Hermes Irineu Del Monego
Radio Resource Management in 4G Networks:
A Strategy Based on Mobility Tendency
and Packet Length Sensibility
A thesis submitted in partial ful llment of the requirements for the degree of Doctor of Philosophy (PhD) in the Doctoral Program in Electrical and Computer Engineering Supervisors José Manuel Soares Oliveira, PhD.
Assistant Professor, Faculdade de Economia, Universidade do Porto, Portugal
Manuel Alberto Pereira Ricardo, PhD.
Associate Professor, Faculdade de Engenharia, Universidade do Porto, Portugal
Departamento de Engenharia Electrotécnica e de Computadores Faculdade de Engenharia da Universidade do Porto
Hermes Irineu Del Monego
Radio Resource Management in 4G Networks:
A Strategy Based on Mobility Tendency
and Packet Length Sensibility
This Thesis has been formally discussed and approved on July 15, 2011 Thesis jury:
President Artur Pimenta Alves, PhD.
Full Professor, Faculdade de Engenharia, Universidade do Porto, Portugal
External Examiners Richard Demo Souza, PhD.
Adjunct Professor, Departamento Acadêmico De Engenharia Elétrica, Univer-sidade Tecnológica Federal do Paraná, Brasil
Jorge Botelho Costa Mamede, PhD.
Adjunct Professor, Departamento de Engenharia Eletrotécnica, Instituto Su-perior de Engenharia do Porto, Portugal
Internal Examiner Mário Jorge Moreira Leitão, PhD.
Associate Professor, Faculdade de Engenharia, Universidade do Porto, Portugal
Supervisors José Manuel Soares Oliveira, PhD.
Assistant Professor, Faculdade de Economia, Universidade do Porto, Portugal
Manuel Alberto Pereira Ricardo, PhD.
To my wife Maurici Luzia and our kids Andressa and Victor
O homem é completamente feliz quando descobre em seu interior que a fé e a ciên-cia caminham juntas para a edi cação do seu ser! (Monego, H.I.)
Acknowledgements
Acknowledgments are something extremely personal, where I must express my emotion and gratitude for those that helped and encouraged me to continue " ght-ing". So, I feel needed to write in my natural tongue, i.e., Brazilian Portuguese.
Tudo começou lá por 2004 com um sonho antigo de estudar doutoramento no exterior. Fui amadurecendo, analisando possibilidades e procurando meios para que pudesse realizar tal sonho. Neste caso, a FEUP juntamente com o INESC Porto ofereceram-me toda a estrutura necessária, não deixando dúvidas de que minha decisão fora acertada.
Tomei por base algo que dizia meu pai Quem não sonha não realiza. Neste momento, a palavra mais importante neste texto é de agradecimento em retribuição aos que de alguma forma ajudaram-me a realizar este projeto de doutoramento.
Primeiramente agradeço a Deus por conservar minha sanidade, dar-me força e perseverança. Depois, agradeço aos meus pais Guerino Del Monego (grazie babbo per tutto, per avermi fatto vedere che nella vita si possono riuscire qualcosa lavor-ando e rispettlavor-ando gli altri, in memoriam) e Alvina Maria Bernardes Del Monego (La ringrazio mamma per avermi dato la vita, sopratutto, l'amore e dedicazione, in memoriam), simplesmente pela concepção da vida.
An-últimos quatro anos apoiando-me pacientemente é inestimável. Vocês zeram o possível para que eu continuasse a trabalhar para completar esta tarefa árdua, onde eu de maneira alguma jamais seria capaz de tê-la superado sem vocês. Vossa compreensão, amor e apoio conduziram-me através dos desa os, fornecendo-me o suporte necessário para conclusão deste projeto. Eu vos amo e sou grato por terem estado sempre disponíveis para mim. Agora, deixem-me retribuir colocando-me a vossa disposição para todo o sempre.
Agradeço aos meus professores orientadores José Manuel Oliveira pela paciência e incentivo pessoal para continuar minha jornada. Também ao professor Manuel Ricardo pela serenidade, certeza dos objetivos e pelo grau de sabedoria com que ajudou-me no desenvolvimento deste trabalho de doutoramento. Ao professor José Ruela pelo carinho, con ança e acolhimento no INESC Porto. Ao prof. Richard Demo pelo grande incentivo pessoal e ajuda durante meu percurso acadêmico. Ao Marcelo Segatto pela companhia durante nossa estada no Porto. Ao Adriano Bresolin pela amizade e companhia nas horas difíceis. Agradeço o suporte prestado pela FCT, onde foi fundamental para a realização deste trabalho.
Cabe aqui também, agradecer aos alguns amigos do INESC Porto e da FEUP que passaram pela minha vida acadêmica e de alguma forma marcaram-na pos-itivamente e também aos meus colegas da UTFPR. Agradeço especialmente ao Gustavo Carneiro pela valiosa ajuda com o NS3 e também pela serenidade e pa-ciência nas explicações sobre o assunto.
Finalmente, agradeço aos meus irmãos, pelo orgulho que sentem por mim e pelo incentivo na execução deste projeto.
Abstract
The concept of Fourth Generation (4G) networks is characterized by the integra-tion of dierent heterogeneous networks including cellular networks, such as the Universal Mobile Telecommunications System (UMTS) and the recent Long Term Evolution (LTE), Wireless Local Area Networks (WLANs), usually identi ed as IEEE 802.11 Wireless Fidelity (WiFi), and metropolitan wireless access networks, such as the Worldwide Interoperability for Microwave Access (WiMAX). The in-tegration of these networks forms one global access network, enabling call transfer-ence from one interface to another, seamlessly to the user. Helping this integration trend, multimode terminals, capable to access multiple network technologies, are starting to appear.
In a context where one telecommunications operator administrates dierent network technologies in the same physical location, a joint and e cient manage-ment of those networks resources is desired. This will certainly improve the service oered to the users and, at the same time, increase the operators' revenue.
The objective of this thesis consists in the development of a new Radio Resource Management (RRM) strategy to e ciently manage the available resources in an heterogeneous network environment. Two original contributions were produced in this thesis. The rst contribution can be identi ed as a new RRM strategy
MTend, focus in the distribution of the incoming calls among radio interfaces according to the characteristics of the calls. The distribution decision is based on the length of the packets associated with each call, following at the same time an hando avoidance policy. Additionally, in a scenario of low available resources, the strategy introduces the possibility of renegotiating requests of new calls or reallocating existing calls from one network to another.
A second contribution of this thesis is the network simulation model. This model has been developed for our simulation tests and for the evaluation of the new RRM strategy, being the use of virtual interfaces its main innovation. The simulation model implementation is available as a free contribution on the Network Simulator Version 3 (NS-3) core.
The performance of the MTend strategy is evaluated by comparing this new strategy with two well-known strategies used in scenarios where the UMTS and WLAN networks are interconnected. The results discussed address the call block-ing probability, the in uence of the packet length in the performance of the RRM strategy, the hando performance and a revenue analysis.
Resumo
O conceito de redes de quarta geração (4G) é caracterizado pela integração de difer-entes redes heterogéneas, incluindo redes celulares, como a rede Universal Mobile Telecommunications System (UMTS) e a recente Long Term Evolution (LTE), Wireless Local Area Networks (WLANs), normalmente identi cadas como redes IEEE 802.11 Wireless Fidelity (WiFi), e redes de acesso sem os metropolitanas, como a Worldwide Interoperability for Microwave Access (WiMAX). A integração destas redes constitui um acesso à rede global, permitindo a transferência de cha-madas de uma interface para outra, de forma transparente para o utilizador. Ajudando essa tendência de integração, têm sido desenvolvidos cada vez mais terminais multi-modo capazes de aceder a diferentes tecnologias de rede.
