Semester

Fall

Date of Graduation

2013

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Lane Department of Computer Science and Electrical Engineering

Committee Chair

Yaser P. Fallah

Committee Co-Chair

Parviz Famouri

Committee Member

Tim Menzies

Abstract

Cooperative vehicle safety (CVS) systems operate based on broadcast of vehicle position and safety information to neighboring cars. The communication medium of CVS is a Dedicated Short Range Communication (DSRC) wireless channel. One of the main challenges in large scale deployment of CVS systems is the issue of scalability. To address the scalability problem, several congestion control methods have been proposed and are currently under field study. These mechanisms adapt transmission rate and power, based on network measures such as: Channel Busy Ratio (CBR), packet reception rate and vehicles tracking error. Channel Busy Ratio (CBR) is defined as the ratio of time that the channel is sensed busy during a time slot. We examine two such algorithms named Linear Memoryless Range Control (LMRC) and Gradient Descent Range Control (GRC). The dynamic behavior of these algorithms over time and space has been studied to evaluate temporal stability and spatial fairness. Moreover we have introduced a novel congestion control mechanism named Stateful Utilization-Based Power Adaptation (SUPRA) which is fundamentally a stateful version of LMRC algorithm to control power of transmission in contrast to Range Control algorithms. The control function of SUPRA has the ability to be tailored to different road conditions from low to high densities and different rates of transmission. The stability of the algorithm is proven through complete analysis of control function and verified in numerous simulation runs for typical road scenarios.Fairness is another issue which is probable to happen in different scenarios. An Unfair situation is when cars having the same density and rate of transmission, do not have analogous share of the channel. We have proposed a distributed mechanism to resolve the issue of unfairness. In this method each node sends out its sensed CBR along with safety messages to neighboring nodes, so each node will have access to all CBRs received from neighbors as well as its own measured CBR. This will provide a wide-ranging view of the whole channel and consequently adaptation of range/power of transmission will be done based on an aggregation of all these CBR values.

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