Digital Underwater Acoustic Communications

Lufen Xu, Tianzeng Xu

• Publisher: Academic Press
• Year: 2016
• ISBN:
  9780128030295
• Topic: Technology & Engineering
• Subtopic: Signals & Signal Processing
• Index: Technology & Engineering

Digital Underwater Acoustic Communications focuses on describing the differences between underwater acoustic communication channels and radio channels, discusses loss of transmitted sound in underwater acoustic channels, describes digital underwater acoustic communication signal processing, and provides a comprehensive reference to digital underwater acoustic communication equipment.

This book is designed to serve as a reference for postgraduate students and practicing engineers involved in the design and analysis of underwater acoustic communications systems as well as for engineers involved in underwater acoustic engineering.

• Introduces the basics of underwater acoustics, along with the advanced functionalities needed to achieve reliable communications in underwater environment
• Identifies challenges in underwater acoustic channels relative to radio channels, underwater acoustic propagation, and solutions
• Shows how multi-path structures can be thought of as time diversity signals
• Presents a new, robust signal processing system, and an advanced FH-SS system for multimedia underwater acoustic communications with moderate communication ranges (above 20km) and rates (above 600bps)
• Describes the APNFM system for underwater acoustic communication equipment (including both civil and military applications), to be employed in active sonar to improve its performance

Chapter 1

Introduction

Abstract

The development of digital underwater acoustic communications is introduced briefly, and then a special emphasis is placed on the essential differences between underwater acoustic communication channels and radio channels. The peculiarities existing in the former mean that it is necessity to explore some innovative signal processing systems employed in digital underwater acoustic communications. According to the peculiarities of the channels, by combining some key techniques, which urgently need to be solved in civil underwater acoustic communications, it is possible to establish an innovative, adaptive, pseudo-random frequency modulation abbreviated system to be employed effectively in the communications. Obtaining an optimum detection result is expected. A communication sonar equation will also be derived. A specific example to show how to use this equation to select the relative parameters in designing a frequency hopping spread spectrum (FHSS) system communication sonar is included.

Keywords

Civil digital underwater acoustic communications; Communication sonar equation; Digital underwater acoustic communications; Innovative signal processing system; Peculiarities of the channels

Digital underwater acoustic communications for civil applications will be discussed in this book. An appendix on ultrasonic sensing systems in the air medium will also be included.

After reviewing the development of underwater acoustic communications, the emphasis in this chapter will be focused on describing the differences between underwater acoustic communication channels and radio channels. The peculiarities existing in the former mean that it is necessity to explore some innovative signal processing systems employed in digital underwater acoustic communications, which is also a basic premise to establish new digital underwater acoustic communication equipment. Also, a communication sonar equation will be derived, which provides the references for predicting the performances of present and new communication sonars being designed. An active sonar equation against noise background will also be included. A specific example to show how to use this equation to select the relative parameters in designing an FHSS system communication sonar is also introduced.

In this chapter, the general idea of the book will be summarized, and the role of each chapter in overall will be coherently defined.

1.1. Overview of Underwater Acoustic Communication Development

Formation and development of a discipline come from practical needs. The urgent needs from both navy military activities and ocean resource exploitations have become a strong driving force for the development of underwater acoustic communications.

Modern undersea warfare belongs to the war of information technology. Underwater acoustic communications are the important methods of information acquisition, transmission, and control.

The main military applications for underwater acoustic communications are as follows [1,2]: the communications between submarines, submarines and surface ships, submarines and shore base stations, and submarines and underwater combating platforms, as well as military divers; in addition, there are military applications for communication among nodes in military underwater acoustic networks, submarines (now as mobile nodes) and nodes, and so forth.

To meet the urgent needs of the peaceful uses of the ocean, the applications of underwater acoustic communications have been rapidly extended from current military to civil fields. The typical applications are as follows:

1. Underwater acoustic communications among surface command ships and divers performing underwater exploration, rescue, and salvage [3]. Generally, short-range (such as a few kilometers) voice and image communications are required. Moreover, services must be designed to be small in size and light in weight to facilitate the divers to carry and operate them. Therefore, higher operating frequencies, such as 20 kHz or more, will be selected.

2. Multimedia communications between surface ships and the various types of underwater robots, AUVs (autonomous underwater vehicle), deep submergences, etc. [4]. These communication equipments generally work in the deep sea, and where there are good conditions of vertical sound transmission, the coherent detection system can be used (such as DPSK (differential phase shift keying)). Communication distances are thus greater (eg, more than several kilometers), and transmission rates are also higher, so real-time voice or even color image communication can be achieved [5].

3. Applications of underwater acoustic communications to the exploration and utilization of marine mineral resources [4], such as underwater monitoring of offshore oil drilling platforms, underwater acoustic data telemetry of oil wells, underwater positioning, and monitoring for laying pipelines. These types of underwater acoustic communications belong to high-frequency, short-range, and point-to-point types; operating conditions are better, and thus it is easier to design corresponding communication sonars.

4. Underwater acoustic data (including remote control commands) communications for the a...