Research On User Pairing Algorithms Of The Virtual MIMO System In LTE Uplink

With the rapid development of mobile communication technologies, the current radio channel resources have becoming increasingly intensive. And how to improve the utilization rate of channel effectively has always been an important issue for the researchers in the field of mobile communication. Due to the great potentialities shown by MIMO in improving the system capacity and channel utilization, it has received researchers’extensive attention and has been listed as one of the compulsory key technologies in the3GPP LTE program.Due to many factors such as UE’s size, cost and power consumption, It’s hard for MIMO to be used in uplink transmission of LTE. As a good solution to solve the problem, Virtual MIMO is such a technology that selects several independent single-antenna UEs to form a group, and then let them to transmit data using the same time/frequency resource. As a result, it achieves spatial multiplexing gain and diversity gain well, and improves the system capacity and channel utilization effectively. As the key point of Virtual MIMO, the quality of the user pairing algorithm affects the system performances directly.In view of the great application prospects shown by Virtual MIMO, this paper mainly focused on the research of user pairing algorithm of Virtual MIMO, and proposed two improved schemes of SUP algorithm on the basis of extensive research on it. The main work of this paper are listed as follows:(1) General analysis of the evolution about3GPP LTE Program was carried out, then the network architecture and technical characters of LTE System were studied. Accordingly, the application background of Virtual MIMO was introduced.(2) A lot of fundamental research work involved the principles, generating methods, system model and technical characters of OFDMA, SC-FDMA and MIMO were carried out extensively, and the necessity of application for Virtual MIMO was derived finally.(3) First, we analyzed the channel capacity of Virtual MIMO. Then the research involved in many aspects such as the principles, pairing process, the merits and drawbacks of several classical user pairing algorithms of Virtual MIMO were carried out, and the system throughputs and user fairness of the several typical algorithms was simulated and analyzed.(4) This dissertation gives some analysis on one kind of SUP algorithm and points out the drawbacks in fairness of it. Referring to the drawbacks shown by SUP algorithm, two modifications were proposed in this paper. The first one is SUP Semi-orthogonal user pairing algorithm based on SNR threshold. In this scheme, the users whose SNR are under the threshold should be transmitted in a direct way, and the others should be transmitted in pairs according to the SUP algorithm. In the second modification, the Proportional fairness criteria has been introduced to the SUP algorithm instead of the previous SINR pairing criteria. Finally, the simulation results show that the modifications have been improved in fairness compared to the original algorithm and the system throughout is very close, which provides a good algorithm scheme options for practical engineering applications.