Of course, coordinating the digital conversations becomes more complex. Under this system, instead of linking one handset and one base station, your mobile would hold two conversations with two base stations. Those would then talk to each other through the hard-wired “backhaul” of the network, to make sure no mistakes are made. If your “hap-” and “birth-” head off in one direction, while “-py” and “-day” go the other, you want to be sure they both get picked up and sent together to your aunt as a complete birthday greeting.
Nevertheless, tests by Interdigital show that the method greatly increases the throughput for users at the edge, without impacting on customers more deeply embedded within the conventional cells. The company is currently working with a series of partners to bring the technology to market.
Network intelligence
Other ideas raise the complexity of communication even further. For example, one of the hottest topics in mobile communications now is so-called cognitive radio.
The idea stems from observations that - despite much of the radio spectrum being carefully allocated to different uses - much of it is idle for large periods of the day. Cognitive radio proposes a handset smart enough to sniff the radio environment, and opportunistically sneak into any bandwidth that was momentarily free, much as a pedestrian crossing a crowded precinct would seek out a path through the gaps in the crowd, negotiating a path step-by-step.
Anant Sahai of Berkeley University has been drawing up maps of spectrum use across the United States, to get an idea of the opportunities for cognitive radio.
“There's a lot of spectrum allocated to government that's underutilised. For a very good reason. If the band is allocated, for example, for emergencies, then most of the time there aren't emergencies, and it's not used. So obviously there's a lot of spectrum that could be used for mobile phones and other data services at those times.”
“The challenging question,” adds Gerald MaGuire of the Royal Institute of Technology in Stockholm, part of the original team who proposed the idea, “is whether that kind of spectrum can be shared dynamically, in such a way that if the services did need it, they can reclaim it very quickly.”
At the moment, spectrum allocations come tied to very tight technical restrictions making sure that one user's equipment doesn't cut across another user's allocation. With cognitive radio, Maguire warns, that licensing would have to extend to the software that does the decision making and retuning the frequencies – software that would be loaded onto millions of handsets, and might be hacked.
Trust will be a very important issue, agrees Sahai.
“In the old days, when you were you allocated a particular band, you were the only one using that band, and you only had to trust yourself and the entities you control. When you talk about cognitive radio, it becomes very interesting because there are multiple users, and they don't all belong to the same system, so you have to be able to build trust between them.”
This is one reason why full-blown cognitive radio, which might roam across the whole spectrum, may be a long way off.
‘Low hanging fruit’
But shades of cognitive radio are already visible in the campaign to free up TV “white spaces”, already high up the political agenda in the United States.
White spaces are the safety zones that separate TV broadcasters who are transmitting on the same frequency in different cities. But that means that across the world, huge amounts of spectrum is going to waste.
