An asynchronous spread spectrum (SS) modem in the 2.45-GHz band has been implemented using an efficient ZnO-SiO2-Si surface acoustic wave (SAW) convolver. The design of the highly efficient SAW convolver was developed at Tohoku University and commercially available devices have been manufactured by Clarion Co., Japan. The modem can operate under full 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 from a preferred pair of MSequences of a period 127, and the code rate is 14 MHz. The demodulation is carried out asynchronously, utilizing the coherent correlation characteristics of the SAW convolver. The main interference caused by a transmitted signal in the modem itself is effectively reduced by an RF isolator and the SS process gain. We have experimentally confirmed a sufficient self-jamming rejection capability: a bit error rate of 10”6 is observed at -78.3 dB of a desired to undesired signal ratio using an artificial transmission line.
|Number of pages
|IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
|Published - 1993 Sept