The Future of Automotive Data Connectivity

Today's cars can perceive the world around them and take actions according to the perceived results. They bring unprecedented experience to drivers and passengers in terms of safety, comfort, convenience and interactivity. Year after year, they keep making progress in this respect.

However, if there is no accurate data connection, the car can't do any of the above. Data connection is the "nervous system" of the car, which is responsible for linking various sensors and actuators all over the car to the car computing platform, that is, the "brain" of the car. As sensors and calculations become more sophisticated and complex, and the general trend of software-defined vehicles, the bandwidth requirement for data connection is increasing rapidly, and it is beyond the application range of traditional vehicle network performance.

We have experienced explosive growth of data in other fields (such as data center, office and home). The decades of experience and lessons brought by them provide reference for the new challenge of defining automobile data network. However, the car-gauge products or technologies have their own unique requirements, and the exploration to meet these requirements with the safest and most cost-effective solutions will lay the foundation for greater innovation.

A New Type of Network

The vehicle-mounted network architecture is facing unprecedented pressure. Traditional point-to-point analog connection is gradually giving way to digital connection. High-resolution radar and camera need higher bandwidth and speed. Inside the automobile, the amount of data exchange between electronic control units (ECU) will be larger and larger. With the development of software-defined cars, these demands will increase day by day.

In order to adapt to these emerging requirements, data connection technology must solve some special challenges of vehicle applications:

Electromagnetic Interference (EMI)

The limited physical space inside the vehicle increases the possibility of electromagnetic interference. So many electronic and electrical components are close to each other, it is necessary to resist the electromagnetic "noise" that may be emitted by other components, and avoid the noise itself when designing the data network.

Delay Sensitivity

If there is a delay in the data sent by one of the sensors, it may be difficult to fuse the data with the data of other sensors to obtain the real-time image of the surrounding environment of the vehicle, thus affecting the decision of higher-level autonomous driving.

Fail-Safe Requirements

High-level self-driving cars must be able to recover from failures in a controlled way. The network solution should be able to bypass the faulty node and ensure that the vehicle continues to drive safely until it stops safely.

Weight

Every gram of weight lost from the vehicle will make the car more efficient and possibly lower in cost. In addition, the wiring that takes up less space can make room for other components, thus loading more functions.

At present, a variety of data connection network technologies have been developed in the industry, and they meet the demand of data connection in an unprecedented way.

Automobile Ethernet

In the field of IT, Ethernet has a long and extremely successful history. Ethernet was invented in 1973 and standardized in 1985 by the Institute of Electrical and Electronics Engineers (IEEE). Later, it began to dominate the local area network (LAN) used in commercial fields, and resisted the competition of all other similar technologies (such as token ring network). For decades, Ethernet has been proved to be a universal and flexible standard network, which promotes the progress of communication field. Different versions of Ethernet rely on coaxial cable, optical fiber and unshielded twisted pair respectively, and the speed is also increased from 10M bit/s to over 100g bit/s. After decades of application, people have a good understanding of Ethernet and made good improvements.

As the in-vehicle network began to connect more in-vehicle computing resources, the application of Ethernet became a natural choice, so in 2016, IEEE released the first automotive Ethernet standard IEEE 802.3bw, or 100Base-T1. Although the bandwidth of 100M bit/s is equivalent to that of 100Base-TX introduced in 1995, there are still some key differences in the car version.

Both standards operate on unshielded twisted pair, that is, two copper wires are twisted together along the length of the cable. This has the effect of generating less electromagnetic radiation and crosstalk, avoiding interference with other wires or components, and resisting interference from other sources.

However, the 100Base-TX uses two twisted pairs, while the automobile Ethernet only needs one pair, so the weight and cost are lower. This pair of lines is "balanced", that is, the signals have equal but opposite voltages. The transmitting signal and the receiving signal are conducted on one twisted pair instead of two different twisted pairs like 100Base-TX.

