Experience replay is a crucial technology for off-policy deep reinforcement learning, which uses a portion of memory as the replay buffer to store previous experience samples for the later policy update. Since each experience sample can be used multiple times, experience replay drastically improves the utilization rate of experience samples. However, how to effectively combine experience replay with multi-agent reinforcement learning is still an open challenge. In multi-agent reinforcement learning, the decision of the agent needs to consider the dynamic information of the environment as well as the behavior of other agents. If the policies of other agents change, updating the current policy with previous experience samples may deteriorate the agents' subsequent decisions. Some methods use a small-capacity replay buffer to store recent experience samples. Although this avoids the problem that the experience sample in the replay buffer is not compatible with the current policy, it will reduce the diversity of experience samples in the replay buffer, that resulting in agents unable to learn the optimal strategy. This paper eases this conflict by enhancing the experience selection mechanism: 1) we use the reservoir retention algorithm to increase the diversity of experience samples in the replay buffer; 2) we use prioritized experience replay to alleviate the problem that the experience sample in the replay buffer is not compatible with the current policy. The experimental results on the covert communication problem confirm the effectiveness of our proposed method.
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