This paper investigates asymmetric spatial modulation (ASM) for multi-user multiple-input multiple-output (MIMO) systems operating in the near-field (NF) region. Considering spherical-wave propagation, closed-form expressions for the average bit error probability (BEP) of both users are derived under maximum likelihood (ML) detection. The analytical framework is validated through Monte Carlo simulations using five million transmitted symbols. Numerical results compare the near-field (NF) and far-field (FF) channel models. When users are located in the NF region, for example at a distance of 0.2 m from the array, the NF model achieves lower BER across the entire signal-to-noise ratio range. At an SNR of 20 dB, the BER gap between NF and FF increases from approximately 1.65e-3 for 16 transmit antennas to about $\mathbf{5. 0 1 e}-\mathbf{3}$ for 32 transmit antennas. The proposed ASM scheme also provides comparable BEP performance for the two users while enabling simultaneous transmission within the same MIMO resource block. These results show that near-field spatial characteristics can be effectively exploited for multi-user transmission in large-scale and high-frequency MIMO systems.
Quynh Nhu Nguyen, Do Hoang Anh, Thai-Hoc Vu et al.· IEEE International Conferenc...· 0 citations
In single-input single-output downlink systems, the common and private streams in rate-splitting multiple access (RSMA) fully overlap in the power domain, causing strong inter-private interference. Under imperfect successive interference cancellation (SIC), this interference significantly increases users’ decoding error probability. To overcome this limitation, we propose a semi-rate-splitting multiple access (SRMA) scheme that distributes private streams across two distinct bandwidth/time regions rather than fully overlapping them. To evaluate the proposed SRMA, we formulate two design problems: 1) maximizing the minimum ergodic capacity (EC) among users and 2) minimizing the system connection outage probability (COP). Both problems jointly optimize the rate-split ratio, power allocation coefficient, and partitioned-resource factor. To address the non-convexity in these problems, we employ successive convex approximation and analytical reformulation to relax them into tractable convex problems with closed-form solutions. Monte-Carlo simulations demonstrate that SRMA outstandingly improves COP performance while achieving EC levels comparable to RSMA and outperforming conventional non-orthogonal multiple.
Thai-Hoc Vu, Anh-Tu Le, Miroslav Voznak· IEEE Wireless Communications...· 0 citations
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