Research On Reducing Peak-to-Average Power Ratio Of OFDM System In Power Line Communications

Power Line Communications, also called PLC, refers to a mode of transmission of signals, such as language and data etc., by power lines. Orthogonal Frequency Division Multiplexing, also called OFDM, is a critical technology for the realization of PLC. The OFDM, which has an excellent resistance against multipath fading and interference, is an important technique of data transmission. However, the Peak-to-Average Power Ratio (PAPR) of the OFDM is high, which lead to the low system performance. It is necessary to take a mearsure to reduce the PAPR of the OFDM. The current study analyzed the causes of high PAPR. This thesis mainly concentrates on the reduction of PAPR in OFDM.Firstly, in the paper, an improved scaled selective mapping (SLM) is proposed to reduce PAPR based on scaled SLM. In the scheme, some of the input signals were scaled to low amplitudes by new decision circle. The analysis of theory demonstrated that, the modified scheme can reduce much more PAPR. The simulation results showed that, having ensured the performance of bit error rate (BER) in PLC channels, the modified scheme can reduce PAPR. The scheme, which has the same effect as the traditional SLM, makes up for the deficiencies of scaled SLM, Also the scheme does not require side information transmission, and the transmission efficiency is pretty much improved.Secondly, in this paper, another scheme is also proposed, which combines improved scaled SLM method with companding technique. In this scheme, the input signals are dealed with improved scaled SLM first, and then disposed by companding technique. The simulation results showed that the proposed scheme reduces PAPR of OFDM system remarkably compared with the improved scaled SLM scheme. The proposed scheme is valuable to be applied, and the transmission efficiency is high.Finally, the paper bring partial transmit theory in companding technique with two kickpoints, partial transmit companding scheme with two kickpoints is proposed to reduce the PAPR of OFDM in PLC. In the scheme, the signals are dealed with partial transmit first to reduce the PAPR, and then disposed by companding technique with two kickpoint to reduce much nore PAPR. The simulation results show that the proposed scheme reduces more PAPR of the system compared with the improved companding technique.