Veli-Matti Kolmonen

Non-Stationary Narrowband MIMO Inter-Vehicle Channel Characterization in the 5-GHz Band

In this paper, we describe measurements and models of 30 × 30 narrowband multiple-input-multiple-output (MIMO) vehicle-to-vehicle (V2V) radio propagation channels at 5.3 GHz. Four environments were considered: a campus, a highway, a suburban area, and an urban area. Since the scattering environment may rapidly change in V2V communications, we first investigate the validity of the wide-sense stationarity (WSS) assumption for such channels using the correlation matrix distance (CMD), which is a metric for the characterization of the MIMO channel nonstationarity. Moreover, statistical channel models were developed for these environments, which take into account the non-stationary behavior of the measured V2V channels. The large-scale fading was found to be lognormally distributed, whereas the small-scale fading was characterized by the flexible Weibull distribution. Finally, the non-stationary behavior of both large-scale fading and small-scale fading statistics was investigated.

Angular and Shadowing Characteristics of Dense Multipath Components in Indoor Radio Channels

The dense multipath components (DMC) represent the part of the radio channel that cannot be characterized by using the specular components (SC). In this paper, the propagation characteristics of the DMC are analyzed in indoor environments based on extensive channel measurements. The results show that the contribution of the DMC to the total received power can vary as much as between 10% and 95%, being generally higher in non-line-of-sight than in line-of-sight scenarios. However, it was found that the DMC have a well distinguishable structure in the angular domain in all the investigated scenarios and, furthermore, the propagation mechanisms of the SC and DMC have large similarities. In addition, the effect of shadowing objects on the SC and DMC has been investigated.

Experimental Propagation Channel Characterization of mm-Wave Radio Links in Urban Scenarios

The 71-76- and 81-86-GHz bands, which are a part of the millimeter-wave (mm-wave) E-band (60-90 GHz), are allocated worldwide for ultrahigh-capacity point-to-point communications. Here, a geometry-based single-bounce channel model is developed for E-band point-to-point link applications and is verified by channel measurements. A measurement campaign was performed in a street canyon scenario, which is one very interesting possible new usage environment for E-band radio links, where reflected signals can cause more severe multipath fading compared to traditional open environments. The measurement results and the geometry of the measurement locations were used to determine the parameters of the developed channel model. The model can be used to estimate the characteristics of the radio channel such as excess delay, power level, and angular distribution of the multipath components. The channel model was validated by comparing the measured and modeled root mean square (RMS) delay spread, which is an important parameter for very broadband radio systems. All the modeled and measured mean values of RMS delay spread were in the range of 0.089-0.125 ns, revealing a good agreement between the channel model and the measurements.

Analysis and Modeling on co- and Cross-Polarized Urban Radio Propagation for Dual-Polarized MIMO Wireless Systems

Cross-polarization coupling is an important radio propagation characteristic in dual-polarized multiple-input multiple output (MIMO) systems. Still, few studies analyze the polarimetric properties of the radio channel in relation to the actual propagation conditions and processes taking place in urban environment. The topic is studied in the present paper with the aid of dual-polarized MIMO measurements and ray tracing simulations. Several scenarios are considered, and the impact of the different propagation characteristics (LOS, NLOS, link-distance, presence of diffuse-scattering, angular distribution of the signal, etc.) on cross-polarization coupling is analyzed. Generally, a fairly high degree of coupling is observed due to multipath propagation and especially to diffuse scattering. Surprisingly, it does not appear to depend on link distance.

Multi-Link MIMO Channel Modeling Using Geometry-Based Approach

Geometry-based stochastic channel models (GSCMs) are extended to support multi-link simulations by applying the concept of common clusters. This novel approach aims to control the correlation between different links, inter-link correlation, by adjusting the amount of power simultaneously propagating via the same clusters in the different links. The behavior of common clusters is analyzed based on dual-link channel measurements, and a multi-link GSCM is developed based on common clusters. In addition, the effects that the common clusters have on inter-link correlation and on sum rate capacity are investigated based on simulations. Finally, comparison between simulations and measurements is done in order to indicate the validity of the proposed multi-link GSCM.

