FULL-DUPLEX TRANSMISSION OPERATION OF A 2.45-GHZ ASYNCHRONOUS SPREAD-SPECTRUM MODEM USING A SAW CONVOLVER

An asynchronous spread spectrum (SS) modem in the 2.45-GHz band has be en implemented using an efficient ZnO-SiO2-Si surface acoustic wave (S AW) convolver. The design of the highly efficient SAW convolver was de veloped at Tohoku University and commercially available devices have b een manufactured by Clarion Co., Japan. The modem can operate under fu ll duplex transmission in the same frequency range of the 2.45-GHz SS band. The SS modem is based on a direct-sequence/code-shift-keying (DS /CSK) method for the modulation. Pseudonoise (PN) codes are chosen fro m a preferred pair of m-sequences of a period 127, and the code rate i s 14 MHz. The demodulation is carried out asynchronously, utilizing th e coherent correlation characteristics of the SAW convolver. The main interference caused by a transmitted signal in the modem itself is eff ectively reduced by an RF isolator and the SS process gain. We have ex perimentally confirmed a sufficient self-jamming rejection capability: a bit error rate of 10(-6) is observed at -78.3 dB of a desired to un desired signal ratio using an artificial transmission line.