The Theory Of Generalized Orthogonal Spreading Code And Its Applications In Multi-rate QS-CDMA Systems

In code-division multiple-access(CDMA)systems,the autocorrelation and cross-correlation(including periodic/aperiodic correlation and periodic/aperiodic partial correlation)properties of the spreading sequences employed play an important role on the level of the self-interference(SI),multiple access interference (MAI)and adjacent cell interference(ACI),therefore directly influence the performance and capacity of the CDMA systems.The theoretic bounds and the design of spreading sequences are two main issues in the theory of spreading sequences.In this thesis,the periodic and aperiodic partial correlation theoretic bounds of the zero correlation zone(ZCZ)or generalized orthogonal(GO)sequence are investigated and some GO sequences with good correlation properties are constructed.Based on the constructed sequences,some multirate quasi-synchronous CDMA(QS-CDMA)system models are proposed,and their interferences and performances are analyzed.Based on the concept of the GO spreading sequences,combining "weight vector method" and the concept of the low/zero correlation zone(LCZ/ZCZ),the theoretic bounds on periodic/aperiodic partial correlation of GO complex roots of unity sequences are investigated.The mathematic inequalities based on some parameters such as sequence length,the number of sequences,maximal periodic/aperiodic partial autocorrelation sidelobe and maximal periodic/aperiodic partial crosscorrelation are derived.The bounds are then generalized to those of normal complex roots of unity sequences.It has been proved that the new bounds include the existing bounds on GO sequences,such as Tang-Fan bounds and Peng-Fan bounds,and the existing bounds on normal sequences such as Paterson bounds, Sarwate bounds and Welch bounds,as special cases.Based on Z-complementary codes,the OVSF-ZCZ codes which not only have orthogonal variable spreading factor property but also have ZCZ property are constructed.Generalized pairwise Z-complementary(GPZ)codes which can be combined with quadratic phase shift keying(QPSK)are constructed.The correlation properties of OVSF-ZCZ codes and GPZ codes are investigated in detail. Furthermore,a construction of GO signature waveforms called GPZ-Chip waveforms are proposed based on GPZ codes and different waveforms,and the properties of GPZ-Chip waveforms are discussed as well.Two multirate single cell QS-CDMA system models are proposed,one is based on the binary phased shift keying(BPSK)modulation and variable spreading factor spreading technique;the other is based on QPSK modulation and multi-code technique.The OVSF-ZCZ codes are applied to the first multirate QS-CDMA system model and the corresponding bit error rate(BER)performance are analyzed. The numerical results show that the system performance can be improved significantly compared to those systems employing OVSF codes or ZCZ sequences, due to the fact that the multipath interference can be reduced dramatically.The GPZ-Chip waveforms are applied into the second multirate QS-CDMA system model and the BER performance are analyzed.The numerical results show that the performance can be improved very much compared to those of system employing the concatenated WH/m sequences with rectangular chip waveform,due to the fact that the multipath interference can be significantly reduced or even eliminated.Based on generalized loosely synchronous(GLS)sequence sets,the GOS sequence sets whose correlation properties are similar to those of GLS sequence sets are constructed.Furthermore,GLS-Chip waveforms,a new construction of GO waveforms,are investigated based on GLS sequences and different chip waveforms. The correlation properties of the GLS-Chip waveforms are discussed in detail.Both the GOS sequence sets and the GLS-Chip waveforms can be applied to the multirate multicell QS-CDMA systems.Two multirate multicell QS-CDMA system models are then proposed.When the GOS sequence sets and GLS-Chip waveforms are applied to these system models, the corresponding interferences and BER performances are investigated and analyzed.The numerical results show that the system capacity can be improved compared with that of the systems employing GLS sequences(waveforms),it is because both of the ACI and multipath interference can be reduced much or eliminated.