Concatenated space-time block codes and TCM, turbo TCM, convolutional as well as turbo codes

2001

IEEE Trans. Commun.

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Abstract-The performance of the proposed radial basis function (RBF) assisted turbo-coded adaptive modulation scheme is characterized in a wideband channel scenario. We commence by introducing the novel concept of the Jacobian RBF equalizer, which is a reduced-complexity version of the conventional RBF equalizer. Specifically, the Jacobian logarithmic RBF equalizer generates its output in the logarithmic domain and hence it can be used to provide soft outputs for the turbo-channel decoder. We propose using the average magnitude of the log-likelihood ratio (LLR) of the bits in the received transmission burst before channel decoding as the channel quality measure for controlling the mode-switching regime of our adaptive scheme. [7]. However, there is little information concerning its potential in either BbB AQAM or in forward error correction (FEC)-coded scenarios, despite the advantageous interactions of RBF-aided DFE BbB AQAM in conjunction with turbo FEC, which were demonstrated in our preliminary work [8]. Hence in this contribution, we set out to document these interactions. IndexThe symbol-spaced channel output can be defined by (1) where ; channel impulse response (CIR); channel's input sequence; noiseless channel output.Paper approved by C. Schlegel, the Editor for Coding Theory and Techniques of the IEEE Communications Society. Manuscript received April 5, 2000; revised March 20, 2001. This work was supported by the EPSRC, the U.K., and the Commission of the European Communities, Brussels, Belgium.The authors are with the Department of Electronics and Computer Science, University of Southampton, Highfield Southampton SO17 1BJ, U.K. (e-mail: lh@ecs.soton.ac.uk).Publisher Item Identifier S 0090-6778 (01) [17] promoted the employment of RBF based equalizers, which exhibit a structure identical to that of the optimal Bayesian symbol-decision based equalizer. Therefore, RBF equalizers can rely on optimal detection theory [18]. In this contribution, we use a decision feedback assisted RBF equalizer, which involves its previous decisions for either RBF subset center selection [17] or space translation [19], [20], in order to reduce its computational complexity. Both versions of the DFE realize the same optimal solution, but the space translation based version [19], [20] requires less storage for the RBF centers, since the centers corresponding to different decision feedback vectors are equivalent in the translated space [19], [20]. Therefore the latter version is preferred in hardware implementations.BbB AQAM schemes [21] employ a higher-order modulation scheme in a certain transmission burst, when the channel quality is favorable, in order to increase the throughput and conversely, a more robust, lower-order modulation scheme is utilized in those transmission bursts, where the instantaneous channel quality drops [1]. The performance benefits of the RBF DFE [17] have been documented in the context of AQAM over dispersive wideband mobile channels in [22], [23], demonstrating that a certain target bit error rate ...

Section: Turbo-coded Rbf-equalized -Qam Performance Resultsmentioning

confidence: 99%

Burst-by-burst adaptive turbo-coded radial basis function-assisted decision feedback equalization

Yee

Liew

2001

IEEE Trans. Commun.

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“…On the other hand, from the family of STB codes, only Alamouti's G 2 code is employed in the system, since it was shown in [5] and [24] that the best performance is achieved by concatenating the unity-rate STB code G 2 with TC codes rather than its lower rate counterparts using a higher number of antennas. Furthermore, although turbo BCH codes, trellis coded modulation (TCM) and convolution codes were also used in the investigations of [5], [24]; again, the best performer was the TC code at a given implementational complexity. For convenience, the transmission matrix of the space-time block code G 2 is reproduced here as…”

Section: Space-time Coded Transmission Over Wideband Channelsmentioning

confidence: 99%

“…In this section, we present the parameters of the space-time codes and the channel codecs employed in the system, which are summarized in Table I. On the other hand, from the family of STB codes, only Alamouti's G 2 code is employed, since we have shown in [24] that the best performance in the set of investigated schemes was obtained by concatenating the STB code G 2 with TC codes. The transmission matrix of the code is shown in (1), while the number of transmitters used by the STB code G 2 is two, which is identical to the number of transmitters in the STT codes shown in Table I.…”

Section: B Space-time and Channel Codec Parametersmentioning

confidence: 99%

Space-Time Trellis and Space-Time Block Coding Versus Adaptive Modulation and Coding Aided OFDM for Wideband Channels

Liew

IEEE Trans. Veh. Technol.

