Multipath Propagation Of Radio Waves Research Articles

Instantaneous Extraction of Indoor Environment from Radar Sensor-Based Mapping

In this paper, we propose a method for extracting the structure of an indoor environment using radar. When using the radar in an indoor environment, ghost targets are observed through the multipath propagation of radio waves. The presence of these ghost targets obstructs accurate mapping in the indoor environment, consequently hindering the extraction of the indoor environment. Therefore, we propose a deep learning-based method that uses image-to-image translation to extract the structure of the indoor environment by removing ghost targets from the indoor environment map. In this paper, the proposed method employs a conditional generative adversarial network (CGAN), which includes a U-Net-based generator and a patch-generative adversarial network-based discriminator. By repeating the process of determining whether the structure of the generated indoor environment is real or fake, CGAN ultimately returns a structure similar to the real environment. First, we generate a map of the indoor environment using radar, which includes ghost targets. Next, the structure of the indoor environment is extracted from the map using the proposed method. Then, we compare the proposed method, which is based on the structural similarity index and structural content, with the k-nearest neighbors algorithm, Hough transform, and density-based spatial clustering of applications with noise-based environment extraction method. When comparing the methods, our proposed method offers the advantage of extracting a more accurate environment without requiring parameter adjustments, even when the environment is changed.

Use of a spatially distributed in-phase antenna to increase the noise immunity of signal reception

Objectives. Radio-technical information transmission systems are widely used in various sectors of our life, not only for telecommunications and associated domestic needs, but also for the functioning of various special services, such as emergency response units, which increasingly use robotic complexes in the course of their work. In the event of an emergency, robot devices can be used to get in under rubble, in concrete pipes or other municipal facilities, which typically result in a sharp deterioration of the necessary conditions for the propagation of radio waves. In this regard, the problem of ensuring reliable communication with the robotic complex becomes rather acute. The aim of the present work is to reduce the effect of multipath propagation of radio waves in the communication channel under complex interference conditions.Methods. The methods of statistical radio engineering and mathematical modeling are used according to optimal signal reception theory.Results. The presented model for a multi-element, spatially-distributed, in-phase receiving antenna of various configurations, featuring an electronically adjustable radiation pattern, is designed to ameliorate the multipath nature of signal propagation. A simulation of a multipath communication channel was carried out in the presence of one main and three reflected beams of radio wave propagation, as well as with harmonic interference at two angles of its arrival and different frequency detuning relative to the frequency of the useful signal. The probability of a bit error when receiving discrete information using the proposed antenna is estimated.Conclusions. The proposed signal processing algorithm on the receiving side can be used to partially compensate for the influence of the multipath effect. As a result, the noise immunity of information reception in comparison with reception on an omnidirectional antenna with one antenna element increases: for a bit error probability of 10−3, the energy gain ranges from 2 dB for two beams to 7–10 dB for three or four beams. In the presence of concentrated harmonic interference in the radio channel, its simultaneous spatial (by the antenna) and spectral (by the demodulator) filtering is also observed, the effectiveness of which depends on the direction of arrival and the frequency detuning of the interference, which also leads to a significant decrease in the error probability.

CONSIDERATION OF MULTIPATH IN MODELING THE FIELD OF SECONDARY ELECTROMAGNETIC RADIATION ON INFORMATIZATION OBJECTS

The paper considers the features of the formation of the resulting field of spurious electromagnetic radiation at informatization objects, taking into account the multipath propagation of radio waves, evaluates the achievable error values for determining the attenuation coefficient using known methods for determining the attenuation of the field of spurious electromagnetic radiation based on a deterministic model of radio wave propagation inside the building. The need for a significant refinement of the method for determining the attenuation coefficient is shown, since, in a known form, it is suitable only for measurements in free space and gives very significant errors in urban conditions and inside buildings, or the use of adaptive reception methods when receiving signals (for example, diversity reception), which allows to significantly reduce the level of interference dips in the resulting electromotive force.

