Should there be a strong focus on having just one network inside the car?
Cars in the 1960s such as the Hillman Hunter (Figure 1), built by the Hillman Motor Car Company based in Coventry, England, had only about 50 wires totaling about 100 feet in length in their harness. Compare that to today’s cars that have more than 1500 wires that can total close to 1.5 miles in length and weigh more than 100 pounds. The harness may be getting heavier; automotive manufacturers state that the weight has jumped by about 30% in just one model evolution, with the integration of autonomous technologies. So, there should to be a strong focus on having just one network inside the auto, right?
Well, the answer is complicated.
Bandwidth Requirements for the Future IVN
The requirements for the in-vehicle network (IVN) include high bandwidth, low latency, and high reliability to operate in the harsh operating environment of the automobile. Over the years, there has been multiple technologies such as analog, controller area network (CAN), FlexRay, local interconnect network (LIN), low voltage differential signaling (LVDS), and media oriented systems transport (MOST) that have been used for the IVN (Figure 2).
When we look at next-generation applications, these legacy technologies cannot support the bandwidth requirements; moreover, some are proprietary and high in cost.
To get a better understanding of the bandwidth requirements, remember the approximate bit rate of a video stream can be calculated as:
So, for an Advanced Driver-Assistance Systems (ADAS) camera capturing a 1080p image with a color depth of 24-bits and transmitting at 30 fps, the bit rate to be supported equals:
The Table below shows typical volumes of data from the different sensors involved in autonomous driving:
SENSOR | DATA/SENSOR |
Camera | 500-3500 Mbps |
Lidar | 20-100 Mbps |
Radar | 0.1-15 Mbps |
Ultrasound | 0.01 Mbps |
Multiple Competing Standards for the IVN
Is the IVN Ethernet, SERDES, or Both?
Some automotive manufacturers and Tier 1 suppliers feel for a few initial years; we may see both standards. However, after that, automotive Ethernet with data rates up to 100Gbps will subsume all others.
Kirsten Matheus, engineer at BMW, might have a slightly different point of view. She has suggested that SERDES is necessary and the right technology for ADAS sensor connections that carry asymmetric data point-to-point; whereas Ethernet is a networking technology good for other automotive applications. Considering that Kirsten played a key role in the standardization of automotive Ethernet, her views should hold some weight (Source: Automotive SerDes Alliance kick-off, May 2019, Salt Lake City).
Automotive OEMs that are trying to finetune their IVN roadmaps, could adopt one of two strategies:
Testing of the IVN
As far as testing of the IVN is concerned, it is important to test transmitter, receiver, and channel performance. With hundreds of tests to be performed, automated compliance test software with interpretation of specifications, repeatable results, setup wizards with user-friendly GUIs, and report generation are just as important for automotive engineers as technical specs such as bandwidths, sampling speeds, and signal resolution.
Transmitter testing is completed mostly with an oscilloscope to ensure signals being sent are not the cause of impurities; while receiver testing is completed to check accurate detection of input signals—using signal stimulus or arbitrary waveform generators. Impedance and return loss measurements are important in time and frequency domains to ensure reliable system performance and to diagnose signal integrity issues.
Conclusion
The automotive industry has come a long way since the days of the Hillman Hunter. Advances towards autonomous and connected vehicles bring challenges that must be addressed by the in-vehicle network. The multiplicity of sensors, controls, and interfaces required for ADAS and new infotainment features require high-bandwidth connections—traditional networks such as CAN, MOST, and FlexRay will not suffice. With the advent of new standards such as automotive Ethernet and SERDES, faster data communications are possible and the needs of future connected vehicles can be met.
About the Author
Alan A. Varghese is responsible for automotive technology and marketing at Keysight Technologies.
Prior to Keysight, Alan served as an industry and technology analyst covering wireless, IoT, automotive, semiconductors, cable and optical, image and video, artificial intelligence and machine learning markets. He advised companies on their strategy and roadmaps, did specialized market/technology research, and SWOT and business model analyses. He started his career as a digital signal processing engineer working on handset modems, and holds a MSEE in wireless communications and DSP from Rensselaer Polytechnic Institute, Troy, New York.