LTE vs. WiMAX: A technical comparison and analysis of ...cradpdf.drdc-rddc.gc.ca/PDFS/unc116/p536469_A1b.pdf · LTE vs. WiMAX: A technical comparison and analysis of their PHY and

LTE vs. WiMAX: A technical comparison and analysis of their PHY and MAC layers Michelle Wang and Jean-François Beaumont

Defence R&D Canada – Ottawa

Technical Memorandum DRDC Ottawa TM 2011-121

November 2011

LTE vs. WiMAX: A technical comparison andanalysis of their PHY and MAC layers

Michelle Wang

Jean-Francois Beaumont

Defence R&D Canada – OttawaTechnical Memorandum

DRDC Ottawa TM 2011-121

November 2011

Principal Author

Original signed by Michelle Wang

Michelle Wang

Approved by

Original signed by Bill Katsube

Bill KatsubeHead/Communications and Navigation Electronic Warfare

Approved for release by

Original signed by Chris McMillan

Chris McMillanChair/Document Review Panel

c© Her Majesty the Queen in Right of Canada as represented by the Minister ofNational Defence, 2011

c© Sa Majeste la Reine (en droit du Canada), telle que representee par le ministrede la Defense nationale, 2011

Abstract

This report presents a technical comparison and analysis of two developing pre-fourthgeneration (pre-4G) wireless communications systems: the long term evolution (LTE)and the worldwide interoperability for microwave access (WiMAX). This analysis isused to speculate on the possible evolutionary directions of 4G systems since thedeveloping direction of the earlier generations of wireless communications systemshas been historically strongly directed by their technological aspects. Special focus islaid on the air interface, especially the physical (PHY) layer and media access control(MAC) layers as defined by the open system interconnection (OSI) model. Thehigher layers are briefly discussed to provide a better understanding of the overallsystems’ operation. The two pre-4G systems appear to use similar technologies thatare optimized for each system. Because of the technological similarity, other factorssuch as business and marketing, may then be more important determinants of thepre-4G systems’ survival in the 4G systems evolution.

Resume

Ce rapport presente une comparaison technique et analyse de deux systemes de com-munications sans fil pre-quatrieme generation (pre-4G) en cours de developement :long term evolution (LTE) et worldwide interoperability for microwave access (Wi-MAX). Cette analyse est utilisee pour speculer sur les directions d’evolution possiblesdes systemes 4G parce que l’orientation du developement des generations precedentesdes systemes de communications sans fil a ete historiquement fortement influenceepar leurs aspects technologiques. Une attention speciale est apportee a l’interfacehertzienne, notamment les couches physique et de controle d’acces au support tel quedefinis par le modele d’interconnexion de systemes ouverts. Les couches superieuressont brievement discutees pour fournir une meilleure comprehension de l’operationgenerale des systemes. Les deux systemes pre-4G semblent utiliser des technologiessimilaires qui sont optmisees pour chaque systeme. En raison de la similarite techno-logique, d’autres facteurs tel que les affaires et la commercialisation, peuvent etre parconsequent des determinants plus importants de la survie des systemes pre-4G dansl’evolution des systemes 4G.

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Executive summary

LTE vs. WiMAX: A technical comparison and analysisof their PHY and MAC layers

Michelle Wang, Jean-Francois Beaumont; DRDC Ottawa TM 2011-121; Defence

R&D Canada – Ottawa; November 2011.

The objective of this report is to perform a technical analysis and comparison ofthe technological choices of pre-fourth generation (pre-4G) wireless communicationssystems and then to speculate on the possible evolutionary directions of 4G systems.The two most popular pre-4G systems at the time of writing this report are analyzed:the long term evolution (LTE) and the worldwide interoperability for microwaveaccess (WiMAX). Special focus is given to the air interface, especially the physicallayer and the media access control (MAC) layer, which are referred as the air interfaceof WiMAX. These same two layers of LTE are analyzed for a fair comparison withthat of WiMAX. Only the high level of operations are discussed to limit the scope ofthis study.

The driving force of the 4G wireless communications technologies appears to be theInternet. Currently, most broadband Internet services are offered by wired and fixedaccess systems. The flexibility of broadband access will likely be demanded by usersof an Internet on the go service. This type of internet service and the operationalrequirements defined by the international mobile telecommunication (IMT)-Advancedinitiative, determine the functions and properties of 4G systems.

Analyzing the most current standards and related documents of the systems revealsa high degree of similarity between the two pre-4G systems. In terms of system archi-tectures, both systems make use of a two-tier architecture: a network architecture forInternet protocol (IP)-based traffic and a more efficient air interface. The IP-basednetwork architecture exclude circuit-switched (CS) components. The air interfacesof both system include a set of key enabling technologies: orthogonal frequency divi-sion multiple access (OFDMA), multiple-input multiple-output (MIMO) and smartantennas. The MAC implementation of both system is designed to support the funda-mental layer-2 requirement: resource management. Resources are centrally controlledat the eNB of LTE and the base station (BS) of WiMAX. Processing functions suchas header compression and hybrid automatic repeat request (HARQ) are used to en-hance performance. As a result, mobile broadband systems appear to be convergingin their air interfaces and network architectures to support the need of broadbandservices and are frequently called IP-OFDMA broadband systems. Because of thesimilar technological choices, other factors such as business and marketing may thenbe more important determinants of the pre-4G systems’ survival in the 4G systemsevolution.

DRDC Ottawa TM 2011-121 iii

Sommaire

LTE vs. WiMAX: A technical comparison and analysisof their PHY and MAC layers

Michelle Wang, Jean-Francois Beaumont ; DRDC Ottawa TM 2011-121 ; R & D

pour la defense Canada – Ottawa ; novembre 2011.

L’objectif de ce rapport est d’effectuer une analyse et comparaison technique des choixtechnologiques des systemes de communications sans fil pre-quatrieme generation(pre-4G) et de speculer sur les directions d’evolution possibles des systemes 4G. Lesdeux systemes pre-4G les plus populaires au moment d’ecrire ce rapport sont ana-lyses : long term evolution (LTE) et worldwide interoperability for microwave access(WiMAX). Une attention speciale est apportee a l’interface hertzienne, notammentla couche physique et la couche de controle d’acces au support (MAC), qui sontdesignees comme etant l’interface hertzienne du systeme WiMAX. Les memes deuxcouches du systeme LTE sont analysees pour obtenir une comparaison equitable aveccelle du systeme WiMAX. Seul les operations de niveau superieur sont discutees pourlimiter la portee de cette etude.

L’element moteur des technologies de communications sans fil 4G semble etre l’In-ternet. Actuellement, la plupart des services Internet a haut debit sont offerts parle biais des systemes cables et a acces fixe. La flexibilite des systemes a large bandesera vraisemblablement demandee par les utilisateurs d’un service Internet mobile.Ce type de service Internet et les exigences operationnelles definies par l’initiativetelecommunications mobiles internationales evoluees (TMI evoluees), determinent lesfonctions et proprietees des systemes 4G.

L’analyse des standards les plus actuels et des documents connexes des systemesrevele un degre eleve de similitude entre les deux systemes pre-4G. En terme d’archi-tectures de systeme, les deux systemes utilisent une architecture a deux niveaux : unearchitecture de reseau pour le trafic base sur le protocole Internet (IP) et une interfacehertzienne plus efficace. L’architecture de reseau basee sur IP exclue les composants decommutation de circuits. Les interfaces hertziennes des deux systemes comprennentun ensemble de technologies habilitantes cles : multiplexage par repartition orthogo-nale de la frequence (OFDM), entree multiple sortie multiple (MIMO) et antennesintelligentes. La mise en oeuvre de la couche MAC des deux systemes est concuepour supporter l’exigence fondamentale de la deuxieme couche : la gestion des res-sources. Le controle des ressources est centralise a la station de base pour LTE (eNB)et WiMAX (BS). Les fonctions de traitement tel que la compression d’en-tete et lademande de repetition automatique hybride (HARQ) sont utilisees pour ameliorer lesperformances. Par consequent, les systemes mobiles a large bande semblent converger

iv DRDC Ottawa TM 2011-121

au niveau de leur interfaces hertziennes et architectures de reseau pour supporter lebesoin de services a haut debit et sont frequemment appeles systemes a large bandeIP-OFDMA. En raison de choix technologiques similaires, d’autres facteurs tel queles affaires et la commercialisation peuvent etre par consequent des determinants plusimportants de la survie des systemes pre-4G dans l’evolution des systemes 4G.

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vi DRDC Ottawa TM 2011-121

Table of contents

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i

Resume . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i

Executive summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

Sommaire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

Table of contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

List of figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x

List of tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2 Wireless technology evolution . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.1 LTE background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.1.1 Evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.1.2 Standardization . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.2 WiMAX background . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.2.1 Evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.2.2 Standardization . . . . . . . . . . . . . . . . . . . . . . . . . 11

3 LTE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.1 System overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.1.1 EPS network elements . . . . . . . . . . . . . . . . . . . . . 16

3.1.1.1 EPC . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.1.1.2 E-UTRAN . . . . . . . . . . . . . . . . . . . . . . 18

3.1.1.3 UE . . . . . . . . . . . . . . . . . . . . . . . . . . 19

3.1.2 EPS interfaces . . . . . . . . . . . . . . . . . . . . . . . . . 20

3.1.3 EPS protocol architecture . . . . . . . . . . . . . . . . . . . 21

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3.1.4 E-UTRAN protocol architecture . . . . . . . . . . . . . . . . 24

3.1.5 Channel structure . . . . . . . . . . . . . . . . . . . . . . . . 26

3.2 PHY layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.2.1 Time and frequency structures of radio resources . . . . . . 28

3.2.2 PHY layer model . . . . . . . . . . . . . . . . . . . . . . . . 33

3.2.2.1 Transport-channel processing . . . . . . . . . . . . 34

3.2.2.2 Physical-channel processing . . . . . . . . . . . . . 38

3.2.3 Interaction with upper layers . . . . . . . . . . . . . . . . . 42

3.3 MAC layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

4 WiMAX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

4.1 System overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

4.1.1 Functional elements . . . . . . . . . . . . . . . . . . . . . . . 47

4.1.1.1 CSN . . . . . . . . . . . . . . . . . . . . . . . . . 48

4.1.1.2 ASN . . . . . . . . . . . . . . . . . . . . . . . . . 49

4.1.2 Reference points . . . . . . . . . . . . . . . . . . . . . . . . 50

4.1.3 Protocol architecture . . . . . . . . . . . . . . . . . . . . . . 51

4.1.4 Interaction between protocol layers of IEEE 802.16 and thehigher layer . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

4.2 PHY layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53


4.2.2 Physical-layer processing . . . . . . . . . . . . . . . . . . . . 55

4.2.2.1 Randomizing . . . . . . . . . . . . . . . . . . . . . 55

4.2.2.2 FEC . . . . . . . . . . . . . . . . . . . . . . . . . 56

4.2.2.3 Interleaver . . . . . . . . . . . . . . . . . . . . . . 56

4.2.2.4 Repetition . . . . . . . . . . . . . . . . . . . . . . 56

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4.2.2.5 Modulation . . . . . . . . . . . . . . . . . . . . . . 57

4.2.2.6 OFDMA . . . . . . . . . . . . . . . . . . . . . . . 57

4.2.2.7 Advanced antenna technologies . . . . . . . . . . . 58

4.3 MAC layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

4.3.1 Service-specific convergence sublayer . . . . . . . . . . . . . 60

4.3.2 MAC common part sublayer . . . . . . . . . . . . . . . . . . 61

4.3.3 Security sublayer . . . . . . . . . . . . . . . . . . . . . . . . 62

5 Comparison of LTE and WiMAX . . . . . . . . . . . . . . . . . . . . . . . 63

5.1 System overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

5.1.1 Functional elements . . . . . . . . . . . . . . . . . . . . . . . 63

5.1.2 Interfaces and reference points . . . . . . . . . . . . . . . . . 64

5.1.3 Protocol architecture . . . . . . . . . . . . . . . . . . . . . . 64

5.1.4 Interaction between protocol layers . . . . . . . . . . . . . . 66

5.2 PHY layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66


5.2.2 Physical-layer processing . . . . . . . . . . . . . . . . . . . . 67

5.3 MAC layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

5.4 Comparison summary . . . . . . . . . . . . . . . . . . . . . . . . . . 68

6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

Annex A: List of LTE standards . . . . . . . . . . . . . . . . . . . . . . . . . 81

Annex B: List of EPS interface . . . . . . . . . . . . . . . . . . . . . . . . . . 85

List of acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

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List of figures

Figure 1: Access technologies . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Figure 2: Mobile broadband evolution . . . . . . . . . . . . . . . . . . . . . 5

Figure 3: Network range expansion . . . . . . . . . . . . . . . . . . . . . . . 6

Figure 4: IEEE 802 standards . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 5: EPS architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 6: EPS overall architecture . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 7: From UMTS to evolved UMTS . . . . . . . . . . . . . . . . . . . . 17

Figure 8: EPS feature distribution . . . . . . . . . . . . . . . . . . . . . . . 18

Figure 9: S1 and LTE-UE user plane . . . . . . . . . . . . . . . . . . . . . . 21

Figure 10: S1 and LTE-UE control plane . . . . . . . . . . . . . . . . . . . . 22

Figure 11: Protocol model for S1 and X2 interfaces . . . . . . . . . . . . . . 22

Figure 12: S1 interface user and control planes . . . . . . . . . . . . . . . . . 23

Figure 13: X2 interface user and control planes . . . . . . . . . . . . . . . . . 23

Figure 14: Radio interface protocol architecture . . . . . . . . . . . . . . . . 24

Figure 15: Downlink DLL structure . . . . . . . . . . . . . . . . . . . . . . . 25

Figure 16: Uplink DLL structure . . . . . . . . . . . . . . . . . . . . . . . . . 25

Figure 17: Downlink channel mapping . . . . . . . . . . . . . . . . . . . . . . 26

Figure 18: Uplink channel mapping . . . . . . . . . . . . . . . . . . . . . . . 27

Figure 19: Frame structure type 1 . . . . . . . . . . . . . . . . . . . . . . . . 28

Figure 20: Frame structure type 2 (for 5 ms switch-point periodicity) . . . . 29

Figure 21: UL and DL resource grid . . . . . . . . . . . . . . . . . . . . . . . 30

Figure 22: Mapping of a resource grid . . . . . . . . . . . . . . . . . . . . . . 32

x DRDC Ottawa TM 2011-121

Figure 23: Physical layer model for UL-SCH transmission . . . . . . . . . . . 34

Figure 24: Transport channel processing for DL-SCH, PCH and MCH . . . . 35

Figure 25: Transport channel processing for BCH . . . . . . . . . . . . . . . 35

Figure 26: Transport channel processing for UL-SCH . . . . . . . . . . . . . 36

Figure 27: Overview of uplink physical-channel processing . . . . . . . . . . . 38

Figure 28: Overview of physical channel processing for two transmit antennas 39

Figure 29: Generic OFDMA and SC-FDMA processing chain . . . . . . . . . 40

Figure 30: Time domain view of data transport . . . . . . . . . . . . . . . . . 43

Figure 31: MAC structure overview, UE side . . . . . . . . . . . . . . . . . . 45

Figure 32: WiMAX system architecture . . . . . . . . . . . . . . . . . . . . . 48

Figure 33: Functional view of ASN Profile C . . . . . . . . . . . . . . . . . . 50

Figure 34: IEEE 802.16e-2005 protocol reference model . . . . . . . . . . . . 51

Figure 35: Protocol layer architecture for control, IP-CS and ETH-CS signal 52

Figure 36: Example of TDD frame structure for mobile WiMAX . . . . . . . 54

Figure 37: WiMAX PHY transmission chain . . . . . . . . . . . . . . . . . . 55

Figure 38: FEC and HARQ for WiMAX . . . . . . . . . . . . . . . . . . . . 56

Figure 39: PDU and SDU in a protocol stack . . . . . . . . . . . . . . . . . . 59

Figure 40: MAC PDU format . . . . . . . . . . . . . . . . . . . . . . . . . . 60

Figure 41: WiMAX PHY and MAC layers protocol stack . . . . . . . . . . . 61

Figure 42: Protocol layer architectures for LTE and WiMAX . . . . . . . . . 65

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List of tables

Table 1: LTE technical specifications . . . . . . . . . . . . . . . . . . . . . 9

Table 2: IEEE 802 WGs and TAGs . . . . . . . . . . . . . . . . . . . . . . 12

Table 3: Evolution of the IEEE 802.16 standard . . . . . . . . . . . . . . . 14

Table 4: UE categories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Table 5: Slot structure for normal and extended cyclic prefix . . . . . . . . 31

Table 6: Resource block characteristics . . . . . . . . . . . . . . . . . . . . 31

Table 7: Channel coding schemes for transport channels . . . . . . . . . . . 37

Table 8: Channel coding schemes for control informations . . . . . . . . . . 37

Table 9: OFDMA parameters . . . . . . . . . . . . . . . . . . . . . . . . . 41

Table 10: MAC function location and direction association . . . . . . . . . . 46

Table 11: WiMAX radio resource characteristic . . . . . . . . . . . . . . . . 54

Table 12: WiMAX OFDMA parameters . . . . . . . . . . . . . . . . . . . . 58

Table 13: Comparison of LTE 3GPP Release 8 and WiMAX R1.0 (IEEE802.16e-2005) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

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1 Introduction

Cellular technology has significantly evolved since its introduction in the early 1980’s.First generation (1G) cellular phones were basic circuit switch analog systems de-signed for voice transmission only. Second generation (2G) phones brought furtherimprovements with the introduction of digital systems, performing both voice anddata transmission at low rates. Today’s third generation (3G) systems are multi-function devices, such as the iPhone, which can make phone calls as well as retrievee-mail, store and play music, surf the Web and stream video files. Although the thirdgeneration is a big improvement over the first two, the primary function of the deviceis still to transmit voice on a digital circuit switch system, with the added capabilityto carry Internet protocol (IP) traffic at moderate data rates.

