Decision feedback equalizer (DFE)-aided turbo-coded wideband adaptive quadrature amplitude modulation (AQAM) is proposed, which is capable of combating the temporal channel quality variation of fading channels. A procedure is suggested for determining the AQAM switching thresholds and the specific turbo-coding rates capable of maintaining the target bit-error rate while aiming for achieving a highly effective bits per symbol throughput. As a design alternative, we also employ multiple-input/multiple-output DFE-aided space-time trellis codes, which benefit from transmit diversity and hence reduce the temporal channel quality fluctuations. The performance of both systems is characterized and compared when communicating over the COST 207 typical urban wideband fading channel. It was found that the turbo-coded AQAM scheme outperforms the two-transmitter space-time trellis coded system employing two receivers; although, its performance is inferior to the space-time trellis coded arrangement employing three receivers.

This paper presents a turbo equalization (TEQ) scheme, which employs a radial basis function (RBF)-based equalizer instead of the conventional trellis-based equalizer of Douillard et al. (1995). Structural, computational complexity, and performance comparisons of the RBF-based and trellis-based TEQs are provided. The decision feedback-assisted RBF TEQ is capable of attaining a similar performance to the logarithmic maximum a posteriori scheme in the context of both binary phase-shift keying (BPSK) and quaternary phase-shift keying (QPSK) modulation, while achieving a factor 2.5 and 3 lower computational complexity, respectively. However, there is a 2.5-dB performance loss in the context of 16 quadrature amplitude modulation (QAM), which suffers more dramatically from the phenomenon of erroneous decision-feedback effects. A novel element of our design, in order to further reduce the computational complexity of the RBF TEQ, is that symbol equalizations are invoked at current iterations only if the decoded symbol has a high error probability. This techniques provides 37% and 54% computational complexity reduction compared to the full-complexity RBF TEQ for the BPSK RBF TEQ and 16QAM RBF TEQ, respectively, with little performance degradation, when communicating over dispersive Rayleigh fading channels.

A reduced complexity trellis-based turbo equalizer known as the in-phase (I)/quadrature-phase (Q) turbo equalizer (TEQ-IQ) invoking iterative channel impulse response (CIR) estimation is proposed. The underlying principle of TEQ-IQ is based on equalizing the I and Q component of the transmitted signal independently. This requires the equalization of a reduced set of separate I and Q signal components in comparison to all of the possible I/Q phasor combinations considered by the conventional trellis-based equalizer. It was observed that the TEQ-IQ operating in conjunction with iterative CIR estimation was capable of achieving the same performance as the full-complexity conventional turbo equalizer (TEQ-CT) benefiting from perfect CIR information for both 4- and 16-quadrature amplitude modulation (QAM) transmissions, while attaining a complexity reduction factor of 1.1 and 12.2, respectively. For 64-QAM, the TEQ-CT receiver was too complex to be investigated by simulation. However, by assuming that only two turbo equalization iterations were required, which is the lowest possible number of iterations, the complexity of the TEQ-IQ was estimated to be a factor of 51.5 lower than that of the TEQ-CT. Furthermore, at BER = 10/sup -3/ the performance of the TEQ-IQ 64-QAM receiver using iterative CIR estimation was only 1.5 dB away from the associated decoding performance curve of the nondispersive Gaussian channel.

The decision feedback equaliser (DFE) aided turbo coded wideband adaptive quadrature amplitude modulation (AQAM) is capable of accommodating the temporal channel quality variation of fading channels. By contrast, the family of multiple-input-multiple-output (MIMO) DFE aided space-time trellis codes benefits from transmit diversity and hence it is capable reducing, rather than accommodating the temporal channel quality fluctuations. The performance of both systems is characterised and compared when communicating over the COST 207 typical urban (TU) wideband fading channel. It was found that the turbo coded AQAM scheme outperforms the two-transmitter space-time trellis coded (STTC) system employing two receivers, although its performance becomes inferior to that of a STTC arrangement employing more than two receivers.

