FDD and TDD Single-User Capacity Bounds

Multiple antennas increase significantly the capacity of wireless links under the assumption of perfect channel state information (CSI). In practice, however, in time division duplex (TDD) or frequency division duplex (FDD) systems, the available CSI is obtained with training and/or limited feedback and hence, is not perfect. In this work, we derive tight capacity bounds for the uplink and downlink of TDD/FDD systems with multiple antennas at the base station and a single-antenna user. We also present a performance comparison between the two systems based on the achievable rates and discuss further issues for a relevant comparison.