commtech talks: optical access architectures for backhauling of broadband mobile networks


1. The data storm

2. Challenges and opportunities

3. Solutions: HetNet, small cells, BBU centralization

4. A closer look to BBU centralization(CPRI backhauling)

5. BBU centralization CAPEX/OPEX analysis

6. Conclusions

AGENDA


New Devices/Ecosystem

data munching devices exhausting data and signaling capacity

The data storm

New Connections

Global Mobile Traffic in 5 years

(forecast for period 2011-2016)

25X

New Consumers

people will be directly touched by connectivity in 2015

5 Billion

New Communities and Cloud Services

empowered users connected in social communities

100s Millions


Challenges …

0

10

20

30

40

50

2005 2006 2007 2008 2009 2010 2011 2012 2013 2014

$/sub/month

Data ARPU

Network Cost

Data Traffic

Service Provider network economics

Source: Bell Labs Analysis


… and opportunities

Mobile backhaul connection by fiber reaching 42% in 2016.

Mobile Backhaul Connections by medium

0

1,000,000

2,000,000

3,000,000

4,000,000

5,000,000

6,000,000

7,000,000

8,000,000

9,000,000

10,000,000

2010 2011 2012 2013 2014 2015 2016 2017

copper

fiber

air

total

Source: Infonetics Research, March 2012


Solutions: HetNet

From homogeneous coverage paradigm to inhomogeneous

• Different wireless technologies, such as W-CDMA , LTE and Wi-Fi

• Flexible radio access options, such as macros, small cells and Wi-Fi.

• Cost-effective for capacity and coverage needs in all environments.

• Mitigates interference and allows for intelligent traffic management features


Solutions: small cells

NGNM definition: “Small cells are operator managed base stations with a lower transmission power and coverage area than macro cells, used to complement them in order to improve the service level by easing congestion with more capacity and enhancing coverage”

Macro

Typical Small

Cell locations

� Small cells typically below

rooftop 3-6m above street level

� In a Het-Net scenario, macro-

sites may double up as

aggregation sites for small cells

� ‘Last mile’ backhaul therefore

provides connectivity between

macro sites and small cell sites

� Connection must meet QoS

requirements…


Solutions: mobile backhauling models

Remote

Radio

Head

(on tower)

All-in-one

(BaseBand

integrated

in Radio Head)Small cell

(Macrocell)

Conventional BBU

IP mobile

backhaul

Wireless

packet coreControllers

Centralized baseband

IP

IP

IP

CPRI

over fiber

IP

RF only sites

IP

Multi-band

Remote

Radio Head

with any

BaseBand


Solutions: IP backhauling options and metrics

MEANINFRASTRUCTURE AND TECHNOLOGY CAPABILITY

Option Bandwidth (Mb/s) Latency (ms)

Copper

DSL - 2 pair bonding with vectoring and phantom mode 1500 m 100 down, 20 up 3



Microwave11-23 GHz (up to 16 Km at 11 GHz) 254 bits per frame

305 down, 306 up per radio

∼∼∼∼ 0.15 per hop

80 GHZ (up to 1.5Km) 1000 ∼∼∼∼ 0.15 per hop

Fiber

TDM PON 10000 down, 2500 up

(shared among ONTs)∼∼∼∼ 1

B&W point to point 10000 0.005/Km

CWDM 8x 10000 per channel 0.005/Km


Solutions: BBU centralization (CPRI backhauling)Traditional versus centralized architectures

Ethernet backhauling

Cabinet

Backhaul network

BBU

RU

CPRI BH i/f

CO

BBU

RU

CPRI

Backhaul network

CPRI

CPRI backhauling


Common Public Radio Interface (CPRI)

CPRI Backhaul

CPRI over fiber

Radio

Equipment

(RE)

Radio

Equipment

Controller

(REC)

Centralized Base Band Unit (BBU)

RF Only

History

• The Common Public Radio Interface (CPRI) is an industry cooperation, operative since 2003, defining a publicly available specification for the internal interface of radio base stations between the Radio Equipment Control (REC) and the Radio Equipment (RE).

• Cooperating parties are: Ericsson AB, Huawei, NEC, Alcatel Lucent and Nokia Siemens Networks (Nortel left on 2009)

What is

• A digitized and serial p2p radio interface, mapping the sampled antenna signals (I/Q data), possibly related to different mobile technologies, into containers.

• Mobile technologies supported include: GSM, UMTS, WiMax, LTE …

• Single-hop and multi-hop topologies (between REC and RE) are allowed.

