Research On The Performance Of Precoding Multi-user MIMO Indoor Visible Light Communication Systems

Light-emitting diodes (LED) are expected to be the substitute of conventional incandescent andfluorescent lamp due to its lower power consumption, high efficiency and longer lifetime. Visiblelight communication (VLC) is a technique which combines lighting and data communication. Atpresent, the main challenage of VLC is the limited bandwidth of LED, typically several MHz.However, according to the revelant international standard, sufficient illuminance is required forindoor environment, which enables the received optical signal to achieve a relatively highsingal-to-noise-ratio (SNR). Hence, the multiple input multiple output (MIMO) technique appearsattractive to achieve high data rate in VLC systems and it has attracted mamy researchers’interests.Multi-user interference (MUI) is the main factor which affects the performances of multi-user(MU) MIMO indoor VLC system. This thesis focused on the existing MUI issuse in indoorMU-MIMO VLC systems to do preliminary research. The scheme of precoding MU-MIMO indoorVLC system is proposed. We investigated the limitation of block diagonalization (BD) algorithm inVLC systems and its corresponding solutions. Performances of the proposed system are analyzed indetails.In this thesis, we first introduced the fundamental theory of indoor VLC system, including theproperties of white LED, the characteristic of VLC channel, and the noise at optical receiver. Basedon a typical indoor VLC system, the distribution of illuminance at receiving plane is investigated.Secondly, the configuration of precoding MU-MIMO indoor VLC system is proposed in thisthesis. The transmitter, channel and receiver of the proposed system are described in details. Thelimitation of BD algorithm in VLC system is analyzed.Finally, in order to improve performances of the proposed system, three corresponding solutionsare proposed to reduce the channel correlation of MU-MIMO indoor VLC systems, i.e., utilizingdifferent field of view (FOV) for optical detectors which belong to single user terminal; tiltedoptical detector and multidirectional optical receiver with different FOV. Based on these solutions,the bit error rate (BER) and SNR performances are investigated. In addition, the impact of userterminals’ mobility on the proposed system is analyzed in this thesis, with consideration of themobility of user terminals in practical indoor VLC system.