Performance analysis of μ-law companding & SQRT techniques for M-QAM OFDM systems

Orthogonal Frequency Division Multiplexing (OFDM) is an efficient transmission technique for high data rate communication systems. The major problem of OFDM system is Peak to Average Power Ratio (PAPR) which reduces the efficiency of the system and increases the system complexity. In this paper, logarithmic based companding (i.e, mu law) and Square rooting companding (SQRT) have been suggested as simple and effective PAPR reduction techniques for OFDM. This paper analyzes mu law and SQRT companding OFDM signal on M ary QAM modulation technique. Simulation results show that the SQRT OFDM system is an effective technique in reducing PAPR and improved BER performance than OFDM system with mu-law companding transform. Comparison among mu law and SQRT companding techniques is made for the best suited companding technique for PAPR reduction in OFDM system. The Simulation result also shows that by modulating a signal at a fixed subcarriers for different modulation technique, the error in the transmitted data increases rapidly whereas in case of fixed modulation techniques, increasing the number of subcarriers the PAPR increases at the transmit, the bit error rate (BER) in the transmitted data is constant and varies by a small fraction.