Decision feedback equaliser based on fuzzy logic

A method for reducing the effect of error propagation in a decision feedback equaliser (DFE) by using fuzzy logic is presented. A simple membership function is proposed and adaptively determined from data. Simulation results are presented to show that the combination of the DFE and fuzzy logic is promising     

Performance improvement in decision feedback equalisers by using`soft decision'

One method to combat intersymbol interference (ISI) in digital transmission is to use a decision feedback equaliser (DFE). It is well known that a major part of the errors made by a DFE is due to the fact that the equaliser makes instantaneous decisions without taking into account data received later. It is therefore obvious that the performance of a DFE could be improved by allowing some type of `soft decision'. A method to introduce `soft decisions' in a decision feedback equaliser is presented. The method gives a performance improvement in SNR of about 1.5 dB with almost no increase in complexity compared to an ordinary DFE     

Decision feedback equaliser design using support vector machines

The conventional decision feedback equaliser (DFE) that employs a linear combination of channel observations and past decisions is considered. The design of this class of DFE is to construct a hyperplane that separates the different signal classes. It is well known that the popular minimum mean square error (MMSE) design is generally not the optimal minimum bit error rate (MBER) solution. A strategy is proposed for designing the DFE based on support vector machines (SVMs). The SVM design achieves asymptotically the MBER solution and is superior in performance to the usual MMSE solution. Unlike the exact MBER solution, this SVM solution can be computed very efficiently     

Neural network-based decision feedback equaliser with latticestructure

The effect of whitening the input data in a multilayer perceptron-based decision feedback equaliser (DFE) is evaluated. It is shown from computer simulations that whitening of the received data employing adaptive lattice channel equalisation algorithms improves the convergence rate and bit error rate performances of multilayer perceptron-based DFEs     

Performance of decision feedback equaliser on measured indoor radio channels

The measured multipath profiles from five different factories are used for the performance analysis of a binary phase shift keying (BPSK) modem, with and without a decision feedback equaliser (DFE). Both average bit error rate and outage probability are calculated as the performance criteria.<>     

Iterative decision feedback equalisation of linearly precoded OFDM systems

An iterative extension of the decision feedback equaliser (DFE) receiver for linearly precoded OFDM is proposed, which improves the performance significantly, but requires a Cholesky factorisation for each iteration every time the channel changes. Next, a lower complexity form for Hadamard precoded systems is proposed, which requires just one Cholesky factorisation per OFDM symbol, with no loss in performance     

Wavelet based decision feedback equaliser

A decision feedback equaliser (DFE) structure based on wavelets (WBDFE) is presented. The WBDFE shows faster convergence than the conventional DFE, with a very small increase in computation. In addition, the WBDFE has good time-frequency localisation, and is suitable for time-varing channels     

Mitigating error propagation effects in a decision feedbackequalizer

We present an approximate analysis approach to the computation of the 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     

Pole-zero decision feedback equalization with a rapidly convergingadaptive IIR algorithm

A decision feedback equalizer (DFE) containing a feedback filter with both poles and zeros is proposed for high-speed digital communications over the subscriber loop. The feedback filter is composed of a relatively short FIR filter that cancels the initial part of the channel impulse response, which may contain rapid variations due to bridge taps, and a pole-zero, or IIR, filter that cancels the smoothly decaying tail of the impulse response. Modifications of an adaptive IIR algorithm, based on the Steiglitz-McBride (1965) identification scheme, are proposed to adapt the feedback filter. A measured subscriber loop impulse response is used to compare the performance of the adaptive pole-zero DFE, assuming a two-pole feedback filter, with a conventional DFE having the same number of coefficients. Results show that the pole-zero DFE offers a significant improvement in mean squared error relative to the conventional DFE. The speed convergence of the adaptive pole-zero DFE is comparable to that of the conventional DFE using the standard least mean square (LMS) adaptive algorithm     

运用误差反馈的判决反馈均衡器的性能分析

判决反馈均衡器（Decision Feedback Equalizer，DFE）能补偿具有严重符号间干扰（Inter Symbol Interference，ISI）的信道，且不存在线性均衡器增强噪声的影响。而在其基础上改进的运用误差反馈的DFE，可利用误差反馈滤波器来减少传统DFE中存在的误差信号的相关性，同时其硬件实现的复杂度没有明显提高。理论分析和仿真表明，这种方法比传统的DFE更有效，特别是针对信道有严重符号间干扰的情况。     

