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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Taking an in-depth look at the mobile communications ecosystem, this book covers the two key components, i.e., Network and End-User Devices, in detail. Within the network, the sub components of radio access network, transmission network, core networks, services and OSS are discussed; component level discussion also features antenna diversity and interference cancellation techniques for smart wireless devices. The role of various standard development organizations and industry forums is highlighted throughout. The ecosystem is strengthened with the addition of the Technology Management (TM) component dealing mostly with the non-technical aspects of the underlying mobile communications industry. Various aspects of TM including technology development, innovation management, knowledge management and more are also presented. * Focuses on OFDM-based radio technologies such as LTE & WiMAX as well as MBWA (Mobile Broadband Wireless Access) * Provides a vital addition to the momentum of EVDO and its migration towards LTE * Emphasis on radio, core, operation, architectural and performance aspects of two next generation technologies - EPS and WiMAX * Includes discussion of backhaul technologies and alternatives as well as issues faced by operators switching to 3G and Next Generation Mobile Networks * Cutting-edge research on emerging Gigabit Ethernet Microwave Radios and Carrier Ethernet transport technologies Next Generation Mobile Communications Ecosystem serves as a practical reference for telecom associated academia and industry to understanding mobile communications in a holistic manner, as well as assisting in preparing graduate students and fresh graduates for the marketplace by providing them with information not only on state-of-the-art technologies and standards but also on TM. By effectively focusing on the key domains of TM this book will further assist companies with improving their competitiveness in the long run. Importantly, it will provide students, engineers, researchers, technology managers and executives with extensive details on various emerging mobile wireless standards and technologies.
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Contents
Cover
Title Page
Copyright
Deication
Preface
About the Author
1: Introduction
1.1 Mobile Communications Ecosystem
1.2 Book Overview
Reference
2: OFDM and OFDMA
2.1 Introduction
2.2 Technical Background
2.3 Principles of OFDM
2.4 OFDM Advantages
2.5 OFDM Impairments and Potential Remedies
2.6 Multi Access Scheme OFDMA
2.7 Why OFDMA for NGMN
2.8 Summary Insights
References
3: 3GPP Evolved Packet System (EPS)
3.1 Introduction
3.2 3GPP Releases
3.3 GPP LTE
3.4 LTE Air Interface
3.5 PHY Layer (Layer 1)
3.6 Layer 2
3.7 RRC (sublayer of Layer 3)
3.8 EPS Architecture
3.9 Key Attributes of E-UTRA
3.10 LTE Performance
3.11 3GPP Roadmap Evolution
3.12 Industry Outlook
3.13 Summary Insights
References
4: IEEE WiMAX
4.1 Introduction
4.2 Air Interface
4.3 Advanced Features of Mobile WiMAX
4.4 Network Architecture
4.5 Performance
4.6 WiMAX Certification
4.7 Industry Outlook
4.8 Next Steps/Evolution
4.9 Summary Insights
References
5: 3GPP2 CDMA2000 1xEV-DO
5.1 Introduction
5.2 1xEV-DO (Revisions 0 and A)
5.3 EV-DO Revision B
5.4 UMB (EV-DO Revision C)
5.5 CDMA450
5.6 EV-DO Network Architecture
5.7 EV-DO Revisions Comparison
5.8 CDMA2000 Evolution and Migration to 3GPP LTE
5.9 Industry Outlook
5.10 Summary Insights
References
6: IEEE 802.20 Mobile-Fi
6.1 Introduction
6.2 MBWA Requirements and Characteristics
6.3 The 802.20 Standard
6.4 Air Interface – Wideband Mode
6.5 Physical Layer Specifications – Wideband Mode
6.6 625k-MC (625kiloHertz-spaced MultiCarrier) Mode
6.7 802.20 Network Architecture
6.8 Performance
6.9 Industry Outlook
6.10 Summary Insights
References
7: Transmission Networks
7.1 Introduction
7.2 Market Drivers and Challenges
7.3 Backhaul Network
7.4 Metro Regional and Aggregation Transport Networks
7.5 Backbone Transport Network
7.6 Transport Network Evolution
7.7 Industry Outlook
7.8 Summary Insights
References
8: Core Networks and Operations Support Systems
8.1 Introduction
8.2 Core Network
8.3 Operations Support Systems (OSS)
8.4 Industry Outlook
8.5 Summary Insights
References
9: IMS, Services and Applications
9.1 Introduction
9.2 What is IMS?
9.3 3GPP IMS
9.4 3GPP IMS and WiMAX
9.5 3GPP2 Multi Media Domain (MMD)
9.6 IMS in Other Standard Bodies
9.7 Common IMS
9.8 Protocols
9.9 Services and Applications
9.10 Challenges
9.11 IMS Absence in Existing 3G Networks
9.12 Advance Services and Applications
9.13 Mobile Content Development
9.14 Key SDOs and Forums
9.15 Industry Outlook
9.16 Summary Insights
References
10: Smart Wireless Devices
10.1 Introduction
10.2 3G Wireless Devices’ Components
10.3 Mobile Software Platform
10.4 RF and Processors
10.5 Signal Processing
10.6 User Interface
10.7 Power Supply
10.8 Mobile Device Management
10.9 Mobile Performance Enhancement Techniques
10.10 Device Development Organizations
10.11 Devices (3GPP, 3GPP2, and WiMAX)
10.12 Industry Outlook
10.13 Summary Insights
References
11: E2E Network Architecture and Mobility Management
11.1 Introduction
11.2 E2E EPS Architecture
11.3 E2E WiMAX Architecture
11.4 Mobility Management
11.5 EPS and WiMAX Interworking
11.6 EPS and EV-DO (HRPD) Interworking
11.7 WiMAX and EV-DO Interworking
11.8 Key Interoperability Challenges
11.9 Fixed Mobile Convergence
11.10 Industry Outlook
11.11 Summary Insights
Reference
12: Technology Management
12.1 Introduction
12.2 Technology Strategy
12.3 Technology Development
12.4 New Product Development (NPD)
12.5 Innovation Management
12.6 Knowledge Management
12.7 Cultural Management
12.8 Technology Foresight
12.9 Technology Roadmapping
12.10 Technology Commercialization
12.11 Managed Services
12.12 Hypothetical Case
12.13 Industry Outlook
12.14 Summary Insights
Reference
13: Recap and Future Outlook
13.1 Chapter Recap
13.2 Formalization of TM for Mobile Communications Ecosystem
13.3 4G
13.4 Mobile Network Infrastructure Sharing
13.5 Connecting the Next Billion Users
13.6 Green Power for Mobile
13.7 Media and Telecom Convergence
13.8 Future Outlook
Reference
Index
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Library of Congress Cataloging-in-Publication Data
Asif, Saad Z. Next generation mobile communications ecosystem : technology management for mobile communications / Saad Z. Asif. p. cm. Includes bibliographical references and index. ISBN 978-0-470-74746-9 (cloth) 1. Mobile communication systems. I. Title. TK5103.2.A848 2010 621.3845′6–dc22 2010018740
A catalogue record for this book is available from the British Library.