In order to continue supporting voice and data at higher data rates, cellular systemsmust shift to a new network architecture. Voice and data will no longer be separateentities in 4G systems. They will be combined on a single packet-based all-IP corenetwork to support high speed multimedia applications such as mobile TV, videoconferences, fast web browsing, telemedicine, large file transfer and bank services.Envisioned data rates to support these advanced services are on the order of a fewhundred Mb/s to 1 Gb/s for high and low mobility respectively. The power and size ofthe Internet are therefore, driving the fourth generation (4G) cellular system require-ments. In order to meet the performance levels required by these Internet servicessuch as spectral efficiency, low latency and seamless handover between cells, severalkey technologies have been developed to help meeting the requirements [1]. Someof the key technologies are orthogonal frequency division multiple access (OFDMA),multiple-input multiple-output (MIMO) and smart antennas.

In addition to the service demand, the operational requirements of 4G systems areofficially defined by the international telecommunication union (ITU) as the interna-tional mobile telecommunication (IMT)-Advanced initiative. Only systems meetingthe IMT-advanced requirements will be considered as 4G systems. Three standardshave been proposed for the development of 4G systems. These standards are: thirdgeneration partnership project(3GPP) long term evolution (LTE), worldwide inter-operability for microwave access (WiMAX) and ultra mobile broadband (UMB).

LTE is an evolution of the global system for mobile communications/universal mobiletelecommunication system (GSM/UMTS) family and specifies the next generationmobile broadband access. LTE will likely be the 4G technology of choice for mostof the major cellular carriers based on the GSM/UMTS family. 3GPP Release 8defines the base standards for LTE. Future releases of 3GPP standards will continueto upgrade LTE.

WiMAX is considered as both 3.5G and 4G technology. It does not follow either the

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GSM or code division multiple access (CDMA) family. It has been standardized bythe WiMAX Forum in conjunction with the Internet engineering task force (IETF)and the institute of electrical and electronics engineers (IEEE). The initial plans forWiMAX were to provide high speed broadband wireless access where the provisionof wired access was inconvenient or expensive. WiMAX was initiated by the IEEE802.16d-2004 standard and there have been hundreds of WiMAX installations world-wide supporting this standard. Subsequently, the mobile WiMAX standard approvedin 2005 (IEEE802.16e–2005) was designed to support high-speed mobile Internet ac-cess and other data intensive applications. This report is primarily concerned withmobile WiMAX and not fixed WiMAX (IEEE 802.16d-2004).

UMB was proposed by Qualcomm, the same manufacturer that originally designedthe CDMA family of systems, the North American counterpart of the GSM/UMTSfamily. UMB was based on the IEEE 802.20 standard. At the moment, no majorcarrier has agreed to upgrade their network to comply with this standard. Therefore,it is very unlikely that UMB will be considered at all as a competing 4G standard.

In terms of technology, WiMAX and LTE are very similar since they have an OFDMA-based air interface, which is optimized for IP. This air interface is referred to as IP-OFDMA. These IP-OFDMA based systems are also frequently referred to as mobilebroadband systems [1, 2]. However, in terms of market introduction, they are ona different timescale as WiMAX has appeared before LTE, giving it a window ofopportunity. WiMAX’s early adaptors are new entrants and computer chip manufac-turers, particularly Intel which has been involved in the early development of WiMAXchipsets. On the other hand, LTE’s adaptors are mobile operators and mobile equip-ment manufacturers. Therefore, the two technologies will currently be deployed andmarketed in different countries for different purposes. WiMAX is currently beingdeployed and LTE is expected to be widely deployed by 2012 or 2013 [3]. The world’sfirst commercial LTE network was launched in December 2009 by TeliaSonera inSweden and Norway [4].

The aim of this report is to perform a technical comparison of LTE and WiMAXsystems, more specifically of their physical (PHY) and media access control (MAC)layers as defined by the international organization for standardization /open systeminterconnection (ISO/OSI) model. The PHY and MAC layers are the focus sincethey are referred as the air interface of WiMAX. These same two layers of LTE areanalyzed for a fair comparison with that of WiMAX.

These pre-4G systems are converging in the air interface and the networking architec-ture to support delivery of multimedia services; however, they are at various stagesof evolution. On that note, since both LTE and WiMAX are still currently understandardization, the technical content of this report is based on the stabilized ver-sions of the standards available at the time of writing: 3GPP Release 8 and WiMAX

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Release 1.0 (IEEE 802.16e-2005) [5] as well as the WiMAX Forum Network Architec-ture Release 1.0. As a result, the view presented here may be different from the mostcurrent standard. However, the general standard framework presented in this reportstill holds. The specifications do not describe the rationale behind the technologicalchoices. This report includes additional references to disclose some of the rationales.

Section 2 presents a brief discussion on the ongoing standardization effort at the3GPP, 3GPP2 and WiMAX forum to define mobile broadband standards. Section 3and Section 4 cover protocol layers of LTE and WiMAX, with an emphasis on thePHY andMAC layers. The higher layers are only briefly discussed. Section 5 discussesthe similarities and differences among the two standards. A table summarizing thesesimilarities and differences is included at the end of the section. Section 6 thenconcludes the report.


2 Wireless technology evolution

Figure 1 [6] shows that communications systems are evolving to offer higher per-formance and efficiency in a mobile environment. Numerous systems exist due totrade-offs between system parameters such as range, bit rate and mobility [1]. Pa-rameters may be adjusted by each system to meet performance requirements

Figure 1: Access technologies

The driving force behind communications systems evolution has been the broad adop-tion of wired broadband Internet services [1, 6, 7]. Communications technologies arenow at the stage to offer mobile accesses with broadband services. The convenienceand capability of broadband accesses will likely drive the same users to seek similarbroadband services and applications wherever they go [8]. This evolutionary path ofcommunications systems is also referred to as mobile broadband. Broadband impliesan internet connection that allows different types of services such as data transfer,voice and video at high speeds. Mobile broadband is therefore, pushing these ser-vices to mobile devices such as cellular phones, laptops and personal digital assistants(PDAs) [9].

Since the IP protocol is the key to the Internet, WiMAX and LTE (Figure 2 [6]) useIP-based architectures. In addition to IP-based architectures, both systems employimportant technologies, including OFDMA, MIMO, smart antennas and software de-fined radios to achieve higher performance. As a result, the air interfaces and networkarchitectures of mobile broadband systems appear to be converging to support therequirements of broadband services. This type of mobile broadband systems is fre-quently called IP-OFDMA broadband system.


Figure 2: Mobile broadband evolution

Figure 2 charts the roadmap for the mobile broadband systems. Several differenttechnologies offer solutions to the requirements of the mobile broadband systems andto the trade-off function between the various system parameters (i.e. range, bit rateand mobility). Contenders come primarily from two industrial markets: broadbandaccess and cellular communications.

The first worldwide launch of the mobile broadband system was WiMAX, which isinfluenced by the broadband-access standard body, IEEE. WiMAX evolved from thewireless access standard (IEEE 802.16d-2004) and is based on the IEEE 802.16e -2005 standard. Therefore, it inherits functionalities optimized for broadband dataservices. On the other hand, the cellular-communications standards are based on3GPP and 3GPP2. The successors of 3.5G are [10]: 3GPP’s high speed packet access(HSPA) and 3GPP2’s evolution-data only (EVDO). The EVDO standard appears tofollow the evolution path of 3GPP or IEEE and will likely create unification in thediverse standards [1]. The LTE standard is 3GPP’s answer to the mobile-broadbandrequirements and inherits both the capabilities and restrictions of the legacy cellularsystems. The most significant challenge that 3GPP faces is the need to support higherdata rates since the legacy standards are designed mostly for mobile voice. Similarly,IEEE faces the challenge to support mobility.

The remainder of this section provides an introduction to wireless-broadband andcellular evolution, followed by the development of LTE and WiMAX.

In the late 1990s, IEEE created the 802.16 working group to create an air interface forbroadband wireless accesses (BWAs) [11,12] on a metropolitan area network (MAN),


previously implemented on a shorter range local area network (LAN) (Figure 3 [13]).The working group leveraged the data over cable service interface specification (DOC-SIS) standard, which was developed to permit high-speed data transfer over cable.The modified standard was introduced as IEEE802.16d in 2004, targeted fixed ap-plications and is also known as fixed WiMAX. In 2005, IEEE 802.16d was furtherenhanced to provide mobility support. This standard is known as IEEE 802.16e ormobile WiMAX.

Figure 3: Network range expansion

The world’s first mobile WiMAX deployment was commercially offered in Korea in2007 [11] under the name of “WiBro”. WiMAX is supported by a broad industrialbase. The competition among numerous vendors, ranging from small companiesto big manufacturers such as Motorola, Samsung, Intel and Cisco [14], potentiallyresults in lower cost. It also has backing from traditional cellular companies such asSprint/XOHM and Clearwire.

IEEE has the history of developing diverse standards for wireless local area networks(WLANs), such as Wireless Fidelity (WiFi) also known as IEEE 802.11 wirelessnetworking. On one hand, it developed WiMAX standard, which is sometimes called“WiFi on steroids”, to offer higher data rate while on the other hand also increase


coverage and mobility for its BWA technologies. This made WiMAX a competitorfor cellular system traffic and customers.

Cellular technologies have progressed through a sequence of generations and are aboutto reach their 4G. Although each generation is supported by several different accesstechnologies, the technology set of each generation is focused on providing a standardlevel of service.

– In 1980, 1G systems delivered the basic mobile voice using frequency division mul-tiple access (FDMA).

– In the early 1990s, 2G introduced digital transmission and most popular systemsemployed time division multiple access (TDMA) and CDMA technologies.

– From 2000, 3G sought higher digital data transmission speeds offered by CDMA.– Finally, 4G systems have been developed to support broadband services for mobiledevices.

The standardization and deployment of LTE has been slower than that of WiMAX.To facilitate quick acceleration to 4G, 3GPP made a strategic choice for an IP-basedarchitecture that does not support backward compatibility for circuit-switched (CS)services. This allows new mobile broadband operators, who have not been followingthe cellular evolution path, to enter the cellular industry.

LTE has backing from most of the traditional cellular companies covering the majorityof the cellular market [14]. LTE is also supported by most WiMAX manufacturerswith the exception of Intel. Cisco is a new entrant to LTE since it started exploringLTE in late 2009 [15]. Due to the large number of cellular subscribers, the cost ofLTE will probably be low as well.

In summary, both LTE and WiMAX are pre-4G standards. Because of the early evo-lution and adoption of mobile WiMAX, in October 2007, the IEEE 802.16e standardis included in the international mobile telecommunication 2000 (IMT 2000) specifica-tion [16], created to harmonize 3G cellular systems. Cellular technologies are movingtoward higher mobility and speeds. These systems are being developed by the tra-ditional cellular industry as well as the computer industry, which originally workedon the WLAN standards. In order for systems to be considered as 4G, they shouldadhere to the IMT-Advanced specification.

2.1 LTE background3GPP is evolving its UMTS standard to accommodate increasing mobile usage. Theevolution consists of two parts. The air interfaces inherited from the GSM/enhanceddata rates for GSM evolution (EDGE) and UMTS/HSPA technologies with enhance-


ments to support wider bandwidths. The evolving UMTS network architecture re-duces network level elements when compared with UMTS [17].

The new OFDMA-based air interface is frequently referred to as the evolved UMTSterrestrial radio access network (E-UTRAN) since the UMTS air interface is called theuniversal terrestrial radio access network (UTRAN). E-UTRAN is backward compat-ible with UTRAN. In addition to the air interface, 3GPP also defines a new IP-basednetwork architecture. The network architecture is termed as the evolved packed core(EPC) network that aims to provide support for packet data. EPC is also referredto as the system architecture evolution (SAE). The entire system is termed as theevolved packet system (EPS) that is also known by another acronym, the evolvedUMTS. The EPS is therefore, basically the concatenation of the E-UTRAN air inter-face and EPC network.

2.1.1 Evolution

3GPP started evolving its 3G mobile systems with the 3GPP TSG radio access net-work (RAN) evolution workshop in November 2004 [18]. More than 40 contributionswith view points and proposals on the evolution of UTRAN were made by operators,manufacturers and research institutes. Following the workshop, 3GPP started a studywith the objective of developing a new radio access technology – reduced cost perbit, increased service provisioning, flexible use of existing and new frequency bands,simplified architecture and open interfaces as well as reasonable terminal power con-sumption [19]. The most important issue of the study was the need for agreement onthe E-UTRAN requirements and was settled in June 2005.

The LTE standardization was then split into two parts – the RAN working groupfocusing on the air interface and the radio while the system architecture (SA) grouptackling the network architecture, EPC. LTE’s performance was evaluated in 2007.The evaluation showed LTE’s ability to meet the targets for peak data rates, celledge user throughput, spectrum efficiency, as well as VoIP and multimedia broadcastmulticast service (MBMS) performance.

In December 2007, 3GPP approved the first full set of specifications for LTE. In 2008,it made a functional freeze on the content of the specifications [20]. Functional freezemeans that new functionalities can not be added but the agreed content will be fi-nalized in a later release. The functional freeze ended in December 2008. After thefunctional freeze, the standard had all the content ready for a protocol freeze, whichguaranteed backward compatibility. In March 2009, the backward-compatibility ver-ification was completed with the 3GPP Release 8 specifications. The LTE specifica-tions is planned to disallow any changes before the actual roll-out.

The world’s first commercial LTE network was launched in December 2009 by Telia-


Sonera in Sweden and Norway [4]. The actual downlink (DL) and uplink (UL) peakdata rates are 42.7 Mb/s and 5.3 Mb/s with a delay of 37 msec, which are not close tothe specified requirements, 100 Mb/s and 50 Mb/s with a delay of 5 msec. However,this performance is better than some wired internet service providers (ISP) servicethat normally is 5Mb/s DL and 1Mb/s UL. Although the LTE specifications arestill a 3G-related standard in terms of, for example the peak data rate, it is 3GPP’sroadmap to the 4G requirements.

2.1.2 Standardization

The official LTE standards are composed of technical specifications (TS) and technicalreports (TR) published by 3GPP. All 3GPP specifications have a specification numberconsisting of 4 or 5 digits (e.g. 09.02 or 29.002). The first two digits define theseries [21]. For series numbered from 1 to 13, two more digits are allowed. For seriesfrom 21 to 55, three more digits are assigned. The specific application of LTE appearsmostly in series 36. Table 1 provides the scope of the 36-series technical specificationsand the associated 3GPP group responsible to maintain it.

Table 1: LTE technical specifications

Specification index Description of contents 3GPP groupTS 36.1xx Equipment requirements such as termi-

nals, base stations and repeatersRAN 4 3GPP

TS 36.2xx Physical layer RAN 1 3GPPTS 36.3xx Layers 2 and 3: MAC, RLC, PDCP and

RRCRAN 2 3GPP

TS 36.4xx Infrastructure communications RAN 3 3GPPTS 36.5xx Conformance testing RAN 5 3GPP

The following documents that describe the overall network architecture as well asgeneral procedures such as network attachment, session setup and mobility are main-tained by the SA2 3GPP group:

– TS 23.401, general packet radio service (GPRS) Enhancements for E-UTRAN Ac-cess

– TS 23.402, Architecture Enhancements for Non-3GPP Accesses

Moreover, 3GPP also produced a number of TRs, which record working assumptionsand agreements until actual specifications are made available:

– TR 24.801: 3GPP System Architecture Evolution; CT WG1 Aspects


– TR 29.804: CT WG3 Aspect of 3GPP System Architecture Evolution– TR 29.803: 3GPP System Architecture Evolution; CT WG4 Aspects– TR 32.816: Telecommunication Management; Study on Management of LTE andSAE

– TR 32.820: Telecommunication Management: Study on Charging Aspects of 3GPPSystem Evolution

– TR 33.821: Rationale and Track of Security Decisions in LTE/SAE

All documents can be found in http://www.3gpp.org/ftp/Specs. A list of the 36-series documents, the 53 TSs and 20 TRs, in effect as of November 2009 is providedin Annex A at the end of this report.

