Susana Loredo

Echo identification and cancellation techniques for antenna measurement in non-anechoic test sites

This paper focuses on the measurement of the antenna radiation patterns when fully anechoic conditions are not available and, as consequence, some undesirable echoes are initially present in the measure. Two techniques are analyzed and compared, which - starting from data measured in the frequency domain - allow the echo contributions to be identified and the antenna radiation pattern to be retrieved. The accuracy of both techniques is evaluated at the frequency of 22 GHz by comparison with measurements obtained in an anechoic chamber.

Accuracy analysis of GO/UTD radio-channel modeling in indoor scenarios at 1.8 and 2.5 GHz

Ray-tracing techniques have been widely used as simulation tools for the design and planning of wireless systems, both in urban microcells and in indoor picocells, due to the site-specific nature of those environments. However, the value of such tools depends on the accuracy of the predictions when compared to measurements in real-world propagation environments. In this paper, the accuracy of a ray-tracing technique based on a full three-dimensional implementation of GO/UTD is analyzed, by comparison between measurements and simulations carried out for different indoor wireless-propagation environments and in different frequency bands. The narrowband analysis shows that both the mean level of the received signal and the statistical behavior of its variations about the mean can be accurately estimated. In the wideband analysis, the comparison between measured and simulated power-delay profiles shows that both the amplitude and arrival times of the main multipath components can be well predicted. The statistical distributions of the measured and simulated wideband parameters are also compared, showing good agreement.

An accurate and efficient method based on ray-tracing for the prediction of local flat-fading statistics in picocell radio channels

Ray-tracing techniques have proven to be very useful for the analysis and design of wireless systems both in urban microcells and in indoor picocells. At present, the optimization of these techniques enables not only the signal mean level but also the local statistics to be estimated accurately, which is of great practical importance. A wide range of comparisons between measurements and simulations confirming this have been carried out by the authors, and some examples are presented. The most interesting contribution of this paper is that starting from the signal information at one single point, obtained using ray-tracing techniques, it is possible to estimate the signal statistics in a local area of that point. This possibility substantially reduces the local statistics calculation time, confirming the idea that an efficient site specific channel model might be feasible. Finally, it is also shown that ray-tracing techniques are able to accurately estimate the first- and second-order statistics in those environments where the Clarke (1968) or isotropic scattering model is not applicable.

Indoor MIMO Channel Modeling by Rigorous GO/UTD-Based Ray Tracing

This paper presents a multiple-input-multiple- output (MIMO) channel model based on rigorous ray-tracing techniques, which is based on a full 3-D implementation of geometric optics and the uniform theory of diffraction (3-D GO/ UTD). Results obtained from measurements and simulations of the correlation matrix and capacity of a 2 times 2 MIMO system in specific indoor environments at a frequency of 2 GHz are presented. The channel capacity has been calculated for the different local areas considered in open- and office-area scenarios, starting from the measurements carried out there, as well as from the ray-tracing simulated channels. The rigorous and quantitative comparison between measurements and simulations shows that the model accuracy is sufficient for the analysis and design of the different aspects of the full MIMO system. The results from the ray-tracing model can also be used to extract general statistical characteristics and parameterize statistical models for different types of environments, without the need to carry out large and costly measurement campaigns. In addition, the measured data are used to study the impact of the channel on the achievable capacity of a 2 times 2 MIMO system in typical indoor scenarios at 2 GHz.

Measurement of Low-Gain Antennas in Non-Anechoic Test Sites through Wideband Channel Characterization and Echo Cancellation [Measurements Corner]

The measurement of an antenna in a reverberant or semi-anechoic chamber, or even in an anechoic chamber with non-ideal absorbing material, will include the effects of multipath propagation, which will be evident in a distorted radiation pattern. In those situations, an improvement of the measurement can be achieved through removal or compensation of the undesired contributions. A simple technique to eliminate those contributions, based on the well-known Fourier transform algorithm, is used in this paper. It starts from measurements of the systems response in the frequency domain, followed by Fourier transformation of data to the time domain, detection and gating of undesired echoes in the time domain, back to the frequency domain, and retrieval of the antenna radiation pattern at the frequency of interest. The method is evaluated under different measurement conditions.

Measurement and Statistical Analysis of the Temporal Variations of a Fixed Wireless Link at 3.5 GHz

This paper presents the measurement and statistical analysis of the temporal variations of the radio channel defined by a fixed link at 3.5 GHz in suburban areas. The analysis provides the required information about the temporal stability of the channel, the probability of occurrence and depth of fades, the Doppler spectrum and, in general, the influence of the environment on the signal behaviour. In particular, the effect of fast traffic on a motorway in the neighbourhood of the receiver is investigated, obtaining some general conclusions particularly useful in wireless communication systems design.

Radiation Pattern Retrieval in Non-Anechoic Chambers Using the Matrix Pencil Algorithm

In this paper, the Matrix-Pencil method is used to retrieve the radiation pattern of several antennas measured in difierent semi- anechoic scenarios using low directive probes, where the existence of re∞ected contributions can severely disturb the measurement. Starting from data measured in the frequency domain, this method allows the direct path to be identifled and the radiation pattern of the antenna to be retrieved with good accuracy in all the cases under study.

Polarization diversity in indoor scenarios: an experimental study at 1.8 and 2.5 GHz

The paper presents the results of a set of measurements carried out in order to research the behaviour of a polarization diversity scheme in indoor environments in the 1.8 and 2.5 GHz bands. To this end, parameters such as the cross-correlation coefficient and the cross-polarization discrimination between the individual signals received in each of the combiner branches are analysed. By simulating various types of combiners, the improvement produced by the combination in the statistical behaviour of the signal, and the decrease of the bit error rate after the combination are also analysed.

A Simple Model for Analyzing Transmitarray Lenses

A new model for characterizing a complex system formed by a feeding horn and a transmitarray lens is presented in this paper. This model characterizes the spillover radiation and is capable of analyzing its effect on the radiation pattern. Both the contribution of the lens and the spillover radiation are modeled as planar arrays. The proposed model shows good agreement with the results obtained in simulations using a commercial full-wave software. In addition, some features, such as the characterization of the feeding element, are included in this model, in order to improve its accuracy. Finally, the limits of applicability are also discussed throughout this paper. Thus, it is possible to set up the boundaries, in terms of F/D ratio and number of elements, within which the model is reliable.

Echo Characterization Based on Maximum-Likelihood Estimation for Antenna-Measurement Correction [Measurements Corner]

Antenna measurement systems could be affected by multipath effects resulting in reflected beams that might modify the measured values. In this paper, the use of the Maximum Likelihood estimator provides the basis of several post-processing methods able to estimate the echo parameters in imperfect antenna measurements. Once the reflections are characterized, these parameters are used to correct the measured values and to retrieve the actual radiation pattern corresponding to the antenna under test. Some different techniques are proposed in order to perform such cancellation. Experimental validation is also presented to show the accuracy of the described methods.