4th GENERATION OF WIRELESS NETWORKS (LTE)

Table of Contents
Abbreviation…………………………………………………………………………………….ii
List of figures……………………………………………………………………………………v
List of Tables…………………………………………………………………………………….vi
I.

GENERAL INTRODUCTION... ..................................................................................................... 1

II.

Chapter 01: Wireless Evolution towards 4th G .................................................................................. 2
INTRODUCTION…………………………………………………………………………………2
WIRELESS EVOLUTION………………………………………………………………...............3

1.
2.

III. Chapter 02: 4th Generation "LTE"……………………………………………………………………17
1.
2.
3.

Introduction………………………………………………………………………………….17
Features and capabilities………………………………………………………………….….20
4G (LTE) the Technologies and Techniques………………………………………..……….21
3.A.LTE: The Downlink: ......................................................................................................... 21
1.OFDMA ............................................................................................................................ 21
2.OFDMA Parameterization ................................................................................................. 23
3.Downlink data transmission ............................................................................................... 27
4.Downlink reference signal structure and cell search ........................................................... 28
5.Downlink Hybrid ARQ (Automatic Repeat Request) ......................................................... 31
3.B. LTE: The Uplink: ............................................................................................................. 32
1.SC-FDMA ........................................................................................................................ 32
2.SC-FDMA parameterization ............................................................................................. 33
3.Uplink Data transmission .................................................................................................. 35
4.Uplink reference signal structure....................................................................................... 38
5.Uplink Hybrid ARQ (Automatic Repeat Request) ............................................................. 39
3.C. LTE: MIMO Concepts .................................................................................................... 40
3.D. LTE Protocol Architecture……………………………………………………………..…45
3.E. Evolution Of Applications And Services………………………………………………….47

4.

Conclusion…………………………………………………………………………………51

IV. GENERAL CONCLUSION .......................................................................................................... 52
V.

REFERENCES……………………………………………………………………………………….53

i

ABBREVIATION
4G
ACK
ARQ
BCCH
BCH
CAPEX
CCCH
CCDF
CCO
CDD
CP
C-plane
CQI
CRC
C-RNTI
CS
DCCH
DCI
DFT
DL
DL-SCH
DRS
DRX
DTCH
DTX
DVB
DwPTS
eNB
EDGE
EPC
E-UTRA
E-UTRAN
FDD
FFT
GERAN
GP
GSM
HARQ
HRPD
HSDPA
HSPA
HSUPA
IFFT
IP
LCID
LTE
MAC

4th Generation
Acknowledgement
Automatic Repeat Request
Broadcast Control Channel
Broadcast Channel
Capital Expenditures
Common Control Channel
Complementary Cumulative Density Function
Cell Change Order
Cyclic Delay Diversity
Cyclic Prefix
Control Plane
Channel Quality Indicator
Cyclic Redundancy Check
Cell Radio Network Temporary Identifier
Circuit Switched
Dedicated Control Channel
Downlink Control Information
Discrete Fourier Transform
Downlink
Downlink Shared Channel
Demodulation Reference Signal
Discontinuous Reception
Dedicated Traffic Channel
Discontinuous Transmission
Digital Video Broadcast
Downlink Pilot Timeslot
E-UTRAN NodeB
Enhanced Data Rates for GSM Evolution
Evolved Packet Core
Evolved UMTS Terrestrial Radio Access
Evolved UMTS Terrestrial Radio Access Network
Frequency Division Duplex
Fast Fourier Transform
GSM EDGE Radio Access Network
Guard Period
Global System for Mobile communication
Hybrid Automatic Repeat Request
High Rate Packet Data
High Speed Downlink Packet Access
High Speed Packet Access
High Speed Uplink Packet Access
Inverse Fast Fourier Transformation
Internet Protocol
Logical channel identifier
Long Term Evolution
Medium Access Control

Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila

ii

MBMS
MIMO
MME
MU-MIMO
NACK
NAS
OFDM
OFDMA
OPEX
PAPR
PBCH
PCCH
PCFICH
PCH
PDCCH
PDCP
PDN
PDSCH
PDU
PHICH
P-GW
PHY
PMI
PRACH
PS
PUCCH
PUSCH
QAM
QoS
QPSK
RACH
RAN
RA-RNTI
RAT
RB
RF
RI
RIV
RLC
ROHC
RRC
RRM
RTT
S1
SAE
SC-FDMA
SDMA
SDU
SFBC

Multimedia Broadcast Multicast Service
Multiple Input Multiple Output
Mobility Management Entity
Multi User MIMO
Negative Acknowledgement
Non Access Stratum
Orthogonal Frequency Division Multiplexing
Orthogonal Frequency Division Multiple Access
Operational Expenditures
Peak-to-Average Power Ratio
Physical Broadcast Channel
Paging Control Channel
Physical Control Format Indicator Channel
Paging Channel
Physical Downlink Control Channel
Packet Data Convergence Protocol
Packet Data Network
Physical Downlink Shared Channel
Protocol Data Unit
Physical Hybrid ARQ Indicator Channel
PDN Gateway
Physical Layer
Precoding Matrix Indicator
Physical Random Access Channel
Packet Switched
Physical Uplink Control Channel
Physical Uplink Shared Channel
Quadrature Amplitude Modulation
Quality of Service
Quadrature Phase Shift Keying
Random Access Channel
Radio Access Network
Random Access Radio Network Temporary Identifier
Radio Access Technology
Radio Bearer
Radio Frequency
Rank Indicator
Resource Indication Value
Radio Link Control
Robust Header Compression
Radio Resource Control
Radio Resource Management
Radio Transmission Technology
Interface between eNB and EPC
System Architecture Evolution
Single Carrier – Frequency Division Multiple Access
Spatial Division Multiple Access
Service Data Unit
Space Frequency Block Coding


iii

SISO
S-GW
SR
SRS
SU-MIMO
TDD
TD-SCDMA
TPC
TS
TTI
UCI
UE
UL
UL-SCH
UMTS
U-plane
UpPTS
UTRA
UTRAN
VoIP
WCDMA
W LAN
X2

Single Input Single Output
Serving Gateway
Scheduling Request
Sounding Reference Signal
Single User MIMO
Time Division Duplex
Time Division-Synchronous Code Division Multiple Access
Transmit Power Control
Technical Specification
Transmission Time Interval
Uplink Control Information
User Equipment
Uplink
Uplink Shared Channel
Universal Mobile Telecommunications System
User plane
Uplink Pilot Timeslot
UMTS Terrestrial Radio Access
UMTS Terrestrial Radio Access Network
Voice over IP
Wideband Code Division Multiple Access
Wireless Local Area Network
Interface between eNBs


iv

List of Figures
Figure 1 : IMTS brief case phone from the 1970‟s ............................................................. 3
Figure 2 : 2G Wireless Infrastructures ................................................................................ 5
Figure 3 : Mobile network architecture .............................................................................. 6
Figure 4 : 2.5 G Wireless Infrastructures ............................................................................ 7
Figure 5 : Path to 3G Wireless infrastructure ..................................................................... 8
Figure 6 : 3G Architecture ................................................................................................ 10
Figure 7 : Speed of 3G Networks ..................................................................................... 11
Figure 8 : Evolution in Data Transmission Rate ............................................................... 12
Figure 9 : Requirements for 4G system ............................................................................ 13
Figure 10 : 4G system ....................................................................................................... 14
Figure 11 : Frequency-time representation of an OFDM Signal ...................................... 22
Figure 12 : OFDM useful symbol generation using an IFFT ........................................... 22
Figure 13 : OFDM Signal Generation Chain .................................................................... 23
Figure 14 : Frame structure type 1 .................................................................................... 23
Figure 15 : Frame structure type 2 (for 5ms switch-point periodicity) ............................. 24
Figure 16: Downlink Resource grid .................................................................................. 26
Figure 17 : OFDM A time-frequency multiplexing (example for normal cyclic prefix) . 28
Figure 18 : Downlink reference signal structure (normal cyclic prefix) .......................... 29
Figure 19 : Primary/secondary synchronization signal and PBCH structure (frame
structure type 1/FDD, normal cyclic prefix) ..................................................................... 30
Figure 20 : Primary/secondary synchronization signal and PBCH structure (frame
structure type2/TDD, normal cyclic prefix)...................................................................... 30
Figure 21: ACK/NACK bundling in TD-LTE .................................................................. 31
Figure 22 : Block diagram of DFT-s-OFDM (localized transmission) ............................ 33
Figure 23 : Uplink resource grid ....................................................................................... 34
Figure 24 : Intra-subframe hopping, Type 1 ..................................................................... 37
Figure 25 : Intra-subframe hopping, Type 1 (blue, UE1) and Type 2 (green, UE3) ........ 38
Figure 26 : PHICH principle ............................................................................................. 40
Figure 27 : Spatial multiplexing (simplified).................................................................... 41
Figure 28: Transmit diversity (SFBC) principle ............................................................... 44
Figure 29 : Architecture of LTE radio access (E-UTRAN) and core network (EPC) ...... 45
Figure 30 : Link layer structure for the downlink ............................................................. 47
Figure 31 : Mobile applications with technical requirements and growth drivers ........... 48


v

List of Tables
Table 1: Data rate and spectrum efficiency requirements defined for LTE ..................... 20
Table 2: Uplink-Downlink configurations for LTE TDD ................................................. 24
Table 3 : Special Sub frame configurations in TD-LTE ................................................... 25
Table 4: Number of resource blocks for different LTE bandwidths (FDD and TDD) ..... 26
Table 5 : Downlink frame structure parameterization (FDD and TDD) .......................... 27
Table 6: Number of HARQ processes in TD-LTE (Downlink) ....................................... 31
Table 7: Uplink frame structure parameterization (FDD and TDD) ................................ 34
Table 8 : Possible RB allocation for uplink transmission ................................................. 35
Table 9 : Contents of DCI format 0 carried on PDCCH ................................................... 36
Table 10 : Transmission Modes in LTE as of 3GPP Release 8 ........................................ 42
Table 11 : Precoding codebook for 2 transmit antenna case ............................................ 43


vi

I.

