Can Multi-User MIMO Measurements Be Done Using a Single Channel Sounder?

In this paper, we consider the question whether mobile multi-user MIMO measurements can be emulated by sequentially measuring each point-to-point link with a single channel sounder. The crucial aspect of this approach is whether it is practically feasible to keep the environment sufficiently static between sequential measurement runs. We investigate this aspect in the context of an outdoor-to-indoor MIMO channel measurement campaign. To quantify the degree to which the surroundings can be kept static between sequential measurements, we focus on measurement repeatability. We performed the same fixed-outdoor to mobile-indoor measurement several times, and then compared the outcomes for different runs. As measures of similarity, we employ the collinearity between channel matrices, collinearity between spatial correlation matrices, and relative condition numbers. Our measurements showed that the similarity regarding the channel matrices is quite high. The results also indicates a strong dependence on the accuracy of the positioning of the measurement equipment and on the exact position of the channel sampling. In terms of channel correlation matrices, we find that the similarity of the correlations at the MS is quite good, and the similarity of the correlations at the BS is very high, which leads to a sufficient similarity of the full correlation matrix. Therefore, the best answer to the question in the title is as so often, “it depends”. Our results indicate that the single channel-sounder approach is definitely feasible when the focus is on channel statistics, i.e. the spatial correlation matrices. When channel matrices are of interest, the approach is only applicable to a limited degree.