Research On Sequence Design For Quasi-synchronous Code-Division Multiple Access Systems

In code division multiple access (CDMA) systems, the correlation properties of thespreading sequences employed play an improtant role on the level of the interference,therefore directly influence the performance and capacity of the CDMA systems.Therefore, the designing of spreading sequences with good auto-correlation andcorss-correlation is one of the key points of the CDMA systems.In this thesis, we give a study on designing of spreading sequences forquasi-synchronous CDMA (QS-CDMA) systems. Several sequence sets withzero-correlation zone or low-correlation zone such as ZCZ sequence sets, optimal LCZsequence sets, quaternary LCZ sequence sets, ZCZ complementary sequence sets and twodimensional ZCZ array sets are constructed.The construction methods of cyclically distinct zero-correlation zone (ZCZ) orlow-correlation zone (LCZ) sequence sets are studied. A new construction of shiftsequence sets is presented at first, based on these shift sequence sets one can get manycyclically distinct ZCZ or LCZ sequence sets by utilizing the interleaving technique. Morethan that, mutually orthogonal sets of zero-correlation zone sequences are also constructedbased on these shift sequence sets.The construction methods of optimal LCZ sequence sets are studied. Based onpseudorandom sequences, a new construction of column sequence sets is presented at first.With these column sequence sets, a new class of optimal LCZ sequence sets whoseparameters can reach the Tang-Fan-Matsufuji bound is constructed.The construction methods of quaternary LCZ sequence sets are studied. Based on theinverse Gray mapping and a binary sequence with ideal two-level auto-correlationfunction, a new method to extend the number of quaternary LCZ sequence sets ispresented. And based on the shift sequences, a new construction of quaternary LCZsequence sets with larger set size is presented.The construction methods of mutually orthogonal ZCZ sequence sets are studied.Based on DFT matrices, two mutually orthogonal ZCZ sequence sets are constructed. A construction method of ZCZ sequence set is improved, which can provide many mutuallyorthogonal optimal ZCZ sequence setsThe construction methods of ZCZ complementary sequence sets are studied. Basedon orthogonal matrices and the interleaving iteration, two constructions of zero correlationzone aperiodic complementary sequence(ZACS) sets are presented. Based on binaryperiodic complementary sequence sets, we also constructed binary and quaternary zerocorrelation zone periodic complementary sequence(ZPCS) sets. The resultant binaryZPCS set is constructed by the interleaving technique and shift sequences. And theresultant quaternary ZPCS set is based on the inverse Gray mapping.The construction methods of two dimensional array sets are studied. Based on thebinary two dimensional array with ideal auto-correlation, a class of quaternary twodimesional array sets with zero-correlation zone are constructed by using the inverse Graymapping. Two methods for constructing two-dimensional ZCZ periodic complementaryarray set are also presented. The proposed methods are based on two-dimensional periodiccomplementary array sets (PCAS) and the interleaving technique.