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DDT-based Chaotic Interleaver Aided Cooperative OFDM System

Typically, interleaver is used to recover information signal from outage where errors in burst form is transformed into single errors. The best interleaver should have the optimal properties of spread and dispersion. Therefore, this paper reports a method to design highly dispersive and systematic interleaver. The interleaver is designed using an incremental approach, which uses a Chaotic Logistic Map (CLM) to generate interleaver positions and utilizes the counter-based difference distribution table (DDT) that has been used in cryptanalysis, in order to achieve highly random and disperse interleaver positions by avoiding bad positions that produce repetitive pairs in the output. The proposed interleaver is implemented in single input single out (SISO) and cooperative Orthogonal frequency division multiplexing (OFDM) system. The performance of the proposed interleaver is evaluated in terms of spread, dispersion, bit error rate (BER) as a function of the burst error length and BER versus channel signal-to-noise-ratio (SNR). The performance of the proposed interleaver is compared with chaotic interleaver, block interleaver and with Matlab® random interlaever. The results show that the proposed interleaver outperforms all the interleavers considered in the simulations and there is 1 dB to 3.5 dB improvement in different scenarios of length of burst errors in terms of BER for proposed SISO OFDM systems. More specifically, the employment of the proposed interleaver in the cooperative OFDM system gives improvement of about 2.75 dB to 3.5 dB at BER = 10−2, as compared to the non cooperative OFDM systems when having the burst error length of 5 bits, 10 bits and 15 bits.