Num contexto em que um operador de telecomunicações administre diferentes tecnologias de rede no mesmo local físico, a gestão conjunta e e ciente dos recursos de rede é a solução mais desejada. Essa gestão conjunta vai certamente melhorar o serviço oferecido aos utilizadores e, ao mesmo tempo, o aumento das receitas do operador.
O objectivo desta tese consiste em desenvolver uma estratégia de gestão de recursos de rádio para gerir e cientemente os recursos disponíveis em redes hetero-géneas. Esta tese produziu duas contribuições originais. A primeira contribuição
rádio adequada para gerir e cientemente recursos de redes heterogéneas. Esta nova estratégia, chamada MTend, caracteriza-se pela distribuição das chamadas entre as interfaces de radio de acordo com as suas características. A decisão de distribuição é baseada no comprimento dos pacotes associados a cada chamada, seguindo ao mesmo tempo uma política de prevenção de handos. Além disso, em cenários em que os recursos de rede são escassos, a estratégia prevê a possibilidade de renegociar os pedidos de novas ligações ou realocar as chamadas existentes de uma rede para outra.
Uma segunda contribuição desta tese é o modelo de simulação de rede. Este modelo foi desenvolvido para avaliar a nova estratégia de gestão de recursos de rádio, sendo o uso de interfaces virtuais a sua principal inovação. A implementação do modelo de simulação foi disponibilizada como uma contribuição gratuita para o Network Simulator Version 3 (NS-3).
O desempenho da estratégia MTend é avaliado comparando a nova estratégia com duas estratégias conhecidas e utilizadas em cenários onde as redes UMTS e WLAN estão interligadas. A análise de resultados cobre aspectos tais como a probabilidade de bloqueio de chamadas, a in uência do tamanho do pacote de tráfego no desempenho da estratégia RRM, o desempenho de hando e uma análise das receitas associadas a cada estratégia.
Contents
List of Figures xviii
List of Tables xix
List of Acronyms xxi
1 Introduction 1
1.1 Overview . . . 1
1.2 Research Context . . . 3
1.3 Research Objectives . . . 4
1.4 Contributions of this Thesis . . . 5
1.5 Thesis Outline . . . 5
Chapter References . . . 7
2 Wireless Communications Architectures 9 2.1 Introduction . . . 9
2.2 Cellular Technology . . . 10
2.2.1 Cellular Concept . . . 10
2.2.1.1 Cell Signal . . . 11
2.2.1.2 Frequency Reuse . . . 13
2.2.1.3 Movement from Cell to Cell . . . 14
2.2.2 Cellular System Evolution . . . 15
2.2.2.1 First Generation . . . 15
2.2.2.2 Second Generation . . . 16
2.2.2.3 From 2G to 3G Evolution Way . . . 17
2.2.2.4 UMTS to HSPA Evolution . . . 18
2.2.2.5 LTE Convergence . . . 20
2.3 Wireless LAN Technology . . . 23
2.3.1 The 802.11a Standard . . . 26
2.4.2 Interconnection Based on 3GPP Standardization . . . 31
2.5 Summary . . . 33
Chapter References . . . 34
3 Radio Resource Management 39 3.1 Introduction . . . 39
3.2 General Concepts . . . 41
3.2.1 Radio Resource Unit . . . 41
3.2.2 QoS in Mobile Networks . . . 42
3.2.3 Scheduling . . . 43
3.2.4 Hando Techniques . . . 44
3.2.4.1 Horizontal Hando . . . 44
3.2.4.2 Vertical Hando . . . 45
3.3 Radio Resource Management in Cellular Networks . . . 46
3.3.1 CAC on 3G Cellular System . . . 47
3.3.2 CAC Based on Load Factor . . . 48
3.4 Radio Resource Management in 802.11 Networks . . . 55
3.4.1 CAC on WLAN Interface . . . 55
3.4.2 CAC based on Measurements . . . 56
3.5 Multi-Radio Resource Management . . . 57
3.6 Analysis of Literature . . . 59
3.6.1 Existing RRM Strategies . . . 62
3.6.1.1 Management Based on Covered Area (CovAr) . . . 62
3.6.1.2 Management Based on Load Balancing (LBal) . . . 62
3.6.2 Quick View of Literature . . . 63
3.7 Summary . . . 65
Chapter References . . . 67
4 Proposed Radio Resource Management Strategy 75 4.1 Introduction . . . 75
4.2 MTend Strategy . . . 76
4.2.1 Decision Algorithm . . . 78
4.2.2 Call Renegotiation Mechanism . . . 80
4.2.3 Call Reallocation Mechanism . . . 82
4.3 Simulation Model . . . 82
4.3.1 Scenario Based on Static Users . . . 84
4.3.2 Scenario Based on Mobile Users . . . 86
4.3.3 Implementation Model . . . 87
4.3.5 Tunneling and Mobility Support . . . 88
4.3.6 Network Stack . . . 89
4.3.7 NS-3 Based Simulation Framework . . . 90
4.4 Summary . . . 94
Chapter References . . . 95
5 Simulations and Result Analysis 99 5.1 Introduction . . . 99
5.2 Simulation Framework Evaluation . . . 100
5.3 Call Blocking Probability Analysis . . . 102
5.3.1 Real Time Tra c . . . 102
5.3.2 Real Time and Non-Real Time Tra c . . . 105
5.4 Renegotiation and Reallocation Analysis . . . 107
5.4.1 Call Renegotiation . . . 108
5.4.2 Call Reallocation . . . 109
5.5 Calls Distribution among Interfaces . . . 110
5.6 Packet Length Analysis . . . 113
5.7 Call Blocking Probability Analysis in a Mobile Scenario . . . 118
5.8 Revenue Analysis . . . 122
5.9 Summary . . . 127
Chapter References . . . 129
6 Conclusions and Future Work 131 6.1 Work Revisited . . . 131
6.2 Original Contributions . . . 134
6.2.1 A New Joint Radio Resource Management Strategy . . . 134
6.2.2 Network Simulation Model . . . 134
6.3 Future Work . . . 135 Chapter References . . . 137 General Bibliography 139 Chapter 1 . . . 139 Chapter 2 . . . 140 Chapter 3 . . . 143 Chapter 4 . . . 150 Chapter 5 . . . 152 Chapter 6 . . . 153 A Term De nitions 157 A.1 Block Error Rate (BLER) . . . 157
A.5 Geometry Factor, G . . . 160
A.6 Ec/I0 . . . 161
A.7 Ec/Ior . . . 161
List of Figures
1.1 Hotspot scenario . . . 4
2.1 Cellular common architecture . . . 12
2.2 Three sector reuse frequency . . . 13
2.3 Handover direction . . . 15
2.4 AMPS cellular system . . . 16
2.5 GSM/GPRS/EDGE and UMTS general architecture . . . 18
2.6 HSPA and LTE evolution . . . 21
2.7 LTE overall architecture . . . 22
2.8 Functional split between E-UTRAN and MME/GW . . . 23
2.9 Enterprise wireless network infrastructure . . . 24
2.10 Residential wireless network architecture . . . 25
2.11 Internet wireless network access block structure . . . 26
2.12 3GPP generic architecture for the interconnection of 3G and WLAN networks . . . 31
2.13 3GPP functional blocks architecture for the interconnection of 3G and WLAN networks . . . 33
3.1 Covered area strategy . . . 63
3.2 Load balancing strategy . . . 64
4.1 Joint multi-radio resource management algorithm . . . 79
4.2 Call renegotiation mechanism . . . 81
4.3 Calls transference between interfaces using the reallocation mechanism 83 4.4 MTend algorithm (including the network allocator and the renego-tiation and the reallocation mechanism) . . . 84
4.5 ηmax distribution according to users location - inside/outside hotspot 86 4.6 User distribution according to the users location - inside/outside hotspot . . . 87
5.1 Calls distribution between UMTS and WLAN . . . 101
5.2 Call blocking probability with RT tra c . . . 105
5.3 Call blocking probability with RT and NRT tra c . . . 107
5.4 Percentage of renegotiation tries . . . 108
5.5 Reallocation mechanism . . . 109
5.6 Percentage of voice calls accepted in UMTS . . . 111
5.7 Percentage of video streaming accepted in WLAN . . . 111
5.8 Percentage of FTP calls accepted in WLAN . . . 112
5.9 Percentage of www calls accepted in WLAN . . . 112
5.10 Average occupation ratio for packet lengths of 50, 500, 1000 and 1500 bytes . . . 113
