7/30/2019 129454451 Lelliwa LTE Technology
1/323
Table of Contents
3
LTE/LTE/LTE/LTE/EEEEPSPSPSPSTechnologyTechnologyTechnologyTechnology
Book revision 4.0.2
TableofContentsTableofContentsTableofContentsTableofContentsChapterChapterChapterChapter PagePagePagePage
1. Introduction ....... 5
2. Architecture .. 27
3. OFDMA & SC-FDMA ..... 49
4. E-UTRAN ..... 95
5. Core Network .... 133
6. Policy control & charging ..... 167
7. Traffic cases .. 177
8. Security . 213
9. EPS Management .. 237
10. Services ..... 249
11. CS Fallback and SMSoSGs .. 297
12. Acronyms & abbreviations ....... 313
7/30/2019 129454451 Lelliwa LTE Technology
2/323
LTE/EPS Technology
4
This page is intentionally left blank
7/30/2019 129454451 Lelliwa LTE Technology
3/323
1 Introduction
5
ChapterChapterChapterChapter1111
IntroductionIntroductionIntroductionIntroduction
TopicTopicTopicTopic PagePagePagePage
Introduction........................................................................................................7
HSPA + ............................................................................................................12
LTE / E-UTRAN.............................................................................................. 17
EPS / SAE........................................................................................................24
IMS ..................................................................................................................25
7/30/2019 129454451 Lelliwa LTE Technology
4/323
LTE/EPS Technology
6
This page is intentionally left blank
7/30/2019 129454451 Lelliwa LTE Technology
5/323
1 Introduction
7
IntroductionIntroductionIntroductionIntroductionThis chapter discusses the evolution and migration of wireless-data
technologies from EDGE to LTE as well as the evolution of underlying
wireless approaches. Progress happens in multiple phases, first with EDGE,
and then UMTS, followed by evolved 3G capabilities such as HSDPA,
HSUPA, HSPA+, and eventually LTE. Meanwhile, underlying approaches
have evolved from TDMA to CDMA, and now from CDMA to Orthogonal
Frequency Division Multiple Access (OFDMA), which is the basis of Long
Term Evolution (LTE).
TDMA,CDMAandOFDMATDMA,CDMAandOFDMATDMA,CDMAandOFDMATDMA,CDMAandOFDMA
Many times, one technology or the other is positioned as having fundamental
advantages over another. However, any of these three approaches, when fully
optimized, can effectively match the capabilities of any other. For example,
GSM, which is based on TDMA, thanks to innovations like synchronized
frequency hopping, AMR, and EDGE for data performance optimisation,
GSM is able to effectively compete with the capacity and data throughput of
CDMA based systems.
Today, the main question is whether OFDM provide any inherent advantage
over TDMA or CDMA. For systems employing less than 10 MHz of
bandwidth, the answer no. Because it transmits mutually orthogonal
subchannels at a lower symbol rate, the fundamental advantage of OFDM is
that it elegantly addresses the problem of Inter Symbol Interference (ISI)
induced by multipath and greatly simplifies channel equalization. As such,
OFDM systems, assuming they employ all the other standard techniques for
maximizing spectral efficiency, may achieve slightly higher spectral
efficiency than CDMA systems. However, advanced receiver architectures,including options such as practical equalization approaches and interference
cancellation techniques, are already commercially available in chipsets and
can nearly match this performance advantage. It is with larger bandwidths (10
to 20 MHz), and in combination with advanced antenna approaches such as
Multiple Input Multiple Output (MIMO) or Adaptive Antenna Systems
(AAS), that OFDM enables less computationally complex implementations
than those based on CDMA.
Hence, OFDM is more readily realizable in mobile devices. However, studies
have shown that the complexity advantage of OFDM may be quite small (that
is, less than a factor of two) if frequency domain equalizers are used for
7/30/2019 129454451 Lelliwa LTE Technology
6/323
LTE/EPS Technology
8
CDMA-based technologies. Still, the advantage of reducing complexity is one
reason 3GPP chose OFDM for its LTE project. It is also one reason newer
WLAN standards, which employ 20 MHz radio channels, are based on
OFDM. In other words, OFDM is currently a favoured approach underconsideration for radio systems that have extremely high peak rates. OFDM
also has an advantage in that it can scale easily for different amounts of
available bandwidth. This in turn allows OFDM to be progressively deployed
in available spectrum by using different numbers of subcarriers.
An OFDMA technology such as LTE can also take better advantage of wider
radio channels (for example, 10 MHz) by not requiring guard bands between
radio carriers (for example, HSPA carriers). In recent years, the ability of
OFDM to cope with multipath has also made it the technology of choice for
the design of Digital Broadcast Systems (DBS).
In 5 MHz of spectrum, as used by UMTS/HSPA, continual advances with
CDMA technology (realized in HSPA+) through approaches such as
equalization, MIMO, interference cancellation, and high-order modulation
will allow CDMA to largely match OFDMA-based systems.
Because OFDMA has only modest advantages over CDMA in 5 MHz
channels, the advancement of HSPA is a logical and effective strategy. In
particular, it extends the life of operators large 3G investments, reducing
overall infrastructure investments, decreasing capital and operational
expenditures, and allowing operators to offer competitive services.
3GPPevolutionaryapproach3GPPevolutionaryapproach3GPPevolutionaryapproach3GPPevolutionaryapproach
Rather than emphasizing any one wireless approach, 3GPPs evolutionary
plan is to recognize the strengths and weaknesses of every technology and to
exploit the unique capabilities of each one accordingly. GSM, based on a
TDMA approach, is mature and broadly deployed. Already extremely
efficient, there are nevertheless opportunities for additional optimizations and
enhancements.
Standards bodies have already defined evolved EDGE, that doubles the
performance of current EDGE systems.
The evolved data systems for UMTS, such as HSPA and HSPA+, introduce
enhancements and simplifications that help CDMA based systems match the
capabilities of competing systems, especially in 5 MHz spectrum allocations.
Given some of the advantages of an OFDM approach, 3GPP has specified
OFDMA as the basis of its LTE effort. LTE incorporates best-of-breed radio
techniques to achieve performance levels beyond what will be practical with
CDMA approaches, particularly in larger channel bandwidths. However, in
the same way that 3G coexists with 2G systems in integrated networks, LTE
7/30/2019 129454451 Lelliwa LTE Technology
7/323
1 Introduction
9
systems will coexist with both 3G systems and 2G systems. Multimode
devices will function across LTE/3G or even LTE/3G/2G, depending on
market circumstances.
2006 2007 2008 2009 2010 2011
3GPP GSM EDGE Radio Access Network Evolution
3GPP UMTS Radio Access Network Evolution
EDGE
DL: 474 kbps
UL: 474 kbps
Evolved EDGE
DL: 1.9 Mbps
UL: 947 kbps
HSDPA
DL: 14.4 Mbps
UL: 384 kbps
In 5 Mhz
HSDPA/HSUPA
DL: 14.4 Mbps
UL: 5.76 Mbps
In 5 Mhz
Rel 7 HSPA+
DL: 28 Mbps
UL: 11.5 Mbps
In 5 Mhz
Rel8 HSPA+
DL: 42 Mbps
UL: 11.5 Mbps
In 5 Mhz
3GPP Long Term Evolution
LTE 2X2 MIMO
DL: 173 MbpsUL: 58 Mbps
In 20 Mhz
LTE 4X4 MIMO
DL: 326 MbpsUL: 86 Mbps
In 20 Mhz
EV-DO Rev 0DL: 2.4 MbpsUL: 153 kbps
In 1.25 Mhz
EV-DO Rev ADL: 3.1 MbpsUL: 1.8 Mbps
In 1.25 Mhz
EV-DO Rev BDL: 14.7 MbpsUL: 4.9 Mbps
In 5 Mhz
UMB 2X2 MIMODL: 140 MbpsUL: 34 Mbps
In 20 Mhz
CDMA 2000 Evolution
UMB 4X4 MIMODL: 280 MbpsUL: 68 Mbps
In 20 Mhz
Fixed WiMAX
Wave 1DL: 23 Mbps
UL: 4 Mbps
10 Mhz3:1 TDD
Wave 2DL: 46 Mbps
UL: 4 Mbps
10 Mhz3:1 TDD
Mobile WiMAX Evolution
IEEE 802.16m
Figure 1-1 Different wireless technologies and their evolution
The development of GSM and UMTS/HSPA happens in stages referred to as
3GPP releases, and equipment vendors produce hardware that supports
particular versions of each specification. It is important to realize that the
3GPP releases address multiple technologies. For example, R7 optimizes
VoIP for HSPA but also significantly enhances GSM data functionality with
Evolved EDGE. A summary of the different 3GPP releases follows:
Release 99 ( completed) - First deployable version of UMTS.
Enhancements to GSM data (EDGE). Provides support for
GSM/GPRS/EDGE/WCDMA radio-access networks.
Release 4 (completed). Multimedia messaging support. First steps
toward using IP transport in the CN.
Release 5 (completed): HSDPA. First phase of IMS. Full ability to useIP-based transport instead of just ATM in the CN.
Release 6 (completed): HSUPA. Enhanced multimedia support
through Multimedia Broadcast/Multicast Services (MBMS).
Performance specifications for advanced receivers. WLAN integration
option. IMS enhancements. Initial VoIP capability.
