Direct sequence spread spectrum digital communication system employing sequence changing during transmission and transmitter and receiver implementing same

摘要

A digital signal receiver comprises receiver and demodulator means producing from the received signal a succession of complex elements. It produces sequences of successive complex elements consisting of conjugate elements of homologous elements used at the transmitting end. The sequences so used at the receiving end are synchronized to the homologous sequences used at the transmitting end. The complex elements obtained at the output of the demodulator are multiplied by a corresponding sequence of successive complex elements so produced and synchronized. The resultant complex elements appearing during the duration of an information symbol are summed over said duration to produce an estimate of the original information symbols used at the transmitting end. The complex elements obtained at the output of the demodulator are analyzed to identify a marking introduced at the transmitting end. Selector means ae controlled in response to the marking so identified in such a way as to retain the same sequence of conjugate complex elements or to change sequence. Successive sequence changes occur at random times determined by the receiver exclusively by analyzing said markings but in a deterministic order shown intrinsically to the receiver. The marking may consist in the relative values (the same or opposite values) assigned to the first two elements of the sequence for each information symbol.