| LTE(Long Term Evolution) has chosen MIMO and OFDM as its physical layer technology, which absorbs the achievements in development of the multi-antenna theory and DSP technology, breaking bottleneck of capacity of wireless systems and improving the communication reliability as well. Precoding technology is one of the key applications of multi-antenna technology, however, in the LTE system, it has its limitations, for commercial LTE systems nowadays continue to use the precoding codebook which was defined in Release8, this codebook is fit for the SU-MIMO model, but with the requirement increase, MU-MIMO model will be an important way of further improving system performance, unluckily, but codebook in Release8can’t be able to provide sufficient support to MU-MIMO. Furthermore, the performance of MU-MIMO is very sensitive to channel information, the original CSI feedback model needs modification as well, as a result, LTE-A, which is the evolution of LTE, regards the improvement of multi-antenna technology as an important direction.We first present the model of downlink precoding system of LTE-A system, and analyze its impacts on system performance theoretically. Then introduce the design of codebook in release8with the analysis of its features and defects, by analyzing the8antennas codebook in release10, we introduce the important direction of release12-design of codebook of4antennas. We have chosen two of the most typical cases as a compare, and proposed our own scheme, which is a double stage codebook scheme. The simulation results show that our scheme is better than the other designs considering the gains and overhead.For MU-MIMO systems, channel information deviation will affect system performance greatly. At present, while scheduling multiple users, the channel state information(CSI) which is the base of scheduling, is derived from the uplink feedback from these users, but this CSI information doesn’t include any interferences between users which were scheduled in the same resource block, as a result, the base stations have to estimate the interference itself so as to implement link adaptation, which lead to great deviation mentioned above. LTE-Advanced system is considering a new kind of CSI feedback model to support MU-MIMO, so we choose the most famous one-BCI scheme to do our feasible research. We compare the CSI estimation scheme which is used most currently with BCI scheme under our simulation platform, and the results shows that BCI scheme needs further research and modification so as to support more other scenarios. |
PDF Full Text Request