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Beamsteering Could Cut Mobile Power Consumption By Half
Mobile devices that channel their signal in a specific direction can cut their power consumption by more than half, a new study finds.
Switch on your mobile phone, netbook or tablet and it’ll start hunting for another node to connect to. Once this connection is established, however, your device will broadcast to the world, sending data in every conceivable direction even though most of it falls on deaf ears.
Surely there’s a better way of communicating. There sure is, say Hang Yu and buddies at Rice University in Houston: broadcast only in the direction of the next node. Simple really.
The challenge, of course, is to do this in a way that saves power and that doesn’t dramatically increase the size of the device. Today, Yu and co show us how.
Electrical engineers have long known how to steer radio beams by broadcasting with several antennas. The trick is to make the signals from all the antennas interfere and combine so that they form a narrow beam. Fairly straightforward changes to these signals then steer the beam.
There are two problems with this method that have prevented it being used in mobile devices. First, having two or more antennas is bulky. Second, each antenna circuit requires its own power and although there is a drop in the transmitted power, it’s not always clear that the overall power budget is lower.
So beamsteering has only really been used with bulky transmitters connected to the mains.
Yu and co say it needn’t be like this. They point out for a start that antenna technology has shrunk to the point that an extra two or three could easily be incorporated into a device the size of an iPad, Kindle or netbook.
They go on to show that the tradeoff between power eaten up by the extra antenna circuits and the transmitted power works in favour of the mobile device. That’s an important consideration.
There’s another problem too. A netbook beaming a signal with four antennas at a nearby wifi node could drown out other users. So there’s also a trade-off that needs to be made between all the users and that’s harder to manage.
But Yu and pals have a solution to this problem too, in the form of a piece of software called BeamAdapt. This sits on all the mobile devices, negotiating between them to discover the broadcast settings that achieves the best transmission for everyone.
They’ve tested BeamAdapt on small network and on a larger simulated one and believe it works well. “BeamAdapt can reduce client power consumption by 40% and 55% with two and four antennas, respectively, while maintaining the same network throughput,” they say.
That’s a significant power reduction, which will turn the heads of more than a few mobile device makers. Yu and pals also show that the beamsteering works while the devices are moving and rotating (although it’s not clear how robust it would be in practice).
The problem, of course, is that the benefit is hard to realise unless everyone uses this software. And it only takes a few refusals to ruin the airwaves for others.
The way round this is build this technology into a future comms standard. That’s feasible but it’ll require significantly more testing to ensure the technique can work in the real world, perhaps combined with various other potential standards being lined up for the future. Bottom line: don’t hold your breath.
Ref: arxiv.org/abs/1012.2830: Beamsteering on Mobile Devices: Network Capacity and Client Efficiency
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