Seamless integration of camera systems into ADAS with MOST technology

ADAS are becoming an integral part of the car – interfaces to many different clusters of the car’s electric/electronic systems. Similar to the human body, this requires the implementation and networking of a large number of functions: sensors such as cameras, radar and ultrasound, as well as processing units and actuators. Given the complexity of the use scenarios and the different vehicle areas that must exchange information, the importance of a sufficient network infrastructure for system efficiency is self-evident. From a functional perspective, driver assistance systems have begun to expand the scope of traditional infotainment systems.

As shown in Figure 1, “Evolution of Electric/Electric Architecture”, the driver assistance field is gradually becoming an integral part of the electric/electronic ecosystem. ADAS and infotainment systems will develop in tandem in the future.

Figure 1: Evolution of electric/electronic architecture

Typical emerging driver assistance applications include:

- Parking assistance

- Collision warning

- Traffic sign monitoring

- Lane Departure Warning

- Advanced Lane Guidance

- Pedestrian warning

- Night Vision

- Adaptive cruise control

- Pre-collision warning

Driver assistance systems place special demands on the network.

Features include:

- Transmission of control, video, data packets and IP data

- Highest quality service

- Hard real-time determinism and low latency

- Flexible topologies such as star, daisy chain and ring

- High bandwidth

- Remote control function

- Security

- Stability and maturity

In addition to the items listed above, cost efficiency is also a key metric.

Multi-channel solution

Typically, driver assistance systems must process a wide variety of sensor data. To cope with this complexity, it is often necessary to find a layered approach with different levels of abstraction and timing constraints. There is a lot of raw data in the low level, which requires high bandwidth and consistent and fast transmission. The middle level needs to transmit objects and attributes. Finally, the highest level will give the parsed data. A typical mapping of MOST technology is shown in Figure 2 "MOST technology data transmission mechanism".

Figure 2: MOST technology data transmission mechanism

Multi-channel network systems enable all services including control data, streaming data and packet data to be used in parallel over one network. When necessary, these services can be easily synchronized in a very deterministic way.

The third generation of MOST specification introduces a MOST technology network with a rate of 150 Mbps. This network supports IP data communication and provides automotive-ready Ethernet channels that comply with the IEEE 802.3 standard, with channel bandwidth freely configurable in the range of 0 to nearly 150 Mbps. MOST technology is open to a variety of IP-based applications, including seamless integration of wireless mobile devices and communication between vehicles and vehicles and infrastructure.

The MOST technology framework and functional module concept includes clear application programming interfaces that standardize the interfaces of driver assistance applications and sensors such as cameras.

Flexible star topology for camera system integration

Figure 3 shows a multi-camera system based on a MOST150 network, which includes four high-definition cameras. A maximum of 150 Mbps of bandwidth can be allocated to the video stream of each camera. The entire data stream bandwidth of MOST150 can be used for each camera link individually. The camera system can be expanded to eight cameras, using a total of 1.2 Gbps of data stream bandwidth. The surround view cameras are connected to the central node of the star topology via coaxial cables.

Figure 3: Multi-camera system based on MOST technology network

The 360-degree car top-view system (Figures 4 and 5) uses a small camera with a MOST technology interface to provide a resolution of one million pixels and a high dynamic range. This type of camera is based on a cost-effective design consisting of an image sensor chip and a MOST technology interface chip. With the remote control function, no memory chip or additional microcontroller is required to operate the camera.

Figure 4: Top view demonstration system based on MOST150 coaxial cable

Figure 5: Top view

With the inherent synchronization brought by the TDMA mechanism, the MOST technology multi-channel network solution ensures real-time determinism and ultra-low video latency (less than 10 milliseconds), thus fully meeting the needs of ADAS.

The MOST150 technology has been validated by corresponding studies in cooperation with TUV Germany. MOST150 has a safety layer concept according to IEC 61508 and ISO 26262 standards and is suitable for fail-safe applications.

Multiply the bandwidth of multiple MOST150 branches

The network interface controller located in the central node has multiple ports that can allocate up to 150 Mbps of data flow bandwidth to each network branch. Different branches can be established using any topology including star, ring, tree or daisy chain, and they can be hot-swapped or disconnected without affecting the streaming data transmission of other parts of the system.

Low latency data streaming

Sending a video stream from a camera to a renderer means transferring a large amount of video data over a long period of time. The continuous data stream cannot be interrupted or delayed. MOST technology transfers the data stream with guaranteed bandwidth and ultra-low latency. It does not require an additional communication processor or addressing overhead, nor does it waste bandwidth by splitting the data into multiple packets, which then need to be checked each time the packet passes through the device along the path.

Coaxial Cable

Utilizing coaxial cable, this solution enables bidirectional communication and power over the same cable, thus providing a scalable electrical physical layer for the ADAS automotive sector. Coaxial cable is an industry standard cable for transmitting high-frequency signals. It provides shielding itself and is a low-cost standard cable and connector. It uses an automated plug-in structure, which enables lower assembly costs compared to shielded copper twisted pair cables. The coaxial solution has been EMC-certified and has an operating speed of up to several Gbps, making it a future-oriented physical layer.

Camera Design

Figure 6 shows the block diagram of the camera module. The image sensor is directly connected to the MOST interface. The camera is controlled via I2C and GPIO using the remote control function. The video data is sent to the MOST interface and then transmitted over the MOST network with the highest quality of service.

Figure 6: Camera block diagram

Remote control function

The camera module takes advantage of the new remote control feature added to the MOST specification. This new feature reduces the software stack that typically requires microcontrollers and memory in peripheral nodes such as displays and cameras. For example, the remote control feature supports the control port used as an I2C bus master. The I2C bus master manages the read and write operations of the image sensor and other on-board slave devices (if present). The I2C read and write operations are handled remotely through the MOST control channel. In addition, GPIOs are also handled remotely through the MOST technology control channel. For example, they can be used as reset pins in the camera. GPIO events are automatically reported through the MOST network. Existing processing power in the electrical control unit (ECU) of the overhead view system is used to run the control software for all cameras.

Centralizing all control software in the ECU of the overhead system can significantly simplify the development process, because in this case only one software instance needs to be developed and deployed. This device architecture helps to optimize system partitioning, save board space and even reduce power consumption of remote devices.

Stability and maturity

Today, MOST technology has been proven to be robust in 150 vehicle models on the road. Cars using the latest MOST150 network have been on the road since 2012.

MOST technology provides a cost-effective system solution approach for ADAS with the following key benefits:

- Determinism and ultra-low latency achieved through TDMA mechanism

- The data streaming feature of MOST supports continuous transmission of video data streams without data packaging or buffering

- Highest quality service

- Supports multiple data types: control, packet, data stream and IP data

- Flexible topologies such as star, daisy chain and ring

- Proven vehicle coaxial physical layer

in conclusion

This article shows that MOST technology networks can provide an optimal solution for camera systems such as overhead view systems. The multi-channel network scheme supports the parallel transmission of control messages, video data streams, and packet data such as object lists over the same link. The flexible framework supports star and ring topologies and a mixture of the two. The data flow characteristics of MOST technology are based on a TDMA mechanism, which supports real-time data streaming and provides ultra-low latency and the highest quality of service. MOST technology can allocate up to 150 Mbps bandwidth for each camera's data stream, and in the ECU of the overhead view system, when using a star architecture consisting of eight cameras, up to 1.2 Gbps of bandwidth can be used to transmit video data to the central processor. The technology uses proven automotive coaxial cables and connectors and can be powered by the same cable. MOST technology has been used in more than 150 car models on the road and can provide a stable and mature choice for camera systems.