Content-Aware RSMA-Enabled Pinching-Antenna Systems for Latency Optimization in 6G Networks

The Pinching Antenna System (PAS) has emerged as a promising technology to dynamically reconfigure wireless propagation environments in 6G networks. By activating radiating elements at arbitrary positions along a dielectric waveguide, PAS can establish strong line-of-sight (LoS) links with users, significantly enhancing channel gain and deployment flexibility, particularly in high-frequency bands susceptible to severe path loss. To further improve multi-user performance, this paper introduces a novel content-aware transmission framework that integrates PAS with rate-splitting multiple access (RSMA). Unlike conventional RSMA, the proposed RSMA scheme enables users requesting the same content to share a unified private stream, thereby mitigating inter-user interference and reducing power fragmentation. We formulate a joint optimization problem aimed at minimizing the average system latency by dynamically adapting both antenna positioning and RSMA parameters according to channel conditions and user requests. A Content-Aware RSMA and Pinching-antenna Joint Optimization (CARP-JO) algorithm is developed, which decomposes the non-convex problem into tractable subproblems solved via bisection search, convex programming, and golden-section search. Simulation results demonstrate that the proposed CARP-JO scheme consistently outperforms Traditional RSMA, NOMA, and Fixed-antenna systems across diverse network scenarios in terms of latency, underscoring the effectiveness of co-designing physical-layer reconfigurability with intelligent communication strategies.

💡 Research Summary

The paper addresses two fundamental challenges of future 6G wireless networks: severe path loss in millimeter‑wave and terahertz bands, and the inefficiency of conventional multiple‑access schemes when many users request the same content. To tackle the first issue, the authors employ a Pinching Antenna System (PAS). A PAS consists of a dielectric waveguide along which a radiating element (the “pinching antenna”) can be activated at any point, thereby creating a direct line‑of‑sight (LoS) link to a user regardless of obstacles. This physical re‑configurability dramatically improves channel gain compared with fixed‑position antennas, especially at high frequencies where blockage is common.

For the second issue, the paper introduces a content‑aware version of Rate‑Splitting Multiple Access (RSMA). Traditional RSMA splits each user’s message into a common part (shared by all users) and a private part (dedicated to each user). In multicast or video‑streaming scenarios, many users request the same file, yet conventional RSMA still generates a separate private stream for each user, causing unnecessary power fragmentation and inter‑user interference. The proposed content‑aware RSMA groups users requesting the same file into a single private stream. Consequently, the number of private streams is reduced, the allocated power per stream is higher, and interference is mitigated. The common stream still serves all users, but its rate is limited by the worst‑case channel; therefore, optimizing the antenna position can improve that worst‑case channel and lift the common‑stream bottleneck.

The system model comprises a single base station equipped with one dielectric waveguide of length (L_W). A pinching antenna is placed at a variable location (\Phi_{\text{Pin}} = (x_{\text{Pin}},0,d)) along the guide. (K) users are randomly distributed in a rectangular area on the ground. There are (I) distinct content files; each file (i) has size (L_i) and a set of requesting users (\mathcal{K}_i). The transmission uses a common power (h_0) for the shared stream and private powers (P_i) for each content‑aware private stream. The achievable rates are (R_0) (common) and (R_i) (private), leading to a per‑content latency (T_i = L_i/(R_0+R_i)). The objective is to minimize the weighted average latency across all contents, subject to a total transmit‑power budget, per‑user QoS constraints, and the requirement that users requesting the same file share a private stream.

Mathematically, this yields a non‑convex optimization problem because the antenna position, power allocation, and rate allocation are tightly coupled. Direct solution is intractable. The authors therefore propose the CARP‑JO (Content‑Aware RSMA and Pinching‑antenna Joint Optimization) algorithm, which decomposes the problem into two tractable sub‑problems:

1. RSMA Resource Allocation Sub‑problem (fixed antenna position).
   – Private powers (P_i) are optimized via a bisection search that satisfies the total‑power constraint while maximizing the sum of private rates.
   – The common power (h_0) is searched over a one‑dimensional grid; for each candidate, the common rate (R_0) is obtained by solving a convex program that enforces that every user can decode the common stream (i.e., the rate does not exceed the worst‑case SINR).
   – The overall latency for the current antenna location is then computed.

2. Antenna Positioning Sub‑problem (fixed RSMA allocation).
   – The antenna’s x‑coordinate is searched along the waveguide using golden‑section search, which efficiently finds the position that minimizes the latency evaluated by the RSMA sub‑problem. At each candidate position, the RSMA allocation is re‑computed, ensuring that the coupling between geometry and power/rate is fully captured.

The two sub‑problems are iterated until convergence, yielding a near‑optimal joint solution.

Simulation results explore a range of system parameters: total transmit power (10–40 W), user density (10–100 users), service‑area size, and the proportion of users requesting the same content. Across all scenarios, CARP‑JO consistently outperforms three baselines: (i) traditional RSMA without content awareness, (ii) NOMA with the same PAS hardware, and (iii) a fixed‑antenna system employing conventional RSMA. The average latency reduction ranges from 20 % to 35 %, with the greatest gains observed when the multicast ratio is high (i.e., many users request identical files). The results also show that optimizing the antenna location can improve the worst‑case channel gain by up to 6 dB, directly translating into higher common‑stream rates.

Beyond performance numbers, the paper contributes several conceptual insights:

• Physical‑Layer Reconfigurability as a Degrees‑of‑Freedom for MAC Design. By moving the antenna, the system can shape the spatial distribution of channel gains, effectively balancing the rates of common and private streams.
• Content‑Level Stream Sharing Reduces Power Fragmentation. Grouping users by requested file eliminates redundant private streams, which is especially beneficial in bandwidth‑limited, high‑frequency bands where every dB of SNR matters.
• Joint Optimization Framework. The decomposition into convex and one‑dimensional searches demonstrates a practical pathway to solve otherwise intractable cross‑layer problems, making the approach amenable to real‑time implementation with modest computational resources.

The authors conclude by outlining future research directions: extending the model to multiple simultaneous pinching antennas, incorporating user mobility and dynamic content popularity, and applying machine‑learning‑based predictors to anticipate content requests and pre‑position the antenna proactively. Overall, the paper presents a compelling case for co‑designing reconfigurable hardware and intelligent multiple‑access protocols to meet the ultra‑low‑latency demands of 6G networks.