Communications

Characterization of the Angle, Delay and Polarization of Multipath Signals for Indoor Environments

A high-resolution channel sounding technique has been used to investigate the cross-polarization of electromagnetic waves in the 5-6 GHz band. Experiments were performed in two non-line-of-sight indoor locations, and it was found that there is a strong dependency of the cross-polarization of multipath components on the elevation angle-of-arrival. For a vertically polarized transmitting antenna, clusters of co-polarized multipath components were confined predominantly to the region around the horizontal plane that contains the virtual line-of-sight between transmitter and receiver. In contrast, cross-polarized signals were detected for a variety of elevation angles with considerable power levels. The surroundings of the receiver were identified as the principal source of depolarized signals. In addition, time dispersion analysis of the multipath signals led to the determination of the AoAs where there is a strong correspondence between co- and cross-polarized signals as a consequence of the partial depolarization of MPCs. This work supports the exploitation of the joint space and polarization diversities in indoor propagation scenarios to improve the system performance.

DOI: 10.1109/TAP.2008.927507

High Resolution Spatiotemporal Characterization of Electric Field Polarization for Indoor Wireless Environments

The effects of the electric field polarization on the received power are investigated based on high resolution measurements of the indoor wireless channel. The results presented here were obtained using a channel sounding testbed, which was specially designed to study the radio propagation in the 5-6 GHz frequency band with high resolution in terms of angle-of-arrival (AOA) and time-of-arrival (TOA). Measurements were made at different indoor locations and the influence of the receiver surroundings on polarization cross-coupling was analyzed as a function of the azimuthal and elevation AOA. Significant cross-coupling was measured in locations where multi-paths arrive with oblique AOA with respect to the horizontal plane (thetas=90deg). The cross-polarization was characterized with high resolution in azimuth and elevation, which enabled the study of the spatial distribution of depolarized multipaths. The amount of power due to cross-polarized multipaths was estimated for a vertically polarized transmitter antenna located in different indoor environments. The advantages of using multi-element antennas and polarization diversity were made evident, as well as the importance of the relative location of transmitter and receiver and the 3-D distribution of the nearest scatterers.

DOI: 10.1109/CCECE.2006.277655

Indoor Wireless Reception Improvement Using Cross-polarized Multipath Signals

Previous work has noted the distinct characteristics of vertically and horizontally polarized multipath components for indoor non-line-of-sight environments. Using measured data, the receiver signal-to-noise ratios for coherent and non-coherent combining of the co- and cross-polarized multipath components are compared to those obtained with omnidirectional reception for vertical or horizontal polarizations. It is seen that significant improvements in SNR can be achieved using intelligent combining with polarization diversity. Furthermore, it is observed that when the receiver is unable to resolve multipath components, coherent combination of both orthogonally polarized signals components provides a consistent advantage over vertically or horizontally polarized omnidirectional reception. At higher bandwidths, the increased resolution improves the performance of all techniques however the dual polarization multipath combining retains its relative advantage over the other techniques.

DOI: 10393/19635

Multibeam Selection for Indoor MIMO Systems: Two Cases of Study

The performance of multiple-input multiple-output (MIMO) systems using beam selection is investigated in this paper. Based on the results of a channel sounding campaign carried out at the University of Manitoba for line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios, it was possible to contrast the results of transmitter, receiver and joint beam selection in rich scattering environments. The channel was characterized in the 1-2.4 GHz frequency band with a multipath delay resolution better than 5.8 ns. The beam selection was performed by exhaustive search method. The results led us to important conclusions regarding the beam selection procedure and its potential to improve the indoor channel capacity. In LOS, the single input single output (SISO) system that favours the maximum power direction of arrival (DOA) maximizes the capacity. Capacity improvements are observed by increasing the number of receiver beams (RBs) only at high signal-to-noise ratios (SNRs) for omnidirectional transmission. The best performance in transmitter beam selection in LOS is observed by increasing the number of transmitter beams (TBs) for high SNRs. In the case of NLOS, the capacity performance is improved when more than a single beam is used in either, transmitter or receiver side. The joint transmitter-receiver beam selection exhibits best capacity performance only for large SNRs in LOS while the SISO systems outperforms any joint beam selection alternative for low SNRs. In contrast, in NLOS environments, the use of joint beam selection shows a constant capacity performance improvement starting from lower SNR than in the LOS case.

DOI: 10.1109/TAP.2007.893380