A Reliable Singular-Vector Pre-Coded OFDM-DCSK System Over Doubly Selective Fading Channels

In this letter, we put forth a novel strategy to boost the reliability of orthogonal frequency division multiplexing differential chaos shift keying (OFDM-DCSK) systems over doubly selective fading channels. Provided the accessibility of channel state information, singular value decomposition is exploited to partition the channel into distinct sub-channels, which is realized by multiplying the right singular vectors by the symbol matrix at the transmitter. Subsequently, the sub-channel associated with the largest singular value is allocated to the reference chaotic sequence, leading to a higher signal-to-noise ratio (SNR) of demodulated symbols and lower bit error rate (BER) at the receiver. Inspired by the water-filling principle, the BER can be further reduced by permuting the symbols in a strategic manner. This approach of channel decomposition integrated with symbol reallocation, referred to as singular-vector pre-coded OFDM-DCSK (SVP-OFDM-DCSK), is able to escalate the SNR over doubly selective channels, ultimately enhancing the system reliability. The BER of the SVP-OFDM-DCSK system is also analyzed. Simulation results demonstrate that the proposed system with and without symbol permutation step achieves lower BERs than existing schemes over doubly selective fading channels.