流体天线辅助的噪声调制：基于方差的无线通信的空间分集
Fluid Antenna-Aided Noise Modulation: Spatial Diversity for Variance-Based Wireless Communication
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中文总结 AI 辅助
该研究将噪声调制与流体天线系统结合，推导了其平均误码率，证实流体天线可恢复噪声调制的分集增益，且存在固有误码率下限。
中文摘要 AI 辅助
噪声调制（NoiseMod）将信息编码在类噪声发射波形的方差中，而非其幅度、相位或频率，这对超低功耗和隐蔽链路颇具吸引力。其主要缺陷在于，与传统调制不同，它在瑞利衰落下无分集：误码率（BEP）仅以1/(N_sδ)的形式衰减，其中N_s为每比特的噪声样本数，δ为有用信号与热噪声的方差比。与此同时，流体天线系统（FAS）已被证实可通过在N_p个紧密间隔的端口间切换的单个辐射元件恢复大量选择分集，且无需额外的射频链。本文将二者结合：为NoiseMod接收机配备流体天线，并推导其平均误码率。对于理想化的相互独立端口，我们通过端口包络的顺序统计量获得精确的闭式误码率；对于符合Jake模型的物理上准确的空间相关情况，我们采用Khammassi等人提出的两阶段信道近似构建半解析误码率。我们通过全信号级蒙特卡洛仿真验证了两种情况，并表明：（i）当端口弱相关时，FAS恢复的分集阶数随端口数N_p的增加而增长；（ii）一旦流体天线孔径Wλ固定，N_p增长时该增益会饱和，这与FAS的中断概率饱和现象类似，现于误码率中观测到；（iii）存在一个与天线分集阶数无关、仅由N_s和方差比α决定的固有、与相关（及δ）无关的误码率下限。
英文摘要
Noise modulation (NoiseMod) encodes information in the \emph{variance} of a transmitted noise-like waveform rather than in its amplitude, phase, or frequency, and is attractive for ultra-low-power and covert links. Its main weakness is that, unlike classical modulation, it exhibits \emph{no} diversity under Rayleigh fading: its bit error probability (BEP) decays only as $1/(N_sδ)$, where $N_s$ is the number of noise samples per bit and $δ$ the useful-to-thermal noise variance ratio. Independently, fluid antenna systems (FAS) have been shown to recover substantial selection diversity from a single radiating element that switches among $N_p$ closely spaced ports, without extra radio-frequency chains. This paper combines the two: we equip a NoiseMod receiver with a fluid antenna and derive its average BEP. For idealized, mutually independent ports, we obtain an exact closed-form BEP via order statistics of the port envelopes. For the physically accurate, spatially correlated case governed by Jake's model, we build a semi-analytical BEP using the two-stage channel approximation of Khammassi \emph{et al.} We validate both regimes against full signal-level Monte Carlo simulation and show that (i) FAS restores a diversity order that grows with the number of ports $N_p$ when ports are weakly correlated, (ii) this gain saturates once the fluid-antenna aperture $Wλ$ is fixed and $N_p$ grows, mirroring the outage-probability saturation reported for FAS, now observed for BEP, and (iii) an intrinsic, correlation-independent (and $δ$-independent) BEP floor set only by $N_s$ and the variance ratio $α$ persists regardless of the antenna diversity order.
