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SAVO GLISIC BEATRIZ LORENZO

ARTIFICIAL INTELLIGENCE AND QUANTUM COMPUTING FOR ADVANCED WIRELESS NETWORKS

SavoG.Glisic

WorcesterPolytechnicInstitute,Massachusetts,USA

BeatrizLorenzo

UniversityofMassachusetts,Amherst,USA

Thiseditionfirstpublished2022 ©2022JohnWiley&SonsLtd

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CoverDesign:Wiley

CoverImage:©AF-studio/GettyImages;CourtesyofSavoGlisic;©YuichiroChino/Moment/GettyImages

Setin9.5/12.5ptSTIXTwoTextbyStraive,Pondicherry,India 10987654321

Contents

Preface, xiii

PartIArtificialIntelligence, 1

1Introduction, 3

1.1Motivation, 3

1.2BookStructure, 5 References, 11

2MachineLearningAlgorithms, 17

2.1Fundamentals, 17

2.1.1LinearRegression, 17

2.1.2LogisticRegression, 18

2.1.3DecisionTree:RegressionTreesVersusClassificationTrees, 20

2.1.4TreesinRandPython, 23

2.1.5BaggingandRandomForest, 24

2.1.6BoostingGBMandXGBoost, 25

2.1.7SupportVectorMachine, 26

2.1.8NaiveBayes,kNN,k-Means, 29

2.1.9DimensionalityReduction, 35

2.2MLAlgorithmAnalysis, 37

2.2.1LogisticRegression, 37

2.2.2DecisionTreeClassifiers, 39

2.2.3DimensionalityReductionTechniques, 48 References, 52

3ArtificialNeuralNetworks, 55

3.1Multi-layerFeedforwardNeuralNetworks, 55

3.1.1SingleNeurons, 55

3.1.2WeightsOptimization, 57

3.2FIRArchitecture, 60

3.2.1SpatialTemporalRepresentations, 60

3.2.2NeuralNetworkUnfolding, 60

3.2.3Adaptation, 62

3.3TimeSeriesPrediction, 68

3.3.1AdaptationandIteratedPredictions, 68

3.4RecurrentNeuralNetworks, 69

3.4.1FiltersasPredictors, 69

3.4.2FeedbackOptionsinRecurrentNeuralNetworks, 71

3.4.3AdvancedRNNArchitectures, 77

3.5CellularNeuralNetworks(CeNN), 81

3.6ConvolutionalNeuralNetwork(CoNN), 84

3.6.1CoNNArchitecture, 85

3.6.2LayersinCoNN, 87 References, 95

4ExplainableNeuralNetworks, 97

4.1ExplainabilityMethods, 99

4.1.1TheComplexityandInteroperability, 99

4.1.2GlobalVersusLocalInterpretability, 100

4.1.3ModelExtraction, 101

4.2RelevancePropagationinANN, 103

4.2.1Pixel-wiseDecomposition, 104

4.2.2Pixel-wiseDecompositionforMultilayerNN, 107

4.3RuleExtractionfromLSTMNetworks, 110

4.4AccuracyandInterpretability, 112

4.4.1FuzzyModels, 113

4.4.2SVR, 120

4.4.3CombinationofFuzzyModelsandSVR, 123 References, 129

5GraphNeuralNetworks, 135

5.1ConceptofGraphNeuralNetwork(GNN), 135

5.1.1ClassificationofGraphs, 136

5.1.2PropagationTypes, 137

5.1.3GraphNetworks, 143

5.2CategorizationandModelingofGNN, 144

5.2.1RecGNNs, 144

5.2.2 ConvGNNs, 147

5.2.3GraphAutoencoders(GAEs), 152

5.2.4STGNNs, 155

5.3ComplexityofNN, 156

5.3.1LabeledGraphNN(LGNN), 157

5.3.2ComputationalComplexity, 164

Appendix5.ANotesonGraphLaplacian, 170 Appendix5.BGraphFourierTransform, 173 References, 175

6LearningEquilibriaandGames, 179

6.1LearninginGames, 179

6.1.1LearningEquilibriaofGames, 182

6.1.2CongestionGames, 184

6.2OnlineLearningofNashEquilibriainCongestionGames, 196

6.3MinorityGames, 202

6.4NashQ-Learning, 204

6.4.1 Multi-agentQ-Learning, 205

6.4.2Convergence, 207

6.5RoutingGames, 211

6.5.1NonatomicSelfishRouting, 211

6.5.2AtomicSelfishRouting, 214

6.5.3ExistenceofEquilibrium, 216

6.5.4ReducingthePOA, 218

6.6RoutingwithEdgePriorities, 220

6.6.1ComputingEquilibria, 222 References, 224

7AIAlgorithmsinNetworks, 227

7.1ReviewofAI-BasedAlgorithmsinNetworks, 227

7.1.1TrafficPrediction, 227

7.1.2TrafficClassification, 228

7.1.3TrafficRouting, 230

7.1.4CongestionControl, 231

7.1.5ResourceManagement, 233

7.1.6FaultManagement, 234

7.1.7QoSandQoEManagement, 235

7.1.8NetworkSecurity, 236

7.2MLforCachinginSmallCellNetworks, 237

7.2.1SystemModel, 238

7.3Q-Learning-BasedJointChannelandPowerLevelSelectioninHeterogeneousCellular Networks, 243

