White Space Spectrum for Rural Broadband – Part I

Microsoft has announced that they want to use white space spectrum to bring broadband to rural America. In today and tomorrow’s blog I’m going to discuss the latest thoughts on the white space spectrum. Today I’ll discuss the hurdles that must be overcome to use the spectrum and tomorrow I will discuss in more detail what I think Microsoft is really proposing.

This spectrum being called white space has historically been used for the transmission of television through the air. In the recent FCC incentive auction the FCC got a lot of TV stations to migrate their signals elsewhere to free up this spectrum for broadband uses. And in very rural America much of this spectrum has been unused for decades.

Before Microsoft or anybody can use this spectrum on a widespread basis the FCC needs to determine how much of the spectrum will be available for unlicensed use. The FCC has said for several years that they want to allocate at least one channel of the spectrum for unlicensed usage in every market. But Microsoft and others have been pushing the FCC to allocate at least three channels per market and argue that the white space spectrum, if used correctly, could become as valuable as WiFi. It’s certainly possible that the Microsoft announcement was aimed at putting pressure on the FCC to provide more than one channel of spectrum per market.

The biggest issue that the FCC is wrestling with is interference. One of the best characteristics of white space spectrum is that it can travel great distances. The spectrum passes easily through things that kill higher frequencies. I remember as a kid being able to watch UHF TV stations in our basement that were broadcast from 90 miles away from a tall tower in Baltimore. It is the ability to travel significant distances that makes the spectrum promising for rural broadband. Yet these great distances also exacerbate the interference issues.

Today the spectrum has numerous users. There are still some TV stations that did not abandon the spectrum. There are two bands used for wireless microphones. There was a huge swath of this spectrum just sold to various carriers in the incentive auction that will probably be used to provide cellular data. And the FCC wants to create the unlicensed bands. To confound things, the mix between the various users varies widely by market.

Perhaps the best way to understand white space interference issues is to compare it to WiFi. One of the best characteristics (and many would also say the worse characteristics) of WiFi is that it allows multiple users to share the bandwidth at the same time. These multiple uses cause interference and so no user gets full use of the spectrum, but this sharing philosophy is what made WiFi so popular – except for the most crowded environments anybody can create an application using WiFi and knows that in most cases the bandwidth will be adequate.

But licensed spectrum doesn’t work that way and the FCC is obligated to protect all spectrum license holders. The FCC has proposed to solve the interference issues by requiring that radios be equipped so that unlicensed users will first dynamically check to make sure there are no licensed uses of the spectrum in the area. If they sense interference they cannot broadcast, or, once broadcasting, if they sense a licensed use they must abandon the signal.

This would all be done by using a database that identifies the licensed users in any given area along with radios that can search for licensed usage before making a connection. This sort of frequency scheme has never been tried before. Rather than sharing spectrum, like WiFi, the unlicensed user will be only allowed to use the spectrum when there is no interference. As you can imagine the licensed cellular companies, which just spent billions for this spectrum are worried about interference. But there are also concerns by churches, city halls and musicians who use wireless microphones.

It seems unlikely to me that in an urban area with a lot of usage on the spectrum that unlicensed white space spectrum is going to be very attractive. If it’s hard to make or maintain an unlicensed connection then nobody is going to try to use the spectrum in a crowded-spectrum environment.

The question that has yet to be answered is if this kind of frequency plan will work in rural environments. There have been a few trials of this spectrum over the past five years, but those tests really proved the viability of the spectrum for providing broadband and did not test the databases or the interference issue in a busy spectrum environnment. We’ll have to see what happens in rural America once the cellular companies start using the spectrum they just purchased. Because of the great distances in which the spectrum is viable, I can imagine a scenario where the use of licensed white space in a county seat might make it hard to use the spectrum in adjoining rural areas.

And like any new spectrum, there is a chicken and egg situation with the wireless equipment manufacturers. They are not likely to commit to making huge amounts of equipment, which would make this affordable, until they know that this is really going to work in rural areas. And we might not know if this is going to work in rural areas until there have been mass deployments. This same dilemma largely sunk the use fifteen years ago of the LMDS and the MMDS spectrums.

The white space spectrum has huge potential. One channel can deliver 30 Mbps to the horizon on a point-to-point basis. But there is no guarantee that the unlicensed use of the spectrum is going to work well under the frequency plan the FCC is proposing.

Recovering Television Spectrum

Rabbit_Ears)Lately, the FCC finds itself in sales mode as it works to convince television station owners to sell their existing spectrum. For those not familiar with what the FCC is doing, this process is being referred to as an incentive auction for the 600 MHz band of spectrum. This spectrum today is owned by UHF TV stations.

This is spectacular spectrum and probably has the best characteristics for delivering wireless data. The spectrum easily carries to the horizon and it blasts through just about anything. I remember as a kid watching TV in a basement from a transmitter that was on a mountain on the far horizon. There is no better spectrum for the cellular companies than these bands.

This is called an incentive auction because TV stations are not being mandated to leave this spectrum. So the FCC is now engaged in a series of regional meetings to try to convince the stations to sell their spectrum. The auctions are expected to be lucrative, and station owners and the FCC will share the auction revenues. The AWS auction last November was wildly successful for the FCC. The FCC had set a minimum threshold on the spectrum at just over $10 billion and the final auction raised over $34 billion, and AWS spectrum is not even close to the great coverage characteristics of the 600 MHz spectrum. The TV spectrum should be far more lucrative since this is basically the holy grail of spectrum.

But many stations are hesitant to sell their spectrum, even at the billions they are likely to reap. The FCC has put together a complicated proposal to ‘repack’ the spectrum so that a station that sells its spectrum can stay on the air. But that is the part of the whole process that has stations nervous. It’s possible that a station could be given a slice of spectrum that is used by somebody else, such as sharing the space with wireless microphones. The repacked spectrum also doesn’t have as much of a cushion around each channel as exists today, which makes stations worried about out-of-band interference.

Having no interference is vital for television stations for several reasons. Historically, local stations got their revenues from advertising, and the rates they can charge are based upon how many theoretical eyeballs can watch them plus their rating in the local market. TV transmission is a tricky thing. For homes near the base transmitter, the power of most TV stations can overpower most interference. But, as you get to the further edges of the transmission path interference becomes a real issue. And in TV, interference is manifested by poor reception and pixelization. So TV stations are worried that their effective delivery circle will get smaller and that there will be significant interference in parts of that area.

The financial issue is further complicated by the fact that local stations (or their corporate owners) today make a lot of money from local transmission agreements. These are fees that are charged to cable providers that want to retransmit their station on cable systems. The fear here is the same in that they are worried that cities near the fringes of their service area might argue that they no longer owe retransmission fees due to degraded quality.

Unfortunately there is no way to pre-test the delivery in one of the repacked blocks. Spectrum engineering is really complicated stuff and the quality of a transmission will vary widely in different pockets of a spectrum delivery area based upon local conditions. The only way to test it is to send out the signal and see what kinds of complaints you get from viewers.

The FCC is putting everything they have into these meetings with Chairman Tom Wheeler attending most of these regional meetings to talk with television station owners. There are already a number of stations that have said that they are interested in joining the auction, but the FCC needs a significant number of them to join before the auction can proceed.

Big cellular companies won’t be the only ones to benefit from the spectrum; the FCC has promised that there will be slices of this spectrum set aside for WiFi and other public uses. So the whole country is on hold waiting to see if the FCC can convince enough stations to move. The billions that the stations can collect from the auction is certainly an incentive, but we are going to have to wait to see how many of them actually make the big leap. It ought to be an interesting summer.