Performance Evaluation of RU and RIS Based on OTA Mode Near Field and Bistatic Measurement Systems

In 5G O-RAN, a radio unit (RU) is connected to an upper-layer network element through an eCPRI interface, relying on digital modulation for data transmission. Therefore, unlike conventional 4G antenna system verification processes, RU radiation pattern testing in this data transmission mode necessitates novel testing approaches. Moreover, millimeter-wave signals in 5G undergo severe transmission losses and lack effective multipath channel characteristics, leading to poor base station coverages in this frequency range. The reconfigurable intelligent surfaces (RIS), an emerging technology that exploits the channel properties for the dynamic manipulation of the propagation environments, is a promising solution to the abovementioned problem. However, evaluating the effectiveness of the dynamic energy transfer for the RIS is a crucial challenge in the development of this technology. This paper presents the novel configuration based on the combined near-field and bistatic measurement systems at Taiwan Tech for RU and RIS performance verifications. We propose a near field measurement system to verify the radiation pattern of the RU in data transmission operation. Also, we integrate a compact antenna test range (CATR) and the planar near field scanner to form the bistatic measurement system and conduct performance evaluation of the scattering characteristics of the object under test. Those testing approaches can more accurately evaluate, verify, and optimize RF coverages of the network deployment for 5G and beyond.