Feasibility of adaptive 4×4 MIMO system using channel reciprocity in FDD mode

The knowledge of state information (CSI) is necessary to be known at transmitter in a multiple input multiple output (MIMO) system in order to improve the capacity performance. Among methods to realize CSI at transmitter, the use of reciprocity principle is the most attractive technique for implementation. This is because CSI at transmitter is easily estimated by the reverse channel where the forward and reverse channels are symmetrically considered in time, frequency and location. In frequency division duplex (FDD) mode, forward and reverse links are allocated by different frequency thus channel reciprocity fails under this condition. In this paper, the capacity performances of adaptive 4times4 MIMO system based on measured data are presented. Also the feasible method to compensate the differences between TDD and FDD channels is studied. The results reveal that the capacity of adaptive MIMO system in FDD mode can be improved by compensation technique.