Enhanced Wi-Fi RTT Ranging: A Sensor-Aided Learning Approach

The fine timing measurement (FTM) protocol is designed to determine precise ranging between Wi-Fi devices using round-trip time (RTT) measurements. However, the multipath propagation of radio waves generates inaccurate timing information, degrading the ranging performance. In this study, we use a neural network (NN) to adaptively learn the unique measurement patterns observed at different indoor environments and produce enhanced ranging outputs from raw FTM measurements. Moreover, the NN is trained based on an unsupervised learning framework, using the naturally accumulated sensor data acquired from users accessing location services. Therefore, the effort involved in collecting training data is significantly minimized. The experimental results verified that the collection of unlabeled data for a short duration is sufficient to learn the pattern in raw FTM measurements and produce improved ranging results. The proposed method reduced the errors in raw distance measurements and well-calibrated ranging results requiring the collection of ground truth data by 47–50% and 17–29%, respectively. Consequently, positioning errors were reduced by 17–30% compared to the well-calibrated ranging scenario.

SOLAR TERMINATOR
 AND IONOSPHERIC PROPAGATION OF RADIO WAVES

The paper provides a review of studies devoted to the peculiarities of the propagation of radio waves in the ionosphere in the area of the solar terminator, which is the only global and regular source of acoustic-gravitational waves and other disturbances of the ionosphere. It describes the results of theoretical works devoted to the study of perturbations created by the solar terminator in the area of the difference in the intensity of solar radiation in the atmosphere. The paper gives a review of experimental studies of the effects created by the solar terminator in the entire thickness of the atmosphere. These effects, in particular, include the multipath propagation of radio waves, their phase variations, and variations in amplitudes during the propagation of radio waves in the area of the solar terminator. In the interests of science and practice, a number of problems have been proposed for the further study of wave perturbations arising as a result of the movement of the temperature gradient at sunrise and sunset hours.

Investigation of the parameters of traveling ionospheric disturbances using a chirp ionosonde

This article presents the results of experimental studies of parameters of natural traveling ionospheric disturbances of “sickle” type observed at mid-latitudes using linear frequency modulation ionosondes. Technical parameters of the ionosondes used are given. Experiments were carried out on slightly inclined paths in the central part of Russia in 2015 - 2020 in the daytime. The transmitting station was located in the village of Vasilsursk, Nizhny Novgorod Region. Registration was carried out in the city of Nizhny Novgorod. Examples of ionograms obtained in the course of measurements with different structure of perturbations are given. Estimates of development times of disturbances and their frequency range have been made. The structure of the received signal is analyzed. Based on the results of a complex experiment using a network of synchronously operating ionosondes of the same type, the data obtained were analyzed and direction and magnitude of propagation velocity of the phase front of moving disturbance were determined. A possible mechanism for the imitation of one-way vertical motion of a traveling disturbance characteristic of the mid-latitude ionosphere is discussed within the framework of multipath propagation of radio waves.

Research efficiency use of orthogonal double polarization MIMO antennas in drone communication

The article considers possible variants of application of various MIMO schemes for the communication with the drone or unmanned aerial vehicle. The model of multipath propagation of radio waves taking into account polarization parameters of antennas is given. The main focus is on the use of MIMO technology with polarization-orthogonal channels and channels with double polarization. The evaluation of the efficiency of using full polarization reception in comparison with MIMO channels of one polarization is given. Attention is paid to the presence of cross-polarization solution between the channels.

Algorithm of Low-Flying Target Tracking in Monopulse Radar Stations Based on a Unscented Kalman Filter

Using the model of multipath propagation of radio waves and the method of unscented Kalman filtering, a nonlinear adaptive algorithm for tracking low-flying targets in a monopulse radar station has been developed. This algorithm, in contrast to the extended Kalman filter, makes it possible to compensate for significant autocorrelated interference in measurements of the elevation angle of low-flying targets, arising from reflections of radio waves from the underlying surface. The results of simulation of the proposed algorithm are presented.

