Improved bounds for error recovery times of decision feedback equalization (original) (raw)
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An improved decision feedback equalization using a priori information
International Journal of Adaptive Control and Signal Processing, 2009
This paper addresses the exhaustive computational complexity of the maximum-a-posteriori equalizer and the inefficiency of the conventional decision feedback equalizer (DFE) algorithm in iterative equalization, especially when the higher-level modulation is used with severely distorted Inter Symbol Interference channels. The new method proposed here improves the bit error rate (BER) performance by computing the extra metric rn+1 using the feedback symbols from previous iteration and combining it with a priori information of the symbols. After each iteration, the hard-detected symbols are saved in the memory as a priori data for next iteration. We verified the proposed algorithm for Binary Phase Shift Keying and 8-phase shift keying modulation. The promising simulation results show that the BER performance given by the proposed low complexity DFE algorithm improved dramatically throughout the iterations when the conventional DFE has only insignificant improvement in the process of iterative equalization. Copyright © 2009 John Wiley & Sons, Ltd.
Error propagation and recovery in decision-feedback equalizers for nonlinear channels
IEEE Transactions on Communications, 2001
Nonlinear intersymbol interference is often present in communication and digital storage channels. Decision-feedback equalizers (DFEs) can decrease this nonlinear effect by including appropriate nonlinear feedback filters. Although various applications of these types of equalizers have been published in the literature, the analysis of their stability and error recovery has not appeared. In this letter, we consider a DFE with a nonlinear feedback filter based on a discrete Volterra series. We extend error propagation, error probability, stability, and error recovery time results for th-order nonlinear channels.
Mitigating error propagation effects in a decision feedback equalizer
IEEE Transactions on Communications, 2001
We present an approximate analysis approach to the computation of probability of error and mean burst error length for a decision feedback equalizer (DFE) that takes into account feedback of decision errors. The method uses a reduced-state Markov model of the feedback process and is applicable to linear modulation formats. We use this technique to analyze a DFE design that mitigates the effects of feedback error by incorporating a soft decision device into the feedback path and a norm constraint on the feedback filter weights. We apply the DFE design and analysis approach to a dispersive multipath propagation environment.
MMSE decision feedback equalizer from channel estimate
The 13th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, 2002
In digital radio transmission over frequency selective channels, the Minimum Mean-Square Error Decision Feedback Equalizer (MMSE-DFE) is widely recognized as an efficient equalization scheme. In order to compute the coefficients of the feedforward and feedback filters of the MMSE-DFE, both the channel impulse response (CIR) and the variance of the noise have to be estimated. The estimate of the CIR is usually performed by the standard least-square method, where a known training sequence is employed. Then, the estimated CIR is used to evaluate the variance of the noise. In this paper the use of the two above estimates for MMSE-DFE is studied. In particular, an unbiased estimate of the variance of the noise is described.
IEEE Transactions on Communications, 1995
A coherent receiver with a decision-feedback equalizer (DFE) operating on a Rayleigh fading channel under a suitable adaptive algorithm is considered. In the analysis of a DFE, a common assumption is that the receiver has perfect knowledge of the channel impulse response. However, this is not the case in practice, and for a rapidly fading channel, errors in channel tracking can become significant. We analyze theoretically the impact of these errors on the performance of a multichannel DFE. T h e expressions obtained for the achievable average MPSK bit error probabilities depend on the estimation error covariance. In order to specify this matrix, we focus on a special case when a Kalman filter is used as an optimal channel estimator. In this case, the probability of bit error can b e assessed directly in terms of channel fading model parameters, the most interesting of which is the fading rate. Our results show the penalty imposed by imperfect channel estimation, as well as the fading-induced irreducible error rates. I. INTRODUCTION Due to its low computational complexity and nearoptimal performance, the decision-feedback equalizer (DFE), operating under a suitable adaptive algorithm, is used in a variety of time-dispersive fading channels, such as a mobile radio channel, a troposcatter channel, or an underwater acoustic channel. It is well-known that the critical issue for its performance in a rapidly changing channel is the tracking capability of the underlying adaptive algorithm. Although a vast body of literature has been devoted to the performance analysis of the DFE, it seems that none addresses the impact of fading-induced imperfect channel tracking. The goal of this analysis is to determine the performance limitations of a coherent receiver which incorporates a DFE, under the conditions that only the statistical properties of the channel are known to the receiver. The primary factor which causes the degradation of the DFE performance from the matched filter bound is the
Sparsity Enhanced Decision Feedback Equalization
IEEE Transactions on Signal Processing, 2012
For single-carrier systems with frequency domain equalization, decision feedback equalization (DFE) performs better than linear equalization and has much lower computational complexity than sequence maximum likelihood detection. The main challenge in DFE is the feedback symbol selection rule. In this paper, we give a theoretical insight on multiple symbol selection, based on sparsity and we present a simple algorithm for DFE. The algorithm converges fast and has a low computational cost. We show how the initial solution can be obtained via convex relaxation instead of linear equalization, and illustrate the impact that the choice of the initial solution has on the bit error rate performance of our algorithm. The algorithm is applicable in several existing wireless communication systems (SC-FDMA, MC-CDMA, MIMO-OFDM). Numerical results illustrate significant performance improvement in terms of bit error rate compared to the MMSE solution.
Iterative Equalization with Decision Feedback based on Expectation Propagation
IEEE Transactions on Communications
This paper investigates the design and analysis of minimum mean square error (MMSE) turbo decision feedback equalization (DFE), with expectation propagation (EP), for single carrier modulations. Classical non iterative DFE structures have substantial advantages at high-data rates, even compared with turbo linear equalizers-interference cancellers (LE-IC), hence making turbo DFE-IC schemes an attractive solution. In this paper, we derive an iterative DFE-IC, capitalizing on the use of soft feedback based on expectation propagation, along with the use of prior information for improved filtering and interference cancellation. This turbo iterative DFE-IC significantly outperforms turbo LE-IC, especially at high-spectral efficiency and also exhibits performance improvements over existing DFE-IC variants. The proposed scheme can also be self-iterated, as done in the recent trend on EP-based equalizers, and it is shown to be an attractive alternative to linear self-iterated receivers. For timevarying (TV) filter equalizers, an efficient matrix inversion scheme is also proposed, considerably reducing the computational complexity relative to existing methods. Using finite-length and asymptotic analysis on a severely selective channel, the proposed DFE-IC is shown to achieve higher rates than known alternatives, with better waterfall thresholds and faster convergence, while keeping a similar computational complexity.
Decision feedback equalizers for high speed data communications
2003
This work shows the performance of different decision feedback equalizers (DFEs) for high-speed data transmission over a telephone line. The analyzed structures are: the interference intersymbol-predictive decision feedback equalizer (ISI-DFE), the decision feedback equalizer with noise predictor (NP-DFE) and the hybrid-type DFE (H-DFE).