Spectrum Sharing between DSRC and WiFi: A Repeated Game Approach

We model the coexistence of Dedicated Short Range Communications (DSRC) and WiFi networks, when they access a shared wireless medium, as a repeated game. Both the networks use a similar CSMA/CA like medium access mechanism. However, while a DSRC network cares for the freshness of status updates and desires to minimize the age of received updates, a WiFi network would like to maximize throughput. We define the stage game, which is parameterized by the average age of the DSRC network at the beginning of the stage, and derive its mixed strategy Nash equilibrium. We study the evolution of the equilibrium strategies over time and the resulting average discounted payoffs of the networks. It turns out that DSRC's requirement of timely updates works in favour of WiFi, making spectrum sharing with DSRC favorable for a WiFi network in comparison to sharing with another WiFi network. Specifically, as we show, the equilibrium strategy has the DSRC network, given its requirement of timeliness, occasionally refrain from transmitting during a stage. Such stages allow the WiFi network competition free access to the medium.