RF Propagation Research Articles

RF Propagation Model for Wireless Sensor Network of MARs

NASA exploration mission on Mars includes the use of rovers and sensors communicating via wireless sensor networks. The network components have a limited range of transmission, low power consumption, low price and a small lifespan. A wireless network's performance is mainly dependent on the RF environment. A Wireless Sensor Network (WSN) on the Mars ground is planned to deploy wireless sensors capable of operating under harsh environmental conditions to detect few properties of regolith on the Martian surface. The main interest property is dielectric permittivity and permeability. Since communicating on the Mars is a difficult and challenging task, the behavior of communications surfaces can be predicted by a channel model. So, efforts have been put to Develop a channel propagation Model to know the behavior of communication channel on the atmosphere of Mars. In order to study the model for radio propagation on Mars, two sites were selected from Gale crater and Meridian Planum at different sites for the Mars with near-flat surfaces, a certain area with peaks and a region with few craters.

Highly Portable, Low-Cost SDR Instrument for RF Propagation Studies

Software-defined radio (SDR) instruments can be used to replace bulky and expensive spectrum analyzers for RF field measurements. Using the commercial off-the-shelf (COTS) equipment, a low-cost, portable SDR instrument for measuring RF propagation has been created and tested. In the U.K., parts of the very high-frequency (VHF) spectrum have been repurposed for the use of Internet-of-Things devices; the instrument developed here is designed to meet the use case of performing an urban propagation study in VHF and UHF short range devices bands in a fast and low-cost manner. Design of the hardware and software is discussed, as well as the calibration of the instrument. The results of a test propagation study are given for the completed instrument. It is shown that the SDR instrument is capable of performing the study to a high degree of agreement with a commercial spectrum analyzer, thus validating the approach. The readings of the received power taken by the instrument are shown to agree with the readings taken at the same locations with a commercial spectrum analyzer to within an average of 1.4 dB at 71 MHz and 1.1 dB at 869.525 MHz. From the measurements taken, log-distance models were able to be produced with a path-loss exponent of 2.44 and a log-normal shadowing standard deviation of 8.5 dB at 71 MHz, and a path-loss exponent of 4.06 and a log-normal shadowing standard deviation of 8.8 dB at 869.525 MHz.

An updated applied formulation for the Goubau transmission line

The Goubau line is a unique transmission line that consists of only a single conductor. Its unique properties make it a solid candidate for low-loss RF propagation and wireless power transfer applications. However, the applied theory of this line that has been established thus far is missing key details of the line's characteristics. Namely, no discussion has been made on the Goubau line's ohmic current distribution or its effective characteristic impedance that would be used in RF/microwave circuit analysis scenarios. Furthermore, the method previously used to solve the waveguide mode is laborious and obsolete when considering current computational methods. In this work, an updated, efficient mode solution process for the Goubau line will be presented, and the current, loss, and characteristic impedance of the line will be discussed. Additionally, all other waveguide parameters such as wave velocity, guide wavelength, propagation constant, etc. will be investigated.

Study on indoor RF Propagation Model with Doppler Effect

Study on indoor RF Propagation Model with Doppler Effect

A Methodology to Study the Effect of Smoke and Fire on Indoor RF Propagation

An indoor wireless network comprises of multiple devices connected wirelessly in a small geographical area, giving mobility to the connected devices. RF signal associated with wireless networks suffers from many propagation losses. It becomes essential to estimate losses at different locations, in the intended coverage area, to attain the desired performance seamlessly. It helps in the optimal device placement in the wireless networks. In the application, in addition to the propagation losses, there is a need to estimate the loss induced by the presence of smoke and fire, individually, in an indoor environment. This paper first deals with the design of a heatmap generating tool, in MATLAB, which gives the approximate signal strength at different locations on a given floor for a given transmitter. Then the paper discusses the formation of plasma in fast flaming fires and presents the path loss due to it. This path loss is incorporated in the heatmap generating tool and a heatmap is generated for our office ground floor for the case of a flaming fire. The paper also describes a testbed, setup in our office premises, to study the scattering loss caused by smoke particles.

