Wireless telecommunication techniques are a prerequisite for information exchange between moving objects and stationary systems. Wireless communication is primarily realised using electromagnetic waves, however, short distances can also be bridged using infrared communication. The coverage of very large areas encounters several problems which originate from the characteristics of electromagnetic waves. In an idealised scenario electromagnetic waves spread equally in all directions. The intensity of electromagnetic waves reduces quadratically with the distance to the transmitter. In real-life, reflections, absorptions, scattering, refractions, and electromagnetic perturbations reduce the intensity of electromagnetic waves significantly. Thus, the reduction of intensity reduces in the fourth power with the distance. That is, in order to double the geographic coverage, a 16 times stronger transmitter is needed. As electromagnetic waves with equal frequencies sent by different transmitters interfere with another, radio communication requires the reservation of the used radio frequencies. However, frequency ranges are limited and wireless telecommunication techniques have to appropriately deal with this problem.
The most important wireless telecommunictaion techniques for transport telematics applications are: