Design And Realization Of Several Spreading Sequence Sets

It is well-known that sequences with good periodic auto-correlation and cross-correlation functions find their applications in the field of spread spectrum communications, CDMA systems, channel estimations, synchronizations, system identifications, radar and sonar systems, etc. There are many different kinds of sequences and it is clear that different applications may require different sequences with specific properties. The thesis mainly discusses ZCZ sequences, perfect sequences and the modified Chu sequences.Firstly, essential concepts associated with sequences design, including periodic and aperiodic correlation functions, contemporary applications for spreading sequences in CDMA systems, and Sanxingdui Coding System Project are introduced Afterwards, optima] periodic sequences, good aperiodic sequences and complementary sequences are reviewed and the flowcharts of the program to generate and analyze these sequences are given.Secondly, the concept of zero correlation zone (ZCZ) is presented, which can be employed in quasi-synchronous CDMA (QS-CDMA) to eliminate the multiple access interference and multi-path interference. Then, several sets of ZCZ sequences, including LA and LS code sequences used in LAS-CDMA systems, and theoretical periodic limit for ZCZ/LCZ sequences are described. These ideas, in fact, open a new direction in spreading sequence design.Thirdly, a set of modified Chu sequences is proposed with similar correlation properties to those of normal Chu sequences except for a special case. Compared with Chu sequences, the modified Chu sequences have a smaller alphabet size. In addition, perfect sequences, Frank sequences and Chu sequences, are also discussed.Finally, the thesis concludes by summarizing the main contributions of the research and presenting directions for future work.