Improved iterative FD-CE and turbo equalisation for doubly-selective high-frequency channel

In this study, the authors investigate joint iterative frequency-domain channel estimation (FD-CE) and turbo equalisation for doubly selective high-frequency channel. The performance of time and FD turbo equalisers (TD/FD-TE) by applying them to Appendix C of military standard (MIL-STD)-188-110C is compared. Compared to TD-TE, FD-TE has reduced computational complexity; however, its performance degrades for time-varying channels. To improve the performance of FD-TE, we propose a new iterative CE scheme which can be used jointly with FD-TE. We employ low-complexity FD least mean-square algorithm in iterative process. By the use of soft information fed back from the decoder from the previous iteration, we improve the quality of the channel estimate over iterations. Simulation results show that at bit error rate (BER) of 1×10 -5 the proposed algorithm improves the performance of FD-TE ~2.5 and 3.5 dB for 8 phase shift keying (PSK) and 16 quadrature-amplitude modulation (QAM), respectively. Also, we study the impact of CE error on the performance of FD-TE. For 16QAM when SNR values are more than 20 dB, there is a gain between 1 and 3 dB when we consider the variance of CE error.