Wavelet analysis and artificial intelligence for diffuse indoor optical wireless communications

Dickenson, Robert (2007) Wavelet analysis and artificial intelligence for diffuse indoor optical wireless communications. Doctoral thesis, Northumbria University.

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Abstract

This thesis investigates the use of Wavelet Analysis and Artificial Intelligence as elements of a diffuse indoor infrared (IR) optical wireless communications receiver. The work presented employs MatlabTM enabled simulations to explore the effects of inter symbol interference (ISI) and fluorescent light interference on a receiver using these techniques. The results are compared with those obtained from traditional receiver architectures. IR devices have been commonplace in most households as remote control handsets for domestic entertainment equipment for many years. More recently, IR communication systems have been deployed in mobile phones, laptop computers and computer peripheral devices largely for the purpose of short range point-to-point data transfers. Since the late 1970's there has been consistent interest and research in the use of the IR part of the spectrum for short-range Wireless Local Area Networks (WLAN). IR offers a number of potential advantages over radio frequency systems such as unregulated and re-usable bandwidth, inherent security, resistance to multipath fading and the availability of mass produced, low cost emitters and detectors. However, significant problems still persist to impede the widespread and popular deployment of IR enabled LANs. The work presented in this thesis focuses on the use of the largely software enabled techniques of Wavelet Analysis and Artificial Intelligence (Wavelet-AI) as novel alternatives to mitigating the difficulties associated with diffuse indoor IR communication systems. Indoor IR wireless links usually have to operate in the presence of intense noise generated by ambient light sources. The source can be natural sunlight from doors and windows, or artificial light from incandescent and fluorescent fittings. In addition to contributing to the generation of shot noise, artificial light sources can also impose a periodic interference signal that can significantly impair the performance of an optical link. Electrical high pass filtering is a typical mitigating technique that is effective at reducing the interference signal. Unfortunately it also introduces a performance degrading phenomenon known as baseline wander. Using well established interferer models the results of original Wavelet-AI inclusive simulations are presented and compared with those of typical receiver architectures with and without electrical high pass filtering. The performance of Wavelet-AI based receiver was found to be superior to traditional unfiltered receiver architecture in the presence of artificial light interference. At low to medium data rates the Wavelet-AI receiver was also found to outperform all but one case of the traditional receiver architecture employing electrical high pass filtering. The results of baseline wander simulations with On-and-Off keying (00K) modulation and the Wavelet-Al receiver architectures is presented and shows that the Wavelet-AI architecture is far more tolerant to baseline wander. In diffuse or non-directed links multipath propagation induced ISI can impose a significant performance penalty for data rates above approximately 10 Mb/s. Typical compensation techniques include the use of equalisers such as the zero-forcing equaliser (ZFE), the minimum mean square equaliser (MMSE) and the decision feedback equaliser (DFE), usually implemented as digital filters. The results of original Wavelet-Al inclusive simulations are presented and compared with those of typical receiver architectures with and without filtering and equalisers. In all cases the simulation results show that the Wavelet-Al receiver architecture performance is superior to the non-equalised traditional receiver. The Wavelet-AI receiver results show a very similar performance to the equalised traditional OOK receiver and the equalised Level 4 Pulse Position Modulation (4-PPM) receiver. However, between a 2 dB and 4 dB optical power penalty was incurred for the 8-PPM Wavelet-AI case. This result may not...

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