FAS channels are represented as AR(p) Gauss-Markov processes to derive the optimal MMSE interpolator, a tight lower bound on required observations, and a Kalman filter achieving that optimum with O(N) complexity.
Cramer-Rao Bounds for Activity Detection in Conventional and Fluid Antenna Systems
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abstract
In this letter, we develop a unified Cram\'{e}r-Rao bound (CRB) framework to characterize the fundamental performance limits of transmission activity detection in fluid antenna systems (FASs) and conventional multiple fixed-position antenna (FPA) systems. To facilitate CRB analysis applicable to activity indicators, we relax the binary activity states to continuous parameters, thereby aligning the bound-based evaluation with practical threshold-based detection decisions. Closed-form CRB expressions are derived for two representative detection formulations, namely covariance-oriented and coherent models. Moreover, for single-antenna FASs, we obtain a closed-form coherent CRB by leveraging random matrix theory. The results demonstrate that CRB-based analysis provides a tractable and informative benchmark for evaluating activity detection across architectures and detection schemes, and further reveal that FASs can deliver strong spatial-diversity gains with significantly reduced complexity.
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cs.IT 1years
2026 1verdicts
UNVERDICTED 1representative citing papers
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Beyond Covariance: Generative Spatial Correlation Modeling and Channel Interpolation for Fluid Antenna Systems
FAS channels are represented as AR(p) Gauss-Markov processes to derive the optimal MMSE interpolator, a tight lower bound on required observations, and a Kalman filter achieving that optimum with O(N) complexity.