History and Development of Automotive Ethernet
In IT, Ethernet has a long and extremely successful history. Invented in 1973 and standardized by the Institute of Electrical and Electronics Engineers (IEEE) in 1985, Ethernet has since come to dominate local area networks used in business and fend off competition from all other competing technologies such as Token Ring. For decades, Ethernet has proven to be a versatile and flexible standard network that drives advancements in communications. Different versions of Ethernet run on coaxial cables, fiber optics, and unshielded twisted pair wires, and speeds have also increased from 10M bit/s to over 100G bit/s. After decades of application, people's understanding of Ethernet
The solution is already very adequate and a good improvement has been made.
As the in-vehicle network begins to connect more in-vehicle computing resources, the application of Ethernet has become a natural choice, so in 2016, IEEE released the first automotive Ethernet standard IEEE 802.3bw, or 100Base-T1. Although 100M bit/s bandwidth is comparable to 100Base-TX introduced in 1995, there are still key differences in the automotive version.
Both of these standards run on unshielded twisted pair, which is two copper wires twisted together along the length of the cable. This has the effect of producing less electromagnetic radiation and crosstalk, avoiding interference with other wires or components, and resisting interference from other sources.
However, 100Base-TX uses two twisted pairs, whereas Automotive Ethernet uses only one pair, resulting in lower weight and cost. This pair of wires is "balanced", meaning that the signals have equal but opposite voltages. Both the transmit signal and the receive signal are conducted on one set of twisted pairs, instead of using two different sets of twisted pairs like 100Base-TX.
In the 100Base-TX standard, a maximum length of 100 meters is also specified, which is followed by subsequent Ethernet standards. Automotive Ethernet has a specified maximum length of only 15 meters. Clearly, automotive applications do not require long distances between network components in the car, and the shorter the length, the lighter the wiring.
Another key difference is the encoding done by the transceivers at both ends of the cable.
The 100Base-TX standard uses Multi-Level Baseband Coding (MLT-3), which encodes bits on the wire by cycling through three voltage levels, while Automotive Ethernet uses three-level Pulse Amplitude Modulation (PAM- 3), By bit-encoding the amplitude of the signal pulse, more bits can be encoded in each clock cycle. Combined with other encoding techniques, the final frequency can be reduced from 125 MHz to 66.6 MHz, again helping to prevent EMI and crosstalk.
Subsequent Developments in Automotive Ethernet
The 100M bit/s of the IEEE 802.3bw standard can satisfy many basic automotive applications, so it is widely used today. But higher speeds will be required as engineers consider higher-definition video streaming and the aggregation of data from multiple sensors onto common cables.
Shortly after IEEE 802.3bw was finalized, the IEEE officially ratified the 802.3bp standard, or 1000Base-T1, which enables gigabit speeds over shielded or unshielded twisted-pair wire. This standard shares much in common with its predecessor, but at a frequency nearly 10 times higher, at 600 MHz. This means the cables are more susceptible to crosstalk, so engineers need to design systems with special care to control electromagnetic noise throughout the vehicle, rigorously testing and shielding where required. The standard will provide sufficient bandwidth for the next two to three generations of platforms.
In 2020, IEEE formulated the 802.3ch standard, which can also support Gigabit Ethernet at standard rates such as 2.5G bit/s, 5G bit/s and 10G bit/s within a distance of 15 meters. Shielded twisted pair cables will be sufficient for the above transmission speeds, but frequencies above 7 GHz may require shielded parallel pair cables to minimize EMI issues.
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