Multibeam Propagation Research Articles

THE METHOD OF ADJUSTING THE MULTI-FREQUENCY PROBING RADAR SIGNAL PARAMETERS AND THE TROPOSPHERIC RADIO WAVEGUIDE CHARACTERISTICS

Peculiarities of air circulation in the coastal zone of large reservoirs (large lakes or inland seas such as the Black and Azov Seas) can lead to a significant departure from the standard spatial distribution of meteorological and, accordingly, radiophysical characteristics of air.
 As a result, it is possible for regions of space with an abnormally low attenuation level of radio waves of certain frequency ranges to appear – tropospheric radio waveguides (TWG). The appearance of TWG leads to multi-beam propagation of radio waves and fluctuations of radar signals. Fluctuations of the radar signal lead to a decrease in the range of detection of aerial objects by radars. For single-frequency radar signals, it is only possible to estimate the degree of distortion and the amount of radar detection range loss. A paradoxical situation arises when, due to TWG, it is possible to increase the range of detection of aerial objects, but due to the distortion of the radar signal in TWG, the detection performance decreases. For multi-frequency signals, it is potentially possible to adjust the parameters of the radar signal with the parameters of the radar channel (in this case, the tropospheric radio waveguide).
 The adjustable parameters of a multifrequency signal include: the number of frequency components; bandwidth of the frequency component; average frequency of the frequency component; signal duration; period.
 The characteristics of TWG, on which the parameters of the multifrequency signal depend, include: the lower transmission frequency of TWG; the upper transmission frequency of TWG; the delay time of the rays in the TWG.
 The bandwidth and beam delay values can be obtained directly by emitting and receiving a test multi- frequency pilot signal, but this method requires the presence of a reference reflector in space, which is difficult to implement in practice.
 The electrophysical characteristics of the tropospheric waveguide can be determined from the data of meteorological observations. The method developed in the article allows, based on the known characteristics of the tropospheric waveguide, to determine and adjust the parameters of a multi-frequency signal, which reduces the fluctuations of the sounding signal and increases the aerial objects detection rang.

On the possibility of detection and classification of noise sources based on analysis of their trajectories at the output of adaptive spatial processing

To detect and classify objects, the source trajectories detected in the process of hydroacoustic observation are used, which contain information about the measured parameters of objects, which are their classification attributes. The analysis of these attributes allows to make a decision about the class of the observed object, for example, a surface or underwater source. As the measured object parameters are used their energy characteristics, parameters of the observed trajectory (bearing, speed of change in bearing and other possible trajectory parameters). In this case, the correctness and speed of the decision on classification depends on the quantity and quality of used classification signs, which are determined by both parameters of the observed object, and the features of sound propagation from the source to the observation device.For signal detection and resolution, we further consider fast projective adaptive algorithms, the use of which, as applied to the problems of in-situ experimental signal detection was considered in [1], [4]. The goal of this class of algorithms is to provide a high probability of detection and accurate measurement of the parameters of the source trajectories under the conditions of a model of multi-beam propagation and scattering in the real ocean environment [5]-[8]. The proposed work is a continuation of the work [1], [4], and aims to ensure the use of experimental field data not only for detection, but also for the classification of the observed sources.The subject of the study are the results of the full-scale experiment of hydroacoustic noise direction finding, given earlier and described in detail in [1], [4]. For the experiment was used antenna of L = 56 vertical daisy chains (of 10 elements each), equidistantly spaced horizontally. The antenna was installed at a depth of 200 meters in the coastal marine zone of the coastal wedge near the shipping lanes. The elements of the flat antenna were affected by signals from surface ships moving ncontrollably in the observation area and one underwater source.A singular decomposition of sampled antenna element data was used to construct adaptive algorithms. Modification of the initial results of singular decomposition allows to create algorithms that provide priority conditions for extraction of separate components of the observed (e. g., weakest) signals when constructing direction finding terrain.In this regard, in addition to the non-adaptive direction finding relief, it is proposed to form three variants of direction finding relief, each of which solves part of the general problem of selection and classification of individual varieties of observed signals:– Initial, corresponding to the energy of the signals of the input sample with amplified components of the weakest signals (overview algorithm);– direction finding relief, which uses an algorithm to detect weak and scattered signals;– direction finding terrain, which highlights the coherent components of signals.Analysis of the trajectories of more than 30 sources in the episode of two hours and forty minutes has been carried out, which increased the reliability of the detection and measurement accuracy of the parameters of the observed objects. Joint analysis of the trajectories of sources based on different variants of the bearing relief allowed to improve the conditions for the detection of weak signals and to make classification decisions using the classification attribute of the width of the area of fluctuations of the surface target trajectory for signals with a strong scattered component.

