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In this paper, we consider a multiple-input–multiple-output (MIMO) system consisting of one source, one destination, and one eavesdropper, where each node is equipped with an arbitrary number of antennas. To improve the security of source–destination transmissions, we investigate the antenna selection at the source and propose the optimal antenna selection (OAS) and suboptimal antenna selection (SAS) schemes, depending on whether the source node has the global channel state information (CSI) of both the main link (from source to destination) and the wiretap link (from source to eavesdropper). Moreover, the traditional space–time transmission (STT) is studied as a benchmark. We evaluate the secrecy performance of STT, SAS, and OAS schemes in terms of the probability of zero secrecy capacity. Furthermore, we examine the generalized secrecy diversity of the STT, SAS, and OAS schemes through an asymptotic analysis of the probability of zero secrecy capacity as the ratio between the average gains of the main and wiretap channels tends to infinity. This is different from the conventional secrecy diversity that assumes an infinite signal-to-noise ratio (SNR) received at the destination under the condition that the eavesdropper has a finite received SNR. It is shown that the generalized secrecy diversity orders of the STT, SAS, and OAS schemes are the product of the number of antennas at source and destination. Additionally, numerical results show that the proposed OAS scheme strictly outperforms both the STT and the SAS schemes in terms of the probability of zero secrecy capacity. [ABSTRACT FROM PUBLISHER]

This work proposes a novel linear programming approach for the joint detection and decoding of LDPC-based space-time (ST) coded signals in multi-antenna orthogonal frequency division multiplexing (OFDM) systems. While traditional receivers typically decouple the detection and decoding processes as two disjunctive blocks or require iterative turbo exchange of extrinsic information between the soft detector and decoder, we formulate a joint linear program (LP) by exploiting the constraints imposed on the data symbols, training symbols, noise subspace as well as channel code. In consideration of the vast amount of LDPC parity check inequalities, we further present an adaptive procedure to significantly reduce the complexity of the joint LP receiver. Our LP-based receivers outperform existing receivers with substantial performance gains. Moreover, the proposed joint LP receiver demonstrates strong robustness when pilot symbols are sparsely arranged on subcarriers. [ABSTRACT FROM PUBLISHER]

We study fast lattice decodability of space-time block codes for n transmit and receive antennas, written very generally as a linear combination \sum _{i=1}^{2l} s_{i} A_{i} , where the s_{i} are real information symbols and the Ai are n\times n~ \mathbb {R} -linearly independent complex-valued matrices. We show that the mutual orthogonality condition AiA\vphantom {RRRaj}^{*} + AjAi^{*}=0 for distinct basis matrices is not only sufficient but also necessary for fast decodability. We build on this to show that for full-rate ( l = n^2 ) transmission, the decoding complexity can be no better than S^n^2+1 , where S is the size of the effective real signal constellation. We also show that for full-rate transmission, g -group decodability, as defined by Jithamithra and Rajan, is impossible for any g\ge 2 . We then use the theory of Azumaya algebras to derive bounds on the maximum number of groups into which the basis matrices can be partitioned so that the matrices in different groups are mutually orthogonal—a key measure of fast decodability. We show that in general, this maximum number is of the order of only the 2-adic value of n arise from a division algebra, which is most desirable for diversity, we show that the maximum number of groups is only 4. As a result, the decoding complexity for this case is no better than S^{\lceil l/2 \rceil } for any rate l$ . [ABSTRACT FROM AUTHOR]

Motivated by the space-time diversity transmission technique in wireless communications, a novel probabilistic quantum relay communication scheme in the quantum noisy channel is proposed in order to maximize the correct information transmission and the range of quantum communication, in which quantum signal sequences that carrying two-particle entangled states are transmitted from two senders to two relays and then retransmitted to the receiver after space-time encoded by relays. The quantum signal states can be restored via filtering out the channel noise with two-dimensional Bell measurements by the receiver. Analysis and discussions indicate that our scheme can increase and approximately double the range of quantum communication while not to reduce too much quantum signal-to-noise ratio, and meanwhile the security can be guaranteed under strongest collective attacks and LOCC attacks. [ABSTRACT FROM AUTHOR]

