A Data Link Layer Protocol for Hybrid Vehicular Sensor Networks Using Practical Mobility Models with Real Maps
Safety applications in Hybrid Vehicular Sensor Networks (HVSN) require robust transmission of messages in order to deliver safety to roads and drivers as intended. Since moving vehicles are equipped with wireless sensors that utilize and share the unreliable wireless channel for communication, the transmission of safety messages must be coordinated to minimize or completely eliminate collision of exchanged packets. The first step on the way of achieving that is through the Media Access Control (MAC) layer which is responsible for managing the access to the shared media safely and without collisions.
This thesis aims at designing and implementing a HVSN MAC protocol to help exchange safety and control messages between the network elements, i.e. vehicles’ on board sensors and road side sensor units. The Time Division Multiple Access (TDMA) is one of the media access techniques used for eliminating collisions. However, it imposes few challenges in implementation, namely, rescheduling and time synchronization among communicating nodes.
In this proposed protocol, we provide a complete solution for such problems. Instead of dividing the time frame between just the available nodes, the protocol provides fixed schedules or time frames with enough time slots that are able to accommodate the maximum number of vehicles that may fit in one segment at a time. Such arrangement eliminates the need for re-scheduling and unnecessary processing. The synchronization problem is solved as well, with coordination from the network controller which is the road side unit.
Since we are dealing with HVSN, the protocol has not only considered the network or the communication part, but also included the vehicles’ behavior in the design process, through realistic mobility modeling. The mobility model and the protocol operations are employed on a small real map where vehicles interact and communicate.
Moreover, a new Packet Delivery Ratio calculation method that considers the vehicles’ mobility in the analysis is applied to practically evaluate the protocol performance.
The devised MAC protocol is characterized by several features; first, it is a collision free MAC protocol that does not require the re-configuration of time slots division as well as it accounts for the time synchronization problem. Second, the protocol is one of the initial works that employs the IEEE 802.11p in HVSN and utilizes its features and specifications. Third, the design is comprehensive and it is built and based on a realistic mobility model that helped in assessing the protocol performance through a unique TDMA mobility based-PDR calculation method.