Relationship Between Capacity and Pathloss for Indoor MIMO Channels

MIMO transmission systems exploit scattering in the radio channel to achieve high capacity for a given SNR. A high pathloss is generally expected for channels with rich scattering, suggesting that a high SNR and rich multipath are competing goals. The current work investigates this issue based on measurements obtained with a 16×32 MIMO channel sounder for the 5.8 GHz band. The measurements were carried out in various indoor scenarios where different sizes of both the transmitter and receiver antenna arrays are investigated, 1×1 up to 16×32. A moderate correlation between pathloss and median capacity was found. However, the higher richness can not compensate for the decrease in capacity due to increased pathloss. Assuming a fixed Tx power, the median capacity was found to depend approximately linearly on the pathloss. The slope of the linear relation depends on the effective rank of the channel, which in turn was found to be approximately linearly dependent on the number of antennas, assuming a symmetric MIMO channel

MIMO — STUDY PROPAGATION FIRST!

Despite many valuable contributions to the theory and practice of MIMO communication systems from various scientific fields, we want to emphasize the outstanding importance of propagation aspects when dealing with MIMO systems. Radio propagation forms the basis for any radio channel including MIMO systems. On the one hand, popular mathematical models and commonly applied statistical assumptions sometimes turn out to neglect important properties of MIMO radio channels. On the other hand, detailed knowledge and investigations of MIMO specific phenomena (e.g. keyholes) do not imply practical relevance. By means of four specific examples we argue that studying propagation is indispensable in order to stay in touch with real MIMO channels. 1

Power and Complex Envelope Correlation for Modeling Measured Indoor MIMO Channels: A Beamforming Evaluation

Abstract — The multivariate complex normal distribution is often employed as a tractable and convenient model for MIMO wireless systems. Several models may result depending on how the covariance matrix is specified, i.e. power or complex envelope correlation and full or separable (Kronecker) correlation. This paper investigates the differences of the various models by applying a joint transmit/receive beamformer to recent wideband MIMO radio channel measurements at 5.2 GHz. It is found that the Kronecker model, especially for power correlation, significantly alters the joint beamformer spectrum. A multipath clustering model is applied whose parameters are estimated directly from the measured data. The clustering model is able to match capacity pdfs, and resulting simulated joint beamformer spectra look more realistic than those generated with conventional separable correlation functions. I