In this paper, we propose a wavelet based watermarking system. The system uses wavelet transform for red, green and blues channel independently. We use space-time coding for encoding the watermark message before data embedding. The bit-error-rate of the recovered message is calculated. The embedding factor is selected in such a way that the host video maintains the same quality with/without using space-time coding. The developed system is further examined, when host video faces compression and noise addition. The result shows the effectiveness of the proposed watermarking system, especially when space-time coding is used. [ABSTRACT FROM AUTHOR]

In this paper, we provide a unified framework for the asymptotic performance analysis of space-time codes (STCs) in correlated Ricean fading and non-Gaussian noise and interference. In particular, we derive simple and asymptotically tight expressions for the pairwise error probability (PEP) of coherent and differential STCs which are valid for any type of noise and interference with finite moments and detection with general Mahalonobis distance (MD) metrics including Euclidean distance (ED) and noise decorrelating (ND) metrics. These PEP expressions can be combined with truncated union bounds to obtain accurate asymptotic approximations for the bit, symbol, and frame error probabilities of STCs. We show that while the diversity gain of an STC is independent of the type of noise and the type of MD metric used, the coding gain is not and depends on certain moments of the noise and interference. We provide closed-form expressions for these moments for several practically relevant types of noise and interference. We show that for correlated noise significant performance gains can be achieved with the ND metric compared to the ED metric. While noise correlations are beneficial at high signal-to-noise ratios if they can be exploited by the metric, they are harmful if this is not the case and the simple ED metric is employed. All our analytical findings are confirmed by simulations for various popular STCs and several different types of noise and interference. [ABSTRACT FROM AUTHOR]

Turbo coded unitary space-time modulation (USTM) can provide large coding gain as compared to uncoded USTM. Because the noncoherent space-time maximum a posteriori demodulator is very complicated, in this letter, we propose a new low-complexity noncoherent iterative space-time demodulator for the USTM constructed from pilot symbol-assisted modulation. The proposed demodulator utilizes both hard and soft decisions from the turbo decoder to simplify the computational task as well as produce reliable soft outputs. Several examples demonstrate that this demodulator has both low complexity and good error performance. [ABSTRACT FROM AUTHOR]

This paper introduces a new class of space-time codes that achieve coding gain without a trellis or any form of inter-block dependency. The construction of the new codes starts from an existing (parent) space-time block code (STBC). Then by increasing the constellation size followed by expurgation of the expanded codebook, a better code is obtained at the original transmission rate. This method can be applied to a wide variety of space-time block codes, including orthogonal codes and quasi-orthogonal codes. A multi-stage design algorithm is presented, and for orthogonal parent codes, an efficient decoding algorithm is developed, and its decoding complexity is analyzed. Despite altering the regular structure of the orthogonal code, the decoding complexity is only affected by a constant factor. [ABSTRACT FROM AUTHOR]

The authors give a construction of multiblock space-time block codes from cyclic division algebras with a given nth root of unity as the nonnorm element. The construction uses local class field theory. Multiblock codes with M blocks can achieve an M-fold increase in diversity. [ABSTRACT FROM AUTHOR]

A novel noncoherent block coding scheme, called noncoherent block-coded MPSK (NBC-MPSK), was proposed recently. In this paper, we present further research results on NBC-MPSK. We first focus on the rotational invariance (RI) of NBC-MPSK. Based on the RI property of NBC-MPSK with multistage decoding, a noncoherent near-optimal linear- complexity multistage decoder for NBC-MPSK is proposed. Then we investigate a tree-search ML decoding algorithm for NBC- MPSK. The derived algorithm is shown to have low complexity and excellent error performance. In this paper, we also utilize the idea of the NBC-MPSK to design noncoherent space-time block codes, called noncoherent space-time block-coded MPSK (NSTBC-MPSK). For two transmit antennas, we propose a signal set with set partitioning and derive the minimum noncohent distance of NSTBC-MPSK with this signal set. For the decoding of NSTBC-MPSK, we modify the ML decoding algorithm of NBC-MPSK and propose an iterative hard-decision decoding algorithm. Compared with training codes and unitary space-time modulation, NBC-MPSK and NSTBC-MPSK have larger mini- mum noncoherent distance and thus better error performance for the noncoherent ML decoder. [ABSTRACT FROM AUTHOR]

