High-frequency wireless communications, such as in the 60 GHz Wireless Personal Area Networks currently being developed, tend to be limited to short-range communications because of the level of absorption of the signals by oxygen in the air. For this and other reasons, this technology is most suitable for personal area networks that have multiple devices communicating with each other within a small area. In many applications, this will lead to a dense operating environment, in which multiple such networks that are adjacent and overlapping will tend to interfere with each other. To reduce the level of this interference, communications tend to be directional and prescheduled. But some communications, by their very nature, need to be omnidirectional and unscheduled. Choosing one or the other usually requires trading off the advantages and disadvantages of each.