Digital Underwater Acoustic Communications

280 Pages·2016·30.23 MB·English

by  Lufen Xu

DIGITAL
UNDERWATER
ACOUSTIC
COMMUNICATIONS
Tianzeng Xu
Lufen Xu
AMSTERDAM(cid:129)BOSTON(cid:129)HEIDELBERG(cid:129)LONDON
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About the Authors
TianzengXuisaprofessorandthesupervisor Ministry of Science and Technology of the
of a Ph.D. program at the College of Ocean and People’sRepublic of China.
Earth Sciences of Xiamen University and Key Lufen Xu is a senior engineer and master
Laboratory of Underwater Acoustic Communi- instructorattheCollegeofOceanandEarthSci-
cation and Marine Information Technology, encesofXiamenUniversityandKeyLaboratory
Ministry of Education. He had been appointed of Underwater Acoustic Communication and
as director of the Subtropical Marine Institute, MarineInformationTechnology,MinistryofEd-
Head of Oceanography Department, Xiamen ucation. He is vice dean of teaching and the
University and vice chairman of the China researchsectionofmarinephysicsofthecollege.
Marine Physical Society.
The advanced worker of national high-new
technical developing (863) program vested by
vii
Foreword
Underwater acoustic communications have basic premise for establishing innovative digital
covered the areas of national defense and civil underwater communication equipment that can
ocean development and exploration. Therefore, adapt topeculiar underwateracoustic channels.
they have been highly valued by maritime na- The contents discussed in this book will
tions in the past several decades. mainly focus on digital underwater acoustic
Analogunderwateracousticcommunications communications forcivil applications.
have played an important role for many years. Military underwater acoustic communication
However,theyhavesomedrawbackslikeunsta- has its own special requirements and corre-
ble communication quality. To adapt peculiar sponding difficulties. For example, it requires
underwater acoustic communication channels, long-rangeandstrictlyconfidentialcommunica-
digital underwater acoustic communications tion,whichsometimesappliestohigh-speedmo-
have raised vast concerns and achieved crucial bilecommunication.However,theappliedfields
developments and massive technological break- and operating specifications between military
throughs. With regard to many underwater and civil underwater acoustic communications
acoustic communication fields, like underwater crosseachother.Inparticular,thetheoreticalba-
data transmission in an underwater acoustic sis is generally identical. Therefore,the contents
network,digitalcommunicationshavegradually discussed in this book have a common
replacedanalog ones. significance.
In principle, digital underwater acoustic Thisbookhasfourchaptersandanappendix.
communications are an extension and develop- Afterreviewingthedevelopmentofunderwater
ment from digital radio communications. How- acoustic communications, Chapter 1 is focused
ever, there are many essential differences ondescribingthedifferencesbetweenunderwa-
betweenunderwateracousticandradiocommu- ter acoustic communication channels and radio
nication channels, including randomly variant ones. The peculiarities existing in the former
spatial-temporal-frequency parameters, large indicatethenecessitytoexploresomeinnovative
attenuation, severe multipath effects, a strict signal processing systems employed effectively
band-limiting property, high noise level, and in digital underwater acoustic communications.
low sound velocity. In particular, underwater After that, a communication sonar equation
acoustic communication channels are generally will be derived, and an active sonar equation
not linear nor time-invariant. Therefore, some against noise background will also be included.
present advanced signal processing systems, A specific example to show how to use the
suchasmatchedfilter,orevensomebasicprinci- communication sonar equation to select the
ples,likeShannontheorem,inradiocommunica- relative parameters in designing an improved
tions cannot perfectly be employed, and they FH-SS (Frequency-Hopped Spread-Spectrum)
especially cannot be copied mechanically in system communication sonar will be provided.
underwater acoustic communications. So, Lawsoftransmittedsoundinunderwateracous-
exploring innovative signal processing systems tic channels will be discussed in Chapter 2,
to suitably employ in peculiar underwater includingsoundtransmissionloss,multipathef-
acoustic communication channels is a valuable fects, sound scattering and fluctuations, and
and challenging research topic, which is also a noise in the sea, especially their impacts on
ix
x
FOREWORD
digital underwater acoustic communications and (3) a rapid, adaptive channel-modifying
and the possible countermeasures to adapt to net that can adapt to underwater acoustic
them. They are the physical basis for designing communication channels having a random
innovative digital underwater acoustic commu- spatial-temporal-frequency variability.