This correspondence introduces a new approach to design space-time convolutional codes (STCCs) with large constellation size in systems with any number of transmit antennas. Our design procedure is based on utilizing quadrature phase-shift keying (QPSK) STCCs as component codes, and, consequently, unlike existing techniques, the search space does not grow exponentially with the constellation size. Our approach is further based on the fact that an n × m multiple-input multiple-output (MIMO) system is equivalent to n distinct 1 × m systems. By employing a common design for each individual 1 × m system, we arrive at an approach whose complexity does not grow with the number of transmit antennas. To describe our approach, we first demonstrate that a system employing an STCC can be implemented with only a single transmit antenna when there are multiple receive antennas. The idea is to transmit more than one symbol from a single transmit antenna during a symbol period by superimposing the encoded symbols on top of each other. This objective is achieved by inducing randomness into the system, that creates additional channel paths, called virtual paths. The design of the distributions of the induced random variables is studied for slow Rayleigh and Rician fading channels by utilizing an upper bound on the pairwise block error probability. Simulation results evaluate the performance of this technique for the case of two transmit antennas and several different number of receive antennas, a spectral efficiency of 4 b/s/Hz for slow Rayleigh and Rician fading channels. [ABSTRACT FROM AUTHOR]

Abstract: In this letter, novel space–time (ST) trellis codes are developed for quaternary continuous phase frequency shift keying (CPFSK) modulation systems (i.e., ) with large number of receiver antennas in quasi-static fading channels. The ST codes are obtained from the code search algorithm applying the maximizing minimum squared Euclidean distance criterion (MMSEDC). The simulation results show that a significant performance gain can be obtained from the ST codes of the code search algorithms compared to the codes obtained from the delay diversity (DD) scheme for CPFSK modulation systems. [Copyright &y& Elsevier]

Fully diverse constellations, i.e., a set of unitary matrices whose pairwise differences are nonsingular, are useful in multiantenna communications especially in multiantenna differential modulation, since they have good pairwise error properties. Recently, group theoretic ideas, especially fixed-point-free (fpf) groups, have been used to design fully diverse constellations of unitary matrices. Here, we give systematic design methods of space-time codes which are appropriate for three-transmit-antenna differential modulation. The structures of the codes are motivated by the special unitary Lie group SU(3). One of the codes, which is called the AB code, has a fast maximum-likelihood (ML) decoding algorithm using complex sphere decoding. Diversity products of the codes can be easily calculated, and simulated performance shows that they are better than group-based codes, especially at high rates and as good as the elaborately designed nongroup code. [ABSTRACT FROM AUTHOR]

The potential promised by multiple transmit antennas has raised considerable interest in space-time coding for wireless communications. In this paper, we propose a systematic approach for designing space-time trellis codes over flat fading channels with full antenna diversity and good coding advantage. It is suitable for an arbitrary number of transmit antennas with arbitrary signal constellations. The key to this approach is to separate the traditional space-time trellis code design into two parts. It first encodes the information symbols using a one-dimensional (M, 1) nonbinary block code, with M being the number of transmit antennas, and then transmits the coded symbols diagonally across the space-time grid. We show that regardless of channel time-selectivity, this new class of space-time codes always achieves a transmit diversity of order M with a minimum number of trellis states and a coding advantage equal to the minimum product distance of the employed block code. Traditional delay diversity codes can be viewed as a special case of this coding scheme in which the repetition block code is employed. To maximize the coding advantage, we introduce an optimal construction of the nonbinary block code for a given modulation scheme. In particular, an efficient suboptimal solution for multilevel phase-shift-keying (PSK) modulation is proposed. Some code examples with 2-6 bits/s/Hz and two to six transmit antennas are provided, and they demonstrate excellent performance via computer simulations. Although it is proposed for flat fading channels, this coding scheme can be easily extended to frequency-selective fading channels. [ABSTRACT FROM AUTHOR]