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7 and 13 GHz ENG Will Complicate Fixed Services Sharing

The FCC issued a Further Inquiry into Fixed Service Sharing of the 6875-7125 MHz and 12700-13200 MHz bands for Wireless Backhaul that seeks "focused comment on "certain issues raised in the Commission's Wireless Backhaul proceeding."

In addition to further discussion of the feasibility of sharing, the Inquiry asked for comments on "limiting the frequency ranges available for Fixed Service (FS) in order to ensure the continuation of electronic newsgathering operations."

The FCC noted that "Both supporters and opponents of the proposal express concerns about how to protect existing electronic news-gathering operations using TV pickup stations from interference due to FS operations, and whether meaningful FS operation in the bands will be possible given the potential for such interference."

The FCC said there was little concern about the ability of FS to coexist with fixed Broadcast Auxiliary Service (BAS) and Cable Relay Service (CARS) operations in filed comments. One item I didn't see in the discussion was that ENG/TV Pickup has coexisted with fixed BAS and, to a lesser extent, CARS. The reason this works is that local SBE coordinators know where the fixed BAS links are located, and stations involved cooperate by either using their own fixed frequencies for ENG use on different paths or otherwise ensure that ENG paths do not illuminate the receive point of other stations' fixed links. One thing that makes coordination easier is that fixed BAS links usually terminate at the main antenna farm for transmitters or at a few relay sites in a market, unlike FS links with locations throughout a market.

The Inquiry asks if a portion of the 7 and 13 GHz bands should be reserved exclusively for BAS and CARS operations. Broadcasters, for example, can operate broadcast auxiliary facilities on a short-term basis as secondary operations with local coordination, but without prior Commission authorization.

The FCC proposed reserving two 25 MHz channels for BAS and CARS use in each band. That proposal would maintain status quo in the 7075-7125 MHz and 13.15-13.20 GHz bands. The FCC also seeks comment on other alternatives for reserving BAS/CARS spectrum and "how alternative technologies for providing video coverage of live events may affect the need to exclude FS from a portion of these bands."

Channelization is another issue.

FS operations have used 25 MHz channels, but the FCC proposed allowing a variety of bandwidths. Several commenters indicated that allowing 10 and 30 MHz channels would preclude operation on multiple 25 MHz channels used by BAS and result in wasted spectrum. The FCC sought comments on whether the maximum channel bandwidth in these bands should be limited to 25 MHz. Two channel plans were proposed, one based on existing 25 MHz channels and another from the Fixed Wireless Communications Coalition (FWCC) based on 28 MHz, which it said comes from the ITU.

Coordination for BAS and FS is different. Temporary BAS operation is allowed using informal frequency coordination; FS requires more detailed procedures that are not appropriate for newsworthy events. Reserving spectrum for BAS might help in some markets, but two 25 MHz channels are unlikely to be sufficient for larger markets or big events.

One concern with the original proposal was that it could apply minimum capacity and loading requirements to links used for relay remote news feeds. The FCC clarified this, stating these requirements would apply to Part 101 links only, not BAS Part 74 and CARS Part 78 links. It also pointed out that Section 101.141(a)(5) exempts transmitters carrying digital video motion material from the Part 101 capacity and loading requirements.

An attachment to the Further Inquiry includes nationwide maps showing all active BAS and CARS facilities within the specified bands, excluding special temporary authority (STA) BAS TV pickup operations. When a center point and radius were specified as the area of operation, this data was used. For "other" areas of operation, a 90 km radius was used. It isn't surprising these plots show little "white space" in the most populated areas.

Comments are due June 27, 2011.

Doug Lung is one of America's foremost authorities on broadcast RF technology. He has been with NBC since 1985 and is currently vice president of broadcast technology for NBC/Telemundo stations.