Resource Allocation for Multi-UAV Relay Networks in 6G Semantic Communication
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摘要: 针对6G多无人机中继网络在动态环境下面临的通信资源受限与传输效能瓶颈,该文引入语义通信范式以降低系统对高带宽的依赖,并提出一种基于两阶段混合强化学习的联合资源优化方法。首先,综合考虑语义符号数量、无人机飞行轨迹、功率控制与信道分配,构建了以最大化语义通信服务质量和长期用户公平性为目标的资源优化模型。其次,设计了两阶段资源分配框架,利用改进的容量感知K均值算法进行负载均衡预部署以规避无效探索,并采用带参数共享的循环独立近端策略优化算法求解动态联合策略。仿真结果表明,该文所提方法具有良好的收敛性,能在保证用户公平性的同时有效提升语义传输效率并降低传输时延。Abstract:
Objective Sixth-generation (6G) mobile networks aim to achieve global seamless coverage through space-air-ground integrated architectures. In this context, Unmanned Aerial Vehicles (UAVs) can serve as mobile aerial relay nodes to support massive ground user access in complex environments. However, traditional data-oriented communication paradigms incur high bandwidth overhead, making them difficult to apply under the limited spectrum resources of UAV networks. In addition, traditional centralized resource allocation methods struggle with real-time implementation due to highly dynamic network topologies and the complex coupling of multi-dimensional resources. To address these challenges, semantic communication has emerged as a new paradigm that extracts the essential meaning of information at the transmitter and reconstructs it at the receiver, thereby reducing redundant data traffic. Although semantic communication provides a feasible solution, existing semantic-driven resource allocation methods primarily focus on static ground networks or single-UAV scenarios, often overlooking the coverage limitations and co-channel interference in multi-UAV collaborative networks. Therefore, an intelligent joint resource optimization model and a distributed resource allocation framework are needed for multi-UAV relay networks. By jointly optimizing multi-dimensional resources, such a framework can improve semantic transmission efficiency and ensure long-term user fairness, thereby supporting intelligent resource scheduling in 6G integrated networks. Methods This study formulates a joint resource optimization model for multi-UAV relay networks under the semantic communication paradigm ( Fig.1 ), coupling the number of semantic symbols, UAV trajectories, transmission power, and channel allocation. To evaluate semantic transmission quality, the proposed model introduces a Semantic Communication Quality of Service (SC-QoS) metric, which integrates Semantic Quantization Efficiency with normalized transmission delay. The optimization objective is formulated as a Mixed Integer Nonlinear Programming problem that maximizes the weighted sum of system-wide SC-QoS and long-term user fairness evaluated by Jain's fairness index. To solve this problem, a Two-Stage Hybrid Reinforcement Learning (TS-HRL) framework is proposed (Fig.2 ). The first stage employs a Capacity-Aware K-means (CA-K-means) algorithm for heuristic UAV pre-deployment. By introducing a dynamic distance compensation term based on residual capacity, this algorithm guides edge users toward low-load UAVs, achieving load balancing among UAV clusters while preserving spatial proximity. The second stage models the dynamic scheduling problem as a Decentralized Partially Observable Markov Decision Process and solves it using a Recurrent Independent Proximal Policy Optimization with Parameter Sharing (R-IPPO-PS) algorithm (Algorithm 1). This algorithm leverages Long Short-Term Memory (LSTM) networks to aggregate historical trajectories and observations, thereby capturing hidden environmental states. Furthermore, the multi-agent parameter-sharing mechanism reduces model complexity with respect to the agent scale, while the preference decoupling strategy converts discrete channel allocation decisions into continuous preference variables to facilitate model training.Results and Discussions The proposed TS-HRL framework is evaluated in a dynamic environment with randomly moving ground users. The convergence analysis shows that the proposed method achieves a higher initial reward and reaches a stable state with fewer iterations than the random deployment, memoryless allocation, and Enhanced Independent Soft Actor-Critic (EI-SAC) baselines ( Fig.3 ). By