5.11 Average transmission time for packet lengths of 50, 500, 1000 and 1500 bytes . . . 115
5.12 Average throughput for MTend, LBal and CovAr strategies . . . 117
5.13 Call blocking probability considering mobile users . . . 120
5.14 Hando analysis . . . 121
5.15 Distribution of applications by the UMTS and WLAN interfaces, by the MTend strategy . . . 124
5.16 Distribution of applications by the UMTS and WLAN interfaces, by the LBal strategy . . . 124
5.17 Distribution of applications by the UMTS and WLAN interfaces, by the CovAr strategy . . . 125
5.18 Revenue obtained in UMTS and WLAN interfaces by the three JRRM strategies . . . 126
List of Tables
2.1 HSPA evolution through 3GPP releases . . . 20
2.2 Modulation coding scheme to 802.11a standard . . . 28
2.3 Brief description of 802.11 group of standards . . . 29
3.1 Parameters used in the uplink load factor calculation . . . 52
3.2 Parameters used in the downlink load factor calculation . . . 53
3.3 Literature analysis of RRM strategies . . . 65
4.1 UMTS and WLAN eligibility degrees according to the user mobility criterion . . . 79
4.2 Applications bit rates and their renegotiation alternatives . . . 81
4.3 Calls per user per hour used in the simulations . . . 85
5.1 Gain of MTend strategy in respect to LBal and CovAr for RT tra c 104 5.2 Gain of MTend strategy in respect to LBal and CovAr for RT & NRT tra c . . . 107
5.3 Throughput gain of MTend in respect to LBal and CovAr, consid-ering dierent packet lengths . . . 118
5.4 Gain of MTend strategy in respect to LBal and CovAr considering mobile users . . . 121
5.5 Prices for the three analyzed services expressed in MU . . . 123 5.6 Total revenue gain of MTend strategy in respect to LBal and CovAr 127
List of Acronyms
2G Second Generation . . . 17 2.5G 2.5 Generation . . . 17 3G 3rd Generation . . . 1
3GPP 3rd Generation Partnership Project . . . 2 AMPS Advanced Mobile Phone System . . . 14 AMR-WB Adaptive Multi Rate - WideBand . . . 81 AP Access Point . . . 23 ARQ Automatic Repeat Request. . . .158 BER Bit Error Rate . . . 158 B3G Beyond 3G . . . 39 BLER BLock Error Rate . . . 157 BS Base Station . . . 11 CAC Call Admission Control. . . .3 CBP Call Blocking Probability . . . 102 CBR Constant Bit Rate. . . .85 CDMA Code Division Multiple Access. . . .11 COFDM Coded OFDM. . . .41 CovAr Covered Area . . . 63 CRC Cyclic Redundancy Check. . . .157 CRRM Common Radio Resource Management . . . 59 DPCCH Dedicated Physical Control Channel. . . .158 DSL Digital Subscriber Line . . . 26 DSMIPv6 Dual Stack Mobile IPv6 . . . 87
DTX Discontinuous transmission . . . 52 EDCA Enhanced Distributed Channel Access . . . 55 EDGE Enhanced Data rates for GSM Evolution . . . 61 eNB E-UTRAN NodeB. . . .21 ETSI TISPAN Telecommunications and Internet converged Services and
Protocols for Advanced Networking. . . .60 E-UTRAN Evolved UTRAN . . . 20 FEC Forward Error Correction . . . 27 FCC Federal Communications Commission. . . .26 FDD Frequency Division Duplex . . . 158 FSK Frequency Shift Keying. . . .16 FM Frequency Modulation. . . .16 FDMA Frequency Division Multiple Access. . . .11 FIFO First In First Out . . . 43 FQ Fair Queuing . . . 43 FTP File Transfer Protocol . . . 78 SAR Segmentation and Reassembly. . . .77 AMD Acknowledged Mode Data . . . 77 PU Packet Units . . . 77 GERAN GSM EDGE Radio Access Network . . . 42 GGSN Gateway GPRS Support Node . . . 17 GMSK Gaussian Minimum Shift Keying . . . 17 GPRS General Packet Radio Service . . . 17 GSM Global System for Mobile Communications . . . 11 GTP GPRS Tunnelling Protocol . . . 89 GW Gateway . . . 21 HA Home Agent . . . 88 HoA Home Address. . . .89 HCCA HCF Controlled Channel Access. . . .55 HCF Hybrid Coordination Function. . . .55
HSDPA High-Speed Downlink Packet Access . . . 19 HSPA High-Speed Packet Access . . . 18 HSUPA High-Speed Uplink Packet Access. . . .19 IEEE Institute of Electrical and Electronics Engineers . . . 55 IETF Internet Engineering Task Force . . . 45 IIS Intelligent Interface Selection . . . 91 IMS IP Multimedia Subsystem . . . 21 IP Internet Protocol . . . 21 IPv4 IP version 4 . . . 88 ISM Industrial, Scienti c, Medical . . . 25 ISIM IMS Subscriber Identity Module . . . 32 ISO International Organization for Standardization . . . 42 ISP Internet Service Provider . . . 58 ITU International Telecommunication Union . . . 81 JRRM Joint Radio Resource Management . . . 75 LAN Local Area Network . . . 23 LBal Load Balancing . . . 65 LTE Long Term Evolution. . . .20 MAC Medium Access Control . . . 25 MBMS MultiMedia Broadcast/Multicast Service . . . 19 MIMO Multiple-input Multiple-output . . . 19 MIPv4 Mobile Internet Protocol version 4. . . .88 MME Mobility Management Entity . . . 21 MRRM Multi-Radio Resource Management. . . .75 MRAT Multi Radio Access Technology. . . .64 MS Mobile Station . . . 10 MSC Mobile Switching Center . . . 11 MTend Mobile Tendency . . . 76 MTU Maximum Transmission Unit . . . 77 NAMPS Narrowband Advanced Mobile Phone System . . . 14 NAS Non-Access Stratum. . . .22
NRT Non-Real Time Tra c. . . .85 NS-3 Network Simulator Version 3 . . . 5 OFDM Orthogonal Frequency Division Multiplexing. . . .27 MU Monetary Unit . . . 122 P2P Peer-to-Peer. . . .93 PDA Personal Digital Assistant . . . 2 PDG Packet Data Gateway . . . 32 PDMA Polarization Division Multiple Access. . . .12 PDN Packet Data Network. . . .21 PDP Packet Data Protocol . . . 43 PDU Protocol Data Unit . . . 77 P-GW PDN Gateway . . . 21 PHY Physical layers . . . 25 PPP Point-to-Point Protocol. . . .90 PQ Priority Queuing . . . 43 QoS Quality of Service . . . 2 RAT Radio Access Technology . . . 39 RATs Radio Access Technologies. . . .59 RLOC Re-allocation of Calls. . . .64 PKLN Packet Length Analysis . . . 64 RNG Renegotiation of Resources . . . 64 VTH Vertical Hando . . . 64 RLC Radio Link Control. . . .43 RM Resource Management. . . .93 RNC Radio Network Controller . . . 19 RNS Radio Network Subsystem. . . .43 RRM Radio Resource Management . . . 3 RRU Radio Resource Unit . . . 41 RT Real Time Tra c . . . 84 SAE System Architecture Evolution . . . 21
SDU Service Data Units . . . 77 SGSN Serving GPRS Support Node . . . 17 S-GW Serving Gateway . . . 21 SIP Session Initiation Protocol. . . .45 SMS Short Message Service . . . 47 SSID Service Set Identi er . . . 32 TACS Total Access Communication System . . . 41 TCP Transmission Control Protocol . . . 85 TDMA Time Division Multiple Access . . . 12 UDP User Datagram Protocol. . . .85 UE User Equipment . . . 21 UICC USIM Integrated Circuit Card. . . .32 UMTS Universal Mobile Telecommunications System . . . 3 U-NII Unlicensed National Information Infrastructure . . . 26 USIM Universal Subscriber Identity Module. . . .32 UTRAN UMTS Terrestrial Radio Access Network . . . 5 VBR Variable Bit Rate . . . 85 WAG WLAN Access Gateway . . . 32 WCDMA Wideband CDMA . . . 11 WFQ Weighted Fair Queuing . . . 43 WiMAX Worldwide Interoperability for Microwave Access . . . 135 WLAN Wireless Local Area Networks . . . 2 WLAN-NAA WLAN-Network Access Application . . . 32 WRR Weighted Round Robin. . . .43 www World Wide Web. . . .47
1
Introduction
This thesis presents a research work on Multi-Radio Resource Management. This rst Chapter provides the context of the research, its objectives, the principal contributions of this work, and an outline of the remainder of the thesis.