Print ISBN: 9780470747469 ePDF ISBN: 9780470972168 oBook ISBN: 9780470972182
Set in 9/11pt Times by Aptara Inc., New Delhi, India
To my lovely daughters Maha and Shiza
Preface
In the name of Allah, the Most Merciful, the Most Compassionate
I am using this opportunity to share some of the technical and management experiences that I have gained while working for the three leading telecommunication service providers of the world. During my tenure at Sprint (USA), Pakistan Mobile Communications Limited (an Orascom Telecom Company) and currently with Telenor Pakistan (Telenor Group), I have come across a number of learning opportunities not only as a technologist but also as a people manager and as a strategist.
The book takes an in-depth look at the Mobile Communications Ecosystem which traditionally includes elements of end-user devices, radio access network, transport network, core network, operational support systems (OSS) and services. Based on my experiences, I believe that this ecosystem can be strengthened by including Technology Management to the value chain.
Technology Management (TM) is the norm of the game in all the organizations associated with technology and innovation driven mobile communications industry; whether it is practiced full heartedly or ineffectively it’s a different matter. TM mostly deals with non engineering elements like technology strategy, technology roadmapping, innovation management, etc.
Moving on, the book takes a deeper look at the two prevailing Next Generation Radio Access Technologies (standards) – 3GPP 3G-LTE and IEEE WiMAX and it also discusses their respective evolution towards 4G (IMT-Advanced). Besides radio technologies, a chapter is dedicated each for transport network, core network and OSS, services, devices and TM. The role of various standard development organizations and industry forums is highlighted throughout the book.
Chapter 1 introduces the enhanced mobile communications ecosystem model along with an overview of the book. Chapter 2 looks into OFDMA which is the newest form of multiple access technique used in both 3G-LTE and WiMAX and also envisioned for future 4G (IMT-Advanced) systems.
Chapter 3 to Chapter 6 looks into four different radio access techniques namely 3G-LTE, WiMAX, 3GPP2 EV-DO and IEEE MBWA respectively. 3G-LTE is the evolution of UTRAN (UMTS Terrestrial Radio Access Network) while WiMAX is the newest 3G radio access technology incorporated in IMT-2000. The continuous downfall of CDMA, death of UMB and absence of 3GPP2 from IMT-Advanced has made EV-DO not only an orphan but also left it without an offspring. At the same time the worldwide presence of EVDO cannot be ignored and its migration towards 3G-LTE has been discussed in chapter 5. IEEE MBWA has so far received very little attention but its importance cannot be ignored.
Chapter 7 looks into several bottlenecks associated with associated with transmission networks. The two emerging transport technologies namely Gigabit Ethernet and Carrier Ethernet are discussed in detail. Chapter 8 provides details of core networks and operational support systems. The evolution of 3GPP core networks with respect to different releases along with EPS and WiMAX management reference models are discussed. The details of Next Generation OSS are also discussed in Chapter 8.
Chapter 9 describes IMS (IP Multimedia Subsystem) and advance services like M-Commerce, Mobile TV, etc. Chapter 10 looks into various components of wireless devices including mobile software platform, radio frequency, processors, etc. Chapter 11 describes the end-to-end network architecture of EPS and WiMAX along with the mobility management aspects. The topic of fixed mobile convergence is also discussed in Chapter 11. Chapter 12 looks into the various branches of Technology Management and their relevance to the mobile communications industry.
Chapter 13 provides a recap of previous chapters, validation of TM for the mobile industry and some industry trends including network sharing, convergence of media and telecom, green power for mobile, etc. It also touches upon providing a high level forecast for the next 10 years by dividing into three periods (2010–2012; 2013–2015 and 2016–2020).
I strongly believe that mobile communications standards should be integrated into engineering, technology, and computing curricula which is not the case today. It will bring the academia further closer to the industry. At the same time the telecom firms can further strengthened their health by injecting time and money in the various domains of the TM.
From the bottom of my heart I would like to thank my wife for her everlasting support, my parents for their undying support and never-ending prayers, and my brother for his assistance in proofreading this book.
Lastly, I hope you will enjoy reading this book and reap immense benefits from it.
About the Author
Saad Z. Asif has twelve years of experience in evaluating telecommunications standards, state-of- the- art wireless technologies and engineering of fiber optic systems.
He began his career in 1998 as an engineer in Sprint Nextel (formerly Sprint) Transmission Engineering group where he engineered DWDM systems. A year later he moved to the Radio Access Development (RAD) group within Sprint Technology Development (formerly Technology Research & Development), an organization situated in Overland Park, KS, USA. In RAD, he accessed and conducted POC (proof-of-concept) trials on a number of wireless technologies including 3G (CDMA2000), interference cancellation, antenna diversity and smart antennas. He also led a team in conducting POC tests for EV-DO technology and played a major role in designing Sprint’s wireless high speed data strategy.
In 2006 he joined Technology Development (TD) group of Mobilink (an Orascom Telecom Company), Pakistan as a Manager TD. In that role his primary focus was on WiMAX where he led a team to conduct POC tests and fulfill regulatory requirements.
Since 2008 he has worked as a Manager Transmission Strategy in Telenor Pakistan in Islamabad. His current focus is on Gigabit Ethernet radios and Carrier Ethernet technologies and providing long-term strategy (direction) for the transmission network. He also led a team to launch the first Village Connection system in Pakistan. He also actively contributes to Telenor Group’s CONTEST (Common Technology and Strategy) program.
Mr. Asif is the author of the book Wireless Communications Evolution to 3G and Beyond published in 2007 by Artech House, USA. He has also published ten papers on wireline and wireless technologies. He, as a co-patentee, holds four US patents and has additional patent applications pending with the US Patent and Trade Office. He is also listed as a scientist in the ‘Productive Scientists of Pakistan – 2009’ directory, published by Pakistan Council for Science and Technology. He is also a senior member of the IEEE.
Mr. Asif received a BS and an MS in Electrical Engineering from Oklahoma State University in 1996 and 1997, respectively. He also received an MS in Engineering Management from the University of Kansas in 2001.
1
Introduction
Mobile Communications is one of the most valuable innovations of the twentieth century. It started in the 1970s and became one of the most common forms of communications in the mid 2000s. Mobile wireless communications is continuously evolving and mobile phone is all set to become the Third Screens after TV and computer.
It is a single technology that enables voice communications like traditional landline, broadband data communications like DSL (Digital Subscriber Line), financial services like banks and infotainment like TV. The journey started with first generation analog systems and moved to second generation digital telephony with GSM (Global System for Mobile Communications), USDC (US Digital Cellular), CDMAOne (Code Division Multiple Access) and PDC (Pacific Digital Cellular) systems. The journey continued with the migration to third generation (3G) systems in the early 2000s. The three 3G standards are CDMA2000, TD-SCDMA (Time Division – Synchronous CDMA) and UMTS (Universal Mobile Telecommunications Systems) [1].
Contrary to what is stated by many industry players both EPS (Evolved Packet System) and WiMAX (Worldwide Interoperability for Microwave Access) are part of ITU (International Telecommunications Union) IMT-2000 (International Mobile Telecommunications) framework and are not 4G technologies. IMT-2000 is a framework from the ITU for 3G wireless phone standards throughout the world that deliver high-speed multimedia data as well as voice. EPS is an evolution of UMTS systems while WiMAX is a new technology and both can be considered as the last leg to 4G.
