Synchronous spread-spectrum multiplex communication system using a modified M-sequence

An attempt is made to improve the frequency efficiency of spread spectrum (SS) communication by reducing the correlation between spreading codes. Proper selection of spreading codes and maintenance of synchronization between the codes are demonstrated to yield a zero-correlation value. The resulting disappearance of interchannel interference raises the possibility of synchronous SS communication with as many multiplex channels as in a TDMA system. A modified M-sequence is obtained using a dc offset to an M-sequence that reduces the autocorrelation sidelobe to zero. The bit-shifted modified M-sequences are implemented as spreading codes for each channel. Attention is given to the effects of bandwidth restriction and noise in the transmission channel, and selection of an appropriate filter is proven an acceptable method of eliminating the transmission noise.