Pinching-Antenna-based Communications: Spectral Efficiency Analysis and Deployment Strategies

Abstract: A multiple-waveguide pinching-antenna (PA)-based multi-user communication system is investigated. With a given number of PAs, two deployment strategies are considered, namely the centralized PA deployment, where all PAs are switched between waveguides to serve users in a time-division manner to avail of beamforming gain, and the distributed PA deployment, where a single PA is deployed on each waveguide to simultaneously serve multiple users by leveraging the multiplexing gain. The spectral efficiency (SE) achieved by each deployment strategy is analyzed: i) For the centralized deployment, the positioning strategy of PAs on each waveguide is determined first with the aim of maximizing the channel gain of the corresponding nearest served user. Based on this, the corresponding system SE is derived. ii) For the distributed deployment, the system SE under the maximum ratio transmission (MRT) is first obtained. To obtain an analytically tractable form, the stationary phase method is utilized to approximate the system SE. The approximation result reveals that the average inter-user interference can be negligible with a large waveguide spacing and thus the simple MRT is appealing for PA-based multi-user communications. Furthermore, the system SEs achieved by the two strategies are compared in both the high and low signal-to-noise ratio (SNR) regimes. Our analysis suggests that at high SNRs, the distributed deployment is superior to achieve the maximal system SE, while the centralized deployment is more suitable for the low-SNR regime. Finally, the theoretical analysis is verified through simulations.