Human Abdomen Path-Loss Modeling and Location Estimation of Wireless Capsule Endoscope Using Round-Trip Propagation Loss

A highly accurate location estimation of a capsule endoscope in the gastrointestinal tract in the range of several millimeters is a challenging task, as radio-frequency signals encounter high power loss and a highly dynamic channel propagation environment. Therefore, an accurate path-loss model is required for the development of accurate localization algorithms. This paper presents an in-body path-loss model for the human abdomen region at 2.4 GHz. To develop the path-loss model, electromagnetic simulations using the finite-difference time-domain method were carried out on three different anatomical human models from the Virtual Family. A mathematical expression for the path-loss model was proposed based on analysis of the measured loss at different capsule locations inside the small intestine. The proposed path-loss model is a good approximation to model in-body RF propagation, since real measurements are not completely practical for the capsule-endoscope subject. Based on the proposed path-loss model, the article also presents the 2-D location estimation of a capsule endoscope inside the small intestine using the trilateration method as well as the non-linear least squares algorithm. It is shown that with 90% probability, the location estimation error is less than 4 cm.

Influence of AlN Growth Temperature on the Electrical Properties of Buffer Layers for GaN HEMTs on Silicon

Despite the fact that a lower growth temperature is generally considered as a drawback for achieving high crystal quality, the necessity to reduce the nucleation temperature of AlN on Silicon has permitted Molecular Beam Epitaxy (MBE) to demonstrate high performance for GaN transistors operating at high frequency. Compared to Metal‐Organic Vapor Phase Epitaxy (MOVPE), the control of the interface between the AlN nucleation layer and the substrate is easier and the reduced growth temperature allows to obtain a more electrically resistive interface while keeping good crystal quality. Moreover, it is shown that further reducing the growth temperature within the nucleation and stress mitigating layers has a noticeable impact on the lateral and vertical buffer leakage currents. At the same time the buffer of MBE grown HEMT structures exhibits low RF propagation losses (below 0.5 dB mm−1 up to 70 GHz). Also, results obtained with structures regrown by MOVPE on MBE AlN‐on‐Si templates confirm that the thermal budget is critical for the resistivity of AlN/Si. On the other hand, the insertion of a 1.5 μm thick Al0.05Ga0.95N layer within a 2 μm HEMT structure significantly improves the vertical breakdown voltage up to 740 V permitting to compare favorably with MOVPE epilayers with similar total thickness.

A Review on Investigation and Assessment of Path Loss Models in Urban and Rural Environment

This paper aims at providing a clear knowledge of Path Loss (PL) to the researcher. The important data have been extracted from the papers and mentioned in clear and precise manner. The limited studies were based on identification of PL due to FM frequency. Majority of studies based on identification of PL considering telephonic frequency as a source. In this paper the PL in urban and rural areas of different places due to various factors like buildings, trees, antenna height, forest etc. have been studied. The common parameters like frequency, model and location based studies were done. The studies were segregated based on various parameters in tabular format and they were compared based on frequency, location and best fit model in that table. Scatter chart was drawn in order to make the things clearer and more understandable. However, location specific PL models are required to investigate the RF propagation in identified terrain.

Improving Physical Layer Security in Wireless Communication Using Hybrid Techniques

As per the conception of RF (Radio) propagation, wireless communications can be easily overheard by unauthorized users for interception and thus wireless communication are highly vulnerable to eaves dropping attacks by exploitation of physical characteristics of wireless channels. The propose work is focused on development of diversity techniques to enhance physical layer security, marking a paradigm Shift from conventional artificial noise generation and beam forming techniques. Artificial noise techniques are highly power hungry and require on additional degree of power capacity which is not suitable for better operated system. Thus work is focused at development of a new techniques using variable length cryptography in which MAC (Medium Access Control)/ address of the wireless nodes for key generation purposes. Also, it is proposed, that the keys for communication encryption are randomized by a global time source such as GPS or internal master RTC (Real Time Clock). This unique feature allows a high degree of security as keys are truly random due to Millisecond level synchronization key randomization using a global accurate time source facility highly secure communication in a closed group. Also, the author has proposed key expiry time, after elapse station of such time, all key will have to be farce fully regenerated.

