Research On The Performance Of Indoor Visible Light Communication System Based On THP Algorithm

Visible light communication(VLC) is a technique which is based on the white light-emitting diode(LED) and combines lighting and data communication. VLC is widely considered to be the new wireless communications technique, but there are still some limitations. The main challenge of VLC is the limited bandwidth of LED, which limits the transmission rate. Therefore, the multi-user multiple input multiple output(MU-MIMO) indoor VLC system has been proposed. However, multi-user interference(MUI) is the main factor which affects the performances of MU-MIMO indoor VLC system.Precoding is an effective method to eliminate MUI. A linear precoding MU-MIMO indoor VLC system has been proposed utilizing block diagonalization(BD) algorithm. Although BD precoding algorithm can eliminate MUI with simple linear operations and singular value decomposition(SVD), the performance of optical detectors belonging to single user terminal differs significantly. Tomlinson-Harashima precoding(THP) algorithm is generally considered as a much better scheme in MIMO systems. Therefore, in this paper, we utilize THP and optimized THP(OTHP) schemes to eliminate MUI in MU-MIMO indoor VLC system.Firstly, this thesis introduces the fundamental theory of indoor VLC system based on white LED. And the modulation characteristic and properties of white LED is analyzed.Secondly, the fundamental theories of BD, THP and OTHP are introduced. In order to reduce the channel correlation of this system, different field of view(FOV) of optical detectors which belong to single user terminal is adopted. The bit error rate(BER) performance comparison of BD, THP and OTHP algorithms in VLC system is analyzed. Simulation results show that the OTHP algorithm could achieve better performance.Finally, in order to further reduce the correlation of the optical detectors, titled detector and multidirectional optical receiver with different FOV have been adopted. Based on these solutions, the BER performance of the MU-MIMO VLC system using OTHP is investigated. In addition, the impact of user terminals’ mobility on the system is analyzed.