CAR-TO-CAR COMMS
ENSURING SAFETY THROUGH RF TESTING
Dr Thomas BrĂźggen, Project Manager, RF Test Systems for Intelligent Transport Systems, Rohde & Schwarz
To ensure safety-related data is received even under poor conditions, radio systems must adhere to minimum standards and be verified using RF tests.
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oad safety has improved steadily as a result of many inventions. Mechanical systems such as safety belts and airbags, as well as electronic safety equipment such as ABS and ESP, have decreased the number of accidents and their consequences in the past decades. In order to further reduce the number of accidents, new technologies are needed. Critical traffic situations can be detected before they occur through the wireless exchange of information between vehicles (V2V communications), as well as with the traffic infrastructure and all traffic participants (V2X communications). For example, all vehicles that drive through a crossing can exchange information about speed and direction. This makes it possible to detect potential collisions, issue appropriate warnings and autonomously initiate early countermeasures. However, this scenario can only become reality if there is a reliable wireless exchange of information between the vehicles, even under poor transmit conditions and without line of sight.
34 Critical Comms - Jul/Aug 2016
If a single piece of information is missed, one or more of the vehicles will gain an inaccurate view of the actual situation, conceivably with deadly consequences.
Possible interference Wireless communications systems can be affected by different types of interference. Many of these are known collectively as fading. This includes shadowing and interference caused by physical effects such as scattering, diffraction, refraction and reflection, which cause multipath propagation of the signal (Figure 1). In other words, multiple versions of the same signal are received at the antenna at different times and with different signal levels and interference. Superpositioning of the individual signals at the receive antenna can distort, attenuate or even cancel out the received signal. Traffic participants are also continuously moving, which adds a time variant to the fading scenario. All receivers inside vehicles are confronted with continually changing conditions and signal qual-
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