Abstract
A soft-decision 8-DPSK modulation format is introduced in a concatenated coding scheme and the performance of the resulting system is evaluated over a slow Rayleigh fading HF ionospheric link in the presence of Additive White Gaussian noise (AWGN). Well-known Ungerboeck TCM techniques are used as inner codes and a Reed–Solomon block code as outer code. The coded/modulated signal is differentially encoded before transmission to combat random phase changes caused by the channel. Soft-decision demodulator's output is used as an input to a modified Viterbi decoder that calculates the Euclidean distances of the received signal from an 8-PSK constellation adapted to the signal's amplitude variations. Block interleaving techniques are necessary to randomise long bursts of errors caused by the fading channel. Simulation results show that significant coding gains are achieved with a minor bandwidth expansion over uncoded, diversity or other coded systems. Finally, the interesting effects of interleaving on the performance of the proposed systems are analysed.
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