An asynchronous multi-channel spread spectrum transceiver using a SAW convolver

The authors have developed a compact spread-spectrum (SS) wireless modem using a SAW (surface acoustic wave) convolver. They utilized the efficient ZnO-SiO₂-Si Sezawa-wave convolver. The SS modem was based on the DS/FSK (direct sequence/frequency shift keying) method, where the PN (pseudonoise) code length was 127 chips and the chip rate was 14 MHz. The demodulation method of the SS modem was a perfectly asynchronous one, which was useful for its application to wireless communication under a very weak signal. The total number of channels of the DS/FS method was confirmed to be more than 200000 within a 28-MHz SS band. Under the 1989 transmitted-power limits in Japan (0.05 μW/120 kHz:500 μV/m at 3 m in the frequency range below 322 MHz), the SS modem proved to be reliable over a distance greater than 110 m. Furthermore, the asynchronous SS modem of 1-W transmission power with a 900-MHz SS band in the US proved to be reliable over a distance as great as 8 km