Quasi-independent frequency hopping - A new spread spectrum multiple access technique

The design and performance analysis of a multiple access, spread spectrum communication technique that uses an adaption of frequency hopping (FH) is presented. This technique has features that enable it to cope with frequency-following jamming. Conventional FH systems use parallel frequency hopping (PFH) in which channels are assigned via frequency division multiple access (FDMA) and hopped as a composite. The present paper describes two alternative pure FH techniques in some detail. Independent frequency hopping (IFH) uses M-ary FSK modulation, block codewords (different for each multiple access channel), and M independently hopping tone banks, permitting a matched-filter, soft-limiter diversity combining receiver to reliably detect the correct symbol. This technique requires M dehopping synthesizers at the receiver, an impracticability for large M. Quasi-independent frequency hopping (QIFH) is a generalization of IFH which achieves the same results but uses fewer than M (any integer factorization of M is possible) hopping groups. The number of simultaneous QIFH channels is shown to be proportional to the number of channel symbols per information symbol transmitted.