Radio Propagation - Science topic

Research in electronic approaches that address rural connectivity deficits in cost-efficient ways would be of interest to countries that host rural populations in remote locations. (E-health is one such approach.)

Indeed Dear Ait Mansour El Houssain

v = 1/ sqrt (epsilon_0 mu_0 ) with these 2 (permitivity & permitivity)values being the physical properties of the vacuum, but there is not a set of equations where these 2 constants are not given, your capture WaveFunction.png shows then inside of the couple field equations.

For an electromagnetic wave in vacuum, group velocity is equal to phase velocity, but in other media rather than vacuum, light speed is not universal & in addition electric fields exists in metalic surfaces, inside metals E_ins is zero.

Dear Emmanouil,

It is true that empty is a dangerous word in nowadays physics. The question is that EM waves need to have a vacuum with electromagnetic properties as a permittivity and permeability with different values than zero. Another thing is how such values can exist providing electric and magnetic dipolar polarizations of it. Casimir effect shows clearly that empitiness has a limit in the real (physical) vacuum that we can reach.

The following article might be helpful for you:

i didnt

Dear Gheorghe Zaharia,

look at this article, it may be helpful for your topic.

The answer to the question is, supposedly by 2020.

There are multiple different trials ongoing or planned for 5G, in different parts of the world. I doubt anyone has pinned down exactly what techniques will become the standard(s), although some candidates often mentioned are massive MIMO and FBMC, as well as channels up in the multiple GHz and multiple 10s of GHz.

On the other hand, you also seem to have answered your own question?

Dear Rhorom,

Please check the following link and pdf attachment for said query

Good Luck

I already replied to your question about what software you could use, so I'll keep this short. To calculate the polarization, first and foremost, you will need a good electron density and magnetic field model. The calculation itself is just a simplification of the Appleton-Hartree equation for the HF case. Ionospheric Radio by Keneth Davies is an excellent reference for the derivation from first principles and goes through a few nice case examples. Ultimately, you'll have a few constants sitting in front of a line integral of the electron density with the magnetic field vector dotted to the signal orientation. I would write out the equation, but Research Gate doesn't have an equation editor in here and the equation itself is pretty simple to find or derive. 

If you're not interested in actually developing your own software for this, please see my response to your software question. IONORT is probably your best option, but simpler models exist in VOACAP, ICEPAC, and REC533; however, recent work has shown that these are not particularly good options (https://www.researchgate.net/publication/277974727_Comparison_of_observed_and_predicted_MUF%283000%29F2_in_the_Polar_cap_region_MUF%283000%29F2_in_the_Polar_Cap_Region).

There was a very interesting (from a history-of-technology perspective) article approved for public release last year. The title is: Stealth, countermeasures and ELINT, 1960–1975. Google the title and you'll find the article.

I think there's a problem, although the received power does not seem all that low to me. Not when the transmit and receive antennas are omnidirectional. In fact, your result is probably way optimistic!

You can find articles that fully derive the simplified equation. This one gives a good summary:

Another one:

The reflected wave will be 180 degrees out of phase with the wave hitting the ground. So as you would expect, with large angles differentiating the direct path from the reflected path (which leads to large differences in the length of the propagation paths), you'll get areas of constructive and destructive interference, and consequently there won't be a simplified power equation independent of these angles.

The supposedly "critical" distance is defined differently in the two articles above. The first one claims, for your lambda and heights, 9 meters or more makes the simple equation valid. Good enough. The second article claims 45 meters, which makes your 10 meters too short for the equation to be valid.

Ignoring that, both put the n value you name at 4, not 2.

Pr = Pt * Gt * Gr * ht^2 * hr^2 / (lambda * d^4)

And that makes sense. The path loss should be quite rapid, compared with free space propagation. At larger distances, with the reflected wave 180 degrees out of phase with the incident wave to ground, and the reflected and LOS paths becoming pretty close to the same length, these two waves will be consistently almost 180 degrees out of phase with one another. You would not expect an inverse square law to apply, as if in free space propagation, right?