Temperature and Specific Absorption Rate Distribution in the Human Head Exposed to RF Propagation at Different Distances and Angles

Normal 0 21 false false false TR X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Normal Tablo"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin-top:0cm; mso-para-margin-right:0cm; mso-para-margin-bottom:8.0pt; mso-para-margin-left:0cm; line-height:107%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri",sans-serif; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi; mso-fareast-language:EN-US;} This paper presents specific absorption rate (SAR) obtained inside a human head and the thermal effects due to exposure to a cellular phone. The cellular phone radiating at 900 MHz and 1800 MHz frequencies was modeled by microstrip patch antenna and its output power was chosen according to the worst-case scenario. By the aid of finite element method (FEM) based COMSOL Multiphysics software program, not only the effect of distance between the antenna and the head model but also the effect of antenna’s angle relative to the head on SAR and the temperature distribution in the head model were investigated. It was shown in the study that the distance and the angle of the antenna to the head had significant importance on the SAR values and the temperature increase in the head. As a result of the simulation, it was found that SAR values at 900 MHz were under the safety limit values whereas at 1800 MHz were under the limits when the distance between the antenna and the head was 0.2 cm. Furthermore, it was noted that the temperature increase on the head was in good agreement with the other studies.

Empirical modeling of plasma clouds produced by the Metal Oxide Space Clouds experiment

The Advanced Research Project Agency (ARPA) Long-Range Tracking And Instrumentation Radar (ALTAIR) radar at Kwajalein Atoll was used in incoherent scatter mode to measure plasma densities within two artificial clouds created by the Air Force Research Laboratory (AFRL) Metal Oxide Space Clouds (MOSC) experiment in May 2013. Optical imager, ionosonde, and ALTAIR measurements were combined to create 3-D empirical descriptions of the plasma clouds as a function of time, which match the radar measurements to within 15%. The plasma clouds closely track the location of the optical clouds, and the best fit plasma cloud widths are generally consistent with isotropic neutral diffusion. Cloud plasma densities decreased as a power of time, with exponents between −0.5 and −1.0, or much more slowly than the −1.5 predicted by diffusion. These exponents and estimates of total ion number from integration through the model volume are consistent with a scenario of slow ionization and a gradually increasing total number of ions with time, reaching a net ionization fraction of 20% after approximately half an hour. These robust representations of the plasma density are being used to study impacts of the artificial clouds on the dynamics of the background ionosphere and on RF propagation.

Wi-Fi 환경에서 가상 Access Point를 이용한 실내 위치추정 알고리즘의 성능분석

실내 Wi-Fi환경에서 위치추정 정확도를 향상시키기 위한 위치추정에 대한 연구가 수년 동안 계속되어 오고 있다. 핑거프린트 기법 및 전파모델은 실내 위치추정에 있어서 매우 중요한 기술이다. 추가적인 하드웨어 없이 저비용으로 핑거프린트 기법을 사용하는 다양한 위치추정 시스템에 대한 연구가 진행되고 있다. 그러나 실내 위치추정 모델에서 VAP (virtual access points) 개념을 사용하여 이러한 목표를 실현한 사례는 매우 드물다. 본 논문은 Wi-Fi 환경의 핑거프린트 기반에서 VAP를 사용한 실내 위치추정 시스템의 아이디어를 제시하였다. 이 아이디어의 핵심은 실제 실내 Wi-Fi 환경에서 VAP를 사용하여 AP의 역할을 수행 할 수 있다. 제안 알고리즘의 성능분석을 위하여 4개의 시나리오를 사용하여 실험한 결과, 1개의 AP 대신에 2개의 VAP를 사용했을 때 가장 우수한 결과가 도출되었으며, 실험의 3번째 경우인 3개의 AP와 2개의 VAP를 사용했을 때 3.99 미터의 가장 낮은 위치오차가 발생하였음을 확인하였다. In recent years, indoor localization has been researched for the improvement of its localization accuracy capability in Wi-Fi environment. The fingerprint and RF propagation models has been the main approach in determining indoor positioning. With the use of fingerprint, a low-cost, versatile localization system can be achieved without the use of external hardware. However, only a few research have been made on virtual access points (VAPs) among indoor localization models. In this paper, the idea of indoor localization system using fingerprint with the addition of VAP in Wi-Fi environment is discussed. The idea is to virtually add APs in the existing indoor Wi-Fi system, this would mean additional virtually APs in the network. The experiments of the proposed algorithm shows the positive results when 2VAPs are used compared with only APs. A combination of 3APs and 2VAPs in the 3rd case had the lowest average error of 3.99 among its 4 scenarios.