1.1 Overview
I
n the last years, the cellular communications system has evolved greatly, mainlymoved by the increase of applications and user requirements. The growth of demand in this area is attributed to facilities and usability of services through cellular networks. Since the rst experiments with radio communications in the end of XIX century, the road to truly mobile radio communications has been quite long. To have a better understanding of the complex 3rd Generation (3G)mobile-communications systems used today, it is also important to understand where they came from and how cellular systems have been developed [1]. The mobile techno-logy developments have also changed, from being a national or regional concern, to becoming a very complex task undertaken by global standards developed by
organizations such as the 3rd Generation Partnership Project (3GPP).
The boom of 3GPP networks was accompanied by an increased usage of Wire-less Local Area Networks (WLAN) and nowadays there are an increasing number of places where cellular and WLAN networks co-exist and are interconnected. These places are known as hotspots. Today it is easy to imagine that anyone can leave home carrying his device (e.g., a Personal Digital Assistant (PDA), a mobile station or a portable computer) connected to a WLAN, and that it switches to a cellular system automatically. This concept is known as seamless connection, and it is characterized by a technology change imperceptible to the user.
Future wireless scenarios will be characterized by the coexistence of a vari-ety of heterogeneous wireless access technologies. There will be complex protocol stacks, supporting a number of applications and services with dierent Quality of Service (QoS) demands and, in addition, requiring multi-mode terminal capabilit-ies to access such networks. Each network diers from the others by aspects such as air interface technology, cell-size, services, bit rate capabilities, or coverage. These wireless scenarios oer great opportunities to be exploited with advantage for both the network operators and the end users. Additionally, the multi-radio technology also enables the use of several access techniques simultaneously, not necessarily administered by the same network operator. In such an environment, the support for fast handovers between dierent radio access networks would facil-itate service continuity when the user moves through the dierent access networks. From a network operator perspective, it is very important to use the resources ef- ciently because the available radio resources are scarce and the revenue must be maximized.
1.2. Research Context 3
1.2 Research Context
The e cient Radio Resource Management (RRM) is an important research topic of the telecommunications systems. However, this optimal e ciency is hard to reach since RRM depends on management strategies, on Call Admission Control (CAC) algorithms and on heterogeneous network controller algorithms [2]. Usually, the RRM algorithm is concerned to improve the system performance and to provide QoS to the users. The family of RRM algorithms can be divided into power control, admission control, load control, and packet scheduling functionalities. The RRM algorithms can be de ned based on the interference levels in the air interface [3].
The mobile communications area is one of the most important technological areas [4]. Technological advances and market developments in the mobile com-munications area have been driven by multiple factors including the successful in-terconnection of heterogeneous networks. The network operators want to provide best quality of service to the users connected to their networks and, consequently, increase the number of customers. The interconnection of heterogeneous networks can give an important contribution to this task. 3GPP launched, through re-lease 8, an architecture for interconnecting Universal Mobile Telecommunications System (UMTS) and WLAN, which are presently the main commercial network technologies. In this context, new radio resource management strategies are re-quired [5, 6]. The work presented in this thesis was done in the perspective of a telecommunications operator that administrates heterogeneous networks resources. Consequently, a special attention was given to the work developed and proposed by 3GPP.
1.3 Research Objectives
The fundamental question behind this work is: "How can we manage heterogen-eous radio resources so that call blocking can be reduced and unnecessary handos avoided?". In order to answer this question, the main goal of this thesis has been de ned to study and develop a new strategy for RRM in heterogeneous networks. We investigate a scenario where the UMTS and the WLAN networks are intercon-nected, forming an hotspot environment (Figure 1.1). In this study, we assume that the WLAN network does not integrate any mechanism for QoS support.
Figure 1.1: Hotspot scenario
After the new strategy is de ned, it should be evaluated and compared with the reference strategies in this area. This evaluation and comparison became then another important objective of this thesis.
In order to compare our approach with concurrent ones, the UMTS and WLAN interconnection architecture de ned by 3GPP should be implemented in a network simulation environment.
1.4. Contributions of this Thesis 5
1.4 Contributions of this Thesis
This work produced two original contributions. The rst contribution can be identi ed as a new radio resource management strategy suitable for e ciently manage heterogeneous resources. This new strategy focus on the distribution of the incoming calls among interfaces according to the characteristics of the calls. The distribution decision is based on the length of the packets associated with each call, following at the same time an hando avoidance policy. A second contribution of this thesis is the network simulation model. This model has been developed for our simulation tests and for the evaluation of the new radio resource management strategy. The simulation model implementation is available as a free contribution on Network Simulator Version 3 (NS-3) core.
1.5 Thesis Outline
The remainder of this thesis is organized as follows. Chapter 2 presents the state-of-the-art on the technologies associated to our work. Firstly, we will describe the wireless access networks technologies, starting by cellular technology and its evolution. After, we will describe the WLAN evolution and its standard. A special attention is given to the interconnection between UMTS Terrestrial Radio Access Network (UTRAN) and WLAN, which was made by 3GPP.
The principal objective of Chapter 3 is to present the technologies devoted to RRM. The CAC algorithms of UMTS and WLAN technologies will be analyzed, as well as the performance of those algorithms acting together. Other topics, such as QoS applications and handover techniques, will be discussed in this chapter.
Finally, some related work in the area of RRM will be presented.
Chapter 4 presents the proposed RRM strategy giving a detailed explanation of the policies followed by the strategy. In the same Chapter we describe the network simulation model implemented in NS-3.
