This work presents a first comprehensive analysis of the impact of vector coded caching (VCC) in multi-user multiple-input multiple-output (MU-MIMO) systems with multiple receive antennas and variable pathloss — two key factors that critically influence systems with inherent MU unicasting behavior. We investigate two widely adopted precoding strategies: (i) block-diagonalization (BD) at the transmitter combined with maximal ratio combining (MRC) at the receivers, and (ii) zero-forcing (ZF) precoding. Our analysis explicitly accounts for practical considerations such as channel fading, channel state information (CSI) acquisition overhead, and fairness-oriented power allocation. Our contributions span both analytical and simulation-based fronts. On the analytical side, we derive analytical expressions for the achievable throughput under BD-MRC and ZF, highlighting the performance benefits of equipping multi-antenna users with cache-aided interference management. Specifically, we develop a low-complexity BD-MRC optimization method that leverages matrix structure to significantly reduce the dimensionality involved in precoding computation, followed by solving the associated max-min fairness problem through an efficient one-dimensional search. In the massive MIMO regime, an asymptotic expression for the achievable throughput over Rayleigh fading channels is also derived. Simulations validate our theoretical results, confirming that VCC delivers substantial performance gains over optimized cacheless MU-MIMO systems. For example, with 32 transmit antennas and 2 receive antennas per user, VCC yields throughput improvements exceeding 300%. These gains are further amplified under imperfect CSI at the transmitter, where VCC’s ability to offload interference mitigation to the receivers ensures robust performance even in the face of degraded CSI quality and elevated acquisition costs.

This paper investigates the integration of coded caching (CC) into fluid antenna (FA) multiple access (FAMA) systems to overcome their fundamental performance limitations. While FAMA has demonstrated strong interference suppression capabilities without relying on precoding, its delivery rate saturates in the high signal-to-noise ratio (SNR) regime due to residual multi-user interference, and it requires at least as many transmit antennas as served users. On the other hand, CC eliminates multi-user interference by jointly designing caching and delivery phases, but suffers from the well-known worst-user bottleneck, especially under wireless fading channels and low SNR conditions. To overcome the interference-limited nature of FAMA and the worst-user bottleneck in CC, we consider a CC-enabled FAMA framework. The proposed approach enables interference-free transmission to multiple users using a single transmit antenna, and leverages adaptive port selection at the users to combat channel fading. We analyze the average rates and effective gains of XOR-based CC and the recently developed aggregated CC (ACC) schemes under the FAMA framework, and derive simple closed-form approximations that accurately characterize the performance. Furthermore, we rigorously prove that, in the limit where the number of FA ports grows without bound while maintaining sufficient spatial diversity, the effective multiplexing gains in the low-SNR limit of both XCC- and ACC-enabled FAMA asymptotically achieve the nominal gain that is only attainable under high-SNR conditions with traditional antennas. Simulation results show that the proposed architecture outperforms both conventional FAMA and traditional-antenna CC schemes, achieving significant spectral efficiency gains in a wide range of SNR regimes.

We propose a new class of coded caching schemes for wireless networks, which we term as non-orthogonal multiple access (NOMA) aided aggregated coded caching (NACC), which manages to alleviate both the uneven channel bottleneck as well as the shared-cache limitation. In particular, NACC uses an aggregation principle to efficiently serve users with unequal channel strengths, as well as uses for the first time the NOMA principle to simultaneously transmit to multiple users that share the same exact cache state. This transmission strategy represents an efficient utilization of NOMA within the coded caching framework. We analyze the high-SNR transmission performance of the proposed scheme and derive analytical expressions for the achievable rate and the effective gain, providing a qualitative understanding of its spectral efficiency. Our numerical results for urban Micro-cell environments abiding by$5\mathrm{G}$standards, demonstrate that NACC achieves - with a single transmit antenna - the same spectral efficiency as a multi-user (MU) multicasting system with 32 transmit antennas, while it also matches the spectral efficiency of traditional MU unicasting system with 8 transmit antennas.

We introduce an energy-efficient downlink rate splitting multiple access (RSMA) scheme, employing a simple matched filter (MF) for precoding. We consider a transmitter equipped with multiple antennas, serving several single-antenna users at the same frequency-time resource, each with distinct message requests. Within the conventional 1-layer RSMA framework, requested messages undergo splitting into common and private streams, which are then precoded separately before transmission. In contrast, we propose a novel strategy where only an MF is employed to precode both the common and private streams in RSMA, promising significantly improved energy efficiency and reduced complexity. We demonstrate that this MF-precoded RSMA achieves the same delivery performance as conventional RSMA, where the common stream is beamformed using maximal ratio transmission (MRT) and the private streams are precoded by MF. Taking into account imperfect channel state information at the transmitter, we proceed to analyze the delivery performance of the MF-precoded RSMA. We derive the ergodic rates for decoding the common and private streams at a target user respectively in the massive MIMO regime. Finally, numerical simulations validate the accuracy of our analytical models, as well as demonstrate the advantages over conventional RSMA.

