Decoding Based On Coding To Reduce PAPR Of OFDM Systems

OFDM(Orthogonal frequency division multiplexing),employing multicarriers modulation (MCM) technique, enables it to transmit signals by using orthogonal multiple subcarriers and has ability of resisting multipath interference. OFDM scheme has been adopted in several recent digital wireless broadcast and network standards, including digital audio broadcasting (DAB),digital video broadcasting over terrestrial network(DVB) and Wireless Local Area Network(WLAN). However, high Peak-to-Average Power Ratio(PAPR) of the transmitted signal is a major drawback of OFDM. Therefore, linear amplifiers with wide dynamic range are required in OFDM transmitters, and they are expensive and inefficient. Amplifier's non-linearity will cause nonlinear distortion and spread of the spectrum of the transmitted signal. Consequently, it is important to reduce PAPR of OFDM by an appropriate technique.Mainly focuses on the techniques of PAPR reduction, I have achieved the following work:(l)The paper first analyzes the basic theory and key technique of OFDM system. Then, the definition add distribution of PAPR is presented in detail.(2) On the basis,the paper sumrnarizes the most popular three kinds of PAPR reducing techniques, including:Clipping technology,Coding technology and non-distorting technology. Also,the paper makes thorough compare of these methods,and draws conclusions. Particularly,strong emphasis is cast on the basic theory of block coding and method of Golay complementary sequence and use MATLAB software to achieve simulation.(3)The paper mainly extends the ordered statistic decoding(OSD) algorithm to the model suitable for block codes over Z Mwith PAPR reduction in OFDM systems,gives the simulation and comparsion of computation complexity. According to the drawbacks (most of the cadidate codewords are processed at phase-i of order-I reprocessing),the paper use more information about N-K reliability values out the MRB and improves the algorithm. It proved that the computation complexity of the improved algorithm is far smaller than the former.At last, the thesis is summarized and an expectation of the further work is given.