Design of the Radiation Pattern of Infrared Short-Range Communication Systems for Electronic-Toll-Collection Applications

This paper proposes a very simple method for enhancing the performance of infrared electronic-toll-collection systems. Using two typical low-cost commercial LEDs with different half-intensity angles Phi_1/2 = 22deg and 10deg, the radiation pattern of the emitting module of an infrared short-range communication system for electronic-toll-collection applications is designed. This enables us to construct a system that has an extended communication region and can withstand high signal attenuation. When the module is fabricated with a proper combination of the numbers of these two different LEDs, together with a suitable mounting angle of each LED, an effective radiation pattern is obtained. The mounting angle of each LED is found with the aid of an optimization algorithm. The performances of three different designs are compared in terms of signal strength, communication length, and 2-D communication region. The results show that a module consisting of ten LEDs divided into three groups, with each group having a proper mounting angle and containing an appropriate number of LEDs, can have much better performance than conventional single-group unidirectional designs. The influence of the defect of the radiation pattern, which may happen on many LEDs, on system performance is also discussed. The results of the analysis are confirmed by experimental measurements.