Eng. Rebeca - Maria COLDA. PhD Thesis Abstract. CONTRIBUTiONS TO THE OPTIMIZATION OF THE USAGE OF RADIO RESOURCES IN WIRELESS SYSTEMS

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1 Investeşte în oameni! FONDUL SOCIAL EUROPEAN Programul Operaţional Sectorial Dezvoltarea Resurselor Umane Axa prioritară: 1 Educaţia şi formarea profesională în sprijinul creşterii economice şi dezvoltării societăţii bazate pe cunoaştere Domeniul major de intervenţie: 1.5 Programe doctorale si postdoctorale în sprijinul cercetării Titlul proiectului: Proiect de dezvoltare a studiilor de doctorat în tehnologii avansate- PRODOC Cod Contract: POSDRU 6/1.5/S/5 Beneficiar: Universitatea Tehnică din Cluj-Napoca Eng. Rebeca - Maria COLDA PhD Thesis Abstract CONTRIBUTiONS TO THE OPTIMIZATION OF THE USAGE OF RADIO RESOURCES IN WIRELESS SYSTEMS Scientific Advisor: Prof. dr. eng. Tudor PALADE PhD Thesis Evaluation Committee: PRESIDENT: - Prof.dr.eng. Dorin Petreuş - Prodean, Faculty of Electronics, Telecommunications and Information Technology, Technical University of Cluj-Napoca; MEMBERS: - Prof.dr.eng. Tudor Palade - Scientific Advisor, Technical University of Cluj-Napoca; - Prof.dr.eng. Ion Bogdan - Reviewer, The Gh. Asachi Technical University of Iaşi; - Researcher Gr.I.PhD.eng. Ştefan-Victor Nicolaescu - Reviewer, National Communications Research Institute of Bucharest; - Prof.dr.eng. Corneliu Rusu - Reviewer, Technical University of Cluj-Napoca. 2011

2 1. Introduction The efficient use of radio resources in wireless systems represents a major research axis with respect to the development of existing communication networks. Since the radio resources are limited and the demand for more and more complex wireless services is increasing, adequate management techniques must be applied in order to be able to offer the necessary support required by simultaneous applications with different QoS (Quality of Service) requirements. Radio resource management (RRM) techniques aim at controlling essential transmission parameters such as: transmission power, modulation and coding techniques, bandwidth allocation method, subchannel allocation method, packet scheduling at the radio interface according to the application requested parameters and admission control. The aim in applying all of these resource self-organization techniques is to maximize the usage of the radio interface, and thus the number of users that can be served by the network at a certain instance of time, while keeping the applications QoS requirements at a certain predefined level Scope of the thesis The scope of the thesis was to identify the optimal values of some physical network configuration parameters, such as to obtain a maximum data transfer rate while maintaining the applications requested parameters. To achieve this goal, several issues were addressed in the thesis with respect to the radio resource management of broadband wireless systems, mainly focusing on IEEE (WiMAX) systems. A special attention was given to link adaptation techniques, which rely on the dynamic configuration of certain key transmission parameters according to the variable radio channel s conditions, given some constraints imposed by the communication system. In the thesis, two such link adaptation techniques were discussed. In the first step, it was assumed the existence of a real time feedback loop, allowing the exploit of the transmitter s adaptive potential by means of an AMC (Adaptive Modulation and Coding) scheme. The implementation of such a technique was done considering a realistic Mobile WiMAX scenario, and also the QoS requirements of some specific applications. The conducted analyses, developed around this concept of dynamic network awareness and dynamic control of the available resources based on the received feedback information, will be extremely important for the development of future wireless systems characterized by high data rate services having strictly QoS demands. In the second part of the thesis, a more detailed analysis was performed, considering the effective transmission of a JPEG 2000 coded image over a MIMO open loop system. The design of efficient RRM schemes for assuring an optimal error protection has become a challenging issue in the context of limited spectrum resources, where high compression techniques are employed thus making the code-stream more sensitive to transmission errors. The aim was to propose a link adaptation scheme, exploiting both the image content to be transmitted, as well as different available MIMO STBC (Space Time Block Coding) techniques. Different UEP Technical University of Cluj-Napoca - 2 -