Release 7 (completed): Provides enhanced GSM data functionality
with Evolved EDGE. Specifies HSPA Evolution (HSPA+), which
includes higher order modulation and MIMO. Also includes fine-
tuning and incremental improvements of features from previous
7/30/2019 129454451 Lelliwa LTE Technology
8/323
LTE/EPS Technology
10
releases. Results include performance enhancements, improved
spectral efficiency, increased capacity, and better resistance to
interference. Continuous Packet Connectivity (CPC) enables efficient
always-on service and enhanced uplink VoIP capacity as well asreductions in call setup delay for PoC. Radio enhancements include 64
QAM in the downlink DL and 16 QAM in the uplinks.
Release 8 (under development): Further HSPA Evolution features
such as simultaneous use of MIMO and 64 QAM. Specifies OFDMA-
based 3GPP LTE. Defines Evolved Packet System (EPS), previously
called System Architecture Evolution (SAE).
CoreCoreCoreCore----NetworkEvolutionNetworkEvolutionNetworkEvolutionNetworkEvolution
3GPP is defining a series of enhancements to the CN to improve network
performance and the range of services provided and to enable a shift to all-IP
architectures. One way to improve CN performance is by using flatter
architectures. The more hierarchical a network, the more easily it can be
managed centrally; however, the trade-off is reduced performance, especially
for data communications, because packets must traverse and be processed by
multiple nodes in the network. To improve data performance and, in
particular, to reduce latency, 3GPP has defined a number of enhancements in
R7 and R8 that reduce the number of processing nodes and result in a flatter
architecture.
In R7, an option called one-tunnel architecture allows operators to configure
their networks so that user data bypasses a serving node and travels directly
via a gateway node. There is also an option to integrate the functionality of
the RNC controller directly into the NodeB.
For R8, 3GPP has defined an entirely new CN, called the Evolved Packet
System (EPS), earlier known under different name System Architecture
Evolution (SAE).
The key features and capabilities of EPS include:
reduced latency and higher data performance through a flatter
architecture,
support for both LTE radio access networks and interworking with
GERAN/UTRAN,
the ability to integrate non-3GPP networks such as WiMAX,
optimization for all services provided via IP,
7/30/2019 129454451 Lelliwa LTE Technology
9/323
1 Introduction
11
ServiceEvolutionServiceEvolutionServiceEvolutionServiceEvolution
Not only do 3GPP technologies provide continual improvements in capacity
and data performance, they also evolve capabilities that expand the services
available to subscribers. Key service advances include Fixed-Mobile
Convergence (FMC), IMS, and broadcasting technologies. This section
provides an overview of these topics, and the appendix provides greater detail
on each of these items.
FMC refers to the integration of fixed services (such as telephony provided by
wire line or WiFi) with mobile cellular-based services. Though FMC is still in
its early stages of deployment by operators, it promises to provide significant
benefits to both users and operators. For users, FMC will simplify how they
communicate, making it possible for them to use one device (for example, a
cell phone) at work and at home, where it might
connect via a WiFi network or a femtocell. When mobile, users connect via a
cellular network. Users will also benefit from single voice mailboxes and
single phone numbers as well as the ability to control how and with whom
they communicate. For operators, FMC allows the consolidation of core
services across multiple-access networks. For instance, an operator could
offer complete VoIP-based voice service that supports access
via DSL, WiFi, or 3G. FMC has various approaches, including enabling
technologies such as Unlicensed Mobile Access (UMA), femtocells, and IMS.
With 3GGP UMA, GSM/UMTS devices can connect via WiFi or cellularconnections for both voice and data.
An alternative to using WiFi for the fixed portion of FMC is femtocells.
These are tiny base stations that cost little more than a WiFi access point and,
like WiFi, femtocells leverage a subscriber's existing wire line broadband
connection (for example, DSL). Instead of operating on unlicensed bands,
femtocells use the operators licensed bands at very low power levels. The
key advantage of the femtocell approach is that any single mode mobile
communications device a user has can now operate using the femtocell.
IMS is another key technology for convergence. It allows access to coreservices and applications via multiple-access networks. IMS is more powerful
than UMA, because it supports not only FMC but also a much broader range
of potential applications. Though defined by 3GPP, both 3GPP2 and WiMAX
have adopted IMS. IMS allows the creative blending of different types of
communications and information, including voice, video, IM, presence
information, location, and documents. It provides application developers the
ability to create applications that have never before been possible, and it
allows people to communicate in entirely new ways by dynamically using
multiple services. For example, during an interactive chat session, a user
could launch a voice call. Or during a voice call, a user could suddenly
7/30/2019 129454451 Lelliwa LTE Technology
10/323
LTE/EPS Technology
12
establish a simultaneous video connection or start transferring files. While
browsing the Web, a user could decide to speak to a customer-service
representative. IMS will be a key platform for all-IP architectures for both
HSPA and LTE.Another important new service is support for mobile TV through what is
called multicast or broadcast functions. 3GPP has defined multicast/broadcast
capabilities for both HSPA and LTE.
HSPA+HSPA+HSPA+HSPA+
OFDMA systems have attracted considerable attention through technologies
such as 3GPP LTE and WiMAX. However, as already discussed earlier,
CDMA approaches can match OFDMA approaches in reduced channel
bandwidths. The goal in evolving HSPA is to exploit available radio
technologies, enabled by increases in digital signal processing power, to
maximize CDMA-based radio performance. This not only makes HSPA
competitive, it significantly extends the life of sizeable operator infrastructure
investments.
Wireless and networking technologists have defined a series of enhancements
for HSPA, some of which are specified in R7 and some of which are beingstudied for R8.
HSPA+ features:
Advanced receivers (type 1, 2, 3, 3i)
MIMO (2x2)
Continuous Packet Connectivity (CPC)
Higher order modulation (64QAM DL, 16QAM UL)Flatter architecture
Integrated RNC/Node B
Robust Header Compression (ROHC)
Figure 1-2 HSPA+ features
7/30/2019 129454451 Lelliwa LTE Technology
11/323
1 Introduction
13
AdvancedreceiversAdvancedreceiversAdvancedreceiversAdvancedreceivers
One important area is advanced receivers, where 3GPP has specified a
number of advanced designs. These designs include Type 1, which uses
mobile Rx diversity; Type 2, which uses channel equalization; and Type 3,
which includes a combination of Rx diversity and channel equalization. Type
3i devices will employ interference cancellation. Note that the different types
of receivers are release-independent. For example, Type 3i receivers will
work and provide a capacity gain in a R5 network.
The first approach is mobile Rx diversity. This technique relies on the optimal
combination of received signals from separate receiving antennas. The
antenna spacing yields signals that have somewhat independent fading
characteristics. Hence, the combined signal can be more effectively decoded,
which results in an almost doubling of downlink capacity when employed inconjunction with techniques such as channel equalization. Receive diversity is
effective even for small devices such as PC card modems and smartphones.
Current receiver architectures based on rake receivers are effective for speeds
up to a few megabits per second. But at higher speeds, the combination of
reduced symbol period and multipath interference results in inter-symbol
interference and diminishes rake receiver performance. This problem can be
solved by advanced receiver architectures with channel equalizers that yield
additional capacity gains over HSDPA with receive diversity. Alternate
advanced receiver approaches include interference cancellation andgeneralized rake receivers (G-Rake). Different vendors are emphasizing
different approaches. However, the performance requirements for advanced-
receiver architectures are specified in 3GPP R6. The combination of mobile
Rx diversity and channel equalization (Type 3) is especially attractive,
because it results in a large capacity gain independent of the radio channel.
What makes such enhancements attractive is that the networks do not require
any changes other than increased capacity within the infrastructure to support
the higher bandwidth. Moreover, the network can support a combination of
devices, including both earlier devices that do not include these enhancements
and later devices that do. Device vendors can selectively apply these
enhancements to their higher performing devices.
MIMOMIMOMIMOMIMO
Another standardized capability is Multiple Input Multiple Output (MIMO), a
technique that employs multiple transmit antennas and multiple receive
antennas, often in combination with multiple radios and multiple parallel data
streams. The most common use of the term MIMO applies to spatial
multiplexing. The transmitter sends different data streams over each antenna.
7/30/2019 129454451 Lelliwa LTE Technology
12/323
LTE/EPS Technology
14
Whereas multipath is an impediment for other radio systems, MIMO actually
exploits multipath, relying on signals to travel across different
communications paths. This results in multiple data paths effectively
operating somewhat in parallel and, through appropriate decoding, in amultiplicative gain in throughput.
UENode B
Figure 1-3 MIMO (2x2)
Tests of MIMO have proven very promising in WLANs operating in relative
isolation, where interference is not a dominant factor. Spatial multiplexing
MIMO should also benefit HSPA hotspots serving local areas such as
airports, campuses, and malls, where the technology will increase capacity
and peak data rates. However, in a fully loaded network with interference
from adjacent cells, overall capacity gains will be more modest - in the range
of 20 to 33 percent over mobile Rx diversity. Relative to a 1x1 antenna
system, however, 2x2 MIMO can deliver cell throughput gains of about 80
percent. 3GPP has standardized spatial multiplexing MIMO in R7.
Although MIMO can significantly improve peak rates, other techniques such
as Space Division Multiple Access (SDMA) - also a form of MIMO - may be
even more effective than MIMO for improving capacity in high spectralefficiency systems using a reuse factor of 1.
CPCCPCCPCCPC
In R7, Continuous Packet Connectivity (CPC) enhancements reduce the
uplink interference created by the DPCCHs of packet data users when those
users have no data to transmit. This, in turn, increases the number of
simultaneously connected HSUPA users. CPC allows both discontinuous
uplink transmission and discontinuous downlink reception, where the mobile
7/30/2019 129454451 Lelliwa LTE Technology
13/323
1 Introduction
15
can turn off its receiver after a certain period of HSDPA inactivity. CPC is
especially beneficial to VoIP on the uplink, which consumes the most power,
because the radio can turn off between VoIP packets.
