OFDM for Underwater Acoustic Communications

Chapter 18OFDM Modem Development

Chapters 9 to 17 have presented OFDM receiver designs in various system setups. The algorithm development relies on simulations and offline processing of data sets collected from field experiments. To build a real communication system with multiple nodes, acoustic modems with real time processing need to be developed. This chapter describes the modem implementation aspect and presents some example designs of OFDM based acoustic modems.

18.1 Components of an Acoustic Modem

Implementation of an acoustic modem goes much beyond algorithm development. To have a standalone underwater acoustic modem which support point to point communications, the following components are needed.

• Hardware. A hardware platform involves various units.
  • A transducer or multiple transducers that can convert the electronic signals into acoustic signals.
  • A hydrophone or an array of hydrophones that can convert the acoustic signals into electronic signals. Note that a transducer can be used for both transmission and reception. If so, transmit-receive (TR) switch mechanism needs to be incorporated.
  • A digital signal processing board that contains DSP chips, and A/D, D/A converters. Communication algorithms are often run inside a DSP chip, and hence an acoustic modem can be viewed as a software defined modem.
  • Power amplifier with matching circuits to the transducer.
  • Preamplifier circuits with interface to the hydrophones.
  • Waterproof housing with the desired depth rating and ...