nication signal processing systems. Digital Many notable books have been published in
underwater acoustic communication signal thefieldofunderwateracoustics;however,there
processing will be described in Chapter 3. After are not any monographs or systematic reports
discussing some signal processing schemes about digital underwater acoustic communica-
employed in digital underwater acoustic com- tion. Despite the fact that the first author is
munications at present, the explorations estab- over 70years old, he invited his daughter to
lishing innovative digital underwater acoustic writethisbookbasedonyearsofteachingexpe-
communication systems are emphatically dis- riences, including two doctor’s degree courses:
cussed. According to the peculiarities of under- “Applied Underwater Acoustics” and “Under-
water acoustic communication channels, by water Acoustic Data Transmissions.” Especially
combiningsomekeytechniques,whichurgently relevant was the experience of research and
need to be solved in civil underwater acoustic development, including undertaking and
communications, it is possible to establish an participating in five topics with respect to a na-
innovative, adaptive pseudo-random frequency tional high, new technical developing program
modulation (abbreviated as APNFM) system to (since to make some contributions to this pro-
beemployedindigitalunderwateracousticcom- gram, one has to be chosen as an advanced
munications. It may be expected to adapt to worker by National Science and Technology
peculiar underwater acoustic communication Committee and win the third prize), and it is
channelsandobtainanapproximatelyoptimum our wish to use that to add a brick and a tile
detection result at the criterion of maximum for building the edifice of Underwater Acoustic
output SNR against a random multipath inter- Communications. At the same time, the authors
ferenceandnoisebackground.Digitalunderwa- hopethecommunicationsdevelopwithoutinter-
ter acoustic communication equipment will be ruption, and become more and more mature in
discussedinChapter4,including three types of servicetohumanitytoexploreandusetheocean
civil digital underwater acoustic communica- in a peacefulway.
tion equipment developed by the authors: (1) Duringtheprocessofwritingthisbook,theau-
underwater acoustic telecontrol communication thors had consulted many brilliant works and
equipment in which a digital time correlation theses, and they received some inspirations
accumulation decision system has been from them. At the same time, the authors want
employed; (2) underwater acoustic multimedia togiveheartfeltthankstocolleaguesfortheirsup-
communication equipment in which an portandhelpduringthelengthyworkprocess.
improved FH-SS system has been used; and This book is designed to serve as a reference
(3) a digital underwater acoustic communica- book for postgraduate students and practicing
tion prototype in which an innovative APNFM engineers involved in the design and analysis
system has been employed. There are three of underwater acoustic communications, as
innovative key parts in APNFM: (1) adaptive wellasrelativeunderwateracousticengineering.
total time sampling processing for PN As a background, we presume that the readers
(Pseudo-random)sequencesinsteadoftheusual have a prior knowledge of underwater acoustic
synchronical schemes; (2) an adaptive Rake physics and digital communications.
receiver to adapt complicated and rapid vary- As we all know, the Monkey King in Journey
ing multipath effects and utilize its energy; to the West can freely travel in the ocean to visit
xi
FOREWORD
hisfriendDragonKingintheCrystalPalace,but basis for designing ultrasonic sensing systems
itisalsoaregrettablethingthat hecannotcarry employedintheairmedium.Next,threenewul-
out underwatercommunicationwithhis master trasonicsensingsystemsdevelopedwillemphat-
and apprentices. ically be discussed in this appendix, which are
The authors believe that with unremitting ef- ultrasonic ranging and bearing sensing system
fortswecanalsotravelthroughtheoceansome- employedinconcretejettingmanipulators,ultra-
day and live in the man-made“Crystal Palace.” sonicterrainobstaclessensingsystememployed
Moreover, people can be guided by tortoises in mobile robots, and ultrasonic navigating
and dance with whales. Furthermore, like the sensing system employed in automatic guided
people who live on the earth, everyone can vehicles.Thisappendixissuitableforpracticing
haveanunderwatermobilephonetocommuni- engineers and postgraduate students as a refer-
cate with their relatives and friends in multi- ence in ultrasonic sensing systems and their
media ways at anytime and anywhere. If the applications.