The recent introduction of vector coded caching has revealed that multi-rank transmissions in the presence of receiver-side cache content can dramatically ameliorate the file-size bottleneck of coded caching and substantially boost performance in error-free wire-like channels. In this work, we employ large-matrix analysis to explore the effect of vector coded caching in realistic wireless multi-antenna downlink systems. For a given downlink MISO system already optimized to exploit both multiplexing and beamforming gains, and for a fixed set of antenna and SNR resources, our analysis answers a simple question: What is the multiplicative throughput boost obtained from introducing reasonably-sized receiver-side caches that can pre-store information content? The derived closed-form expressions capture various linear precoders, and a variety of practical considerations such as power dissemination across signals, realistic SNR values, as well as feedback costs. The schemes are very simple (we simply collapse precoding vectors into a single vector), and the recorded gains are notable. For example, for 32 transmit antennas, a received SNR of 20 dB, a coherence bandwidth of 300 kHz, a coherence period of 40 ms, and under realistic file-size and cache-size constraints, vector coded caching is here shown to offer a multiplicative throughput boost of about 310% with ZF/RZF precoding and a 430% boost in the performance of already optimized MF-based (cacheless) systems. Interestingly, vector coded caching also accelerates channel hardening to the benefit of feedback acquisition, often surpassing 540% gains over traditional hardening-constrained cacheless downlink systems.

We investigate the performance of coded caching in land mobile-satellite (LMS) systems, where a satellite station with full access to a content library serves K cache-aided land users. The promising gains that coded caching provides for the error-free shared-link Broadcast Channel are known to suffer in some low signal-to-noise ratio (SNR) scenarios. For this reason, we analyze to what extent the coded caching gains are preserved in LMS systems, which are governed by low-to-moderate SNR due to the long propagation distances. We model the satellite-terrestrial channels through the widely adopted Shadowed-Rician fading, and we show that the coded caching gains are partially preserved even in the low-SNR limit due to the existence of line-of-sight (LOS) components, which allows us to double the goodput of LMS communication at low SNR. These results illustrate the potential of coded caching in LMS systems and motivate further research to design adapted and practical coded caching schemes for LMS systems.

We address the worst-user bottleneck of wireless coded caching, which is known to severely diminish cache-aided multicasting gains due to the fundamental worst-channel limitation of multicasting. We consider the quasi-static Rayleigh fading Broadcast Channel, for which we first show that the effective coded caching gain of the standard XOR-based coded-caching scheme completely vanishes in the low signal-to-noise ratio (SNR) regime. Then, we reveal that this collapse is not intrinsic to coded caching. We do so by presenting a novel scheme that can fully recover the coded caching gains by capitalizing on one aspect that has remained unexploited to date: the shared side information brought about by the effectively unavoidable file-size constraint. As a consequence, the worst-user effect is dramatically ameliorated, as it is substituted by a much more subtle worst-group-of-users effect, where the suggested grouping is fixed, and it is decided before the channel or the demands are known. Furthermore, the theoretical gains are completely recovered as the number of users increases, and this is done without any user selection technique. We analyze the rate performance of the proposed scheme and derive approximations which prove to be very precise. Importantly, this novel approach can be translated to other coded caching schemes and scenarios, including decentralized scenarios.

We investigate the use of coded caching in the single-cell downlink scenario where the receiving users are randomly located inside the cell. We first show that, as a result of having users that experience very different path-loss, the real gain of the original coded caching scheme is severely reduced. We then prove that the use of shared caches - which, we stress, is a compulsory feature brought about by the subpacketization constraint in nearly every practical setting - introduces a spatial-averaging effect that allows us to recover most of the subpacketization-constrained gains that coded caching would have yielded in the error-free identical-link setting. For the ergodic-fading scenario with different pathloss, we derive tight approximations of the average (over the users) rate and of the coded caching gain by means of a basic high-SNR approximation on the point-to-point capacity. These derived expressions prove very accurate even for low SNR. We also provide a result based on the regime of large number of users which is nonetheless also valid for settings with few users. These results are extensively validated using Monte-Carlo simulations that adhere to 3GPP recommendations on system parameters for urban micro or macro cells.

