Practical implementation of multiple-input multiple-output visible light communication systems
Wireless data transmission occurs everywhere and the global data traffic is growing rapidly. Current radio frequency (RF) spectrum resource is becoming saturated and our current RF based wireless communication system will not meet the demands for data traffic in the future. Research efforts have been put into increasing the spectral efficiency of existing RF networks. Techniques such as multiple-input multiple-output (MIMO), have been well studied. However, it is still insufficient for the rapid growth of the wireless data traffic. The visible light (VL) spectrum is over 1000 times wider than the size of the entire 300 GHz RF spectrum, therefore, it is a viable alternative resource. The spread of light emitting diode (LED) lighting infrastructures provides a good opportunity for visible light communication (VLC). VLC turns the LEDs into high speed wireless data transmitter while retaining their illumination function. VLC has drawn much attention in recent years. MIMO techniques have also been studied in VLC. However, there have only been a few studies that compared practical MIMO VLC systems with theoretical studies. In this thesis, several practical implementations of the MIMO VLC system have been presented. First, a generalised space shift keying (GSSK) system, which is a simple form of spatial modulation (SM), has been presented. The performance of the field programmable gate array (FPGA) based real-time system has been studied against different transmitter (Tx) and receiver (Rx) numbers. The performance against mobility has also been evaluated. Up to 16 transmitters have been used and the result shows high spectral efficiency is achievable with the low complexity implementation of GSSK. Second, an investigation of an ultra-high speed wavelength division multiplexing (WDM) VLC system using inexpensive, low-complexity front-end components has been developed. We have used ordinary off-the-shelf red, green, blue and yellow (RGBY) LEDs in surface-mount technology (SMT). The result shows that a data rate of over 15 Gbits/s can be achieved by using proper optimising procedures on the inexpensive commercially available components. This study has confirmed the potential of high achievable capacities of VLC systems. Third, the first MIMO VLC system using organic photovoltaics (OPVs) has been implemented featuring simultaneous data communication and energy harvesting. Record data rates of 102 Mbits/s for a single pixel and 146 Mbits/s for a 2-by-2 MIMO set-up have been presented. The first system model for MIMO OPV VLC system has been proposed. The model has been validated with experimental results. The scalability of the system has also been discussed.