Research On Precoding Techniques Of LOS MIMO In Millimeter Wave Communication System

LOS MIMO system has the advantages of increasing the channel capacity and improving the system performance, and the influence of antenna array position is a little influence on channel capacity of the system in LOS MIMO, so we can see that it has a broad application prospect. But when the phase of the direct pathes in LOS MIMO system are close, the correlation of each channel becomes large. So detecting the signals in recever becomes difficulty. What is worse, the capacity of system will be lower, when the system is covered. In order to taking advantage of the LOS MIMO system and reducing the complexity of signal detection in receiver, more and more people start to focus on precoding technology in LOS MIMO system which has nice performance and low complexity.This paper will show the characteristics of the channel model in LOS MIMO systems to us, through comparing the channel model of the LOS MIMO and the NLOS MIMO systems. And we can see that channel capacity in LOS MIMO system is larger than it in NLOS MIMO system when the other environmen factors are the same. The distance between the antennas has influence on channel capacity in LOS MIMO systems, and this paper will show the fixed distance between the antennas in certain conditions.Three precoding algorithms based on NLOS MIMO which were proposed by previous are simulated in LOS MIMO systems. On the basis of the optimization of channel capacity, a new precoding algorithm in LOS MIMO single-user systems is proposed through calculation and analysis in this paper. This algorithm combines the characteristics of the LOS MIMO channel model. And this algorithm has been simulated with some other traditonal algorithm in LOS MIMO systems with different antenna array. The simulation results show that the new algorithm has better performance in bit error rate. Finally, the new algorithm can be simplified in the uniform circular array LOS MIMO systems.Four precoding algorithms based on NLOS MIMO multiuser systems which were proposed by previous are simulated in LOS MIMO multiuser systems. The simulation results show that the signal leakage noise ratio(SLNR) algorithm has optimal performance in LOS MIMO multiuser systems. Because SLNR algorithm has great advantage in eliminating interference between users, this paper proposes a improved algorithm combined with the precoding algorithm which is proposed in the third chapter. The improved algorithm has the advantage of SLNR, at the same time it also has the advantage of the new algorithm proposed in three chapter which can eliminate interference between antennas of one user. This algorithm has been simulated with SLNR algorithm in LOS MIMO multiuser systems. The simulation results show that the new algorithm has better performance in both bit error rate and channel apacity.