Recent Advances in RF Propagation Modeling for 5G Systems

Recent Advances in RF Propagation Modeling for 5G Systems

A Dynamic Model of Silicon Bragg Grating Modulators

We present a dynamic model of silicon Bragg grating modulators that takes into account the distributed feedback of the grating coupled to depletion-based phase-shifters. We further consider the on-chip degradation of the radio-frequency excitation. This dynamic model allows the optimization of the grating design parameters such as its strength and length. We apply the proposed model to uniform Bragg grating modulators and show that grating modulators operated in reflection have larger 3 dB E/O bandwidth (BW), while gratings operated in transmission have larger optical modulation amplitude. As a result, higher speed on–off keying signal will be obtained using the reflection port while higher quality multi-level pulse amplitude modulation signal should be obtained in transmission, albeit at a lower baud rate. We also show that longer gratings have larger 3 dB modulation BW but noisier responses. Finally, we find that optical propagation losses results in either higher driving voltage or reduced modulation BW. The model is experimentally validated and we examine how RF propagation losses also limit the E/O BW.

An Empirical Study on the Performance of Wireless OFDM Communications in Highly Reverberant Environments

Reverberation chambers are closed reflective spaces that can emulate highly reverberant electromagnetic environments. The electromagnetic environment is primarily determined by the size of the cavity, effective conductivity, and leakage via apertures. In this effort, we investigate the performance of wireless OFDM communications in relation to the latter two by controlling the loading of a reverberation chamber and the effective aperture into a coupled cavity. A software defined radio measurement platform was used to assess the communication performance through a selection of link-level metrics including error vector magnitude, post processing signal-to-noise ratio, and throughput. The degradation of link quality is quantified for increasingly diffuse environments, as well as the improvement when leveraging a maximal ratio combining receiver diversity scheme. The link quality was found to improve in both the reverberation chamber and the coupled cavity for larger effective apertures. This result was analyzed using a time-dependent model for RF propagation in coupled cavities.

Correction Terms of Ground and Water Reflection Surfaces for Perera’s Breakpoint Distance Model

Wireless localization techniques based on received signal strength require highly accurate prediction of path loss. This has led to revisit existing breakpoint distance models for path loss prediction. Dual-slope path loss models for line-of-sight propagation have been verified by many measurement campaigns. Breakpoint distance is the distance that separates the two different trends in path loss levels. Many prediction breakpoint distance models have already been proposed in literature. Perera’s breakpoint distance model has been verified with some of the published measurement results. In this work, we provide correction terms for ground and water reflection surfaces for both horizontal and vertical polarization. The correction terms generalize application of Perera’s model in terms of applicability ranges and RF propagation scenarios. The correction terms are based on analyzing and modeling of extracted patterns of prediction error.

