Performance Improvement of OFDM System Using New Scrambling Technique with Precoded Methods

Abstract

One of the challenging issues for Orthogonal Frequency Division Multiplexing (OFDM) system is its high Peak to Average Power Ratio (PAPR). This degrades performance of the system. In this paper, a new scrambling algorithm to reduce PAPR is presented. The new algorithm uses chaos system to generate several Chaos Binary Sequences (CBS) that scrambled with the data symbols to get several sequences. Only one sequence is chosen with smallest PAPR value for transmission. To reduce the PAPR more and improve Bit Error Rate (BER) performance of the new scrambling algorithm, precoded methods are used. Two precoded methods are presented in this work: Discrete Cosine Transform (DCT) and Walsh Hadamard Transform (WHT). Simulation results using MATLAB show that when number of subcarriers is 1024 and number of CBS is 8, the PAPR is approximately equal to 7 db by using new scrambling technique only. While the PAPR is approximately reduced by 1 db when using WHT with new technique. Finally, when using DCT with new technique, the PAPR is approximately reduced by 3.8 db. Also DCT with new technique gives better BER performance than WHT with new technique.