Nevertheless the evolution is ongoing and migration to 4G is just starting with the request from ITU-R for the submission of IMT-Advanced or 4G proposals. These proposals are currently under evaluation and 4G technology or technologies will be standardized in 2011.
1.1 Mobile Communications Ecosystem
The traditional mobile communications ecosystem mainly comprises of technologies, standards and networks and it deals with the management of technlogies in a less effective fashion. Though technology management is recognized it is not as such practiced as it should be in the world of mobile communications. We made an attempt in this book to place technology management in its right place and give it a structured role in the overall ecosystem. We have explicitly added the component of technology management in the ecosystem so that the academia and importantly the mobile industry can start to consider TM as an integrated element of the business.
Thus, the mobile communications ecosystem is divided into three concrete elements namely the End-User Device, the Network and Technology Management (TM). This enhanced ecosystem in presented in Figure 1.1.
Figure 1.1 Enhanced mobile communications ecosystem
1.1.1 Devices
Device is one of the most critical elements of the food chain as the user experience ultimately drives the value of network. Devices come in various forms and shapes starting from simply traditional cell phones to iPhones and BlackBerrys.
1.1.2 Networks
3G networks consists of five major components, namely radio access network, transmission/transport network, core network, service element (Applications), OSS (operational support systems). The component of Information Technology which plays a supportive for the telecom network is not as such discussed in the book.
Radio Access Network (RAN): The RAN connects the end user devices to the core network that is, it sits between the device and the core network. The term RAN is typically used in GSM/UMTS networks. An equivalent term in CDMA2000 systems is air interface along with those components governing the networking of base stations and their connection to the core network. The air interface is the radio-based communication link between the mobile station and the active base transceiver station. RAN consists of two main components namely BTS (Base Transceiver Station) or NodeB and BSC (Base Station Controller) or RNC (Radio Network Controller). A BSC/RNC serves multiple BTS/ NodeBs [1].Transmission Network: Like its name, it provides the transmission of traffic from the user to mobile network and from the network either to PSTN or to another mobile user or to the Internet (or application servers). Transmission systems include microwaves, leased line, fiber, and so on.Core Networks: Core Network lies between RAN and OSS. It can be either circuit switched for voice communications or packet switched for data services. The mapping between RAN to Core Network is one-to-many. Core Network elements consist of MSCs (Mobile Switching Centers), SGSN (Serving GPRS GPRS (General Packet Radio Service) Support Node), PDSN (Packet Data Serving Node), GGSN (General GPRS Support Node), and so on. Each MSC, SGSN and PDSN can serve multiple BSCs/RNCs. PDSN and GGSN connect the users to Internet or third party application servers [1].Service Element (Applications): In 3G networks, users can get access to external Packet Data Networks (e.g., Internet) or in-house applications that are present on separate servers via core network.OSS: It provides OAM&P (operations, administration, maintenance and provisioning) functionality. It acts as the watchman that monitors the network and takes actions to rectify in case something goes wrong with the network on a 24/7/365 basis.1.1.3 Technology Management
TM deals with a number of soft elements of the mobile communications business. This field is vast and contains both technical and people elements, including, but not limited to, technology development, knowledge management, managed services, and so on.
1.2 Book Overview
We have made an attempt in this book to give a holistic picture of a Next Generation Mobile Communications ecosystem. Holistic means that we not only discuss technologies, standards and networks, but also the technology management component which is necessary to manage underlying technologies and networks in an effective fashion.
The book consists of 13 chapters including the current chapter that is, Chapter 1 Introduction. It provides details of various radio, transmission, core network, and OSS technologies and standards. Additionally, a chapter is dedicated to the principles of technology management. Briefly (and as shown in Figure 1.2) some information about the chapters is as follows:
Figure 1.2 Chapters overview
1.2.1 Chapter 2 OFDM and OFDMA
Chapter 2 looks into OFDM (orthogonal frequency division multiplexing) and OFDMA (OFD Multiple Access) techniques. OFDMA is at the heart of both 3GPP (Third Generation Project Partner) EPS and IEEE (Institute of Electrical and Electronics Engineers) WiMAX technologies. OFDMA is a departure from CDMA which is used in all the three 3G systems mentioned earlier. OFMDA is also the proposed multiple access technique for 4G mobile systems.
1.2.2 Chapter 3 3GPP Evolved Packet System (EPS)
Chapter 3 discusses 3GPP EPS technology that consists of a new radio access called E-UTRAN (Enhanced UMTS Terrestrial Radio Access Network) which is commonly known as 3G-LTE (Long Term Evolution) and an enhanced core network called EPC (Enhanced Packet Core). The radio interface of EPS that is, 3G-LTE is primarily discussed in this chapter along with its performance and key features. The evolution towards LTE-Advanced (4G candidate) is also briefly touched upon in the chapter.
1.2.3 Chapter 4 IEEE 802.16 WiMAX
The IEEE 802.16 WiMAX technology, the competitor to 3G-LTE is discussed in Chapter 4. The air interface of WiMAX along with its performance in the lab and field environments are presented. The WiMAX certification process conducted by WiMAX Forum and its evolution towards IEEE 802.16m (4G candidate) are also presented in the chapter.
1.2.4 Chapter 5 3GPP2 CDMA2000 1xEV-DO
Chapter 5 discusses 3GPP2 EV-DO (Evolution Data Optimized) technology which is based on CDMA. The two revisions of EV-DO (1xEV-DO Rev 0 and 1xEV-DO Rev A) have been deployed in many parts of the world and there are more than 145 million users of EV-DOEV-DO. The key features of these two single carrier technologies have been discussed in the chapter. Details of multicarrier EV-DOEV-DO Revision B along with its performance are provided. The key elements of UMB (Ultra Mobile Broadband) or EV-DO Revision C which is based on OFDMA are listed. After failing to get any meaningful support from the industry, UMB an evolution to EV-DO and a potential competitor to 3G-LTE and WiMAX has been discontinued. This failure has demanded the EV-DO industry to find a new evolution path and this has turned out to be 3GPP 3G-LTE for the most players. The evolution of EV-DO is discussed in detail in the chapter.
1.2.5 Chapter 6 IEEE 802.20 Mobile-Fi
Chapter 6 looks into IEEE 802.20 MobileFi technology, which is also known as MBWA (Mobile Broadband Wireless Access). It was initially proposed to counter WiMAX. Though the standard was completed in 2007, it has so far failed to develop into any meaningful industry support until the writing of this book. The chapter goes on to describe MBWA air interface, architecture and performance.
1.2.6 Chapter 7 Transmission Networks
The key aspects of transmission or transport systems are described in Chapter 7. The transmission networks can be divided into three segments, namely access (backhaul) network, metro or regional network and core (backbone) network. This segmentation is not standard and could vary from operator to operator and country to country. The key bottleneck of today’s broadband networks is mobile backhaul. A number of technological alternatives are provided to address this challenge. In addition, some backhaul planning guidelines are presented in the chapter as well. Several technologies that can be used in metro and backbone segments are also presented.
1.2.7 Chapter 8 Core Networks and OSS
Chapter 8 discusses two elements of the mobile networks, namely core networks and operational support systems. The evolution of 3GPP core networks with respect to different releases (Rel.99 to Rel.8) has been discussed in detail. We also briefly touched upon the core networks of EV-DO, WiMAX and MBWA. The role of various Standard Development Organizations (SDOs) and industry forums on OSS is discussed. Details of TMN (Telecommunications Management Network) and Next Generation OSS (NGOSS) are also provided in the chapter. Lastly, management reference models of both EPS and WiMAX are described in the episode.
