PAPR Reduction in OFDM System Using Partial Transmit Sequence (PTS) and Precoding Techniques

Abstract

In recent time, the demand for multimedia data services has grown up rapidly. One of the most promising multi-carrier system, Orthogonal Frequency Division Multiplexing (OFDM) forms basis for all 4G wireless communication systems due to its large capacity to allow the number of subcarriers, high data rate and ubiquitous coverage with high mobility. OFDM is significantly affected by peak-to-average-power ratio (PAPR). Unfortunately, the high PAPR inherent to OFDM signal envelopes will occasionally drive high power amplifiers (HPAs) to operate in the nonlinear region of their characteristic curve. The nonlinearity of the HPA exhibits amplitude and phase distortions, which cause loss of orthogonality among the subcarriers, and hence, inter-carrier interference (ICI) is introduced in the transmitted signal. Not only that, high PAPR also leads to in-band distortion and out-of-band radiation. This thesis emphasis mainly on the PAPR reduction of OFDM system using partial transmits sequence (PTS) and precoding techniques. Some other techniques such as amplitude clipping have low-complexity; on the other hand, they suffer from various problems such as in-band distortion and out-of-band expansion. Signal companding methods have low-complexity, good distortion and spectral properties; however, they have limited PAPR reduction capabilities. Advanced techniques such as coding, partial transmit sequences (PTS) and selected mapping (SLM), have also been considered for PAPR reduction. Such techniques are efficient and distortionless, nevertheless, their computational complexity is high. Also, the precoding is an attractive technique to the PAPR problem which approaches that of single carrier system. This technique has low complexity as well as it is data independent. So, it does not require new processing and optimization for each transmitted block. We proposed a combine technique of precoding and PTS to reduce the PAPR. This hybrid combined technique reduces PAPR effectively and also minimizes the complexity of PTS technique which arises due to number of subblocks. In PTS scheme, as the number of subblocks increases, the IFFT operation to be performed for subblocks also increases. Simulation results have shown that the decrement of PAPR of proposed scheme is more than PTS and precoding methods as well as the complexity reduced significantly. The out of band radiation of proposed scheme is less than original OFDM as shown in power spectral density (PSD) simulation result.