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The relationship between the age of information (AoI) and the mean squared error (MSE) in optimisation problems has been widely investigated for various Gaussian Markov models. Recently, we put the AoI in an information-theoretic context and proposed a mutual information-based value of information (VoI) framework to characterise how valuable the status updates are. In this letter we consider general noisy Gaussian models and investigate the connection between the VoI and MSE. We show that the VoI can be presented by a logarithmic function of the MSE. We also study the rate of change of the two with respect to the signal-to-noise ratio (SNR) and the AoI. The results hold for both discrete-time and continuous-time stationary Gaussian processes. This letter illuminates a useful relationship between information theory and signal processing theory in the presence of the AoI and additive noise, and provides a possible way to infer the information value by estimating the MSE for practical applications. [ABSTRACT FROM AUTHOR]

In this paper, we propose two novel modulation concepts based on a simple maximum distance separable (MDS) code and show that these concepts can achieve better error performance than index modulation (IM) and related schemes. In the first concept, we use amplitude and phase levels to form a simple MDS code, whereas, in the second one, in-phase and quadrature components of codeword elements are used to construct the MDS code. We depict practical schemes for using the proposed concepts with orthogonal frequency division multiplexing (OFDM). We analyze the performance in terms of the minimum Euclidean distance and bit error rate. We also show that the proposed techniques exhibit desirable properties such as efficient low-complexity detection, very simple bits-to-symbols, and symbols-to-bits mappings, and a better error performance when compared to the OFDM-IM and related schemes. More importantly, contrary to the vast majority of IM studies that focus on showing the superiority of the IM techniques against conventional modulation techniques, we show that modulation concepts based on a well-known MDS code can achieve better error performance than the IM and related schemes while exhibiting a structure as simple as these schemes. [ABSTRACT FROM AUTHOR]

In this paper, we derive closed-form expressions for significant statistical properties of the link signal-to-noise ratio (SNR) and the separation distance in mobile ad hoc networks subject to Ornstein-Uhlenbeck (OU) mobility and Rayleigh fading. In these systems, the SNR is a critical parameter as it directly influences link performance. In the absence of signal fading, the distribution of the link SNR depends exclusively on the squared distance between nodes, which is governed by the mobility model. In our analysis, nodes move randomly according to an Ornstein-Uhlenbeck process, using one tuning parameter to control the temporal dependency in the mobility pattern. We derive a complete statistical description of the squared distance and show that it forms a stationary Markov process. Then, we compute closed-form expressions for the probability density function (pdf), the cumulative distribution function (cdf), the bivariate pdf, and the bivariate cdf of the link SNR. Next, we introduce small-scale fading, modeled by a Rayleigh random variable, and evaluate the pdf of the link SNR for rational path loss exponents. The validity of our theoretical analysis is verified by extensive simulation studies. The results presented in this work can be used to quantify link uncertainty and evaluate stability in mobile ad hoc wireless systems. [ABSTRACT FROM AUTHOR]

This article proposes zero-forcing (ZF) beamforming strategies that can simultaneously deal with active and passive eavesdroppers in visible light communication (VLC) systems. First, we propose a ZF beamforming scheme that steers a transmission beam to the null space of active eavesdroppers’ (AEDs) channel, while simultaneously considering the SNRs for a legitimate user (UE) and passive eavesdroppers (PEDs) residing at unknown locations. To find an eigenmode related to the optimal beamforming vector, we adopt an inverse free preconditioned Krylov subspace projection method. For unfavorable VLC secrecy environments, the proposed ZF beamformer appears to be incapable of effectively coping with the PEDs due to the strict condition that the data transmission must be in the null space of the AEDs’ channel matrix. Hence, an alternative beamforming scheme is proposed by relaxing the constraint on the SNRs of the AEDs. The related optimization problem is formulated to reduce the secrecy outages caused by PEDs, while simultaneously satisfying the target constraints on the SNRs of the UE and the AEDs. To simplify the mathematical complexity of the approach, Lloyd’s algorithm is employed to sample the SNR field, which in turn discretizes the problem, thus making it tractable for practical implementation. The numerical results show that both the exact and relaxed ZF beamforming methods achieve superior performance in the sense of secrecy outage relative to a benchmark ZF scheme. Moreover, the proposed relaxed ZF beamforming method is shown to cope with PEDs better than the exact ZF beamforming approach for unfavorable VLC environments. [ABSTRACT FROM AUTHOR]

This paper considers physical layer security enhancement mechanisms that utilize simultaneous beamforming and jamming in visible light communication systems with a randomly located eavesdropper under the assumption that there are multiple light-emitting diode (LED) transmitters and one intended user. When an eavesdropper with an augmented front-end receiver is present, the jamming is very useful for preventing the eavesdropper from wiretapping the information since it is not possible to extract only the information component from the received signal if the jamming signal is random. Thus, in this paper, an optimization problem is formulated with a focus on the signal-to-interference-plus-noise ratio for the legitimate link, and it is solved by a heuristic method called the concave–convex procedure. Then, a ternary scheme is proposed, which is less complicated than the full (joint) scheme, and it is optimized by adopting a formulation based on an assignment problem, the solution of which is effectively obtained by the so-called tabu search procedure. In addition, the problem of maximizing the average secrecy rate is investigated by utilizing a continuous LED model, which significantly relaxes the complication that rises from calculating the expectation with respect to the location of the eavesdropper. Our analysis and simulation results show that the proposed simultaneous beamforming and jamming strategies (both joint and ternary) are good proxies for maximizing the average secrecy rate by utilizing the statistical information on the eavesdropper’s random location. [ABSTRACT FROM AUTHOR]

