The Feher quadrature phase shift keying (FQPSK) modulation is significantly susceptible to frequency and phase offsets under low signal-to-noise ratios. In this study, the authors proposed a serially concatenated sign...
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The Feher quadrature phase shift keying (FQPSK) modulation is significantly susceptible to frequency and phase offsets under low signal-to-noise ratios. In this study, the authors proposed a serially concatenated signalling scheme with FQPSK modulation and low-density parity-check coding, which could efficiently resist residual frequency offset by employing an intended compensation algorithm. The designed maximum-likelihood estimation-enabled compensation algorithm is incorporated into the iterative concatenated demodulation-decoding process by using soft-input-soft-output-based maximum-a-posteriori-probability criterion. On the other side, the codeword sequence to be transmitted at the sender is re-arranged in a pre-configured order different from original codeword, in order to help the compensation algorithm diminish the impacts of frequency offsets. Simulation results show that the bit error rate of the proposed scheme can be improved efficiently up to three orders of magnitude with the frequency offsets from 100 to 700 ppm.
A new method to improve the bit error rate (BER) performance by optimising the bit energy is proposed in this study. This method is mainly based on a formula derived from the union bound that can estimate the BER for ...
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A new method to improve the bit error rate (BER) performance by optimising the bit energy is proposed in this study. This method is mainly based on a formula derived from the union bound that can estimate the BER for every bit in the codeword sequence. Then by mathematical optimisation and assisted with a BER distribution, the energy for every bit can be optimised so that the average BER achieves the minimum value. Compared with other methods, this method considering all the codewords with minimum Hamming weights and their multiplicity to each bit of the codewords. The simulation examples show that the average BER is improved not only at high signal-to-noise ratio (SNR), but also at low and moderate SNRs.
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