Coded multiple chirp spread spectrum system and overlay service

An asynchronous spread-spectrum system called coded multiple chirp is proposed, and the possible spread-spectrum overlay over an analog FM-TV is investigated by computer simulation. In the proposed system, multiple single-sloped up and down chirps are encoded by a PN code and decoded by deciphers (pulse compression filters) followed by a digital code correlator. Performance of the proposed system, expressed in probability of bit error and code miss probability, is similar to that of noncoherent FSK using codewords, if sufficient compression gain is used. In the overlay where chirp is used to overlay an FM-TV channel, two chirp signals with data rate up to 25 kb/s could be overlaid in a 36 MHz satellite transponder without significant mutual interference. Performance estimates for a VSAT earth station operating at C-band show that a 2.4 m antenna and 300 mW transmitter could send a 2.4 kb/s signal to a large central earth station over an occupied channel.<>