Let’s talk about the second spatial diversity technique which is called the feedback or the
scanning diversity. What is the basic principle? It scans all the signals in a fixed sequence until
one with the SNR more than a predetermined threshold is identified. So we need to set a
threshold before we start the operation and then we go into the scanning mode.
Consider M independent Rayleigh fading channels available at the receiver, so here we have the
block diagram for the scanning diversity, we have the different antenna elements goes to the
receiver, finds the short term average, comparator with a preset threshold and then keep on
jumping from one antenna element to the other in a predefined fashion until your threshold is
reached and then you stop. So you do not have to go through the entire cycle to locate the
maximum as long as your threshold is satisfied, you are in business.