In this paper, we investigate the performance of wireless-powered communication (WPC) systems operating under the harvest-then-transmit protocol with a three-piecewise nonlinear energy harvesting (EH) model, which explicitly captures the sensitivity and saturation behavior of practical EH circuits. In parallel, we adopt a versatile fading characterization by assuming Nakagami-mchannels in the EH phase and generalized Gamma channels in the information transfer phase, the latter being of practical interest as it unifies several standard fading distributions and accurately approximates fading environments in next-generation networks. Based on this setting, we develop a novel analytical framework that yields, for the first time, exact analytical expressions for the average throughput in the delay-limited, delay-tolerant, and Quality of Service (QoS) delay-constrained transmission modes. We then apply the developed framework to study the throughput of WPC-enabled reconfigurable intelligent surface-assisted systems as a direct application example. We conduct extensive Monte-Carlo simulations under various system configurations to confirm the accuracy of the analytical results. Our results show that nonlinear EH effects yield a more realistic benchmark for the average throughput compared to the conventional linear EH model, particularly under stringent sensitivity and saturation constraints.

Thermal noise modulation (TNM) encodes information in thevarianceof Johnson noise, enabling ultra-low/zeropower operation with intrinsic physical-layer security. While recent demonstrations have focused on binary TNM, its twolevel alphabet fundamentally limits spectral efficiency. This paper develops anM-ary TNM (M-TNM) framework that maps symbols to multiple variance levels, thereby conveying (log2M) bits per channel use. We first establish a structural property of the optimal detector: for zero-mean Gaussian classes with ordered variances, the maximum-likelihood (ML) decision regions are contiguous in the energy statistic and each symbol’s boundaries depend only on its two adjacent variance levels. Leveraging this result, we derive closed-form expressions for theoptimalML detection thresholds and the associatedexactaverage symbol error rate (SER) forM-TNM. We then formulatevariance-constellation optimization—the selection and spacing of symbol variances—as a SER-minimization problem under practical constraints. Analytical results are validated via extensive Monte Carlo simulations, which show near-perfect agreement with theory and demonstrate substantial BES reductions for optimized constellations compared with naïve (e.g., uniformly spaced) variance levels. The proposedM-TNM framework thus improves spectral efficiency while preserving TNM’s energy and security promise, positioning variance-domain modulation as a viable physical-layer technique for bandwidth-limited, large-scale Internet of Things (IoT) deployments.

This work investigates the bit error probability (BEP) of thermal noise modulation (TNM) in Rayleigh fading channels. TNM has emerged as a promising ultra-low-power modulation scheme, where information is conveyed through variations in thermal noise variance. Existing studies provide only approximate BEP expressions and assume perfect channel state information (CSI) at the receiver. Furthermore, current detection strategies require per-symbol threshold adjustments, which, along with CSI estimation, introduce significant computational overhead for power-constrained devices. To address these limitations, we propose a fixed-threshold detection strategy that eliminates the need for channel estimation and threshold adaptation. Additionally, we derive an exact closed-form BEP expression for TNM under Rayleigh fading and formulate the problem of optimal threshold selection as an optimization task, solvable using efficient line-search techniques such as gradient descent. The accuracy of our analytical results is validated through Monte Carlo simulations, demonstrating strong agreement with theoretical predictions. These contributions provide a more precise characterization of TNM performance in fading environments, paving the way for its practical implementation in energy-efficient wireless systems.

Reconfigurable intelligent surfaces (RIS) can be crucial in next-generation communication systems. However, designing the RIS phases according to the instantaneous channel state information (CSI) can be challenging in practice due to the short coherent time of the channel. In this regard, we propose a novel algorithm based on the channel statistics of massive multiple input multiple output systems rather than the instantaneous CSI. The beamforming at the base station (BS), power allocation of the users, and phase shifts at the RIS elements are optimized to maximize the minimum signal-to-interference and noise ratio (SINR), guaranteeing fair operation among various users. In particular, we design the RIS phases by leveraging the asymptotic deterministic equivalent of the minimum SINR that depends only on the channel statistics. This significantly reduces the computational complexity and the amount of controlling data between the BS and RIS for updating the phases. This setup is also useful for electromagnetic fields (EMF)-aware systems with constraints on the maximum user’s exposure to EMF. The numerical results show that the proposed algorithms achieve more than 100 % gain in terms of minimum SINR, compared to a system with random RIS phase shifts, when 40 RIS elements, 20 antennas at the BS and 10 users, are considered.

