Lasse Vuokko

Comparison of MIMO antenna configurations in picocell and microcell environments

This paper presents the results achieved with a dual-polarized multiple-input multiple-output (MIMO) measurement system in the 2 GHz range. Results from continuous measurement routes were used in evaluating and comparing different MIMO antenna configurations. Different pattern and polarization diversity possibilities were studied using two methods: elements were selected from the antenna arrays used in measurements, and as another option, in the mobile station the incident waves were estimated and used in different dipole antenna arrays. The capacity limit seems to be higher in an indoor picocell than in an outdoor microcell environment. At the mobile station, directive elements result in 35% higher average capacities than those of the omnidirectional elements; however, the capacity of the directive elements also depends on the azimuth direction of arrival of the incident field. Dual-polarized antenna configurations have approximately 14% higher capacities than copolarized configurations. Increasing the number of mobile antenna elements increases the capacity in those environments where the angular spread of the incident field is large. Increasing the distance between elements at the fixed station increases the capacity - especially in microcells where signals arrive from specific directions.

5.3 GHz MIMO radio channel sounder

A radiowave propagation measurement system for wideband multichannel multiple-input-multiple-output (MIMO) measurements at 5.3 GHz is presented. The MIMO channel matrix of size 32/spl middot/32 can be measured using microwave switches at the transmitter (TX) and the receiver (RX). The system is capable of measuring direction of departure and direction of arrival with a dual polarization in both TX and RX. The antenna configuration can be selected to include a planar array or semispherical groups at each end of the link. A high-power switch is used at TX to enable large measurement distances. Results from a calibration in an anechoic chamber and from the measurement campaigns are shown.

Analysis of Multipath Propagation in Urban Environment Through Multidimensional Measurements and Advanced Ray Tracing Simulation

A multidimensional analysis of multipath propagation in urban micro- and macro-cellular environment has been carried out. Multidimensional measurement data, including path-loss, delay spread and direction-of-arrival are compared with simulations performed with a 3D ray tracing model which takes diffuse scattering into account. The results are analyzed highlighting the dominant propagation mechanisms in the different cases and model performance/shortcomings. In particular, the results show that diffuse scattering plays a key role in urban propagation, with an impact on both narrowband and wideband parameters in most cases. Also, the accuracy and the characteristics of environment representation can have a significant impact on prediction even in simple topologies.

Measurement of Large-Scale Cluster Power Characteristics for Geometric Channel Models

Directional urban radio channel measurements are analyzed in this paper. The mean powers, the shadow fading, and the lifetimes of individual propagation clusters extracted from the measured data are studied. The cluster shadow fading is an input parameter of several directional channel models, but measured values for the fading have not been published previously. Also, measured numbers of strong, significant propagation clusters are essential for the channel models.

Clusters extracted from measured propagation channels in macrocellular environments

The urban physical propagation environment around the mobile station is often described as a multipath environment, where power is received through diffractions over rooftops and building corners, reflections from walls and scattering in general from other surrounding objects. Since there are only finite number of these scatterers, the waves are received in clusters each originating from one of the scattering sources. To study these scatterers, direction-of-arrival data measured along continuous routes in two small macrocellular environments were analyzed. Multipaths received with approximately the same directions and delays were combined as clusters. Therefore each of the clusters corresponds to the signal received from one scatterer. This paper focuses on both the identification of the physical scatterers in the surrounding environment and studying the radio wave propagation in more detail, including the amount of significant scatterers in terms of contributed power, XPR values, and delay and azimuth spreads of the individual clusters. The results show that there are only a few dominant scatterers. They were usually building corners and walls, and building structures over the rooftop level. The delay and azimuth spreads inside the clusters were small, and depolarization was almost negligible. Both propagation over the rooftop level and propagation along the street canyons were significant in the considered environments.

Comparison of MIMO Antenna Configurations: Methods and Experimental Results

In this paper, the methods for comparing multipleinput-multiple-output (MIMO) antenna configurations using measured radio channels are considered. The expression of mutual information (MI) is factorized to give better understanding of the ability of MIMO antenna systems to transfer signal power, as well as to utilize parallel channels. An appropriate power normalization of channel matrices is shown to have a profound impact on the ranking of particularly directive MIMO antennas. It was found that the ability to transfer signal power from the transmitter to the receiver, instead of the rank properties, dominates in outage MI over a wide range of signal-to-noise ratios. The largest differences in outage MI between the antennas were found at low outage-probability levels, particularly in the line of sight. It was also verified that dual-polarized antenna systems are more robust for environmental variations but more sensitive for antenna orientation in comparison with single-polarized antenna systems both in eigenvalue dispersion and transferred signal power. At low outage-probability levels, the highest MI was achieved with vertically polarized dipole antennas.

Polarization Behaviours at 2, 5 and 60 GHz for Indoor Mobile Communications

The behaviours of linear polarizations at 2.15, 5.3 and 61.7 GHz in corridors are studied in this paper. It shows that there is no significant difference between the received powers for vertical and horizontal polarizations. Depolarization is obvious at 2.15 GHz due to different antenna type is applied at the receiver, and it is more serious in non-line-of-sight (NLOS) cases.

Study of different mechanisms providing gain in MIMO systems

In this paper, measurements are used as the experimental basis for evaluation of MIMO antenna configurations at 2.15 GHz. At the transmitting fixed station, the effects of increasing the number of channels and increasing the inter-element spacing in MIMO systems are studied. The goal of the paper is to find out how MIMO channels could be exploited better. We have performed radio channel sounder measurements using antenna arrays of directive and dual-polarized elements. Three potential MIMO environments have been included in the study. We found that increasing the distance between transmitting antenna elements or increasing the number of elements decreases eigenvalue spread and improves MIMO performance.

Clusterization of measured direction-of-arrival data in an urban macrocellular environment

Measured wideband direction-of-arrival data from urban macrocellular environment were clusterized. The clusterization was done by manual inspection. To understand the physical propagation channel, the source points of the extracted clusters were located to the local environment surrounding the mobile station. Some key parameters were calculated for each of the extracted clusters and for the residual power. By combining these parameters with the estimates of the cluster source points, assumptions on the propagation mechanisms of the clusters were drawn. According to the results the most significant sources are building structures above the average building height and corners of the buildings. This result is inline with previous studies in the urban propagation. Only a few significant clusters were found, in this study three clusters out of 14 extracted clusters contributed nearly 60% of the received power, while 19% of the power remained outside the clustering. Most of the clusters follow the Rician distribution with relatively high K-factor, while the residual power was Rayleigh distributed. There was only slight depolarization from the transmitted vertical polarization. One of the clusters was a clear exception with a negative XPR.

Experimental investigations of MIMO propagation channels

Recent results from information theory have predicted large data rates for MIMO (multiple output-multiple input) mobile radio systems (e.g [I]). However, the achievable capacity is defined by the availability of parallel propagation channels in the multipath environment. For example, the keyhole effect [2] could reduce the theoretical capacity. Obviously, radio channel measurements are needed to investigate the development and characteristics of parallel separate propagation paths. Both detailed understandmg on the most important propagation phenomena and information on the statistical properties of the channel are needed to support the development of MIMO radio systems. Essential properties of the MIMO channel measurement systems are