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Ofcom Future Options for Efficient Backhaul 23 January 2007

Ofcom – 23 January 2007

Ofcom Future Options for Efficient Backhaul 23 January 2007

© PA Knowledge Limited 2007

PA Consulting Group Cambridge Technology Centre

Melbourn Herts SG8 6DP

Tel: +44 1763 261 222Fax: +44 1763 260 023www.paconsulting.com

Report No: Prepared For:

EIQ-06-0003-D_B Ahmad Atefi

Version: Issue B

i

EIQ-06-0003-D_B Ofcom – 23 January 2007

EXECUTIVE SUMMARY

INTRODUCTION

Ofcom commissioned this report to address what it saw as the potential problem of backhaul links forming a bottleneck and hindering the evolution and future development of wireless communications networks in the UK. For the purposes of this report, backhaul is defined as the final link from a radiating access point (e.g. cellular base station, WLAN access point, etc) to a network node.

Backhaul linkCore

Network

Traffic Aggregation Point& Fibre PoP

WirelessBase Station

Figure 1: Definition of Backhaul

Backhaul is increasingly becoming the constraining factor in high data-rate modern communications systems. For example, it is commonplace for many Wi-Fi nodes capable of data rates of 54Mbits/s to be backhauled through ADSL connections of perhaps a few Mbits/s.

The scope of this report is to investigate backhaul technologies, techniques and requirements over the next 10 to 20 years. The main objectives are to:

• Predict how different backhaul technologies and techniques will evolve and develop over the coming years, and compare them with each other (e.g. in terms of cost, capacity, range, availability) over that time.

• Identify potential future requirements placed on backhaul networks (in the next 10 to 20 years) and what large-scale disruptive changes might occur.

• Identify key hurdles and limits for dramatically lowering future backhaul costs and deploying any given technology very cheaply and ubiquitously.

• Produce a backhaul technologies roadmap for the next 10 – 20 years, identifying: − What possible routes are available to ubiquitous, low cost backhaul − The likely time scales − What actions if any are needed to enable this.

CONCLUSIONS

We see a number of ways in which demand for wireless communications could develop. The most challenging of these for backhaul is where networks have to provide high-capacity personal services (e.g. Video-on-Demand). For these challenging scenarios, there will be a need for high-density, high-capacity backhaul networks.

Executive Summary…

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We foresee the potential need in the future for urban meshed wireless MANs (Metropolitan Area Networks), supporting very dense base station deployments, for example with street-level micro-base stations at every junction. This scenario would see multiple backhaul links per base station, where each link is operating at high capacity over distances up to a few hundred metres, putting in place a very high capacity meshed wireless transmission network, providing backhaul to optical fibre Points-of-Presence for all wireless base stations and access points across a city.

This report concludes that high-capacity Point-to-Point (PtP) Microwave will be the preferred technology for the final link to outdoor base stations (BTSs) in future backhaul networks.

• PtP Microwave is typically used today to link large macro-BTSs over ranges of a few kilometres. These links will evolve to provide higher capacity over shorter distances, working over multiple hops to connect street-level base stations.

• The choice of PtP Microwave will be on the basis of reduced costs: − Reduced overall costs by avoiding leased lines − Quick and cheap to install compared to digging trenches − Low cost of scaling up capacity to BTSs as it is required

• Wireless will be able to deliver the link capacities required

• Combinations with flexible, auto-configured, multi-hop mesh-type topologies will be needed for street-level micro- and pico-BTSs in urban & suburban Non-Line-Of-Sight (NLOS) environments.

• There will be enough PtP spectrum to support such very high capacity networks

High-speed DSL will be used for indoor pico-BTS deployments where available due to its low cost.

Optical Fibre and xDSL will otherwise be used on a link-by-link basis to connect outdoor BTSs only where they provide a lower life-time cost than PtP Microwave.

The final link to the BTS will become shorter as Fibre-To-The-Cabinet (FTTC) pushes fibre further into the access network, increasing the number of fibre PoPs.

Other technologies considered (Point-to-MultiPoint Microwave, WiMAX, Free-Space Optics, Satellite, Power-Line Communications) will only have niche roles in the future.

APPROACH

In this report, we investigate whether the logical evolution paths for different technologies are likely to meet the future requirements for backhaul networks and, if not, how the gap(s) might be filled. To understand this, we compare the two following approaches:

1. Investigate the current state of the art and predictable evolution of the technologies over the coming years

2. Brainstorm potential future scenarios for wireless communications usage and what implications these have for backhaul requirements


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Approach 1Approach 2

Do they meet?

Time2006 2007 2008 2009 2010 2011 2016 2017 2018 2019

Comparison by:- Cost- Range- Capacity- Availability Tech 1

Tech 2

Tech 3

Tech 4

Scenario 1

Scenario 2

Scenario 3

Scenario 4

Time2006 2007 2008 2009 2010 2011 2016 2017 2018 2019


Tech 2

Tech 3

Tech 4

Scenario 1

Scenario 2

Scenario 3

Scenario 4

Figure 2: Approach to Work

FUTURE BACKHAUL REQUIREMENTS

We identify a number of possible Future Scenarios and how different cellular and WiFi deployment types support them. The following backhaul requirements were derived for different deployment types and scenarios:

Urban

SuburbanRural

AreaType

166666

No. of Operators

Backhaul Req’s per BTS per Scenario (Mbit/s)

103060WiFi Pico-BTS102030Cellular Pico-BTS103060Cellular Micro-BTS2080228Cellular Macro-BTS2080228Cellular Macro-BTS40180228Cellular Macro-BTS

LowMediumHighDeployment Type

Urban

SuburbanRural

AreaType

166666

No. of Operators

Backhaul Req’s per BTS per Scenario (Mbit/s)

103060WiFi Pico-BTS102030Cellular Pico-BTS103060Cellular Micro-BTS2080228Cellular Macro-BTS2080228Cellular Macro-BTS40180228Cellular Macro-BTS

LowMediumHighDeployment Type

Table 1: Future Backhaul Requirements

Typical GSM backhaul capacity per base station today is from 2 Mbit/s up to 12 Mbit/s for the largest macro-base stations. Newer provisioning on 3G networks today typically allows for scaling up to 34 Mbit/s to macro-base stations, based on expected traffic growth with HSDPA.

Note that this study concentrated on public access wireless; corporate in-building use is not within the scope of work and we assume that major buildings will continue to be served by leased line / optical fibre.

LIKELY ROLE OF DIFFERENT TECHNOLOGIES

From looking at how different technologies meet the technical, logistical and cost requirements for meeting these backhaul requirements, we identify the potential for each to play a major role in future backhaul networks as follows:


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Yes – In conjunction with mesh radio techniques in NLOS environments

PtP Microwave

No – Limited in range and by location of nearest transformerPower-Line CommunicationNo – Limited capacitySatelliteNo – Not reliable enough for practical deploymentsFree Space OpticsNo – Another flavour of PtMPWiMAXProbably Not – Not appropriate for NLOS micro- and pico-BTSsPtMP MicrowaveYesxDSLYesOptical Fibre

Likely to have a major future role?Backhaul TechnologyYes – In conjunction with mesh radio techniques in NLOS environments

PtP Microwave

No – Limited in range and by location of nearest transformerPower-Line CommunicationNo – Limited capacitySatelliteNo – Not reliable enough for practical deploymentsFree Space OpticsNo – Another flavour of PtMPWiMAXProbably Not – Not appropriate for NLOS micro- and pico-BTSsPtMP MicrowaveYesxDSLYesOptical Fibre

Likely to have a major future role?Backhaul Technology

Table 2: Likely Role of Technologies in Future Backhaul Networks

We identify key hurdles and limitations that are stopping each technology from providing cheaper and more ubiquitous backhaul networks in the future and recommend potential areas of further research that Ofcom could sponsor to help overcome these hurdles.

Specifically, we believe that there is a role for Ofcom to play in:

• Stimulating targeted research into PtP microwave, particularly including mesh networks.

• Understanding the business case for meshed wireless metropolitan area networks (MANs).

Other specific recommendations are included in the main report.

Finally, this report sets out the predicted roadmap over time of key drivers and requirements that backhaul networks will have to meet, explaining their impact and implications over the time scales of 5 years, 10 years and 15 – 20 years.

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TABLE OF CONTENTS

Executive Summary i

1. Introduction 1-1 1.1 Background 1-1 1.2 Scope and Objectives 1-1 1.3 Approach to Work 1-2 1.4 Structure of the Report 1-3

2. Market Drivers 2-4 2.1 Access Technologies 2-5 2.2 Services and Applications 2-6

3. Technology Comparison 3-7 3.1 Technical Summary 3-7 3.2 The Likely Role of Technologies in Future Backhaul Networks 3-8 3.3 Cost Comparison 3-10

4. Current and Emerging Backhaul Technologies 4-15 4.1 Optical Fibre 4-16 4.2 Point-to-Point Microwave 4-19 4.3 Point-to-MultiPoint Microwave 4-22 4.4 DSL 4-24 4.5 WiMAX 4-28 4.6 Free Space Optics 4-31 4.7 Satellite 4-33 4.8 Power-Line Communications 4-34

5. Future Scenarios 5-35 5.1 Future Drivers of Wireless Telecoms Usage 5-36 5.2 Usage Scenarios 5-38 5.3 Mobile Network Capacity 5-45 5.4 Can the Deployment Types support each Scenario? 5-47 5.5 Required Backhaul Capacity 5-50 5.6 The Ability of Technologies to meet the Backhaul Requirements 5-53

6. Technology Hurdles and Areas for Further Research 6-60 6.1 Hurdles and Obstacles 6-60 6.2 Areas for Further Research 6-67

7. Wired vs. Wireless 7-69 7.1 Will there be a “Shift in Power”? 7-69 7.2 What will be the Nature of the Change? 7-69 7.3 Will there be enough spectrum? 7-70

8. Backhaul Roadmap 8-73 8.1 In 5 Years Time 8-75 8.2 In 10 Years Time 8-75 8.3 In 15 to 20 Years Time 8-76

Appendices APPENDIX A: Industry Interviews A-77 APPENDIX B: Backhaul Developments outside the UK B-85 APPENDIX C: Glossary of Terms C-87

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1. INTRODUCTION

1.1 BACKGROUND

Ofcom commissioned this report to address what it saw as the potential problem of backhaul links forming a bottleneck and hindering the evolution and future development of wireless communications networks in the UK.

Backhaul is increasingly becoming the constraining factor in high data-rate modern communications systems. For example it is commonplace for many Wi-Fi nodes capable of data rates of 54Mbits/s to be backhauled through ADSL connections of perhaps a few Mbits/s.

Backhaul accounts for a significant proportion of network cost and is a critical parameter for evaluating network performance. For operators, therefore, choosing the correct backhaul technology for their current and future requirements can be critical to their success.

1.2 SCOPE AND OBJECTIVES

For the purposes of this report, backhaul is defined as the final link from a radiating access point (e.g. cellular base station, WLAN access point, etc) to a network node.

Backhaul linkCore

Network



Figure 3: Definition of Backhaul

The scope of this report is to investigate backhaul technologies, techniques and requirements over the next 10 to 20 years. The main objectives are to:

• Predict how different backhaul technologies and techniques will evolve and develop over the coming years, and compare them with each other (e.g. in terms of cost, capacity, range, availability) over that time.

• Identify potential future requirements placed on backhaul networks (in the next 10 to 20 years) and what large-scale disruptive changes might occur.


• Produce a backhaul technologies roadmap for the next 10 – 20 years, identifying: − What possible routes are available to ubiquitous, low cost backhaul − The likely time scales − What actions if any are needed to enable this.

1. Introduction

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It should be noted that the priority of this study is to concentrate on the future and consider where backhaul technologies and markets are going in the longer term, rather than focus too directly on the predictable evolution over the next few years.

The desired benefits of this report are to:

• Inform Ofcom’s spectrum requirement planning team on likely changes in demand for wireless backhaul

• Inform industry of the potential for more efficient and/or cheaper technologies & techniques currently or soon to be available to them

• Help produce actions plans for overcoming likely hurdles that may obstruct migration to more efficient and cost-effective technologies and techniques.

1.3 APPROACH TO WORK

We adopt a two-pronged approach to this project:

1. Investigate the current state of the art and predictable evolution of the technologies over the coming years

2. Brainstorm potential future scenarios for wireless communications usage and what implications these have for backhaul requirements

We then compare the future scenarios against the predictable evolution to see if the logical evolution paths are likely to meet the future requirements

Approach 1Approach 2

Do they meet?

Time2006 2007 2008 2009 2010 2011 2016 2017 2018 2019


Tech 2

Tech 3

Tech 4

Scenario 1

Scenario 2

Scenario 3

Scenario 4

Time2006 2007 2008 2009 2010 2011 2016 2017 2018 2019


Tech 2

Tech 3

Tech 4

Scenario 1

Scenario 2

Scenario 3

Scenario 4

Figure 4: Approach to Work

In the process of producing this report, we have carried out a number of industry interviews with players on both the supplier and user sides of the backhaul industry. These have been used to inform and substantiate our findings and conclusions.

1. Introduction

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1.4 STRUCTURE OF THE REPORT

This report is structured as follows:

• Section 1 looks at the wireless access technologies and networks using backhaul and identifies what will be the main sectors and users that will drive developments in backhaul technologies.

• Section 1 provides a technical and cost comparison between the different backhaul technologies considered in this report and concludes which are likely to play the major roles in future backhaul networks.

• Section 1 provides an overview of each of the backhaul technologies, giving information on general usage, technical characteristics, future developments and applicability to backhaul networks.

• Section 0 considers future scenarios for wireless telecommunications usage and what requirements may be placed on backhaul networks 10 to 20 years from now. It concludes which technologies will be able to support the different scenarios and deployment types.

• Section 1 looks at the main obstacles and hurdles stopping each technology becoming the natural choice for providing future cheap and ubiquitous backhaul networks in the future. It also suggests further areas of research that Ofcom could consider sponsoring to help overcome these hurdles.

• Section 1 looks at how the use of wired and wireless technologies is likely to change over time and whether there is likely to be a significant shift from one to another. It considers what impact this is likely to have on the UK’s current plans for spectrum management for wireless backhaul.

• Section 1 provides a summarising overview of the whole report and lays out a roadmap for how backhaul networks are predicted to evolve over the next 10 to 20 years.

• The Appendices cover feedback received from industry interviews carried out for this report and provide an overview of backhaul developments outside the UK.

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2. MARKET DRIVERS

Backhaul network costs are primarily driven by two basic concepts:

• Capacity per link

• Number of links

Therefore, when looking at the drivers behind developing cheap, ubiquitous future backhaul networks, the markets that will drive these developments will be those requiring the largest volumes in terms of link capacities and link numbers.

This section looks at the different wireless communications markets that use backhaul technologies today and assesses their current and likely future roles in driving developments in backhaul networks.

2. Market Drivers

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2.1 ACCESS TECHNOLOGIES

This section looks at the base station access technologies that backhaul technologies are currently serving, both licensed and unlicensed. The larger the market each technology represents, the more likely it is to drive future backhaul options towards greater efficiency.

Access

Technology Size of Market Backhaul Capacity per BTS

2G 50K – 60K 2G BTSs in the UK across the main mobile operators.

Typically 2 Mbit/s to 4 Mbit/s required. Very large urban BTSs could require up to 12 Mbit/s.

3G Currently 30K – 40K 3G Node Bs in the UK. This number is likely to grow to 60K – 70K.

3G HSDPA will require 12 Mbit/s – 30 Mbit/s for typical macro-base station deployments.

Note that downlink capacities will be higher than uplink and may require asymmetric backhaul for maximum efficiency.

3G LTE Base station numbers for 3G Long-Term Evolution (LTE) will be similar to current 3G (i.e. 60K – 70K). Widespread deployment should be seen by 2011 – 2013.

3G LTE macro-base stations will require between 30 Mbit/s – 120 Mbit/s, with very large urban base stations potentially requiring up to 240 Mbit/s backhaul capacity.

Again, asymmetric backhaul solutions may be appropriate for maximum efficiency.

WiFi / WLAN There are currently nearly 10,000 WiFi hotspots in the UK and this is likely to increase enormously over time with the trend towards Metro-WiFi networks.

Current backhaul on WiFi hotspots is typically only 2 Mbit/s residential ADSL.

WiFi today (802.11a/g) has the potential to require up to 30 Mbit/s on the backhaul link if run to capacity.

Future WiFi (802.11n) has the potential to require up to 150 Mbit/s on the backhaul if run to capacity.

WiMAX Mobile WiMAX may be rolled out in the UK and achieve mass-market volumes. Deployments are likely to be similar to cellular operators, with up to 10K BTSs per operator.

Fixed WiMAX (providing residential and business broadband access services) deployments will be much smaller in number.

Depending on planning assumptions, Mobile WiMAX base stations will likely require backhaul capacities of 20 Mbit/s – 50 Mbit/s.