1.2.8 Chapter 9 IMS, Services and Applications
Chapter 9 is divided into two segments – IMS (IP Multimedia Subsystem) and Advanced Applications. It provides details of 3GPP IMS and 3GPP2 MMD (Multi Media Domain). The role of other SDOs and Forums on IMS has been listed along with the concept of Common IMS that will address the interoperability between the different IMS standards and future IMS-enabled networks. It also looks into the challenges that have delayed the rollout of IMS and issues that have so far caused its absence in 3G networks. A number of advanced applications including M-Commerce, Mobile TV, Location based Services, and Machine to Machine have been extensively described in the chapter. Mobile Content Development is the next topic that is investigated followed by a list of key SDOs and Forums that are working on the development of these applications.
1.2.9 Chapter 10 Smart Wireless Devices
Chapter 10 looks into the various components of mobile wireless devices. The key aspects of multiple mobile software platforms including Symbian, Windows Mobile, Andriod, and so on, are described. The critical elements of RF (radio frequency) and baseband processors along with their integration are discussed. The additional device components that are discussed include speech coders, logic control, UICC (Universal Integrated Circuit Card), user interface and power supply. The importance of mobile device management and role of various device development SDOs and forums is highlighted. The chapter also looks into some mobile performance enhancement techniques including smart antennas, antenna diversity, interference cancellation, and so on. The last section provides snapshots of some smart 3GPP, 3GPP2, and WiMAX devices along with their key attributes.
1.2.10 Chapter 11 E2E Network Architecture and Mobility Management
This chapter describes the end-to-end network architecture of EPS and WiMAX. Next, aspects of mobility management of EPS and WiMAX along with their interworking with EV-DO are described. A section is dedicated to discuss key network interoperability challenges. Lastly, Fixed Mobile Convergence and the associated challenges are illustrated.
1.2.11 Chapter 12 Technology Management
Chapter 12 discusses various aspects of technology management and their relevance to mobile communications. The principles of TM like technology strategy, technology development, innovation management, cultural management, and so on, are described. Lastly, a hypothetical case involving a startup 4G radio equipment manufacturer is used to illustrate these various principles.
1.2.12 Chapter 13 Recap and Future Outlook
This chapter primarily focuses on eight topics – summarizing what has been discussed in the previous chapters, discussing 4G, justifying the enhanced mobile communications model presented in Chapter 1, briefly describing some key industry trends including Infrastructure Network Sharing, Convergence of Media and Mobile, Connecting the Next Billion Users and Renewal Energy, and finally providing a 30 000 foot view on the future of mobile communications.
Reference
1. Asif, S.Z. (2007) Wireless Communications Evolution to 3G and Beyond, Artech House, Inc., Norwood, MA.
Next Generation Mobile Communications Ecosystem: Technology Management for Mobile Communications Saad Z. Asif © 2011 John Wiley & Sons, Ltd
2
OFDM and OFDMA
2.1 Introduction
The wireless communications industry is evolving from circuit switched systems to all IP packet centric platforms. A common theme for this evolution is the use of OFDM (Orthogonal Frequency Division Multiplexing) and associated multiple access technique called OFDMA (Orthogonal Frequency Division Multiple Access). A major difference between 3G and NGMN (Next Generation Mobile Networks) is that all 3G networks are based on CDMA while NGMN (like 3G-LTE and WiMAX) are based on OFDMA. Thus, it becomes important that we learn about OFDM first before we dive into NGMN.1
Multi carrier modulation systems, of which OFDM is a key example, were first developed in the 1950s for military applications. However, the low cost implementation of OFDM only became possible with the advances in Digital Fourier Transform (DFT) in the 1980s. Further along in history, it was not until the 1990s that we witnessed the first wireless OFDM based standard – the Digital Audio Broadcasting (DAB). Next we highlight some historical perspectives [1] in the development of OFDM:
1958: Kineplex, a military multi-carrier high frequency communication system (R.R. Mosier and R.G. Clabaugh).1966: R. W. Chang at Bell Labs published the OFDM paper “Synthesis of band-limited orthogonal signals for multi-channel data transmission.”1970: First patent (US3488445 “Orthogonal Frequency Multiplex Data Transmission System”) issued to R. W. Chang on OFDM.1971: Weinstein and Ebert proposed the use of FFT (Fast Fourier Transform) and guard interval.1985: Cimini described use of OFDM for mobile communications.1985: Telebit Trailblazer Modem introduced incorporating a 512 carrier Packet Ensemble Protocol.1987: Alard & Lasalle: C-OFDM (Coded OFDM) for digital broadcasting.1988: Thomson-CSF LER, first experimental Digital TV link in OFDM in Paris.1989: First OFDM international patent application PCT/FR 1989/00546 “Emitter, Transmission Method and Receiver” was filed in the name of THOMSON-CSF, et al.1990: Thomson-CSF LER, first OFDM equipment field test, 34 Mbps in an 8 MHz channel in Paris area.1993: Morris: Experimental 150 OFDM wireless LAN (local area network).1994: US patent 5282222, “Method and apparatus for multiple access between transceivers in wireless communications using OFDM spread spectrum.”1995: ETSI DAB (Digital Audio Broadcasting), first OFDM based standard.1997: ETSI DVB-T (Digital Video Broadcasting- Terrestrial) standard.1999: IEEE 802.11a and HIPERLAN/2 wireless LAN standards.2000: Proprietary fixed wireless access (Vector-OFDM, Flash-OFDM, and so on).2002: IEEE 802.11g standard for wireless LAN.2004: IEEE 802.16-2004 standard for fixed wireless MAN (Fixed WiMAX).2004: ETSI DVB-H (Digital Video Broadcasting – Handheld) standard.2005: IEEE 802.16e (Mobile WiMAX) standard.2007: First demonstration of OFDMA based 3G-LTE air interface.2007: 3GPP2 specified OFDMA for Ultra Mobile Broadband (UMB) standard.2008: IEEE 802.20 (MobileFi) standard.2009: TeliaSonera launched first 3GPP 3G-LTE system in December.The focus of this chapter is on OFDM and OFDMA. In Section 2.2 a technical background on OFDM is presented while Section 2.3 discusses principles of OFDM. In the following two sections we list the advantages and impairments associated with OFDM. Section 2.6 provides a brief overview of OFDMA and Section 2.7 listed the justifications why OFDM is required for packet-based networks like NGMN. The concluding remarks are provided in Section 2.8.
2.2 Technical Background
A single carrier system modulates information onto one carrier by altering frequency, phase or amplitude of the carrier. For digital signals, the information is in the form of bits, or collections of bits called symbols, that are modulated onto the carrier. As higher bandwidths (data rates) are used, the duration of the bits or symbol (collection of bits) of information becomes smaller. The system becomes more susceptible to interference from external sources and losses due to impulse noise, signal reflection, and so on. The type of interference due to spurious emissions, inter-modulation products, and so on, is called frequency interference.
