Optimizing the Control Channel Interval of the DSRC for Vehicular Safety Applications

Dedicated short-range communication (DSRC) technology has been adopted by the IEEE community to enable safety and nonsafety applications for vehicular ad hoc networks. To better serve these two classes of applications, the DSRC standard divides the bandwidth into seven channels. One channel, which is called the control channel (CCH), serves safety applications, and the other six channels, which are called service channels, serve nonsafety applications. The DSRC standard specifies a channel-switching scheme to allow vehicles to alternate between these two classes of applications. The standard also recommends that vehicles should visit the CCH every 100 ms, which is called the synchronization interval (SI), to send and receive their status messages. It is highly desirable that these status messages be delivered to the neighboring vehicles reliably and within an acceptable delay bound. It is obvious that increasing the time share of the CCH from the SI will increase the reliability of safety applications. In this paper, we propose two algorithms to optimize the length of the control channel interval (CCI) such that nonsafety applications have a fair share of the SI interval. One algorithm, which is called optimal channel access, is proposed to allow vehicles to access the channel with a derived optimal probability such that the successful transmission rate is maximized. The second algorithm, which is called the mobility- and topology-aware algorithm, is an adaptive scheme proposed to change the DSRC parameters based on the road and network conditions to allow the coexistence of safety and nonsafety applications on the DSRC. Vehicles will execute both algorithms in a distributed manner to achieve a high success rate within the selected CCI interval. The simulation results show that using the two new algorithms keeps the CCI below half of the SI in all scenarios while maintaining a high success rate for safety messages. This will give nonsafety applications the opportunity to work in the second half of the SI interval without jeopardizing the critical safety applications.