Overlapped Code Division Multiple Access Network Research

In wireless communications, various multiplexing technologies are employed to improve the spectrum efficiency. Furthermore, because of the channel fading, diversity techniques should be used to improve the reliability of wireless transmission. Advanced code division multiple access technology named overlapped code division multiple access technology is studied in this thesis.this overlapped code division multiple access system uses spreading codes,which of perfect autocorrelation and crosscorrelation characteristic,thus can eliminate the interference between network cells,also have better performance than traditional code division multiple access system.in this system,overlapped multiplex technology is employed to improve codes utilization.overlapped multiplex is a new technolgy which can improve system capacity.multiple antenna technology is also used in this new network system.Main component discussed in this paper is construction of Overlapped Code Divide Multi Access(OVCDMA) Multi-cell simulation system and application of detection algorithm in receiver. A group of orthogonal Codes are designed, Different groups of codes are distributed to different cells to ensure that signal from different cells are orthogonal. Inside a cell different shifts of one group of code are used as user addresses. This overlapped design has two advantages. First it can enhance codeword utilization. Second, coding gain can be obtained. In the construction of system, multi-antenna is also considered. Multi Input Multi Output (MIMO) is introduced to OVCDMA system to obtain diversity gain. System can achieve higher capacity and reliability.In the receiver, sequence detection algorithm like Viterbi Algorithm (VA) can be used to recover transmitted data. Though being the optimal sequence decoder, VA is too complex to be used in practical because of the large constraint length in frequency-selective channel. Other two sub-optimal sequence decoders Fano and Stack decoder are used in system. Complexities of these two decoders are independent from constraint length. Another important aspect of this paper is the usage of Multi User Detection (MUD) algorithm in OVCDMA system. MUD is different from conventional detection because it treats interference from other users as constraint rather than destructive distribution. MUD is widely used in 3G communication systems. Single subcarrier Frequency Domain Equalization (FDE) is a technique which is used in LTE standards. it has an advantage in performance comparing with OFDM. FDE is also an aspect of this paper.In this paper principle of OVCDMA is described in details. Several types of detection algorithm is introduced from its theory to the application in OVCDMA system. After the theoretical analysis lots of simulation results are also provided. Analyzing from this simulation results, OVCDMA can completely eliminate interference from other cells. It can provided a remarkable performance with high spectrum efficiency。...