Reduced Complexity I/Q Turbo Detection for Space-Time Trellis-Coded Systems

Abstract

A reduced-complexity turbo-detection scheme, referred to here as the R-TD arrangement, is proposed for employment in space-time trellis-coded (STTC) systems using the inphase/quadrature-phase (I/Q) cancellation technique that was previously developed for single-transmitter and single-receiver systems. The R-TD scheme decomposes the received signal into its constituent I and Q signal components and detects these components separately; hence, reducing the number of possible signal combinations to be “tested” by the detector. The R-TD scheme is capable of approaching the performance of the conventional turbo detector (F-TD), while achieving a complexity reduction factor of 3 and 862 for a four-phase-shift-keying 32-state STTC system, denoted as STTC(4,32), communicating over two- and five-path Rayleigh-fading channels, respectively, exhibiting a symbol-spaced and equal-tap-weight channel-impulse response. In order to investigate the benefits of employing channel coding in conjunction with STTC schemes, the R-TD principle was also invoked in convolutional-coding-aided STTC schemes. It was observed that, at a given throughput, the turbo-detected “nonchannel-coded” STTC(4,32) system required a similar signal-to-noise ratio to that of the R = 1/2 and constraint length K = 7 convolutional-coded STTC(16,16) scheme for achievingthe bit error rate (BER) of 10^-5. At a higher target, BER of 10^-3, the “nonchannel-coded” STTC(4,16) and STTC(4,32) schemes outperformed the channel-coded STTC(16,16) system by 0.8 and 2.3 dB, despite having a factor of 19 or 11 lower complexity, respectively.
Index Terms—Inphase, iterative equalization and decoding, quadrature phase, reduced complexity, serial concatenated codes, space–time trellis coding(STTC), turbo equalization/detection.

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ORCID for L. Hanzo: orcid.org/0000-0002-2636-5214

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