Maximum Likelihood Sequence Estimation Detector Research Articles

Comparison of Advanced Detection Techniques for QPSK Signals in Super-Nyquist WDM Systems

We compare the performance of detecting quadrature-phase-shift-keying (QPSK) in a super-Nyquist wavelength division multiplexing system as a QPSK and quadrature duobinary (QDB) signal using maximum likelihood sequence estimation (MLSE) and maximum a posteriori (MAP) criterion with both simulations and experiments. Three different detection schemes are studied: 1) QPSK detection with a multitap linear equalizer followed by a MLSE or MAP detector; 2) QPSK detection with only a MLSE or MAP detector; and 3) QDB detection with a MLSE or MAP detector, where a multitap linear equalizer and a delay-&-add operation are placed before the MLSE/MAP detector to convert a QPSK signal to a QDB signal. Our simulations and experiments show that the QDB detection with multitap MLSE does not provide better performance than that with two-tap MLSE, and the QDB detection with two-tap MLSE has better filtering tolerance than the QPSK detection with linear equalization followed by a multitap MLSE/MAP detector.

Sub-optimum MLSE detector with a folded state-transition trellis preselection stage

The maximum-likelihood sequence estimation (MLSE) multiuser detector has very good performance but at the expense of the exponentially increasing number of states with the number of users. A scheme that exploits the feature of power-equality in the downlink to reduce the number of states involved has been previously proposed by the authors. In the paper, the folded-trellis detector is combined with MLSE. The main idea here is to use the folded trellis which has a linear complexity to preselect a subset of the bit-combinations and then apply MLSE to this much smaller set.

A comparison of GSM receivers for fading multipath channels with adjacent and co-channel interference

We evaluate and compare several data detection schemes used in GSM systems. In particular, we compare the performance of decision feedback equalization (DFE) and nonlinear data directed estimation (NDDE) to that of maximum likelihood sequence estimation (MLSE). Establishing the performance of the basic NDDE detector is a first step in investigating the applicability of block transmission techniques to GSM systems. Our simulation results, obtained both for fading multipath channels and adjacent- and co-channel interference scenarios, suggest that the NDDE offers certain performance advantages over the DFE, and the performance of both detectors is comparable to that of the MLSE for the SNR region of interest in practical systems. Thus, they both represent viable alternatives to the MLSE detector.

Soft-decision feedback equalizer for continuous phase modulated signals in wideband mobile radio channels

A combination of a decision feedback equalizer (DFE) and a Viterbi processor for the equalization of continuous phase modulated (CPM) signals transmitted over wideband mobile radio channels is described. The equalizer structure allows soft-decision to be made and incorrect decisions to be changed in the feedback filter of the DFE. The provision of soft decisions significantly alleviates the catastrophic effect of error propagation due to error bursts caused by the fading channel. Simulation results show that the proposed equalizer approaches the performance of the more complicated maximum likelihood sequence estimation (MLSE) detector to within 2.0 dB and 2.5 dB at bit error rates (BERs) of 10/sup -2/ and 10/sup -3/ in a two-path Rayleigh fading channel while the complexity is reduced to half of that of the MLSE detector.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>