7.3.1StochasticNoncooperativeGame, 247

7.3.2Multi-AgentQ-Learning, 248

7.3.3Q-LearningforChannelandPowerLevelSelection, 250

7.4MLforSelf-OrganizingCellularNetworks, 252

7.4.1LearninginSelf-Configuration, 254

7.4.2RLforSONCoordination, 256

7.4.3SONFunctionModel, 257

7.4.4ReinforcementLearning, 260

7.5RL-BasedCaching, 267

7.5.1SystemModel, 267

7.5.2OptimalityConditions, 271

7.6BigDataAnalyticsinWirelessNetworks, 274

7.6.1EvolutionofAnalytics, 275

7.6.2Data-DrivenNetworkOptimization, 276

7.7GraphNeuralNetworks, 279

7.7.1NetworkVirtualization, 279

7.7.2GNN-BasedDynamicResourceManagement, 282

7.7.3LearningandAdaptation, 285

7.8DRLforMultioperatorNetworkSlicing, 291

7.8.1SystemModel, 291

7.8.2SystemOptimization, 295

7.8.3GameEquilibriabyDRL, 296

7.9DeepQ-LearningforLatency-LimitedNetworkVirtualization, 302

7.9.1SystemModel, 304

7.9.2LearningandPrediction, 306

7.9.3DRLforDynamicVNFMigration, 310

7.10Multi-ArmedBanditEstimator(MBE), 317

7.10.1SystemModel, 317

7.10.2SystemPerformance, 323

7.11NetworkRepresentationLearning, 327

7.11.1NetworkProperties, 328

7.11.2UnsupervisedNRL, 332

7.11.3Semi-SupervisedNRL, 340 References, 344

PartIIQuantumComputing, 361

8FundamentalsofQuantumCommunications, 363

8.1Introduction, 363

8.2QuantumGatesandQuantumComputing, 372

8.2.1QuantumCircuits, 376

8.2.2QuantumAlgorithms, 381

8.3QuantumFourierTransform(QFT), 386

8.3.1QFTVersusFFTRevisited, 391 References, 396

9QuantumChannelInformationTheory, 397

9.1CommunicationOvera Channel, 398

9.2QuantumInformationTheory, 401

9.2.1DensityMatrixandTraceOperator, 401

9.2.2QuantumMeasurement, 404

9.3 ChannelDescription, 407

9.3.1 ChannelEntropy, 410

9.3.2SomeHistory, 412

9.4 ChannelClassicalCapacities, 414

9.4.1CapacityofClassicalChannels, 415

9.4.2ThePrivateClassicalCapacity, 419

9.4.3TheEntanglement-AssistedClassicalCapacity, 420

9.4.4TheClassicalZero-ErrorCapacity, 421

9.4.5Entanglement-AssistedClassicalZero-ErrorCapacity, 427

9.5 ChannelQuantumCapacity, 431

9.5.1PreservingQuantumInformation, 431

9.5.2QuantumCoherentInformation, 433

9.5.3ConnectionBetweenClassicalandQuantumInformation, 434

9.6QuantumChannelExamples, 437

9.6.1ChannelMaps, 437

9.6.2Capacities, 440

9.6.3QChannelParameters, 440 References, 445

10QuantumErrorCorrection, 451

10.1StabilizerCodes, 458

10.2SurfaceCode, 465

10.2.1TheRotatedLattice, 468

10.3Fault-TolerantGates, 471

10.3.1FaultTolerance, 472

10.4TheoreticalFramework, 474

10.4.1ClassicalEC, 474

10.4.2TheoryofQEC, 478

10.ABinaryFieldsandDiscreteVectorSpaces, 492

10.BSomeNoisePhysics, 494 References, 496

11QuantumSearchAlgorithms, 499

11.1QuantumSearchAlgorithms, 499

11.1.1TheDeutschAlgorithm, 499

11.1.2TheDeutsch–JozsaAlgorithm, 499

11.1.3Simon’sAlgorithm, 500

11.1.4Shor’sAlgorithm, 500

11.1.5QuantumPhaseEstimationAlgorithm, 501

11.1.6Grover’sQuantumSearchAlgorithm, 502

11.1.7Boyer–Brassard–Høyer–TappQSA, 504

11.1.8Dürr–HøyerQSA, 505

11.1.9QuantumCountingAlgorithm, 506

11.1.10QuantumHeuristicAlgorithm, 507

11.1.11QuantumGA, 507

11.1.12Harrow–Hassidim–LloydAlgorithm, 508

11.1.13QuantumMeanAlgorithm, 508

11.1.14QuantumWeightedSumAlgorithm, 509

11.2PhysicsofQuantumAlgorithms, 510

11.2.1ImplementationofDeutsch’sAlgorithm, 511

11.2.2ImplementationofDeutsch–JozsaAlgorithm, 513

11.2.3BernsteinandVazirani’sImplementation, 514

11.2.4ImplementationofQFT, 515

11.2.5EstimatingArbitraryPhases, 516

11.2.6ImprovingSuccessProbabilityWhenEstimatingPhases, 518

11.2.7TheOrder-FindingProblem, 518

11.2.8ConcatenatedInterference, 522 References, 541

12QuantumMachineLearning, 543

12.1QMLAlgorithms, 543

12.2QNNPreliminaries, 547

15.2.2Multiple-ObjectiveOptimizationModel, 713 x Contents

12.3QuantumClassifierswithML:Near-TermSolutions, 550

12.3.1TheCircuit-CentricQuantumClassifier, 552

12.3.2Training, 558

12.4GradientsofParameterizedQuantumGates, 560

12.5ClassificationwithQNNs, 568

12.5.1Representation, 570

12.5.2Learning, 572

12.6QuantumDecisionTreeClassifier, 575

12.6.1ModeloftheClassifier, 575 AppendixMatrixExponential, 579 References, 585

13QCOptimization, 593

13.1HybridQuantum-ClassicalOptimizationAlgorithms, 593

13.1.1QAOA, 598

13.2ConvexOptimizationinQuantumInformationTheory, 601

13.2.1RelativeEntropyofEntanglement, 607

13.3QuantumAlgorithmsforCombinatorialOptimizationProblems, 609

13.4QCforLinearSystemsofEquations, 614

13.4.1AlgorithminBrief, 616

13.4.2DetailedDescriptionoftheAlgorithm, 618

13.4.3ErrorAnalysis, 620

13.5QuantumCircuit, 625

13.6QuantumAlgorithmforSystemsofNonlinearDifferentialEquations, 628 References, 632

