Time Triggered Scheduling Algorithm for Real-Time Wireless Systems

Time Sensitive Networking (TSN) is a group of standards to improve reliability, minimize jitter and ensure bounded latency by using scheduled traffic for safety critical real-time applications. Recently, the incorporation of Time-Triggered (TT) wireless technology into this kind of networked systems has been proposed because of its flexibility and easy design. Despite these benefits, the mutual interference between signals must be considered depending on the transmission intervals and the spatial proximity. Interference may prevent reception, cause the corruption of signals or affect on the signal quality. Most of the scheduling algorithms consider either the perspective of scheduling and routing restrictions, or the impact of interference on the wireless scheduling solutions. To address the interference restrictions besides the scheduling and routing restrictions, a Wireless Heuristic List Scheduler (WHLS) is proposed in this paper to determine the schedule. In this algorithm, TT messages of the computational jobs use the optimal routes with minimum latency from all available routes. In addition, the message is fragmented according to the time-slot size and assigned to several time-slots. In each time-slot all messages can be transmitted simultaneously by using a physical interference model. WHLS supports multi-cast communication while respecting the precedence constraints between computation jobs and periodicity restrictions. To evaluate the proposed scheduler, a basic List Scheduler (LS) that uses a static route (the least hop count) is implemented. The experimental results show that WHLS outperforms LS in all simulation tests, where schedulability, make span and execution time are used as parameters.