Analysis of multipath impulse response of diffuse and quasi-diffuse optical links for IR-WLAN

This paper studies the variation on the power budget, in an infrared optical link for indoor channels with multipath propagation. The multipath propagation produces heavy distortion over the received signal and reduces the maximum baud rate for a given bit error rate. Focusing on IR wireless local area network (IRWLAN), we study some emitter and receiver configurations. In order to allow computer portability these links can be diffuse or quasi-diffuse. These channels do not rely upon the line-of-the-sight path. This works deals not only with the total received power, but with its time and spatial distribution. This paper considers the channel as characterized by its channel transfer function in a deterministic way. This is a good approximation if the variations in the environmental conditions are slow enough compared with the baud rate of the communication system. The source is an IR emitter diode (IRED) with different values of directivity, pointing to a reflecting surface, while the receiver is a photodiode characterized through its field of view (F.O.V.) value. The results show that an optical Q-diffuse link improves the performances of a diffuse one. We use for the comparative analysis the RMS spread delay of the impulse response, the spatial distribution of received power and its standard deviation from the mean. We present extensive simulation results, an emitter configuration and the first measured results obtained using an APD as receiver