Mitigating error propagation of MMSE-DFE by joint parameter optimization

A joint optimization of the decision feedback equalizer (DFE) filter weights and an erasure slicer is proposed in this letter. The feedback weights of the DFE are constrained with an accurate mean square error (MSE) model as the criterion. An erasure slicer is adopted to further decrease error propagation. Two consecutive 1-D optimizations are shown as good as that of a single 2-D optimization. Simulation results verify the performance improvements of the proposed scheme.     

Joint coding and decision feedback equalization for broadbandwireless channels

This paper introduces a new approach for joint convolutional coding and decision feedback equalization (DPE). To minimize error propagation, the DFE uses a combination of soft decisions and delayed tentative decisions to cancel intersymbol interference (ISI). Soft decisions are obtained by passing the DFE output through a (soft) nonlinear device. This simple method is shown to perform almost as well as an optimum soft feedback approach on wireless channels with diversity. Tentative decisions from the Viterbi decoder are used to cancel ISI due to multipath with large delays, thus remedying the increasing effect of error propagation in channels with large delay spreads. We consider the use of this soft/delayed feedback DFE (S/D-DFE) technique in broadband wireless channels (with delay spreads up to several tens of the symbol period) typical in high-bitrate mobile data applications. Simulation results indicate that the proposed joint coding and S/D-DFE technique performs to within 1-2 dB [in required signal-to-noise ratio (SNR)] of an ideal coded DFE without error propagation. When combined with antenna diversity and a reduced-complexity DFE concept with adaptive feedforward tap assignment, it provides high packet throughput against Rayleigh fading, severe delay spreads, and high Doppler rates     

Introducing erasures in decision-feedback equalization to reduceerror propagation

A simple modification of the decision feedback equalizer (DFE) slicer is proposed to reduce the effect of error propagation. A comparison of the performance of the modified DFE and conventional DFE is made for specific channels. On these channels, the modified DFE performs only marginally better than the conventional DFE in terms of average error probability, but may offer some advantages in terms of error probability conditioned on specific input sequences and in terms of the distribution of error burst lengths. Some examples are given, concerning binary PAM and multilevel quadrature amplitude modulation (M-QAM) systems     

Decision feedback demodulation-based adaptive linear equalisers fordifferentially coherent DPSK systems

The authors propose to combine linear feedback equalisation and decision feedback demodulation for the equalisation of differentially coherent PSK signalling. By modifying the equaliser output based on the decision feedback demodulation before feeding back, the proposed equaliser can be made to behave like one with a decision feedback structure. Indeed, computer simulation results demonstrate that this equaliser performs much better than existing equalisers, such as linear equalisers for differentially coherent detection. Furthermore its performance is even comparable to that of a decision feedback equaliser with coherent detection     

基于多用户反馈的判决反馈均衡器的研究

本文提出的一种新颖的基于多用户反馈的判决反馈均衡器,解决了在CDMA多用户检测中传统自适应判决反馈均衡器误码率高、系统容量小的缺点.它由具有误差反馈滤波器的判决反馈均衡器(Decision Feedback Equalizer with Error Feedback Filter,DFE-EFF)构成,并在判决后反馈多用户数据抵消多址干扰(多用户反馈干扰抵消).文中给出其结构图,分析各种判决反馈均衡算法.理论证明,具有误差反馈滤波器的多用户反馈干扰抵消判决反馈均衡器(多用户反馈干扰抵消DFE-EFF)较各种判决反馈均衡器为最优,它能同时有效处理ISI,MAI和噪声的干扰.仿真结果表明,在误码率性能和系统容量两方面,多用户反馈干扰抵消DFE-EFF比DFE、DFE-EFF均有较大改善.     

