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					                                                  GUEST EDITORIAL

                                      LTE PART I: CORE NETWORK

     Kalyani Bogineni    Reiner Ludwig       Preben Mogensen        Vish Nandlall

     Vojislav Vucetic      Byung K. Yi          Zoran Zvonar

C      urrent cellular networks based on Third Generation
       Partnership Project (3GPP) and 3GPP2 technolo-
gies provide evolution from circuit-switched technologies,
                                                                 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 (E-
originally developed for voice communications, to packet-        UTRAN). The completion of the SAE/LTE Release 8
switched technologies. Next-generation networks need to          specifications represents a milestone in the development of
deliver IP-based services (voice, video, multimedia, data,       standards for the mobile broadband industry.
etc.) for all kinds of user terminals while moving between          The EPC is a multi-access core network based on the
fixed (fiber, DSL, cable) and wireless (3GPP-based,              Internet Protocol (IP) that enables operators to deploy
3GPP2-based, IEEE-based) access technologies, and roam-          and operate one common packet core network for 3GPP
ing between various operator networks. Users expect the          radio access (LTE, 3G, and 2G), non-3GPP radio access
network to originate, terminate, and maintain a session          (HRPD, WLAN, and WiMAX), and fixed access (Ether-
while the user is moving and roaming. Services have to be        net, DSL, cable, and fiber). The EPC is defined around
delivered to users based on serving network functionality        the three important paradigms of mobility, policy manage-
(quality of service [QoS], bandwidth, etc.), availability, and   ment, and security. The EPC provides user terminals with
user preferences. The network and users must be protect-         optimized handover schemes between different radio
ed through various authentication, encryption, and other         access technologies (e.g., between LTE and HRPD). Stan-
security mechanisms at the access, network, and applica-         dardized roaming interfaces enable operators to offer their
tion layers. Mobility has to be provided through coordinat-      subscribers global services connectivity across a range of
ed link, network, and application layer mobility                 different access technologies. The network-controlled and
mechanisms that ensure user expectations of service per-         class-based QoS concept of the EPC is based on 3GPP’s
formance are met. Requirements on the radio technology           policy and charging control (PCC) framework. This maxi-
include improved performance as well as reduced system           mizes operator control over all PCC/QoS functions that
and device complexity. 3GPP Release 8 specifies the archi-       are distributed across different network elements, includ-
tecture to meet the above requirements.                          ing the user terminal.
   3GPP has finalized the Release 8 specifications of the           The LTE radio access is based on orthogonal frequen-
3GPP evolved packet system (EPS). The two key work               cy-division multiplexing (OFDM) and supports different
items of 3GPP Release 8 are the service architecture evo-        carrier frequency bandwidths (1.4–20 MHz) in both fre-
lution (SAE) and long term evolution (LTE). The stan-            quency-division duplex (FDD) and time-division duplex
dardization work on those two work items, which started in                                            (Continued on page 42)

40                                                                                  IEEE Communications Magazine • February 2009
                                                 GUEST EDITORIAL