GENERAL INTRODUCTION
The objective of the current communication systems is the distribution and

transfer of the everyday augmented massive volumes of data presented in many forms
and types of Multimedia applications such as web browsing, video and audio streaming
and data transfer wirelessly at high Broadband speed. Ensuring the availability and the
proper functioning of these services requires the transmission of signals on the mobileradio channel, and regardless of the position and mobility of the user.
Crossing the channel, these signals will be exposed to the phenomena of
multipath and frequency shift by the Doppler Effect and many other unpredicted
phenomenons altering and changing the information totally and beyond recognition. They
provide distortion and induce degradation of the quality of communication and therefore
limited and low Broadband speed and this issue led to many handicaps in the world of
communication rendering it the most invested and based on research domain by many
R&D companies and facilities in the present time and the future.
Transmission techniques were created and developed by many pioneers in the
field of telecommunications and were designed primarily to address these issues and
problems. And one of the current time techniques and methods lead to the wireless
revolutionary telecommunication system LTE based on the 4th generation of mobile and
wireless communication and known also as beyond 3G.
Our goal in this project is to introduce this revolutionary technology, and it‟s
current impacts and future one‟s on human kind, and to do so many chapters were set and
put on action to give you a proper introduction in a fairly presented dissertation.
The dissertation is structured as follows.in the first chapter a brief introduction to
the world of telecommunication in the mobile and wireless communication systems.
Next, we introduce the previous technologies to the 4th generation (LTE), from
the most primitive way of telecommunication till evolved Second Generation, next to
Third Generation.
Thereafter the evolution towards Fourth Generation is described in the second
chapter with the Release 8 (LTE). The most important features of this release are
explained in the corresponding subsections as well as the improvements in the
throughput, the specifications and the modifications regarding previous releases.


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Chapter 01: Wireless Evolution towards 4
1.

G

INTRODUCTION

This paper discusses the challenge of evolving the core network of today‟s 2G
and 3G networks to enable the unprecedented growth in voice and data expected with
the migration to 4G wireless networks. The introduction of packet core infrastructure
into digital wireless networks offers both challenges and opportunities for wireless
service providers and its users.
Despite the economic situation and recent world events, the basic drivers of
growth in mobile computing are as strong as ever. In fact, telecommuting and
decentralized workforces are options many companies are looking at increasingly as they
reevaluate their physical security vulnerabilities and develop risk management plans.
Mobile devices have become significantly more powerful, and in many
cases smaller and lighter versions are available for handheld. Storage and processor
speeds have advanced as expected. While 3G haven‟t quite been implemented totally,
designers are already thinking about the deployment of 4G technologies across the Globe.
The hope once envisioned for 3G as a true broadband service has all but dwindled
away. It is apparent that 3G systems, while maintaining the possible 2-Mbps data rate in
the standard, will realistically achieve 384-kbps rates. To achieve the goals of true
broadband cellular service, the systems have to make the leap to a fourth-generation (4G)
network. This is not merely a numbers game. 4G is intended to provide high speed, high
capacity, low cost per bit, IP based services.
The goal is to have data rates up to 20 Mbps, even when used in such scenarios as
a vehicle traveling 200 kilometers per hour. New design techniques, however, are needed
to make this happen, in terms of achieving 4G performance at a desired target of onetenth the cost of 3G. That‟s the goal of 4G. In short, Fourth Generation (4G) mobile
devices and services will transform wireless communications into on-line, real-time
connectivity. 4G wireless technologies will allow an individual to have immediate access
to location-specific services that offer information on demand at an amazingly high speed
and low cost.
Welcome to the world of amazing realities of an amazingly high-speed data
communication and mobile technology at a very low cost. That‟s The 4th G.


2

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2.

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WIRELESS EVOLUTION
A. First generation

In the MTS/IMTS world, if a user travelled outside the coverage area of a base
station, any ongoing call dropped and would have to be re-established when the user reentered system coverage area. In the cellular world, users had smooth and relatively
seamless mobility over multiple cells. A major underlying success factor for cellular and
its seamless mobility control technique was the availability of the microprocessor, which
provided sophisticated, intelligent control at both the mobile and network. In 1983, the
first commercial cellular system, the Advanced Mobile Phone Service (AMPS) was
deployed in the Chicago area. AMPS is typically referred to as 1st Generation Cellular.
In addition to aggressive spatial frequency reuse and instantaneous mobility management
techniques, regulators in the United States provided AMPS with a substantial quantity of
radio spectrum. Instead of 8 or 16 channels per metropolitan area, AMPS now had 666
channels available which provided a capacity increase of over a million times in large
metropolitan areas. AMPS was still FM in the beginning, but now many more phone
numbers were available and adoption was rapid throughout the 1980‟s and early 1990‟s.
Similar technologies were developed and deployed around the globe, e.g. the Nordic
Mobile Telephone Service (NMT) in 1981, Total Access Communication System
(TACS) and Extended TACS (ETACS) in Europe.

Figure 1 : IMTS brief case phone from the 1970‟s

During the years 1983 through about 1986, cellular mobile equipment was still
expensive. A typical automotive installation brought a fixed cost of $2,000 to $4000 US
Dollars plus the monthly subscription fees to the mobile operator. Incremental costs of
making and receiving calls was on top of the cost of equipment and service. Therefore,

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even after the introduction of the AMPS cellular system, the primary market segment for
mobile telephony was still largely commercial users. But with the availability of
equipment and phone numbers, there was an element of high-end personal users entering
the cellular user community as well. Throughout the 1980‟s and 1990‟s, the learning
curve brought down the cost of manufacturing equipment (Freeman, 1997). With lower
costs came lower prices, and with lower prices came greater demand. By the early
1990‟s, most middle class adults owned mobile telephone equipment of some kind.
B. Second Generation (2G)
The second generation of digital mobile phones appeared about ten years later to
First Generation mobile phones, along with the first digital mobile networks. During the
second generation, the mobile telecommunications industry experienced exponential
growth both in terms of subscribers as well as new types of value -added
services. Mobile phones are rapidly becoming the preferred means of personal
communication, creating the world's largest consumer electronics industry. This way the
telecommunication industry experienced for the first time the growth and profits of
mobile telecommunication with advancement of technology. This prompted them to build
more powerful communication means.
The second generation (2G) of the wireless mobile network was based on lowband digital data signaling. The most popular 2G wireless technology is known as Global
Systems for Mobile Communications (GSM). GSM systems, first implemented in 1991,
are now operating in about 140 countries and territories around the world. An estimated
248 plus million users now operate over GSM systems. GSM technology is a
combination of Frequency Division Multiple Access (FDMA) and Time Division
Multiple Access (TDMA). The first GSM systems used a 25MHz frequency spectrum in
the 900MHz band. FDMA is used to divide the available 25MHz of bandwidth into 124
carrier frequencies of 200 kHz each. Each frequency is then divided using a TDMA
scheme into eight timeslots. The use of separate timeslots for transmission and reception
simplifies the electronics in the mobile units. Today, GSM systems operate in the
900MHz and 1.8 GHz bands throughout the world with the exception of the Americas
where they operate in the 1.9 GHz band.
In addition to GSM, a similar technology, called Personal Digital
Communications (PDC), using TDMA -based technology, emerged in Japan. Since then,
several other TDMA-based systems have been deployed worldwide and serve an
estimated 89 million people worldwide. While GSM technology was developed in
Europe, Code Division Multiple Access (CDMA) technology was developed in North
America. CDMA uses spread spectrum technology to break up speech into small,
digitized segments and encodes them to identify each call. CDMA systems have been

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implemented worldwide in about 30 countries and serve an estimated 44 million
subscribers.

Figure 2 : 2G Wireless Infrastructures

While GSM and other TDMA-based systems have become the dominant 2G
wireless technologies, CDMA technology is recognized as providing clearer voice quality
with less background noise, fewer dropped calls, enhanced security, greater reliability
and greater network capacity.
The Second Generation (2G) wireless networks mentioned above are also mostly
based on circuit-switched technology. 2G wireless networks are digital and expand
the range of applications to more advanced voice services, such as Called Line
Identification. 2G wireless technology can handle some data capabilities such as fax and
short message service at the data rate of up to 9.6 kbps, but it is not suitable for web
browsing and multimedia applications.


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Figure 3 : Mobile network architecture

What improvements were needed? Fundamentally, wireless users wanted even
more from their mobile sets:








Email and fast internet access
Synchronization of mobile personal management tools with popular
personal management software such as Microsoft Outlook, Lotus
Organizer or Symantec ACT!
Location-based services such as navigation and mobile yellow pages
Robust "buddy" features such as messaging
Video
Global roaming, etc.

To meet these demands, network operators and wireless equipment manufacturers
alike were turning toward a third generation (3G) of wireless systems that deliver higher
data rates based on packet transmission and new modulation formats. But the path toward
3G, though evolving, was far from clear. In fact, there are many parallel paths, and at
least one, probably two, generations of transitional technologies. A first step in realizing
the benefits associated with a packet core is to understand that voice gateways can play a
crucial role. Packet media gateways are part of a new generation of switching technology
that enables the integration of wireless (2G/2.5G/3G), fixed IP, PSTN and IN-based
services. There are three key elements to this next-generation switching architecture:
core IP/ATM switches/routers, media gateways in which wireless is just another
access method, and call servers and application platforms.