HigherordermodulationHigherordermodulationHigherordermodulationHigherordermodulation
Another way of increasing performance is to use higher order modulation.
HSPA uses 16 QAM or QPSK on the downlink and QPSK on the uplink. But
radio links can achieve higher throughputs, adding 64 QAM on the downlink
and 16 QAM on the uplink. Higher order modulation requires a better SNR,
which is enabled through other enhancements such as receive diversity and
equalization.
FlatterarchFlatterarchFlatterarchFlatterarchitectureitectureitectureitecture
Another way HSPA performance can be improved is through a flatter
architecture. In R7 there is the option of a one-tunnel architecture by which
the network establishes a direct transfer path for user data between RNC and
GGSN, while the SGSN still performs all control functions. This brings
several benefits such as eliminating hardware in the SGSN and simplified
engineering of the network.
Node B
SGSN
RNC
GGSN
Node B
SGSN
RNC
GGSN
Node B
SGSN
GGSN
control planeuser plane
Figure 1-4 HSPA+ possible architectures
7/30/2019 129454451 Lelliwa LTE Technology
14/323
LTE/EPS Technology
16
IntegratedRNC/NodeBIntegratedRNC/NodeBIntegratedRNC/NodeBIntegratedRNC/NodeB
There is also an integrated RNC/NodeB option where RNC functions are
integrated in the Node B. This is particularly beneficial in femtocell
deployments, as an RNC would otherwise need to support thousands of
femtocells. The integrated RNC/NodeB for HSPA+ has been agreed as an
optional architecture alternative for packet-switched based services. Support
of circuit-switched services in HSPA+ must be deployed using the traditional
hierarchical architecture.
These new architectures, are similar to the EPS architecture, especially on the
packet-switched core network side where they provide synergies with the
introduction of LTE.
ROHCROHCROHCROHC
The size of the full IPv6 header together with Real-time Transport Protocol /
User Datagram Protocol (RTP/UDP) header is 60 bytes, while the size of a
typical voice packet is 30 bytes. Without header compression two-thirds of
the transmission would be just headers. IP header compression can be applied
to considerably improve the efficiency of VoIP traffic is HSPA.
Robust Header Compression (ROHC) is a standardized method to compress
the IP, UDP, RTP, and TCP headers of IP packets. This compression scheme
differs from other compression schemes such as IETF RFC 1144 and RFC2508 by the fact that it performs well over links where the packet loss rate is
high, such as wireless links.
The ROHC in the 3GGP is a part of R4. With ROHC, the required data rate
for VoIP is reduced from close to 40 kbps down to below 16 kbps.
HSPA+capabilitiesHSPA+capabilitiesHSPA+capabilitiesHSPA+capabilities
Depending on the features implemented, HSPA+ can exceed the capabilities
of IEEE 802.16e-2005 (mobile WiMAX) in the same amount of spectrum.This is mainly because HSPA MIMO supports closed-loop operation with
precode weighting, as well as multicode word MIMO, and enables the use of
SIC receivers. It is also partly because HSPA supports Incremental
Redundancy (IR) and has lower overhead than WiMAX.
7/30/2019 129454451 Lelliwa LTE Technology
15/323
1 Introduction
17
peak data rate
11.5 Mbps42.2 MbpsHSPA+ R8 2x2MIMO/64QAM/16QAM
11.5 Mbps28.0 MbpsHSPA+ R7 2x2MIMO/16QAM/16QAM
11.5 Mbps21.1 MbpsHSPA+ R7 64QAM/16QAM
5.76 Mbps14.4 MbpsHSPA R6
ULDLtechnology
peak data rate
11.5 Mbps42.2 MbpsHSPA+ R8 2x2MIMO/64QAM/16QAM
11.5 Mbps28.0 MbpsHSPA+ R7 2x2MIMO/16QAM/16QAM
11.5 Mbps21.1 MbpsHSPA+ R7 64QAM/16QAM
5.76 Mbps14.4 MbpsHSPA R6
ULDLtechnology
Figure 1-5 HSPA+ capabilities
HSPA+ will also more than double HSPA capacity as well as reduce latency
below 25 ms. Sleep to data-transfer times of less than 200 ms will improve
users always-connected experience, and reduced power consumption with
VoIP will result in talk times that are more than 50% higher.
From a deployment point of view, operators will be able to introduce HSPA+
capabilities through either a software upgrade or hardware expansions to
existing cabinets to increase capacity.
LTE/LTE/LTE/LTE/EEEE----UTRANUTRANUTRANUTRAN
Although HSPA and HSPA+ offer a highly efficient broadband-wireless
service, 3GPP is working on a project called Long Term Evolution (LTE) as
part of R8. LTE will allow operators to achieve even higher peak throughputs
in higher spectrum bandwidth. Work on LTE began in 2004, with an official
work item started in 2006 and a completed specification expected in early
2008. Initial possible deployment is targeted for 2009.
RequirementsfortheLTEsystemRequirementsfortheLTEsystemRequirementsfortheLTEsystemRequirementsfortheLTEsystem
LTE is focusing on optimum support of Packet Switched (PS) services. Main
requirements for the design of an LTE system were identified in the beginning
of the standardisation work on LTE and have been captured in 3GPP TR
25.913. They can be summarized as follows:
Data rate: Peak data rates target 100 Mbps DL and 50 Mbps UL for
20 MHz spectrum allocation, assuming 2 receive antennas and 1
transmit antenna at the terminal (these requirement values are already
exceeded by the current LTE specification),
7/30/2019 129454451 Lelliwa LTE Technology
16/323
LTE/EPS Technology
18
Throughput & spectrum efficiency: Target for downlink average
user throughput per MHz and for spectrum efficiency is 3-4 times
better than release 6. Target for is 2-3 times better than release 6.
Latency: The one-way transit time between a packet being availableat the IP layer in either the UE or radio access network and the
availability of this packet at IP layer in the radio access network/UE
shall be less than 5 ms. Also C-plane latency shall be reduced, e.g. to
allow fast transition times of less than 100 ms from camped state to
active state.
Channel bandwidth: Scalable bandwidths of 5, 10, 15, 20 MHz shall
be supported. Also bandwidths smaller than 5 MHz shall be supported
for more flexibility, i.e. 1.4 MHz and 3 MHz.
Interworking: Interworking with existing UTRAN/GERAN systems
and non-3GPP systems shall be ensured. Multimode terminals shall
support handover to and from UTRAN and GERAN as well as inter-
RAT measurements. Interruption time for handover between E-
UTRAN and UTRAN/GERAN shall be less than 300 ms for real time
services and less than 500 ms for non real time services.
Multimedia Broadcast Multicast Services (MBMS): MBMS shall
be further enhanced and is then referred to as E-MBMS.
Costs: Reduced CAPEX and OPEX including backhaul shall be
achieved. Cost effective migration from release 6 UTRA radio
interface and architecture shall be possible. Reasonable system and
terminal complexity, cost and power consumption shall be ensured.
All the interfaces specified shall be open for multi-vendor equipment
interoperability.
Mobility: The system should be optimized for low mobile speed (0-15
km/h), but higher mobile speeds shall be supported as well including
high speed train environment as special case.
Spectrum allocation: Operation in paired (Frequency Division
Duplex / FDD mode) and unpaired spectrum (Time Division Duplex /
TDD mode) is possible.
Co-existence: Co-existence in the same geographical area and
collocation with GERAN/UTRAN shall be ensured. Also, co-
existence between operators in adjacent bands as well as cross-border
coexistence is a requirement.
Quality of Service: End-to-end Quality of Service (QoS) shall be
supported. VoIP should be supported with at least as good radio and
7/30/2019 129454451 Lelliwa LTE Technology
17/323
1 Introduction
19
backhaul efficiency and latency as voice traffic over the UMTS circuit
switched networks
Network synchronization: Time synchronization of different network
sites shall not be mandated.
data rate: DL 100 Mbps & UL 50 Mbps (already exceeded),
throughput & spectrum efficiency: DL 3-4 x R6, UL 2-3 x R6),
channel bandwidth (5, 10, 15, 20 MHz and smaller),
interworking (GERAN/UTRAN and non-3GPP),
MBMS,
cost reduction,
mobility (optimised for low speeds 0-15 km/h),
spectrum allocation (FDD & TDD),
QoS,
time synchronisation between sites not mandatory.
Figure 1-6 Requirements for the LTE system
LTEtechnologyoverviewLTEtechnologyoverviewLTEtechnologyoverviewLTEtechnologyoverviewLTE uses OFDMA on the downlink, which is well suited to achieve high peak
data rates in high spectrum bandwidth. WCDMA radio technology is basically
as efficient as OFDM for delivering peak data rates of about 10 Mbps in 5
MHz of bandwidth. However, achieving peak rates in the 100 Mbps range
with wider radio channels would result in highly complex terminals, and it is
not practical with current technology. This is where OFDM provides a
practical implementation advantage. Scheduling approaches in the frequency
domain can also minimize interference, thereby boosting spectral efficiency.
approach is also highly flexible in channelization, and LTE will operate invarious radio channel sizes ranging from 1.25 to 20 MHz.
On the uplink, however, a pure OFDMA approach results in high Peak to
Average Ratio (PAR) of the signal, which compromises power efficiency and,
ultimately, battery life. Hence, LTE uses an approach called SC-FDMA,
which is somewhat similar to OFDMA but has a 2 to 6 dB PAR advantage
over the OFDMA method used by other technologies such as IEEE 802.16e.
