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Small Cells in a Big City

Deploying multipoint microwave to backhaul a small cell network

Dr John Naylon, Chief Technology Officer,

Cambridge Broadband Networks Limited

www.cbnl.com Commercial in confidence 2

• Choosing from the famous

‘backhaul toolbox’

• Observations from a live small

cell deployment using

multipoint microwave

• Conclusions

Topics Covered

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Backhaul Toolbox

Commercial in confidence 3

Fibre

WiFi / Unlicensed

Multipoint NLoS

P-P Microwave

Multipoint Microwave

Bonded Copper

P-P 60GHz

(E-Band)

P-P 70/80GHz

Satellite

Free-Space Optical

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Backhaul Toolbox


Fibre

WiFi / Unlicensed

Multipoint NLoS

P-P Microwave


Bonded Copper

P-P 60GHz

(E-Band)

P-P 70/80GHz

Satellite

Free-Space Optical

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Choosing from the Toolbox

1. The solution has to work − Not just today, but sustainably as the access network evolves

2. It has to be cost-effective to deploy en masse


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The Solution Has To Work: Spectrum Considerations


Source: "Frequency Band Review for Fixed

Wireless Service", for Ofcom, Nov 2011,

http://goo.gl/7S26p

Sub 6GHz: 1.54 GHz for licensed and unlicensed fixed & mobile

Microwave: 16.4GHz for terrestrial fixed links

millimetre wave 18.3GHz

Unlicensed Light licensed

Link licenced (PTP) Area Licensed (PMP)

Area Licensed Unlicensed

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Sub 6GHz: 1.54 GHz for licensed and unlicensed fixed & mobile

Area Licensed Unlicensed

• Access share of < 6GHz has risen from 1% to 10% in 20

years

• Regulators are seeking to release 500MHz (~10%) more

• Backhaul gets economically squeezed out of < 6GHz

• Unlicensed could be a possibility today … but tomorrow?

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Microwave: 16.4GHz for terrestrial fixed links

millimetre wave 18.3GHz

Unlicensed Light licensed

Link licenced (PTP) Area Licensed (PMP)

• Microwave and millimetre wave offer future-proof capacity

• Tried and tested backhaul technologies for macro network

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Backhaul Toolbox


Fibre

WiFi / Unlicensed

Multipoint NLoS

P-P Microwave


Bonded Copper

P-P 60GHz

(E-Band)

P-P 70/80GHz

Satellite

Free-Space Optical

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Core

Core


Cost Effective Deployment: What’s New About Small Cells?

Macro cells Small cells

Lots of aggregation in

the RAN

Little aggregation in

the RAN

Many more

sites

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Small cells

Core


Cost Effective Deployment: Coping with Many More Sites

• Three major determinants

of solution cost:

• Frequency

• Topology

• Licensing


Cost Effective Deployment: Cost versus Frequency

• RF parts get significantly

more expensive at high

frequencies

• e.g. 71—76GHz PA is 5×

the cost of a 16—33GHz PA

at the same volume

• Low yield, demanding

device geometry, less

volume, awkward packages

• Reflected in equipment

costs!

Frequency (GHz)

$0

$20

$40

$60

$80

$100

$120

$140

$160

0 20 40 60 80 100

$0

$20

$40

$60

$80

$100

$120

$140

$160

0 20 40 60 80 100

Volume Cost: Low Noise Amplifier

Volume Cost: RF Power Amplifier

Sources: Hittite Microwave Corp, Digikey


Cost Effective Deployment: Less is More

• P-P topologies (star, ring,

tree) need 2 ODUs per link

• Multipoint needs a single

sectoral ODU and one

directional ODU per link

• Mean number of links per

multipoint sector is 4:

5 ODUs with multipoint

8 ODUs with P-P

• 40% fewer ODUs deployed:

significant cost saving

Point-to-point Topology

Multipoint Topology


Cost Effective Deployment: The Licensing Continuum

• Regulator ‘round-trip time’

and high per-link license

fees mean that:

• Traditional, link-licensed

microwave is too expensive

and too slow for small cells

• Area licensed, light

licensed and unlicensed are

all workable

• None is completely “free”

due to internal coordination Bureaucracy per link

Cost per

link

Unlicensed

Light Licensed

Area Licensed

Link Licensed

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Core

Core


Cost Effective Deployment: Aggregation

Macro cells Small cells

Lots of aggregation in

the RAN

Little aggregation in

the RAN

Many more

sites

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Why Does Aggregation Matter?

• Mobile backhaul traffic is already quite bursty, because it is data dominated:


HSPA+ Macro Node B backhaul traffic Peak:

Mean:

Ratio:

23.31 Mbps

5.54 Mbps

4.20 Mbps

Mbps

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Bursty Traffic is Hard to Carry Efficiently

• Efficiency = mean channel utilisation

peak channel capacity =

1 peak to mean ratio

= 25% average



Mean:

Ratio:

23.31 Mbps

5.54 Mbps

4.20 Mbps

Mbps

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Looking at Data… 60s Resolution




= 25% average



Mean:

Ratio:

Mbps

23.31 Mbps

5.54 Mbps

4.20 Mbps

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Looking at Data… 15m Resolution




= 28% average



Mean:

Ratio:

20.03 Mbps

5.54 Mbps

3.62 Mbps

Mbps

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Looking at Data… 1h Resolution




= 37% average



Mean:

Ratio:

15.04 Mbps

5.54 Mbps

2.71Mbps

Mbps


Small Cell Backhaul Traffic

Mbps

Live small cell network • Much higher peak-to-mean

(as expected)

• A dedicated (point-to-point)

tail link in this example

would have 4% utilisation

• Does this matter if the

spectrum is unlicensed?

• Yes: this figure is the

utilisation of the expensive

box at each end as well!

Peak:

Mean:

Ratio:

32.67 Mbps

1.37 Mbps

23.85 Mbps

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Multipoint Backhaul: Packet Switched not Circuit Switched


• Point-to-point links are statically provisioned circuits

• Packet switching (multipoint) much more efficient for data

• Statistical multiplexing gain increases in small cell networks

Mbps Mbps

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Multipoint Backhaul for Small Cells: Less Waste, More Gain


Sta

tistical m

ultip

lexin

g g

ain

Peak-to-mean ratio of backhaul traffic

• Multipoint efficiency advantage increases as traffic

becomes more bursty (like in a small cell network)

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Multipoint Backhaul for Small Cells: Less Waste, More Gain


Sta

tistical m

ultip

lexin

g g

ain

Nodes per multipoint backhaul sector

• Multipoint efficiency advantage increases as network gets

denser (like in a small cell network)

www.cbnl.com

VectaStar

Backhaul

lightRadio

• Building on years of macro backhaul experience CBNL are deploying

and trialling small cell backhaul with numerous operators and vendors

Current CBNL Small Cell Activities


Metro

WiFi

VectaStar

Backhaul

LTE Picocell

Antennas

VectaStar

Backhaul

27 27 27

Conclusions

•Small cell backhaul is different:

many more cells to backhaul, non-

traditional locations and even

burstier data

• Both microwave and millimetre

wave, P-P and multipoint, can “do

the job” for small cell backhaul

• Good end-user quality of

experience requires much more

backhaul capacity than there is low

frequency backhaul spectrum

• Multipoint microwave for small cell

tail links offers significant cost

savings through higher utilisation of

equipment and spectrum

VectaStar from Cambridge Broadband Networks is the market leader in multipoint microwave

cbnl.com/smallcells

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