Multiuser MIMO E-SDM Systems: Performance Evaluation and Improvement in Time-Varying Fading Environments

Abstract

In the paper, performance of multiuser multipleinput multiple-output eigenbeam-space division multiplexing (E-SDM) systems in the downlink transmission is evaluated in both uncorrelated and correlated time-varying fading environments based on computer-generated data. In the ideal case, using the block diagonalization (BD) scheme, inter-user interference can be completely eliminated at each user; and using the E-SDM technique for each user, optimal resource can be allocated, and spatially orthogonal substreams can be obtained. In realistic environments, however, due to the dynamic nature of the channel and the processing delay at both the transmitter and the receiver, the channel change during the delay may cause existence of interuser interference even if the BD scheme is used. In addition, the change may also result in large inter-substream interference and no longer lead the allocated data resource for each user to the optimal condition. As a result, system performance may be degraded seriously. To overcome the problem, we propose a method of channel extrapolation to compensate for the channel change. Applying our proposed method, simulation results show that much better system performance can be obtained than the conventional case.

Performance Evaluation of a Multi-User MIMO System With Prediction of Time-Varying Indoor Channels

“…This is the same configuration as that we used in our measurements that will be stated later. General and detail description of the multi-user MIMO system is given in reference [25]. We express transmit (TX) symbols for the MS1 and MS2 as s 1 (t) and s 2 (t), respectively.…”

“…However, when multi-stream transmission is used, the interference cannot be suppressed at the MS sides and system performance can be seriously degraded. Now, we describe the channel prediction scheme [25]. In this paper, we assume a TDD system such as HIPERLAN/2 [27].…”

“…Also, we applied the linear channel prediction scheme to a multi-user MIMO E-SDM system, and examined the BER performance using computer-generated data. The simulations were done assuming the Jakes' model, and it was shown that the channel prediction method significantly improves the BER performance [25]. In actual propagation environments, however, we may have line-of-sight (LOS) components, and scatterers are not distributed uniformly.…”

Multi-user MIMO system with channel prediction for time-varying environments

“…The TX weight matrices are determined by the BD and E-SDM techniques. The detail description of the techniques is given in reference [9].…”

“…It has been clarified that the BER performance is significantly degraded in time-varying environments. To mitigate this problem, we have proposed a linear channel prediction scheme, and have shown by computer simulations that the BER performance is greatly improved [9]. The prediction scheme is simple to implement, and the computational complexity is small.…”