Effect of multi-beam propagation on free-space coherent optical communications in a slant atmospheric turbulence

Based on the multi-beam propagation theory, a mathematic model of log-intensity fluctuation variance under multi-beam propagation in slant path atmospheric turbulence near the ground for free-space optical communication is established. Taking single beam, double beam, three beam, and four beams as examples, the intensity fluctuation characteristics of single beam and multi-beam are obtained, and the relationship between the log-intensity fluctuation and the bit error rate (BER) of the heterodyne detection coherent optical communications based on binary phase shift keying modulation is deduced. The results show that, with the increase of beam number, the variance of signal log-intensity fluctuation is significantly mitigated, and the BER of the system is significantly reduced. It proves that the multi-beam propagation method can be effectively applied to the long-distance coherent optical communications, and improve the performance of the system.

Радіолокаційне вимірювання кутів місця цілей над морем методом Matrix Pencil з урахуванням впливу завад багатопроменевого поширення і теплових шумів РЛС

Subject and Purpose. The Matrix Pencil method is investigated as a means of increasing the accuracy of measuring the angles of low-altitude targets above sea level. The aim of the study was to evaluate its effectiveness in the conditions of interference created by multi-beam propagation, represented by mirror and diffuse reflection of radio waves from the sea surface, and thermal noise of radar receiving channels, and to justify measures to achieve high efficiency in different combinations. and obstacle levels. Methods and Methodology. The study was conducted by computer simulation. It covered the sea waves, which met the conditions of both specular and strong diffuse reflection, as well as different levels of thermal noise in the receiving channels of the radar. Typical conditions were used in the simulation: the length of the route – 2000 m, the height of the center of the receiving antenna at sea level – 12 m, the width of the antenna beam – 1°, the angular height of the target – 0.3°. The effectiveness of the method was determined by comparing it with the previously studied method of root-MUSIC under identical conditions. Results. The data on the errors of measuring the place angle when using different a priori parameters of the Matrix Pencil method are obtained. Recommendations for the choice of these parameters have been developed to minimize errors in measuring the angles of the place. The advantages and disadvantages of the Matrix Pencil method in comparison with the root-MUSIC method are noted. Conclusion. The obtained results can be used in the development of radars designed to support low-altitude objects above sea level.

Экспериментальное исследование самоорганизующегося акустического канала связи

This paper presents the results of an experimental study of the adaptive communication system with phase separation. Adaptation is carried out by methods of machine learning and consists in transmitters phases regulation. An acoustic waveguide with a tunable metasurface is used as a propagation medium. In the case of multi-beam propagation and the presence of significant inter-symbol interference the transmission rate of 1 kbit/s was achieved. The adaptation time of the investigated system to sudden changes in the channel parameters does not exceed 10 cycles of training, even in case of significant fading.

ESTIMATION OF BIT ERROR PROBABILITIES OF COMMUNICATION SYSTEMS WITH FM BROADBAND SIGNALS

Today, wireless communication is one of the most promising areas in the field of communications. Modern radio communication systems and facilities operate in a complex electronic environment. The development of next-generation wireless networks depends on both transmitting and receiving equipment, which must provide the high data rates needed to maintain a reliable level of interference protection. The main factors influencing the quality of radio communication are natural and intentional interference in the radio wave propagation channel, multi-beam propagation, bandwidth limitation and the need for asynchronous access. One of the possible methods of partial solution of the above problems is the use of extended spectrum communication systems. The article investigates the effectiveness of different types of phase modulation used for Direct Sequence Spread Spectrum systems. An idealized channel with additive white Gaussian noise was chosen as the radio wave propagation channel. It has been observed that Binary phase shift keying radio systems achieve better Bit error rate values than other systems. The research was conducted in the environment of dynamic interdisciplinary modeling of complex technical systems - Simulink (the main tool for model-oriented design), whose main interface is a graphical tool for charting and a flexible set of libraries of functional blocks. The simulation results showed that for a given data rate and under the influence of AWGN on the propagation channel, DSSS-BPSK was more resistant to the negative effects of white noise. Future research will focus on evaluating the effectiveness of the SSS communication system in the event of different types of interference.

