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86 a high-speed serial link over a lighter shielded twisted-pair cable (STP) rather than coaxial. This would carry higher speed camera data up to 12 Gbit/s around the vehicle in point-to-point links. Ethernet Although Ethernet is increasingly accepted as the mainstream technology for the backbone network in an autonomous vehicle, there are still issues with its adoption because of the complexity and weight of the harness. Traditional Ethernet cables used for 100Base-TX, based on two differential pair wires and isolated by transformers, are too expensive for automotive applications. Moreover, the Category 5 cable used in offices for Gigabit Ethernet doesn’t meet automotive EMI standards, making the current low-cost Ethernet unsuitable for in-car comms. Data transport also has to support synchronisation, traffic shaping and fixed latency, but standard Ethernet doesn’t have that kind of support unless new protocol stacks are implemented. So, the 100Base-T1 IEEE 802.3bw standard provides 100 Mbit/s over a UTP bidirectional cable that meets automotive emissions requirements. The EMI is reduced by using the superposition, specific encoding and scrambling schemes. To support automotive applications, Ethernet needs additional software that provides determinism. This can be achieved by the AVB protocol, developed within the IEEE 802.1 standard; the IEEE is the organisation in charge of the second layer in the ISO/OSI model to provide time synchronisation and traffic shaping to carry audio and video content reliably. AVB led to the definition of a set of protocols known as time-sensitive networking (TSN), providing Ethernet with real-time support. IEEE 802.3bw plus TSN can provide deterministic comms to the cabin on an autonomous vehicle, and is evolving to a new 1000Base-T1 standard that can reach 1 Gbit/s. The latest protocol standards are moving to 5, 10 and 25 Gbit/s; 50 Gbit/s versions are also being developed. Industrial and enterprise applications in data centres have been driving the development of high-speed Ethernet protocols, but the automotive market needs simpler, more rugged implementations. That means there are more interface standards being defined. Ethernet interface standards There are several key interface standards for automotive Ethernet as data rates grow. The media-independent interface (MII) was originally defined as a standard interface to connect a Fast Ethernet 100 Mbit/s digital media access control (MAC) block to the PHY chip that handles the physical interface. This was standardised as IEEE 802.3u, and allows different types of physical interfaces such as UTP, STP or fibre without redesigning or replacing the MAC, which is clocked at 25 MHz to provide the 100 Mbit/s throughput. This MII design has been extended for reduced signals and increased speeds, both of which are needed in automotive designs. The reduced media- independent interface (RMII) cuts down the number of pins on the MAC and PHY, while the gigabit media-independent interface (GMII) supports higher speeds and is a spin-off from a reduced gigabit April/May 2020 | Unmanned Systems Technology Multiple screens in the cabin of a driverless vehicle increase the vehicle’s data requirements (Courtesy of Panasonic) Optical fibre can be used to deliver data at up to 25 Gbit/s in an autonomous vehicle (Courtesy of KDPOF)