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CSIRO, BUPT China Co-Operate on Wireless

Richard Chirgwin

With CSIRO's announcement that it's working with Chinese researchers to improve the energy efficiency of wireless networking technologies, it's worth looking at why such a move is necessary in the first place.

The CSIRO side of the project will be led by Dr Jay Huo, whom I also interviewed for A Series of Tubes. China's contribution, meanwhile, will come from the Beijing University of Posts and Telecommunications.

The two groups are to work together on technologies that will reduce the number of base stations needed for wireless networks, which would go at least part of the way to addressing the electricity consumption (and therefore carbon footprint) of those networks.

So why, a reasonable reader might ask, would we consider wireless communications to be “non-green”?

The answer takes us back to the mathematics that lies at the bottom of networking – Shannon's Law. As discussed in earlier articles, Shannon's Law defines the limits of a network's capacity, as a function of bandwidth, signal-to-noise ratio, and power.

Wireless networks suffer from noise: not only is there the background noise of their environment (which grows in proportion to the signal, the further you get from the base station). There's also the noise of network activity: to any user of a wireless channel, every other user looks like noise, and reduces the available capacity to the individual communication.

The result is this: to transfer a given amount of data

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in a relatively noisy wireless environment is likely to demand more power than to transfer the same amount on a quieter channel, like wired Ethernet (this ignores a host of other variables, but is good enough to get the idea across).

Wireless networks get around the noise problem in a variety of ways. The three most common are to develop more sophisticated modulation techniques (improving the signal-to-noise ratio); to increase the transmitter power (also improving the signal-to-noise ratio), or to increase the number of base stations (so as to dedicate more capacity to fewer users).

Two of these three – more power and more base stations – directly increase the electricity demands of the network.

At least in the first instance, the focus of the CSIRO-China collaboration will be to improve the footprint of the wireless network, thus reducing the number of base stations a network requires.

Announcing the research agreement, Dr Jay Guo said that base stations typically consume around 80% of the power in a wireless network, with 3G networks in Australia able to consume between 5 million and 10 million kilowatt-hours per year.

That figure is likely to rise. Recent years have seen strong growth in 3G-based Internet connectivity. As more users gravitate to those networks, and as their traffic increases, two outcomes are likely.

The first relates to the duty cycle of the base stations. With more users and more traffic, the base stations will spend more time transmitting and receiving communications, and less time idle. This will increase the power demands of those base stations.

The second is that to cope with growing traffic, especially in high-traffic areas, carriers will have to increase the number of cells in base stations (which involves adding more transmitters and receivers to those base stations), also increasing the power demands.

There are in the vicinity of 20,000 mobile network base station locations in Australia at the moment across the networks of Telstra, Optus, Vodafone and Hutchison, so growth either in the number of locations or the number of base stations installed in those locations will have a significant impact on electricity consumption.

CSIRO's efforts will tackle the problem of base station capacity in a variety of ways: improving the antennas, better signal processing, and developing new network protocols.