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C. Second Generation (2G+/2.5) Wireless Networks
As stated in a previous section, the virtual explosion of Internet usage has
had a tremendous impact on the demand for advanced wireless data communication
services. However, the effective data rate of 2G circuit -switched wireless systems is
relatively slow -- too slow for today's Internet. As a result, GSM, PDC and other TDMA based mobile system providers and carriers developed 2G+ technology which was
packet-based and increases the data communication speeds to as high as 384kbps.
These 2G+ systems are based on the following technologies: High Speed CircuitSwitched Data (HSCSD), General Packet Radio Service (GPRS) and Enhanced Data
Rates for Global Evolution (EDGE) technologies. HSCSD is one step towards 3G
wideband mobile data networks. This circuit-switched technology improves the data rates
up to 57.6kbps by introducing 14.4 kbps data coding and by aggregating 4 radio channels
timeslots of 14.4 kbps.
To meet the needs of today‟s subscribers, wireless service providers are in the
process of upgrading their 2G networks to 2.5 G networks. These 2.5G networks continue
to use the 2G architecture to deliver voice and circuit-switched data applications while
adding a packet data overlay to support additional packet data services. Upgrading
a 2G wireless infrastructure to support 2.5G enables subscribers on this network to attain
data rates up to 170 kbps, a substantial increase over 2G data rates.
Choosing a multi-service core network solution that efficiently handles multiple
traffic types (e.g., packet data, voice, etc.) not only gives the operator the capability of
providing new services with increased data rates, but also saves on TDM voice
expenditures as previously outlined.

.

Figure 4 : 2.5 G Wireless Infrastructures

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D. Moving Towards 3G
The "path to 3G" (see Figure 5) begins with several parallel 2G paths depicting
the currently deployed technologies. It has become increasingly apparent that subscribers
will not wait until the final 3G technologies have been deployed. For this reason, many of
the 2.5G standards were been developed for deployment in the interim. Surprisingly,
many of these, notably GPRS, EDGE, and IS136B/HS, may offer sufficient capabilities
to satisfy end user customers for years to come. It seems likely that, short term,
significantly more rather than fewer standards will emerge and be used concurrently,
often running on adjacent or common carrier frequencies. The 2.5G transition period
promises to be even more complex than today's 2G market.
As we look at the "road map" (Figure 5) of the transition from 2G to 3G, it's
important to note that the journey begins with several parallel 2G paths (GSM, CDMA,
etc.), which split into even more paths before converging, ideally, on a single 3G
standard. HSCSD (High-speed Circuit-Switched Data) and GPRS (General Packet Radio
Service) will share the market with emerging variants of IS-136 and IS-95. The 2.5G
transition period promises to be even more complex than today's 2G market.

Figure 5 : Path to 3G Wireless infrastructure

As Figure 5 implies, equipment manufacturers and network operators will
continue to need test solutions for multiple standards during the 2.5G period, even more
so than they have in the past. Given that many different standards will exist, equipment
manufacturers must be able to adopt flexible design and manufacturing processes to meet

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changing demands. For many equipment manufacturers it may be necessary to design and
manufacture GSM, TDMA, CDMA One, HSCSD, GPRS, EDGE, EGPRS, IS-136B/HS,
and IS-95B phones and network elements concurrently, often building them on the
same manufacturing lines.
E. Third Generation (3G) Wireless Networks
3G wireless technology represents the convergence of various 2G wireless
telecommunications systems into a single global system that includes both terrestrial and
satellite components. One of the most important aspects of 3G wireless technologies is its
ability to unify existing cellular standards, such as CDMA, GSM, and TDMA, under one
umbrella. The following three air interface modes accomplish this result: wideband
CDMA, CDMA2000 and the Universal Wireless Communication (UWC -136) interfaces.
Wideband CDMA (W-CDMA) is compatible with the current 2G GSM networks
prevalent in Europe and parts of Asia. W-CDMA will require bandwidth of between 5
MHz and 10 MHz, making it a suitable platform for higher capacity applications. It can
be overlaid onto existing GSM, TDMA (IS-36) and IS95 networks. Subscribers are
likely to access 3G wireless services initially via dual band terminal devices. W-CDMA
networks will be used for high-capacity applications and 2G digital wireless systems will
be used for voice calls.
The second radio interface is CDMA 2000, which is backward compatible with
the second generation CDMA IS-95 standard predominantly used in US.
The third radio interface, Universal Wireless Communications – UWC-136, also
called IS-136HS, was proposed by the TIA and designed to comply with ANSI-136,
the North American TDMA standard. 3G wireless networks consist of a Radio Access
Network (RAN) and a core network. The core network consists of a packet-switched
domain, which includes 3G SGSNs and GGSNs, which provide the same functionality
that they provide in a GPRS system, and a circuit -switched domain, which includes 3G
MSC for switching of voice calls. Charging for services and access is done through the
Charging Gateway Function (CGF), which is also part of the core network. RAN
functionality is independent from the core network functionality. The access network
provides a core network technology independent access for mobile terminals to different
types of core networks and network services. Either core network domain can access any
appropriate RAN service; e.g. it should be possible to access a “speech” radio access
bearer from the packet-switched domain.


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Figure 6 : 3G Architecture

3G: what's new? Is 3G is designed to deliver







A wide range of market-focused applications
Long-term market-driven creativity, an innovative value chain and real
user benefits, driving genuine market demand
Advanced, lightweight, easy-to-use terminals with intuitive interfaces·
Instant, real-time multimedia communications
Global mobility and roaming
A wide range of vendors and operators, offering choice, competition and
affordability
High-speed e-mail and Internet access


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The Speed

Figure 7 : Speed of 3G Networks

3G enabled users to transmit voice, data, and even moving images. In order to
realize these services, 3G improves the data transmission speed up to 144Kbps in a highspeed moving environment, 384Kbps in a low-speed moving environment, and 2Mbps in
a stationary environment. 3G provides services like Internet connection, transmission of
large-scale data and moving contents photographed by digital cameras and videos, and
software downloading.
At present, maximum data transmission speed is 64Kbps offered in 3G services,
and it was expected that by toward early 2001, 384Kbps would be possible. At the early
stage of 3G services, a 144Kbps-transmission speed is expected. By around 2005 when
3G is in general use; a maximum speed of 2Mbps will be possible.
2.

What are the standards saying?

It is important to understand what people mean when they talk about an
all-IP network. For instance, does it play at the transport, service or application level?
Clearly the ultimate goal and one of the prime reasons for adopting IP as a unifying
protocol is convergence on a single protocol at the application layer. For example, the
architectural principles for the all -IP UMTS network clearly state that the UMTS core
network shall be independent of the underlying trans-port mechanism. More specifically,
for the IP transport layer, Layer 2 options are ATM, PPP or MPLS. Therefore, wireless
operators have several options with regard to implementing the initial packet core
infrastructure, as long as the core can be evolved to support the high bandwidth
requirements of the future. Streams of traffic on each physical facility (between the end user and the network or between network switches) Virtual circuits can be statically
configured as permanent virtual circuits (PVC) or dynamically controlled via signaling.
While 3G haven‟t quite arrived, designers are already thinking about 4G technology.
With it comes challenging RF and base band design headaches.

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Figure 8 : Evolution in Data Transmission Rate

Cellular service providers are slowly beginning to deploy third-generation
(3G) cellular services. As access technology increases, voice, video, multimedia, and
broadband data services are becoming integrated into the same network. The hope once
envisioned for 3G as a true broadband service has all but dwindled away. It is
apparent that 3G systems, while maintaining the possible 2-Mbps data rate in the
standard, will realistically achieve 384-kbps rates. To achieve the goals of true broadband
cellular service, the systems have to make the leap to a fourth-generation (4G) network.
This is not merely a numbers game. 4G is intended to provide high speed, high capacity,
low cost per bit, IP based services.
The goal is to have data rates up to 20 Mbps, even when used in such scenarios as
a vehicle traveling 200 kilometers per hour. New design techniques, however, are needed
to make this happen, in terms of achieving 4G performance at a desired target of onetenth the cost of 3G. The move to 4G is complicated by attempts to standardize on a
single 3G protocol. Without a single standard on which to build, designers face
significant additional challenges.
F. Multi carrier modulation
To achieve a 4G standard, a new approach is needed to avoid the divisiveness
we've seen in the 3G realms. One promising underlying technology to accomplish this is
multi carrier modulation (MCM), a derivative of frequency-division multiplexing.
MCM is not a new technology; forms of multi carrier systems are currently used
in DSL modems, and digital audio/video broadcast (DAB/DVB). MCM is a base band
process that uses parallel equal bandwidth sub-channels to transmit information.

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Normally implemented with Fast Fourier transform (FFT) techniques, MCM's
advantages include better performance in the inter symbol interference (ISI) environment,
and avoidance of single -frequency interferers. However, MCM increases the peak-toaverage ratio (PAVR) of the signal, and to overcome ISI a cyclic extension or guard band
must be added to the data.
G. Fourth Generation Wireless Systems(All-IP)
Reasons to Have 4G
 Support interactive multimedia services: teleconferencing, wireless
Internet, etc.
 Wider bandwidths, higher bit rates.
 Global mobility and service portability.
 Low cost.
 Scalability of mobile networks.

Figure 9 : Requirements for 4G system

What's New in 4G?
Entirely packet-switched networks
 All network elements are digital.
 Higher bandwidths to provide multimedia services at lower cost (up to
100Mbps).
 Tight network security.

