Optical wireless communication systems employing dual header pulse interval modulation (DH-PIM)
Indoor optical wireless communication systems have been shown to be viable alternatives to radio systems for indoor networks because optical wireless systems offer a huge unlicensed bandwidth, high data rates, secure connectivity, immunity to electromagnetic interference and prevention from multipath fading. However, optical wireless systems are subject to multipath distortion and are governed by eye safety standards. Therefore, a modulation scheme is required that is capable of providing high speed and good immunity to multipath dispersion on indoor optical channels. In this thesis, a critical review of optical wireless systems and suitable modulation schemes has been presented. A new modulation scheme called dual header pulse interval modulation (DH-PTh1) is presented. A comprehensive theoretical analysis supported by computer simulations has been carried out to study characteristics of DH-PTh1. Novel expressions for the DH-PTh1 pulse train, symbol length, bandwidth requirement, packet transmission rate, transmission capacity, Fourier transform, power spectral density, slot and packet error rates and power requirement and penalty due to multipath propagation have been presented. Results from the analyses have been compared with OaK, PPM and DPTh1 modulation schemes. It has been shown that DH-PTh1 is a viable alternative scheme for indoor optical wireless communications, due to its built-in symbol synchronisation and relatively easy slot synchronisation. Compared with PPM and DPIM, DH-PIM offers shorter symbol lengths, improved transmission rates, increased transmission capacity, improved bandwidth requirement and better immunity to multipath dispersion when the dispersion is high. However these features are at the expense of a slightly higher optical power requirement and increased probability of error. The proposed scheme is suitable for applications where there is a need for high throughput.
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