TV Broadcast Services

Currently ~1,100 TV broadcast masts across the UK, of which ~50 are major sites. No likely increase in masts in the future.

~300 Mbit/s backhaul capacity needed towards the broadcast mast. Major sites require fully duplicated redundant backhaul.

Tetra O2 Airwave has ~1,000 sites covering the UK.

2 Mbit/s backhaul capacity per site meets current requirements.

Analogue PMR

There are ~20,000 PMR base stations in the UK (excluding on-site base stations where backhaul is not an issue).

Very low capacities required, typical remote base stations may have a simple voice circuit connection.

Table 3: Size and Impact of Access Technology on Backhaul Requirements

2. Market Drivers

2-6


It is clear from this that:

• 2G and 3G cellular networks currently dominate the market for backhaul links.

• There has been significant growth in WLAN / WiFi hotspots in recent years, but these services have not typically been profitable enough to warrant investment in high capacity or high quality backhaul links. However, this market has the potential to achieve significant market growth and could see very large growth in traffic volumes and associated backhaul requirements.

• WiMAX is still somewhat of an unpredictable technology in terms of what market share it will win. Again, it has the potential for mass market success and with that, the potential for generating a large backhaul network requirement.

• Other wireless access technologies (Broadcast services, Tetra, PMR) do not currently represent a large slice of the backhaul market in the UK and are equally unlikely to do so in the future.

2.2 SERVICES AND APPLICATIONS

The services and applications that will be carried over the access networks above are also changing in nature. The new services appearing either now or in the next few years place additional demands on access networks, which need to increasingly support:

• Increasing capacity – as well as predictable growth in major services such as voice and SMS, there will be largely unpredictable growth in new services (video services, TV services, messaging) that have the potential to achieve mass market success and, in doing so, see very large increases in overall network traffic to be supported and backhauled.

• Mixed traffic – the evolution to packet based networks requiring support of both IP and TDM traffic.

• Higher data rate services – networks are evolving to support much higher peak end-user data rates and such services need to be supported in the backhaul network to avoid the backhaul becoming the bottleneck in service support.

• Differential services – the ability to automatically provide bandwidth based on traffic priority.

• Asymmetric bandwidth – end users typically consume more data that they produce, therefore requiring higher downlink capacity that uplink.

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3. TECHNOLOGY COMPARISON

This section brings together the features and analysis of the different technologies considered to provide a high-level comparison between them on the basis of their applicability to backhaul in wireless communications networks. In more detail, it:

• Summarises the characteristics of each technology based on the more detailed descriptions in Section 1.

• Identifies those technologies likely to play a major role in future backhaul networks.

• Provides a comparison of these technologies to identify further likely trends and drivers based on costs.

3.1 TECHNICAL SUMMARY

This section summarises the current and emerging backhaul technologies and their associated characteristics, based on their current capabilities and predictable evolution as described in Section 4. Each characteristic for each technology is classified on a qualitative scale:

• ● – Very Good

• ◕ – Good

• ◑ – Acceptable

• ◔ – Poor

• ○ – Very Poor

The characteristics in the table below come under the following headings:

• Technical characteristics – Range, Capacity, Reliability − These need to be at least acceptable. Since backhaul in wireless

communications is primarily a cost, rather than adding a specific value to the end-service, backhaul technologies only have to be good enough to meet these technical performance requirements.

• Cost – Ideally, cost should be as good as possible (i.e. as low as possible)

• Logistical – Local Availability, Speed of Rollout − These need to be at least acceptable, but are less critical than the technical or

cost criteria when choosing a technology for backhaul networks.

Further detail on the reasoning behind each classification is given in Section 1.

3. Technology Comparison

3-8


Characteristic

Technology Range Capacity Reliability Cost Local Availability

Speed of Rollout

Optical Fibre ● ● ● ◔ ◕ ◔

PtP Microwave ◕ ◕ ● ◑ ◕ ◕

PtMP Microwave ◑ ◑ ● ◑ ◑ ●

DSL ◔ ◔ ◑ ● ◔ ●

WiMAX ◑ ◔ ● ◑ ◑ ◕

Free-Space Optics ○ ● ○ ◕ ◕ ●

Satellite ● ○ ◕ ○ ◕ ◕

Power-Line Comms ○ ◔ ◔ Unknown ◔ ◔

Table 4: Comparison of Backhaul Technology Characteristics

3.2 THE LIKELY ROLE OF TECHNOLOGIES IN FUTURE BACKHAUL NETWORKS

As stated above, backhaul technologies only have to be good enough to meet the technical performance requirements of range, capacity and reliability. Once that technical standard has been met, operators will likely go for the cheapest, most cost-effective solution available to them. With this in mind, the key messages from the table above therefore are:

• Only three technologies (Optical Fibre, PtP Microwave, PtMP Microwave) score at least “Acceptable” or better on all three technical characteristics.

• Only two technologies (DSL, Free-Space Optics) score at least “Good” or better on cost.

• WiMAX, Satellite and Power-Line Comms can be immediately discounted as having any major role in future backhaul and will not drive the market. This is on the basis that they display neither acceptable technical nor good cost characteristics.


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This is summarised in the following table:

Meeting Technical Performance Requirements

Meeting Cost Requirements Meeting Neither

Optical Fibre

PtP Microwave

PtMP Microwave

DSL

Free-Space Optics

WiMAX

Satellite

Power-Line Comms

Table 5: Technologies meeting Technical and Cost Requirements

Note that technologies identified as ‘Meeting Technical Performance Requirements’ or ‘Meeting Cost Requirements’ may also meet the other necessary requirements in certain types of deployment (eg. DSL for short links in urban areas).

Of the technologies meeting either the technical or cost requirements, further examination suggests that PtMP Microwave and Free-Space Optics will also not have a major role in future backhaul networks. The reasons for this are:

• PtMP Microwave is directly competing with PtP Microwave in its applications in backhaul networks. However, PtP provides better range and capacity, while PtMP has not proven it can provide lower costs in the UK. Furthermore, PtMP configurations are less appropriate to use for street-level micro- and pico-base stations, which are likely to increase greatly in numbers in the coming years.

• Free-Space Optics limitations in range and reliability are so great that even with a low cost per link, it is unlikely that operators will be able to find suitable uses for it.

This leaves three technologies that are likely to dominate future backhaul networks and drive the market:

• PtP Microwave strikes a good balance between good enough technical performance with reasonable costs. It provides operators with an opportunity to build out their own networks and avoid service provider leased line solutions if desired. Future developments with mesh topologies should also enable its use for backhauling street-level micro- and pico-base stations.

• DSL has significant technical limitations, but its cost base is so low that it will be an obvious choice for operators where it is available and delivers the technical performance required. It may have a major future role to play in backhauling micro- and pico-base stations, especially where the base station is mounted on or in a building where copper pairs are already present.

• Optical fibre has excellent technical performance, but the time and cost required to dig in trenches for new deployments are a major limitation. Lack of open access to existing operators’ optical PoPs also means that optical tail circuits are in practice only available as leased lines from service providers. However, optical fibre will continue to have a major role in future backhaul networks, both where fibre is already available and where other solutions (primarily PtP Microwave or DSL above) cannot actually provide lower costs.


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The table below summarises these findings to clearly state whether or not each technology is likely to play a major role in future backhaul networks. Backhaul Technology Likely to have a major future role?

PtP Microwave Yes (in conjunction with advances in mesh radio techniques)

Optical Fibre Yes

xDSL Yes

PtMP Microwave Probably Not – Competes directly with PtP Microwave, and is not appropriate for NLOS micro- and pico-BTSs

Free Space Optics No – Not reliable enough for practical deployments

WiMAX No – In effect another flavour of PtMP and is primarily aimed at end-user services.

Satellite No – Limited capacity

Power-Line Communication No – Limited in range and by location of nearest transformer

Table 6: Likely Role of Technologies in Future Backhaul Networks

3.3 COST COMPARISON

This section provides a high-level comparison of the costs of those technologies likely to have a major role in future backhaul networks providing the final link to the base station. It highlights key messages and implications of the cost analysis for use of each technology in future. This analysis is intended to complement the wider findings in the technical review and comparison of the technologies.

3.3.1 The Main Backhaul Options

From Section 3.2, only three technologies are foreseen to have a major role in shaping backhaul networks of the future, based on meeting the technical requirements. Those three technologies are:

• Point-to-Point Microwave Radio

• Optical Fibre

• DSL (e.g. VDSL2)

These technologies will provide the great majority of final links to the wireless base stations of the future. That final link will reduce to 1km – 1.5 km, as optical fibre pushes further out into the access network through Fibre-To-The Cabinet (FTTC).

3.3.2 Overall Approach to Cost Comparison

The difference between future scenarios lies in the final link to the base station. Once backhauled to a fibre PoP, the rest of the access network is common across the three options. Therefore, the cost modelling in this section concentrates on the difference between the options for the final link to the base station, as shown in the figure below.


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Backhaul link:- PtP Microwave- DSL (VDSL2)- Optical Fibre

Network

Fibre to the Cabinet




Network





NetworkNetwork




Figure 5: Focus of Cost Comparison on Final Link to Base Station

In comparing the costs of the different technical options for the final link, we:

• Try to consider costs, not prices, where possible. − For example, we do not look at leased line prices, we try to consider the cost

of installing the link.

• Calculate NPV values to allow both Capex and Opex items to be considered. − Looking at a range of years (5, 10, 15) to calculate Net Present Values

(NPVs), it was found that increasing the number of years does not significantly change the cost comparison between the different technologies.

− A 5-year NPV is used in the main analysis below as it strikes a balance between the strategic view that operators are taking on backhaul transmission, against the desire to minimise investment in the short term.

− A discount rate of 14% was used to calculate all NPV figures.

• Look at the cost for a range of data rates − Operators are greatly concerned about the cost of scaling up capacity as

future traffic levels grow.

3.3.3 Cost Items Considered

For the final link, there are a number of costs to be considered:

• Equipment at either end of the link − Line cards (optical, DSL), DSL router, PtP Microwave radios and antennas

• The cost of the physical transmission medium − Optical fibre, LLU payments per copper pair, spectrum licensing fees

• Installation − Installing equipment, digging trenches for new fixed links

• Operation & Maintenance − Supplier support contracts, technical staffing requirements


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For each of the three technologies, we have used typical present-day figures for the different capex and opex cost items as detailed below:

PtP Microwave Optical Fibre DSL

PtP Equipment: Exchange-end port on line card

£35 DSL Router £200

- 8 Mbit/s £4,511 Jumpering & connection £48 Line Card £30

- 34 Mbit/s £6,000 BTS-end termination equipment

£120

- 155 Mbit/s £9,000 Installation @ BTS end £100

- 622 Mbit/s £18,000 Dig cost/m (urban) £62.30

Installation £3,000 Dig cost/m (suburban) £45.00

Dig surveying cost/m £4.00

Laying fibre in duct cost/m £1.60

Fibre cable cost/m £0.30

Average link length (metres) 500m

Table 7: Capex Cost Assumptions

PtP Microwave Optical Fibre DSL

Supplier Support 5% of capex



O&M £500 O&M £200 O&M £100

Site Rental £1,000 LLU Rental £96

Spectrum Licensing £500

Table 8: Opex Cost Assumptions

3.3.4 Impact of a future Meshed Wireless MAN Scenario

In contrast to the standard PtP microwave link considered above, we also consider a future scenario for meshed PtP radio, where an urban mesh is put in place with street-level micro-BTSs at every junction. This is illustrated below and is also dealt with in more detail in Section 7.3.1, when looking at the impact of this scenario on spectrum requirements.


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Building

BTSLink

Key:

Channel #

Building

BTSLink

Key:

Channel #

Figure 6: Future Meshed Wireless MAN Scenario

This scenario results in an average of two links per BTS, where each link is operating at high-capacity, high-frequency and operating over 200m – 500m. As a result, equipment costs are lower (see Section 0), as are installation, O&M and site rental costs.

This illustrates one of the potential strengths in PtP Microwave. There is the prospect of equipment prices being driven down due to technology advances and the manner in which wireless networks will be deployed in the future (dense micro- and pico-BTS deployments). This will have a knock-on impact on a number of associated costs that affect the life-time cost of the link. The capex and opex assumptions for this are as follows:

PtP Equipment £1,000

Installation £200

Table 9: Capex Cost Assumptions


O&M £100

Site Rental £100

Spectrum Licensing Free*

* - assumed to be in lightly licensed spectrum

Table 10: Opex Cost Assumptions

3.3.5 Cost Comparison

As discussed above, capex and opex costs were considered over a five year period and a Net Present Value calculated to show the cost comparison between the different technologies. The graph below shows those costs of investing in the different technologies for different data rates and overlays the cost of the future Meshed Wireless MAN scenario on the costs based on present-day assumptions


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Cost of different Backhaul Rates using different Technologies

£0

£5,000

£10,000

£15,000

£20,000

£25,000

£30,000

£35,000

£40,000

8 Mbit/s 34 Mbit/s 155 Mbit/s 622 Mbit/s

Data Rate

5 Ye

ar N

PV (£

'K)

PtP Microwave

VDSL2

Optical Fibre (urban, all dug)

Optical Fibre (urban, 20%dug)Optical Fibre (suburban, alldug)Optical Fibre (suburban, 20%dug)Meshed Wireless MANscenario

Figure 7: Cost Comparison of different Backhaul Technologies

This shows that:

• DSL is the easily the cheapest option, but is limited on data rates supported (as well as other technical and logistical limitations discussed elsewhere).

• PtP Microwave costs are based on typical figures for a cellular macrocell backhaul link today. These costs are dominated by equipment costs, installation and site rental.

• Optical fibre costs are dominated by the cost of digging trenches for new fibre installation. We consider different scenarios above for: − Urban vs. suburban − All new dig vs. 20% new dig

• If optical fibre has to be fully dug in for the entire link length, then PtP microwave is cheaper up to the point where STM-4 (622 Mbit/s) data rates have to be supported.

• If optical fibre is available to within 100m (the 20% dig scenario for fibre in the graph above) of the BTS, then it is cheaper than PtP microwave.

• The graph above shows that for this scenario, the cost of a meshed microwave backhaul network could come in significantly cheaper than optical fibre, even if fibre is available within 100m of the BTS.

• Since optical fibre link costs are dominated by the cost of digging trenches, there is not the same prospect of optical fibre link costs reducing to the same extent.

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4. CURRENT AND EMERGING BACKHAUL TECHNOLOGIES

This chapter looks at the different transmission technologies that could be used in backhaul networks. The technologies discussed are:

• Optical fibre

• Point-to-Point (PtP) Microwave

• Point-to-MultiPoint (PtMP) Microwave

• DSL

• WiMAX

• Free Space Optics (FSO)

• Satellite

• Power-Line Communications

For each technology, we consider:

• General Usage

• Technical Characteristics − Range, capacity, reliability, cost, local availability, speed of rollout

• Future Developments

• Applicability to Backhaul Networks − Strengths & weaknesses

4. Current and Emerging Backhaul Technologies

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4.1 OPTICAL FIBRE

4.1.1 General Usage

Optical fibre is widely used in core or backbone networks in the UK for very high data-rate transmission (up to 10 Gbit/s). As a result, a lot of optical fibre is laid around the UK, typically as large pipes linking cities and main areas of commerce.

However, use of optical fibre in the access network is more patchy and typically only on a link-by-link basis, where the need for high data-rate access is required and where the cost of installation is not prohibitive. For example, in large commercial areas, optical fibre is also widely used to provide high-speed access into large corporates and businesses.

Optical fibre is also widely used in cellular 2G and 3G backhaul today, along with Point-to-Point microwave radio.

Competition for optical fibre in the UK is reasonably high in the provision of backbone transmission and in high-value, high-speed access for large corporates and businesses in the major commercial areas. However, competition in the wider access market across the UK is not very strong and such customers wishing to get an optical fibre tail circuit to any given location generally find they do not have a lot of options.

The use of optical fibre links in the access network is almost exclusively through the rental of leased lines from a service provider. The barriers to entry for a wireless communications operator to build out their own optical fibre in their backhaul network are very high:

• The time and cost required to dig in new trenches and ducts for optical fibre is very high.

• A large number of optical Points of Presence (PoPs) are required around the country in order to minimise the distance (and therefore cost) of any digging for new trenches. Since the principles of Local Loop Unbundling (LLU) only apply to copper pairs and not to optical tail circuits, operators have no right to connect back their own optical fibre backhaul links to BT’s local exchanges or other fibre PoPs.

All this means that, in practice, the use of optical fibre in the access network is a service provider-only solution.


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4.1.2 Technical Characteristics Characteristic Comment

Range In practice, no limitation – The operating range of optical fibre circuits meets all the requirements of backhaul networks.

Capacity In practice, no limitation – Optical fibre links can operate up to 10 Gbit/s and are available at virtually any data rate from 2 Mbit/ upwards.

Reliability Excellent

Cost High – The cost to dig in new fibres is very high. Also, leased line solutions are currently perceived in the market as being expensive.

