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Abstract - A special form of frequency shift keying (FSK) efficiently and robustly allows multiple uncoordinated users to communicate at command and control data rates as part of an ad-hoc network in the underwater acoustic channel. Differential Frequency Hopping (DFH) is a spread spectrum scheme, where the transmitted tone depends on the current data symbol and on the previous transmitted tone. Received symbols in DFH coding depend on the frequency transition between two sequentially received tones, where the possible sequence for a valid message is governed by a carefully designed code. Multiple user access is achieved by assigning orthogonal codes to each user. DFH has been shown to be superior to other coding schemes considering the joint constraints of maximizing multiple user access, good resistance to jamming, and minimizing required transmitted levels. DFH modulation also eases reliance on Media Access Control algorithms because of robustness to co-channel interference. Doppler-robust demodulation via training-free, adaptive synchronization for mobile platforms is presented and discussed, using both simulations and data collected during WHOI's MACE10 experiment. BibTex - @ARTICLE{EgnorJUA2011, TITLE = {Differential frequency hopping (DFH) modulation for underwater mobile ad-hoc networks [U]}, AUTHOR = {D. Egnor and G. S. EdelsonL. Cazzanti and A. K. Das}, JOURNAL = {U.S. Navy Journal of Underwater Acoustics}, note = {accepted for publication.} } |