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Trends affecting automotive RF system tests

Posted: 27 Apr 2016     Print Version  Bookmark and Share

Keywords:wireless communication  car-to-car  C2C  eCall  ISO 26262 

ISO 26262 prescribes the requirements for guaranteeing the functional safety of a system, starting from its specification, through design, implementation, integration, verification, validation, and finally to production release. Under the specifications of ISO 26262, equipment is required to achieve a certain ASIL (automotive safety integrity level) grade: this is a risk classification scheme defined by the standard.

The application of ISO 26262 to systems that include a radio is going to dramatically intensify and prolong the testing that RF engineers will need to perform. RF engineers are going to have to develop models which capture and characterise every possible risk which a failing or malfunctioning RF system presents to the operation of the vehicle. They will need to exhaustively catalogue the failure modes of the radio. And they will then need to devise and document testing regimes that verify, with a very high level of confidence, both the risk of failure, and the way in which the radio will handle each failure mode.

In other words, the complexity and duration of RF tests will be far beyond those experienced by most RF engineers working in industry today.

Testing for dynamic network topologies
As has been shown, ADAS and driver information systems of various kinds are going to become increasingly important features in passenger vehicles. Today, these make considerable use of cameras. But in low visibility, for instance because of heavy rain or snow, their operation might be impaired. Even road markings might be impossible to see in snow or ice.

To provide supplementary or more reliable information about road conditions and the operation of the vehicle, car manufacturers are going to implement comprehensive C2I (Car-to-Infrastructure) and C2C communications systems, based on the IEEE 802.11 standards and mobile telephone technology.

Mobile telephone networks are useful for automotive communications because they already cover large parts of the globe, are highly standardised, and provide a robust communications link for fast-moving user equipment.

Legacy technologies such as 2G and 3G will be needed for in-car telephony, browsing the internet and the eCall (European) emergency communications system, described below. But their relatively low bandwidth and high latency make them unsuitable for real-time applications such as the control of autonomous cars. New mobile phone technologies however – LTE (4G) and 5G – will meet the requirement for real-time C2I communications.

In C2C communication, the technology for co-operative Intelligent Transport Systems (ITS) is derived from the IEEE 802.11 wireless local area networking (WLAN) standard which is also the basis for Wi-Fi. A specific frequency spectrum in the 5.9GHz range has been allocated to it in Europe, in line with similar allocations in the US. As soon as two or more cars or ITS stations are in range, they will connect automatically and set up an ad hoc network in which all ITS stations know the location, speed and direction of the surrounding stations, and will be able to share messages, warnings and information.

As the communication range of a WLAN connection is limited to a few hundred metres, every vehicle also acts as a router for message forwarding. The routing algorithm will be based on the position of the vehicles, and can handle rapid changes to the ad hoc network topology (table).

The implementation of C2C wireless communications thus calls not only for robust RF performance, a physical layer function which can readily be verified with the use of an instrument such as a spectrum analyser – the MS2830A from Anritsu is a good example. The system designer must also implement a sophisticated test plan for verifying the protocol layer performance, to show that it can handle rapid changes in network topology without dropping packets or losing connections. As above, standard test specifications might not capture the full depth of testing required under the provisions of ISO 26262, and this looks set to demand a new approach to the design and implementation of test routines from automotive RF engineers.

Table: Transfer rates, modulation schemes and coding rates specified in the IEEE 802.11p standard, for a 10MHz channel bandwidth.

eCall: another safety-critical technology
The European Union's eCall system, and the similar ERA-GLONASS (in Russia) combines mobile communications and satellite positioning to provide fast, reliable assistance to motorists in the event of an accident.

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