Multi-user THSS system for indoor wireless optical communications with angle-diversity detection

Abstract

In this paper, an infrared wireless communications system based on THSS techniques employing angle-diversity detection is studied via simulation. Although the system is designed to operate at infrared wavelengths, it can also be used for Visible Light Communications (VLC). Time-Hopping codification is based on splitting the symbol period into several short slots. In order to specify which slots are used to transmit and which are not, the use of maximum length sequences is considered. The remaining time slots can be used by other users so as to provide the system with multiple access capabilities. In this paper, a 2-PPM modulation scheme is selected because it yields good results in infrared systems as well as in VLC. Furthermore, the THSS system allows for selecting the number of pulses per symbol to be transmitted and makes use of an optimum maximum-likelihood receiver for AWGN channels with the ability to choose between hard or soft decision decoding. The system designed allows for comparing the performance based on the computation of the bit error rate (BER) as a function of the pulse energy to noise power spectral density ratio, for different configurations in single-user and multi-user environments. The results show a significant enhancement when angle-diversity receivers are used as compared to employing receivers using a single-element detector with a wide field of view (FOV). In this paper, two angle-diversity structures are compared: conventional and sectored receivers. Although the sectored receiver exhibits better BER than the conventional receiver, its implementation is more complex.