Simplified parallel decision feedback equalisation for CCITT V.32/V.32 bis coded modems

A simplified parallel decision feedback equaliser (SPDFE) with the 32/64/128 AMPM CCITT trellis code is considered. The SPDFE detector consists of a whitened matched filter (WMF) and a reduced parallel decision feedback equaliser incorporated in the Viterbi decoder. The bit error rate simulation results show substantial improvement over the conventional detector with a linear equaliser and a separate Viterbi algorithm, although the implementation complexity remains the same.<>     

Diversity Combining and Equalization with TCM for Wireless Communications

This paper presents an equalization structure in which antennadiversity, adaptive decision feedback equalization (DFE), interleavingand trellis-coded modulation (TCM) can be effectively combined to combatboth ISI and cochannel interference in cellular mobile radioenvironments. The feedback filter of the DFE can use either tentative orfinal decision symbols of the TCM Viterbi decoding to cancel tail ISIwith the square root Kalman algorithm. A performance bound on theaverage pairwise error probability for TCM under perfect interleavingand equalization is obtained by analysis. Some simulation results whichillustrate the potential of the proposed system will also be given. Inparticular, a performance comparison between the proposed method anduncoded QPSK modulation will be undertaken.     

Novel Techniques to Minimize the Error Propagation of Decision Feedback Equalizer in 8VSB DTV System

In this paper, novel and yet simple techniques are presented to minimize the error propagation caused by the large precursors and postcursors of the decision feedback equalizer (DFE) in 8VSB DTV system. A technique that selects a reference tap (symbol timing of DFE) from an estimated channel impulse response (CIR) is presented to minimize the effect of the large precursors. Another technique that selects the reference tap position, i.e., decision delay in a feedforward filter (FFF), from the estimated CIR and the amplitude of the selected reference tap is proposed to minimize the effect of large postcursors. The combined structure of a feedback filter (FBF) and Viterbi decoder for use in 8VSB DTV system is also proposed to replace the past unreliable decision symbols in FBF as well as to reduce the decision error probability. Simulation results show that our proposed DFE can prevent effectively the error propagation, in particular, by changing the reference tap and its position in FFF according to the channel condition. It is also shown that an echo removing capability of the proposed DFE, where 400 and 620taps are used for the FFF and FBF, respectively, is greater than that of conventional DFEs by about -20 mus in the single pre-echo of -10 dB channel and by about 10 mus in the single post-echo of -1 dB channel     

Joint equalization and coding for intersymbol interference channels

We present a novel scheme that combines decision feedback equalization (DFE) with high-rate error-detection coding in an efficient manner. The proposed scheme is shown to considerably outperform the conventional practice on channels with high SNR, such as those encountered in twisted-pair telephony systems. In order to analyze the performance of our method, we introduce an approximate mathematical model taking into account the error propagation phenomenon. Based on this model, upper and lower bounds on the overall probability of error are developed. These show that a simple low-redundancy error-detecting code, when properly integrated with the equalizer, can make the overall probability of error several orders of magnitude lower than that obtained with the conventional DFE, or with a DFE followed by an error-correcting code. Computer simulations of the proposed method have been performed for several channels, including the so-called high-bit-rate digital subscriber line (HDSL) test-loop 4, which is known to have a considerable amount of intersymbol interference. For all these channels, our results show that a reduction in the probability of error by more than three orders of magnitude can be obtained using codes of rate 0.96 and above. This, in turn, translates into power savings (coding gain) of 2.5 to 3 dB     

Near‐Optimum Blind Decision Feedback Equalization for ATSC Digital Television Receivers

This paper presents a near‐optimum blind decision feedback equalizer (DFE) for the receivers of Advanced Television Systems Committee (ATSC) digital television. By adopting a modified trellis decoder (MTD) with a trace‐ back depth of 1 for the decision device in the DFE, we obtain a hardware‐efficient, blind DFE approaching the performance of an optimum DFE which has no error propagation. In the MTD, the absolute distance is used rather than the squared Euclidean distance for the computation of the branch metrics. This results in a reduction of the computational complexity over the original trellis decoding scheme. Compared to the conventional slicer, the MTD shows an outstanding performance improvement in decision error probability and is comparable to the original trellis decoder using the Euclidean distance. Reducing error propagation by use of the MTD in the DFE leads to the improvement of convergence performance in terms of convergence speed and residual error. Simulation results show that the proposed blind DFE performs much better than the blind DFE with the slicer, and the difference is prominent at the trellis decoder following the blind DFE.