Development of communication models of wireless environment in emergency situations

Two-point communication model of the wireless environment with one-beam and multi-beam propagation of radio waves were developed. The specified models make it possible to create various particular two-point communication models of wireless environment, taking into account the assigned geometry of location of shadowing and scattering structures in the environment. The practical use of the proposed models is limited to arbitrary points of radiation and reception in the environment, taking into account location of directional aerials in them. To study known multipoint technologies under conditions of emergency situations, we developed the multipoint communication models with one-beam and multibeam propagation of radio waves from each radiation point to each reception point, predetermined by the presence of shadowing and scattering structures in the environment. The developed multipoint models make it possible to create specific models at the physical level for various multi-aerial technologies, taking into consideration the use of aerial arrays of arbitrary configuration at the transmitting and receiving sides. Verification of the developed communication models of the wireless environment was performed. It was found that the use of directional aerials at the transmitting and receiving sides of the wireless environment in the presence of considerable shadowing and scattering structures makes it possible to significantly improve noise immunity. It is noted that with the use of the developed communication models, it is possible to carry out in-depth examination of the physical level with a view to developing a reliable and stable architecture of communications under conditions of emergency situations.

WOCDMA系统中基于多光束传输技术的大气闪烁抑制方法

We propose employing multi-beam propagating technology to mitigate the influence of atmospheric scintillation to the wireless optical code division multiple access (WOCDMA) system and then deduce the bit error rate (BER) formulas of systems in weak and strong scintillations, respectively. According to simulation experiment results, multi-beam propagation can improve the system performance very well compared with single-beam propagating technique. Moreover, the more beams we use, the better the performance we get. When the received optical power is –30 dBm, the BER of the system employing four beams is 5 and 1 dB lower than that of using single-beam propagating technique in weak and strong scintillations, respectively.

Interference origin of the fine structure in the dynamic spectra of solar radio bursts

The multibeam propagation of radio waves in the solar plasma is analyzed, because the emission from a solar flare passes through an inhomogeneous solar atmosphere on its way to the observer. A formula (a mathematical model) for calculating the structure of the dynamic spectrum for flare radio bursts has been obtained. Comparison of the calculated spectra with the observed ones shows that the results of interference explain the formation of a zebra structure and the separation of its stripes into individual spikes, describe the time profile of the spikes, and explain the properties of fibers, ropes of fibers, and chains of “point” bursts. The similarity of the dynamic spectra testifies that the fine structure of the spectra is formed not in the emission source but as a result of the propagation of waves through the solar corona and interplanetary space.

Influence of Radio Wave Propagation on the Properties of Solar Microwave Bursts

Scintillation of radio signals passing through the solar corona is considered. An expression describing the dynamic spectrum of these scintillations on the basis of multibeam propagation of radio waves is derived. Properties of the analytically calculated spectrum are shown to coincide with zebra-structure properties of solar radio bursts. It is determined that the time profile of the scintillations caused by multibeam propagation may appear as impulses of emission or absorption or may have a sawtooth form. It is concluded that assuming specific emission source features is not the only way to explain the zebra structure, since the effect of multibeam propagation of radio waves through the solar corona and interplanetary space yields a simple explanation of the phenomenon discussed.

Methods of imitational computer modeling of decameter communication channels

Imitational models of one-dimensional discrete communication channels with and without edge distortions of message fragments and of one-dimensional discrete-continuous, two-dimensional linear and nonlinear, and three-dimensional continuous linear (space and time) communication channels are suggested that allow comparative tests of decameter communication systems to be performed on paths under conditions of multibeam propagation in the presence of every possible additive noise component.

First application of the radioholographic method to wave observations in the upper atmosphere

Wave phenomena in the upper atmosphere can be studied using the high‐precision Global Positioning System (GPS) radio navigational field. In this paper, basic principles, accuracy, and vertical resolution of the radioholographic technique for studies of ionospheric wave phenomena are presented for the general case when the orbits of the satellites are arbitrary. Results of testing of the radioholographic method are discussed using orbital station MIR and geostationary satellites (MIR/GEO) and GPS/Meteorology (GPS/MET) radio occultation data. The radioholographic method has high vertical (12–30 m) and angular (4–8 μrad) resolution, which has been validated by directly observing multibeam propagation in the atmosphere and revealing signals, reflected from the sea, in GPS/MET and MIR/GEO radio occultation data. We show that this method allows one to determine the vertical profile of the electron density and monitoring wave structures in the upper atmosphere. As an example of this approach, observations of the summer Antarctic mesosphere on 7 February 1997 are presented. We show, by combining phase and amplitude analysis, that a vertical resolution of 0.3–0.5 km reveals wavelike structures with spatial periods from 1–2 km to 8–10 km in the vertical electron density distribution in the D and E regions. Variations in the gradient of the electron density from ±5 × 103 to ±8 × 103 el/(cm3 km) at altitudes of 72–95 km were observed. The obtained results demonstrate the high‐technology level of the radioholography approach and open new perspectives for radio occultation experiments: measurements of the characteristics of the natural processes in the atmosphere, mesosphere, and ionosphere and observations of the state of the sea surface by measuring parameters of reflected signal simultaneously with radio occultation experiments.

