Experimental study of depolarization and antenna correlation in tunnels in the 1.3 GHz band

Measurements have been carried out in a low-traffic road tunnel to investigate the influence of the polarization of the transmitting and receiving antennas on the channel characteristics. A real-time channel sounder working in a frequency band around 1.3 GHz has been used, the elements of the transmitting and receiving arrays being dual-polarized patch antennas. Special emphasis is made on cross-polarization discrimination factor and on the spatial correlation between array elements which has a great influence on the performances of transmit/receive diversity schemes. Various polarizations both at the transmitter and the receiver have been tested to minimize this spatial correlation while keeping the size of the array as small as possible

Experimental investigation of V2I radio channel in an arched tunnel

This paper describes the results of the experimental radio channel sounding campaign performed in an arched road tunnel in Le Havre, France. The co-polar and cross-polar channels measurements are carried out in the closed side lane, while the lane along the center of the tunnel is open to traffic. We investigate the channel characteristics in terms of: path loss, fading distribution, polarization power ratios and delay spread. All these parameters are essential for the deployment of vehicular communication systems inside tunnels. Our results indicate that, while the H-polar channel gain attenuates slower than the V-polar channel due to the geometry of the tunnel, the mean delay spread of the H-polar channel is larger than that of the V-polar channel

Channel correlation-based approach for feedback overhead reduction in massive MIMO

For frequency-division duplex multiple-input-multiple-output (MIMO) systems, the channel state information at the transmitter is usually obtained by sending pilots or reference signals from all elements of the antenna array. The channel is then estimated by the receiver and communicated back to the transmitter. However, for massive MIMO, this periodical estimation of the full transfer matrix can lead to prohibitive overhead. To reduce the amount of data, we propose to estimate the updated channel matrix from the knowledge of the full correlation matrix at the transmitter made during some initialization time and the instantaneous measured channel matrix of smaller size, characterizing the link between the user and a limited number of reference array elements. The proposed algorithm is validated with measured massive MIMO channel transfer functions at 3.5GHz between a $9 \times 9$ uniform rectangular array and different user positions. Since measurements were made in static conditions, the criteria chosen for evaluating the performance of the algorithm are based on a comparison of the predicted channel capacity calculated from either the measured or estimated channel matrix

Statistics of multipath component clustering in an office environment

In this paper, directional MIMO measurements in an indoor office environment are presented. A 5-D ESPRIT estimation algorithm is used to extract parameters associated with discrete propagation paths, such as their azimuth of arrival, azimuth of departure, delay, and power. The estimated path parameters are grouped into clusters using the statistical K-power-means algorithm. Statistical distributions are determined for the path parameters within individual clusters and for their change between clusters. To validate the distributional choices, the goodness-of-fit to the proposed distributions is verified using statistical hypothesis tests with sufficient power

Robustness of high-resolution channel parameter estimators in presence of dense multipath components

The estimation accuracy of specular multipath components in radio channels that include dense multipath is investigated. Classical multipath estimation algorithms such as ESPRIT and SAGE do not include dense multipath in their signal model whereas recent ones, such as RiMAX, do. These estimation algorithms are applied to a priori known synthetic channels which include both specular components (SCs) and dense multipath components (DMCs). The estimation errors of the SCs are computed as a function of the DMC power to evaluate the estimator's robustness. The results of this work clearly indicate large estimation errors for the SC parameters when the estimator does not include DMCs in its data model

Accuracy of specular path estimates with ESPRIT and RiMAX in the presence of measurement-based diffuse multipath components

This paper presents performance results of three high-resolution parameters estimation algorithms: ESPRIT, SAGE and RiMAX. MIMO indoor radio channels which include measurement-based time-delay diffuse multipath scattering (DMC) were emulated to evaluate the estimation performance of both algorithms. The impact of the DMC on the parameter estimation accuracy is studied by adjusting its power with respect to the specular component. For all discussed scenarios, it is clearly demonstrated that RiMAX outperforms ESPRIT and SAGE which do not include DMC estimation into their data model. The preliminary results clearly highlight the importance of DMC and the necessity to account for its presence in data models to accurately estimate the channel parameters. Otherwise, very poor estimates of the coherent component parameters are expected which would in turn result in wronged propagation prediction models

Flexible real-time MIMO channel sounder for multidimensional polarimetric parameter estimation

This paper describes the architecture of a fully parallel multiple-input multiple-output (MIMO) channel sounder. It has been designed to give in real-time the full polarimetric channel matrix which is then exploited to display, for example, the bi-directional channel characteristics as the angle of arrival (AoA) and angle of departure (AoD) of the multipath components. This 16x16 sounder, working at a center frequency of 1.35 GHz, uses an OFDM transmission scheme with an 80 MHz bandwidth. Applications of this sounder are then illustrated by studying the outdoor to indoor propagation characteristics

MIMO in tunnel : impact of polarization and array orientation on the channel characteristics

Polarimetric characteristics of the propagation channel in a straight tunnel and in a frequency band around 1.3 GHz, are deduced from measurements using a real-time MIMO channel sounder. Emphasis is on the cross-polarization discrimination factor and, for a MIMO configuration, on the correlation between transmitting and receiving array elements, depending on the array orientation and on the polarization of the transmitting elements