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Efficient Mobile Backhaul

Next generation thinking

John Naylon

Mobile World Congress, Barcelona - 29 February 2012

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'08 '09 '10 '11 '12 '13 '14 '15

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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