Frequency Division Multiplexing (FDM) extends the concept of SCM (single carrier modulation) by using multiple sub-carriers within the same single channel (spectrum). FDM allows the division of total data that needs to be sent into various sub-carriers offering various advantages over SCM. First, the data do not have to be divided evenly nor does it have to originate from the same information source. Second, it allows separate modulation/demodulation scheme to a particular type of data. Thirdly, having multiple narrowband sub-carriers instead of one wideband carrier simplifies the equalization2 process that operates upon a signal at the receiving end.
Beside the advantages, FDM does have some drawbacks, in particular the requirement of a guard band between modulated sub-carriers to prevent the spectrum of one subcarrier from interfering with another. Each sub-carrier is separated by a guard band to ensure that they do not overlap. These sub-carriers are then demodulated at the receiver by using filters to separate the bands (as shown in Figure 2.1). These guard bands lower the system’s effective information rate when compared to a single carrier system with similar modulation.
Figure 2.1 FDM with seven sub-carriers using filters
OFDM is a well known multi carrier modulation scheme used in 3GPP 3G-LTE, Wireless LANs, WiMAX and has been specified for 3GPP2 UMB and IEEE 802.20 MobileFi networks. Multi-carrier modulation is a method of transmitting data by splitting it into several components, and sending each of these components over separate carrier signals. The individual carriers have narrow bandwidth, but the composite signal can have broad bandwidth.
A functional block diagram of multi carrier modulation is shown in Figure 2.2. First, the serial data bits carrying information are converted to parallel bit streams. This simply means that a stream of data elements received in time sequence, that is, one at a time, are converted into a data stream consisting of multiple data elements transmitted simultaneously. Then, every block of N data bits entering the multi carrier modulation will be multiplexed onto N channels where each of these blocks is modulated by a different carrier signal. The carrier signals (φ1, φ2, φN) are carefully selected subject to various conditions and they differ from one scheme to another. Since the focus is on OFDM, these carrier signals will be orthogonal in time. In OFDM, the sub-carrier frequencies are chosen so that the sub-carriers are orthogonal to each other, meaning that cross-talk between the sub-channels is eliminated and inter-carrier guard bands are not required [2-4].
Figure 2.2 MCM scheme.
Reproduced with permission from Dawid and Rethnakaran © 2003 Synopsys [3].
2.3 Principles of OFDM
OFDM is a combination of modulation and multiplexing:
Modulation – a process of conveying a message signal inside another signal that can be physically transmitted. Modulation is the systematic variation of some attribute of the carrier, such as amplitude, phase, or frequency, in accordance with a function of the message signal.
Multiplexing – a process where multiple digital data streams are combined into one signal over a shared medium.
The letter O in OFDM implies orthogonality among the sub-carriers that results in the elimination of guard bands required by FDM. Once the sub carriers are made orthogonal to each other, the interference among them is also eliminated. The term orthogonality means that the sub-carriers are perpendicular to each other in a mathematical sense allowing the spectrum of each subcarrier to overlap another without interfering with it. Figure 2.3 shows the effect of orthogonality by reducing the bandwidth required as compared to FDM. The bandwidth is reduced by removing guard bands and allowing their spectra to overlap each other.
Figure 2.3 OFDM with seven sub-carriers.
2.3.1 OFDM System Model
OFDM is a multicarrier block modulation scheme where data symbols are grouped and transmitted in parallel by employing a large number of orthogonal sub-carriers. OFDM is realized through the Discrete Fourier Transform (DFT) and its inverse (IDFT). The computation of DFT and IDFT are themselves performed by Fast Fourier Transform (FFT) techniques.
Figure 2.4 shows the transmitter and receiver chain of an OFDM modem. Contrary to SCM, the OFDM modulation is performed on a block-by-block basis. At the transmitter, a block of source symbols in the frequency domain is first serial-to-parallel converted onto K sub-carriers. These sub-carriers are input to an IFFT (Inverse FFT) block that brings the signal into a time domain. The orthogonal waveform is carried out using an IFFT and a parallel to serial converter. The output of the converter is the summation of all sub-carriers. Following the converter, certain points (symbols) are appended to the beginning of the sequence as a cyclic prefix. The purpose is to allow multipath to settle before the main data arrives at the receiver. The length of the cyclic prefix is often equal to the guard interval. The resulting samples are then shaped, converted to analog and transmitted. Each transmitted block over the channel is referred to as on OFDM symbol [4,5].
Figure 2.4 OFDM system model.
Reproduced with permission from Li and Li © 2005 John Wiley and Sons, Ltd [5]
At the receiver, an FFT block is used to reverse the operation. In particular, the sampled signals are first processed to determine the starting point of a block and the proper demodulation window. Next, CP which also contains ISI (Inter symbol interference) is removed and then the sequence is serial to parallel converted. The converted sequence is input to the FFT. The output of the FFT are the symbols are modulated on the K sub-carriers, each multiplied by a complex channel gain. Finally, different demodulation schemes can be used to recover the information bits.
2.3.2 OFDM Mathematical Realization
As stated earlier, the computation of DFT and IDFT are themselves performed by Fast Fourier Transform (FFT) techniques. These mathematical operations are widely used for transforming data between the time-domain and frequency-domain. These transforms are interesting from the OFDM perspective because they can be viewed as mapping data onto orthogonal sub-carriers. The details on Fourier Transforms can be found in [6].
Consider a data block x(n), where n is the block index, consists of n data symbols that is,
A conventional OFDM modulation is employed at the transmitter. The baseband transmitted signal xk at the output of the IFFT can be written as [7]:
where is the data symbol, and e(j2πnk)/N, k = 0, 1, 2, …… , N − 1, represents the corresponding orthogonal frequencies of N sub-carriers. Thus, a group of n different data symbols is mapped onto N sub-carriers via the IFFT processor. Note that IFFT has TOFDM seconds to complete its operation. The duration TOFDM for an OFDM symbol is N. Ts, where Ts is the time period of a data symbol [3,7].
At the receiver, the OFDM signal is mixed with a local oscillator signal. Assuming it is Δf above the carrier frequency of the received OFDM signal due to a frequency estimation error or Doppler velocity, the baseband FFT demodulator output is given by:
where represents the received signal at the input to the FFT processor, ωk is the AWGN (Additive White Gaussian Noise), and dm is the output of the FFT processor. The term e(j2πk/N)ΔfT, k = 0, 1, 2, …, N − 1, represents the corresponding frequency offset of the received signal at the sampling instants, and ΔfT is the frequency offset to subcarrier frequency spacing ratio [7].
2.4 OFDM Advantages
OFDM has a number of advantages that work well in providing high speed data services for NGMN [2,5].
