Sequence Design And Applications In Broadband Wireless Communications

Due to the demand of high data rate for future wireless services and limited spectrum resources,future wireless communication systems are required to provide strong interference-resistant ability,high spectrum efficiency,high freedom degree and flexibility.CDMA is a mature technology which has been broadly applied in 3G systems.The generalized conception of CDMA includes TDMA,FDMA and OFDMA as special cases. However,the interference-limited problem of traditional CDMA systems is serious,especially in broadband communications.Interference cancelation is one of the key technologies of CDMA systems.Since the auto-/cross-correlation properties of spreading sequences are directly related to the interference intensity,break through from the spreading sequences would be a direct and effective way to solve the interference-limited problem in CDMA system.First,the fundamental parameters and metrics of spreading sequences are introduced. Two new metrics are proposed to provide guidance for sequence design and performance analysis in later chapters.The definition of GO code is given to include all the existing orthogonal codes in a generalized frame.The development of various orthogonal spreading sequences is summarized,based on which the new sequence design criterion is proposed.Then,we study the sequence design and application in synchronized spreading spectrum systems.Perfect complementary(PC)code spreading and offset-stack modulation have been proposed in the CDMA system which can support multi-rate services flexibly. We analyze the multipath separation condition theoretically and propose a non-recursive receiver,which achieves interference-free performance and avoids the error propagation caused by the recursive receiver.By investigating the distribution of ZCZ of the Loosely synchronized(LS)code,We propose a new code allocation algorithm to improve the robustness of LS-CDMA system against channel deterioration.Different from the existing GO codes whose ZCZ length must be the power of 2,m-ZCZ code proposed by the author is a kind of GO code whose ZCZ length can be selected in integer field.We give the cyclic construction method for m-ZCZ code,and design the application style for m-ZCZ code in CDMA system.To support more users,we also propose a code with minimum ZCZ length of one,called ZCZ-one code.We study the code allocation scheme and the bandwidth allocation between spreading and coding,enable the new system with both large capacity and strong interference-resistant ability.Channel estimation is important for the above systems to realize interference-free performance ,hence we study the pilot-based channel estimation for general GO code based synchronized system.The impact of accuracy of channel estimation on system performance is theoretically analyzed,based on which the parameters such as pilot power and pilot number are optimized.Next,a novel GO code called Intergroup complementary(IGC)code is proposed for asynchronized spreading spectrum systems.IGC code has group-wise correlation properties ,based on which we propose a new code allocation scheme to match the ZCZ length with the relative time delay between users.Simulation results show that IGC-CDMA system has better BER performance and spectral efficiency than both traditional gold code based CDMA system and PC code based interference-free CDMA system.At last,two hybrid multiple access systems are studied.For MC-CDMA system,we analyze the relation between interference intensity and spectral correlation properties of the sequences.Then we design a novel sequence called generalized Walsh(GW)code with spectral ZCZs.The GW code based MC-CDMA system is then proposed,which can effectively eliminate interference and support multi-rate services flexibly with variable spreading factor GW(VSF-GW)code.For MIMO-CDMA system,we employ PC code spreading and delay multiplexing technique.The resultant system can eliminate interferences from both other users and other antennas.