14QuantumDecisionTheory, 637

14.1PotentialEnablersforQc, 637

14.2QuantumGameTheory(QGT), 641

14.2.1Definitions, 642

14.2.2QuantumGames, 651

14.2.3QuantumGameforSpectrumSharing, 660

14.3QuantumDecisionTheory(QDT), 665

14.3.1Model:QDT, 668

14.4PredictionsinQDT, 676

14.4.1UtilityFactors, 679

14.4.2ClassificationofLotteriesbyAttractionIndices, 681 References, 688

15QuantumComputinginWirelessNetworks, 693

15.1QuantumSatelliteNetworks, 693

15.1.1Satellite-BasedQKDSystem, 695

15.1.2QSNArchitecture, 696

15.1.3RoutingandResourceAllocationAlgorithm, 699

15.2QCRoutingforSocialOverlayNetworks, 706

15.2.1SocialOverlayNetwork, 707

15.3QKDNetworks, 713

15.3.1QoSinQKDOverlayNetworks, 715

15.3.2AdaptiveQoS-QKDNetworks, 716

15.3.3RoutingProtocolforQKDNetwork, 721 References, 726

16QuantumNetworkonGraph, 733

16.1OptimalRoutinginQuantumNetworks, 733

16.1.1NetworkModel, 735

16.1.2Entanglement, 736

16.1.3OptimalQuantumRouting, 738

16.2QuantumNetworkonSymmetricGraph, 744

16.3QWs, 747

16.3.1DQWL, 748

16.3.2PerformanceStudyofDQWL, 749

16.4MultidimensionalQWs, 753

16.4.1TheQuantumRandomWalk, 755

16.4.2QuantumRandomWalksonGeneralGraphs, 757

16.4.3Continuous-TimeQuantumRandomWalk, 760

16.4.4SearchingLarge-ScaleGraphs, 763 References, 769

17QuantumInternet, 773

17.1SystemModel, 775

17.1.1RoutingAlgorithms, 777

17.1.2QuantumNetworkonGeneralVirtualGraph, 781

17.1.3QuantumNetworkonRingandGridGraph, 782

17.1.4QuantumNetworkonRecursivelyGeneratedGraphs(RGGs), 786

17.1.5RecursivelyGeneratedVirtualGraph, 787

17.2QuantumNetworkProtocolStack, 789

17.2.1Preliminaries, 789

17.2.2QuantumNetworkProtocolStack, 795

17.2.3Layer3 – ReliableStateLinking, 801

17.2.4Layer4 – RegionRouting, 806 References, 814

Index, 821

Preface

Atthisstage,itisanticipatedthat6Gwirelessnetworkswillbebasedonmassiveuseofmachine learning(ML)andartificialintelligence(AI),while7Gwillalreadyincludehybridsofclassicaland quantumcomputing(QC)technologies.Inanticipationofthisevolution‚ wehavestructuredthe booktocontinuouslymove,throughaseriesofchapters,fromthepresentationofMLalgorithmsto thefinalchaptercoveringtheprinciplesofquantuminternet.Inthisprocess,wealsoprovidechapterscoveringthecomplexrelationshipbetweenthetwotechnologies,ontopicssuchasquantum ML,quantumgametheory,andquantumdecisiontheory.ThefocusofthebookisnotontheproblemhowtoconstructaquantumcomputerbutratherhowQCtechnologyenablesnewparadigms inthemodeling,analysis,anddesignofcommunicationnetworks,whatisnowadaysreferredtoas QC-enabledcommunications.Thesenewparadigmsbenefitfromthesignificantcomputation speedupenabledbythecomputingparallelismofquantumcomputersandthenewquantum searchalgorithmsdevelopedsofarforbigdataprocessing.Quantumcryptographyandquantum keydistribution(QKD)enablenewsolutionstotheproblemofsecurityinadvancednetworks. Thisbookisalsodesignedtofacilitateanewconceptineducationinthisfield.Insteadofthe classicalapproachofprovidingalistofproblemsattheendofachapter,weintroduceaseries ofdesignexamplesthroughoutthebookthatrequireteamworkbyagroupofstudentsforsolving complexdesignproblems,includingreproductionoftheresultspresentedinthebook.This approachturnedouttoberatherpopularwithourstudentsatUniversityofMassachusettsat Amherst.Wehopethatthebookprovidesusefulmaterialfornotonlystudentsbutalsofor researchers,educators,andregulatoryprofessionalsinthisfield.

TheAuthors January2021

Amherst,Massachusetts

1.1Motivation

Owingtotheincreaseinthedensityandnumberofdifferentfunctionalitiesinwirelessnetworks, thereisanincreasingneedfortheuseofartificialintelligence(AI)inplanningthenetworkdeployment,runningtheiroptimization,anddynamicallycontrollingtheiroperation.Machinelearning (ML)algorithmsareusedtopredicttrafficandnetworkstateinordertoreserveresourcesfor smoothcommunicationwithhighreliabilityandlowlatencyinatimelyfashion.Bigdatamining isusedtopredictcustomerbehaviorandpre-distribute(caching)theinformationcontentacrossthe networkinatimelyfashionsothatitcanbeefficientlydeliveredassoonasitisrequested.IntelligentagentscansearchtheInternetonbehalfofthecustomerinordertofindthebestoptions whenitcomestobuyinganyproductonline.ThisbookreviewsML-basedalgorithmswithanumberofcasestudiessupportedbyPythonandRprograms.Itdiscussesthelearningalgorithmsused indecisionmakingbasedongametheoryandanumberofspecificapplicationsinwirelessnetworkssuchaschannel,networkstate,andtrafficprediction.

WebeginthebookwithacomprehensivesurveyofAIlearningalgorithms.Thesealgorithmsare usedinthepredictionofthenetworkparametersforefficientnetworkslicing,customerbehavior forcontentcachingacrossthenetwork,orforefficientnetworkcontrolandmanagement.Subsequently,wefocusonnetworkapplicationswithanemphasisonAI-basedlearningalgorithmsused forreachingequilibriaingamesusedamongdifferentpartiesinavarietyofnewbusinessmodelsin communicationnetworks.Thisincludescompetitionbetweennetworkoperators,serviceproviders,orevenusersindynamicnetworkarchitecturesofuser-providednetworks.

ThebookalsocoversindetailanumberofspecificapplicationsofAIfordynamicreadjusting networkbehaviorbasedontheobservationofitsstate,trafficvariation,anduserbehavior.This includeschannelandpowerlevelselectionincellularnetworks,networkself-organization,proactivecaching,bigdatalearning,graphneuralnetwork(GNN),andmulti-armedbanditestimators.