7/30/2019 129454451 Lelliwa LTE Technology
18/323
LTE/EPS Technology
20
LTE capabilities include:
Downlink peak data rates up to 326 Mbps with 20 MHz bandwidth.
Uplink peak data rates up to 86.4 Mbps with 20 MHz bandwidth.
Operation in both TDD and FDD modes.
Scalable bandwidth up to 20 MHz, covering 1.25, 2.5, 5, 10, 15, and
20 MHz. Channels that are 1.6 MHz wide are under consideration for
the unpaired frequency band, where a TDD approach will be used.
Increased spectral efficiency over R6 HSPA by a factor of two to four.
Reduced latency, to 10 ms RTT between user equipment and the
eNodeB, and to less than 100 ms transition time from inactive to
active.The overall intent is to provide an extremely high-performance radio-access
technology that offers full vehicular speed mobility and that can readily
coexist with HSPA and earlier networks. Because of scalable bandwidth,
operators will be able to easily migrate their networks and users from HSPA
to LTE over time.
peak data rate
86.4 Mbps326.4 Mbps4x4 MIMO/64QAM
57.6 Mbps172.8 Mbps2x2 MIMO/16QAM
ULDLLTE configuration
peak data rate
86.4 Mbps326.4 Mbps4x4 MIMO/64QAM
57.6 Mbps172.8 Mbps2x2 MIMO/16QAM
ULDLLTE configuration
Figure 1-7 LTE bitrates (20 MHz channel)
OFDMOFDMOFDMOFDM
Orthogonal Frequency Division Multiplexing (OFDM) uses a large number of
narrow sub-carriers for multi-carrier transmission. The basic LTE downlink
physical resource can be seen as a time-frequency grid, as illustrated in
Fig 1-6. In the frequency domain, the spacing between the subcarriers, f, is
15 kHz. The number of subcarriers ranges from 75 in a 1.25 MHz channel to
1,200 in a 20 MHz channel. In addition, the OFDM symbol duration time is
1/f + cyclic prefix. The cyclic prefix is used to maintain orthogonally
between the sub-carriers even for a time-dispersive radio channel.
One resource element carries QPSK, 16QAM or 64QAM. With 64QAM, each
resource element carries six bits.
7/30/2019 129454451 Lelliwa LTE Technology
19/323
1 Introduction
21
The OFDM symbols are grouped into resource blocks. The resource blocks
have a total size of 180 kHz in the frequency domain and 0.5 ms in the time
domain. Each 1ms TTI consists of two slots (Tslot).
Each user is allocated a number of so-called resource blocks in the timefrequency grid. The more resource blocks a user gets, and the higher the
modulation used in the resource elements, the higher the bit-rate.
Which resource blocks and how many the user gets at a given point in time
depend on advanced scheduling mechanisms in the frequency and time
dimensions. The scheduling mechanisms in LTE are similar to those used in
HSPA, and enable optimal performance for different services in different
radio environments.
f
t 12 subcarriers, 180 kHz
Oneslot
(Tslot=0.5ms,7O
FDMsym
bols)
Resource block
(12 x 7 = 84 resource elements)
Resource element
QPSK 2 bits,
16QAM 4 bits,
64QAM 6 bits,
15 kHz
Figure 1-8 OFDMA concept
The basic principle of OFDM is to split a high-rate data stream into a number
of parallel low-rate data streams, each a narrowband signal carried by a
subcarrier. The different narrowband streams are generated in the frequency
domain and then combined to form the broadband stream using a
mathematical algorithm called an Inverse Fast Fourier Transform (IFFT) thatis implemented in DSPs.
By having control over which subcarriers are assigned in which sectors, LTE
can easily control frequency reuse. By using all the subcarriers in each sector,
the system would operate at a frequency reuse of 1; but by using a different
one third of the subcarriers in each sector, the system achieves a looser
frequency reuse of 1/3. The looser frequency reduces overall spectral
efficiency but delivers high peak rates to users.
In the uplink, LTE uses a pre-coded version of OFDM called Single Carrier
Frequency Division Multiple Access (SC-FDMA). This is to compensate for a
7/30/2019 129454451 Lelliwa LTE Technology
20/323
LTE/EPS Technology
22
drawback with normal OFDM, which has a very high PAR. High PAR
requires expensive and inefficient power amplifiers with high requirements on
linearity, which increases the cost of the terminal and drains the battery faster.
SC-FDMA solves this problem by grouping together the resource blocks insuch a way that reduces the need for linearity, and so power consumption, in
the power amplifier. A low PAR also improves coverage and the cell-edge
performance.
AdvancedantennasAdvancedantennasAdvancedantennasAdvancedantennas
Advanced antenna solutions that are introduced in HSPA+ are also used by
LTE. Solutions incorporating multiple antennas meet next-generation mobile
broadband network requirements for high peak data rates, extended coverage
and high capacity.
Advanced multi-antenna solutions are key components to achieve these
targets. There is not one antenna solution that addresses every scenario.
Consequently, a family of antenna solutions is available for specific
deployment scenarios. For instance, high peak data rates can be achieved with
multi-layer antenna solution such as 2x2 or 4x4 MIMO whereas extended
coverage can be achieved with beam-forming.
ProtocolsProtocolsProtocolsProtocols
The LTE physical layer solely provides shared channels to the higher layers
using a 1 ms TTI. LTE relies on rapid adaptation to channel variations,
employing rate adaptation and HARQ with soft-combining in much the same
way as is done in HSPA. The use of OFDM and SC-FDMA makes it possible
to exploit variations in both the frequency and time domains.
The architecture of the radio interface protocol is based on that for HSPA.
The names of the protocols are the same, in fact, and the functions are similar.
Some distinctions stem from differences in the multiple access techniques of
LTE and HSPA. Others relate to the fact that LTE is a packet-only system(that is, there are no requirements to support the legacy circuit-switched
domain). Fig. 1-8 and Fig. 1-9 show the architecture of the LTE radio
interface protocol. Note: Apart from the NAS protocols, all radio interface
protocols terminate in the eNodeB on the network side.
Packet Data Convergence Protocol (PDCP) handles the header compression
and security functions of the radio interface; the Radio Link Control (RLC)
protocol focuses on lossless transmission of data; and the Media Access
Control (MAC) protocol handles uplink and downlink scheduling and HARQ
signalling. Similarly, the Radio Resource Control (RRC) protocol handles
radio bearer setup, active mode mobility management, and broadcasts of
7/30/2019 129454451 Lelliwa LTE Technology
21/323
1 Introduction
23
system information, while the NAS protocols deal with idle mode mobility
management and service setup.
IP
PDCP
RLC
MAC
PHY
UE
RLC
MAC
PHY
eNode B
PDCP
IP
GW
IP
Figure 1-9 LTE protocols (user plane)
NAS
RRC
RLC
MAC
PHY
UE
RLC
MAC
PHY
eNode B
RRC
NAS
MME
PDCP PDCP
Figure 1-10 LTE protocols (control plane)
The RTT for E-UTRAN is around 7 ms, one way delay 3,5 ms and HARQ
RTT 5 ms.
UE eNode B
1 ms 1.5 ms 1 ms
1 ms 1 ms1.5 ms
TTI + framealignment
HARQ RTT 5 ms
Figure 1-11 LTE user plane delay
7/30/2019 129454451 Lelliwa LTE Technology
22/323
LTE/EPS Technology
24
EPS/SAEEPS/SAEEPS/SAEEPS/SAE
3GPP is defining EPS (previously called SAE) in R8 as a framework for anevolution of the 3GPP system to a higher-data-rate, lower-latency packet-
optimized system that supports multiple radio-access technologies. The focus
of this work is on the PS domain, with the assumption that the system will
support all services - including voice - in this domain.
Although it will most likely be deployed in conjunction with LTE, EPS could
also be deployed for use with HSPA+, where it could provide a stepping-
stone to LTE. EPS will be optimized for all services to be delivered via IP in a
manner that is as efficient as possible - through minimization of latency
within the system, for example. It will support service continuity acrossheterogeneous networks, which will be important for LTE operators that must
simultaneously support GSM/GPRS/EDGE/UMTS/HSPA customers.
One important performance aspect of EPS is a flatter architecture. For packet
flow, EPS includes two network elements, called Evolved Node B (eNodeB)
and the Access Gateway (AGW). The eNode B (base station) integrates the
functions traditionally performed by the RNC, which previously was a
separate node controlling multiple Node Bs. Meanwhile, the AGW integrates
the functions traditionally performed by the SGSN. The AGW has both
control functions, handled through the Mobility Management Entity (MME),
and user plane (data communications) functions. The user plane functionsconsist of two elements: a serving gateway that addresses 3GPP mobility and
terminates eNode B connections, and a Packet Data Network (PDN) gateway
that addresses service requirements and also terminates access by non-3GPP
networks.
The MME, serving gateway, and PDN gateways can be collocated in the same
physical node or distributed, based on vendor implementations and
deployment scenarios. The EPS architecture is similar to the HSPA One-
Tunnel Architecture, discussed in the HSPA+ section, which allows for
easy integration of HSPA networks to the EPS. EPS also allows integration ofnon-3GPP networks such as WiMAX. EPS will use IMS as a component. It
will also manage QoS across the whole system, which will be essential for
enabling a rich set of multimedia-based services.
Elements of the EPS architecture include:
Support for legacy GERAN and UTRAN networks connected via
SGSN.
Support for new radio-access networks such as LTE.
