Transmission bandwidth control schemes for direct sequence/spread spectrum systems in the presence of periodic partial-band interference

When a processing gain of a direct sequence spread spectrum (DS/SS) system is too small to suppress nar rowband interferences and the interference power is much higher than that of the desired signal, an adaptive filter [5-7] cannot compensate for the uncorrelated interference signals because the filter coefficients cannot be updated. In this case, if the interfered bands are known, a notch or bandpass filtering is useful. However, such frequency domain filtering in the receiver may suppress not only the interfering signals but also the desired one. Prefiltering in the transmitter [8] cannot achieve the same performance as DS/SS systems without a bandpass-fllter in the absence of interference. This paper proposes and investigates a scheme of controlling the transmission bandwidth and its power spectral density using two spreading sequences in order to improve the performance in the presence or absence of high-power periodical partial-band interference. Two concrete systems also are proposed: a spreading sequence serial transmission system using different spreading 81 sequences; and a spreading sequence selectable ARQ system. In the former system, the transmitter does not consider the phase of the periodical partial-band interfer ence in the receiver. Therefore, the system is realized easily because of the rather loose timing control require ment on the penalty of bit rate and because it does not require backward channels. On the other hand, in the latter system, 75 percent of the transmitted data are not degraded by the interference because of the more careful channel state selection at the transmitter than the former system.