I thought 8-PSK modulation were only used on the Ka-band spotbeams for now at least?
Because their higher PFD beam footprint compensates for the loss in signal robustness by going to a higher level modulation.
Ka CONUS beams still all use QPSK though due to their lower PFD footprint.
Note: Although I notice that Ku band CONUS transponder 24 at 119 (D7S) is using 8-PSK for Spanish MPEG-4 MEGA HD (ch. 405) and TFTw HD (ch. 408).http://www.lyngsat.com/DirecTV-7S.html
Assuming the LyngSat entry is accurate of course ...
EDIT: Then again looking at the formula for satellite data throughput I posted back in January. http://www.dbstalk.c...11&d=1327482283
I suppose they really had to go to an 8-PSK modulation level to achieve something close (~37 mb/s) to the typical ~39 mb/s data rate for Ka band CONUS HD programs mentioned earlier in this thread.
With a 24 Mhz wide transponder on Ku band, they only had the SD standard SR of 20,000 KiloSym./sec. to work with instead of the normal 30,000 KS/sec. on Ka band for HD afforded to them by the larger 36 Mhz wide transponders employed there.
Edited by HoTat2, 13 June 2012 - 09:30 AM.