7/30/2019 129454451 Lelliwa LTE Technology
23/323
1 Introduction
25
The Serving Gateway that terminates the interface toward the 3GPP
radio-access networks.
The PDN gateway that controls IP data services, does routing,
allocates IP addresses, enforces policy, and provides access for non-3GPP access networks.
The MME that supports UE context and identity as well as
authenticates and authorizes users.
The Policy Control and Charging Rules Function (PCRF) that
manages QoS aspects.
AGW
LTE
eNode B
PDN GW
Serving GW
HSS
PCRF
IP networks /IMS / services
WCDMA/HSPAGSM
non-3GPPaccess
SGSN
MME
Figure 1-12 EPS / SAE architecture
IMSIMSIMSIMS
IMS is a service platform that allows operators to support IP multimedia
applications. Potential applications include video sharing, PoC, VoIP,
streaming video, interactive gaming, and so forth. IMS by itself does not
provide all these applications. Rather, it provides a framework of application
servers, subscriber databases, and gateways to make them possible. The exact
services will depend on cellular operators and application developers that
make these applications available to operators.
The core networking protocol used within IMS is Session Initiation Protocol
(SIP), which includes the companion Session Description Protocol (SDP)
used to convey configuration information such as supported voice codecs.
7/30/2019 129454451 Lelliwa LTE Technology
24/323
LTE/EPS Technology
26
Other protocols include Real-time Transport Protocol (RTP) and Real Time
Streaming Protocol (RTSP) for transporting actual sessions. The QoS
mechanisms in UMTS is an important component of some IMS applications.
Although originally specified by 3GPP, numerous other organizations aroundthe world are supporting IMS. These include the Internet Engineering
Taskforce (IETF), which specifies key protocols such as SIP, and the Open
Mobile Alliance (OMA), which specifies end-to-end service-layer
applications. Other organizations supporting IMS include the GSM
Association (GSMA), the ETSI, CableLabs, The Parlay Group, the ITU, the
American National Standards Institute (ANSI), the Telecoms and Internet
converged Services and Protocols for Advanced Networks (TISPAN), and the
Java Community Process (JCP).
IMS is relatively independent of the radio-access network and can, and likelywill, be used by other radio-access networks or even by wireline networks.
As shown in Fig. 1-13, IMS operates just outside the packet core.
Call Session Control Function (CSCF)(SIP proxy)
HSS
Media Gateway
Control Function
Media ResourceFunction (MRF)
SIPApplication
Server (AS)
IMS
DSL3GPP CN WiFi
Figure 1-13 IMS architecture
The benefits of using IMS include handling all communication in the packet
domain, tighter integration with the Internet, and a lower cost infrastructure
that is based on IP building blocks and common between voice and data
services. This allows operators to potentially deliver data and voice services at
lower cost, thus providing these services at lower prices and further driving
demand and usage.
IMS applications can reside either in the operators network or in third-party
networks, including enterprises. By managing services and applications
centrally, and independently of the access network, IMS can enable network
convergence. This allows operators to offer common services across 3G,
WiFi, and even wireline networks.
7/30/2019 129454451 Lelliwa LTE Technology
25/323
2 Architecture
27
ChapterChapterChapterChapter2222
ArchitectureArchitectureArchitectureArchitecture
TopicTopicTopicTopic PagePagePagePage
Non-roaming architecture ................................................................................ 29
Roaming architecture .......................................................................................37
Arch. for non-3GPP access .............................................................................. 39
Interfaces..........................................................................................................41
Geographical network structure....................................................................... 43
Identities........................................................................................................... 45
7/30/2019 129454451 Lelliwa LTE Technology
26/323
LTE/EPS Technology
28
This page is intentionally left blank
7/30/2019 129454451 Lelliwa LTE Technology
27/323
7/30/2019 129454451 Lelliwa LTE Technology
28/323
LTE/EPS Technology
30
Some additional nodes are also required for interworking with other (non
LTE) radio access technologies. Example of such node is SGSN that is used
for interworking with GERAN and UTRAN.
MMEMMEMMEMME
The Mobility Management Entity (MME) is in charge of all control plane
functions related to subscriber and session management. From that
perspective, the MME supports as follows:
Non-access Stratum Signalling (NAS) i.e. signalling between UE and
the Evolved Packet Core (EPC) network this relates to all signalling
procedures related with terminal location management (tracking area
update procedure) and procedures used to setup a packet data context(connection for user data) and negotiate associated parameters like
Quality of Service (QoS).
Inter Core Network (CN) node signalling for handling mobility
between different types of 3GPP access networks, i.e. signalling with
SGSN exchanged over S3 interface.
Security procedures this relates to end-user authentication, end-user
equipment check, as well as initiation and negotiation of ciphering and
integrity protection algorithms.
Tracking Area (TA) list management.
Idle UE reachability, e.g. control and execution of paging
transmission.
Selection of other CN nodes:
o S-GW and PDN-GW for the purpose of user data transmission,
o MME for handovers with MME change,
o SGSN for handovers to GERAN or UTRAN.
Roaming, i.e. MME handles interface toward subscribers HPLMNHLR.
The MME is linked through the S6a interface to the HSS which supports the
database containing all the user subscription information.
7/30/2019 129454451 Lelliwa LTE Technology
29/323
2 Architecture
31
GatewaysGatewaysGatewaysGateways
Two logical Gateways exist: Serving GW (S-GW),
PDN GW (P-GW).
The P-GW and the S-GW may be implemented in one physical node or
separated physical nodes.
MME
E-UTRAN
P-GWS-GW
S1-U
S1-MME
S11
IP/IMS
SGi
S6a HSS
Figure 2-2 S-GW and P-GW in one physical node
Also the S-GW and the MME may be implemented in one physical node or
separated physical nodes.
MME
E-UTRAN
P-GWS-GW
IP/IMSSGi
S6a HSS
S5
S1
Figure 2-3 MME and S-GW in one physical node
SSSS----GWGWGWGW
The Serving Gateway (S-GW) is the gateway which terminates the interface
towards E-UTRAN. For each UE associated with the EPS, at a given point of
time, there is a single S-GW.
The functions of the S-GW, include:
Packet routeing and forwarding,
Transport level packet marking in the uplink and the downlink, e.g.
setting the DiffServe Code Point, based on the QoS Class Identifier
(QCI) of the associated EPS bearer,
Downlink packet buffering and initiation of network triggered
service request procedure for Idle UEs,
7/30/2019 129454451 Lelliwa LTE Technology
30/323
LTE/EPS Technology
32
The local mobility anchor point for inter-eNodeB handover and
assistance in packet reordering during inter-eNodeB handover,
Mobility anchoring for inter-3GPP mobility (relaying the traffic
between 2G/3G system and P-GW,
Charging and accounting,
Lawful interception.
PPPP----GWGWGWGW
The PDN GW is the gateway which terminates the SGi interface towards the
PDN. If a UE is accessing multiple PDNs, there may be more than one PDN
GW for that UE.
PDN GW functions include:
Transport level packet marking in the uplink and the downlink,
UE IP address allocation,
Per-user based packet filtering (by e.g. deep packet inspection),
UL and DL service level charging ,
UL and DL service level rate enforcement,
UL and DL service level gating control,
Lawful Interception,
DHCP functions,
SGSNSGSNSGSNSGSN
The Serving GPRS Support Node (SGSN), in addition to the functions
handled earlier in 2G/3G network, is responsible for:
Inter EPC node signalling for mobility between 2G/3G and E-
UTRAN,
PDN and Serving GW selection,
MME selection for handovers to E-UTRAN.
PCRFPCRFPCRFPCRF
The Policy and Charging Rules Function (PCRF). PCRF functions are
described in more detail later in this book.
7/30/2019 129454451 Lelliwa LTE Technology
31/323
2 Architecture
33
HSSHSSHSSHSS
The Home Subscriber Server (HSS) is the concatenation of the HomeLocation register (HLR) and the Authentication Centre (AuC) two functions
being already present in 2G GSM and 3G UMTS networks. The HLR part of
the HSS is in charge of storing and updating when necessary the database
containing all the user subscription information, including:
user identification and addressing this corresponds to the
International Mobile Subscriber Identity (IMSI) and Mobile
Subscriber ISDN Number (MSISDN),
user profile information this includes service subscription states and
user-subscribed Quality of Service (QoS) information (such asmaximum allowed bit rate or allowed traffic class),
The AuC part of the HSS is in charge of generating security information from
user identity keys. This security information is provided to the HLR and
further communicated to other entities in the network. Security information is
mainly used for:
mutual network-terminal authentication,
radio path ciphering and integrity protection, to ensure data and
signalling transmitted between network and the terminal is neither
eavesdropped nor altered.
Introduced from the very beginning of the GSM network standardisation,
HLR and AuC boxes were eventually joined together in a single HSS node as
IMS was defined by the 3GPP. In its extended role, the HSS of Evolved
UMTS networks integrates both HLR and AuC features, including classical
MAP features (for support of CS and PS sessions), IMS-related functions, and
all necessary functions related to the new EPC.
2G/3G PS domain2G/3G CS domain
IMS EPC
HLR
AUC
HSSI/S-CSCF
GMSC
VLR SGSN
GGSN
MMES6a
Gc
S6b
Gr
Cx
C
D
Figure 2-4 HSS structure and external interfaces
7/30/2019 129454451 Lelliwa LTE Technology
32/323
LTE/EPS Technology
34
There are actually three main cases in which the HSS is actively involved:
At user registration the HSS is interrogated by the corresponding CN
node as the user attempts to register to the network in order to check
the user subscription rights. This can be done by either the MSC, theSGSN, I-CSCF or the MME, depending on the type of network and
registration being requested;
In the case of terminal location update as the terminal changes
location areas, the HSS is kept updated and maintains a reference of
the last known are;
In the case of user-terminated session request the HSS is
interrogated and provides a reference of the CN node corresponding to
the current user location.
