Resource Allocation & Physical Layer Security in Wireless Communication Systems

112 Pages·2015·0.86 MB·English

Resource Allocation & Physical Layer
Security in Wireless Communication
Systems
Sotiris Karachontzitis
Department of Computer Engineering & informatics
University of Patras
This dissertation is submitted for the degree of
Doctor of Philosophy
at the
University of Patras
University of Patras July 2015

Acknowledgements
First of all, I would like to sincerely thank my advisor Professor Kostas Berberidis for his
leading and his generous support and encouragement during my PhD course. I will always
bedeeplyindebtedtohimfortheopportunitytopursuemydoctoraldissertationandtogrow
upasaresearchscientist. Iamalsogratefultomyco-advisorProfessorIoannisKrikidisfor
his constant guidance and his invaluable contribution in time, motivation and ideas, with-
out of which it would be impossible for me to finish this work. I would like to express
my special thanks to Professor Anastasios Dagiuklas and Dr. Stelios Timotheou for their
valuable guidance and contributions during our collaborative research. Both of them are
considered not only as brilliant professionals and colleagues but also as best friends. Fur-
ther, I would like to thank my committee members, Professor Angeliki Alexiou, Professor
Theodore Antonakopoulos, Professor Emmanouel Psarakis and Professor Emmanouel Var-
varigos for their precious time and their valuable comments and suggestions. Also, I thank
the members of the Signal Processing and Communications Lab, past and present, for all
the time we shared together during my stay at the Lab. Finally, I would like to thank my
parents for their unconditional support in my life and my sweet Angel for her continuous
understandingandlove. Thankyouall!

Abstract
In this thesis, the problem of resource allocation is investigated in multiuser, multi-antenna
downlink wireless systems in which spatial multiplexing is employed in the physical layer.
The thesis consists of two main parts; in the first, the interest is focused on optimizing
system’s performance in terms of users’ transmission rate. Under this context, a low-
complexity but highly performing user selection algorithm is presented for the flat-fading
channel,whenzero-forcingbeamformingisemployedattheBSandtheaimistomaximize
system’s throughput. For the more interesting case where the transmission is performed si-
multaneouslyoveranumberofparallelsubchannels,twofairness-awareresourceallocation
problemsareinvestigatedinthesensethatcertainQoSconstraintsareconsidered. Typically,
this kind of problems fall within the NP class because of the integer nature of the involved
user selection procedure. Hence, several near-optimal and heuristic solutions are proposed.
In the second part of the thesis, the concept of physical layer security is integrated into the
resource allocation procedure and the secrecy rate becomes the critical quantity of the con-
sideredproblems. Theconsideredsetupconsistsofamultiuserdownlinksysteminwhicha
passive eavesdropper tries to wiretap the message of one or more users. First, the problem
ofsecrecyratebalancingisinvestigatedforaSISOdownlinksysteminwhichtransmission
is performed over a set of parallel subchannels. Under the assumption that each subchan-
nel is occupied exactly by one user, several optimal, near-optimal and heuristic solutions
are proposed for several different problem settings. By assuming a multiantenna BS, the
resource allocation problem is further enriched with spatial multiplexing within each sub-
channel. Thus,thethesisiscompletedwiththeinvestigationoftwosuchproblemsinwhich
secrecy-rateQoSconstraintsarealsotakenintoconsideration.

