3-d Directional Wideband Dual-polarized Measurement of Urban Mobile Radio Channel with Synthetic Aperture Technique

Realistic spatial channel models are essential for development of future wideband mobile communication systems, particularly when adaptive antennas at the base stations are considered. Channel models are prerequisite for the performance evaluation of different adaptive antenna solutions and estimation of the obtained capacity gain. Realistic models require channel measurements to prove their assumptions and allow appropriate parameter selection. Considerations of different measurement techniques and an extensive literature list can be found in [1]. In this paper we present a novel concept for spatial radio channel measurements at the base station site in urban environment. It combines RF switching and synthetic aperture technique and allows the full 3-D channel characterization. A high-resolution 2-D Unitary ESPRIT algorithm is used for estimation of azimuth and elevation angles of the incoming waves, and a high delay resolution is obtained using a wideband channel sounder with 2154 MHz carrier frequency. The used dual-polarized microstrip patch array allows the separation of horizontally and vertically polarized wave components. Spatial measurements at the base station (BS) site with a planar array are especially interesting because the directions of arrival (DOA) are more discrete from the BS point of view. A measurement campaign was carried out using three different receiver array (base station) sites in urban environment (downtown Helsinki), below, at, and above the roof-top level. The antenna heights and positions correspond well to urban macroand microcell antenna installations of the operational networks. 20-30 transmitter (mobile) locations at ground level were measured for each site. Transmitter using an omnidirectional discone antenna was always at 1.5 m above the street level. The main goal of the measurement campaign was to improve understanding of the urban propagation mechanisms, such as the roles of 'street-canyon-' and 'over-therooftop-' propagation. The measurement campaign is described in more detail in [2].