Research On The Symbol Level Overlapped Gaussian Coded Multiple Access

The spectral efficiency is the important objective in the future mobile communication systems, and the multiplexing technique is one of the most important ways to improve the system's spectral efficiency. Overlapped Code Division Multiple Access (OVCDMA) is based on the generalized complementary orthogonal code, in theory, OVCDMA system's adjacent cell interference is zero, and codeword utilization can be much larger than 1, which means we can get a high system capacity and spectrum efficiency.In order to solve the adjacent cell interference of TD-SCDMA, Professior Daoben Li proposed a new networking design scheme: TD-OVCDMA. Accoding to the four-color theorem, only 4 generalized complementary sequences are needed in the OVCDMA networking, which can eliminate adjacent cell interference, at the same time interference between homochromatic cells is a little large. Therefore we must find a way to reduce it, in this thesis a new way of multiple access proposed by Professor Daoben Li is introduced:Overlapped Gaussian Coded Multiple Access (OVGMA), it can realize the channel capacity sharing in the real sense.OVGMA uses specific gaussian sequences to make original undifferentiated homochromatic signals orthogonal, without system's bandwidth expansion or changes of information transmitting rate and data flow structure. Multiuser detection is OVGMA's theoretical basis, and OVGMA system performs far better than IDMA system.This thesis is mainly about the research on the symbol level OVGMA, including the following four parts: In chapter 1, the evolution of 4G mobile communication is introduced at the beginning, and then an overview of key technologies that may be employed in 4G mobile communications is given, and there are brief explainations of four-color theorem and interference between homochromatic cells. The organization of following chapters is mentioned at the end of this chapter.In chapter 2, several kinds of pseudorandom sequence (PN) is introduced, and due to the nonideal correlation of the spreading codes, in traditional CDMA system there exists MAI all the time, then do a specific analysis of non-adjacent cell interference in OVCDMA networking, presented the link level TD-OVCDMA scheme, and in the end compared TD-OVCDMA four-color theorem networking scheme to the ITU-LTE networking model.In chapter 3, the fundamental principles of OVGMA are introduced at the beginning, including symbol level OVGMA and sequencial level OVGMA. After that the simulation of uncoded OVGMA system is performed, then use convolutional codes with short coding constraint length to cooperate the symbol level OVGMA system, system simulations using TPC codes with long coding constraint length are performed afterwards, all compared with IDMA systems and the excellent performance of OVGMA is proved. At last the performance comparision between system with TPC coding and LTE-Turbo coding is made, and the influence on system performance by using diffrent guassian sequences.In chapter 4, a summary of this thesis and a prospect of the research in future are made.