Alternatives for Supporting Multiple Cryptographically-Isolated User Groups in Frequency-Hopping Systems

Most traditional coded and interleaved frequency-hop systems either avoid multiple-access interference through the use of orthogonal hopping patterns or tolerate the MAI that results from non-orthogonal hopping patterns. While the former method typically has better performance, all the users' hopping patterns must be coordinated to maintain orthogonality. Because the processing gain of frequency-hop systems relies on the secrecy of the hopping pattern, having a potentially large number of users with knowledge of coordinated hopping patterns may be undesirable. Rather, multiple smaller groups that are cryptographically isolated from each other are preferred. In this paper, we discuss alternatives for supporting multiple such cryptographically-isolated user groups in frequency-hopping spread spectrum systems. Tradeoffs among interference rejection, data rate, and number of supportable users are considered for a variety of channel access schemes and hopping pattern designs. In addition, the impact of improved receiver capabilities, such as multiuser detection, to the trade space is investigated.