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This paper proposes a genetic algorithm (GA) combined with ray tracer to generate a cell-free topology of massive MIMO (mMIMO) for the optimal focusing performance serving multiple users. The realistic hardware impairment, for instance the non-ideal power amplifier, is taken into account of the system modeling and topology optimization. To the best of our knowledge, this is the first attempt to apply GA in optimizing the hardware-impaired multi-user cell-free mMIMO. Although the demonstrated numerical analysis is for indoor scenario, the proposed approach is transferable for generic scenarios. In GA, the base station (BS) antennas’ placement is encoded with an adjusted binary matrix representation, which is straightforward for the subsequent genetic operations. The explored candidates by GA can evolve beyond the parents, where the fitness of individuals is evaluated dynamically via a ray tracer radio channel simulator. Compared to the traditional GA, our proposed GA can find better solutions with a faster convergence speed. The algorithm provides near-optimal results in experiments, applicable to generic environment with multiple mobile users and different signal-to-interference-plus-noise ratios. [ABSTRACT FROM AUTHOR]

Featured Application: The presented numerical approach can be directly applied to the estimation of the compliance boundary of the antenna array base stations and the downlink human EMF exposure assessment in the networks served by such base stations. In the near future, wireless coverage will be provided by the base stations equipped with dynamically-controlled massive phased antenna arrays that direct the transmission towards the user. This contribution describes a computational method to estimate realistic maximum power levels produced by such base stations, in terms of the time-averaged normalized antenna array gain. The Ray-Tracing method is used to simulate the electromagnetic field (EMF) propagation in an urban outdoor macro-cell environment model. The model geometry entities are generated stochastically, which allowed generalization of the results through statistical analysis. Multiple modes of the base station operation are compared: from LTE multi-user codebook beamforming to the more advanced Maximum Ratio and Zero-Forcing precoding schemes foreseen to be implemented in the massive Multiple-Input Multiple-Output (MIMO) communication protocols. The influence of the antenna array size, from 4 up to 100 elements, in a square planar arrangement is studied. For a 64-element array, the 95th percentile of the maximum time-averaged array gain amounts to around 20% of the theoretical maximum, using the Maximum Ratio precoding with 5 simultaneously connected users, assuming a 10 s connection duration per user. Connection between the average array gain and actual EMF levels in the environment is drawn and its implications on the human exposure in the next generation networks are discussed. [ABSTRACT FROM AUTHOR]

The goal of this paper is to experimentally assess the field enhancement and hotspot size of radio frequency electromagnetic fields created by the Maximum Ratio Combining (MRC) precoding scheme using lab measurements at 3.5, 5.5 and 11 GHz. MRC is an adaptive precoding scheme used by Massive Multiple Input Multiple Output systems, one of the enabling techniques of the fifth generation of telecommunications (5G). A virtual antenna array was used to compare MRC with two passive precoding schemes: the Random Phase Model (RPM) and the Centerline Beam Model (CBM). The field enhancement going from CBM to MRC was largest in obstructed line of sight (OLOS), ranging from 1.9 to 7.4 dB. The field enhancement going from RPM to MRC was about 9.5 dB across frequency bands in both line of sight (LOS) and OLOS. The hotspot size, quantified by the full width at half maximum (FWHM), ranged from 0.5 wavelengths to one wavelength. [ABSTRACT FROM AUTHOR]

A novel localization framework is presented based on ultra-wideband (UWB) channel sounding, employing a triangulation method using the geometrical properties of propagation paths, such as time delay of arrival, angle of departure, angle of arrival, and their estimated variances. In order to extract these parameters from the UWB sounding data, an extension to the high-resolution RiMAX algorithm was developed, facilitating the analysis of these frequency-dependent multipath parameters. This framework was then tested by performing indoor measurements with a vector network analyzer and virtual antenna arrays.The estimated means and variances of these geometrical parameters were utilized to generate multiple sample sets of input values for our localization framework. Next to that, we consider the existence of multiple possible target locations, which were subsequently clustered using a Kim–Parks algorithm, resulting in a more robust estimation of each target node. Measurements reveal that our newly proposed technique achieves an average accuracy of 0.26, 0.28, and 0.90 m in line-of-sight (LoS), obstructed-LoS, and non-LoS scenarios, respectively, and this with only one single beacon node. Moreover, utilizing the estimated variances of the multipath parameters proved to enhance the location estimation significantly compared to only utilizing their estimated mean values. [ABSTRACT FROM PUBLISHER]

