Research On Selected Mapping To Reduce PAPR In OFDM System

Orthogonal Frequency Division Multiplexing(OFDM) is a kind of Multicarrier Modulation technology. It has a lot of advantages, such as powerful immunity, high spectrum efficiency, higher data transmission speed and so on. DFT can greatly reduce the complexity of the receiver. This technology is considered as the core technology of the future 4G wireless communications. However, the high peak-to-average power ratio(PAPR) of OFDM signals results in nonlinear distortion and degradation of bit error ratio(BER) performance, which is the obstacle of utilities of OFDM. So it is necessary for us to research the PAPR reduction algorithms.The ways to reduce PAPR are generally divided into three sorts: Pre-distortion, Coding and Multiple signal representation. The detailed study and simulation are done in this thesis. These ways will be properly chosen for practical systems according to the need of the system, because each way has its advantage and disadvantage. At numerous methods of reducing peak-to-average power ratio(PAPR), the selected mapping(SLM) is a well effective method. In this thesis, the SLM methods of reducing PAPR of OFDM are researched. Some valuable conclusions are acquired. The main contents are as follows:1. An adaptive choosing the copy-frame number model of SLM is proposed. In the SLM, it needs more IFFT process whose number is equal to copy-frame number, this cause the high complexity of the system. An adaptive choosing the copy-frame number model of SLM is proposed in this thesis. At the basic of the PAPR meets some qualification, it can choose out the very suit copy-frame number of system though the adaptive choosing the copy-frame number arithmetic. This makes the systemic complexity keeping in the lowest floor, and at the same time reduces the PAPR effectively.2. An improved IFFT algorithm of SLM is proposed. Selective mapping (SLM) is a better way in reducing peak-to-average power ratio(PAPR) of the OFDM system, unfortunately it needs to calculate the additional V-1 times IFFT operations, which causes the high complexity of the system. An improved IFFT algorithm can reduce the complexity of the system, whilst it can reduce the multiplication operation of real domain in IFFT and make the SLM-OFDM system avoiding large IFFT operation. The analysis of the complexity and simulation results show that the proposed method can not only simplify the computation, improve the efficiency of operations, but also can reduce the PAPR effectively.