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What is 4G?
4G takes on a number of equally true definitions, depending on whom you are
talking to. In simplest terms, 4G is the next generation of wireless networks that will
replace 3G networks sometimes in future. In another context, 4G is simply an
initiative by academic R&D labs to move beyond the limitations and problems of 3G
which is having trouble getting deployed and meeting its promised performance and
throughput. In reality, as of first half of 2002, 4G is a conceptual framework for or a
discussion point to address future needs of a universal high speed wireless network that
will interface with wire line backbone network seamlessly. 4G is also represents the hope
and ideas of a group of researchers in Motorola, Qualcomm, Nokia, Ericsson, Sun, HP,
NTT DoCoMo and other infrastructure vendors who must respond to the needs of
MMS, multimedia and video applications if 3G never materializes in its full glory.

Figure 10 : 4G system

Motivation for 4G Research Before 3G Has Not Been Deployed?






3G performance may not be sufficient to meet needs of future highperformance applications like multi-media, full motion video, wireless
teleconferencing. We need a network technology that extends 3G
capacities by an order of magnitude.
There are multiple standards for 3G making it difficult to roam and
interoperate across networks. We need global mobility and service
portability
3G is based on primarily a wide-area concept. We need hybrid networks
that utilize both wireless LAN (hot spot) concept and cell or base-station
wide area network design.


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


1.

2.

3.

4.

5.

We need wider bandwidth
Researchers have come up with spectrally more efficient modulation
schemes that cannot be retrofitted into 3G infrastructure
 We need all digital packet networks that utilize IP in its fullest form with
converged voice and data capability.
Specification:
o 4G can provide 10 times increase in data transfer over 3G.
o This speed can be achieved through OFDM.
o OFDM can not only transfer data at speed of more than
100mbps, but it can also eliminate interference that impairs
high speed signals.
Applications:
o 4G will provide for a vast no. of presently nonexistent application
for mobile devices.
o 4G device will differ from present day mobile device in that there
will be navigation menus.
o 4G will provide a seamless network for users who travel &
required uninterrupted voice/data communication.
Need of 4G:
o Firstly 3G‟s maximum data transfer rate of 384 kbps to 2 mbps is
much slower than 20mbps to 100mbps of 4G.
o With its use of existing technologies & communication
standards, 4G present a comparably inexpensive standard.
o 4G will utilize most of the existing wireless communication
infrastructure.
Issue in 4G:
o Access
o Handoff
o Location co-ordination
o Resource co-ordination to add new user
o Support for quality of service.
o Wireless securities & authentication.
o Network failure & backup.
o Pricing and billing.
Technique used in 4G:
o OFDM
o UWB(Ultra Wide Band)
o Millimeter wireless.
o Smart Antennas


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o Long term power prediction.
o Scheduling among users.
o Adaptive modulation and power control.
6. Advantages and Disadvantages of 4G :
Advantages:
o Support for interactive multimedia voice, streaming video, internet &
other broadband services.
o IP based mobile system.
o High speed, high capacity & low cost per bit.
o Global access, service portability & scalable mobile services.
o Better scheduling and call admission control technique.
o Ad-hoc & multi-hop network.
o Better spectral efficiency.
o Seamless network of multiple protocols & air interfaces.
Disadvantages:
o Expensive
o Battery uses are more hard to implement
o Need complicated hardware.
4G mobile phone technology promises faster communication Speeds (100 Mbps
to 1 Gbps), capacity and diverse usage formats. These formats would provide richer
content and support for other public networks such as optical fiber and wireless local area
networks.


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1. Introduction

Fourth generation wireless (4G) is an abbreviation for the fourth generation of
cellular wireless standards and replaces the third generation of broadband mobile
communications. The standards for 4G, set by the radio sector of the International
Telecommunication Union (ITU-R), are denoted as International Mobile
Telecommunications Advanced (IMT-Advanced).
An IMT-Advanced cellular system is expected to securely provide mobile service
users with bandwidth higher than 100 Mbps, enough to support high quality streaming
multimedia content. Existing 3G technologies, often branded as Pre-4G (such as mobile
WiMAX and 3G LTE), fall short of this bandwidth requirement. The majority of
implementations branded as 4G do not comply with the full IMT-Advanced standard.
The premise behind the 4G service offering is to deliver a comprehensive IP
based solution where multimedia applications and services can be delivered to the user
anytime and anywhere with a high data rate, premium quality of service and high
security. Seamless mobility and interoperability with existing wireless standards is
crucial to the functionality of 4G communications. Implementations will involve new
technologies such as Femto cell and Pico cell, which will address the needs of mobile
users wherever they are and will free up network resources for roaming users or those in
more remote service areas.
Two competing standards were submitted in September 2009 as technology candidates
for ITU-R consideration:



LTE Advanced - as standardized by the 3GPP
802.16m - as standardized by IEEE

These standards aim to be:






Spectrally efficient
Able to dynamically allocate network resources in a cell
Able to support smooth handover
Able to offer high quality of service (QoS)
Based on an all-IP packet-switched network

WiMax is touted as the first 4G offering. It is an IP based, wireless broadband access
technology, also known as IEEE 802.16. WiMax services offer residential and business
customers with basic Internet connectivity.


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Present implementations of WiMAX and LTE are largely considered a stopgap solution
offering a considerable boost, while WiMAX 2 (based on the 802.16m specification) and
LTE Advanced are finalized. Both technologies aim to reach the objectives traced by the
ITU, but are still far from being implemented.
Mobile networks have become an important means of Internet access recently,
although these networks were primarily designed for voice transmission between two
users. With the establishment of the third generation of mobile networks (e.g. UMTS –
Universal Mobile Telecommunications System, CDMA2000 – Code Division Multiple
Access 2000) and their upgrades (e.g. HSPA – High-Speed Downlink Packet Access,
EVDO – Evolution-Data Optimized), data rates have been continuously increasing but
still have not reached those of fixed networks. At the same time, the amount of user data
transferred and the number of mobile Internet users have also increased.
The increasing amount of transferred data and new applications such as mobile
games and television, Web 2.0 and video streaming have motivated the 3GPP (Third
Generation Partnership Project) organization to start the LTE project. The project‟s aim
is to issue a series of recommendations (called Release 8) for new radio access that will
support recent trends in mobile communications.
Although often designated as a fourth-generation (4G) mobile technology, LTE
actually does not yet meet the requirements to be a 4G mobile network [1], [2] so it is
often designated as 3.9 G. Nevertheless, LTE will bring improvements in efficiency and
quality of service, lower operator costs, better utilization of the frequency spectrum and
integration with existing open standards. LTE will introduce characteristics to mobile
networks similar to those in fixed networks.
Most of the UMTS networks worldwide have been already upgraded to High
Speed Packet Access (HSPA) in order to increase data rate and capacity for packet data.
HSPA refers to the combination of High Speed Downlink Packet Access
(HSDPA) and High Speed Uplink Packet Access (HSUPA).While HSDPA was
introduced as a 3GPP Release 5 feature, HSUPA is an important feature of 3GPP
Release 6. However, even with the introduction of HSPA, evolution of UMTS has not
reached its end.
HSPA+ is a significant enhancement in 3GPP Release7, 8, 9 and even
10.Objective is to enhance performance of HSPA based radio networks in terms of
spectrum efficiency, peak data rate and latency, and exploit the full potential of
WCDMA based 5MHz operation. Important Release7 features of HSPA+ are downlink
MIMO (Multiple Input Multiple Output), higher order modulation for uplink (16QAM)
and downlink (64QAM), improvements of layer 2 protocols, and continuous packet

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connectivity. Generally spoken these features can be categorized in data-rate or capacity
enhancement features versus web-browsing and power saving features. With higher
Release 8, 9 and 10 capabilities like the combination of 64QAM and MIMO, up to four
carrier operations for the downlink(w/o MIMO), and two carriers operation for the
uplink are now possible. This increases downlink and uplink data rates up to theoretical
peaks of 168 Mbps and 23 Mbps, respectively. In addition the support of circuit-switched
Services over HSPA (CS over HSPA) has been a focus for the standardization body in
Terms of improving HSPA+ functionality in Release 8 [3].
However to ensure the competitiveness of UMTS for the next decade and beyond,
Concepts for UMTS Long Term Evolution (LTE) have been first time introduced in
3GPP Release 8. Objectives are higher data rates, lower latency on the user plane and
control plane and a packet-optimized radio access technology. LTE is also referred to as
E-UTRA (Evolved UMTS Terrestrial Radio Access) or E-UTRAN (Evolved UMTS
Terrestrial Radio Access Network). Based on promising field trials, proving the concept
of LTE as described in the following sections, real life LTE deployments significantly
increased from the start of the first commercial network in end 2009.As LTE offers also
a migration path for 3GPP2 standardized technologies (CDMA2000®1xRTT and 1xEVDO) it can be seen as the true mobile broadband technology.
This application note focuses on LTE/E-UTRA technology. In the following, the
terms LTE, E-UTRA or E-UTRAN are used interchangeably. LTE has ambitious
requirements for data rate, capacity, spectrum efficiency, and latency. In order to fulfill
these requirements, LTE is based on new technical principles. LTE uses new multiple
access schemes on the air interface: OFDMA (Orthogonal Frequency Division Multiple
Access) in downlink and SC-FDMA (Single Carrier Frequency Division Multiple
Access) in uplink . Furthermore, MIMO antenna schemes form an essential part of LTE.
In order to simplify protocol architecture, LTE brings some major changes to the
Existing UMTS protocol concepts. Impact on the overall network architecture including
the core network is referred to as 3GPP System Architecture Evolution (SAE).
LTE includes an FDD (Frequency Division Duplex) mode of operation and a
TDD (Time Division Duplex) mode of operation. LTE TDD which is also referred to as
TD LTE provides the long term evolution path for TD-SCDMA based networks.