2.2 WiMAX backgroundWiMAX-compliant systems are based on two system profiles [22, 23]: fixed and mo-bile. The standard for the fixed system profile is IEEE 802.16d-2004 and the standardfor the mobile system profile is IEEE 802.16e-2005, which is actually an amendmentto the 802.16d-2004 standard to support mobility. The 802.16 standards define thePHY layer and the MAC layer (which is also known as the air interface) of a WiMAXsystem in an OSI model. The end-to-end networking of WiMAX networks is sep-arately defined by the WiMAX Forum network working group (NWG). To ensureinteroperability of WiMAX Forum certified products [24], a subset of 802.16 featurescalled a system profile is also defined.

This document focuses on the current WiMAX implementation, mobile WiMAX.Section 2.2.1 provides more information on the mobile WiMAX evolution while Sec-tion 2.2.2 gives an overview of the IEEE 802.16 standardization.

2.2.1 Evolution

As mentioned earlier, mobile WiMAX is an IEEE 802.16-based technology main-tained by the WiMAX Forum. The goal of the WiMAX forum is to develop end-to-end specifications for interworking and interoperability and its specifications helppromote compatibility of WiMAX equipment and systems [25]. WiMAX Release 1.0certification began in January 2007 [26, 27].

The mobile WiMAX specifications are divided into three stages:

– The stage-1 specifications specify recommendations and requirements for WiMAXnetworks from the perspective of network operators who intend to deploy compati-ble networks. It provides information such as business/usage scenarios, deployment


models, functional requirements and performance guideline for the end-to-end sys-tem [28].

– The stage-2 documents specify how the stage-1 requirements are implemented atthe architecture level [29].

– The stage-3 specifications details protocols and procedures required to implementthe architecture-level specifications [30].

The most current version of the specification is Release 1.5. Further performanceenhancements are planned for mobile WiMAX Release 2.0 which is based on theIEEE 802.16m standard.

Release 1.0 of the mobile WiMAX standard is based on the IEEE 802.16e-2005 stan-dard. It reduces the scope of the IEEE802.16e-2005 standard to a smaller set of designchoices for implementation. The WiMAX Forum does scope reduction by specifyingsystem profiles which define a subset of mandatory and optional features from theIEEE802.16e-2005 standard [31, 32]. Mobile WiMAX Release 1.5 is based on theIEEE 802.16-2009 standard and is an extension of Release 1.0 [33]. Mobile WiMAXRelease 2.0 is based on the IEEE 802.16m standard and is backward compatible withRelease 1.0 and Release 1.5.

2.2.2 Standardization

While 3GPP was developing solutions to meet the requirements of mobile broadbandaccesses, the IEEE 802 LAN/MAN standards committee (LMSC) also made a similarattempt. In the late 1990s, the IEEE 802.16 WG was set up to standardize BWAsfor wireless metropolitan area networks (WMAN). At the same time, the IEEE 802LMSC also established the IEEE 802.20 WG to work on a nearly identical focus of theIEEE 802.16 WG. Table 2 [34] shows the status of the IEEE 802 WGs and technicaladvisory groups (TAGs), in effect as of 2009. The relationship between some of theIEEE 802 standards is shown in Figure 4 [35]. The IEEE 802 standards define onlythe data link and PHY layers of the OSI reference model.


Table 2: IEEE 802 WGs and TAGs

Number NameStatus inApril 2009

802.1 Higher Layer LAN Protocols WG Active802.2 Logical Link Control WG Inactive802.3 Ethernet WG Active802.4 Token Bus WG Disbanded802.5 Token Ring WG Inactive802.6 Metropolitan Area Network WG Disbanded802.7 Broadband TAG Disbanded802.8 Fiber Optic TAG Disbanded802.9 Integrated Services LAN WG Disbanded802.10 Security WG Disbanded802.11 Wireless LAN WG Active802.12 Demand Priority WG Disbanded802.13 (Not used)802.14 Cable Modem WG Disbanded802.15 Wireless Personal Area Network (WPAN) WG Active802.16 Broadband Wireless Access WG Active802.17 Resilient Packet Ring WG Active802.18 Radio Regulatory TAG Active802.19 Coexistence TAG Active802.20 Mobile Broadband Wireless Access (MBWA) WG Active802.21 Media Independent Handoff WG Active802.22 Wireless Regional Area Networks WG Active


Figure 4: IEEE 802 standards

The IEEE 802.16 standard has evolved through various editions. Initially, the focusof the standard was on line of sight (LOS) operations for fixed wireless subscriber sta-tions. Since the first publication of the standard in 2001, the scope has been expandedto cover non line of sight (NLOS) scenarios, supporting mobility and accounting forhigher data rates as shown in Table 3 [36]. The IEEE 802.16e-2005 specification [5]is a supplement to the IEEE 802.16d-2004 specification [37], and so the two are com-binedly referred to as IEEE 802.16-2004&E. The IEEE 802.16-2004&E specifies fivetypes of physical layers. WiMAX considers only OFDM and OFDMA physical layersof the IEEE 802.16-2004&E standard [38].

The most current IEEE 802.16 version is IEEE 802.16-2009 [39], which is amendedby IEEE 802.16j-2009 [40] for multihop relay. The IEEE 802.16-2009 standard waspublished in May 2009 and is the second revision of IEEE 802.16 following IEEE802.16-2001 and IEEE 802.16d-2004. It consolidates previous IEEE 802.16 revisions:IEEE802.16d-2004, IEEE 802.16e-2005, IEEE 802.16-2004/Cor1-2005, IEEE 802.16f-2005 and IEEE 802.16g-2007 [41]. The IEEE 802.16m is currently in draft stageand being designed to meet the requirements of IMT-Advanced. Its goal is to pushdata rates up to 100 Mb/s for mobile subscribers and 1Gb/s for fixed accesses whilemaintaining backward compatibility with existing WiMAX radios [26].


Table 3: Evolution of the IEEE 802.16 standard

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3 LTE

This section presents the EPS evolution as introduced in Release 8 of the 3GPPstandard [42]. The section starts with a system overview a better understandingof the entire network. Next, it briefly presents the protocol layers of the EPS andthen finally, concentrates on the MAC layer and the PHY layer of the air interface.The referenced specifications are cited when appropriate through the section whenappropriate.

3.1 System overviewFigure 5 [43] shows an EPS architecture. The system elements specific to the EPS areEPC (MME/S-GW) and E-UTRAN as shown in Figure 6 [44]. The EPC comprisesa mobile management entity (MME) and a serving gateway (S-GW) together with apacket data network gateway (PDN-GW). The E-UTRAN contains only evolved nodeBs (eNBs). The communication between user equipments (UEs) and eNBs is one-to-one but communication between eNBs and EPCs are meshed (meaning that all eNBsand EPCs may be linked together). Section 3.1.1 provides a more in-depth view ofEPC and E-UTRAN and the corresponding interfaces are described in Section 3.1.2.

Figure 5: EPS architecture


Figure 6: EPS overall architecture

The EPS network architecture is based on the transmission control protocol (TCP)/IPprotocol to enable personal computer (PC)-like services. The architecture is designedwith the goal of supporting packet-switched (PS) traffic, which allows internet servicessuch as VoIP and multimedia messaging. The result is a simplified flatter architecturethat is in contrast to a multi-node network architecture of the 3G systems as shownin Figure 7 [45]. The architecture is considered simplified whereby most of the radionetwork controller (RNC) functionalities are merged with the NodeB to create theeNB [1]. Also, all of the UMTS core network functions go into two elements, the MMEfor control signaling and the logical gateways (S-GW/PDN GW) for data signaling.Since the EPC is all-IP, all services (including voice) are delivered as PS traffic. Asa result, the CS part of the UMTS system is abandoned.

The functional split between eNB and EPC is shown in Figure 8 [44]. The functionsof an EPC, an eNB and an UE are summarized on the figure. The white boxes insidethe eNB, MME and GWs depict the functional entities of the control plane and theshaded boxes depict the protocol layers of the air interface. The protocol architectureof the air interface is split into two planes, the user and control plane. Generally, theuser plane carries traffic signaling while the control plane carries control signaling.

3.1.1 EPS network elements

This section briefly describes the network entities of the EPC and E-UTRAN asshown in Figure 6. Only the network nodes specific to EPS are presented here.


Figure 7: From UMTS to evolved UMTS

3.1.1.1 EPC

The EPC is composed of several functional entities as shown in Figure 8. The mainrole of a MME is to provide control-plane functions related to subscriber and sessionmanagement. In addition, the EPC has two logical gateway entities, the S-GW andthe PDN-GW.

MME A MME and a S-GW may be implemented in one physical node or separatedphysical nodes. The MME [43] transfers only control signalling and hence, IP pack-ets do no go through the MME. The main functions of a MME are idle-mode UEreachability, tracking area list management, roaming, authentication, authorization,PDN-GW/S-GW selection, bearer management, security negotiation and non-accessstratum (NAS) signalling.

S-GW A S-GW is the termination point of packet data transmission towards E-UTRANs. For each UE associated with the EPS, there is only one single S-GWserving at a giving point of time. There is no communication among S-GWs sincea S-GW is designed as an enforcement point that acts on notifications coming fromMMEs. The S-GW functions as a local mobility anchor forwarding and receivingpackets to and from eNBs and the serving UEs [46]. Since the S-GW is the anchoringpoint for UEs travelling among 3GPP accesses, it provides data traffic in case of lawfulinterception. It is responsible for storage of the context of the UEs and replication.


Figure 8: EPS feature distribution

PDN-GW Similar to an S-GW, a PDN-GW is the termination point of packet datatransmission towards packet data networks. It provides connectivity to external PDNssuch as the Internet or hosted services such as IP multimedia subsystem (IMS) andpacket-switched streaming service (PSS). The PDN-GW also operates as an anchorfor mobility between 3GPP and non-3GPP accesses such as WiMAX, 3GPP2 andWLAN through various sets of interfaces. The PDN-GW serves several IP functionssuch as address allocation, policy enforcement, packet filtering and routing [47,48].

3.1.1.2 E-UTRAN

3GPP uses the traditional OSI model to define the air interface, E-UTRAN. eNBsare connected to each other in a meshed way through the X2 interface to supportmultiple cells while the individual eNB is responsible for its coverage area. Due to theelimination of RNC in the E-UTRAN, eNB now has to implement both the NodeBfunctions as well as control functions traditinally implemented in a RNC. Therefore,the eNB provides the user-plane (PDCP/RLC/MAC/PHY) and control-plane (RRC)protocols towards the UE, shown in Figure 8. Several main functions of the eNBare header compression, ciphering and reliable delivery of packets. On the control


side, the eNB incorporates functions such as admission control and radio resourcemanagement. The meshed network, E-UTRAN, provides the following functions[43,44]:

– Transfer of user data– Radio channel ciphering and deciphering– Integrity protection– Header compression– Mobility control functions– Handover– Paging– Positioning

– Inter-cell interference coordination– Connection setup and release– Load balancing– Distribution function for NAS messages– NAS node selection function– Synchronization– MBMS function– Rate enforcement and bearer level admission control– Transport level packet marking

eNB The eNB is the only element interfacing with an UE in a LTE network. Ithosts a user plane to carry user data and a control plane to control the connectionbetween the UE and the network.

From a functional perspective, the eNB provides a set of legacy features related tophysical-layer procedures for transmission and reception over the air. This includesradio channel modulation/demodulation and coding/decoding. Because of the factthat an RNC’s function is integrated into the eNB, the eNB has to support functionsbeyond the physical layer. According to the OSI model, the eNB provides layer-2supports to ensure proper transfer of user data and layer-3 supports to route user-plane data. For more information, refer to the 3GPP standard, [44] where all thefunctions of the eNB are described in detail.

3.1.1.3 UE

As shown in Figure 8, the UE has the user-plane protocol layers, consisting of packetdata convergence protocol (PDCP), radio link control (RLC), MAC and PHY layers,to connect to the eNB. The control plane contains the NAS layer and the RRC layerfor communication with the MME and eNB respectively. This 3GPP standard, [49],defines five UE categories, differentiated by bit-rate capabilities. The UE categories


are shown in Table 4 [20]. Further terminal categories may be defined in later 3GPPreleases.

Table 4: UE categories

3.1.2 EPS interfaces

Interfaces connect logical nodes (elements) in an EPS network. Annex B lists mostof the interfaces defined for the EPS-integrated architecture (an example shown inFigure 5) and is collected from several releases of TS 23.401. Because of the multi-plicity of logical nodes in the architecture, the same interfaces have different namesor reliance on previous 3GPP systems in different releases of the standard.

Three new interfaces, S1, X2, and LTE-UE are defined exclusively for E-UTRAN.All are functionally split into user plane and control plane for transferring user dataand control messages respectively. LTE-UE is the radio interface, connecting a UE toits network. The X2 interface defines the user and control plane protocols for eNBs,which are interconnected in a meshed fashion. The main role of X2 is to minimizepacket loss while the UE moves. Any unsent or unacknowledged packets queued inthe previous eNB are forwarded to the new eNB through the X2 interfaces. The S1interface defines the user and control plane protocols for eNB communication withthe MME (S1-MME interface) and the S-GW (S1-U interface).


3.1.3 EPS protocol architecture

Figure 9 and Figure 10 [50] present the model introduced by the TS 24.301 standardat the beginning of 2G [51] which is still being applied to the evolution of UMTS.The structure is based on the principle that the layers and planes are logically inde-pendent. This model presents two layers: the access stratum (AS) and the non accessstratum (NAS) that span over several entities (UE, E-UTRAN and EPC). This OSI-like separation allows the standardization body to alter protocol stacks to fit furtherrequirements. For example, when 3G/UMTS was defined in 1999, the 2G/GSMNAS layer was augmented to meet the requirement of the UMTS system. Similarly,the broadband global area network (BGAN) system replaces the air interface of theUMTS’s AS layer for transmission over satellites. The actual implementation of theoverall protocol stack may be analyzed by a packet analyzer such as the WireSharksoftware that has implemented some of the 3GPP TS 24.301 specification [52].

Figure 9: S1 and LTE-UE user plane

Generally, an AS layer corresponds to features linked to radio interfaces. For theradio interface of an EPS, the AS features are supported by the PHY, MAC, RLC,PDCP, and RRC protocol layers defined in documents TS 36.2xx and TS 36.3xx. Forthe S1 and X2 interfaces, the AS features are defined in TS 36.41x and TS 36.42xrespectively.

As shown in Figure 11, the AS layers specific to the S1 and X2 interfaces are furthersplit into two main parts: the radio network layer and the transport network layer.This separation allows independent development in the application part and transportpart of the system. The user and control planes for S1 and X2 are shown in Figure 12and Figure 13 respectively [44].


Figure 10: S1 and LTE-UE control plane

Figure 11: Protocol model for S1 and X2 interfaces


Figure 12: S1 interface user and control planes

Figure 13: X2 interface user and control planes

In contrast, a NAS layer corresponds to functions that are independent of the accesstechnologies. For LTE, the NAS layer’s protocols are performed between an UE anda MME. These protocols consist of the EPS mobility management (EMM) protocoland the EPS session management (ESM) protocol. EMM is responsible for controlof mobility and security while ESM handles EPS bearer control.


3.1.4 E-UTRAN protocol architecture

The LTE radio interface is composed of the PHY, data link, and network layers. TheData Link Layer (DLL) is implemented by the PDCP, RLC and MAC parts, whilethe Network Layer (NL) is supported by the RRC protocol. Figure 14 [53] showsthe E-UTRAN protocols around the PHY layer and also indicates three categoriesof information channels between protocol layers, the transmitter and the receiver.They are the physical, transport and logical channels. SC-FDMA and OFDM are thesignal formats for the physical channels. Section 3.1.5 describes the channel structurein more detail.