Whyquantumcomputing?Theever-reducingtransistorsizefollowingMoore’slawisapproachingthepointwherequantumeffectspredominateintransistoroperation.Thisspecifictrend impliesthatquantumeffectsbecomeunavoidable,hencemakingresearchonquantumcomputing (QC)systemsanurgentnecessity.Infact,aquantumannealingchipsetisalreadycommercially availablefromD-Wave1.

Apartfromthequantumannealingarchitecture,gate-basedarchitecture,whichrelieson buildingcomputationalblocksusingquantumgatesinasimilarfashiontoclassicallogicgates,

isattractingincreasingattentionduetotherecentadvancesinquantumstabilizercodes,whichare capableofmitigatingthede-coherenceeffectsencounteredbyquantumcircuits.Intermsofimplementation,IBMhasinitiallyproduced53-qubitsquantumcomputer[1]andplanstohave1-million qubitsby2030[2].D-WaveTwo512qubitprocessors[3]arebuiltinGoogleandNASAquantum computer.Withthisrecentdevelopments,Quantumcomputinghasbecomeacommercialreality anditmaybeusedinwirelesscommunicationssystemsinordertospeedupspecificprocessesdue toitsinherentparallelizationcapabilities.

Whereasaclassicalbitmayadoptthevalues0or1,aquantumbit,orqubit,mayhavethevalues |0>,|1>,oranysuperpositionofthetwo,wherethenotation|>isthecolumnvectorofaquantum state.Iftwoqubitsareused,thenthecompositequantumstatemayhavethevalues|00>,|01>, |10>,and|11>simultaneously.Ingeneral,byemployingbbitsinaclassicalregister,oneoutof b2 combinationsisrepresentedatanytime.Bycontrast,inaquantumregisterassociatedwithb qubits,thecompositequantumstatemaybefoundinasuperpositionofallb2 valuessimultaneously.Therefore,applyingaquantumoperationtothequantumregisterwouldresultinaltering allb2 valuesatthesametime.Thisrepresentstheparallelprocessingcapabilityofquantum computing.

Inadditiontosuperiorcomputingcapabilities,multiplequantumalgorithmshavebeenproposed,whicharecapableofoutperformingtheirclassicalcounterpartsinthesamecategories ofproblems,byeitherrequiringfewercomputationalsteps,orbyfindingabettersolutionto thespecificproblem.Inthisbook,wewillfocusontheemploymentofquantumalgorithms inclassicalcommunicationsystems,whichisnowadaysreferredtoasquantum-assisted communications.

Inthefollowingsections,werevisittheMLmethodsinthecontextofquantum-assistedalgorithmsforMLandthequantummachinelearning(QML)framework.Quantumprinciplesbased onemergingcomputingtechnologieswillbringinentirelynewmodesofinformationprocessing. Anoverviewofsupervised,unsupervised,andreinforcementlearning(RL)methodsforQMLis presentedinthissegmentofthebook.

Currently,5Gnetworkshaveenteredintothecommercializationphase,whichmakesitappropriatetolaunchastrongefforttoconceptualizethefuturevisionofthenextgenerationofwireless networks.Theincreasingsize,complexity,services,andperformancedemandsofcommunication networksnecessitateplanningandconsultationforenvisioningnewtechnologiestoenableand harmonizefutureheterogeneousnetworks.AnoverwhelminginterestinAImethodsisseenin recentyears,whichhasmotivatedtheprovisionofessentialintelligenceto5Gnetworks.However, thisprovisionislimitedtotheperformanceofdifferentisolatedtasksofoptimization,control,and management.Therecentsuccessofquantum-assistedanddata-drivenlearningmethodsincommunicationnetworkshasledtotheircandidatureasenablersoffutureheterogeneousnetworks. Thissectionreviewsanovelframeworkfor6G/7Gnetworks,wherequantum-assistedMLand QMLareproposedasthecoreenablersalongwithsomepromisingcommunicationtechnology innovations.

Therelevanceoftheresearchfieldsintegratedthroughoutthisbookcanbeeasilyrecognized withintheNationalScienceFoundation(NSF)listofresearchprioritiesinscienceandtechnology: These10areasspecifiedbyNSFinclude(i)AIandML;(ii)highperformancecomputing,semiconductors,andadvancedcomputerhardware;(iii)quantumcomputingandinformationsystems; (iv)robotics,automation,andadvancedmanufacturing;(v)naturaloranthropogenicdisasterprevention;(vi)advancedcommunicationstechnology;(vii)biotechnology,genomics,andsynthetic biology;(viii)cybersecurity,datastorage,anddatamanagementtechnologies;(ix)advanced

energy;and(x)materialsscience,engineering,andexplorationrelevanttootherkeytechnology areas.The10areaswouldberevisitedeveryfouryears.

1.2BookStructure

ThefirstpartofthebookcoversselectedtopicsinML,andthesecondpartpresentsanumberof topicsfromQCrelevantfornetworking.

Chapter2(MachineLearningAlgorithms):Thischapterpresentsanintroductorydiscussionof manybasicMLalgorithmsthatareoftenusedinpracticeandnotnecessarydirectlyrelatedtonetworkingproblems.However,theywillpresentalogicalbasisfordevelopingmoresophisticated algorithmsthatareusednowadaystoefficientlysolvevariousproblemsinthisfield.Thesealgorithmsincludelinearregression,logisticregression,decisiontree(regressiontreesvs.classification trees),andworkingwithdecisiontrees[4]inRandPython.Inthischapter,weanswerthequestions:Whatisbagging?Whatisrandomforest?Whatisboosting?Whichismorepowerful:GBMor XGBoost?WealsoexplainthebasicsofworkinginRandPythonwithGBM,XGBoost,SVM(supportvectormachine),NaiveBayes,kNN,K-means,randomforest,dimensionalityreductionalgorithms[5,6],gradientboostingalgorithms,GBM,XGBoost,LightGBM,andCatBoost[7,8].

