Decentralized spacing control of a string of multiple vehicles over lossy datalinks

Aircraft formation flying and highway vehicle platooning are examples of spacing control of multiple vehicles. To achieve string stability with a linear static controller, state information of a reference vehicle in addition to the immediately preceding vehicle must be available to all vehicles. Possibly, the most efficient way to achieve this is by using wireless datalinks. Wireless datalinks however suffer from random momentary drop-outs. This effect on spacing control has not been specifically addressed. This paper shows that, by performing estimation during communication drop-outs, a weak form of string stability can be guaranteed. It also shows that the worst-case communication drop-out scenario is when alternate vehicles (instead of all of them) in a string suffer from drop-outs simultaneously. Numerical design results show a trade-off between performance and robustness against communication drop-outs. It is also found that moderately reliable links are sufficient for spacing control so long as they recover quickly when they fail.