Multi-Hop UAV Ad Hoc Network Access Control Protocol: Deep Reinforcement Learning-Based Time Slot Allocation Method
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摘要: 无人机自组织网络中,各个节点的流量不均衡,容易导致网络拥塞和时隙资源利用率低的问题。本该文研究了无人机自组网中饱和节点和不饱和节点共存的场景下的接入控制问题,旨在让更多的节点共享不饱和节点的空闲时隙,提升网络的吞吐量。针对无人机多跳自组织网络接入控制问题,该文提出一种基于深度强化学习的多跳无人机自组织网络MAC协议(DQL-MHTDMA),将饱和节点联合为一个大智能体,学习网络拓扑信息和时隙占用规律,选择最优的接入动作,实现每个时隙上的最大吞吐量或最佳能效。仿真结果表明,所提DQL-MHTDMA协议能够学习时隙的占用规律,并且可以感知多跳拓扑,在多种不饱和流量到达规律下获得最优的吞吐量或最佳的能量效率。Abstract:
Objective Unmanned Aerial Vehicle (UAV) ad hoc networks have gained prominence in emergency and military operations due to their decentralized architecture and rapid deployment capabilities. However, the coexistence of saturated and unsaturated nodes in dynamic multi-hop topologies often results in inefficient time-slot utilization and network congestion. Existing Time Division Multiple Access (TDMA) protocols show limited adaptability to dynamic network conditions, while conventional Reinforcement Learning (RL)-based approaches primarily target single-hop or static scenarios, failing to address scalability challenges in multi-hop UAV networks. This study explores dynamic access control strategies that allow idle time slots of unsaturated nodes to be efficiently shared by saturated nodes, thereby improving overall network throughput. Methods A Deep Q-Learning-based Multi-Hop TDMA (DQL-MHTDMA) protocol is developed for UAV ad hoc networks. First, a backbone selection algorithm classifies nodes into saturated (high-traffic) and unsaturated (low-traffic) groups. The saturated nodes are then aggregated into a joint intelligent agent coordinated through UAV control links. Second, a distributed Deep Q-Learning (DQL) framework is implemented in each TDMA slot to dynamically select optimal transmission node sets from the saturated group. Two reward strategies are defined: (1) throughput maximization and (2) energy efficiency optimization. Third, the joint agent autonomously learns network topology and the traffic patterns of unsaturated nodes, adaptively adjusting transmission probabilities to meet the targeted objectives. Upon detecting topological changes, the agent initiates reconfiguration and retraining cycles to reconverge to optimal operational states. Results and Discussions Experiments conducted in static (16-node) and mobile (32-node) scenarios demonstrate the protocol’s effectiveness. As the number of iterations increases, the throughput gradually converges towards the theoretical optimum, reaching its maximum after approximately 2,000 iterations ( Fig. 5 ). In Slot 4, the total throughput achieves the theoretical optimum of 1.8, while the throughput of Node 4 remains nearly zero. This occurs because the agent selects transmission sets {1, 8} or {2, 8} to share the channel, with transmissions from Node 1 preempting Node 4’s sending opportunities. Similarly, the total throughput of Slot 10 also attains the theoretical optimum of 1.8, resulting from the algorithm’s selection of conflict-free transmission sets {1} or {2} to share the channel simultaneously. The throughput of the DQL-MHTDMA algorithm is compared with that of other algorithms and the theoretical optimal value in odd-numbered time slots under Scenario 1. Across all time slots, the proposed algorithm achieves or closely approximates the theoretical optimum, significantly outperforming the traditional fixed-slot TDMA algorithm and the CF-MAC algorithm. Notably, the intelligent agent operates without prior knowledge of traffic patterns in each time slot or the topology of nodes beyond its own, demonstrating the algorithm’s ability to learn both slot occupancy patterns and network topology. This enables it to intelligently select the optimal transmission set to maximize throughput in each time slot. In the mobile (32-node) scenario, when