Research On Scheduling Strategy Of CAN Protocol For Automotive Network

As the rapid development of electronic control technology, computer network technology and communication technology in vehicle, automobile is developing towards multifunctional direction, the trend of intelligence and network is becoming more and more evidential. Vehicle is composed of several intricate sub-systems and its whole performance depends on the cooperative operation of all sub-systems. Through the development for many years, Controller Area Network (CAN) has become backbone of multi-hierarchy network in vehicle, so, researches on automotive network key theories based on CAN protocol have profound significances on further development of intellectualization and network trend for vehicle.CAN bus is multi-master system base on event-trigger mechanism, the maximum bandwidth of CAN bus is limited to1MB/s, CAN protocol adopt bit by bit non-destructive arbitration technology in Medium Access Control layer, concerning the complicated vehicle utilization environment, there remains many requirements and demanding on predictability, real-time, reliability and bandwidth resources utilization ability of CAN protocol network. Therefore, how to design scheduling algorithm to improve real-time and flexible ability of various requirement, and how to ensure network dependability by real time analysis, how to improve bandwidth resource utilization have become a challenging topic in vehicle network designing.Automotive network designing based on CAN protocol constitutes of phases of vehicle body network designing, power train network designing and whole vehicle network designing, in this thesis, the research on modeling and optimization etc certain key scheduling theories of in those different phases are explored. The main works are as follows:1. As functionality of vehicles increases in complexity, the demand on the in-vehicle networks increases as well. Maximum bus utilization often becomes the communication bottleneck. To solve these problems, a data reduction change first (DRCF) algorithm to reduce the amount of data and schedule messages to be transferred on vehicle body CAN bus is introduced. The principle of data encoding, decoding and scheduling algorithm is given. Through simulation, the performance of this new algorithm method will be shown in terms of message latency, transmission efficiency and bus utilization.2. Aiming at improving response ability of lower priority messages and network utilization, adopt dynamic scheduling Earliest Deadline First(EDF) in power train high speed CAN bus designing, EDF scheduling is hardly to imply on Controller Area Network bus because the large scope of deadline of CAN bus messages while the bit sizes in CAN frame is limited, and it is necessary to guarantee strict time synchronization in all nodes so that all nodes can update their deadline priorities at the same time. To solve these problems, EDF algorithm based on CAN bus arbitration is proposed. The principle of EDF and schedulability analysis method is given.3. The event-triggered part of time-triggered controller area network (TTCAN) can not bound the response time of a given sporadic message accurately, when designing TTCAN distributed real-time system of automotive, it is necessary to analysis the transformation time of messages in advance to ensure the real-time properties of messages. Based on above analysis, the response time model of sporadic message in TTCAN system is proposed. Visual technology is an effective way for engineering designing and analysis, in this paper, the method of real-time analysis of sporadic messages in TTCAN asynchronous phase, and visualization software based on this method for real-time analysis of TTCAN with Visual C#is designed. Finally, the software is used to real-time analysis for an automotive TTCAN control system.4. Controller area network can not deal with event-triggered traffic and time-triggered traffic simultaneously and efficiently in real time system. To solve this problem, and considering the flexibility of in vehicle network designing and scheduling, flexible time triggered CAN (FTTCAN) was introduced to manage the power transmission system, then, FTTCAN and CAN that manage vehicle body system are used to build up the whole in-vehicle network by linking with gateway, the method of allotting messages in Scheduling Table in synchronous phase was introduced, the analysis result of system performances such as real time performance and dependability verifies the proposed scheme is feasible, and has perfect performance.5. To meet high performances of automotive time-triggered CAN real-time control bus, a key problem is how to distribute time windows within system matrix of TTCAN, a new correlative periods loading(CPL) scheduling optimization algorithm based on average loading was proposed, and the scheduling strategy was explained concretely. The CPL scheduling algorithm aimed to make event-triggered messages of system gain more transmission times by minimizing the space occupied by time-triggered messages.6. In view of the problems of uncertainty in scheduling periodic signals and the permanent block of lower priority message by higher one in the controller area network of electric vehicle control system, a compound-scheduling algorithm based on time-triggered controller area network is proposed, in which CPL algorithm is used to schedule periodic signals, and for scheduling random signals a modified earliest deadline first algorithm,.i.e. EDF scheduling priority programming algorithm is adopted. The methods of constructing the system matrix of TTCAN and schedulability analysis are also given. Finally the network performance of electric vehicle control system is analyzed, verifying the good scheduling performance of the compound scheduling algorithm proposed.7. To study designing and exploitation strategy of vehicle electric system, in order to establish contact between in-vehicle network and outside network, an information CAN experiment system make up of GPS, GPRS and traveling data recorder is designed, data collection and long distance monitor etc function will be realized trough the experiment system. System designing, simulation and integration testing of experiment system are studied through the experiment system.