Digital interfaces are driving data in the automotive sector
The software-defined vehicle is fast becoming a reality. Engineers continue to explore the dramatic rise of in-vehicle networking and how it evolves to meet automotive industry demand.
Vehicle design has changed considerably over the past 40 years. What started with mechanical enhancements of power steering and anti-lock brakes also led to an evolution in electrical controls and gauges.
Our modern vehicles may still meet Henry Ford’s purpose, but they operate entirely differently. They are a hotbed of interconnected electronic systems, and this trend is accelerating with the growth of battery-electric vehicles and fully autonomous self-driving capabilities.
The electronic control unit (ECU) has been a key vehicle function since the mid-1970s when it optimized the management of the engine's fuel injection and timing. Electronic systems found their way into more vehicle functions, from the transmission to comfort controls and suspension to traction controls. As this happened, the number of ECUs increased. Initially, each ECU performed a single function, with little or no interaction.
Once the number of ECUs in some vehicle models reached over 150, the automotive industry spent the next two decades consolidating them into domains, such as body and drivetrain. The increasing use of sensors and interaction between disparate functions has emphasized the need for better in-vehicle networking.
In-vehicle networking evolution
Industry-standard connection between ECUs, sensors and actuators already exists. In the mid-1990s, the Society of Automotive Engineers (SAE) established the J1939 specification for ECU interconnectivity. This standard introduced the message-based controller area network (CAN) protocol, which has been used for high-speed, in-vehicle networking for decades. Together with CAN, other legacy lower-speed serial bus and multi-drop network protocols such as FlexRay, Media Oriented System Transport (MOST), and Local Interconnect Network (LIN) are at the center of attention as automotive E/E (electrical/electronic) architecture engineers struggle to keep up with the demand for high-speed networks.
When introduced, the maximum data rate for CAN was only 150 kb/s. Over time, improvements led to the development of the 10 Mb/s CAN-FD (flexible data rate) standard. The recently ratified CAN XL standard extends bandwidth up to 20 Mb/s.
Even with double the data rate, technologies such as advanced driver assistance systems still demand more. Vision-based sensors, front-facing mmWave radar, and LiDAR are becoming extremely popular for safety and security functions. Examples include lane departure warning, emergency braking and adaptive cruise control. These all require ultra-reliable, high-bandwidth, low-latency networking to operate effectively.
Ethernet, the dominant IP-based enterprise networking protocol, has been adapted for automotive purposes. The essential differences between Ethernet and Automotive Ethernet (100Base-T1, 1000Base-T1, and 10Base-T1S - 10 Mb/s to 1 Gb/s) are in the physical layer. The benefit is lower-cost, more compact, and much lighter single shielded or unshielded twisted pair cables. This Ethernet approach is called single-pair Ethernet (SPE), a physical media interface that’s also gaining rapid adoption in other market sectors, such as industrial automation.
But more electronic systems still require more copper wiring. Heavy looms are needed to interconnect ECUs, sensors, actuators and infotainment human machine interfaces. This presents automotive E/E executives with challenges.
The additional weight of cabling and systems is a significant challenge, particularly for battery electric vehicles, where the weight dictates range. Wiring harnesses are getting heavier, bulkier, and increasingly complex to design and fit. Consequently, automotive engineers are migrating platforms from a domain-based approach toward a zonal architecture.
From domain-centric approach to fully zone-based architecture
With an increasing interdependence on interconnected systems, the role of a single-vehicle server or gateway is gaining popularity. As such, the software-defined vehicle is fast becoming a reality.
A domain wiring approach uses costly, lengthy and heavy wiring harnesses. A zonal system uses a redundant Ethernet network backbone to serve each zone and connect all major vehicle functions.
Engineers are removing chaotic domain wiring and replacing it with a central server and a zonal architecture. (Source: NXP)
Aggregating multiple ECU functions into a central server and off-loading or delegating specific edge tasks (window controls, etc.) to zonal controllers — all linked with an automotive Ethernet backbone — saves weight and reduces complexity. This approach also allows for converting some vehicle functions into software services, leading toward the software-defined vehicle, a goal deemed necessary for a fully autonomous vehicle.
Besides the physical layer benefits of automotive Ethernet, the protocol brings several desirable features and recent enhancements originally developed for industrial applications. Of note is time-sensitive networking (TSN), which delivers a deterministic network behavior essential for critical safety functions.
There is no doubt that, in time, Ethernet will replace CAN. In the meantime, the automotive industry will continue to deploy CAN and other slower-speed networks. CAN suits several applications which, as yet, Ethernet is either too costly or too complex to replace.
Aside from the rise of the Ethernet protocol for in-vehicle networking, the need for high-speed application-specific interface protocols opens the opportunity for new standards. An example is the Mobile Industry Processor Interface (MIPI) A-PHY, an asymmetrical point-to-point or daisy-chain interface protocol that provides an ultra-high speed unidirectional data link of up to 16 Gb/s and power delivery using a single unshielded twisted pair (UTP) cable. MIPI A-PHY is the only automotive interface natively supporting the MIPI CSI-2 camera and DSI-2 display interfaces. The interface is ideal for advanced driver assistance systems and infotainment applications.
In-vehicle networking accelerates
Vehicle technologies have advanced considerably over the past 40 years. Sleek, intuitive and informative touchscreens have replaced analog gauges and switches. Modern vehicles are also much safer, featuring ADAS functions such as emergency braking and blind spot detection.
Because it generates so much data, the car is often described as a data center on wheels. And just like any data center, our cars rely on reliable and robust networking to operate safely and reliably.