Kimmo Kalliola

Angular power distribution and mean effective gain of mobile antenna in different propagation environments

We measured the elevation angle distribution and cross-polarization power ratio of the incident power at a mobile station in different radio propagation environments at 2.15 GHz frequency. A novel measurement technique was utilized, based on a wideband channel sounder and a spherical dual-polarized antenna array at the receiver. Data were collected over 9 km of continuous measurement routes, both indoor and outdoor. Our results show that in non-line-of-sight situations, the power distribution in elevation has a shape of a double-sided exponential function, with different slopes on the negative and positive sides of the peak. The slopes and the peak elevation angle depend on the environment and base-station antenna height. The cross-polarization power ratio varied within 6.6 and 11.4 dB, being lowest for indoor and highest for urban microcell environments. We applied the experimental data for analysis of the mean effective gain (MEG) of several mobile handset antenna configurations, with and without the users head. The obtained MEG values varied from approximately -5 dBi in free space to less than -11 dBi beside the head model. These values are considerably lower than what is typically used in system specifications. The result shows that considering only the maximum gain or total efficiency of the antenna is not enough to describe its performance in practical operating conditions. For most antennas, the environment type has little effect on the MEG, but clear differences exist between antennas. The effect of the users head on the MEG depends on the antenna type and on which side of the head the user holds the handset.

Statistical characterization of urban spatial radio channels

We present a statistical analysis of wideband three-dimensional channel measurements at base station locations in an urban environment. Plots of the received energy over azimuth, elevation, and delay planes suggest that the incident waves group to clusters in most measured transmitter positions. A super-resolution algorithm (Unitary ESPRIT) allows one to resolve individual multipath components in such clusters and hence enables a detailed statistical analysis of the propagation properties. The origins of clusters-sometimes even individual multipath components-such as street apertures, large buildings, roof edges, or building corners can be localized on the city map. Street guided propagation dominates most of the scenarios (78%-97% of the total received power), while quasi-line-of-sight over-the-rooftop components are weak(3%-13% of the total received power). For this measurement campaign, in 90% of the cases, 75% of the total received power is concentrated in the two strongest clusters, but only 55% in the strongest one. Our analysis yields an exponential decay of power with 8.9 dB//spl mu/s, and a standard deviation of the log-normally distributed deviations from the exponential of 9.0 dB. The power of cross-polarized components is 8 dB below copolarized ones on average (vertical transmission).

Real-time 3-D spatial-temporal dual-polarized measurement of wideband radio channel at mobile station

This paper describes a measurement system enabling the complete real-time characterization of the wideband radio channel. The system is based on a wideband radio channel sounder and a spherical antenna array, and it aims to describe the three-dimensional (3-D) spatial radio channel seen by the mobile terminal, including polarization. This information is highly valuable in designing antennas for mobile terminals. The spatial properties of the measurement system are analyzed through test measurements in an anechoic chamber. The system has a 40/spl deg/ spatial resolution and a 17 dB cross polarization discrimination. The values are well above those of a small mobile terminal antenna. The dynamic range in the spatial domain is 12 dB. The measurement is very fast, which makes real-time channel acquisition practical at normal mobile speeds.

Wideband 3D characterization of mobile radio channels in urban environment

This paper describes three-dimensional (3D) radio channel measurements at the base station site in an urban environment. We introduce a measurement concept which combines an RF switched receiver array and a synthetic aperture technique and allows full 3D characterization of the channel. Additionally, dual-polarized patch antennas as array elements enable full determination of the polarization properties of the impinging signals. We describe measurements at over 70 different transmitter positions and three receiver array sites with different sectors and antenna heights. Our results show that the received energy is concentrated within identifiable clusters in the azimuth-elevation-delay domain. We demonstrate that the observed propagation mechanisms are mainly determined by the environment close to the base station. Street canyon propagation dominates also when the receiver array is at or even above rooftop level with the studied measurement distances. Thus, the azimuth spectrum at the BS site is fairly independent of the location of the mobile. Signal components propagating over the rooftop are often related to reflections from high-rise buildings in the surroundings.

