CSI Reference Signal Multiplexing Using Carrier Frequency Swapping for FDD High-Order MIMO SDM

This paper proposes channel state information - reference signal (CSI-RS) multiplexing employing carrier frequency swapping for frequency division duplex (FDD) high-order multiple-input multiple-output (MIMO) spatial division multiplexing (SDM). In the proposed CSI-RS multiplexing method, the carrier frequency of a fast Fourier transform (FFT) block for multiplexing time division duplex (TDD) CSI-RSs within a subframe is swapped between the downlink and uplink. By using the proposed TDD CSI-RS multiplexing method, the CSI for performing precoding and link adaptation is estimated in the reverse link by taking advantage of the channel reciprocity feature. By using the proposed TDD CSI-RS multiplexing method, the RS overhead is decreased according to the increase in the number of simultaneously accessing sets of user equipment for multiuser MIMO. Moreover, the proposed TDD CSI-RS multiplexing method does not need fast feedback signals that track instantaneous channel response including the channel quality indicator (CQI), rank indicator (RI), and precoding matrix indicator (PMI) except for the slow feedback of the average interference level from the surrounding cells.