Studies Of FlexRay Network Reliability Based On Static Segment Parameters Optimization

For cars, people have put forwards higher requirements in terms of many aspects, such as safety, comfort, economy, environmental protection and so on. These ever-increasing needs have made cars keep on developing towards electronic, networked and intelligent direction. A new generation of automotive electronic control system possesses more complicated network structure and communicate larger amount of data. In this case, the system must be designed with higher reliability and faster function expansion speed. Traditional vehicle network is difficult to satisfy the requirements of this system. As the next the next generation of on-board network protocol, the functional security of Flex Ray is of great importance. We choose the network reliability of FlexRay as the entry point in this thesis. The main work is as follows:In order to improve the network reliability, we analyze FlexRay network static segment reliability and set up active retransmission mechanism in the application layer. Considering from these two points of view: static segment parameter optimization and message retransmission optimization, message retransmission scheduling success ratio is improved by optimizing network bandwidth utilization and cutting down time slots consumption.Under the constraints of network bandwidth utilization, we propose the signal priority packing method for static segment parameter optimization. In this way, invalid bandwidth consumption can be reduced effectively. On the basis of packed signals, time slots multiplexing method is used to optimize the distribution of frame identifiers(FID) and reduce the consumption number of time slots. Before creating message retransmission mechanism, network bandwidth utilization can be optimized by static segment parameter optimization. Thus, under the same condition of network reliability, message retransmission network bandwidth consumption will decrease.Reliability contribution rate is defined as a criterion to select retransmission messages. Retransmission reliability contribution and network bandwidth retransmission consumption are both taken into consideration when computing reliability contribution rate. By using this criterion, we setup message retransmission sequence to enhance efficiency of reliability improvement. Meanwhile we establish reference message retransmission sequence which is used to bring down message retransmission scheduling failures. For message retransmission sequence scheduling, the allocation of retransmission frame identifiers is optimized by adopting message multiplexing mechanism. Calculations show that this message retransmission scheme can effectively lower bandwidth consumption and reduce the number of time slots when improving reliability. What’s more, it can also reduce message retransmission sequences scheduling failures, so as to improve the reliability of Flex Ray network.