Marina Barbiroli

Ray-Tracing-Based mm-Wave Beamforming Assessment

The use of large-size antenna arrays to implement pencil-beam forming techniques is becoming a key asset to cope with the very high throughput density requirements and high path-loss of future millimeter-wave (mm-wave) gigabit-wireless applications. Suboptimal beamforming (BF) strategies based on search over discrete set of beams (steering vectors) are proposed and implemented in present standards and applications. The potential of fully adaptive advanced BF strategies that will become possible in the future, thanks to the availability of accurate localization and powerful distributed computing, is evaluated in this paper through system simulation. After validation and calibration against mm-wave directional indoor channel measurements, a 3-D ray tracing model is used as a propagation-prediction engine to evaluate performance in a number of simple, reference cases. Ray tracing itself, however, is proposed and evaluated as a real-time prediction tool to assist future BF techniques.

Evaluation of exposure levels generated by cellular systems: methodology and results

During the past years, the number of antenna installations has considerably increased mainly as a consequence of the great diffusion of cellular systems. While the emissions of mobile terminals principally concern cellular system users, the exposure due to base stations (BSs) is permanent and spread over the entire territory. In this paper, a flexible approach for the evaluation of exposure levels generated by cellular systems BSs is proposed. Both a conceptual method for the evaluation of the overall exposure level and a site specific method for the computation of the field in the surroundings of BS antennas are proposed. This last method is based on a combination of three different propagation models which enable an accurate evaluation of the field both close to the antenna and farther off. The validity of the approach is checked by comparison with measurements in single-antenna and multiantenna cases.

Ray tracing propagation modeling for future small‐cell and indoor applications: A review of current techniques

Applied for the first time to mobile radio propagation modeling at the beginning of the nineties, ray tracing is now living a second youth. It is probably the best model to assist in the design and planning of future short-range, millimeter-wave wireless systems, where the more limited propagation environment with respect to UHF frequencies allows to overcome traditional high-CPU time limitations while the higher operating frequency makes ray-optics approximations less drastic and allows to achieve an unprecedented level of accuracy. An overview of ray tracing propagation modeling is given in this paper, with a special attention to future prospects and applications. In particular, frontiers of ray-based propagation modeling such as extension to diffuse scattering, multidimensional channel characterization, multiple-input multiple-output (MIMO) capacity assessments, and future applications such as real-time ray tracing are addressed in the paper with reference to the work recently carried out at the University of Bologna.

A new statistical approach for urban environment propagation modeling

Field prediction is an essential component of the planning process of cellular radio systems. This task is particularly time- and money-consuming in the urban environment, where cell size is of the order of a few hundred meters, and the influence of the city structure (building size and dimension, street width, orientation, etc.) cannot be neglected in the field prediction. For this reason, traditional statistical models such as the well-known Okumura-Hata, cannot be used in this environment, and the prediction is accomplished by means of accurate but time-consuming methods, such as ray-tracing, which require detailed and very expensive databases of the building and street layout of the city under investigation. In this correspondence, we propose a new methodology, which is based on the decomposition of propagation in its basic mechanisms, corresponding to different propagation planes, which can be treated independently from each other. This allows us to build a model which is as simple, fast, and easy to use as the traditional statistical models, with the advantage that it requires only a few statistical parameters thus realizing the need of high-resolution databases.

Assessment of Population and Occupational Exposure to Wi-Fi Systems: Measurements and Simulations

In this study, the impact of Wi-Fi access points is investigated in terms of electromagnetic field exposure evaluations. Installations, typically present in common living contexts, have been analyzed by means of both wideband and narrow-band measurements and simulation-prediction tools. The obtained results show that exposure due to these systems is compliant with the limits provided by regulation.