3-D double-directional radio channel characterization for urban macrocellular applications

We measured the spatial properties of the three-dimensional (3D) double-directional radio channel in urban macrocell environments separately at both ends of the link. In this paper, we study propagation conditions pertaining to reception and transmission at the mobile terminal, measured using a wideband channel sounder and a dual-polarized spherical antenna array. We were able to refine the results of the measurements conducted at the base station, and extend the study to full double-directional 3D channels. Individual propagation paths could be identified precisely, in some cases even considerable scattering from lampposts was observed. Our results show that over-rooftop-dominated propagation often occurs via building roofs with LOS to the base station antenna, acting as strong secondary signal sources. Based on measurements along continuous routes we demonstrate that the dominant propagation mechanisms can vary considerably when the mobile moves in the environment. We also present typical directional properties of the 3D radio channel at the mobile terminal in urban macrocell environments characterized by street canyons, showing how the angular distribution of energy is correlated with the excess delay.

Signal Power Distribution in the Azimuth, Elevation and Time Delay Domains in Urban Environments for Various Elevations of Base Station Antenna

We investigate signal power distribution in the azimuth-of-arrival, elevation-of-arrival and time-of-arrival domains for various positions of the base station antenna located below the rooftop as well as at rooftop level. This article is based on a multiparametric stochastic model we introduced in 2004, as combination of a statistical part, describing an array of buildings randomly distributed at the terrain, and a waveguide model, describing a grid of straight streets with buildings along them. Joint signal power distributions in azimuth-time delay and elevation-azimuth planes are obtained and compared to high-resolution 3-D measurements carried out in downtown Helsinki. A good agreement between theoretical predictions and the measurements is obtained basically, and also regarding the wave-guiding effect and antenna height dependencies. A satisfactory physical explanation, which accounts for the character of the specific building topography, the height and tilt of the antennas, is found. Finally, we present a numerical experiment of changing the base station antenna height, its directivity, and tilt. By this we show that the proposed stochastic approach allows to predict and control a-priori main parameters of smart antenna based only on knowledge of specific features of built-up terrain

Characterization system for radio channel of adaptive array antennas

This paper describes a multichannel measurement system for the analysis of the radio channel of adaptive array antennas. It provides real-time recording of signals from multiple input channels. Due to this multielement reception, the incidence angles of the received signal components can be resolved. Wideband sounding provides the delay information. This allows the characterization of the two-dimensional radio channel of adaptive antenna systems in realistic environments. The system is based on a complex wideband radio channel sounder and a fast RF switch. As an example, the system allows measurement of complex impulse responses for a 16-element array with 17 ns delay resolution, and a delay range of 4.3 /spl mu/s for a 26 m/s mobile speed. The continuously recorded path lengths can be over one hundred meters. Practical channel measurements have been performed with a linear array of 8 elements. In these measurements the received signal components could be separated with 13/spl deg/ angular and 20 ns delay resolution. The developed method provides a novel approach to the two-dimensional analysis of the mobile environment.

Path-Loss Models for Urban Microcells at 5.3 GHz

Based on wideband 5.3 GHz measurements performed in downtown Helsinki, Finland, empirical path-loss models for regular urban street grids were developed for future beyond 3G (B3G) wireless radio systems.

Spatial characterization of urban mobile radio channels

We present statistical evaluations of wideband spatial dual-polarized radio channel measurements. Some 80 different street-level transmitter positions in downtown Helsinki, Finland, were measured. We chose three different receiver array sites below, at, and above the rooftop level of the surrounding urban environment. A super-resolution algorithm allows the determination of the directions of arrival of incident radio waves at a 16/spl times/62 elements base station antenna array. The main conclusion of our investigations is that the incident waves tend to cluster in azimuth, elevation and/or delay, which we justify by detailed statistical evaluations. Clustering is mainly defined by the surroundings of the base station. The cumulative distribution function of the powers of these clusters shows that in 90% of all cases, 75% of the total received power is concentrated in the two strongest clusters. Street guided propagation dominates at all three receiver sites, even if the base station is above the rooftop level.

Azimuth, elevation, and time-delay distributions in wireless communication channels

We investigate the wave-propagation characteristics in urban environments as functions of the angle-of-arrival distribution, both in the azimuth and elevation planes. We also take into consideration the time delays for various base-station antenna elevations. We combine a statistical multi-parametric model, describing randomly distributed buildings, and a waveguide model, describing a grid of crossing streets with buildings lining the sides to create a new stochastic model. The joint probability of signal distributions in the azimuth-elevation, azimuth-time delay, and elevation-time delay planes are obtained and compared with high-resolution three-dimensional experiments carried out in urban areas in Helsinki, Finland. A good agreement between experimental and theoretical results is obtained