High Spectral Efficiency: OFDM achieves high spectral efficiency by using orthogonal sub-carriers. Orthogonality allows sub-carriers’ spectra to overlap which in turn enables transmission of more data than FDM over the same fixed bandwidth.Resistance against fading and interference: OFDM is relatively robust against interference since it usually affects only a fraction of the sub-carriers. Frequency-selective fading on the other hand can affect each subcarrier’s performance. However, since the bandwidth of each subcarrier is small, the performance loss of these sub-carriers can be accommodated with efficient coding. OFDM facilitates coding and interleaving across sub-carriers in the frequency domain that can provide robustness against burst errors.Reduced Computational Complexity: The FFT and IFFT reduce the modem complexity and the processing requirements grow only slightly higher than linearly with data rate or bandwidth. With the FFT, the number of operations in each OFDM symbol is in the order of N log2N. The implementation complexity of single carrier systems with an equalizer is at least NLe, where Le is the number of taps in the equalizer.Modulation and Coding: OFDM allows different modulation and coding schemes for each subcarrier. This capability improves the end-user performance in comparison to when only one modulation and one or few code rates are used. OFDM is well suited for adaptive modulation and coding, which allows the system to make the best of the available channel conditions.2.5 OFDM Impairments and Potential Remedies
This section will look into various impairments of the OFDM systems including frequency and phase offsets, channel estimations, phase noise, High PAPR (peak to average power ratio), and so on [2,4,5,8].
2.5.1 Frequency Offset
In communication systems a local oscillator (LO) and a mixer are used at the transmitter to convert lower frequencies onto a higher frequency carrier. The receiver reverses the operation to extract the lower frequency content. If the LOs at both ends do not use the exact same frequency, the result will be an offset in the frequency.
Frequency synchronization in OFDM is carried out in two phases, namely acquisition and tracking. The acquisition range is used in the initial phase while accuracy and stability is more important during the tracking stage. A frequency offset at the OFDM receiver can cause losses in subcarrier orthogonality, and thus introduce inter-channel interference (ICI). In Fourier transformation theory this phenomenon is known as DFT Leakage.
The two common frequency offset estimation methodologies are pilot-based and non-pilot based. To ensure an adequate acquisition range, many practical OFDM systems employ concentrated pilot symbols while continuous pilot sub-carriers are also available for frequency tracking purposes. Pilot-based approaches are more reliable and accurate than non-pilot (blind) based techniques. Whereas non-pilot techniques eliminate the overhead of the system which is associated with pilot-based approaches.
2.5.2 Phase Offset
The changes in the phase also cause offsets and loss of orthogonality at the receiver. Phase changes mainly occur due to multipath fading over the radio interface. The minor phase shifts can be corrected by an equalizer while larger ones can cause ambiguity in bit interpretations.
2.5.3 Sampling Offset
Sampling offset can occur in both time and frequency domains. A sampling time offset occurs if the transmitter and receiver are slightly out of sync. Due to this offset, the sampling of the received signal takes place at different times. This means that the samples taken at the receiver could not be perfectly matched to an OFDM symbol. The OFDM symbol boundaries can be distinguished by using a cyclic prefix. As long as the OFDM symbol boundaries are maintained, a sampling time offset is equivalent to a linear phase shift, which in most cases can be handled by the receiver.
A sampling frequency offset occurs when sampling takes place less frequently or more frequently than expected. In other words it occurs when the A/D converter output is sampled either too fast or too slow. In an OFDM system with many parallel sub-carriers, a sampling frequency offset on one sub-carrier causes inter-(sub)-carrier interference in the time domain, since one sampling interval overlaps that of another sub-carrier. It can be corrected by generating an error term that is used to drive a sampling rate converter.
2.5.4 High Peak to Average Power Ratio (PAPR)
A process OFDM signal can have large peaks resulting in a large dynamic range and a high PAPR. For multi-carrier systems, the PAPR value is often expressed in terms of statistics because the probability that all sub-carriers will simultaneously reach peak amplitude is low, even though the simultaneous peak amplitude value is large. If the received signal level is very high it can saturate receiver amplifiers or D/A converters; the result will be a distorted signal. The distortion will increase the SNR needed to maintain adequate performance. Linearity requirements in both the receiver and transmitter must be adjusted to account for PAPR. One way to combat a high PAR on the downlink is to leave the sub-carriers empty that do not need to send information. Thus, no unnecessary energy is added to the transmitted signal.
2.5.5 Phase Noise
The phase noise effects the OFDM signal reception in two ways namely inter-carrier interference (ICI) and common phase error (CPE). The ICI can be modeled as Gaussian noise (additive white noise) and it is difficult to remove due to its noise-like characteristics. CPE rotates all sub-carriers equally and can be easily corrected by estimating such rotation through continuous pilot tones embedded in OFDM symbols.
2.5.6 I/Q Imbalance
Commonly, the OFDM signals are combined with high order modulation (64-Quadrature Amplitude Modulation) to maximize spectral efficiency and achieve broadband data rates. Sophisticated signal processing algorithms are needed to avoid imperfections that are typically present in low-cost direct conversion RF receivers.
The analog in-phase and quadrature (I/Q) modulators and demodulators are often used in OFDM communications. These I/Q modulators and demodulators have imperfections that result in an imperfect match between the two baseband signals, I and Q, which represent the complex carrier. For example, gain mismatch might cause the “I” signal to be slightly smaller than the “Q.”
When the frequency response of the baseband I and Q channel signal paths are different, and I/Q channel mismatch takes place, there is a [5] proposed a pilot-based scheme to determine the compensation parameters for I/Q imbalance estimation.
2.6 Multi Access Scheme OFDMA
Channelization protocols are commonly used in today’s cellular and high speed data services. The communications between the devices and base station take place using multiple channels. The channel is defined by how the frequency, time and code domains are divided and shared by terminals and base station. Currently TDMA (Time Division Multiple Access), FDMA (Frequency Division Multiple Access) and CDMA (Code Division Multiple Access) are the three major medium access control schemes used in the cellular world. TDMA and FDMA were used in analog mobile phone systems and in 2G digital GSM systems while CDMA is used in three 3G systems namely W-CDMA, CDMA2000 and TD-SCDMA (China 3G standard).
FDMA was deemed unsuitable for broadband applications since each user occupies multiple frequencies to transmit data and those frequencies cannot be used by other users. However, the rise of OFDM contributed by the less complex implementation procedures of IFFT/FFT, give FDMA an opportunity to become a multiple access scheme for broadband communications. The use of IFFT/FFT allows systems and terminals to combine multiple frequencies (sub-carriers) at the baseband leading to OFDMA (Orthogonal Frequency Division Multiple Access).
OFDMA is a modulation and access technique that combines both TDMA and FDMA technologies. OFDMA works by assigning a subset of sub-carriers (subchannels) to individual users. Each OFDMA user transmits symbols using sub-carriers that remain orthogonal to those of other users. More than one subcarrier can be assigned to one user to support high rate applications. It provides multiplexing of user data streams onto the downlink subchannels and uplink multiple access by means of uplink subchannels.
2.7 Why OFDMA for NGMN
OFDMA has a number of advantages over other multiple access schemes which has led to its adoption for NGMN. In particular, OFDMA and MIMO (Multiple Input Multiple Output) are synergistically integrated to offer broadband services. It also plays a key role in enabling Multiple Antenna technologies at the base station and subscribers’ stations. Some key attributes of OFDMA are as follows [5].
In OFDMA, the multiple access is not only supported in the time domain by means of OFDM symbols, but also in the frequency domain by means of sub-carriers (Figure 2.5), just like traditional FDMA minus the guard band overhead. As a result it can support more users and gives less delay.Figure 2.5 OFDMA in frequency and time domain.