• Three different information flows (User Plane data, Control and Management Plane data, and Synchronization Plane data) are TDM multiplexed over the CPRI.

• Seven different options for CPRI line bite rates are defined, as multiple of lower line rate: (1) 614, 4 Mb/s, (2) 1228.8 Mbit/s, (3) 2457.6 Mbit/s, (4) 3072.0 Mbit/s, (5)

4915.2 Mbit/s, (6) 6144.0 Mbit/s, (7) 9830.4 Mbit/s.


CPRI throughput examples

How evaluating CPRI throughput:

• N. of sectors for each cell site: 3

• N. of MIMO TX antennas

• for WCDMA: 2

• for LTE: 4

• Sampling rate: 7.68 Mb/s for WCDMA

15.36 Mb/s for LTE 10MHz



• Sample width: 8 bit/sample for WCDMA

15 bit/sample for LTE

• I/Q multiplication factor: 2

5 MHz

WCDMA carriers

0 10 20 30

0 0 5.530 11.059 16.614

1 737 6.267 11.796 17.351

2 1.475 7.004 12.534 18.089

3 2.212 7.741 13.271 18.826

4 2.949 8.479 14.008 19.563

LTE spectral bandwidth [MHz]

CPRI unidirectional throughput [Mb/s]

(non compressed)

CPRI unidirectional throughput [Mb/s]

(compressed)

5 MHz

WCDMA carriers

0 10 20 30

0 0 2.048 4.096 6.153

1 273 2.321 4.369 6.426

2 546 2.594 4.642 6.699

3 819 2.867 4.915 6.973

4 1.092 3.140 5.188 7.246

LTE spectral bandwidth [MHz]

• Compression rate: 2.7


Centralized BBU Deployment Pros&Cons

Benefits: • Reduced OPEX (clustering):

• Fewer cell site visits (e.g.

centralized upgrades)

• Reduced site costs (site

rental) and civil works for

new sites

• Eliminate heating and

cooling of enclosure

• Improved security (no

cabinets to break into)

• Improved X2 performance

(no transmission delay

among BBUs in a pool)

• Load balancing lowers CAPEX

(pooling)

• Improved spectral efficiency

(CoMP)

CPRIover fiber

Centralized

BBU

CPRIover fiber

Centralized

BBU

Challenges: • CPRI backhaul demands

high bandwidth capacity

(up to 10G) for circuit-

based traffic

• Need for optical infra-

structure

• Bandwidth

compression

algorithms can

effectively reduce costs

• Strict transmission latency

and jitter requirements

• Low entry cost with ability

to scale

• Effectively leveraging

existing fiber (e.g. GPON

overlay)


The business case for BBU centralization

• The total incremental costs of a C-RAN architecture in urban environments reduce after the first year, moving towards 70% of traditional RAN costs in the final years

• OPEX reduction eventually outweighs initial CAPEX increase

source:


A synopsis of CPRI backhauling architectures

Fiber rich

context

P2P fibers

RRH-BBU

Need for CPRI

multiplexing

at cell site

Y N

WDM or

TDM

muxing

WDM TDM• Purely passive solution possible

• CPRI compression not needed

• With colored or colorless optics

• Active solution

• CPRI compression lowers costs

• Proprietary or std multiplexing

P2P

TREE

RING

P2P fibers RRHP2P fibers RRH--BBUBBU CPRI multiplexingCPRI multiplexing


CPRI

(AxC)

COMPR.

DECOMPR.

CPRI

MUX

DEMUX

OPTICAL

NETWORK

TERMINATION

CPRI

or SUB-CPRI

SWITCHING

CPRI

MUX

DEMUX

OPTICAL

LINE

TERMINATION

CPRI

(AxC)

COMPR.

DECOMPR.

CPRI

(AxC)

COMPR.

DECOMPR.

CPRI

MUX

DEMUX

OPTICAL

NETWORK

TERMINATION

CPRI

or SUB-CPRI

SWITCHING

CPRI

MUX

DEMUX

OPTICAL

LINE

TERMINATION

CPRI

(AxC)

COMPR.

DECOMPR.

