Downlink Performance Analysis of Pinching Antenna Systems: WDMA or NOMA?

TL;DR

This paper develops an analytical framework comparing WDMA and NOMA in downlink pinching antenna systems, revealing their performance trade-offs across different SNR regimes and user distributions.

Contribution

It introduces a unified channel model and derives closed-form expressions for outage probability and achievable rate, providing new insights into access scheme performance in PASS.

Findings

NOMA outperforms WDMA at high SNR due to SIC.

WDMA offers more reliable performance at low to moderate SNR.

WDMAs performance is highly sensitive to user spatial distribution.

Abstract

This paper presents an analytical framework for downlink pinching antenna systems (PASS) employing waveguide division multiple access (WDMA) and non-orthogonal multiple access (NOMA). A unified channel model is developed to capture antenna deployment, user spatial distribution, and path loss. Closed-form and single-integral expressions for the outage probability and average achievable rate are derived and validated via Monte Carlo simulations. The results show that NOMA achieves higher spectral efficiency at high transmit signal-to-noise ratio (SNR) due to successive interference cancellation (SIC), whereas WDMA offers more reliable performance at low to moderate SNR but suffers from an outage floor and rate saturation at high SNR. Moreover, WDMA performance is more sensitive to the user spatial distribution due to the spatially dependent inter-waveguide interference. These findings provide design insights for access-scheme selection and antenna placement in PASS.