Academic Year 2011/2012           ELECTRICAL AND COMPUTER ENGINEERING           THE INSTITUTE OF TELECOMMUNICATIONS    FAC...
Modelling and Simulation of Scheduling Algorithms in                     LTE NetworksAbstract:This thesis is based on the ...
Modelowanie i symulacja działania procedur           rezerwacji zasobów w sieciach typu LTEStreszczenie:W pracy podjęto st...
CURRICULUM VITAEPersonal Details:Name:          Dinesh MannaniDate of Birth: 28-02-1990Nationality: IndianWork Experience:...
AcknowledgementThis Bachelors thesis is the final step in obtaining my Bachelor‟s Degree in Electrical andComputer Enginee...
Table of Contents1. Introduction ............................................................................................
Figures ListFig. 1 : OFDM and OFDMA [28].....................................................................................
Fig. 47 : Resource allocation by RR algorithm for 3 users in uplink Case 4........................... 48Fig. 48 : Resource...
Abbreviations3GPP – 3rd Generation Partnership ProjectLTE – Long Term EvolutionMMOG – Multimedia Online GamingHSPA – High ...
PHICH – Physical Hybrid ARQ Indicator ChannelHARQ – Hybrid Automatic Retransmission RequestRS – Reference SignalCIR – chan...
1. IntroductionThis chapter is dedicated to the introduction to the concept of 3rd Generation PartnershipProject (3GPP) Lo...
essentially the same overall complexity as OFDMA. Like OFDM, SC-FDMA also consists ofsub-streams but it transmits on sub-c...
1.2.2 Thesis goalsThe main purpose of this thesis is to verify and compare selected downlink and uplinkschedulers in LTE M...
2. An Overview of LTEThis chapter will provide an insight into the technical details of Long Term Evolution asunderlined b...
shall be maintained at speeds from 120 km/h to 350 km/h (or even up to 500 km/h dependingon the frequency band).Spectrum e...
Fig. 1 : OFDM and OFDMA [28]The full potential of OFDMA is utilised by proper scheduling as it allows the resources to beu...
2.3 LTE Frame StructureAs per the description of LTE frame structure in [28] the downlink and uplink transmissionsare grou...
always reserved for downlink transmission. UpPTS and the subframe immediately followingUpPTS are reserved for uplink trans...
Fig. 5 : LTE Downlink channels [18]We will be discussing the role and description of the physical downlink channels [28]in...
Physical Hybrid Automatic Retransmission Request (HARQ) Indicator Channel(PHICH)PHICH carries Acknowledge (ACK)/Not Acknow...
We will be discussing the role and description of the physical uplink channels [28] involvedin LTE:Physical Uplink Control...
Fig. 7 : Single user MIMO transmission principle [8]In LTE all the device categories with exception of the simplest, suppo...
3. Selected Issues of SchedulingThis chapter along with explaining the concept of scheduling will give details of the vari...
In LTE networks, the role of resource scheduling is very important because greatperformance gain can be achieved by proper...
The main advantage of this kind of scheduling is the relative ease in its implementationwhereas the major disadvantage is ...
3.1.3 Proportional Fair SchedulingThis algorithm assigns the PRBs to the UE with the best relative channel quality i.e. ac...
4. Simulations and TestingThis chapter is meant for the analysis of the scheduling algorithms we have discussed in theearl...
Testing Scenarios                                                  Downlink                                               ...
Multipath Model                                                                                   3GPP model          Envi...
The SNIR values have been limited to the range of -2 dB to 25 dB like in a realistic scenarioso as to derive results which...
Case 2: 3 Users, Stationary, Using Round Robin, Max SNIR and Proportional Fairscheduling algorithmsIn this case we simulat...
Fig. 18 depicts the allocation of resources by Round Robin algorithm in which each user getsallocated the same number of r...
Fig. 20 shows how the PF algorithm first starts out by allocating equal no. of resources toeach user and then eventually s...
each user irrespective of their SNIR values, in Fig. 19 we see the Max SNIR scheduler allotsmore resources to the users ha...
MaxSNIR Scheduler allocations                    16                    14                    12                    10     ...
We can notice the difference between the Fig. 20 and Fig. 25 both depicting the allocation asper PF with the channel of ch...
between fairness and achieving the Maximum throughput. The throughput results are a bitbetter due to the fact all users ar...
MaxSNIR Scheduler allocations                    16                    14                    12                    10     ...
MAX SNIR scheduler            Number of allocated PRB                                      1500                           ...
Scenario UplinkCase 1: Single user, Stationary, Using Round Robin, Max SNIR and Proportional Fairscheduling algorithmsIn t...
Modeling and simulation of scheduling algorithms in lte networks by dinesh mannani
Modeling and simulation of scheduling algorithms in lte networks by dinesh mannani
Modeling and simulation of scheduling algorithms in lte networks by dinesh mannani
Modeling and simulation of scheduling algorithms in lte networks by dinesh mannani
Modeling and simulation of scheduling algorithms in lte networks by dinesh mannani
Modeling and simulation of scheduling algorithms in lte networks by dinesh mannani
Modeling and simulation of scheduling algorithms in lte networks by dinesh mannani
Modeling and simulation of scheduling algorithms in lte networks by dinesh mannani
Modeling and simulation of scheduling algorithms in lte networks by dinesh mannani
Modeling and simulation of scheduling algorithms in lte networks by dinesh mannani
Modeling and simulation of scheduling algorithms in lte networks by dinesh mannani
Modeling and simulation of scheduling algorithms in lte networks by dinesh mannani
Modeling and simulation of scheduling algorithms in lte networks by dinesh mannani
Modeling and simulation of scheduling algorithms in lte networks by dinesh mannani
Modeling and simulation of scheduling algorithms in lte networks by dinesh mannani
Modeling and simulation of scheduling algorithms in lte networks by dinesh mannani
Modeling and simulation of scheduling algorithms in lte networks by dinesh mannani
Modeling and simulation of scheduling algorithms in lte networks by dinesh mannani
Modeling and simulation of scheduling algorithms in lte networks by dinesh mannani
Modeling and simulation of scheduling algorithms in lte networks by dinesh mannani
Modeling and simulation of scheduling algorithms in lte networks by dinesh mannani
Modeling and simulation of scheduling algorithms in lte networks by dinesh mannani
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This thesis is mainly to understand the scheduling algorithms for LTE by means of modeling and simulation of the process and in the end verify the results by conducting tests in a LTE test environment. Furthermore, work out a method to examine LTE scheduling performance evaluation for teaching purposes.


The analysis of these scheduling algorithms has been done through simulations executed on a MATLAB-based system level simulator from IS-Wireless, which is part of 4G University Suite with their verification in a LTE network test environment

For more information about 4G University Suite, please have a look http://is-wireless.com/products/4g-university-suite.