Wideband MIMO Car-to-Car Radio Channel Measurements at 5.3 GHz

Measurements of car-to-car (C2C) radio channels with 60 MHz bandwidth at 5.3 GHz have been performed in Helsinki, Finland. We focused on 30x30 multiple-input multiple- output (MIMO) measurements, conducted in four environments (urban, sub-urban, campus and highway), under quasi-realistic traffic conditions. As first results, we present in this paper the delay spread statistics for each investigated environment. The largest values of root-mean-square (RMS) delay spread, roughly 2 mus, were obtained in the urban environment. The narrowband channel fading statistics have also been derived using composite distributions, in order to assess the global fading statistics.

Characterization of Quasi-Stationarity Regions for Vehicle-to-Vehicle Radio Channels

We analyze the nonwide-sense-stationarity (nonWSS) of vehicle-to-vehicle (V2V) radio channels using three metrics: 1) the correlation matrix distance (CMD); 2) the wideband spectral divergence (SD); and 3) the shadow fading correlation. The analysis is based on measurements carried out at 5.3 GHz using a 30 × 4 MIMO system in suburban, urban, and underground parking areas. Several factors such as the existence of a line-of-sight (LOS), the speed of cars, and the antenna array size and configuration are considered in the analysis of non-WSS. It is found that quasi-stationarity region ranges from 3 to 80 m in different V2V scenarios, and is strongly affected by the above factors. Based on the comparison of the equivalent quasi-stationarity region size estimated by the three metrics, it is suggested to use SD and shadowing correlation metrics for systems with small electrical array apertures and to use CMD metric only for arrays with large electrical apertures.

Wideband Measurement-Based Modeling of Inter-Vehicle Channels in the 5-GHz Band

In this paper, we describe a model for the fading of Vehicle-to-Vehicle (V2V) radio propagation channels, based on an extensive measurement campaign that has been conducted at 5.3 GHz in four different environments (i.e. on a campus, on a highway, in suburban and urban areas) around Helsinki (Finland) in August 2007. Owing to the well known non-stationary behavior of the V2V channel, we considered a Geometry-based Stochastic Channel Modeling (GSCM) approach rather than a more classical tapped-delay line one. The fading of the time-variant scatterer contributions is modeled as the combination of a distance-decaying process and two stochastic small- and large-scale fading processes. The complete parametrization of the V2V channel model is provided in the paper.

Dependence of Error Level on the Number of Probes in Over-the-Air Multiprobe Test Systems

Development of MIMO over-the-air (OTA) test methodology is ongoing. Several test methods have been proposed. Anechoic chamber-based multiple-probe technique is one promising candidate for MIMO-OTA testing. The required number of probes for synthesizing the desired fields inside the multiprobe system is an important issue as it has a large impact on the cost of the test system. In this paper, we review the existing investigations on this important topic and end up presenting rules for the required number of probes as a function of the test zone size in wavelengths for certain chosen uncertainty levels of the field synthesis.

Reproduction of Arbitrary Multipath Environments in Laboratory Conditions

We discuss the synthesis of arbitrary multipath environments in a spherical volume of space (test zone), with a limited number of feed antennas (probes). The probes can be of any type, e.g., simple dipoles. The required number of probes is proportional to the area of the sphere enclosing the test zone. The signal received by a two-port mobile terminal antenna model placed in the test zone is examined through simulations, using measured real-world propagation channel data. We study how the received signal and the channel capacity are affected by truncation errors and a certain noise level in the probe excitations. This kind of synthesis enables the testing of mobile terminals under realistic operating conditions in laboratory environments. The synthesis is not limited to far-field scenarios, but near-field effects can be generated as well.