Juan D. Sánchez-Heredia

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.

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.

Sample-Selection Method for Arbitrary Fading Emulation Using Mode-Stirred Chambers

Mode-stirred chambers (MSCs) consist of one or more resonant cavities coupled in some way in order to allow the measurement of different antenna parameters such as antenna efficiency, correlation, diversity gain, or multiple-input multiple-output (MIMO) capacity, among others. In a single-cavity MSC, also known as a reverberation chamber (RC), the environment is isotropic and the amplitude of the signal is Rayleigh distributed. Real environments, however, rarely follow an isotropic Rayleigh-fading scenario. Previous results have shown that a Rician-fading emulation can be obtained via hardware modification using an RC. The different methods lack from an accurate emulation performance and are strongly dependent upon chamber size and antenna configurations. With the innate complexity of more-than-one-cavity MSC, the coupling structure generates sample sets that are complex enough so as to contain different clusters with diverse fading characteristics. This letter presents a novel method to accurately emulate a more realistic Rician-fading distribution from a Rayleigh-fading distribution by selecting parts of the sample set that forms different statistical ensembles using a complex two-cavity multi-iris-coupled MSC. Sample selection is performed using a genetic algorithm. Results demonstrate the potential of MSCs for versatile MIMO fading emulation and over-the-air (OTA) testing. The method is patent protected by EMITE Ing., Murcia, Spain.

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.

Measuring Distributed MIMO System in Reverberation Chamber

Reverberation chambers have in recent years been validated as efficient tools for measuring multiple-input-multiple-output (MIMO) systems. Nowadays, cooperative systems are beginning to gain attention as the key to reach high speeds in the wireless environment. These systems often implement the so-called distributed MIMO. A simple method is proposed for characterizing distributed MIMO systems in reverberation chambers. Results for capacity and correlation are shown for three different distributed MIMO systems.

Sample Selection Algorithms for Enhanced MIMO Antenna Measurements Using Mode-Stirred Reverberation Chambers

Mode-stirred reverberation chambers (MSRCs) are a useful tool for measuring several wireless-related MIMO antenna parameters. In a conventional single-cavity MSRC, the emulated fading environment is isotropic and the amplitude of the signal is Rayleigh distributed. Previous contributions have enhanced the emulation capabilities of MSRCs so as to include the ability to emulate Rician- and non-isotropic fading environments. In this contribution, arbitrary amplitude probability density functions (PDF) emulation using a MSRC is presented by selecting parts of the sample set that forms different statistical ensembles. Several algorithms are presented and compared in terms of computation time and power accuracy using simulated as well as measured data from different MSRCs to obtain Rician, on-body and amplitude PDFs of standardized models. The technique is patent-protected by EMITE.

HSDPA Throughput Performance With Limited Number of Signal Paths

Over-the-air characterization of wireless devices is performed using specific channel models. Channel models define the distribution of the incident signals over angle and polarization, but always assuming a large number of signal paths. However, in some real cases, the number of signal paths can be limited. This letter studies the effect of the number of signal paths on the high-speed downlink packet access (HSDPA) throughput, using a commercial phone. Differences in performance are found, depending on the number of signal paths. This highlights the importance of the number of signal paths in the characterization of wireless devices.

Mode-stirred chamber sample selection technique applied to antenna correlation coefficient

This work was supported in part by the Spanish National R & D Programme through TEC 2008-05811 and by Fundacion´ Seneca, the R & D coordinating agency for the Region of ´ Murcia (Spain) under the 11783/PI/09 and 11610/IV2/09 Projects.

Radiative MRI Coil Design Using Parasitic Scatterers: MRI Yagi

Conventionally, radio frequency (RF) coils used for magnetic resonance imaging (MRI) are electrically small and designed for near-field operation. Therefore, existing antenna design techniques are mostly irrelevant for RF coils. However, the use of higher frequencies in ultrahigh field MRI allows for antenna design techniques to be adapted to RF coil designs. This communication proposes the use of parasitic scatterers to improve the performance of an existing 7T MRI coil called the single-sided adapted dipole (SSAD) antenna. The results reveal that scatterers arranged in a Yagi fashion can be applied to reduce local specific absorption rate maxima of a reference SSAD by 40% with only a 6% decrease in the propagated

Arbitrary fading emulation using mode-stirred reverberation chambers with stochastic sample handling

B_{1}^{+}