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Modeling and simulation of scheduling algorithms in lte networks by dinesh mannani

  1. 1. Academic Year 2011/2012 ELECTRICAL AND COMPUTER ENGINEERING THE INSTITUTE OF TELECOMMUNICATIONS FACULTY OF ELECTRONICS AND INFORMATION TECHNOLOGY WARSAW UNIVERSITY OF TECHNOLOGY Bachelor of Science Thesis Modeling and Simulation of Scheduling Algorithms in LTE Networks Dinesh Mannani Supervisor: Dr. Mirosław Słomiński, Associate Professor Consultant: Dr. Sławomir Pietrzyk, IS-Wireless........................................................... Evaluation........................................................... Signature of the Head of Examination Committee Warsaw, January 2012
  2. 2. Modelling and Simulation of Scheduling Algorithms in LTE NetworksAbstract:This thesis is based on the study of scheduling algorithms in LTE (Long Term Evolution).LTE is an evolution of the UMTS (Universal Mobile Telecommunications System)standardised by the 3GPP (3rd Generation Partnership Project) in its Rel. 8 for thedevelopment of wireless broadband networks with very high data rates. It enables mobiledevices such as smartphones, laptops, tablets to access internet at a very high speed dataalong with lots of multimedia services. The future of LTE lies in being implemented invarious electronic devices to exchange data wirelessly at very high speeds.Technically, the Long Term Evolution provides a high data rate and can operate in differentbandwidths ranging from 1.4MHz up to 20MHz. In terms of features the latest Release ofLTE (Rel. 10 – LTE-Advanced) aims to deliver enhanced peak data rates to support advancedservices and applications (100 Mbit/s for high and 1 Gbit/s for low mobility [25], low latency(10ms round-trip delay), improves system capacity and coverage, supports multi-antenna andreduces operating costs [1] by introducing concepts like SON and allowing seamlessintegration with existing mobile network systems.Scheduling is basically the process of making decisions by a scheduler regarding thedistribution of resources (time and frequency) in a telecommunications system among itsusers. The Max SNIR, the Proportional Fair and the Round Robin scheduling algorithmshave been considered and discussed in this dissertation. The analysis of these schedulingalgorithms has been done through simulations executed on a MATLAB-based system levelsimulator from IS-Wireless called LTE MAC Lab (aka Matlab version of 4G System Lab)with their verification in a LTE network test environment (deployed in the Institute ofTelecommunications within the Smart City of TPSA in the Warsaw University of Technology).I have examined the impact on the throughput and the fairness results of each schedulingalgorithm.This thesis is mainly to understand the scheduling algorithms for LTE by means of modellingand simulation of the process and in the end verify the results by conducting tests in a LTEtest environment. Furthermore, work out a method to examine LTE scheduling performanceevaluation for teaching purposes. 2
  3. 3. Modelowanie i symulacja działania procedur rezerwacji zasobów w sieciach typu LTEStreszczenie:W pracy podjęto studia dotyczące nowoczesnych sieci telekomunikacyjnych zgodnych zestandardem Long Term Evolution ( LTE), opracowanym i rozwijanym przez Konsorcjum 3rdGeneration Partnership Project (3GPP), które pozwalają już obecnie na osiąganie wsieciach telefonii komórkowej dużych szybkości transferu danych (do 100 Mb/s w kierunku doabonenta i do 50 Mb/s w kierunku zwrotnym) z małymi opóźnieniami. W szczególnościskupiono się na zagadnieniach związanych z analizą procesu rezerwacji zasobówtransmisyjnych w tych sieciach.Do analizy porównawczej wybrano trzy, rekomendowane dla tych sieci, algorytmy: The MaxSNIR Scheduling Algorithm, The Proportional Fair Scheduling Algorithm i The Round RobinScheduling Algorithm. Analizy przeprowadzono z wykorzystaniem profesjonalnego narzędziaprogramistycznego – Symulatora LTE MAC Lab (aka Matlab version of 4G System Lab)firmy IS-Wireless oraz niedawno otwartego na Wydziale Elektroniki i TechnikInformacyjnych (WEiTI) Politechniki Warszawskiej Laboratorium LTE, przygotowanego wewspółpracy z firmą HUAWEI Polska Sp. z o.o., Telekomunikacją Polską S.A. i Orange LabsPoland.Uzyskane w pracy wyniki zostaną wykorzystanie w zajęciach dydaktycznych na studiach 1-i 2-stopnia WEiTI prowadzonych z wykorzystaniem ww. Laboratorium LTE oraz badaniachi testach wykonywanych przez studentów w środowisku sieciowym „Miasteczka TestowegoTelekomunikacji Polskiej w Politechnice Warszawskiej”. 3
  4. 4. CURRICULUM VITAEPersonal Details:Name: Dinesh MannaniDate of Birth: 28-02-1990Nationality: IndianWork Experience:1. Intern Business Development Team at IS–Wireless, Warsaw, Poland  01-07-2011 to 30-09-20112. English Teacher (Native)  Since 03-2011Career Highlights:1. School Prefect  Head of the Student Union  Represented school at various public events  worked in a team environment to represent students2. President Computer Club at School  Responsible for handling web-designing projects  Responsible for time-management of other participants3. President English Literary Society at School Represented the school at various debate competitions4. Experience in Hospitality Industry5. Experience in website and graphics designingEducation: Completed schooling from Birla Vidya Mandir, Nainital, India o 04-2004 to 03-2008 BSc. in Electrical and Computer Engineering (specialization – Telecommunications) at Warsaw University of Technology (Politechnika Warszawska). Thesis: “Scheduling Algorithms in LTE networks” o 10-2008 to 02-2012Skills:  Knowledge of LTE/WiMax network technologies.  Knowledge of various Routing and internet protocols.  Knowledge about Business Development and CRM  Fluent in English, Hindi.  Working knowledge of Polish.  Working knowledge of Visual Basic, HTML, JavaScript, flash, SQL.  Designing magazines, graphics etc. ………………………….. Signature of the student 4
  5. 5. AcknowledgementThis Bachelors thesis is the final step in obtaining my Bachelor‟s Degree in Electrical andComputer Engineering with specialisation in Telecommunications at the Warsaw Universityof Technology.The thesis was conducted under the supervision of Dr. Mirosław Słomiński, AssociateProfessor in the Telecommunications Department of the Faculty Electronics and InformationTechnology at the Warsaw University of Technology (Politechnika Warszawska). I haveworked on my Bachelor‟s thesis from June, 2011 to January 2012. Here I would like toexpress my sincere gratitude to all those who have provided me with encouragement andguidance during this thesis.First of all I am particularly indebted to Dr. Mirosław Słomiński, my supervisor. He has beena great support since the beginning of the thesis and showed trust in me when I firstapproached him with the aim of finishing my thesis within one working semester. In somecircumstances where I had some unexpected problems during my project he was there to finda solution and provide useful guidance. Further, I want to express my gratitude toDr. Sławomir Kukliński, who was always ready to share his knowledge and experience in thefield of LTE.Secondly, I would like to thank Dr. Sławomir Pietrzyk CEO of IS-Wireless and his team, forlending me invaluable knowledge support along with granting a trial license for their toolLTE MAC Lab. Their help and suggestions have proved as important as the license itself. Iespecially would like to thank Mr. Marcin Dryjański a specialist with IS-Wireless, who hasbeen constantly providing me with concrete suggestions on working with the thesis alongwith answering all questions that I had. 5
  6. 6. Table of Contents1. Introduction .......................................................................................................................... 11 1.1 Background .................................................................................................................... 11 1.2 Motivation and goals of the thesis ................................................................................. 12 1.2.1 Motivation ............................................................................................................... 12 1.2.2 Thesis goals ............................................................................................................. 13 1.3 Thesis Scope .................................................................................................................. 132. An Overview of LTE ........................................................................................................... 14 2.1 LTE requirements .......................................................................................................... 14 2.2 Multiple Access Techniques .......................................................................................... 15 2.2.1 Downlink - Orthogonal Frequency Division Multiple Access (OFDMA) ............. 15 2.2.2 Uplink - Single Carrier - Frequency Division Multiple Access (SC-FDMA) ........ 16 2.3 LTE Frame Structure ..................................................................................................... 17 2.4 LTE Downlink Physical Channels ................................................................................. 18 2.5 LTE Uplink Physical Channels ...................................................................................... 20 2.6 Multiple Input Multiple Output ..................................................................................... 213. Selected Issues of Scheduling .............................................................................................. 23 3.1 Selected Scheduling Algorithms .................................................................................... 