Since optical fibre use is primarily through leased lines, the cost base is dominated by ongoing opex costs (leased line rental charges).

Local Availability Good – Optical fibre can be laid to most places in the UK.

Speed of Rollout Poor – Where fibre is not currently available, the time to install a new link is high. Furthermore, gaining permission to dig new trenches can also take a long time, especially in metropolitan areas.

Table 11: Technical Characteristics of Optical Fibre

4.1.3 Future Developments

The advent of Metro Ethernet has the potential to push optical fibre further into the access network and to drive prices down. Metro Ethernet provides high-speed access services, typically to large multi-site corporate customers.

• Metro Ethernet is typically delivered using optical fibre links, and so is pushing optical fibre further into the access network.

• Metro Ethernet is also currently priced significantly lower than leased lines for equivalent data rates (typically up to 60% lower). While service levels are not comparable between leased lines and Metro Ethernet, the likely future growth in IP-based data traffic in wireless communications will see services such as Metro Ethernet become more applicable to the backhaul market.

Passive Optical Network (PON) topologies and technologies are lowering the cost of widespread deployment of optical fibre, delivering higher data rates and increasing the range of the PON tree structure. The latest standard is GPON (Gigabit PON1), delivering up to 2.4 Gbit/s over distances up to 20km. Other work is ongoing looking at further increasing data rates or distance supported2.

Fibre-To-The-Cabinet (FTTC) – Broadband Internet access services will continue to see increased peak data rates offered, as well as increased traffic levels. The requirement to support higher data rates and traffic levels will likely see the deployment of high-data rate DSL services (e.g. ADSL2+, VDSL, VDSL2) from the street cabinet, with optical fibre deployed out to the cabinets to provide the necessary capacity for the link back to the Multi-Service Access Node (MSAN) at the local exchange.

1 ITU G.984 series recommendations

2 BT Technology Journal Vol.24 No. 2 April 2006


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4.1.4 Applicability to Backhaul Networks

Optical fibre is currently widely used in cellular backhaul networks and is likely to continue to be a major player in the future. Its main strengths and weaknesses can be summarised as follows:

Strengths:

• Range and capacity are not a limit for optical fibre and are sufficient for all backhaul purposes.

• Optical fibre is very reliable and generally available across the UK.

Weaknesses:

• The time and cost needed to dig trenches in order to deploy new fibre is very high.

• Access to a large number of optical PoPs is required to minimise the cost of new build. This places a very high barrier to entry for wireless operators to build out their own optical fibre backhaul links, making this a service provider-only solution in practice.

• Leased lines are perceived as being very expensive, especially for scaling up of capacity to a base station.

• Lack of competition in provision of fibre tail circuits.

Optical fibre’s strengths lie in its technical performance, more than adequately meeting the technical requirements of future backhaul networks. Its weaknesses are a combination of logistical (digging trenches) and competitive hurdles (service provider-only solution, leased lines perceived as expensive).


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4.2 POINT-TO-POINT MICROWAVE

4.2.1 General Usage

There are nearly 50,000 licensed Point-to-Point (PtP) microwave links in the UK today and the majority of these are currently being used in cellular backhaul. These links are deployed both by cellular operators building and owning their own microwave backhaul network and by service providers building and operating microwave networks on behalf of customers.


Range Highly dependent on operating frequency and modulation scheme used. Typical ranges are:

• 4 km at 38 GHz

• 10 km at 13 GHz

• 40 km at 6 GHz

Capacity Ofcom licenses PtP links up to STM-4 (622 Mbit/s) data rates today. Unlicensed Gigabit Ethernet radio links are also available today.

High data-rate links typically operate in high-frequency spectrum (e.g. > 10 GHz).

Reliability Very good.

Cost Reasonable – dominated by up-front capex for equipment and installation. Good scalability of capacity for cost.

Local Availability Good for serving tower-mounted macro-BTSs at any frequency.

Not good for serving street-level microcells due to the requirement for low-frequency Non-Line-of-Sight (NLOS) spectrum

Speed of Rollout Very good

Table 12: Technical Characteristics of PtP Microwave


Technical developments are expected to provide some incremental improvements in the performance of PtP microwave systems over the next two to five years:

• Automatic Transmit Power Control (ATPC) will improve frequency re-use distances.

• Adaptive Modulation and Coding (AMC) will increase link capacity during good propagation conditions.

• MIMO is not expected to deliver significant benefits for outdoor PtP links as it works better in high-multipath environments (e.g. indoor offices).

• Adaptive Antenna Systems (AAS) are not expected to deliver significant benefits for PtP systems.


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• New repeater technologies or FEC gains may provide incremental improvements to link capacities.

• Higher-order modulation schemes (up to 256-QAM) may deliver increased data rates.

Overall though, it is not expected that any “step changes” in link capacities or ranges will be delivered over the next five years through such technology developments.

As further micro- and pico-base stations are deployed further to deliver higher capacity, link distances are likely to reduce significantly. This will see use of higher-frequency spectrum (e.g. > 50 GHz) capable of delivering high capacity links over short distances (e.g. < 2 km).

High-frequency systems (> 50 GHz) promise future reductions in equipment prices

• The use of metallised plastics can significantly reduce component costs at these frequencies.

• Antenna sizes (and costs) reduce greatly.

• Wide channel spacing (e.g. > 2 GHz, easier to accommodate at higher frequencies) simplifies diplexer requirements and reduces cost.

• Radio links that operate in the oxygen absorption band (55 GHz to 67 GHz) are available that have highly simplified structures based on the assumption that frequency re-use will still be very high due to the high signal attenuation at these frequencies. Such systems may have no power amplifier, no FEC, run simple modulation schemes (QPSK, 8-QAM) and deliver Ethernet services (rather than traditional E1 links). − Prices for such 60 GHz radio links are around £2K - £4K today for 125 Mbit/s

up to Gigabit-Ethernet rate. Forecasts are for these prices to drop below £1K per link as volumes increase.

A migration to Ethernet-based transmission links is expected as traffic volumes migrate to IP-based transmission, resulting in simpler and cheaper equipment.

Combinations of PtP microwave with mesh topologies may be used in the future to allow use of high-frequency, high-capacity Line-Of-Sight (LOS) spectrum to backhaul micro- and pico-base stations over a limited number of hops in urban areas.

Ofcom is allocating a further 10 GHz of PtP spectrum, with the 70 GHz and 80 GHz band planned to be opened up in 2007.

Ofcom is also moving towards a lightly licensed regime for higher frequency bands, which should simplify the planning and administration of PtP links in these bands.


PtP Microwave is currently widely used in cellular backhaul networks and is likely to remain a major player in the future. Its main strengths and weaknesses can be summarised as follows:

Strengths:

• Capacity, range and reliability are adequate to meet operator requirements.


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• Can be deployed by the wireless operator for themselves, allowing leased line solutions to be avoided if desired.

• The cost of scaling up capacity is quite low, which is highly relevant given predicted growth in traffic volumes with the growth of HSDPA and WiFi hotspots.

Weaknesses:

• Equipment prices are quite high for current systems used in cellular backhaul.

• Achievable link range becomes limited at higher frequencies.

• The majority of PtP spectrum is only suitable for LOS spectrum, limiting its use primarily to tower-mounted macro-base stations.

PtP Microwave’s strengths lie in meeting the technical performance requirements of backhaul networks, while providing operators with a cost-effective solution that they can build out themselves rather than rely entirely on service-providers. Its weaknesses are limits on operating range, poor support for street-level base stations and relatively high equipment prices.


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4.3 POINT-TO-MULTIPOINT MICROWAVE

4.3.1 General Usage

The most common use of Point-to-MultiPoint (PtMP) microwave is in delivering broadband access services to residential and business customers. There is some minor use of PtMP in backhaul networks, but this is not widespread in the UK.

PtMP microwave competes directly with PtP microwave in the cellular backhaul market. Hub base station costs are higher than one end of a PtP link, while the CPE-end is lower cost. If enough outlying CPEs (connected to wireless access base stations) can be connected back to the hub base station, then PtMP systems can deliver a lower average cost per link than PtP. However, in practice, UK cellular operators have not seen the opportunity for strategic deployment of PtMP systems in their networks.


Range Highly dependent on operating frequency and modulation scheme used. Typical ranges are:

• 3 km at 26 GHz

• 10 km at 3.5 GHz

As a rule of thumb, PtMP systems deliver roughly half the range of an equivalent PtP system.

Capacity Reasonable – Expect up to STM-1 per sector in the near future, with four to eight sector per hub base station.

PtMP systems lend themselves to sharing capacity between outlying CPEs, which will be useful as bursty data traffic increases.

Reliability Very good

Cost Reasonable – Cost per link depends on the number of outlying CPEs that can be served by a hub base station.

Local Availability Suitable for tower-mounted macro-base stations.

Not very suitable for street-level micro- and pico-base stations. Low-frequency spectrum can operate in a NLOS environment, but capacity may be limited for future traffic volumes. High-frequency LOS spectrum cannot operate in a NLOS environment.

Speed of Rollout Very good. Specifically very good for ad-hoc deployment of outlying CPEs as the hub base station is already present.

Table 13: Technical Characteristics of PtMP Microwave


Adaptive Modulation and Coding (AMC) will directly deliver advantages to PtMP systems, allowing the balancing of resources between links experiencing different and varying propagation conditions.

Rollouts of PtMP are being seen more in developing countries (e.g. South Africa) in urban environments, where base station density is high enough to make it economical.


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PtMP is not a major player in backhaul networks today and is not likely to be in the future. Its strengths and weaknesses can be summarised as follows:

Strengths:

• Balancing of resources between outlying CPEs to support bursty data traffic.

• Cost-effective in a dense base station environment when serving a high enough number of outlying CPEs.

• Can provide a useful solution in a green-field environment where it provides full coverage of a wide area.

Weaknesses:

• Range is limited compared to PtP microwave.

• Does not operate appropriately for street-level micro- and pico-base stations.

• Capacity is limited and at the hub-end it has to be shared between a number of outlying CPEs.

Cellular operators have not generally been able to see where base station density is high enough in combination with achieving LOS links back to a single hub base station to justify the widespread deployment of PtMP systems in the UK. Further increases in base station density are likely to be achieved through deployment of micro- and pico-base stations, rather than denser macro-base station deployments. This will count against the widespread use of PtMP in the future, as it does not provide the coverage required in the NLOS environment of small, street-level base stations.


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4.4 DSL

4.4.1 General Usage

DSL is generally used in the UK to provide residential broadband access services, with data rates up to 7 Mbit/s offered. Higher grade services are also generally available, providing business-grade services (e.g. VPN, lower contention, etc).

All DSL in use in the UK today is ADSL and is highly asymmetric, with much higher data rates on the downlink than on the uplink. Residential ADSL is also highly contended (typically 50:1), so the average data rate provided can be much lower than the peak data rate.

In backhaul markets today, standard residential ADSL is typically used to backhaul WiFi hotspots today because of its low price. This illustrates the problem that WiFi offers a theoretical 54 Mbit/s over the air to end-users, but is in practice limited on the backhaul by a 2 Mbit/s ADSL link that is also contended by 50:1.

There is also some minor use of Symmetric DSL (SDSL) today to provide leased line services where available, typically to micro-base stations located on or in buildings.


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Range Poor, and highly dependent on data rate to be offered. See graph below:

• ADSL 5 km

• ADSL2+ 3 km

• SHDSL 3 km

• VDSL 1 km

• VDSL2 1 km

Capacity Limited and highly dependent on range to be offered. See graph below:

• ADSL 7 Mbit/s down, 800 kbit/s up

• ADSL2+ 24 Mbit/s down, 1 Mbit/s up

• SHDSL 5.6 Mbit/s up/down

• VDSL 55 Mbit/s down, 15 Mbit/s up

• VDSL2 100 Mbit/s

Reliability Acceptable – DSL runs over the copper pairs in the ground, which have been there for up to 30 years. Copper pairs can get corroded and impaired through water leakage, so not all links will perform as well as others.

Cost Very good – DSL is highly regulated and competitive, with Local Loop Unbundling (LLU) opening up the market to many smaller players.

Local Availability Poor – DSL only works up to a certain distance from the local exchange. While lower data rate services (today’s ADSL) works up to 5 km and can cover the majority of the UK’s population, future high data rate DSL technologies will be very limited on range. This will severely limit the ubiquitous availability of these services.

If DSL becomes widely and heavily used, links may start to suffer from cross-talk, or interference between the copper pairs – this will further restrict operating ranges. DSL is currently designed for sporadic use, rather than continuous use.

Also, wireless base stations are often mounted on street-lamps, on towers or other places where copper pairs are not typically present. This presents a logistical problem in providing DSL services to wireless base stations.

Speed of Rollout Very good if copper pairs are already available at or near the location where it is needed. Poor, if copper pairs are not readily available.

Table 14: Technical Characteristics of DSL


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0

50

100

150

200

250

0 500 1000 1500 2000 2500 3000 3500Reach / m

Rat

e / M

Bit/

s

DS ADSL2+ (2.2 MHz)

DS VDSL1 (12 MHz)

DS VDSL2 (30MHz)

AWGN/-140dBm/Hz/ANSI-TP1

Symmetrical 100Mbit/s due to 30MHz bandwidth

ADSL-like long reach performance due to Trellis coding and Echo Cancellation

Improved mid range performance through Trellis/Viterbi coding and Generic Convolutional Interleaver

1600 3300 4900 6600 8200 9900 11,500Reach / ft*

* Numbers are rounded

Source: DSL Forum presentation on VDSL2

Figure 8: Capacity vs. Range for high data-rate DSL Technologies


Future deployments of DSL in the UK may see ADSL2+ or VDSL2 rolled out to provide high data-rate services offered (24 Mbit/s, 55 Mbit/s or even 100 Mbit/s).

Since the range of these technologies and data rates is highly limited, it may be necessary to offer them from the street cabinet, or Principal Connection Point (PCP), to reduce the range needed to serve the surrounding population.

• DSL from the local exchange needs to operate up to 5 km – 7 km typically to serve the surrounding population. DSL from the cabinet needs to operate up to 1 km – 1.5 km to serve the same population.

Offering high data rate DSL services from the cabinet is a likely driver for the widespread deployment of Fibre-To-The-Cabinet (FTTC) across the UK.


There is widespread use of ADSL to backhaul WiFi hotspots today and the use of SDSL to cellular base stations is just beginning. DSL offers very cheap connectivity and is likely to play a major role in future backhaul networks where it is available and delivers the capacities required.

Strengths:

• Very low costs per link

• Copper pairs generally available to all buildings in the UK.


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Weaknesses:

• Capacity is limited both today (7 Mbit/s) and in the future (55 Mbit/s to 100 Mbit/s), compared to optical fibre and microwave radio.

• Range – high data-rate services only work typically up to 1 km.

• Asymmetry – most DSL technologies are highly asymmetric and may not suit wireless communications if uplink capacities are not much lower than downlink.

• Reliability – DSL links are only as reliable as the copper pairs providing them. Much of the copper access network in the UK is old and may be corroded and suffer from water leakage.

• Local Availability – Copper pairs are not available everywhere. They are typically present at houses and buildings, not towers or street-lamps where base stations may be located.

DSL’s strength lies in its low cost. Where it is available and meets the technical performance requirements of backhaul networks, it will be an obvious choice of technology. It’s weaknesses in capacity vs. range, reliability and location of copper pairs mean that it will not always be easily available.


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4.5 WIMAX

4.5.1 General Usage

WiMAX comes in two main forms:

• Fixed WiMAX (IEEE 802.16-2004), which was developed for fixed access services, PtP and PtMP backhaul.

• Mobile WiMAX (IEEE 802.16e-2005), which was developed for mobile access services.

WiMAX deployments are generally point-to-multipoint, with sectored base stations serving a wide area. Point-to-point configurations are possible, but uncommon.

There are some small deployments of Fixed WiMAX technology in the UK (Pipex recently announced a commercial deployment in Milton Keynes). These networks are primarily aimed at delivering end-user services to residential and business customers.

Mobile WiMAX is still being standardised and operating spectrum for mobile WiMAX services is not currently licensed in the UK. While Mobile WiMAX can also be used to deliver fixed services, such as backhaul, in practice it is expected that this spectrum will be primarily used to deliver end-user access services.

There is no use of WiMAX for backhaul networks in the UK today.


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Range Good in PtP configuration, Reasonable in PtMP configuration – Up to 50 km, but increasing range reduces link capacity.

Capacity Poor - Theoretically up to 70 Mbit/s, but with a 20 MHz channel over a short range. Practical data rates over longer distances and with smaller channel bandwidths will be proportionally lower.

Channel bandwidths of 1.75 MHz, 3.5 MHz, 5 MHz, 7 MHz, 10 MHz and 20 MHz are supported.

Reliability Good – as good as PtP or PtMP microwave.

