Summary
International Symposium on Antennas and Propagation
2010
Session Number:3TD4
Session:
Number:3TD4-4
Characteristic Evaluation of Dual Polarized 4x4 MIMO through Propagation Measurement
Yuki Hirota, Shinobu Nanba, Yoji Kishi,
pp.-
Publication Date:2010/11/23
Online ISSN:2188-5079
Summary:
The Multiple-Input Multiple-Output (MIMO) system employed in mobile WiMAX and 3GPP Long Term Evolution (LTE) has a high-speed wireless data transmission capability without increasing the bandwidth. MIMO achieves a high information-theoretic capacity with multiple antennas in transmitter (Tx) and receiver (Rx) site [1]. It is because the efficiency by spatial multiplexing of MIMO increases linearly according to the number of antennas. It is important to estimate the efficiency of spatial multiplexing represented by the eigenvalues of channel matrix for MIMO because the capacity is calculated by Signal-to-Noise Ratio (SNR) and the eigenvalues. There are the spatial multiplexing and the polarized multiplexing for MIMO. The spatial multiplexing efficiency of MIMO is especially large in a non-line-of-sight (NLOS) environment because the spatial correlation among multiple propagation channels is relatively low [2]. However, the capacity of the spatial multiplexing for 2x2 MIMO with single polarized antennas (SP-MIMO) is degraded in a LOS environment because the spatial correlation is relatively high. On the other hand, it is confirmed that the polarized multiplexing of MIMO with the orthogonal-dual polarized-antenna (DP-MIMO) is effective in a line-of-sight (LOS) environment under outdoor conditions [3]. The DP-MIMO uses a vertical (V) and horizontal (H) polarization. It achieves lower channel correlation than SP-MIMO even in a LOS environment thanks to the orthogonality of V and H polarizations in an ideal LOS environment. DP-MIMO also offers reasonable efficiency in an NLOS environment because the channel correlation is low [3]. The propagation characteristics of DP-MIMO with increasing the number of antennas have been researched widely. The results of experimentally measured channel characteristics by the dual-polarization 4x4 MIMO are shown [4][5]. In particular, it is said that the strong direct wave results in two dominant eigenvalues due to the polarization in the LOS environment [5]. These papers explain the phenomenon that only the two eigenvalues are high and the other eigenvalues are low in LOS even though 4 or more antennas is used. However, the measurement results given in this paper differ from their results. Some of the 3rd and 4th eigenvalues measured by our experiments in the LOS are as high as in the NLOS. The others of the eigenvalues are surely low in the LOS. These results imply that the eigenvalues in DP-MIMO cannot be characterized only by the LOS or NLOS environments. This paper evaluates the measured eigenvalues characteristics for 4x4 DP-MIMO in a LOS or an NLOS environment. Moreover, the relation between the eigenvalues and the correlation between the antennas is analyzed. The next section describes the measurement environment. Section III presents and discusses the measurement results. Section IV presents the conclusions