3 (Unequal Error Protection) strategies were proposed, leading to the best tradeoff between the robustness to errors and the image visual quality. 2. Contributions to the Optimization of the Usage of Radio Resources in Wireless Systems 2.1. Contributions Summary 1. Identification of efficient radio resource management techniques suited for broadband wireless access systems, targeting IEEE systems. The work presented in chapter 2 is dedicated to a theoretical study of the main resources that can be exploited in a wireless system. A specific analysis was performed mainly targeting IEEE (WiMAX) systems, one of the most important wireless systems that mark the evolution towards 4G systems. First of all, the entities responsible for RRM in the WiMAX network architecture have been identified. Afterwards, a detailed analysis was performed with respect to the way the OFDM subcarriers can be grouped into subchannels, the minimum frequency resource unit that can be allocated dynamically to a user depending on the channel conditions and the application QoS requirements. Then, several mechanisms were investigated with respect to: (1) power optimization both for the uplink (UL) direction, by means of water-filling or downlink direction (DL) by means of a series of algorithms that involve a compromise between the maximum transfer rate and the necessary needed power, as well as the fairness of resource allocation among the users (MSR, MF, PRC, PF), (2) power-saving modes (sleep and idle) needed especially for battery equipped devices, (3) bandwidth request and allocation methods adapted both to the type of service requested as well as to the degree of radio channel loading, (4) admission control, depending both on the available resources as well as on the QoS demands that must be fulfilled. A special attention was paid to link adaptation techniques, in particular to the AMC and HARQ (Hybrid ARQ) techniques. [Colda10r1], [Colda08] 2. Development of a realistic transmission chain, adapted for the case of a Mobile WiMAX system. The entire simulated Mobile WiMAX transmission chain, presented in chapter 3, was developed in accordance to the IEEE standard specifications as well as to that of the WiMAX Forum. The first step involved the modeling of the broadband radio channel with emphasis on the ITU-R set of empirical channel models, this set of models being subsequently extended by a number of other channel models developed for different current technologies such as LTE (Long Term Evolution). The second step involved the specification of the QoS requirements characterizing different types of applications. Next, the influence of two parameters upon the system performance was investigated: the proper choice of the cyclic prefix, parameter through which a satisfactory compromise must be assured between the required immunity Technical University of Cluj-Napoca - 3 -

4 against multipath propagation and the amount of useful data that can be transmitted, and the coding scheme, a suitable coding scheme being required in order to cope with the irreducible error rate induced both by the channel selectivity as well as by the Doppler spread that appears due to user mobility. [Colda10c], [Colda10r2], [Nicolaescu10], [Colda09a], [Colda09b], [Colda09c] 3. Implementation of the AMC link adaptation technique based on the QoS requirements of different types of applications. The importance of applying such a technique resides from exploiting the radio channel s dynamics by appropriately adapting the current transmission mode (modulation and FEC coding rate), given some minimum QoS requirements that must be maintained. The AMC technique was implemented with respect to the maximum tolerated error rate and to the minimum needed transfer rate that must be fulfilled. From simulations were determined: the SNR threshold values needed for the transition from one transmission mode to another, the maximum possible transmission rate, both per connection and per user, the maximum operating distance for each transmission mode, as well as the needed receiver sensitivity to trigger a particular transmission mode. The conducted analyses lead to the development of lookup tables, for different channel models, that based on the existence of a real feedback loop could be implemented at the transmitter, thus providing an optimum radio resource management. The performances obtained by applying the AMC technique were evaluated also for the case of a fast fading channel, modeled by means of the ITU-R mix of channels, as well as compared with a temporal diversity scheme based on repetition coding. [Puşchiţă11], [Colda10a], [Colda10b], [Colda10c], [Colda10r2], [Nicolaescu10] 4. Theoretical approach of the problems imposed by image transmission over wireless channels, in case of open-loop MIMO systems. If until now an optimization of the system was done with respect to some general QoS specifications, in chapter 4 a more detailed analysis is carried on concerning the actual transmission of an image over an error prone wireless channel. The following steps were performed: (1) study of the existing JPEG 2000 error protection mechanisms both at the entropic and packet level, (2) study of the error protection mechanisms present in the JPEG 2000 Wireless (JPWL) amendment of the JPEG 2000 compression standard, and more specifically to the way a differentiated error protection scheme (UEP) can be established by manipulating the information present in the EPB (Error Protection Block) and ESD (Error Sensitivity Descriptor) markers, (3) study of different MIMO STBCs that can be applied to further enhance the link reliability. The performance of different MIMO transmission techniques was investigated from the following categories: orthogonal codes (Alamouti STBC), algebraic number theory based codes (DAST Diagonal Algebraic Space Time Code) and perfect codes (Golden code). Technical University of Cluj-Napoca - 4 -

