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(4G) cellular, including LTE, is the latest in an ongoing series of innovations that respond to ever-changing wireless market
demands, which began with analog cellular almost 30 years ago.
First Generation Cellular Networks
All of the First Generation (1G) mobile systems provided voice services based on analogue radio transmission techniques.
These first generation technologies used Frequency Division Multiple Access (FDMA), which had inherent limitations in the
use of radio channels.
Second Generation Cellular Networks
Second Generation (2G) mobile
systems are characterized by digitization and compression of speech. This allowed many more mobile users to be accommodated
in the radio spectrum through either time (GSM) or code (IS-95 CDMA) multiplexing.
Third Generation Cellular Networks
The Third Generation (3G) cellular networks
appeared in 2000, with the first commercial deployment launched by DoCoMo on Oct. 1, 2001, and was designed to offer high
speed data and multimedia connectivity to users. A distinct difference between 2G and 3G technologies was the appearance of
a packet data core network, where the access network was shared by circuit and packet domains.
4G Networks – the next step
The overall goal of 4G systems is to provide
a converged network compatible with the Next Generation Network (NGN) vision of convergence. This kind of network integrates
mobility management, security and QoS management mechanisms for both fixed and mobile broadband accesses, independent of the
access technology. Though the Release 8 version of LTE does not strictly meet the ITU's definition of a 4G system, its architecture
and underlying technologies provide a solid foundation for the Release 10 (R10) LTE-Advanced system, which does describe
a fully compliant 4G system.
The figure below illustrates a simplified view of the overall LTE architecture which is marked by the elimination
of the circuit-switched domain and a simplified access network. The functional entities depicted in this figure can be physically
co-located, or reside in dedicated hardware according to the network operator's needs.
The LTE system is comprised of two networks:
the E-UTRAN and the Evolved Packet Core (EPC). The result is a system characterized by its simplicity, a non-hierarchical
structure for increased scalability and efficiency, and a design optimized to support real-time IP-based services.
The access network, E-UTRAN is characterized
by a network of Evolved-NodeBs (eNBs) which support OFDMA and advanced antenna techniques. Each eNB, having an IP address,
is part of the all-IP network. In the absence of radio network controllers, which were present in earlier generation access
networks, the eNBs in LTE collaborate to perform functions such as handover and interference mitigation.
Similarly, the all-IP packet core network enables the deployment
and efficient delivery of packet-oriented multimedia services, through the IP Multimedia Subsystem (IMS). This results in
lower costs and rapid deployment of new services for network operators.
While there are recognizable parallels to the 3GPP UMTS packet core network, the
EPC is a significant departure from the legacy packet core which enables growth in packet traffic, higher data rates, and
lower latency, and support for interworking with several wireless access technologies.
The EPC Architecture
LTE's packet domain is called the Evolved
Packet Core (EPC). It is a flat all-IP system designed for:
Much higher packet data rates
The ability to optimize packet flows within all kinds of operational scenarios
having to do with bandwidth rationing and charging schemes
Explicit support for multiple radio access technologies in the interests of seamless
nodes are defined to meet these goals: the Mobility Management Entity (MME), the Home Subscriber Server (HSS), the Serving
Gateway (S-GW), the Packet Data Network Gateway (P-GW), the Policy and Charging Rules Function (PCRF), and the evolved Packet
Data Gateway (ePDG).
Somewhat analogous to the distribution
of control and bearer data of the MSC found in 3GPP R4, LTE separates control from bearer in the design of the EPC. The Mobility
Management Entity (MME), which supports many functions for managing mobiles and their sessions, also controls establishment
of EPS bearers in the selected gateways.
The Serving Gateway (S-GW) is responsible for anchoring the user plane for inter-eNB handover and inter-3GPP mobility.
An S-GW functionally resembles a 3G SGSN without the mobility and session control features. It routes data packets between
the P-GW and the E-UTRAN.
Packet Data Network Gateway (P-GW) acts as a default router for the UE, and is responsible for anchoring the user plane for
mobility between some 3GPP access systems and all non-3GPP access systems.
The Home Subscriber Server is the master data base that stores subscription-related
information to support call control and session management entities.
The Policy and Charging Control Function (PCRF) is the single point of policy-based
QoS control in the network. It is responsible for formulating policy rules from the technical details of Service Date Flows
(SDF) that will apply to a user's services, and then passing these rules to the P-GW for enforcement. The evolved Packet
Data Gateway (ePDG) is used for interworking with un-trusted non-3GPP IP access systems.
IMS – Key to Service Delivery
3GPP has developed a complete service network system for mobile networks,
which they call the IP Multimedia Subsystem (IMS). It is a complete, SIP-based control architecture that includes charging,
billing and bandwidth management. As such, it defines its own formal interfaces with the IETF for any protocol extensions.
