Prefiltered Low Complexity Tree Detection for Frequency Selective Fading Channels

Abstract

We target M-ary data sequence estimation over time-variant frequency selective fading channels. Recently, we proposed a low complexity breadth first tree detector, termed improved M-algorithm (IMA). Unlike the M-algorithm (MA), it takes the whole energy of the received symbol of the current step into account when choosing survivors. Unknown future symbols overlap with postcursors of the current symbol and are modelled as additive Gaussian noise in the metric. Thus, unlike the standard MA, IMA works well without an energy compacting Front End Prefilter (FEP) even in frequency-selective channels, whereas a FEP is crucial for ordinary reduced state sequence estimators such as the Delayed Decision Feedback Sequence Estimator (DDFSE) and Reduced State Sequence Estimator (RSSE). However, although not explicitly needed, we show that the complexity of IMA can be reduced even more applying a FEP, because the first channel tap has increased energy, and the effective channel would be even shorter, so that the influence of future symbols on the postcursors is smaller, enabling the tree detector to chose the paths through the tree more precisely. We propose to make use of the cepstrum to compute the FEP via a minimum phase target impulse response. We use the GSM/EDGE modulation format here, in order to enable other researchers to compare their results. Simulation results indicate that for the given application, IMA is superior to RSSE with similar complexity.

Design and Optimization of a Digital Baseband Receiver ASIC for GSM/EDGE

“…Then, the MMSE-DFE [12] and cepstrum method [15] (recently proposed for GSM/EDGE in [16]) have been implemented, and the parameters have been optimized, such that these algorithms provide the same BER performance at certain SNR points In Fig. 7 the complexity of the different algorithms in terms of number of complex-valued multiplications and additions is compared 3 .…”

Recursive Detection of M-ary Signals over Fast Varying Mobile Communication Channel

“…Several articles discuss the problem of detection of M-ary signals [5][6][7][8]. In [5] the authors derived an exact expression for the symbol error probability (SEP) for coherent detection of M-ary PSK signals using array of antennas with optimum combining.…”

“…They consider a Rayleigh flat fading channel. In [6], a low complexity breadth first tree detector, termed improved M-algorithm (IMA) is proposed. The authors showed that IMA works well without an energy compacting front end prefilter (FEP) even in frequency-selective channels.…”

“…If the channel exhibits intersymbol interference (ISI) in the received data, adaptive equalizers [1][2][3], that use adaptive algorithms [4], are used to recover the received signal and to remove the ISI. When the channel is rapidly varying, tracking these variations becomes a challenging problem and hence the equalizer may not be able to track the channel.Several articles discuss the problem of detection of M-ary signals [5][6][7][8]. In [5] the authors derived an exact expression for the symbol error probability (SEP) for coherent detection of M-ary PSK signals using array of antennas with optimum combining.…”