Figure 14: Radio interface protocol architecture

Figure 15 and Figure 16 [44] show the DLL structures at an eNB. A similar butsimplified layout also exists at the UE. One of the reasons for simplification is thatthe UE is not required to serve multiple entities. Service access points (SAPs) aremarked with circles between sublayers. The SAPs between the MAC sublayer andthe RLC sublayer provide the logical channels while the SAPs between the PHYlayer and the MAC sublayer provide the transport channel. The logical channels arecharacterized by the type of information transferred. Two types of logical channelsexist: control channels for control-plane data and traffic channels for user-plane data.The transport channels are characterized by how the information is transferred overthe radio interface. The figures also show several instances of radio bearers. Since theradio bearers consist of a defined combination of logical and transport channels, theyare also characterized by parameters describing the type of information and QoS.On the user-plane side, one of those groupings may be VoIP, video stream and best-effort file transfer, while on the control plane side, they are used for different control


signalling. In addition to prioritization relative to the parameters of the channelsand the bearers, the DL traffic is further scheduled and prioritized among UEs bythe MAC sublayer.

Figure 15: Downlink DLL structure

Figure 16: Uplink DLL structure


3.1.5 Channel structure

There are three types of channels: logical, transport and physical. Comparing theLTE channels to the UMTS channels [54] shows that the logical channels are similar.The transport and physical channels of LTE are simpler in structure compared tothose of UMTS.

Channels are used to transfer data among the PHY, MAC and RLC layers, as shownin Figure 14. The physical-channel communication exchanges are in the form ofmeasurements – channel quality indication (CQI) and control commands that adaptthe radio transmission to the state of the channel – adaptive modulation and coding(AMC). The PHY layer uses the transport channels to transfer data to the MAC layer.The transport channels are defined by their transport format set, which specifies therequired processing options, such as channel coding, interleaving and rate matching.The MAC layer assigns logical channels to be used by the RLC layer. A logical channelis defined by the type of information it carries. The logical channels are furtherdivided into two groups: control channels for transfer of control-plane informationand traffic channels for transmission of user-plane information. Figure 17 [2] shows thechannels used in the DL while Figure 18 presents the channels for the UL. Multicastchannels are grayed out in Figure 17 because they are not being specified in Release8 of the LTE standard.

Figure 17: Downlink channel mapping


Figure 18: Uplink channel mapping

3.2 PHY layerLTE defines radio resources in both the time and frequency domains. In order tosupport channel sensitive scheduling and to achieve low packet transmission latency,a LTE transmission is based on the one-msec duration of a subframe, which is alsocalled transmission time interval (TTI). In the frequency domain, the PHY layer ofLTE uses OFDMA to support flexible bandwidth deployments in diverse spectrumarrangements. LTE is designed to support bandwidths in increments of 180 kHzstarting from a minimum bandwidth configuration of 1.08 MHz. The PHY layer isbased on OFDMA in DL and SC-FDMA in UL. Both time division duplex (TDD)and frequency division duplex (FDD) are specified to carry information.

The PHY layer provides data transport services for higher layers. Processing appli-cable to the data depends on the quality of the channels in question. Section 3.2.2uses the UL-SCH channel as an example to demonstrate a cross-layer model thatshows the processing and interaction of the PHY layer. An overview of the channelprocessing is then presented using generic structures.


3.2.1 Time and frequency structures of radio resources

All LTE signals derive their timing from the basic time unit Ts [55]:

Ts = 1/(15000× 2048) seconds

The following list summarizes the symbols that are used in the LTE specifications todescribe the PHY layer:

(k, l) Resource element with frequency-domain index k and time-domainindex l

Ts Basic time unitNsymb Number of symbols in a transmission time slotNDL

symb Number of OFDM symbols in a downlink slotNUL

symb Number of SC-FDMA symbols in an uplink slotNRB

SC Resource-block size in the frequency domain, expressed as a numberof subcarriers

NTA Timing offset between uplink and downlink radio frames at an UE,expressed in units of Ts

NRB Number of available RBs in a transmission link of a specific channelbandwidth

BWchannel Channel bandwidthBWconfig Transmission bandwidth configuration (occupied bandwidth)Δf Subcarrier spacing

In the LTE system, UL and DL data transmissions are scheduled on a one-msecsubframe basis as shown in Figure 19 and Figure 20 [55]. A subframe consists oftwo consecutive equal-duration (0.5 msec) slots. A radio frame consists of 20 slots,numbered from 0 to 19 or 10 sub-frames, numbered from 0 to 9.

Figure 19: Frame structure type 1


Figure 20: Frame structure type 2 (for 5 ms switch-point periodicity)

Three duplexing modes are supported: full-duplex FDD, half-duplex FDD, and TDD.Figure 19 shows the frame structure that is applicable to FDD. In the half-duplexFDD operation, a UE cannot transmit and receive at the same time while there are nosuch restrictions in the full-duplex FDD mode. Figure 20 shows the frame structurethat is used for TDD.

Figure 21 [55] shows the relationship between UL and DL frames of an UE that usesthe type 1 frame. The transmission of a UL frame from the UE starts NTA × Ts

seconds before that of the corresponding DL frame to the UE. This timing offset isadjusted for each UE to ensure that UL transmissions from multiple UEs arrive atthe serving eNB at the same time. In addition to the time-domain constrains on theradio resource, LTE also has a set of frequency-domain constrains. As a result, LTEassigns transmission recourses in time-frequency units, referred to as recourse blocks(RBs).

All RBs in one of the available channel bandwidths constitute a resource grid. Eachentry in the resource grid is referred to as a resource element defined by the index pair(k, l), where k and l are the indices in the frequency and time domain respectively.Therefore, a resource block consists of NRB

SC ×Nsymb resource elements [56] .

In the time domain, a RB has a 0.5-msec slot duration. Each slot is further dividedinto NUL

symb SC-FDMA symbols or NDLsymb OFDM symbols for the UL and the DL

respectively. Depending on the channel delay spread requirements, a slot consists of7 or 6 symbols for the normal cyclic prefix (CP) and the extended CP respectively.To preserve the slot timing of 0.5 msec, when the normal CP is used, the first symbolin a slot has a longer CP than the remaining six symbols as shown in Table 5 [55].

LTE supports a set of six channel bandwidths as described in Table 6 [55]. Therelationship between BWchannel and BWconfig is shown in Figure 22 [56,56]. BWconfig

is given by BWconfig = NRB × NRBSC × Δf . It is smaller than BWchannel to allow a

guard band preventing out-of-band radiation.


Figure 21: UL and DL resource grid


Table 5: Slot structure for normal and extended cyclic prefix

Table 6: Resource block characteristics


Figure 22: Mapping of a resource grid


3.2.2 PHY layer model

The PHY layer offers data transport services to higher layers by performing thefollowing functions [57]:

– Error detection on the transport channel and indication to higher layers– Forward error correction (FEC) encoding/decoding of the transport channel– Hybrid ARQ soft-combining– Rate matching of the coded transport channel to physical channels– Mapping of the coded transport channel onto physical channels– Power weighting of physical channels– Modulation and demodulation of physical channels– Frequency and time synchronisation– Radio characteristics measurements and indication to higher layers– MIMO antenna processing/ transmit diversity/ beamforming– Radio frequency (RF) processing

Access to these services is through the use of transport and physical channels. Thecombination of services varies according to the quality of the channel in question.Each set of transport and physical channels, therefore, offers a unique combinationof services and baseband processing.

Figure 23 [57] uses the UL-SCH channel as an example to show basic basebandprocessing in terms of operations. The processing chain is divided into two parts: thetransport-channel and physical-channel processing. Section 3.2.2.1 gives an overviewon the operations of the transport-channel processing chain while Section 3.2.2.2focuses on the physical-channel processing chain.

Furthermore, Figure 23 gives a cross-layer model of the physical layer to capture thecharacteristics of the physical layer from the point of view of higher layers. The pro-cessing steps that are configurable by the higher layers are highlighted in blue. In thecase of an UL transmission, the signaling of transport format and resource allocationis partly made at the network side. The network transports this information to theUE over the air. The information may be multiplexed with the hybrid automatic re-peat request (HARQ) information and then used by the uplink transmission controlin the UE to configure the physical-channel processing.

One transport-block of data is delivered to/from the physical layer every TTI. Inthe UE side, after adding cyclic redundancy check (CRC), channel coding is appliedaccording to the implicit information given by the combination of transport formatand resource assignment. Depending on the HARQ type, the HARQ may have controlover coding and rate matching (RM). The transport data is then handled by thephysical-channel processing according to the UL transmission control in the UE. Onthe network side, the MAC scheduler uses indications such as channel state and


Figure 23: Physical layer model for UL-SCH transmission

error indications to configure the physical-channel processing of both the UE and thenetwork side.

3.2.2.1 Transport-channel processing

Major operations supported by different transport channels are summarized in figures24, 25 and 26 [58]. The operations that are common to all transport channels, exceptthe BCH, are as follows:– Transport block CRC attachment– Code block segmentation and code block CRC attachment– Channel coding of data and control information– Rate matching– Code block concatenationThe code block segmentation and concatenation steps are used for large-size infor-mation blocks. Block sizes used on the BCH are small; so the segmentation andconcatenation steps are not required for the BCH processing.

The UL channel has two additional operations: data and control multiplexing aswell as channel interleaving. Data and control information is multiplex to ensurethe presence of the control information on both slots in a subframe. The channelinterleaver is specified for the frequency diversity when hopping is enabled in a UL [2].


Figure 24: Transport channel processing for DL-SCH, PCH and MCH

Figure 25: Transport channel processing for BCH


Figure 26: Transport channel processing for UL-SCH

The major channel coding schemes are summarized in tables 7 and 8 [58]. Turbocoding is used for large data packets from DL and UL data transmission, paging andMBMS transmissions. A tail biting convolutional code, a repetition code or a blockcode are used for DL/UL control (DCI, UCI, CFI and HI) and broadcast control(BCH).


Table 7: Channel coding schemes for transport channels

Table 8: Channel coding schemes for control informations


3.2.2.2 Physical-channel processing

After transport-channel processing, the coded sequence of bits then go through thephysical-channel processing procedures as shown in Figure 27 [55].

Figure 27: Overview of uplink physical-channel processing

Unlike the UL transmission chain shown above, the DL transmission chain supportstransmission diversity as shown in Figure 28 (for the case of a processing chain withtwo transmit antennas) [55]. The transmit diversity scheme in the LTE system isdefined in terms of layer mapping and precoding.


Figu

re28

:Overview

ofphysicalchan

nel

processingfortw

otran

smitan

tennas


Scrambling The scrambling step reduces the effect of fading that disrupts datatransport. Scrambling is applied to all of DL and UL physical channels, except thephysical random access channel (PRACH). All DL channels, except the MCH, havetransport-channel specific scrambling such that the scrambling sequences used in onecell are different from the neighbour cells. This ensures interference randomizationamong cells. All MCH channels of the cells involved in a specific multicast broad-cast signal frequency network (MBSFN) transmission have a common scramblingsequence. The scrambling sequences used in the UL are UE-specific.

Modulation Modulation of scrambled bits generates complex-valued modulationsymbols. Depending on the physical channel considered, supported modulationschemes vary. The UL channels support binary phase shift keying (BPSK), QPSK,16- quadrature amplitude modulation (QAM) and 64-QAM while the DL channelssupport QPSK, 16-QAM and 64-QAM.

OFDMA LTE uses OFDMA in the DL and SC-FDMA in the UL [2, 17]. The useof SC-FDMA results in reduction of peak-to-average power ratio which translates todecreased battery consumption in mobile terminals. The trade-off, however, is theincreased complexity in both mobile and base-station design. The base station needsadaptive equalization to mitigate multipath. The basic processing chain of a SC-FDMA transmitter (as shown in Figure 29 [59]) is more complicated than an OFDMAtransmitter. The two transmitters, however, have a significant degree of similaritysince many of the functional blocks are common to both. Figure 29 duplicates aportion of the physical-channel processing chain shown in figures 27 and 28 forcomparison.

Figure 29: Generic OFDMA and SC-FDMA processing chain

The transform precoding of Figure 27 corresponds to the M -point discrete Fouriertransform (DFT) operation in Figure 29.The size of DFT processor relates to thenumber of scheduled subcarriers used for transmitting a symbol. It is defined as:M = NRB

sc ×α, where α is the number of resource block allocated for the transmission.


The resource element mapping operation corresponds to the subcarrier mapping inFigure 29. It assigns DFT outputs to subcarriers of resource blocks. Subcarriers areassigned according to localized or distributed resource blocks. In the localized type,the DFT outputs are assigned to adjacent subcarriers. In the distributed type, thedata are spaced across the channel bandwidth. Although both types are specified inthe standard [55], the localized type is favoured by early LTE deployments [59].

The signal generation step corresponds to the remainder of the processing chain inFigure 29: N -point inverse discrete Fourier transform (IDFT), Cyclic prefix & pulseshaping and radio front-end (RFE). The sizes of IDFT processor, N , supported by theLTE systems are specified in the E-UTRAN BS standard [56] and shown in Table 9.The cyclic prefix addition provides multipath mitigation. The pulse shaping stepprevents spectral regrowth. The RFE converts digital signal to analog and then toRF.

Table 9: OFDMA parameters

Layer mapping and precoding Layer mapping assigns the complex-valued modu-lation symbols to one of several transmission layers, and precoding transforms thesymbols on each layer for transmission on antenna ports. The two steps are relatedto transmission diversity and spatial multiplexing. The transmission diversity allowsimprovement of link performance and reduces delays introduce by scheduling [60].LTE employs the space frequency block coding (SFBC) as a transmission diversityscheme.

Multiple transmitting antennas in combination with multiple receiving antennas areused to create spatial multiplexing which increases data rate. The spatial multiplexingallows transmission of different data streams simultaneously on the same RB. Thedata streams can belong to one user (SU-MIMO) or to different users (MU-MIMO).The SU-MIMO increases the data rate of one user while the MU-MIMO increasesoverall capacity. LTE defines the following parameters for the spatial multiplexing[20]:

– For DL, up to four layers


– For UL, single layer– For UL and DL, the MU-MIMO is supported

As a result, both the SU-MIMO and MU-MIMO schemes are supported by the DLwhile the UL supports only the MU-MIMO scheme. Supporting only MU-MIMOat UL reduces terminal complexity while taking advantage of two or more transmit-ting antennas. The MU-MIMO scheme requires only one transmit antenna at UEside. The UEs share the same resource block by applying mutually orthogonal pi-lot patterns. The MU-MIMO is also referred to as spatial division multiple access(SDMA).

3.2.3 Interaction with upper layers

Figure 30 [61] shows the data flow between the protocol layers in the time domain.The MAC layer passes data to/from the PHY layer in one-msec TTI sub-frames. Theprotocol layers work together to make effective use of radio recourses in the fixed timeperiod. Starting from the top of the protocol stack, the PDCP layer treats each IPpacket as a PDCP service data unit (SDU) and then adds a PDCP header to theIP packet to make it a PDCP protocol data unit (PDU). Those PDCP PDUs arethen passed to the RLC layer for reassembly and/or segmentation. The relationshipbetween RLC SDUs and PDUs is configurable and defined in the radio interfaceprotocol [54]. Then, the MAC layer adds a MAC header and padding to the data.The data is received as transport blocks (TBs) by the PHY layer. Finally, the TB isallocated physical resource for transmission over the air. The IP packet is decodedby following this process in the reverse order.


Figure 30: Time domain view of data transport


3.3 MAC layerThe MAC layer controls access to a shared medium (radio resources). To ensureeffective use of the radio spectrum in a fixed period of time (a TB), dynamic allocationof the radio resources is made using the following functions [62].

– Mapping between logical channels and transport channels– Multiplexing of MAC SDUs from one or different logical channels onto TBs to bedelivered to the physical layer on transport channels

– Demultiplexing of MAC PDUs from TBs delivered by the physical layer on trans-port channels

– Scheduling information reporting– Error correction through HARQ– Priority handling between UEs by means of dynamic scheduling– Priority handling between logical channels of one UE– Logical channel prioritization– Transport format selection

To ensure flexible spectrum assignment, protocol layers exchange management mes-sages and the supporting eNB centrally controls the DL and UL spectrum. Becauseof the DL and UL channel separation, the MAC layer is also designed uniquely forboth transport directions. Figure 31 [62] shows an overview of the MAC structure atthe UE side to illustrate the interaction of the MAC functions.

The MAC is mainly responsible for mapping logical channels and transport channels.Variables of mapping are transport format selection such as coding and modulation,which determine data rate and scheduling (time-slot allocation). On DL, the MAClayer of the eNB specifies transport formats by sending the UE modulation codingscheme (MCS) in each TB and the MCS is used by the UE to prepare the PHYfor the next TB. Transport formats are chosen according to MAC measurementsregarding the UE’s status and conditions. The UE sends MAC measurements tothe eNB using control messages. Once the MAC of the UE interprets the transportformat and schedule, it works in combination with the PHY to perform HARQ forerror recovery. The PHY is responsible for retention and recombination and the MACperforms management and signalling of the HARQ process. An adaptive HARQ isused for both UL and DL data transmissions. This means that modulation, codingand resource allocation can change on retransmission. When a valid TB is availablefrom the HARQ process, the TB may need to be demultiplexed since it may containseveral channels.

