In this paper, we investigate the downlink performance of multi-cell RSMA-enabled ISAC networks in which base stations (BSs), communication users, and sensing targets are spatially distributed according to independent Poisson point processes (PPPs). Each BS simultaneously serves multiple users using RSMA while exploiting the common stream as a dual-functional communication and sensing waveform. The users are equipped with FAS that selects the best antenna port to maximize the received signal quality. Closed-form analytical expressions are derived for the ergodic sum-rates by combining stochastic geometry, order statistics, and Laplace-transform-based interference analysis. Furthermore, a tractable approximation for the average radar SINR is developed by characterizing the statistical properties of the common precoder. Leveraging the derived analytical expressions, a low-complexity analytical resource allocation framework is proposed to jointly optimize the RSMA power allocation, the communication-sensing beam tradeoff, and the number of scheduled users while sat- isfying the sensing quality-of-service constraint. Compared with conventional iterative optimization approaches, the proposed analytical design significantly reduces computational complexity while achieving nearly identical communication performance. Simulation results verify the accuracy of the developed analytical expressions and demonstrate substantial improvements in both RSMA sum-rate and sensing performance over conventional transmission schemes.
This paper investigates the sum-rate maximization problem for downlink rate-splitting multiple access (RSMA) systems equipped with pattern-reconfigurable fluid antennas (PRFA). Two PRFA models are developed: a deployable discrete-selection PRFA (DS-PRFA) model with finite predefined radiation modes, and an idealized continuous-optimization PRFA (CO-PRFA) model based on spherical harmonic expansion that serves as a performance upper bound. The sum-rate maximization problem is formulated by jointly optimizing digital, analog, and antenna-domain precoders along with RSMA power allocation. To solve this non-convex problem, we propose alternating optimization algorithms based on the weighted minimum mean square error (WMMSE) transformation and block coordinate descent with per-antenna decoupling. For DS-PRFA optimization, closed-form solutions are derived, while for CO-PRFA optimization, a preconditioned Riemannian conjugate gradient method is developed on the spherical manifold. Simulation results under the considered settings show that the proposed tri-hybrid RSMA framework with PRFA improves sum-rate performance compared with conventional hybrid precoding, where the CO-PRFA provides an idealized upper benchmark compared with practical DS-PRFA due to the more flexible reconfigurability.
Yijin Pan, Yifeng Ji, Anzheng Tang et al.· IEEE Open Journal of the Com...· 0 citations
In integrated sensing and communication (ISAC) systems, stringent sensing performance constraints can severely limit the power available for communication. Hybrid reconfigurable intelligent surfaces (HRISs) with capabilities of both passive reflection and active signal amplification can significantly improve communication performance in the power-limited regime. This motivates us to analyze and optimize the performance of an HRIS-aided multiple-input-multiple-output (mMIMO) ISAC system. We first estimate the effective uplink/downlink channels using the minimum mean square error method. We then derive closed-form expressions for the communication sum-rate and sensing Cram\'er-Rao lower bound (CRLB). It is shown that under the equal power allocation strategy, the CRLB remains independent of the HRIS coefficients. Then, we formulate a joint optimization problem of power allocation and HRIS beamforming to maximize the communication sum-rate while ensuring specified sensing CRLB constraints. To solve the formulated non-convex problem, we propose an alternating optimization algorithm based on fractional programming and successive convex approximation. Extensive simulations validate our analysis and proposed algorithm, showing significant improvements in both communication and sensing performances enabled by the HRIS. For example, an HRIS with only $4$ active elements offers $97.30\%$ improvement in the communication sum-rate, while ensuring a sensing CRLB constraint of $-30$ dB.