24 3.1.1 Round Robin Scheduling ........................................................................................ 24 3.1.2 Max SNIR Scheduling ............................................................................................ 25 3.1.3 Proportional Fair Scheduling .................................................................................. 264. Simulations and Testing ....................................................................................................... 27 4.1 LTE MAC Lab System Level Simulator: An overview ................................................ 27 4.1.1 Simulation Scenarios .............................................................................................. 27 4.1.2 Simulation Results and Analysis ............................................................................ 28 4.2 LTE network test environment ...................................................................................... 50 4.2.1 Testing Scenarios .................................................................................................... 50 4.2.2 Testing Results and Analysis .................................................................................. 505. A Student Lab Experiment................................................................................................... 57 5.1 Simulation Tools ............................................................................................................ 57 5.2 Investigation of scheduling algorithms with LTE MAC Lab Matlab tool..................... 57 5.3 Summary of abilities to be gained during the experiment ............................................. 586. Conclusions and future work ............................................................................................... 59 6.1 Conclusion ..................................................................................................................... 59 6.2 Future work .................................................................................................................... 607. References ............................................................................................................................ 61 7.1 CD contents .................................................................................................................... 62 6
  7. 7. Figures ListFig. 1 : OFDM and OFDMA [28]............................................................................................ 16Fig. 2 : OFDM and SC-FDMA [28] ........................................................................................ 16Fig. 3 : LTE frame structure [18] ............................................................................................. 17Fig. 4 : Frame Type 2 [27] ....................................................................................................... 18Fig. 5 : LTE Downlink channels [18] ...................................................................................... 19Fig. 6 : LTE Uplink Channels [18] .......................................................................................... 20Fig. 7 : Single user MIMO transmission principle [8] ............................................................. 22Fig. 8 : Multi-user MIMO transmission principle [8] .............................................................. 22Fig. 9 : Layer 2 functionalities for dynamic packet scheduling, link adaptation, and HARQManagement [8] ....................................................................................................................... 23Fig. 10 : Flow Chart for Round Robin Algorithm ................................................................... 24Fig. 11 : Flow chart for Max SNIR algorithm ......................................................................... 25Fig. 12 : Flow chart for Proportional Fair Algorithm .............................................................. 26Fig. 13 : A tree diagram for all the scenarios under consideration for simulations ................. 28Fig. 14 : PRB allocation based on SNIR values for single user downlink Case 1................... 29Fig. 15 : Resource Allocation for a single user in downlink Case 1 ........................................ 30Fig. 16 : Throughput Results for single user in downlink Case 1............................................ 30Fig. 17 : PRB allocation based on SNIR values for 3 users .................................................... 31Fig. 18 : Resource allocation by RR algorithm for 3 users in downlink Case 2 ...................... 31Fig. 19 : Resource allocation by Max SNIR algorithm for 3 users in downlink Case 2 .......... 32Fig. 20 : Resource allocation by Max SNIR algorithm for 3 users in downlink Case 2 ......... 32Fig. 21 : Comparison of PRB allocation in all three algorithms over time Case 2 .................. 33Fig. 22 : Comparison of throughput obtained from all three algorithms Case 2 ..................... 33Fig. 23 : Resource allocation by RR algorithm for 3 users in downlink Case 3 ...................... 34Fig. 24 : Resource allocation by Max SNIR algorithm for 3 users in downlink Case 3 .......... 35Fig. 25 : Resource allocation by PF algorithm for 3 users in downlink Case 3....................... 35Fig. 26 : Comparison of PRB allocation in all three algorithms over time Case 3 .................. 36Fig. 27 : Comparison of throughput obtained from all three algorithms Case 3 ..................... 36Fig. 28 : Resource allocation by RR algorithm for 3 users in downlink Case 4 ...................... 37Fig. 29 : Resource allocation by Max SNIR algorithm for 3 users in downlink Case 4.......... 38Fig. 30 : Resource allocation by PF algorithm for 3 users in downlink Case 4....................... 38Fig. 31 : Comparison of PRB allocation in all three algorithms over time downlink Case 4.. 39Fig. 32 : Comparison of throughput obtained from all three algorithms downlink Case 4 ..... 39Fig. 33 : PRB allocation based on SNIR values for single user in uplink Case 1 ................... 40Fig. 34 : Resource Allocation for a single user in uplink Case 1............................................. 41Fig. 35 : Throughput results of single user in uplink Case 1 ................................................... 41Fig. 36 : PRB allocation based on SNIR values for 3 users .................................................... 41Fig. 37 : Resource allocation by RR algorithm for 3 users in uplink Case 2........................... 42Fig. 38 : Resource allocation by Max SNIR algorithm for 3 users in uplink Case 2 .............. 42Fig. 39 : Resource allocation by PF algorithm for 3 users in uplink Case 2 ........................... 43Fig. 40 : Comparison of PRB allocation in all three algorithms over time uplink Case 2 ...... 43Fig. 41 : Comparison of throughput obtained from all three algorithms uplink Case 4 .......... 44Fig. 42 : Resource allocation by RR algorithm for 3 users in uplink Case 3........................... 45Fig. 43 : Resource allocation by Max SNIR algorithm for 3 users in uplink Case 3 .............. 45Fig. 44 : Resource allocation by PF algorithm for 3 users in uplink Case 3 ........................... 46Fig. 45 : Comparison of PRB allocation in all three algorithms over time uplink Case 3 ...... 46Fig. 46 : Comparison of throughput obtained from all three algorithms uplink Case 3 .......... 47 7
  8. 8. Fig. 47 : Resource allocation by RR algorithm for 3 users in uplink Case 4........................... 48Fig. 48 : Resource allocation by Max SNIR algorithm for 3 users in uplink Case 4 .............. 48Fig. 49 : Resource allocation by PF algorithm for 3 users in uplink Case 4 ........................... 48Fig. 50 : Comparison of PRB allocation in all three algorithms over time uplink Case 4 ...... 49Fig. 51 : Comparison of throughput obtained from all three algorithms uplink Case 4 .......... 49Fig. 52 : Throughput results from Download within 5m of eNodeB: 100 MB file ................ 51Fig. 53 : Throughput results from Download within 5m of eNodeB: 200 MB file ................ 51Fig. 54 : Throughput results from Download within 5m of eNodeB: 500 MB file ................ 52Fig. 55 : Throughput results from Download within 5m of eNodeB: 1 GB file..................... 52Fig. 56 : Throughput results from HTTP Download with user 3 at cell edge ......................... 53Fig. 57 : Throughput results from HTTP Download with user 1 & 3 at cell edge .................. 53Fig. 58 : Throughput results from HTTP Download with all 3 users at cell edge ................... 54Fig. 59 : Throughput results from FTP Download within 5m of eNodeB : 500 MB file ........ 54Fig. 60 : Throughput results from FTP Download with user 3 at cell edge ............................ 55Fig. 61 : Throughput results from FTP Download with user 1 & 3 at cell edge ..................... 55Fig. 62 : Throughput results from FTP Download with all 3 users at cell edge ...................... 56Tables ListTable 2.1 : Bandwidth and Resource blocks specifications [1] ............................................... 18Table 4.1 summary of simulation parameters used for all the testing scenarios ..................... 28Table 4.2 : LTE Test Environment Test 1 ............................................................................... 51Table 4.3 : LTE Test Environment Test 2 ............................................................................... 51Table 4.4 : LTE Test Environment Test 3 ............................................................................... 52Table 4.5 : LTE Test Environment Test 4 ............................................................................... 52Table 4.6 : LTE Test Environment Test 5 ............................................................................... 53Table 4.7 : LTE Test Environment Test 6 ............................................................................... 53Table 4.8 : LTE Test Environment Test 7 ............................................................................... 54Table 4.9 : LTE Test Environment Test 8 ............................................................................... 54Table 4.10 : LTE Test Environment Test 9 ............................................................................. 55Table 4.11 : LTE Test Environment Test 10 ........................................................................... 55Table 4.12 : LTE Test Environment Test 11 ........................................................................... 56 8