Reproduced from Li and Li © 2005 John Wiley and Sons, Ltd [5]
2.7.1 OFDMA Advantages
A lot of R&D hours have been invested in finding the true potential of different multiple access schemes. OFDMA which is the newest of the three (TDMA and CDMA being the other two) has been recognized as the most feasible multiple access technique for broadband data services, as we will see in this section. OFDMA provides a number of advantages over CDMA and TDMA but at the same time they do have some shortcomings as discussed earlier. We will briefly discuss the key advantages of OFDMA over TDMA and CDMA in this section [9].
2.7.1.1 Scalability
On the top of the list is the scalability factor that OFDMA provides over CDMA and TDMA. OFDMA subcarrier structure supports a wide range of bandwidth. The scalability is achieved by adjusting FFT size3 to channel bandwidth while fixing the sub-carrier frequency spacing. For example, in WiMAX, sub-carrier spacing is fixed to 10.94 kHz while FFT size varies (128, 256, 512, 1024, 2048) with the different channel bandwidth sizes (1.25, 2.5, 5, 10, 20 MHz) respectively.
One immediate advantage stemming from scalability is the flexibility of deployment. OFDMA systems can be deployed in various frequency band intervals to flexibly address the need for various spectrum allocation and usage model requirements. TDMA and CDMA based systems however, do not provide such flexibility in the traditional sense. For example, CDMA2000 and EV-DO mainly offer 1.25 MHz channel bandwidth while channel bandwidth is fixed to 5 MHz in WCDMA and HSPA systems.
2.7.1.2 Robustness to Multipath
In OFDMA systems, subchannels maintain orthogonality in multi-path channels. The number of multi-path components does not limit the performance of the system as long as all these multi-paths are within the cyclic prefix window. OFDMA systems therefore more robust towards multipath effects than other multiple access schemes.
In CDMA systems, RAKE receivers only have a fixed number of receive fingers and one finger corresponds to one multipath component. After detecting the multipath components the Rake receiver coherently combines them. RAKE receivers operate based on the assumption that the average interference in a large window is small. The assumption can lead to incorrect conclusions due to the presence of other impairments such as frequency offset, Doppler effect4 and lack of time synchronization. The CDMA interference can be mitigated by equalizer, however complexity increases rapidly with system bandwidth. Therefore, in broadband wireless systems where multipath effect is very common, OFDMA systems are considered to be more robust and less complex than CDMA systems.
2.7.1.3 Downlink Multiplexing
OFDMA, due to its orthogonal nature, does not require very robust power control and can utilize maximum available power in downlink transmission. When channel is frequency selective, OFDMA allows users to be scheduled to their best subchannels respectively within the same OFDMA symbol while the TDMA system does not have such flexibility.
2.7.1.4 Uplink Multiple Access
OFDMA uplink access is performed through orthogonal sub-channels. By eliminating intra-cell interference, an OFDMA system can achieve higher reverse-link capacity than a traditional CDMA system. OFDMA uplink can also take advantage of frequency selectivity the same way as downlink does by allocating best sub-channels to the respective access users to further improve the overall system performance.
2.7.1.5 Smart Antenna Benefits
Smart Antenna techniques MIMO (Multiple Input Multiple Output), Receive Diversity and Transmit Diversity can be applied to both CDMA and OFDMA systems. These techniques provide higher capacities as well as better coverage.
For CDMA systems, the function of RAKE receiver makes it harder to deploy MIMO systems in its full capacity. However, CDMA networks do incorporate antenna receive diversity both at the base station and at the mobile station. Since MIMO gives higher capacities and better spectral efficiencies than the receive diversity technique, OFDMA systems are fundamentally superior to CDMA systems.
2.7.1.6 Spectral Efficiency
When the operator has 10 MHz or more bandwidth, OFDMA based systems are more spectral efficient than CDMA systems. If bandwidth is less than 5 MHz, then CDMA provides higher spectral efficiency than OFDMA systems. Beyond high traffic metro areas, OFDM-based systems are not as such economical since the spectrum and network will most likely remain under utilized.
2.7.1.7 Higher Capacity
In OFDMA, the influence of narrow-band interference is not the same for all users. The consequence of this is that some users can operate at higher interference values than others, and the number of users which can operate at a given performance level is an increasing function of the signal-to-interference ratio (SNR). The results indicated in [9] showed that OFDMA can accommodate a significant number of users at SNR values far below those which break TDMA and CDMA.
2.8 Summary Insights
This chapter provided an overview of OFDM and OFDMA which are and expected to be used with Next Generation Networks. The principles of OFDM, pros and cons and remedies for the impairments were presented. The benefits of OFDMA over CDMA and TDMA were also provided. Both the Next Generation Mobile Technologies that is, 3G-LTE and WiMAX are based on OFDMA; the thing that industry is to waiting to see whether or not OFDMA in its current form will become part of IMT-Advanced (4G) networks or will the industry unveil a totally out of the box solution (access scheme) for futuristic 4G/5G networks.
References
1. Wikipedia. available at http://en.wikipedia.org/wiki/Main_Page.
2. Edstrom, P. 2007) MS Thesis COS/CCS 2007-19: Overhead impacts on long-term evolution radio networks. KTH Information and Communication Technology, May 31.
3. Dawid, H., and Rethnakaran, P. 2003) Orthogonal frequency division multiplexing Digital Communication Solutions, Synopsys Inc, November 1.
4. Liwin, L., and Pugel, M. 2001) The Principles of OFDM. RF Design Magazine, January.
5. Li, H., and Li, G. 2005) OFDM-Based Broadband Wireless Networks: Design and Optimization, John Wiley & Sons Inc., Malden, MA.
6. Ludeman, L.C. 1986) Fundamentals of Digital Signal Processing, Harper & Row Publishers, Inc., New York, NY.
7. Yeh, H., Chang, Y., and Hassibi, B. 2007) A scheme for cancelling intercarrier interference using conjugate transmission in multicarrier communication systems. IEEE Transactions on Communications, 6(1),3–7.
8. Cutler, B. 2002) Effects of physical layer impairments on OFDM systems RF Design Magazine, May.
9. Moeneclaey, M., Baldel, M., and Sari, H. 2001) Sensitivity to multiple-access techniques to narrow band interference. IEEE Transactions on Communications, 49(3), 497–505.
10. Alamouti, S., and H. Yin 2006) OFMDA: A Broadband Wireless Access Technology. 2006 IEEE Sarnoff Symposium, Nassau Inn in Princeton, NJ, USA, March 27–28, pp. 1–4.
1 We have mainly considered EPS and WiMAX as part of NGMN. Next Generation Mobile Communications Ecosystem: Technology Management for Mobile Communications Saad Z. Asif ©2011 John Wiley & Sons, Ltd
2 Equalization is the process of using passive or active electronic elements or digital algorithms for the purpose of altering (originally flattening) the frequency response characteristics of a system. An equalization filter is a filter, usually adjustable, meant to compensate for the unequal frequency response of some other signal processing circuit or system [1].
3 FFT size is the length of FFT.
4 The Doppler effect (or Doppler shift) is the change in frequency of a wave for an observer moving relative to the source of the wave.