For the UL direction, most of the DL MAC operations are reversed. The most sig-nificant difference is the random-access process that is used for initial transmission.There are two types of random accesses: contention based and non-contention based,


Figure 31: MAC structure overview, UE side

where the contention-based process is subject to failure while the other is not. Ta-ble 10 [62] summarized the MAC functions in both transport directions of the UEand eNB sides.


Table 10: MAC function location and direction association

MAC function UE eNB Downlink Uplink

Mapping between logical channels and X X Xtransport channels X X X

MultiplexingX X

X X

DemultiplexingX X

X X

Error correction through HARQX X X

X X XTransport format selection X X XPriority handling between UEs X X XPriority handling between logical

X X Xchannels of one UELogical channel prioritization X XScheduling information reporting X X


4 WiMAX

This section presents mobile WiMAX as documented in IEEE 802.16-2004&E [5,37],WiMAX Forum Stage 2 and Stage 3 specifications for Release 1.0 Version 4, andWiMAX Forum mobile system profile Release 1.0 [31]. Only the aspects of IEEE802.16 standards that are relevant to mobile WiMAX will be discussed. Discrepan-cies between different versions of the standards are common and so the referencedspecifications are cited when appropriate. The structure of this section is similar tothat of Section 3. It starts with an overall system-level description, then describesprotocol layers and finally, concentrates on the air interfaces: PHY and MAC layers.

4.1 System overviewThe WiMAX network has simple and flat architecture when compared to other cel-lular network architecture. WiMAX architecture also does not have to support anybackward compatibility with previous standards, such as LTE with UMTS and GSM.It is composed of two parts: a radio network and a core network. The WiMAX ra-dio network is called access service network (ASN) which consists of base stations(BSs) and access services network gateways (ASN-GWs). The WiMAX core net-work, connectivity services network (CSN), uses typical IP-network nodes such as anauthentication, authorization and accounting (AAA) server and a home agent (HA),which acts similar to a dynamic host configuration protocol (DHCP) server in a wiredIP network.

4.1.1 Functional elements

Figure 32 [29] shows a more detailed reference model that defines functional elementsand reference points for interoperability between vendors. Functional entities aregrouped into three elements: mobile station (MS), ASN and CSN. A device that ismobile WiMAX-enabled is denoted as MS. On the network side, mobile WiMAX in-troduces two key elements: an ASN and a CSN which are comparable to a RAN anda core network of a 3G network in terms of functionality. Functionally speaking, theASN handles all aspects of the radio interface to maintain connectivity between MSsand the network. The CSN provides most of the backend functions to provide IPconnectivity to subscribers such as authentication, IP address management, billingand mobility to the ASN. Generally, the ASN providers are also known as network ac-cess providers (NAP) and the CSN providers are also called network service providers(NSP). The NAP deploys radio networks while the NSP hosts network services suchas streaming and Internet accesses.


Figure 32: WiMAX system architecture

4.1.1.1 CSN

A CSN is defined as a set of network functions that provide IP connectivity to sub-scribers [29]. It is typically an all-IP network based on standard IP protocols andelements such as routers/switches, AAA servers, user databases and interworkinggateways. CSN is defined with the following functions:

– MS IP address and endpoint parameter allocation– Internet access– AAA proxy or server– Policy and admission control based on user subscription profiles– ASN-CSN tunneling support– Billing and inter-operator settlement– Inter-CSN tunneling for roaming– Inter-ASN mobility– WiMAX services such as location based services, connectivity for peer-to-peer ser-vices, IP multimedia services and lawful intercept services


4.1.1.2 ASN

An ASN is defined with a set of network functions for providing wireless access tosubscribers. It comprises of network entities such as one or more BSs and one ormore ASN-GWs. A single ASN may connect to multiple CSNs and vice versa. Thisarchitectural design allows the ASNs and CSNs to be owned by different businessentities. The defined set of network functions are mapped to a BS and an ASN-GWaccording to three different profiles in Release 1.0 of the standard [29]: Profile A,Profile B and Profile C. Some of the ASN functions are as follows:

– AAA message relay– Network discovery and selection of preferred NSP for subscribers– Providing layer-2 connectivity and relay functions to establish layer-3 connectivitywith a MS

– Radio resource management– Mobility control functions: ASN anchor mobility, CSN anchor mobility and ASN-CSN tunneling

– Paging– Quality of Service

The distribution of ASN functions for Probile C is shown in Figure 33 [29] as anexample. The three ASN profiles are summarized as follows. Profile A separatesthe function set among the BS and ASN-GW similar to a 3G RAN. The ASN-GWacts as a central controller and serves several BSs. Therefore, most of the decision-making tasks such as mobility control and radio resource management are handledby the ASN-GW. Profile B groups the BS and ASN-GW into a single entity. Thisimplementation is similar to LTE’s E-UTRAN that merges the RNC and NodeB ofUMTS to create the eNB. Profile C, similar to Profile A, distributes the functionset among the BS and ASN-GW. The BS, however, are assigned with more decision-making tasks.

BS The WiMAX BS is a logical entity that embodies a full instance of the WiMAXMAC and PHY layers according to the IEEE 802.16-2004&E standard as well as someASN functions. A BS instance represents one sector with one frequency assignment.One physical implementation of a BS may have multiple BS instances since the BSis defined as a logical entity. A single BS is associated with exactly one ASN-GWbut it is required to have connectivity to several ASN-GWs for load balancing orredundancy. Its key function is scheduling for UL and DL resource management [29].

ASN-GW The WiMAX ASN-GW is also a logical entity that represents an ag-gregation of functions such as control-plane functions and security functions. Eachfunctional entity works with a corresponding function in a BS instance, a residentfunction in a CSN or a function in another ASN. The ASN-GW functions may be


Figure 33: Functional view of ASN Profile C

decomposed into two groups: the enforcement point (EP) and the decision point(DP) [29].

4.1.2 Reference points

A reference point (RP) [29] is a conceptual link that connects two groups of functionsreside in different functional entities such as ASN, CSN and MS or in different businessentities such as NAP or NSP. R6 to R8 RPs are called inter-ASN informative RPssince they are between internal functional entities of an ASN and the other RPs arecalled normative RPs. The following RPs are defined:

R1 : Defined between a MS and an ASN.


R2 : Defined between a MS and a CSN for authentication and IP host configurationmanagement of roaming procedures.

R3 : Defined between an ASN and a CSN to support AAA, policy enforcement andmobility managements. It also transfers user data between the ASN and theCSN.

R4 : Defined between two ASN-GWs. This interface defines mobility procedurewhen a MS crosses an ASN boundary.

R5 : Defined between two CSNs for roaming procedures.

R6 : Defined between a BS and an ASN-GW.

R7 : Defined between a DP and an EP of an ASN-GW.

R8 : Defined between two BSs. This interface defines mobility procedures when aMS crosses a BS boundary.

4.1.3 Protocol architecture

Figure 34 [25] shows the protocol layers of mobile WiMAX . IEEE 802.16e-2005 islimited to the control/data-plane aspects of the radio interface. The IEEE 802.16protocol layering consists of only the MAC layer (part of the link layer) and thePHY layer. The management-plane functions are supplemented by IEEE 802.16f andIEEE 802.16g. The WiMAX NWG adds radio access control and transport functionsto IEEE 802.16 to make an end-to-end system.

Figure 34: IEEE 802.16e-2005 protocol reference model


Figure 35: Protocol layer architecture for control, IP-CS and ETH-CS signal

Figure 35 [29] shows the end-to-end architecture and the protocol layers of a mobileWiMAX network. Control signal are carried by the control protocol stack while datasignal are carried by the data paths. The PHY and MAC specification of IEEE 802.16are used by the R1 RP between the MS and BS. The control signal are handled bythe IEEE 802.16 control layer (.16 Ctrl) at the R1 RP and by the control layers ofthe ASN or CSN (ASN ctrl and CSN ctrl) at the rest of the network. The remainderof the control protocol stack are provider-specific, as long as the implementationscomply with the mobile WiMAX specification.

Data, transmitted by the IP layer, are carried in messages called IP datagrams. IPdatagrams are transferred through the IP-convergence sublayer (IP CS) or Ether-net (ETH) CS data paths. The IP CS carries IP datagrams directly in the payloadof 802.16 PDUs while the ETH CS needs to encapsulate IEEE 802.3 frames, whichcarries the IP datagrams, in the payload of 802.16 PDUs. The generic routing en-capsulation (GRE) is used to route traffic within an ASN.


4.1.4 Interaction between protocol layers of IEEE 802.16 and thehigher layer

To support a wide range of BWA applications, the MAC and PHY layers of IEEE802.16 provides functions such as classification, resource allocation and burst profiles[5,37]. The 802.16 MAC provide multiple service types for the transport of protocolssuch as IP protocol, IEEE 802.3 from the higher layer. Issues of transport efficiencyare addressed by adapting PHY parameters, such as modulation and coding schemes,to facilitate the delivery of data with appropriate QoS constraints.

4.2 PHY layerMobile WiMAX organizes it radio resource in time-frequency building blocks whichare further described in Section 4.2.1. The duration and shape of transmission de-pends on the amount of resource that the BS is assigned. OFDMA access techniqueis used in both UL and DL transmissions. This access technique allows flexible band-width deployment ranging from 1.25 MHz to 20 MHz. Although IEEE 802.16-2004&Esupports TDD, FDD and half-duplex FDD, most of the mobile WiMAX system pro-files, defined in Release 1.0 [31], are based on TDD. Since this report is based on theRelease 1.0, Section 4.2.1 focuses on the TDD structure.

The PHY layer of mobile WiMAX offers a set of baseband processing which is cov-ered in Section 4.2.2. Although IEEE 802.16-2004&E specifies several PHY layerprocessing chains, mobile WiMAX uses just the OFDMA chain, which is also theonly processing covered by Section 4.2.2.

4.2.1 Time and frequency structures of radio resources

The WiMAX PHY layer is responsible for mapping modulated data symbols andpilots onto subcarriers to form OFDMA symbols [5, 31, 37]. Several subcarriers aregrouped into subchannels. The subchannels are then organized into slots that areused to form bursts. The DL/UL bursts from different users are mapped into frames.Figure 36 [36] shows an example of a TDD frame that is divided into a DL subframeand an UL subframe to accommodate both DL and UL traffic.

Mobile WiMAX supports a set of channel bandwidths (BW ), frame durations andslot structures. Channel bandwidths can be a multiple of 1.25, 1.75, 2, or 2.75 MHzto a maximum of 20 MHz. Table 11 lists the bandwidths, slot structures and framedurations supported by mobile WiMAX. The frame structure is quite flexible in termsof how multiple users are multiplexed. A single frame may contain bursts of variablesizes and shapes. Burst allocations are controlled by the DL-MAP and UP-MAPmessages which are dynamic and change from frame to frame.


Figure 36: Example of TDD frame structure for mobile WiMAX

Table 11: WiMAX radio resource characteristic

A slot is the minimum resource allocation unit. It is defined in time-frequency dimen-sions. The time dimension refers to the OFDMA symbol number and the frequencydimension refers to the subchannel logical number. The definition of the slots dif-fers for transmission directions (DL and UL) and subchannel schemes – partial usagesubchannel (PUSC), full usage subchannel (FUSC) and AMC.

As shown in Figure 36, each frame begins with a preamble, followed by a DL sub-frame, a guard or a transmit/receive transition gap (TTG) and an UL subframe.The downlink subframe starts with a preamble that is for one symbol duration. Thepreamble enables physical-layer functions such as time/frequency synchronization andinitial channel estimation. The frame control header (FCH) follows the preamble toprovide frame configuration information such as the length of the DL-MAP message.


The DL-MAP, which follows the FCH, specifies the burst allocation for different usersin the downlink subframe and the location of the UL-MAP message. The UL-MAPmessage specifies the burst allocation information for the next uplink subframe.

The UL subframe is made up of UL bursts from different users. A portion of the ULsubframe is set asides for MAC functions such as ranging, channel quality estimationfor CQI transfer to the BS scheduler and HARQ acknowledgements.

4.2.2 Physical-layer processing

In order to strengthen the robustness of communications in mobile wireless envi-ronments, WiMAX supports several modulation and coding schemes that can beconfigured on a burst-by-burst basis according to channel conditions. This is knownas adaptive modulation and coding (AMC). Figure 37 [5] shows a physical-layer pro-cessing chain for the support of channel coding and modulation.

Figure 37: WiMAX PHY transmission chain

To effectively change the coding and modulation to the most appropriate ones, theAMC techniques require awareness of channel quality which is usually provided bya channel estimation process at the receiver and a feedback process to report theestimate to the transmitter. For mobile WiMAX systems, a MS periodically reportchannel status to the BS using CQI messages that provides feedback on the DL-channel quality. For the UL, the BS makes a channel-quality estimate based on thequality of the received signal. Then, the BS uses both the UL and DL estimatesto choose a coding and modulation scheme that makes the best use of the availableradio resources. A combination of modulation and coding scheme is defined as aburst profile in mobile WiMAX. The following subsection details each block of theprocessing chain.

4.2.2.1 Randomizing

Data from the MAC layer are first randomized or scrambled by using a pseudo-randombinary sequence (PRBS) generator. The randomizing process is applied to all dataon the DL and UL, except the FCH and preamble. The PRBS generator polynomialis 1 + x14 + x15 and the period of the generator is 215 − 1. It is initialized on eachFEC block.


4.2.2.2 FEC

IEEE 802.16 [5, 37] specify several FEC methods as mandatory requirements or asoptions. The mandatory coding method is convolutional coding (CC) and the optionalcoding methods are convolutional turbo coding (CTC), block turbo coding (BCT)and low density parity check (LDPC). Mobile WiMAX [31], however, requires CTCto be mandatory.

HARQ is a variation of ARQ mechanisms and is implemented at the physical layertogether with FEC as shown in Figure 38 [5]. IEEE 802.16e-2005 defines two HARQtechniques that are classified in terms of the combining method: chase and incremen-tal redundancy. Release 1.0 mobile WiMAX chooses to support only chase combiningHARQ.

Figure 38: FEC and HARQ for WiMAX

4.2.2.3 Interleaver

The interleaving step is used to protect the transmission against fading. Interleavingis usually used together with FEC to facilitate error correction. The encoded databits are interleaved by a block interleaver that is made of two steps [5, 37]. The firststep makes sure that adjacent coded bits are mapped to non-adjacent subcarriers.The second step ensures that adjacent coded bits are mapped alternately to more orless significant bits of the constellation. The two interleaving steps are defined bytwo permutations.

4.2.2.4 Repetition

Repetition is described by the IEEE 802.16e-2005 [5] standard only for the OFDMAphysical layer processing. It is intended to further increase the signal margin over themodulation and FEC mechanisms.

Two variables are used to control the repletion step: R is called the repetition factorand K is the number of required slots before applying repetition. In short, the databits obtained after the interleaving step are divided into slots and each group of bits


designated for a slot is repeated R times to form R contiguous slots. The numberof allocated slots (NS) is calculated as the followings for UL and DL transmissionsseparately. For UL, NS is a whole multiple of R. For DL, NS is in the range of R×Kto R×K + (R− 1). For example, when R = 6 and K = 10, NS for the burst can befrom 60 to 65 slots. This repetition scheme only applies to QPSK modulation.

4.2.2.5 Modulation

Modulation schemes applied to UL and DL transmissions vary according to the chan-nel state and are determined by the serving BS. QPSK, 16-QAM and 64-QAM aremandatory for the DL while only QPSK and 16-QAM are mandatory for the UL.

4.2.2.6 OFDMA

Once the FEC encoding and modulation processing is done, the data bits are mappedto OFDMA subcarriers and then put through a processing similar to that of Figure 29.Subcarriers are assigned in groups known as subchannels.

Two types of subchannels are defined depending on the methods of grouping subcar-riers. One is called the distributed-based subchannel, which selects subcarriers thatspace across the channel bandwidth and then group the selected subcarriers togetherto form a subchannel. The distributed-based subchannel is further divided into twotypes: PUSC and FUSC. The PUSC is partially allocated to multiple transmittersand the FUSC is fully allocated to one transmitter. The other subcarrier-groupingmethod is called the adjacent-based subchannel or band AMC subchannel. It selectssubcarriers in adjacent frequencies.

