Radial basis function decision feedback equaliser assisted burst-by-burst adaptive modulation

2001

IEEE Trans. Commun.

Self Cite

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: B Simulation Resultsmentioning

confidence: 99%

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

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Yee

Liew

2001

IEEE Trans. Commun.

Self Cite

“…An alternative neural-network radial basis function (RBF) DFE-based AQAM modem design was proposed in [9], where the RBF DFE provided the channel quality estimates for the modem mode switching regime.…”

Section: Background and Motivationmentioning

confidence: 99%

Adaptive modulation techniques for duplex OFDM transmission

Keller

IEEE Trans. Veh. Technol.

2000

Self Cite

260

107

Abstract-The design tradeoffs of turbo-coded burst-by-burst adaptive orthogonal frequency division multiplex (OFDM) wideband transceivers are analyzed. We demonstrate that upon aiming for a higher throughput a higher proportion of low-quality OFDM subcarriers has to be used for the transmission of inherently vulnerable high-order modem modes, transmitting several bits per subcarrier. Upon invoking turbo coding and adjusting the modem mode switching regime near-error-free performance can be achieved at the cost of a reduced throughput. Various blind modem mode detection techniques have also been investigated and the most complex channel coding trellis-based detection algorithm was found to be the most powerful. Last, the design tradeoffs of spectral pre-equalization have been explored and qualtified. We concluded that AOFDM provides a convenient framework for adjusting the required target integrity and throughput both with and without turbo channel coding.

“…In [57], a TEQ scheme was proposed, which employs a radial basis function (RBF)-based equalizer [52], [58], [59] instead of the classic trellis-based equalizer of Douillard et al [33]. It was shown with the aid of plausible graphical examples in [52] that at the output of a dispersive fading channel the phasor constellation points may become linearly nonseparable even in the absence of noise and in this scenario only nonlinear receivers, such as the RBF-based TEQ, are capable of operating without an error floor.…”

Section: B Turbo Equalization Of Time-variant Wireless Channelsmentioning

confidence: 99%

Turbo Decoding and Detection for Wireless Applications

Woodard²,

Robertson

2007

Proc. IEEE

Future iterative receivers will be designed using EXIT charts for near-capacity operation over dispersive wireless channels at the lowest possible complexity and delay. More specifically, we commence by discussing the turbo principles, which have been shown to be capable of performing close to Shannon's capacity limit. We continue by reviewing the classic maximum a posteriori probability decoder. These discussions are followed by studying the effect of a range of system parameters in a systematic fashion, in order to gauge their performance ramifications. In the second part of this treatise, we focus our attention on the family of iterative receivers designed for wireless communication systems, which were partly inspired by the invention of turbo codes. More specifically, the family of iteratively detected joint coding and modulation schemes, turbo equalization, concatenated spacetime and channel coding arrangements, as well as multi-user detection and three-stage multimedia systems are highlighted.