LTE trials mount in problematic sub-1GHz bands
German and US carriers focus on low frequencies, but business case may be tough
Published: 27 May, 2010
Deutsche Telekom plans to begin a user trial of LTE in its newly acquired 800MHz spectrum in Germany this year, hard on the heels of Telefonica O2 in the UK and Germany. With Verizon Wireless deploying LTE initially in 700MHz, the early focus is very much on low frequencies, even though many experts question whether carriers really can get a decent return on their investment in these bands.
A new study from network planning firm Aircom finds that US carriers could save $1.2bn by relying on HSPA+ instead of building out LTE. And Tommy Ljunggren - head of mobile networks at the only commercial LTE carrier, TeliaSonera - was dismissive of Europe's 800MHz digital dividend band at the recent LTE World Summit. This was echoed by supplier NEC, whose director of global LTE strategy, Dr Sharam Niri, told MobileEurope: "Why would you do it? It's not a useful solution in Europe - you don't see the benefits of LTE - you can't achieve much more throughput than with good HSPA coverage. So what are you offering?"
The answer is that many carriers do not have optimal spectrum for LTE, and they have different and sometimes conflicting objectives for building 4G. One is to reduce the cost of delivery of heavy duty data services by investing in the higher capacity and greater spectral efficiency of the new technologies. But these profitable data services rely on intensive build-outs to cover areas of high demand and population - which means the smaller cells and higher capacity of frequencies above 2GHz.
However, in some cases carriers cannot get their hands on that optimal mobile data spectrum, as in the US, where the 2.5GHz band is largely controlled by Clearwire, and the new allocations for Verizon and AT&T are in 700MHz. For high frequency capacity, they will have to refarm 3G bands or wait for new allocations. Niri added in the interview that cellcos were coming round to the idea that LTE "will not map onto the macro 3G network, and will require a roll-out of far smaller cell sizes of between 100 and 200 meters".
The other reason for the focus on low bands is that many carriers have rural coverage targets to meet, as in Germany. The large cells of 800MHz are ideal for covering sparse populations, though arguable HSPA+ would be a more efficient technology choice, as Aircom claims. These rural targets may be in commercial conflict with the real profit potential for LTE, urban data.
However, Deutsche Telekom says it will start user trials in underserved areas this year, an exercise already begun, even before the recent auctions, by Vodafone Germany. And UK regulator Ofcom has granted O2 a trial license to begin LTE testing in the 800MHz band, using equipment from Huawei. O2 is already carrying out trials in 2.6GHz, and now wants to evaluate LTE in the digital dividend spectrum. Licenses in both bands will be auctioned simultaneously, probably near the end of this year. The 800MHz test will take place in the northern English city of Carlisle during the third quarter, partly to assess interference potential between between mobile LTE and existing television broadcast services.
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