EEEE----UTRANUTRANUTRANUTRAN
Coming back to the first releases of the UMTS standard, the UTRAN
architecture was initially very much aligned with GSM access network
(GERAN) concepts. As described in Fig. 2-5, the UTRAN network is
composed of the radio equipment (known as NodeB or Base Station) in
charge of transmission and reception over the radio interface, and the Radio
Network Controller (RNC) in charge of NodeB configuration and radio
resource allocation. A single RNC may possibly control a large number of
NodeBs over the Iub interface.
In addition, an inter-RNC Iur interface was defined to allow UTRAN call
anchoring at the RNC level and macro-diversity between different NodeBs
controlled by different RNCs. Macro-diversity was a consequence of
CDMA-based UTRAN physical layer, as means to reduce radio interference
and preserve network capacity. The initial UTRAN architecture resulted in a
simplified NodeB implementation, and a relatively complex, sensitive, high-
capacity and feature-rich RNC design. In this model, the RNC had to support
resources and traffic management features as well as a significant part of theradio protocols. Compared with UTRAN, the E-UTRAN OFDM-based
structure is quite simple. It is only composed of one network element: the
evolved NodeB (eNodeB).
7/30/2019 129454451 Lelliwa LTE Technology
33/323
2 Architecture
35
Core Network
Iur
Iub Iub
Iu Iu
RNCRNC
IubIub
NodeB NodeB
NodeBNodeB
Core Network
X2
S1
eNodeB eNodeB
S1
UTRAN E-UTRAN
Figure 2-5 UTRAN and E-UTRAN architectures
The 3G RNC inherited from the 2G BSC has disappeared from E-UTRAN
and the eNodeB is directly connected to the Core Network (CN) using S1
interface. As a consequence, the features supported by the RNC have been
distributed between the eNodeB and the CN entities.
An eNodeB can be implemented either as a single-cell equipment providing
coverage and services in one cell only, or as a multi-cell node, where each cell
is covering a given geographical sector.
omnidirectional eNodeB sectorised eNodeB
Figure 2-6 Omnidirectional and sectorised eNodeBs
A new X2 interface has been defined between eNodeBs, working in a meshed
way (meaning that all NodeBs may possibly be linked together). The main
purpose of this interface is to minimise packet loss due to user mobility. As
the terminal moves across the access network, unsent or unacknowledged
packets stored in the old eNodeB queues can be forwarded to the new eNodeB
thanks to the X2 interface.
7/30/2019 129454451 Lelliwa LTE Technology
34/323
LTE/EPS Technology
36
S1
Tx Re-Tx
HO
Tx Re-Tx
X2
Core Network
S1
Figure 2-7 X2 interface
From a high-level perspective, the new E-UTRAN architecture is actually
moving towards WLAN network structures and WiFi or WiMAX base
stations functional definition. eNodeB as WLAN access points support
all L1 and L2 features associated to the E-UTRAN OFDM physical interface,
and they are directly connected to the network routers. There is no more
intermediate controlling node (as the 2G BSC or 3G RNC was).
This has a merit of a simpler network architecture (fewer nodes of different
types, which means simplified network operation) and allows betterperformance over the radio interface.
From the functional perspective, the eNodeB supports a set of legacy features,
all related to physical layer procedures for transmission and reception over the
radio interface:
modulation and de-modulation,
channel coding and decoding.
Besides, the eNodeB includes additional features, coming form the fact that
there are no more Base Station controllers in the E-UTRAN architecture:
radio resource control: this relates to the allocation, modification and
release of resources for the transmission over the radio interface
between the user terminal and the eNodeB.
mobility management: this refers to a measurement processing and
handover decision.
full L2 protocol: this refers detection and possibly correction of errors
that may occur in the physical layer (this function in UTRAN was
fully or for some services partially handled by RNC).
7/30/2019 129454451 Lelliwa LTE Technology
35/323
2 Architecture
37
RoamingarchitectureRoamingarchitectureRoamingarchitectureRoamingarchitecture
This section describes the case, both the visited and the home networks areEPC networks. Other cases, i.e. migration routes to this target roaming
architecture are left by 3GPP for further studies. Two alternative architectures
are shown, depending on whether UE traffic has to be routed to the HPLMN
or not.
UsertrafficroutedtotheHPLMNUsertrafficroutedtotheHPLMNUsertrafficroutedtotheHPLMNUsertrafficroutedtotheHPLMN
Fig. 2-8 presents the EPC architecture support for roaming cases. In this
example, a user has subscribed to HPLMN A, but is currently under the
coverage of the VPLMN B. This kind of situation may happen while the user
is travelling to another country, or in case in which a national roaming
agreement has been set up between operators, so as to decrease the investment
effort for national coverage. In such a roaming situation, part of the session is
handled by the VPLMN. This includes E-UTRAN access network support,
session signalling handling by the MME, and user plane routing through the
local S-GW. Thanks to local MME and S-GW, the VPLMN is then able to
built and send charging tickets to the subscriber home operator ,
corresponding to the amount of data transferred and QoS allocated.
UTRAN
SGSN
MME
E-UTRAN
P-GWS-GW
PCRF
S1-U
S1-MME
S11
S8
S10
HSSS6a
S4 S12
OperatorsIP
Services(e.g. IMS,
PSS, etc.)
SGi
Gx
Rx
LTE-Uu
GERAN
UE
S3
MME
VPLMN HPLMN
Figure 2-8 Roaming architecture (HPLMN routed traffic)
However, since the terminal user has no subscription with the VPLMN, the
Visited EPC needs to be linked to the HSS of the user home network, at least
to retrieve the user-specific security credential needed for authentication and
ciphering. In the roaming architecture , the session path goes through the
7/30/2019 129454451 Lelliwa LTE Technology
36/323
LTE/EPS Technology
38
Home P-GW over the S8 interface, so as to apply policy and charging rules in
the home network corresponding to the users subscription parameters.
The S8 interface is in fact a roaming variant of S5 reference point, to support
both signalling and data transfer between S-GW located in VPLMN andP-GW located in the HPLMN.
Briefly, in such a model, the VPLMN provides the access connectivity (which
also involves the basic session signalling procedures supported by the Visited
MME, with the support of the Home HSS), whereas the HPLMN still
provides the access to external networks, possibly including IMS-based
services.
UsertrafficnotrUsertrafficnotrUsertrafficnotrUsertrafficnotroutedtotheHPLMNoutedtotheHPLMNoutedtotheHPLMNoutedtotheHPLMN
In the previous model, the call is still anchored to the Home IASA, hence the
home routed traffic denomination. The user packet routing in such a scheme
may, however, be quite inefficient in terms of cost and network resources as
the Home P-GW and Visited S-GW may be very far from each other. This is
the reason why the 3GPP standard also allows the possibility of the user
traffic to be routed via a Visited P-GW, as an optimisation. This may be very
beneficial in the example of public Internet access as routing the traffic to
the HPLMN does not add any value to the end user and even more in the
case of an IMS session established between a roaming user and a subscriber
of the visited network. In the last case, local traffic routing avoids a complete
round trip of user data trough the HPLMN anchors.
Fig. 2-9 and describe possible network architecture in the case where the
traffic is routed locally or the local breakout case. Both gateways are part
of the VPLMN.
HomeOperatorsServices
UTRAN
SGSN
MME
E-UTRAN
P-GWS-GW
vPCRF
S1-U
S1-MME
S11
S5
S10
HSS
S6a
S4 S12
VisitedOperators
PDNSGi
Gx
Rx
LTE-Uu
GERAN
UE
S3
MME
VPLMN HPLMN
hPCRF
S9
Rx
Figure 2-9 Roaming architecture (local breakout)
7/30/2019 129454451 Lelliwa LTE Technology
37/323
2 Architecture
39
If the networks make use of PCRF, one of the possible solutions is that the
enforcement of the HPLMN policies (QoS and charging policies) by the
Visited P-GW is performed through the interaction of Home and Visited
PCRF. Possibly, the Visited PCRF may add/modify policies according tothose defined in the VPLMN. The related reference point between PCRFs is
referred as S9.
ArchArchArchArch....fornonfornonfornonfornon----3GPPaccess3GPPaccess3GPPaccess3GPPaccess
A non-3GPP IP Access Network is defined as atrusted non-3GPP IP Access
Network if the 3GPP EPC system chooses to trust such non-3GPP IP accessnetwork. The 3GPP EPC system operator may choose to trust the non-3GPP
IP access network operated by the same or different operators, e.g. based on
business agreements.
Note that specific security mechanisms may be in place between the trusted
non-3GPP IP Access Network and the 3GPP EPC to avoid security threats. It
is assumed that an IPSec tunnel between the UE and the 3GPP EPC is not
required.
On the contrary, an untrusted non-3GPP IP Access Network is an IP access
network where 3GPP network requires use of IPSec between the UE and the3GPP network in order to provide adequate security mechanism acceptable to
3GPP network operator. An example of such untrusted non-3GPP IP access is
WLAN and it is made trusted in the Interworking WLAN specifications
developed within 3GPP.
In the current standardisation documents, a trusted non-3GPP IP access is also
referred to as the non-3GPP IP access, and an untrusted non-3GPP IP accesses
are accommodated by is also referred to as the WLAN 3GPP IP access.