Cost Equipment prices should be relatively low given WiMAX standardisation. However, spectrum is likely to be quite expensive as WiMAX is primarily aimed at providing high-value end-use services.

Fixed WiMAX has operating profiles for 2.4 GHz, 3.5 GHz and 5.8 GHz. Mobile WiMAX’s operating profile is at 2.5 GHz.

Local Availability Suitable for backhauling tower-mounted macro-base stations.

Not very suitable for street-level micro- and pico-base stations. Low-frequency spectrum can operate in a NLOS environment, but capacity may be limited for future traffic volumes. High-frequency LOS spectrum cannot operate in a NLOS environment.

Speed of Rollout Good.

Table 15: Technical Characteristics of WiMAX


WiMAX is a recently developed technology that is technically advanced. It uses Adaptive Modulation and Coding (AMC) to deliver high data rates in good propagation conditions. Adaptive Antenna Systems (AAS) are an option within the standards that provide range increases for sectorised antennas.

Given that Mobile WiMAX in particular is still being standardised and deployments are unlikely to be seen before end-2007, there are no future developments foreseen for Mobile WiMAX beyond proving the technology and standards work in commercial deployments.


WiMAX is not currently used in backhaul networks and is very unlikely to be a major player in the future backhaul market.

Strengths:

• Good operating range.

• Operates in NLOS spectrum, providing good coverage and range.

• International standardisation and industry support should see relatively cheap equipment.

• Technically advanced, delivering good spectral efficiency.


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Weaknesses:

• Expensive and limited spectrum, likely aimed at end-user services and not the backhaul market.

• Capacity is low compared to optical fibre or PtP microwave.

WiMAX’s strengths lie in delivering service in NLOS environments over a reasonable range. Its weaknesses for backhaul lie in its low capacity for future backhaul purposes.


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4.6 FREE SPACE OPTICS

4.6.1 General Usage

Free Space Optics (FSO) is not a widely used technology in the UK. A typical use is to connect buildings over short distances where line-of-sight (LOS) can be guaranteed (e.g. connecting buildings on a business park). High data-rate transmission links can be supported in this way.

FSO uses lasers to transmit data in the terahertz spectrum range, therefore strict LOS conditions are needed.

FSO is not currently used in any backhaul networks by wireless operators in the UK.


Range Very poor – practical link ranges are restricted to less than 1 km.

Capacity Excellent – data rates up to 10 Gbit/s can be supported.

Reliability Very poor – FSO link transmission is effectively cut off by fog and is massively reduced by rain, reducing link reliability below levels acceptable to cellular operators today.

Cost Good – equipment is not expensive and relatively small, reducing cost of installation and site rental.

Local Availability Easily deployed anywhere, but requirements for strict LOS limit practical uses.

Speed of Rollout Very good.

Table 16: Technical Characteristics of Free-Space Optics


There is some speculation within the industry that FSO might have a role to play in backhaul networks through its use in parallel with another technology (e.g. cheap microwave links) to give high capacity and reliability with low cost.

Beyond this speculation, no specific future developments for FSO have been identified.


FSO is not currently used to backhaul wireless communications networks and is very unlikely to be a major player in the future. Its strengths and weaknesses can be summarised as follows:

Strengths:

• Very high capacity

• Low cost

• Speed of deployment

Weaknesses:


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• Low range

• Poor reliability, completely cut off by fog

FSO’s weaknesses mean that it simply does not meet the technical performance requirements of backhaul networks. Therefore, its strengths never come into play.


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4.7 SATELLITE

4.7.1 General Usage

Satellite is primarily used for broadcast services in the UK, taking advantage of its large footprint and relatively low capacity. Use of satellite for two-way, individual telecommunications is typically restricted to very remote areas (e.g. oil platforms in the North Sea) and to low data rates.

Satellite is not used at all in backhaul networks today.


Range Excellent – satellite footprints cover the entire UK.

Capacity Very poor

Reliability Good

Cost Very expensive

Local Availability Generally excellent, but not very suitable for use to street-level micro-base stations and not at all for indoor base stations.

Speed of Rollout Good, assuming the satellite resources are already available.

Table 17: Technical Characteristics of Satellite


The advent of mobile TV could see a role for satellite in providing the final link to the base station, as this service plays into the strength of satellite in delivering broadcast services over a very wide area.


Satellite does not play any role in backhaul networks in the UK today and is very unlikely to have any significant role in the future.

Strengths:

• Range – able to serve the most remote areas.

• Good support for broadcast services over a wide area.

• Good speed of deployment

Weaknesses:

• Very low capacity for individual end-user services.

• Very expensive

The weaknesses of satellite mean that it does not meet the performance requirements for backhaul networks in the UK and so will never be a major driver.


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4.8 POWER-LINE COMMUNICATIONS

4.8.1 General Usage

Power-Line Communications (PLC) has been around for many years, but is virtually unused in the UK. It’s most common use is to provide communications inside a house by transmitting data over the electrical wiring and accessing the data by plugging into the power sockets.

There is no use of PLC in any backhaul networks in the UK.


Range Poor – limited by the location of the nearest transformer.

Capacity Good at very short distances (>20m), but poor over longer distances (>100m)

Reliability Poor – PLC provides an inherently very noisy environment.

Cost Unknown

Local Availability Poor – limitations on range and location of nearest transformer mean that setting up a link between any two useful points is very difficult.

Speed of Rollout Poor

Table 18: Technical Characteristics of Power-Line Communications


No one in the UK wireless communications industry even mentioned PLC during the industry interviews carried out for this report until prompted.


PLC is not used at all in backhaul networks today and is very unlikely to have any role in the future. Its strengths and weaknesses can be summarised as follows:

Strengths:

• Useful capacity over very short distances.

• General availability of power sockets within a house to provide connection points.

Weaknesses:

• Poor capacity over longer distances.

• Poor reliability.

• Limited by location of nearest transformer, meaning setting up an end-to-end link between any two points is difficult.

PLCs weaknesses mean that it does not meet the performance requirements for backhaul networks and its strengths are not particularly relevant.

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5. FUTURE SCENARIOS

This section looks at the potential impact and implications of future scenarios for backhaul networks. It identifies how future use of wireless communications may develop over the next 10 to 20 years and what requirements this will place on backhaul networks. This is used to compare against the analysis of Section 1 that looks at the more predictable evolution of backhaul technologies. The purpose is to see whether the evolution of existing backhaul technologies is likely to be able to support these future requirements, or whether there is a discontinuity between those future requirements and the ability of technologies to support them.

The following sub-sections cover:

• An overview of future drivers that will drive wireless telecoms usage.

• A description of different scenarios that can be identified from these drivers and their impact on wireless traffic.

• A summary of the known current network load and medium-term potential network capacities.

• The impact of these scenarios on potential base station deployments (density and capacity) and future backhaul networks.

• Conclusions on which technologies are likely to have a significant role in supporting these future scenarios.

5. Future Scenarios

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5.1 FUTURE DRIVERS OF WIRELESS TELECOMS USAGE

This section looks at what drivers at a personal, social and technology level will affect future use of wireless communications.

5.1.1 Personal / Life-Style Drivers

These are drivers based around how people will choose to live their lives and what preferences they have. Driver Effect

Willingness to pay & Value-for-money

People have limited money to spend, this may lead to tiered service levels.

Work / Life fusion & balance

No offices, home-working, merging of work and personal data and communications.

Personalisation & individualism

Individual content desired, reduction in broadcast and increase in unicast / multicast.

Shared & user-generated content

A huge increase in sources of data, greater specialisation in content accessed, closed user groups and communities

Automation of daily life Standard chores and data-checking carried out automatically

Information to/from cars The car as entertainment / data hub

Table 19: Personal / Life-Style Drivers

5.1.2 Externally-Imposed / Anxiety Drivers

These drivers are based around the impact of external activities or events on individuals, both imposed from outside and the individual’s perception of and reaction to them. Driver Effect

Personal safety & anxiety The need for security and authentication – driven as much by individual anxiety as imposed by outside organisations (e.g. government, insurance companies), protection and proof of id and personal data.

Privacy Protection of individual data and identity

Health & safety Concern over personal health & safety, how to monitor and check

Government Imposition of information and data requirements on the individual

Information to/from cars Intelligent transport

Table 20: Externally-Imposed / Anxiety Drivers

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5.1.3 Social Changes / Drivers

Changes in society as a whole will also have impacts on wireless usage. These drivers reflect changes in culture across large groups of people. Driver Effect

Breakdown & change of family structure

Dispersed families, increased mesh of relationships to maintain.

Maintaining virtual relationships

Virtual friends you’ve never met in person.

Social inclusion Equal access available to all people wherever they are.

Ageing consumers Increasing proportion of population are older and not so technically literate.

Distribution channels for goods

Traditional channels are migrating to the Internet.

Table 21: Social Changes / Drivers

5.1.4 Technology Drivers

Finally, advances in technology itself will drive changes in future wireless communications. Driver Effect

Device technology Improvements in display, memory, usability and multimedia delivery.

Thin clients & centralised applications

Balance local vs. central storage, potential for increase in communications needed.

Cashless society Minor and major transactions carried out without cash or cards

New services Location-based services, TV to phones, Push content, etc, will all drive new use of wireless services.

Table 22: Technology Drivers

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5.2 USAGE SCENARIOS

From the drivers identified in Section 5.1 above, five different scenarios are identified for future telecoms usage:

• All-You-Can-Eat Society

• Entertainment Society

• The Interactive society

• The Governed Society

• Stay-As-Is Society

The following sub-sections provide an overview of these scenarios, their key drivers and the predicted impact on traffic volumes generated.

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5.2.1 Scenario 1 – “All-You-Can-Eat Society”

This scenario is based on the premise that future wireless communications will be like using broadband at home today. Users will have “all-you-can-eat” access, will break down the traditional barriers between work and home, and full access to your own data, wherever it is (on your own / hosted / work server, etc.)

The main drivers behind this are:

• Willingness to Pay & Value-for-money

• Personalisation & individualism

• Shared & user-generated content

• Automation of daily life

• Social inclusion

• Device technology

• Thin clients & centralised applications

This will see a huge increase in data volumes generated and consumed by the individual, which will be taken for granted and used by default. However, the service offering is still set by the service provider, this possibly restricts capacities (e.g. excluding VOD).

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This sees a ~350 times increase over today’s offered traffic, with total traffic for the UK of 4,200 Gbit/s, dominated by the upload & download of work and personal data. This is based on predicted traffic volumes shown in the table below: Activity Usage

Automation of daily life Average: 10 MByte/day/person

• Background data, effectively machine-to-machine

Work & personal life Average: 150 MByte/day/person

• Upload & download of work & personal data, use of thin clients, synchronising of data, etc. Could be highly asymmetric at any one time. Effectively person-to-machine or machine-to-person.

• Assumes:

− 10M users @ 500 MByte/day



− 5 busy hours a day

Personal Communications

Average: 40 mE/person

• Assuming all video-telephony @ 100kbit/s

Table 23: “All-You-Can-Eat Society” Traffic Volumes

5.2.2 Scenario 2 – “Entertainment Society”

This scenario sees individualised entertainment services delivered to wireless users as the norm. These services will be delivered to people, not places, providing entertainment on the move. Handheld TV will be a mass-market service, with Video-on-Demand (VoD) to mobile users, delivered seamlessly with other channels.



• Shared & user-generated content

• Information to cars – the car as entertainment / data hub

• Maintaining virtual relationships

• Distribution channels for goods

• Device technology

This will result in a huge increase in demand for personalised entertainment, with much greater specialisation and distribution of sources and destinations. It would see the biggest bandwidths, with users setting the agenda and potentially highly asymmetric and sustained high data rates.

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This sees a ~3,000 times increase over today’s offered traffic, with total traffic for the UK of ~35,000 Gbit/s, dominated by Video-on-Demand. This is based on predicted traffic volumes shown in the table below: Activity Usage

Video-on-Demand Average: 2 hours/day/person @ 2 Mbit/s

• Individually streamed HDTV (travelling, at work, at home) to 75% of population, spread over 6 busy hours a day.

Audio Average: 2 hours/day/person @ 128 kbit/s

• Hi-fi quality audio streamed (travelling, at work, at home) to 75% of population, spread over 15 hours.

Broadcast Average: 600 Mbit/s per key site

• 64-QAM Digital TV transmission over 96 MHz from 60 key sites across the UK

Other activities already described in Scenario 1

Automation of daily life, upload & download of work and personal data, interpersonal communications.

Table 24: “Entertainment Society” Traffic Volumes

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5.2.3 Scenario 3 – “The Interactive Society”

This scenario suggests that society develops much higher levels of interactivity, with interactive games, virtual friends and full situational awareness of where friends are (e.g. MySpace / LinkedIn).



• Personal safety & anxiety

• Privacy – while highly interactive, need to choose who & how to interact

• Breakdown & change of family structure

• Maintaining virtual relationships

• Location-based services

This will see a massive increase in communications to establish and maintain relationships, much greater awareness of context and situation included and taken for granted. The traffic generated will be reasonably symmetric with requirements for very low latencies.

This sees a ~500 times increase over today’s offered traffic, with total traffic for the UK of ~6,000 Gbit/s, dominated by Interactive Gaming. This is based on predicted traffic volumes shown in the table below: Activity Usage

Interactive gaming Average: 2 hours/day/person @ 1 Mbit/s

• High quality video, to 25% of population, spread over 6 hours a day

Video calling Average: 80 mE/person @ 200 kbit/s

• Very high use of video calling, group calling, plus context information included (location, presence)

Context signalling Average: 0.5 MByte/hour/person

• Constant signalling of a person’s context (location, presence, privacy preferences, etc) to the network to support interactivity of services

Table 25: “The Interactive Society” Traffic Volumes

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5.2.4 Scenario 4 – “The Governed Society”

This scenario suggests wireless delivery of “big” central services (e.g. health, tax, insurance, education, road charging, etc) imposed by the government.

Drivers:

• Personal safety & anxiety

• Privacy

• Health & safety

• Information to/from cars – intelligent transport

• Social inclusion

• Thin clients & centralised applications

• Cashless society

This will see big centralised IT systems, with a huge numbers of small transactions. Emergent behaviour will see users take up services because it makes things easier or cheaper (e.g. lower health insurance if you have your health monitored).

This sees a ~70 times increase over today’s offered traffic, with total traffic for the UK of ~840 Gbit/s, dominated by Education services. This is based on predicted traffic volumes shown in the table below: Activity Usage

Education Average: 100 MByte/day

• Delivery of education material to 20% of population, spread across 5 hours.

Personal monitoring Average: 10 KByte every 30 secs

• Monitoring health, location, transactions, etc of 100% of population. Lots of small transactions, but effectively machine-to-machine raw data.

Intelligent transport Average: 10 KByte every 30 secs

• Monitoring speed, location, congestion, road charging, etc. for ~40M vehicles. Again, lots of small transactions, but effectively machine-to-machine raw data.

Table 26: “The Governed Society” Traffic Volumes

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5.2.5 Scenario 5 – “Stay As-Is Society”

This scenario suggests that people retrench to a simpler life style, using technology as an enabler, rather than being driven by it. We no longer live in a gadget society and follow a greener, environmentally-friendly life style. An aging population is not so tech-savvy.

Although valid, this is not a scenario that will push the envelope for telecoms usage and therefore is not considered further.

5.2.6 Impact on Overall Traffic

These scenarios represent a huge increase compared to today’s traffic. Today’s GSM networks in the UK are dominated by simple voice, with a total peak load of 12 Gbit/s generated across all networks (assuming voice (~10kbit/s) @ 20mErlang/sub in Busy Hour (BH), with ~60M subscribers). Scenario National Offered

Traffic (Gbit/s) Average Traffic

per Person (kbit/s)

Normalised Traffic

Increase

Main Driver of Traffic

GSM today 12 0.2 1 Voice

All-You-Can-Eat

4,200 70 350 Upload & download of work and personal data

Entertainment 35,000 583 2,917 Video-on-Demand

Interactive 6,000 100 500 Interactive Gaming

Governed 840 14 70 Education services

Table 27: Growth in National Traffic based on Future Scenarios

Note that average traffic per person in the table above is calculated assuming a UK population of 60 million people.

This table shows that it is not difficult to envisage traffic volumes growing by up to 500 times, and perhaps even up to 3,000 times if very high data rate individualised services (e.g. Video-on-Demand) really achieve mass-market success.

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5.3 MOBILE NETWORK CAPACITY

Whereas Sections 5.1 and 5.2 above have focused on users and traffic generated, this section looks at wireless access technologies and considers what capacities they can offer.

