Improving Bandwidth Utilization in a 1 Tbps Airborne MIMO Communications Downlink

105 Pages·2013·0.82 MB·English

by  Jonathan D. Hill

IMPROVINGBANDWIDTHUTILIZATIONINA1TBPS
AIRBORNEMIMOCOMMUNICATIONSDOWNLINK
THESIS
JonathanD.Hill,Captain,USAF
AFIT-ENG-13-M-25
DEPARTMENT OF THE AIR FORCE
AIR UNIVERSITY
AIR FORCE INSTITUTE OF TECHNOLOGY
Wright-Patterson Air Force Base, Ohio
DISTRIBUTIONSTATEMENTA.
APPROVEDFORPUBLICRELEASE;DISTRIBUTIONUNLIMITED
The views expressed in this thesis are those of the author and do not reflect the official
policyorpositionoftheUnitedStatesAirForce,theDepartmentofDefense,ortheUnited
StatesGovernment.
This material is declared a work of the U.S. Government and is not subject to copyright
protectionintheUnitedStates.
AFIT-ENG-13-M-25
IMPROVINGBANDWIDTHUTILIZATIONINA1TBPS
AIRBORNEMIMOCOMMUNICATIONSDOWNLINK
THESIS
PresentedtotheFaculty
DepartmentofElectricalandComputerEngineering
GraduateSchoolofEngineeringandManagement
AirForceInstituteofTechnology
AirUniversity
AirEducationandTrainingCommand
inPartialFulfillmentoftheRequirementsforthe
DegreeofMasterofScienceinElectricalEngineering
JonathanD.Hill,B.S.E.E.
Captain,USAF
March2013
DISTRIBUTIONSTATEMENTA.
APPROVEDFORPUBLICRELEASE;DISTRIBUTIONUNLIMITED
AFIT-ENG-13-M-25
IMPROVINGBANDWIDTHUTILIZATIONINA1TBPS
AIRBORNEMIMOCOMMUNICATIONSDOWNLINK
JonathanD.Hill,B.S.E.E.
Captain,USAF
Approved:
/signed/ 8Mar2013
RichardK.Martin,PhD(Chairman) Date
/signed/ 15Mar2013
LtColJamesA.Louthain,PhD(Member) Date
/signed/ 14Mar2013
MajMarkD.Silvius,PhD(Member) Date
AFIT-ENG-13-M-25
Abstract
ForwardErrorCorrection(FEC)techniquesarecomparedfordifferentMultiple-Input
Multiple-Output (MIMO) configurations of a high altitude, extremely wide bandwidth
radiofrequencydownlink. MonteCarlosimulationsarecompletedinMATLAB® withthe
aim of isolating the impacts of turbo codes and Low-Density Parity Check (LDPC) codes
on system throughput and error performance. The system is modeled as a transmit-only
static array at an altitude of 60,000 feet, with no interferers in the channel. Transmissions
are received by a static receiver array. Simulations attempt to determine what modulation
typesshouldbeconsideredforpracticalimplementation,andwhatFECcodesenablethese
modulationschemes. Theantennaconfigurationsusedinthisstudyare[44:352],[62:248],
and [80:160] transmitters to receivers. Effects from waveform generation, mixing, down-
conversion,andamplificationarenotconsidered.
Criteria of interest were Bit-Error Rate (BER) and throughput, with the maximum
allowable value of the former set at 1×10-5, and the latter set at a 1 terabits per second
(Tbps) transfer rate for a successful configuration. Results show that the best performing
system configuration was unable to meet both criteria, but was capable of improving over
Brueggen’s 2012 research, which used Reed-Solomon codes and a MIMO configuration
of [80:160], by 18.6%. The best-case configuration produced a throughput rate of 0.83
Tbps at a BER of less than 1×10-8, by implementing a rate 2⁄ LDPC code with Quadrature
3
AmplitudeModulation(QAM)constellationof16symbols.
iv
Acknowledgments
Anyone who worked with me at any time during the process of completing this
program or producing this document, even in the form in now presently exists, knows I
would not have made it without their constant support, and a serious amount of Divine
intervention. With this in mind, I would like to thank my parents, friends, instructors, and
especially Dr. Martin for helping me through. There is an old saying that goes something
like this: “Whoever ignores instruction despises himself, but he who listens to reproof
gainsintelligence.”Toeveryonewhohaschallengedmetogrow,whetherinsideoroutside
ofacademia,thankyou.
