Distributing the construction of a multiple-input multiple-output (MIMO) system among more than one mobile user reduces hardware and processing complexity at the terminal end, and may result in improved channel propagation conditions, particularly those related to spatial correlation. In this paper, measured outdoor propagation data is used to study a 4 × 4 virtual MIMO system formed from a two-user 4×4 classical system using only two of the antennas at each constituent user. The capacity, if-factor, and spatial correlation are evaluated for 226 possible pairs of users whose channels were measured while standing and walking. The proportions of pairings that result in a capacity increase and if-factor and correlation reductions over both, only one and neither of the constituents are determined. It is found that correlation reduction appears to be a stronger sign of capacity improvement than is if-factor reduction. When choosing a partner for a given single user, results show that it is easier to improve these three parameters as the user's value of them becomes poorer, so thresholds applicable to this data set are found which specify values of capacity, if, and correlation beyond which at least 50% of possible pairings improve matters.
Sponsorship: The authors wish to acknowledge the partners to the Mobile VCE MIMO Propagation Elective for enabling collection of the propagation data, M. Hunukumbure whose analysis was essential groundwork for this study, and K. Stevens for his innovative support of the measurement campaign. Thanks are also due to
the anonymous reviewers, whose comments have improved the paper.
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- K-factor, capacity, correlation, virtual MIMO