lte part i: core network - IEEE Xplore

LYT-GUEST EDIT-Bogineni

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GUEST EDITORIAL

LTE PART I: CORE NETWORK

Kalyani Bogineni

Reiner Ludwig

Preben Mogensen

Vojislav Vucetic

Byung K. Yi

Zoran Zvonar

C

urrent cellular networks based on Third Generation Partnership Project (3GPP) and 3GPP2 technologies provide evolution from circuit-switched technologies, originally developed for voice communications, to packetswitched technologies. Next-generation networks need to deliver IP-based services (voice, video, multimedia, data, etc.) for all kinds of user terminals while moving between fixed (fiber, DSL, cable) and wireless (3GPP-based, 3GPP2-based, IEEE-based) access technologies, and roaming between various operator networks. Users expect the network to originate, terminate, and maintain a session while the user is moving and roaming. Services have to be delivered to users based on serving network functionality (quality of service [QoS], bandwidth, etc.), availability, and user preferences. The network and users must be protected through various authentication, encryption, and other security mechanisms at the access, network, and application layers. Mobility has to be provided through coordinated link, network, and application layer mobility mechanisms that ensure user expectations of service performance are met. Requirements on the radio technology include improved performance as well as reduced system and device complexity. 3GPP Release 8 specifies the architecture to meet the above requirements. 3GPP has finalized the Release 8 specifications of the 3GPP evolved packet system (EPS). The two key work items of 3GPP Release 8 are the service architecture evolution (SAE) and long term evolution (LTE). The standardization work on those two work items, which started in

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Vish Nandlall

2005, has led to specifications of the evolved packet core (EPC) and a new radio access network referred to as the evolved universal terrestrial radio access network (EUTRAN). The completion of the SAE/LTE Release 8 specifications represents a milestone in the development of standards for the mobile broadband industry. The EPC is a multi-access core network based on the Internet Protocol (IP) that enables operators to deploy and operate one common packet core network for 3GPP radio access (LTE, 3G, and 2G), non-3GPP radio access (HRPD, WLAN, and WiMAX), and fixed access (Ethernet, DSL, cable, and fiber). The EPC is defined around the three important paradigms of mobility, policy management, and security. The EPC provides user terminals with optimized handover schemes between different radio access technologies (e.g., between LTE and HRPD). Standardized roaming interfaces enable operators to offer their subscribers global services connectivity across a range of different access technologies. The network-controlled and class-based QoS concept of the EPC is based on 3GPP’s policy and charging control (PCC) framework. This maximizes operator control over all PCC/QoS functions that are distributed across different network elements, including the user terminal. The LTE radio access is based on orthogonal frequency-division multiplexing (OFDM) and supports different carrier frequency bandwidths (1.4–20 MHz) in both frequency-division duplex (FDD) and time-division duplex (Continued on page 42)

IEEE Communications Magazine • February 2009


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GUEST EDITORIAL (Continued from page 40) (TDD) modes. This provides great flexibility for operators to use existing and future radio spectrum allocations. The LTE radio access is based on shared channel access providing peak data rates of 75 Mb/s in the uplink direction and 300 Mb/s in the downlink direction. Improved coverage and battery lifetime have been key goals in the development of the LTE specifications. Unlike the 2G/3G 3GPP radio access networks, which are connected to the circuit-switched domain of the 3GPP core network, the EUTRAN is only connected to the EPC. The E-UTRAN protocols and user plane functions have therefore been optimized for the transmission of traffic from IP-based real-time and non-real-time applications/services. Part I of this Feature Topic will focus on the 3GPP Release 8 EPC, the standard that is the flat SAE architecture. This new architecture is designed to optimize network performance, reduce total cost of ownership, increase cost efficiency, and facilitate the uptake of mass market IP-based services. The system is considered “flat” as there are only two nodes in the SAE architecture user plane: the LTE base station (eNodeB) and the gateway, as shown in Fig. 1. The flat architecture reduces the number of nodes involved in the signaling and media paths. With incorporation of radio network controller (RNC) functionality inside eNodeB, handovers will be negotiated and managed directly between eNodeBs, which will mimic those currently employed in 3G UTRAN networks. A key difference from current networks is that the EPC is defined to support IP packet-switched traffic only. Interfaces are based on IP protocols. This means that all services will be delivered through packet connections, including voice. To this end, voice call continuity between circuit-switched voice systems and packet-switched voice over IP systems has received particular attention in Release 8. It is assumed that voice services will be implemented through the use of an IP multimedia subsystem (IMS). The article “Voice Call Handover Mechanisms in Next-Generation 3GPP Systems,” coauthored by Apostolis Salkintzis, Mike Hammer, Itsuma Tanaka, and Curt Wong, provides an overview of the voice call handover techniques and mechanisms that enable handover at any time in the call. They also present scenarios in handover that are also known as single radio voice call continuity (SR-VCC) and circuit-switched fallback (CSFB). The techniques described in this article enable mobility and service continuity between existing and future access networks; that is, interworking from E-UTRAN access to UTRAN/GERAN or 1xRTT access. Access selection is based on combinations of operator policies, user preferences, and access network conditions Existing 3GPP (GSM and WCDMA/HSPA) and 3GPP2 (CDMA 1xRTT, EVDO) systems are integrated with the EPS through standardized interfaces providing optimized mobility with LTE. This means a signaling interface between the signaling GPRS service node (SGSN) and the evolved core network for 3GPP systems, and a signaling interface between the code-division multiple access (CDMA) RAN and the EPC for 3GPP2 systems. Such integration will support both dual and single radio handover

