Communication - Delay Spread                                 Home : www.sharetechnote.com

 

 

 

Even though a same signal is transmitted from single transmission antenna, the signal may go through various different path. Each of the different path may cause different travel distance if the signal get reflected by one or more obstacles (like buildings) and in some case different path may has different physical property of propagation media, so it is higly likely that the signal traveling through different path would arrive at the reciever antenna at different timing. So if you send a signal from a transmitter antenna and measure the arrival time at the reciever antenna which is a certain distance away from the transmitter antenna, you would get multiple different arrival timing.

If you plot those arrival timing on the axis of time, you would see a certain variation (spread) of those values. This spread is called 'Delay Spread'.

 

I think this is enough for the definition for layman. If you want to dig into further details and go through some mathematical model of these delay spread see the following. (I will put description later)

 

 

If I plot the signals detected by a reciever antenna in time vs amplitude plot, it can be represented as follows. As you see here, you will see multiple copies of the same signal coming in with different timing and different amplitue. Using these time variation and amplitude variation, we can defined several different criteria (metrics) to define the nature of the channel. To introduce these criteria (metric) is the main purpose of this page.

 

 

 

Max Delay Spread

 

 

 

Problems with Max Delay Spread

 

 

 

Average Delay Spread

 

 

 

 

 

 

  

 

Variance of Delay

 

 

 

 

 

 

 

RMS Delay Spread

 

 

 

Reference :

 

[1] Lecture 20: Max Delay Spread

    Prof. Aditya K. Jagannatham

    Dept. of Electrical Engineering

 

[2] Lecture 21: RMS Delay Spread

    Prof. Aditya K. Jagannatham

    Dept. of Electrical Engineering

 

[3] Lecture 22: Delay Spread and Inter Symbol Interference

    Prof. Aditya K. Jagannatham

    Dept. of Electrical Engineering