(Continued from page 40)
                                                                           2G/3G                                    LTE
(TDD) modes. This provides great flexibility for operators
to use existing and future radio spectrum allocations. The           CDMA/GSM/UMTS
LTE radio access is based on shared channel access pro-              Control            User                  Control        User
viding peak data rates of 75 Mb/s in the uplink direction             Plane             Plane                  Plane         Plane
and 300 Mb/s in the downlink direction. Improved cover-
age and battery lifetime have been key goals in the devel-                      HA /                             Serving / PDN
                                                                               GGSN                                gateway
opment 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 E-
UTRAN is only connected to the EPC. The E-UTRAN
protocols and user plane functions have therefore been                         PDSN /
                                                                                SGSN                            MME
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 architec-
ture. This new architecture is designed to optimize net-                       BSC /
work performance, reduce total cost of ownership, increase                     RNC
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
                                                                                BTS /
Fig. 1. The flat architecture reduces the number of nodes                      NodeB                                eNodeB
involved in the signaling and media paths. With incorpora-
tion of radio network controller (RNC) functionality inside
eNodeB, handovers will be negotiated and managed
                                                                I Figure 1. From hierarchical to a simpler, flatter network.
directly between eNodeBs, which will mimic those current-
ly employed in 3G UTRAN networks.
    A key difference from current networks is that the EPC      and allow for flexible migration to LTE. It should also be
is defined to support IP packet-switched traffic only. Inter-   noted that wireless LAN or WiMAX radio access could
faces are based on IP protocols. This means that all ser-       also be integrated into the EPC. The article “Network-
vices will be delivered through packet connections,             Based Mobility Management in the Evolved 3GPP Core
including voice. To this end, voice call continuity between     Network,” coauthored by Irfan Ali, Alessio Casati, Kuntal
circuit-switched voice systems and packet-switched voice        Chowdhury, Katsutoshi Nishida, Eric Parsons, Stefan
over IP systems has received particular attention in Release    Schmid, and Rahul Vaidya, covers network mobility and
8. It is assumed that voice services will be implemented        functions that enable operators to provide a common set of
through the use of an IP multimedia subsystem (IMS). The        services and mobility at the IP layer across various access
article “Voice Call Handover Mechanisms in Next-Genera-         networks.
tion 3GPP Systems,” coauthored by Apostolis Salkintzis,            Release 8 also includes a class-based QoS concept. This
Mike Hammer, Itsuma Tanaka, and Curt Wong, provides             provides a simple yet effective solution for operators to
an overview of the voice call handover techniques and           offer differentiation between packet services. The policy
mechanisms that enable handover at any time in the call.        and charging rules function (PCRF) handles QoS manage-
They also present scenarios in handover that are also           ment, and also controls rating and charging. Subscriber
known as single radio voice call continuity (SR-VCC) and        management and security is the responsibility of the home
circuit-switched fallback (CSFB). The techniques described      subscriber server (HSS). Javier Pastor, Stefan Rommer,
in this article enable mobility and service continuity          and John Stenfelt authored the article “Policy and Charg-
between existing and future access networks; that is, inter-    ing Control in the Evolved Packet System,” and address
working from E-UTRAN access to UTRAN/GERAN or                   how to provide access agnostic policy control that can be
1xRTT access. Access selection is based on combinations         applied to a variety of access networks, including E-
of operator policies, user preferences, and access network      UTRAN, UTRAN, GERAN, eHRPD, and WiMAX. This
conditions                                                      article covers an overview of policy and control functions
    Existing 3GPP (GSM and WCDMA/HSPA) and 3GPP2                and the corresponding implementation in EPS 3GPP
(CDMA 1xRTT, EVDO) systems are integrated with the              Release 8. The article “QoS Control in 3GPP Evolved
EPS through standardized interfaces providing optimized         Packet System,” authored by Hannes Ekström, is about
mobility with LTE. This means a signaling interface             QoS concepts that enable network operators and service
between the signaling GPRS service node (SGSN) and the          providers with effective techniques to enable subscriber
evolved core network for 3GPP systems, and a signaling          and services differentiation, and maintain the QoS across
interface between the code-division multiple access             the end-to-end systems.
(CDMA) RAN and the EPC for 3GPP2 systems. Such inte-               The security mechanisms in wireless systems were
gration will support both dual and single radio handover        essential functional elements of GSM and UMTS. Howev-

42                                                                                       IEEE Communications Magazine • February 2009
                                                               GUEST EDITORIAL

