The IEEE 802.15.4 protocol is designed to flexibly support both real-time and contention-based services. When the beacon model is enabled, Guaranteed Time Slot (GTS) scheduling can provide contention-free access to latency-sensitive services based on the time division multiple access mechanism. This characteristic makes IEEE 802.15.4 the appropriate candidate for Vehicular Sensor Networks in which mobile nodes need to exchange packets with roadside units within a limited duration. In this paper, using network calculus theory, we analyzed the relationship between time slots utilization and corresponding access parameters, such as packet arrival rate, burst size and vehicles' mobility extent. Then, for a given number of vehicles preparing to access a roadside unit, we proposed a Time-Sensitive Weighted Round Robin scheduler (TS-WRR) to improve the multiple-access performance which can take the service delay requirement, packet arrival rate and vehicular mobility level into account. Next, the weight determination and time-slot allocation strategy of TS-WRR were issued in detail which incorporate the special limitations and application requirements in a V2I(Vehicle-toInfrastructure) communication environment. To make our model feasible for testing, we also elaborately demonstrated the implementation procedure with pseudo-code and simulator design. Numerical results show that our TS-WRR scheduler outperforms some classic schedulers such as FCFS and WRR as well as two latest works, i.e. i-GAME and ARG-GAS in terms of delay guarantee and GTS utilization maximization in Vehicular Sensor Networks.
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