Analysis of field strength levels near base station antennas

A new hybrid algorithm to evaluate the field strength levels around base stations antennas of cellular mobile radio systems is presented in the paper. The method allow a correct evaluation of near and far radiated field by means of the combination of different propagation models. The field intensity level is compared with measurements for some typical urban base stations and an analysis of the impact of the presence of buildings or other objects is also performed. We identify the areas around the antennas where the field strength level exceeds the exposure limits specified in the IRPA Guidelines of 1988 and CENELEC ENV 50166-2 report of 1995. As a result of this analysis we propose a preliminary classification of different installations based on few fundamental parameters related to the antenna characteristics and to the environment topology.

Synchrophasors-Based Distributed Secondary Voltage/VAR Control via Cellular Network

The impact of the increasing connection of distributed generation to medium voltage (MV) feeders, with particular reference to photovoltaic (PV) units, justifies the investigation on secondary voltage/VAR control (VVC) schemes able to improve the utilization of available control resources and to reduce reactive power flows. The paper deals with a secondary VVC scheme based on a distributed multi-agent approach that requires only the estimation of the reactive power flows between the buses where the PV units with reactive power control capability are connected. Phasor Measurement Units (PMUs) are used to get the relevant information. In general, distributed control approaches are expected to work adequately even by using communication infrastructures with lower performances than those required by centralized approaches. The paper addresses such an issue by the analysis of the distributed VVC performance when a shared cellular network is used for the cooperative adjustment of PV inverters reactive power outputs and of tap positions of transformers equipped with on-load tap changers. The analysis is carried out by using a specifically developed ICT (Information and Communications Technology)-power co-simulation platform. It is shown that the VVC scheme has adequate performances also in the presence of significant levels of background traffic and data loss.

Analysis of Outdoor-to-Indoor Propagation at 169 MHz for Smart Metering Applications

An experimental work aimed at assessing the outdoor-to-indoor propagation losses at 169 MHz is described in this paper. The building penetration loss, often considered as an additional constant value to be added to propagation losses in previous studies, is here on the contrary regarded as a random variable; its cumulative distribution is extracted from the measured data and is found to be approximately Gaussian. Moreover, in order to account for the critical installation conditions which may be experienced by indoor wireless devices in particular applications (e.g., wireless smart metering), an additional loss term, here indicated as installation loss, is introduced and its value is investigated in some reference cases. The achieved results are also embedded into a statistical procedure similar to those commonly adopted for wireless cellular networks planning.

Ray Tracing RF Field Prediction: An Unforgiving Validation

The prediction of RF coverage in urban environments is now commonly considered a solved problem with tens of models proposed in the literature showing good performance against measurements. Among these, ray tracing is regarded as one of the most accurate ones available. In the present work, however, we show that a great deal of work is still needed to make ray tracing really unleash its potential in practical use. A very extensive validation of a state-of-the-art 3D ray tracing model is carried out through comparison with measurements in one of the most challenging environments: the city of San Francisco. Although the comparison is based on RF cellular coverage at 850 and 1900 MHz, a widely studied territory, very relevant sources of error and inaccuracy are identified in several cases along with possible solutions.

Smart Metering Wireless Networks at 169 MHz

Intelligent metering systems are being rolled-out on a large-scale worldwide, enabling consumer to make informed choices about consumption patterns and energy saving, while supporting the development of new retail services and products. Unfortunately, the lack of established and shared international standards represents a serious hindrance to be overcome for a complete development of a profitable market. The identification of suitable communication protocols and cost-effective network architectures represent a challenging aspect. In this framework, different network design solutions for wireless smart metering systems at 169 MHz are considered and investigated in this paper, aiming at cost efficient deployment based on extensive re-use of existing infrastructures in urban scenarios, namely, macro-cellular and lighting networks. Coverage assessment and frequency planning issues are addressed, together with an ad hoc measurement campaign carried out to fill the gap in the knowledge of urban propagation in the 169 MHz band. Results show that cost-effective deployment of the intelligent metering network is achievable. Notably, a spatial reuse factor larger than the overall number of available frequency channels might be necessary, thus meaning that the spectral resources shall be also allocated according to a time division scheme, where the hubs are switched off at turn. Anyway, this requirement should not affect the overall reading rate in practical applications.