This paper presents a qualitative study of FlexRay and Ethernet in in-vehicle communication networks. Although both protocols have experienced fast growth in the past years, they still have some important deficiencies that deserve attention. This qualitative study has not only outlined the important shortcomings of in-vehicle FlexRay and Ethernet, but also identified their unique competitive edges, respectively. Intensive analyses of both protocols are carried out from three key perspectives: system cost, data transmission capacity and fault detection capability. Some improving approaches have also been pointed out. It is revealed that at the current stage FlexRay is better than Ethernet in transmitting time critical signals deterministically, but has higher cost and complexity. Ethernet, though less deterministic than FlexRay, possesses much greater bandwidth and can transmit data at quite small latency and jitter. This qualitative study has indicated that both protocols need further improvement to meet the requirements of future in-vehicle networks, yet Ethernet may lead the development and expand faster.
I. INTRODUCTIONEncoded communication channels have long been used to transmit signals among different controllers in in-vehicle networks. The typical motivations for this fact are: 1) To reduce cable cost. Since wire harness subsystem is the third most expensive and heaviest subsystem after engine and chassis [1], adopting coded communication is obviously a wise strategy to follow. 2) To save package space. As vehicles are built smaller in size but more enriched in functions, routing of wire harness has become increasingly challenging. 3) To cater the demands for higher bandwidth. Nowadays some luxury cars, even not fully featured, already have more than 70 ECUs and 2500 signals to transmit [2], letting alone accommodating the rising demands from ADAS and infotainment systems. 4) To enhance communication safety. Digital transmission has unparalleled advantages in resisting external disturbance over traditional point-to-point analog wires. Moreover, digital signals can be encrypted to further enhance data security in transmission.After LIN (Local Interconnect Network) and CAN (Controller Area Network), FlexRay and Ethernet are two most recently developed wired in-vehicle communication networks. FlexRay was firstly public released in 2004 and has gradually become an ISO standard after 2009. FlexRay is commonly understood as the protocol for X-by-Wire applications, and can provide deterministic communication for chassis and vehicle dynamic controls. BMW is the first