leveraging LSTM-based historical information and CA-K-means topology initialization, the proposed method reduces invalid exploration and improves convergence stability. Compared with traditional bit-based communication, the semantic communication framework increases Semantic Spectral Efficiency (S-SE) by 3.6 times, reduces transmission delay by 92.1%, and improves fairness by 14.3% (Fig.4 ). Within the semantic communication paradigm, compared with the memoryless and heuristic schemes, the proposed method improves S-SE by 92.7% and 51.9%, reduces transmission delay by 13.5% and 57.7%, and improves fairness by 17.3% and 39.7%, respectively. Although the EI-SAC baseline achieves a fairness index of 0.93, its S-SE remains relatively low. In contrast, the proposed TS-HRL framework maintains a high fairness level while achieving an S-SE approximately 4.3 times higher than that of EI-SAC. Compared with random deployment, the proposed method improves S-SE by 11.3% with only a marginal 1.1% decrease in fairness, demonstrating a better trade-off between transmission efficiency and fairness. As the number of users increases from 10 to 40, most baselines show decreases in S-SE and fairness due to intensified co-channel interference and spectrum constraints (Fig.5 ). In contrast, the adaptive scheduling and global fairness reward mechanisms of the proposed method mitigate performance degradation and maintain the average transmission delay below 0.1 ms. These results indicate that the proposed method improves overall system performance while ensuring long-term user fairness.Conclusions This paper investigates joint resource allocation and trajectory planning in dynamic 6G multi-UAV relay networks by integrating the semantic communication paradigm. A joint optimization model coupling the number of semantic symbols, UAV trajectory, power control, and channel allocation is formulated to maximize system SC-QoS and long-term user fairness. To address the high-dimensional coupling of the formulated problem, a TS-HRL framework is proposed. This framework combines CA-K-means pre-deployment with the R-IPPO-PS algorithm to handle multi-dimensional resource scheduling under partial observability. Simulation results verify the convergence, stability, and scalability of the proposed method under different user densities. Through distributed cooperation among UAVs, the proposed method enhances semantic transmission efficiency and reduces transmission delay while ensuring long-term service fairness among ground users. These findings provide a viable approach for intelligent resource allocation in UAV-assisted semantic communication for future space-air-ground integrated networks. -
1 基于R-IPPO-PS的联合资源分配算法
输入:最大回合数$ {N}_{\text{eps}} $,回合内时隙数T,每次参数更新迭代数
$ {N}_{\text{epoch}} $输出:优化后的共享网络参数$ \theta ,\phi $ (1) 初始化参数$ \theta $,$ \phi $,同步旧策略参数$ {\theta }_{\text{old}}\leftarrow \theta $,初始化经验回
放池D(2) 对于每个回合$ e\in \{1,2,\cdots ,{N}_{\text{eps}}\} $: (3) 获取初始观测$ {\boldsymbol{o}}_{m}[0] $,初始化LSTM的隐藏状态$ {\boldsymbol{h}}_{m}[0] $与
细胞状态$ {\boldsymbol{c}}_{m}[0] $(4) 对于每个时隙$ t\in \{1,2,\cdots ,T\} $: (5) 通过MLP与LSTM更新隐藏状态$ ({\boldsymbol{h}}_{m}[t],{\boldsymbol{c}}_{m}[t]) $,采
样独立动作$ {\boldsymbol{a}}_{m}[t] $(6) 执行联合动作,获取奖励$ {r}_{m}[t] $与下一时刻观测
$ {\boldsymbol{o}}_{m}[t+1] $(7) 结束循环 (8) 获取本回合的交互轨迹$ {\tau }_{m} $,采用GAE计算优势函数
$ \widehat{A}[t] $,并将完整交互数据存入D(9) 对于每次训练迭代$ j\in \{1,2,\cdots ,{N}_{\text{epoch}}\} $: (10) 从D中抽取小批量数据,最大化总目标函数
$ J(\theta ,\phi ) $,联合更新参数$ \theta $与$ \phi $(11) 结束循环 (12) 更新旧策略参数$ {\theta }_{\text{old}}\leftarrow \theta $,并清空经验回放池D (13) 结束循环 表 1 仿真参数设置
参数 参数值 载波频率 $ {f}_{\text{c}}=2.4 $ GHz 热噪声功率谱密度 $ {n}_{0}=1.27\times {10}^{-20} $ W/Hz LoS路径损耗指数 $ {\eta }_{\text{a}}=9.61 $ NLoS路径损耗指数 $ {\eta }_{\text{b}}=0.16 $ 语义保真度阈值 $ {\xi }_{\text{th}}=0.8 $ 每回合最大步数 T=600 时隙持续时间 $ {\delta }_{t}=0.1 $ s 表 2 训练参数设置
参数 参数值 MLP隐藏层 [256, 256, 128] MLP激活函数 ReLU LSTM隐藏单元数 256 LSTM序列长度 40 学习率 $ \alpha =1.5\times {10}^{-5} $ 折扣因子 $ \gamma =0.85 $ GAE参数 $ \lambda =0.95 $ PPO裁剪阈值 $ \epsilon =0.09 $ SC-QoS权重系数 $ {w}_{1}=1.0,{w}_{2}=1.0 $ 优化目标权重系数 $ {w}_{\text{sc}}=1.0,{w}_{\text{f}}=1.0 $ -
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