A Hard Real-Time Testbed for Distributed TDMA-Based MAC Protocols in VANETs

Recent years, a number of distributed TDMA-based MAC protocols have been proposed for Vehicular Ad-hoc Networks (VANETs), and most of them were evaluated only in the simulations. However, according to the measurement-based works, the wireless communication of VANETs in the real world is extremely unstable, which significantly impacts the performance of the MAC protocols. Therefore, it is important to evaluate them in the real world environment. In this paper, we design and implement a hard real-time testbed for distributed TDMA-based MAC protocols in VANETs. The testbed consists of five parts: the commercial off-the-shelf Network Interface Card (NIC), the high-accuracy GPS receiver for time synchronization, the collaboration of Linux and the Field-Programmable Gate Array (FPGA) subsystem, the revised ADHOC MAC protocol in the FPGA subsystem for the controlling of the TDMA access, and the Unmanned Ground Vehicle (UGV) for the mobility control. The testbed achieves the hard real-time data delivery for high-priority packets by handling the interactions with the NIC in the FPGA, and allowing the FPGA to process the high-priority tasks and Linux to process the low-priority tasks. Results of the measurements show that the transmission delay of the high-priority packets is bounded and the TDMA access is functional.