Empirical Model of Radio Wave Propagation in the Presence of Vegetation inside Greenhouses Using Regularized Regressions.

Spain is Europe’s leading exporter of tomatoes harvested in greenhouses. The production of tomatoes should be kept and increased, supported by precision agriculture to meet food and commercial demand. The wireless sensor network (WSN) has demonstrated to be a tool to provide farmers with useful information on the state of their plantations due to its practical deployment. However, in order to measure its deployment within a crop, it is necessary to know the communication coverage of the nodes that make up the network. The multipath propagation of radio waves between the transceivers of the WSN nodes inside a greenhouse is degraded and attenuated by the intricate complex of stems, branches, leaf twigs, and fruits, all randomly oriented, that block the line of sight, consequently generating a signal power loss as the distance increases. Although the COST235 (European Cooperation in Science and Technology - COST), ITU-R (International Telecommunications Union—Radiocommunication Sector), FITU-R (Fitted ITU-R), and Weisbberger models provide an explanation of the radio wave propagation in the presence of vegetation in the 2.4 GHz ICM band, some significant discrepancies were found when they are applied to field tests with tomato greenhouses. In this paper, a novel method is proposed for determining an empirical model of radio wave attenuation for vegetation in the 2.4 GHz band, which includes the vegetation height as a parameter in addition to the distance between transceivers of WNS nodes. The empirical attenuation model was obtained applying regularized regressions with a multiparametric equation using experimental signal RSSI measurements achieved by our own RSSI measurement system for our field tests in four plantations. The evaluation parameters gave 0.948 for R2, 0.946 for R2 Adj considering fifth grade polynomial (20 parameters), and 0.942 for R2, and 0.940 for R2 Adj when a reduction of parameters was applied using the cross validation (15 parameters). These results verify the rationality and reliability of the empirical model. Finally, the model was validated considering experimental data from other plantations, reaching similar results to our proposed model.

АЛГОРИТМ ОЦЕНКИ И КОРРЕКЦИИ ПАРАМЕТРОВ МНОГОЛУЧЕВОГО КАНАЛА ПРИ ДЕМОДУЛЯЦИИ СИГНАЛОВ OFDM

OFDM signals form the basis of the radio interface of 4G mobile networks. Among the most well-known systems using OFDM signals, the LTE / LTE-Advanced, IEEE 802.11, IEEE 802.16 family, as well as DVB-T, DVB-T2 digital television standards, should be noted. Due to the high spectral efficiency and noise immunity in channels with multipath propagation of radio waves, OFDM signals are also used in other systems under development. Radio systems with OFDM signals have two significant drawbacks: the high peak factor (PAPR), which reduces the efficiency of the radio transmitter, and the high sensitivity of the demodulator to frequency synchronization errors. Because of them, in the LTE system in the Up lines (from a subscriber - mobile station – MS - to the base station - BS), the SC-OFDM transmission method is used instead of the classical OFDM, which reduces the spectral efficiency. High-speed user movement in an environment with many diffusers characteristic of dense urban development leads to frequency dispersion, when a Doppler spectrum occurs near each subcarrier of the OFDM signal. In addition, in any radio communication system, there are random fluctuations in the phase of the radio signal caused by the instability of the generators of the radio receiver and radio transmitter. As a result, the orthogonality of the subcarriers is violated and mutual interference between them (ICI - inter-carrier interference) occurs. This can significantly impair the noise immunity of the transmission system. Therefore, an integral part of the demodulator processing the OFDM signal is the channel parameter estimation and correction unit (adaptive equalizer). There are two categories of equalizers that determine the parameters of the channel – in the frequency domain and in the time domain. Since the OFDM signal demodulators use the fast Fourier transform at the subcarrier separation stage, as well as the pilot subcarriers being contained in the signal structure, it is advisable to consider equalizers that calculate the channel parameters in the frequency domain for efficient hardware implementation and good performance. Such an equalizer joins in with a demodulator after the stage of fast Fourier transformation. Traditionally for OFDM signals, an adaptive equalizer is built based on approximation of frequency description of channel by averaging of results obtained on the pilot subcarrier. Frequency dependence of total phase change of multibeam signal is not considered in such methods. Accordingly, good results can be expected at the dense location of the pilot subcarrier that reduces frequency efficiency in turn. An offered method allows considering a frequency-dependent phase change and interference losses, arising due to addition of copies of the signal from the different ways of distribution. It is special topically in systems with a small number of the pilot subcarriers.

