Performance Analysis and Peak-to-Average Power Ratio Reduction of Concatenated LDPC Coded OFDM system Using low complexity PTS

OFDM suffers with two major drawbacks, poor bit error rate (BER) performance in fading environment and high value of peak to average power ratio (PAPR). OFDM system can be combined with channel coding schemes to improve BER in fading environment. Convolution codes, Reed Solomon (RS) and Turbo codes are widely used channel codes, but in recent studies low density parity check codes (LDPC) have outperformed every other code in terms of error correction capabilities. High PAPR increases circuit complexity and reduce RF amplifier efficiency. Partial Transmit Sequence (PTS) is one of the most preferred techniques for PAPR reduction, however in PTS scheme the computation of optimal phase factors necessitates exhaustive searching among all allowable phase factors. This leads to exponential increase in computation complexity with the increase in number of sub-blocks. In this paper a coded OFDM scheme with LDPC-RS concatenated codes using PTS is proposed. The design improves BER performance compared to traditional RS-convolution concatenated codes and the proposed modified PTS scheme reduces the computation complexity in terms of reduced complex multiplications and additions by significant margin and at the same time maintaining same PAPR reduction as conventional PTS scheme. OFDM system used in the paper complies with IEEE 802.11 a standard.