Reduced-complexity downlink (dl) signal demodulation using reciprocity reference signals for mimo wireless communication systems

A base station for use in a multiuser (MU) multiple-input-multiple-output (MIMO) wireless communication system to reduce complexity of downlink signal demodulation by user equipment (UE) of the system, the base station comprising:

• a plurality of antennas;
• receive circuitry, coupled to the plurality of antennas, that receives from the UE an uplink (UL) reciprocity reference signal (RRS);
• processing circuitry configured to:
• acquire uplink (UL) channel state information (CSI) of a MIMO channel between the base station and the UE using the UL-RRS received from the UE;
• derive downlink (DL) CSI from the UL CSI;
• and
• perform MIMO pre-equalization based on the DL CSI;
• and
• transmit circuitry, coupled to the plurality of antennas, configured to transmit MIMO pre-equalized orthogonal frequency-division multiplexing (OFDM) radio subframes and to send DL-RRS to enable the UE to derive a single complex phasor estimate using the DL RRS for use in performing downlink reciprocity correction of the MIMO pre-equalized OFDM subframes received from the base station and to enable the UE to perform downlink data demodulation of the downlink reciprocity corrected OFDM subframes without performing additional MIMO equalization.

A user equipment (UE) for use in a multiuser (MU) multiple-input-multiple-output (MIMO) wireless communication system with reduced complexity of downlink signal demodulation of signals received from a base station by the UE, the UE comprising:

• transmit circuitry that transmits an uplink (UL) reciprocity reference signal (RRS) to enable the base station to acquire uplink UL channel state information (C SI) of a MIMO channel between the base station and the UE using the UL-RRS and to derive downlink (DL) CSI from the UL CSI;
• receive circuitry configured to:
• receive from the base station orthogonal frequency-division multiplexing (OFDM) radio subframes transmitted by the base station using MIMO pre-equalization based on the DL CSI;
• perform downlink reciprocity correction of the OFDM subframes received from the base station using a single complex phasor estimate;
• and
• perform downlink data demodulation of the downlink reciprocity corrected OFDM subframes without performing MIMO equalization additional to the MIMO pre-equalization performed by the base station.