2006

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Abstract-The achievable performance of channel coded spacetime trellis (STT) codes and space-time block (STB) codes transmitted over wideband channels is studied in the context of schemes having an effective throughput of 2 bits/symbol (BPS) and 3 BPS. At high implementational complexities, the best performance was typically provided by Alamouti's unity-rate G 2 code in both the 2-BPS and 3-BPS scenarios. However, if a low complexity implementation is sought, the 3-BPS 8PSK space-time trellis code outperfoms the G 2 code. The G 2 space-time block code is also combined with symbol-by-symbol adaptive orthogonal frequency division multiplex (AOFDM) modems and turbo convolutional channel codecs for enhancing the system's performance. It was concluded that upon exploiting the diversity effect of the G 2 space-time block code, the channel-induced fading effects are mitigated, and therefore, the benefits of adaptive modulation erode. In other words, once the time-and frequency-domain fades of the wideband channel have been counteracted by the diversity-aided G 2 code, the benefits of adaptive modulation erode, and hence, it is sufficient to employ fixed-mode modems. Therefore, the low-complexity approach of mitigating the effects of fading can be viewed as employing a single-transmitter, single-receiver-based AOFDM modem. By contrast, it is sufficient to employ fixed-mode OFDM modems when the added complexity of a two-transmitter G 2 scheme is affordable.

“…As seen at the bottom of Fig. 18, Alamouti's ST block code [41] and [55] is applied across the frequency domain, since it was found in [41] and [58] that from a wide-ranging set of combined channel coding and ST coding schemes, this particular combination exhibited the largest coding gain at a given complexity and at an effective throughput of 2-and 3-BPS. A pair of the adjacent subcarriers belonging to the same ST encoding block is assumed to have the same channel quality.…”

Section: E Concatenated Space-time Block-coded and Turbo-coded Symbomentioning

confidence: 99%

“…The optimum set of switching levels should satisfy (58) where , and were given in (31), (28), and (8), respectively. The following results are helpful in evaluating the partial differentiations in (58): (59) (60) (61) Using (59) and (60), the partial differentiation of , defined in (28) with respect to , can be written as (62) where is the BPS throughput of an -ary modem.…”

Section: Appendix C Relationship Between Optimum Switching Levelsmentioning

confidence: 99%

Optimum mode-switching-assisted constant-power single- and multicarrier adaptive modulation

Choi

IEEE Trans. Veh. Technol.

2003

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119

Abstract-A set of optimum mode-switching levels is derived for a generic constant-power adaptive-modulation scheme based on a closed-form expression of the average bit error ratio (BER) and the average bits-per-symbol (BPS) throughput of the adaptive-modulation scheme. This results in a constant BER, variable-throughput arrangement. The corresponding BPS throughput performance and the achievable signal-to-noise ratio (SNR) gain are investigated for the optimum mode-switching assisted constant-power adaptive-modulation schemes employing various diversity schemes, including maximal ratio combining (MRC) receive-antenna diversity, a two-dimensional RAKE receiver, as well as transmit-diversity aided space-time (ST) coding, when communicating over various fading scenarios. The BPS throughput of our constant-power adaptive quadrature amplitude modulation (AQAM) scheme approaches the throughput of variable-power variable-rate AQAM within 1 dB. However, the achievable throughput gain of the adaptive-modulation scheme, in comparison to conventional fixed-mode modems, is substantially reduced as the diversity order of the receiver is increased. Hence, adaptive modulation constitutes a lower complexity alternative to multiple-transmitter and receiver-based systems when considering the range of techniques that can be used for mitigating the effects of the channel-quality fluctuations imposed by wireless channels.Index Terms-Adaptive modulation, adaptive quadrature amplitude modulation (AQAM), fading counter measures, Lagrangian optimization for adaptive modulation, optimum switching levels for adaptive modulation.