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BER performance of LDPC-coded nonlinear OFDM systems

It is widely known that the peak-to-average power ratio (PAPR) problem inherited in orthogonal frequency division multiplexing (OFDM) signals can cause severe bit error rate (BER) performance degradation. However, most of the work reported in the literature considers the uncoded BER performance, which might be misleading due to the over estimation of the impact of the resulted interference due to the high power amplifier (HPA) nonlinearity. Consequently, this work considers the impact of the HPA on the performance of a low density parity check (LDPC) coded OFDM systems. Extensive Monte Carlo simulations have been conducted using various LDPC codes with different codeword lengths and rates. The simulation results demonstrate that the BER performance degradation due to the signal distortion caused by the HPA is not as severe as it is usually claimed. Surprisingly, the coding gain loss for LDPC code that has a high error correction capability is less than 0.5 dB, with a moderate input back-off (IBO) of 4 dB. For less powerful codes, the coding gain reduction was about 1 dB. The effect of the unique structure of LDPC codewords on the PAPR was isolated by fragmenting the LDPC codewords into smaller packets each of which consists of 128 subcarriers.