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MOST in future automotive connectivity

MOST in future automotive connectivity

Technology News |
By eeNews Europe



To easily and seamlessly integrate upcoming applications requires a flexible and upgradable network that forms a stable, robust backbone. For example, there is more and more focus on a growing number of IP-based applications. The requirements for bandwidth are driven by applications such as fast software updates of the different control devices, fast media access to onboard mass storage systems (HDD/SSD), mobile with USB connected consumer electronics devices and WLAN or LTE connected car-to-x applications.

For driver assistance camera systems, the uncompressed transfer of video data is required, which additionally presumes high transfer rates. It is important that common data formats are supported. Furthermore, the network concept should be inherently scalable and extendable with respect to speed; the amount and characteristics of the data channels and application-specific interfaces should be chosen appropriately.

Infotainment

In-car applications are in transition. The scope of infotainment is continuously extended and optimized – take, for example, rear seat entertainment in HD quality with Blu-ray. The challenge is to keep pace with the developments of the consumer industry and the requirements of the users: the diversity of entertainment applications is multiplying rapidly, and users today cultivate a digital lifestyle where they always carry their entertainment systems everywhere. It is necessary, therefore, to connect these external systems and services with the car network. The focus is on the efficient and innovative migration of the features of entertainment electronics like internet radio and video and online connection via WiFi, UMTS and LTE.

Data Streaming

The car industry has focused for more than ten years on the MOST standard for audio and video communication. From the start, the network was conceived for the streaming of data to different devices, to ease the load on entertainment systems in cars. For communication between the outside world and the car, internet protocol (IP) is gaining increasing importance, where data streams in the IT world use different IP packet based protocols. The MOST Ethernet packet channel fits into the "Open Systems Interconnect" (OSI) Reference Model for network communication of the International Organization for Standardization (ISO). The latest MOST Technology connects infotainment and data IP frames and already complies with IEEE802.x specifications (Fig. 1).

Fig. 1: Modified OSI Reference Model that includes MOST and Ethernet (Source: Microchip Technology). For full resolution click here.

With MOST, the appropriate network architecture for a broad range of current and future IP-based applications, such as the support of Apps to Connected Services and general internet access, is already available. The network supports standards for consumer electronics, like UPnP (Universal Plug-n-Play) and DLNA (Digital Living Network Alliance), as well as standards for automotive diagnostics over IP (DoIP).

Driver Assistance

Driver assistance systems (ADAS) are gaining popularity and within the euroFOT study (June 2012) they were also credited with a positive impact on driving behavior, fuel efficiency, traffic security and overall cost savings (www.eurofot-ip.eu). There will be a quick increase in the number of cars that have driver assistance functions integrated, such as camera systems, distance alert and lane departure warnings, in addition to information functions like navigation systems, traffic information and function warnings. There is no question that an ADAS network for seamless integration is needed.

There is already a consensus between many OEMs and Tier 1 suppliers that there will be a new cluster in the electric/electronic ECO system. A flexible multiplex approach like MOST delivers a holistic, optimal system solution. Current MOST Technology already fulfills the requirements for merging infotainment and driver assistance and the coming generation will incorporate even higher bandwidth. In particular, applications that share the attention of the driver need an appropriate network that supports easy and seamless integration of the infotainment and driver assistance domains.

Speed

Real market requirements of a broad user group are always integrated into the decisions of the MOST Cooperation regarding the development of new functions and features, speed grades and physical layers. The technical and economical optimum is always aimed for, instead of the technically feasible extreme. The real needs are determined based on the data content that car makers expect will be truly brought into the car.

For this, the overall system costs have to be considered, including an automotive qualified network interface controller, the physical medium and the connector systems. The challenge is to find the balance between the highest data rates, robustness and cost. The amount of bandwidth mainly results from the requirements for the uncompressed transmission of camera signals, display content and high speed applications like USB 3.0. As a consequence of these factors, the targeted bandwidth for the next generation of MOST is 5 Gbit/s.

In addition to the data network speed, the interfaces of the network interface controller to the CPU or GPU also have to be considered: with growing data rates, bottlenecks and consequently data jams have to be expected. In addition to efficient general purpose interfaces like USB or PCI, for the transmission of uncompressed or compressed video and audio data there is demand for improvement by means of application-specific interfaces.

With them, in the future, data can be transported directly from a source to a sink without protocol overhead, additional CPU load or the uncertainties of software stacks. In contrast to most networks, MOST does not require additional communication processors, but offers the transport of application-specific data streams with guaranteed bandwidth and latency that the multiplex architecture inherently offers.

Physical Layer

With the targeted data transmission rate of 5 Gbit/s at the optical physical layer, we reach the limits of Polymer Optical Fiber (POF), which MOST has deployed so far. Therefore, different companies are already investigating the automotive suitability of the fiber glass technology that is already successfully used in the consumer and telecommunications industry.

In the electrical domain, the coaxial standard recently introduced for MOST offers a scalable physical layer. With it, new options open up into the automotive domains, particularly ADAS, as this physical layer allows for bidirectional communication and power supply across the same cable. Coaxial is the industry standard cable for transport of high frequency signals. It has inherent shielding and provides low-cost and standard cables and connectors. Its symmetric construction enables automated connector assembly allowing lower assembly cost than shielded twisted pairs of copper wires (STP).

Depending on bandwidth and cable/connector quality it offers low reflections up to 100m distance. Coaxial standard already works up to several Gbit/s and it is fully integrated in the INIC. Thus, the coaxial standard provides the EMC-proof and low-cost electrical physical layer for MOST (Fig. 2).

