Broader Broadband For 4G Networks?

FCC contemplates relaxation of out-of-band emission limits in the 2.5 GHz band.

The FCC has proposed to relax out-of-band emission limits for the Broadband Radio Service (BRS) and the Educational Broadband Service (EBS), operating in the 2496-2690 MHz band (a/k/a the 2.5 GHz band). These services were formerly known as MMDS and ITFS. Their spectrum is now largely leased to Clearwire, Nextwave, and others for 4G mobile broadband services.

Clearwire is the largest current user of the band. It relies on WiMAX technology, which typically utilizes 10 MHz channels. But Clearwire and other service providers are thinking that wider bandwidths might be in order. Clearwire would like to migrate to WiMAX2, while other service providers (and maybe Clearwire as well in the future) are considering Long Term Evolution-Avanced (LTE). Both WiMAX2 and LTE contemplate channel bandwidths of 40-100 MHz.

At first blush, there doesn’t seem to be much reason why the FCC should not allow operators to choose their own bandwidth, and thereby improve 4G broadband performance. Except for one thing: it isn’t as easy – or cheap – to mask out-of-band emissions as sharply when using a broader desired bandwidth as it is when using narrower bandwidth. Faced with this conundrum, the Wireless Communications Association International (WCAI) asked the FCC to loosen the mask.

Ouch! cried some of the people who use adjacent bands for things like Mobile Satellite and TV Broadcast Auxiliary Services. Don’t tread on me!  Spicing things up, one developer/manufacturer of LTE-Advanced gear chimed in that it can produce 20 MHz bandwidth equipment that complies with the existing out-of-band limits. In this manufacturer’s view, no relaxation of the current mask is necessary because the equipment it makes will take care of the problem even at the broader bandwidths. 

According to WCAI, however, other equipment manufacturers support the proposed relaxation as “an appropriate and reasonable trade-off between form factor, battery consumption, and performance”. Worry not, says WCAI, because our mobile units normally don’t occupy the entire bandwidth, and they keep their power low to conserve battery capacity – so overall, the benefits of a relaxed mask outweigh the risks.

What shall we do with no consensus, the FCC asks? A mitigation rule is already in place that requires base stations to comply with a tighter emission mask within 60 days of receiving a documented interference complaint. Mobile devices operate with lower power and do seem to be less of a threat. So the Commission reasons that maybe it can lighten up – but should it also anticipate future bandwidths even wider than 20 MHz, and should it change mobile mask limits to make it easier and cheaper to make those ever-smarter devices without which no self-respecting teenager or twenty-something would be seen on the street?

Comments will be due 30 days after the proposals are published in the Federal Register, with Reply Comments only 15 days later. Those short times suggest the FCC does not expect a major brouhaha. It remains to be seen whether they guessed right.