Multi-Antenna Cooperation In LTE-Advanced System

Along with the fast development of data communications and multimedia services, as well as the increasing demand for high mobility services, the fourth generation mobile communication - LTE-Advanced facing mobile computing and mobile multimedia, began to rise. One of the core issues of LTE-Advanced wireless communication system is how to provide higher data transmission rates within the limited spectrum resources. In order to resolve this problem, LTE-Advanced applies many new technologies including multiple input multiple output (MIMO). What's more, multi-user MIMO (MU-MIMO) and coordinated multi-point (CoMP), rather than single-user MIMO, have received more attention in LTE-Advanced.MU-MIMO and CoMP technologies of LTE-Advanced system are studied in this paper. The innovative research achievements are listed as follows.(1) The channel reciprocity is unavailable in CoMP-FDD system. To solve this problem, an effective channel compression feedback scheme was proposed, which could raise the spectrum efficiency by 20%, while increasing only 6 bits feedback overhead. The row and column of the downlink physical channel matrix were compressed, using eigenvector of the channel matrix and codebook. Then, joint precoding algorithm on the fed back channel information was applied at the cooperative base stations for further inter-cell interference mitigation.(2) To ease the multi-user interference, a novel use paring scheme was proposed, which could increase average cell throughput, especially cell-edge users'performance. Only users under certain correlation constraint would get paired. Thus, the desired signal strength could be saved from mitigating the multi-user interference. (3) To solve the precoding matrix designing of CoMP system, a simplified algorithm was proposed, which can satisfy the requirement of per base station transmit power limit while only degrading the performance lightly when compared to the total power limit. In this scheme, the optimal precoding matrix was multiplied by a diagonal matrix at the left side to adjust each antenna's transmit power and normalize each base station's transmit power.(4) Since channel estimation errors always exist in real system, the modeling methods were designed to compare the different effect of two kinds of errors, sounding reference signal (SRS) and demodulation RS (DM-RS), on system performance. Besides, the reason of this difference was analyzed.(5) To avoid the interference between paired users of uplink MU-MIMO system, the power control algorithm was improved. This algorithm could conserve the resource by cutting the redundant transmit power, and improve the transmission quality by ensuring user orthogonality.(6) In order to receive the desired signals correctly at the collaborative base stations, a new power control scheme was proposed, which could increase average cell and cell-edge spectrum efficiency by 6% and 10% respectively. The calculation method of pathloss factor was amended in the power control formula, and the traditional pathloss compensation method based on main serving base station was changed to that based on multiple base stations from the CoMP cluster.