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Efficient Mobile Backhaul
Next generation thinking
John Naylon
Mobile World Congress, Barcelona - 29 February 2012
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Microwave Fibre Copper
The Problem Space: Mobile Backhaul
• Need to connect mobile base stations
(node Bs) to core network − Could use copper, fibre or microwave radio
− Microwave is the dominant choice
− ~0.5M new microwave backhaul connections
per annum
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Worldwide Mobile
Backhaul Connections Source: Infonetics Research
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The Problem Space: Mobile Backhaul Traffic Properties
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Sample backhaul demands for 3 tri-cell node Bs in a live, busy HSPA+ network:
Can we exploit statistical properties of this data to
make our backhaul more efficient?
Mbps
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First Property: Data is Bursty
• Data is bursty, i.e. has sharp transient peaks and a much lower mean − This characteristic is driven by user and application behaviour
− Burstiness still present when traffic is aggregated within a node B/eNode B
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Node B backhaul traffic Peak:
Mean:
Ratio:
23.31 Mbps
5.54 Mbps
4.20 Mbps
Handset traffic (10 Devices) Peak:
Mean:
Ratio:
12.07 Mbps
1.44 Mbps
8.37 Mbps
Handset traffic (one iPhone 4) Peak:
Mean:
Ratio:
11.44 Mbps
0.14 Mbps
79.20 Mbps
Mbps
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First Property: Data is Bursty (2)
• Network-wide average of peak-to-mean ratio is approximately 4:1 in this
HSPA+ example network
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− Major implication for efficiency since it is
mandatory to provision backhaul that can
accommodate the offered peak load
− However if we have a dedicated link the
mean utilisation de facto cannot be greater
than the mean offered load
− Therefore the mean utilisation will be
approximately in the ratio of 1:4 to the
peak, i.e. approximately 25%
− So the data’s properties mean that:
Dedicated backhaul
links are 75% idle!
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Mbps
• Peak bandwidth demand does not occur simultaneously at adjacent node Bs
Second Property: Peak Demand is not Synchronised
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− Peaks are of short duration (seconds, not
hours like the daily ‘swells’)
− Peaks arise from random, independent
actions of network end users
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• Peak bandwidth demand does not occur simultaneously at adjacent node Bs
Second Property: Peak Demand is not Synchronised (2)
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− Peaks are of short duration (seconds, not
hours like the daily ‘swells’)
− Peaks arise from random, independent
actions of network end users
− In the studied HSPA+ network, average
cross-correlation factor of pairs of node Bs
in geographical proximity is 0.16 indicating
very weak correlation (network-wide
correlation is even lower, at 0.06)
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Point-to-Point
• Non-uniform data rate and absence of correlation lets us share, or multiplex,
resources instead of using dedicated resources (just as we do in the RAN)
Using These Properties to Improve Backhaul Efficiency
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Point-to-Multipoint
Shared radio +
antenna for all links
Dedicated radio +
antenna per link Dedicated RF
channel per link
Shared RF channel
for all links
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• We examine measured backhaul profiles from a group of eight node Bs − Live network, large middle-eastern operator, heavy data usage
− HSPA+ tri-cellular node Bs
− Theoretical maximum throughput 64.8Mbps per site
• Consider the amount of spectrum needed for each of the two topologies − Use the bare minimum of spectrum to carry exact data profile (no ‘headroom’)
Savings from Point-to-Multipoint Architecture: Spectrum
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Savings from Point-to-Multipoint Architecture: Spectrum
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Peak:
Mean:
11.29 Mbps
2.47 Mbps
Point-to-Point Microwave Radio, Star Topology Point-to-Multipoint Microwave Radio
Cumulative Peak: 11.3 Mbps
Cumulative Mean: 2.5 Mbps
Cumulative Peak: 11.3 Mbps
Cumulative Mean: 2.5 Mbps
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Savings from Point-to-Multipoint Architecture: Spectrum