This paper considers secrecy enhancement mechanisms in visible light communication (VLC) systems with spatially distributed passive eavesdroppers (EDs) under the assumption that there are multiple LED transmitters and one legitimate user equipment. Based on certain amplitude constraints, we propose a beamforming scheme to improve secrecy performance. Contrary to the case where null-steering is made possible by using knowledge of the ED locations, the proposed beamforming when only statistical information about ED locations is available directs the transmission along a particular eigenmode related to the intensity of the ED process and the intended channel. Then, a LED selection scheme that is less complicated than beamforming is provided to reduce the secrecy outage probability (SOP). An approximate closed-form for the SOP is derived by using secrecy rate bounds. All the analysis is numerically verified by Monte-Carlo simulations. The analysis shows that the beamformer yields superior performance to LED selection. However, LED selection is still a highly efficient alternative scheme due to the complexity associated with the use of multiple transmitters in the full beamforming approach. These performance trends and exact relations between system parameters can be used to develop a secure VLC system in the presence of randomly distributed EDs. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a novel relay selection scheme for orthogonal frequency-division multiplexing systems by combining conventional bulk and per-subcarrier selection schemes and analyze its outage performance over equally spatially correlated channels. Specifically, the combined selection scheme selects only two relays at the first attempt and performs per-subcarrier selection over these two relays. We analyze the asymptotic outage performance of the combined selection scheme in the high signal-to-noise ratio (SNR) region and prove a generalized theorem. This theorem states that the combined selection can achieve an optimal outage probability equivalent to the per-subcarrier selection at a high SNR without using the full set of available relays for selection. This unique property is termed the equivalence principle, and it holds for all correlation conditions. To explore this principle, we consider three examples: decode-and-forward, fixed-gain amplify-and-forward (AF), and variable-gain AF relay systems. Furthermore, two extended applications, i.e., antenna selection and branch selection, are also considered to reveal the feasibility and the expandability of the equivalence principle. Our analysis is verified by Monte Carlo simulations. The proposed combined selection and the proved theorem provide a general and feasible solution to the tradeoff between system complexity and outage performance when relay selection is applied. [ABSTRACT FROM AUTHOR]

We develop an approximation for the outage probability of a parallel channel where the subchannel statistics satisfy mild conditions. The main result is in the form of a functional of the density function that describes the statistics of the subchannel powers. The error of the approximation is quantified to be O(\gamma^-n(q+1)-2), where $\gamma$ is the end-to-end SNR of a given subchannel, $n$ is the number of subchannels, and $q$ represents the inherent subchannel diversity. We illustrate the versatility and accuracy of the approximation by studying different statistical subchannel models, which reflect practical wireless communication systems, including line-of-sight links (Rician fading), transmissions affected by interference, and relay systems subject to amplifier distortion. [ABSTRACT FROM PUBLISHER]

A theorem that describes the high signal-to-noise ratio outage behavior of fixed-gain amplify-and-forward relay systems is given. Qualitatively, the theorem states that the outage probability decays according to a power law, where the power is dictated by the poles of the moments of the underlying per-hop fading distributions. The power-law decay is dampened by a logarithmic factor when the leading pole (furthest to the right in the plane) is of order two or more. The theorem is easy to apply, and several examples are presented to this effect. [ABSTRACT FROM PUBLISHER]

We study the effect that anisotropic radiation has on the probability that a dense, two-dimensional (2-D) random network is fully connected. To this end, we provide a thorough analytical treatment of the connectivity of wireless ad hoc networks with beamforming using a newly established theory of connectivity reported in , where we assume the network experiences small-scale fading according to the well-known two-wave with diffuse power (TWDP) model. We calculate the connectivity mass related to various radiation patterns, and show that isotropic radiation is optimal when the path loss exponent is greater than two, but single-sector directed transmission yields superior performance for other cases. We exploit our analysis to design optimal radiation patterns in the sense that connectivity is maximized, which can be used as masks to perform antenna pattern synthesis. Our results exhibit a property of universality with respect to the small-scale fading model since they do not depend on the TWDP fading parameters. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the asymptotic performance of per-tone, bulk, and joint bulk/per-tone transmit antenna selections in orthogonal frequency-division multiplexing systems employing orthogonal space–time block coding (OSTBC). In particular, we show that the diversity and coding gains of all three systems are identical. This is a remarkable result since it demonstrates that systems with M transmit antennas operating in the high signal-to-noise ratio regime can achieve optimal performance while only employing enough radio frequency circuitry to convey OSTBC over L < M antennas on all subcarriers, thus offering significant savings over conventional approaches. [ABSTRACT FROM PUBLISHER]

In this paper, we show that there exists an arbitrary number of power allocation schemes that achieve capacity in systems operating in parallel channels comprised of single-input multiple-output (SIMO) Nakagami-m fading subchannels when the number of degrees of freedom L (e.g., the number of receive antennas) tends to infinity. Statistical waterfilling — i.e., waterfilling using channel statistics rather than instantaneous channel knowledge — is one such scheme. We further prove that the convergence of statistical waterfilling to the optimal power loading scheme is at least \mathcalO( 1/( L log L) ) , whereas convergence of other schemes is at worst \mathcalO( 1/ log L) . To validate and demonstrate the practical use of our findings, we evaluate the mutual information of example SIMO parallel channels using simulations as well as new measured ultrawideband channel data. [ABSTRACT FROM PUBLISHER]