Ph.D. Thesis Self-Optimization of Radio Resources on IEEE 802.11 Networks Ph.D. Candidate: Eduard Garcia Villegas Ph.D. Advisor: Josep Paradells Aspas Wireless Networks Group (WNG) — Telematics Department Universitat Polit`ecnica de Catalunya (UPC) July 2009 Acknowledgements At first glance, anyone may easily infer that the most evident results of the last five years of my life are an incipient alopecia and a loss of shape. I hope that the reader of this thesis would pay regard to other commendable achievements. These achievements are not the fruit of my effort alone since many people have helped me throughout these years. I would like to express my gratitude to those who stood beside me and supported me. Firstly I am particularly indebted to Professor Josep Paradells, who envisioned this thesis five years ago. He has guided me ever since to forge what you hold in your hands, and I wish to enjoy his verve for many years to come. I also like to acknowledge the advice and support of Rafael Vidal, which goes back to even before I “hatched” as an engineer. He has generously read and commented on almost every line I wrote during this thesis. I am grateful to Elena L´opez for her “tech support” with the simulator - which I suggest to rename as Elena’s WLAN incredible simulator (Elwis) -. Many thanks are to Marilet de Andrade for putting up with my “not-always-enjoyable” mood and for sitting with me in the same office without committing murder. I would also like to thank the reviewers (Jeff, H´ector Velayos and Pedro Ruiz) for their valuable and insightful comments that indubitably helped to improve the quality of this document. There are many others that I hope they accept this multicast acknowlegement: to the membersoftheWNG, to my pupils (TFC/PFC), to the inhabitants of the lab 322, to the marauders of the C3, to my colleagues at the EPSC, to all the guardiola keepers,... THANK YOU! ii iii Contents 1 Introduction 1 1.1RadioResourceManagement(RRM)..................... 2 1.1.1 Dynamic RRM mechanisms for IEEE 802.11 WLANs ........ 4 1.1.1.1 Rateselection......................... 4 1.1.1.2 Loadbalancing........................ 5 1.1.1.3 Frequencychannelallocation................ 5 1.1.1.4 Powercontrol......................... 7 1.2 Implementation platforms ........................... 7 1.3Scopeandstructureofthisthesis....................... 10 1.3.1 Contributions and publications .................... 11 2 IEEE 802.11 Wireless LANs 13 2.1TheBasics.................................... 13 2.1.1 TheElements.............................. 13 2.1.2 TheTopologies............................. 14 2.1.2.1 IBSS.............................. 14 2.1.2.2 ESS.............................. 14 2.2TheServices................................... 15 2.2.1 Distribution of messages ........................ 15 2.2.2 Associationservices........................... 17 2.2.2.1 Scanning ........................... 17 2.2.2.2 Roaming ........................... 18 2.2.3 Security................................. 18 2.2.4 SpectrumManagement......................... 19 iv CONTENTS 2.3 Medium Access Control ............................ 19 2.3.1 MACFrameFormat.......................... 20 2.3.2 CarrierSensemechanism........................ 21 2.3.3 DCFbasedMAC............................ 21 2.3.3.1 BasicAccess......................... 22 2.3.3.2 Four-wayhandshake(RTS/CTS).............. 23 2.4PhysicalLayer.................................. 23 2.4.1 DSSS................................... 24 2.4.1.1 PLCPFrameFormat..................... 24 2.4.1.2 Legacy 802.11 DSSS ..................... 25 2.4.1.3 HighRateDSSS....................... 25 2.4.2 OFDM.................................. 26 2.4.2.1 Modes............................. 27 2.4.2.2 PLCPFrameFormat..................... 27 2.4.2.3 OFDMinthe2.4GHzband................. 28 2.5 Alphabet Soup . ............................... 29 3 Characterizing the environment 37 3.1 Propagation ................................... 37 3.1.1 Indoor propagation ........................... 38 3.1.2 Outdoor propagation .......................... 39 3.1.3 Coverageestimations.......................... 40 3.1.4 Multipathchannel........................... 42 3.1.5 Measurementcampaigns........................ 43 3.2Errormodels.................................. 45 3.2.1 OFDM.................................. 45 3.2.2 DSSS................................... 47 3.2.3 CCK................................... 48 3.3Interferenceandcoexistence.......................... 50 3.3.1 Non-802.11 interference ......................... 51 3.3.2 Receiverdesign............................. 52 3.3.2.1 Timing recovery and header processing ........... 53 CONTENTS v 3.3.2.2 Dynamicrangeselection................... 53 3.3.3 Channelscheme............................. 