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2G/3G

LTE

CDMA/GSM/UMTS Control Plane

User Plane HA / GGSN

PDSN / SGSN

Control Plane

User Plane

Serving / PDN gateway

MME

BSC / RNC

BTS / NodeB

eNodeB

■ Figure 1. From hierarchical to a simpler, flatter network.

and allow for flexible migration to LTE. It should also be noted that wireless LAN or WiMAX radio access could also be integrated into the EPC. The article “NetworkBased Mobility Management in the Evolved 3GPP Core Network,” coauthored by Irfan Ali, Alessio Casati, Kuntal Chowdhury, Katsutoshi Nishida, Eric Parsons, Stefan Schmid, and Rahul Vaidya, covers network mobility and functions that enable operators to provide a common set of services and mobility at the IP layer across various access networks. Release 8 also includes a class-based QoS concept. This provides a simple yet effective solution for operators to offer differentiation between packet services. The policy and charging rules function (PCRF) handles QoS management, and also controls rating and charging. Subscriber management and security is the responsibility of the home subscriber server (HSS). Javier Pastor, Stefan Rommer, and John Stenfelt authored the article “Policy and Charging Control in the Evolved Packet System,” and address how to provide access agnostic policy control that can be applied to a variety of access networks, including EUTRAN, UTRAN, GERAN, eHRPD, and WiMAX. This article covers an overview of policy and control functions and the corresponding implementation in EPS 3GPP Release 8. The article “QoS Control in 3GPP Evolved Packet System,” authored by Hannes Ekström, is about QoS concepts that enable network operators and service providers with effective techniques to enable subscriber and services differentiation, and maintain the QoS across the end-to-end systems. The security mechanisms in wireless systems were essential functional elements of GSM and UMTS. Howev-



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GUEST EDITORIAL er, most of the focus was placed on the radio path. Through evolution of cellular systems, security aspects have evolved to include several network functionalities as well. In EPS architecture, security is more robust in order to encompass end-to-end security both in the radio as well as the core, and additionally spanning across multiple access networks (inter Radio Access Technology). The article “Network Access Security in Next Generation 3GPP Systems” by C. B. Sankaran is a tutorial covering key attributes that are essential for services offered by the operator related to network access security, including inter-radio access technology (inter-RAT). Several trial activities in LTE are already underway globally. The article “Multisite Field Trial for LTE and Advanced Concepts,” coauthored by Ralf Irmer, HansPeter Mayer, Andreas Weber, Volker Braun, Michael Schmidt, Michael Ohm, Andre Zoch, Carsten Jandura, Patrick Marsch, and Gerhard Fettweis, presents LTE performance in a multisite field trial. It includes an overview of LTE standards, and the industry alliances and initiatives driving the requirements and performance (e.g. NGMN and LSTI). Among the requirements defined by NGMN for LTE are increased peak and average data rates, reduced latency, high spectral efficiency, and cell edge throughput. Results from simulation and field tests are provided in this article on key performance indicators such as throughput and latency. Radio interface physical layer features enabling performance, including vhannel coding and physical channel mapping, MIMO diversity, as well as UE physical layer capabilities, are presented in the results. As summarized above, Part I covers several key aspects of the EPS architecture. Part II of this Feature Topic will focus on RAN technology and standards.

