Improvement on Doppler Reconstruction in Multiprobe OTA Setups for Directional-Antenna Devices

This article proposes an improved channel reconstruction method to increase the accuracy of Doppler emulations when measuring directional multi-antenna devices in over-the-air (OTA) testing at millimeter wave (mmWave) bands. In real radio channels, the Doppler spectrum depends on incoming ray angles. In OTA testing, the target Doppler spectrum is accurately created when assessing omni-directional antenna terminals using the conventional prefaded signal synthesis (PFS) method. However, the devices under test (DUTs) may consist of directional antennas that produce different gains in impinging angles. Since the PFS method ignores the dependence of the Doppler spectrum on the DUT antenna element pattern, it will lead to inaccurate channel emulation, thus affecting the link performance of the DUT. Therefore, an improved PFS method is proposed by considering the impact of the DUT antenna element pattern. Specifically, the rays within a cluster mapped to active probes are divided into multiple subsets, each of which is weighted to synthesize the cluster. The objective function with constraints between the target temporal covariance and emulated one is established to obtain all subset weights. Simulation results verify that the proposed channel emulation method is superior to the existing PFS technique for Doppler emulation while not degrading the emulated spatial characteristics using the proposed optimization strategy.