  9. 9. Abbreviations3GPP – 3rd Generation Partnership ProjectLTE – Long Term EvolutionMMOG – Multimedia Online GamingHSPA – High Speed Packet Access3G – Third Generation of Cellular Wireless StandardsGSM – Global System for Mobile CommunicationUMTS – Universal Mobile Telecommunications SystemUTRA –UMTS terrestrial radio accessE-UTRA – Evolved UMTS terrestrial radio accessUTRAN – UMTS Terrestrial Radio Access NetworkE-UTRAN – Evolved UMTS Terrestrial Radio Access NetworkMIMO – Multiple Input Multiple OutputFDD – Frequency Division DuplexTDD – Time Division DuplexOFDM – Orthogonal Frequency Division MultiplexingOFDMA – Orthogonal Frequency Division Multiple AccessSC-FDMA – Single Carrier Frequency Division Multiple AccessFDMA – Frequency Division Multiple AccessPAPR – Peak to Average Power RatioBS – Base StationeNodeB – Base StationMS – Mobile StationUE – User EquipmentRB – Resource BlockRE – Resource ElementSNIR – Signal to Noise-Interference RatioRR – Round RobinPF – Proportional FairCQI – Channel Quality IndicatorTPSA – Telekomunikacja Polska S.A.DL – DownlinkUL – UplinkHSDPA – High Speed Downlink Packet AccessC.D.F – Cumulative Distribution FunctionEUL – Enhanced UplinkSC – Single CarrierSISO – Single Input Single OutputMME – Mobility Management EntitySGW – Serving GatewayPGW – PDN GatewayCP – Cyclic PrefixDwPTS – Downlink Pilot Time SlotGP – Guard PeriodUpPTS – Uplink Pilot Time SlotPBCH – Physical Broadcast ChannelPCFICH – Physical Control Format Indicator ChannelPDCCH – Physical Downlink Control Channel 9
  10. 10. PHICH – Physical Hybrid ARQ Indicator ChannelHARQ – Hybrid Automatic Retransmission RequestRS – Reference SignalCIR – channel impulse responsePRN – pseudorandom numberP-SS and S-SS – Primary and Secondary Synchronization SignalDC – Dedicated ControlACK – AcknowledgeNACK – Not AcknowledgePDSCH – Physical Downlink Shared ChannelPMCH – Physical Multicast ChannelPUCCH – Physical Uplink Control ChannelPUSCH – Physical Uplink Shared ChannelPRACH – Physical Random Access ChannelWCDMA – Wideband Code Division Multiple AccessPHY – Physical layerMAC – Medium Access ControlRLC – Radio Link ControlRRC – Radio Resource ControlIEEE – Institute of Electrical and Electronics Engineers4G – Fourth Generation of Cellular Wireless StandardsSNR – Signal to Noise RatioPS – Packet SchedulerTTI – Transmission Time IntervalMCS – Modulation and Coding SchemeQoS – Quality of ServiceAMC – Adaptive modulation and codingPRBs – Physical Resource BlocksRRM – Radio Resource ManagementCCI – co-channel interferenceVoIP – Voice over Internet ProtocolQPSK – Quadrature Phase-Shift KeyingQAM – Quadrature Amplitude Modulation 10
  11. 11. 1. IntroductionThis chapter is dedicated to the introduction to the concept of 3rd Generation PartnershipProject (3GPP) Long Term Evolution (LTE) and technological features associated with it.The first section, 1.1, of this chapter will discuss the background information on the subjectof LTE and scheduling. The motivation and goals for the thesis have been discussed in thesections 1.2 and 1.3 respectively with the last section 1.3 presenting the outline of the thesis.1.1 BackgroundOver the recent years we have seen mobile broadband become a reality as more and moreinternet users are getting accustomed to having broadband access wherever they go, and notjust at home or in the office. Multimedia applications such as Multimedia Online Gaming(MMOG), mobile TV, Web 2.0, streaming contents through the Internet have gathered moreattention by the internet generation and have motivated the 3GPP to work on the LTE whichis a successor to High Speed Packet Access (HSPA) currently being used in the 3rdGeneration of Cellular Wireless Standards (3G) networks. LTE is an answer to deliver betterapplications and services to mobile users which consume a lot of bandwidth.The 3GPP is the organisation which stipulates and standardises the specifications for LTEalong with Global System for Mobile Communication (GSM) and 3G Universal MobileTelecommunications System (UMTS) terrestrial radio access (UTRA) systems. It startedwork on the evolution of 3G mobile system in November 2004, and the project came to beknown as LTE. The main focus of this initiative to introduce LTE was on enhancing theUTRA and optimizing 3GPP‟s radio access architecture. A lot of research has been carriedout since 2004 and proposals have been presented on the evolution of the UTRAN. Thespecifications related to LTE are formally known as the evolved UMTS terrestrial radioaccess (E-UTRA) and evolved UMTS terrestrial radio access network (E-UTRAN), but are ingeneral referred as project LTE.The end of year 2008 saw the Release 8 of the 3GPP, which cites the stable specifications forLTE, being frozen. The initial deployment of LTE began in 2010 with many operatorsadopting it gradually. According to Release 8 specs, LTE supports peak rates of 300Mb/swhich could be achieved with the help of Multiple Input Multiple Output (MIMO) and aradio-network delay of less than 5ms. In addition to that it operates on both FrequencyDivision Duplexing (FDD) and Time Division Duplexing (TDD) and can be deployed indifferent bandwidths depending on the availability of spectrum. In TDD configuration theuplink and downlink operate in same frequency band whereas with FDD configuration theuplink and downlink operate in different frequency bands.Orthogonal Frequency Division Multiplexing (OFDM) has been adopted as the downlinktransmission scheme for the 3GPP LTE [11]. The transmission which occurs from the basestation to the User Equipment is referred to as downlink whereas vice-versa uplink. OFDMdivides the transmitted high bit-stream signal into different sub-streams and sends these overmany different/parallel sub-channels. For uplink transmission scheme the 3GPP selected SC-FDMA (Single Carrier – Frequency Division Multiple Access). An uplink is a transmissionfrom the mobile station to the base station. SC-FDMA is a modified form of OrthogonalFrequency Division Multiple Access (OFDMA) and has similar throughput performance and 11
  12. 12. essentially the same overall complexity as OFDMA. Like OFDM, SC-FDMA also consists ofsub-streams but it transmits on sub-channels in sequence not in parallel which is the case inOFDM, which prevents power fluctuations in SC-FDMA signals i.e. low Peak to AveragePower Ratio (PAPR). A base station (BS) is called an Evolved NodeB (eNodeB) in the LongTerm Evolution and a mobile station (MS) is called a User Equipment (UE) in the Long TermEvolution.The data transmission in LTE is organized as physical resources which are represented by atime-frequency resource grid consisting of Resource Blocks (RB). Resource blocks consist ofa no. of Resource Elements (RE). One of the major functionalities that have been assigned tothe BS is scheduling which is carried out by scheduler. The scheduler is responsible forassigning the time and frequency resources to the different UE under the BS coverage. It doesthat by allotting the RBs which are the smallest elements that can be assigned by a scheduler.In the thesis we will be discussing the major scheduling algorithms that are used by theschedulers, they are, Max Signal to Noise-Interference Ratio (SNIR) Scheduling, RoundRobin (RR) Scheduling and Proportional Fair (PF) Scheduling. In brief, the Max SNIRscheduling assigns the resource blocks to the user with the highest Channel Quality Indicator(CQI-received as a feedback from the UE by the BS) on that RB. In Round Robin schedulingthe UEs are assigned the resource blocks in turn (one after another) without taking the CQIinto account, allocating resources to the users equally. In Proportional Fair Scheduling theUEs are assigned the resource blocks on the basis of the best relative channel quality i.e. acombination of CQI & level of fairness desired.The Max SNIR Scheduling, RR Scheduling and PF Scheduling have been simulated in aMATLAB-based System Level Simulator (LTE MAC Lab) from IS-Wireless. Theperformance of these scheduling algorithms in terms of throughput is analysed. We haveconsidered various scenarios for proper analysis in the thesis. Furthermore, the algorithmshave been analysed with their implementation in an LTE network test environment (deployedin the Institute of Telecommunications within the Smart City of TPSA in the WarsawUniversity of Technology).1.2 Motivation and goals of the thesis1.2.1 MotivationThe rise of the wireless industry in the past years along with the innovation of technologiesbringing large amount of multimedia services to the mobile devices led me to work in a fieldwhere I could be a part of this wireless revolution. With LTE the future of mobile broadbandbecomes brighter and clearer. According to various statistics, LTE would be the leadingtechnology to serve mobile broadband to the majority of cellular users in the coming years [6,7].Time and Frequency being scarce resources, the impact and importance of scheduling is veryhigh in a LTE network. To work on such a topic will not only help me to understand thepresent technology and solutions but also help develop a better solution for the future. 12