Monkey King knew that, he wouldbe jealous. Itshouldbepointedoutthattheauthorspub-
The appendix includes relative ultrasonic lishedDigitalUnderwaterAcousticCommunication
sensing systems in the air medium. The rules in Chinese in 2010. Now, we have carried out
with respect to ultrasonic radiation, transmis- some supplements and expect a wider range
sion,scattering,andreceivingintheairmedium of interchanges, if it is published in English,
will first be described briefly. It is a physical becauseit has beentranslated by the authors.
C H A P T E R
1
Introduction
Digital underwater acoustic communications 1.1 OVERVIEW OF UNDERWATER
for civil applications will be discussed in this ACOUSTIC COMMUNICATION
book. An appendix on ultrasonic sensing sys- DEVELOPMENT
tems in the air medium willalso be included.
Afterreviewingthedevelopmentofunderwa- Formation and development of a discipline
ter acoustic communications, the emphasis in come from practical needs. The urgent needs
thischapterwillbefocusedondescribingthedif- from both navy military activities and ocean
ferences between underwater acoustic commu- resource exploitations have become a strong
nication channels and radio channels. The drivingforceforthedevelopmentofunderwater
peculiarities existing in the former mean that it acoustic communications.
is necessity to explore some innovative signal Modernunderseawarfarebelongstothewar
processing systems employed in digital under- ofinformationtechnology.Underwateracoustic
water acoustic communications, which is also a communications are the important methods of
basic premise to establish new digital underwa- information acquisition, transmission, and
ter acoustic communication equipment. Also, a control.
communication sonar equation will be derived, The main military applications for underwa-
which provides the references for predicting ter acoustic communications are as follows
theperformancesofpresentandnewcommuni- [1,2]: the communications between submarines,
cation sonars being designed. An active sonar submarines and surface ships, submarines and
equation against noise background will also be shore base stations, and submarines and under-
included. A specific example to show how to water combating platforms, as well as military
usethisequationtoselecttherelativeparameters divers; in addition, there are military applica-
indesigninganFHSSsystemcommunicationso- tions for communication among nodes in mili-
nar is also introduced. tary underwater acoustic networks, submarines
In this chapter, the general idea of the book (now as mobile nodes) and nodes, and so forth.
willbesummarized,andtheroleofeachchapter Tomeettheurgentneedsofthepeacefuluses
in overall will becoherently defined. of the ocean, the applications of underwater
DigitalUnderwaterAcousticCommunications
http://dx.doi.org/10.1016/B978-0-12-803009-7.00001-5 1 ©2017ChinaOceanPress.PublishedbyElsevierInc.Allrightsreserved.
2
1. INTRODUCTION
acoustic communications have been rapidly parameters.Inthistypeofmarineobservation
extended from current military to civil fields. station,thevarioussensorsofoceanographic
The typical applications are as follows: parametersandadatacommunicationsonar
arearrangedinanunderwaterplatform.
1. Underwateracousticcommunicationsamong
Samplingvesselsregularlyvisitthesestations
surface command ships and divers
andsendcommandsinthevicinityofthe
performing underwater exploration, rescue,
underwaterplatformtoacquiretherelative
and salvage [3]. Generally, short-range (such
parametersbyusingunderwateracousticdata
as a few kilometers) voice and image
communications.Comparedwiththe
communications are required. Moreover,
traditionalfieldmeasurementsbyusing
servicesmust bedesigned to besmallin size
surveyingships,thevesselshavethe
and lightin weight tofacilitate the divers to
outstandingadvantagesofsavingtime,effort,
carry and operate them. Therefore,higher
andcost.
operating frequencies,such as 20kHz or
5. Formation of civil underwater acoustic
more, will beselected.
networks [6]. The oceanographic parameters
2. Multimediacommunicationsbetweensurface
acquiredby asinglebuoy-based ocean
ships and the various types of underwater
observatory station mentioned earlier can
robots, AUVs (autonomous underwater
only get a single pointdata; thus in-depth
vehicle), deep submergences, etc. [4]. These
analyses of marine environmental variations
communication equipments generally work
andnumericalpredictionsareverydifficult.If
in the deepsea, and where there are good
anunderwater networkis formed, the
conditionsofverticalsoundtransmission,the
multilevelparameters will bemeasured in
coherent detection system canbe used (such
every node. Then by applying underwater
as DPSK (differential phase shift keying)).
