Research on the solution of realizing vehicle-mounted media-oriented transmission system

According to research, driver assistance systems can have a positive effect on the driver's driving behavior and safety, and can also protect the environment and improve traffic efficiency. With the rapid growth of navigation functions, traffic information functions, camera systems, distance control, and route keeping, system functions are no longer independent, but rather show a cooperative relationship, and seamless integration between functions is the goal to be pursued.

Advanced driver assistance systems (ADASS) are connected to many different in-vehicle electronic systems. Just like the human body, the various assistance system functions in the car must also cooperate with each other: sensors (radar, camera, ultrasound); processing units; actuators (steering wheel, brake pedal, electronic stability control, airbags). So many systems are complicated to use, which requires information exchange between system functions. Obviously, sufficient network infrastructure construction is crucial to improve the efficiency of driver assistance systems. The functional scope of driver assistance systems is gradually expanding and will become an integral part of the E/E ecosystem.

In order for driver assistance systems and entertainment information systems to work together seamlessly, specific requirements need to be met in terms of network technology. These prerequisites are the need for highly integrated multi-channel networks; real-time confirmation and low latency; flexible scalability structure; high bandwidth; security and stability. Therefore, multi-channel networks with inherent synchronization are preferred.

Further advantages include technological maturity, cost-effectiveness, flexible topology and parameters in the Media Oriented Transport System (MOST). The Media Oriented Transport System enables the simultaneous transmission of all functional data streams, which are synchronized.

The latest generation of media oriented transmission system MOST150 can support IP protocol data communication and provide Ethernet channels for cars with configurable bandwidth from 0 to 150 megabytes per second. In this way, MOST provides data transmission channels for applications based on IP communication, including wireless network devices, C2C devices and C2X devices.

The MOST architecture adopts the concept of functional modules, including programming interfaces with clear functions, which can standardize entertainment interaction applications and sensor interfaces.

Packet transmission

Ethernet connection is suitable for connecting to computer systems in unstable network connections. It can achieve the purpose of data transmission in a wider range. Each data packet is encapsulated and re-addressed and controlled to reach the destination, and the transmission speed is very fast.

IP address connections are very helpful for sending e-mails, browsing the web, and moving data. The problem with the carrier sense multiple access with collision detection (CSMA/CD) architecture in Ethernet is that when a collision occurs, it may be detected, and when there is too much data participating in Ethernet, its transmission rate will be greatly reduced, sometimes resulting in multiple reconnections to the network. The system is uncertain, and the delay of network transmission varies greatly. Audio, video, and other applications that require continuous operation will seriously affect the user experience once they are interrupted, so the disadvantages of Ethernet connection are obvious.

Control information data must arrive within a predetermined time, and can be buffered to keep the network smooth, but devices such as on-board cameras or sensors in driver assistance systems are related to driving safety, so no buffering is allowed and all data must be real-time data. The compromise solution requires additional hardware, and the so-called data buffering method is only in the theoretical stage and is not suitable for real-time transmission.

All network interfaces need to be connected to switches, increasing hardware equipment and costs more than current Ethernet transceivers. Ethernet Audio Video Bridging adds hardware to distribute clocks, provide timestamp messages for each time packet, and provide mechanisms for reserving bandwidth and optimizing data packets.

Streaming

IP packets require a lot of overhead to address and send information. Adding addressing information and interrupting the packet transmission and then checking the packet passing through a device wastes a lot of bandwidth. The delay of the packet passing through the system is also uncertain. They need to decompress the packet and put the data into a continuous data stream to process the data through the A/V decoder.

For this type of transport, streaming and media-oriented transport have clear advantages. The media-oriented transport control channel is used to place data in a frame, and a renderer can read the data of this frame at any time. Once this is set up, only A/V data can be transmitted, without any addressing or timing information.

With MOST150, there is no need to force all data into a specific format to fit a single transport protocol, as it features a dedicated Ethernet channel that can transmit standard Ethernet packets across the MOST network without having to go through a high-level Ethernet stack.

The MOST150 intelligent network interface controller (INIC) even has an Ethernet-style media access control (MAC) address, so that Ethernet packets can be extracted in the right place and passed to other standard Ethernet devices, without the need for switches or any other hardware devices. Stream data can be transmitted in parallel.

The strengthening of the entire automotive network management infrastructure will help cars better utilize Ethernet data transmission capabilities. A complete tool chain for automotive development and manufacturing systems already exists and is ready to add Ethernet capabilities to MOST.

The MOST streaming channel does not require a separate stack data structure. Data can simply be transmitted into the network. Low transmission delay is a good thing for automatic data acquisition systems. The transmission delay from one terminal to another, including compressed data and decompressed data, is only a few milliseconds.

MOST includes all the software layers of the automotive industry and does not require new automotive network management stack data structures. From a technical point of view, there is no need to define the type of network infrastructure required for the car. Both packet transmission and stream transmission are adaptable, and designers can use the best transmission scheme according to actual conditions.