BIOGRAPHIES KALYANI BOGINENI ([email protected]) is principal architect at Verizon Communications with extensive experience in architecture and design of telecommunications networks for wireless and wireline technologies as well as various application technologies. She has published extensively in IEEE/ACM peer-reviewed journals and conferences. She has been on the Technical Program Committees for several conferences, and has been a reviewer for various IEEE journals and magazines for over 18 years. She is an active speaker on next-generation converged networks at various conferences and panels. Recently she has been active in the development of 3GPP standards for 4G technologies focused on the development of converged networks for multiple access technologies with IP-based mobility management mechanisms, policy-driven roaming architectures, and converged security architectures. She has B.Tech and M.E. degrees in electrical engineering, an M.S. degree in computer engineering, and a Ph.D. in electrical and computer engineering. REINER LUDWIG received his Diploma and doctoral degree in computer science from the University of Technology, Aachen, Germany, in 1994 and 2000, respectively. He joined Ericsson in 1994 working within the Research Department on cross-layer aspects of wireless packet-based networks. He has worked within the Internet Engineering Task Force (IETF), where he coauthored standards on operating end-to-end protocols across wireless access networks. More recently, he has been actively involved in the standardization of the policy and QoS framework of the 3GPP EPS, including link layer aspects of the LTE radio access. He currently holds an expert posi-


tion in the Systems and Technology Department of Ericsson’s Business Unit Networks, where he is responsible for policy and QoS control for fixed and mobile access networks. P REBEN M OGENSEN received his M.Sc.E.E. and Ph.D. degrees in 1988 and 1996, respectively, from Aalborg University (AAU), Denmark. Since 1999 he has been a part time professor in the Department of Electronic Systems, AAU, where he heads the Radio Access Technology (RATE) research section. He also holds a part time position as principal engineer at Nokia Siemens Networks, Aalborg, where he is involved in LTE and LTE-Advanced standardization research. He is author or co-author of more than 170 technical publications within a wide range of areas, including radio wave propagation, advanced antenna technologies, receiver design, frequency assignment, radio resource management, and packet scheduling. VISH NANDLALL is the chief technical officer for Carrier Networks at Nortel. He is responsible for Nortel’s technology vision in 4G and in particular LTE, and has shaped Nortel's product and standards strategy in this field, advocating seamless intertechnology handoff and flat network topologies. He has spent the last 15 years in architecture roles within Nortel, most recently as chief architect for Nortel's CDMA and EVDO wireless access division, contributing to the launch of high-speed data services in North America and Eastern Europe. Prior to his life in wireless, he contributed to Nortel's Metro Optical and DMS product lines, providing key technologies in core computing and private line services. His current research is in cross-layer design for cellular interference control and scheduling in direct relay systems. VOJISLAV VUCETIC received his Ph.D. degree from Imperial College, London, United Kingdom. In 1988 he joined AT&T Bell Laboratories, where he worked on software design and software architecture for data communications systems, and network designs for data carrier networks internationally. In 1998 he joined Cisco, where he worked as a consulting engineer supporting U.S.-based and international service providers. He also contributed to metro Ethernet and cable-based VoIP development activities. Currently he is a senior manager in the Carrier Standards and Architecture group. He leads a group that is responsible for coordinating industry and standards activities with Cisco carriers’ development organizations and service providers. His current focus is on architecture and protocols for accessagnostic IP-based networks to support 3GPP, 3GPP2, WiMaX, and other access technologies. BYUNG K. YI, senior executive vice president of LG Electronics, has over 32 years of experience in research and development of communication and space systems. He has been working on 3G and 4G wireless communication systems. He served as TSG-C chair of 3GPP2 for two terms, developing cdma2000 air interface specifications, and served as a co-chair of Working Group 5 of 3GPP2 TSG-C, developing 1xEV/DV wireless standards. Under his leadership, TSG-C published three important air interface standards, cdma2000 Rev. D, and High Rate Packet Data (HRPD) Revs. A and B. He is currently heading the LGE North America R&D center, developing mobile terminals for North American carriers. He was in charge of small satellite system engineering for distributed low earth orbiting telecommunication and remote sensing applications at Orbital and CTA as a chief engineer. He taught graduate courses for nine years at George Washington University as an adjunct professor. His current interests are wireless and space communication systems, iterative decoding, and space system engineering. He holds eight U.S. patents and five international patents in the areas of iterative decoding and handoff schemes for cellular-based systems. ZORAN ZVONAR () is director of systems engineering, MediaTek Wireless, and a MediaTek Fellow. He received a Dipl.Ing. in 1986 and an M.S. degree in 1989 from the Department of Electrical Engineering, University of Belgrade, Serbia, and a Ph.D. degree in electrical engineering from Northeastern University, Boston, Massachusetts, in 1993. From 1994 to 2008 he pursued industrial carrier within Analog Devices. He was a member of the core development team for the baseband platform and RF direct conversion transceiver wireless product families, and has been a recipient of the company’s highest technical honor of ADI Fellow. Since January 2008 he has been with MediaTek focused on the design of algorithms and architectures for cellular standards, with applications to integrated chip set solutions and real-time software. He is the Editor of the Radio Communications Series in IEEE Communications Magazine and has served as Guest Editor and the member of the editorial boards for a number of professional journals in wireless communications.

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