A reduced complexity turbo equalizer, TEQ-IQ, which uses the in-phase/quadrature-phase cancellation technique developed for single-transmitter and single-receiver systems, is proposed for space-time trellis coded (STTC) systems. The TEQ-IQ scheme is capable of approximating the performance of the conventional turbo equalizer (TEQ-CT), while achieving complexity reduction factors of 1.4 and 468.2 for a 4PSK 32-state STTC system communicating over two-path and five-path symbol-spaced and equal tap weight Rayleigh fading channels, respectively.

The performance of turbo-equalized Global System of Mobile Communications/General Packet Radio Service (GSM/GPRS)-like videophone transceivers is studied over dispersive fading channels as a function of the number of turbo equalization iterations. Iteration gains up to 6 dB were attained. The operating channel signal-to-noise ratio (SNR) required for maintaining a peak SNR loss of less than 1 dB was reduced by 3.2 dB for the one-slot system and by 4.1 dB for the four-slot system. The proposed system is capable of providing low-resolution videophone services over GSM/GPRS.

Turbo equalizers have been shown to be successful in mitigating the effects of inter-symbol interference introduced by partial response modems and by dispersive channels for code rates of R/spl les/ 1/2. We comparatively studied the performance of a range of binary phase-shift keying turbo equalizers employing block-turbo codes, namely Bose-Chaudhuri-Hocquenghen (1960, 1959) turbo codes, convolutional codes, and convolutional turbo codes having high code rates, such as R=3/4 and R=5/6, over a dispersive five-path Gaussian channel and an equally weighted symbol-spaced five-path Rayleigh fading channel. These turbo equalization schemes were combined with an iterative channel estimation scheme in order to characterize a realistic scenario. The simulation results demonstrated that the turbo-equalized system using convolutional turbo codes was the most robust system for all code rates investigated.

The performance of turbo-equalised GSM/GPRS-like videophone transceivers is studied over dispersive fading channels as a function of the number of turbo-equalisation iterations. Iteration gains in excess of 4 dB were attained. The proposed system is capable of providing low-resolution videophone services over GSM/GPRS.

A novel reduced complexity trellis-based equaliser, referred to as the in-phase/quadrature-phase equaliser (I/Q-EQ), is proposed. The I/Q-EQ is employed in the context of turbo equalisation (TEQ-IQ) and with the aid of iterative channel estimation. The performance of the TEQ-IQ is characterized in a noise limited environment over an equally-weighted, symbol-spaced three-path Rayleigh fading channel. The TEQ-IQ achieved the same performance as the conventional turbo equaliser, while achieving a complexity reduction by a factor of 1.25 and 7.17 for 4-QAM and 16-QAM, respectively.

A reduced-complexity radial basis function (RBF) aided neural-network based turbo equalization (TEQ) scheme is proposed for employment in a serially concatenated convolutional coded and systematic space time trellis coded (CC-SSTTC) arrangement. A two-path Rayleigh fading channel having a normalised Doppler frequency of 3.3615/spl times/10/sup -5/ was used. The BER performance of the RBF-CC-SSTTC(4,4) scheme employing a transmission burst consisting of 100 symbols using a space-time-trellis (STT) interleaver of at least 400 symbols and eight turbo equalization iterations was found to be similar to that of the CC-SSTTC system using a trellis-based TEQ, which attains the optimum performance. However, the Jacobian RBF based TEQ provided a complexity reduction factor of 14.

Space-time block codes provide substantial diversity advantages for multiple transmit antenna systems at a low decoding complexity. We concatenate space-time codes with convolutional codes (CC), turbo convolutional codes (TC), turbo BCH codes (TBCH), trellis coded modulation (TCM) and turbo trellis coded modulation (TTCM) schemes for achieving a high coding gain. The associated performance and complexity of the the coding schemes is compared.

Space-time block codes provide substantial diversity advantages in multiple transmit antenna assisted systems at a low decoding complexity. In this contribution, we concatenate space-time codes with three turbo coding schemes, namely turbo BCH (TBCH) codes, turbo convolutional (TC) codes and turbo trellis coded modulation (TTCM) schemes for the sake of achieving significant coding gain. The issues of mapping coded bits of the TBCH and TC schemes to different protection classes of various multilevel modulation schemes is also addressed. Finally, the performance and associated complexity of the three turbo schemes is compared.