Conference Paper

Analysis of propagation mechanisms based on direction-of-arrival measurements in urban environments at 2 GHz frequency range

Radio Lab., Helsinki Univ. of Technol., Espoo
DOI: 10.1109/APS.2002.1016295 Conference: Antennas and Propagation Society International Symposium, 2002. IEEE, Volume: 1
Source: IEEE Xplore

ABSTRACT In cellular mobile communications propagation environments are usually defined roughly by base station location, distance from the base station, and local environment around the mobile station. In this paper a rough categorization of the main propagation mechanisms was done based on the direction of arrival information of each incident wave at the mobile. Three propagation mechanisms, or classes, were specified; propagation along street canyons, propagation directly from transmitter over rooftops in a vertical plane, and other mechanisms as the third class. The first two classes correspond to propagation planes of quasi-3D-models, and the last class presents the proportion of power which quasi 3D-models cannot predict. The categorization is based on a constant elevation boundary for street canyon propagation and tracing of the transmitter's azimuth direction with a small margin for over rooftop propagation. The study of the significance of different propagation mechanisms is based on measurements in several different city environments at 2 GHz frequency range. The measured data consist of microcell and small macrocell measurements and the distance between transmitter and receiver varies from 100 m to 550 m.

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    ABSTRACT: A directional wideband measurement campaign was performed in urban macrocells at 2 GHz using a channel sounder and a 8-sensor linear antenna array at the base station. Directions of arrival at the Base Station (BS) were estimated by beamforming using the antenna array. Directions of arrival at the Mobile Station (MS) were estimated by beamforming using parts of the measurement route. Global parameters (delay spread, azimuth spread at BS, maximum factor and street canyon factor) were processed from the Azimuth-Delay Power Profiles (ADPP) at BS and MS. In this paper, we compare the statistics of these four parameters with the statistics of those simulated by the 3GPP-SCM system-level model and the statistics of those reported in the literature. We find an acceptable agreement between our measurements and the SCM model except for the delay spread and the street canyon factor. The azimuth spread at BS mean value (9.5°) and delay spread mean value (0.250 µs) are also in accordance with values reported in other references. Azimuth spreads are ranged from 7° to 11°, and delay spreads are ranged from 0.1 µs to 1 µs. From a statistical analysis of global parameters, we show that most of the measured propagation channels can be classified in three main categories: low spatial diversity at MS and BS, high spatial diversity at MS and BS, low spatial diversity at BS and high spatial diversity at MS.
    EW 2007 : 13th European Wireless Conference; 01/2007
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    ABSTRACT: Sophisticated measurement data, including path-loss, delay spread and direction-of -arrival, are analyzed and compared with simulations performed with an advanced 3D ray tracing model which takes diffuse scattering into account. The results show that diffuse scattering plays a key role in urban propagation, with a particular impact on the time delay- and on the angular- spread of the signal at the receiver. I - INTRODUCTION Since the great majority of mobile radio communications take place nowadays in urban environment, the study of urban radio propagation is of crucial importance for both the design and the deployment of present and future mobile radio systems. Urban propagation is a complex phenomenon which involves several mechanisms of interaction between the radio wave and the environment. According to the Geometrical Optics (GO) approach, two basic mechanisms are usually identified and separately modeled: diffraction due to building and rooftop edges and reflection due to the ground and building walls. However, the GO approach is based on the hypothesis that building walls and edges are homogeneous and smooth. This hypothesis is evidently not valid in real urban environment. Deviations in building walls from smooth homogeneous layers, the presence of "small" objects such as windows, balconies, irregular bricks, internal beams etc. contribute to the scattering of the impinging radio power in unpredictable ways, also because the cited "irregularities" are generally unknown (1). Diffuse scattering of the radio wave is especially relevant in the case of far buildings, which are very unlikely to produce significant reflection/diffraction effects due to the very narrow spread of the reflection cone. Unfortunately, far buildings are of major importance in the determination of channel dispersion and thus the wideband behavior of the urban mobile radio channel cannot be understood without