I'd say, assuming 10 meters is indeed past the critical distance, that your received power will be more like 0.051 mW. (!!) (Still, that's -13 dBm, which is not all that weak of a signal, in the greater scheme of things.)

I do research in both the optical and the radio frequency domains.  They behave identically because they must both obey Maxwell's equations.  There are two sources of differences, however.  First, materials can have very different properties.  Metals work great at RF, but are very lossy at optical frequencies.  Second, they work at much different size scales so the devices look different simply because of our manufacturing methods at those different size scales.

Akram,

The solution you are looking for is called a Disk-Cone Antenna. It takes the form of an inverted cone with a disk on top. Think of a funnel turned upside down with a disk at the top. These are truely wideband antennas that are omnidirectional in the horizontal plane. They require very accuract fabrication as you progress to higher frequencies and wider bandwidths. A fractional-wavelength antenna will also work but you sacrifice a lot of gain at the lower frequencies which makes it insensitive to low signal levels. Good luck.

Hi,

The problem is not trivial if you are using a signal transmitted by your own station via a bent-pipe repeater (as in most geo satellites) but simpler if you are receiving a beacon signal. Which case applies to you ?

see for example

Excess attenuation measurement on an earth-space path in Colombia. Analysis of one year measurement results.

Luis D. Emiliani, J.Agudelo, E.Gutierrez, J.Restrepo, C.Fradique-Mendez

10th Ka and Broadband Communications Conference, Vicenza, Italy; 10/2004

Hi,

Your question is already very specific and asking for the m-parameter of Nakagami. But the selection of a radio propagation model depends mostly on the scenario that you want to simulate and finally investigate. Several measurement campaigns have proposed more specific radio propagation model for V2V Communication, e.g.:

Abbas, Taimoor, et al. "A Measurement Based Shadow Fading Model for Vehicle-to-Vehicle Network Simulations." arXiv preprint arXiv:1203.3370 (2012).

Christoph Sommer, David Eckhoff, Reinhard German and Falko Dressler, "A Computationally Inexpensive Empirical Model of IEEE 802.11p Radio Shadowing in Urban Environments," Proceedings of 8th IEEE/IFIP Conference on Wireless On demand Network Systems and Services (WONS 2011), Bardonecchia, Italy, January 2011, pp. 84-90.

Michele Segata, Bastian Bloessl, Stefan Joerer, Christoph Sommer, Renato Lo Cigno and Falko Dressler, "Vehicle Shadowing Distribution Depends on Vehicle Type: Results of an Experimental Study," Proceedings of 5th IEEE Vehicular Networking Conference (VNC 2013), Boston, MA, December 2013, pp. 242-245.

Felix Erlacher, Florian Klingler, Christoph Sommer and Falko Dressler, "On the Impact of Street Width on 5.9 GHz Radio Signal Propagation in Vehicular Networks," Proceedings of 11th IEEE/IFIP Conference on Wireless On demand Network Systems and Services (WONS 2014), Obergurgl, Austria, April 2014, pp. 143-146.

He, Ruisi, et al. "Vehicle-to-Vehicle Propagation Models With Large Vehicle Obstructions." 1-12.

I hope this papers help you to understand why radio channel modeling for vehicular networks is more than just using the "right" parameters for the Nakagami Model.

Cheers,

Stefan Joerer

This ITU recommendation document may also be helpful.

Search for  FR-REC-P.526-7-200102-S!!MSW-E.doc

We usually validate measurement results using residuals. Residuals are the difference between the values obtained from the measurements and other measurements carried out in different environments. Sometimes it may be necessary to gather repeated data in the same environment or conditions and use them as a basis for the comparison. Plots of the residuals usually give a graphic illustration of the consistency of the data. If the residuals alternate about the zero position (between positive and negative values about zero) then the measurements represents the initial measurement significantly. However a quantitative way to validate the model is to use the RMS errors observed by comparing the two measurement values. If a model was developed from the field measurements, the model can also be validated using the residuals obtained by subtracting the model generated values from the validation data values. RMS errors can also be used. F-test and t test can also provide additional means of checking the model performance.