TrustedNonTrustedNonTrustedNonTrustedNon----3GPPIPAccess3GPPIPAccess3GPPIPAccess3GPPIPAccess
Fig. 2-10 represents the network architecture providing IP connectivity to the
EPC using non-3GPP type of access. This architecture is independent from
the access technology, which could be WiFi, WiMAX or any other kind of
access type. This picture applies to the trusted WLAN access, corresponding
to the situation where the WLAN network is controlled by the operator itself
or by another entity (local operator or service provider) which can be trusted
due to the existence of mutual agreements.
7/30/2019 129454451 Lelliwa LTE Technology
38/323
LTE/EPS Technology
40
Trustednon 3GPPIP Access
HSS
3GPP AAA
Server
MME
E-UTRAN
PCRF
OperatorsIP
(services:IMS, PSS,
etc)Wx
Ta
P-GWS2a
S7
SGi
Rx
Non-3GPPnetwork
3GPPnetwork
S-GW
Figure 2-10 Trusted Non-3GPP IP Access architecture
As described below, some new network nodes and interfaces are needed to
support non-3GPP access types. In contrast, on terminal side, no changes are
required except some slight software adaptations. This comes from the fact
that Authentication Authorisation and Accounting (AAA) mechanisms for
mutual authentication and access control are based on known IETF protocols
but make use of the 3GPP UICC stored credentials.
The 3GPP AAA Servers role is to act as an inter-working unit between the
3GPP world and IETF standard-driven WLAN networks from the securityperspective. Its purpose is to allow end-to-end authentication with WLAN
terminals using 3GPP credentials. For that reason, the 3GPP AAA Server has
an access to the HSS through Wx interface, so as to retrieve user-related
subscription information and 3GPP authentication vectors.
From the 3GPP AAA Server, the Ta interface has been defined with the
trusted access network, aiming at transporting authentication, authorization
and charging-related information in a secure manner.
From the user plane perspective, the user data are transmitted from the
WLAN to the P-GW through the new S2a interface. As in legacy EPCarchitecture, the P-GW still serves as an anchor point for the user traffic.
In such a model, the 3GPP Anchor and MME UPE nodes are not needed any
more. Terminal location management is under the responsibility of the
WLAN Access as well as the packet session signalling and does not need any
support from 3GPP EPC nodes (aside from the provision of 3GPP security
credentials). In the example of a 802.11 WiFi access point, user association
(the process by with a WiFi terminal connects to an access point), security
features as well as radio protocols are handled by the access point itself.
7/30/2019 129454451 Lelliwa LTE Technology
39/323
2 Architecture
41
In addition to the trusted model, the standard defines another model, for the
situations where WLAN is untrusted. This model is described in Fig. 2-11. As
an example, this may correspond to a business entity deploying a WLAN for
its internal use and willing to offer 3GPP connectivity to some of itscustomers. In such a case, the WLAN-3GPP interconnection looks a bit
different due to additional mechanism to maintain legacy 3GPP infrastructure
security and integrity.
Untrustednon 3GPP
IP Access
HSS
3GPP AAA
Server
MME
E-UTRAN
PCRF
Operators
IP(services:
IMS, PSS,
etc)
Wx
Ta
P-GW SGi
Rx
Non-3GPP
network
3GPP
network
S-GW
ePDGWn
Wm
S2b
S7
Figure 2-11 Untrusted Non-3GPP IP Access architecture
This model introduced a evolved Packet Data Gateway (ePDG) node which
concentrates all the traffic issued or directed to the WLAN network. Its main
role is to establish a secure tunnel for user data transmission with the terminal
using IPSec and filter unauthorised traffic.
In this model, the new Wm interface is introduced for the purpose of
exchanging user-related information from the 3GPP AAA Server to the
ePDG. This will allow the ePDG to enable proper user data tunnelling and
encryption to the terminal.
InterfacesInterfacesInterfacesInterfaces
It is important to note, that the interfaces shown in Fig. 2-1 are logical
interfaces, i.e. they have no close relation with the physical network structure
and transmission. The connectivity between nodes will be handled by IP
network, operating on longer distances on top of SDH transmission network
and possibly on shorter distances on Carrier Ethernet, Gigabit Ethernet or
7/30/2019 129454451 Lelliwa LTE Technology
40/323
LTE/EPS Technology
42
even ADSL technologies. In such case the logical interface between two
nodes exist if only they are able to exchange information across IP network.
This means also, that they are aware of their functions and IP addresses,
which are configured either statically by means of O&M commands ordynamically by means of some signalling protocols.
SGSN
MMEP-GW
S-GW
PCRF
HSS
EIR
eNodeB
eNodeB
P-GW
S-GW
MME
eNodeB
Figure 2-12 Interfaces & connectivity
The protocol stacks used across the EPS interfaces are listed in Fig. 2-13.
Diameter/SCTP/IPP-GW PCRFGx
GTP-C/UDP/IPMME/SGSNMSCSv
SGsAP/SCTP/IPMME MSCSGs
Diameter/SCTP/IPSGSN HSSS6b
IPS-GW PDNSGi
S1-AP/SCTP/IPeNB
MMES1-MME
Diameter/SCTP/IPPCRF AFRx
X2-AP/SCTP/IPeNB eNBX2
Diameter/SCTP/IPMME EIRS13
GTP-U/UDP/IPS-GW RNCS12
GTP-C/UDP/IPMME S-GWS11
GTP-C/UDP/IPMME MMES10
Diameter/SCTP/IPvPCRF hPCRFS9
GTP/UDP/IP or PMIPvS-GW hP-GWS8
Diameter/SCTP/IPMME HSSS6a
GTP/UDP/IP or PMIPS-GW P-GWS5
GTP/UDP/IPS-GW SGSNS4
GTP-C/UDP/IPMME SGSNS3
GTP-U/UDP/IPeNB S-GWS1-U
Protocol stackNodesInterface
Diameter/SCTP/IPP-GW PCRFGx
GTP-C/UDP/IPMME/SGSNMSCSv
SGsAP/SCTP/IPMME MSCSGs
Diameter/SCTP/IPSGSN HSSS6b
IPS-GW PDNSGi
S1-AP/SCTP/IPeNB
MMES1-MME
Diameter/SCTP/IPPCRF AFRx
X2-AP/SCTP/IPeNB eNBX2
Diameter/SCTP/IPMME EIRS13
GTP-U/UDP/IPS-GW RNCS12
GTP-C/UDP/IPMME S-GWS11
GTP-C/UDP/IPMME MMES10
Diameter/SCTP/IPvPCRF hPCRFS9
GTP/UDP/IP or PMIPvS-GW hP-GWS8
Diameter/SCTP/IPMME HSSS6a
GTP/UDP/IP or PMIPS-GW P-GWS5
GTP/UDP/IPS-GW SGSNS4
GTP-C/UDP/IPMME SGSNS3
GTP-U/UDP/IPeNB S-GWS1-U
Protocol stackNodesInterface
Figure 2-13 Protocols on EPS interfaces
7/30/2019 129454451 Lelliwa LTE Technology
41/323
2 Architecture
43
GeographicalnetworkstructureGeographicalnetworkstructureGeographicalnetworkstructureGeographicalnetworkstructure
For all mobiles not being in idle mode, location management is still animportant item, as the network needs to know the current terminal location at
any time in case of mobile-terminated session setup or push services.
However, idle mode procedures do not require the network to know each
terminal location with the high degree of accuracy (such as the cell level). For
that reason, the concept of Tracking Area (TA) has been introduced.
Basically, a TA is defined as a set of contiguous cells. The identity of the TA
the cell belongs to, or Tracking Area Identity (TAI), is part of the system
information broadcast on Broadcast Control Channel (BCCH). As in the
3GPP definition, TAs do not overlap each other. When the network needs tojoin the terminal, a paging message is sent in all the cells which belong to the
Tracking Area.
The current terminal TA is signalled to the EPC at initial registration and
when UE changes the zones. In addition, the current TA is periodically
updated, even if it does not change, so that the EPC network does not keep
alive a context for a terminal which is no longer reachable in the network.
This can happen if the terminal fails to de-register or runs out of coverage.
As an enhancement to UMTS, the standard leaves the possibility for the
terminal to be registered into multiple TAs. In this situation , the terminaldoes not perform any TA update as long as it remains under the coverage of
the TAs it was registered to (like TA1, TA2 and TA3 in Fig. 2-14), with the
exception of periodic TA update. This multi-TA registration mechanism helps
to reduce the number of TA updates that the network has to process for
terminals located at the edge of TAs.
TA#3
TA#7
TA#8
TA#9
TA#1
TA#2
TA#4
TA#5
TA#6
TA update
Figure 2-14 Tracking Area (TA)
7/30/2019 129454451 Lelliwa LTE Technology
42/323
LTE/EPS Technology
44
The list of TAs that the UE is registered to is communicated by the network
during the TA update process. The UE considers it is registered to the whole
TA list until it enters a TA which does not belong to the list, or gets an update
list from the network, e.g. on the occasion of periodic TA update.The concept of location area, such as the TA, is not new to EPS, a sit was
introduced at the beginning of GSM system. Letter on, when GPRS and
UMTS were introduced, this principle become more complex. In UMTS, as
presented in Fig. 2-15, no less than four types of areas are being used:
Location Area (LA), which is a type of area supported by the CS CN
domain,
Routing Area (RA), which is the equivalent of the LA for the PS CN
domain,
UTRAN Registration Area (URA), which is a registration area for the
use of the UMTS access network,
Cell, which provides the best accuracy localisation information.