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2. Features and capabilities
The LTE project targets the following features and capabilities of the evolved radio
access network (E-UTRAN – Evolved Universal Terrestrial Radio Access Network) [4]:
Peak data rates of 100 Mb/s on the downlink and 50 Mb/s on the uplink within a
20 MHz spectrum allocation.
Control plane capable of carrying signalization for 200 simultaneously active
users for spectrum allocations up to 5 MHz and for at least 400 users for higher
spectrum allocations.
Switch time between idle and active state shorter than 100 ms.
Radio access network latency below 10ms.
Spectral efficiency 5 bit/s/Hz on the downlink and 2.5 bit/s/Hz on the uplink.
Table 1: Data rate and spectrum efficiency requirements defined for LTE

Downlink (20 MHz)
Unit
Mbps
bps/Hz
Requirement
100
5
2x2 MIMO
172.8
8.6
4x4 MIMO
326.4
16.3

Uplink (20 MHz)
Unit
Mbps
Bps/Hz
Requirement
50
2.5
16QAM
57.6
2.9
64QAM
86.4
4.3

Radio access network optimized for mobile user speeds up to 15 km/h. The
system should support high performance for speeds up to 120 km/h. Links should
be maintained at speeds up to 350 km/h, or up to 500 km/h depending on the
frequency band.
The system should support the targeted performance within a 5 km range. A slight
degradation in performance is tolerated within a 30 km range. Ranges up to 100
km or even more should not be precluded by the specifications.
Enhanced broadcast and multicast transmissions compared to HSPA standards.
Scalable bandwidth allocation of 1.25 MHz, 1.6 MHz, 2.5 MHz, 5 MHz, 10 MHz,
15 MHz and 20 MHz . Bandwidths narrower than 5 MHz enable a smooth
transition to the spectrum of the previous generations of mobile systems.
Deployment in frequency bands of the previous generations of mobile systems:
450 MHz, 700 MHz, 800 MHz, 900 MHz, 1600 MHz, 1700 MHz, 1900 MHz,
2100 MHz and other. Because a large set of frequency bands is available, global
roaming will be possible.
Support for paired and unpaired spectrum for FDD (Frequency Division Duplex),
TDD (Time Division Duplex) and the combination of both. The advantage of
combined TDD and FDD use are simplified terminals at the expense of higher
data rates that could be achieved with the frequency duplex.
Interoperability with existing mobile systems at the same location on adjacent
channels. The time needed for handover between E-UTRAN and other radio


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access networks must be shorter than 300 ms for real time services and 500 ms for
other services.
The architecture of E-UTRAN must be packet-based, but it must also support
real-time services.
Support for various types of services (e.g. VoIP – Voice over IP, data transfer).
Reasonable system and terminal complexity, cost and power consumption.

3. 4G (LTE) The Technologies And Techniques
LTE is based on existing technologies that were not widely used in mobile
communications in the past. The reason was in their large processing requirements,
which, due to technological progress, are no longer problematic. LTE introduces new
models of multiplexing and multiple access techniques on a radio interface, such as
OFDM (Orthogonal Frequency Division Multiplex) and OFDMA (Orthogonal
Frequency Division Multiple Access) on the downlink and SC-FDMA (Single Carrier
Frequency Division Multiple Access) on the uplink.
Advanced antenna techniques, such as MIMO (Multiple-Input Multiple-Output),
are also important in LTE. MIMO increases radio network throughput by transmitting
multiple data streams simultaneously within the same frequency band.
The signals propagate along different paths, which is a common phenomenon in mobile
communications. The receiver separately receives the signals with different delays,
creating parallel channels.

A.

LTE: The Downlink:
1.

OFDMA

As opposed to single-carrier systems, OFDM does not demand higher symbol
rates to achieve higher data rates [5], [6].
The downlink transmission scheme for E-UTRA FDD and TDD modes is based
on conventional OFDM. In an OFDM system, the available spectrum is divided into
multiple carriers, called subcarriers. Each of these subcarriers is independently modulated
by a low rate data stream. OFDM is used as well in WLAN, WiMAX and broadcast
technologies like DVB. OFDM has several benefits including its robustness against
multipath fading and its efficient receiver architecture.
Figure 11 shows a representation of an OFDM signal. In this figure, a signal with
5MHz bandwidth is shown, but the principle is of course the same for the other E-UTRA
bandwidths. Data symbols are independently modulated and transmitted over a high
number of closely spaced orthogonal subcarriers [7]. In E-UTRA, downlink modulation

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schemes QPSK, 16QAM, and 64QAM are available. In the time domain, a guard
interval is added to each symbol to combat Inter-Symbol Interference (ISI) due to
channels delay spread. The delay spread is the time between the symbol arriving on the
first multi-path signal and the last multi-path signal component, typically several µs
dependent on the environment (i.e. indoor, rural, suburban, city center). The guard
interval has to be selected in that way, that it is greater than the maximum expected delay
spread. In E-UTRA, the guard interval is a cyclic prefix which is inserted prior to each
OFDM symbol.

Figure 11 : Frequency-time representation of an OFDM Signal

In practice, the OFDM signal can be generated using IFFT (Inverse Fast Fourier
Transform) digital signal processing. The IFFT converts a number N of complex data
Symbols used as frequency domain bins in to the time domain signal. Such an N-point
IFFT is illustrated in Figure 12 where a (mN+n) refers to the nth subcarrier modulated
data symbol, during the time period mTu < t ≤ (m+1) Tu.

Figure 12 : OFDM useful symbol generation using an IFFT

The vector sm is defined as the useful OFDM symbol. It is the time superposition of the
N narrowband modulated subcarriers. Therefore, from a parallel stream of N sources of
data, each one independently modulated, a waveform composed of N orthogonal


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Subcarriers is obtained, with each subcarrier having the shape of a frequency sinc
function (see Figure 11).
Figure 13 illustrates the mapping from a serial stream of QAM symbols to N
parallel streams, used as frequency domain bins for the IFFT. The N-point time domain
blocks obtained from the IFFT are then serialized to create a time domain signal.

Figure 13 : OFDM Signal Generation Chain

In contrast to an OFDM transmission scheme, OFDMA allows the access of multiple
Users on the available bandwidth. Each user is assigned a specific time-frequency
resource. As a fundamental principle of E-UTRA, the data channels are shared channels,
i.e. for each Transmission Time Interval (TTI) of 1ms, a new scheduling decision is
taken regarding which users are assigned to which time/frequency resources during this
TTI.

2.

OFDMA Parameterization

Two frame structure types are defined for E-UTRA:
 Frame structure type 1 for FDD mode,
 And frame structure type 2 for TDD mode.
For the frame structure type 1, the 10ms radio frame is divided into 20 equally sized slots
of 0.5ms. A sub frame consists of two consecutives lots, so one Radio frame contains ten
sub frames .This is illustrated in Figure 14.

Figure 14 : Frame structure type 1

Ts (sampling time) is expressing the basic time unit for LTE, corresponding to a
Sampling frequency of 30.72MHz. This sampling frequency is given due to the defined
subcarrier spacing for LTE with f =15 KHz and the maximum FFT size to generate the
OFDM symbols of 2048.


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Selecting these parameters ensures also simplified Implementation of multi standard
devices, as this sampling frequency is a multiple of the chip rate defined for WCDMA
(30.72MHz/ 8=3.84Mcps) and CDMA2000®1xRTT (30.72MHz/ 25=1.2288Mcps).
For the frame structure type 2, the 10ms radio frame consists of two half-frames
of Length 5ms each. Each half-frame is divided into five sub frames of each 1ms, as
Shown in Figure 15 below. All sub frames which are not special sub frames are defined
as two slots of length 0.5ms in each sub frame. The special sub frames consist of the
three fields DwPTS (Downlink Pilot Time Slot), GP (Guard Period), and UpPTS
(Uplink Pilot Time Slot). These fields are already known from TD-SCDMA and are
maintained in LTE TDD. DwPTS, GP and UpPTS have configurable individual lengths
and a total Length of 1ms.

Figure 15 : Frame structure type 2 (for 5ms switch-point periodicity)

Seven uplink-downlink configurations with either 5ms or 10ms downlink-to-uplink
switch-point periodicity are supported. In case of 5ms switch-point periodicity, the
special sub frame exists in both half-frames. In case of 10ms switch-point periodicity
The special sub frame exists in the first half frame only. Sub frames 0 and 5 and DwPTS
Are always reserved for downlink transmission. UpPTS and the sub frame immediately
Following the special sub frame are always reserved for uplink transmission. Table 2
Shows the supported uplink-downlink configurations, where ”D” denotes a sub frame
reserved for downlink transmission, “U” denotes a sub frame reserved for uplink
transmission, and “S” denotes the special sub frame.
Table 2: Uplink-Downlink configurations for LTE TDD

Uplink-Downlink
Configuration
0
1
2
3
4
5
6

Downlink to Uplink
Switch point periodicity
5 ms
5 ms
5 ms
10 ms
10 ms
10 ms
5 ms

0
D
D
D
D
D
D
D

1
S
S
S
S
S
S
S


2
U
U
U
U
U
U
U

Subframe number
3 4 5 6 7
U U D S U
U D D S U
D D D S U
U U D D D
U D D D D
D D D D D
U U D S U

8
U
U
D
D
D
D
U

9
U
D
D
D
D
D
D

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There is always a special sub frame when switching from DL to UL, which provides a
Guard period. Reason being is that all transmission in the UL from all the different UEs
must arrive at the same time at the base station receiver. When switching from UL to
DL only the base station is transmitting so there is no guard period needed. Beside UL
DL configuration there is also 9 special sub frame configurations. And the length of the
DwPTS, Guard Period (GP) and UpPTS is given in numbers of OFDM symbols. As it
can be seen there are Different lengths for GP, which is necessary to support different
cell size, up to 100km.
Table 3 : Special Sub frame configurations in TD-LTE

Normal cyclic prefix in downlink
Extended cyclic prefix downlink
Special
UpPTS
UpPTS
Subframe
Guard Normal Extended
Guard Normal Extended
Config. DwPTS Period Cyclic
Cyclic DwPTS Period
Cyclic
Cyclic
prefix
prefix
Prefix
Prefix
In uplink In uplink
0
3
10
3
8
1
9
4
8
3
1
1
1
1
2
10
3
9
2
3
11
2
10
1
4
12
1
3
7
2
2
5
3
9
8
2
6
9
3
9
1
2
2
7
10
2
8
11
1
It can be also extracted that downlink and uplink in TD-LTE can utilize different cyclic
prefixes, which is different from LTE FDD. Figure 16 shows the structure of the
downlink Resource grid for both FDD and TDD.