5 [Colda11], [Colda11r3] 5. Development of adaptive image transmission strategies, suited for a MIMO system, by exploiting both the image content to be transmitted as well as the error performance of different MIMO STBC techniques. The necessity of applying such differentiated error protection strategies, according to the contribution of each data packet to the overall image quality, comes from the desire to assure the best possible image quality adapted to the variable radio channel conditions. Thus, in chapter 5, the following steps have been performed: (1) development of an image transmission system, incorporating also MIMO facilities, by means of an interconnection between the OpenJPEG simulator used for the image encoding / decoding processes and Matlab, (2) implementation and comparison of the above mentioned MIMO STBC techniques, (3) comparison of different predefined error protection mechanisms present both in JPEG 2000 and JPWL with the aim of proving their ineffectiveness in case of wireless fading channels, (4) assessment of the image quality with progressive decoding, both at the packet level and layer level and (5) establishment, based on simulations and objective and subjective image quality evaluation methods, of different UEP strategies both at the packet level and layer level. It will be shown that significant improvements in terms of connection reliability, especially for low to medium SNR values, can be obtained not only by choosing a suitable UEP scheme but also by combining it with an optimal STBC code. [Colda11], [Colda11r3] 2.2. General Conclusions Since the radio resources are limited and the data requirements keep increasing, link adaptation techniques through which a higher spectral efficiency as well as a better resource management can be achieved have emerged as powerful tools for the development of future wireless broadband networks. Although in the current communications standards a framework for RRM (Radio Resource Management) is usually defined, the actual RRM implementation algorithms are left to the development of the equipment manufacturers, representing a topic upon which a closer investigation is required. Moreover, in applying such a method aiming to optimize the resource consumption the accurate estimation of the transmission medium plays an important role. Besides that, the RRM problem should be addressed at a system level, and not only locally, as it is necessary to monitor the impact of a locally applied technique with respect to the performance of the whole system. Concerning the link adaptation techniques, it was shown that in applying such a technique usually an optimum compromise must be reached between the application QoS requirements that should be minimally fulfilled and the level of protection needed to efficiently cope both with the adverse channel conditions as well as the user mobility. Technical University of Cluj-Napoca - 5 -

