Research On MU-MIMO User Pairing Technology In LTE

With the rapid development of new communication services, the requirement of the information capacity and transmission rate of the wireless communication system becomes higher and higher. At present, the available frequency resource is limited. Keep using the traditional way of communication could not cope with the explosive growth of requirements of communication speed and quality. It is a very important research topic that how to transmit information faster and more accurate with the limited time and frequency resources in wireless communication system.MIMO(Multiple Input Multiple Output) technology can significantly improve the channel capacity in wireless system, therefore MIMO is widely used in the 3GPP LTE(Long Term Evolution) system. In LTE uplink, however, because of the limitation of user terminal size, power and so on, most of the terminal configures only a transmitting antenna. If using the traditional MIMO technology, the system performance is limited by the number of transmitting antenna. It can’t take the advantages of MIMO to improve channel capacity. Therefore, in view of the limited number of transmitting antenna scenarios in LTE uplink, several users will be combined to form a MU-MIMO(Multiuser Multiple Input Multiple Output) system, which can achieve the better channel capacity performance as traditional MIMO in uplink transmission. MU-MIMO technology in the uplink transmission is also known as V-MIMO(Virtual Multiple Input Multiple Output). MU-MIMO technology can also be used in the LTE downlink transmission,it will be a few users to unite as a user pairing. All users in a user pairing use the same time and the same frequency resources of the system in downlink transmission. Existing research showed that the performance of MU-MIMO user pairing technology is related to three aspects, including user pairing algorithm, precoding method in senders in downlink transmission, signal detection method in receiver in uplink transmission. Therefore, this paper mainly study MU-MIMO user pairing technology from the above three aspects in LTE system. First introduced basic methods and performed simulations on them, and come up with some better solutions.MU-MIMO user pairing technology is mainly used to improve the performance of LTE system physical resource scheduling method. In the paper, we firstly introduce concepts related to MU-MIMO user pairinging technology in the physical layer of LTE system, including frame structure, resource block, the transmission technologies in LTE uplink and downlink. In addition, we also describe an overview of the MU-MIMO user pairing, common channel model of LTE system. Before introducing MU-MIMO user pairing methods, we introduce and simulate the signal detection methods and precoding methods in MU-MIMO transmission. The signal detection methods of MU-MIMO transmission include two kinds of linear detection and SIC(successive interference cancellation) detection. The precoding methods include inverse precoding, dirty paper precoding, block diagonalization precoding, Tomlinson-Harashima precoding. On this basis, the basic user pairing algorithms are analyzed and simulated, including random pairing, channel gain pairing(Matrix norm pairing), channel capacity pairing, orthogonal pairing, determinant pairing, simple Zero-force precoding pairing(block diagonalization pairing). According to the requirements and constraints of different scenarios, we finally come up with two kinds of MU-MIMO user pairing methods and two methods to reduce the computing complexity of user pairing. Improved MU-MIMO user pairing methods includes the simple bit error rate pairing, improved bit error rate pairing. Kuhn-Munkres algorithm is used to reduce the computing complexity of simple bit error rate pairing when considering two users pairing. Clustering method is used to reduce the computing complexity of improved bit error rate pairing compared with the exhaustive method, which can be used to pair users more than two. The two improved user pairing algorithms are all simulated and analysized. Simulation results shows that both simple bit error rate pairing and improved bit error rate pairing have markedly improved performance and acheived low complexity in LTE system compared with basic user pairing algorithm.