Smriti Uniyal, Tian-Yu Fang, M. di Renzo et al.· 0 citations
Fluid antenna systems (FASs) have recently emerged as a promising reconfigurable antenna technology for future wireless networks, owing to their unique ability to exploit fine-grained spatial channel variations within a compact aperture. In this paper, a single-input multiple-output (SIMO) FAS employing maximum-ratio combining (MRC) is investigated under the block-diagonal correlation model, where the ports of FAS are partitioned into independent blocks and the strongest port within each block is selected for MRC combining. Exact outage probability (OP) expressions are first derived in both convolution and characteristic-function forms. To gain further insights, closed-form high-SNR asymptotic expressions are developed, from which the diversity order is shown to approximate the number of ports. This result reveals that block partitioning influences only the coding gain and can therefore be optimized without compromising the diversity performance. For the ergodic rate (ER), a Gamma-matching approximation together with a tighter Jensen-based approximation is derived in closed form. Simulation results corroborate the analytical framework and demonstrate that: i) increasing either the number of ports or the number of blocks improves the system performance; ii) the diversity order depends solely on the number of ports; and iii) the proposed SIMO-FAS achieves comparable or superior outage performance to conventional MRC receivers despite employing fewer combining branches.
A modulation- and receive-filter-aware framework for the sensing-interference management in multi-cell OFDM-ISAC systems is developed and closed-form signal-to-interference-plus-noise ratio (SINR) expressions for each range--Doppler bin under matched filtering (MF) and reciprocal filtering (RF).
Kaitao Meng, Kawon Han, C. Masouros et al.· 0 citations
Slow fluid antenna multiple access (sFAMA), enabled by the fluid antenna system (FAS), has recently emerged as a practical and low-complexity paradigm for supporting massive wireless connectivity. While existing studies have characterized its physical-layer performance under one-shot transmission, its interaction with retransmission protocols and the resulting networking performance remain largely unexplored. In this paper, we study a downlink hybrid automatic repeat request (HARQ)-assisted sFAMA framework, termed HARQ-sFAMA, in which each user performs distinguished port selection in every HARQ round and combines the received signals across multiple rounds to improve decoding reliability. We develop a comprehensive analytical framework to characterize the outage probability, average packet waiting time, and energy efficiency of the proposed system. The analysis reveals how HARQ exploits the spatial reconfigurability of FAS to simultaneously enhance reliability and improve queueing performance. Numerical results corroborate the theoretical analysis and demonstrate that the HARQ-sFAMA system significantly outperforms conventional one-shot sFAMA in terms of reliability, delay, and energy efficiency. These findings suggest that the integration of HARQ and sFAMA provides a promising pathway toward a practical and standards-compatible massive access solution for future wireless networks.
Sixu Han, Kai-Kit Wong, Hanjiang Hong et al.· arXiv.org· 1 citation
In this paper, we propose an fluid antenna (FA)-enhanced interference exploitation symbol-level precoding (SLP) for downlink multi-user multiple-input single-output (MU-MISO) systems, focusing on transmitter-side fluid antenna systems (Tx-FAS) that allow flexible spatial correlation effects while preserving user portability. First, we derive an explicit expression for the achievable rate of SLP under finite-alphabet inputs, and further establish a closed-form upper bound that quantifies the theoretical rate improvement achieved by spatial reconfigurability of Tx-FAS. Subsequently, a joint optimization problem involving SLP design and Tx-FAS port selection is formulated to maximize the minimum user signal-to-interference-plus-noise ratio (SINR) under strict transmit power constraints. Due to the highly non-convex nature of the problem, we devise a genetic algorithm (GA) to efficiently obtain a near-optimal solution. Moreover, based on the optimal channel structure of SLP, we further develop a low-complexity algorithm with a spatial filtering mechanism to obtain a sub-optimal solution to the considered problem. Simulation results confirm that the proposed FAS-enhanced SLP scheme delivers notable performance improvements over both conventional precoding techniques and the FAS-only transmission approach.
Guorui Wei, Ang Li, Xiao-Yan Hu et al.· IEEE Transactions on Communi...· 0 citations
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