The FCC continues its examination of the best use of spectrum and released a Notice of Inquiry on August 4 looking at the 900 MHz band of spectrum. They want to know if there is some better way to use the spectrum block. They are specifically looking at the spectrum between 896–901 MHz and 935-940 MHz.

The FCC first looked at this frequency in 1986 and the world has changed drastically since then. The frequency is currently divided into 399 narrowband channels grouped into 10-channel blocks. This licensed use of the spectrum varies by MTA (Major Trading Area), where channels have been allocated according to local demand from commercial users.

One of the more common uses of the spectrum is for SMR service (Specialized Mobile Radio), which is the frequency that’s been used in taxis and other vehicle fleets for many years. The other use is more commonly referred to as B/ILT purposes (Business/Industrial Land Transportation). This supports radios in work fleets, and is used widely to monitor and control equipment (such as monitoring water pumps in a municipal water system). The frequency was also widely used historically for public safety / police networks using push-button walkie-talkies (although cellphones have largely taken over that function).

The FCC currently identifies 2,700 sites used by 500 licensees in the country that are still using B/ILT radios and technologies. These uses include security at nuclear power plants including public alert notifications, flood warning systems, smart grid monitoring for electric networks, and for monitoring petroleum refineries and natural gas distribution systems.

But we live in a bandwidth hungry world. One of the characteristics of this spectrum is that it’s largely local in nature (good for distances of up to a few miles, at most). When mapping the current uses of the frequency it’s clear that there are large portions of the country where the spectrum is not being used. And this has prompted the FCC to ask if there is a better use of the spectrum.

Typically the FCC always finds ways to accommodate existing users and regardless of any changes made it’s unlikely that they are going to cut off use of the spectrum in nuclear plants, electric grids and water systems. But to a large degree the spectrum is being underutilized. Many of the older uses of the spectrum such as walkie-talkies and push-to-talk radios have been supplanted by newer technologies using other spectrum. With that said, there are still some places where the old radios of this type are still in use.

The FCC’s action was prompted by a joint proposal by the Enterprise Wireless Alliance (EWA) and Pacific DataVision (PDV). This petition asks for the frequency to be realigned into three 3 MHz bands that can be used for wireless broadband and two 2 MHz bands that could be used to continue to support the current narrowband uses of the spectrum. They propose that the broadband channels be auctioned to a single user in each BTA but that the narrowband uses continue to be licensed upon request in the same manner as today.

This docket is a perfect example of the complexities that the FCC always has deal with in changing the way that we use spectrum. The big question that has to always be addressed by the FCC is what to do with existing users of the spectrum. Any new allocation plan is going to cause many existing users to relocate their spectrum within the 900 MHz block or to spectrum elsewhere. And it’s generally been the practice of the FCC to make new users of spectrum pay to relocate older uses of spectrum that must be moved. And so the FCC must make a judgement call about whether it makes monetary sense to force relocation.

The FCC also has to always deal with technical issues like interference. Changing the way the spectrum will be used from numerous narrowband channels to a few wideband channels is going to change the interference patterns with other nearby spectrum. And so the FCC must make a determination of the likelihood of a spectrum change not causing more problems than it solves.

This particular band is probably one of the simpler such tasks the FCC can tackle. While the users of the spectrum perform critical tasks with the current spectrum, there is not an unmanageable number of current users and there are also large swaths of the US that have no use at all. But still, the FCC does not want to interfere with the performance at nuclear plants, petroleum refineries or electric grids.

For anybody that wants to read more about how the FCC looks at spectrum, here is the FCC Docket 17-200. The first thing you will immediately notice is that this document, like most FCC documents dealing with wireless spectrum, is probably amongst the most jargon-heavy documents produced by the FCC. But when talking about spectrum the jargon is useful because the needed discussions must be precise. But it is a good primer on the complications involved in changing the way we use spectrum. There has been a recent clamor from the Congress to free up more spectrum for cellular broadband, but this docket is a good example of how complex of an undertaking that can be.