Remember wireless cable?

Fri, 11/30/2001 - 7:00pm
Jeffrey Krauss, wireless guru and President of Telecommunications and Technology Policy

By Jeffrey Krauss, 
Wireless Guru and 
President of Telecommunications 
and Technology Policy

You remember wireless cable, right? Well, after the last couple of years of FCC decisions, and particularly the September 2001 bequest of mobile authority, you wouldn't know it anymore. Wireless cable, formally known as Multichannel Multipoint Distribution Service (MMDS), occupies the frequencies between 2500 and 2690 MHz. Originally, these frequencies were allocated to educational institutions for the delivery of classroom lectures. Then the FCC allocated some of the band for commercial use, for delivery of pay television.

The band can carry 31 6-MHz analog video channels. Depending on the city and the time of day, some of the channels are still used for delivering classroom lectures. But long ago, the FCC allowed the wireless cable operators to lease spare capacity from the schools, to supplement the MMDS licenses they already held. That wasn't enough to allow wireless cable to become a full competitor to cable TV, because 31 channels is not enough anymore.

A few years ago, the FCC allowed MMDS operators to transmit digital video, which potentially provided a lot more channel capacity. But by then, DirecTV and Echostar had established the DBS market, with even more channel capacity. So the MMDS engineers came up with the idea of two-way transmissions to support Internet access, employing cellular frequency reuse and using some channels for the upstream return path. This led to one of the most complex and contentious FCC proceedings of the 1990s. There were many school systems that saw a need only for one-way video distribution, and they were concerned about interference from nearby two-way transmitters. With a cellular network design, there would be hub transmitters all over town, instead of one single broadcast site. And if a video receiver that was receiving a weak distant video signal happened to be near a hub transmitter operating on an adjacent channel, the video receiver might receive interference. Eventually, the two-way proponents and the schools agreed on a very complex set of computations that a licensee must submit, showing that there will be neither adjacent channel interference in the same market nor co-channel interference into nearby markets.

But there has been very little real business development of two-way services so far. Sprint and Worldcom bought many of the MMDS licenses when they were auctioned by the FCC. Sprint has MMDS licenses and contracts in 90 markets, covering 30 million households, but so far has built two-way networks in only 14 markets, and recently announced a freeze on the rollout of fixed wireless markets. Worldcom has licenses and contracts in 160 markets, covering 40 percent of U.S. homes, but it has deployed networks in only five markets.

One reason for the slow deployment is that the current MMDS technology requires line-of-sight (LOS) radio paths between transmitters and receivers. LOS technology requires outdoor antennas, which are expensive to install. Non-line-of-sight capability is needed to support user-installable subscriber set-top units. The next generation of MMDS technology, still under development, will include non-LOS capabilities. Technically, non-LOS takes an additional 15 dB to 20 dB of signal strength more than LOS to cover a two- to three-mile path. Some of the technologies being developed to achieve this include adaptive antenna beamforming using phased array antennas; stacked CDMA codes (redundant transmission of the same data at the same time); and COFDM coding techniques.

But until September, there was a cloud over the MMDS frequencies. In some countries, these frequencies will be used for third-generation (3G) land mobile, the next advance in cellular phone design. The United States has to decide what frequencies will be used for 3G here, and 2500-2690 MHz was one of the candidates. That meant that potentially, the FCC could have taken away some of the MMDS frequencies from existing licensees and auctioned them off for 3G use to Verizon, Cingular and AT&T Wireless. This uncertainty slowed down the rollout plans of Sprint and Worldcom.

In September, the FCC took the MMDS frequencies off the table, so far as 3G is concerned. The educational community had exerted political pressure to avoid losing its spectrum. The big surprise was that the FCC decided to allow existing licensees to conduct mobile operations on these frequencies. So instead of Verizon, Cingular and AT&T Wireless getting these frequencies for 3G, Sprint and Worldcom get to use them for that.

It is far too soon to know whether these frequencies will actually be used for mobile operations. The FCC said that detailed service rules will be adopted later, after a full analysis of interference issues. And in the same way that they had to be dragged kicking and screaming into the two-way Internet access technical agreement, the schools will be sure to impede progress. And maybe the fixed two-way wireless Internet access business will take off, using all the MMDS frequencies for fixed links.

But Teligent and Winstar tried that business, and ran into trouble. Cellular mobile demand, on the other hand, is booming. And high-speed Internet access for mobile devices is a key element in the next generation of cellular mobile technology. It may take a few years, but I sure wouldn't be surprised to see Sprint, Worldcom and other MMDS operators migrate from a fixed to a mobile business. For them, Christmas came in September.


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