This work investigates a multi-user, multi-antenna uplink wireless system, in which multiple users transmit signals to a base station. Prior research has explored the potential for linear growth in spectral efficiency by employing multiple transmit and receive antennas. This gain depends heavily on the quality of channel state information and the number of uncorrelated antennas. However, spatial correlations, arising from closely-spaced antennas and channel aging effects, stemming from the difference between the channel state at pilot and data time instances, can substantially counteract these benefits, and degrade the transmission rate, especially in non-stationary environments. To address these challenges, this work introduces a real-time beamforming framework to compensate for the spatial correlation and channel aging effects. First, a channel estimation scheme leveraging temporal channel correlations and considering mobile device velocity and antenna spacing is developed. Subsequently, an expression approximating the average spectral efficiency, which depends on pilot spacing, pilot and data powers, and beamforming vectors, is obtained. By maximizing this expression, optimal parameters are identified. Numerical results demonstrate the effectiveness of the proposed approach compared to prior works. Interestingly, the optimal pilot spacing remains unaffected by large-scale channel parameters and the velocities of interfering users. The impact of interference components also diminishes with an increasing number of transmit antennas.

Recovering signals that are sparse in a transform domain–so-called analysis-sparse vectors–from undersampled measurements is a fundamental problem in compressed sensing. In many practical scenarios, such as imaging, geophysics, and communications, the distribution of transform coefficients is known in advance, providing valuable prior information. Weighted ℓ1 analysis offers a natural framework to exploit this knowledge, yet a principled method for choosing the weights has remained unsolved. In this work, we propose a distribution-aware framework for weight design. Using convex geometric tools, we establish a computable and nearly tight upper bound on the expected number of Gaussian measurements needed for exact recovery. This bound depends only on two accessible summaries of the prior in the analysis domain: marginal support probabilities and expected signs. Minimizing it yields a near-optimal weight vector that is stable, scale-invariant, and applicable a priori, without iterative tuning. Our theory accurately predicts recovery thresholds and shows how prior knowledge can be converted into provable measurement savings. Extensive simulations confirm substantial reductions in the number of required measurements and reconstruction error relative to unweighted ℓ1 analysis, with the largest improvements observed for coherent and redundant operators. Overall, this work establishes a rigorous and practical recipe for leveraging distributional priors in analysis-based compressed sensing.

We present a unified framework for semantic communication under bounded privacy leakage, in which an encoder must reveal selected information about a source while restricting the disclosure of correlated private data. In contrast to prior work that merely injects noise over a fixed representation, we co-design both the semantic mapping and the noise mechanism. Leveraging extended versions of the Functional Representation Lemma (FRL) and the Strong Functional Representation Lemma (SFRL), we model how the disclosed data arise from the original source and correlated private data. We then formulate a new optimization problem to align the resulting distributions with a 'goal' distributionbalancing accuracy for the user's task and privacy constraints on sensitive data. Furthermore, we propose two distinct mapping strategies that map the original signal domain to a compact semantic space. Our numerical results verify the effectiveness of this joint design, demonstrating significant benefits over conventional methods for privacy-constrained semantic communication.

In this paper, we propose a novel goal-oriented method for identifying stationary Internet of Things (IoT) devices, with the performance robust to the number of inactive devices. We start by formulating a two-dimensional atomic norm minimization problem that captures the angular group-sparsity of the wireless channel. Building on this, we propose a goal-oriented optimization problem that retains only the angular information required to identify active stationary IoT devices. This problem is then reformulated as an equivalent semi-definite programming (SDP) problem, enabling efficient detection of active users. Unlike traditional methods that rely on orthogonal preambles or pilot assignments for joint active user detection and channel estimation, our approach operates without pilots, enabling blind identification of the line-of-sight angles of active stationary devices. Simulation results demonstrate that the proposed method achieves high detection accuracy and low false alarm rates, offering a scalable and robust solution for enabling massive connectivity in future wireless networks.

Integrated sensing and communications (ISAC) is a promising component of 6G networks, fusing communication and radar technologies to facilitate new services. Additionally, the use of extremely large-scale antenna arrays (ELAA) at the ISAC common receiver not only facilitates terahertz-rate communication links but also significantly enhances the accuracy of target detection in radar applications. In practical scenarios, communication scatterers and radar targets often reside in close proximity to the ISAC receiver. This, combined with the use of ELAA, fundamentally alters the electromagnetic characteristics of wireless and radar channels, shifting from far-field planar-wave propagation to near-field spherical wave propagation. Under the far-field planar-wave model, the phase of the array response vector varies linearly with the antenna index. In contrast, in the near-field spherical wave model, this phase relationship becomes nonlinear. This shift presents a fundamental challenge: the widely-used Fourier analysis can no longer be directly applied for target detection and communication channel estimation at the ISAC common receiver. In this work, we propose a feasible solution to address this fundamental issue. Specifically, we demonstrate that there exists a high-dimensional space in which the phase nonlinearity can be expressed as linear. Leveraging this insight, we develop a lifted super-resolution framework that simultaneously performs communication channel estimation and extracts target parameters with high precision.

