Monday, December 31, 2012

Harm claim thresholds for satellite earth stations

I'm reasonably confident at this point about deriving harm claim thresholds for cellular neighbors and TV receivers (see e.g. the TPRC 2012 paper Here's a first cut (a few months old, but I'm behind on blogging...) at thresholds for satellite earth stations.

For satellite systems with mobile receivers (e.g. satellite navigation systems like GPS) the harm claim threshold would resemble that for a cellular system: a profile of aggregate field strength over a spatial region, for the licensed block and a range of frequencies above and below it, observed at some height(s) above ground level, that must be exceeded at more than a given percentage of locations and times for a claim of harmful interference to go forward. Since the desired signal level from the satellite is known and relatively constant, the harm claim thresholds would be informed by the in-block and out-of-block protection ratios required by the receiver.

Some satellite earth station receivers have fixed locations specified in their license. In such cases, the harm claim threshold needs to be defined only at the location of the earth station, and not over a spatial region.

If the location of the transmitter is known, as in the case of geostationary satellites, the harm claim thresholds could vary in azimuth, with more interfering energy allowed from (say) a northerly direction if the satellite is in the southern sky; cf. the Northpoint case.  Satellite earth stations with low elevation angles have a significant difference in gain in azimuth that can exceed 10 dB.  The harm claim thresholds would therefore vary with azimuth. If the pointing direction, say α, is fixed in the license, then there would be a low harm claim threshold for azimuth direction [α-10, α+10] degrees, and a higher one for the remaining directions. For earth stations that change their pointing direction because they are intended to operate with different satellites at different times, the low threshold azimuth range would have to be wider to encompass the full range of pointing directions.

Since satellite antennas are highly directional, their off-axis gain is minimal more than 10 degrees off-axis (Morgan & Gordon 1989, Figure 3.74). Most earth stations operate with a minimum elevation angle of 5 degrees. The harm claim thresholds could therefore be specified for a partition of incoming elevation angles, for example 0 to 10 degrees, 10 to 20 degrees, and greater than 20 degrees.

Having added satellite earth stations, one begins to see the permutations of receiver and transmitter protection regimes. Let us refer to the assignment being given thresholds as R (the receiving system), and the neighboring system(s) as T (since adjacent transmissions impact receivers in R):
  • TV: Incumbent (television ) in R; R's transmitter location fixed, R's receiver location arbitrary 
  • Earth station: Incumbent (satellite) in R; R's transmitter location fixed or arbitrary; R's receiver location fixed 
  • Cellular: New allocation in R, incumbent (cellular) in T; T's transmitter location arbitrary, T's receiver location arbitrary
  • GPS: Incumbent (satellite) in R; R's receiver location arbitrary. Harm claim thresholds for GPS would assume T's transmitter locations are arbitrary 

I'm grateful to Rich Currier for his tutorials; all the errors and misconceptions are mine.

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