  13. 13. 1.2.2 Thesis goalsThe main purpose of this thesis is to verify and compare selected downlink and uplinkschedulers in LTE MAC Lab (aka Matlab version of 4G System Lab provided by IS-Wireless) with their implementation in an LTE network test environment (deployed in theInstitute of Telecommunications within the Smart City of TPSA in the Warsaw University ofTechnology). The simulation part of the thesis enables us to understand the schedulingalgorithms for the LTE networks in much more detail and gain experience in modelling andsimulation of such networks in detail. During this thesis a detailed study of the networkarchitecture and layers being proposed for LTE networks is carried out.One of the main contributions of this dissertation is to work out a method to examine LTEscheduling performance evaluation for teaching purposes.1.3 Thesis ScopeThis thesis is organized in 7 chapters. The rest of the chapters are organized as follows:Chapter 2 gives an overview of LTE. Chapter 3 describes the concept of scheduling alongwith the description of the scheduling algorithms under consideration. Chapter 4 discussesthe simulation and testing scenarios and results. Chapter 5 presents teaching proposals in theform of a laboratory experiment. Finally chapter 6 draws the conclusion and givesrecommendations for future works. Chapter 7 details the various sources and references ofstudy. 13
  14. 14. 2. An Overview of LTEThis chapter will provide an insight into the technical details of Long Term Evolution asunderlined by the 3GPP. The chapter starts with describing the LTE requirements, thetransmission schemes used for uplink and downlink, followed by other important featureslike MIMO.2.1 LTE requirementsThe 3GPP has laid out specific requirements that need to be fulfilled by LTE which are listedin [10], with some of them listed below:Peak Data Rates:E-UTRA should support significantly increased instantaneous peak data rates. The supportedpeak data rate should scale according to size of the spectrum allocation.Note that the peak data rates may depend on the numbers of transmit and receive antennas atthe UE. The targets for downlink (DL) and uplink (UL) peak data rates are specified in termsof a reference UE configuration comprising:a) DL capability – 2 receive antennas at UEb) UL capability – 1 transmit antenna at UEFor this baseline configuration, the system should support an instantaneous downlink peakdata rate of 100Mb/s within a 20 MHz downlink spectrum allocation (5 bps/Hz) and aninstantaneous uplink peak data rate of 50Mb/s (2.5 bps/Hz) within a 20MHz uplink spectrumallocation.Latency:A user plane latency of less than 5 ms one-way and a control plane transition time of less than50 ms from dormant to active mode and less than 100 ms from idle to active mode.User throughput:Downlink:2-3 times higher downlink throughput than High Speed Downlink Packet Access (HSDPA)Release 6 at the 5% point of the Cumulative Distribution Function (C.D.F).3-4 times higher average downlink throughput than HSDPA Release 6.The user throughput should scale with the spectrum bandwidth.Uplink:2-3 times higher uplink than Release 6 Enhanced UL at the 5% point of the CDF.2-3 times higher average uplink throughput than Release 6 Enhanced UL (EUL).The user throughput should scale with the spectrum bandwidth provided that the Maximumtransmit power is also scaled.Mobility:LTE shall support mobility across the cellular network and should be optimized for 0 to 15km/h. Furthermore, should support also higher performance at 15 and 120 km/h. Connection 14
  15. 15. shall be maintained at speeds from 120 km/h to 350 km/h (or even up to 500 km/h dependingon the frequency band).Spectrum efficiency:3-4 times higher spectrum efficiency (in bits/s/Hz/site) in downlink and 2-3 times higher inuplink, compared to Release 6 HSDPA and EUL respectively.Bandwidth/Spectrum flexibility:LTE should support several different spectrum allocation sizes such as: 1.25 MHz, 1.6 MHz,2.5 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz. in both uplink and downlink where thelatter is used to achieve the highest peak data rate, with both TDD and FDD modes. It shouldalso support the flexibility to modify the radio resource allocation for broadcast transmissionaccording to specific demand or operator‟s policy.Furthermore the communication can take place both in paired (FDD) and unpaired (TDD)bands. Paired frequency bands means that the uplink and downlink transmissions use separatefrequency bands, while in the unpaired frequency bands downlink and uplink share the samefrequency band.Coverage:Cell ranges up to 5 km support the above targets; up to 30 km will suffer some degradation inthroughput and spectrum efficiency and up to 100 km will have overall performancedegradation.Given some of the advantages of an OFDM approach, 3GPP has specified OFDMA as thebasis of its LTE effort.2.2 Multiple Access Techniques3GPP LTE have selected different transmission schemes in uplink and downlink due tocertain characteristics. OFDMA has been selected for downlink i.e. from eNodeB to UE andSC-FDMA has been selected for uplink i.e. for transmission from UE to eNodeB [12].2.2.1 Downlink - Orthogonal Frequency Division Multiple Access(OFDMA)For downlink transmission LTE uses OFDMA which splits the data stream into many slowerdata streams that are transported over many carriers simultaneously. The main advantage ofmany slow but parallel data streams is that it leads to elongation of the transmission stepswhich in turn help to avoid the issues of multipath transmission on fast data streams. Thisscheme helps allocate radio resources to multiple users based on frequency (subcarriers) andtime (symbols) using OFDM. For LTE, OFDM subcarriers are typically spaced at 15 kHz andmodulated with QPSK, 16-QAM, or 64-QAM modulation. 15
  16. 16. Fig. 1 : OFDM and OFDMA [28]The full potential of OFDMA is utilised by proper scheduling as it allows the resources to beused between multiple users flexibly by sharing the subcarriers, with differing bandwidthavailable to each user versus time.2.2.2 Uplink - Single Carrier - Frequency Division Multiple Access (SC-FDMA)For uplink transmission the use of OFDMA is not ideal because of its high PAPR when thesignals from multiple subcarriers are combined and hence as a result an alternative to OFDMwas sought for use in the LTE uplink. And as we know power consumption is a keyconsideration for UE terminals and for this there was a need to adopt a transmission schemewhich wouldn‟t comprise with the requirements of LTE without putting too much pressure onthe power consumption of UEs. The solution came up in the form of SC-FDMA that suitsvery well with the LTE uplink requirements. The transmitter and receiver architecture isnearly the same as OFDMA. Furthermore it also offers the same degree of multipathprotection. Fig. 2 : OFDM and SC-FDMA [28]In SC-FDMA instead of dividing the data stream and putting the resulting substreams directlyon the individual subcarriers, the time-based signal is converted to a frequency-based signalwith an FFT function. This distributes the information of each bit onto all subcarriers that willbe used for the transmission and thus reduces the power differences between the subcarriers[18]. 16
  17. 17. 2.3 LTE Frame StructureAs per the description of LTE frame structure in [28] the downlink and uplink transmissionsare grouped in (radio) frame of length 10 milliseconds (ms). Each radio frame is divided into10 subframes of 1ms duration each, with the subrame being further divided into 2 slots thatare 0.5 ms each. Each slot consists of 7 or 6 OFDM symbols for normal or extended cyclicprefix used respectively [5]. The LTE frame structure is illustrated in the Fig. 3.The smallest modulation structure in LTE is one symbol in time vs. one subcarrier infrequency and is called a Resource Element (RE). Resource Elements are further aggregatedinto Resource Blocks (RB), with the typical RB having dimensions of 7 symbols by 12subcarriers. The RE and RB structure is also shown in Fig. 3. The number of symbols in a RBdepends on the Cyclic Prefix (CP) in use. During the use of normal CP the RB contains sevensymbols, whereas in case of extended CP which is used due for extreme delay spread ormultimedia broadcast modes, the RB contains six symbols. Fig. 3 : LTE frame structure [18]Due to the spectrum flexibility two frame types are defined for LTE, with Type 1 being usedin FDD while Type 2 is being used in TDD. Type 1 frames consist of 20 slots with slotduration of 0.5 ms as discussed previously; whereas Type 2 frames contain two half frames,where at least one of the half frames contains a special subframe carrying three fields ofswitch information including Downlink Pilot Time Slot (DwPTS), Guard Period (GP) andUplink Pilot Time Slot (UpPTS). If the switch time is 10 ms, the switch information occursonly in subframe one. If the switch time is 5 ms, the switch information occurs in both halfframes, first in subframe one, and again in subframe six. Subframes 0 and 5 and DwPTS are 17
