I. Why is Ethernet only being used in automobiles now?
Automotive Ethernet is a physical network used to connect components within a vehicle using a wired network. It meets market requirements for electromagnetic interference/radio frequency interference (EMI/RFI), including requirements for network emissions and compliance with radio frequency interference (RFI) regulations.
To fully meet automotive requirements, the IEEE 802.3 and 802.1 groups are working on several new specifications and revisions. Until some specific IEEE specifications are adopted, there are currently provisional specifications.
BroadReach is a provider of open Ethernet solutions from Broadreach. This 100Mbps physical implementation uses technology from 1G Ethernet to enable 100Mbps transmission over a single pair of bidirectional transmissions (using echo cancellation), and uses more advanced coding to reduce the baseband to 66MHz (from 125MHz), thus enabling Ethernet to meet automotive EMI/RFI specifications. AVnu adopted the audio/video bridging standard prior to the IEEE 802.1 standardization process.
Although Ethernet has been around for over 20 years, it was previously unusable in automobiles due to the following limitations:
Ethernet does not meet the OEM/RFI requirements of the automotive market. Ethernet at 100 Mbps (and above) has too much radio frequency "noise," and it is also susceptible to "external" noise from other devices within the vehicle. Ethernet cannot guarantee latency reduction to the low microsecond range. This is intended to replace communication with any sensors/control devices requiring fast response times. Ethernet lacks a method for controlling bandwidth allocation across different streams, therefore it cannot be used to transmit shared data from multiple types of sources. Ethernet lacks a method for synchronizing time between devices and allowing multiple devices to sample data simultaneously.
II. Understanding the Automotive Ethernet Transmission Channel
Today, automotive networks have evolved to include mature PHY layer protocols such as CAN(FD), LIN, FlexRay, and MOST, as well as widely used link transmission methods based on LVDS/USB technology. However, over time, these protocols and technologies have gradually become inadequate for current transmission needs. For example, CAN(FD) and LIN have maximum transmission rates of 2 Mbit/s and 19.2 Mbit/s respectively, far from meeting the demands of large-scale applications. They are still used for powertrain ECU control only due to their high stability and fast response. FlexRay supports relatively low data transmission rates and is more complex than CAN(FD) and LIN. Coupled with weak promotion from relevant organizations, even with a high degree of protocol completion, few manufacturers have actually adopted it in their chassis or transmission systems.
Due to its excellent transmission properties, optical fiber has always been favored by some manufacturers for its use in automotive applications. In the 1990s, there was a surge in demand for automotive audio transmission. Before the application of optical fiber, there was no suitable transmission system to support it. At that time, Japanese plastic optical fiber technology was maturing, and the fragility of traditional glass optical fiber was being overcome. Taking advantage of this favorable situation, the MOST protocol, based on optical transmission, emerged. It quickly experienced significant development and was even briefly used for video data transmission. However, although its maximum speed eventually reached MOST150, accompanied by the introduction of lower-cost coaxial solutions, the high monopoly nature of MOST resulted in poor scalability and compatibility.
By 2012, the 150 Mbit/s speed was no longer sufficient to meet the higher transmission demands of high-definition video, image data, and high-definition and ultra-high-definition cameras used in ADAS applications. For example, a typical 720P high-definition camera, without compression, requires a transmission rate of approximately 1.6 Gbps. The inherent EMI resistance and high-speed support of LVDS links have made them extremely popular in similar applications in recent years. USB, with its more specific connection methods and testing procedures, is also widely used for trunk transmission in automotive networks. However, both LVDS and USB significantly increase the complexity of vehicle wiring and the types of specialized cables used.
Given the above circumstances and current situation, automotive engineers have been considering whether it's possible to introduce a widely applicable protocol that supports high-speed transmission, standardizes link connection methods, reduces the types of links in the vehicle, lowers costs, and allows for easy and streamlined connectivity to the world. Ultimately, Ethernet, born in the 1970s, was chosen due to its various adaptable characteristics. Admittedly, the birth of automotive Ethernet had an element of chance, but it was precisely because of the initial decision and persistence of BMW engineers that automotive Ethernet has been able to develop healthily and rapidly to its current state.
