Bidirectional Soft-Decision Feedback Turbo Equalization for MIMO Systems


This paper proposes a bidirectional soft-decision feedback turbo equalizer for severe triply selective fading channels. The proposed bidirectional soft-decision feedback equalizer (Bi-SDFE) uses a time reversed SDFE in conjunction with a normal SDFE to harvest time-reverse diversity and mitigate error propagation. A simple and effective linear combining scheme is derived for combining the extrinsic information on the two SDFEs for multiple-input-multiple-output (MIMO) systems with multilevel modulation. The bit-error-rate (BER) simulation results show that the proposed Bi-SDFE exhibits a lower signal-to-noise-ratio (SNR) threshold than the original SDFE and outperforms the well-known exact turbo minimum mean square error (MMSE) linear equalizers (LEs) at medium-to-high SNRs. Moreover, both extrinsic information transfer (EXIT) chart analysis and BER simulation results show that the Bi-SDFE achieves better performance than the original SDFE, whereas the Bi-SDFE uses only half the number of iterations of the SDFE. Therefore, the total computational complexity of the Bi-SDFE is similar to that of the original SDFE, which is a linear function of the channel length, MIMO size, and modulation constellation size. The performance gain of the proposed Bi-SDFE is also verified through an underwater acoustic (UWA) communication experiment with tough channel conditions.


Electrical and Computer Engineering


National Science Foundation (U.S.)


This work was supported by the National Science Foundation under Grant ECCS 0846486 and Grant ECCS 1408316

Keywords and Phrases

Bit error rate; Codes (symbols); Communication channels (information theory); Equalizers; Error analysis; Errors; Fading channels; Feedback control; Mean square error; MIMO systems; Modulation; Optical communication; Signal to noise ratio; Telecommunication repeaters; Underwater acoustics; Bit error rate simulations; Extrinsic information transfer charts; Minimum mean square errors (MMSE); Modulation constellation sizes; Selective fading channel; Signal to noise ratio thresholds (SNR); Soft decision feedback; Turbo equalizations; Decision feedback equalizers; Bidirectional soft-decision feedback equalizer (Bi-SDFE); Multiple-input multiple-output (MIMO); Underwater acoustic (UWA) communication

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Article - Journal

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© 2016 Institute of Electrical and Electronics Engineers (IEEE), All rights reserved.

Publication Date

01 Jul 2016