Studying On Reducing Peak-to-Average Ratio Of MC-CDMA

Capacity and performance of mobile radio systems essentially depend on the choice of the multiple access scheme. A novel and promising wireless digital modulation/multiple access technique called Multicarrier CDMA is studied in this thesis, including reducing the peak-to-average ratio, which is one of its key techniques.MC-CDMA is combination of OFDM and CDMA, thus advantages of both techniques are exploited. With MC-CDMA, each data modulated chip of the user specific spreading code is mapped onto a separate subcarrier after spreading and scrambling, so that the chips of the spreading code and, hence, the data symbol is transmitted in parallel on multiple subcarriers. Spreading codes ensure the MC-CDMA a multiuser system. The application of MC-CDMA enables one to avoid ISI and ICI in the detection process, resulting in advantages of frequency diversity.The peak-to-average ratio (PAR) of signals decides the volume of PA in some cases. High PAR restricts the use of MC-CDMA base station, which is obstacle of utilities of MC-CDMA.This thesis researches on reducing the PAR of MC-CDMA from two different points.On one side, this thesis studies behaviors of MC-CDMA with Golay complementary sequences as spreading sequences. Simulation Indicates that the PAR of MC-CDMA can be upper bounded 6dB by using Golay complementary sequences and S-R sequences as spreading sequences, which is much superior to m sequences and Hadamard sequences.On the other side of view, compared with the old Basic Selected Mapping method, this thesis proposes some other selected mapping algorithms and compares the performances based analysis and simulation. Analysis indicates that Circular Shift Block Selected Mapping algorithm may have well foreground of application with the number of bits required to represent side information much less with little loss of performance.