Hey everyone, thanks for coming back to Wi Fi fundamentals with location and analytics. This course will help you to muster the air. This video starts are ranging serious. We will learn the techniques used in Wi Fi to measure how far am I from my access point who is close to me. And is there anyone around or in my store. There are so many use cases where Wi Fi ranging comes handy.
It is also the basis for location which we will also learn we will look at those use cases and analyze them in our analytics part. There are three main methods to get ranging and location from an RF signal. There's this signal strength method the time of arrival method And the angle based method, we will start with the single strength method. But to understand it clearly, we have to know what is the free space path loss. Let's start the distance our signal travels is related directly to its path loss. In order to understand ranging, we must understand the free space path loss theory.
Free space path loss helps us to determine the received power in different distances assuming a line of sight and path free of obstacles. free space path loss is the loss in signal strength of an electromagnetic wave that would result from a line of sight path through free space. Usually It is air with no obstacles nearby to cause reflections or diffraction. it degrades over distance following the inverse square law and frequency laws. The higher the frequency, the higher the loss. We can determine the signal value from a transmitting device with a known measure power and frequency in different distances.
As we can see, we have an access point that operates both in the five gigahertz frequency and the 2.4 gigahertz frequency. That is the equation for free space path loss in DBS. free space path loss depends on two parameters distance based on the inverse square law and frequency Based on the wavelength, we can determine the relationship between them using the formula above. D equals to distance F is our frequency. And k is a constant that depends on the unit of distance and frequency. if D is in kilometres, and F frequency is in megahertz, then k are constant is 32 point 44.
So we input the value of one meter into the formula, and our frequency is 2412 megahertz, which is actually channel one in a Wi Fi access point that operates in the 2.4 gigahertz frequency. The outcome will be 40 dB of loss. Let's see how it looks in Google Sheets. A very simple way to calculate free space loss is Google Sheets. So if we have an equation that says that the free space loss in decibels is actually 20 lock 10 times the distance, which is one meter away from our access point, plus 20 lock 10 times the frequency, which is 2.4 gigahertz plus our constant, we can look at the equation and see that the result is a 40 Db loss. So let's assume that our access points operates with a 20 dBm of power 20 dBm equals to 100 millivolt for a Wi Fi signal open rating the 2.4 gigahertz.
Within the first one meter, over 40 dB of energy is lost the level of exposure one meter away only one meter away, is below minus 20 dBm. But our signal doesn't stop here, it goes farther away and away. And each obeys the inverse square law. If we double the distance from one meter to two meters away from the access point, the power reduces four times six dB. If you have a signal that operates at a five gigahertz frequency, it loses about 47 Db one meter away. Remember, the higher the frequency, the bigger the loss to meters away the power decreases four times and the loss is 53 Db and so on.
Next up more free space path loss examples. See you soon