Abstract
This paper investigates the impact of devices under test (DUTs) with directional antennas on the recreated channel in the over-the-air (OTA) testing for massive multiple-input multiple-output (MIMO) devices using prefaded signal synthesis (PFS) technique. Assuming the uplink in real radio environments, the directional receiver (Rx) antenna patterns would affect the gains in different incoming directions, thereby affecting the spatial characteristics of the target channel. A typical multi-probe anechoic chamber (MPAC) setup for massive MIMO base stations (BSs) is studied, where a limited number of probe antennas are distributed over the probe wall to emulate the target channel by proper probe weighting. The directional antenna patterns would have nonnegligible effects on the emulated spatial characteristics which may become inaccurate for DUTs with directional antennas and thus need to be re-examined. Therefore, the reconstructed channel with the PFS technique will be investigated under the MPAC setup in this paper, with particular focus on the DUTs with directional antennas. The deviations between the covariance matrix of the Rx antennas under the target channel and the covariance matrix under the reconstructed channel are used as the metric to evaluate the performance of the reconstructed channel, and the optimal probe weights are also re-determined. Furthermore, given beamforming capability of massive MIMO BSs, the impact of the BS antenna patterns on angular spectrum is investigated as well. In addition, since the reconstructed channel needs to not only reflect the spatial characteristics of Rx antennas but also reflect the spatial characteristics of transmitter antennas and propagation environment, the end-to-end channel capacities are evaluated. Simulation results under various scenarios show that the accuracies of the reconstructed channel in terms of spatial correlation, angular spectrum and channel capacity can be improved by using the re-optimized probe weights when directional antenna patterns of the DUTs are taken into account.
Highlights
Massive multiple-input multiple-output (MIMO) is one of the key technologies of the fifth-generation (5G) mobile communication system [1], which relies on deploying a large number of antennas at base stations (BSs)
The channel capacity of the reconstructed channel is investigated to examine the emulated channel in the case of directional antenna devices
Uniform line array (ULA) on the Tx side consists of 4 ideal dipole antennas, and uniform rectangular array (URA) on the Rx side is composed of 8 × 8 directional antennas under four scenarios, where the 3dB beamwidths of the antenna elements are 10◦, 30◦ and 65◦, respectively
Summary
Massive multiple-input multiple-output (MIMO) is one of the key technologies of the fifth-generation (5G) mobile communication system [1], which relies on deploying a large number of antennas at base stations (BSs). Due to the above arguments, the power imbalance of different channels can be ignored in both the real radio environment and the OTA testing, and the covariance matrices of spatial channels can be constructed as the metric to investigate the impact of the DUT antenna patterns on the spatial characteristics of the reconstructed channel, with particular focus on a limited number of probe antennas. Two optimization metrics, namely, the covariance matrix and the angular spectrum of the spatial channels, will be discussed, respectively, to investigate the impact of the DUT antenna patterns on the test zone performance under a limited number of probe antennas in the massive MIMO OTA testing. It is clear that (9) is a convex programming problem with linear constraints, which can be solved by convex optimization techniques readily
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