Spectrum-sharing backscatter communication (SSBC) systems are among the most prominent technologies for ultralow power and spectrum-efficient communications. In this article, we propose an underlay SSBC system, in which the secondary network is a backscatter communication system. We analyze the performance of the secondary network under a transmit power adaption strategy at the secondary transmitter, which guarantees that the interference caused by the secondary network to the primary receiver is below a predetermined threshold. We first derive a novel analytical expression for the cumulative distribution function (CDF) of the instantaneous signal-to-noise ratio of the secondary network. Capitalizing on the obtained CDF, we derive novel accurate approximate expressions for the ergodic capacity, effective capacity, and average bit-error rate. We further validate our theoretical analysis using the extensive Monte Carlo simulations.

This paper derives the asymptotic distribution of the normalized$k$-th maximum order statistics of a sequence of non-central chi-square random variables with non-identical non-centrality parameters. We demonstrate the utility of these results in characterizing the signal-to-noise ratio in three different applications in wireless communication systems where the statistics of the$k$-th maximum channel power over Rician fading links are of interest. Furthermore, we derive simple expressions for the asymptotic outage probability, average throughput, achievable throughput, and average bit error probability. The proposed results are validated via extensive Monte Carlo simulations.

We analyze the asymptotic average and effective throughputs of a multiuser diversity scheme for a secondary multiuser network consisting of multiple secondary users (transmitters) and one secondary receiver. Considering a transmit power adaptation strategy at the secondary users to satisfy the instantaneous interference constraint at the primary receiver, the secondary receiver selects the k-th best secondary user for transmission, namely, the one with the k-th highest signal-to-noise ratio (SNR). We use extreme value theory to show that the k-th highest SNR converges uniformly in distribution to an inverse gamma random variable for a fixed k and large number of secondary users. We use this result to derive closed-form asymptotic expressions for the average and effective throughputs of the k-th best secondary user.

The effective rate is an important metric that takes delay quality of service (QoS) requirements into consideration while analyzing the performance of wireless systems. In this paper we analyze the effective rate of multiple-input single-output (MISO) systems with transmit antenna selection (TAS) subject to Rayleigh fading. Specifically, we derive an analytical expression for the effective rate of MISO/TAS systems and closed form expressions for the effective rate in asymptotically high and low signal-to-noise ratio (SNR) regimes. Furthermore, we analyze the effective rate of MISO/TAS systems with large number of transmit antennas and derive an asymptotic analytical expression for it.

We analyze the asymptotic average throughput of a multiuser diversity (MD) scheme, in the limit of large number of users, for free space optical (FSO) communication systems over a gamma-gamma fading channel. It is assumed that the FSO system consists of an optical transmitter (central node) equipped with K transmit apertures to serve K users (one transmit aperture for each user). It is also assumed that each user is equipped with N receive apertures and equal gain combining (EGC) is employed at the user's receiver. In MD, the central node serves only one user which has the largest channel gain among the K users, while other users remain silent. Using extreme value theory (EVT), we derive a simple and tight upper bound on the asymptotic average throughput of the considered FSO system. Moreover, the asymptotic average bit error rate (BER) is investigated and a closed form approximation for the average BER of the FSO system with MD#x002F;EGC scheme is obtained.

The IEEE 802.15.7 standard for visible light communication (VLC) includes the use of run-length-limited codes to mitigate modulation-induced flickering and the further use of coding to improve bit error rate performance. In this paper, we introduce algorithms to design codes using finite-state machines, which provide simultaneously a coding gain while also mitigating flicker. The codes have the additional advantage of being optimally soft-decision decodable using the Viterbi algorithm. To compare the flicker mitigation performance of different codes, we further introduce a mathematical measure of flicker based on the power spectrum of the transmitted signals. We discuss tradeoffs between flicker mitigation, code rate, and coding gain, design several codes, and compare their error rate and flicker mitigation performance to some codes in the VLC standard.

The IEEE 802.15.7 standard on visible light communications (VLC) proposes color-shift-keying (CSK) as a way to increase data rate while keeping a constant optical power. In this paper, we propose two algorithms to design codes by finite state machines (FSM) using newly introduced CSK constellations. These codes ensure a constant perceived color eliminating the use of the scrambler proposed by the standard. Furthermore, they achieve about 1 to 3 dB of coding gain compared with the standard constellations and are optimally and efficiently softdecision decodable using the Viterbi algorithm.

In this paper we derived the probability density function of the product of independent non-identically distributed Weibull RVs. The derivation is based on the use of the Mellin transformation along with the Residue theorem to evaluate the attained complex integral. The resultant integrands have only elementary functions, such as exponentials and algebraic power functions and can, therefore, be explicitly evaluated to any degree of accuracy using any symbolic mathematics based software. The distribution of the product of independent and identically distributed (i.i.d) Weibull RVs are also evaluated. The proposed method avoids the computational burden of residuals of a product of functions. Hence our results are expected to be of significant practical use to evaluate the error rate performance of any Mary orthogonal faded systems in indoor and outdoor wireless environments.