Table of contents
Listoffigures ix
Listoftables xi
ListofAlgorithms xiii
1 Introduction 1
1.1 Precodinginmultiantenna downlinkchannel . . . . . . . . . . . . . . . . . 1
1.1.1 Beamforming transmission . . . . . . . . . . . . . . . . . . . . . . 2
1.1.2 Nonlineartechniques . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Transmissionoverparallelchannels . . . . . . . . . . . . . . . . . . . . . 6
1.3 Physicallayersecurity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.4 Thesisoutline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.5 Author’s publicationlist . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2 ResourceAllocationinmultiuser,multiantennadownlinkchannelusingSDMA 15
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.2 Alow-complexity userselectionalgorithm formaximizing throughput . . . 18
2.3 Resourceallocationschemesinsystemsthattransmitoverparallelsuchannels 24
2.3.1 Throughput maximization underindividual userrateconstraints . . 24
2.3.2 Maximizeusers’ratebalancing . . . . . . . . . . . . . . . . . . . 32
2.4 Throughput maximization byperforming resourceallocationonchunkbasis 35
3 Secrecy rate balancing over parallel channels in the presence of passive eaves-
dropping 41
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.2 Theproblem ofsecrecyratebalancing . . . . . . . . . . . . . . . . . . . . 44
3.2.1 Optimalpowerallocationforfixedsubchannelassignment . . . . . 45
3.3 Optimal resourceallocationinthecaseofmoreusersthansubchannels . . . 50
3.4 Resourceallocationschemesinthecaseoflessusersthansubchannels . . . 54
3.4.1 Optimality intwospecialcases . . . . . . . . . . . . . . . . . . . . 54
viii Tableofcontents
3.4.2 Anear-optimal solutionbasedonlinearpiecewiseapproximation . 56
3.4.3 Low-complexity heuristics . . . . . . . . . . . . . . . . . . . . . . 57
4 Throughput maximization in multiantenna systems under secrecy rate con-
straints 63
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.2 Userselectiontomaximizesecrecythroughput underpassiveeavesdropping 66
4.2.1 Powerallocationforfixedtransmissiongroupofusers . . . . . . . 67
4.2.2 Lowcomplexity resourceallocationschemes . . . . . . . . . . . . 70
4.3 Simultaneoussecrecyandthroughput maximization usingSDMA . . . . . 73
4.3.1 Aresourceallocationschemebasedondualoptimization . . . . . . 74
4.3.2 Decoupling the subproblems of subchannel assignment and power
allocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
5 Summary&futurework 85
5.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
5.2 Futurework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
5.2.1 ResourceallocationinmassiveMIMOsystems . . . . . . . . . . . 87
5.2.2 Physicallayersecurityinheterogeneouscellularnetworks . . . . . 87
References 91
List of figures
1.1 Wiretapchannelmodel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1 Throughput ofCUSA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.2 ComparisonofthroughputbetweenCUSAandotheruserselectionalgorithms. 23
2.3 Piecewiselinearapproximation ofalogarithmic function f(w). . . . . . . . 27
2.4 Throughput ofRSRA-OPA/FSAvsP forN =4andU =6. . . . . . . . . 31
T
2.5 Throughput RSRA-RB-OPA/FSAvsP forU =6andT =3. . . . . . . . 34
T x
2.6 Inter-subchannelcorrelationprofileinasystemwhichtransmitsoveranum-
berofparallelsubchannels. . . . . . . . . . . . . . . . . . . . . . . . . . . 36
2.7 Throughput vsP forB =0.5MHz,U =100andT =4,8. . . . . . . . . 38
T c x
2.8 Throughput ofchunk-basedresourceallocationschemes. . . . . . . . . . . 40
3.1 System setup; the eavesdropper wiretaps the transmitted message within
eachdata-bearingsubchannel. . . . . . . . . . . . . . . . . . . . . . . . . 44
3.2 SecrecyrateofOptimalResourceAllocationAlgorithm. . . . . . . . . . . 52
3.3 Approximation ofsecrecyrateformula inhighpowerregime. . . . . . . . . 55
3.4 Secrecy rate per user of MILP-OPA/FSA versus the number of segments in
linearapproximation ofsecrecyformula,N =6andK =5. . . . . . . . . . 60
3.5 Secrecyrateperuserofthepresentedresourceallocationschemes. . . . . . 62
4.1 Secrecythroughput ofS/CUSAandCUSAwitheavesdropperselected. . . 72
4.2 System setup; spatial multiplexing between a normal and a secure sensitive
user. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
4.3 ConvergencebehaviorofSOA. . . . . . . . . . . . . . . . . . . . . . . . . 79
4.4 Feasibilityofthepresentedresourceallocationschemes. . . . . . . . . . . 83
4.5 Throughput ofthepresentedresourceallocationschemes. . . . . . . . . . . 84