Frequency-hop multiple-access systems with limited per-hop multi-user detection

Robust frequency hop (FH) waveforms perform forward error correction coding across multiple time-frequency slots (referred to as hops). The typical assumption for FH receivers is that only one signal per hop can be recovered by the demodulator. In terms of multiple-access interference (MAI), this typically leads to one of two design choices for FH systems. One option is to mitigate MAI statistically; namely, through the use of nonorthogonal hopping. With nonorthogonal hopping, from time to time multiple users´ signals occupy the same hop. Because coding is performed across many hops, this interference does not necessarily preclude correct decoding, and the corresponding performance degradation may be deemed acceptable. The advantage of this approach is that one user´s hopping sequence does not depend on the hopping sequence of one or more of the other users, which reduces the required level of coordination among the users. The second option is to completely avoid MAI through the use of orthogonal hopping sequences. Such sequences ensure that at most one user signal is present in each hop, which complements the capabilities of a single-user detector, but additional coordination is required among the users.