Technology for providing electromagnetic compatibility requirements for mobile wireless systems

The subject of study is the process of ensuring electromagnetic compatibility requirementsof mobile wireless communication systems. The goal is the development of ultra-wideband communication technology, which provides a reduction in the level of interference electromagnetic environment of mobile devices, occupying a random position relative to each other. The technology is based on the principle of direct transmission of low-power encoded pulses in a very wide frequency band without a carrier frequency. The task is to reduce the level of interference electromagnetic environment and compensate for distortions of the information signal caused by intersymbol interference and multipath radio wave propagation. Methods used: methods of analytical, simulation and temporary positional-pulse coding. The following results are obtained. A technology has been developed to ensure the electromagnetic compatibility requirements of mobile wireless communication systems, which includes the method of temporary position-pulse coding and the method of shimmering polarization of information signals. The minimum required number of pulses encoding an information bit is proved, which ensure its recovery. A technical solution is proposed for the design of the antenna system for signals with shimmering polarization. The possibility of joint noiseless operation in the same frequency range of both traditional communication systems and systems using ultra-wideband signals is shown. Conclusions. The use of the proposed technology of ultra-wideband signals, shimmering polarization of signals and the antenna system with the communication systems of mobile devices allows increasing the signal-to-noise ratio at the receiver input, which reduces the level of electromagnetic radiation, thus providing the electromagnetic compatibility requirements of mobile wireless communication systems. Efficiency of the developed technology application is conditioned by the possibility of realizing a high density of communication channels per square meter of the working area. By reducing the level of the information signal relative to white noise in the operating frequency range, simultaneous noise-free operation of both narrow-band traditional communication systems and communication systems using ultra-wideband signals is carried out. Implementation of the technology for ensuring the electromagnetic compatibility requirements of mobile wireless communication systems makes it possible to ensure their implementation at all stages of the development and implementation of mobile wireless communication systems.

Compensation of Multipath Interference in a Separated Passive Time and Frequency Synchronization Systems

Multipath propagation of radio waves negatively affects to the performance of telecommunications and radio navigation systems [1, 3]. When performing time and frequency synchronization tasks of spatially separated standards, the multi­path signal propagation aggravates the probabi­lity of a correct synchronization and introduces an error. The presence of a multipath signal reduces the signal-to-noise ratio in the received signal, which in turn causes an increase in the synchronization error. The mathematical models of multipath interference suppression in the time and in the frequency domain are presented in the article. Compared to time processing, processing in the frequency domain reduces computational costs. The operation of suppression in the time domain has been verified experimentally.

