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The article reviews the exhibition "Gainsborough's House" featuring the works of John and Mary Gainsborough at the house in Sudbury, Suffolk, England starting November 21, 2022.

Space-time trellis coding is an established diversity technique that reduces the effects of multipath fading over wireless communication channels. Here, we consider high rate space-time trellis codes (STTC) with continuous phase frequency shift keying (CPFSK). We present optimized rate-2/3 STTC implemented with 3 transmit antennas. These codes provide system throughputs of 4 and 6 bits per channel use with 4-ary and 8-ary CPFSK respectively. Simulated error rate performance of the optimized codes with receive diversity is presented. We show that although the schemes do not achieve full transmit diversity, they provide excellent coding gains compared to full rank schemes that have equivalent throughput, but higher order modulations and greater complexity. Index Terms--Space-time trellis coding, continuous phase modulation, spectrally efficient signals.

An iterative approach is developed for decoding Space Time Trellis Codes (STTCs) in frequency selective Multiple Input Multiple Output (MIMO) channels. The method uses the Partitioned Viterbi Algorithm (PVA) as an equaliser for the MIMO system. It is used iteratively with a STTC decoder that provides soft outputs using the Soft Output Viterbi Algorithm (SOVA). It is shown through simulation that the iterative procedure achieves a performance within 2.0dB of Maximum Likelihood (ML) decoding, at a FER of [10.sup.-2], but suffers a small diversity loss. It is also shown that the complexity of the iterative approach is lower than that of ML decoding. Index Terms--MIMO systems, space-time coding, equalization, reduced complexity, Viterbi.

A sequence-based multiple-input-multiple-output receiver incorporating channel estimation and tracking for a frequency selective fading environment is developed. It employs near-maximum likelihood sequence estimation using the partitioned Viterbi algorithm and offers linearly increasing complexity with the number of transmit antennas. The receiver implements channel estimation and tracking using a vector-polynomial-based generalized recursive least squares algorithm. The resulting integrated receiver can operate in a continuously time-varying Rayleigh or Rician fading environment. Simulation results show that it offers a good tradeoff between complexity and performance. Further complexity reduction can be achieved using tentative decisions as reference signals to the estimator and a reduced complexity form of the estimator. Index Terms--Channel estimation, equalizers, fading channels, mobile communication, multiple-input-multiple-output (MIMO) systems.

An adaptive equalizer structure based on a state space formulation and maximum likelihood sequence estimation (MLSE) is developed for a time-varying, frequency-selective channel. Differential phase shift keying (DPSK) is assumed at the transmitter and effective differential decoding is performed at the receiver. The standard models of a time-varying linear channel and the Karhunen-Loeve (KL) expansion underpin the receiver structure. Analytical and simulation results for the receiver are shown. The resulting receiver is a per-survivor structure. Index Terms--Adaptive equalizers, Kalman filtering, Viterbi detection.

This paper presents a multiple-input-multiple-output (MIMO) receiver design with integrated channel estimation and tracking for a time-varying frequency-selective Rician or Rayleigh fading environment. It first extends a polynomial-predictor-based channel estimation and tracking approach to a MIMO system. The structure and complexity of the estimator are similar to that of an optimum estimator using a Kalman filter, but it does not require a priori knowledge of the channel statistics. It employs a fixed-state transition matrix using precomputed polynomial coefficients and can be used in a Rician fading environment without recontiguration. It is integrated with a MIMO minimum-mean-squared-error decision feedback equalizer, and simulation results show that the system performance using the estimator can be made comparable to that employing a Kalman estimator under a broad range of channel conditions. Index Terms--Equalizers, estimation, fading channels, mobile communication, multiple-input-multiple-output (MIMO) systems.

We develop space-time trellis coded (STC) schemes using continuous-phase modulation (CPM). We employ the Rimoldi model of CPM to create a decomposed model of STC-CPM. The decomposition separates the coding from the modulation. The space-time encoding and the inherent CPM encoding is combined into a single trellis encoder on the ring of integers modulo-p. This is followed by a bank of memoryless modulators. The model allows the search for good space-time codes to take into account the inherent encoding of the modulation. Index Terms--Continuous phase modulation, space-time coding, ring convolutional codes.

