An asynchronous spread spectrum wireless-modem using a SAW convolver

The authors have developed a compact spread-spectrum (SS) wireless modem using a SAW (surface acoustic wave) convolver (the efficient ZnO-SiO₂-Si Sezawa wave convolver). The SS modem was based on a DS (data-scanning) method, where the PN (pseudonoise) code length was 127 bits and the code rate was 14 MHz. The demodulation method of the SS modem was a completely asynchronous one, which was very useful for application to wireless communication under the very weak signals. From 1989 in Japan, the allowed electric field of a transmitter without a license will be less than 500 μV/m at 3 m in the frequency range less than 322 MHz. Under this restriction the usual narrowband FM modem was effective only within a distance less than 11 m. The SS modem proved to be reliable for distances as far as 110 m