54 3.3.3.1 Regulatorydomains..................... 54 3.3.3.2 Spreadsignals......................... 56 3.3.4 Adjacentchannelinterference..................... 59 3.3.4.1 Effects of utilization on interference measurements .... 61 3.3.5 Co-channelinterference......................... 63 3.4Simulationenvironment............................ 65 3.4.1 Open-sourcesimulators......................... 66 3.4.2 SIPTE11simulator........................... 68 3.4.2.1 InterferenceManagement.................. 69 3.4.2.2 Input/Output interfaces ................... 70 3.4.2.3 Scenariogeneration...................... 71 3.4.3 Common assumptions ......................... 72 3.4.4 Conclusions............................... 74 4 Throughput and capacity models 77 4.1 Single user .................................... 78 4.2 Single cell .................................... 81 4.3 Multiple cells .................................. 85 4.3.1 Effect of packet errors in saturation throughput ........... 86 4.3.2 Effect of co-channel interference .................... 87 4.3.3 Modeling of a link adaptation algorithm . ............. 90 4.3.4 Practicalevaluation........................... 95 4.4Conclusions................................... 96 5 Dynamic frequency assignments in WLANs 99 5.1Relatedwork.................................. 99 5.2Proposedapproach...............................102 5.2.1 Partially overlapping channels .....................103 5.2.2 Algorithm................................104 5.2.2.1 Client-drivenenhancement..................106 vi CONTENTS 5.2.3 Implementationissues.........................106 5.2.3.1 Distributed architecture ...................108 5.2.3.2 Centralizedarchitecture...................109 5.2.3.3 Client-driven.........................109 5.2.4 Evaluation................................110 5.2.4.1 Algorithmperformance...................110 5.2.4.2 Practicalmeasurements...................111 5.2.4.3 Simulations..........................114 5.3Conclusions...................................115 6 Load Balancing in WLANs 119 6.1LoadMetrics..................................120 6.1.1 Numberofactiveusers.........................120 6.1.2 Packetloss................................120 6.1.3 Carriedtraffic..............................122 6.1.4 Load information in IEEE 802.11 standards .............122 6.1.4.1 Service Time and Medium Access Delay ..........123 6.1.4.2 Channelbusytime......................125 6.1.4.3 AvailableAdmissionCapacity................127 6.1.5 AvailableAdmissionCapacity.....................127 6.1.5.1 Definitions ..........................128 6.1.5.2 Algorithm...........................129 6.1.5.3 Evaluation..........................130 6.1.5.3.1 Analyticalmodels.................131 6.1.5.3.2 Simulations.....................131 6.1.5.3.3 Practicalmeasurements..............134 6.1.6 Conclusions...............................137 6.2 Load Balancing techniques ...........................138 6.2.1 Relatedwork..............................139 6.2.2 Client-drivenapproach.........................141 6.2.2.1 Implementation details ....................141 6.2.2.1.1 Active scanning ...................142 CONTENTS vii 6.2.2.1.2 Passive scanning ..................142 6.2.2.1.3 Out-of-band signaling (centralized) ........143 6.2.2.2 Evaluation..........................144 6.2.2.2.1 Scenario.......................144 6.2.2.2.2 Saturation......................145 6.2.2.2.3 Degreeofsaturation................147 6.2.2.2.4 Fairnessvs.Throughput..............149 6.2.2.2.5 Testbed.......................150 6.2.3 Cell Breathing ..............................151 6.2.3.1 Distributed load balancing algorithm with cell breathing . 152 6.2.3.2 Implementation issues ....................154 6.2.3.3 Performanceevaluation...................155 6.2.3.3.1 Scenario.......................156 6.2.3.3.2 Simulationresults.................156 6.2.4 Conclusions...............................158 7 Resource Management in WLANs 161 7.1StandardizedRadioResourceManagement..................162 7.1.1 IEEE 802.11h: Spectrum Managed ..................163 7.1.1.1 TPC..............................163 7.1.1.2 DFS..............................164 7.1.1.3 ActionFrames........................165 7.1.1.4 Newinformationinmanagementframes..........166 7.1.2 IEEE 802.11k: Radio Measurements .................166 7.1.2.1 New responsibilities for the old STAs ............167 7.1.2.2 Actionframes.........................168 7.1.2.3 Newinformationinmanagementframes..........171 7.1.3 IEEE 802.11v: Network management .................172 7.1.3.1 Powersavingandtrafficfiltering..............172 7.1.3.2 Measurement,eventanddiagnosticreporting.......172 7.1.3.3 Presence procedures .....................173 7.1.3.4 Associationcontrol......................174 viii CONTENTS