Iterative Design and Detection of a DFE in the Frequency Domain

Abstract

Error-propagation phenomena and computational complexity of the filters' design are important drawbacks of existing decision-feedback equalizers (DFE) for dispersive channels. In this paper, we propose a new iterative block DFE (IBDFE) which operates iteratively on blocks of the received signal. Indeed, a suitable data-transmission format must be used to allow an efficient implementation of the equalizer in the frequency domain, by means of the discrete Fourier transform. Two design methods are considered. In the first method, hard detected data are used as input of the feedback, and filters are designed according to the correlation between detected and transmitted data. In the second method, the feedback signal is directly designed from soft detection of the equalized signal at the previous iteration. Estimators of the parameters involved in the IBDFE design are also derived. From performance simulations on a wireless dispersive fading channel, we observed that the IBDFE outperforms existing DFEs. Moreover, the IBDFE exhibits a reduction of the computational complexity when compared against existing schemes, both in signal processing and in filter design

Performance of Iterative Soft Decision Feedback Equalizers for Single-Carrier Transmission

“…Recently, iterative detection and decoding schemes [6][7][8][9][10][11] that utilize the soft-decisions provided by iterative channel decoders have been considered with technology development in low cost computing hardware. Especially, in [6], maximum likelihood sequence estimator (MLSE) is used for the soft-in/soft-out detection, while those in [7][8][9][10][11] utilize soft-decision feedback and interference cancellation.…”

“…Especially, in [6], maximum likelihood sequence estimator (MLSE) is used for the soft-in/soft-out detection, while those in [7][8][9][10][11] utilize soft-decision feedback and interference cancellation. In complexity point of view, MLSE has a complexity exponentially increasing with the channel length, and the scheme in [6] is not suitable for practical application even though it generally outperforms all other schemes.…”

“…In complexity point of view, MLSE has a complexity exponentially increasing with the channel length, and the scheme in [6] is not suitable for practical application even though it generally outperforms all other schemes. In this sense, the soft-decision feedback cancellation schemes in [7][8][9][10][11] look more feasible for practical application at a reasonable computational cost.…”

“…Based on this observations, we, in this paper, consider to use turbo equalization techniques using the decision feedback equalizer in time-domain [2,3] and in frequency domain [10,11] by replacing the immediate hard-decision with the soft-decisions fed-back from channel decoder. Using log-likelihood ratio (LLR) feedback from channel decoder, we extract the soft decision as a posteriori mean and the reliability information as a posteriori variance, which are then used to cancel the residual interference.…”

Multiuser Detection for the Uplink of Prefix-Assisted DS-CDMA Systems Employing Multiple Transmit and Receive Antennas

“…The receiver is particularly simple at the downlink: since all spreading codes are affected by the same multipath channel, the receiver can be based on a linear FDE (Frequency-Domain Equalizer), operating at the chip level, followed by the despreading procedure [7]. The performances can be further improved if the linear FDE is replaced by a more powerful IB-DFE (Iterative BlockDecision feedback Equalization) [8], [9], especially for fully loaded scenarios and/or in the presence of strong interference levels [10].…”