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Figure 16: Downlink Resource grid

In the frequency domain, 12 subcarriers form one Resource Block (RB). With a
subcarrier spacing of 15 kHz a RB occupies a bandwidth of 180 kHz. The number of
resource blocks, corresponding to the available transmission bandwidth, is listed for the
six different LTE bandwidths in Table 4.
Table 4: Number of resource blocks for different LTE bandwidths (FDD and TDD)

Channel Bandwidth [MHz]
1.4
3
5
10
15
20
Number of resource blocks
6
15
25
50
75
100
To each OFDM symbol, a cyclic prefix (CP) is appended as guard time, compare
Figure11. One downlink slot consists of 6 or 7 OFDM symbols, depending on whether
Extended or normal cyclic prefix is configured, respectively. The extended cyclic prefix
Is able to cover larger cell sizes with higher delay spread of the radio channel, but
reduces the number of available symbols. The cyclic prefix lengths in samples and µs are
summarized in Table 5.


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Table 5 : Downlink frame structure parameterization (FDD and TDD)

Resource
Block size

Number
Of
Symbols

12
12

7
6

Configuration
Normal cyclic prefix
Ext cyclic prefix

Cyclic prefix
Length in
samples

Cyclic prefix length
in µs

160 for first symbol
144 for other symbols
512

5.2 µs for first symbols
4.7 µs for other symbols
16.7 µs

With a sampling frequency of 30.72 MHz 307200 samples are available per radio
Frame (10ms) and thus 15360 per time slot (0.5ms). Due to the maximum FFT size
Each OFDM symbol consists of 2048 samples. With usage of normal cyclic prefix
Seven OFDM symbols are available or 7*2048=14336 samples per time slot. The
remaining 1024 samples are the basis for cyclic prefix. It has been decided that the first
OFDM symbol uses a cyclic prefix length of 160 samples, where the remaining six
OFDM symbols using a cyclic prefix length of 144samples. Multiplying the samples
With the sampling time TS, results in the cyclic prefix length in µs.
Please note that for E-MBMS another cyclic prefix of 33.3µs is defined for a different
Subcarrier spacing off =7.5 kHz in order to have a much larger cell size.

3.

Downlink data transmission

Data is allocated to a device (User Equipment, UE) in terms of resource blocks,
i.e. one UE can be allocated integer multiples of one resource block in the frequency
domain. These resource blocks do not have to be adjacent to each other. In the time
domain, the scheduling decision can be modified every transmission time interval of 1ms.
All scheduling decisions for downlink and uplink are done in the base station (enhanced
NodeB, eNodeB or eNB).The scheduling algorithm has to take in to account the radio
link quality situation of different users, the overall interference situation, Quality of
Service requirements, service priorities, etc. and is a vendor-specific implementation.
Figure 17 shows an example for allocating downlink user data to different users (UE1-6).
The user data is carried on the Physical Downlink Shared Channel (PDSCH). The
PDSCH(s) is the only channel that can be QPSK, 16 QAM or 64 QAM modulated.


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Figure 17 : OFDM A time-frequency multiplexing (example for normal cyclic prefix)

4.

Downlink reference signal structure and cell search

The downlink reference signal structure is important for initial acquisition and
cell search, coherent detection and demodulation at the UE and further basis for channel
estimation and radio link quality measurements. Downlink reference signal provide
further help to the device to distinguish between the different transmit antenna used at the
eNodeB.
Figure18 shows the mapping principle of the downlink reference signal structure
for up to four transmit antennas. Specific pre-defined resource elements in the timefrequency domain are carrying the cell-specific reference signal sequence. In the
frequency domain every six subcarrier carries a portion of the reference signal pattern,
which repeats every fourth OFDM symbol.


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Figure 18 : Downlink reference signal structure (normal cyclic prefix)

The reference signal sequence is derived from a pseudo-random sequence and
results in a QPSK type constellation. Frequency shifts are applied when mapping the
reference signal sequence to the subcarriers, means the mapping is cell-specific and
distinguish the different cells.
During cell search, different types of information need to be identified by the UE:
symbol and radio frame timing, frequency, cell identification, overall transmission
bandwidth, antenna configuration, and cyclic prefix length. The first step of cell search in
LTE is based on specific synchronization signals. LTE uses a hierarchical cell search
scheme similar to WCDMA. Thus, a primary synchronization signal and a secondary
synchronization signal are defined. The synchronization signals are transmitted twice per
10 ms on predefined slots; see Figure 19 for FDD and Figure 20 for TDD. In the
frequency domain, they are transmitted on 62 subcarriers within 72 reserved subcarriers
around the unused DC subcarrier. The 504 available physical layer cell identities are

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grouped into 168 physical layer cell identity groups, each group containing 3 unique
identities (0, 1, or2). The secondary synchronization signal carries the physical layer cell
identity group, and the primary synchronization signal carries the physical layer identity
0, 1, or 2.

Figure 19 : Primary/secondary synchronization signal and PBCH structure (frame structure type 1/FDD,
normal cyclic prefix)

Figure 20 : Primary/secondary synchronization signal and PBCH structure (frame structure type2/TDD, normal
cyclic prefix)

As additional help during cell search, a Physical Broadcast Channel (PBCH) is
available which carries the Master Information Block (MIB). The MIB provides basic
physical layer information, e.g. system bandwidth, PHICH configuration, and system
frame number. The number of used transmit antennas is provided in directly using a
specific CRC mask. The PBCH is transmitted on the first 4 OFDM in the second time
slot of the first sub frame on the 72 subcarriers centered around DC subcarrier. PBCH
has 40ms transmission time interval, means a device need to read four radio frames to get
the whole content.


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Downlink Hybrid ARQ (Automatic Repeat Request)

Downlink Hybrid ARQ is also known from HSDPA. It is a retransmission
protocol. The UE can request retransmissions of data packets that were incorrectly
received on PDSCH. ACK/NACK information is transmitted in uplink, either on Physical
Uplink Control Channel (PUCCH) or multiplexed with in uplink data transmission on
Physical Uplink Shared Channel (PUSCH). In LTE FDD there are up to 8 HARQ
processes in parallel. The ACK/NACK transmission in FDD mode refers to the downlink
packet that was received four sub frames before. In TDD mode, the uplink ACK/NACK
timing depends on the uplink/downlink configuration.
Table 6: Number of HARQ processes in TD-LTE (Downlink)

TDD UL/DL
Configuration
0
1
2
3
4
5
6

Number of HARQ processes for normal
HARQ operation
7
4
2
3
2
1
6

Number of HARQ processes for
subframe bundling operation
3
2
N/A
N/A
N/A
N/A
3

Two modes are supported by TD-LTE acknowledging or non-acknowledging data
Packets received in the downlink: ACK/NACK bundling and multiplexing. Which mode
is used, is configured by higher layers. ACK/NACK bundling means, that ACK/NACK
information for data packets received in different sub frames is combined with logical
AND operation.

Figure 21: ACK/NACK bundling in TD-LTE


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LTE: The Uplink:
1.

SC-FDMA

During the study item phase of LTE, alternatives for the optimum uplink
transmission scheme were investigated. While OFDMA is seen optimum to fulfill the
LTE requirements in downlink, OFDMA properties are less favorable for the uplink. This
is mainly due to weaker peak-to-average power ratio (PAPR) properties of an OFDMA
signal, resulting in worse uplink coverage and challenges in power amplifier design for
battery operated handset, as it requires very linear power amplifiers.
Thus, the LTE uplink transmission scheme for FDD and TDD mode is based on
SCFDMA [5], [8] (Single Carrier Frequency Division Multiple Access) with cyclic
prefix. SCFDMA signals have better PAPR properties compared to an OFDMA signal.
This was one of the main reasons for selecting SC-FDMA as LTE uplink access scheme.
The PAPR characteristics are important for cost-effective design of UE power amplifiers.
Still, SC-FDMA signal processing has some similarities with OFDMA signal processing,
so parameterization of downlink and uplink can be harmonized.
There are different possibilities how to generate an SC-FDMA signal. DFT spread
OFDM (DFT-s-OFDM) has been selected for E-UTRA. The principle is illustrated in
Figure22. For DFT-s-OFDM, a size-MDFT is first applied to a block of M modulation
symbols. QPSK, 16QAM and 64QAM are used as uplink E-UTRA modulation schemes,
the latter being optional for the UE. The DFT transforms the modulation symbols in to
the frequency domain. The result is mapped on to the available number of subcarriers.
For LTE Release8 uplink, only localized transmission on consecutive subcarriers is
allowed. An N-point IFFT where N > M is then performed as in OFDM, followed by
addition of the cyclic prefix and parallel to serial conversion.