The next fifth generation (5G) of wireless communication networks comes with a set of new features to satisfy the demand of dataintensive applications: millimeter-wave frequencies, massive antenna arrays, beamforming, dense cells, and so forth. In this paper, we investigate the use of beamforming techniques through various architectures and evaluate the performance of 5G wireless access networks, using a capacity-based network deployment tool. This tool is proposed and applied to a realistic area in Ghent, Belgium, to simulate realistic 5G networks that respond to the instantaneous bit rate required by the active users. The results show that, with beamforming, 5G networks require almost 15% more base stations and 4 times less power to provide more capacity to the users and the same coverage performances, in comparison with the 4G reference network. Moreover, they are 3 times more energy efficient than the 4G network and the hybrid beamforming architecture appears to be a suitable architecture for beamforming to be considered when designing a 5G cellular network. [ABSTRACT FROM AUTHOR]

This work presents an analysis of dense multipath components (DMC) in an industrial workshop. Radio channel sounding was performed with a vector network analyzer and virtual antenna arrays. The specular and dense multipath components were estimated with the RiMAX algorithm. The DMC covariance structure of the RiMAX data model was validated. Two DMC parameters were studied: the distribution of radio channel power between specular and dense multipath, and the DMC reverberation time. The DMC power accounted for 23% to 70% of the total channel power. A significant difference between DMC powers in line-of-sight and nonline-of-sight was observed, which can be largely attributed to the power of the line-of-sight multipath component. In agreement with room electromagnetics theory, the DMC reverberation time was found to be nearly constant. Overall, DMC in the industrial workshop is more important than in office environments: it occupies a fraction of the total channel power that is 4% to 13% larger. The industrial environment absorbs on average 29% of the electromagnetic energy compared to 45%–51% for office environments in literature: this results in a larger reverberation time in the former environment. These findings are explained by the highly cluttered and metallic nature of the workshop. [ABSTRACT FROM PUBLISHER]

The demonstration of compliance with guidelines for human exposure to base-station antennas can be a time consuming process or often results in overly conservative estimates. To alleviate this burden and reduce the overestimation, approximation formulas for the whole-body average specific absorption rate (SAR) and the peak spatial SAR of human bodies using readily available basic antenna parameters have been developed and validated in this study. The formulas can be used for adults standing in the radiating near field of base-station antennas operating between 300 MHz and 5 GHz, at distances larger than 200 mm. It is shown that the 95th-percentile absorption for the human population can be well approximated by the absorption mechanism and statistical data of weight, height, and body-mass index of the human population. The validation was performed numerically using three anatomical human models (Duke, Ella, and Thelonious) exposed to 12 generic base-station antennas in the frequency range 300 MHz to 5 GHz at six distances between 10 mm and 3 m. From the 432 evaluated configurations, the estimation formulas for adult models are proven to be conservative in predicting the SAR exposure values of the two adults, but as expected not of the child. [ABSTRACT FROM AUTHOR]

Measurements and simulations of the vehicle penetration loss (VPL) at 600, 900, 1800, and 2400 MHz are presented. The measured average penetration loss varies from 3.2 to 23.8 dB, depending on frequency, illuminated vehicle side, and in-vehicle antenna orientation. VPL tends to follow a lognormal distribution. Reported penetration loss values are compared to previous measurements from the literature. [ABSTRACT FROM AUTHOR]

A comparison between the safety distances of a base station antenna using electromagnetic field and the specific absorption rate (SAR) assessment is made. The input power in the antenna is determined such that the electromagnetic fields and the SAR equal the reference levels and the basic restrictions, respectively, at a certain distance. Up to about 10 W the localized SAR delivers the largest safety distances when the electric field averaged in a volume is considered. This means that from 10 W and up the SAR does not need to be determined to obtain the largest safety distances. Safety distances based on the SAR will be smaller than those obtained from the electromagnetic fields when the maximum field value in a plane is considered. [ABSTRACT FROM AUTHOR]

Abstract: In this letter, measurements of the industrial power delay profile are presented. Measurements are performed through frequency-domain channel sounding in the range from 800MHz to 4GHz and by using the virtual antenna array method. Received power as a function of delay clearly exhibits clustering and is for this reason fitted to the well-known Saleh–Valenzuela model. With this, new statistical modifications to the rates of power decay in the Saleh–Valenzuela model are presented. It is found that the model''s parameters do not seem to differ significantly between LOS and NLOS. Small-scale fading is Rayleigh distributed except for the first arriving delay tap, for which a Nakagami- distribution provides a better fit. [Copyright &y& Elsevier]