Radar measurement of ionospheric scintillation in the polar region

AbstractThis paper considers several estimators that use radar data to measure the S4 scintillation index that characterizes the severity of amplitude scintillation that may occur during RF propagation through ionospheric irregularities. S4 is defined to be the standard deviation of the fluctuations in received power normalized by division by the mean power. Estimates of S4 are based on radar returns obtained during track of targets which may themselves have intrinsic radar cross‐section fluctuations. Key to this work is the consideration of thresholding, which is used in many radars to remove (from further processing) signals whose SNR is considered too low. We consider several estimators here. The “direct” estimator attempts to estimate S4 through the direct calculation of the mean and standard deviation of the SNR from a number of radar returns. The maximum likelihood (ML) estimator uses multiple hypothesis testing and the assumption of Nakagami‐m statistics to estimate the scintillation index that best fits the radar returns from some number of pulses. The ML estimator has perfect knowledge of the number of radar returns that are below the threshold. The direct estimator is accurate for the case where there is no threshold and there are many returns or samples from which to estimate S4. However, the direct estimator is flawed (especially for strong scintillation) if deep fades that fall below the radar threshold are ignored. The modified ML estimator here is based on the ML technique but is useful if the count of missed returns is unavailable. We apply the modified ML estimator to several years of radar tracks of large calibration satellites to obtain the statistics of UHF scintillation as viewed from the early warning radar at Thule, Greenland. One‐way S4 was measured from 5000 low Earth orbit tracks during the 3 year period after solar maximum in May 2000. The data are analyzed to quantify the exceedance or the level of scintillation experienced at various probabilities. For example, from Thule during the period from December 2001 to February 2002, the probability exceeds 5% that the one‐way scintillation index at UHF is greater than 0.7. On a daily basis this translates into 1.2 h a day of strong scintillation. Unfortunately, there are insufficient data to obtain equivalent information for the winter of solar maximum when the scintillation is likely to be most severe.

DE 2: localization based on the rotating RSS using a single beacon

Wireless localization technology has become an important research area of pervasive computing applications. This paper presents $$DE ^{2 }$$DE2 (direction estimation and distance estimation), a wireless localization approach that is responsive to the scenario where only a single beacon is available to locate multiple position-unknown targets. Unlike the previous work which needs a priori knowledge of the scenario during the training phase by manual recording (taking significant human efforts), or uses a certain number of beacons during the localization phase to reach a certain accuracy (leading to high energy consumption and reducing network lifecycle), $$DE ^{2 }$$DE2 leverages a single beacon without many prior human efforts to locate multiple targets. The intuition underlying $$DE ^{2 }$$DE2 is that, direction and distance constraints between an unknown position and the single beacon are adequate to determine the unknown position. When a person rotates around an RF receiver (the single beacon), the human body acts as a signal-blocking obstacle. It causes the signal from a transmitter (position-unknown) to the single receiver to attenuate in a certain scope. The blocking effect caused by human body can be utilized to obtain the direction constraint between the unknown position and the single beacon. And we call the signal strength which is perceived by the receiver during the person's rotation as rotating received signal strength (RSS). Moreover, a corresponding distance constraint is also concluded in the rotating RSS according to the RF propagation model. $$DE ^{2 }$$DE2 pushes the limit of minimum beacons needed for localization without much pre-configuration effort. To demonstrate the utility of $$DE ^{2 }$$DE2, we implement $$DE ^{2 }$$DE2 in real-world single beacon wireless networks. The results show that these applications can significantly benefit from $$DE ^{2 }$$DE2.

Response surface methodology based power consumption and RF propagation analysis and optimization on XBee WSN module

One of the most important issues in wireless sensor networks (WSN) is reduction of power consumption, prolonging the network lifetime (for battery powered networks) or reducing the induced $$\hbox {CO}_{2}$$CO2 emissions (for grid powered networks). Power consumption reduction can be achieved in various ways: transmitter power control, duty cycling, data reduction and others. This paper analyses the impact of several parameters on power consumption of Digi's XBee PRO of shelf WSN modules. To determine the conditions for transmitter power control, this paper presents measurement analysis for indoor RF propagation in order to determine the minimum received signal strength for high data transfer reliability. Measurement analysis is conducted using response surface methodology and the conclusions based on the respective measurement results are given resulting in a mathematical model of the node's power consumption. Also, optimization of power consumption is shown for various parameters using desirability functions, where optimal parameters for minimum power consumption are presented.

Military Communications [Guest Editorial

New and diverse types of threats and military conflicts mean that the requirements for military communications continue to evolve. These requirements, along with reduced military spending, impose considerable challenges on researchers and developers of military communications systems. These challenges are exacerbated by technical and environmental limitations, which include harsh RF propagation environments, severe spectrum limitations, topological variability, mobility, and stringent security requirements. Adding to these fundamental challenges is the fact that military networks need to support a wide variety of applications with needs ranging from time-sensitive delivery to reliable large volume data dissemination. Information will emanate from a large range of sources, including remote sensors and unmanned vehicles, both aerial and terrestrial.