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Figure 22 : Block diagram of DFT-s-OFDM (localized transmission)

The DFT processing is therefore the fundamental difference between SC-FDMA
and OFDMA signal generation. This is indicated by the term “DFT-spread-OFDM”. In
an SC-FDMA signal, each subcarrier used for transmission contains information of all
Transmitted modulation symbols, since the input data stream has been spread by the DFT
transform over the available subcarriers. In contrast to this, each subcarrier of an
OFDMA signal only carries in formation related to specific modulation symbols. This
Spreading lowers the PAPR compared to OFDMA as used in the downlink. It depends
now on the used modulation scheme (QPSK, 16QAM, later on also 64QAM) and the
Applied filtering, which is not standardized as in WCDMA for example.

2.

SC-FDMA parameterization

The LTE uplink structure is similar to the downlink. In frame structure type 1, an
uplink radio frame consists of 20 slots of 0.5 ms each, and one subframe consists of two
slots. The slot structure is shown in Figure 23 Frame structure type 2 consists also of
ten subframes, but one or two of them are special subframes. They include DwPTS, GP
and UpPTS fields, see Figure 14. Each slot carries 7 SC-FDMA symbols in case of
normal cyclic prefix configuration and 6 SC-FDMA symbols in case of extended cyclic
prefix configuration. SC-FDMA symbol number 3 (i.e. the 4th symbol in a slot) carries
the demodulation reference signal (DMRS), being used for coherent demodulation at the
eNodeB receiver as well as channel estimation.

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Figure 23 : Uplink resource grid

Table7 shows the configuration parameters.
Table 7: Uplink frame structure parameterization (FDD and TDD)

Configuration

Number of
symbols

Cyclic prefix length in
samples

Cyclic prefix length in
µs

Normal cyclic prefix

7

Ext. cyclic prefix

6

160 for 1st symbol
144 for other symbols
512

5.2 µs for 1st symbol
4.7 µs for other symbols
16.7 µs


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Uplink Data transmission

Scheduling of uplink resources is done by eNodeB. The eNodeB assigns certain
time/frequency resources to the UEs and informs UEs about transmission formats to use.
The scheduling decisions may be based on QoS parameters, UE buffer status uplink
channel quality measurements, UE capabilities, UE measurement gaps, etc. In uplink,
data is allocated in multiples of one resource block. Uplink resource block size in the
frequency domain is 12 subcarriers, i.e. the same as in downlink. However, not all integer
multiples are allowed in order to simplify the DFT design in uplink signal processing.
Only factors 2, 3, and 5 are allowed. Table 8 shows the possible number of RB that can
be allocated to a device for uplink transmission.

Table 8 : Possible RB allocation for uplink transmission

1
15
40
81

2
16
45
90

3
18
48
96

4
5 6 8 9 10 12
20 24 25 27 30 32 36
50 54 60 64 72 75 80
100

In LTE Release 8 only contiguous allocation is possible in the downlink
transmissions with resource allocation type 2. The number of allocated RBs is signaled to
the UE as RIV. The uplink transmission time interval is 1 ms (same as downlink). User
data is carried on the Physical Uplink Shared Channel (PUSCH). DCI (Downlink Control
Information) format 0 is used on PDCCH to convey the uplink scheduling grant. The
content of DCI format 0 is listed in Table 9.


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Table 9 : Contents of DCI format 0 carried on PDCCH

Information type
Flag for format 0/ format1A
Differentiation
Hopping flag

Number of bits on
PDCCH
1
1

Resource block assignment
and hopping resource
allocation

Depending on
resource block
allocation type

Modulation and coding
scheme and redundancy
version

5

New date indicator

1

TPC command for scheduled
PUSCH

2

Cyclic shift for
demodulation reference
signal
Uplink index (TDD only)

3

CQI request

1

2

Purpose
Indicates DCI format to UE
Indicates whether uplink frequency
hopping is used or not
Indicates whether to use type 1 or type 2
frequency hopping and index of starting
resource block of uplink resource
allocation as well as number of
contiguously allocated resource blocks
Indicates modulation scheme and,
together with the number of allocated
physical resource blocks, the transport
block size indicates redundancy version
to use
Indicates whether a new transmission
shall be sent
Transmit power control (TPC) for
adapting the transmit power on the
Physical Uplink Shared Channel
(PUSCH)
Indicates the cyclic shift to use for
deriving the uplink demodulation
reference signal from the base sequence
Indicates the uplink subframe where the
scheduling grant has to be applied
Requests the UE to send a channel quality
indication (CQI)aperiodic CQI
reporting

Frequency hopping can be applied in the uplink. The uplink scheduling grant in
DCI format 0 contains a 1 bit flag for switching hopping ON or OFF. By use of
frequency hopping on PUSCH, frequency diversity effects can be exploited and
interference can be averaged. The UE derives the uplink resource allocation as well as
frequency hopping information from the uplink scheduling grant that was received four
subframes before. LTE supports both intra- and inter-subframe frequency hopping. It is
configured per cell by higher layers whether either both intra- and inter-subframe
hopping or only inter-subframe hopping is supported. In intra-subframe hopping (inter
slot hopping), the UE hops to another frequency allocation from one slot to another
within one subframe. In inter-subframe hopping, the frequency resource allocation
changes from one subframe to another, depending on a pre-defined method. Also, the UE
is being told whether to use type 1 or type 2 frequency hopping.

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The available bandwidth i.e. 50 RB is divided into a number of sub-bands, 1 up to
4. This information is provided by higher layers. The hopping offset, which comes as
well from higher layers, determines how many RB are available in a sub-band. The
number of contiguous RB that can be allocated for transmission is therefore limited.
Further the number of hopping bits is bandwidth depended, 1 hopping bit for bandwidths
with less than 50 RB, 2 hopping bits for bandwidth equals and higher 50 RB.
The UE will first determine the allocated resource blocks after applying all the
frequency hopping rules. Then, the data is being mapped onto these resources, first in
subcarrier order, then in symbol order.
Type 1 hopping refers to the use of an explicit offset in the 2nd slot resource
allocation. Figure 24 shows an example, of a complete radio frame for a 10 MHz signal
applying a defined PUSCH hopping offset of 5 RB and configuring 4 sub-bands.

Figure 24 : Intra-subframe hopping, Type 1

Type 2 hopping refers to the use of a pre-defined hopping pattern. The hopping is
performed between sub-bands (from one slot or subframe to another, depending on
whether intra- or inter-subframe are configured, respectively). In the example (Figure 25)
the initial assignment is 10 RB with an offset of 24 RB.


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Figure 25 : Intra-subframe hopping, Type 1 (blue, UE1) and Type 2 (green, UE3)

4.

Uplink reference signal structure

There are two types of uplink reference signals:
The demodulation reference signal (DMRS) is used for channel estimation in the
eNodeB receiver in order to demodulate control and data channels. It is located on the 4 th
symbol in each slot (for normal cyclic prefix) and spans the same bandwidth as the
allocated uplink data.
The sounding reference signal (SRS) provides uplink channel quality
information as a basis for scheduling decisions in the base station. The UE sends a
sounding reference signal in different parts of the bandwidths where no uplink
data transmission is available. The sounding reference signal is transmitted in the last
symbol of the subframe. The configuration of the sounding signal, e.g. bandwidth,
duration and periodicity, are given by higher layers.
Both uplink reference signals are derived from so-called Zadoff-Chu sequence
types. This sequence type has the property that cyclic shifted versions of the same
sequence are orthogonal to each other. Reference signals for different UEs are derived by
different cyclic shifts from the same base sequence.


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The available base sequences are divided into groups identified by a sequence
group number u. within a group, the available sequences are numbered with index v. The
sequence group number u and the number within the group v may vary in time. This is
called group hopping, and sequence hopping, respectively.
Group hopping is switched on or off by higher layers. The sequence group
number u to use in a certain timeslot is controlled by a pre-defined pattern.
Sequence hopping only applies for uplink resource allocations of more than five
resource blocks. In case it is enabled (by higher layers), the base sequence number v
within the group u is updated every slot.

5.

Uplink Hybrid ARQ (Automatic Repeat Request)

Hybrid ARQ retransmission protocol is also used in LTE uplink. The eNodeB has
the capability to request retransmissions of incorrectly received data packets.
ACK/NACK information in downlink is sent on Physical Hybrid ARQ Indicator
Channel (PHICH). After a PUSCH transmission the UE will therefore monitor the
corresponding PHICH resource four subframes later (for FDD). For TDD the PHICH
subframe to monitor is derived from the uplink/downlink configuration and from PUSCH
subframe number.
The PHICH resource is determined from lowest index physical resource block of
the uplink resource allocation and the uplink demodulation reference symbol cyclic shift
associated with the PUSCH transmission, both indicated in the PDCCH with DCI format
0 granting the PUSCH transmission.
A PHICH group consists of multiple PHICHs that are mapped to the same set of
resource elements, and that are separated through different orthogonal sequences. The UE
derives the PHICH group number and the PHICH to use inside that group from the
information on the lowest resource block number in the PUSCH allocation, and the cyclic
shift of the demodulation reference signal. The UE can derive the redundancy version to
use on PUSCH from the uplink scheduling grant in DCI format 0, see Table 9.
8 HARQ processes are supported in the uplink for FDD, while for TDD the
number of HARQ processes depends on the uplink-downlink configuration.