6 2.3. List of Publications Books [Nicolaescu10] Ş.-V. Nicolaescu (editor), T.-P. Palade, A. Moldovan, E. Puşchiţă, R. Colda, I. Vermeşan (included in the list of contributors), Wireless access networks: Resource allocation and dynamic self-organization (Reţele wireless de acces: Alocarea dinamică şi autoorganizarea resurselor), Printech Publishing House, Bucharest 2010, ISBN , 402 p. Selective Research Papers [Colda11] [Puşchiţă11] [Colda10a] [Colda10b] [Colda10c] [Colda09a] R. Colda, C. Perrine, J.-P. Cances, R. Vauzelle, T. Palade, Content-Based Image Unequal Error Protection Strategies for an Open Loop MIMO System, submitted to Int l J. of Communications, Network and System Sciences, September E. Puşchiţă, T. Palade, R. Colda, I. Vermeşan, A. Moldovan, Radio Resource Adaptive Adjustment in Future Wireless Systems Based on Application Demands, Submitted to International Journal of Computers, Communications & Control (IJCCC), Mai R. Colda, T. Palade, I. Vermeşan, A. Moldovan, E. Puşchiţă, Link Adaptation in Mobile WiMAX Systems under the ITU-R Mix of Channels, Proceedings of the 14 th WSEAS International Conference on COMMUNICATIONS, July 2010, Corfu Island, Greece, ISSN , ISBN , pp R. Colda, T. Palade, E. Puşchiţă, A. Moldovan, I. Vermeşan, PER-Based Analysis of a Mobile WiMAX System, Proceedings of the 18 th International Conference on Microwave, Radar and Wireless Communications (MIKON), June 2010, Vilnius, Lituania, ISBN , pp R. Colda, T. Palade, E. Puşchiţă, I. Vermeşan, A. Moldovan, Mobile WiMAX: System performance on a vehicular multipath channel, Proceedings on the 4 th European Conference on Antennas and Propagation (EuCAP), April 2010, Barcelona, Spain, ISBN , pp.1-5. R. Colda, T. Palade, E. Puşchiţă, I. Vermeşan, A. Moldovan, Ş.-V. Nicolaescu, BER Performance Evaluation of a Mobile WiMAX System over an ITU-R Pedestrian B Multipath Channel, ACTA TEHNICA NAPOCENSIS - Electronics and Telecommunications, Volume 50, Number 3, 2009, ISSN , CNCSIS B+, pp Technical University of Cluj-Napoca - 6 -

7 [Colda09b] [Colda09c] [Colda08] R. Colda, T. Palade, E. Puşchiţă, I. Vermeşan, A. Moldovan, ITU-R channel model analysis for a Mobile WiMAX system, Proceedings of the 15 th International Scientific Conference Nicolae Bălcescu Land Forces Academy, Noiembrie 2009, Sibiu, ISSN , pp R. Colda, T. Palade, E. Puşchiţă, I. Vermeşan, A. Moldovan, Ş.-V. Nicolaescu, Evaluation of the transmission efficiency of pedestrian and vehicular environments under the IEEE e standard (Evaluarea eficienţei transmisiilor în medii cu deplasare pedestră şi vehiculară în standard IEEE e), Telecommunications Magazine, Year LII / Nr.1/2009, CNCSIS D, Agir Publishing House, Bucharest, ISSN , pp R. Colda, T. Palade, E. Puşchiţă, Broadband wireless access and mobility solution using IEEE : concepts and architecture, ACTA TEHNICA NAPOCENSIS - Electronics and Telecommunications, Volume 49, Number 4, 2008, ISSN , CNCSIS B+, pp Scientific Research Reports [Colda10r1] [Colda10r2] [Colda11r3] R. Colda, Study on radio resources in wireless systems (Studiu asupra resurselor radio în sisteme wireless), Scientific Research Report 1, Technical University of Cluj-Napoca, Romania, February R. Colda, Analysis of radio resource management methods in wireless systems (Analiza modalităţilor de gestiune a resurselor din cadrul sistemelor wireless), Scientific Research Report 2, Technical University of Cluj- Napoca, Romania, July R. Colda, Contributions to the optimization of the usage of the radio resources in wireless systems (Contribuţii la eficientizarea utilizării resurselor din cadrul sistemelor wireless), Scientific Research Report 3, Technical University of Cluj-Napoca, Romania, April Participation in Research Projects Eureka: Multilink Architecture for Multiplay Services (MARCH), Eureka Cluster Project, No. CP-013 / 2008, Development period: PN 2: Integrated Wireless Platform for Broadband Local Access and Mobility, with Resources Self-Organization (Platformă wireless integrată de acces local pentru bandă largă şi mobilitate, cu auto-organizarea resurselor (PABMAR)), Contract No / , Development period: Technical University of Cluj-Napoca - 7 -