acousticdatacommunication amongthe
Communication distances are thus greater
nodes, the parameters willbe transmitted by
(eg, more than several kilometers), and
the antenna on the surface buoyof the
transmission rates are also higher, so real-
gateway node into radiochannels and
timevoice or even color image
collectedby a shorestation datacenter.
communication can beachieved [5].
Therefore,multiparameter, large area,
3. Applicationsof underwater acoustic
simultaneous, continuous, and long-term
communications tothe explorationand
valuabledata can beobtained.
utilization of marine mineralresources [4],
suchasunderwatermonitoringofoffshoreoil People are ready to capture the formation of
drilling platforms, underwater acoustic data an autonomous oceanographic sampling
telemetry of oil wells,underwater network[7,8].Thisnetworkwillprovidetheex-
positioning, and monitoring for laying change of data, such as control, telemetry, and
pipelines.Thesetypesofunderwateracoustic video signals, among network nodes. The
communications belong to high-frequency, networknodes,stationaryandmobileunderwa-
short-range, and point-to-point types; ter vehicles or robots, will be equipped with
operating conditions are better,and thus various surveying instruments, such as current
it is easier todesign corresponding meters, seismometers, sonars, and video cam-
communication sonars. eras. A remote user can gather various oceano-
4. Underwateracousticdata(includingremote graphic data using direct computer access via a
controlcommands)communicationsforthe radio link to a central network node based on a
automaticmonitoringofmarineenvironmental surface buoy.
3
1.1 OVERVIEWOFUNDERWATERACOUSTICCOMMUNICATIONDEVELOPMENT
Inaddition,underwateracousticcommunica- occur anytime and anywhere. Adapting
tionscanalsobeusedinsomeotherfields,such communication functionsto underwater
asmarinedisasterforecasting,thepositioningof acousticcommunication environments that
ablackboxfromaplanecrash,orthecommuni- randomly vary in spatial,temporal, and
cation between underwater tour boats and the frequency aspects isvery difficult.
shore station. The application fields of civil un- 4. Military underwater acoustic
derwater acoustic communications can be ex- communicationsmay beapplied to high-
pected to be rapidly extended in the future. speed mobileones. In these cases, there exist
Theappliedfieldsandperformancespecifica- dramaticchangesin the communication
tions between military and civil underwater environments,largeDopplerfrequencyshifts,
acoustic communications cross each other, and the high noise levels of theships [10].In
whereas more are essentially different. particular, since the usualunderwater
Military underwater acoustic communica- acousticsignal processing schemes,such as
tions have their own special requirements and the matchedfilter and OFDM(orthogonal
corresponding difficultiesrealizing robust ones. frequencydivisionmultiplexing),donothave
frequency shift adaptability, realizing high-
1. Military underwateracoustic quality mobile underwater acoustic
communicationsgenerallyrequirelong-range communicationsis quite difficult.
propagation.Iftheinformationtobeobtained 5. Military underwater acoustic
is more distant, there is a wider range for communicationshave a requirement to be
acting opportunity. strictly confidential. Ifthis difficult problem
2. Military underwateracoustic cannot beovercome, perhaps transmitted
communications generally require high data sound power and the corresponding
rates.Oncetheinformationisreceivedfaster, communication distanceshave tobereduced
actions can beobtained in anadvanced to exchange forthe improvement of
amount of time. confidential communication performance [1].
Compatibly satisfyingthe long range,r, 6. Military underwater acoustic
and the high rate,R, underwater acoustic communicationsgenerallyneed multimedia
communications canbe quite difficult. Based information to adapt to differentapplied
on the experimental results acquired by fields. Installing a lot of different
American scholars, anupperlimit product communication equipment(including
between R (kbps) and r (km) [9] isgivenby different transducer-amplifier of power
modules) in the shipswith limitedspacesis
R (cid:1)40 (1.1)
r
generally not allowed.Thus,the
compatibility problemsof different
Generally,itisdifficult toreachthisupper
communication media, communication
limit. For example,whenR¼1kbps is
sonar, and activesonar transducers, etc.,
required, communication distance would be
would cautiously besolved [1].
less than 40km.