Salt water is a medium that has a high relative dielectric permittivity (around 80) and is also able (rather poorly) to behave as electrical conductor. Conductivity (around 4 siemens/m) involves losses when a wave propagates in such a medium. Penetration depth of radiowaves are however strongly dependant of the wavelength/ frequency spectrum of the transmitted wave. Submarine electromagnetic transmissions are possible only at a few Hertz or a few tens of Hertz (depending on numerous factors including the distance of course). The right figure of merit is the skin depth (defined in many standard textbooks)

For radio sound broadcasting in the upper HF broadcast bands (6 to 30 MHz) both horizontally and vertically polarized antennas will work, although horizontal polarization is more common. This is logical is, as these frequencies are generally used to reach far away (500-5000 km) areas by means of ionospheric radio wave propagation. This calls for directional antennas to beam the energy towards the coverage area, both in the horizontal and the vertical plane. Using horizontal polarization gives addition antenna gain due to the ground reflection near the antenna.

For radio sound broadcasting in the tropical bands (2 to 3 MHz) or in the lower shortwave bands (3 to 7 MHz) the antennas used may also be horizontally polarized antennas suspended at 0.1 to 0.2 lambda above ground. These antennas radiated straight upwards and that radiation is reflected by the ionosphere to cover a continuous area around the transmitter with a radius of 300-500 km (typically) with excellent signal strength. This propagation mechanism is called Near Vertical Incidence Skywave (NVIS).

In the higher medium wave (1 to 1.5 MHz) ionospheric radio wave propagation is still possible at nighttime and sufficiently high horizontally polarized antennas would work at night to cover longer distances. Vertical polarization may also be used for this. Daytime absorption in the ionosphere, however, is very high.

NVIS would be possible at nighttime, but suspending horizontal antennas much lower than 0.1 lambda above ground requires either an extensive ground screen or the amount of power lost into the ground below the antenna will be very high.

Ionospheric propagation is not possible or not practical at frequencies below 1 MHz. Therefore most broadcast station on long or medium wave (0.1 - 1.5 MHz) are designed for ground wave propagation, for which vertically polarized antennas work best. These antennas also need extensive ground screens, as the ground is part of the antenna itself and ground losses directly cause reduction of the antenna efficiency.

Antenna gain, ground losses and voltages between antenna and earth for horizontal and vertical antennas with `thin´ elements can be modeled quite well with free Method of Moments (MoM) antenna packages such as NEC-2 or NEC-4. Be sure to use Sommerfeld ground, and please compare your results with good antenna books (Kraus, Jasik) to avoid common simulation pitfalls. If your simulation are contradicting common theory, they might be wrong :-)

The critical frequency of the ionosphere is not a fixed value. It roughly varies with time of day, day of the year, and the 11-year long solar cycle. Short term variation is influence by many factors, of which the solar radiation and the earth magnetic field are the main drivers.

Solar flares may disturb the more usual arrangement of the ionosphere, and can be seen as anomalies in ionospheric radio wave propagation, sometimes even totally disrupting all ionospheric propagation.

The critical frequency of the F-layer is measured near real-time by ionosonde stations. Please take a look at them, they are very informative. The following link is from an ionosonde in Belgium, but there are several in your area as well:

Is your interest driven by radio wave propagation issues, or earth science interest?

Atmospheric pressure as well as the air density decreases with the altitude and this is mainly associated with the gravity that keeps more atmospheric mass near to the earth surface and it decreases upward. Higher you go in the altitude (say 100 m in your case) less air remains above u thats why you observe less pressure.