  18. 18. always reserved for downlink transmission. UpPTS and the subframe immediately followingUpPTS are reserved for uplink transmission. Other subframes can be used for either uplink ordownlink. Frame Type 2 is illustrated in Fig. 4. Fig. 4 : Frame Type 2 [27]The number of RBs that can fit within a given channel bandwidth varies proportionally to thebandwidth. Logically, as the channel bandwidth increases, the number of RBs can increase.The transmission bandwidth configuration is the maximum number of Resource Blocks thatcan fit within the channel bandwidth with some guard band [28]. The table 2.1 shows theLTE bandwidth and resource configuration. Table 2.1 : Bandwidth and Resource blocks specifications [1]We can notice here that subcarrier spacing remains same in all bandwidth configurations. Thebest results in terms of throughput can be achieved by the bandwidth with maximum amoutof RBs.2.4 LTE Downlink Physical ChannelsAs in other networks like UMTS, all higher layer signalling and user data traffic areorganized by the means of proper channels. In LTE the downlink channels have been definedin [28] the following way: 18
  19. 19. Fig. 5 : LTE Downlink channels [18]We will be discussing the role and description of the physical downlink channels [28]involved in LTE:Physical Broadcast Channel (PBCH)The PBCH is used to send cell-specific system identification and access control parametersevery 4th frame (40 ms) using Quadrature Phase Shift Keying (QPSK) modulation. Thestructure of PBCH is independent of the actual network bandwidth.Physical Downlink Shared Channel (PDSCH)The PDSCH is used to transport user data and is designed for high data rates. The ResourceBlocks associated with this channel are shared among users via OFDMA. The various optionsfor modulation include QPSK, 16- Quadrature Amplitude Modulation (QAM), and 64-QAM.Spatial multiplexing is exclusive to the PDSCH.Physical Control Format Indicator Channel (PCFICH)The PCFICH is used to inform the UE how many OFDM symbols will be used for the controlinformation in PDCCH in a subframe. The number of symbols used ranges from 1 to 3. ThePCFICH uses QPSK modulation.Physical Downlink Control Channel (PDCCH)The PDCCH is used to inform UE about the uplink and downlink resource schedulingallocations. It maps onto resource elements in up to the first three OFDM symbols in the firstslot of a subframe and uses QPSK modulation. The value of the PCFICH indicates thenumber of symbols used for the PDCCH.Physical Multicast Channel (PMCH)The PMCH carries multimedia broadcast information with the use of modulation includingQPSK, 16-QAM, or 64-QAM. Multicast information can be sent to multiple UEsimultaneously. 19
  20. 20. Physical Hybrid Automatic Retransmission Request (HARQ) Indicator Channel(PHICH)PHICH carries Acknowledge (ACK)/Not Acknowledge (NACKs) in the downlink inresponse to uplink transmissions in order to request retransmission or confirm the receipt ofblocks of data from the UE. ACKs and NACKs are implemented in HARQ mechanism.Reference Signal (RS)Reference signal is used by UE for downlink channel estimation. It allows the UE todetermine the channel impulse response (CIR). RS‟s are the product of a two-dimensionalorthogonal sequence and a two-dimensional pseudo-random sequence. Since there are 3different sequences available for the orthogonal sequence and 170 possible sequences for thepseudorandom number (PRN), the specification identifies 510 RS sequences. The RS uses thefirst and fifth symbols under normal CP operation, and the first and fourth symbols forextended CP operation; the location of the RS on the subcarriers varies.Primary and Secondary Synchronization Signal (P-SS and S-SS)UEs use the Primary Synchronization Signal (P-SS) for timing and frequency acquisitionduring cell search. The PSS carries part of the cell ID and provides slot timingsynchronization. It is transmitted on 62 of the reserved 72 subcarriers (6 Resource Blocks)around Dedicated Control (DC) on symbol 6 in slot 0 and 10 and uses one of three Zadoff-Chu sequences. UEs use the Secondary Synchronization Signal (S-SS) in cell search. Itprovides frame timing synchronization and the remainder of the cell ID, and is transmitted on62 of the reserved 72 subcarriers (6 Resource Blocks) around DC on symbol 5 in slot 0 and10. The S-SS uses two 31-bit binary sequences and BPSK modulation.2.5 LTE Uplink Physical ChannelsIn LTE the uplink channels have been defined in [28] the following way: Fig. 6 : LTE Uplink Channels [18] 20
  21. 21. We will be discussing the role and description of the physical uplink channels [28] involvedin LTE:Physical Uplink Control Channel (PUCCH)The PUCCH carries uplink control information and is never transmitted simultaneously withPUSCH data. PUCCH conveys control information including channel quality indication(CQI), ACK/NACK responses of the UE to the HARQ mechanism, and uplink schedulingrequests.Physical Uplink Shared Channel (PUSCH)Uplink user data is carried by the PUSCH. Resources for the PUSCH are allocated on a sub-frame basis by the UL scheduler. Subcarriers are allocated in units of RBs, and may behopped from sub-frame to sub-frame. The PUSCH may employ QPSK, 16-QAM, or 64-QAM modulation.Physical Random Access Channel (PRACH)The PRACH carries the random access preamble and coordinates and transports randomrequests for service from UE‟s. The PRACH channel transmits access requests (bursts) whena wireless device desires to access the LTE network (call origination or paging response).Uplink Reference SignalThere are two variants of the UL reference signal. The demodulation reference signalfacilitates coherent demodulation, and is transmitted in the fourth SC-FDMA symbol of theslot. A sounding reference signal is also used to facilitate frequency dependent scheduling.Both variants of the UL reference signal use Constant Amplitude Zero Autocorrelation(CAZAC) sequences.2.6 Multiple Input Multiple OutputA major step in order to increase the data transmission rates was achieved by includingMIMO in the first release of LTE. LTE supports multiple antenna operation both in terms oftransmit diversity as well as spatial multiplexing with up to four layers. The use of MIMOwith OFDMA has some favourable properties compared to Wideband Code DivisionMultiple Access (WCDMA) because of its ability to cope effectively with multi-pathinterference [8]. The main features of MIMO help in improving the network performance as,transmit diversity can be used to increase the robustness of communication in fading channelsby transmitting multiple replicas of the transmitted signal from different antennas whereasspatial multiplexing can help increase the peak data rates as compared to the non-MIMOscenarios by a factor of 2 to 4, depending on the eNodeB and the UE antenna configuration. 21
  22. 22. Fig. 7 : Single user MIMO transmission principle [8]In LTE all the device categories with exception of the simplest, support MIMO capability. Fig. 8 : Multi-user MIMO transmission principle [8]The eNodeBs can also have multiple antennas without any adverse impact on the non-MIMOUE as all devices can cope with the transmit diversity up to four antennas. 22
  23. 23. 3. Selected Issues of SchedulingThis chapter along with explaining the concept of scheduling will give details of the variousdownlink and uplink scheduling algorithms used in LTE.In general terms, scheduling is basically the process of making decisions by a schedulerregarding the assignment of various resources (time and frequency) in a telecommunicationssystem between users. In LTE the scheduling is carried out at eNodeB by dynamic packetscheduler (PS) which decides upon allotment of resources to various users under its coverageas well as transmission parameters including modulation and coding scheme (MCS). Asearlier discussed, LTE defines 1 ms subframes as the Transmission Time Interval (TTI)resulting in the scheduling of resources every 1 ms. It means after every 1 ms the assignmentof resources could change depending upon various factors including CQI (Channel QualityIndicator) sent as a feedback by the user to the eNodeB.The process of selecting the transmission parameters and Modulation and Coding Scheme(MCS) is known as Link Adaption (LA). Link adaption along with scheduling of resources ismeant to maximize the cell capacity, while making sure that the minimum Quality of Service(QoS) requirements are met and there are adequate resources also for best-effort bearers withno strict QoS requirements [8]. LA adjusts the data rate with the help of Adaptive modulationand coding (AMC) by matching the modulation and the channel coding scheme on resourcesassigned by the scheduler. In situations with advantageous channel conditions, AMC selects ahigher modulation order and coding rate and vice versa. Fig. 9 : Layer 2 functionalities for dynamic packet scheduling, link adaptation, and HARQ Management [8] 23
  24. 24. In LTE networks, the role of resource scheduling is very important because greatperformance gain can be achieved by properly observing the amount of radio resourcesassigned to each user. As the 3GPP hasn‟t standardised any scheduling algorithm, we are freeto choose and implement any algorithm that would meet the expected our QoS. Whilechoosing or designing a scheduling algorithm many factors such as expected QoS level, thebehaviour of data sources, and the channel status have to be kept in mind. The problembecomes more complex in the presence of users with different requirements in term ofbandwidth, tolerance to delay, and reliability [13].3.1 Selected Scheduling AlgorithmsThere are various scheduling methods that have been developed over time to enhance theprocess of scheduling. But in this thesis, we shall be concentrating on particularly threealgorithms which have been implemented in the software environment provided for testing byIS-Wireless.Among them are:–Round Robin,–Max SNIR, and–Proportional Fair.3.1.1 Round Robin SchedulingThis scheduling method is based on the idea of being fair in the long term by assigning equalno. of Physical Resource Blocks (PRBs) to all active UEs. It operates by assigning the PRBsto UEs in turn i.e one after another without taking into account their CQI. Hence the users areequally scheduled. For e.g. If we have 4 users U1, U2, U3, U4 and PRBs, this algorithm willassign the resources in the following manner: U1, U2, U3, U4, U1, and U2. It can beillustrated by the following flow chart: Fig. 10 : Flow Chart for Round Robin Algorithm 24
