Mengyu Qian, Xidong Mu, Li You, Michail Matthaiou
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 thecentralized PA deployment, where all PAs are switched between waveguides to serve users in a time-division manner to avail of beamforming gain, and thedistributed 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 location strategy of PAs on each waveguide is determined first with the aim of maximizing the channel gain of the 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, which is challenging to analyze due to the inter-user interference. 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 in the high-SNR regime, 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. Numerical results demonstrate that i) with the aid of the stationary phase method, the approximation of the system SE proves to be highly accurate overall; and ii) compared to the centralized deployment, the distributed deployment generally achieves a higher SE but at the cost of a low energy efficiency.