access icon free Design of light-emitting-diode array for solving problems of irregular radiation pattern and signal attenuation for infrared electronic-toll-collection systems

© The Institution of Engineering and Technology
Received 20/05/2013, Accepted 05/04/2014, Revised 31/03/2014, Published 01/07/2014

Infrared light emitting diodes (LEDs) with a half-intensity angle Φ1/2 ≃ 10° are suitable for electronic-toll-collection (ETC) applications. However, the radiation patterns of commonly available low-cost commercial infrared LEDs are irregular to some extent, which result in difficulties to construct an infrared ETC system with a proper communication area. Most low-cost infrared LEDs with a half-intensity angle Φ1/2 ≃ 10° exhibit a common irregularity in their radiation pattern – a notch in the central radiant direction. The adverse influence bccause of such irregularities can be reduced by a proper design of an LED array in the emitter. High attenuation for the infrared signal of some windshields is also a serious problem for infrared ETC systems, which leads to severe shrinkage of the communication area if the emitter has not been properly designed. In this study, the authors present some successful designs with the aid of an optimisation algorithm to adjust the mounting angle of each constituent LED. In spite of the aforementioned irregularity, the proposed design still exhibits good performance in terms of the ability to withstand high signal attenuation and extended communication area in the vehicle-travelling direction.

Inspec keywords: optimisation; infrared detectors; road pricing (tolls); light emitting diodes; error statistics; intelligent transportation systems

Other keywords: LED notch compensation; irregular radiation pattern; light emitting diode array design; half intensity angle adjustment; central radiant direction; mounting angle adjustment; optimisation algorithm; infrared electronic-toll-collection system; vehicle travelling direction; commercial infrared LED; signal attenuation; bit error rate; ETC system; emitter; received signal strength; ETC requirements; ETC mounting configuration; cosine function; on-board unit; road side unit

Subjects: Light emitting diodes; Photodetectors; Optimisation techniques; Optimisation techniques; Traffic engineering computing; Other topics in statistics; Other topics in statistics

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