High-speed networking for driver assistance over MOST

  • 16-Oct-2012 08:43 EDT
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Henry Muyshondt has been instrumental in introducing the MOST networking technology into the automotive industry. He has worked to bring together the automotive and consumer electronics industries and has led MOST Cooperation and Consumer Electronics Association (CEA) efforts to bridge the gap between these industries.

Studies have reported that driver-assistance functions may have a positive effect on driver behavior and the potential to impact road safety, traffic efficiency, and environmental conservation. Along with features such as navigation systems, traffic information, and function warnings, the number of vehicles with driver-assistance functions such as camera systems, distance controls, or lane departure warnings will rapidly increase. Consequently, the need for the seamless integration of infotainment and driver assistance becomes evident.

Advanced driver-assistance systems (ADASs) interface with many different clusters of electric/electronic systems in the car. Comparable to the human body, numerous functions have to be implemented and networked: sensors (for example, radar, cameras, or ultrasonic); processing units; and actuators such as steering, brakes, electronic stability program, and airbags. Regarding 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 essential for the efficiency of the system. ADASs have started to enlarge the functional range of infotainment systems and will become an integral part of the E/E ecosystem.

For driver-assistance and infotainment systems to work together seamlessly, special requirements at the network level are necessary. These prerequisites are characterized by high integration of a multichannel network; hard real-time determinism and low latency; flexible topology; high bandwidth; safety aspects; as well as robustness and maturity. Consequently, a multichannel network approach with inherent synchronicity will be the first choice.

Further advantages such as maturity, cost efficiency, and flexible topology are additional arguments for MOST (media-oriented system transport) technology. MOST 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.

MOST150, the latest generation of MOST, enables IP (Internet protocol) data communication, providing the automotive-ready Ethernet channel according to IEEE 802.3 with freely configurable bandwidth from 0 to nearly 150 Mbit/s. In this way, MOST is open to a broad variety of IP protocol based applications, including the seamless integration of wireless mobile devices or car-to-car and car-to-infrastructure communication.

The MOST Framework, with its function block concept, comprises a clear application programming interface. It is able to standardize both interfaces between infotainment applications and sensor interfaces such as cameras in ADAS.

Packet transmission

Ethernet was developed to connect computing systems that could be widely separated and did not necessarily have reliable connections among them. Each packet of information had to be encapsulated with addressing and control information so that it could be rerouted. The information has to reach the destination without any time limitations.

This IP communication is very useful for e-mail, web browsing, and moving data that are not time critical or time sensitive. The problem with the fundamental CSMA/CD (Carrier Sense Multiple Access with Collision Detection) architecture of Ethernet is that it is impossible to predict when there will be a collision and, as more devices participate, the more time and thus bandwidth is wasted backing off and trying again. The system is nondeterministic, and there can be wide variations in latency. Audio and video and any other application with a continuously flowing stream of data, however, cannot afford to be interrupted.

Control messages have to arrive within a predetermined timeframe. Buffering can help, but it introduces delays that are unacceptable for applications such as cameras or other driver-assistance functions where latency is a safety issue. The tradeoff is that additional hardware is needed and buffering and determinism is only a statistic, rather than a hard real-time feature.

All network interfaces need to connect to a switch, adding hardware and cost beyond the actual Ethernet transceiver. Ethernet AVB (Audio Video Bridging) adds hardware to distribute clocks, provide timestamps for each packet that is transmitted, and provide mechanisms for bandwidth reservation and packet prioritization.

Stream transmission

The addressing information used in IP packets results in significant amounts of overhead. Adding addressing information and breaking up the data into packets that then need to be examined every time they go through a device along the route results in a lot of wasted bandwidth. Also, packets may not always move through the system with exact latency and determinism. In addition, they need to be unpacked and the data joined into a continuous stream for the various A/V decoders to process it.

For such transmissions, the streaming and isochronous channels of MOST have a distinct advantage. The MOST control channel is used to set up where the data is going to be placed within a frame, and where a renderer can pick up the data it needs. Once this setup is completed, only actual A/V data is transmitted, without any overhead for addressing or timing information.

With MOST150, there is no need to force all data into a particular format to fit a single transmission protocol since it has a dedicated Ethernet channel within its frame. This channel can take a standard Ethernet packet without any special processing by the higher levels of the Ethernet network management stacks, and send it over the MOST network.

MOST150 Intelligent Network Interface Controllers (INIC) even have Ethernet-style MAC (Media Access Control) addresses so that the Ethernet packets can be extracted at the right location and passed on to other standard Ethernet devices without any need for central switch hubs and additional hardware. Streaming data can then be sent in parallel.

The whole automotive network management infrastructure currently in place can be leveraged when adding Ethernet capabilities to the vehicle. Complete tool chains geared for automotive development and manufacturing systems already exist and are ready to add Ethernet capabilities to the current set of MOST functions.

The MOST streaming channels do not require separate processing stacks. Data can just be pumped down into the network. This results in very low latency transmissions that are well suited for ADAS. End-to-end delays, including compression and decompression, are just a few milliseconds.

MOST includes all the software layers needed for the car industry and does not require new automotive network management stacks. From a technical perspective, there is no need to argue what kind of infrastructure the vehicle needs. Both packet and stream transmissions can be accommodated, and the designer can take advantage of the best solutions to the problems. MOST provides a single physical layer that supports the advantages that each technology brings to the vehicle.

Henry Muyshondt, Technical Liaison of the MOST Cooperation and Senior Director of Business Development at SMSC, wrote this article for AEI.

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