Reliable and Secure Communications Through Compact Ultra-Massive Antenna Arrays

TL;DR

This work analyzes the performance of the CUMA network in terms of the outage probability and the ergodic rate and derives closed-form expressions for the secrecy outage probability and suggests that a simple imperfect interference cancelation mechanism at the legitimate receiver may substantially increase the secrecy performance.

Abstract

Compact Ultramassive Antenna Array (CUMA) is a pioneering paradigm that leverages the flexibility of the Fluid Antenna System (FAS) to enable a simple multiple access scheme for massive connectivity without the need for precoding, power control at the base station or interference mitigation in each user's equipment. In order to overcome the mathematical intricacy required to analyze their performance, we use an asymptotic matching approach to relax such complexity with a remarkable accuracy. First, we analyze the performance of the CUMA network in terms of the outage probability (OP) and the ergodic rate (ER), deriving simple and highly accurate closed-form approximations to the channel statistics. Then, we evaluate the potential of the CUMA scheme to provide secure multi-user communications from a physical layer security perspective. Leveraging a tight approximation to the signal-to-interference-ratio (SIR) distribution, we derive closed-form expressions for the secrecy outage probability (SOP). We observe that the baseline CUMA (without side information processing) exhibits limited performance when eavesdroppers are equipped with a CUMA of the same type. To improve their secure performance, we suggest that a simple imperfect interference cancellation mechanism at the legitimate receiver may substantially increase the secrecy performance. Monte Carlo simulations validate our approximations and demonstrate their accuracy under different CUMA-based scenarios.

Figures (7)

• Figure 1: (a) Conventional CUMA downlink system with a MIMO BS communicating with the $U_\mathrm{B}$ FAS-enabled UEs, (b) a CUMA-aided secure scheme with a MIMO BS communicating with $U_\mathrm{B}$ FAS-enabled legitimate UEs in the presence of $U_\mathrm{E}$ FAS-enabled eavesdropper UEs.
• Figure 2: ER vs. the number of users, $U$, for different operating frequencies under rich scattering. Markers denote Monte Carlo Simulations, whereas the solid line represents the proposed approximation given in \ref{['eq14cuma']}.
• Figure 3: OP of any typical UE of the CUMA network by varying $U$ with a fixed frequency operation of $f=6$ GHz under rich scattering. Markers denote Monte Carlo Simulations, whereas the solid line represents the proposed approximation given in \ref{['eq15cuma']}.
• Figure 4: SOP vs. the threshold rate, $R_{\rm S}$, by assuming $f=6$ GHz, $\delta_i=1$, and $U=20$. Markers denote Monte Carlo Simulations, whereas the solid line represents the proposed approximation given in \ref{['cumaeq17']}.
• Figure 5: SOP vs. the number of users, $U$, with $f=26/40$ GHz, $\delta_i=1$, and $R_\mathrm{S}=1$. Markers denote Monte Carlo Simulations, whereas the solid line represents the proposed approximation given in \ref{['cumaeq17']}.

Theorems & Definitions (12)

• Proposition 1
• proof
• Proposition 2
• proof
• Proposition 3
• proof
• Proposition 4
• proof
• Remark 1
• Proposition 5