Table 12 shows parameters supported by mobile WiMAX. The characteristics of anOFDMA symbol are determined by the following primitive parameters:

– BW , the channel bandwidth– n, sampling factor: This parameter is used to determine the sampling frequencyto bandwidth ratio, the subcarrier spacing and the useful symbol time. n is 8/7for channel bandwidths that are a multiple of 1.75 MHz and 28/25 for channelbandwidths that are a multiple of 1.25, 1.5, 2, 2.75 MHz.

– G, the guard time ratio or the CP to “useful” time ratio: IEEE 802.16e–2005 sup-ports 1/32, 1/16, 1/8 and 1/4 while mobile WiMAX supports only 1/8.

Once the primitive parameters are specified, other parameters of Table 12 can bederived. IEEE 802.16e–2005 specifies the support of several fast Fourier transform(FFT) lengths: 128, 512, 1024 and 2048. Mobile WiMAX fixes its subcarrier spacing,Δf that is set to 10.94 kHz and OFDMA symbol duration that is set to 102.9 μs [36].


Table 12: WiMAX OFDMA parameters

Parameter Unit Value

Channel bandwidth (BW) MHz 1.25 5 10 20FFT size 128 512 1024 2048Subcarrier spacing (Δf) kHz 10.94Useful symbol time (Tb) μs 91.4Guard time (Tg) μs 11.4OFDMA symbol time (TS) μs 102.8

This subcarrier spacing supports delay spread up to 20 μs and mobility up to 120km/h at 3.5 GHz. The other parameters are calculated using the following equations:

– NFFT , FFT size: NFFT = (n× BW )/Δf– Tb, useful symbol time: Tb = 1/Δf– Tg, guard time: Tg = Tb ×G– TS, OFDMA symbol time: TS = Tb + Tg

4.2.2.7 Advanced antenna technologies

Mobile WiMAX uses multiple antenna technologies and diversity schemes to increasethroughput and reliability of transmissions. A space time coding (STC) is chosenas an optional transmission diversity scheme to provide higher order diversity in DLtransmissions. Multiple antennas working together with spatial division multipleaccess (SDMA) are used in the DL and only SDMA is used in the UL. SDMA is alsoreferred to as the collaborative spatial multiplexing in WiMAX.


4.3 MAC layerFigure 39 [37] shows data unit exchange in general. There are two types of dataunits involved: protocol data unit (PDU) and service data unit (SDU). A PDU istransferred between peer entities of the same protocol layer. It is the data unitgenerated from a SDU unit for the next lower layer in the downward direction. Forexample shown on Figure 40, a MAC SDU is appended with a MAC header and aCRC to form a MAC PDU for the PHY layer. In the upward direction, it is the dataunit received from the previous lower layer. A SDU is obtained by stripping the headerand CRC from the PDU. It can be exchanged directly between two adjacent protocollayers. It is received from the previous higher layer on the downward direction andsent to the next higher layer on the upward direction.

In general, the data unit between the MAC sublayers and the PHY layer of WiMAXair interface (shown in Figure 34) follows the same naming convention. The MAClayer passes data to/from the PHY layer in each burst interval. A MAC PDU is ofvariable length, which depends on the amount of carried payload. When packing isturned on for a connection, a PDU can contain multiple SDU units.

Figure 39: PDU and SDU in a protocol stack


MAC header MAC SDU(s) CRC

MS

B

LSB

Figure 40: MAC PDU format

Figure 41 shows the PHY and MAC layers for WiMAX. The MAC layer includesthe service-specific convergence sublayer (CS) that interfaces to higher layers, theMAC common part sublayer (CPS) that carriers out the key MAC functions andthe security sublayer (privacy sublayer) that locates below the CPS. The MAC layeris defined to enable simultaneous connections to shared resources in the OSI model.This objective is supported by MAC-layer functions such as reliable transfer of framesand coordination attempts to shared radio resources from multiple subscribers in amobile WiMAX network. To support those tasks, the CS classifies transmitting dataand associates each application stream with a particular connection. This connection-oriented feature of mobile WiMAX ensures tight control of resource allocation andQoS for individual applications. The CPS of a BS is responsible for the performanceof the overall system while supporting the QoS of individual connections.

In addition to traditional layer-2 functions of the OSI model, the security sublayer ofthe mobile WiMAX MAC layer provides subscribers with privacy and authenticationacross the broadband network. Functions of the three sublayers are further describedin the following sub-sections.

4.3.1 Service-specific convergence sublayer

The CS resides on the top of the other two MAC sublayers. It performs the followingfunctions to utilize the services of the MAC CPS via the MAC SAP [5, 37]. The CSaccepts higher layer protocol PDUs and processes the external-network data to finallygenerate CS PDUs to the appropriate MAC SAP. Processing includes classifying theexternal network data to associate them to the proper MAC service flow identifier(SFID) and connection identifier (CID).

The IEEE 802.16e-2005 standard defines two CSs to interface with two types ofexternal networks: asynchronous transfer mode (ATM) network and packet network.However, the WiMAX Forum Mobile System Profile Release 1.0 [31] excludes theATM CS; hence, a discussion of the ATM CS is omitted. The packet CS is defined forpacket services such as IPv4, IPv6, Ethernet and virtual local area network (VLAN).


Figure 41: WiMAX PHY and MAC layers protocol stack

The classifying and associating process enable QoS and bandwidth allocation servicesprovided by the CPS layer.

In addition, the CS is defined with optional functions such as payload header sup-pression (PHS) to enhance efficiency by suppressing payload header information andrebuilding suppressed payload header information. The packet CS supports robustheader compression (ROHC) and enhanced compressed real-time transport protocol(ECRTP) header compression.

4.3.2 MAC common part sublayer

The MAC CPS is the main body of the MAC layer. It provides the core MACfunctionalities, such as resource allocation & QoS management, connection & sessionprocessing, data transfer processing and ARQ [5,37]. Similar to a cellular system, theCPS is designed to support point-to-multipoint architecture. The BS in a WiMAXnetwork acts as the central controller handling multiple independent users simultane-ously. On the downlink, the downlink scheduler of the BS manages bandwidth. Theuplink bandwidth is shared among all of the MSs in the same cell or sector and so


that it is allocated by the BS to the MSs upon request. The CPS of the BS performsbandwidth management based on service requirements. A service request is mappedto a service flow which is unidirectional and is associated with a negotiated set ofQoS parameters from upper layer applications. Some of the QoS parameters arebandwidth and delay. A 32-bit SFID is used to identify the service flow within theMS. The scheduler of the BS arranges the network resources to meet the performancedemand according to the requested QoS parameters.

A WiMAX network is called connection-oriented since all services flows are mappedto connections at the MAC layer. Connections are referenced with a 16-bit CID.When data are sent between the MS and the BS, the service flow is implicitly definedby the CID. Therefore, the SFID is not carried in the data packets between the MSand the BS.

Since the CPS is responsible for overall connection and session processing, it definesa complete messaging structure to achieve this function. Upon entering the network,the MS is assigned with different types of management connections that reflect dif-ferent QoS performances depending on the management requirements. There arethree types of management connections: basic, primary and secondary. The basicconnection is for the transfer of short and time-critical management messages. Theprimary connection is used to exchange longer and more delay-tolerant messages.The secondary management connection is used for the transfer of standard-basedmanagement messages. Each connection is associated with a particular CID. In addi-tion, other CIDs are defined for network operations such as initial ranging, multicastbroadcast and etc.

To deliver data to the lower layer, the MAC CPS processes the MAC SDUs receivedfrom the CS through the MAC SAP and constructs the MAC PDUs. Other advancedfeatures such as HARQ, AMC and fast feedback schemes are designed to enhancethroughput and coverage of an 802.16-based network.

4.3.3 Security sublayer

The security sublayer is built into the WiMAX radio-interface protocol stack andhas two component protocols: encapsulation protocol and privacy key management(PKM) protocol. The encapsulation protocol applies cryptographic transformationto MAC PDUs traveling between a MS and a BS. This provides users with privacy orconfidentiality across the network. The PKM protocol provides secured distributionof keying data from the BS to the MS. This secures network services from theft andalso provides authentication [5, 37].


5 Comparison of LTE and WiMAX

This section briefly compares the overall systems of LTE and WiMAX, then theprotocol layers and finally, the air interfaces. Table 13 summarizes the comparison.

5.1 System overviewSome similarities among the LTE and WiMAX system architectures are as follows.Both WiMAX and LTE are architecturally split into two parts: a radio network anda core network. Similar to LTE, mobile WiMAX is also an all-IP system that carriesonly IP packets.

However, The WiMAX ASN consists of BSs and ASN-GWs while the LTE radio net-work consists of only eNBs. For LTE, the rationale behind eliminating the RNC islikely to reduce latency by distributing the RNC processing load into multiple eNBs.As a result, set up times from idle can meet the performance requirement of less than100 msec specified in [63]. In contrast to the LTE’s radio network, mobile WiMAX al-lows developers three ASN configurations. A possible advantage of separated entitiesis that the network capacity can grow independently. Consequently, operators mayimplement the air-interface entities topologically separated or collocated dependingon the considered bandwidth latencies and congestion. WiMAX’s core network isalso slightly different from LTE’s. The WiMAX core network, CSN, uses typical IP-network nodes. In contrast, LTE defines a core network called EPC which includesunique entities such as MME and S-GW.

5.1.1 Functional elements

Despite the different evolution paths taken by the WiMAX Forum and 3GPP, the LTEEPS architecture still resembles the WiMAX architecture in terms of functionalityset [12].

– BS and eNB: Functionally speaking, a BS and an eNB are similar. Both of themare the only elements interfacing with subscriber devices. The main functions thatrelate to the creation of connectivity are radio resource management and scheduling.They provide air interfaces into PS networks by IP tunneling to an access gateway.The significant difference is the physical-layer processing since the BS is based onIEEE 802.16 and the eNB is based on 3GPP releases.

– MME/S-GW and ASN-GW: Functionally speaking, the MME/S-GW and the ASN-GW are similar since both of them provide mobility between radio interfaces (eNBin LTE and BS in WiMAX), security and QoS functions. The differences are:LTE defines the MME for control-plane traffic and the S-GW for user-plane trafficwhile WiMAX uses the ASN-GW to handle both traffic types. The protocols and


messages used between the radio interfaces differ as well since they are defined bycorresponding specifications.

– PDN-GW and HA: The functions of the PDN-GW and the HA are similar sinceboth of them provide mobility between access gateways (S-GW in LTE and ASN-GW in WiMAX). Differences in protocols arise again from corresponding specifi-cations.

5.1.2 Interfaces and reference points

The RPs of WiMAX and the interfaces of LTE are functionally similar since both ofthem connect network elements.

– Communications between radio interfaces (BS in WiMAX and eNB in LTE): R8and X2 eliminate the need to route traffic through a core network when appropriate.This reduces the latency in handovers and the dependency to the core network.

– Communications between the radio and the core network: S1 is defined for LTEand R6 is defined for WiMAX.

– Mobility support: LTE and WiMAX provide mobility procedures for seamless con-nectivity. For LTE, S1-U is for handovers among eNBs, S2 is for handovers tonon-3GPP access technologies, S10/S4 are for handovers to 3GPP access networksand S5 is for handovers to different gateways. For WiMAX, R8 and R6 are forhandovers among BSs, R4 is for handovers to different ASNs and R2/R5 are forhandovers to different CSNs.

5.1.3 Protocol architecture

Figure 42 [26] shows the protocol stacks of LTE next to that of WiMAX and furtherillustrates the similarities and differences between the two. LTE has more layers andproprietary protocols comparing to WiMAX. The tunneling protocols used by LTEand WiMAX to encapsulate user data are also different. WiMAX uses GRE whileLTE uses the GPRS tunnelling protocol (GTP) and the proxy mobile IP (PMIP)-based S5/S8.

Figure 42 shows the protocol stacks only for user data and a comparison of the control-plane protocol stacks is given as the followings. LTE defines two control-plane stacksfor subscribers. One is for RRC messages between an UE and an eNB and the other isfor NAS messages between an UE and a MME. In comparison, a WiMAX subscriberdoes not communicate directly with an ASN-GW. The MS uses procedures definedby IEEE 802.16 to communicate with the BS and the BS talks to the ASN-GW usinga R6 RP defined by the WiMAX forum.

Both IEEE and 3GPP assume sublayering for their wireless systems because the DLLdesign of the OSI model provides the functional and procedural means to transfer


Figure 42: Protocol layer architectures for LTE and WiMAX

data only between wired entities such as the Ethernet. The OSI-layered modeling isnot sufficient on its own to cope with the scarcity and harshness of radio medium.Another reason for sublayering comes from the need to accommodate changes orevolutions in the PHY layer [64].

Although sublayers are defined differently among different standards, the sublayersare divided according to the higher-level services and functions. Generally, the DLLsof most wireless standards are divided into at least two sublayers. The DLL functionsthat are constrained by the specific characteristics of the corresponding PHY aregrouped in one layer while the medium-independent functions are in the other.

E-UTRAN groups the DLL functions independent of the physical aspects of theradios interface such as in-sequence delivery into the RLC and PDCP layers, whilethe medium-dependent functions such as scheduling are part of the MAC layer. Thesublayered model dates back to when IEEE defined the LAN standardization. TheIEEE 802 network is based on the logical link control (LLC) sublayer, a uniforminterface for the data link service. Beneath the LLC sublayer is the MAC sublayerdesigned for the particular medium such as the Ethernet and WiFi [65]. Similarly,WiMAX puts the DLL independent functions into the CS and security sublayer whilethe dependent funcitons into the MAC CPS.


5.1.4 Interaction between protocol layers

BothWiMAX and LTE are designed to support a wide range of BWA applications. Tosupport these varieties of services, LTE defines the logical channels to carry differenttypes of information and the transport and physical channels to dynamically processthe data according to performance requirements. The MAC and PHY layers of IEEE802.16 provide similar functions in the forms of classification, resource allocation andburst profiles.

5.2 PHY layer5.2.1 Time and frequency structures of radio resources

Both LTE and WiMAX are defined to support a wide range of bandwidths. This ismade possible by using OFDMA modulation and resource allocation schemes that arescalable in both time and frequency domains. To support two-way communications,both LTE and WiMAX specify frame structures for TDD and FDD.

The frame duration of LTE is 1 msec while that of WiMAX is 5 msec. Generallyspeaking, the complexity of implementations grows as the timing requirement getsstricter. However, the shorter frame duration reduces latency. Consequently, theperformance of HARQ and AMC are also improved.

Both WiMAX and LTE have TDD and FDD defined in their specifications. How-ever, Release 1.0 mobile WiMAX is defined as a TDD system and most of the LTEdeployments are expected to be FDD [36]. The reasons for this difference in deploy-ment preference were resource availability and technological focus. Previous cellulardeployments were FDD-based. As a result, the cellular operators have unused orin-used spectrum allocation for FDD deployments. Also, this legacy partly explainsexisting cellular operators’ preference to migrate towards LTE. On the other hand,one of the main objects of broadband wireless accesses is to support multimediadata transport. The TDD technology adapted by mobile WiMAX operators enablesflexibility in choosing UL-to-DL data rate ratios which support the asymmetric na-ture of multimedia traffic in general. On the other hand, FDD is more adequatefor symmetric traffic such as live voices which have been the main service of cellularcommunication systems.

Other technical aspects of TDD and FDD systems are as follows:

– FDD uses paired spectrum, one for DL and the other for UL. TDD does not havethis requirement.

– TDD is more suited for applying antenna technologies than FDD. TDD systemsoffer the ability to exploit channel reciprocity that is usually required by beam-forming technologies to estimate channel quality. Diversity and MIMO techniques,


however, are applicable to both TDD and FDD.– TDD and FDD device manufacturers face different design challenges. TDD requiressynchronization between transceivers. TDD has advantages over FDD in that somedevices can be shared among the transmitter and the receiver.

5.2.2 Physical-layer processing

Both WiMAX and LTE use a MAC scheduler to dynamically adjust coding andmodulation schemes of each transmission according to the channel conditions. Inaddition to supporting a variety of coding and modulation schemes, the PHY-layerprocessing chains of both systems have a lot in common. Both of them have thefollowing processing steps: CRC attachment, channel coding schemes such as CCand CTC, scrambling/interleaving, data modulation techniques such as QPSK, 16-QAM and 64-QAM and OFDMA modulation. Smart antenna technologies such astransmission diversity and multiple antennas are designed into both systems. WhileWiMAX uses STC, LTE uses a variation of STC called SFBC. Both systems usemultiple antenna and SDMA in the DL and only SDMA in the UL. SDMA is referredto as MU-MIMO in LTE and collaborative spatial multiplex in WiMAX.