The IP Multimedia Subsystem (IMS) is
intended to occupy the core of tomorrow's converged networks. The IMS is the chief enabler that could accelerate network convergence
with the promise of flexible service delivery. Mobile operators will count on LTE to implement cost-effective network changes
as preparation for IMS. Deploying SIP-based control architectures on broadband wireless IP-based LTE naturally implies services
ought to reside in the IMS.
to 4G Core Network Migration
With operators worldwide deploying High Speed Packet
Access (HSPA) services, 3G has finally arrived and is now gaining momentum. As 3G enjoys its success, the evolution in the
radio and core network space continues with Long Term Evolution (LTE) and Evolved Packet System (EPS) leading the way forward
to the 4G revolution. The heralded “anytime, anywhere” access and entertainment medium shall become a reality
The mobile video and mobile TV era,
with “always on” expectations, brings in the need for a robust and modular network infrastructure that can help
get new voice and data services to market at lower cost and in less time than in the current reality. But, while the 4G revolution
is focusing on the air interface and access network side of the equation, the core network also has to revive itself with
new architecture enhancements in order to keep up with seemingly unrealistic data speeds and related issues. How the evolved
core sustains the challenge will be key in determining the user experience of new services.
This paper talks about the shift of existing infrastructure for 3G core to 4G,
and the benefits and impact on the communications industry of AdvancedTCA on the wireless core network.
3G Core Network Realities
Today’s wireless industry aims at providing voice and data services in the next generation of converging communications
networks. The goal is the performance gain to meet the demands of ever increasing data speeds and network traffic at lower
operational costs. The specific requirement is to build stable and flexible infrastructure that leverages open, standards-based
interfaces that enable “Triple Play” voice, video, and data. Before we discuss implementation specific, however,
let’s start with an overview of 3G core network functional elements.
The 3G packet core architecture consists of the Universal Mobile Telecommunications System (UMTS) packet-switched
(PS) domain – or General Packet Radio Service (GPRS) Support Nodes (GSN), the Gateway GSN (GGSN) and the Serving GSN
(SGSN). These elements constitute the interface between the radio system and fixed networks for packet-switched services.
The GSN performs all necessary functions in order to handle the packet transmission to and from the mobile stations.
The SGSN (Serving GPRS Support Node) supports mobility management
functions within the network. The signaling and packet data from the access nodes, namely the Radio Network Controller (RNC),
is forwarded to the SGSN. The SGSN handles functions of data packet processing, such as forwarding, tunneling the data to
the GGSN in the user plane, along with the control plane functions of authentication, SS7 signaling to the HLR, and mobility
management. An SGSN platform requires computing capability for processing the signaling messages as well as network interface
modules to handle intensive control protocol processing and to support the interfaces to the other network elements.
An SGSN platform also needs high performance packet processing capacity to tunnel the data in the user plane. Similarly,
a GGSN (Gateway GPRS Support Node) has to take care of intensive packet processing, channeling the data in and out of the
wireless network to the external packet data entities.
In a Cutt Newsletter (2004) issue it is mentioned that while current 3G services
are working to enable transactional wireless communications like location-based services, wireless shopping, personal services,
email and multimedia data transfer, these are at much lower speeds compared to the 100 MBPS to 1 GBPS of 4G. As demand builds
for high-quality, streaming video and audio, only 4G systems will be able to accommodate growing consumer and business expectations.
Japan, China and South Korea plan to work together with developing new technologies like fourth-generation mobile phones says
Japanese local papers.
Ongoing talks have been underway for the last several months
to discuss how to work together in the best possible way including
those for the 2008 Beijing Olympics and future Internet systems, said an official at the
telecommunications ministry.A 4G orientated meeting was held in Seoul in March with officials from the above countries, where they agreed to
share information and work together on developing 4G mobile phones. In Eliza Evans and others (2004) the implications
of 4G network are discussed in detail.
They predict that if implemented, the projected 4G technology may facilitate
a true IP cellular network. 4G mobile phone technology supports Internet Protocol version 6 (IPv6) and promises faster communication
speeds (100 megabits per second), capacity and diverse usage formats. These formats would provide richer content and support
for other public networks such as optical fibre and wireless local area networks. 4G is currently only an ideal.
Still, some companies are incorporating new technological advances into cellular technology, something that some companies
are calling “3.5G.” 3.5G technology, the convergence of cellular and wireless LAN technologies, has led to a handset
that makes calls using Voice over Internet Protocol (VoIP) when a 802.11 network is available (for example, when at home or
at the office), then switches to a 3G cellular network when mobile.
4G networks may replace all existing 2.5G and 3G networks, perhaps even before a full deployment of 3G. Multiple 3G standards
are springing up that would make it difficult for 3G devices to be truly global. A strong need exists to combine both the
wireless (LAN) concept and cell or base station wide area network design.
4G is seen as the solution that will bridge that gap and thereby provide a much
more robust network.