||In this Thesis, we propose a Cluster-based TDMA (CBT) scheme for Vehicular Ad-hoc Networks (VANET). In the CBT, the collision problems can be solved when packets are transmitted at the same time.|
In the Intra-cluster communications, the VANET Coordinator (VC) is determined by randomly choosing a number of zero or one. Other VANET Nodes (VNs) then randomly select different time slots to transmit their Bandwidth Requests (BRs). If more than two VNs choose the same slots for BRs, collision will occur. The failed VNs will continue to issue BRs in the next TDMA frames. After the time slots are scheduled by VC, all VNs can use the designated time slots to send data. In the Inter-cluster communications, when two clusters are approaching to each other, two VCs must exchange Slot Allocation MAP (SAM) using the random zero-or-one scheme. The VCs successfully receive SAM must reschedule the time slots.
For the purpose of performance evaluation, we calculate the average time slots of selecting VC and the average time slots required for successful BRs. We also compute the average time slots required for successfully transmitting SAM and the average time slots required for broadcasting SAM to all VNs. Finally, we calculate the average time slots required for waiting before data transmission. To validate the mathematical results, we perform a simulation written in C++. When comparing the mathematical results to the simulation results, we observe that in the average time slots required for BR, the former is larger than the latter. This is because in the mathematical equations it is difficult to specify which time slots are used by VNs to transmit BRs. However, the rest of performance comparisons, the two results are very close.