Chapter3(ArtificialNeuralNetworks):Wearewitnessingtherapid,widespreadadoptionofAI [9]inourdailylife,whichisacceleratingtheshifttowardamorealgorithmicsociety.Ourfocusis onreviewingtheunprecedentednewopportunitiesopenedupbyusingAIindeployingand optimizationofcommunicationnetworks.Inthischapter,wewilldiscussthebasisofartificialneuralnetworks(ANNs)[10]includingmultilayerneuralnetworks,trainingandbackpropagation, finite-impulseresponse(FIR)architecturespatialtemporalrepresentations,derivationoftemporal backpropagation,applicationsintimeseriesprediction,auto-regressivelinearprediction,nonlinearprediction,adaptationanditeratedpredictionsaswellasmultiresolutionFIRneural-networkbasedlearningalgorithmappliedtonetworktrafficprediction.Trafficpredictionisimportantfor timelyreconfigurationofthenetworktopologyortrafficreroutingtoavoidcongestionornetwork slicing.

Chapter4(ExplainableNN):EvenwiththeadvancementsofAIdescribedinthepreviouschapter,akeyimpedimenttotheuseofAI-basedsystemsisthattheyoftenlacktransparency.Indeed, theblack-boxnatureofthesesystemsallowspowerfulpredictions,buttheycannotbedirectly explained.ThisproblemhastriggeredanewdebateonexplainableAI(XAI)[11–14].

XAIisaresearchfieldthatholdssubstantialpromiseforimprovingthetrustandtransparencyof AI-basedsystems.ItisrecognizedasthemainsupportforAItocontinuemakingsteadyprogress withoutdisruption.ThischapterprovidesanentrypointforinterestedresearchersandpractitionerstolearnkeyaspectsoftheyoungandrapidlygrowingbodyofresearchrelatedtoXAI.Here, wereviewtheexistingapproachesregardingthetopic,discusstrendssurroundingrelatedareas,and presentmajorresearchtrajectoriescoveringanumberofproblemsrelatedtoExplainableNN.This,in particular,includessuchtopicsasusingXAI:theneedandtheapplicationopportunitiesforXAI; explainabilitystrategies:complexity-relatedmethods,scoop,andmodel-relatedmethods;XAImeasurement:evaluatingexplanations;XAIperception:humanintheloop; XAIantithesis:explainorpredictdiscussion;towardmoreformalism;human-machineteaming;explainabilitymethods composition;otherexplainableintelligentsystems;andtheeconomicperspective.

Chapter5(GraphNeuralNetworks):Graphtheoryisabasictoolformodelingcommunication networksintheformG(N,E),whereNisthesetofnodesandEthesetoflinks(edges)interconnectingthenodes.Recently,themethodologyofanalyzinggraphswithMLhavebeenattracting

increasingattentionbecauseofthegreatexpressivepowerofgraphs;thatis,graphscanbeusedto representalargenumberofsystemsacrossvariousareasincludingsocialscience(socialnetworks) [15,16],naturalscience(physicalsystems[17,18]andprotein–proteininteractionnetworks[19]), knowledgegraphs[20],andmanyotherresearchareas[21]includingcommunicationnetworks, whichisourfocusinthisbook.Asauniquenon-EuclideandatastructureforML,graphanalysis focusesonnodeclassification,linkprediction,andclustering.GNNsaredeep-learning-basedmethodsthatoperateongraphdomain.Duetoitsconvincingperformanceandhighinterpretability, GNNhasrecentlybeenawidelyappliedgraphanalysismethod.Inthischapter,wewillillustrate thefundamentalmotivationsofGNNsanddemonstratehowwecanusethesetoolstoanalyzenetworkslicing.ThechapterincludesGNNmodeling,computationofthegraphstate,thelearning algorithm,transitionandoutputfunctionimplementations,linearandnonlinear(non-positional) GNN,computationalcomplexity,andexamplesofWebpagerankingandnetworkslicing.

Chapter6(LearningEquilibriaandGames):Acomprehensivenetworkoptimizationalso includesthecostofimplementingspecificsolutions.Moregenerally,allnegativeeffectscaused byacertaindecisioninthechoiceofnetworkparameterssuchascongestion,powerconsumption, andspectrummisuse,canbemodeledasacost.Ontheotherhand,mosteconomictheoryrelies onequilibriumanalysis,makinguseofeitherNashequilibriumoroneofitsrefinements[22–31]. OnejustificationofthisistoarguethatNashequilibriummightariseasaresultoflearningand adaptation.Inthischapter,weinvestigatetheoreticalmodelsoflearningingames.Avarietyof learningmodelshavebeenproposed,withdifferentmotivations.Somemodelsareexplicitattempts todefinedynamicprocessesthatleadtoNashequilibriumplay.Otherlearningmodels,suchas stimulusresponseorreinforcementmodels,wereintroducedtocapturelaboratorybehavior.These modelsdifferwidelyintermsofwhatpromptsplayerstomakedecisionsandhowsophisticated playersareassumedtobehave.Inthesimplestmodels,playersarejustmachineswhousestrategies thathaveworkedinthepast.Theymaynotevenrealizetheyareinagame.Inothermodels,players explicitlymaximizepayoffsgivenbeliefsthatmayinvolvevaryinglevelsofsophistication.Thus,we willlookatseveralapproachesincludingbestresponsedynamics(BRD),fictitiousplay(FP),RL, jointutilityandstrategylearning(JUSTE),trialanderrorlearning(TE),regretmatchinglearning, Q-learning,multi-armedbandits,andimitationlearning.

Chapter7(AIAlgorithmsinNetworks):Finally,attheendofPartIofthebook,inthischapterwe presentanextensivesetofexamplesofsolvingpracticalproblemsinnetworksbyusingAI.This includesasurveyofspecificAI-basedalgorithmsusedinnetworks,suchasforcontrolledcaching insmallcellnetworks;channelandpowerlevelselection;controllingnetworkself-organization; proactivecaching;bigdatalearningforAI-controlledresourceallocation;GNNforpredictionof resourcerequirements;andmulti-armedbanditestimatorsforMarkovchannels.

