An application of SAW convolvers to spread-spectrum transmission of packet voice

A spread-spectrum system for the transmission of packet voice is presented. A continuously variable slope delta (CVSD) modulator is used to encode speech signals at 16 kilobits per second (kbps). The resulting binary data stream is transmitted in bursts containing 1024 message bits. The bit rate within a bursts is 84 kbps, with binary code shift keying (CSK) being employed for data representation. The spreading modulation is direct-sequence (DS) with a code rate of 21.4 MHz. The receiver signal processing is based on the application of SAW elastic convolvers to programmable matched filtering of the continuously changing code patterns. Synchronization is accomplished with the aid of an 11-bit preamble preceding each data packet. Experimental results on the performance of the spread spectrum modem are presented and compared with theory.