er, most of the focus was placed on the radio path.                              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
Through evolution of cellular systems, security aspects                          mobile access networks.
have evolved to include several network functionalities as
well. In EPS architecture, security is more robust in order                      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
to encompass end-to-end security both in the radio as well                       has been a part time professor in the Department of Electronic Systems,
as the core, and additionally spanning across multiple                           AAU, where he heads the Radio Access Technology (RATE) research section.
                                                                                 He also holds a part time position as principal engineer at Nokia Siemens
access networks (inter Radio Access Technology). The                             Networks, Aalborg, where he is involved in LTE and LTE-Advanced stan-
article “Network Access Security in Next Generation                              dardization research. He is author or co-author of more than 170 technical
3GPP Systems” by C. B. Sankaran is a tutorial covering                           publications within a wide range of areas, including radio wave propaga-
                                                                                 tion, advanced antenna technologies, receiver design, frequency assign-
key attributes that are essential for services offered by the                    ment, radio resource management, and packet scheduling.
operator related to network access security, including
inter-radio access technology (inter-RAT).                                       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,
   Several trial activities in LTE are already underway                          and has shaped Nortel's product and standards strategy in this field, advo-
globally. The article “Multisite Field Trial for LTE and                         cating seamless intertechnology handoff and flat network topologies. He
                                                                                 has spent the last 15 years in architecture roles within Nortel, most recently
Advanced Concepts,” coauthored by Ralf Irmer, Hans-                              as chief architect for Nortel's CDMA and EVDO wireless access division, con-
Peter Mayer, Andreas Weber, Volker Braun, Michael                                tributing to the launch of high-speed data services in North America and
Schmidt, Michael Ohm, Andre Zoch, Carsten Jandura,                               Eastern Europe. Prior to his life in wireless, he contributed to Nortel's Metro
                                                                                 Optical and DMS product lines, providing key technologies in core comput-
Patrick Marsch, and Gerhard Fettweis, presents LTE per-                          ing and private line services. His current research is in cross-layer design for
formance in a multisite field trial. It includes an overview                     cellular interference control and scheduling in direct relay systems.
of LTE standards, and the industry alliances and initiatives
                                                                                 VOJISLAV VUCETIC received his Ph.D. degree from Imperial College, London,
driving the requirements and performance (e.g. NGMN                              United Kingdom. In 1988 he joined AT&T Bell Laboratories, where he
and LSTI). Among the requirements defined by NGMN                                worked on software design and software architecture for data communica-
                                                                                 tions systems, and network designs for data carrier networks international-
for LTE are increased peak and average data rates,                               ly. In 1998 he joined Cisco, where he worked as a consulting engineer
reduced latency, high spectral efficiency, and cell edge                         supporting U.S.-based and international service providers. He also con-
throughput. Results from simulation and field tests are                          tributed to metro Ethernet and cable-based VoIP development activities.
                                                                                 Currently he is a senior manager in the Carrier Standards and Architecture
provided in this article on key performance indicators such                      group. He leads a group that is responsible for coordinating industry and
as throughput and latency. Radio interface physical layer                        standards activities with Cisco carriers’ development organizations and ser-
features enabling performance, including vhannel coding                          vice providers. His current focus is on architecture and protocols for access-
                                                                                 agnostic IP-based networks to support 3GPP, 3GPP2, WiMaX, and other
and physical channel mapping, MIMO diversity, as well as                         access technologies.
UE physical layer capabilities, are presented in the results.
                                                                                 BYUNG K. YI, senior executive vice president of LG Electronics, has over 32
   As summarized above, Part I covers several key aspects                        years of experience in research and development of communication and
of the EPS architecture. Part II of this Feature Topic will                      space systems. He has been working on 3G and 4G wireless communica-
focus on RAN technology and standards.                                           tion 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
                              BIOGRAPHIES                                        leadership, TSG-C published three important air interface standards,
                                                                                 cdma2000 Rev. D, and High Rate Packet Data (HRPD) Revs. A and B. He is
KALYANI BOGINENI (Kalyani.Bogineni@VerizonWireless.com) is principal archi-      currently heading the LGE North America R&D center, developing mobile
tect at Verizon Communications with extensive experience in architecture         terminals for North American carriers. He was in charge of small satellite
and design of telecommunications networks for wireless and wireline tech-        system engineering for distributed low earth orbiting telecommunication
nologies as well as various application technologies. She has published          and remote sensing applications at Orbital and CTA as a chief engineer. He
extensively in IEEE/ACM peer-reviewed journals and conferences. She has          taught graduate courses for nine years at George Washington University as
been on the Technical Program Committees for several conferences, and            an adjunct professor. His current interests are wireless and space communi-
has been a reviewer for various IEEE journals and magazines for over 18          cation systems, iterative decoding, and space system engineering. He holds
years. She is an active speaker on next-generation converged networks at         eight U.S. patents and five international patents in the areas of iterative
various conferences and panels. Recently she has been active in the devel-       decoding and handoff schemes for cellular-based systems.
opment of 3GPP standards for 4G technologies focused on the develop-
ment of converged networks for multiple access technologies with IP-based        ZORAN ZVONAR () is director of systems engineering, MediaTek Wireless, and
mobility management mechanisms, policy-driven roaming architectures,             a MediaTek Fellow. He received a Dipl.Ing. in 1986 and an M.S. degree in
and converged security architectures. She has B.Tech and M.E. degrees in         1989 from the Department of Electrical Engineering, University of Bel-
electrical engineering, an M.S. degree in computer engineering, and a Ph.D.      grade, Serbia, and a Ph.D. degree in electrical engineering from Northeast-
in electrical and computer engineering.                                          ern University, Boston, Massachusetts, in 1993. From 1994 to 2008 he
                                                                                 pursued industrial carrier within Analog Devices. He was a member of the
REINER LUDWIG received his Diploma and doctoral degree in computer sci-          core development team for the baseband platform and RF direct conver-
ence from the University of Technology, Aachen, Germany, in 1994 and             sion transceiver wireless product families, and has been a recipient of the
2000, respectively. He joined Ericsson in 1994 working within the Research       company’s highest technical honor of ADI Fellow. Since January 2008 he
Department on cross-layer aspects of wireless packet-based networks. He          has been with MediaTek focused on the design of algorithms and architec-
has worked within the Internet Engineering Task Force (IETF), where he co-       tures for cellular standards, with applications to integrated chip set solu-
authored standards on operating end-to-end protocols across wireless             tions and real-time software. He is the Editor of the Radio Communications
access networks. More recently, he has been actively involved in the stan-       Series in IEEE Communications Magazine and has served as Guest Editor
dardization of the policy and QoS framework of the 3GPP EPS, including           and the member of the editorial boards for a number of professional jour-
link layer aspects of the LTE radio access. He currently holds an expert posi-   nals in wireless communications.

IEEE Communications Magazine • February 2009                                                                                                                 43

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