ИСПОЛЬЗОВАНИЕ РАЗВЕТВЛЕННОГО БИСПЕКТРАЛЬНО-ОРГАНИЗОВАННОГО КОДА В НЕСТАЦИОНАРНЫХ КАНАЛАХ СВЯЗИ С ЗАМИРАНИЯМИ

One of the main problems in modern wireless telecommunication systems and networks is the transmission and reception of signals in a multipath environment. Due to the nonideal impulse response of the communication channel, the frequency selective fading of the transmitted signal occurs. Diffraction and interference effects create a complex non-stationary structure of the electromagnetic field, which varies greatly in space and time. The method of branched BIS is organized - redundant coding, which allows you to receive and recognize a signal in a digital communication system in the presence of additive Gaussian noise, multipath propagation of radio waves, fading, random signal delays, as well as random changes in Doppler frequency shift. The advantages of the bispectral signal processing method include the ability to identify and evaluate the phase relationships of the spectral components in the observation, high noise immunity with respect to additive Gaussian noise and invariance to random signal time delays. The proposed method is based on solving the problem of multi-alternative detection and distinguishing of known triple signals against the background of interference according to test statistics – estimating the amplitude bispectrum by comparing the corresponding peak values of bi-amplitudes at the output of the matched bispectral filter. Since the bi-amplitude serves as a measure of the contribution of the frequency-phase dependences specified in a polyharmonic signal, the reception rule is to choose a triplet as the solution of a bispectrically organized signal, whose frequency dependencies are most similar to the frequency dependencies in the adopted oscillation. The aim of the work is to substantiate the advantages of using a branched bispectrically-organized code in digital radio communication systems in conditions of fading and multipath propagation of radio waves in comparison with the known redundant code. The results of computer statistical modeling of communication systems with the proposed coding method and the known one show a lower probability of symbol error for branched bispectrically-organized redundant coding under conditions of multipath radio propagation channels within the considered Rice and Rayleigh fade models. Computer simulations performed to show that the proposed method of branched bispectrically-organized redundant coding improves noise immunity in the propagation of radio waves in a channel with additive white Gaussian noise and also in a multipath radio link with fast and slow fading compared to the known frequency-redundant system-prototype.

Algorithm for received signal in multipath propagation conditions

This article discusses the received signal reception algorithm under conditions of multipath propagation of radio waves. As well as an analytical expression of the effectiveness of this algorithm is derived from the point of view of SNR.

METHOD OF CODING INFORMATION DISTRIBUTED BY WIRELESS COMMUNICATION LINES UNDER CONDITIONS OF INTERFERENCE

The subject matter of the paper is the processes of analysis and evaluation of the effectiveness of information coding methods in wireless systems. The aim is to improve noise immunity of information messages under conditions of powerful electromagnetic interference, with the help of complex signal-code constructions. The objective is to develop a method for noise-immune encoding in a wireless information transmission system, providing increase in information transmission rate. The methods used: Simulation and digital signal coding. The following results have been obtained: A method for encoding information transmitted via wireless communication lines in presence of interference. For signal coding, it is proposed to use Gaussian monocycle with time-dependent position-pulse modulation (PPM). It is shown that for organization of independent channels within a single frequency band, it is practical to use a system of orthogonal codes. Pulses of the useful information signal accumulated in a receiver correlator provide significantly increase in signal-to-noise ratio, allowing transmission of information over a wide frequency range well below the noise level. As a result of encoding information in wireless information transmission systems with the help of ultra-short pulse signals, the effectiveness of the proposed method is a quantitatively and qualitatively evaluated. Conclusion. Using Pulse Position Modulation coding in wireless information transmission systems allows transmitting large volumes of information with high transmission rate and high noise immunity of the communication channel as well as protecting the channel from message interception. Ability to work with low radiating power and high signal capacity to penetrate various obstacles ensure fulfilment of electromagnetic compatibility requirements as well as stable communication in conditions of multipath radio wave propagation. A possibility that powerful electromagnetic disturbances accompanying a lightning discharge may have catastrophic impact on the information transmission channel is also eliminated.

Method for Enhancing the Accuracy of Frequency Offset Estimation in OFDM Modulation Based Communication Systems

The paper proposes a method for enhancing the accuracy of estimation of frequency offset for OFDM modulation based communication systems. An increase accuracy of the proposed method is achieved at the expense of combined use of pilot and information symbols of OFDM signal. The main factors determining the accuracy of proposed method were identified. Mathematical simulation of the proposed method was performed for a multipath radio wave propagation channel. The proposed method efficiency was shown in comparison with existing methods for the estimation of frequency offset. Advantages and disadvantages of existing and proposed methods were described. The relationships of the root-mean-square error of frequency offset estimation as a function of the signal-to-noise ratio were built for the proposed and existing methods. The attainable high accuracy of frequency offset estimation by employing the proposed method makes its use expedient in control and measuring equipment. Conclusions have been made regarding the simulation results obtained and the expediency of proposed method applications.

