Seamless Integration of Video Camera Systems in ADAS with MOST Technology
The ADAS are on their way to becoming an integral part of the vehicle—with interfaces to many different clusters of electric/electronic systems in the car. Comparable to the human body, numerous functions have to be implemented and networked: sensors such as cameras, radar and ultrasonic, as well as processing units and actuators. Taking into account the complexity of the use cases and the different vehicle areas that have to exchange information, it is obvious that an adequate network infrastructure is of essential importance for the efficiency of the system. From a functional point of view, driver-assistance systems have started to enlarge the range of classical infotainment systems.
As shown in Fig. 1 “Evolution of E/E Architecture” the driver assistance domain is becoming an integral part of the E/E ecosystem. ADAS and infotainment systems are expected to grow together in the future.
Fig. 1: Evolution of E/E Architecture
Typical emerging driver-assistance applications include:
- Parking Assistance
- Collision Warning
- Traffic-Sign Monitor
- Lane-Departure Warning
- Advanced Lane Guidance
- Pedestrian Warning
- Night Vision
- Adaptive Cruise Control
- Pre-Crash Warning
Driver assistance systems lead to special requirements at the network level.
These are characterized by:
- Transfer of control, video, packet and IP data
- Highest quality of service
- Hard real-time determinism and low latency
- Flexible topologies, such as star, daisy chain and ring
- High bandwidth
- Remote-Control features
- Safety aspects
- Robustness and maturity
Beyond this list, cost efficiency is a key requirement.
The next section demonstrates that a multi-channel network approach with an underlying TDMA mechanism is an excellent choice.
Multi-Channel Approach
Typically, driver-assistance systems have to deal with a variety of sensor data. In order to cope with the complexity, you often find a hierarchical approach with different abstraction levels and timing constraints. On the lower level, there is a high amount of raw data where high bandwidth as well as coherent and fast transmission is required. On the medium level, objects and attributes need to be transported. Finally, on the highest level, interpretation data will flow. A typical mapping to MOST technology is shown in Fig. 2 “MOST Technology Data Transport Mechanisms.”
Fig. 2: MOST® Technology Data Transport Mechanisms
A multi-channel network allows the parallel usage of all services for control data, streaming data and packet data, through one network. These services are easily synchronized, if necessary, in a highly deterministic way.
The 3rd generation of the MOST Specification [1] introduces the MOST technology network with 150 Mbit/s. It enables IP data communication, providing the automotive-ready Ethernet channel according to the IEEE 802.3 standard with freely configurable bandwidth from 0 to nearly 150 Mbit/s. MOST technology is open to a broad variety of IP-protocol-based applications, including seamless integration of wireless mobile devices as well as car-to-car and car-to-infrastructure communication.
The MOST technology framework with its Function Block concept, comprises a clear application programming interface. It is able to standardize the interfaces of driver-assistance applications and sensors, such as cameras.
Flexible Star Topology for Camera System Integration
Fig. 3 shows a MOST150-network-based, multi-camera system with four high-definition video cameras. Up to 150 Mbit/s can be allocated for each camera’s video stream. The full streaming bandwidth of MOST150 can be independently used for each camera link. The video camera system can be extended to eight cameras, using up to 1.2 Gbit/s total streaming bandwidth. The surround-view cameras are connected to a central node in a star topology, over a coaxial cable.
Fig. 3: MOST® Technology network-based multi-camera system
The 360-degree automotive top view system (Fig. 4, 5) uses small-footprint, one megapixel high-dynamic-range cameras with a MOST technology interface. The cameras are based on a cost-efficient design consisting of an image sensor chip and a MOST technology interface chip. By using the Remote Control Feature, neither a memory chip nor an additional microcontroller are required to run the camera.
Fig. 4: Top-view demo system based on MOST150 coaxial cabling
Fig. 5: Top view screen
The MOST technology multi-channel network approach, with its inherent synchronicity due to the TDMA mechanism, is perfectly adapted for ADAS, since it assures real-time determinism and ultra-low video latency at less than 10 milliseconds.
MOST150 technology has already been proven by corresponding studies, in cooperation with the German TÜV [2]. With a safety-layer concept, MOST150 enables fail-safe applications, according to the IEC 61508 and ISO 26262 standards [3].
Multiplying Bandwidth to Several MOST150 Branches
A network interface controller with multiple ports in the central node can allocate up to 150 Mbit/s streaming bandwidth in each network branch. The different branches can then be built with any topology—including star, ring, tree or daisy-chain—and can be hot plugged or disconnected without influencing the flow of streaming data in the rest of the system.