  25. 25. The main advantage of this kind of scheduling is the relative ease in its implementationwhereas the major disadvantage is the fact that it does not take into account user CQIfeedback, which may lead to lower and unequal throughput.3.1.2 Max SNIR SchedulingThe Max SNIR scheduling algorithm assigns the PRBs to the UE with the highest CQI onthat RB obtained in the form of feedback from the UE. Hence, for this method to workproperly the UE must feedback the CQI to the eNodeB. This algorithm helps in improvingthe user throughput by assigning the PRB to the UE with good channel quality as a resultenhancing its peak data performance. The scheduling process can be seen in flow chart: Fig. 11 : Flow chart for Max SNIR algorithmMax SNIR algorithm can increase the cell capacity at the expense of the fairness. In thisscheduling strategy, UEs located far from the eNodeB (i.e. cell-edge) are unlikely to bescheduled. 25
  26. 26. 3.1.3 Proportional Fair SchedulingThis algorithm assigns the PRBs to the UE with the best relative channel quality i.e. acombination of CQI & level of fairness desired. There are various versions of PF algorithmbased on values it takes into account. Main goal of this algorithm is to achieve a balancebetween Maximising the cell throughput and fairness, by letting all users to achieve aminimum QoS (Quality of Service). Fig. 12 : Flow chart for Proportional Fair AlgorithmThe above Fig. 12 depicts one of the possible methods of implementing proportional fairalgorithm. Such an algorithm is designed to be better in terms of average user throughput aswell as being fair to most of the users and meeting the minimum QoS requirements during thescheduling process. 26
  27. 27. 4. Simulations and TestingThis chapter is meant for the analysis of the scheduling algorithms we have discussed in theearlier section by means of simulations and practical experiments. The analysis has beencarried out by comparing the throughput for different scenarios (different schedulingschemes, different environment models and different number of users). Along with thesimulations, the practical work will be carried out in LTE network test environment(deployed in the Institute of Telecommunications within the Smart City of TPSA in theWarsaw University of Technology). This practical test environment is designed to analyse theLTE network performance. A detailed description of each used tool is given in this chapter.Then graphical representations of the performance of these scheduling algorithms in terms ofthroughputs are plotted.4.1 LTE MAC Lab System Level Simulator: An overviewAccording to the materials [24] provided by IS-Wireless: The Matlab version of 4G SystemLab™ also known as LTE MAC Lab belongs to the category of system-level simulators trulyreflecting the behaviour of a modelled radio access network. A tool user selects andconfigures the LTE radio interface, chooses appropriate channel and traffic models, definesthe network to be analysed, makes the choice on the set of Radio Resource Management(RRM) functionalities and runs the simulation. The tool is time-driven and models, with highaccuracy, all the events that happen within a radio network. This includes terminals mobility,cell selection / reselections, attach, random access, admission control, handovers, powercontrol, scheduling and many more. Special attention is given to co-channel interference(CCI) control, where functionalities managing CCI can be easily modelled and verified. Aftersimulation, user-defined network statistics collected over defined observation time windoware available as reports for post processing.The role played by RRM features in LTE, LTE-Advanced will be far greater than in previouswireless systems. Therefore decision to put special emphasis on appropriate modelling ofRRM features was taken. This constitutes the cornerstone of 4G System Lab™ anddifferentiates it significantly from the classical RNP tools. LTE MAC Lab provides plenty ofrepresentative algorithms for RRM and CCI control. It is a continuously evolving product. Inthe near future it will include features belonging to 3GPP Rel 9 and more importantly to Rel10 – also known as LTE-Advanced.4.1.1 Simulation ScenariosIn order to verify and compare the scheduling algorithms with the help of LTE MAC Lab, wehave selected no. of scenarios. These scenarios are meant to help us understand the workingof the scheduling algorithms in downlink and uplink. We investigate the performance of thescheduling algorithms in terms of resource allocations and throughput for different scenarios(different scheduling methods, different channel models and different number of users). Hereis a chart depicting the cases that are considered: 27
  28. 28. Testing Scenarios Downlink Uplink Proportional Proportional Round Robin Max SNIR Round Robin Max SNIR Fair Fair ...... ........ ....... ....... ....... MultipleSingle User Users Stationary High Mobile One user at cell edge Fig. 13 : A tree diagram for all the scenarios under consideration for simulations The scenarios have been selected to analyse the impact of the scheduling algorithms in different conditions, hence understand their functioning in much more detail. 4.1.2 Simulation Results and Analysis In this section all the simulation results are presented along with their analysis. During the simulations we will be set some basic default parameters which are depicted below: Table 4.1 summary of simulation parameters used for all the testing scenarios Parameters Value Number of Equipment (UEs) 1or 3 Number of base station 1 Bandwidth 3 MHz Channel type Stationary and Vehicular (Highly Mobile) Simulation length 150 TTI Scheduling algorithms Round Robin, Max SNIR and Proportional Fair 28
  29. 29. Multipath Model 3GPP model Environment Type Urban Frequency 850 MHZ Model Type 3GPP model Base Station height 20 m Base Station Antenna Characteristic Omnidirectional User Equipment height 1.5 m BLER 10^(-1) FFT Size 256 Transmission Scheme SISOThe parameters have been considered so as to create the most appropriate simulationenvironment that is relative to real scenarios.Downlink ScenarioCase 1: Single User, High mobility, Using Round Robin, Max SNIR and Proportional Fairscheduling algorithmsIn this first case we simulate a single user and we show the resource allocations and userthroughput for different SNIR values. We have plotted graph depicting the SNIR measuredfor each PRB which eventually impacts the scheduling along with a single graph depictingthe resource allocations and throughput, respectively, for different scheduling algorithms(RR, Max SNIR, PF) as in case of single user the scheduling algorithm does not impact theresource allocations as all resources are allocated by default to the single user. Measured SNIR for 1 user in Downlink in the frequency axis (3 MHz band) 25 User 1 20 15 SNIR in dB 10 5 0 0 2 4 6 8 10 12 14 16 PRB number Fig. 14 : PRB allocation based on SNIR values for single user downlink Case 1 29
  30. 30. The SNIR values have been limited to the range of -2 dB to 25 dB like in a realistic scenarioso as to derive results which reflect the real life situation. Scheduler allocations for single user 16 14 12 10 PRB 8 6 4 2 20 40 60 80 100 120 140 TTI Fig. 15 : Resource Allocation for a single user in downlink Case 1All the resources are assigned to the single user as no scheduling algorithm kicks in untilthere is more than a single user under an eNodeB. Throughput vs TTI for 1 user 6 User 1 5 4 Mbit/s 3 2 1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 TTI * 10 Fig. 16 : Throughput Results for single user in downlink Case 1Fig. 15 depicts the allocation of resources to the user which in our case is complete allocationfor single user, followed by Fig. 16 which shows user throughput achieved. We observe thatthe throughput is limited to around 4.5 – 5 Mbps because of various factors such as SNIRvalues. We can reach a Maximum throughput of 13.2 Mb/s, if all conditions are favourable. 30
  31. 31. Case 2: 3 Users, Stationary, Using Round Robin, Max SNIR and Proportional Fairscheduling algorithmsIn this case we simulate 3 users and we show the resource allocations and user throughput fordifferent SNIR values. We have plotted graph depicting the initial SNIR measured for eachPRB which eventually impacts all the scheduling algorithms followed by plots depicting theresource allocations and throughput for different scheduling algorithms (RR, Max SNIR, PF). Measured SNIR for 3 users in Downlink in the frequency axis (3 MHz band) 25 User 1 User 2 User 3 20 15 SNIR in dB 10 5 0 0 2 4 6 8 10 12 14 16 PRB number Fig. 17 : PRB allocation based on SNIR values for 3 users This figure is valid for all multi-user cases, as the initial SNIR settings will remain same throughout our simulation experiments in order to compare data collected properly. Round Robin Scheduler allocations 16 14 12 10 PRB 8 6 4 2 20 40 60 80 100 120 140 TTI Fig. 18 : Resource allocation by RR algorithm for 3 users in downlink Case 2 31
  32. 32. Fig. 18 depicts the allocation of resources by Round Robin algorithm in which each user getsallocated the same number of resources. MaxSNIR Scheduler allocations 16 14 12 10 PRB 8 6 4 2 20 40 60 80 100 120 140 TTI Fig. 19 : Resource allocation by Max SNIR algorithm for 3 users in downlink Case 2We can observe that the allocation of resources in Fig. 19 is as per the SNIR values of eachuser; hence the higher a user has SNIR the more resources get allocated to it. Proportional Fair Scheduler allocations 16 14 12 10 PRB 8 6 4 2 20 40 60 80 100 120 140 TTI Fig. 20 : Resource allocation by Max SNIR algorithm for 3 users in downlink Case 2 32
