Analysis of CSMA Based Broadcast Communication in Vehicular Networks with Hidden Stations

This thesis studies the congestion problem at the Medium Access Control (MAC) layer of the IEEE 802.11p system in highway scenarios using an analytical approach. Using the Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) protocol, the IEEE 802.11p system suffers from the hidden station problem. This thesis provides formal definitions for the hidden station condition and the hidden station problem and develops an analytical methodology for CSMA protocols to investigate the interaction between stations in mutual channel sensing range and hidden to each other. Analytical models are developed for broadcast communication using the generic CSMA protocol and the IEEE 802.11p MAC protocol with a one-dimensional (1-D) homogeneous network topology. Simulation studies prove the accuracy of the models in analyzing the reliability performance and the efficiency performance of CSMA broadcast communication with hidden stations.

The performance of Cooperative Awareness Message (CAM) in IEEE 802.11p network is analyzed for highway scenarios using the developed analytical models. The study reveals that in a hidden station scenario the reliability performance of the CAM broadcast communication deteriorates with increased topological distance between the transmitter and the receiver. This study provides quantitative analysis of this performance with respect to network density, frame length, traffic load and settings of the IEEE 802.11p MAC protocol. Analysis of the mean update interval of CAM at a receiver vehicle discovers though in general the performance degrades with increased network density, the update interval of CAM frames from a particular vehicle in the vicinity of the receiver, e.g. with a topological distance less than 8 between the transmitter and the receiver, can be easily maintained below 1 second by using control mechanisms like transmit power control, transmit rate control and link control. The analytical models developed in this work provide quantitative guidance on optimizing protocol parameters and utilization of these control mechanisms.