Combined Decision Feedback Equalizer Research Articles

Power Optimization of an 11.75-Gb/s Combined Decision Feedback Equalizer and Clock Data Recovery Circuit in 0.18-$\mu\hbox{m}$ CMOS

An 11.75-Gb/s combined decision feedback equalizer (DFE) and clock data recovery circuit in a 0.18-μm CMOS is presented. Various techniques are applied to reduce the chip power consumption. In particular, the feedback path of the DFE is merged with an Alexander phase detector (PD). An analysis on the speed requirements of various blocks in the PD and DFE circuits is performed to determine the optimum power dissipation of each one. It is shown that the chip power consumption is reduced by 31% compared to a conventional design. The chip is capable of equalizing copper cable channels with up to 12-dB loss at the 5.875-GHz Nyquist frequency and consumes 101 mW (not including output buffers) with a 1.8-V supply voltage.

Frequency domain feed-forward filter combined DFE structure in single carrier systems over time-varying channels

Most of the researches about frequency domain equalization assume that the single carrier wireless communication system works over static channels. However, with more and more requests for mobile wireless reception, we have to consider the case of time-varying channels. In this paper, we propose a frequency domain feed-forward filter combined decision feedback equalizer over time-varying channels (FD-DFE-TV) for single carrier systems. Moreover, some complexity reducing techniques are provided to lower the additional computational burden brought by the disposal in time-varying channels. Simulations show that the proposed method can effectively lower the system error floor thus has superior performance than existing FD-DFE structure in time-varying environment, especially in high speed mobile reception.

Adaptive DFE control with differential LMS algorithm

In order to implement high-speed, high-quality land-mobile digital communications, it is necessary to simultaneously satisfy both the trackability of the frequency-selectivity fading and the simplification of the algorithm. In this study, we propose the use of the differential LMS algorithm, which is applied to the decision feedback equalizer (DFE) as the adaptive algorithm. It can be expected that the introduction of the differential algorithm will make it possible to upgrade the tracking of propagation channels that can be approximated by the simplified Markov process. By using this algorithm, we designed an LMS-DFE having a simple configuration, and evaluation of the propagation characteristics by computer simulation has shown that, compared to the conventional LMS-DFE, it has better robustness to fluctuations and makes it possible to reduce the error floor by half. In addition, we also examined a diversity combined DFE and obtained similar results. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 84(1): 99–108, 2001

Soft-output equalization and TCM for wireless personal communication systems

This paper investigates the use of a maximum a posteriori probability (MAP) algorithm to realize soft-output equalization in a concatenated equalization and trellis-coded modulation (TCM) decoding-based wireless communication system. Specifically, we first begin with a general MAP algorithm and then focus on studying Bahl's (1974) MAP and Lee's (1974) MAP algorithms. We then propose a modified version of Lee's MAP algorithm which is much simpler than the original, in terms of complexity, and is more practical. In particular, a very simple channel estimation method which employs orthogonal training sequences is proposed. In order to improve the system performance, equal-gain combining and selection diversity are also considered. Finally, we compare the performance of the MAP algorithm-based equalization with our previously proposed equalization scheme, which combines decision feedback equalization and TCM.

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.