Block diagonalization for multiuser MIMO TDD downlink and uplink in time-varying channel

Block diagonalization (BD) is a downlink multiuser multiple-input multiple-output (MIMO) communication strategy that utilizes transmitter channel state information (CSI). This paper proposes a practical uplink MIMO scheme for time division duplex (TDD) systems to co-exist with BD so that the CSI of the BD channel is used also in the uplink transmission. It is shown that the precoded pilot symbols are sufficient in both uplink and downlink to satisfy the needs of both transmission and reception. The capacity of the system is analyzed in conjunction with linear receivers in a time-varying fading channel. The effect of using transmit and receive CSI estimated from noisy pilot symbols is studied. According to the results the proposed uplink transmission strategy provides capacity gain over non-precoded transmission, without being sensitive to channel time variations and CSI estimation errors.