# Why is bandwidth inversely proportional to mulitpath interference?

I have a project related to Signals of Opportunity and during my research on the communication signals that can be used for navigation purpose I saw that as references are given below signals that have smaller bandwidth give larger positional errors due to multipath effect. However, I could not find the reason why smaller bandwidthed signals are more prone to multipath effect compared to larger bandwithed signals. Could anyone point to any resources or give an explanation for why that is the case?

References: "The net bandwidth of FM signal is much narrower than even the GPS C/A code. This narrowness allows potential multipath errors." from https://navi.ion.org/content/69/2/navi.521

• What you claim is wrong. Narrowband signals are less prone to multipath. Sep 23 at 21:37
• Any time you mention "I saw that..." you should cite your source. Please edit your question to cite where you heard that signals with smaller bandwidths give larger positional errors when there is multipath. Please give a URL or two, or if it's printed matter cite them sufficiently to find them. Especially if it's printed matter, quote the relevant sentence, paragraph, and/or equations. Sep 23 at 22:24
• It's interesting. Narrower channel bandwidth (in the frequency domain) means a larger time width (and less precise estimation of time of arrival) of a single, pulse-like signal. Dunno exactly how that relates to multipath interference, but it seems to me that the wider width of a pulse means that the superposition of multiple-path arrivals would be messier because of overlapping of the multiple pulses received. But this is not my field, so I am not contradicting either Marcus or Tim. They know better than me. Sep 23 at 23:52
• @robertbristow-johnson you hit the nail on its proverbial head: while narrow bandwidth means wide autocorrelation of the signal and thus worse positional accuracy, the necessary flight time difference to shift the correlation peak to the next "range bin", if you will, would be so large that statistically, you can be pretty sure that echo would be sufficiently attenuated compared to the path you want to observe that you don't lose much info on the main path. When doing a wideband observation, you need to find a wb equalizer that restores your pulse, and then read the range from the eq taps. Sep 24 at 9:37
• @TimWescott For example in the experiment carried out by Sage Trudeau and Hope Hong from Lincoln Laboratory they ended up FM signals with narrow with gives larger error compared to HDTV signals. You can reach the results of the experiment at the 16th and 17th pages from events.gnuradio.org/event/18/contributions/252 . Sep 24 at 11:39