Inparticular,weconsiderAI-basedalgorithmsfortrafficclassification,trafficrouting,congestion control,resourcemanagement,faultmanagement,QualityofService(QoS)andQualityofExperience(QoE)management,networksecurity,MLforcachinginsmallcellnetworks,Q-learningbasedjointchannelandpowerlevelselectioninheterogeneouscellularnetworks,stochasticnoncooperativegame,multi-agentQ-learning,Q-learningforchannelandpowerlevelselection,ML forself-organizingcellularnetworks,learninginself-configuration,RLforSONcoordination,SON functionmodel,RL,RL-basedcaching,systemmodel,optimalityconditions,bigdataanalyticsin wirelessnetworks,evolutionofanalytics,data-drivennetworksoptimization,GNNs,networkvirtualization,GNN-baseddynamicresourcemanagement,deepreinforcementlearning(DRL)for multioperatornetworkslicing,gameequilibriabyDRL,deepQ-learningforlatencylimitednetworkvirtualization,DRLfordynamicVNFmigration,multi-armedbanditestimator(MBE), andnetworkrepresentationlearning.

Chapter8(FundamentalsofQuantumCommunications): Duringthelastfewyears,theresearch communityhasturneditsattentiontoquantumcomputing[32–36]withtheobjectiveofcombining itwithclassicalcommunicationsinordertoachievecertainperformancetargets,suchasthroughput,roundtripdelay,andreliabilitytargetsatalowcomputationalcomplexity.Aswewilldiscussin moredetailinthischapter,therearenumerousoptimizationproblemsinwirelesscommunications systemsthatmaybesolvedatareducednumberofcostfunctionevaluations(CFEs)byemploying quantumalgorithms.Althoughwedonotattempttocovertheproblemsofquantumcomputer designitself,inthischapterwewilldiscussthebasicsofQCtechnologyinordertounderstand betterhowthistechnologycanenablesignificantimprovementsinthedesignandoptimization ofcommunicationnetworks.Thesefundamentalsincludediscussionsonthequbitsystem,algebraicrepresentationofquantumstates,entanglement,geometrical(2D,3D)representationof quantumstates,quantumlogicalgates,tensorcomputing,theHadamardoperatorH,andthePauli andToffoligates.

Chapter9(QuantumChannelInformationTheory):Quantuminformationprocessingexploits thequantumnatureofinformation.Itoffersfundamentallynewsolutionsinthefieldofcomputer scienceandextendsthepossibilitiestoalevelthatcannotbeimaginedinclassicalcommunication systems.Forquantumcommunicationchannels,manynewcapacitydefinitionsweredevelopedin analogywiththeirclassicalcounterparts.Aquantumchannelcanbeusedtoachieveclassicalinformationtransmissionortodeliverquantuminformation,suchasquantumentanglement.Inthis chapter,wereviewthepropertiesofthequantumcommunicationchannel,thevariouscapacity measures,andthefundamentaldifferencesbetweentheclassicalandquantumchannels [37–43].Specifically,wewilldiscusstheprivacyandperformancegainsofquantumchannels, thequantumchannelmap,theformalmodel,quantumchannelcapacity,classicalcapacitiesof aquantumchannel,thequantumcapacityofaquantumchannel,quantumchannelmaps,and capacitiesandpracticalimplementationsofquantumchannels.

Chapter10(QuantumErrorCorrection):Thechallengeincreatingquantumerrorcorrection codesliesinfindingcommutingsetsofstabilizersthatenableerrorstobedetectedwithoutdisturbingtheencodedinformation.Findingsuchsetsisnontrivial,andspecialcodeconstructionsare requiredtofindstabilizerswiththedesiredproperties.Wewillstartthissectionbydiscussing howacodecanbeconstructedbyconcatenatingtwosmallercodes.Otherconstructionsinclude methodsforrepurposingclassicalcodestoobtaincommutingstabilizerchecks[44–47].Here, wewilloutlineaconstructionknownasthesurfacecode[48,49].Therealizationofasurfacecode logicalqubitisakeygoalformanyquantumcomputinghardwareefforts[50–54].Thecodesbelong toabroaderfamilyofso-calledtopologicalcodes[55].Inthisframework,withinthischapterwe willdiscussstabilizercodes,surfacecodes,therotatedlattice,fault-tolerantgates,faulttolerance, theoreticalframework,classicalerrorcorrection,andthetheoryofquantumerrorcorrectionin additiontosomeauxiliarymaterialonbinaryfieldsanddiscretevectorspaces,andnoisephysics.

Chapter11(QuantumSearchAlgorithms):Theappetiteforfaster,morereliable,greener,and moresecurecommunicationscontinuestogrow.Thestate-of-the-artmethodsconceivedforachievingtheperformancetargetsoftheassociatedprocessesmaybeaccompaniedbyanincreaseincomputationalcomplexity.Alternatively,degradedperformancemayhavetobeacceptedduetothe lackofjointlyoptimizedsystemcomponents.Inthischapter,weinvestigatetheemploymentof quantumcomputingforsolvingproblemsinwirelesscommunicationsystems.Byexploitingthe inherentparallelismofquantumcomputing,quantumalgorithmsmaybeinvokedforapproaching theoptimalperformanceofclassicalwirelessprocesses,despitetheirreducednumberofCFEscostfunctionevaluations.InChapter8,wehavealreadydiscussedthebasicsofquantumcomputingusing linearalgebra,beforepresentingheretheoperationofthemajorquantumalgorithmsthathavebeen

proposedintheliteratureforimprovingwirelesscommunicationssystems.Furthermore,inthe followingchapters,wewillinvestigateanumberofoptimizationproblemsencounteredbothin thephysicalandnetworklayerofwirelesscommunications,whilecomparingtheirclassicaland quantum-assistedsolutions.Morespecifically,inthischapterwewilldiscussthefollowing:quantum searchalgorithms(QSAs)forwirelesscommunicationssuchastheDeutschalgorithm,theDeutsch–Jozsaalgorithm,Simon’salgorithm,Shor’salgorithm,thequantumphaseestimationalgorithm, Grover’sQSA,theBoyer–Brassard–Høyer–TappQSA,theDürr–HøyerQSA,quantumcounting algorithm,quantumheuristicalgorithm,quantumgeneticalgorithm,Harrow–Hassidim–Lloyd algorithm,quantummeanalgorithm,andquantum-weightedsumalgorithm.

