Path loss model:

• Path loss model is a major part in the analysis and design of link budget of a telecommunication system. Path loss is the reduction in power density of an electromagnetic wave as it propagates through space. It may be due to many effects such as reflection, diffraction, absorption and medium loss etc.
• Path loss models describe the signal attenuation between transmit and a receive antenna as a function of the propagation distance and other parameters. Some models include many details of the ground profile to estimate the signal attenuation, whereas others just consider carrier frequency and distance. Antenna heights are other critical parameters.

There are various types of path loss models in which few are two ray ground path model, free space path model and long distance path model .From these models, free space path loss model is explained below.

Free-space path loss:

• The free space path loss model is in appropriate to apply to wireless cellular operation because any type of wireless communication, the signal circulates with distance. Therefore, an antenna with a fixed area will receive less signal power the beyond it is from the transmitting antenna.

• Free-space path loss is proportional to the square of the distance between the transmitter and receiver (d) and also proportional to the square of the frequency of the radio signal,$\large{\lambda}$.

The equation for FSPL is      

$ \large\ FSPL= \Big({\dfrac{4d\Pi}{\lambda}\Big)^2 }\ldots{}\ldots{}\ldots{}\ldots{}\ldots{}\ldots{}1 equ$

As we know,

 $\large{\lambda=\dfrac{c}{f}}$

 Therefore, equation 1 becomes

    $\large\ FSPL= \Big({\dfrac{4df\Pi}{c}\Big)^2 }\ldots{}\ldots{}\ldots{}\ldots{}\ldots{}\ldots{}2 equ$

Where,                                                                           

$\large{\lambda}$is the signal wavelength (in meters),

$\large{f}$is the signal frequency (in hertz),

$\large{d}$ is the distance from the transmitter (in meters),

 $\large{c}$ is the speed of light in a vacuum, 2.99792458 × 108 meters per second.

This equation is only accurate in the far field where spherical spreading can be assumed.