Digital underwater communications are becoming increasingly important, with numerous applications emerging in environmental monitoring, exploration of the oceans, and military missions. Until the mid-nineties, the research was focused on hardware and on communication transmitters and receivers for the transmission of raw bits. In network terminology, this is known as the physical layer. A breakthrough was achieved in the mid-nineties by Stojanovic et al. , who showed that phase-coherent communication is feasible by integrating a phase-locked loop into a decision-feedback equalizer . Such a receiver can be applied to a single hydrophone, although robust operation at high data rates, say >1 kbit/s, generally requires the presence of a (vertical) hydrophone array for reception. Indeed, multichannel adaptive equalizers have proven to be versatile and powerful tools. If the use of a receive array is impractical, as in multinode networks, then frequency-shift keying (FSK) is often used as a fairly robust modulation for single-receiver systems [3, 4, 5]. However, the corresponding data rates are of the order of 100 bit/s. Although progress is still reported on the physical layer, for example on multicarrier modulations or covert communications, a basic set of modulations and receiver algorithms is now available to support research on higher levels in network architectures.
KeywordsMedium Access Control Autonomous Underwater Vehicle Doppler Power Covert Communication Multicarrier Modulation
- 3.Freitag L, Grund M, von Alt C, Stokey R, Austin T (2005) A shallow water acoustic network for mine countermeasures operations with autonomous underwater vehicles. In: Proceedings Underwater Defense Technology (UDT), Amsterdam, NetherlandsGoogle Scholar
- 4.Partan J, Kurose J, Levine BN (2007) A survey of practical issues in underwater networks. SIGMOBILE Mob Comput Commun Rev 11(4):23–33Google Scholar
- 5.Rice J, Green D (2008) Underwater acoustic communications and networks for the US Navy’s Seaweb program. In: Proceedings 2nd international conference on sensor technologies and applications (SENSORCOMM), Cap Esterel, France, pp 715–722Google Scholar
- 6.Been R, Hughes DT, Vermeij A (2008) Heterogeneous underwater networks for ASW: technology and techniques. In: Proceedings Underwater Defense Technology (UDT), Glasgow, UKGoogle Scholar
- 8.Brady D, Preisig JC (1998) Wireless communications—signal processing perspectives. Prentice Hall, Upper Saddle River, Chapter 8, pp 330–379 Google Scholar
- 9.van Walree P (2011) Channel sounding for acoustic communications: techniques and shallow-water examples. FFI-rapport 2011/00007, Forsvarets ForskningsinstituttGoogle Scholar