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Orthogonal frequency division multiplexing(OFDM) is a prominent technique for providing high Quality of service(QOS) to the users by mitigating the fading of signals and also for providing high data rates in multimedia services. But Peak to Average power ratio(PAPR) is a major technical challenge in OFDM which reduces the efficiency of RF Power amplifiers. In this paper, we describe the PAPR reduction techniques in OFDM signals and compare their performance.

A fast block motion estimation algorithm is proposed using modified diamond search patterns. This algorithm utilizes the directions and magnitudes of motion vectors between interblocks and uses a smaller number of search points than conventional diamond search patterns. Simulation results show that the proposed method significantly improves computational speed over other fast motion estimation algorithms without degradation of distortion.

A modified alternative signal technique for reducing peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing systems employing offset quadrature amplitude modulation (OFDM-OQAM) is proposed. Lower PAPR reduces the complexity of digital to analog converters and results in increasing the efficiency of power amplifiers. The main objective of the algorithm is to decrease PAPR with low complexity. The alternative signal method involves the individual alternative signal (AS-I) and combined alternative signal (AS-C) algorithms. Both the algorithms decrease the peak to average power ratio of OFDM-OQAM signals and AS-C algorithm performs better in decreasing PAPR. However the complexity of AS-C algorithm is very high compared to that of AS-I. To achieve reduction in PAPR with low complexity, modified alternative signal technique with sequential optimisation (MAS-S) is proposed. The quantitative PAPR analysis and complexity analysis of the proposed algorithm are carried out. It is demonstrated that MAS-S algorithm simultaneously achieves PAPR reduction and low complexity.