Chapter 5 analyzes the simulation results by comparing the proposed RRM strategy with two alternative strategies. The result discussed cover the call block-ing probability, the in uence of the tra c packet length in the performance of the RRM strategy, the hando performance, and a revenue analysis.
Finally, Chapter 6 presents the nal conclusions of this work, and points out future work directions.
1.5. Chapter References 7
Chapter References
[1] Dahlman, E., Parkvall, S., Skold, J., Beming, P. 3G Evolution, 2nd Edition:
HSPA and LTE for Mobile Broadband. Academic Press, 2008.
[2] Pérez-Romero, J., Sallent, O., Agustí, R. Radio Resource Management Strategies in UMTS. John Wiley & Sons, Ltd, 2005.
[3] Holma, H., Toskala, A. WCDMA For UMTS - HSPA Evolution and LTE. John Wiley & Sons, Ltd, 2007.
[4] Vulic, N., de Groot, S.H., Niemegeers, I. A Framework for Integration of Dierent WLAN Technologies at UMTS Radio Access Level. In Proceed-ings of the 4th annual IEEE International Conference on Pervasive Computing and Communications Workshops, (PERCOMW '06), p. 436. IEEE Computer Society, 2006.
[5] 3GPP. 3GPP System to Wireless Local Area Network (WLAN) Interworking. TR-23.234 v.7.5.0, Services and System Aspects Group, March 2007.
[6] 3GPP. Mobility Between 3GPP-Wireless Local Area Network (WLAN) In-terworking and 3GPP Systems (Release 8). TS-23.327 v.8.2.0, Services and System Aspects Group, December 2008.
2
Wireless Communications
Architectures
The goal of this Chapter is to present a review of wireless communications systems, giving a special attention to the technologies involved in our work. Firstly, we will describe the main alternatives for wireless access networks technologies. We start by the cellular technology and its evolution, and then we cover the WLAN set of standards commonly designated by 802.11. We nalize this Chapter giving a special attention to the interconnection between UTRAN and WLAN, which is under release by 3GPP.
2.1 Introduction
The recent evolutions in telecommunications have been in uenced by the crescent need of users to access their subscribed services in mobile environments. This demand has determined two complementary research lines in this area. On one hand, multimode terminals have been developed, being capable to access dierent network technologies, particularly wireless technologies, such as UMTS, WLAN,
or Bluetooth. On the other hand, the interconnection of dierent access networks has been researched and de ned, enabling call transference from one interface to another, seamlessly to the user. The future wireless network is envisioned as a convergence of various wireless access technologies, enabling users to be al-ways best connected to the Internet and continue using their applications without transmission disruption while they are moving between dierent wireless access technologies. In such environment, it is a critical issue for mobile nodes to in-telligently select access network and maintain active connections while they are roaming between dierent wireless access technologies.
This Chapter is organized as follows. Section 2.2 presents an overview of cel-lular technology, its components and its evolution path. An overview of WLAN technology and its standardization is made in Section 2.3. Finally, Section 2.4 addresses the interconnection between WLAN and UMTS, outside and inside the 3GPP scope.
2.2 Cellular Technology
2.2.1 Cellular Concept
Cellular telephony is designed to provide communications between two moving units, called Mobile Station (MS), or between one mobile unit and one stationary unit, often called a land unit. A service provider must be able to locate and track a caller, assign a channel to the call, and transfer the channel from base station to base station as the caller moves out of range [1]. To make this tracking possible, each cellular service area is divided into small regions called cells. Each
2.2. Cellular Technology 11 cell contains an antenna and is controlled by a solar or AC powered network station, called the Base Station (BS). Each BS is normally controlled by a switching o ce, known by Mobile Switching Center (MSC). The MSC coordinates communication between all the base stations and the telephone central o ce. It is a computerized center that is responsible for connecting calls, recording call information, and billing (see Figure 2.1).
Cell size is not xed and can be increased or decreased depending on the popu-lation of the area. The typical radius of a cell is depending on system (e.g., Global System for Mobile Communications (GSM),Wideband CDMA (WCDMA)). High-density areas require smaller cells than low-High-density areas to meet tra c demands. Once determined, cell size is optimized to prevent the interference of adjacent cell signals. The transmission power of each cell is kept low to prevent its signal from interfering with those of other cells [2].
The increased capacity in a cellular network, compared with a network with a single transmitter, comes from the fact that the same radio frequency can be reused in a dierent area for a dierent transmission. If there is a single plain transmitter, only one transmission at time can be made on a given frequency. Unfortunately, there is inevitably some level of interference from the signal from the other cells working in the same frequency.
2.2.1.1 Cell Signal
In order to distinguish signals from several dierent transmitters, Frequency Divi-sion Multiple Access (FDMA) and Code DiviDivi-sion Multiple Access (CDMA) were developed. With FDMA, the transmitting and receiving frequencies used in each cell are dierent from the frequencies used in each neighboring cell. The principle
Figure 2.1: Cellular common architecture
of CDMA is more complex, but achieves the same result; the distributed trans-ceivers can select one cell and listen to it. Other available methods of multiplexing such as Polarization Division Multiple Access (PDMA) and Time Division Mul-tiple Access (TDMA) cannot be used to separate signals from one cell to the next since the eects of both vary with position and this would make signal separation practically impossible. Time division multiple access, however, is used in com-bination with either FDMA or CDMA in a number of systems to give multiple channels within the coverage area of a single cell.
2.2. Cellular Technology 13 2.2.1.2 Frequency Reuse
In general, neighboring cells cannot use the same set of frequencies for commu-nication because it may create interference for the users located near the cell boundaries. However, the set of frequencies available is limited, and frequencies need to be reused. Adjacent cells must utilize dierent frequencies, however there is no problem with two cells su ciently far apart operating on the same frequency. The elements that determine frequency reuse are the reuse distance and the reuse factor. The reuse distance, D is calculated as:
Figure 2.2: Three sector reuse frequency
D = R√3N (2.1)
where R is the cell radius and N is the number of cells per cluster. Cells may vary in radius in the ranges (1 km to 30 km). The boundaries of the cells can also overlap between adjacent cells and large cells can be divided into smaller cells. The frequency reuse factor is the rate at which the same frequency can be used in the network. It is 1/K (or K according to [3]) where K is the number of cells which cannot use the same frequencies for transmission. Common values for
the frequency reuse factor are 1/3, 1/4, 1/7, 1/9 and 1/12 (or 3, 4, 7, 9 and 12 depending on notation). In case of N sector antennas on the same base station site, each with dierent direction, the base station site can serve N dierent sectors. N is typically 3. A reuse pattern of N/K denotes a further division in frequency among N sector antennas per site. Some current and historical reuse patterns are 3/7 (North American Advanced Mobile Phone System (AMPS)), 6/4 (Motorola Narrowband Advanced Mobile Phone System (NAMPS)), and 3/4 (GSM) [4].
CDMA based systems use a wider frequency band to achieve the same rate of transmission as FDMA, but this is compensated by the ability to use a frequency reuse factor of 1, for example using a reuse pattern of 1/1. In other words, adjacent base station sites use the same frequencies, and the dierent base stations and users are separated by codes rather than frequencies. While N is shown as 1 in this example that does not mean the CDMA cell has only one sector, but rather that the entire cell bandwidth is also available to each sector individually.
