понедельник, 21 июня 2010 г.

OFDM, COFDM: Link-11, Tadil-A, Alligator

Link-11, Tadil-A, Alligator
MIL-STD 188-203-1A, Sh-110, Br-75, Ch-14+1+Pilot, pi/4 DQPSK, k = 7/15 = 0.466(6)

Author: SergUA6
Band Width ~2400 Hz
Low Range ~500 Hz, shift is possible, recieved in SSB
Baud Rate 75 Hz in channel
n-Ary (PSK/MPSK) pi/4 DQPSK in he channel
Count of Carriers 14 frequency manipulation in the block + 1 channel + 1 pilot-tone
Step between carriers 110 Hz in the block, 550 among the block and one morePilot tone(s) 1 pilot tone ~550 Hz, shift is possible, recieved in SSB
RX mode SSB

pic.1 Generall view

pic.2 Graphical spectrum

pic.3 Structure of the short start and generall parameteres of the signal

pic.4 Constellation in the channel

Link-11, Tadil-A, Alligator - is not rare signal on the air. this signal is characteristic enough for ear. It can be easily identified, because similar stuff is hardly can be found. There are two sorts of such signal, with rather long burst as in the example and with the short one. Both sorts of this signal has identical parametres, except lengh, for LINK-11 short, it does not exceed 300 msec, and usually an order 80-100 msec. Technical speed makes 15*75*2 = 2250 bps.