JonathanD.Hill
v
TableofContents
Page
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
TableofContents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi
ListofFigures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
ListofTables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii
ListofSymbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiv
ListofAcronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv
I. IntroductionandProblemStatement . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 ProblemStatement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4 MethodologyOverview . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.5 Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
II. TheoreticalBasisandFoundationalConcepts . . . . . . . . . . . . . . . . . . . 7
2.1 BasicCommunicationSystemArchitecture . . . . . . . . . . . . . . . . . 7
2.2 Interleaving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2.1 BlockInterleaving . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2.2 ConvolutionalInterleaving . . . . . . . . . . . . . . . . . . . . . . 9
2.2.3 Non-UniformInterleaving . . . . . . . . . . . . . . . . . . . . . . 10
2.3 ForwardErrorCorrection . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.3.1 BlockCodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3.2 Reed-SolomonCodes . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3.3 ConvolutionalEncoders . . . . . . . . . . . . . . . . . . . . . . . 12
2.3.3.1 Non-SystematicConvolutionalCodes . . . . . . . . . . . 12
2.3.3.2 RecursiveSystematicConvolutionalCodes . . . . . . . . 13
2.3.4 ConvolutionalDecoding . . . . . . . . . . . . . . . . . . . . . . . 15
2.3.4.1 MaximumLikelihoodDecoding . . . . . . . . . . . . . 15
2.3.4.2 ViterbiAlgorithm . . . . . . . . . . . . . . . . . . . . . 16
vi
Page
2.3.5 TurboCoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.3.6 TurboEncoderStructure . . . . . . . . . . . . . . . . . . . . . . . 17
2.3.7 TurboDecoding . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.3.7.1 ModifiedBCJRAlgorithm . . . . . . . . . . . . . . . . 19
2.3.7.2 IterativeDecoding . . . . . . . . . . . . . . . . . . . . . 23
2.3.8 Low-DensityParityCheckCodes . . . . . . . . . . . . . . . . . . 23
2.3.9 DecodingLDPCCodes . . . . . . . . . . . . . . . . . . . . . . . . 24
2.4 Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.4.1 Phase-ShiftKeying . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.4.2 QuadratureAmplitudeModulation . . . . . . . . . . . . . . . . . . 25
2.5 Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.5.1 RayleighFadingChannel . . . . . . . . . . . . . . . . . . . . . . . 27
2.5.2 RiceanFadingChannel . . . . . . . . . . . . . . . . . . . . . . . . 28
2.6 MIMOCommunicationSystems . . . . . . . . . . . . . . . . . . . . . . . 29
2.6.1 ChannelCapacity . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.6.1.1 SISOCapacity . . . . . . . . . . . . . . . . . . . . . . . 29
2.6.1.2 MIMOCapacity . . . . . . . . . . . . . . . . . . . . . . 30
2.6.2 MaximumLikelihoodSignalDetection . . . . . . . . . . . . . . . 30
2.6.3 SignalDetectionbyMeansofSingularValueDecomposition . . . . 30
2.6.4 InverseChannelDetection . . . . . . . . . . . . . . . . . . . . . . 31
2.6.5 MinimumMean-SquaredErrorDetection . . . . . . . . . . . . . . 32
2.7 MultipathModeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
2.7.1 Two-RayGroundReflectionModel . . . . . . . . . . . . . . . . . 33
2.7.2 TappedDelayLineChannelModel . . . . . . . . . . . . . . . . . 33
2.8 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
III. ExperimentalConfiguration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.1 SystemModel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.1.1 SystemParameters . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.1.2 AntennaConfigurations . . . . . . . . . . . . . . . . . . . . . . . 36
3.2 ErrorCorrectionCodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.2.1 Non-UniformInterleaver . . . . . . . . . . . . . . . . . . . . . . . 38
3.2.2 ConvolutionalCoding . . . . . . . . . . . . . . . . . . . . . . . . 39
3.2.3 TurboEncoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.2.4 TurboDecoding . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.2.4.1 DemultiplexingandPunctureRemoval . . . . . . . . . . 43