2.2.1.3 Movement from Cell to Cell
In a cellular system, as the distributed mobile transceivers move from cell to cell during an ongoing continuous communication, switching from one cell frequency to a dierent cell frequency is done electronically without interruption and without a base station operator or manual switching. This is called the handover or han-do (see Section 3.2.4). Typically, a new channel is automatically selected for the mobile unit on the new base station which will serve it. The mobile unit then automatically switches from the current channel to the new channel and com-munication continues. The exact details of the mobile system's move from one base station to the other varies considerably from system to system (see on the
2.2. Cellular Technology 15 Figure 2.3 for how a mobile phone network manages handover).
A service provider usually has limited coverage. Neighboring service providers can provide extended coverage through a roaming contract, enabling to have access to communication and to be reached where there is no coverage from its home service provider.
Old sig nal New sign
al
Figure 2.3: Handover direction
2.2.2 Cellular System Evolution
Since the cellular system was created, a constant evolution in the device architec-ture, system networks and services has been observed. This evolution was always driven by the need of better system capacities than the actual system can oer. The following Subsections give a brief description of this evolution path.
2.2.2.1 First Generation
In the late 70 the rst generation was designed for voice communication using analog signals. The AMPS is one of the leading analog cellular systems in North America. It uses FDMA to separate channels in a link. The system uses two
separate analog channels, one for forward (base station to mobile station) commu-nication and one for reverse (mobile station to base station) commucommu-nication. The band between 824 and 849 MHz carries reverse communication; the band between 869 and 894 MHz carries forward communication (see Figure 2.4). Each band is divided into 832 channels. However, two providers can share an area, which means 416 channels in each cell for each provider. Out of these 416, 21 channels are used for control, which leaves 395 channels. AMPS has a frequency reuse factor of 7; this means only one-seventh of these 395 tra c channels are actually available in a cell. For transmission, AMPS uses Frequency Modulation (FM) and Frequency Shift Keying (FSK) for modulation. Voice channels are modulated using FM, and control channels use FSK to create 30 kHz analog signals [1].
Figure 2.4: AMPS cellular system
2.2.2.2 Second Generation
To provide higher-quality on mobile voice communications, the second generation of the cellular phone network was developed. While the rst generation was de-signed for analog voice communication, the second generation was mainly dede-signed for digitized voice. The GSM is an European standard that was developed in the early 80 to provide a common second-generation technology for all Europe (see
2.2. Cellular Technology 17 Figure 2.1). Although GSM was created as a pan-European project, it quickly attracted worldwide interest and was deployed in a great number of countries out-side Europe [5]. The aim was to replace a number of incompatible rst-generation technologies. GSM uses two bands for duplex communication. Each band is 25 MHz in width, shifted toward 900 MHz, and divided into 124 channels of 200 kHz, separated by guard bands. Each 270.8 kbit/s digital channel modulates a car-rier using Gaussian Minimum Shift Keying (GMSK) (a form of FSK used mainly in European systems); the result is a 200-kHz analog signal. Finally 124 analog channels of 200 kHz are combined using FDMA [1].
2.2.2.3 From 2G to 3G Evolution Way
Evolution is a common term used in the context of cellular networks. The evolution from Second Generation (2G) to 3G network means the introduction of data trans-portation over cellular system. The development in this area started during the second half of the 1990s, with General Packet Radio Service (GPRS) introduced in GSM cellular technology and other developments, such as the Japanese standard. These technologies are often known as 2.5 Generation (2.5G) and considered an evolution of GSM [6]. The success of iMode, the Japanese data network, gave a very clear alert of the great potential for applications over packet data in mobile systems, in spite of, the fairly low data rates supported at the time. With the ad-vent of 3G and the enhancements on the radio interface of UTRAN, a new range of services came, that actually were only hinted at with 2G and 2.5G (see Figure 2.5). From GSM to GPRS, some modi cations are made in terms of architecture, such as the introduction of the Serving GPRS Support Node (SGSN) and the Gateway GPRS Support Node (GGSN) [7]. These modules are responsible by
packet tra c compatibility and allow MSs to use the packet switching network. In order to allow the UTRAN to use the network through GPRS network, appropriate interfaces have been developed. Few modi cations at the hardware level have been made, only, or in the majority of cases, software adequacy was enough to make the system versatile. It was the way found to give compatibility to the system, at the same time, reducing the nancial impact. Otherwise, it would be too expensive if the 3G system had been started from the scratch (see Figure 2.5) [7].
PRO FESSI ON AL W OR KSTATI ON
PRO FESSI ON AL W OR KSTATI ON PR OFES SIO NAL WO RKST ATIO N
PR OFES SIO NAL WO RKST ATIO N
PR OFES SIO NAL WO RKST ATIO N PRO FESSI ON AL W OR KSTATI ON
PROFESSIONAL WORKSTATION PROFESSIONAL WORKSTATION
EN TER PRI SE6 0 0 0
-E NT-ER PRI S-E6 0 0 0 -P D N In te rn e t In tr a n e t ISDN PSTN X.25
Figure 2.5: GSM/GPRS/EDGE and UMTS general architecture
2.2.2.4 UMTS to HSPA Evolution
3GPP has developed the architecture of UMTS towards standardization of a new system capable of increasing the speed of the tra c data with QoS. These in-vestigations converged to a new technology, designated by High-Speed Packet
2.2. Cellular Technology 19 Access (HSPA)1. The normalization of HSPA occurred in two stages, in the
down-link direction (from the network to the user) and the updown-link direction (from the user to the network). In the downlink, the so-called High-Speed Downlink Packet Access (HSDPA) was standardized as part of 3GPP Release 5. In the uplink, High-Speed Uplink Packet Access (HSUPA) was part of the 3GPP Release 6, where enhanced uplink packet data support has been introduced. The 3GPP Release 6 also brought e cient support for broadcast services into WCDMA through the in-troduction of the MultiMedia Broadcast/Multicast Service (MBMS), suitable for applications like mobile TV and multimedia contents. The HSDPA can reach an initial peak rate of 1.8 Mbit/s in the terminals, and can potentially reach more than 10 Mbit/s. In HSUPA, the peak rate at an early stage can vary from 1 to 2 Mbit/s. It is expected that, in a second phase, the data rate can vary between 3 and 5 Mbit/s.
In Release 7, with the introduction of Multiple-input Multiple-output (MIMO), HSDPA and HSUPA can reach until 28 and 11 Mbit/s respectively, (Table 2.1 [5]). This evolution marks a new phase on HSPA known as HSPA+. The HSPA was
developed over the architecture of the WCDMA network, on the same carrier. Thus, the HSPA and the WCDMA can share all elements of core and radio net-work, including the BS, the Radio Network Controller (RNC), the SGSN and the GGSN. Similarly, WCDMA and HSPA also share the locations of base stations and all the elements of antennas. With the evolution of WCDMA to HSPA, few adjustments at the hardware level are needed, both in base stations and in the RNC, to support high data rate. However, some software packages are needed to adapt the WCDMA to HSPA. Due to the share structure between WCDMA and
HSPA, the cost of changing from one technology to another is very low compared with the construction of a new standard for the network [8]. Thus, the research in this area can evolve to develop technologies that can contribute for a better support of QoS across the network [9].