Chapter12(QuantumMachineLearning):Inthischapter,weprovideabriefdescriptionofquantummachinelearning(QML)anditscorrelationwithAI.WewillseehowthequantumcounterpartofMLismuchfasterandmoreefficientthanclassicalML.Trainingthemachinetolearnfrom thealgorithmsimplementedtohandledataisthecoreofML.Thisfieldofcomputerscienceand statisticsemploysAIandcomputationalstatistics.TheclassicalMLmethod,throughitssubsetsof deeplearning(supervisedandunsupervised),helpstoclassifyimages,recognizepatternsand speech,handlebigdata,andmanymore.Thus,classicalMLhasreceivedalotofattentionand investmentsfromtheindustry.Nowadays,duetothehugequantitiesofdatawithwhichwedeal everyday,newapproachesareneededtoautomaticallymanage,organize,andclassifythesedata. ClassicalML,whichisaflexibleandadaptableprocedure,canrecognizepatternsefficiently,but someoftheseproblemscannotbeefficientlysolvedbythesealgorithms.Companiesengagedin bigdatabasesmanagementareawareoftheselimitations,andareveryinterestedinnew approachestoaccomplishthis.TheyhavefoundoneoftheseapproachesinquantumML.However, theinterestinimplementingthesetechniquesthroughQCiswhatpavesthewayforquantumML. QML[56–59]aimstoimplementMLalgorithmsinquantumsystemsbyusingquantumproperties suchassuperpositionandentanglementtosolvetheseproblemsefficiently.ThisgivesQMLanedge overtheclassicalMLtechniqueintermsofspeedoffunctioninganddatahandling.IntheQML techniques,wedevelopquantumalgorithmstooperateclassicalalgorithmsusingaquantumcomputer.Thus,datacanbeclassified,sorted,andanalyzedusingthequantumalgorithmsofsupervisedandunsupervisedlearningmethods.Thesemethodsareagainimplementedthrough modelsofaquantumneuralnetworkorsupportvectormachine.Thisisthepointwherewemerge thealgorithmsdiscussedinPartsIandIIofthisbook.Inparticular,wewilldiscussQMLalgorithms,quantumneuralnetworkpreliminaries,quantum,classifierswithML:near-termsolutions, thecircuit-centricquantumclassifier,training,gradientsofparameterizedquantumgates,classificationwithquantumneuralnetworks,representation,learning,thequantumdecisiontreeclassifier,andthemodeloftheclassifierinadditiontosomeauxiliarymaterialonmatrixexponential. Chapter13(QuantumComputingOptimization):Convexitynaturallyarisesinmanysegmentsof quantuminformationtheory;thesetsofpossiblepreparations,processes,andmeasurementsfor quantumsystemsareallconvexsets.Manyimportantquantitiesinquantuminformationare definedintermsofaconvexoptimizationproblem,suchasquantifyingentanglement[60,61]. Sincethesetofseparableorunentangledstatesisconvex,ameasureofentanglementmaybe definedforentangledstatesoutsideofthisset,givenasuitable “distance” measure,suchasthe minimumdistancetoastateinside.Perhapsthemostwellknownofthesequantitiesistherelative entropyofentanglement.Inaddition,inthechapterwediscussanumberofoptimizationalgorithmsincludingoptimizationforhybridquantum-classicalalgorithms,thequantumapproximate optimizationalgorithm(QAOA),convexoptimizationinquantuminformationtheory,relative entropyofentanglement,quantumalgorithmsforcombinatorialoptimizationproblems,QCfor linearsystemsofequations,adesignexample(QCformultipleregression),andaquantumalgorithmforsystemsofnonlineardifferentialequations.

Chapter14(QuantumDecisionTheory):Theclassicaldecision-makingprocessismostlybased onexpectedutilitytheory,anditsperformancesignificantlydegradesinscenariosinvolvingrisk anduncertainty[62].Inmostoftheclassicaldecision-makingprocesses,thepossibilityofmakingcorrectpredictionscanbestronglyaffect edbythenatureofthesurroundingenvironment suchastheunknownstochasticorvaryingenvironment.Furthermore,inscenarioshaving incompleteorpartiallyreliableinformationorincompletepreferencerelations,anyprediction islikelytobejustpartialandqualitative.Toaddressthis,quantumdecisiontheory(QDT)seems tobeapromisingapproachandhasbeenalreadyinvestigatedintheexistingliterature[62,63]. Also,theprocessofrepresentingallstepsofa decisionprocessmathematicallyinordertoallow quantitativepredictionissignificantnotonlyforthedecisiontheorybutalsofordevelopingartificialquantumintelligence,whichcanworkonlyfortheoperationsdefinedinmathematical terms[64].

WiththerecentadvancesinquantuminformationandQC,therehasbeenatrendofformulating classicalgametheoryusingquantumprobabilityamplitudestowardanalyzingtheimpactofquantumsuperposition,entanglement,andinterferenceontheagents’ optimalstrategies[65].Quantum gametheory(QGT)ingeneralreplacestheclassicalprobabilitiesofgametheorywithquantum amplitudesbycreatingthepossibilityofneweffectsarisingfromentanglementorsuperposition. Themaindifferencebetweentheclassicalgameandthequantumgameisthatclassicalgamesperformcalculationsintheprobabilityspace,whereasquantumgamesoperateintheHilbertspace. Quantumgametheoretictechniquescanbeutilizedforinvestigatingsuitablesolutionsinquantum communication[66]andquantuminformationprocessing[67].Inthisregard,anarticle[65]providedanintroductiontoquantumtheoryalongwithsomerelatedworksanddiscussedsomewellknownquantumgamesincludingthequantumpennyflip,Eisert’squantumprisoners’ dilemma, andquantumParrondogames.Furthermore,arecentarticle[68]analyzedtheexistingworkson quantumgamesfromthreeperspectives,namely,co-authorship,co-occurrence,andco-citation, andalsoreviewedthemainquantumgamemodelsandapplications.Underthisumbrella,the chapterdiscussesQGT,definitions,quantumgames,adesignexample(quantumroutinggames), quantumgameforspectrumsharing,QDT,amodel(QDT),predictionsinQDT,utilityfactors,and classificationoflotteriesbyattractionindices.

