Reduced complexity sequence detection

The paper deals with the design of suboptimal receivers for data transmission over frequency selective channels. The complexity of the optimum detector, that is the maximum likelihood sequence detector (MLSD), turns out be exponential in the channel memory. Hence, when dealing with channels with long memory, suboptimal receiver structures must be considered. Among suboptimal methods, a technique that allows reduction of the complexity is the delayed decision feedback sequence detector (DDFSD). This receiver is based on a Viterbi processor where the channel memory is truncated. The memory truncation is compensated by a per-survivor decision feedback equalizer. In order to achieve good performance, it is crucial to operate an appropriate prefiltering of the received sequence before the DDFSD. Our contribution is to extend the principles of MLSD and DDFSD to the case where the prefilter is the feedforward filter of a minimum mean-square error decision feedback equalizer (MMSE-DFE). Moreover performance evaluation of the MMSE prefiltered DDFSD is addressed. The union upper bound is used to evaluate the probability of first-event error. Simulation results show that our proposed design of the MMSE-DDFSD gives substantial benefits when a severe frequency selective channel is considered

Fast Time-Varying Dispersive Channel Estimation and Equalization for 8-PSK Cellular System

In this paper, a novel channel-estimation scheme for an 8-PSK enhanced data rates for GSM evolution (EDGE) system with fast time-varying and frequency-selective fading channels is presented. via a mathematical derivation and simulation results, the channel impulse response (CIR) of the fast fading channel is modeled as a linear function of time during a radio burst in the EDGE system. Therefore, a least-squares-based method is proposed along with the modified burst structure for time-varying channel estimation. Given that the pilot-symbol blocks are located at the front and the end of the data block, the LS-based method is able to estimate the parameters of the time-varying CIR accurately using a linear interpolation. The proposed time-varying estimation algorithm does not cause an error floor that existed in the adaptive algorithms due to a nonideal channel tracking. Besides, the time-varying CIR in the EDGE system is not in its minimum-phase form, as is required for low-complexity reduced-state equalization methods. In order to maintain a good system performance, a Cholesky-decomposition method is introduced in front of the reduced-state equalizer to transform the time-varying CIR into its minimum-phase equivalent form. via simulation results, it is shown that the proposed algorithm is very well suited for the time-varying channel estimation and equalization, and a good bit-error-rate performance is achieved even at high Doppler frequencies up to 300 Hz with a low complexity

Equalization of multi-Gb/s chip-to-chip interconnects affected by manufacturing tolerances

Electrical chip-to-chip interconnects suffer from considerable intersymbol interference at multi-Gb/s data rates, due to the frequency-dependent attenuation. Hence, reliable communication at high data rates requires equalization, to compensate for the channel response. As these interconnects are prone to manufacturing tolerances, the equalizer must be adjusted to each specific channel realization to perform optimally. We adopt a reduced-complexity equalization scheme where (part of) the equalizer is fixed, by involving the channel statistics into the equalizer derivation. For a 10 cm on-board microstrip interconnect with a 10% tolerance on its parameters, we point out that 2-PAM transmission using a fixed prefilter and an adjustable feedback filter, both with few taps, yields only a moderate bit error rate degradation, compared to the all-adjustable equalizer; at a bit error rate of 1e-12 these degradations are about 1.1  dB and 3  dB, when operating at 20 Gb/s and 80 Gb/s, respectively

Combating channels with long impulse response using combined turbo equalization and turbo decoding.

by Chan Yiu Tong.Thesis (M.Phil.)--Chinese University of Hong Kong, 2000.Includes bibliographical references (leaves 56-[59]).Abstracts in English and Chinese.Chapter 1 --- Introduction --- p.1Chapter 1.1 --- Communications and Coding Technology --- p.2Chapter 1.2 --- The Emerge of Turbo Codes --- p.3Chapter 1.3 --- The Extension of Turbo Principle --- p.3Chapter 1.4 --- Receiver Structures for Practical Situations --- p.4Chapter 1.5 --- Thesis Overview --- p.5Chapter 2 --- ISI Channel Model and Channel Equalization --- p.6Chapter 2.1 --- A Discrete Time ISI Channel Model --- p.6Chapter 2.1.1 --- Optimum Maximum Likelihood Receiver --- p.8Chapter 2.1.2 --- The Whitened Matched Filter --- p.11Chapter 2.2 --- Equalization Techniques for Combating ISI --- p.13Chapter 2.2.1 --- Linear MMSE Equalizer --- p.13Chapter 2.2.2 --- MLSE Equalizer in Viterbi Algorithm --- p.15Chapter 3 --- An Overview of Turbo Codes --- p.18Chapter 3.1 --- The Turbo Encoder --- p.19Chapter 3.2 --- The Turbo Interleaver --- p.21Chapter 3.3 --- The Iterative Decoder --- p.22Chapter 3.3.1 --- The MAP Algorithm --- p.23Chapter 3.3.2 --- The Max-Log MAP Algorithm --- p.25Chapter 3.3.3 --- The Log-MAP Algorithm --- p.28Chapter 4 --- Receivers for Channels with Long Impulse Responses --- p.29Chapter 4.1 --- Shortcomings for the Existing Models --- p.30Chapter 4.2 --- Proposed System Architecture --- p.30Chapter 4.2.1 --- Optimized Model for Channel Shortening Filter --- p.31Chapter 4.2.2 --- Method One - Separate Trellises for EQ and DEC --- p.35Chapter 4.2.3 --- Method Two - Combined Trellises for EQ and DEC --- p.37Chapter 5 --- Performance Analysis --- p.40Chapter 5.1 --- Simulation Model and Settings --- p.40Chapter 5.2 --- Performance Expectations --- p.43Chapter 5.3 --- Simulation Results and Discussions --- p.49Chapter 6 --- Concluding Remarks --- p.55Bibliography --- p.5

Intersymbol and Intercarrier Interference in OFDM Transmissions through Highly Dispersive Channels

This work quantifies, for the first time, intersymbol and intercarrier interferences induced by very dispersive channels in OFDM systems. The resulting achievable data rate for \wam{suboptimal} OFDM transmissions is derived based on the computation of signal-to-interference-plus-noise ratio for arbitrary length finite duration channel impulse responses. Simulation results point to significant differences between data rates obtained via conventional formulations, for which interferences are supposed to be limited to two or three blocks, versus the data rates considering the actual channel dispersion