5.3.1 Increases in Mobile Network Capacity

3G LTE has the potential for a ~100 x increase in capacity over GSM today, as shown in the table below. Such future cellular networks will deliver increases in capacity/cell through:

• Use of more spectrum

• Better spectral efficiency

• Better frequency re-use

Technology Spectrum Spectral Efficiency (bits/s/Hz)

Frequency Re-Use

Capacity per Cell (Mbit/s)(1)

Normalised Capacity Increase

GSM 110 MHz 0.384(2) 1/9 4.7 1

HSDPA 130 MHz 1.1 1 143 30

3G LTE 240 MHz(3) 1.93 1 456 97

Table 28: Potential Growth in Mobile Network Capacity

This table assumes that:

• 2 x 240MHz FDD mobile spectrum available in the UK: − GSM has 2 x 35MHz in 900MHz band, 2 x 75MHz in 1800MHz band − UMTS has 2 x 60MHz in 1900MHz band, 2 x 70MHz in 2.5GHz band

• (1) All spectrum is available to the cell (i.e. considering national capacity and ignoring how spectrum may be divided among operators)

• (2) GSM in practice predominantly delivers 9.6 kbit/s voice

• (3) 3G LTE will re-use GSM spectrum as well as 3G spectrum

5.3.2 Increasing Base Station Density

Further increases in geographic capacity (i.e. capacity/km2) can be delivered through increasing the BTS density (e.g. micro- or pico-BTSs).

Four main types of base station (BTS) deployments are considered to meet the demands of the preceding future scenarios:

• Cellular macro-BTS

3 3GPP TR25.814 v.7.1.0 Table 8.1.2.2.2.2-2, average of downlink performance results

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• Cellular micro-BTS

• Cellular pico-BTS

• WiFi pico-BTS

This follows from Section 2.1, which concluded that cellular and WiFi networks will dominate future wireless communications.

Within these deployment types, it is assumed that:

• Macro-cells are the only option for national coverage.

• Micro- and pico-cell deployments are used for urban coverage only. − Micro-cells will be predominantly outdoors, while pico-cells will be deployed

both indoors and outdoors. Both will be below roof-level.

• WiFi pico-BTSs are assumed to deliver up to 150 Mbit/s to the end-user − Based on current 802.11n standards, with an average cell over-the-air data

rate of ~300 Mbit/s, but with average end-user cell capacity of roughly half that due to MAC and PHY overheads (in line with overheads experienced on 802.11 a/g today).

Due to their smaller cell size, micro- and pico-BTSs can deliver greater capacity in the same area as a macro-BTS. The table below shows the geographic capacity (capacity per cell divided by cell area) for the different deployment types and illustrates how much greater capacity per km2 is delivered by micro- and pico-BTSs. Area Type Deployment Type Capacity

per cell (Mbit/s)(1)

Typical Cell Range (m)

Cell Area (km2)

Geographic Capacity

(Mbit/s/km2)

Rural Cellular Macro-BTS 456 4500 21.2 22

Suburban Cellular Macro-BTS 456 900 0.848 540

Cellular Macro-BTS 456 400 0.168 2,700

Cellular Micro-BTS 456 100 0.0314 15,000

Cellular Pico-BTS 456 20 0.0013 360,000 Urban

WiFi Pico-BTS 150 40 0.0050 30,000

Table 29: Geographic Capacity of different Base Station Deployment Types

• (1) Assuming 3G LTE for cellular capacity and all spectrum is available to the cell (i.e. considering national capacity and ignoring how spectrum may be divided among operators).

• For calculating cell area, macro-BTSs are assumed to have 3 sectors (or cells) per BTS, micro- and pico-BTSs have only 1 sector (or cell) per BTS.

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5.4 CAN THE DEPLOYMENT TYPES SUPPORT EACH SCENARIO?

This section brings together both the offered traffic volumes predicted by the different scenarios and the offered capacity of the different base station deployment types of the previous sections. By using typical population densities for different area types, it is possible to compare the offered traffic with the offered capacity in each area type.

The population densities that can be supported by each deployment type can be calculated based on:

• The traffic generated per person by each scenario

• The cell area and capacity for each deployment type

These can then be compared against typical population densities for different area types as shown in the table below: Area Type Population Density

(People/km2)

Urban 9,000 Population density of Inner London - 2.86M people in 319 km2

Suburban 2,000 Population density of Bromley (outer London) - 300K people in 150 km2

Rural 240 Population density of Mid Bedfordshire - 122K people in 503 km2

Table 30: Typical Population Densities of different Area Types

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5.4.1 Offered Traffic vs. Offered Capacity for different Scenarios and Deployment Types

The table below takes the traffic per person for each scenario from Section 5.2.6 and compares it to the geographic capacity offered by each deployment type from Section 5.3.2. This allows the calculation of the population density that can supported for each combination of scenario and deployment type.

• For example: − The All-You-Can-Eat scenario generates 70 kbit/s per person − A rural macro-cell provides a geographic capacity of 22 Mbit/s/km2 − 22 Mbit/s divided by 70 Kbit/s = 307 − This means up to 307 people per km2 can be supported by a rural macro-cell

for this scenario (as shown in the top left-hand green cell in the table below). − This figure is greater than the typical population density for a rural area of 240

people/km2, so in this case the deployment type can support the scenario.

The table below shows the potential population densities supported by each deployment type for each scenario and compares it against the typical population density for that area type.

• Red indicates that the required population density from the previous slide cannot be supported by that deployment type, green indicates that it can.

All-You-Can-

Eat Entertainment Interactive Governed

Total Offered Traffic (Gbit/s) 4,200 35,000 6,000 840

Traffic per Person (kbit/s) 70 583 100 14

Geographic Capacity

(Mbit/s/km2)

Required Population

Density Potential Population Density supported (People/km2)

Rural macro-cell 22 240 307 37 215 1,540

Suburban macro-cell 540 2,000 7,680 922 5,380 38,400

Urban macro-cell 2,700 9,000 38,900 4,670 27,200 194,000

Urban micro-cell 15,000 9,000 207,000 24,900 145,000 1,040,000

Urban pico-cell 360,000 9,000 5,180,000 622,000 3,630,000 25,900,000

WiFi pico-cell 30,000 9,000 426,000 51,200 298,000 2,130,000

Table 31: Potential Population Densities supported by different Deployment Types

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The second table below shows essentially the same information as the previous slide, but this time in terms of the factor by which a given deployment type can support the typical population density for an area type and the offered traffic for the different scenarios.

For example:

• From the table above, a rural macro-cell can support up to 307 people/km2 for the All-You-Can-Eat scenario.

• The typical population density for a rural area is 240 people/km2.

• 307 divided by 240 equals 1.28

• This means that for this particular combination of scenario and deployment type, the offered capacity exceeds the offered traffic by a factor of 1.28 (as shown in the top left-hand green cell in the table below).

All-You-

Can-Eat Entertainment Interactive Governed

Total Offered Traffic (Gbit/s) 4,200 35,000 6,000 840

Traffic per Person (kbit/s) 70 583 100 14

Geographic Capacity

(Mbit/s/km2)

Required Population

Density Potential Over-Capacity Factor Possible

Rural macro-cell 22 240 1.28 0.15 0.90 6.40

Suburban macro-cell 540 2,000 3.84 0.46 2.69 19.2

Urban macro-cell 2,700 9,000 4.32 0.52 3.02 21.6

Urban micro-cell 15,000 9,000 23.0 2.76 16.1 115

Urban pico-cell 360,000 9,000 576 69.1 403 2,880

WiFi pico-cell 30,000 9,000 47.4 5.68 33.2 237

Table 32: Potential Over-Capacity Factors for different Deployment Types

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5.5 REQUIRED BACKHAUL CAPACITY

This section looks at the offered traffic per base station for each scenario and uses it to assess what the required backhaul capacity is for each combination. For this, it is important to realise that backhaul capacity depends on offered traffic, not theoretical BTS capacity.

In practice, not all the available spectrum will be used at a single BTS. We assume that:

• The UK is likely to have 6 cellular operators, each with separate backhaul.

• A single WiFi operator is assumed, following the model of the Metro-WiFi network where the city or town invests in its own infrastructure.

This results in the average offered traffic per operator’s BTS as shown in the table below. Also shown in brackets is the predicted required backhaul capacity to serve the offered traffic. All-You-Can-

Eat Entertainment Interactive Governed

Average Users/BTS

Average Offered Traffic per BTS - Mbit/s

(Instantaneous Backhaul Capacity required per BTS – Mbits) Rural macro-BTS

2,545 180 (180) 1,500(228) 250 (228) 36 (40)

Suburban macro-BTS

848 59 (80) 490 (228) 85 (80) 12 (20)

Urban macro-BTS

754 53 (80) 440 (228) 75 (80) 11 (20)

Urban micro-BTS

47 3.3 (30) 28 (60) 4.7 (30) 0.7 (10)

Urban pico-BTS

2 0.1 (20) 1.1 (30) 0.2 (20) 0.0 (10)

WiFi pico-BTS

45 3.2 (30) 26 (60) 4.5 (30) 0.6 (10)

Table 33: Average Offered Traffic per Base Station

In the table above:

• Average users/BTS is calculated as the BTS area served (from Section 5.3.2) multiplied by the typical population density for that area type (from Section 5.4). − For example, a rural macro-BTS with three sectors serves 3 x 21.2 km2 = 63.6

km2. The typical population density for rural areas is 240 people/km2. We assume 6 equal operators, each with a subscriber density of 40 people/km2. So a rural macro-BTS typically serves 63.6 x 40 = 2,545 users.

• Average offered traffic per BTS is calculated as the average number of users/BTS multiplied by the average traffic per person for that scenario. − For example, a rural macro-BTS serves 2,545 users on average. For the All-

You-Can-Eat scenario, each user generates 70 kbit/s on average. So a rural macro-BTS has an average offered traffic of 2,545 x 70 kbit/s = 180 Mbit/s.

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• Where offered traffic is high (e.g. for macro-BTSs), the required backhaul is set to match the offered traffic.

• Where offered traffic levels are low (e.g. for for micro- and pico-BTSs), backhaul capacities are set by the need to support a useful number of simultaneous users of the highest data-rate services (e.g. 2 Mbit/s for VoD in the Entertainment scenario, 1 Mbit/s for Interactive Gaming in the Interactive Scenario). − In practice, this is effectively a judgement call rather than a formal

dimensioning exercise. The averaging effects of looking at population densities breaks down to some extent when looking at small cell areas and the variations in actual user numbers and offered traffic volumes become proportionally higher. This is reflected in setting backhaul capacity requirements that also proportionally higher than the average offered traffic.

• Where the offered traffic exceeds network capacity for macro-BTSs, the backhaul requirements are limited to 228 Mbit/s, which is the limit of the BTS air interface (assuming a maximum of 40 MHz per operator and the spectral efficiency of 3G LTE from Section 5.3.1).

5.5.1 Key Points

Key points from the preceding tables are that:

• Typical macro-cell deployments will not deliver the capacity required for the Entertainment scenario in any area type without large increases in BTS density − The Interactive scenario would require a slightly denser BTS deployment to

support the data rates and population densities required in rural areas. − Macro-cells could provide national coverage (rural, suburban and urban) for

either the All-You-Can-Eat or the Governed scenarios without reducing typical cell sizes.

• In metropolitan areas, micro-cellular coverage is capable of supporting all four scenarios, even the Entertainment society

• Pico-BTS coverage (either cellular or WiFi) can easily support all scenarios in urban environments. − To support the Entertainment scenario, cellular pico-BTSs would average

offered traffic of only 1 Mbit/s, WiFi pico-BTSs would average ~26 Mbit/s. Either is significantly below the maximum BTS capacity available.

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5.5.2 Backhaul Requirements – Working Assumptions

From the previous section, we take the following backhaul requirements:

High (Mbit/s) Medium (Mbit/s) Low (Mbit/s)

Rural Cellular Macro-BTS 228 180 40

Suburban Cellular Macro-BTS 228 80 20

Cellular Macro-BTS 228 80 20

Cellular Micro-BTS 60 30 10

Cellular Pico-BTS 30 20 10 Urban

WiFi Pico-BTS 60 30 10

Table 34: Future Backhaul Requirements by Scenario

• High equates primarily to the Entertainment scenario − This can be limited by the maximum potential BTS capacity, as opposed to the

potential offered traffic)

• Medium generally equates to the All-You-Can-Eat and Interactive scenarios

• Low equates to the Governed scenario

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5.6 THE ABILITY OF TECHNOLOGIES TO MEET THE BACKHAUL REQUIREMENTS

This section considers the ability of different technologies to support the backhaul requirements for the different high / medium / low scenarios derived in Section 5.5.2 above for each deployment type.

It provides a qualitative assessment of how applicable and suitable each technology is based on a combination of technical, logistical and cost considerations. The key to the assessment is as follows: Score Level of Suitability

● The technology is entirely suitable – it provides appropriate capacity, range & reliability, it’s easy to deploy and provides at least a reasonable cost.

◕ The technology is mostly suitable – it meets most of the technical, logistical and cost considerations, but at least one of these criteria is only just acceptable.

◑ The technology could be used, but is not ideal and might not be the first choice – it meets some of the technical, logistical and cost requirements, but fails to meet others.

◔ The technology is largely unsuitable – it fails to meet the majority of the technical, logistical and cost considerations.

○ The technology is not suitable – it is not an appropriate technology to provide the backhaul for that combination of scenario and deployment type.

Table 35: Key to Qualitative Assessment of Technologies

Building on the conclusions from Section 3.2, we only consider here those technologies that were identified as likely to play a major role in future backhaul networks. These are:

• Optical Fibre

• DSL

• PtP Microwave

Note that for this section we split PtP Microwave into two categories:

• PtP Microwave – the traditional configuration today of single point-to-point links.

• Meshed PtP Microwave – a future configuration combining mesh techniques with multiple point-to-point hops that could be used to backhaul street-level micro- and pico-base stations in an urban environment.

This allows us to consider separately how future developments in mesh radio techniques could change the suitability of PtP microwave to support backhaul in urban environments in particular.

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5.6.1 Macro-BTS Deployment

PtP Microwave will be the preferred option for the final link to macro-BTSs. It will be capable of delivering the capacities required, will avoid the logistical problems of digging in fibre and allows operators to own and operate their own network (avoiding the ongoing operating costs of leased line solutions). High Med Low Technology Comment

◑ ◑ ◑ Optical Fibre

Fibre is likely to progressively push out from the core, increasing the number of fibre PoPs and reducing the average link distance to the nearest BTS.

It will continue to be limited by the cost and time needed to dig the final 50m to 200m.

◕ ◕ ● PtP Microwave

Can deliver up to STM-4 (622 Mbit/s) today. Suitable for the LOS environment with macro-BTSs. High capacity per BTS will limit daisy-chain and ring topologies due to capacity overhead.

There wlll be an impact on spectrum management and planning, with much greater capacity per link required compared to today’s norms.

○ ○ ○ Meshed PtP Microwave

Mesh networks unlikely to be useful in macro-BTS deployments, where LOS is available and BTS density will not be so high.

○ ◔ ◑ DSL xDSL technologies will struggle to deliver such capacities (80 – 228 Mbit/s) over useful distances for the high and medium scenarios, but would be suitable for the low scenario (20 – 40 Mbit/s).

Table 36: Suitability of Backhaul Technologies to Macro-BTS Deployment

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5.6.2 Micro-BTS Deployment

PtP Microwave will be the preferred option for the final link to micro-BTSs if combining it with limited mesh topologies can help it operate in NLOS environments. DSL will be a real alternative where it is available. However, both DSL and optical fibre may have logistical problems in getting the connection to the BTS, while operators may also wish to avoid the operating costs of leased line solutions. High Med Low Technology Comment


Fibre is likely to progressively push out from the core, increasing the number of fibre PoPs and reducing the link distance to the nearest BTS. Again, fibre will continue to be limited by cost and time required to dig the final 50m to 200m.

◔ ◔ ◔ PtP Microwave

Capacity should not be an issue. The NLOS environment will be an issue – the use of planned rings and daisy-chains to get back to a fibre PoP via a small number of hops could help this, but would be very difficult to manage.

Big impact on spectrum management and planning, with much greater capacity per link and a big increase in the number of links required compared to today’s standards.

◕ ◕ ◕ Meshed PtP Microwave

Limited mesh networks may have a role to play in backhauling micro-BTSs back to fibre PoPs via a small number of hops.

◑ ◑ ◑ DSL xDSL technologies will be able to deliver such capacities (10 – 60 Mbit/s) over useful distances, but may still be limited by BTSs typically being located on street lamps and not buildings, where copper pairs are present.

Table 37: Suitability of Backhaul Technologies to Micro-BTS Deployment

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5.6.3 Cellular Pico-BTS Deployment

DSL will be the preferred option for the final link to indoor pico-BTSs. PtP Microwave will be the preferred option for outdoor pico-BTSs, if combining it with mesh topologies can help it operate in NLOS environments. Optical fibre may be too costly for the final link to pico-BTSs. Also, operators may wish to avoid leased line solutions (such as DSL and optical fibre) and opt for microwave where possible. High Med Low Technology Comment


Fibre is likely to progressively push out from the core, increasing the number of fibre PoPs and reducing the link distance to the nearest BTS. Again, fibre will continue to be limited by cost and time required to dig the final 50m to 200m.