An Indoor Positioning System Based on the Dual-Channel Passive RFID Technology

In the Internet-of-Things era, it will be increasingly important to accurately and efficiently locate an object in the real world as well as identify it in the virtual world. However, it is not easy to accurately locate an indoor target using radio technology because the multipath propagation of radio waves in an indoor environment may lead to serious position estimation errors. In addition, when each target has a transceiver or each reader operates in its high-power mode, the overall power consumption of the whole system is considerable. In this paper, a dual-channel low-power passive RFID positioning system is proposed to solve this problem. The probability for accurately locating a target within 0.5 m from its real position can reach 96.7% in this system. The positioning area of this work is bigger than those of the prior arts. The total RF radiation power of one block of the proposed system is 23.14 dBm, which is the lowest among reported RFID positioning systems. Furthermore, this proposed architecture can be easily expanded to a large system.

Minimum-value distribution of random electromagnetic fields for modeling deep fading in wireless communications

In this work, we presented a theoretical investigation of the minimum-value distribution inside complex electromagnetic environments. In particular, a statistical model for characterizing the minimum value of the complex-value field or power inside a dynamic mode-tuned or mode-stirred reverberation chamber is presented and discussed. Such an EM environment serves as an emulator of multipath radiowave propagation for indoor/outdoor wireless communication channels. It is found that, for both overmoded and undermoded regimes, the generalized extreme value distribution leads to the reverse Frechet and Weibull types for complex-value (Cartesian and total) fields and for the total energy (or intensity). These distributions are stable and follow from the convergent behavior of the lower tail for their corresponding parent distribution of the Cartesian field magnitude, namely a χ 2. On the other hand, received power exhibits a Pareto-type distribution because of the unbounded left tail of the negative exponential parent distribution.

Compact Built-In Handset MIMO Antenna Using L-Shaped Folded Monopole Antennas

A compact built-in handset antenna for multiple-input multiple-output (MIMO) system at 2GHz, comprising two elements array of newly proposed L-shaped folded monopole antenna (LFMA), is evaluated under the multipath radio wave propagation environments. By analyzing the fundamental characteristics, mean effective gain (MEG), correlation, and channel capacity, the significant enhancement in the capability, as a handset MIMO antenna under practical use conditions, was confirmed. The performances were also compared to those of an array antenna comprising two planar inversed-F antenna (PIFA) elements in order to verify the effectiveness of the proposed antenna. The results show that the equivalent or improved performances can be realized, by using the proposed LFMA array with a compact size, taking only the volume of 44% of a PIFA array. The LFMA array provides almost the same bandwidth and enhanced isolation compared with a PIFA array, and the sufficiently low correlation and acceptable effective gain are obtained under the multipath radio wave propagation environments. In addition, a greater channel capacity than a PIFA array is achieved especially when the proposed LFMA array is inclined for the display-viewing mode, and moreover, an almost doubled increase in the channel capacity is obtained by using MIMO transmission compared with single-input single-output (SISO). This study also show that the MEG has much effects on the channel capacity, rather than the correlations, for the proposed antenna.

Microwave Propagation Factor at Small Grazing Angle Over Sea: Transient Domain

The peculiarities of the field of centimeter and millimeter radio waves over rough see surface are investigated in the transition domain of small grazing angles, below which it is necessary to use the model of multiple knife-edge (Fresnel) diffraction on the wave crest, and beyond which — the Kirchgoff approximation method. It is shown that multipath propagation of radio waves is applicable in this model. The particularities of coherent and incoherent components of the field forward scattering as a function from the radio path geometry and the parameters of sea roughness are analyzed.