While their efficiency is adequate for present applications, the use of spread spectrum coding has the potential of greatly expanding the capacity of PR networks. In addition to increased capacity, spread spectrum can provide message privacy for those applications that need it. Because the technology involved is so interesting, this report will examine the nature of these systems even though they are not yet in use. They used PR to communicate with the different islands of Hawaii. Since 1980, when the FCC made a temporary allocation of frequency space to this purpose, an amateur packet radio network has sprouted up in this country, today with thousands of users.
Several users use the same data channel for efficiency.
When a pair of messages from separate users appear on the network simultaneously, the packets collide and the information from both is lost. Then both packets have to be resent. A normal packet network is structured into clusters. A group of users locally work form a cluster and communicate over the same channel to each other. For communication to users outside of the local group, one of the local computers must act as a clusterhead.