This paper studies optical communications using subcarrier phase shift keying (PSK) intensity modulation through atmospheric turbulence channels. The bit error rate (BER) is derived for optical communication systems employing either on/off key (OOK) or subcarrier PSK intensity modulation. It is shown that at BER = [10.sup.-6] and a scintillation level of [sigma] = 0.1, an optical communication system employing subcarrier BPSK is 3 dB better than a comparable system using fixed-threshold OOK. When [sigma] = 0.2, an optical communication system employing subcarrier BPSK achieves a BER = [10.sup.-6] at SNR = 13.7 dB, while the BER of a comparable system employing OOK can never be less than [10.sup.-4]. Convolutional codes are discussed for optical communication through atmospheric turbulence channels. Interleaving is employed to overcome memory effect in atmospheric turbulence channels. An upper bound on BER is derived for optical communication systems employing convolutional codes and subcarrier BPSK modulation. Index Terms--Atmospheric turbulence, coding, laser, scintillation.

Lattice coding of orthogonal frequency-division multiplexing (OFDM) systems is considered. Mapping of multilevel construction lattices to OFDM blocks is shown, and a methodology for probabilistic analysis of multistage generalized minimum distance (GMD) decoding of the received OFDM blocks is shown. As a case study, transmission of points from a 128-dimensional Barnes-Wall lattice is considered. Tight approximations to the system-error rate are obtained and verified by simulation. It appears that GMD decoding of lattice-encoded OFDM provides high coding gain at low complexity. Index Terms--Frequency-selective channels, generalized minimum distance (GMD) decoding, orthogonal frequency-division multiplexing (OFDM) systems, sphere packings and lattices.

For a power limited orthogonal frequency-division multiplexing (OFDM) system transmitting a large number N of subcarriers over a Rayleigh-fading channel, the distribution of the instantaneous capacity is shown to be approximately Gaussian. The mean and variance of the approximating distribution are derived. It is also shown that, in the limit as N [right arrow] [infinity], the capacity approaches a constant value equal to the capacity of the infinite-bandwidth Gaussian channel. Index Terms--Channel capacity, orthogonal frequency-division multiplexing (OFDM), Rayleigh-fading channels.

A study presents a robust channel-order estimation algorithm that will work over a wide range of signal-to-noise ratios (SNRs) and correlated channels. The performance is clearly superior to the minimum description length (MDL) algorithm that operates within a small range of SNRs and fails completely when the channels are correlated.

The iterative decoding structure and component maximum a posteriori decoders used for decoding binary concatenated codes can be extended to the nonbinary domain. This paper considers turbo codes over nonbinary rings, specifically ternary, quaternary, penternary, hexernary, and octernary codes. The best rate-l/2 component codes are determined using a practical search algorithm. The performance of the resulting rate-l/3 turbo codes on an additive white Gaussian noise channel using q-ary phase-shift keying modulation is given. Index Terms--Nonbinary turbo codes, ring codes.

The box and match decoding algorithm (BMA) significantly reduces the computational complexity of the ordered statistic decoding algorithm at the expense of increased memory requirements. In this letter, a soft-input/soft-output version of the BMA is developed. Additional complexity-reduction techniques are also described. Index Terms--Iterative decoding, list decoding, product codes.

This paper describes a new approach to list-based soft-input soft-output (SISO) decoding based on order-i reprocessing. Approximations to both the log-maximum a posteriori (MAP) and max-log-MAP algorithms are developed. Additional decoding steps are proposed to correct common types of errors remaining after iterative decoding. These steps can significantly improve performance at low bit-error rates in later iterations. The proposed algorithms offer a wide range of complexity versus performance tradeoffs, which are explored through Monte Carlo simulations of product code decodings. The algorithms improve performance over previous approaches. Index Terms--Iterative decoding, list decoding, product codes.

Single parity-check (SPC) codes are applied in both parallel and serial concatenated structures to produce high-performance coding schemes. The number of concatenations or stages M is increased to improve system performance at moderate-to-low bit-error rates without changing the overall code parameters (namely, code rate and code block length). Analytical bounds are presented to estimate the performance at high signal-to-noise ratios. The SPC concatenated codes are considered with binary phase-shift keying and with 16-quadrature amplitude modulation bit-interleaved coded modulation on the additive white Gaussian noise channel and the independent Rayleigh fading channel. Simulations show that the four-stage serial or parallel concatenated SPC codes can outperform or perform as well as 16-state turbo codes, respectively. Furthermore, decoding complexity is approximately 9-10 times less complex than that of 16-state turbo codes. The convergence behavior of both serial and parallel concatenated SPC codes is also discussed. Index Terms--Bit-interleaved coded modulation (BICM), parallel concatenation, serial concatenation, single parity-check (SPC) codes, turbo codes.

