Design of a Convolver-Based Packet Voice Spread Spectrum System
M. Kowatsch · 1984
A spread spectrum system for the transmission of packet voice has been developed. Using a continuously variable slope delta (CVSD) modulator, speech signals are encoded at 16 kbit/s. The encoder output data stream is split into blocks of 1024 bits, which are t ransmitted in bursts at a data rate of 84 kbit/s. For data representation binary code shift keying (CSK) is employed. The spreading modulation is direct-sequence (DS) with a chip rate of 21.4 MHz. The receiver design is based on the application of two SAW elastic convolvers to programmable matched filtering of the continuously changing code patterns. The alignment of received signal and local reference is accomplished by means of an 11-bit preamble preceding each data packet. Experiments are in good agreement with theoretical predictions, measures of performance being the probability of burst loss and the bit error probability in an additive white Gaussian noise channel.