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Performance of long-distance VHF-band communication links based on scattering from perturbed Ionosphere. מציגים : יואב צידון שי ביטון מנחה : פרופ ' נתן.

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Presentation on theme: "Performance of long-distance VHF-band communication links based on scattering from perturbed Ionosphere. מציגים : יואב צידון שי ביטון מנחה : פרופ ' נתן."— Presentation transcript:

1 Performance of long-distance VHF-band communication links based on scattering from perturbed Ionosphere. מציגים : יואב צידון שי ביטון מנחה : פרופ ' נתן בלאונשטיין

2 Background and motivation Background and motivation It is well known that the regular ionosphere allows to send information at long distance due to scattering from its regular structure. This can be done only at HF- frequency band. It is well known that the regular ionosphere allows to send information at long distance due to scattering from its regular structure. This can be done only at HF- frequency band. In history many researches and studies were made trying to find a way to send information in higher frequency (VHF) for long distance (out of sight) and by this to increase the range between the ground terminals. In history many researches and studies were made trying to find a way to send information in higher frequency (VHF) for long distance (out of sight) and by this to increase the range between the ground terminals. The problem is that : VHF (radio frequencies above 30 MHz) has the tendency to penetrate the ionosphere making them unsuitable for long distance propagation. The problem is that : VHF (radio frequencies above 30 MHz) has the tendency to penetrate the ionosphere making them unsuitable for long distance propagation.

3 Background and motivation cont. In the recent decade a new possibility to send information from ground-based terminals at the VHF- band based on radio scattering from perturbed ionosphere plasma was found. In the recent decade a new possibility to send information from ground-based terminals at the VHF- band based on radio scattering from perturbed ionosphere plasma was found. The plasma perturbations are caused by additional natural phenomena in the atmosphere such as solar activity, magnetic storms, meteors rain etc. The plasma perturbations are caused by additional natural phenomena in the atmosphere such as solar activity, magnetic storms, meteors rain etc.

4 The Ionosphere The top region of the earth's atmosphere where ionization caused by incoming solar radiation affects the transmission of radio waves. It extends from a height of 70 kilometers to 400 kilometers above the surface.

5 The Ionosphere cont. The inhomogeneity of the ionosphere is an important factor in determining VHF-band wave propagation conditions. The inhomogeneity of the ionosphere is an important factor in determining VHF-band wave propagation conditions. Many experiments carried out using ground facilities show that in the normal ionosphere there exists a wide spectrum of irregular inhomogeneities which cause a number of radio physical effects, such as interference, scattering, diffraction and refraction of radio waves. Many experiments carried out using ground facilities show that in the normal ionosphere there exists a wide spectrum of irregular inhomogeneities which cause a number of radio physical effects, such as interference, scattering, diffraction and refraction of radio waves.

6 Scattering Scattering is the process by which small particles suspended in a medium of a different index of refraction diffuse a portion of the incident radiation in all directions. scattering is a major cause of the attenuation of radiation by the atmosphere, but in this project we examined the benefits of the scattering that ’ s allows the VHF-band waves to be sent back to earth, even if it is in a low power form. Scattering is the process by which small particles suspended in a medium of a different index of refraction diffuse a portion of the incident radiation in all directions. scattering is a major cause of the attenuation of radiation by the atmosphere, but in this project we examined the benefits of the scattering that ’ s allows the VHF-band waves to be sent back to earth, even if it is in a low power form.

7 Reflection Reflection is the process by which a surface of discontinuity turns back a portion of the incident radiation into the medium through which the radiation approached. Reflection is the process by which a surface of discontinuity turns back a portion of the incident radiation into the medium through which the radiation approached. To have true reflection, a real discontinuity in the index of reflection is required. This discontinuity must be significant compared to the wavelength of the radiation, or the energy could be returned by way of refraction rather than reflection To have true reflection, a real discontinuity in the index of reflection is required. This discontinuity must be significant compared to the wavelength of the radiation, or the energy could be returned by way of refraction rather than reflection

8 Diffraction Diffraction is the bending and spreading of waves when they meet an obstruction. Diffraction is the bending and spreading of waves when they meet an obstruction. When there is a NLOS between the transmitter and the receiver there are “ shadow regions ”, and due to the diffraction phenomena, the wave will arrive those regions. When there is a NLOS between the transmitter and the receiver there are “ shadow regions ”, and due to the diffraction phenomena, the wave will arrive those regions.

9 Refraction The change in direction of a propagation wave when passing from one medium to another. The change in direction of a propagation wave when passing from one medium to another.