Optimized TDM based CPRI backhauling architecture

CPRI backhauling functional model

Transport network

BBU Pool

CPRIs Line Line CPRIs

Cell site Central Office

• Optional• Proprietary

• TDM/WDM • Optional• Proprietary

• Optional• Proprietaryif sub-CPRI

• TDM/WDM• P2P• PON• Ring

• P2P• PON• Ring

RRH(s)

WDM based CPRI backhauling architecture


CPRI backhauling CAPEX/OPEX analysisModels

CPRI multiplexing:CPRI multiplexing:

•• TDM up to 10Gb/sTDM up to 10Gb/s

•• CPRI compressionCPRI compression

(about 3 times on (about 3 times on

LTE signals)LTE signals)Cell site CO

Cell siteWDM pt-to-pt(20÷40 Km)

CPRI multiplexing:CPRI multiplexing:

1.1.Fixed DWDMFixed DWDM

2.2.Colorless DWDMColorless DWDM

(SS(SS--WDM)WDM)

WDM colored WDM colored e/oe/o convertersconverters

Passive WDM

MX/DX (AWG)

CO

BBU stack

B&W pt-to-pt(20÷40 Km)

Active TDM MX/DXBBU stack


CPRI backhauling CAPEX/OPEX analysis

Number of cell sites

Normalized network cost

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 300

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

6

Minimally loaded configuration

1

2

4

3

Number of cell sites


0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 300

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

6

Minimally loaded configuration

1

2

4

3

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 300

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

6

Maximally loaded configuration

)

)

)

)

xNumber of cell sites


1

2

4

3

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 300

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

6

Maximally loaded configuration

)

)

)

)

xNumber of cell sites


1

2

4

3

Legenda:

1) p2p fibers connecting RUs and BBUs;

2) TDM multiplexing (with compression);

3) WDM multiplexing with fixed WDM;

4) WDM multiplexing with colorless WDM

(SS-WDM)

• Variable number of cell sites

• 2 scenarios:

1. Minimally loaded:

• mix of CPRI interfaces globally

conveying 33Gb/s (16Gb/s after

compression)

2. Maximally loaded:

• mix of CPRI interfaces globally

conveying 88Gb/s (40Gb/s after

compression)


CPRI backhauling CAPEX/OPEX analysisOPEX considerations

Reliability Scalability Installation aspects In-field upgrades

TDM Acceptable if careful electronic design

Limited by TDM box capacity; it scales with boxes

Either in cabinet or on tower, with need for power supply if not cooling; indoor/outdoor versions needed

Needed

Fixed WDM

Very good; only passive WDM de-multiplexer at cell site (beyond RRHs)

Limited by the number of λs on a fiber (up to 80+80 using C+L bands)

No power/cooling needs for WDM de-mux; complex management of WDM modules (spares for each λ, need for management of fixed colors)

Not needed

SS-WDM Very good; only passive WDM de-multiplexer at cell site (beyond RRHs)

Limited by the number of λs on

a fiber (up to 80+80 using C+L bands)

No power/cooling needs for WDM de-mux; very simple management of WDM modules (only one spare type, no management of fixed colors)

Not needed


Colorless DWDM technology SS-WDM: principle of operation

WDM MX/DX(AWG or TFF)

Distribution Fiber

Remote mirrorReflective-SOA

Data modulation

Self-seeding Laser cavity

Colorless transmitter self-aligns to any available channel of the AWG grid without needing wavelength control and tracking system:

1. The fiber between the R-SOA and the AWG mirror forms a laser cavity

2. The laser wavelength is selected by the AWG port channel

3. The R-SOA is directly modulated with the ONU data stream

Feeder Fiber

ONU transmitter


Colorless DWDM technology SS-WDM: R-SOA operations in the self-seeding cavity

The R-SOA in the cavity performs simultaneously 3 operations:

• Sustain lasing – optical amplification

• ONU data modulation – direct gain modulation

• Cancellation of re-circulating modulation – Nonlinear Gain saturation


Conclusions

• Some mobile market evolution trends have been depicted in their main lines, showing how a sustainable growth constantly needs to leverage on innovation, in order to make operators’ costs and revenues meet on a fair basis

• Specifically, a new mobile backhauling paradigm (BBU centralization or CPRI backhauling) has been described

- Suitable both for macro and small cells

- Allowing for significant OPEX savings at the expense of initial CAPEX increase

• Results from a CAPEX/OPEX analysis have been reported:

- TDM (active) solutions with compression can be generally designed at lower cost than WDM ones and allow for “CPRI independent” monitoring of the optical line

- Low cost/short distance WDM solutions, like SS-WDM, look promising thanks to the possibility of a pure passive add-ons in the cell site; the auto-tuning facility is key for eliminating the OPEX burden implied by the management of different devices for distinct colours

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commtech talks: optical access architectures for backhauling of broadband mobile networks

Documents

alcatel lucent

data traffic

sites copyright

data storm2

radio equipment control

cpri throughput exampleshow

different mobile technologies

serial p2p radio interface