Capacity should not be an issue, but PtP will be limited by the NLOS environment and the likely deployment of BTSs both indoors and outdoors. The use of rings and daisy-chains to get back to a fibre PoP via a small number of hops could help in the NLOS environment, but the density of links will be very difficult to plan.


Mesh networks should have a role to play in backhauling pico-BTSs back to fibre PoPs via a small number of hops. The ad-hoc deployment of pico-BTSs could also benefit from auto-configuring mesh networks, rather than planned ring or daisy-chain topologies.

◕ ◕ ◕ DSL xDSL technologies will be able to deliver such capacities over useful distances. Indoor deployments may easily be connected via copper pair, but outdoor pico-cells may still be limited by typically being located on street lamps, where copper pairs are not present.

Table 38: Suitability of Backhaul Technologies to Cellular Pico-BTS Deployment

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5.6.4 WiFi Pico-BTS Deployment

DSL will be the preferred option for the final link to indoor pico-BTSs. PtP Microwave will be the preferred option for outdoor pico-BTSs, if combining it with mesh topologies can help it operate in NLOS environments. Optical fibre may be too costly for the final link to pico-BTSs. Also, operators may wish to avoid leased line solutions (such as DSL and optical fibre) and opt for microwave where possible. High Med Low Technology Comment


Fibre would be ideal for the capacity required, but will continue to be limited by cost and time required to dig the final 50m to 200m.


Capacity should not be an issue, but PtP will be limited by the NLOS environment and the likely deployment of BTSs both indoors and outdoors. The use of rings and daisy-chains to get back to a fibre PoP via a small number of hops could help in the NLOS environment, but the density of links will be very difficult to plan.


Mesh networks could have a big role to play in backhauling WiFi networks. The ease of “plug-and-play” installation of BTSs would be helped by suitable auto-configuration capabilities. Capacity overheads may be a problem unless the number of hops can be limited.

◑ ◕ ◕ DSL xDSL technologies will be able to deliver such capacities over useful distances. Indoor deployments may easily be connected via copper pair, but outdoor pico-cells may still be limited by typically being located on street lamps, where copper pairs are not present.

Table 39: Suitability of Backhaul Technologies to WiFi Pico-BTS Deployment

5. Future Scenarios

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5.6.5 Backhaul Requirements – Preferred Options

The preferred technology options for the different deployment types against the different scenarios (High / Medium / Low) are summarised in the table below.

• Other potentially suitable technologies are shown in brackets that would act as backup options where the preferred option is not available or suitable.

High Medium Low

Rural Macro-BTS PtP Microwave

(Optical Fibre)

Suburban Macro-BTS

Macro-BTS

PtP Microwave

(Optical Fibre) PtP Microwave

(DSL, Optical Fibre)

Micro-BTS Meshed PtP Microwave

(DSL, Optical Fibre)

Pico-BTS

Urban

WiFi Pico-BTS

Outdoors – Meshed PtP Microwave

Indoors – DSL

Table 40: Preferred Backhaul Technologies for different Deployment Types

In the table above:

• Green = Technically feasible now

• Amber = On technology roadmaps

• Red = Technical development needed

This is because PtP Microwave and Optical Fibre are suitable today and capable of supporting the traffic volumes required. DSL will need to support higher data rates than today’s ADSL, but this is on the DSL roadmap (through ADSL2+, VDSL and VDSL2). Meshed PtP Microwave is not on any specific roadmap, but it is clear that developments towards this are likely in the coming years.

5.6.6 Backhaul Conclusions

Whatever the scenario, wireless technologies will be able to deliver the individual link capacities required, even to large macro-BTSs.

• It is unlikely that optical fibre will have to be used direct to the majority of BTSs.

The final link from the BTS is likely to become significantly shorter as optical fibre progressively pushes further out from the core network, increasing the number of fibre PoPs to which to backhaul.

• This will make microwave more feasible in the final link to the BTS as these have to deliver higher capacity and may have to operate at higher frequencies.

• Dramatic increases in BTS capacity will make daisy-chain or ring topologies difficult to support using wireless solutions due to the capacity overheads required.

5. Future Scenarios

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Mesh radio may have a big role to play with micro- and pico-BTS deployments where a small number of hops may be needed to connect back to a fibre PoP or aggregation point.

• If mesh radio needs to use licensed PtP spectrum for capacity purposes, this may require a different approach to spectrum licensing to allow for ad-hoc types of pico-cell deployment.

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6. TECHNOLOGY HURDLES AND AREAS FOR FURTHER RESEARCH

This section considers the hurdles and obstacles facing each technology that are stopping that technology from becoming more attractive to operators of future backhaul networks, by becoming cheaper, more efficient and/or more widely available. It then identifies and suggests steps and actions that could be taken to help overcome those hurdles and improve the attractiveness of any given technology. Finally, it then recommends whether Ofcom should consider taking any of those steps or actions by proposing areas for further research.

6.1 HURDLES AND OBSTACLES

This section identifies the hurdles and obstacles facing the different technologies considered in this report and what possible interventions could be taken to help overcome them. The hurdles and obstacles identified cover different areas, including:

• Technology

• Logistical

• Market

6.1.1 PtP Microwave

The big challenges facing PtP microwave cover:

• Reducing link costs such as equipment, installation and management costs.

• Combining high-frequency, high-capacity PtP microwave with mesh topologies and techniques to address street-level micro- and pico-base stations

• Overcoming public opposition to, and planning permission issues with deployment of more micro- and pico-base stations and associated antennas.

Specific limitations and hurdles for PtP microwave are: Limitation or Hurdle

Cost of PtP equipment – this is a major component of the overall cost of PtP links

Possible Intervention

Investigate the potential for reduction in equipment costs of PtP Microwave equipment, especially by moving towards higher-frequency operation (e.g. 55GHz and up) and new technologies (e.g. metallised plastics, LTCC).

Action by Ofcom?

Yes – Ofcom could consider researching the potential for reduced equipment costs by moving to higher frequency operation. Any such work should also consider the applicability and operating restrictions presented by such technologies.

6. Technology Hurdles and Areas for Further Research

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Limitation or Hurdle

Ease and cost of installation – installation of PtP links is another major cost component.


Research into auto-configuring “plug-and-play” backhaul links that could allow easy installation, network discovery and configuration. This could be particularly useful for unplanned deployment of pico-BTSs.

Action by Ofcom?

Yes – Ofcom could lead research into tools and techniques for auto-configuring “plug-and-play” backhaul links and antennas.


Planning permission and public acceptance for antennas


Research into alternatives that would reduce the profile and/or transmit powers of antennas and improve their acceptability to the public and planning councils (e.g. flat-panel antennas for flush mounting on buildings, multi-beam antennas to reduce antenna numbers, reduced antenna sizes due to increased operating frequencies).

Quantification of what improvements in antenna sizes and transmit powers are required to significantly improve public acceptance and reduce planning permission opposition.

Action by Ofcom?

Yes – Ofcom could lead research into:

• Public acceptability of antennas and help set standards that industry could work towards.

• Techniques and technologies that would meet these standards for acceptable deployments of microwave antennas in PtP links.


Successful operation of mesh techniques and topologies with high-frequency PtP spectrum


Investigation into techniques to improve performance of meshed high-frequency PtP backhaul networks to support performance targets and mobility requirements expected of public mobile networks.

Action by Ofcom?


• What performance requirements (e.g. real-time service support, latency, jitter, mobility routing & re-routing) meshed backhaul networks would be required to meet, and what limitations this would place on backhaul mesh topologies.

• What techniques, topologies and algorithms would improve performance of meshed backhaul networks to meet performance requirements.


Complexity of spectrum management, interference planning and licensing of PtP links for relatively ad-hoc and very dense deployment of pico-cell BTSs.


Review Ofcom’s policies on spectrum management and licensing of PtP links for very dense BTS deployments. Ofcom is implementing a lightly licensed regime for frequency bands over 60 GHz, but is even this “hands-off” approach manageable or optimum to support very dense, relatively ad-hoc and potentially rather fluid deployments of future pico-BTSs?

Action by Ofcom?

Yes – Ofcom could review its own policies regarding the lightly licensed regime for high frequency PtP links with a view to assessing its viability for a potential future scenario that sees very dense ad-hoc deployments of pico-BTSs using meshed PtP microwave for backhaul.


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6.1.2 Optical Fibre

The big challenges facing optical fibre cover:

• Encouraging greater deployment and availability of optical fibre and improving competition in its provision in the access network.

• Finding solutions for the re-use of in-building cabling to link to indoor, wall-mounted and roof-mounted base stations.

Specific limitations and hurdles for optical fibre are: Limitation or Hurdle

Time & cost of digging trenches for final link to BTS


Research into lowering the costs of installing fibre in the access network.

Lobby for government funding for the strategic build-out of fibre in the access network.

Action by Ofcom?

Yes – Ofcom could investigate techniques for lowering the costs of installing fibre in the ground, or alternatives such as fibre installed along telephone wires and poles.


Lack of open access for optical tail circuits reduces the options for operators to install their own fibre links, reduces competition and makes optical fibre a service provider only option in practice.


Apply the principles of LLU to optical fibre links.

Action by Ofcom?

Yes – Ofcom could consider whether to enforce third party access to local exchanges, cabinets and PoPs owned by large operators for optical fibre links on the access side.


Lack of clarity in the sharing of in-building cabling. One option to reduce overall backhaul costs is to re-use cabling into and around buildings where BTSs are located. However, practical and workable sharing arrangements of the capacity (who pays for what, who owns what, who is responsible for what?) are not clear.


Define workable standards and arrangements for the sharing of transmission capacity on in-building cabling and communications links into / out of buildings.

Action by Ofcom?

Yes – Ofcom could lead research into practical arrangements for sharing of in-building cabling and communications links into / out of buildings to provide the final link to indoor, wall-mounted or roof-mounted base stations.


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6.1.3 DSL

The big challenges facing DSL cover:

• Overcoming limitations on range vs. capacity

• Encouraging the widespread deployment and availability of advanced DSL technologies such as VDSL2.

• Encouraging competition in the supply of high data-rate DSL technologies.

• Finding solutions for the re-use of in-building cabling to link to indoor, wall-mounted and roof-mounted base stations.

Specific limitations and hurdles for DSL are: Limitation or Hurdle

Range vs. capacity – high data-rate DSL (ADSL2+, VDSL2) is limited to < 1km


Research into techniques to increase capacity and range of DSL technologies beyond VDSL2.

Action by Ofcom?

No – Industry is already leading the development of DSL technology, both through organisations like the DSL Forum and through suppliers of the technology.


Sub-loop unbundling reduces the opportunity for competition. Running DSL from cabinets reduces the competitive options due to the smaller market served from cabinets.


Assess whether sub-loop unbundling limits the potential for competition. If so, investigate whether price regulation is needed on high data-rate DSL services provided from the cabinet?

Action by Ofcom?

Yes – Ofcom could assess to what extent sub-loop unbundling limits competition in the provision of DSL services from the cabinet. If so, Ofcom should investigate whether price regulation is needed for high data-rate DSL services provided from the cabinet.


Cross-talk – higher use of high data-rate DSL will increase the amount of cross-talk suffered and reduce the effective range for any given bit-rate further.


Investigate the extent to which cross-talk limits DSL performance in terms of capacity vs. range and when this will affect DSL networks in practice given forecasts on take-up and usage of broadband services.

Research into techniques to reduce cross-talk and improve the performance of the copper access network to support future growth in broadband DSL services.

Action by Ofcom?

Yes – Ofcom could lead research into when cross-talk is likely to limit DSL performance and services, and into techniques to alleviate this.


Lack of availability of copper pairs at street-lamps where BTSs may be mounted.


Place obligation on BT to provide copper pairs wherever they are requested, even to BTSs mounted on street-lamps.

Action by Ofcom?

No – other solutions are available, and DSL should have to cost in against these solutions.


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6.1.4 PtMP Microwave

The big challenges facing PtMP microwave cover such areas as:

• It is inappropriate to use at street-level where wide-area coverage is not possible due to urban canyons.

• Proving base stations densities are high enough that it provides a more cost-effective solution that PtP microwave.

• Providing sufficient capacity at the hub point to serve the backhaul requirements identified in this report for the different future scenarios.

Specific limitations and hurdles for PtMP microwave are: Limitation or Hurdle

Ineffective to use high-frequency LOS spectrum for street-level micro- and pico-BTS deployments in a NLOS environment.


None.

Action by Ofcom?

No.


Lack of capacity in lower-frequency NLOS spectrum (e.g. < 6 GHz) to support future scenarios


Allocate more spectrum in lower and higher frequency bands for PtMP use.

Action by Ofcom?

No – Allocation of spectrum should be on the basis of demand from the market.


No great increase in macro-BTS density foreseen that could make PtMP microwave more cost-effective than PtP


None.

Action by Ofcom?

No.

6.1.5 Mesh Radio

Specific limitations and hurdles for mesh radio are: Limitation or Hurdle

Lack of understanding of benefits provided by mesh networks to wider community.


Investigate the wider business case for the provision of wireless MAN transport infrastructure in terms of the benefits delivered to local communities (residential and business) and the local economy.

Action by Ofcom?

Yes – Ofcom could lead research into the business case and benefits delivered to a local economy through the provision of a meshed wireless MAN transport network to support various forms of wireless communications.


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6.1.6 WiMAX

The use of WiMAX in backhaul networks is limited primarily by the fact that operators deploying this technology will in practice be focusing on serving end-users directly and not the backhaul market. Limitation or Hurdle

Cost and availability of WiMAX spectrum


Allocate certain WiMAX spectrum for backhaul use only.

Action by Ofcom?

No – Ofcom should not limit the use of WiMAX spectrum to backhaul usage only.


WiMAX is essentially another flavour of PtMP, therefore all hurdles that apply to PtMP Microwave above apply to WiMAX as well.


None.

Action by Ofcom?

No.

6.1.7 FSO

The big challenge facing FSO is to prove that it can provide the reliability required of public networks. Limitation or Hurdle

Reliability and availability that can be achieved (and operator perception of this)


Investigation into ability of FSO links to support the availability and performance targets expected of public mobile networks, and under what circumstances and what scenarios this can be achieved.

Action by Ofcom?


• The potential for reduced link costs by deploying FSO equipment. Any such work should also consider the applicability and operating restrictions presented by such technologies.

• What techniques, topologies and algorithms could improve performance of FSO in backhaul networks to meet performance requirements.


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6.1.8 Power-Line Comms

The big challenge facing Power-Line Comms is to prove it can deliver useful data rates over useful distances to useful locations. Limitation or Hurdle

Limited by location of nearest transformer


None.

Action by Ofcom?

No.


Data-rates that can be supported over longer distances


Investigate techniques to improve the data rates supported by power-line comms over greater distances (e.g. 100m to 1km)

Action by Ofcom?

No – Ofcom should not spend resources on power-line comms as there is no clear application for it in the backhaul market and no demand for it from the market.

6.1.9 Satellite

The big challenges facing the use of satellite in backhaul networks are its limited capacity and high cost. Limitation or Hurdle

Limited capacity compared to traffic volumes foreseen.


Allocate more spectrum to satellite usage.

Action by Ofcom?

No – not appropriate.


Cost of capacity compared to other solutions


Investigate techniques to reduce cost of capacity over satellite, either through improved spectral efficiency or reductions in equipment costs.

Regulate on price or usage of satellite in the backhaul market.

Action by Ofcom?

No – other solutions are available, and satellite should have to cost in against these solutions.


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6.2 AREAS FOR FURTHER RESEARCH

Those areas where Ofcom should consider sponsoring or leading further research are shown in the table below, summarising those areas of research suggested in section 0 above.

Since industry may be focusing on shorter time scales than those addressed by this report (10 to 20 years), the objective of this section is to identify those areas that industry may not be currently addressing adequately. Each of the areas below could make a significant impact on the long-term attractiveness of each technology in backhaul networks if addressed successfully.


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Technology Potential Further Research Area

Consider researching the potential for reduced equipment costs by moving to higher frequency operation. Any such work should also consider the applicability and operating restrictions presented by such technologies.

Lead research into tools and techniques for auto-configuring “plug-and-play” backhaul links and antennas.

Lead research into:

• Public acceptability of antennas and help set standards that industry could work towards.

• Techniques and technologies that would meet these standards for acceptable deployments of microwave antennas in PtP links.

Lead research into:

• What performance requirements (e.g. real-time service support, latency, jitter, mobility routing & re-routing) meshed backhaul networks would be required to meet, and what limitations this would place on backhaul mesh topologies.

• What techniques, topologies and algorithms would improve performance of meshed backhaul networks to meet performance requirements.

PtP Microwave

Review Ofcom’s own policies regarding the lightly licensed regime for high frequency PtP links with a view to assessing its viability for a potential future scenario that sees very dense ad-hoc deployments of pico-BTSs using meshed PtP microwave for backhaul.

Investigate techniques for lowering the costs of installing fibre in the ground, or alternatives such as fibre installed along telephone wires and poles.

