Four-element ultrawideband textile cross array for dual-spatial and dual-polarization diversity

The emergence of miniaturized flexible electronics enables on-duty first responders to collect biometrical and environmental data through multiple on-body sensors, integrated into their clothing. However, gathering these life-saving data would be useless if they cannot set up reliable, preferable high-data-rate, wireless communication links between the sensors and a remote base station. Therefore, we have developed a four-element ultrawideband textile cross array that combines dual-spatial and dual-polarization diversity and is easily deployable in a first responder's garment. The impedance bandwidth of the array equals 1.43 GHz, while mutual coupling between its elements remains below -25 dB. For a maximal bit error rate of 1e-4, the array realizes a diversity gain of 24.81 dB. When applying adaptive subcarrier modulation, the mean throughput per orthogonal frequency division multiplexing (OFDM) subcarrier increases by an extra bit/symbol when comparing fourth- to second-order diversity

Recovering handset diversity and MIMO capacity with polarization-agile antennas

Journal ArticleDesign guidance is provided for multiple-input-multiple- output (MIMO) antenna systems on handsets-a strong prospect for next generation wireless devices. Handheld wireless devices are likely to be rotated out of their optimal polarization, thereby experiencing significant power losses. An existing polarization-agile antenna design and a novel four-spoke extension recover significant fractions of the rotation-induced losses both in switched-antenna diversity and capacity calculations-all but 1 dB of diversity gains at a 99% system reliability, half of the CΕ losses or 80% of the Cο,1 losses. These gains benefit four- and ten-element arrays and remain significant in the presence of 6 dB cross coupling and in volume-restricted arrays. Diversity order investigations also demonstrate a new, non-Rayleigh locus of curves describing patch antennas subject to rotation

Effect of user presence on receive diversity and MIMO capacity for rayleigh-fading channels

The effects of the presence of the user on multipleinput– multiple-output (MIMO) performance for wireless communications systems is investigated through measurements in a reverberation chamber. Measured results have demonstrated that despite a decrement on the envelope correlation coefficient, a degradation of both diversity gain and MIMO capacity are expected when the user is present. While the validity of the correlation coefficients for predicting MIMO performance is limited in the presence of the user, the effects have also been found to be strongly dependent upon frequency, antenna topology, and user characteristics.This work was supported in part by the Fundación Séneca, the R&D coordinating unit of the Autonomous Region of Murcia (Spain) under Projects 2I05SU0033 and TIC-TEC 06/01-0003

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.This work was supported in part by the Fundación Séneca, the R&D unit of the Autonomous Region of Murcia (Spain) under project references TIC-TEC 06/01-0003, 07/02-0005 and 05746/PI/07, and in part by the Spanish National R&D Programme through TEC2007/63470/TCM

Equivalent circuit based calculation of signal correlation in lossy MIMO antennas

Correlation coefficient of received signals across a pair of antennas is a key performance indicator for multiple-input multiple-output (MIMO) systems. For multipath environments with uniform 3D angular power spectrum, the signal correlation between two antennas can be exactly calculated from their 3D radiation patterns. When radiation patterns are unavailable, a simplified approach that only requires the antennas’ scattering parameters can be used instead. However, the simpler method assumes lossless antennas and thus only works well for antennas with high radiation efficiencies. To take into account the antenna loss, the idea of equivalent circuit approximation is used in this paper to analytically separate the lossy components (resistance or conductance) from the lossy antenna arrays, using known scattering parameters and radiation efficiencies. The simplified method using S parameters can then be applied to obtain the correlation coefficient of the equivalent lossless antennas. The effectiveness of the method has been verified on antennas operating at a single mode, such as dipole or patch at its lowest resonant frequency. Good results were also obtained for the measured case of a dual-antenna mobile terminal, consisting of a monopole and a PIFA

Experimental analysis of multidimensional radio channels

In this thesis new systems for radio channel measurements including space and polarization dimensions are developed for studying the radio propagation in wideband mobile communication systems. Multidimensional channel characterization is required for building channel models for new systems capable of exploiting the spatial nature of the channel. It also gives insight into the dominant propagation mechanisms in complex radio environments, where their prediction is difficult, such as urban and indoor environments. The measurement systems are based on the HUT/IDC wideband radio channel sounder, which was extended to enable real-time multiple output channel measurements at practical mobile speeds at frequencies up to 18 GHz. Two dual-polarized antenna arrays were constructed for 2 GHz, having suitable properties for characterizing the 3-D spatial radio channel at both ends of a mobile communication link. These implementations and their performance analysis are presented. The usefulness of the developed measurement systems is demonstrated by performing channel measurements at 2 GHz and analyzing the experimental data. Spatial channels of both the mobile and base stations are analyzed, as well as the double-directional channel that fully characterizes the propagation between two antennas. It is shown through sample results that spatial domain channel measurements can be used to gain knowledge on the dominant propagation mechanisms or verify the current assumptions. Also new statistical information about scatterer distribution at the mobile station in urban environment is presented based on extensive real-time measurements. The developed techniques and collected experimental data form a good basis for further comparison with existing deterministic propagation models and development of new spatial channel models.reviewe