The FCC plans a complicated spectrum auction next year that would reallocate spectrum in the 600 MHz range from broadcast use to mobile communication use. As an incentive, broadcasters could sell their spectrum back to the government and either go out of business or share a 6 MHz channel with another broadcaster. Each station that participates in the auction will set a selling price, and through a complicated decision process the FCC will decide whether to accept that price or not. This is the “reverse auction.” The amount of spectrum that will be cleared of broadcast stations won’t be known for quite some time. It will require a repacking of the remaining broadcast spectrum, so some (many? most?) remaining TV stations will be required to relocate to a different channel.

More or less simultaneously is the “forward auction,” where the cleared spectrum is auctioned off for mobile communications use. The FCC has already established a channel structure for the mobile communications users. It consists of spectrum blocks 5 MHz wide for base-to-mobile links (downlink) and separate blocks 5 MHz wide for mobile-to-base links (uplink). This arrangement is known as frequency division duplex.

The FCC has also floated a set of 12 scenarios with channel plans that go from two mobile communications licenses to 12 licenses. Each scenario lays out the spectrum assignments for the mobile licensees plus several guard bands. Guard bands to limit interference are needed between the highest remaining broadcast channel and the lowest mobile communications block; also on either side of TV channel 37, which is used for radio astronomy, not broadcasting; and also a “duplex gap” of 11 MHz.

A duplex gap is needed by mobile communications technology. It separates the uplink and downlink frequencies. It’s needed so that a mobile radio’s transmitter does not cause interference to its own receiver. There is filtering designed into mobile handsets that protects against such interference, but the smaller the frequency separation, the more expensive the filters. There is consensus that 11 MHz is an acceptable guard band.

As I’ve written in the past, among others harmed by this spectrum auction are wireless microphones and unlicensed white spaces devices (WSDs). Both lost out on spectrum that the FCC had previously allocated for those uses, but then took away to give to licensed mobile communications. While there might still be some post-auction unused TV channels in town that would be shared by wireless mics and WSDs, part of the duplex gap was supposed to be exclusively for wireless mics. That changed in August.

In August, the FCC issued a Public Notice entitled “Broadcast Incentive Auction Scheduled to Begin on March 29, 2016; Procedures for Competitive Bidding in Auction 1000, Including Initial Clearing Target Determination, Qualifying to Bid, and Bidding in Auctions 1001 (Reverse) and 1002 (Forward).” In this document, the FCC decided that TV stations could be relocated to the duplex gap.  We can now review the comments that criticize that decision.

The National Association of Broadcasters has filed a petition for reconsideration of that decision. Broadcasters are major users of wireless mics for live news coverage and sports programming.

Sennheiser, a major manufacturer of wireless mics, referred to “real-time operational requirements” for “hyper-critical links for when there is no ‘second chance,’ i.e., breaking news, film production, professional concerts and theater, and historic political and civic events.” Since any spectrum still available for wireless mics would be shared with WSDs, coordination would be needed, but the coordination procedures would be too time-consuming for breaking news.

And of course, the cable industry is a large user of wireless mics, through ESPN and other programmers.

But that’s not all. Relocating a TV station to the duplex gap almost assures interference problems. The TV station will cause interference into mobile communications receivers.  TV channel 51 occupies 692-698 MHz, the highest frequency still remaining for over-the-air TV broadcasting. It is adjacent to the 700 MHz spectrum band that was previously reallocated from TV broadcasting to mobile communications. There has already been such interference from TV channel 51 broadcasters into mobile receivers.  For example, WJAR-TV in Providence was causing interference to T-Mobile in Boston.

There are other controversies associated with other aspects of the FCC incentive auction.  For example, some Low-Power TV stations may be unable to find a channel for relocation. There are questions about must-carry carriage rights when two stations share a 6 MHz channel.  In addition, there are controversies over bidding procedures, the FCC’s anti-collusion rules, access to the FCC’s software to run simulations, and probably other areas. This road is getting pretty bumpy.