Antonio M. Martínez-González

Integrated planar multiband antennas for personal communication handsets

The advent of new, multistandard mobile phone devices is an important challenge for antenna designers, as they have to implement integrated antennas with multiband operation within a volume that is rapidly shrinking. In the paper, research results concerning the input return loss, radiation characteristics and efficiency of novel internal, planar, multiband patch antennas are presented.

The Role of Polarization Diversity for MIMO Systems Under Rayleigh-Fading Environments

Polarization diversity techniques have not received as much attention as others due to the significant difference in mean signal level between copolarized and cross-polarized branches when one polarization is transmitted. However, multiple-input-multiple-output (MIMO) systems where the multipath fading is only partially correlated could use polarization diversity to provide a high diversity gain. Hence there is a need to fully understand the role of true polarization diversity in such systems. In this letter, progressive (true) polarization diversity performance for 3 times 3 MIMO systems under Rayleigh-fading environments is evaluated through simulations and measurements. True polarization diversity was found to be as significant as spatial diversity at improving diversity gain, and hence MIMO system capacity

Evaluation of True Polarization Diversity for MIMO Systems

MIMO systems where multipath fading is only partially correlated could use polarization diversity to provide a higher diversity gain. Recent letters have proposed the use of tri-polarized antennas and a novel true polarization diversity (TPD) scheme. In this paper, the full potential of TPD is evaluated with both simulations and measurements and compared to conventional orthogonal polarization diversity (OPD). MIMO system performance with respect to capacity and diversity gain is obtained through the use of multimode-stirred chambers for both isotropic and non-isotropic environments. Simulated and measured results in over 591 different MIMO systems show that TPD outperforms conventional OPD for reduced volumes. Likewise, it has been demonstrated that TPD can be effectively combined with spatial diversity to nearly double the diversity gain and MIMO capacity for the same available handset volume.

Emulation of MIMO Nonisotropic Fading Environments With Reverberation Chambers

Some recent publications have extended the emulating capabilities of reverberation chambers. While polarization imbalance has been removed and Ricean-fading environments are now properly emulated, these chambers are still limited to isotropic nonline of sight (NLOS) scattering. By controlling the power received, number of resolvable multipath components (MPC), angular spread (AS), and angle of arrival (AoA), the emulation of real-propagating environments with both isotropic and nonisotropic scattering are demonstrated in this letter using a reverberation chamber with several multiple-input multiple-output (MIMO) arrays.

The Influence of Efficiency on Receive Diversity and MIMO Capacity for Rayleigh-Fading Channels

A previously published guideline for MIMO antenna arrays is refuted. The influence of radiation efficiency on diversity gain and MIMO capacity of wireless communications systems is investigated through simulations and measurements using a reverberation chamber. Integrated antennas on a portable device have efficiencies low enough to disallow typical inter-element correlation assumptions. Both diversity gain and MIMO capacity depend on the number of antennas, SNR and efficiency in a complex way. When the efficiency of antennas is considered, certain system capacity losses are predicted and measured. These losses may be recovered through using more receive elements than commonly recommended or through the addition of a smaller number of more efficient antennas.

Advances in mode-stirred reverberation chambers for wireless communication performance evaluation

Reverberation chambers (RC) are a popular tool for laboratory wireless communication performance evaluation, and their standardization for Over-The-Air (OTA) measurements is underway. Yet, the inherent limitations of single-cavity RCs to emulate isotropic Rayleigh-fading scenarios with uniform phase distribution and high elevation angular spread put their representation of realistic scenarios into jeopardy. Recent advances in the last few years, however, have solved all these limitations by using more general mode-stirred reverberation chambers (MSC), wherein the number of cavities, their stirring and coupling mechanisms, and their software postprocessing algorithms is far from simple, representing a new era for wireless communications research, development, and over-the-air testing. This article highlights recent advances in the development of second-generation mode-stirred chambers for wireless communications performance evaluation.

Diversity Gain and MIMO Capacity for Nonisotropic Environments Using a Reverberation Chamber

Several physical parameters of realistic nonisotropic environments have been recently emulated with reverberation chambers. In this letter, the different performance in terms of diversity gain and multiple-input multiple-output (MIMO) capacity of the same linear MIMO array in different nonisotropic propagating scenarios is demonstrated with a reverberation chamber (RC) for the first time. This could be useful for designing antenna arrays in handset MIMO.

Emulation of MIMO Rician-Fading Environments With Mode-Stirred Reverberation Chambers

Some recent publications have extended the emulating capabilities of mode-stirred reverberation chambers, which are now able to emulate Ricean-fading and non-isotropic environments. Either the need to physically modify existing chambers or multiple sets of measurements is required for these enhancements. In this paper a novel post-processing hybrid tool is presented for the transformation of a Rayleigh-fading emulated environment into a Rician one. The model is tested and compared to outdoor measurements and simulations through the K-factor, correlation, diversity gain and MIMO capacity. Results show an excellent matching performance with no hardware modifications of mode-stirred chambers with just one set of measurements. The method is patent protected by EMITE Ing.

Accurate Estimation of Correlation and Capacity for Hybrid Spatial-Angular MIMO Systems

In this paper, several novel functions for accurately estimating the correlation and the multiple-input-multiple-output (MIMO) capacity of combined spatial and true polarization diversity (TPD) schemes are proposed for the first time. Minimum error estimation of the correlation for a hybrid spatial-TPD linear scheme previously reported cannot be obtained by simple nonlinear least-square estimators, and the use of genetic algorithms (GAs) provides an accurate solution. Channel matrix coefficients and MIMO capacities are analyzed for the diverse optimization strategies employed, which aim to identify the best prediction of MIMO performance. The novel functions are used with previously reported results and validated for Rayleigh fading scenarios with isotropic scattering using a multimode-stirred chamber (MIMO Analyzer). An accurate prediction of high correlation values is concluded to be of extreme importance for the final MIMO performance estimation. This has been found to be particularly important for estimating MIMO capacity with achieved prediction accuracies of 1.1% at SNR = 15 dB. In contrast, the accurate prediction of low correlation values has been found to have a less-important effect on the final capacity-predicting performance.

Multipath Simulator Measurements of Handset Dual Antenna Performance With Limited Number of Signal Paths

Antenna pairs for diversity or MIMO functionality are characterized under the assumption of a certain statistical distribution of the incident signals over angle and polarization, but also assuming a signal environment with a large number of signal paths. In many real-life environments, however, only a few signal paths contain most of the transferred power. A multipath simulator can be used to realize signal environments with a controlled number of signal paths. This paper presents measurements of dual antenna performance using a multipath simulator with 2-16 signal paths. The results are analyzed in terms of statistical power distributions, power imbalance, correlation coefficient, multiplexing efficiency, and diversity gain. Differences in performance depending on the number of signal paths are noted, illustrating the value of considering the number of signal paths in characterization.