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Femtocells, not 4G, will solve spectrum crisis

Ofcom bets big on small cells

4G will improve capacity by only 1.2 times, according to the latest research, so better network topologies will be needed if we're going to get the bandwidth it seems we'll need.

Solving the widely anticipated data crunch will require better-designed networks, rather than new generations of radio standard, according to the latest research (PDF, surprisingly dull) carried out by Real Wireless on behalf of the UK regulator Ofcom.

The independent consultancy reckons that 4G (LTE) deployments will only improve spectral efficiency by about 20 per cent, despite offering much-improved speeds to individual users. So the best way to increase the overall capacity of the mobile networks is to build a lot more base stations rather than depend on magical new technologies to do more with less.

That conclusion isn't very surprising: the later versions of 3G (including HSPA and those other variants that Americans already call "4G") are very spectrally efficient. The limit on 3G is really a physical restriction on how much data one can squeeze into the 5MHz channel defined by the 3G standard.

Some extensions to that standard are already lashing together 5MHz channels for greater speed, but 4G (LTE) is much better at dynamically allocating a channel from 1MHz up to 20MHz in width depending on the application being used. That enables LTE to achieve headline-grabbing speeds for individual users, without being significantly faster than 3G.

The best way to carry more data, therefore, is to transmit it less far, so that frequencies can be reused more readily. If my nearest base station is 10 miles away, then the signal from that transmitter is sent into an area 50 square miles in size, while the one coming from my phone fills a circle of 314 square miles. Put the base station a mile away and those figures drop to a shade over a tenth of a square mile for the base station, and .8 from the handset.

Those figures are our own back-of-an-envelope stuff, but it is obvious that packing base stations closer together means frequencies can be reused more often, and thus the capacity of the network increases proportionally. LTE has many features to facilitate exactly that; OFDM reduces interference from neighbouring cells and LTE enables a very fast soft hand-off between cells, reducing the signalling load on the network.

So we will need 4G to make the future happen. Not because it can carry more data than its predecessors, but because it enables a greater density of base stations to be deployed. Good news for base station manufacturers, but bad news for those who want to know where all those base stations are going to go. ®

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