Seybold's Take: Finding 500 MHz of spectrum

Andrew Seybold In the National Broadband Plan it sent to Congress in March of this year, the FCC pledged to "find" an additional 500 MHz of spectrum for additional wireless broadband services. Since spectrum is a finite resource and almost every bit of it is already in use in the United States, the term "find" really means to look for spectrum that is being used by entities that can be moved to different portions of the spectrum.

The FCC can look at both the commercial spectrum, which is regulated by the FCC, and federal government spectrum, which is used by federal agencies including the military. The last auctions were all for spectrum that was cleared by moving the original license holders. The PCS spectrum (1900 MHz) was originally used for microwave and other short-distance systems. Since wireless engineers had found ways for wireless devices to work on higher portions of the spectrum, the PCS spectrum was the first to be auctioned.

Next came the AWS-1 spectrum. The lower part of the two segments that make up AWS-1 was assigned to the military while the upper portion was used for fixed-point microwave. The military moved its operations to a different portion of the spectrum and the microwave users were moved higher up in the spectrum, many to 6 GHz, with the cost of the relocation being part of the cost of the spectrum to the license winners. The most recent auction for the 700 MHz spectrum was in conjunction with the move of TV stations from analog to digital. During the transition, stations located on channels 52 to 69 were relocated to lower channels.

There is still some spectrum that has not yet been auctioned: the so-called AWS-2 (5X5 MHz of spectrum at 1915 MHz to 1920 MHz and 1995 MHz to 2000 MHz) and the AWS-3 band (a single slice of spectrum between 2210 MHz and 2155 MHz).

The previous FCC administration tried to combine the upper portion of AWS-2 with the AWS-3 spectrum and auction it, requiring the winner to build out a network that would cover 95 percent of the U.S. population over ten years and to provide free broadband lower-speed service to anyone who wanted it (it could charge for higher-speed service). The auction never took place because T-Mobile raised valid concerns that this block of spectrum could cause interference to the AWS-1 spectrum holders and T-Mobile has a lot of AWS-1 spectrum that is being used for its 3G network.

In order for the FCC to "find" 500 MHz of spectrum, there will have to be many changes to the spectrum map as we know it today. The first 300 MHz is to be released for use within five years with the next 200 MHz becoming available within ten years. But where will this spectrum come from?

One answer is to squeeze the TV stations even further down the band. Since each channel occupies 6 MHz of bandwidth, if the FCC decided to move TV stations using channels 31 to 52, for example, that would open up 126 MHz of spectrum. If the TV stations were all pushed down below channel 20, that would open up another 66 MHz for a total of 192 MHz. Because this spectrum occupies the 500 MHz to almost 700 MHz spectrum, it would be even more valuable than the 700 MHz spectrum since it would require even fewer cell sites to cover large areas and its in-building penetration characteristics are near ideal.

The TV broadcasters that are part of the most powerful lobby in Washington DC (NAB) will fight this type of spectrum incursion very hard, but the fact remains that today less than 20 percent of the U.S. population actually receives over-the-air TV broadcasts; everyone else is connected to cable or satellite TV systems. One of the FCC's ideas is to let TV stations opt into moving off a segment of the band in exchange for some of the auction proceeds. The problem with this is that it would be on a city-by-city basis and we would end up with a hodgepodge of different spectrum segments that would be available only on a city-by-city basis.

The best hope for finding more spectrum appears to be a combination of relocating some of the TV channels, moving some license holders higher in frequency, and finding government spectrum that could be turned over for commercial broadband use. Finding 300 MHz of spectrum that will support broadband technologies will not be easy and the FCC certainly will have its hands full trying, even with the Executive Order approving these spectrum allocations.

I believe the FCC will find the first 300 MHz of spectrum, but I am not at all sure where the next 200 MHz will come from. However, there are a number of new technologies emerging: software-defined radios, cognitive radios, database systems for better frequency management, smart antennas, and, of course, advances in technologies that will make more efficient use of the spectrum we have. We cannot make more spectrum, but we can find ways to make more efficient use of what we have.

But at the end of the day, it is important to remember a few things. Even with 500 MHz of additional spectrum, and even with new technologies, there is not enough spectrum available to be able to move the Internet to an entirely wireless system. Wireless will continue to be the last mile, and the wired Internet has it owns capacity issues. We will have to better manage our spectrum and our Internet going forward.

In wireless, capacity boils down to how much spectrum you have available within a single cell sector (120 degrees) and how many people are trying to use that spectrum at the same time. The more customers sharing the spectrum in a given cell sector, the slower everyone's data connection will be, and if the demand is too heavy, some customers won't have any access. We have all had voice calls blocked (fast busy or no connection) and that is usually because there are too many of us in the same general area all trying to use our wireless phones at once. It does not work today and it won't in the future, even with 500 MHz more of spectrum.

Andrew M. Seybold is an authority on technology and trends shaping the world of wireless mobility. A respected analyst, consultant, commentator, author and active participant in industry trade organizations, his views have influenced strategies and shaped initiatives for telecom, mobile computing and wireless industry leaders worldwide.