small cells in a big city
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www.cbnl.com
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
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• 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
Commercial in confidence 4
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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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
Commercial in confidence 5
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The Solution Has To Work: Spectrum Considerations
Commercial in confidence 6
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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The Solution Has To Work: Spectrum Considerations
Commercial in confidence 7
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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The Solution Has To Work: Spectrum Considerations
Commercial in confidence 8
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
www.cbnl.com
Backhaul Toolbox
Commercial in confidence 9
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
www.cbnl.com
Backhaul Toolbox
Commercial in confidence 10
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
www.cbnl.com
Core
Core
Commercial in confidence 11
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
Commercial in confidence 12
Cost Effective Deployment: Coping with Many More Sites
• Three major determinants
of solution cost:
• Frequency
• Topology
• Licensing
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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
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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
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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
Commercial in confidence 16
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:
Commercial in confidence 17
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
Commercial in confidence 18
HSPA+ Macro Node B backhaul traffic Peak:
Mean:
Ratio:
23.31 Mbps
5.54 Mbps
4.20 Mbps
Mbps
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Looking at Data… 60s Resolution
• Efficiency = mean channel utilisation
peak channel capacity =
1 peak to mean ratio
= 25% average
Commercial in confidence 19
HSPA+ Macro Node B backhaul traffic Peak:
Mean:
Ratio:
Mbps
23.31 Mbps
5.54 Mbps
4.20 Mbps
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Looking at Data… 15m Resolution
• Efficiency = mean channel utilisation
peak channel capacity =
1 peak to mean ratio
= 28% average
Commercial in confidence 20
HSPA+ Macro Node B backhaul traffic Peak:
Mean:
Ratio:
20.03 Mbps
5.54 Mbps
3.62 Mbps
Mbps
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Looking at Data… 1h Resolution
• Efficiency = mean channel utilisation
peak channel capacity =
1 peak to mean ratio
= 37% average
Commercial in confidence 21
HSPA+ Macro Node B backhaul traffic Peak:
Mean:
Ratio:
15.04 Mbps
5.54 Mbps
2.71Mbps
Mbps
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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
Commercial in confidence 23
• 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
Commercial in confidence 24
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
Commercial in confidence 25
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)
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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
Commercial in confidence 26
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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