MU-MIMO Channel Model with User Parameters and Correlation between Channel Matrix Elements in Small Area of Multipath Environment


IEICE TRANSACTIONS on Communications   Vol.E103-B   No.12   pp.1421-1431
Publication Date: 2020/12/01
Publicized: 2020/06/22
Online ISSN: 1745-1345
DOI: 10.1587/transcom.2019EBP3171
Type of Manuscript: PAPER
Category: Antennas and Propagation
MU-MIMO channel model,  correlation between users,  movement factor,  user parameter,  5th mobile generation,  

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In a multiple-user MIMO system in which numerous users simultaneously communicate in a cell, the channel matrix properties depend on the parameters of the individual users in such a way that they can be modeled as points randomly moving within the cell. Although these properties can be simulated by computer, they need to be expressed analytically to develop MIMO systems with diversity. Given a small area with an equivalent multi-path, we assume that a user u is at a certain “user point” $P^u(lambda _p^u,xi _p^u)$ in a cell, or (radius $lambda _p^u$ from origin, angle $xi _p^u)$ and that the user moves with movement $M^u(f_{max}^u, xi_v^u)$ around that point, or (Doppler frequency $f_{max}^u$, direction $xi_v^u$). The MU-MIMO channel model consists of a multipath environment, user parameters, and antenna configuration. A general formula of the correlation $ ho_{i - j,i' - j'}^{u - u'} (bm)$ between the channel matrix elements of users u and u' and one for given multipath conditions are derived. As a feature of the MU-MIMO channel, the movement factor $F^{u - u'}(gamma^u,xi_n ,xi_v^u)$, which means a fall coefficient of the spatial correlation calculated from only the user points of u and u', is also derived. As the difference in speed or direction between u and u' increases, $F^{u - u'}(gamma^u,xi_n ,xi_v^u)$ becomes smaller. Consequently, even if the path is LOS, $ ho_{i - j,i' - j'}^{u - u'} (bm)$ becomes low enough owing to the movement factor, even though the correlation in the single-user MIMO channel is high. If the parameters of u and u' are the same, the factor equals 1, and the channels correspond to the users' own channels and work like SU-MIMO channel. These analytical findings are verified by computer simulation.