PAPR Reduction using Frequency Domain Multiplexed Pilot Sequences

We investigate the feasibility of applying the peak-to-average power ratio (PAPR) reduction method using pilot sequences, originally proposed for orthogonal frequency division multiplexing (OFDM) signals, for single-carrier (SC) signals with frequency domain multiplexed (FDM) pilots. The idea is to select the FDM pilot sequence with which the transmitted signal produces the lowest PAPR. We also investigate the applicability of the sum of square error (SSE) selection rule for high order modulation of SC signals. The SSE rule selects the pilot sequence which produces the minimum SSE between the transmitted signal and a pre-defined threshold, proportional to the saturation level of a high power amplifier (HPA). It is found that for both SC and OFDM systems, the PAPR reduction capabilities of orthogonal Walsh-Hadamard (W-H) sequences and cyclic shifted Chu (CS-Chu) sequences are similar for small block size, but not for large block size. Using CS-Chu sequences produces better PAPR reduction capability. With an appropriate choice of the value of input backoff power of a HPA, the SSE selection rule produces similar results as that of the minimum PAPR selection rule. The effects of out-of-band radiation for SC and OFDM signals with PAPR reduction using FDM pilot sequences after HPA depends on the amount of non-linearity portion of the HPA. The out-of-band radiation improvement is obvious for a HPA that approximates a linear clipper.