# A Reliability Scheduling Algorithm for the Static Segment of FlexRay on Vehicle Networks +
## 1 Introduction  
Next-generation automotive systems will be equipped with an increasing number of components, such as electronic control units (ECUs) and sensors, which are connected through various buses. In order to deal with the amount of data and signals between ECUs or sensor nodes, traditional point-to-point communication has been replaced by vehicle networks such as controller area network (CAN) and FlexRay [1]. Modern automotive systems are moving from CAN to FlexRay. FlexRay is an automotive networking standard, and it has been increasingly adopted in the vehicle dynamics domain and inter-domain communications [2]. The advantages of FlexRay are its real-time operation, flexibility, a maximum data rate of up to 10 Mb/s, two communication channels, precise control and fault tolerance when compared with other vehicle networks. These characteristics mean that FlexRay is a fast and dependable network protocol and is often used for new safety features, such as X-by-wire [3] applications, where deterministic performance is critical. In a FlexRay bus, the communication cycle level consists of static segments, dynamic segments, symbol windows, and network idle time. Static segments were designed using a time-division multiple-access (TDMA) mechanism, and are accessed by time-triggering for safety-critical systems such as drive-by-wire, adaptive cruise control(ACC), and anticlock braking systems (ABS) [4; 5]. However, radiation, crosstalk, electromagnetic interference (EMI) and power supply noise in the environment cause a lot of interference for the vehicle network [6]. If a transient fault occurs, it will result in transmission delay, data loss, and a miscalculation in logic, which is very dangerous during driving. However, FlexRay does not have an application layer scheme to avoid transient faults in the static segment. The time slot of the static segment is used to store messages which should be transmitted periodically. Therefore, many studies have been performed on how to offer increased reliability for FlexRay. First, [PERSON] et al. [7] formulated the scheduling problem as a mixed integer linear program. This method improves scheduling by minimizing the latencies of the acknowledgement and re-transmission messages, but this work offers no guarantees for reliability. In contrast to [7], [PERSON] et al. [8] proposed an algorithm which provides formal guarantees that the generated fault-tolerant message is scheduled in the static segment of FlexRay. However, this algorithm cannot generate the optimal retransmission scheme to reduce the slot utilization. In [9], [PERSON] et al. proposed a heuristic algorithm H-I method. They designed an evaluation function to determine which message should be re-transmitted, and its performance is better for bandwidth utilization and execution time than [PERSON]'s method [8]. The work in [10] by [PERSON] et al. proposed a method to ensure the reliability of systems using a reliability three-step (RTS) method. This method cannot satisfy the system reliability goal when the number of messages exceeds 25 because the slot utilization has reached 100%; this means that there is an insufficient number of slots to use in the testing time (\(\tau\)). [PERSON] et al. [11] proposed a frame-packing algorithm based on transmission reliability (FPBTR) to optimize signal combinations and static slot allocations. However, the FPBTR method will have a greater time cost for meeting the demands of the desired reliability. [PERSON] et al. [12] proposed a prompt retransmission mechanism (PRTM) method to ensure the safety-critical communications of FlexRay; they pointed out that retransmission should be studied to optimize the bandwidth utilization. For these reasons, we proposed a new fast reliability scheduling algorithm (FRSA) by considering the low complexity and optimized static slot allocations in [13].