So, I am looking to start a robotics project, but I was looking for advice for one key part. I'd like to build a robot that can follow you as you walk around. So the basic idea of the project is to have some form of beacon, carried or placed by the user, and the robot will direct itself towards the beacon and move towards it. Now the constraints that make it more complicated are that 1) I'd like it to work "anywhere" (We'll assume 2 dimensions for now), so the only two points allowed are the Robot and the beacon. I'd like it to not require additional set-up. 2) I'd like it to not require direct line of sight. I'm assuming a max range, even if it isn't even a very long max range (I'd be happy with a just a few meters), but I'd like it to not automatically fail if something is between the beacon and the robot. 3) The beacon should be relatively low power. I'd like it to be something that a person could carry on their person without difficultly. 4) I'd like it to not cost a fortune.
What are the methods to determine relative direction and distance with only 2 points? I'm not even sure what to call this, so any information would help. I have no clue what type of signal to use for the beacon, or where to even start looking, but I imagine that there is at least some form of established technology for this?