Figure 1: A current-generation vehicle uses multiple communication standards: emerging applications will expand the number considerably. (Image Source: NXP)

It’s not news that the electronic content of an automobile takes up an ever-increasing percentage of its cost. In fact, it is estimated the electronic content will reach 35 percent of vehicle value by 2020, and 50 percent 10 years later (compared to only 15 percent as recently as 1990). Current luxury automobiles include up to 150 electronic control units (ECUs)—modules that control almost every aspect of vehicle operation, from fundamental functions such as engines, transmissions, and brakes, to infotainment and convenience features such as audio, video, and navigation.

Hand-in-hand with the increase in electronic modules has been the growth of networked vehicle communications to reduce wiring, sensor duplication, and weight. Inter-module communication has been steadily growing since the first vehicle added a second ECU and the two began exchanging data. Worldwide, the number of network nodes introduced each year continues to increase (Figure 2), almost doubling between 2016 and 2025. With a forecast growth in vehicle sales of 30 percent over the same period, this represents an increase in the number of nodes per vehicle from around 14 to over 20.

Figure 2: Vehicle networking nodes and nodes/vehicle will show steady growth. (Image Source: IHS Markit)

The variety of automotive requirements has spawned a proliferation in serial communication protocols. Automotive serial communication has a long history. GM’s Assembly Line Diagnostic Link (ALDL) protocol, for example, dates back to 1980: broadcasting at a leisurely 160 bits/sec (bps), it allowed testing of the engine control module during production. In the 1990s, the California Air Resources Board (CARB) required the inclusion of onboard diagnostics (OBD) capability for vehicles sold in California, and OBD-II became mandatory in 1996 for all vehicles sold in the United States. U.S. manufacturers implemented the J1850 serial data standard, with data speeds up to 41.6 kbps, but the OBD-II standard accommodates four additional protocols.

The Controller Area Network (CAN) and Local Interconnect Network (LIN) protocols are the most common standards in vehicles today. CAN dates back to 1986 when Tier-1 supplier Robert Bosch announced it at the SAE Detroit show. It’s now the ISO 11898-2 standard. CAN is a multi-master system that uses bitwise arbitration to resolve bus conflicts; standard high-speed CAN can attain 1 Mbps, but the latest ISO 11898-2 2015 specification includes flexible data rate operation (CAN FD) and can reach 12 Mbps.

CAN hardware is expensive, so in the late 1990s, the low-cost LIN protocol became a popular alternative for data rates up to 20 kbps; with a master-slave topology, it’s primarily used for communication between ECUs and mechatronic units such as seats, mirrors, and sun roofs.

Current vehicles also have low-speed serial networks for specialized applications: PSI-5 and DSI, for example, are used primarily in airbag and safety systems.

ADAS raises the protocol bar

It’s expected that LIN and CAN networks will continue to dominate general-purpose vehicle communication over the next decade, with CAN contributing about 65 percent of nodes and LIN most of the rest, but their speeds can’t satisfy the requirements of many newer applications. As a result, higher bandwidth protocols have begun to appear in automobiles. The options include both automotive versions of general-purpose standards such as Ethernet, and automotive-specific protocols like Media Oriented Systems Transport (MOST) for multimedia applications, and FlexRay for safety-critical systems.

Advanced driver assistance systems (ADAS) are a major contributor to the need for speed. ADAS includes a collection of functions that have a common goal: to help drivers avoid collisions by alerting them to potential problems and taking over control of the vehicle when necessary. Bandwidth-hungry ADAS functions include adaptive cruise control; lane departure warning systems; video, ultrasonic, radar and lidar sensors; online traffic alerts, and many more. ADAS is considered a necessary stepping-stone in the development of a fully autonomous vehicle. 

Figure 3: An ADAS vision system employs multiple protocols to transfer data from video sensors to a vision processor and then to a cockpit display. (Image Source: Texas Instruments)

Figure 3 illustrates the range of protocols needed for a typical ADAS application: an ADAS vision system with multiple remote sensor nodes that transmit high-speed video data to a central module. The system combines the data streams into images for a cockpit display. It can also process the image to extract useful information: detect obstacles, identify traffic signs, etc.

  • Image Sensor: The most widely-used sensor interface is the MIPI Alliance’s CSI-2, although, some image sensors output data in the parallel DVP (digital video port) format. This CSI-2 standard can support a broad range of high-performance applications including high-resolution photography and 1080p, 4K, or 8K video. An industry-standard I2C protocol provides control functions.
  • Serializer/Deserializer (SerDes): In this Texas Instruments design, FPD-Link transmits the high-speed digital video to the central module: it’s a power-over-coax (PoC) protocol that combines power, high-speed video, and low-speed bidirectional communication on a single coaxial cable. FPD-Link III, the latest version, replaces the low-voltage differential signal (LVDS) technology used in earlier generations with current-mode logic (CML), and can transmit data at 3 Gbit/s over cables of 10 meters or longer. MOST and Ethernet, including Power Over Ethernet (PoE), are competing options.
  • Cockpit Display: A variety of protocols can be used to drive the display, including consumer favorite HDMI.

Autonomous Vehicles represent a quantum jump in requirements

The communication protocols we’ve talked about thus far are wired systems, but the next stage will involve a massive increase in wireless communication capability.  

Of course, wireless systems have been in vehicles for years: Remote Keyless Entry (RKE) systems, GM’s OnStar and GPS navigation are just a few examples. However, large-scale communication between vehicles and the rest of the world has been a long time in development.

The first stage is likely to be vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2X) communication using the Dedicated Short-Range Communications (DSRC) bus being pushed by the National Highway Traffic Safety Administration (NHTSA). The expected benefits include a reduction in collisions, fuel savings, and less traffic congestion.

Twenty years after the initial allocation of frequencies (5.9 GHz in the US), the technical standards are mostly finalized, but substantial concerns remain. Although V2V-equipped vehicles are already on the road and major automakers are moving ahead with production plans, completion of the V2X roadside infrastructure is still many years in the future. In addition, the Trump administration is rumored to be less enthusiastic than its predecessor about mandating the adoption of DSRC technology.

While we wait, 5G cellular, which is beginning its rollout this year, may offer ways to achieve the hoped-for benefits at lower cost. The latest 5G specification includes cellular-to-V2X (C-V2X) capability and suppliers are taking note: Qualcomm, for example, has announced its Cellular Vehicle-to-Everything solution, with a reference design based around their 9150 chipset.

Over the next few decades, many automotive futurists predict the end of personal ownership of vehicles, replaced by transportation as a service via ubiquitous autonomous vehicles. These autonomous vehicles are just over the horizon, and will require a vast expansion in wireless capability: Intel’s CEO has estimated that one autonomous vehicle will use up to 4,000 Gb of data per day, and much of that will be carried over the wireless network. Traffic data, information about other vehicles, and extremely detailed real-time maps are just a few of the data that must be transmitted and received. 

The autonomous vehicle passengers will need something to do while they relax on their journey, so let’s not forget to add in extra bandwidth for all those 4K and 8K videos.  Perhaps we should leave that problem to those future engineers who’ll be developing the protocols for 6G and 7G systems.