On Wednesday, November 4, 2020, 08:53:56 AM CST, James Amos <jimamos@...> wrote:
[snip]
> Several mentions were made to summing the different multipath rays for better detection. This >does not work on a single antenna, as the singles get summed at the input!
[snip]
This will be more clear with some numerical experiments, but those will take a while to find time.
The general model of multipath arrivals at a single receiver in Z transform notation of sorts:
D(z) = S*A0*s(z) +S*A1*s(a*z) + S*A2*s(b*z) + ...
with S signal, A0... being path strength and s delay with exponents a,b... over path.
If S=M*PRN where * indicates convolution, then if one one crosscorrelates D(z) with PRN, one then gets the bit for that transmission frame prior to multipath filtering. Without correlation with the PRN the signal sounds like low level white noise. Because the bit frame is long, precise resolution and tracking of multiple arrivals is easy. So the travel time sequence for the arrivals is simple to determine.
If you know the PRN pair used by a station, you can listen for that signal at very low computational cost. There is a very big difference in what is possible if you allow enough time per bit. By using GPS synchronization, multipath at 10-30 seconds per bit is a bit different. You can exploit the additional signal by phase aligning and summing multiple arrivals. This can even be used to separate arbitrary signals on the same frequency if you have enough compute available.
My goal is reliable peer to peer radio mail at a few kB/day.
Have Fun!
Reg
