Hey everyone, thanks for coming back to Wi Fi fundamentals with location and analytics. This course will help you to muster the air. We're moving in into one of the most promising ranging techniques time of arrival, promising as it will result in a more accurate reading that, as you will see later on will help us in positioning, but it is much more complicated to accomplish at least when you compare it to rssi. We will look at how ranging is done using time of arrival. Why is it so complicated? And why do we need to take in concern the speed of light.
We will see how it helps us in positioning and how it become the basis for Wi Fi round trip time of like the most promising positioning technology out there. time of arrival technique is very simple to understand. Whenever a station or an access point sensor frame, a timestamp is attached to that frame. When the frame is received at the other side, another timestamp is attached to the frame the time that passes between the first time stamp the sent frame and the second time stamp, the received frame is the time of propagation, the time it took the frame to arrive to the other side. The equation says the d d is the distance equals to C which is a constant it is the speed of flight about 300,000 kilometres a second times t times the time of propagation. So if for example, our signal travels in the speed of light for a millisecond the distance it travels is 300 kilometres 300,000 kilometres, divide them with a thousandth of a second.
That brings us to 300 kilometres. All right, that was simple. So why is it so complicated? Well, it's complicated because the light travels fast. Just think about it light travels at the speed of 300 million meters a second. Now think about that a nanosecond and nanosecond is zero dot 00000001 of a second, a light travels one feet in a nanosecond.
So, our clocks, our devices clocks, our stations and access points clocks must be synchronized to the nanosecond. time of arrival has two methods for range measurement. The first one was covered here in this video. The second which involves two way arranging, also known as round trip time of flight is the basis for Wi Fi RTT, which we will deal with in the next videos. The advantage of using the time of arrival instead of rssi is that when the signal travels through obstructions such as walls, the time it takes for The signal to travel will be affected only very slightly. In the case of rssi the effect of such obstructions is far greater.
Next up, we are moving to location. See you soon