Hybrid beamforming method for wireless multi-antenna and frequency-division duplex systems

1. A base station (BS) for wireless communication comprising a plural of antennas and radio frequency (RF) transmitting and receiving chains: a plural of base band transmitting paths with a digital to analog converter (DAC) and base band receiving paths with an analog to digital converter (ADC) whereas the number of base band transmitting and receiving paths is less than the number of antennas; and a processor that constructs a subspace for each user equipment (UE) using the principal angle information contained in partial channel state information (CSI) obtained on channels associated with a part of the BS antennas, derives an analog beamforming matrix and/or an analog combining matrix from the subspaces of all the UEs selected for communication with the BS to achieve analog beamforming, and additionally performs a beamforming at the base band, wherein the BS transmits CSI measurement pilots in downlink for each UE to estimate the partial CSI and receives the partial CSI fed back by a UE, and the processor applies a predefined analog beamforming matrix to map the pilot signals to a part of antennas for transmitting CSI measurement pilot in the downlink, wherein the predefined analog beamforming matrix is determined by the number of RF chains, the arrangement of the antenna array and the number of antennas at the BS.

2. A base station (BS) for wireless communication comprising a plural of antennas and radio frequency (RF) transmitting and receiving chains; a plural of base band transmitting paths with a digital to analog converter (DAC) and base band receiving paths with an analog to digital converter (ADC) whereas the number of base band transmitting and receiving paths is less than the number of antennas; and a processor that constructs a subspace for each user equipment (UE) using the principal angle information contained in partial channel state information (CSI) obtained on channels associated with a part of the BS antennas, derives an analog beamforming matrix and/or an analog combining matrix from the subspaces of all the UEs selected for communication with the BS to achieve analog beamforming, and additionally performs a beamforming at the base band, wherein the BS transmits CSI measurement pilots in downlink for each UE to estimate the partial CSI and receives the partial CSI fed back by a UE, and the processor modifies the angles fed back from the UE according to the ratio of carrier frequency in the uplink and downlink and constructs a subspace to represent the uplink CSI of a UE based on the modified angles and associated gains.

3. A base station (BS) for wireless communication comprising a plural of antennas and radio frequency (RF) transmitting and receiving chains: a plural of base band transmitting paths with a digital to analog converter (DAC) and base band receiving paths with an analog to digital converter (ADC) whereas the number of base band transmitting and receiving paths is less than the number of antennas; and a processor that constructs a subspace for each user equipment (UE) using the principal angle information contained in partial channel state information (CSI) obtained on channels associated with a part of the BS antennas, derives an analog beamforming matrix and/or an analog combining matrix from the subspaces of all the UEs selected for communication with the BS to achieve analog beamforming, and additionally performs a beamforming at the base band, wherein the processor estimates the partial CSI using uplink pilots sent from a UE and applies a predefined analog combining matrix to map the received pilot signals at all antenna to RF chains, wherein the predefined analog combining matrix is determined by the number of RF chains, the arrangement of the antenna array and the number of antennas at the BS.