This correspondence investigates the asymptotic performance of single parity-check (SPC) product codes (PCs) from a decoding point of view. Specifically, the probability of bit error is bounded before and after the decoding of each dimension, similar to the analysis of "iterated codes" by Elias. It is shown that the asymptotic probability of bit error can be driven to zero as the number of dimensions, and hence the block length, increases at signal-to-noise ratios (SNRs) within 2 dB of capacity over the additive white Gaussian noise (AWGN) channel. Index Terms--Asymptotic analysis, iterated codes, single parity-check (SPC) product codes (PCs).

This letter presents a simple polynomial predictor-based sequence detector for the Rayleigh nonselective fading channel. Unlike the polynomial predictor-based sequence detector proposed by Borah and Hart, the new receiver is not restricted to constant envelope modulation schemes. Analytical and simulated results are presented. In some instances, the proposed receiver performs within 6 dB of the equivalent maximum-likelihood sequence estimation receiver. Index Terms--Fading channels, sequence estimation.

Previous work on concatenated single parity-check codes has yielded exceptionally good performance despite, or perhaps because of, their weak algebraic structure. In this letter, maximum a posteriori single parity-check decoders are applied to the decoding of systematic binary algebraic block codes. Results for a range of Hamming codes show good performance compared to soft-decision brute force (maximum-likelihood) and algebraic decoding. The decoding complexity of the proposed technique grows only linearly with increasing block length. Index Terms--Concatenated codes, iterative decoding, maximum a posteriori (MAP) decoding, single parity-check (SPC) codes, soft decoding, soft-input-soft-output (SISO).

A technique is described for enumerating incident signals on a uniform linear array (ULA) independent of their correlation in a Raleigh flat fading channel environment. The technique minimizes the number of antennas with reference to the number of signals and adapts dynamically to maintain performance in mobile environments.

Turbo-codes are decoded using iterative decoding algorithms with somewhat elusive convergence properties. In this paper, the modes of convergence observed in an extensive series of turbo-code simulations are categorized by examining the bit convergence behavior for each frame. Based on these results, a new method for decoder termination based on average log-likelihood ratios is presented and compared with other methods. As an application, a selective repeat automatic repeat request (ARQ) system is considered. Index Terms--Decoder convergence, iterative decoding, log-likelihood decoding, stopping criterion, turbo-codes.

To increase wireless system capacity using co-channel signals and multiple receiver antennas, we develop the partitioned Viterbi algorithm (PVA). The PVA estimation complexity increases linearly with each additional co-channel signal rather than exponentially as it does with joint maximum-likelihood sequence estimation (MLSE). The estimation problem involves multiple signals simultaneously transmitted and observed through slow-fading, frequency-selective channels. Although transmission is assumed to be in bursts according to a time-division multiple-access scheme, more than one signal can occupy the same time and frequency slot (these signals are referred to as "co-channel" signals). Separation and estimation of the symbol bursts is accomplished by exploiting channel differences. PVA estimation consists of a set of Viterbi detectors, one per signal, that operate in parallel with cross-coupling to allow approximate interference cancellation by means of tentative decisions. The forward filter of a decision feedback equalizer (DFE) is used to "prefilter" received signals prior to PVA estimation. Prefiltering delays the energy of interfering signals so that tentative decisions become reliable enough to use. Simulation results show PVA performance remains near-optimal with respect to the performance of joint MLSE. Index Terms--Diversity methods, maximum-likelihood estimation, multipath channels, multiuser channels, time-varying channels.

This paper develops an approach to iterative multistage decoding of multilevel codes. This involves passing reliability information to previous and subsequent decoders instead of only hard decisions to subsequent decoders. The paper also develops an adaptive version of the suboptimal soft output decoding algorithm of [1]. This adaptive algorithm provides a gain of approximately 0.24 dB at a bit error rate (BER) of [10.sup.-5] after four iterations and approximately 0.43 dB after ten iterations over the algorithm of [1]. If the adaptive algorithm is used in conjunction with iterative multistage decoding then a gain of approximately 0.62 dB is obtained at a BER of [10.sup.-5] after four iterations and approximately 0.9 dB after ten iterations over the algorithm of [1]. Index Terms--Block turbo codes, iterative decoding, iterative multistage decoding, multilevel codes, product codes.

Hein and Zakhor analyzed the limit-cycle behavior of the low-pass double-loop converter. This brief demonstrates that the limit cycles in a bandpass [Sigma]-[Delta] double-loop converter are identical to the low-pass case. It is shown that the double-loop converter can have two independent limit cycles occurring simultaneously. Simulations confirm that the bandpass converter state variables can be designed to stay within designed bounds, as in the low-pass (baseband) case. Hence, stability is improved as the likelihood of stages saturating and clipping is significantly reduced.

