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Decentralized Resource Sharing and Associationin in Wireless Networks
KTH, School of Electrical Engineering (EES), Automatic Control.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In wireless networks, some of the most important supporting functionalities are decentralized resource sharing and association of clients to access points. These functionalities aim to optimally allocate the available wireless transmission resources, for example, time or spectrum channels, the transmit power, access points, and relaying opportunities, all of which are subject to availability constraints. Decentralized resource sharing and association are designed by a common background theory: optimization problems that are non-convex with mixed integer-real variables, and need to be solved by distributed algorithms over the network nodes. The thesis investigates these optimization problems and establishes novel solution methods based on auction and Lagrangian duality theories. The thesis is divided into two parts: in the first part, the theoretical background of the thesis is given, and novel results on distributed auction theory are established to solve a class of optimization problems with integer variables. These theoretical background and novel results are then used in the second part of the thesis, where published or submitted papers are reported. Specifically, novel solution methods for distributed optimization problems with mixed integer-real variables are in- vestigated for resource sharing and association problems in cognitive radio networks, and in millimeter wave networks.

In the first paper (J1), a non-convex optimization problem with mixed integer and real variables is considered for resource allocation in a cognitive radio network. In this network, unlicensed secondary users can maximize their achievable transmit rates by cooperating with licensed primary users. An optimization problem to maximize the secondary users achievable rates is proposed by controlling the transmit radio power, the secondary users relaying selection, and power splitting of the relays, while guaranteeing primary users performance. A novel distributed solution method is developed to find the solution to such a challenging mixed integer and non-convex problem. The method provides a distributed algorithm for finding the optimal power allocations for secondary users, and a greedy distributed algorithm for finding the associations between primary and secondary users. Optimality and convergence of the solution method are investigated. The numerical results illustrate the performance of the proposed solution methods, and show that they give a near-to-optimal solution.

In the second paper, the solution methods investigated in the first paper are used for mixed integer-real optimization problems in millimeter wave networks. These networks are emerging to enable extremely high data rates wireless communications. The main limiting factors of millimeter wave networks are communication blockage (due to high penetration loss of the transmit signals) and deafness (misalignment between the antenna’s beams of the transmitter and receiver). To minimize these limiting factors, it is imperative to design efficient association between clients and access points. Therefore, a general optimization framework to maximize network throughput considering both blockage and deafness is proposed. The optimization framework considers static networks (i.e., no client mobility) and investigates a novel distributed auction based solution, where the clients and access points act asynchronously to achieve optimal association along with the optimal beamwidth of the antennas. A convergence proof and optimality of the auction algorithm are analyzed.

The optimization framework investigated in the second paper was intended for static networks. In networks with dynamic topologies and channel variations, the dynamic appearance of obstacles or of small misalignments between antenna beams of the transmitters and receivers may trigger the reexecution of the association mechanism, which is time consuming and may be inefficient. This challenge is addressed in the third paper by dynamic distributed association techniques that are robust to wireless channel variations and client mobility. The association problem is formulated as a mixed-integer optimization problem aiming to maximize the network throughput with proportional fairness guarantees. This optimization problem is solved by a distributed dual decomposition algorithm, and by a novel dynamic distributed auction algorithm. A distinguishing novel feature of the proposed algorithms is that the resulting optimal association does not have to be re-computed every time the network changes (e.g., due to client mobility). Instead, it is proved that the algorithm continuously adapts to the network variation and is thus capable to continuously track the optimal solutions. It is shown that the proposed algorithm provably converges to a solution that maximizes the aggregate network utility within a desired bound.

The previous line of research is then extended to the case where, in addition to designing the association clients-access points, also relays nodes are considered. The association of clients to relaying nodes can provide more uniform quality of service by offering robust millimeter waves connection, load balancing, coverage extension, indoor-outdoor coverage, efficient mobility management, and smooth handover operations. The challenges of clientrelay-access point association are addressed in a sequence of two contributions having different optimization goals: the first one considers the throughput maximization, and the second one the load balancing. In the first contribution (presented in the fourth paper of the thesis), a distributed optimization that solves the joint client association and relaying problem is investigated for the throughput maximization. The optimization problem is posed as a novel multi-dimension assignment optimization, for which an original solution method is established by a series of transformations together with a distributed auction solution algorithm. In the second contribution (presented in the fifth paper of the thesis), the joint association and relaying problem is posed as a novel stochastic optimization problem considering the load balancing, and the resource sharing at access points. The problem is solved by a distributed auction algorithm where the clients and relays act asyn- chronously to quickly achieve optimal association. The convergence time and performance bounds of the algorithm are derived in closed-forms. Numerical results quantify the performance enhancements introduced by the relays, and the substantial improvements of the network throughput and fairness among the clients by the proposed association methods compared to existing approaches.

The common thread in the line of research reported in the papers of the thesis is given by the solution methods of mixed integer optimization problems that must be solved in a distributed manner. The core result of the thesis is a novel distributed approach, based on the auction theory, for the computation of the solution of a class of optimization problems. It is shown that such an approach can work in static and dynamic network topologies and exhibits convergence and optimality guarantees by leveraging the specific assumptions of the problems’ constraints. Future study could extend the proposed distributed auction method for more general optimization problems for association, such as generalized assignment problems.

