The Control Plant as A Communication Channel: Implicit Communication for Decentralized LQG Control
For decentralized control systems with asymmetric information, this work provides a novel method to achieve coordination without explicit communication, though it is incremental as it builds on joint source-channel coding.
The paper tackles decentralized LQG control where only the leader knows the target state and no explicit communication exists. It proposes an implicit communication scheme using the control plant as a channel, achieving follower estimation error that decreases to zero and control cost close to the explicit-communication lower bound.
We study a decentralized linear quadratic Gaussian control problem, in which a leader and a follower must steer a linear system to a target state. The target state is known only to the leader, and no explicit communication channel exists between the agents. To address the challenge posed by this asymmetric information structure, we propose an integrated communication and control (ICoCo) framework in which the control plant itself serves as a communication channel: the leader encodes the target state into its control input through an additive communication term, and the follower decodes it from the resulting state trajectory. We design an implicit coordination scheme based on joint source-channel coding ideas, and prove that the follower's estimation error decreases monotonically to zero, enabling the two agents to coordinate increasingly well and ultimately steer the system to the target state. We then formulate the design of the communication power as an optimal control problem to minimize the overall control cost. In the fully actuated leader case, we derive necessary optimality conditions and in the under-actuated case, we solve the problem numerically. Numerical results show that the proposed scheme effectively coordinates the two agents and achieves a control cost close to that of the explicit-communication lower bound.