Chapter15(QuantumComputinginWirelessNe tworks):Inthischapter,wediscussseveral examplesofwirelessnetworkdesignbasedonthetoolsenabledbyquantumcomputing.Both satelliteandterrestrialnetworksareconsidered.Traditionalsecuritytechniquesmostlyfocus ontheencryptionofcommunication,wheresecuritydependsonthemathematicalcomplexity. However,encryptionmethodologiesarebecomi nglessreliableaseavesdroppersandattackers aregainingpowerfulcomputingability.AsalreadydiscussedinChapters8and11,quantum cryptographyisanewcryptographictechnologyforgeneratingrandomsecretkeystobeused insecurecommunication.Quantumcryptographycanprovidecommunicationsecuritybased onthelawsofquantumphysics(e.g.,theno-cloningtheoremanduncertaintyprinciple).However,thequantumkeyhastobedistributedoverthecommunicationnetworktobeusedbythe sendersandreceivers.

Reference[69]demonstratedthefeasibilityofquantumkeydistribution(QKD)overopticalnetworks.SuchaQKDnetworkcanbeconstructedbydistributingend-to-endsecret(quantum)keys throughtrustedrepeaters(e.g.,basedonthepoint-to-pointBB84protocol).References[70,71]also reportedsuchoptical-fiber-basedQKDnetworks,usedtosecuremetropolitanandbackbonenetworks.RecentstudiesdiscussedabouttheintegrationofQKDandclassicalnetworks,suchasQKD overwavelengthdivisionmultiplexing(WDM)networks[72,73]andQKD-enabledsoftwaredefinednetworks(SDN)[74].WhileimplementingQKDinterrestrialopticalnetworks,distributing secretkeysoveralongdistance(e.g.,acrosstheglobe)ischallenging.Single-photonsignals

transmittedoverlong-distanceopticalfibersufferfromhighlossesanddepolarization.Hence,carryingthekeysusingopticalfiberoverlongdistances(e.g.,1000km)isnotaneffectivesolution[75].

Toaddresstheselimitations,anexperimentedfree-spaceQKDhasbeenstudiedinrecentyears. Incontrasttoopticalfibers,thefree-spacephotonwillexperiencenegligiblelossinvacuum,makingitfeasibletodistributesecretkeysoverthousandsofkilometers.Althoughtheopticalbeamofa satellite-to-groundlinkcansufferfromatmosphericloss,mostofthespaceisempty,whichmakes thechannellosslessthanthatforalongfiber[75,76].Thequantumsatellite Micius,launchedin 2016forquantumcommunicationexperiments,hassuccessfullydemonstratedsatellite-to-ground QKDusingsingle-photonsource[77].In2017,agroundfree-spaceQKDexperimentwasconducted usingtelecomwavelengthindaylightanddemonstratedthefeasibilityofinter-satelliteQKDindaylight[78,79].Therefore,satellite-basedQKDisapromisingmethodfordistributingquantumkeys betweentwoultra-long-distancepartiesontheground.

Sincethecoverageandflyovertimeofonesatelliteislimited,agroupofquantumsatellitescanbe usedastrustedrepeaterstoservegroundstations.Recently,researchershaveproposeda “network ofquantumsatellites” torealizeglobal-scalequantumcommunications[80,81].Theauthorsof[78] proposedaQKDsatellitenetworksarchitecturebasedonquantumrepeaters.Theresearchersalso proposedthetrusted-repeater-basedsatelliteQKDscheme[79–83].TheirschemeisbasedonBB84 protocolsincequantumrepeatersarestillfarfrombeingimplemented.Reference[84]investigates thepossibleschemesoffree-spaceQKDusinginter-satellitelinksandanalyzedthepropertiesof satellite-groundlinks.Thesestudiesmotivatedtheconceptpresentedhere[85],whichisacontributiontowardtheadvancementofthestateofthe-artinsatellite-basedQKDnetworks.

Priorstudiesenvisionthataquantum-capablesatelliteconstellationcanbeformedtoconstruct globalQKD(similartotraditionalsatelliteconstellationssuchasIRIDIUM[86]).Inrecentproposals,quantumsatelliteswillusealowearthorbit(LEO)tobenefitfromitslowchannelloss.Buta LEOsatellitecanaccessaparticulargroundstationforalimitedtimeoftheday[87].Thislimited coveragemayleadtoashortageofsecretkeysbetweensatelliteandground.Bycontrast,geostationaryearthorbit(GEO)satellitescanaccessgroundstationscontinuously,allday.However,their signalcansufferfromhighchannellossandalimitedkeygenerationrate.

In2017,GermanresearcherssuccessfullymeasuredquantumsignalsthatweresentfromaGEO toagroundstation[88].Italianresearchershavealsodemonstratedthefeasibilityofquantumcommunicationsbetweenhigh-orbitingglobalnavigationsatellitesandagroundstation[89].The ChineseAcademyofScienceshasfutureprojectstolaunchhigher-altitudesatellites[77–79]. Accordingtotheresearchers,thefuturequantumsatelliteconstellationwillcomprisesatellitesin highandloworbits[90].Thus,combiningbothGEOandLEOsatellitestobuildQKDnetworks isaresearchdirectionworthexploring.Withinthisscope,inthischapterwewilladdressthefollowingproblems:quantumsatellitenetworks,satellite-basedQKDsystem,quantumsatellitenetwork architecture,aroutingandresourceallocationalgorithm,QCroutingforsocialoverlaynetworks, socialoverlaynetworks,amultiple-objectiveoptimizationmodel,QKDNetworks,QoSinQKD overlaynetworks,adaptiveQoS-QKDnetworks,andaroutingprotocolforQKDnetworks.

Chapter16(QuantumNetworkonGraph)

Tofullybenefitfromtheadvantagesofquantum technology,itisnecessarytodesignand implementquantumnetworks[91,92]thatareabletoconnectdistantquantumprocessors throughremotequantumentanglementdistribution.However,despitethetremendousprogress ofquantumtechnologies,efficientlong-distance entanglementdistributionremainsakeyproblem,duetotheexponentialdecayofthecommunicationrateasafunctionofdistance[93,94]. Asolutiontocounteracttheexponentialdecaylo ssistheadoptionofquantumrepeaters[95,96]. Insteadofdistributingentanglementoveralonglink,entanglementwillbegeneratedthrough

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