Consider whether to enforce third party access to local exchanges, cabinets and PoPs owned by large operators for optical fibre links on the access side.

Optical Fibre

Lead research into practical arrangements for sharing of in-building cabling and communications links into / out of buildings to provide the final link to indoor, wall-mounted or roof-mounted base stations.

Assess to what extent sub-loop unbundling limits competition in the provision of DSL services from the cabinet. If so, Ofcom should investigate whether price regulation is needed for high data-rate DSL services provided from the cabinet.

DSL

Lead research into when cross-talk is likely to limit DSL performance and services, and into techniques to alleviate this.

Mesh Radio Networks

Lead research into the business case and benefits delivered to a local economy through the provision of a meshed wireless MAN transport network to support various forms of wireless communications.

FSO Lead research into:

• The potential for reduced link costs by deploying FSO equipment. Any such work should also consider the applicability and operating restrictions presented by such technologies.

• What techniques, topologies and algorithms could improve performance of FSO in backhaul networks to meet performance requirements.

Table 41: Potential Areas for Further Research by Ofcom

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7. WIRED VS. WIRELESS

This section looks at the level of use of wired (e.g. optical fibre, DSL) and wireless (e.g. PtP microwave) technologies in future backhaul networks. It considers the following questions:

• Will there be a “shift in power”, a change in the balance of usage of wired vs. wireless technologies? If so, in which direction?

• What will be the nature of the change in use and how big will it be?

• What will the spectrum requirements for wireless use and what will be the impact on Ofcom’s spectrum planning and management processes?

7.1 WILL THERE BE A “SHIFT IN POWER”?

There will be a migration towards wireless technologies for the provision of the final link to the base station. Section 0 concludes that high-capacity PtP Microwave will be the preferred option for the final link to outdoor base stations, whether macro-, micro- or pico-base stations.

This will be on the basis of reduced costs:

• Reduce overall costs by avoiding leased lines

• Quick and cheap to install compared to digging trenches

• Low cost of scaling up capacity to BTSs as it is required

Wireless will be able to deliver the link capacities required and through combinations with mesh-type topologies will be suitable for micro- and pico-BTSs in urban & suburban Non-Line-Of-Sight (NLOS) environments.

High-speed DSL will be the preferred option for indoor pico-BTS deployments where available.

Optical Fibre and xDSL will otherwise be used on a link-by-link basis to connect outdoor BTSs only where they provide a lower life-time cost than PtP Microwave.

7.2 WHAT WILL BE THE NATURE OF THE CHANGE?

The final link to the base station will become shorter as Fibre-To-The-Cabinet (FTTC) pushes fibre further into the access network, increasing the number of fibre PoPs. This will reduce the final link to an average of 1km – 1.5km for the majority of base stations.

The number of base stations and therefore the number of backhaul links will increase dramatically as micro- and pico-base stations are deployed as the norm to meet future growth in wireless communications traffic.

• The number of base stations, and therefore backhaul links, in urban areas could increase by a factor of between 10 and 20. − The majority of urban cellular coverage and capacity is currently provided by

macro-base stations. It is likely that in 10 – 20 years from now, the majority of cellular coverage and capacity will be provided by micro-cells, which cover much smaller areas; the typical micro-cell range is only 25% of the typical macro-cell range.

7. Wired vs. Wireless

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• If Metro-WiFi networks become prevalent, then the number of base stations and backhaul links could increase even further. WiFi cell ranges are typically only 10% of macro-cell ranges, suggesting contiguous WiFi coverage could require up to 100 times as many base stations and associated backhaul links.

The nature of backhaul link deployment is likely to change as well, becoming far more dynamic and fluid. The rate of change over time in the number of base stations and the number of fibre PoPs to backhaul to will increase significantly. Combined with the use of mesh topologies in dense areas, this will mean that backhaul networks will be much more ad-hoc in nature and will develop, evolve and change much more quickly than we’re used to today. This will make formal planning and management of backhaul networks far more complex.

7.3 WILL THERE BE ENOUGH SPECTRUM?

There is just over 20 GHz of spectrum available for Point-to-Point use in current bands up to and including the 65 GHz band. Ofcom plans to open up the 70 GHz and 80 GHz band in the near future, bringing the total to just over 30 GHz of spectrum.

Levels of congestion of the current PtP spectrum are currently fairly unclear. There can be difficulty in assigning links in certain bands, but other bands are completely clear. Generally though, Ofcom is not getting feedback from industry that there is currently any overall problem with spectrum congestion.

Ofcom publishes Technical Frequency Assignment Criteria documents for each of the PtP bands. These show the following general restrictions:

• Maximum channel bandwidth of 56 MHz in the 15 GHz band and above. CEPT is discussing the use of 56 MHz channels in lower frequency bands.

• Maximum capacity of STM-4 (622 Mbit/s) in 56 MHz, based on system efficiency class 5b – 64-QAM or 128-QAM using Adjacent Channel Co-Polarisation (ACCP)

7.3.1 Impact on Spectrum from increases in Capacity per Link

This section provides a simple analysis of how the current spectrum plans would cope if capacity per link increased significantly to meet the requirements envisaged in the future scenarios in Section 0.

The current spectrum management and licensing schemes are already designed for links up to STM-4 (622 Mbit/s) and could cope with this order of increase in capacity.

It is less clear whether there is sufficient spectrum to cope with a general increase in such capacities. However, considering a simple deployment case that may represent something close to a worst case scenario gives an indication.


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Building

BTSLink

Key:

Channel #

Building

BTSLink

Key:

Channel #

Figure 9: Future Meshed Wireless MAN Scenario

The diagram above considers an urban layout of street-level BTSs (e.g. micro-BTSs), where each BTS can link to four other BTSs.

For costing purposes in the example above, there is an average of 2 PtP microwave links for each BTS. This is independent of the location of the nearest fibre PoP where traffic is backhauled to.

For traffic purposes, if we assume that the central BTS is co-located with a fibre PoP then:

• The traffic from each of the 24 surrounding BTSs is backhauled to this BTS.

• There are four PtP links feeding into the central BTS, so on average the cumulative traffic from 6 BTSs (= 24 BTSs / 4 links) is carried on each of the final PtP links into the central BTS.

• Each BTS generates 30 Mbit/s – 60 Mbit/s (see Section 5.5.2 – Medium to High scenario for urban micro-BTSs)

• Each of the final links into the central BTS carries 180 Mbit/s – 360 Mbit/s total traffic, compared to a link capacity of 622 Mbit/s.

For spectrum requirements purposes, we assume:

• Directionality of antennas means that the same channel can be used for links at right angles to each other. Frequency re-use will therefore be dictated by the number of links in a straight line needed before the same channel can be used again.

• Each link has a capacity of 622 Mbit/s (i.e. STM-4), thus requiring a channel bandwidth of 56 MHz. − Ofcom’s Technical Frequency Assignment Criteria documents (see

http://www.ofcom.org.uk/radiocomms/ifi/tech/tfacs/?a=87101) indicate a Wanted to Unwanted (W/U) ratio of 40 dB is needed for single-entry co-channel interference limits for spectrum efficiency class 5 (necessary for such high capacity links).


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• Over a short distance for the scenario above, the propagation model should follow free-space path loss (i.e. d2), suggesting a frequency re-use factor of 100 (i.e. 10 x Log (1002) = 40 dB). However, free-space path loss will not in practice be sustained for the long distances indicated by such a high frequency re-use. We therefore assume that path loss is likely to be proportional to at least distance cubed (i.e. d3), suggesting a frequency re-use factor of no more than 22 (i.e. 10 x Log (223) = 40 dB) will be possible in practice.

• All links are FDD, so if channel 1 uses f1 and f1’, the frequency re-use factor can be halved by reversing the direction of use of f1 and f1’ for a subsequent link. Therefore a practical frequency re-use factor of 11 can be assumed for the scenario above.

• 8 different operators want to operate separate networks across the entire urban area (with the same frequency re-use, channel bandwidths and separate frequencies).

The amount of spectrum needed to support this scenario is:

Link Capacity 622 Mbit/s

Channel Bandwidth 56 MHz

Factor for symmetric links 2

Frequency re-use factor 11

Total spectrum used per operator 1.23 GHz

Approx. guard band overhead 10%

Total spectrum needed per operator 1.35 GHz

Total spectrum needed for 8 operators ~11 GHz

Table 42: Spectrum Requirements for Future Meshed Wireless MAN Scenario

This compares against the 30 GHz of spectrum available for PtP microwave use once the 70 GHz and 80 GHz bands are opened up. Overall, this suggests that even with huge increases in link density and capacity, there should be sufficient spectrum available to accommodate such a scenario.

7.3.2 Impact of Link Length

This section considers the impact of link lengths decreasing in parallel with increases in link capacity.

Varying link length in the scenario above should not greatly affect the amount of spectrum needed. The amount of spectrum required does not change as the scale of the urban environment is increased or decreased. The frequency re-use factor can remain the same, independent of the actual link length between BTSs.

While higher frequency bands are very limited in operational range, this is not a restriction on the scenario considered above where the BTSs are mounted at street level and typically only one block apart, limiting link lengths to no more than ~200m. In fact, the likely reduction in link lengths will make these bands more appropriate to use.

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8. BACKHAUL ROADMAP

This section pulls together the findings and analysis of the rest of the report by predicting the time scales for the main developments affecting backhaul networks over the next 10 to 20 years.

The roadmap picture below shows the main drivers and requirements that backhaul will have to support in those time scales. These drivers and requirements fall generally into the categories of:

• Cellular traffic and cellular base station deployments

• WiFi traffic and WiFi deployments

• Backhaul technology developments

In the roadmap below, the following key applies:

• – A blue hashed line indicates the period over which the driver or requirement is ramping up to or down from maturity.

• – A blue solid line indicates that the driver or requirement has reached full maturity and the full impact of it will be felt in backhaul networks.

The following sub-sections then provide a more detailed description and analysis of what these developments will mean to backhaul networks in the time scales of 5 years from, 10 years from now and 15 – 20 years from now.

8. Backhaul Roadmap

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5 10 15 20Years

Need to support GSM TDM traffic

3G HSPA increases traffic volumes

3G migrates to all-IP

3G LTE increases traffic volumes further

Cellular coverage mostly through macro-cells

Cellular coverage migrated to mostly micro- and pico-cells

Metro WiFi networks mature

Mesh techniques mature to support real-time services and mobility req’s

Significant traffic hits WiFiand Metro-WiFi networks

Meshed Wireless MAN scenario realised

Migration to PtP microwave (< 40 GHz)

Roll-out of Fibre-To-The-Cabinet (FTTC)

Widespread roll-out of high speed DSL (VDSL2)

Migration to PtP Microwave (> 50 GHz)

Need to support 3G ATM traffic

Driver / Requirement

Gen

eral

Cel

lula

rM

acro

/ M

icro

/ P

ico-

Cel

lsTe

chno

logi

es

5 10 15 20Years

Need to support GSM TDM traffic

3G HSPA increases traffic volumes

3G migrates to all-IP

3G LTE increases traffic volumes further

Cellular coverage mostly through macro-cells

Cellular coverage migrated to mostly micro- and pico-cells

Metro WiFi networks mature

Mesh techniques mature to support real-time services and mobility req’s

Significant traffic hits WiFiand Metro-WiFi networks

Meshed Wireless MAN scenario realised

Migration to PtP microwave (< 40 GHz)

Roll-out of Fibre-To-The-Cabinet (FTTC)

Widespread roll-out of high speed DSL (VDSL2)

Migration to PtP Microwave (> 50 GHz)

Need to support 3G ATM traffic

Driver / Requirement

Gen

eral

Cel

lula

rM

acro

/ M

icro

/ P

ico-

Cel

lsTe

chno

logi

es

Figure 10: Roadmap for Future Backhaul Networks

8. Backhaul Roadmap

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8.1 IN 5 YEARS TIME

In practice cellular operators are already planning for these time-scales. The main points to be drawn from the roadmap above are:

• Cellular backhaul will still have to support GSM TDM traffic and 3G ATM traffic. This will make any migration to cheaper and simpler Ethernet-based products (that carry IP traffic efficiently) difficult in these time scales.

• Cellular traffic volumes will have started to increase significantly through 3G HSPA services, but cellular coverage will still be mostly provided through macro-base stations. Base station backhaul requirements may still be met with 34 Mbit/s links.

• Metro WiFi networks will have matured, with significant traffic volumes being carried on these networks and these networks will have started to deliver the performance needed for real-time services and mobility re-routing support.

• Wireless communications operators will have migrated the majority of their backhaul networks to PtP microwave, operating in much the same manner as today at frequencies of 38 GHz and below. This will be driven by the need to reduce costs and in particular to avoid the ongoing costs of leased line solutions.

8.2 IN 10 YEARS TIME

In ten years from now, backhaul networks will have changed significantly. The main points to be drawn from the roadmap above are:

• Cellular traffic should be all-IP in these time scales. GSM is likely to be defunct will all mobile subscribers on 3G networks. These 3G networks will also have migrated to simpler and lower-cost IP backhaul links, allowing cheaper transmission equipment to be used (e.g. Ethernet-based).

• 3G LTE and perhaps Mobile WiMAX will have reached maturity and increased traffic volumes even further, with large macro-base stations having capacities up to 100 Mbits/ to 200 Mbit/s, requiring equivalent capacities on backhaul links.

• The majority of cellular coverage and capacity will have migrated to micro- and pico-base stations to provide the geographic capacity needed. This will see very large numbers of street-level base stations deployed.

• Metro-WiFI networks will fully support all real-time services and mobility, competing directly with cellular networks. This will increase the number of backhaul links significantly.

• Widespread Fibre-To-The-Cabinet will have become a reality, massively increasing the potential number of fibre PoPs across the UK and reducing the final link to base stations to 1km – 1.5km.

• High-speed DSL technologies (e.g. VDSL2) will become generally available as FTTC reduces the final link range required from the cabinet.

• Use of very high-capacity, high-frequency (> 50 GHz) PtP microwave will be widespread, making use of the shorter distance to a fibre PoP (brought about by FTTC) and advances in meshing technologies to support micro- and pico-base stations in urban areas.

8. Backhaul Roadmap

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• The scenario of an urban meshed Wireless MAN is starting to become a reality, where a metropolitan area has a ubiquitous meshed transmission network able to automatically hop back to the nearest fibre PoP. Base stations (either cellular or WiFi) can easily access these networks and backhaul back to the core network is via a combination of FTTC and meshed PtP microwave over the last kilometre or so.

8.3 IN 15 TO 20 YEARS TIME

In 15 to 20 years time, the full effect of all these developments will have set in. The main points from the roadmap above are:

• All wireless traffic (cellular or WiFi) will be IP-based, allowing simple, cheap packet-switched transmission equipment to be used in backhaul links.

• Traffic volumes will have increased massively on both cellular and WiFi networks, with ubiquitous provision of mobility and QoS for real-time services.

• Backhaul transmission will be via FTTC and either high-speed DSL to indoor pico-base stations or meshed high-frequency (> 50 GHz) PtP microwave radio to outdoor micro- and pico-base stations.

• Urban areas will have fully implemented the concept of a meshed Wireless MAN, with a very high-capacity wireless transmission network providing backhaul to fibre PoPs for all wireless base stations and access points across the city.

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APPENDIX A: INDUSTRY INTERVIEWS

Industry sources are key to a better understanding of how the backhaul market will develop, in terms of market demand, future applications and technology supply. In the process of producing this report, we carried out a number of one-to-one interviews with industry sources, covering suppliers and users across a range of potential backhaul technologies. A key objective of this process was to quantify backhaul requirements and technologies, rather than simply holding general discussions.

This appendix presents the main feedback provided during the interviews, which has been used to inform the overall project, this report and its findings. It should be noted though that this appendix covers all the main comments received. Therefore, individual comments may not agree with each other (where different interviewees had different opinions) and not all comments will agree with the overall findings of the main body of this report.

A.1 INITIAL COMMUNICATION WITH INTERVIEWEES

This section provides a copy of the information provided to interviewees prior to the interview taking place.

A.1.1 The Scope of the Overall Project

For the purposes of this project, backhaul is defined as the link from a radiating access point (e.g. cellular base station, WLAN access point, etc) to a network node. The scope of this project is to investigate backhaul technologies, techniques and requirements over the next 10 to 20 years. The high level aims are to:

• Predict how different backhaul technologies and techniques will evolve and develop over the coming years, and compare them with each other (e.g. in terms of cost, capacity, range, availability) over that time

• Identify potential future requirements placed on backhaul networks (in the next 10 to 20 years) and what large-scale disruptive changes might occur


It should be noted that the purpose and priority of this study is to concentrate on the future and consider where backhaul technologies and markets are going.

A.1.2 Key Questions

The following is an indicative list of the key questions that we would like to discuss. However, this is not intended to be exhaustive and we are keen to allow discussions to address areas not covered here. In particular, some questions are clearly more applicable to the supply or demand side of the market.

