Multi-probe Anechoic Chamber Research Articles

Over-the-Air Testing of MIMO-Capable Terminals: Evaluation of Multiple-Antenna Systems in Realistic Multipath Propagation Environments Using an OTA Method

A new over-the-air (OTA) testing method is required for evaluating multiple-antenna systems in realistic multipath propagation environments. Antenna design and propagation channels are the two key parameters that ultimately determine the multiple-input, multiple-output (MIMO) device performance. As antennas are inherently included in OTA testing, it is important to also consider realistic channel models for MIMO device-performance evaluation. This article shows that the multiprobe anechoic chamber (MPAC) setup is capable of emulating realistic and accurate multipath environments, making it a suitable method for testing terminals equipped with multiple antennas. In comparison to the mode-stirred reverberation chamber (RC) setup that represents an isotropic multipath environment, the MPAC method is capable of generating arbitrary spatial channel models with polarization characteristics.

Emulating Realistic Bidirectional Spatial Channels for MIMO OTA Testing

This paper discusses over the air (OTA) testing for multiple input multiple output (MIMO) capable terminals with emphasis on modeling bidirectional spatial channel models in multiprobe anechoic chamber (MPAC) setups. In the literature, work on this topic has been mainly focused on how to emulate downlink channel models, whereas uplink channel is often modeled as free space line-of-sight channel without fading. Modeling realistic bidirectional (i.e., both uplink and downlink) propagation environments is essential to evaluate any bidirectional communication systems. There have been works stressing the importance of emulating full bidirectional channel and proposing possible directions to implement uplink channels in the literature. Nevertheless, there is no currently published work reporting an experimental validation of such concepts. In this paper, a general framework to emulate bidirectional channels for time division duplexing (TDD) and frequency division duplexing (FDD) communication systems is proposed. The proposed technique works for MPAC setups with arbitrary uplink and downlink probe configurations, that is, possibly different probe configurations (e.g., number of probes or their configurations) in the uplink and downlink. The simulation results are further supported by measurements in a practical MPAC setup. The proposed algorithm is shown to be a valid method to emulate bidirectional spatial channel models.

Covariance-Based Spatial Channel Structure Emulation for MIMO OTA Testing

The paper presents a general framework for recreating the spatial channel structure in a MIMO over-the-air (OTA) multiprobe anechoic chamber testing setup. The idea is to find the power weights of the spatial taps (antenna probes) that minimize a certain distance between the spatial channel covariance matrix corresponding to the desired (continuous) channel and the covariance related to the emulated (discrete) channel within the test area. Unlike previous methods that merely rely on the spatial correlation coefficient, the proposed approach properly accounts for emulating the power imbalance among the antennas-under-test by considering the whole spatial covariance structure. The simulation results validate the improved performance of the suggested approach in terms of emulation accuracy compared to the key emulation methods proposed in the literature.

Probe Selection in Multiprobe OTA Setups

Standardization work for over-the-air (OTA) testing of multiple-input-multiple-output (MIMO) capable terminals is currently ongoing in COST IC1004, 3GPP, and CTIA, where a multiprobe anechoic chamber based method is a promising candidate. Setting up a multiprobe configuration with channel emulators is costly, so finding ways to limit the number of probes while still reproducing the target channels accurately could make the test system both cheaper and simpler to implement. Several probe selection algorithms are presented in this paper to address this issue. The proposed techniques provide a probe selection framework for the channel emulation techniques published in the literature. Simulation results show that good channel emulation accuracy can be achieved with the selected subset of probes for the considered target channel models. The probe selection algorithm is further supported by measurement results in a practical multiprobe setup.

Rician Channel Modeling for Multiprobe Anechoic Chamber Setups

This letter discusses over-the-air (OTA) testing for multiple-input–multiple-output (MIMO)-capable terminals, with emphasis on modeling Rician channel models in the multiprobe anechoic chamber setups. A technique to model Rician channels is proposed. The line-of-sight (LOS) component, within arbitrary polarization and an arbitrary impinging direction, and non-LOS (NLOS) component, with any impinging power angular spectrum (PAS), can be created. Simulation results show that the emulated Rician channels approximate the target models accurately in terms of field envelope distribution, $K$ -factor, Doppler spectrum, and spatial correlation at the receiver (Rx) side.