In this paper, we investigate the transmission probabilities in three cases (depending only on the legitimate receiver, depending only the eavesdropper, and depending on both legitimate receiver and eavesdropper) in quantum key distribution (QKD) systems over free-space optical links. To be more realistic, we consider a generalized pointing error scenario, where the azimuth and elevation pointing error angles caused by stochastic jitters and vibrations in the legitimate receiver platform are independently distributed according to a non-identical normal distribution. Taking these assumptions into account, we derive approximate expressions of transmission probabilities by using the Gaussian quadrature method. To simplify the expressions and get some physical insights, some asymptotic analysis on the transmission probabilities is presented based on asymptotic expression for the generalized Marcum Q-function when the telescope gain at the legitimate receiver approaches to infinity. Moreover, from the asymptotic expression for the generalized Marcum Q-function, the asymptotic outage probability over Beckmann fading channels (a general channel model including Rayleigh, Rice, and Hoyt fading channels) can be also easily derived when the average signal-to-noise ratio is sufficiently large, which shows the diversity order and array gain.

In this work, we address the worst-user bottleneck of coded caching, which is known to diminish any caching gains due to the fundamental requirement that the multicast transmission rate should be limited by that of the worst channel among the served users. We consider the quasi-static Rayleigh fading Broadcast Channel, for which we first show that the coded caching gain of the XOR-based standard coded-caching scheme completely vanishes in the low-SNR regime. Yet, we show that this collapse is not intrinsic to coded caching by presenting a novel scheme that can completely recover the caching gains. The scheme exploits an aspect that has remained unexploited: the shared side information brought about by the file size constraint. The worst-user effect is dramatically ameliorated because it is replaced by the worst-group-of-users effect, where the users within a group have the same side information and the grouping is decided before the channel or the demands are known.

In this paper, we analyze the secrecy performance of the decode-and-forward (DF) relay system in generalized-K fading channels. In a typical four-node communications model, a source (S) sends confidential information to a destination (D) via a relay (R) using DF strategy in two time slots, while an eavesdropper (E) wants to overhear the information from S to D over generalized-K fading channels. To be more realistic, we assume that E can receive the signals of two time slots, and there is no direct link between S and D because of heavy fading. Based on those assumptions, we derive closed-form expressions for the secrecy outage probability (SOP) and ergodic secrecy capacity (ESC) by using a tight approximate probability density function of the generalized-K model. Furthermore, asymptotic expressions for the SOP and ESC are also derived in the high signal-to-noise ratio region, not only because we can get some insights about SOP and ESC, but also because expressions for SOP and ESC can be simplified significantly. The single relay system is subsequently extended into a multi-relay system, where the asymptotic SOP analysis of three proposed relay selection strategies is investigated. Moreover, the security-reliability tradeoff analysis in the multi-relay system is also presented given that S adopts a constant code rate. Finally, the Monte-Carlo simulation is used to demonstrate the accuracy of the derived closed-form expressions.

This paper investigates the secrecy performance of maximal ratio combining (MRC) and selection combining (SC) with imperfect channel state information (CSI) in the physical layer. In a single-input multipleoutput (SIMO) wiretap channel, a source transmits confidential messages to the destination equipped with M antennas using the MRC/SC scheme to process the received multiple signals. An eavesdropper equipped with N antennas also adopts the MRC/SC scheme to promote successful eavesdropping. We derive the exact and asymptotic closed-form expressions for the ergodic secrecy capacity (ESC) in two cases: (1) MRC with weighting errors, and (2) SC with outdated CSI. Moreover, two important indicators, namely high signal-to-noise ratio (SNR) slope and high SNR power offset, which govern ESC at the high SNR region, are derived. Finally, simulations are conducted to validate the accuracy of our proposed analytical models. Results indicate that ESC rises with the increase of the number of antennas and the received SNR at the destination, and fades with the increase of those at the eavesdropper. Another finding is that the high SNR slope is constant, while the high SNR power offset is correlated with the number of antennas at both the destination and the eavesdropper.

We investigate the secrecy outage performance of maximal ratio combining (MRC) in cognitive radio networks over Rayleigh fading channels. In a single-input multiple-output wiretap system, we consider a secondary user (SU-TX) that transmits confidential messages to another secondary user (SU-RX) equipped with M ( M ≥ 1) antennas where the MRC technique is adopted to improve its received signal-to-noise ratio. Meanwhile, an eavesdropper equipped with N ( N ≥ 1) antennas adopts the MRC scheme to overhear the information between SU-TX and SU-RX. SU-TX adopts the underlay strategy to guarantee the service quality of the primary user without spectrum sensing. We derive the closed-form expressions for an exact and asymptotic secrecy outage probability.