In the 100Base-TX standard, the maximum length is 100 meters, which is followed by subsequent Ethernet standards. The specified maximum length of Ethernet for automobiles is only 15m. Obviously, the automobile application does not need a long distance between the network components in the car, and the shorter the length, the lighter the wiring.

Another key difference lies in the coding done by the transceivers at both ends of the cable.

The 100Base-TX standard adopts multi-level baseband coding (MLT-3) technology, which encodes bits on the wires by circularly adopting three voltage levels, while automotive Ethernet adopts three-level pulse amplitude modulation (PAM-3), which encodes bits by the amplitude of signal pulses, so that more bits can be encoded in each clock cycle. Combined with other coding techniques, the final frequency can be reduced from 125 MHz to 66.6 MHz, which also helps to prevent electromagnetic interference and crosstalk.

Subsequent developments in automotive Ethernet

The 100M bit/s of IEEE 802.3bw standard can meet many basic automotive applications, so it is widely used today. However, as engineers consider higher-definition video streams and converge data from multiple sensors on a common cable, higher speed will be an inevitable requirement.

Shortly after the finalization of IEEE 802.3bw, IEEE officially approved the 802.3bp standard, or 1000Base-T1, which can achieve gigabit speed through shielded or unshielded twisted pairs. This standard has a lot in common with the predecessor standard, but its frequency is nearly 10 times higher, reaching 600 MHz. This means that the cable is more susceptible to crosstalk. Therefore, when designing the system, engineers need to pay special attention to control the electromagnetic noise of the whole vehicle, strictly test it and shield it when necessary. This standard will provide enough bandwidth for the next two to three generations of platforms.

In 2020, IEEE formulated the 802.3ch standard, which can support Gigabit Ethernet with standard rates such as 2.5G bit/s, 5G bit/s and 10G bit/s within 15 meters. Twisted-pair shielding can meet the above transmission speeds, but shielding parallel pairs may be required for frequencies exceeding 7 GHz to minimize the electromagnetic interference.

A key advantage of Ethernet is that it is a flexible network that can be easily reconfigured. If something goes wrong, Ethernet routers can send data through different routes. This is important to ensure that the connection of important computing components in the vehicle will not be interrupted.

In vehicle network, equally important is the ability of Ethernet, which uses copper wire as transmission medium, to transmit power with data signals. This feature is called data line power supply (PoDL). The data cable can support up to 500 mA of power, which is enough to meet the needs of some sensors, such as the optimized satellite architecture camera. In this way, the automobile manufacturers only need to lay a pair of wires to connect these sensors, which can meet all their needs, thus making the whole vehicle lighter in weight and simpler in structure.

Some automotive Ethernet devices require higher current, which exceeds the power supply capacity of data lines. These systems combine the high-speed AMEC data port with the traditional DC power line into a single interface, which keeps the simplicity of data line power supply as a single device connection.

Application of Automobile Coaxial Cable

Coaxial cable harness has long been used for data network connection. The center of coaxial Wire Harness contains an insulated wire, which is surrounded by a shielding layer made of conductive materials. It was originally used for Ethernet, and it is still widely used for cable TV connection. Different types of coaxial cables have different performance levels, and specific cables will be selected according to the parameters when they are used in automobiles.

Coaxial wiring looms have robustness and anti-interference, which makes them popular in automotive applications. For more than 20 years, the global interface standard adopted by most automobile OEMs is called FAKRA (Fachkreis Automobil). These connectors work well at the frequency of up to 3 GHz, and can also adapt to the application at 6GHz frequency through the specific design function of the terminal, with the speed of up to 8 Gbit/s.

The latest automotive coaxial cable applications include digital camera systems in vehicles. With the high bandwidth capability of coaxial cable, video signal and camera power transmission can be realized through a single cable.

With the application upgrading from a simple standby camera to a complex vision system, the size of FAKRA interface has become larger and larger. A new generation of smaller coaxial cable connectors is being developed to solve the space problem of vehicles.

