What is Path Loss Coefficient?

[Femto_Engineer]

Hi,

In one of the paper, the received signal power 'P_RX' at a distance 'd' is approximated as:

equation.jpg

Where, 'P_TX' is the transmit power, c is the path loss coefficient and n is the path loss exponent.

Can anyone explain what path loss coefficient really is and what is it based on? I've know about path loss exponent, which tells us how fast a signal decays with distance (usually for free space its approximated to be 2, and for dense urban area the path loss exponent is assumed to be 4), but I could not find anything about path loss coefficient in the text books.


wbr,

[lynt123]

the path loss co-efficient is the calculated value of "free air" obstructions such as dust, humidity etc vs the frequency band being calculated for. Specifically things like rain fade would be one of the factors used in this parameter.

[dekili]

Path loss coefficient in this case is usually based on empirical data and then approximated to fit the measured values if you are using formula that you have. Again, usually, this is considered not to be a precision method for modeling the propagation, but is useful for scientific papers or just to show general concept because it is easy to use in calculations. Value of the exponent depends on many things since it is the only number that influences the path loss in such simple models. If n=2 then it is free space loss and formula is good for such propagation losses. For in-building models and urban models, n goes from 3.5 to 4 and it includes reflection, diffraction, refraction etc... for outdoor models it would also include humidity and all other influences on the propagation. It seems to me that you are reading a paper that is focused on something else and simple propagation model is there not to explain model itself and loos the focus.cheers

[firstmaxim]

Path Loss at a distance x, PLx(dB) =PLo - 10n log (Rx/Ro); Rx is the distance at which you want the Path Loss , PLx to be estimated; Ro is the known distance at which you already know the path loss (PLo). In this equation n refers to the propagation coeffficient, which signifies the rate at which the signal decays.

For a free space model, n =2; however, most mobile environments have different morphologies:dense urban, urban, semi-urban, rural, etc). The rate of decay can range anywhere from 4/4.5 to 2; the highest being for dense urban.