• Is the cost of backhauling traffic a significant cost or limit in wireless networks? − For example, if it reduced significantly, could it change your business model,

deployment plans or network architecture? If so, how? − By how much would backhaul costs have to reduce to have a significant

impact – 10%, 50%, …?

• What backhaul technologies do you currently supply or use?

A:. Industry Interviews

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− Why have you chosen these technologies? What have been the key factors in choosing any particular technology?

− Where and how do you use these technologies? Are there clear breakpoints where you choose one technology over another?

− What other technologies have you considered? How did they compare and what have been the key factors in carrying out the comparison (e.g. cost, range, capacity, availability)?

− What new or emerging technologies do you see as potentially interesting or competitive? Which technologies do you see as coming or going?

• What is the underlying cost structure for your backhaul technology or network? What are the dominant cost items?

• What developments do you see in future years that could improve the attractiveness (e.g. cost, efficiency, performance) of different technologies? − What are the key limitations of different technologies? What is stopping any

given technology becoming the low-cost, ubiquitous backhaul technology of choice?

• What changes in market requirements or drivers can you foresee in the future that will impact on backhaul links? − How will factors such as required capacity, range, cost or availability change

significantly over the next 10 to 20 years? − Do you see anything radical happening in the future that will affect the

backhaul market? For example, what if the market moves towards a very large number of very small base stations for high-capacity coverage – how will backhaul requirements be met efficiently?

− What will backhaul networks look like in 5 years? In 15 years?

• Who else do you think we should talk to, either inside your organisation or outside?

A.2 COMPANIES INTERVIEWED

The following companies provided input and feedback to this project:

• Orange

• Vodafone

• The Cloud

• Pipex

• UK Broadband

• Nortel

• MLL Telecom

• Cambridge Broadband

• National Grid Wireless

• Lucent R&D


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• DSL Forum

• Three UK

• Huber+Suhner

A.3 FEEDBACK FROM INDUSTRY INTERVIEWS

The main feedback provided during the interviews is provided below. This is grouped according to:

• Technology-neutral comments on backhaul networks

• Specific comments on individual technologies

• Suggestions on potential areas for further research

A.3.1 General Themes

What is backhaul? – The definition of backhaul changes between organisations and even between people within the same organisation.

• For this report, we have defined the backhaul link as the final link to/from the wireless base station. However, others, for example, see backhaul stretching from the base station through to (i) a hub aggregation point, (ii) on to the BSC and (iii) on to the MSC in the core.

Time Scales – Organisations (both operators and suppliers) are typically looking out to 3 to 5 years. Discussions on time scales beyond this are generally welcome, but speculative and qualitative, not quantitative.

Drivers of future wireless usage will include:

• Future wireless communications will see increases in capacity to provide “all-you-can-eat” packages.

• There is a move towards best-effort services and providing what people are willing to pay for

Costs:

• Backhaul is a significant cost and limitation on wireless networks. If backhaul was significantly cheaper, there would be different, more distributed architectures with fewer points of failure.

• Operators and suppliers agree that reducing ongoing opex is the key to any business case and decision on backhaul networks. This is about introducing low cost structures for operating, maintaining, managing and expanding the network.

• Equipment capex is not seen as the key factor and most organisations are willing to invest in up-front capex to reduce ongoing opex costs.

• Leased line solutions are currently seen as too expensive. In particular, the cost of scalability with leased line solutions is seen as unacceptable, with large increases in capacity foreseen in the next 3 – 5 years.


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General technical comments included:

• Future backhaul will move to IETF protocols to simplify transmission schemes and allow off-the-shelf equipment to be bought.

• Cellular BTS densities may increase to every couple of hundred metres.

• Backhaul loads for packet networks will be dimensioned around the mean data rate, not the peak data rates claimed by suppliers.

• The introduction of intelligence into the BTS could see local distribution of traffic and a subsequent reduction in the backhaul load.

• Air interface data rates may increase enormously. NTT DoCoMo has publicly stated they believe they can achieve as much as 1 Gbit/s in 4G.

• Future solutions may see different technologies used in parallel to achieve the reliability required.

A.3.2 Optical Fibre

There is general agreement that fibre will push further out from the core network and that Fibre-To-The-Cabinet (FTTC) and maybe something approaching Fibre-To-The-Kerb (FTTK) will be achieved in metropolitan areas in the 10 to 20 year time scales.

Fibre rollout in the access network will likely be on a link-by-link basis as capacity demands it, rather than any nationwide or regional strategy. This will probably see rather patchy and inconsistent coverage, with a risk of a lack of competition in the availability of tail circuits.

There is a general perception that leased line services over optical fibre are too expensive, that there is a lack of competition in its provision and that this is likely to continue in the future.

There is also general agreement that even if a fibre PoP is only 50 to 200 metres away, the cost and time to dig a trench for the final link will continue to be a major limitation.

Optical fibre would be ideal from the point of view of capacity. The latest standards in PONs is GPON, which targets connections of 100 Mbit/s to the end-user.

In the USA, there is a lot of fibre being deployed, often via telegraph poles and power lines to increase speed and reduce cost of rollout.

A.3.3 Point-to-Point Microwave

Wireless hits the physics barrier sooner than wired solutions, so is more limited on capacity.

Wireless links from the BTS may only have to cover 500m, as BTS densities increase and fibre PoPs become more numerous.

PtP solutions can support STM-4 data rates (622 Mbit/s) today.

Connecting back to a fibre PoP would ideally use NLOS links, but it is not practical to get the spectrum for the capacities required. PtP solutions may combine with mesh topologies to backhaul to a fibre PoP over a very limited number of hops.


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PtP is more efficient in use of spectrum over a geographic area than PtMP. However, spectrum and interference management is difficult at hub sites where a number of PtP links converge.

60 GHz radio systems take advantage of the oxygen-absorption band to simplify system structures and drive link costs down.

• 60 GHz link equipment costs are currently as low as £2K – £4K (including both ends of the link) and could get down below $1K with increased volumes.

• Use of metallised plastics hugely reduces component costs compared to systems operating at lower frequencies.

• Suppliers claim 4 x “9”’s availability at 800m link range with data rates between 125 Mbit/s and Gigabit-Ethernet.

• System simplifications include no power amplifier, simple modulation schemes (QPSK, 8-QAM), no forward-error correction, Ethernet transport, wide diplexing (> 2 GHz). This simplifications are based on the assumption that frequency re-use is still very high in this band because the signal attenuation over distance due to oxygen absorption is so high.

Comments on technical developments included:

• Adaptive Coding & Modulation (AMC) – Reducing reliability by a factor of 10 can result in a four-times increase in capacity. This could be useful for best-effort services such as browsing.

• Automatic Power Control in conjunction with AMC will deliver a re-use improvement factor of ~1.7

• MIMO won’t deliver any real improvement for outdoor backhaul links.

• AAS improves range, but may not improve capacity as backhaul links typically already use high-order modulation schemes.

• Some repeater technologies or FEC gains could deliver 20% to 40% to link capacities.

Comments on PtP costs included:

• PtP solutions are relatively cheap (as low as £6K for 16 x 2 Mbit/s link today) and scale economically for costs (less than twice the cost for an STM-1 link).

• Site rental for a microwave antenna will typically be £1K to £1.5K.

• Spectrum licensing fees typically average £500 per link. Ofcom’s licence fees are not so high as to significantly affect the business case for microwave in backhaul networks.

A.3.4 Point-to-MultiPoint Microwave

Increases in BTS densities in metropolitan areas will see a migration to PtMP solutions from PtP if it delivers lower average per-link costs.

PtMP solutions allow the balancing of resources between outlying CPEs. This allows for:

• More efficient use of resources for bursty data traffic by balancing network load between peak and mean traffic levels


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• Greater gains from AMC compared to PtP links

PtMP is good for ad-hoc network design and easily accommodates the introduction of new cell sites.

PtMP will support STM-1 data rates per sector in the next couple of years.

Interference control using interference agility will improve capacity and range in the future.

PtMP is limited by the amount of spectrum available for its use.

PtMP systems are being seen more in developing countries (e.g. South Africa) in urban areas. There is little current use of PtMP among UK operators.

A.3.5 Mesh Networks

If all traffic moves to IP in the backhaul, WiFi and mesh could be a player. But synchronisation and latency problems will continue for legacy 2G (TDM) and 3G (ATM) traffic.

Current weaknesses of mesh networks are the capacity overheads and unpredictable latency due to the number of hops across the network.

One operator’s experience with trialling mesh networks is that they either had:

• Good capacity, but with very slow re-routing, or

• Good re-routing speed, but with a big impact on capacity

There are different views on the applicability of mesh networks:

• Some operators believe that small meshes will be intrinsic to future wireless backhaul to a limited number of fibre PoPs as BTS densities increase and BTSs move to street level (i.e. NLOS environment).

• Other operators believe that mesh networking is not applicable to the carrier environment where WAN coverage is needed.

Mesh networks are easier to manage in TDD than in FDD, as the flow of traffic may not be symmetric.

A.3.6 xDSL

An ongoing problem with DSL and copper pairs is that they go to homes and not to poles where BTSs are typically located.

DSL technologies may be most appropriate for microcellular BTSs that have lower capacities than macrocells.

Sub-loop unbundling extends the range of DSL coverage by pushing the connection point out from the DLE to the street cabinet

• There are ~5,000 DLEs in the UK, but about 88,000 cabinets

• This tends to be a solution that suits the incumbent. A cabinet serves 300 – 400 users and the customer penetration to make this worthwhile needs to be very high.


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DSL from the exchange requires a link distance of 5km – 7km, DSL from the cabinet requires a link distance of 1km – 1.5km/

VDSL2 claims 100 Mbit/s symmetric up to 500m, 55 Mbit/s asymmetric up to 1km.

• Due to range restrictions, VDSL2 may only be rolled out from cabinets, not DLEs.

There is no major technology difference in the costs between ADSL and VDSL2. The increased costs are down to:

• Power and fibre to the cabinet.

• Providing the higher capacities in the network behind the cabinet.

A.3.7 Free-Space Optics

The general view is that Free-Space Optics (FSO) is too unreliable to use in public networks.

There are some suggestions that future solutions could see FSO and cheap microwave used in parallel for back-up, using a combination of technologies to give high capacity and reliability with low cost.

A.3.8 WiMAX

WiMAX will be an access technology. The economies of scale will go into low-cost, low-powered chipsets, not into providing fixed link infrastructure.

A.3.9 Satellite

No operator or supplier saw satellite as having any significant role in future backhaul networks

A.3.10 Areas for Further Research

Some companies have explicitly stated areas that they feel would be worthwhile areas for future research. For example, one operator has contributed to the EU 6th Framework on eMobility on backhaul transmission requirements, identifying priorities for study as:

• Low cost GHz - THz generation and reception

• Microwave adaptive arrays – low cost production of electrically steerable antennas, ideally with no moving parts

• Algorithms for self-configuration and routing in fixed mesh networks

• Techniques for transfer of time and frequency standards

• Techniques to maximise spectrum efficiency in NLOS transmission at lower microwave frequencies

Another operator identified:

• Intelligent meshing in 70 – 80 GHz spectrum

• High-gain flat-panel antennas operating at 28 GHz and up

• Use of 256QAM radio with ATPC and AMC


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A third operator suggested the following areas that they believe would be useful:

• They see a need for multi-point beam-forming antennas, flat panels that could be mounted on buildings, providing up to 6 point-to-point links in different directions. This could get around significant planning permission issues.

• Use of remote repeaters from the BTS can improve coverage. A remote radio head where the signal is mixed up to a higher frequency to be backhauled to the expensive BTS equipment form a sort of "quasi-backhaul". The problem though is how to prevent uplink noise aggregation when using multiple repeaters talking back to the BTS. If the BTS listens to both simultaneously then there is a noise rise - the question is how to reduce this noise rise.

• Ofcom could compile a database of where fibre is in the ground across all providers.

• How to reduce the costs of digging the final trench, even if it is only 50 metres.

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APPENDIX B: BACKHAUL DEVELOPMENTS OUTSIDE THE UK

This appendix provides a short overview of developments in backhaul networks and technologies outside the UK. The main conclusions are:

• The backhaul market everywhere is growing quickly as cellular and WiFi networks and traffic grow. The result is that the market for microwave, fibre and DSL backhaul are all growing worldwide.

• There are similar trends in Europe, the US and the Far East in investment in Next-Generation Networks that are driving investment in deploying optical fibre and high-speed DSL in access networks. These are driven by the residential and business broadband access markets, but will have a knock-on impact on the wireless communications backhaul market through improved local availability of these technologies.

• Countries such as Japan and South Korea in the Far East and the USA appear to be moving towards Fibre-To-The-Cabinet (FTTC) with high-speed DSL for the final link or Fibre-To-The-Home (FTTH) sooner than Europe, with significant migration already underway.

• There is no clear common strategy between operators for deploying FTTH or FTTC in any part of the world. Different operators appear to be convinced of one or the other approach depending on their local circumstances.

B.1 WESTERN EUROPE

Next Generation Networks (NGN) are seeing very high investments in new network infrastructure throughout Western Europe. This has been prompted by incumbent operators reacting to the competitive and pricing pressures they are facing by migrating to lower-cost operating structures. The keys to this are

• Flatter architectures

• Fewer nodes

• Single, simple transport structure

• IETF protocols in the core allowing off-the-shelf equipment to be bought.

A consequence of these new investments will be the upgrading of the core and edge network transmission technologies, with a likely push for optical fibre further into the access network, e.g. through Fibre-to-the-Cabinet (FTTC).

In December 2006, France Telecom announced plans for the roll out of its super fast Fibre-To-The-Home (FTTH) broadband network. The operator said that the early stage deployment phase will run from 2007 to 2008, with the aim of having 150,000 to 200,000 customers connected by the end of 2008 out of a potential client base of 1 million.

B.2 US

Verizon is going through a major investment in rolling out Fibre-to-the-Home (FTTH). Other US operators such as SBC and AT&T are rolling out Fibre-to-the-Cabinet (FTTC) and plan to offer high data-rate DSL services, such as ADSL2+ or VDSL2, to the home.

B:. Backhaul Developments outside the UK

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While these investments are typically targeted primarily at the residential broadband access market, they will also benefit the backhaul market for wireless communications through increasing the availability of optical fibre throughout the access network.

B.3 FAR EAST

South Korea has made major investments in rolling out fibre in urban areas, with very high-speed DSL for the final link to the end-user. Major drivers behind this have been:

• Very dense urban populations, meaning fibre to the basement of apartment blocks allows short copper runs to customers to support very high-speed DSL.

• The South Korean government provided a significant part of the overall investment in upgrading the national network.

In Japan, NTT indicates they are turning on new FTTH subscribers at a higher rate than DSL. NTT is going on the record as shooting for 30MM FTTH subscribers by 2010.

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APPENDIX C: GLOSSARY OF TERMS

3G LTE 3G Long-Term Evolution

AAS Adaptive Antenna Systems

ACCP Adjacent Channel Co-Polarisation

ADSL Asymmetric DSL

ADSL2+ Asymmetric DSL 2+, an improved version of ADSL

AMC Adaptive Modulation and Coding

ATPC Automatic Transmit Power Control

BTS Base Station

CPE Customer Premises Equipment

DLE Digital Local Exchange

DSL Digital Subscriber Loop

FDD Frequency Division Duplex

FEC Forward Error Correction

FSO Free-Space Optics

FTTC Fibre-To-The-Cabinet

FTTH Fibre-To-The-Home

GPON Gigabit PON

HDTV High-Definition TV

HSDPA High-Speed Downlink Packet Access

IP Internet Protocol

LLU Local-Loop Unbundling

LOS Line-Of-Sight

LTCC Low-Temperature Co-fired Ceramics

MAC Medium Access Control

MAN Metropolitan Area Network

mE milli-Erlang

MIMO Multiple-Input, Multiple-Output

MSAN Multi-Service Access Node

NLOS Non-Line-Of-Sight

NPV Net Present Value

O&M Operation & Maintenance

PCP Primary Connection Point

PHY PHYsical

PLC Power-Line Communications

PMR Private Mobile Radio

C:. Glossary of Terms

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PON Passive Optical Network

PoP Point of Presence

PtMP Point-to-MultiPoint

PtP Point-to-Point

QAM Quadrature Amplitude Modulation

QPSK Quadrature Phase Shift Keying

SDSL Symmetric DSL

SHDSL Symmetric High-speed DSL

SMS Short Messsage Service

STM-1 Synchronous Transfer Mode-1 (155 Mbit/s)

STM-4 Synchronous Transfer Mode-4 (622 Mbit/s)

TDD Time Division Duplex

TDM Time Division Multiplexing

VDSL Very-high-bit-rate DSL

VDSL2 Very-high-bit-rate DSL 2, an improved version of VDSL

VOD Video-On-Demand

VPN Virtual Private Network

WLAN Wireless Local Area Network

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