PAPR reduction using the combination of precoding and Mu-Law companding techniques for OFDM systems

The high peak-to-average power ratio (PARR) of OFDM signals is a primary disadvantage that single-carrier modulation does not have. Because of using muti-carrier modulation technique, OFDM systems also exhibit a large out-of-band (OOB) emission that can potentially interfere with neighboring transmissions. The precoding scheme using with more null subcarriers achieves significant better PAPR reduction than that using with less subcarriers. But the use of more null subcarriers promotes out-of-band power emission and reduces the transmission rate. The compander, applying Mu (μ)-Law compression and expansion at the transmitter and receiver, is simple and nonlinear method for reducing PAPR. Although the use of nonlinear companding signal has effective reduction in PAPR, it also promotes OOB emission. This paper presents a combination scheme, which using a combination of precoding by utilizing least null subcarriers in frequency domain and nonlinear companding technique by applying proper Mu-Law characteristic in time domain, for reducing PAPR. Simulation results show that the proposed scheme achieves a beneficial trade-off between the reduction of PAPR and OOB power emission in OFDM systems.