  33. 33. Fig. 20 shows how the PF algorithm first starts out by allocating equal no. of resources toeach user and then eventually shares the resources such that each user is able to attain highestequal throughput. Number of allocated PRB MAX SNIR scheduler 1500 User 1 User 2 1000 User 3 500 20 40 60 80 100 120 140 TTI Round Robin scheduler Number of allocated PRB 1500 User 1 User 2 1000 User 3 500 20 40 60 80 100 120 140 TTI Proportional Fair scheduler Number of allocated PRB 1500 User 1 User 2 1000 User 3 500 20 40 60 80 100 120 140 TTI Fig. 21 : Comparison of PRB allocation in all three algorithms over time Case 2 Throughput vs TTI for 3 users :Downlink Round Robin scheduler 2 User 1 Mbit/s 1 User 2 User 3 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 TTI * 10 Throughput vs TTI for 3 users :Downlink MAX SNIR scheduler 2 User 1 Mbit/s 1 User 2 User 3 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 TTI * 10 Throughput vs TTI for 3 users :Downlink Proportional Fair scheduler 2 User 1 Mbit/s 1 User 2 User 3 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 TTI * 10 Fig. 22 : Comparison of throughput obtained from all three algorithms Case 2In the above plots we can see the how each scheduling algorithm carries out the task ofresource allocation. In Fig. 18 we can see the resources being allocated in a cyclic way to 33
  34. 34. each user irrespective of their SNIR values, in Fig. 19 we see the Max SNIR scheduler allotsmore resources to the users having a higher SNIR than the other and in Fig. 20 we observethe Proportional Fair scheduler assigning resources in terms of fairness in the beginning andthen trying to balance the fairness and best throughput results for each user. In Fig. 21 we cananalyse the allotment of PRB over time using each scheduling algorithm, it also shows thefairness of these algorithms quite clearly. The last Fig. 22 shows the throughput resultsachieved with the help of these scheduling algorithms and helps us compare them. We canobserve that Round Robin algorithm delivers fairness to all the users, the Max SNIRalgorithm has the Maximum throughput but not all users are able to enjoy the best speed andthe Proportional Fair algorithm tries to strike a balance between fairness and achieving theMaximum throughput.Case 3: 3 Users, High Mobile (Vehicular), Using Round Robin, Max SNIR and ProportionalFair scheduling algorithmsIn this case we simulate 3 users moving at a speed of 100 Kmph and we show the resourceallocations and user throughput for different SNIR values. We have plotted graph depictingthe initial SNIR measured for each PRB which eventually impacts all the schedulingalgorithms followed by plots depicting the resource allocations and throughput for differentscheduling algorithms (RR, Max SNIR, and PF).Please refer to Fig. 17 for initial PRB allocations based on SNIR values. Round Robin Scheduler allocations 16 14 12 10 PRB 8 6 4 2 20 40 60 80 100 120 140 TTI Fig. 23 : Resource allocation by RR algorithm for 3 users in downlink Case 3Fig. 23 depicts the allocation of resources by Round Robin algorithm in which each user getsallocated the same number of resources without taking into consideration any otherparameters. 34
  35. 35. MaxSNIR Scheduler allocations 16 14 12 10 PRB 8 6 4 2 20 40 60 80 100 120 140 TTI Fig. 24 : Resource allocation by Max SNIR algorithm for 3 users in downlink Case 3We observe that the allocation of resources in Fig. 24 is still as per the SNIR values of eachuser; the change of speed does not affect the allocations until unless the SNIR also changessignificantly, hence the higher a user has SNIR the more resources get allocated to it. Proportional Fair Scheduler allocations 16 14 12 10 PRB 8 6 4 2 20 40 60 80 100 120 140 TTI Fig. 25 : Resource allocation by PF algorithm for 3 users in downlink Case 3 35
  36. 36. We can notice the difference between the Fig. 20 and Fig. 25 both depicting the allocation asper PF with the channel of channel conditions. MAX SNIR scheduler Number of allocated PRB 1500 User 1 1000 User 2 User 3 500 20 40 60 80 100 120 140 TTI Round Robin scheduler Number of allocated PRB 1500 User 1 1000 User 2 User 3 500 20 40 60 80 100 120 140 TTI Proportional Fair scheduler Number of allocated PRB 1500 User 1 1000 User 2 User 3 500 20 40 60 80 100 120 140 TTI Fig. 26 : Comparison of PRB allocation in all three algorithms over time Case 3 Throughput vs TTI for 3 users :Downlink Round Robin scheduler 2 Mbit/s 1 User 1 User 2 User 3 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 TTI * 10 Throughput vs TTI for 3 users :Downlink MAX SNIR scheduler 3 2 Mbit/s User 1 1 User 2 User 3 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 TTI * 10 Throughput vs TTI for 3 users :Downlink Proportional Fair scheduler 2 Mbit/s 1 User 1 User 2 User 3 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 TTI * 10 Fig. 27 : Comparison of throughput obtained from all three algorithms Case 3We can observe from Fig. 23 that Round Robin algorithm delivers fairness to all the users,the Max SNIR algorithm has the Maximum throughput for user 2 but not all users are able toenjoy the best throughput and the Proportional Fair algorithm tries to strike a balance 36
  37. 37. between fairness and achieving the Maximum throughput. The throughput results are a bitbetter due to the fact all users are located within 7-8 m radius from the base station and thechange of SNIR values has a positive effect in the small time frame under consideration, buteventually as the distance of users from the eNodeB increases there should be degradation inthroughput.Case 4: 3 Users (user 1 at cell edge), High Mobile (Vehicular), Using Round Robin, MaxSNIR and Proportional Fair scheduling algorithmsIn this case we simulate 3 users moving at a speed of 100 Kmph with user 1 at cell edge andwe show the resource allocations and user throughput for different SNIR values. We haveplotted graph depicting the initial SNIR measured for each PRB which eventually impacts allthe scheduling algorithms followed by plots depicting the resource allocations and throughputfor different scheduling algorithms (RR, Max SNIR, and PF).Please refer to Fig. 17 for initial PRB allocations based on SNIR values. Round Robin Scheduler allocations 16 14 12 10 PRB 8 6 4 2 20 40 60 80 100 120 140 TTI Fig. 28 : Resource allocation by RR algorithm for 3 users in downlink Case 4The changes in channel conditions still do not affect the behaviour of RR algorithm as itallocates the resources equally among all users no matter what conditions. 37
  38. 38. MaxSNIR Scheduler allocations 16 14 12 10 PRB 8 6 4 2 20 40 60 80 100 120 140 TTI Fig. 29 : Resource allocation by Max SNIR algorithm for 3 users in downlink Case 4 Proportional Fair Scheduler allocations 16 14 12 10 PRB 8 6 4 2 20 40 60 80 100 120 140 TTI Fig. 30 : Resource allocation by PF algorithm for 3 users in downlink Case 4The above figure depicts the resource block allocation to the users. We observe that User 1 isscheduled equally in the Round Robin algorithm in Fig. , but the Max SNIR algorithm shownin Fig. 29, it has the least allocated resources due to its SNIR values. We also observe that inthe Proportional Fair algorithm depicted in Fig. 30 the algorithm tries to allot more resourcesin order to facilitate higher throughput. 38
  39. 39. MAX SNIR scheduler Number of allocated PRB 1500 User 1 1000 User 2 User 3 500 20 40 60 80 100 120 140 TTI Round Robin scheduler Number of allocated PRB 1500 User 1 1000 User 2 User 3 500 20 40 60 80 100 120 140 TTI Proportional Fair scheduler Number of allocated PRB 1500 User 1 1000 User 2 User 3 500 20 40 60 80 100 120 140 TTI Fig. 31 : Comparison of PRB allocation in all three algorithms over time downlink Case 4 Throughput vs TTI for 3 users :Downlink Round Robin scheduler 2 Mbit/s User 1 1 User 2 User 3 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 TTI * 10 Throughput vs TTI for 3 users :Downlink MAX SNIR scheduler 3 User 1 2 Mbit/s User 2 User 3 1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 TTI * 10 Throughput vs TTI for 3 users :Downlink Proportional Fair scheduler 2 Mbit/s User 1 1 User 2 User 3 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 TTI * 10 Fig. 32 : Comparison of throughput obtained from all three algorithms downlink Case 4As a conclusion we can say that in the downlink the throughput results are not much affectedby the channel conditions provided that SNIR values do not change significantly. The MaxSNIR and RR scheduling algorithms provide consistent results while the PF algorithm tries toachieve the best throughput within available conditions. 39
  40. 40. Scenario UplinkCase 1: Single user, Stationary, Using Round Robin, Max SNIR and Proportional Fairscheduling algorithmsIn this case we simulate a single stationary user. We show the resource allocations and userthroughput for different SNIR values. We have plotted graph depicting the initial SNIRmeasured for each PRB which eventually impacts all the scheduling algorithms followed byplots depicting the resource allocations and throughput for different scheduling algorithms(RR, Max SNIR, and PF). Measured SNIR for 1 user in Uplink in the frequency axis (3 MHz band) 25 User 1 20 15 SNIR in dB 10 5 0 0 2 4 6 8 10 12 14 16 PRB number Fig. 33 : PRB allocation based on SNIR values for single user in uplink Case 1The same settings were chosen for the simulations in uplink also so as to facilitate analysis ofresults. Round Robin Scheduler allocations 16 14 12 10 PRB 8 6 4 2 20 40 60 80 100 120 140 TTI 40

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