Yukitsuna Furuya

DS/CDMA adaptive interference canceller on differential detection in fast fading channel

This paper proposes a multiple-access interference (MAI) canceller for direct-sequence code-division multiple-access (DS/CDMA) mobile radio communications, which can operate effectively in fast fading environments. The proposed canceller consists of a fractionally chip-spaced code-orthogonalizing filter (COF) and a differential detector. The COF adaptively makes its tap coefficients orthogonal to all other users spreading codes by minimizing the mean squared error between the detected and decision signal. After the MAI cancellation, the differential detector removes fast phase variation in the desired carrier due to fading. The proposed adaptive interference canceller (AIC) only uses the desired spreading code and needs no information about other users. Thus, the AIC is practical for its simplicity and promising for future DS/CDMA mobile radio systems.<<ETX>>

Optimum pre-emphasis for FM transmission with frequency-domain voice scrambling

Optimum pre- and de-emphasis are theoretically investigated for FM and PM transmission, including frequency-domain scrambling for voice security. Using a linear system model, the optimum frequency characteristics for pre- and de-emphasis filters are given as functions of the voice signal spectrum, demodulator output noise spectrum, and the scrambling method. Comparisons of the maximum attainable SNR (signal/noise ratio) are made for various cases including plain voice (nonscrambling) and secured voice scrambled by spectrum inversion, reverberation, and DFT (discrete Fourier transform) spectrum transformation, assuming simple voice and noise spectra.<<ETX>>