Design of Wireless Optical MIMO Links

Abstract

Wireless optical MIMO links can achieve very high data transmission rates by exploiting spatial diversity at a grand scale. Although such links can achieve high rates, their practical implementation remains challenging. The difficulty in implementation arises due to the complex transmitter and receiver designs required to overcome the channel impairments. This thesis considers practical transmitter and receiver designs for the wireless optical MIMO channel in the presence of channel impairments. In the first part of the thesis, two techniques to improve channel capacity for wireless optical MIMO channels are presented. The first technique uses multilevel half toning to reduce quantization noise power. For quantization noise-limited systems, increasing the number of quantizer levels provides gains in capacity. For example, at a rate of 200fps, a four-level quantizer gives approximately a two-fold increase in capacity over a binary-level quantizer for all frame sizes considered. The second technique uses higher order noise shaping to shape the quantization noise to the out-of-band spatial frequency spectrum. This technique is shown to be useful when the number of levels is small, i.e., near 2. In the second part of the thesis, the receiver design for wireless optical MIMO channels with magnification is considered. The work done in this part constitute a step towards the practical implementation of such links since it is the first time the effects of spatial transformations are considered. Signal magnification introduces varying spatial frequency inter-channel interference (SF-ICI) at the receiver. A novel receiver design that uses complex windowing with decision feedback equalization is used to equalize the SF-ICI in spatial frequency domain. For SF-ICI limited channels, the novel receiver design achieved a low bit-error rate compared with rectangular windowing with zero-forcing equalization. However, for noise limited channels, rectangular windowing with zero-forcing equalization is the receiver design of choice.