Linearly time-varying fading models are used to investigate differential detection of PSK signals transmitted over frequency-flat fading channels. The structure of the optimal differential PSK detector is derived and an analytical technique is developed to compute its error performance. Results obtained by computer simulation are in excellent agreement with the analytical predictions. Index Terms - Differential phase-shift keying, diversity systems, fading channels, Rayleigh channels.

In this paper we compute the error performance of noncoherent detection receivers for FSK signals transmitted over fast frequency-flat Rician fading channels. Linearly time-varying fading models are used to derive closed-form expressions for the error probability of binary FSK signaling. Error bounds are established for the performance of M-ary orthogonal FSK. Simulation results are in excellent agreement with analytical predictions. Index Terms - Fading channels, frequency-shift keying, noncoherent receivers.

We propose a novel detection scheme for continuous-phase modulation (CPM) signals transmitted over frequency-flat fading channels. Its most significant feature is that it operates without statistical information on the fading channel, and for this reason it is nicknamed 'blind detector.' Its error-rate performance is assessed with minimum shift keying (MSK) and Gaussian MSK (GMSK) schemes and compared with the performance of other decoders. Index Terms - Continuous-phase modulation, fading channels, maximum-likelihood detection.

This paper describes a carrier-frequency offset estimator derived using maximum-likelihood techniques. The estimator is designed for a digital space-diversity receiver, operating in a wide-band frequency-selective multipath fading channel. The estimator is suited to a burst-mode time-division-multiple-access system, because the estimate is formed in an open-loop manner, and relies on a training sequence normally used in burst-mode systems. The main advantage is that it does not require channel state information; rather, it only requires knowledge of the autocorrelation of the channel. Simulation results show the estimator to be unbiased over a wide frequency range. The normalized error standard deviation is shown to be 0.0015 across the frequency offset range for a receiver with four diversity branches, when the normalized channel delay spread is 0.1, the signal-to-noise ratio (SNR) is 10 dB, and the training sequence length is 23 symbols. It is found that, for most parameter configurations, there is approximately a factor of two improvement in the estimate error standard deviation when the antenna diversity is doubled.

This paper develops a receiver structure to perform jointly maximum-likelihood (ML) synchronization, equalization, and detection of a linearly modulated signal transmitted over a time-varying frequency-selective Rician-faded channel, corrupted by additive white Gaussian noise (AWGN). The receiver is particularly suited to a fast-fading channel, where other receivers that rely on estimating the channel cannot track it quickly enough. The signal mean and autocovariance are needed, and a scheme is proposed for estimating these quantities adaptively. The receiver processes the specular and diffuse components (corresponding to the signal mean and autocovariance) separately. Processing the known specular component is the classical detection problem. The unknown diffuse component is processed by predictors [11]. We show that the predictors can achieve synchronization in a novel manner, if synchronization is required. A union bound on the receiver's bit-error rate (BER) is derived, and it tightly bounds simulated BER's in fast fading at high signal-to-noise ratios (SNR's). Index Terms - Dispersive channels, error analysis, linear prediction, maximum-likelihood detection, parameter estimation, Rician channels, synchronization, time-varying channels.

In [1], a maximum-likelihood sequence estimation (MLSE) receiver structure was derived for unknown time-varying frequency-selective Rayleigh-fading channels and uncorrelated diversity sources. In this letter, the receiver design is extended to the case of correlated diversity sources. Correlated diversity sources typically arise with space diversity, where constraints on antenna volume require that diversity antennae be placed too closely together. Analytic and simulated bit-error rate (BER) curves are presented for receivers which exploit and ignore the correlation. In the former case, we find a small BER improvement that reduces with decreasing correlation. However, for a fixed receiver complexity, superior performance is achieved when the correlation is ignored. Index Terms - Correlation, dispersive channels, diversity methods, linear prediction, maximum-likelihood detection, time-varying channels.

Conventional differential detection is known to perform poorly on the fast-fading Rayleigh-fading channel due to the rapid variation of the channel state. The technique of multiple symbol differential detection (MSDD) improves the error performance by detecting over a sequence of symbols and exploiting the inherent correlation of the fading process. To further reduce the error rate, we need to introduce some form of coding. Successful coding for the Rayleigh-fading channel requires interleaving to decorrelate the channel a conflicting requirement to MSDD. In this paper we propose a solution consisting of interleaving blocks of L M-ary phase-shift keying (MPSK) symbols that are multiple symbol differentially detected. The blocks are treated as elements of an [M.sup.L] symbol alphabet over which a multilevel code based on geometrically uniform partitions is defined. Index Terms - Geometrically uniform codes, multiple symbol differential detection, Rayleigh-fading channel.