Table 2.1: HSPA evolution through 3GPP releases HSPA Evolution
R5 (HSDPA) R6 (HSUPA) R7 (HSPA+)
- Downlink improved - Uplink improved - MIMO introduction - Packet-data support - Packet-data support - 28 Mbit/s downlink peak - 14 Mbit/s peak - Reduced delays - 11 Mbit/s uplink peak - ≈3 x R99 capacity - 5.74 Mbit/s peak - Continuous packet
- ≈2 x R99 capacity connectivity - Introduction of MBMS
2.2.2.5 LTE Convergence
In order to be prepared for the future needs, 3GPP has started the activity on the HSPA evolution. The UTRAN long-term evolution project group is look-ing at the market introduction of the Evolved UTRAN (E-UTRAN), belook-ing the resulting speci cation available in Releases 8 and 9 [10, 11]. The objective of Long Term Evolution (LTE) is to provide a high data rate, low latency and packet optimized radio access technology supporting exible bandwidth deploy-ments [12]. In parallel, a new network architecture is designed with the goal to support packet switched tra c with seamless mobility, quality of service and min-imal latency [13]. 3G evolution consists of two parallel tracks: HSPA evolution an LTE. Figure 2.6 illustrates the relation between HSPA evolution and LTE, as it can be seen from Release 8 ahead. To support the new packet data
devel-2.2. Cellular Technology 21 opments provided by the LTE radio interfaces, a new evolved core network has been developed. The work of specifying the core network is commonly known as System Architecture Evolution (SAE) [14, 15]. All the network interfaces
Figure 2.6: HSPA and LTE evolution
are based on Internet Protocol (IP) protocols. The E-UTRAN NodeB (eNB)s are interconnected by means of an X2 interface, while the Mobility Management Entity (MME)/Gateway (GW) entity and the eNBs are interconnected by means of an S1 interface, as shown in Figure 2.7. The S1 interface supports a many-to-many relationship between MME/GW and eNBs [10, 16]. The functional split between eNB and MME/GW is shown in Figure 2.8. Two logical gateway entities called the Serving Gateway (S-GW) and the PDN Gateway (P-GW) are de ned in this gure. The S-GW works as a local mobility anchor receiving and forwarding packets to and from the eNB serving the UE. The P-GW interfaces with external Packet Data Network (PDN)s, such as the Internet and the IP Multimedia Subsystem (IMS). The P-GW also has several IP functions, such as address allocation, packet l-tering, policy enforcement and routing. The MME is used to perform signaling and not to transport user IP packets. An advantage of a separate network entity for signaling is that the network capacity for signaling and tra c can grow inde-pendently [17]. The main functions of MME are idle mode User Equipment (UE)
S1 S1 S1 X2 X2 S 1
Figure 2.7: LTE overall architecture
reachability, including the control and paging retransmission, roaming, authentic-ation, authorizauthentic-ation, P-GW/S-GW selection, bearer management including dedic-ated bearer establishment, security negotiations and Non-Access Stratum (NAS) signaling. Evolved Node-B implements the Node-B functions as well as the pro-tocols traditionally implemented in RNC. The main functions of eNB are header compression, ciphering and reliable delivery of packets. On the control side, eNB incorporates functions, such as admission control and radio resource management. Some of the bene ts of a single node in the access network are reduced latency and the distribution of RNC processing load into multiple eNBs. The 3GPP project is working to allow that the LTE improvements can be seen by all kind of access network technologies in a transparent way [18].
2.3. Wireless LAN Technology 23
Figure 2.8: Functional split between E-UTRAN and MME/GW
2.3 Wireless LAN Technology
A WLAN is a communication system where a user is able to connect to a Local Area Network (LAN) using no wires. WLAN was designed as an alternative to the wired LAN to minimize the need for wired connections (see Figure 2.9). WLAN works similarly to the cellular system, oering a combination of data connectivity and user mobility [19]. As described in Figure 2.10, each Access Point (AP) is a base station that transmits data between the WLAN and the wired network infrastructure. Each AP can support a group of users and provides coverage for a limited distance. The position where the mobile station is localized in relation to the AP impacts the received signal strength. In addition, obstacles and unknown interferences can contribute to the decrease of power received. APs are connected to an intra-wired network via an Ethernet network (e.g, hub or switch). End users
can access the WLAN through equipments that integrate a WLAN adapter, such as PDAs, laptops, or even cellular devices. WLAN enables users to walk seamlessly among APs without dropping their connections. WLANs have gained popularity
Figure 2.9: Enterprise wireless network infrastructure
in a number of vertical markets, including public-space, o ces, retail, hotels, and manufacturing [20, 21, 22]. These industries have pro ted from the advantages oered by the easier use of WLANs. Network administrators can set up or aug-ment networks without installing new wires. The installation exibility, mobility support, simplicity and cost bene ts are some of the advantages of WLANs over the wired networks.
WLANs are seen as a complement to cellular communications when they are in the same covered area. Compared with cellular communications, WLAN has a
2.3. Wireless LAN Technology 25
Wired Networ
k
Figure 2.10: Residential wireless network architecture short range cell and high bit rate.
WLAN and IEEE 802.11 standard are almost synonymous. The original 802.11 was developed during 1991-1997 [23]. The rst release of the standard was accepted in June 1997 and included a speci cation of the Medium Access Control (MAC) layer. Three dierent Physical layers (PHY), the frequency hopping, the Dir-ect Sequence Spread SpDir-ectrum (DSSS) and the infrared have been speci ed in that release. Radio PHYs operate in the 2.4GHz unlicensed Industrial, Scienti c, Medical (ISM) band, which is available globally, and provide up to 2 Mbit/s bit rate. Over time, the DSSS variant became popular among users. The MAC layer works reliably even in environments with a high level of interference. No frequency planning or other kind of radio related parameters are necessary to be set before use, although larger areas with a high number of APs operate more e ciently
when some engineering eort is spent. In order to visualize a coherent network environment, Figure 2.11 describes through a block diagram how can a wireless network user access the Internet through the wireless network. In a typical net-work, the WLAN network bridges the nal meters between the Digital Subscriber Line (DSL) modem and the devices using a xed line Internet connection. The WLAN AP can be combined with a DSL modem [24].
To In te rn et
Figure 2.11: Internet wireless network access block structure
2.3.1 The 802.11a Standard
802.11a2 can provide speeds up to 54 Mbit/s, operating in the 5-GHz Unlicensed
National Information Infrastructure (U-NII) band and occupies 300 MHz of band-width. The Federal Communications Commission (FCC) initially has divided the 300 MHz into three distinct 100 MHz group, each one with a dierent maximum transmission power. The "low" band operates between 5.15 and 5.25 GHz, with
2The 802.11a standard has been considered as the WLAN base standard in the context of our
2.3. Wireless LAN Technology 27 maximum power output of 50 mW. The "middle" band operates between 5.25 and 5.35 GHz, with maximum power of 250 mW. The "high" band operates between 5.73 and 5.83 GHz, with maximum power of 1 W. The low and the middle bands are more indicated for indoor wireless transmission, while the high band is more adequated for transmission among buildings [19, 25]. 802.11a uses the Orthogonal Frequency Division Multiplexing (OFDM) (see Table 2.2) as the principal trans-mission scheme. There are a total of 8 non-overlapping channels de ned in two lower bands, each of which is 20 MHz wide [26]. Each of these channels is divided into 52 sub-carriers and each sub-carrier is approximately 300 kHz wide. Inform-ation bits are encoded and modulated in each sub-carrier, and the 52 sub-carriers are multiplexed together and transmitted in "parallel". Therefore, high data rate is realized by combining many low rate sub-carriers. The transmission of multiple sub-carriers or sub-channels makes the network more scalable than other tech-niques. To limit the channel errors and improve the transmission quality, Forward Error Correction (FEC) was also introduced. Besides, to oer higher data rate and better scalability, another signi cant advantage of OFDM technique is that it improves the interference resistance over the multi-path fading channels. Because of the low symbol rate of each sub-carrier, the eect of delay spread is reduced and thus the multi-path interference is minimized [25].
