A DS/FH Burst Communication Modem based on SAW Elastic Convolvers

This paper presents a burst-type spread spectrum communication modem with binary orthogonal code shift keying (CSK) employed for data modulation. A burst consists of an 8-bit synchronization preamble followed by a block of 1000 message bits, transmitted at 84 kbit/s. The spread spectrum modulation scheme is direct sequence (DS) combined with noncoherent frequency hopping (FH). Each bit of both the preamble and the message portion of a burst is encoded by a different 255-chip Kasami sequence with a chip rate of 21.4 MHz. The hop rate of the carrier is equal to the data rate, the number of frequencies being 13. The total transmission bandwidth is 300 MHz. Receiver signal processing is based on the application of two SAW elastic convolvers to programmable matched filtering. Performance measurements in a simulated communications channel show good agreement with theory.