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Point-to-Point Microwave Radio, Star Topology Point-to-Multipoint Microwave Radio
Peak:
Mean:
15.12 Mbps
4.18 Mbps
Cumulative Peak: 19.5 Mbps
Cumulative Mean: 6.6 Mbps
Cumulative Peak: 26.4 Mbps
Cumulative Mean: 6.6 Mbps
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Savings from Point-to-Multipoint Architecture: Spectrum
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Cumulative Peak: 30.9 Mbps
Cumulative Mean: 14.2 Mbps
Point-to-Point Microwave Radio, Star Topology Point-to-Multipoint Microwave Radio
Peak:
Mean:
17.45 Mbps
7.61 Mbps
Cumulative Peak: 43.9 Mbps
Cumulative Mean: 14.2 Mbps
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Savings from Point-to-Multipoint Architecture: Spectrum
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Cumulative Peak: 42.9 Mbps
Cumulative Mean: 18.9 Mbps
Point-to-Point Microwave Radio, Star Topology Point-to-Multipoint Microwave Radio
Cumulative Peak: 58.4 Mbps
Cumulative Mean: 18.9 Mbps
Peak:
Mean:
14.51 Mbps
4.64 Mbps
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Savings from Point-to-Multipoint Architecture: Spectrum
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Cumulative Peak: 51.7 Mbps
Cumulative Mean: 24.6 Mbps
Point-to-Point Microwave Radio, Star Topology Point-to-Multipoint Microwave Radio
Cumulative Peak: 74.2 Mbps
Cumulative Mean: 24.6 Mbps
Peak:
Mean:
15.83 Mbps
5.69 Mbps
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Savings from Point-to-Multipoint Architecture: Spectrum
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Cumulative Peak: 60.2 Mbps
Cumulative Mean: 31.2 Mbps
Point-to-Point Microwave Radio, Star Topology Point-to-Multipoint Microwave Radio
Cumulative Peak: 92.0 Mbps
Cumulative Mean: 31.2 Mbps
Peak:
Mean:
17.85 Mbps
6.67 Mbps
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Savings from Point-to-Multipoint Architecture: Spectrum
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Cumulative Peak: 67.8 Mbps
Cumulative Mean: 34.2 Mbps
Point-to-Point Microwave Radio, Star Topology Point-to-Multipoint Microwave Radio
Cumulative Peak: 108.0 Mbps
Cumulative Mean: 34.2 Mbps
Peak:
Mean:
15.98 Mbps
2.93 Mbps
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Savings from Point-to-Multipoint Architecture: Spectrum
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Cumulative Peak: 77.9 Mbps
Cumulative Mean: 39.7 Mbps
Point-to-Point Microwave Radio, Star Topology Point-to-Multipoint Microwave Radio
Cumulative Peak: 123.2 Mbps
Cumulative Mean: 39.7 Mbps
Peak:
Mean:
15.18 Mbps
5.49 Mbps
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Spectrum required = bandwidth required in bps
spectral efficiency in bps/Hz
Point-to-Point
• Spectrum required = 15.4 MHz
Savings from Point-to-Multipoint Architecture: Spectrum
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Point-to-Multipoint
• Spectrum required = 9.7 MHz
* 256-QAM assumed
Cumulative Peak: 77.9 Mbps Cumulative Mean: 39.7 Mbps Cumulative Peak: 123.2 Mbps Cumulative Mean: 39.7 Mbps
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Mean channel utilisation (efficiency) = mean bandwidth requirement peak bandwidth requirement
Point-to-Point
• Efficiency = 32.2%
Savings from Point-to-Multipoint Architecture: Spectrum
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Point-to-Multipoint
• Efficiency = 51.0%
Cumulative Peak: 77.9 Mbps Cumulative Mean: 39.7 Mbps Cumulative Peak: 123.2 Mbps Cumulative Mean: 39.7 Mbps
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40% power saving per link
Point-to-Point
37W per radio,
2 radios per link
74W per link
Savings from Point-to-Multipoint Architecture: Power
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Point-to-Multipoint
35W per radio, mean of 4 remotes per
sector ⇒ 1.25 radios per link
44W per link
* Figures reflect market leaders in both categories
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Conclusions
• Mobile broadband backhaul traffic
has specific properties we can exploit
to design more efficient backhaul
networks
• Point-to-multipoint architecture
dramatically improves spectral
efficiency and power efficiency
per link
• Dedicated backhaul links operate at
a very low efficiency: ~25% (!!)
something blah something different
something
• Less equipment deployed means
additional environmental, capex
and opex benefits
VectaStar from Cambridge Broadband Networks is the market leader in point-to-multipoint
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