2.3.2 Overview of Other 802.11 Standard Variants
Similarly to what occurred in a wired networks, where the data transfer rates evolved from 10 Mbit/s to 10 Gbit/s, there was a need to increase the WLAN bit rate too. Therefore, enhancements to the physical layers were developed in the
Table 2.2: Modulation coding scheme to 802.11a standard Data Rate (Mbit/s) Mudulation Scheme Channel Coding Rate
6 BPSK 1/2 Convolutional code 9 BPSK 3/4 Convolutional code 12 QPSK 1/2 Convolutional code 18 QPSK 3/4 Convolutional code 24 16 QAM 1/2 Convolutional code 36 16 QAM 3/4 Convolutional code 48 64 QAM 2/3 Convolutional code 54 64 QAM 3/4 Convolutional code
late 1990s, incorporated to the family of 802.11 standards. Table 2.3 presents a summary of the WLAN standard and their main characteristic [23]. The 802.11b, delivering up to 11Mbit/s, was introduced in September 1999, and 802.11a, around 54Mbit/s, in December 1999 [26]. The paramount popularity of WLAN began with the 802.11b standard around 2000-2001, while the 802.11a has seen quite poor success in the marketplace. Although 802.11a is technically superior, at least regarding bit rates, the 802.11b was a better t to the market, was good enough, and had compatibility with previous 802.11 DSSS installations [27]. Later on (November 2001), the higher speed 802.11a modulations were added to the 2.4 GHz band, producing the 802.11g variant, which runs around to 54 Mbit/s. Today the 802.11g is the most common variant in the marketplace. The enormous number of 802.11b devices causes considerable inertia to the market, and hence most 802.11g equipment also includes the 802.11b radio interface.
2.4. Interconnection of Heterogeneous Access Networks 29 Table 2.3: Brief description of 802.11 group of standards
Working Group Short Description 802.11 Base standard
802.11a 5 GHz extension multi-rate 6 to 54 Mbit/s
802.11b Data rate extension in 2.4 GHz IMS band up to 11 Mbit/s 802.11c ID Bridge addition
802.11d Regulatory domains 802.11e QoS enhancements
802.11f Recommended practices for inter-access point communications 802.11g 54Mbit/s a-like high-speed extension for 2.4 GHz IMS band 802.11h Dynamic channel allocation and power control extensions
for European requirements 802.11i Security enhancements to MAC 802.11j Support for 4.9 GHz bands for Japan 802.11k Radio resources measurements
802.11m Standard maintenance, technical and editorial corrections 802.11n High throughput > 100 Mbit/s extension
802.11p Wireless access in vehicular environments 802.11r Fast BSS transition - i.e., fast handover 802.11s Mesh networks
802.11t Wireless performance prediction 802.11u Inter-working with external networks 802.11v Wireless network management
2.4 Interconnection of Heterogeneous Access
Net-works
QoS provisioning in wireless networking technologies, such as WLAN or 3G net-works, is an object of study that has been exploited in recent years by many researchers. Providing QoS to integrate these technologies around a common core network is one of the biggest challenges in this area.
2.4.1 Interconnection Solutions
In some cases, the WLAN network is used by 2 and 3G as a complementary solu-tion. In [28] is proposed an interconnection architecture using coupling techniques to balance the tra c between the networks. Other similar approaches can be found at [29, 30] and [31]. The main objective of these approaches is to keep the user always connected in all environments. There are two techniques that allow the coupling between 3G and WLAN networks:
• Loose coupling, where each network operates independently and is connected
to each other at the reference point, where GGSN is connected to external packet data network. WLAN does not share any core network nodes of UMTS [32];
• When UMTS and WLAN are tightly coupled, tra c from WLAN ows into
the core network of the UMTS and ows out to the external PDN via SGSN and GGSN. On the other hand, in the loosely coupled case, the users from WLAN can access the UMTS services with guaranteed QoS and seamless mobility. But it is a problem that the capacity of UMTS core network nodes is not enough to accommodate the bulky data tra c from WLAN, since the core network nodes are designed to handle circuit voice calls or low volumes of tra c [33].
The challenges of the interconnection between heterogeneous wireless networks are exploited to demonstrate the ways that lead to an optimized use of networks, for example, in terms of cost, network conditions, type of applications and user preference [34, 35]. These approaches can make balance between network interfaces
2.4. Interconnection of Heterogeneous Access Networks 31 and can be exploited as a way to manage tra c by a network operator.
2.4.2 Interconnection Based on 3GPP Standardization
In Release 7, 3GPP proposes to interconnect the WLAN with 3G technology as a way to minimize the visibility of the vertical hando. In [36] and [37], an archi-tecture of integration between WLAN and 3G is described. Figure 2.12 shows the architecture of this interconnection, where the network operator controls the two interfaces based on IP. In this scenario, an environment where the 3G networks and WLAN are located in the same area is assumed. Thus, the user can, through
Figure 2.12: 3GPP generic architecture for the interconnection of 3G and WLAN networks
its equipment, compatible with the two network technologies, use the 3G network or WLAN transparently. A typical usage scenario is one where the user's equip-ment is connected to a 3G network and detects the Service Set Identi er (SSID) of an available WLAN network, and starts trying to connect to the network through the WLAN interface. If the operator identi es the equipment as a user of its network, it will allow the transmission of information by the 3G network or by the WLAN.
In release 8, the 3GPP group is strongly committed to the standardization of seamless technology in order to enable an operator to provide telecommunica-tions service through heterogeneous networks without the need of user's interven-tion [38]. This release suggests a unit called USIM Integrated Circuit Card (UICC), which is responsible for maintaining the integration between the networks. A UICC can integrate three networks: WLAN-Network Access Application (WLAN-NAA), IMS Subscriber Identity Module (ISIM) and Universal Subscriber Identity Module (USIM) [39, 40].
Recently, 3GPP has launched a new release of the interconnection standard-ization initiative, which incorporates both network technologies into a single ar-chitecture [41]. The goal of this release is to de ne and standardize nodes at the WLAN network that correspond to nodes with similar functions presented in 3G networks. Examples of these nodes are the WLAN Access Gateway (WAG), which has a role similar to the SGSN, and the Packet Data Gateway (PDG), which can be compared to the GGSN (Figure 2.13)3. The main objective of this approach
is to make the interconnection between dierent networks totally indierent to
3The explanation of some interfaces are neglected since they are irrelevant for understanding
2.5. Summary 33
Wu
H2
Figure 2.13: 3GPP functional blocks architecture for the interconnection of 3G and WLAN networks
the interface used by the user, thus enabling it to view the network as a single platform. Furthermore, the decisions taken by the network must be to provide a better usage of the existing resources by the end user.
2.5 Summary
In this Chapter, we analyzed the wireless networks technology giving an overview about cellular networks since the beginning, with GSM, following the evolution until the LTE technology. In addition, an introduction to WLAN networks was also made. This explanation covers the 802.11 standard with focus on the 802.11a standard, because it is the model implemented in NS-3 and it was used in this work [42]. After, we described the interconnection between UMTS and WLAN according to 3GPP releases. Here, we mainly focused on the interconnection ar-chitecture proposed in Release 8, which will be the interconnection approach used in Chapter 4.
Chapter References
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[2] Nawrocki, M.J., Dohler, M., Aghvami, A.H. Understanding UMTS Radio Net-work Modelling, Planning and Automated Optimisation Theory and Practice. John Wiley & Sons, Ltd, 2006.
[3] Forouzan, B.A. Data Communications and Networking. McGraw-Hill, 2008. [4] Chevallier, C., Brunner, C., Garavaglia, A., Murray, K.P., Baker, K.R.
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