3. Military underwateracoustic In contrast, the problems existing in military
communications demand high robustness to underwater acoustic communications are not as
avoidaccidental incidents. However,marine outstandingasinmilitaryones.Civilcommunica-
communication environments are tionequipmentisusuallyoperatedatshorterdis-
complicatedandvaried;whereasunderwater tances and communication time intervals also
warfare and their battlefields are likely to have a great flexibility; thus the compatibility
4
1. INTRODUCTION
problem of either communication distances or underwateracousticcommunicationsonarshave
data rates is not present. Moreover, they usually someparticularrequirementsinsize,weight,po-
belong to fixed points or, at low-speed mobile wer consumption, and cost. In particular, it is
communications, communication environments difficulttoacquirethepriorknowledgeofunder-
that are more stable, so there is a lighter burden water acoustic communication channels for the
on the Doppler frequency shift correction, and civil users. Therefore, such equipment must be
thenoiselevelsarealsolower.Thereisnorequest able to accomplish the communication without
forconfidentialityforsuchcommunicationequip- the prior knowledge of the channels. We see
ment.Aslongasthepermissionsaremetforen- that there are some special difficulties for
ergy consumption, size, and weight, we can designingsuchcivilcommunicationsonars.
maketheinformationdetectionunderthecondi- Thus, even if for civil underwater acoustic
tion of high signal-to-noise ratio (SNR). In addi- communications,achievingmultimediacommu-
tion, we can produce a variety of underwater nications with longer distances, higher data
acoustic communication equipment having rates, and high robustness are still of very diffi-
different specifications and applied fields for cult. Many core techniques critically wait to be
different users. Generally, the complex compati- solved, which will be discussed in this book.
bilityproblemsmentionedearlierdo nothaveto Some particularly difficult problems existing in
beconsidered. military underwater acoustic communications,
Ofcourse,thedegreeofdifficultybetweenmil- such as secure, high-speed mobile communica-
itary and civil underwater acoustic communica- tions, will not be discussed in depth in this
tions is relative. Realizing civil underwater bookbecausethecontentswillfocusonthedig-
acousticcommunicationswithhighperformances ital underwater acoustic communications
is still a difficult task. If the communication dis- against for civil applications.
tances can be extended to be farther, this will As noted earlier, because of the complexity
widely adapt to practical requirements. Some andvariabilityofunderwateracousticchannels,
communicationmediathathavelargeinformation there are many practical difficulties to achieve
contents, such as in image communication, still high-quality underwater acoustic communica-
have high required data rates. For example, we tions. However, driven by actual military and
haddevelopedashallowwaterimagecommuni- civilneeds,theunderwateracousticcommunica-
cation prototype [11]. Although the data rates tion discipline has advanced greatly in the pro-
havereached8kbpsforasimpleblackandwhite cess to overcomethe varied difficulties.
image consisting of 320(cid:3)200(pixels)(cid:3)16(gray From the layout of the communications, sim-
level)withoutusingdatacompression,thetrans- ple, static point-to-point communications have
mission time is still 32s. According to Eq. (1.1), spreadtomobileones;nowunderwateracoustic
the communication distances are below 5km. In networks have been formed, and we are pre-
someseaareas,adversecommunicationenviron- pared to establish land/sea/air three-
ments will be encountered. A signal processing dimensional mobile communication networks.
system with excellent channel adaptability is Fromthecommunicationsystems,theanalog
also needed for ocean developments and utiliza- underwater acoustic communications have
tion.Someappliedfields,suchasthecommunica- gradually been transited to digital ones. More-
tionbetweenasurfacecommandshipandAUVs, over, some advanced radio communication sys-
are still considered mobile. Moreover, the multi- tems, such as spread spectrum [12,13] and
media communications and corresponding OFDM systems have been applied to underwa-
compatibility problems will also be encountered ter acoustic communications. We can achieve
insomeintegralapplyingfields.Inaddition,civil distances above 100km in low data rate digital