Sec.  27.1221   Interference protection.

   (a) Interference protection will be afforded to BRS on a station by station
   basis based on the heights of the stations in the LBS and UBS and also on
   height benchmarking, although the heights of antennas utilized are not
   restricted.

   (b) Height Benchmarking. Height benchmarking is defined for pairs of base
   stations, one in each of two neighboring service areas. The height benchmark
   for a particular station in a service area relative to a base station in an
   adjacent service area is the distance'squared between the station and the
   GSA service area boundary measured along the radial between the respective
   stations, divided by 17. That is, the height benchmark is h[b] = D ^2 /17.
   Interference protection will be afforded on a station by station basis based
   on the actual antenna height above the radial average terrain (calculated
   along the straight line between the two base stations in accordance with
    Sec. 24.53(b) and (c) of this chapter) and this height benchmark.

   (c) Protection for a Receiving-Antenna not Exceeding the Height Benchmark. A
   base station receive-antenna with an HAAT less than or equal to the height
   benchmark relative to a neighbor's transmitting base station will be
   protected if that station's HAAT exceeds its height benchmark. That station
   is required to take such measures to limit the undesired signal at the
   receiving base station to −109dBm or less.

   (d) No Protection from a Transmitting-Antenna not Exceeding the Height
   Benchmark. A base station transmitting-antenna with an HAAT less than or
   equal to the height benchmark relative to a neighbor's receiving antenna is
   not required to protect that receiving station, regardless of the HAAT of
   that station.

   (e) No Protection for a Receiving-Antenna Exceeding the Height Benchmark. A
   base station transmitting-antenna with an HAAT greater than the height
   benchmark relative to a neighbor's receiving antenna is not required to
   protect that receiving antenna if its HAAT is greater than its height
   benchmark.

   [ 69 FR 72034 , Dec. 10, 2004, as amended at  70 FR 1190 , Jan. 6, 2005]