Fig. 2: Coax cable provides fully symmetric cable for well controlled impedance, one inner wire and shield as second wire connector assembly simple (automated)

Multiplex Network

The automotive network of the future requires a powerful and scalable multiplex architecture with free topology configuration. With the expandable multi-protocol approach, different types of data can be transported across the different MOST channel types. For each protocol adequate interfaces are available, for instance I2S, RGB, I2C, MII, CAN, and USB. Several instances are possible per channel. In addition, the mechanism is flexible and expandable with extra channels for future protocols. Even with respect to topology everything is feasible: from star to daisy-chain to tree, different topologies can be assembled, and combinations can also be used (Fig. 3).

Fig. 3: Next generation MOST: simply expandable (Source: Microchip Technology). For higher resolution click here.

The multiport interface controller by Microchip will allocate the true, full bandwidth to every branch. With up to 8 MOST150 network ports and fully featured 150 Mbit/s streaming data per port, a total bandwidth of up to 1.2 Gbit/s is already available today. An additional standard high-speed interface is integrated, compatible with all modern interfaces used by powerful media processors in multimedia operation or driver assistance. The different branches can then be built up of ring or daisy-chain and can be hot-plugged or disconnected without influencing the data communication in the rest of the system. With such architecture, use cases like ADAS, which require a pure star architecture, are also addressed (Fig. 4).

Fig. 4: The multiport interface controller allocates the true, full bandwidth to every branch. (Source: Microchip Technology)

In order to further simplify the network system, a new remote control feature is implemented, allowing the reduction of the number of microcontrollers and amount of memory by obsoleting them in peripheral nodes such as displays, amplifiers and cameras. The outer nodes can be controlled remotely by a central microcontroller – for example, the one in the head unit. Performing all control centrally in the head unit also simplifies the development process considerably, as only one piece of software needs to be developed. Amplifiers and displays run without a local microcontroller and without local software. This significantly lowers costs on the side of the remote devices and helps to optimize in the area of system partitioning, board space or even power dissipation in the remote device (Fig. 5).

Fig. 5: Remote control features obsoletes microcontrollers and software in peripheral nodes (Source: MOST Cooperation)

Future Network Architecture

Let’s have a look at what would happen if the future automotive network architecture was set up again from scratch: the evolution of MOST began with the transmission of audio data. MOST is a synchronous network because this architecture delivers the ultimate audio quality with minimal effort. The first MOST generation started out as an entertainment network and later, after some years, expanded into an infotainment network because navigation systems developed and cars were connected to the internet. With the target of defining one network architecture for all communication in a car, not just the transport of internet data, some real-time capabilities should be added.

Assuming some events or commands have to be sent over the network in real time, these short control messages will be queued into the communication channel, probably resulting in a longer latency than might be acceptable for some control tasks. So mechanisms are necessary to split up longer packets to allow real-time messages to access the communication channel in between, with acceptable latency. A very typical approach, used in a number of industrial Ethernet variants, is to divide the transmission time into time frames and divide these frames into regions for real-time and best effort communication. So it is still packet based communication, but some clearly defined times have been introduced in between where real-time communication can take place. Thus, it is guaranteed that real-time control messages have a chance to get access to the channel and a guaranteed maximum latency is achieved.

The further design process now is evidently well-known. Since the transmission has been divided into time frames and regions in these frames have assigned for best effort and for real-time control, another region for streaming data is defined. This provides the easiest and most effective way to transport audio data at the ultimate quality or to deliver guaranteed bandwidth for video streams.

In the next generation MOST network, the transmission speed will be increased, but the basic architecture principles will stay the same. The basic time frame will be kept at 20µs, but the number of bytes per frame will be increased according to the network speed. At a network speed of around 5 Gbit/s, MOST frames will contain more than 10 kilobytes. This allows the extension of existing channels and the addition of new channels.

Further audio and video channels with much higher bandwidth can be added for the transport of uncompressed video data. Additional instances of existing channels could be, for example, a second control channel that could be reserved for system management purposes or a separate Ethernet channel in order to separate trusted und untrusted IP traffic in an absolutely secure and hacker proof manner.

The next MOST generation will also keep and extend two other unique features of MOST: routing capabilities and application specific interfaces. Application and data specific interfaces such as I2S for audio or TS for video allow delivery of the data in the most effective manner to the devices. No CPU must filter packets; no software stack is in between. The next generation MOST interface controllers will have all well-known data specific interfaces and they will also have the multi-purpose interfaces PCIe, USB or MediaLB. For new data types and application interfaces for uncompressed video, for example YUV or MII/GII, interfaces for Ethernet communication will be added. Next generation MOST network controllers will also provide the flexible routing capabilities between interfaces and network but also between different interfaces.

In summary, it can be said that future network communication in cars will be adapted to growing bandwidth requirements, with a new network speed of 5 Gbit/s. For the physical layer, optical and electrical variants will be at the manufacturer’s disposal. For the optical physical layer, glass fiber is being considered.

For the electrical physical layer, a coaxial cable is the favorite solution, since it offers new functionalities such as the bidirectional data transmission and power supply over the same wire. Thanks to the multiplex architecture with powerful interfaces, multiprotocol channels, synchronicity and low latency of the network, the MOST architecture is ready for the future.

About the Author

Rainer Klos is Director Engineering of Microchip Technology and MOST Cooperation Administrator. Since 1995 he has worked for the development of network standards, ICs, software and tools in the MOST environment.

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