Precoding In Multiuser MIMO System Of Security Communication

To meet the requirements of the continuous development of the business, the MIMO is a proposed by researchers. MIMO can improve the capacity and channel utilization technology. One of the key technology is precoding technology. The performance of the precoding methods are always closely related to performance of MIMO. But the MIMO system is vulnerable to multiple interference. In multiuser MIMO communication system, the interference come from its own user’s antenna interface and other users’ antenna interface.In order to improve the performance,sometimes we also need to add artificial interference. Therefore, how to improve the performance of the system by eliminating interference, improving the capacity, reducing the error rate or reducing the complexity is urgent to consider about. A variety of precoding schemes have their own advantages and disadvantages.In many cases, we cannot achieve the optimal multiple performance at the same time, so we need to take a compromise in the performance indicators. Precoding technology has become the has been a hot area of research for several years.This article mainly revolves the linear multiuser precoding technology with the secure communication background. I have done some research based on the common linear precoding technology and proposed some methods to improve the performance of MIMO.Firstly, under the circumstances that the secure communication system circumstances does not exist the null space, the common algorithm set the channel zero to ensure the requirements to resolve the null space. We can also achieve the optimal capacity by the water filling algorithm for each user. However, by designing of the weighted matrix at the receiver, we can obtain better capacity and the secrecy capacity than previous methods.The design of the weighted matrix at the receiver can be converted to solve the optimal objective function under the constraint condition value. The simulation results show that, this method proposed can improve the sum capacity and security capacity.Besides we can see that under some certain conditions such as the fixed Qos of the users, sending the artificial noise is beneficial to improve the safety performance when the Qos is satisfied.Secondly, we put forward two methods which can improve the performance of the MIMO system.For example, in order to reduce the complexity, we propose a method for multiuser system. To reduce the complexity of algorithm,we use the method of solving the generalized inverse matrix to get the null space and eliminate multiuser interference, then use an decomposition method ofchannel to reduce the error rate. Besides, in order to reduce the error rate, we put forward an another method of MIMO system. Our purpose is to make the equivalent channel more perfect because the unevenness is still a big problem in the common channel decomposition. We can solve the problem by convert the problem to the objective function. As a result he channel is decomposed into uniform channel and the error rate descends. The two kind of method is suitable for different goals. The simulation proves the availability of the two methods.