Research Of Interference Coordination In Massive Distributed MIMO System

With the development of modern mobile communication technology, the data capacity of the communi-cation system has become larger. All kinds of technical researches aim to improve the capacity of the mobile communication system further and make it close to the limitation of channel capacity given by Shannon Channel Capacity Equation. Due to the proposal and development of Turbo code, LDPC, MIMO system, OFDM and so on, the restraining effect of channel noise and fading, which limits the transferring capacity of mobile communication system before, become smaller. On the other hand, because of the scale of mobile communication network becoming larger today, total frequency multiplex is adopted among cells, as frequen-cy multiplexing factor to be 1, to improve the channel capacity. So more interference inside and among cells become a serious obstruction to the improvement of capacity transferred in mobile communication system. The question, that how to deal with interference effectively, has become a hot issue in the theoretical study.In recent theoretical researches, an interference coordination scheme called interference alignment has been put forward, which converts the interference signal to the orthogonal subspace of effective signals in the receiver, so that the interference signal can be separated and will not cause interference to the effective signals waiting to be received. The proposal of this theory attracts widespread attention immediately. This thesis gives a theoretical introduction and simulated analysis of some kinds of distributed interference alignment scheme, such as interference alignment based on minimum leakage of interference, interference alignment based on sorted QR decomposition, interference alignment based on power control, interference alignment based on maximum signal to interference plus noise ratio, interference alignment based on minimum mean square error, interference alignment based on relay and so on. The simulation results show that distributed interference alignment has an excellent performance on improving channel capacity.In the calculation process of interference alignment, channel state information has a large effect on the performance results. So this thesis gives the introduction of the definition and the access of channel state information, especially the process of channel state information quantification and feedback with limited-bits feedback, and discusses the problems to be considered when limited-bits feedback is used in the process of interference alignment. Based on this, the thesis also proposes a limited-bits feedback scheme based on unit circle quantization. The simulation analysis has proved that in some certain system conditions, the limited-bits feedback scheme based on unit circle quantization has better system performance in total chan-nel transmission capacity, with very little cost of computational complexity, than the limited-bits feedback scheme based on tranditional quantization codebook created by LBG algorithm. Because there has error in the process of channel estimation and quantization, it will lead to uncertain channel state information. So this thesis gives discussion and simulation analysis of the effect to the distributed interference alignment per- formance, caused by the uncertainty of channel state information. It shows that the larger the uncertainty of channel state information is, the poorer the performance of channel transferring capacity got by distributed interference alignment algorithm will be.IEEE802.11 protocol sets the transferring standard in the wireless mobile network which is call WIFI. Because of the adoption of Carrier Sense Multiple Access with Collision Avoidance, so when the amount of mobile terminals linked to the base station becomes larger, the interference among users will be more serious and reduce the access rates and transmission efficiency of the system greatly. So this thesis tries to use the improvement of Time Division Multiple Access on the downlink, based on the original IEEE802.11 protocol, to reduce the interference among users and improve the transmission efficiency of the system. This thesis introduces the related concept and realization of the improvement scheme and use OpenWRT platform to do examinations in hardware. The result shows that in the situation of more users, the improvement scheme using approximate time division multiple access in the downlink, has some improvement in the total system transmission rate, compared with the standard scheme in the original protocol.