the relay selection algorithm detects significant topological changes, the protocol is triggered to reselect actions. After each change, the algorithm rapidly converges to optimal action selection schemes and adaptively achieves near-theoretical-optimum maximum throughput across varying topologies (Fig. 9 ). Under the optimal energy efficiency objective policy, energy efficiency in time slot 11 converges after 2,000 iterations, reaching a value close to the theoretical optimum (Fig. 10 ). Compared to the throughput-oriented algorithm, energy efficiency improves from 0.35 to 1. This occurs because the throughput-optimized algorithm preferentially selects transmission sets {1, 8} or {2, 8} to maximize throughput. However, as Node 11 lies within the 2-hop neighborhood of both Nodes 1 and 8, concurrent channel occupancy induces collisions, significantly degrading energy efficiency. In contrast, the energy-efficiency-optimized algorithm preferentially selects an empty transmission set (i.e., no scheduled transmissions), thereby maximizing energy efficiency while maintaining moderate throughput levels. The paper presents statistical comparisons of energy efficiency against theoretical optima across eight distinct time slots in the static (16-node) scenario. As demonstrated in multi-hop network environments, the proposed algorithm achieves or closely approaches theoretical optimum energy efficiency values in all slots. Furthermore, while maintaining energy efficiency guarantees, the algorithm delivers significantly higher throughput compared to conventional TDMA protocols.Conclusions This paper addresses the access control problem in multi-hop UAV ad hoc networks, where saturated and non-saturated nodes coexist. A DQL-MHTDMA is proposed. By consolidating saturated nodes into a single large agent, the protocol learns network topology and time-slot occupation patterns to select optimal access actions, thereby maximizing throughput or energy efficiency in each time slot. Simulation results demonstrate that the algorithm exhibits fast convergence, stable performance, and achieves the theoretically optimal values for both throughput and energy efficiency objectives. -
Key words:
- UAV /
- Multiple access protocol /
- Ad hoc network /
- Deep Reinforcement Learning (DRL)
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1 DQL-MHTDMA(目标:最大吞吐量或者最佳能效)
(1) 运行中继选择算法,选出中继节点 (2) 确定智能体成员集合$ {N_S} $ (3) 初始化参数:初始状态$ {s_0} $,贪心策略中的探索概率$ \varepsilon $,折扣
因子$ \gamma $,调整步进$ \rho $,最小样本数量$ {N_E} $,更新周期$ F $(4) 初始化经验池$ EM $ (5) 初始化QNN的参数$ \theta $ (6) 初始化目标QNN的参数$ {\theta ^ - } $ (7) for t=0,1,2, ···, do 向QNN输入$ {s_t} $,输出$ Q = \left\{ {q\left( {{s_t},a,\theta } \right)\left| {a \in {A_{{s_t}}}} \right.} \right\} $ 采用$ \varepsilon $-贪婪算法从$ Q $中选择动作$ {a_t} $ 执行动作$ {a_t} $,获得$ {z_t} $和$ {r_{t + 1}} $,得到$ {s_{t + 1}} $ 存储$ \left( {{s_t},{a_t},{r_{t + 1}},{s_{t + 1}}} \right) $经验池$ EM $ 训练QNN网络: 从经验池中随机选择$ {N_E} $个样本 for 每一个样本中的经验$ e = \left( {s,a,r,s'} \right) $,do 计算$ y_{r,s'}^{QNN} = r + \gamma \mathop {\max }\limits_{a'} q\left( {s',a';{\theta ^ - }} \right) $ end for 执行梯度下降,在QNN中更新$ \theta $ 如果$ \left( {t/F = = 0} \right) $,更新目标网络$ {\theta ^ - } = \theta $ end 训练 end for 表 1 不饱和节点的时隙占用规律(场景1)
节点
编号发送概率 说明 节点
编号发送概率 说明 4 0.2 随机 12 0.12 随机 5 0.4 随机 13 1/2 周期 7 0.67 随机 14 0.35 随机 9 1/4 周期 15 1/5 周期 10 0.8 随机 16 0.9 随机 11 0.55 随机 表 2 不饱和节点的时隙占用规律(场景2)
节点
编号发送
概率节点
编号发送
概率节点
编号发送
概率3 0.79 13 0.6 23 0.55 4 0.31 14 0.18 24 0 5 0 15 0.23 25 0.45 6 0.2 16 0.26 26 0.65 7 0.23 17 0.65 27 0.63 8 0.53 18 0.24 28 0.08 9 0.17 19 0.19 29 0 10 0.67 20 0.69 30 0.23 11 0.11 21 0.75 31 0 12 0 22 0.28 32 0.91 表 3 超参数设置
参数名称 参数值 历史状态长度$ M $ 20 折扣因子$ \gamma $ 0.9 贪心策略中的探索概率$ \varepsilon $ 0.005~0.010 学习率 1 目标网络的更新频率$ F $ 100 最小样本数量$ {N_E} $ 64 经验池大小 1000 鼓励参数$ \beta $ 12 -
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