In setting a challenging project for a very bright physics and mathematics student, I had to stay one step ahead and go back to fundamentals to work out the availability of a fading path as a function of direct and indirect signals.

This is useful in many applications where the fade margin required for reliable communications in narrowband channels can be characterised as a function of the amplitude of indirect scattered components relative the direct line-of-sight component.

This led me to develop this little fading calculator based upon Marcum’s Q function, which I have implemented as a custom function in a spreadsheet to resemble the Nakagami-Rice distribution as expressed in ITU-R P.1057-4 and plotted in figure 4.

I chose the numerical approximation of the Q function based upon ‘Another Recursive Method of Computing the Q Function’ by W F McGee (IEEE Transactions and Information Theory, July 1970).

The complete example is available for download here.

Well done Callum for solving the problem set and keeping me on my toes!