Hey everyone, thanks for coming back to Wi Fi fundamentals with location and analytics. This course will help you to muster the air. free space path loss is a great model to calculate the received signal. Yet it is a theoretical model that is based on an ideal environment free of obstacles. The real deal is rssi the received signal strength indicator you see it every day in your smartphone and on your laptop. Whenever you connect to a Wi Fi network.
It is the received power the signal amplitude as our wireless card circuitry senses it We have mentioned the training is done using different methods. There's the propagation based method, time based method, angle based method. rssi ranging is done using propagation based methods. Let's see what's ahead, we will look at rssi, how to measure it, how to calculate distances with rssi what our society's impact has on your data rate, and we will look at the physical phenomenon every Wi Fi engineers should be familiar with the inverse square law. Our society is a mechanism by which RF energy is measured by the circuitry of our wireless card. The measurement is done by the energy observed at the antenna and numeric value because between zero and 255 is given, yet no vendor actually measures 256 different values.
Each vendor has its own specific maximum value. Our society is mostly used in a relative manner in the dBm scale. The range of the energy that is measured usually starts at minus 10 dBm. When representing energy less than one meter rssi is shown in a negative DPM number. The receiver wireless card in station or an access point must have a minimum rssi levels in order to conduct a stable connection between the two parties. The minimum level is called the receiver sensitivity There is a direct linkage between rssi and modulation.
Different vendors indicate minimum rssi levels in order to decode modulation scheme and thus connection speeds. at the lowest speeds, the wireless card needs a minimum of rssi or it will not differentiate between RF signal and noise. And 802 11 access point usually transmits power at 20 dBm and can receive power its receiver sensitivity all the way to minus 96 dBm. Now, let's move on to the inverse square law and our SSI power decreases attenuates in distance, this physical phenomenon is known as the inverse square law. The power change is inversely proportional to the square of the distance change from the source. Wow.
Let me make it simpler. So let's imagine an access point that transmits a signal. one meter away, we can measure the intensity of the signal. one meter away would be a reference. And let's imagine that there is an imaginary paper behind it. We move the paper another one meter back.
So the distance actually doubles. We take the factor of change the distance and square it. So if I'm twice as far away, the factor is to the inverse of two is half square. It is one fourth, the intensity is one fourth. The RF signal spreads out and cover a lot more area. The signal has less energy because it has to match a larger area.
If we move the paper another one meter back, the space being covered is a lot bigger, the intensity of our RF signal is decreasing. So the factor now is tree and the inverse of three squared is one ninth the power our society can be used in different ranging applications. It is simple, it is cheap. It doesn't require anything from your side. But be aware. It is not that accurate.
Our signal propagates in the air They meet obstacles in the phase and amplitude changes. Next up our OSI part to see you soon