Overview
A generalized framework is proposed for the novel center-fed pinching antenna system (C-PASS). This framework encompasses the derivation of closed-form expressions for the system's degree of freedom (DoF) and power scaling law. Based on the C-PASS modeling, a sum-rate maximization problem is formulated for the joint optimization of transmit and pinching beamforming. An alternating optimization algorithm is developed to address this non-convex problem.
Research Context
The research focuses on the C-PASS architecture, specifically examining its performance characteristics related to DoF and power scaling. The analysis includes a comparison with existing antenna systems, namely the single-waveguide PASS and multi-waveguide PASS, under various conditions, including high-attenuation regimes. The objective is to understand and optimize the beamforming capabilities of the C-PASS.
Approach
The research approach commenced with the development of a generalized framework for the C-PASS. Within this framework, closed-form expressions were derived for the DoF and power scaling law. These theoretical derivations informed the understanding of the C-PASS's fundamental performance characteristics. The DoF was found to scale linearly with the number of input ports, $M$, and the number of receive antennas, $K$. The power scaling laws indicated a power gain of order $\mathcal{O}(P_T M)$, where $P_T$ represents the transmit power.
Following the modeling phase, a sum-rate maximization problem was formulated. This problem targets the joint optimization of transmit and pinching beamforming, which is characterized as a highly coupled non-convex problem. To solve this, an efficient alternating optimization algorithm was developed. The algorithm updates the transmit precoding and power splitting ratios using derived closed-form solutions. Concurrently, the pinching antenna positions and radiation coefficients are optimized through the application of block coordinate descent (BCD) methods.
Findings
- The derived theoretical results for the C-PASS indicate that the achievable degree of freedom (DoF) scales linearly with $M$, the number of input ports, and $K$, the number of receive antennas.
- The power scaling laws for the C-PASS demonstrate a power gain of order $\mathcal{O}(P_T M)$, with $P_T$ representing the transmit power.
- Numerical results reveal that the single-waveguide C-PASS achieves superior DoF compared to the single-waveguide PASS.
- The single-waveguide C-PASS also demonstrates superior power scaling laws when compared to the single-waveguide PASS.
- In high-attenuation regimes, the single-waveguide C-PASS outperforms the multi-waveguide PASS, yielding a substantial gain exceeding $10$ dB.