Communicating with each other may be in fact more complex. What communication standard do you use. Even more important, what do you communicate? I think this is less realistic than each robot having a beacon of some sort.
Though im not sure, i imagine it would be pretty simple to make a omnidirectional IR beacon. First of all, FIRST already does this on the field. Second, i think it can be even simpler than what FIRST appears to have (several small area beacons) by just shining a single beacon at a reflective sphere (say a 2x ball
)