근거리 무선통신환경에서 스펙트럼 이용효율과 시스템성능 향상을 위한 다중편파 안테나시스템에 관한 연구

Abstract

In this thesis, we propose a novel next generation(4G and 5G) multi-polarized antenna system improving spectrum efficiency and diversity effect by adopting the multi-polarization concept in the conventional mobile frequency band as well as the next generation frequency band. Firstly, we establish a novel wireless channel model modifying conventional mobile radio channel parameters and also try to improve the transmission system performance applying the modified channel parameters. And then, we analyze a novel next generation mobile radio transmission method improving spectrum efficiency. The first goal is to find newly modified wireless channel parameters adopting a characteristic that the circularly polarized wave and polarization diversity system has marked fading reduction effect compared to the linearly polarized waves in the LOS and NLOS environment. Secondly, in order to investigate the polarization diversity effect, we study the propagation characteristic of the conventional and the next generation frequency band through the mobile radio measurements using the several implemented antennas with multi-polarized waves. And also, with regard to the next Femto cell environments, we focus on the analysis of a propagation characteristic in the indoor LOS/NLOS and short range propagation environments.

Finally, in this thesis, in order to certify the fading reduction effect in the UHF/RFID frequency band we implement a multi-polarized micro-strip antenna system with a RF combiner and diversity unit in order to measure the signal strength in short-range radio wave propagation environments. In order to estimate performance of the circular polarization diversity system, we designed and implemented a circular polarization diversity system using the circularly polarized antenna at the transmitting unit. As a result, propagation characteristic measurements were carried out in a short-range radio wave propagation environment. Usually, polarization diversity at a transmitting end does not require antenna spacing because a co-planer antenna implemented by micro-strip substrate can be used. If a micro-strip antenna implemented by two co-planer polarization antennas is used, the diversity system can be easily fabricated. To estimate the fading reduction effect of the fabricated multi-polarized antenna system, we conducted moving measurements in LOS/NLOS indoor radio environments. Selecting a general office size as the measurement environment, we set or remove an obstacle between the transmitter and the receiver in an office room for the purpose of making the LOS/NLOS condition. With the aim of reducing the multipath fading in short range radio wave propagation environment, we proposed a multi-polarized antenna system. From the measured data analysis, it was found that the C-C combination shows better fading reduction result than the cases of V-V and H-H combination in LOS environment, respectively. On the other hand, in the case of NLOS environment, it was found that the polarization diversity effect using the two branches C-V and C-H branches shows better fading reduction effect than the cases of C-C, C-X, V-V and H-H. From the measurement results, it can be inferred that the proposed circular polarization diversity scheme has better diversity gain than that of the conventional linear polarization diversity in short range radio propagation environment. Especially, the XPD value for the case of using circular polarized wave indicated 6∼7dB lower than that of using vertically polarized wave. This means that the XPD value using circularly polarized diversity system expects lower value than that of the case of using linear polarization at a transmitting end.