Research On MU-MIMO Technology For Indoor Visible Light Communication Systems

Because of license-free light spectrum,low-cost devices and immunity to radio frequency(RF)interference,visible light communication(VLC)has become a promising candidate to address the current challenges in wireless communications.Indoor illumination systems are typically equipped with multiple LEDs,which make the multiple-input multiple-output(MIMO)a natural choice for indoor VLC systems.The unique transmission mechanism and special transmission environment of the indoor visible light communication system make the mature multi-user MIMO technology of the wireless electromagnetic wave communication system can not be applied directly.This dissertation studies the multi-user MIMO technology by combining the characteristics of the multi-user indoor visible light communication system itself.The main innovative results obtained of this dissertation are presented as follows.First,this dissertation uses two indicators,the correlation index and the conditional number,to give the quantitative indication of the correlation of MIMO channel in indoor visible light communication systems.Research on the MIMO channel correlation showes that,in the indoor visible light communication system,channel correlation between different PDs belonging to the same user are particularly high,and the FOV diversity scheme has little effect on the reduction of the channel correlation.Second,Based on the light source distribution characteristics of indoor visible light communication system,this dissertation proposes a power-efficient MIMO transmission scheme for MU-MISO visible light communicaton systems.The main idea of this scheme is that the channel matrix used to perform pseudoinverse comes from the set of optical access points(APs)shared by more than one user,instead of the set of all involved serving APs as the existing Zero Force(ZF)precoding schemes often used.By doing this,the waste of power,which is caused by the transmission of one user's data in the un-serving APs,can be avoided.In addition,the size of the channel matrix needs to perform pseudoinverse becomes smaller,which helps to reduce the computation complexity.The simulation results and the theoretical analysis show that the power-efficient MIMO transmission scheme can achieve higher data rate compared with the existing schemes.Third,by incorporating the power-method algorithm and the block diagonalization(BD)algorithm,this dissertation proposes a joint precoding scheme for MU-MIMO visible light communicaton systems.this scheme adopts the iteration method instead of the SVD merhod used in the existing schemes to calculate the eigenvectors corresponding to the largest eigenvalues,which reduces the ca;culation cost.The simulation results indicate that the proposed scheme has almost the same system data rate as that of the traditional schemes.Fourth,in view of the application of multiuser MIMO technology in different scenarios,this dissertation proposes an equivalent ZF precoding scheme and an enhanced equivalent ZF precoding scheme.The contrast results show that the equivalent ZF scheme has an obvious advantage on user rate and has lowest complexity,while the enhanced equivalent ZF scheme has the best system rate performance.These two schemes can be applied to two different scenarios: the equivalent ZF precoding scheme is suitable for the indoor scenario with a small number of users,while the enhanced equivalent ZF precoding scheme is suitable for the indoor scenario with a large number of users.