Low-Latency Streaming
Sending a video stream from the camera to the renderer means that a significant amount of video data is streamed for a prolonged period of time. The continuously flowing streams of data are not interrupted or delayed. MOST technology provides the transport of data streams with guaranteed bandwidth and ultra-low latency. It requires neither additional communication processors, nor addressing overhead, nor the bandwidth-wasting process of breaking up the data into packets that then need to be examined every time they go through a device along the route.
Coaxial Cabling
Using coaxial cables, the solution provides a scalable electrical physical layer for the ADAS automotive domain, as it allows for bidirectional communication and power supply across the same cable. Coaxial cabling is the industry-standard cable for the transport of high-frequency signals. It has inherent shielding and provides low-cost and standard cables and connectors. Its construction enables an automated connector assembly, allowing lower assembly costs than shielded twisted pairs of copper wires. The coaxial approach is EMC proof and already works up to several Gbit/s, making it a future proof physical layer.
Camera Design
Fig. 6 shows the block diagram of the camera module. The image sensor is directly connected to the MOST technology interface. It is controlled through I2C™ and General Purpose Inputs/Outputs (GPIOs) using the Remote Control Feature. The video data is applied to the MOST technology interface and streamed over the MOST technology network with the highest quality of service.
Fig. 6: Camera block diagram
Remote Control Feature
The camera module takes advantage of the new Remote Control Feature that is being added to the MOST technology specification. This new feature allows the reduction of the software stack, which typically demands the use of microcontrollers and memory in peripheral nodes such as displays and cameras. For example, the Remote Control Feature supports a control port that implements an I2C bus master. The I2C bus master manages reads and writes to the imager sensor and other on-board slave devices, if any. The I2C reads and writes are remotely handled through the MOST control channel. Also, GPIOs are remotely handled through the MOST technology control channel. These can be used as reset pin in the camera, for example. GPIO events are automatically reported over the MOST network. Existing processing power in the top-view Electrical Control Unit (ECU) is used to run the controlling software for all cameras.
Centralizing all controlling software in the top-view ECU simplifies the development process considerably, as only one software instance needs to be developed and deployed. This kind of device architecture helps to optimize system partitioning, board space and even power dissipation in the remote device.
Robustness and Maturity
Today, MOST technology has been proven as robust in more than 150 car models that are on the road. Cars with the latest MOST150 networks have been on the road since 2012.
MOST technology provides a cost-efficient, system-solution approach with the following key benefits for ADAS:
- The TDMA mechanism leads to determinism and ultra-low latency
- The streaming nature of MOST supports continuously flowing streams of video data with no need for packetization and buffering
- Highest quality of service
- Wide range of data types: control, packet, stream and IP data
- Flexible topologies, such as star, daisy chain and ring
- Automotive-proven coaxial physical layer
Conclusion
This article has shown that the MOST technology network provides an optimal solution for video camera systems, such as a top view system. The multi-channel-network approach allows the transmission of control messages, video data streams and packet data such as object lists in parallel over the same link. The flexible framework supports both the star and ring topologies, as well as a mixture of the two. The streaming nature of MOST technology, based on a TDMA mechanism, supports real-time streaming with ultra-low latency and the highest quality of service. Up to 150 Mbit/s can be allocated for each camera’s stream, allowing the routing of up to 1.2 Gbit/s of video data into the central microprocessor, in the top view ECU, in the case of an eight-camera star architecture. Automotive-proven coaxial cables and connectors are used. Power can be supplied over the same cable. Being deployed in more than 150 car models on the road, MOST technology also provides a robust and mature choice for video camera systems.
Literature
[1] MOST Specification Rev. 3.0 E2. MOST Cooperation, 2010.
[2] Lisner, J.; Specht, J.: Definitely Safe. Elektronik Automotive. Special Edition March
2010, p. 32-34.
[3] ISO 26262-6:2011 Road vehicles – Functional safety – Part 6: Product development at the
software level.
About the Author
Dr. Ing. Bernd Sostawa is a Senior Manager of Business Development at Microchip Technology Inc. He represents Microchip Technology Inc. in the MOST Cooperation Steering Committee.
Note: MOST is a registered trademark of Microchip Technology Inc. in the USA and other countries. All other trademarks mentioned herein are the property of their respective companies.
Article previously published in Elektronik automotive, MOST Special Edition, May 2014, www.elektroniknet.de.
If you enjoyed this article, you will like the following ones: don't miss them by subscribing to :