10 Natural phenomena causing plasma perturbations solar activity- regarding mostly to Solar variations,which are fluctuations in the amount of energy emitted by the sun. solar activity- regarding mostly to Solar variations,which are fluctuations in the amount of energy emitted by the sun. magnetic storms - A disturbance or fluctuation in the earth's magnetic field, associated with solar flares. It is the effect on the ionosphere of large bursts of charged particles from the sun. magnetic storms - A disturbance or fluctuation in the earth's magnetic field, associated with solar flares. It is the effect on the ionosphere of large bursts of charged particles from the sun. meteors shower- A streak of light in the sky, often called a “ shooting star, ” that occurs when a bit of extraterrestrial matters falls into the atmosphere of the Earth and burns up. meteors shower- A streak of light in the sky, often called a “ shooting star, ” that occurs when a bit of extraterrestrial matters falls into the atmosphere of the Earth and burns up.

11 Free Space Propagation The most basic model of radio wave propagation involves so called "free space" radio wave propagation. In this model, radio waves emanate from a point source of radio energy, traveling in all directions in a straight line, filling the entire spherical volume of space with radio energy that varies in strength. The most basic model of radio wave propagation involves so called "free space" radio wave propagation. In this model, radio waves emanate from a point source of radio energy, traveling in all directions in a straight line, filling the entire spherical volume of space with radio energy that varies in strength. the Free Space Loss can be simply expressed in decibel form : the Free Space Loss can be simply expressed in decibel form :

12 Ionospheric propagation The ionosphere is an ionized plasma around the earth that is essential to sky-wave propagation and provides the basis for nearly all HF and VHF communications beyond the horizon. The ionosphere is an ionized plasma around the earth that is essential to sky-wave propagation and provides the basis for nearly all HF and VHF communications beyond the horizon. The properties of the ionosphere are a function of the free electron density, which in turn depends upon altitude, latitude, season, and primarily solar and magnetic conditions. The properties of the ionosphere are a function of the free electron density, which in turn depends upon altitude, latitude, season, and primarily solar and magnetic conditions. For sky-wave communication over any given path at any given time there exists a maximum usable frequency (MUF) above which signals are no longer refracted, but pass through the F layer of the ionosphere. For sky-wave communication over any given path at any given time there exists a maximum usable frequency (MUF) above which signals are no longer refracted, but pass through the F layer of the ionosphere.

13 Back and Forward Scattering The transmitter is located at the point P1 and the receiver is at the point p2. The transmitter is located at the point P1 and the receiver is at the point p2. The coordinate system is located at the point O inside the scattering volume V consisting small-scale inhomogeneities. The coordinate system is located at the point O inside the scattering volume V consisting small-scale inhomogeneities. We want to check the power of the wave in the receiver regarding the power of the transmitting wave, and all due to the scatter volume and its small- scale inhomogeneities (when l < ג ). We want to check the power of the wave in the receiver regarding the power of the transmitting wave, and all due to the scatter volume and its small- scale inhomogeneities (when l < ג ). l - scale of inhomogeneity. l - scale of inhomogeneity. ג - wave length. ג - wave length.

14 Power of Scatter wave model As mentioned the inhomogeneity is a result of the geomagnetic field and the solar activity in the scatter volume. Meteor trails are also an important variable as they a main cause of the scattering. As mentioned the inhomogeneity is a result of the geomagnetic field and the solar activity in the scatter volume. Meteor trails are also an important variable as they a main cause of the scattering. A few models were developed in the recent decades that tried to develop the formula of the scatter wave power accepted in the receiver when the scatter wave is formed from the inhomogeneity scatter volume. A few models were developed in the recent decades that tried to develop the formula of the scatter wave power accepted in the receiver when the scatter wave is formed from the inhomogeneity scatter volume. We will perform a model that is based on those models and gives a rather accurate formula. We will perform a model that is based on those models and gives a rather accurate formula.

15 Power of scatter wave cont. - Wave length - The density of the plasma disturbances with respect to ambient iononospheric plasma density. - The gain factor of the transmitter and the receiver - The angle between vector of the electric field and the wave vector of the scattered wave S - The effective area of scattering - The angle between the direction of the inhomogeneity and the TOR-plane - the angle TOR

16 Power of scatter wave cont. On the right we get (in dB) the decrease of the power received due to the exponential factor: On the right we get (in dB) the decrease of the power received due to the exponential factor: - Values in the left r - The distance rT = rR (V is small respectively to rT,rR). α - ??

17 Model results As mentioned φ is the angle TOR and its vary according to the location on earth. On Israel - 10° On California - 20° On Russia - 40° On Canada- 60° The graph shows the attenuation of the scatter wave accepted in the receiver. For a longer distance the attenuation will be too strong and the power of the wave will not be usable.

18 Model results ????

19 Summery In the past it was possible to send information threw the ionosphere using only HF-band communication links. In the past it was possible to send information threw the ionosphere using only HF-band communication links. In this project we have shown a model that examine the possibility to use even VHF-band links and by that to increase the distance betweens the ground terminals. In this project we have shown a model that examine the possibility to use even VHF-band links and by that to increase the distance betweens the ground terminals. The model shows that indeed this possibility is existing but still the power in the receiver is pretty low and require a very high transmitting power. The model shows that indeed this possibility is existing but still the power in the receiver is pretty low and require a very high transmitting power.

20 Questions??


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