An asynchronous spread spectrum (SS) wireless modem has been implemented using an efficient (ZnO-SiO2-Si surface acoustic wave (SAW) convolver. The modem is based on a direct-sequence/frequency-shift-keying (DS/FSK) method for the modulation. The demodulation is carried out asynchronously utilizing the coherent correlation characteristics of the SAW convolver. In order to improve the narrowband interference rejection capability, we propose a new technique based on the reference signal control. A notched-reference-signal circuit and a self-convolution canceler are implemented in the SS modem for the reference signal control. It was found that the antijam capability for narrowband interference is at least -24 dB of desired-to-undesired power ratio (D/U); the improvement of the antijam capability is 16 dB up as compared with our previous SS modem.
|Number of pages||7|
|Journal||IEICE Transactions on Communications|
|Publication status||Published - 1993 Aug|