These "mini coaxial cable" connectors are much smaller than the current interfaces, which can improve the density of connectors at the equipment end of the same size. In the automotive industry, there are two kinds of micro coaxial cable definition interfaces. In addition, Amber actively participates in the formulation of standards of the International Organization for Standardization (ISO) and the American Automotive Research Council (USCAR) to ensure that Kable-X`s products are suitable for any global application.

Another feature of micro coaxial cable systems is that they support bandwidth far exceeding that of current automobile products. Although FAKRA can support frequencies as high as 6GHz, the micro coaxial cable can support applications from 9 GHz to 15GHz, which means that the bandwidth can reach more than 20 Gbit/s.

The future automotive computing system will include a large number of coaxial cables, which are used to transmit data between more complex on-board computing platforms.

Peripheral Interconnect Bus (PCI-E)

Another technology being considered for some automotive application scenarios is PCI Express. PCI Express, founded in 2003, is a bus interface, which is mainly used to connect peripheral devices to computer motherboards. The latest version of PCI Express can support the transmission rate of up to 128 gigabytes per second.

The maximum distance of PCI is very short, only half a meter, but it doesn't need a transceiver, so it can save costs.

PCI Express may be an ideal solution for ecus close to each other in vehicles.

Other Network Technologies

It seems to be a good choice for fiber-optic cars, but they have some shortcomings, which may hinder their wide application. Optical fibers use optical pulses to transmit data through glass or plastic fibers, which means that they do not generate electromagnetic radiation and are not susceptible to interference from other sources. However, power cannot be transmitted through the optical fiber data line, which means that the components need additional power transmission. Optical fiber is often expensive, which requires a transceiver to convert electrical signals into optical pulses. The manufacturing process cost is also very high. More importantly, the bending radius of the optical fiber line is limited. How to make the optical fiber line pass through the narrow area in the car without excessively bending is a thorny problem.

Another technology that engineers have considered is multi-core cable technology, that is, a cable contains a large number of single wires. The most prominent example is USB Type- C, which has established itself in the PC world and can combine power and data into the same cable. However, the Type-C cable can only be limited to a few meters long, and the manufacturing cost is very high. They also limit the bandwidth to 5Gbit/s per channel, and require the transceiver to divide the data into these channels, thus adding extra cost.

Although more and more data connection schemes such as automobile Ethernet are emerging, some traditional technologies that have been applied in automobiles for many years may continue to be used in simple application scenarios with low data rates. For example, local area network (LIN) only needs relatively economical chipset and connectors. Other relatively economical schemes include controller area network (CAN) (running speed up to 1M bit/s) and variable data rate CAN (CAN-FD) (running speed up to 2M bit/s). FlexRay can support up to 10M bit/s, and it is still used in some security-related applications, but it is expensive and is expected to be phased out.

Recently, the industry has introduced a low-speed automobile Ethernet scheme: 10Base-T1S to meet the needs of these applications. Although most network technologies are symmetrical, there are some in-vehicle applications whose requirements are asymmetrical and only require one-way high bandwidth, such as cameras or high-resolution displays. Asymmetric technologies that have been widely used include Flat Panel Display Link (FPD-Link), Automobile Pixel Link (APIX) and Gigabit Multimedia Serial Link (GMSL).

HDBaseT Automotive is an asymmetric technology, which can realize Ethernet channel transmission of up to 4G bit/s with extremely low delay on 15-meter standard unshielded twisted pair with insulation sheath, and up to 8G bit/s on shielded twisted pair, so it is developing rapidly. Like Ethernet, HDBaseT uses pulse amplitude modulation, so its physical layer is less complex than other technologies, so its weight and cost are relatively low.

This unique perspective has also led us to design the next generation of Smart Vehicle Architecture. Under the framework of SVS, various solutions need to provide a solid foundation for all components of active safety, and lay a foundation for further innovation while reducing vehicle weight.

The emergence of automobile Ethernet, mini coaxial cable and PCI Express provides a broad prospect for manufacturing vehicles that meet the above standards.