Mimo And Interference Coordination In LTE-Advanced Systems

As the smooth evolution of LTE system, LTE-Advanced system is now under the focus of telecommunication research. LTE-Advanced has adopted enhanced Multiple-Input Multiple-Output (MIMO), Coordinated Multiple-Point communication (CoMP), Carrier Aggregation (CA) and Heterogeneous Network (HeNet) as its key technologies. LTE-Advanced can support all the functions of LTE, further optimize the coverage of indoor scenarios, and obtain larger bandwidth with CAas well.Up to eight antennas in the downlink and eight antennas in the uplink are supported in LTE-Advanced systems, leading to up to eight parallel data streams at the same time. So the system is able to achieve higher array gain, multiplexing gain and also diversity gain. Beamforming is one of the MIMO technologies employed in LTE-Advanced, and adaptive switching between single-stream and dual-stream is supported to develop fully of potential of beamforming. But the effect of imperfect Channel State Information (CSI) has been rarely considered in past research. In this paper, a rank adaptive beamforming scheme is proposed for TDD LTE systems with imperfect CSI, in which channel estimation error acts as one of the impact factors of switching threshold, and one parameter of the switching threshold can be dynamically optimized. With the adaptation of switching threshold and the optimization of threshold parameter, more accurate adaptive switching between single-stream and dual-stream can be obtained under imperfect CSI. It is shown by simulation results that the proposed scheme can significantly improve the average cell throughput, resisting the loss by imperfect CSI effectively. In LTE-Advanced system, Orthogonal Frequency Division Multiplexing (OFDM) is used in the downlink, and Single-Carrier Frequency Division Multiple Access (SC-FDMA) is used in the uplink, resulting in no interference for the intra-cell. Therefore, inter-cell interference becomes one of the most important elements of system performance. With heterogeneous nodes introduced, inter-cell interference turns more complicated in HeNets, and traditional Inter-Cell Interference Coordination (ICIC) algorithms are not suit for HeNets. Besides, ICIC schemes in the downlink are unfit for the uplink due to constraint of user equipments. In this paper, an uplink co-channel interference coordination algorithm is proposed for HeNets, where the algorithm is applied at the receiver sides. In this algorithm, the zero space of interference user channel can be obtained with Singular Value Decomposition (SVD), and a supplement matrix is used according to a given metric, so this algorithm can achieve interference elimination or coordination and obtain full multiplexing gain at the same time. The simulation results show that the proposed algorithm outperforms the traditional Zero Forcing (ZF) and Minimum Mean Square Error (MMSE) algorithms.