3
3GPP Evolved Packet System (EPS)
3.1 Introduction
UMTS (Universal Mobile Telecommunication System) refers to the interconnection of a new type of Radio Access Network, the UTRAN (UMTS Terrestrial Radio Access Network), to the adapted pre-Release 99 GSM/GPRS Core Network infrastructure. A new radio interface called W-CDMA (Wideband Code Division Multiple Access) was specified in Release 99. From there onwards, multiple releases have been standardized to continue the evolution of UMTS. HSPA (High Speed Packet Access) was the next step in the evolution and it was standardized in Releases 5-6. After HSPA, 3GPP has also defined Evolved HSPA (HSPA+) in Release 7. The longer term evolution of UMTS/HSPA networks has been named as EPS (Evolved Packet System). EPS is composed of E-UTRAN (Evolved UTRAN) and EPC (Evolved Packet Core) which are commonly known as 3G-LTE (Long Term Evolution) and SAE (System Architecture Evolution) respectively. E-UTRAN is focused on the evolution of the Radio Access Network while EPC looks into the future needs of the core network. EPS is defined primarily in 3GPP Release 8 which was completed in December 2008.
Chapter 3 primarily focuses on E-UTRAN as defined in Release 8, its performance aspects and its evolution. The second section looks into the different releases of 3GPP while the third and fourth sections describe the LTE objectives and LTE air interface respectively. Layers 1–3 are described in Sections 5–7 whereas the key attributes of LTE are listed in Section 3.8. EPS overall architecture and test results are presented in Sections 3.9 and 3.10 respectively. The roadmap of LTE, industry outlook and summary of the chapter are presented in Sections 3.11–3.13 respectively.
3.2 3GPP Releases
The evolution of GSM systems has been standardized by 3GPP in several releases, starting from Release 1999 (R99) and moving towards Release 4 (Rel-4), Release 5 (Rel-5) all the way to Release 10 (Rel-10). Each release primarily corresponds to a new radio access technology, but not always, as can be witnessed from Figure 3.1. These releases also include enhancements to the previous radio technologies and to the rest of the network that were introduced in the earlier releases. This section will highlight some of the key features that have been introduced from Rel-99 to Release-7. Enhancements that are part of Rel-8 and Rel-9 are discussed in Section 3.3 3GPP LTE while Rel-10 enhancements are discussed in the Section 3.10 3GPP Roadmap Evolution:
R99: First WCDMA enabler with voice and data support and was functionally frozen in March 2000.Rel-4: First 3GPP release that supports EDGE (Enhanced Data Rates for GSM Evolution) and TD-SCDMA (Time Division – Synchronous CDMA) and was functionally frozen in March 2001.Rel-5: First 3GPP release that supports HSDPA (High Speed Downlink Packet Access), IP transport in radio access network and IP Multimedia Subsystem (IMS) and was functionally frozen in June 2002.Rel-6: Release 6 is the first 3GPP release that supports HSUPA (High Speed Uplink Packet Access) and was functionally frozen in March 2005.Rel-7: HSPA+ radio technology was first defined in Release 7 and its activities were frozen as of December 2007.Rel-8: First 3GPP release that supports EPS and was functionally frozen in December 2008.Rel-9 and Rel-10: These releases are still in operation and have not been frozen.Figure 3.1 3GPP releases.
Note: DL = Downlink; UL = Uplink
3.2.1 Key Aspects of Rel-99
W-CDMA [1] was the first step towards 3G for GSM-based 2G/2.5G systems. The major difference between W-CDMA and GSM/GPRS systems was in terms of multiple access technique. W-CDMA utilized CDMA while GSM/GPRS and even EDGE applied the principles of FDMA and TDMA. The key highlights of W-CDMA and R-99 are as follows [2]:
New Radio: CDMA based UTRAN was introduced as an evolution to GSM. CDMA, the new access technique, supports both FDD and TDD modes of duplex. An advanced BSC termed as RNC (Radio Network Controller) was also part of R-99. The radio channels in W-CDMA are 5 MHz wide as compared to the 200 kHz channels of GSM/GPRS. The chip rate1 is 3.84 Mcps (mega chips per second) and frame length is 10 ms.Higher Data Rates Support: Another key enhancement of 3G systems is the support for higher data rates in both downlink and uplink. R-99 supports up to 2 Mbps in both directions in a 5 MHz channel.Handovers: The W-CDMA systems have the capability to handover to GSM/GPRS networks where UMTS coverage is not available.Core Network backward compatibility: The R99 inherits a lot from the GSM model on the core network side. The core network of R99 is an evolution of GSM core network which is based on MAP (Mobile Application Part). In addition to UTRAN, R99 also supports the legacy GSM BSS radio access network. This backward compatibility feature assists the legacy mobiles to operate in 3GPP R99 networks in a seamless fashion.3.2.2 Key Aspects of Rel-4
Rel-4 is associated with the inception of TD-SCDMA (Time Division Synchronous CDMA) and EDGE (Enhanced Data rates for GSM Evolution) radio technologies. The details of 3GPP Rel-4 can be found in [3].
Support for EDGE: EDGE is a TDM-based technology that provides the evolution for 2G IS-136 and GSM systems. GERAN or GSM/EDGE Radio Access Network is capable of supporting 473.6 kbps with 8-PSK (Phase Shift Keying) modulation scheme. EDGE does not require a new spectrum and it is also known as EGPRS (Enhanced GPRS) since it can coexist with GPRS provided necessary upgrades are implemented. It uses the same network elements, interfaces, protocols and procedures as GPRS with minor differences primarily in the RAN and mobility management.Support for TD-SCDMA: TD-SCDMA or UTRA/UMTS-TDD 1.28 Mcps Low Chip Rate (LCR), is China’s home grown 3G technology. The TD-SCDMA radio interface is integrated in 3GPP Rel-4 and is part of IMT-TC (IMT-Time Code) family of air interfaces. TD-SCDMA is based on CDMA, supports 2 Mbps in a 1.6 MHz channel bandwidth and uses UMTS core network. The details on TD-SCDMA can be found in [1].Support for a variety of mobile equipment: Rel-4 network architecture supports a variety of handheld devices ranging from voice (circuit-switched) only handsets to multimedia terminals and data air-cards (for laptops), and so on.Improved Speech Support in CS Domain: Rel-4 features enhanced speech support, for example with Transcoder-Free Operation and Tandem Free Operation.2 These enhancements provide transmission efficiency and cost reduction in the core network and are applicable to both GSM and UMTS systems.3.2.3 Key Aspects of Rel-5
The two key features of Rel-5 are IMS (IP Multimedia Subsystem) and HSDPA (High Speed Downlink Packet Access). The details of Rel-5 can be found in [4] while some brief information is as follows:
New Radio HSDPA: In Rel-5, techniques like adaptive modulation and coding, hybrid ARQ (automatic repeat request), and so on, help in facilitating HSDPA [1]. It supports a peak data rate of 14.4 Mbps and 384 kbps in downlink and uplink respectively.Support for IMS: Rel-5 supports a special core network subsystem, which is called the IMS [1]. The IMS is an open signaling system, based on standard Internet technology, which supports the migration of Internet applications (like VoIP, video conferencing, messaging, etc.) to the mobile environment and offers enhanced service control capabilities. All IMS entities are located in the Core Network. These entities and procedures are used to support real-time and multimedia IP applications using Session Initiation Protocol (SIP).GERAN Iu-ps Interface: Rel-5 introduces the Iu-ps interface for GERAN, which allows GERAN to connect directly to the UMTS packet core network.
