Research On PAPR Reduction In OFDM Systems

OFDM(Orthogonal frequency division multiplexing), employing multicarriers modulation (MCM) technique, enable 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.Firstly, three kinds of techniques, including pre-distortion techniques, coding techniques, and scrambling techniques, are introduced to reduce high PAPR on the basis of the principle of OFDM system. However, these techniques have some certain limitations. There is no technique can get all effective result in reducing PAPR, decreasing computation complexity and improving system performance.And then, aiming at solving the problem of PAPR reduction, two new methods of reducing PAPR of OFDM are presented in the thesis. The first is trellis structure search with the Cascade Pseudo-random partition method. The trellis factor search exhibits different PAPR reduction performances PTS with a variant constraint length LC , and the application of the Cascade Pseudo-random partition method improves the performance of the system. The second is the improved Dual Layered search based on random subblock, which change the whole search to Sub-Optimal search in the first Layer and use Pseudo-random partition method. This method reduces the computation complexity of the Dual Layered search and reduces PAPR of OFDM efficiently. Both of the methods canl reduce PAPR and the computation complexity effectively.At last, the thesis is summarized and an expectation of the further work is given.