5.3 MAC layerSince the MAC layer of WiMAX covers the whole layer 2 of the OSI model whilethe MAC sublayer of LTE is only a part of the layer 2, the WiMAX MAC layerhas more functions. Data units are passed among sublayers in the same namingconversion, SDU and PDU. Although the duration of frames is fixed for both systems,the transmission interval is fixed for LTE and is variable for WiMAX. Functionallyspeaking, the MAC layers of both LTE and WiMAX provide functions to supportthe traditional layer-2 objective of the OSI model in terms of resource management.Resource management is optimized by adapting centralized control at the eNB of LTEand the BS of WiMAX. In addition to traditional layer-2 functions, the WiMAXMAClayer also provides function to support security features such as integrity protectionand authentication.

Some functional overlaps between LTE and WiMAX are:

– ROHC at the PDCP layer of LTE is provided by the CS of WiMAX.– Control channels of LTE are functionally similar to management CIDs of WiMAX.They are defined to support network specific operations.

– HARQ is supported to enhance network performance.


5.4

Com

pari

son

sum

mar

y

Tabl

e13

:Com

parison

ofLTE3G

PPRelease

8an

dW

iMAX

R1.0(IEEE802.16e-2005)

Issu

eLTE

(3GPP

Release

8)

WiM

AX

R1.0

(IEEE

802.16-2004&E)

Definition

–LTE

is3G

PP’s

radio

stan

dard

tooff

erbroad

ban

daccesses

tomob

iledevices.

–It

isbased

ontheEPSarchitecture

which

issimilar

totheIP

-OFDMA

technology.

–W

iMAX

isgoverned

bytheW

iMAX

Fo-

rum

tooff

erbroad

ban

daccesses

tomob

ile

devices

such

asPDAsan

dlaptops.

–It

isbased

ontheIP

-OFDMA

technology

whichis

oneof

theIM

T-2000familymo-

bilewirelessinterfacestan

dards.

Tim

ing

–Thesystem

requirem

ents

weredefined

in2005.

–Thebackward-com

patibilityverification

ofthebaselinestan

dard,3G

PP

Release

8,was

complete

in2009.

–Theworld’sfirstcommercial

LTEnetwork

was

launched

in2009.

–The

baseline

stan

dard,

IEEE

802.16e-

2005,was

finalized

in2006.

–Thesystem

requirem

ents

weredefined

in2006.

–TheIP

-based

core

networkdefinitionwas

completedin

2007.

–Thefirstcommercial

deploymentof

aMo-

bileW

iMAXnetwork,W

iBro,was

realized

in2007.


Standard

–LTE

isbased

onthe36-seriesdocuments

intheform

sof

technical

specification

san

dtechnical

reports

published

by3G

PP.

–Theairinterfaceis

defined

bythe3G

PP

RAN

grou

p–Theend-to-end

perform

ance

isregu

lated

bythe3G

PPSA

grou

p.

–Theairinterfaceis

coveredbytheIE

EE

802.16

stan

dardpublished

byIE

EE.

–Theend-to-end

perform

ance

isregu

lated

bytheW

iMAX

forum.

–Release

1.0of

themob

ileW

iMAX

stan

-dardisbased

onIE

EE802.16e-2005.

Ecosystem

–Mem

bersof

the3G

PPstan

dardbody

–Mostmob

ileop

erators

–Mem

bersof

theW

iMAX

Forum

consist

ofbothcomputerindustry

andcellularindus-

try

–IE

EE

Legacy

–GAM/G

PRS/U

MTS/H

SPA

–Non

e

Network

archi-

tecture

–Two-tier

architecture:EUTRANan

dEPC

–Flatter

architecture

since

centralized

con-

troller(R

NC)is

elim

inated

infavourof

adistributedsystem

–Two-tier

architecture:ASN

andCSN

–Several

ASN

profile

fordifferentdegrees

ofcontrol

rangingfrom

centralized

todis-

tributed


CoreNetwork

–All-IPEUTRAN

network,EPC

–W

iMAX

Forum’s

all-IP

network

which

consistsof

nodes

common

totrad

itional

IP-based

networks

Com

munication

betweennetwork

elem

ents

–Interfaces

–Reference

points

Cellradius

–5k

m–2-7km

Functionsof

the

MAC

layer

–Sublayeringof

layer2:PDCP,RLC

and

MAC

–PMP

supportwith

thecentralized

con-

troller,an

eNB

–QoS

support

–Sublayeringof

layer2:

CS,CPSan

dsecu-

rity

–PMP

supportwith

thecentralized

con-

troller,aBS

–QoS

support,header

compression,security

features

HARQ

–Yes

–Yes

Cellcapacity

–Morethan

200userat

a5-MHzban

dwidth

–Morethan

400users

forlarger

ban

dwidths

–100-200users


Mob

ility

–Upto

250km/h

–Upto

120km/h

Latency

–Linklayer:

smallerthan

5msec

–Han

doff

:sm

allerthan

50msec

–Linklayer≈

20msec

–Han

doff

:35-50msec

Multicast/

Broad

cast

–Release

9.0

–Release

1.0

Rad

ioresource

structure

–Tim

e-frequency

unit:

(OFDMA

symbol

index,subcarrierindex)

–Divisions:

slot,subfram

e,resourceelem

ent

andresourceblock

–Tim

e-frequency

unit:

(OFDMA

symbol

index,subchan

nel

index)

–Divisions:

slot,burstan

dsubfram

e

Chan

nel

ban

d-

width

–Scalable

–1.4,

3,5,

10,16

and20

MHz

–Ban

dwidth

configu

ration

increm

ent:

0.18

MHz

–Scalable

upto

20MHz

–Ban

dwidth

increm

ents:

1.25,1.75,2

or2.75

MHz

Framesize

–1msec

–5msec


Multiple

access

technology

–DL:OFDMA

–UL:SC-FDMA

–DL:OFDMA

–UL:OFDMA

Duplexing

–FDD

andTDD

–TDD

inRelease

1.0

–TDD

andFDD

inRelease

1.5

Subcarriermap

-ping

–Localizedan

ddistributed

–Localizedan

ddistributed

Subcarrier

hop

-ping

–Yes

–Yes

Data

modula-

tion

–BPSK,QPSK,16-Q

AM

and64-Q

AM

–QPSK,16-Q

AM

and64-Q

AM

Subcarrierspac-

ing

–7.5an

d15

kHz

–10.94kHz

FFT

size

–128,

256,

512,

1024,1536,2048

–128,

512,

1024,2048

OFDMA

symbol

duration

–71.8,71.3,83.2

and166.6μs

–102.9μs


Chan

nel

coding

–Con

volution

alcodingforcontrol

inform

a-tion

,K=7,

R=1/3

–Con

volution

alturbocodingfordatainfor-

mation,K=4,

R=1/3,

6144

bits/block

–Block

andrespective

coding

–Con

volution

alcoding

for

fram

econtrol

headers

–Con

volution

alturbocodingfordataan

dcontrol

inform

ation

–Option

al:BCT

andLDPC

coding

Smart

antenna

technologies

–Multi-layerprecoded

spatialmultiplexing,

spacefrequency

block

coding

–MIM

O

–Beamform

ing,

spacetimecodingan

dspa-

tial

multiplexing

–MIM

O


6 Conclusion

The aim of this report was to perform a technical comparison and analysis of twopre-4G mobile broadband systems: LTE and WiMAX. In order to limit the scopeof this activity, special focus was given to the air interface, especially the PHY andMAC layers as defined by the OSI model. The higher layers of these systems werebriefly discussed to provide a better understanding of their overall operation.

The analysis of the two systems reveals a high degree of similarity. From a systemstandpoint, both systems have similar functional decompositions such as the sepa-ration of radio access network and IP core network although the specific protocolsused between those networks are different. Both systems also have similar air inter-faces designed to aim at efficient spectrum usage. The MAC layers are responsiblefor the layer-2 functions of the OSI model. The PHY layers use similar processingtechnologies that are optimized for their specific frame sizes and subcarrier spacings.

The MAC-layer implementations of both systems vary considerably; the MAC layerof WiMAX covers the entire layer 2 of the OSI model while the MAC sublayer of LTEis only a part of the layer 2. As a result, the WiMAX MAC layer design providesmore functionalities than the LTE MAC layer implementation. However, both MAClayer implementations are designed to support the fundamental layer-2 requirement:resource management. Resources are centrally controlled at the eNB of LTE and theBS of WiMAX.

The PHY-layer implementations of both WiMAX and LTE use AMC to dynamicallyadjust system parameters of each transmission according to the channel conditions.Their physical layer processing chains also have many signal processing functions incommon, such as CRC check, turbo coding, interleaving, scrambling, OFDMA andMIMO. System parameters are adjusted for each implementation to control over-heads and flexibility of the technology choices. Processing functions such as headercompression and HARQ are used to enhance performance.

Since LTE and WiMAX use similar technologies, their performance approximationsare comparable. Their specific implementation choices control overheads and flexibil-ity of the technologies. Consequently, efficiencies of the two systems are slightlydifferent. Currently, LTE efficiency is slightly better than WiMAX Release 1.0[10, 12, 14, 66]. However, the two systems have been learning from and competingwith each other to improve their future revisions. In fact, with the next revision oftheir standards, these two pre-4G systems are aiming to meet the ITU IMT-Advancedrequirements to be eventually considered as 4G systems. These requirements wereestablished to support low to high mobility applications with data rates (100 Mb/sfor high and 1 Gb/s for low mobility) allowing high-quality multimedia within a widerange of services and platforms. Better cell spectral efficiency in all four cell envi-


ronments (indoor, microcellular, urban and high speed), scalable bandwidth up to40 MHz, lower latency, lower handover interruption times and higher VoIP capac-ity are all key factors that should contribute to provide significant improvements inperformance and quality of service.

All three standardization communities mentioned earlier, namely 3GPP, IEEE andWiMAX Forum, are developing solutions and specifications to be submitted to theITU for the IMT-Advanced requirements. 3GPP is currently working on definingLTE-Advanced. The LTE-Advanced study item appears to be defining the content for3GPP Release 10 [67]. In the late 2009, IEEE submitted a candidate radio interfacetechnology for IMT-Advanced [68]. The proposal is based on the IEEE 802.16mstandard and demonstrates its ability to meet requirements in all four IMT-Advancedcell environments. In April 2010, some member of the WiMAX forum formed theWiMAX 2 collaboration initiative (WCI) to support WiMAX 2 development basedon the IEEE 802.16m standard [69]. The WCI members consist of Alvarion, Beceem,GCT Semiconductor, Intel, Motorola, Samsung, Sequans, XRONet, ZTE and ITRI.

Finally, although the technological aspects of communications systems have alwaysbeen an important factor determining the evolutionary direction of earlier cellular sys-tems, both pre-4G systems are taking similar technological choices aiming at meeting,or even exceeding the performance levels set by the IMT-Advanced requirements. Thebusiness and marketing factors may play a bigger role in determining the survival ofLTE and mobile WiMAX in the 4G evolution. For example, WiMAX was introducedearlier than LTE, which gives WiMAX a window of opportunity. The two systemsappear to be deployed and marketed in different countries for different purposes dueto the customer base of each service provider. WiMAX has been adapted by new en-trants to the mobile broadband services and chip markets while LTE’s providers arecellular operators and equipment manufacturers. Following this observation, keepingtrack of business factors, such as worldwide deployments, number of subscribers, totalrevue and vendor supports helps determining possible evolutions of future wirelesssystems.


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Annex A: List of LTE standards

1. TS 36.101 Evolved Universal Terrestrial Radio Access (E-UTRA); UserEquipment (UE) radio transmission and reception

2. TS 36.104 Evolved Universal Terrestrial Radio Access (E-UTRA); BaseStation (BS) radio transmission and reception

3. TS 36.106 Evolved Universal Terrestrial Radio Access (E-UTRA); FDDrepeater radio transmission and reception

4. TS 36.113 Evolved Universal Terrestrial Radio Access (E-UTRA); BaseStation (BS) and repeater ElectroMagnetic Compatibility (EMC)

5. TS 36.124 Evolved Universal Terrestrial Radio Access (E-UTRA); Elec-tromagnetic compatibility (EMC) requirements for mobile terminalsand ancillary equipment

6. TS 36.133 Evolved Universal Terrestrial Radio Access (E-UTRA); Re-quirements for support of radio resource management

7. TS 36.141 Evolved Universal Terrestrial Radio Access (E-UTRA); BaseStation (BS) conformance testing

8. TS 36.143 Evolved Universal Terrestrial Radio Access (E-UTRA); FDDrepeater conformance testing

9. TS 36.171 Evolved Universal Terrestrial Radio Access (E-UTRA); Re-quirements for Support of Assisted Global Navigation Satellite System(A-GNSS).

10. TS 36.201 Evolved Universal Terrestrial Radio Access (E-UTRA);Long Term Evolution (LTE) physical layer; General description

11. TS 36.211 Evolved Universal Terrestrial Radio Access (E-UTRA);Physical channels and modulation

12. TS 36.212 Evolved Universal Terrestrial Radio Access (E-UTRA);Multiplexing and channel coding

13. TS 36.213 Evolved Universal Terrestrial Radio Access (E-UTRA);Physical layer procedures

14. TS 36.214 Evolved Universal Terrestrial Radio Access (E-UTRA);Physical layer - Measurements

15. TS 36.300 Evolved Universal Terrestrial Radio Access (E-UTRA)and Evolved Universal Terrestrial Radio Access Network (E-UTRAN);Overall description; Stage 2

16. TS 36.302 Evolved Universal Terrestrial Radio Access (E-UTRA);Services provided by the physical layer

17. TS 36.304 Evolved Universal Terrestrial Radio Access (E-UTRA);User Equipment (UE) procedures in idle mode

18. TS 36.305 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Stage 2 functional specification of User Equipment (UE)positioning in E-UTRAN.


19. TS 36.306 Evolved Universal Terrestrial Radio Access (E-UTRA);User Equipment (UE) radio access capabilities

20. TS 36.307 Evolved Universal Terrestrial Radio Access (E-UTRA); Re-quirements on User Equipments (UEs) supporting a release-indepen-dent frequency band.

21. TS 36.314 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Layer 2 - Measurements

22. TS 36.321 Evolved Universal Terrestrial Radio Access (E-UTRA);Medium Access Control (MAC) protocol specification

23. TS 36.322 Evolved Universal Terrestrial Radio Access (E-UTRA);Radio Link Control (RLC) protocol specification

24. TS 36.323 Evolved Universal Terrestrial Radio Access (E-UTRA);Packet Data Convergence Protocol (PDCP) specification

25. TS 36.331 Evolved Universal Terrestrial Radio Access (E-UTRA);Radio Resource Control (RRC); Protocol specification

26. TS 36.355 Evolved Universal Terrestrial Radio Access (E-UTRA);LTE Positioning Protocol (LPP)

27. TS 36.401 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Architecture description

28. TS 36.410 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 layer 1 general aspects and principles

29. TS 36.411 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 layer 1.

30. TS 36.412 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 signalling transport

31. TS 36.413 Evolved Universal Terrestrial Radio Access (E-UTRA) ;S1 Application Protocol (S1AP)

32. TS 36.414 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 data transport

33. TS 36.420 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 general aspects and principles

34. TS 36.421 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 layer 1

35. TS 36.422 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 signalling transport

36. TS 36.423 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 Application Protocol (X2AP)

37. TS 36.424 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 data transport

38. TS 36.440 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); General aspects and principles for interfaces supportingMultimedia Broadcast Multicast Service (MBMS) within E-UTRAN


39. TS 36.441 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Layer 1 for interfaces supporting Multimedia BroadcastMulticast Service (MBMS) within E-UTRAN

40. TS 36.442 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Signalling Transport for interfaces supporting MultimediaBroadcast Multicast Service (MBMS) within E-UTRAN

41. TS 36.443 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); M2 Application Protocol (M2AP)

42. TS 36.444 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); M3 Application Protocol (M3AP)

43. TS 36.445 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); M1 Data Transport

44. TS 36.446 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); M1 User Plane protocol

45. TS 36.455 Evolved Universal Terrestrial Radio Access (E-UTRA);LTE Positioning Protocol A (LPPa)

46. TS 36.508 Evolved Universal Terrestrial Radio Access (E-UTRA)and Evolved Packet Core (EPC); Common test environments for UserEquipment (UE) conformance testing

47. TS 36.509 Evolved Universal Terrestrial Radio Access (E-UTRA) andEvolved Packet Core (EPC); Special conformance testing functions forUser Equipment (UE)

48. TS 36.521-1 Evolved Universal Terrestrial Radio Access (E-UTRA);User Equipment (UE) conformance specification; Radio transmissionand reception; Part 1: Conformance testing

49. TS 36.521-2 Evolved Universal Terrestrial Radio Access (E-UTRA);User Equipment (UE) conformance specification; Radio transmissionand reception; Part 2: Implementation Conformance Statement (ICS)

50. TS 36.521-3 Evolved Universal Terrestrial Radio Access (E-UTRA);User Equipment (UE) conformance specification; Radio transmissionand reception; Part 3: Radio Resource Management (RRM) confor-mance testing

51. TS 36.523-1 Evolved Universal Terrestrial Radio Access (E-UTRA)and Evolved Packet Core (EPC); User Equipment (UE) conformancespecification; Part 1: Protocol conformance specification

52. TS 36.523-2 Evolved Universal Terrestrial Radio Access (E-UTRA)and Evolved Packet Core (EPC); User Equipment (UE) conformancespecification; Part 2: ICS

53. TS 36.523-3 Evolved Universal Terrestrial Radio Access (E-UTRA)and Evolved Packet Core (EPC); User Equipment (UE) conformancespecification; Part 3: Test suites

54. TR 36.800 Universal Terrestrial Radio Access (UTRA) and Evolved


Universal Terrestrial Radio Access (E-UTRA); Extended UMTS /LTE 800 Work Item Technical Report

55. TR 36.801 Evolved Universal Terrestrial Radio Access (E-UTRA);Measurement Requirements

56. TR 36.803 Evolved Universal Terrestrial Radio Access (E-UTRA);User Equipment (UE) radio transmission and reception

57. TR 36.804 Evolved Universal Terrestrial Radio Access (E-UTRA);Base Station (BS) radio transmission and reception

58. TR 36.805 Evolved Universal Terrestrial Radio Access (E-UTRA);Study on minimization of drive-tests in next generation networks

59. TR 36.806 Evolved Universal Terrestrial Radio Access (E-UTRA);Relay architectures for E-UTRA (LTE-Advanced)

60. TR 36.810 Universal Terrestrial Radio Access (UTRA) and EvolvedUniversal Terrestrial Radio Access (E-UTRA); UMTS / LTE 800 forEurope Work Item Technical Report.