URA #1 URA #1 URA #1
RA #1
LA #1
RA #2 RA #3 RA #4 RA #5
LA #2 LA #3
Figure 2-15 UMTS location areas
RA is defined in such a way that a LA may include one or more RA. URA
was introduced to provide flexibility in UTRAN terminal location
management, in connection with the protocol states which were introduced in
the UTRAN RRC layer. As it is managed by the UTRAN, URA has no
relation with the CNs LA and RA.
LA and RA are quite similar to the concept of TA, as being a non-overlapping
group of cells. However, the URA concept has no equivalent in E-UTRAN.
The possibility of defining overlapping URA was introduced as a way to
decrease the signalling load impact of URA update, similarly to the TA list
registration concept presented above.
7/30/2019 129454451 Lelliwa LTE Technology
43/323
2 Architecture
45
From the perspective of the terminal location management, EPS has been
simplified ,a s there is only one type of CN domain (the EPC) and no
registration area has been defined for the access network like the UTRANs
URA. This will also have an impact on RRC state management simplification.
IdentitiesIdentitiesIdentitiesIdentities
Similarly to GSM/UMTS, EPS uses a number of descriptors to identify
subscribers. In Fig. 2-16 the EPS nodes are presented together with the
identities used by these nodes for various identification purposes.
MSISDN
IMSI
IMEI
P-TMSI
UTRAN
SGSN
MME
E-UTRAN
P-GWS-GW
HSS
EIR
GERAN
UE
IMSI IMEI
IMSIIMEI
IMEI
IMSI
IMEI
P-TMSI
PDP
address
IMSIIMEI GUTI
PDP address
PDP
address
GUTI
Static PDP address ?
MSISDNIMSI IMEI
Figure 2-16 EPS identities
IMSIIMSIIMSIIMSI
The unique identity for mobile subscriber is called International MobileSubscriber Identity (IMSI). IMSI consists of three parts:
MCC - Mobile Country Code (three digits),
MNC - Mobile Network Code (2-3 digits),
MSIN - Mobile Station Identification (up to 10 digits).
This number is stored on the SIM and acts acts as the unique database search
key in the HSS, MME and SGSN.
7/30/2019 129454451 Lelliwa LTE Technology
44/323
7/30/2019 129454451 Lelliwa LTE Technology
45/323
2 Architecture
47
TAC SNR
IMEI
spare
Figure 2-19 IMEI
TAC - Type Approval Code - Is a 8 digits length code that
identifies the particular type of the mobile equipment.
SNR - Serial Number (6 digits)
Spare - (1 digit)
The IMEI (14 digits) is complemented by a check digit. The check digit is not
part of the digits transmitted when the IMEI is checked. The Check Digit is
intended to avoid manual transmission errors, e.g. when customers registerstolen mobile equipment at the operator's customer care desk.
GUTI,MGUTI,MGUTI,MGUTI,M----TMSIandSTMSIandSTMSIandSTMSIandS----TMSITMSITMSITMSI
The MME allocates a Globally Unique Temporary Identity (GUTI) to the UE.
The GUTI has two main components:
Globally Unique MME Identifier (GUMMEI) uniquely identifying the
MME which allocated the GUTI,
M-TMSI uniquely identifying the UE within the MME that allocated
the GUTI.
GUTI/IMSI IMSI
GUTIIMSI
IMSI
new GUTI
IMSIGUTI
new GUTI
MME P-GW
HSS
S-GWeNodeBeNodeB
SGSN
Figure 2-20 Globally Unique Temporary Identity (GUTI)
7/30/2019 129454451 Lelliwa LTE Technology
46/323
LTE/EPS Technology
48
GUMMEI is constructed from MCC, MNC and MME Identifier (MMEI).
In turn the MMEI is constructed from an MME Group ID (MMEGI) and an
MME Code (MMEC).
For paging, the mobile is paged with the S-TMSI. The S-TMSI is constructed
from the MMEC and the M-TMSI.
The operator needs to ensure that the MMEC is unique within the MME pool
area and, if overlapping pool areas are in use, unique within the area of
overlapping MME pools.
The GUTI is used to support subscriber identity confidentiality, and, in the
shortened S-TMSI form, to enable more efficient radio signalling procedures.
GUMMEI
MCC MNC MMEGI MMEC M-TMSI
MMEI
S-TMSI
Figure 2-21 GUTI structure
TAITAITAITAI
The Tracking Area Identity (TAI) is the identity used to identify TrackingAreas (TAs). The Tracking Area Identity is constructed from the MCC, MNC
and Tracking Area Code (TAC).
MCC MNC TAC
Figure 2-22 Tracking Area Identity (TAI)
7/30/2019 129454451 Lelliwa LTE Technology
47/323
7/30/2019 129454451 Lelliwa LTE Technology
48/323
LTE/EPS Technology
50
This page is intentionally left blank
7/30/2019 129454451 Lelliwa LTE Technology
49/323
3 OFDMA & SC-FDMA
51
IntroductionIntroductionIntroductionIntroductionMultiple access in telecommunications systems refers to techniques that
enable multiple users to share limited network resources efficiently. A
telecommunications network has finite resources that are usually defined in
terms of bandwidth. When there is more than one user to access such limited
bandwidth, an multiple access scheme must be put in place to control the
share of bandwidth among multiple users so that everyone can use services
provided by the network and to make sure that no single user spends all
available resources.
From a very early stage of modern communications, researchers have been
working on finding the best multiple access scheme to follow the above
simple rule of resource sharing among multiple users. Very visible and
fundamental ways of sharing bandwidth, frequency and time separation, were
chosen as the beginning of multiple access generation.
FDMAFDMAFDMAFDMA
In the first multiple access communications systems, the available frequency
spectrum for a given system was divided into some frequency channels where
each channel occupies a portion of total available bandwidth and is given to a
single user. Multiple users using separate frequency channels could access the
same system without significant interference from other users concurrently
operating in the system. It is the simplest way of having an scheme in a multi-
user system, and it is referred to as Frequency Division Multiple Access
(FDMA).
time
frequencyf1 f2 f3 f4 f5 f6 f7
Figure 3-1 Frequency Division Multiple Access
7/30/2019 129454451 Lelliwa LTE Technology
50/323
LTE/EPS Technology
52
TDMATDMATDMATDMA
With the same concept, Time Division Multiple Access (TDMA) schemes
came to start the digital communications era by dividing the time axis into
portions or time slots, each assigned to a single user to transmit data
information. TDMA schemes thus came into effect through frame and
multiframe concepts: a user could send a large data file within time slots of
periodical frames. Data from a single user always sits in the same time slot
position of a frame, so at the receiver all information from that portion can be
collected and aggregated to shape the original transmitted packet. TDMA,
together with Pulse Code Modulation (PCM), has become an effective way of
sharing the available system resources not only in wireless communications
but in wired communications since then. TDMA has kept its dominance in
wired and wireless systems for many years. Many cellular standards such asthe GSM and GPRS adopted TDMA as their multiple access scheme.
time
frequency
TS 1
TS 2
TS 3
TS 4
Figure 3-2 Time Division Multiple Access
As is clear from the above simple review, in both FDMA and TDMA
techniques the number of channels or time slots is fixed for a given system,
and a single channel is allocated to a single user for the whole period of
communications.
This was not only a concept to have a simple multiple access technique in the
early stage of modern telecommunications, but was based on the dominantservice in mind at the time, voice communications. Having a fixed channel or
time slot assignment could guarantee the service quality for real-time and
constant-bit-rate voice telephony, the main service at that time. By increasing
the number of services from simple voice to more burst data transmissions,
fixed channel assignment has shown its lack of efficiency in utilizing the
scarce spectrum, especially with the exponential increase in number of users.
Researchers started to think of more dynamic channel assignment forms of
TDMA and FDMA that could allocate a channel only when the user wants to
transmit data. While many dynamic channel assignment multiple access
schemes have been invented since then, the fixed upper limit on number of
7/30/2019 129454451 Lelliwa LTE Technology
51/323
3 OFDMA & SC-FDMA
53
users in a TDMA or FDMA system has created a demand for new multiple
access schemes with fewer limitations, particularly for mobile
communications.
CDMACDMACDMACDMA
With this idea in mind, Code Division Multiple Access (CDMA) schemes
based on spread spectrum technology started to come into commercial
systems, different from their original environment mainly in military
applications. In a CDMA system the relatively narrowband users information
is spread into a much wider spectrum using a high clock chip rate. Using
different uncorrelated codes by each user, it is possible to send multiple users
information on the same frequency spectrum without significant difficulty in
detecting the desired signal at the receiver side as long as the correctspreading code is known to the receiver. The signal from each user will have
very low power and be seen by others as background noise. Therefore, as long
as the total power of noise (i.e., multi-user interference) is less than a
threshold, it is possible to detect the desired signal using the spreading code
used to encode the signal at the transmitter. Using spread spectrum
techniques, CDMA has become a dynamic channel allocation multiple access
scheme that has no rigid channel allocation limitation for individual users.
The number of users is also not fixed as in TDMA and FDMA, and a new
user can be added to the system at any time. The upper limit for the maximum
number of simultaneous users in the system using the same frequency
spectrum is decided by the effect of total power of multi-user interference;
thus, adding new users to a CDMA system will only cause graceful
degradation of signal quality. CDMA is thus seen as an multiple access
scheme that has no fixed maximum number of users as opposed to TDMA
and FDMA schemes.
frequency
time
code
code 1
code 2
code 3
code 4
Figure 3-3 Code Division Multiple Access
7/30/2019 129454451 Lelliwa LTE Technology
52/323
LTE/EPS Technology
54
With the ex