We propose a novel pilot-free multi-user uplink framework for integrated sensing and communication (ISAC) in mm-wave networks, where single-antenna users transmit orthogonal frequency division multiplexing signals without dedicated pilots. The base station exploits the spatial and velocity diversities of users to simultaneously decode messages and detect targets, transforming user transmissions into a powerful sensing tool. Each user’s signal, structured by a known codebook, propagates through a sparse multi-path channel with shared moving targets and user-specific scatterers. Notably, common targets induce distinct delay–Doppler–angle signatures, while stationary scatterers cluster in parameter space. We formulate the joint multi-path parameter estimation and data decoding as a 3D super-resolution problem, extracting delays, Doppler shifts, and angles-of-arrival via atomic norm minimization, efficiently solved using semidefinite programming. A core innovation is multi-user fusion, where diverse user observations are collaboratively combined to enhance sensing and decoding. This approach improves robustness and integrates multi-user perspectives into a unified estimation framework, enabling high-resolution sensing and reliable communication. Numerical results show that the proposed framework significantly enhances both target estimation and communication performance, highlighting its potential for next-generation ISAC systems.

The Internet of Things interconnects billions of devices and forms a vast network where users sporadically transmit short messages through multi-path wireless channels. These channels are characterized by the superposition of a small number of scaled and delayed copies of Dirac spikes. At the receiver, the observed signal is a sum of these convolved signals, and the task is to find the amplitudes, continuous-indexed delays, and transmitted messages from a single signal. This task is inherently ill-posed without additional assumptions on the channel or messages. In this work, we assume the channel exhibits sparsity in the delay domain and that independent and identically distributed random linear encoding is applied to the messages at the devices. Leveraging these assumptions, we propose a semidefinite programming optimization capable of simultaneously recovering both messages and the delay parameters of the channels from only a single received signal. Our theoretical analysis establishes that the required number of samples at the receiver scales proportionally to the sum-product of sparsity and message length of all users, aligning with the degrees of freedom in the lifting-type optimization frameworks. Numerical experiments confirm the efficacy of the proposed method in accurately estimating closely-spaced delay parameters and recovering messages.

Several previous works have addressed the inherent trade-off between allocating resources in the power and time domains to pilot and data signals in multiple input multiple output systems over block-fading channels. In particular, when the channel changes rapidly in time, channel aging degrades the performance in terms of spectral efficiency without proper pilot spacing and power control. Despite recognizing non-stationary stochastic processes as more accurate models for time-varying wireless channels, the problem of pilot spacing and power control in multi-antenna systems operating over non-stationary channels is not addressed in the literature. In this paper, we address this gap by introducing a refined first-order autoregressive model that exploits the inherent temporal correlations over non-stationary Rician aging channels. We design a multi-frame structure for data transmission that better reflects the non-stationary fading environment than previously developed single-frame structures. Subsequently, to determine the optimal pilot spacing and power control within this multi-frame structure, we develop an optimization framework and an efficient algorithm based on maximizing a deterministic equivalent expression for the spectral efficiency, demonstrating its generality by encompassing previous channel aging results. Our numerical results indicate the efficacy of the proposed method in terms of spectral efficiency gains over the single frame structure.

The transition toward 6G is pushing wireless communication into a regime where the classical plane-wave assumption no longer holds. Millimeter-wave and sub-THz frequencies shrink wavelengths to millimeters, while meter-scale arrays featuring hundreds of antenna elements dramatically enlarge the aperture. Together, these trends collapse the classical Rayleigh far-field boundary from kilometers to mere single-digit meters. Consequently, most practical 6G indoor, vehicular, and industrial deployments will inherently operate within the radiating near-field, where reliance on the plane-wave approximation leads to severe array-gain losses, degraded localization accuracy, and excessive pilot overhead. This paper re-examines the fundamental question: "Where does the far-field truly begin?"Rather than adopting purely geometric definitions, we introduce an application-oriented approach based on user-defined error budgets and a rigorous Fresnel-zone analysis that fully accounts for both amplitude and phase curvature. We propose three practical mismatch metrics: worst-case element mismatch, worst-case normalized mean square error, and spectral efficiency loss. For each metric, we derive a provably optimal transition distance-the minimal range beyond which mismatch permanently remains below a given tolerance-and provide closed-form solutions. Extensive numerical evaluations across diverse frequencies and antenna-array dimensions show that our proposed thresholds can exceed the Rayleigh distance by more than an order of magnitude. By transforming the near-field from a design nuisance into a precise, quantifiable tool, our results provide a clear roadmap for enabling reliable and resource-efficient near-field communications and sensing in emerging 6G systems.

This paper presents a novel distributed computing framework, DCbMF (Distributed Computing by Matrix Factorization), for the efficient computation of linearly separable functions. Our framework operates within a multicast network of interconnected computing nodes to compute a set of output functions from input data through an efficient three-step process - Map, Shuffle, and Reduce. We cast the computation procedure as a sparse matrix factorization problem to achieve efficient communication and computation. To this end, we formulate an ℓ0 optimization problem that seeks to minimize the number of nonzero elements in each matrix factor. Due to the intractability of ℓ0 minimization, we turn to a relaxed ℓ1 formulation of the problem. We devise a modified alternating direction method of multipliers to solve the biconvex optimization problem and prove the convergence of our algorithm to a stationary solution. The numerical experiments show that DCbMF outperforms similar computing frameworks for linearly separable function computation, achieving a substantial reduction in communication overhead by 98% while maintaining the same computation cost. Notably, leveraging sparse matrix factorization and alternating optimization highlights a fundamental tradeoff between compu-tation and communication costs and paves the way for scalable and efficient distributed computing applications.