Multimedia MOST150´s new features in a series project

MOST is the de-facto standard for connecting infotainment systems in high-end vehicles. In Daimler AG vehicles, MOST25 with a speed grade of 25 Mbit/s has now been used for ten years. However, with the bandwidth of MOST25 almost fully occupied in current systems and with new system requirements for the next generation of infotainment systems, it was necessary to switch to a network with more bandwidth. Therefore, Daimler has decided to build its next generation of infotainment systems based on MOST150, as defined by the MOST Specification 3.0 [3].

The bandwidth provided by MOST150 enables Daimler to realize new features, such as access to Internet services, as well as increased requirements for connectivity to consumer devices. In addition, Daimler has begun to stream video over MOST150, replacing separate dedicated video links. With the bandwidth provided by MOST150, it is possible to create a system where the available audio and video sources can be accessed independently from different seats.

In this paper the experiences with the networking and architectural aspects of the on-going development process at Daimler will be described.

Requirements of the next generation infotainment system

In current systems the head unit provides the user interface for the dri- ver and optionally the co-driver. It interacts with different peripheral devices, for example a high-end audio amplifier or a country-specific digital radio, via the MOST bus. The MOST bus is used to transmit control information as well as the audio streams, including a digital 5.1 surround stream if a DVD is used as a audio source. Additionally, more and more data is transmitted over the asynchronous (packet) channel; for example, it provides metadata for music tracks or the data services for a digital broadcast system. The rear seat entertainment system is to a large extent still a stand-alone system and is not connected to the MOST bus.

The requirements that were the basis for the design of the next generation of infotainment systems can be summarized as follows:

  • Independent access to audio and video sources from all seats.
  • Access to Internet services and increased connectivity to customer devices.
  • Increased bandwidth for new features.

While the current system is basically a master/slave system with all controlling applications running on the head unit, in the next system the functions available for the rear seat passengers will be provided by rear units, which are connected to the head unit via MOST150. User interface and applications for the rear seat passengers will be executed on the rear units. A comparison for the current and the next system architecture is shown in figure 1. The challenges for the management mechanisms of a multi-seat system will be discussed in the next section.

The next Generation of Systems will provide access to Internet services and Web browsing for all seats. Therefore, IP traffic has to be transmitted efficiently over the MOST150 network, especially against the background of increasing data rates of mobile networks (e.g. LTE).

Finally, the bandwidth requirements for existing features have increased to a great extent. Reasons for this are, among others, the use of metadata (including cover art) for music tracks, the data services of digital broadcast radio (e.g. the weather information provided by the Sirius service in the USA [4]), accessing video files on storage media and the access to HTML-based information content provided by one device to the other devices in the system. All of these features have to be provided in a multi-seat context.