An unanswered question...

I had pondered so much about an unanswered question for years when I was in school. My inability to find an answer or even framing the question in a more formal language bothered me intensely from time to time. Fortunately, the question survived somewhere in my mind all these years...
Consider that you and your friend go out for trekking in some dense unknown jungle. Assume each of you are carrying a radio receiver-transmitter. Both your transceiver sets work over a range of frequencies one of which has to be selected explicitly. You and your friend set your transceivers to some agreed upon frequency making sure that you will be able to communicate properly. During the trek, somehow you are lost and your friend isn't anywhere in sight. You need to communicate on the radio. But, unfortunately, you had accidentally changed the frequency of your radio. You don't even remember the frequency value you had agreed upon. You try to call on some frequency. But the absence of an answer can mean that either the frequency is wrong or your friend is out of range. What can you do? What if your friend has been trying to contact you and he thinks he has the wrong frequency and he also changes the frequency knob. What can be the best strategy for you to contact your friend?!...
After almost ten years, I was able to draw the analogy between this problem and the problem of rendezvous in a multi-robot system. I was happy to learn that an entire academic community was doing research on a problem that was lingering in my mind for years!! Having long-lost my interest in solving this problem, the assurance that somebody will find a suitable answer was satisfactory enough!!