61. TR 36.814 Evolved Universal Terrestrial Radio Access (E-UTRA);Further advancements for E-UTRA Physical layer aspects

62. TR 36.815 TR LTE-Advanced feasibility studies in RAN WG463. TR 36.821 Extended UMTS/LTE 1500 Work Item Technical Report64. TR 36.902 Evolved Universal Terrestrial Radio Access Network (E-

UTRAN); Self-configuring and self-optimizing network (SON) usecases and solutions

65. TR 36.903 Evolved Universal Terrestrial Radio Access (E-UTRA);Derivation of test tolerances for multi-cell Radio Resource Manage-ment (RRM) conformance tests

66. TR 36.912 Feasibility study for Further Advancements for E-UTRA(LTE-Advanced)

67. TR 36.913 Requirements for further advancements for Evolved Uni-versal Terrestrial Radio Access (E-UTRA) (LTE-Advanced)

68. TR 36.921 FDD Home eNB RF Requirements Work Item TechnicalReport

69. TR 36.922 LTE TDD Home eNode B (HeNB) Radio Frequency (RF)requirements; Work item Technical Report

70. TR 36.931 RF requirements for LTE Pico NodeB71. TR 36.938 Evolved Universal Terrestrial Radio Access Network (E-

UTRAN); Improved network controlled mobility between E-UTRANand 3GPP2/mobile WiMAX radio technologies

72. TR 36.942 Evolved Universal Terrestrial Radio Access (E-UTRA);Radio Frequency (RF) system scenarios

73. TR 36.956 Evolved Universal Terrestrial Radio Access (E-UTRA);Repeater planning guidelines and system analysis


Annex B: List of EPS interface

The following are LTE Interfaces [43]:

S1-MME : Reference point for the control plane protocol between E-UTRAN andMME.

S1-U : Reference point between E-UTRAN and Serving GW for the per bearer userplane tunnelling and inter eNB path switching during handover.

S2 : Between PDN GW and non-3GPP access. Supports control and mobility pro-cedures for non-3GPP access technologies.

S3 : It enables user and bearer information exchange for inter 3GPP access networkmobility in idle and/or active state.

S4 : It provides related control and mobility support between GPRS Core and the3GPP Anchor function of Serving GW. In addition, if Direct Tunnel is notestablished, it provides the user plane tunnelling.

S5 : It provides user plane tunnelling and tunnel management between Serving GWand PDN GW. It is used for Serving GW relocation due to UE mobility and ifthe Serving GW needs to connect to a non-collocated PDN GW for the requiredPDN connectivity.

S6 : Between the Evolved Packet Core nodes and the HSS. Supports the proceduresfor user subscription data retrieval and location update.

S6a : It enables transfer of subscription and authentication data for authenticat-ing/authorizing user access to the evolved system (AAA interface) betweenMME and HSS.

S7 : Between the PDN GW and the PCRF. Supports the procedures for Policy andCharging rule transfer from the PCRF to the EPC. This interface is based onthe 3GPP R7 Gx definition.

S8 : Inter-PLMN reference point providing user and control plane between the Serv-ing GW in the VPLMN and the PDN GW in the HPLMN. S8 is the interPLMN variant of S5.

S9 : It provides transfer of (QoS) policy and charging control information betweenthe Home PCRF and the Visited PCRF in order to support local breakoutfunction.

S10 : Reference point between MMEs for MME relocation and MME to MME in-formation transfer.

S11 : Reference point between MME and Serving GW.

S12 : Reference point between UTRAN and Serving GW for user plane tunnellingwhen Direct Tunnel is established. It is based on the Iu-u/Gn-u reference pointusing the GTP-U protocol as defined between SGSN and UTRAN or respec-tively between SGSN and GGSN. Usage of S12 is an operator configurationoption.


S13 : It enables UE identity check procedure between MME and EIR.

X2 : Between eNBs. Supports mobility and user plane tunnelling features. Basedon the same user plane protocol as S1.

Gx : It provides transfer of (QoS) policy and charging rules from PCRF to Policyand Charging Enforcement Function (PCEF) in the PDN GW.

SGi : It is the reference point between the PDN GW and the packet data network.Packet data network may be an operator external public or private packet datanetwork or an intra operator packet data network, e.g. for provision of IMSservices. This reference point corresponds to Gi for 3GPP accesses.

Rx : The Rx reference point resides between the AF (Application Function) and thePCRF in the TS 23.203.

SBc : Reference point between CBC and MME for warning message delivery andcontrol functions.

Wn* : Reference point between the untrusted non-3GPP IP access and the ePDG.Traffic on this interface has to be forwarded toward ePDG.


List of acronyms

16-QAM 16-level quadrature amplitude modulation1G First generation2G Second generation3G Third generation3GPP Third generation partnership project4G Forth generation64-QAM 64-level quadrature amplitude modulationAAA Authorization and accountingAES-CCM Advanced encryption standard-counter with cipher block

chaining message authentication codeAM Acknowledge modeAMBR Aggregate maximum bit rateAMC Adaptive modulation and codingAP Application protocolARQ Automatic repeat requestAS Access stratumASN-GW Access service network gatewayATM Asynchronous transfer modeBCCH Broadcast control channelBCH Broadcast channelBCT Block turbo codingBGAN Broadband global area networkBPSK Binary phase shift keyingBS Base stationBWA Broadband wireless accessCBC Cell broadcast serviceCC Convolutional codingCCCH Common control channelCDMA Code division multiple accessCID Connection identifierCMAC/HMACCipher-based message authentication code/keyed-hashing

for message authentication codeCP Cyclic prefixCPS MAC common part sublayerCQI Channel quality indicationCRC Cyclic redundancy checkCS Circuit switchedCSN Connectivity services networkCTC Convolutional turbo codingDCCH Dedicated control channel


DFT Discrete Fourier transformDHCP Dynamic host configuration protocolDHCPv4 Dynamic host configuration protocol service for IPv4DiffServ Differentiated servicesDL DownlinkDLL Data Link LayerDOCSIS Data over cable service interface specificationDP Decision pointDRX Discontinuous receiveDTCH Dedicated traffic channelEAP Extensible authentication protocolECRTP Enhanced compressed real-time transport protocolEDGE Enhanced data rates for GSM evolutionE-MBMS Enhanced multimedia broadcast multicast serviceEMM EPS mobility managementeNB Evolved Node BEP Enforcement pointEPC Evolved packed coreEPS Evolved packet systemESM EPS session managementETH-CS Ethernet convergence sublayerETWS Tsunami warning systemE-UTRAN Evolved UMTS terrestrial radio access networkEVDO Evolution – data onlyFCH Frame control headerFDD Frequency division duplexFDMA Frequency division multiple accessFEC Forward error correctionFFT Fast Fourier transformFUSC Full usage subchannelGPRS General packet radio serviceGRE Generic routing encapsulationGSM Global system for mobile communicationsGTP GPRS tunnelling protocolGTP-U GPRS tunnelling protocol — user data tunnellingHA Home agentHARQ Hybrid automatic repeat requestHARQ Hybrid ARQHSPA High speed packet accessHSS Home subscriber serviceIDFT Inverse discrete Fourier transformIEEE Institute of electrical and electronics engineers


IETF Internet engineering task forceIMS IP multimedia subsystemIMT International mobile telecommunicationIP Internet protocolIP CS IP convergence sublayerISO/OSI International organization for standardization /open system

interconnectionISP Internet service providerLAN Local area networkLDPC Low density parity checkLLC Logical link controlLMSC LAN/MAN standards committeeLOS Line of sightLTE Long term evolutionLTE-Uu S1, X2 and LTE-UE interfacesMAC Media access controlMAN Metropolitan area networkMBMS Multimedia broadcast multicast serviceMBSFN Multicast broadcast signal frequency networkMCCH Multicast control channelMCH Multicast channelMCS Modulation coding schemeMIMO Multiple-input and multiple-outputMME Mobile management entityMPLS Multiprotocol label switchingMS Mobile stationMTCH Multicast traffic channelMU-MIMO Multi user MIMONAP Network access providersNAS Non access stratumNB NodeBNL Network LayerNLOS Non line of sightNSP Network service providersNWG Network working groupOFCS Offline charging systemOFDMA Orthogonal frequency-division multiple accessPBCH Physical broadcast channelPC Personal computerPCCH Paging control channelPCFICH Physical control format indicator channelPCH Paging channel


PCRF Policy and charging rules functionPDA Personal digital assistantPDCCH Physical downlink control channelPDCP Packet data convergence protocolPDN-GW Packet data network gatewayPDSCH Physical downlink shared channelPDU Protocol data unitPHICH Physical hybrid ARQ indicator channelPHS Payload header suppressionPHY PhysicalPKM Privacy key managementPLMN Public land mobile networkPMCH Physical multicast channelPMIP Proxy mobile IPPRACH Physical random access channelPRBS Pseudo-random binary sequencePS Packet switchedPSS Packet-switched streaming servicePUSC Partial usage subchannelPUSCH Physical uplink shared channelQCI QoS class identifierQoS Quality of serviceQPP Quadratic permutation polynomialQPSK Quadrature phase shift keyingRAB Radio access bearerRACH Random access channelRAN Radio access networkRB Recourse blockRF Radio frequencyRFE Radio front-endRLC Radio link controlRM Rate matchingRNC Radio network controllerROHC Robust header compressionRP Reference pointRRC Radio resource controlRRM Radio resource managementRTCP Real-time transport protocolRTD Round-trip delayRTP Real-time protocolSA System architectureSAE System architecture evolution


SAP Service access pointSC-FDMA Single carrier frequency division multiple accessSCH Shared channelSCTP Stream control transmission protocolSDMA Spatial division multiple accessSDU Service data unitSFBC Space frequency block codingSFID Service flow identifierSGSN Serving GPRS support nodeS-GW Serving gatewaySIP Session initiation protocolSTC Space time codingSU-MIMO Single user MIMOTAG Technical advisory groupTB Transport blockTCP Transmission control protocolTDD Time division duplexTDMA Time division multiple accessTR Technical reportTS Technical specificationTTG Transmit/receive transition gapTTI Transmission time intervalUDP User datagram protocolUE User equipmentUL UplinkUM Un-acknowledge modeUMB Ultra mobile broadbandUMTS Universal mobile telecommunications systemUTRAN Universal terrestrial radio access networkVLAN Virtual local area networkVoIP Voice over IPWCI WiMAX 2 collaboration initiativeWG Working groupWiBro Wireless broadbandWiFi Wireless Fidelity (IEEE 802.11 wireless networking)WiMAX Worldwide interoperability for microwave accessWLAN Wireless local area networkWMAN Wireless metropolitan area network




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1. ORIGINATOR (The name and address of the organization preparing thedocument. Organizations for whom the document was prepared, e.g. Centresponsoring a contractor’s report, or tasking agency, are entered in section 8.)


3701, Carling avenue, Ottawa, Ontario, K1A-0Z4

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UNCLASSIFIED

3. TITLE (The complete document title as indicated on the title page. Its classification should be indicated by the appropriateabbreviation (S, C or U) in parentheses after the title.)

LTE vs. WiMAX: A technical comparison and analysis of their PHY and MAC layers

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Wang, M.; Beaumont, J.-F.

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November 2011

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6b. NO. OF REFS (Totalcited in document.)

69

7. DESCRIPTIVE NOTES (The category of the document, e.g. technical report, technical note or memorandum. If appropriate, enterthe type of report, e.g. interim, progress, summary, annual or final. Give the inclusive dates when a specific reporting period iscovered.)

Technical Memorandum

8. SPONSORING ACTIVITY (The name of the department project office or laboratory sponsoring the research and development –include address.)


3701, Carling avenue, Ottawa, Ontario, K1A-0Z4

9a. PROJECT NO. (The applicable research and developmentproject number under which the document was written.Please specify whether project or grant.)

15dg02

9b. GRANT OR CONTRACT NO. (If appropriate, the applicablenumber under which the document was written.)

10a. ORIGINATOR’S DOCUMENT NUMBER (The officialdocument number by which the document is identified by theoriginating activity. This number must be unique to thisdocument.)

DRDC Ottawa TM 2011-121

10b. OTHER DOCUMENT NO(s). (Any other numbers which maybe assigned this document either by the originator or by thesponsor.)

11. DOCUMENT AVAILABILITY (Any limitations on further dissemination of the document, other than those imposed by securityclassification.)

( X ) Unlimited distribution( ) Defence departments and defence contractors; further distribution only as approved( ) Defence departments and Canadian defence contractors; further distribution only as approved( ) Government departments and agencies; further distribution only as approved( ) Defence departments; further distribution only as approved( ) Other (please specify):

12. DOCUMENT ANNOUNCEMENT (Any limitation to the bibliographic announcement of this document. This will normally correspondto the Document Availability (11). However, where further distribution (beyond the audience specified in (11)) is possible, a widerannouncement audience may be selected.)

Unlimited distribution

drakus

Non_Controlled DCD

13. ABSTRACT (A brief and factual summary of the document. It may also appear elsewhere in the body of the document itself. It is highlydesirable that the abstract of classified documents be unclassified. Each paragraph of the abstract shall begin with an indication of thesecurity classification of the information in the paragraph (unless the document itself is unclassified) represented as (S), (C), (R), or (U).It is not necessary to include here abstracts in both official languages unless the text is bilingual.)

This report presents a technical comparison and analysis of two developing pre-fourth generation

(pre-4G) wireless communications systems: the long term evolution (LTE) and the worldwide in-

teroperability for microwave access (WiMAX). This analysis is used to speculate on the possible

evolutionary directions of 4G systems since the developing direction of the earlier generations of

wireless communications systems has been historically strongly directed by their technological

aspects. Special focus is laid on the air interface, especially the physical (PHY) layer and media

access control (MAC) layers as defined by the open system interconnection (OSI) model. The

higher layers are briefly discussed to provide a better understanding of the overall systems’ op-

eration. The two pre-4G systems appear to use similar technologies that are optimized for each

system. Because of the technological similarity, other factors such as business and marketing,

may then be more important determinants of the pre-4G systems’ survival in the 4G systems

evolution.

14. KEYWORDS, DESCRIPTORS or IDENTIFIERS (Technically meaningful terms or short phrases that characterize a document and couldbe helpful in cataloguing the document. They should be selected so that no security classification is required. Identifiers, such asequipment model designation, trade name, military project code name, geographic location may also be included. If possible keywordsshould be selected from a published thesaurus. e.g. Thesaurus of Engineering and Scientific Terms (TEST) and that thesaurus identified.If it is not possible to select indexing terms which are Unclassified, the classification of each should be indicated as with the title.)

Wireless, 4G, WiMAX, LTE, 3GPP, IEEE

LTE vs. WiMAX: A technical comparison and analysis of ...cradpdf.drdc-rddc.gc.ca/PDFS/unc116/p536469_A1b.pdf · LTE vs. WiMAX: A technical comparison and analysis of their PHY and

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