Stable and Fair Power Control in Vehicle Safety Networks

Cooperative vehicle safety (CVS) systems operate based on frequent broadcast of vehicle state (e.g., position, heading, and speed) and safety information to other vehicles over a wireless local area network. Such networks are formed using dedicated short-range communications (DSRC) technology. In crowded networks, the shared wireless channel may become congested and fail to deliver the broadcast information, potentially affecting the reliability of CVS applications. This issue, which is known as a scalability issue, has been identified as one of the challenges to be addressed with high-scale deployment of vehicle safety networks. Several scalability algorithms have been recently introduced and studied in the literature; currently, a select number of algorithms are under study by industry for possible adoption and standardization. One method used by some algorithms is congestion control through power or range adaptation. In this paper, we analyze two existing range control algorithms in terms of time stability and spatial fairness. We derive stability conditions for the main range control scheme that is currently under study. An improved algorithm that relaxes these conditions is then proposed, and its convergence properties are studied in detail. We show that the algorithm is stable and can be controlled to quickly converge to desired operation points. Finally, fairness properties of several power control schemes are studied, and an enhancement method is presented that ensures that spatial fairness is achieved by the presented power control schemes.