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Maximum likelihood (ML) receivers for space-time coded multiple-input multiple-output (MIMO) systems with Gaussian channel estimation errors are proposed. Two different cases are considered. In the first case, the conditional probability density function (PDF) of the channel estimate is assumed Gaussian and known. In the second case, the joint PDF of the channel estimate and the true channel gain is assumed Gaussian and known. In addition to ML signal detection for space-time coded MIMO with ML and minimum mean-squared-error channel estimation, ML signal detection without channel estimation is also studied. Two suboptimal structures are derived. The Alamouti space-time codes are used to examine the performances of the new receivers. Simulation results show that the new receivers can reduce the gap between the conventional receiver with channel estimation errors and the receiver with perfect channel knowledge at least by half in some cases. [ABSTRACT FROM AUTHOR]

The goal of combining beamforming and space-time coding is to obtain full-diversity order and to provide additional received power (array gain) compared to conventional space-time codes. In this work, a class of code constellations is proposed, called generalized partly orthogonal designs (PODs) and both high-rate and low-rate feedback information is incorporated with possible feedback errors. A binary symmetric channel (BSC) model characterizes feedback errors. Two cases are studied: first, when the BSC bit error probability is known a priori to the transmission ends, and second, when it is not known exactly. Based on a minimum pairwise error probability (PEP) design criterion, we design a channel optimized vector quantizer (COVQ) for feedback information and a precoder matrix codebook to adjust the transmission codewords. The attractive property of our combining scheme is that it converges to conventional space-time coding with low-rate and erroneous feedback and to directional beamforming with high-rate and error-free feedback. This scheme also shows desirable robustness against feedback channel modeling mismatch. [ABSTRACT FROM AUTHOR]

This paper presents serially concatenated trellis coded modulations (SCTCMs) that perform consistently close to the available mutual information for periodic erasure channel (PEC), periodic fading channel (PFC) and the 2 x 2 compound matrix channel. We use both the maximum-likelihood decoding criteria and iterative decoding criteria to design universal SCTCMs for the PEC and the PFC. For the space-time channel, by demultiplexing the symbols across the antennas, the proposed universal SCTCMs for the period-2 PFC deliver consistent performance over the eigenvalue skew of the matrix channel. Within the family of channels having the same eigenvalue skew, a time-varying linear transformation (TVLT) is used to mitigate the performance variation over different eigenvectors. The proposed space-time SCTCMs of 1.0, 2.0 and 3.0 bits per transmission require excess mutual information in the ranges 0.11-0.15, 0.23- 0.26 and 0.35-0.53 bits per antenna, respectively. Because of their consistent performance over all channels, the proposed codes will have good frame-error-rate (FER) performance over any quasi-static fading distribution. In particular, the codes provide competitive FER performance in quasi-static Rayleigh fading. [ABSTRACT FROM AUTHOR]

In this paper, a method is proposed to construct spectrally efficient unitary space-time codes for high-rate differential communications over multiple-antenna channels. Unlike most of the known methods which are designed to maximize the diversity product (the minimum determinant distance), our objective is to increase the spectral efficiency. The simulation results indicate that for high spectral efficiency and for more than one receive antenna, the new method significantly outperforms the existing alternatives. In the special case of two transmit antennas, which is the main focus of this paper, the relation between the proposed code and the Alamouti scheme helps us to provide an efficient maximum-likelihood (ML) decoding algorithm. Also, we demonstrate that similar ideas can be applied to designing codes for more than two transmit antennas. As an example, we present a construction for 4-by-4 unitary constellations which has a good performance, compared with the other known codes. [ABSTRACT FROM AUTHOR]

Finding a least-cost path subject to a delay constraint in a network is an NP-complete problem and has been extensively studied. Many works reported in the literature tackle this problem by using ϵ-approximation schemes and scaling techniques, i.e., by mapping link costs into integers or at least discrete numbers, a solution which satisfies the delay constraint and has a cost within a factor of the optimal one, that can be computed with pseudopolynomial computational complexity. In this paper, having observed that the computational complexities of the ϵ-approximation algorithms using the linear scaling technique are linearly proportional to the linear scaling factor, we investigate the issue of finding the optimal (the smallest) linear scaling factor to reduce the computational complexities, and propose two algorithms, the optimal linear scaling algorithm (OLSA) and the transformed OLSA. We analytically show that the computational complexities of our proposed algorithms are very low, as compared with those of ϵ-approximation algorithms. Therefore, incorporating the two algorithms can enhance the ϵ-approximation algorithms by granting them a practically important capability: self-adaptively picking the optimal linear scaling factors in different networks. As such, ϵ-approximation algorithms become more flexible and efficient. [ABSTRACT FROM AUTHOR]

In this paper, we develop a capacity-approaching Cooperative Space-Time Coding (CSTC) scheme employing irregular design for a twin-relay aided network as an extension of our previous work cast in the context of a half-duplex single-relay-aided network. For the sake of recovering the multiplexing loss imposed by a half-duplex three-terminal network, we employ a successive relaying protocol in this paper, where an additional relay node is activated. Hence, in order to design a near-capacity coding system, first the capacity and the achievable information-rate of a specific space-time coding aided scheme are quantified for the successive relaying aided channel. More specifically, the cooperative space-time codes employed at the source and the relays are jointly designed with the aid of EXtrinsic Information Transfer (EXIT) charts for the sake of high-integrity operation at Signal-to-Noise Ratios (SNRs) close to the corresponding successive relaying channel's capacity. Furthermore, unlike in the half-duplex single-relay based system, the destination node performs frame-by-frame Successive Interference Cancellation (SIC) aided iterative detection, in order to mitigate the efforts of multiple-access interference. Finally, our numerical results demonstrate that our proposed Irregular Cooperative Space-Time Coding (Ir-CSTC) scheme is capable of near-capacity operation in the successive relaying aided network, which is an explicit benefit of our joint source-and-relay transceiver design. [ABSTRACT FROM AUTHOR]

The article presents abstracts of papers related to radio transmissions that will be appearing in the forthcoming issues of the journal "IEEE Transactions on Communications." The paper "Performance of Filterbank and Wavelet Transceivers in the Presence of Carrier Frequency Offset," by Tiziano Bianchi, Fabrizio Argenti and Enrico Del Re investigates the performance of a generic filterbank transceiver in the presence of a carrier frequency offset. The paper "Reduced-Complexity Decoding of LDPC Codes," by I. Chen, A. Dholakia, E. Eleftheriou, M. Fossorier and X.-Y. Hu presents information on various log-likelihood-radio-based belief-propagation decoding algorithms and their reduced-complexity derivatives for low-density parity-check codes. The paper "Multistage Iterative Decoding With Complexity Reduction for Concatenated Space-Time Codes," by Andres Reial and Stephen G. Wilson presents a multistage iterative decoding structure that takes full advantage of the concatenated nature of the transmission path, treating the modulator and channel stages as an additional encoder in serial concatenation.