Application of radio holographic method for observation of altitude variations of the electron density in the mesosphere/lower thermosphere using GPS/MET radio occultation data

A radio holographic method for observation of wave phenomena in the upper atmosphere (height interval 60– 120 km ) is described. The radio holography uses coherent properties of the rays propagating through the atmosphere. These properties arise due to the high stability of the GPS signal and its high sensitivity to layered structures in the atmosphere and ionosphere. High angular and vertical resolution of the radio holographic method has been revealed with the use GPS/MET radio occultation data. Multibeam propagation in the troposphere and weak reflections from the ocean surface have been observed with vertical resolution better than 70 m . Radio holographic method gives the possibility to remove the contributions of the upper layers and to identify detailed structures in the electron density altitude profiles in the D- and E-layer of the ionosphere. The main effects connected with the influence of the D- and E-layer on the phase path are correspondingly of the order of 0.5–2 and 10– 30 cm . The instrumental accuracy of the GPS phase path measurements was of the order of 1– 2 mm . The fine structures in the D-layer and the sporadic E-layer have been inferred. They have a vertical spatial period of 1– 2 km, changes in the electron density vertical gradient from ±0.5×10 3 to ±10×10 3 electrons/( cm 3 km) and the electron density variations from 100 el/ cm 3 to 1000 el/ cm 3 . Electron density altitude distribution and its gradient with maximum values ∼45×10 3 el/ cm 3 and ∼20×10 3 electrons/( cm 3 km), respectively, have been observed in an E-layer of the ionosphere at the height interval 92– 100 km . The possibility of a qualitative measurement of the vertical distribution of the horizontal wind velocity in the E-layer region using GPS/MET radio occultation data is considered.

Radio holographic principle for observing natural processes in the atmosphere and retrieving meteorological parameters from radio occultation data

The radio holographic principle is briefly described and tested by using radio occultation data of the GPS/MET and MIR/GEO experiments. Sub-Fresnel spatial resolution ∼12 m/pixel was achieved using focused synthetic aperture radio holographic approach, and direct evidence of multibeam propagation effects in the atmosphere was obtained. The achieved instrumental accuracy in angular distance measurements was near 0.004 milliradian/pixel, and observed angular distance between different rays was equal to 0.3 milliradians. The angular resolution of the radio holographic method depends on the wavelength as λ1 compared to λ1/2 in conventional methods. In general case the principal limit of the vertical resolution may be determined using focused synthetic aperture antenna theory and may achieve a value ∼20–40 m under assumptions of spherical symmetry and quiet atmospheric conditions. Wave structures were discovered in the altitude distribution of the gradient electron density at a height interval of 60–95 km with spatial period 1–2 km and vertical resolution 300–500 m. Good correspondence was found between the temperature profiles revealed by radio holographic analysis and those obtained by traditional retrieval using UCAR GPS/MET data.

Radio occultation data analysis by the radioholographic method

The radioholographic method is briefly described and tested by using data of 4 radio occultation events observed by the GPS/MET experiment on 9 February 1997. The central point of the radioholographic method ( Pavelyev, 1998) is the generation of a radiohologram along the LEO satellite trajectory which allows the calculation of angular spectra of the received GPS radio wave field at the LEO satellite. These spectra are promising in view of detection, analysis and reduction of multipath/diffraction effects, study of atmospheric irregularities and estimation of bending angle error. Initial analysis of angular spectra calculated by the multiple signal classification (MUSIC) method gives evidence that considerable multibeam propagation occurs at ray perigee heights below 20 km and at heights around 80–120 km for the 4 GPS/MET occultation events. Temperature profiles obtained by our analysis (radioholographic method, Abel inversion) are compared with those of the traditional retrieval by the UCAR GPS/MET team (bending angle from slope of phase front, Abel inversion). In 3 of 4 cases we found good agreement (standard deviation σ T ∼1.5°K between both retrievals at heights 0–30 km).