3.2.4.2 IterativeDecoding . . . . . . . . . . . . . . . . . . . . . 43
3.2.4.3 OverflowPrevention . . . . . . . . . . . . . . . . . . . . 44
3.2.5 TurboCoderPerformance . . . . . . . . . . . . . . . . . . . . . . 46
3.2.6 Low-DensityParityCheckCodes . . . . . . . . . . . . . . . . . . 47
3.3 Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
vii
Page
3.4 Demodulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
3.5 Channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
3.5.1 MIMOCross-TalkandNoise . . . . . . . . . . . . . . . . . . . . . 52
3.5.2 FadingandMultipath . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.5.3 Two-RayModel . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.5.4 TappedDelayLineModel . . . . . . . . . . . . . . . . . . . . . . 53
3.6 Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
3.6.1 Throughput . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
3.6.2 ErrorPerformance . . . . . . . . . . . . . . . . . . . . . . . . . . 55
3.7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
IV. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
4.1 AntennaConfigurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
4.2 CodingMethods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
4.2.1 ConvolutionalCodes . . . . . . . . . . . . . . . . . . . . . . . . . 58
4.2.2 TurboCodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
4.2.3 LDPCCodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
4.3 Anomalies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
4.4 MultipathModelAssessment . . . . . . . . . . . . . . . . . . . . . . . . . 64
4.5 SummaryComments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
V. ConclusionsandRecommendations . . . . . . . . . . . . . . . . . . . . . . . . 71
5.1 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
5.2 Trade-OffConsiderations . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
5.3 RelationshiptoPreviousResearch . . . . . . . . . . . . . . . . . . . . . . 72
5.4 FutureResearch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
AppendixA:ViterbiAlgorithmExample . . . . . . . . . . . . . . . . . . . . . . . 74
AppendixB:ImplentationDetails . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
AppendixC:CompleteResults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
viii
ListofFigures
Figure Page
1.1 PhysicalrepresentationofMIMOdownlink . . . . . . . . . . . . . . . . . . . 3
2.1 Genericwirelesscommunicationsystem . . . . . . . . . . . . . . . . . . . . . 8
2.2 StatediagramofaNSCencoderwith K = 3andgeneratorpolynomial[7,5] . . 13
8
2.3 State diagram of a RSC encoder with constraint length of 3 and generator
polynomial[7,5] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
8
2.4 Rate 1⁄ NSC (left) and RSC (right) encoder trellises with K = 3 and generator
2
polynomial[7,5] forboth . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
8
2.5 Basicturboencoderstructure . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.6 Iterativedecodingloopforturbodecoding . . . . . . . . . . . . . . . . . . . . 19
2.7 Branchmetricsoverlaidontothetrellisofa[7,5] RSCcode . . . . . . . . . . 22
8
2.8 Example state metric feeding for a [7,5] RSC code trellis. Following (2.10),
8
(2.12) and the trellis paths in Fig. 2.7, α1 = α1 δ0,1 + α2 δ1,2 and β1 =
k k−1 k−1 k−1 k−1 k
β1 δ0,1 +β3 δ1,1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
k+1 k k+1 k
2.9 ConstellationsforGraycoded8-PSKin(a)and16-QAMin(b) . . . . . . . . . 27
2.10 Theoreticalerrorperformancecomparisonofuncodedmodulationschemesfor
channel E /N values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
b 0
3.1 PhysicalrepresentationofMIMOtransmissionpathways . . . . . . . . . . . . 37
3.2 Experimentalsystemblock-diagram . . . . . . . . . . . . . . . . . . . . . . . 37
3.3 RSCencoderwithconstraintlengthof5andgeneratorpolynomial[37,21] . . 40
8
3.4 Iterativedecodingloopforturbodecoding . . . . . . . . . . . . . . . . . . . . 42
3.5 Performanceofarate1⁄ turbocodecomprisedoftwo K = 5rate1⁄ RSCcodes
2 2
withgenerator[37,21] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
8
3.6 Comparisonofrate1⁄ turboandLDPCcodesimplementedforexperimentation 48
2
ix