Abstract
The advances in programmable and reconfigurable radios have rendered feasible transmitter optimization schemes that can greatly improve the performance of multiple-antenna multiuser systems. Reconfigurable radio platforms are particularly suitable for implementation of transmitter optimization at the base station. We consider the downlink of a wireless system with multiple transmit antennas at the base station and a number of mobile terminals (i.e., users) each with a single receive antenna. Under an average transmit power constraint, we consider the maximum achievable sum data rates in the case of (1) zero-forcing (ZF) spatial prefilter, (2) modified zero-forcing (MZF) spatial prefilter, and (3) triangularization spatial prefilter coupled with dirty-paper coding (DPC) transmission scheme. We show that the triangularization with DPC approaches the closed-loop MIMO rates (upper bound) for higher SNRs. Further, the MZF solution performs very well for lower SNRs, while for higher SNRs, the rates for the ZF solution converge to the MZF rates. An important impediment that degrades the performance of such transmitter optimization schemes is the delay in channel state information (CSI). We characterize the fundamental limits of performance in the presence of delayed CSI and then propose performance enhancements using a linear MMSE predictor of the CSI that can be used in conjunction with transmitter optimization in multiple-antenna multiuser systems.
Highlights
For a wide range of emerging wireless data services, the application of multiple antennas appears to be one of the most promising solutions leading to even higher data rates and/or the ability to support greater number of users
The advances in programmable and reconfigurable radios have rendered feasible transmitter optimization schemes that can greatly improve the performance of multiple-antenna multiuser systems
We considered the maximum achievable sum data rates in the case of the zero-forcing, the modified zero-forcing, and the triangularization spatial prefiltering coupled with the dirty-paper coding transmission scheme
Summary
For a wide range of emerging wireless data services, the application of multiple antennas appears to be one of the most promising solutions leading to even higher data rates and/or the ability to support greater number of users. Multiple-transmit multiple-receive antenna systems represent an implementation of the MIMO (multiple-input multiple-output) concept in wireless communications [1]. Reconfigurable radio platforms are suitable for implementation of transmitter optimization at the base station Such optimization techniques have great potential to enhance performance on the downlink of multiuser wireless systems. After characterizing the fundamental performance limits, we study the performance of the above transmitter optimization schemes with respect to delayed channel state information (CSI).
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