Pairwise Error Probability of Space-Time Codes in Frequency Selective Rician Channels

In this letter, we investigate the performance of space-time codes in frequency selective correlated Rician channels. An exact expression has been derived for the pairwise error probability (PEP) of space-time trellis codes over frequency selective Rician fading channel, which is in the form of a single finite range integral. We also obtain a closed form expression for the PEP when the signal matrices are drawn from some special design and the performance upper bound

Extreme eigenvalue distributions of gamma-Wishart random matrices

This paper derives analytical expressions for the eigenvalues of so-called gamma-Wishart random matrices, which arise in the context of multiple-input multiple-output (MIMO) transmission over land-mobile-satellite (LMS) communication channels. Such matrices are representative of complex noncentral Wishart matrices, but with randomly varying noncentrality parameter following a distribution closely related to the matrix-variate gamma. For these matrices, we derive exact closed form expressions for the distribution functions of the extreme eigenvalues (i.e., the maximum and minimum). These results are remarkably simple, and are useful for the performance analysis of MIMO transmission techniques over LMS channels. © 2011 IEEE

Analysis of the level crossing rates for ordered random processes

Given n independent but not necessarily identical random processes, this paper investigates the general problem of determining how frequently, on average, any given process becomes at least the p-th (p = 1, 2,... , n - 1) largest among all processes. This problem requires determining the level crossing rate (LCR) of a carefully defined ordered process, which we solve by developing a general mathematical framework based on the theory of permanents. Our results are very general and may be applicable for a wide range of engineering applications which involve ordered random processes. To demonstrate the applicability to wireless communications, we present closed-form formulas for the LCR for the case where the processes correspond to time-varying Rayleigh fading channels, and use these to characterize the required switching rate for a particular branch of a generalized selection combining diversity receiver. © 2011 IEEE

Detection of a signal in colored noise: A random matrix theory based analysis

This paper investigates the classical statistical signal processing problem of detecting a signal in the presence of colored noise with an unknown covariance matrix. In particular, we consider a scenario where m-dimensional p possible signal-plus-noise samples and m-dimensional n noise-only samples are available at the detector. Then the presence of a signal can be detected using the largest generalized eigenvalue (l.g.e.) of the so called whitened sample covariance matrix. This amounts to statistically characterizing the maximum eigenvalue of the deformed Jacobi unitary ensemble (JUE). To do this, we employ the powerful orthogonal polynomial approach to determine a new finite dimensional expression for the cumulative distribution function (c.d.f.) of the l.g.e. of the deformed JUE. This new c.d.f. expression facilitates the further analysis of the receiver operating characteristics (ROC) of the detector. It turns out that, for m=n, when m and p increase such that m/p is fixed, there exists an optimal ROC profile for each fixed signal-to-noise ratio (SNR). In this respect, we have established a tight approximation for the corresponding optimal ROC profile

On the Exact Outage Probability of 2×2 MIMO-MRC in Correlated Rician Fading

This paper addresses a classical problem in random matrix theory-finding the distribution of the maximum eigen-value of the correlated Wishart unitary ensemble. In particular, we derive a new exact expression for the cumulative distribution function (c.d. f.) of the maximum eigen-value of a 2 × 2 correlated non-central Wishart matrix with rank-l mean. By using this new result, we derive the exact outage probability of 2 × 2 multiple-input multiple-output maximum-ratio-combining (MIMO-MRC) in Rician fading with transmit correlation and a strong line-of-sight (LoS) component (rank-l channel mean). We also show that the outage performance is affected by the relative alignment of the eigen-spaces of the mean and correlation matrices. In general, when the LoS path aligns with the least eigenvector of the correlation matrix, in the high transmit signal-to-noise ratio (SNR) regime, the outage gradually improves with the increasing correlation. Moreover, we show that as K (Rician factor) grows large, the outage event can be approximately characterized by the c.d.f. of a certain Gaussian random variable

Optimality of beamforming for a correlated MISO relay channel

We analyze the optimality of beamforming in multiple-input single-output relay channels without a direct link between the source and the destination. Assuming that the source has access to the channel correlation information, and that the relay operates in amplify and forward mode with a long term power constraint, we first show that the optimal transmission strategy is to transmit along the eigen-vectors of the transmit correlation matrix. The optimality of beamforming is then studied via the power allocation problem at the source. In particular, we derive a necessary and sufficient condition under which beamforming achieves the capacity. Our results demonstrate that the finite relay gain decreases the range at which beamforming is optimal. ©2010 IEEE

Finite-SNR diversity-multiplexing trade-off of dual hop relay channels

We analyze the diversity-multiplexing trade-off (DMT) of fixed-gain amplify-and-forward (AF) protocols for the dual hop relay channel. Contrary to most prior work, we characterize the finite signal-to-noise ratio (SNR) DMT using a non-asymptotic framework. Our results are based on a new exact closed-form expression which we derive for the distribution of the received SNR, which takes into account the direct transmission link. We also extract the conventional asymptotic DMT as a special case of the finite-SNR result, and demonstrate that the asymptotic DMT can significantly overestimate the level of diversity that is achievable for practical error rates and SNRs. We also present the finite-SNR DMT for decode-and-forward (DF) relaying protocols, and show the interesting result that fixed-gain AF outperforms DF at low SNR. © 2010 IEEE

Two-Way Communications via Reconfigurable Intelligent Surface

The novel reconfigurable intelligent surface (RIS) is an emerging technology which facilitates high spectrum and energy efficiencies in Beyond 5G and 6G wireless communication applications. Against this backdrop, this paper investigates two-way communications via reconfigurable intelligent surfaces (RISs) where two users communicate through a common RIS. We assume that uplink and downlink communication channels between two users and the RIS can be reciprocal. We first obtain the optimal phase adjustment at the RIS. We then derive the exact outage probability and the average throughput in closed-forms for single-element RIS. To evaluate multiple-element RIS, we first introduce a gamma approximation to model a product of Rayleigh random variables, and then derive approximations for the outage probability and the average throughput. For large average signal-to-interference-plus-noise ratio (SINR) \rho, asymptotic analXsis also shows that the outage decreases at the rate (\log(\rho)/\rho) where L is the number of elements, whereas the throughput increases with the rate \log(\rho)

Chemopreventive Effect of Dietary Anthocyanins against Gastrointestinal Cancers: A Review of Recent Advances and Perspectives

Anthocyanins are a group of dietary polyphenols, abundant mainly in fruits and their products. Dietary interventions of anthocyanins are being studied extensively related to the prevention of gastrointestinal (GI) cancer, among many other chronic disorders. This review summarizes the hereditary and non-hereditary characteristics of GI cancers, chemistry, and bioavailability of anthocyanins, and the most recent findings of anthocyanin in GI cancer prevention through modulating cellular signaling pathways. GI cancer-preventive attributes of anthocyanins are primarily due to their antioxidative, anti-inflammatory, and anti-proliferative properties, and their ability to regulate gene expression and metabolic pathways, as well as induce the apoptosis of cancer cells