Improving Robustness and Deployability in Distributed MPC Formation Control: a Framework for Underwater Acoustic Networks

We consider the problem of controlling networks of underwater agents that use acoustic communication channels to exchange information, and that are tasked with maintaining a given formation while following a shared path. We thus propose approaches to robustify already existing distributed control algorithms, i.e., algorithms to transform existing distributed model predictive controllers (DMPC) unsuitable for the underwater realm (e.g., because they assume standard double precision in exchanged data, or because they are designed for synchronous, bidirectional, and reliable communication) into deployable DMPC schemes. The proposed robustification strategies accommodate both time-division and frequency-division medium access schemes, and address the inherent challenges of lossy and broadcast communication over acoustic media. More precisely, we introduce schemes for handling broadcast asynchronous communication, mitigating packet losses, and quantising exchanged data, with the goal of providing strategies that may be incorporated by other distributed formation control schemes. We characterise the data rate savings vs.\ control performance losses that may be achieved through tuning the parameters of the proposed schemes, and provide sensitivity analyses on how controller / communication performance losses are influenced by such parameters. In doing so, we showcase the implementability of the proposed strategies for practical purposes using commercially available full-duplex or half-duplex modems.