communication system comprises one or more transmitters 5 and receivers 7 as shown in fig1 a and 1b respectively although only a single transmitter 5 and a single receiver 7 are shown in the figures embodiments of the present invention also comprise multiple access communication so that there may be two or more transmitters 5 operating simultaneously over the same channel for reception by two or more receivers 7 for multiple access communication interference concerns are overcome by using spread spectrum techniques a particular spread spectrum technique which may be used in the embodiments described herein is the u201c direct sequence u201d spread spectrum dsss technique in a typical dsss transmitter a pseudorandom or pseudonoise pn code sequence generator is used to interface the modulator at the transmitter to spread the transmitted signal a pn code sequence comprises a code sequence of 1 39 s and 0 39 s whose correlation properties are similar to that of white noise a pn code generator 12 is shown as comprising part of the transmitter 5 shown in fig1 a pn code generator 12 provides a pseudorandom code sequence this pseudorandom code sequence is modulated onto an information signal provided by an information source 10 the information signal comprises a plurality of data symbols intended for transmission the modulated signal output from modulator 11 is then optionally processed by a wave shaper 13 to condition the modulated signal prior to being radiated by an antenna 14 there exist a variety of pn code sequence schemes some of the widely used pn sequences are the maximum length shift register sequence or m.