For platoons under the multiple-predecessor following (MPF) topology, communication delays can compromise both the internal stability and string stability. The most straightforward solution to guarantee stability is by increasing the time headway. However, time headway plays a significant role in road capacity and increasing its value is in contrast with the idea of platooning. In this study, internal stability and string stability of platoons suffering from communication delays are investigated and a lower bound for the time headway is proposed. Using this bound, platoons do not need to massively increase the time headway in order to compensate for the effects of communications delays. Finally, we evaluate the proposed lower bound on the time headway and the simulation results demonstrate its effectiveness.

Transmission control protocols (TCPs) are used to control the congestion in the Internet. Various types of TCP protocols have been proposed including TCP Reno, TCP Tahoe and TCP Vegas. Although TCP Reno is widely used for wired communications, TCP Vegas is proved to have better performance in wireless environments. In TCP Reno, to achieve a certain queue level at the intermediate routers, active queue management (AQM) schemes are used. An AQM scheme marks the packets at the intermediate routers and TCP Reno source uses that mark to adjust its speed. However, in TCP Vegas, such scheme is not useable. Consequently, the queue level adjustment is not achievable. A scheme which is employed at the source and adjusts the TCP Vegas parameters dynamically to achieve a certain queue level at the intermediate router is proposed. To the best of the knowledge, this is the first attempt to dynamically adjust the queue levels when TCP Vegas is employed. Our proposed scheme plays the role of AQM in TCP Reno for TCP Vegas. The control scheme presented is designed based on integral backstepping technique and will be applied to the linearised model of TCP Vegas.

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