taking diffuse scattering into account. In the present work diffuse scattering in urban environment is investigated through both the analysis of experimental results and the comparison between measurements and computer simulations. As diffuse scattering is a "non-deterministic" phenomenon, a statistically significant amount of experimental data is required to investigate its existence and relevance. Furthermore, information on the angular distributions of the signals is useful in separating signals propagated via scattering from those undergoing "deterministic" GO propagation phenomena like reflections and diffractions. The experimental part of this paper is based on large amount of measured 3D angular signal distributions giving thus a unique insight into the significance of scattering as a propagation phenomenon. The measurement setup is described in section II. Computer simulations have been performed with an advanced three-dimensional Ray Tracing (RT) program. Diffuse scattering has been modeled according to the effective roughness approach described in (2)(3). The 3D RT algorithm is illustrated in section III. Results (see section IV) show that by introducing scattering in the RT model a good agreement between simulation and measurement can be obtained, especially if power-delay profiled or power-DOA profiles are considered. Moreover, RT with scattering converges more rapidly than traditional RT even with a low order of events (successive reflections / diffractions / scatterings), thus sensibly reducing CPU time.
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    ABSTRACT: In this paper we measured the soft-handover (SHO) probability at and near street crossings in UMTS. Literature quotes two main propagation paths in urban macro-cell sce- narios: along street-canyons and over the rooftops. Due to the fact that propagation along street canyons is one of the main propagation paths we expected high SHO probability at street crossings. To evaluate this effect we measured the active-set-size along a route in the city center of Vienna in three different UMTS networks of three different operators. We analyzed the probability of being in SHO-state and the probability of various active-set-sizes for different distances from street crossing s.The results show that probability of being in SHO does not depend on street crossings. I. I NTRODUCTION In this paper we investigate the SHO probability on or near street crossings in street canyons. We know from various papers (1), (2) that there are two dominant propagation paths in macro-cell scenarios: along the street canyon and deflect ion over the roof tops. Entering the crossing, the mobile would monitor a new strong cell propagating within the crossing street canyon. The decision if a new cell is added to the active-set is only based on a window function comparing different received CPICH (Common Pilot CHannel) energy, given by EC/I0. An unrequired increase of the active-set entering street crossings could be likely. After leaving th e street crossing the mobile would drop the new cell. In an area with high traffic, this would introduce significant unrequir ed signaling traffic (see (3), (4)). There are three so called sets in UTRAN (UMTS Terrestrial Radio Access Network). The active-set consists of the cells the mobile is actively connected to. A cell listed in the cell info list, being no member of the active-set, belongs to the monitored-set. The last set is the detected-set. It cont ains all cells from intra frequency measurements. A handover is a mobility event of a mobile station, initiated by the change from cell A to cell B. There are two fundamental types of hand-over (HO). In hard-HO the mobile removes all connections to the old cell before entering the new one. This type of HO applies to all carrier frequency changes (i.e. cel l A and B have different frequencies). In the SHO mode the mobile equipment is logically and physically attached to several base-stations. In this mode it blocks logical and physical resources. Therefore a wrong decision to add a cell to the active-set will harm the UTRAN network performance. The core-network load will increase in SHO mode too. We assumed that the UTRAN is more restricted and therefore did not extract the intra-RNC and intra-SGSN separately. Figure 1 shows a principle scenario. A mobile terminal is moving in a street canyon, on Street1, which is the main propagation path of Cell1, approaching a street crossing with Street2, which is the main propagation path of Cell2. While the terminal is far away from the crossing only Cell1 is visible. When closing in to the crossing also Cell2 will get visible to the receiver and at some point in time the power of the CPICH may be close enough to add Cell2 to the active-set. After leaving the crossing on Stree t1, the power from Cell2 will again drop into the noise floor and Cell2 will be removed from the active-set again. In this case the radio-link addition of the UMTS terminal only generated additional signaling traffic without featuring any improve ment.