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WIRELESS NETWORK COCAST

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ABSTRACTTitle of dissertation: WIRELESS NETWORK COCAST:COOPERATIVE COMMUNICATIONSWITH SPACE-TIME NETWORK CODINGHung-Quoc Duc Lai, Doctor of Philosophy, 2011Dissertation directed by: Professor K. J. Ray LiuDepartment of Electrical and Computer EngineeringTraditional cooperative communications can greatly improve communicationperformance. However, transmissions from multiple relay nodes are challengingin practice. Single transmissions using time-division multiple access cause largetransmission delay, but simultaneous transmissions from two or more nodes usingfrequency-division multiple access (FDMA), code-division multiple access (CDMA),or distributed space-time codes are associated with the issues of imperfect frequencyand timing synchronization due to the asynchronous nature of cooperation.In this dissertation, we propose a novel concept of wireless network cocast(WNC) and develop its associated space-time network codes (STNCs) to overcomethe foretold issues. In WNC networks, each node is allocated a time slot for itstransmission and thus the issues of imperfect synchronization are eliminated. Toreduce the large transmission delay, each relay node forms a unique signal, a com-bination of the overheard information, and transmits it to the intended destination.The combining functions at relay nodes form a STNC that ensures full spatial diver-sity for the transmitted information as in traditional cooperative communications.Various traditional combining techniques are utilized to design the STNCs, includ-ing FDMA-like and CDMA-like techniques and transform-based techniques with theuse of Hadamard and Vandermonde matrices. However, a major distinction is thatthe combination of information from different sources happens within a relay nodeinstead of through the air as in traditional cooperative communications.We consider a general case of multiuser relay wireless networks, where usernodes transmit and receive their information to and from a common base node withthe assistance from relay nodes. We then apply the STNCs to multiuser cooperativenetworks, in which the user nodes are also relay nodes helping each other in theirtransmission. Since the cooperative nodes are distributed around the network, thenode locations can be an important aspect of designing a STNC. Therefore, wepropose a location-aware WNC scheme to reduce the aggregate transmit power andachieve even power distribution among the user nodes in the network.WNC networks and its associated STNCs provide spatial diversity to dramati-cally reduce the required transmit power. However, due to the additional processingpower in receiving and retransmitting each other’s information, not all nodes andWNC networks result in energy efficiency. Therefore, we first examine the powerconsumption in WNC networks. We then offer a TDMA-based merge process basedon coalitional formation games to orderly and efficiently form cooperative groupsin WNC networks. The proposed merge process substantially reduces the networkpower consumption and improves the network lifetime.WIRELESS NETWORK COCAST:COOPERATIVE COMMUNICATIONS WITH SPACE-TIMENETWORK CODINGbyHung-Quoc Duc LaiDissertation submitted to the Faculty of the Graduate School of theUniversity of Maryland, College Park in partial fulfillmentof the requirements for the degree ofDoctor of Philosophy2011Advisory Committee:Professor K. J. Ray Liu, Chair/AdvisorProfessor Alexander BargProfessor Min WuProfessor Dianne O’LearyProfessor Lawrence Washingtonc° Copyright byHung-Quoc Duc Lai2011PrefaceThis dissertation was submitted to the Faculty of the Department of Electricaland Computer Engineering at the University of Maryland in partial fulfillment ofthe requirements for the degree of Doctor of Philosophy (Ph.D.). The studies werecarried out over a period of over three years, from September 2007 to December2010. The research was mainly supported by the In-house Laboratory IndependentResearch (ILIR) program at the United States Army Research, Development, andEngineering Command (RDECOM) Communications-Electronics Research, Devel-opment, and Engineering Center (CERDEC).Hung-Quoc LaiCollege Park, April 21, 2011iiDedicationTo my wife Lethy and my beloved children:Quoc-Viet, Quoc-Kiet, and Minh-ChauiiiAcknowledgementsAs the first person in my extended family to receive a Ph.D. degree, I owe mygratitude to all the people who have helped me through this long journey, in oneway or another, making this great achievement as much a significant life experienceas a challenging but rewarding intellectual experience.First and foremost, I would like to express my deep gratitude to my advisor,Professor K. J. Ray Liu for his care, guidance, and support. I first knew Professor Liuin Summer 2003 when I worked under his supervision in the Maryland EngineeringResearch Internship Teams (MERIT) program at the Department of Electrical andComputer Engineering, University of Maryland. His research work and his eruditionalways inspire me and were an encouragement for me to continue my education withmy Ph.D. study after I completed my undergraduate. It has been a pleasure to workwith and learn from such an extraordinary individual.I would also like to thank the other members of my dissertation committee.Special thanks are due to Professor Alexander Barg and Professor Min Wu for theirguidance in my research proposal. Their knowledge and insights were extremelyvaluable and greatly enriched my work. I also want to thank Professor DianneO’Leary and Professor Lawrence Washington for agreeing to serve on my dissertationcommittee. To all the committee members, I greatly appreciate their invaluable timereviewing and commenting the manuscript.My colleagues in Signals and Information Group at the University of Marylandhave enriched my graduate life in many ways and deserve a special mention. I wouldivlike to thank every member in the group for their friendship, encouragement, andhelp. I have learned a lot from each one of them, and for that I am deeply grateful.I specially thank Dr. Ahmed Ibrahim, Ms. Zhenzhen Gao, and Mr. Yan Chen forthe research discussions that were all inspiring for me.I would also like to thank Ms. Dorothea Brosius at the Institute for Electronicsand Applied Physics, University of Maryland for providing the LaTex template,which made putting this dissertation together an easy effort.I would like to acknowledge the financial support from the Gates MillenniumScholars for my undergraduate and graduate study.


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