FULL-DUPLEX ASYNCHRONOUS SPREAD-SPECTRUM MODEM USING A SAW CONVOLVER FOR 2.4-GHZ WIRELESS LAN

An asynchronous spread spectrum (SS) modem for 2.4-GHz wireless LAN ha s been implemented using an efficient ZnO-SiO2-Si surface acoustic wav e (SAW) convolver. The design of the highly efficient SAW convolver wa s developed at Tohoku University and commercially manufactured by Clar ion Co., Japan. The modem can operate under full-duplex transmission i n the same frequency range of the 2.4-GHz SS band. The SS modem is bas ed on a direct-sequence/code-shift-keying (DS/CSK) method for the modu lation. Pseudo-noise (PN) codes are chosen from a preferred pair of 12 7-chip m-sequences and the code rate is 14 MHz. The asynchronous demod ulation is simply realized utilizing the coherent correlation characte ristics of the SAW convolver. Under full-duplex transmission, the self -jamming caused by a transmitted signal in the modem itself is effecti vely reduced by an RF isolator and the SS processing gain. The impleme nted modem has been tested using a coaxial cable with attenuator. A bi t error rate of 10(-6) under full-duplex transmission is observed at - 78.3 dB of a desired to undesired signal ratio. The effective range is estimated on the basis of two-path propagation model. From self-jammi ng rejection of -78.3 dB, the effective range under real-time full-dup lex is estimated to be about 200 m.