 

 

 

 

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. , xxi, 41 p.
Series
TRITA-EE, ISSN 1653-5146 ; 2015:117
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-180803ISBN: 978-91-7595-824-8 (print)OAI: oai:DiVA.org:kth-180803DiVA: diva2:896893
Public defence
2016-02-12, E3, Osquarsbacke 14, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20160125

Available from: 2016-01-25 Created: 2016-01-22 Last updated: 2016-02-16Bibliographically approved
List of papers
1.
The record could not be found. The reason may be that the record is no longer available or you may have typed in a wrong id in the address field.
2. User association and the alignment-throughput tradeoff in millimeter wave networks
Open this publication in new window or tab >>User association and the alignment-throughput tradeoff in millimeter wave networks
2015 (English)In: Research and Technologies for Society and Industry Leveraging a better tomorrow (RTSI), 2015 IEEE 1st International Forum on, IEEE Communications Society, 2015, 100-105 p.Conference paper, Published paper (Refereed)
Abstract [en]

Millimeter wave (mmWave) communication is apromising candidate for future extremely high data rate, wirelessnetworks. The main challenges of mmWave communications aredeafness (misalignment between the beams of the transmitterand receiver) and blockage (severe attenuation due to obstacles).Due to deafness, prior to link establishment between a clientand its access point, a time consuming alignment/beam trainingprocedure is necessary, whose complexity depends on the operatingbeamwidth. Addressing blockage may require a reassociationto non-blocked access points, which in turn imposes additionalalignment overhead. This paper introduces a unifying frameworkto maximize network throughput considering both deafness andblockage. A distributed auction-based solution is proposed, wherethe clients and access points act asynchronously to achieveoptimal association along with the optimal operating beamwidth.It is shown that the proposed algorithm provably converges toa solution that maximizes the aggregate network utility withina desired bound. Convergence time and performance boundsare derived in closed-forms. Numerical results confirm superiorthroughput performance of the proposed solution compared toexisting approaches, and highlight the existence of a tradeoffbetween alignment overhead and achievable throughput thataffects the optimal association.

Place, publisher, year, edition, pages
IEEE Communications Society, 2015
Keyword
millimeter wave networks, 5G, association, directionality
National Category
Communication Systems
Research subject
Computer Science; Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-178796 (URN)10.1109/RTSI.2015.7325078 (DOI)000380575200015 ()2-s2.0-84964344604 (Scopus ID)978-1-4673-8166-6 (ISBN)
Conference
IEEE Research and Technologies for Society and Industry,16-18 Sept. 2015, Turin, Italy
Note

QC 20160212

Available from: 2015-12-08 Created: 2015-12-08 Last updated: 2016-11-14Bibliographically approved
3. Dynamic Distributed Association with Fairness in Millimeter Wave Networks
Open this publication in new window or tab >>Dynamic Distributed Association with Fairness in Millimeter Wave Networks
(English)Manuscript (preprint) (Other academic)
National Category
Communication Systems
Identifiers
urn:nbn:se:kth:diva-178713 (URN)
Note

QS 2016

Available from: 2015-12-08 Created: 2015-12-08 Last updated: 2016-01-25Bibliographically approved
4. Distributed Association and Relaying in Millimeter Wave Networks
Open this publication in new window or tab >>Distributed Association and Relaying in Millimeter Wave Networks
(English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248Article in journal (Refereed) Submitted
National Category
Communication Systems
Identifiers
urn:nbn:se:kth:diva-178666 (URN)
Available from: 2015-12-08 Created: 2015-12-08 Last updated: 2017-12-01Bibliographically approved
5. Distrubuted association and relaying with fairness in millimeter wave networks
Open this publication in new window or tab >>Distrubuted association and relaying with fairness in millimeter wave networks
2016 (English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 5, no 12, 7955-7970 p.Article in journal (Refereed) Published
Abstract [en]

Millimeter wave (mmWave) systems are emerging as an essential technology for enabling extremely high data rate wireless communications. The main limiting factors of mmWave systems are blockage (high penetration loss) and deafness (misalignment between the beams of the transmitter and receiver). To alleviate these problems, it is imperative to incorporate efficient association and relaying between terminals and access points. Unfortunately, the existing association techniques are designed for the traditional interference-limited networks, and thus are highly suboptimal for mmWave communications due to narrow-beam operations and the resulting non-negligible interference-free behavior. This paper introduces a distributed approach that solves the joint association and relaying problem in mmWave networks considering the load balancing at access points. The problem is posed as a novel stochastic optimization problem, which is solved by distributed auction algorithms where the clients and relays act asynchronously to achieve optimal client-relay-access point association. It is shown that the algorithms provably converge to a solution that maximizes the aggregate logarithmic utility within a desired bound. Numerical results allow quantification of the performance enhancements introduced by the relays, and the substantial improvements of the network throughput and fairness among the clients by the proposed association method as compared to standard approaches. It is concluded that mmWave communications with proper association and relaying mechanisms can support extremely high data rates, connection reliability, and fairness among the clients.

Place, publisher, year, edition, pages
IEEE Press, 2016
Keyword
relays, Millimeter wave communication, load management, distributed algorithms, user association
National Category
Control Engineering
Research subject
Telecommunication
Identifiers
urn:nbn:se:kth:diva-180826 (URN)10.1109/TWC.2016.2609919 (DOI)000391292500004 ()2-s2.0-85006821278 (Scopus ID)
Note

QC 20170111

Available from: 2016-01-25 Created: 2016-01-25 Last updated: 2017-11-30Bibliographically approved

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