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Figure 26 : PHICH principle

C. LTE: MIMO Concepts
Multiple Input Multiple Output (MIMO) systems form an essential part of LTE in
order to achieve the ambitious requirements for throughput and spectral efficiency.
MIMO refers to the use of multiple antennas at transmitter and receiver side. For
the LTE downlink, a 2x2 configuration for MIMO is assumed as baseline configuration,
i.e. two transmit antennas at the base station and two receive antennas at the terminal
side.
Configurations with four transmit or receive antennas are also foreseen and
reflected in specifications. Different gains can be achieved depending on the MIMO
mode that is used. In the following, a general description of spatial multiplexing and
transmit diversity is provided. Afterwards, LTE-specific MIMO features are
highlighted.
Spatial multiplexing
Spatial multiplexing allows transmitting different streams of data simultaneously
on the same resource block(s) by exploiting the spatial dimension of the radio channel.
These data streams can belong to one single user (single user MIMO / SUMIMO) or to different users (multi user MIMO / MU-MIMO). While SU-MIMO
increases the data rate of one user, MU-MIMO allows increasing the overall capacity.
Spatial multiplexing is only possible if the mobile radio channel allows it.


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Figure 27 : Spatial multiplexing (simplified)

Figure 27 shows a simplified illustration of spatial multiplexing. In this example,
each transmit antenna transmits a different data stream. This is the basic case for spatial
multiplexing. Each receive antenna may receive the data streams from all transmit
antennas. The channel (for a specific delay) can thus be described by the following
channel matrix H:
[

]

In this general description, Nt is the number of transmit antennas, Nr is the
number of receive antennas, resulting in a 2x2 matrix for the baseline LTE scenario.
The coefficients hij of this matrix are called channel coefficients from transmit antenna j
to receive antenna i, thus describing all possible paths between transmitter and receiver
side. The number of data streams that can be transmitted in parallel over the MIMO
channel is given by min {N , N } and is limited by the rank of the matrix H. The
transmission quality degrades significantly in case the singular values of matrix H are not
sufficiently strong. This can happen in case the two antennas are not sufficiently decorrelated, for example in an environment with little scattering or when antennas are too
closely spaced. The rank of the channel matrix H is therefore an important criterion
to determine whether spatial multiplexing can be done with good performance. Note that
Figure 27 only shows an example. In practical MIMO implementations, the data streams
are often weighted and added, so that each antenna actually transmits a
combination of the streams; see below for more details regarding LTE.
Transmit Diversity
Instead of increasing data rate or capacity, MIMO can be used to exploit diversity
and increase the robustness of data transmission. Transmit diversity schemes are already
known from WCDMA Release 99 and will also be part of LTE. Each transmit antenna
transmits essentially the same stream of data, so the receiver gets replicas of the same
signal. This increases the signal to noise ratio at the receiver side and thus the robustness

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of data transmission especially in fading scenarios. Typically an additional antennaspecific coding is applied to the signals before transmission to increase the diversity
effect. Often, space-time coding is used according to Alamouti [9].
Switching between the two MIMO modes (transmit diversity and spatial multiplexing) is
possible depending on channel conditions.
1. Downlink MIMO modes in LTE as of Release 8

Different downlink MIMO modes are envisaged in LTE which can be adjusted
according to channel condition, traffic requirements, and UE capability. The following
transmission modes are possible in LTE:
Table 10 : Transmission Modes in LTE as of 3GPP Release 8

Transmission Mode
TM1
TM2
TM3
TM4
TM5
TM6
TM7

Description
Single Antenna transmission (SISO)
Transmit Diversity
Open-loop spatial multiplexing, no UE feedback (PMI) on MIMO
transmission provided
Closed-loop spatial multiplexing, UE provides feedback on MIMO
transmission
Multi-user MIMO(more than one UE is assigned to the same resource
block)
Closed-loop precoding for rank=1(i.e. no spatial multiplexing, but
precoding is used)
Single-layer beam forming (mandatory TD-LTE, optional LTE FDD)

In LTE spatial multiplexing, up to two code words can be mapped onto different
spatial layers. One code word represents an output from the channel coder. The number
of spatial layers available for transmission is equal to the rank of the matrix H.
Precoding on transmitter side is used to support spatial multiplexing. This is
achieved by multiplying the signal with a precoding matrix W before transmission. The
optimum precoding matrix W is selected from a predefined “codebook” which is known
at eNodeB and UE side. The codebook for the 2 transmit antenna case in LTE is shown in
Table 11. The optimum pre-coding matrix is the one which offers maximum capacity.


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Table 11 : Precoding codebook for 2 transmit antenna case

Codebook index

Number of layers v
1

0
1

2

[ ]
[

[
]

2

[ ]

3

[

]

]

[

]

[

]
-

The codebook defines entries for the case of one or two spatial layers. In case of
only one spatial layer, obviously spatial multiplexing is not possible, but there are still
gains from precoding. For closed-loop spatial multiplexing and v=2, the codebook index
0 is not used.
The UE estimates the radio channel and selects the optimum precoding matrix.
This feedback is provided to the eNodeB. Depending on the available bandwidth, this
information is made available per resource block or group of resource blocks, since the
optimum precoding matrix may vary between resource blocks. The network may
configure a subset of the codebook that the UE is able to select from.
In case of UEs with high velocity, the quality of the feedback may deteriorate.
Thus, an open loop spatial multiplexing mode is also supported which is based on
predefined settings for spatial multiplexing and precoding. In case of four antenna ports,
different precoders are assigned cyclically to the resource elements.
The eNodeB will select the optimum MIMO mode and precoding configuration.
The information is conveyed to the UE as part of the downlink control information (DCI)
on PDCCH. DCI format 2 provides a downlink assignment of two code words including
precoding information. DCI format 2a is used in case of open loop spatial multiplexing.
DCI format 1b provides a downlink assignment of 1 code word including precoding
information. DCI format 1d is used for multi-user spatial multiplexing with precoding
and power offset information.
In case of transmit diversity mode, only one code word can be transmitted.
Antenna transmits the same information stream, but with different coding. LTE employs
Space Frequency Block Coding (SFBC) which is derived from [9] as transmit diversity
scheme. A special precoding matrix is applied at transmitter side. At a certain point in

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time, the antenna ports transmit the same data symbols, but with different coding
and on different subcarriers. Figure 28 shows an example for the 2 transmit antenna
case, where the transmit diversity specific precoding is applied to an entity of two data
symbols d (0) and d (1).

Figure 28: Transmit diversity (SFBC) principle

Cyclic Delay Diversity (CDD)
Cyclic delay diversity is an additional type of diversity which can be used
in conjunction with spatial multiplexing in LTE. An antenna-specific delay is applied to
the signals transmitted from each antenna port. This effectively introduces artificial
multipath to the Signal as seen by the receiver. By doing so, the frequency diversity of
the radio channel is increased. As a special method of delay diversity, cyclic delay
diversity applies a cyclic shift to the signals transmitted from each antenna port.
2. Uplink MIMO
Uplink MIMO schemes for LTE will differ from downlink schemes to take
into account terminal complexity issues. For the uplink, MU- can be used. Multiple user
terminals may transmit simultaneously on the same resource block. This is also referred
to as spatial division multiple access (SDMA). The scheme requires only one transmit
antenna as well as transmitter chain at UE side which is a big advantage. The UEs
sharing the same resource block have to apply mutually orthogonal pilot patterns.
To exploit the benefit of two or more transmit antennas but still keep the UE cost
low, transmit antenna selection can be used. In this case, the UE has two transmit
antennas but only one transmitter chain and power amplifier. A switch will then choose
the antenna that provides the best channel to the eNodeB. This decision is made
according to feedback provided by the eNodeB. The CRC parity bits of the DCI format
0 are scrambled with an antenna selection mask indicating UE antenna port 0 or 1.
The support of transmit antenna selection is an UE capability.


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D. LTE Protocol Architecture
1.

System Architecture Evolution (SAE)

SAE (System Architecture Evolution) is a core network architecture that supports
the characteristics of LTE. SAE introduces a packet switched mobile core network EPC
(Evolved Packet Core) with the following elements:


S-GW (Serving Gateway) and PDN (Packed Data

Network) gateway on the user plane and


MME (Mobility Management Entity) on the control plane.

The elements of EPC can be incorporated into one or more physical nodes, linked
with standardized interfaces, which enable the use of hardware of various manufacturers.
Fig. 29 shows a simplified SAE network architecture.
SAE separates the user and the control plane. The latter is managed especially by
the MME. Because there are no radio network controllers, as individual network elements
in SAE, the base station (eNB, eNodeB) connects directly with the MME or S-GW for
the exchange of user and control information (Fig. 29). Besides routing data towards the
EPC, the eNodeB also schedules and transmits paging messages, selects an MME during
network attachment, etc. The eNodeB communicates with mobile terminals over link
layer protocols and the RRC, and also implements the functionality of the physical layer
presented in the next sections.

Figure 29 : Architecture of LTE radio access (E-UTRAN) and core network (EPC)


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MME is the key control node in the network. It performs the signalization and
controls the entities in various layers of the protocol stack.
The Serving Gateway supports mobility anchoring during inter-eNodeB handover
and inter-3GPP network mobility. It also supports charging and performs routing,
forwarding, buffering, marking and interception of data packets.
The PDN Gateway ensures the connectivity of the mobile terminal with other
packet data networks. The functions of the PDN Gateway include filtering, intercepting
and marking of data packets, DHCP (Dynamic Host Configuration Protocol), support for
charging and traffic shaping.
2. The Upper Layers Of The LTE Protocol Stack
Fig. 30 presents the structure of the link layer for the downlink [10]. The scheme
for the uplink is similar. The SAPs (Service Access Points) of the physical layer are
known as the transport channels, while those of the MAC (Media Access Control)
sublayer are known as logical channels and the SAPs of the link layer are radio bearers.
Transport channels correspond to services provided by the physical layer. These services
are defined by how and with what characteristics data are transported over the radio
interface.
Logical channels correspond to the data transfer services that are offered by the
MAC sublayer and are defined by the type of information they carry. Logical channels
are divided on the control channels that carry data on the control plane and traffic
channels that carry the user plane data.
Radio bearers correspond to the type of information and quality of service at transmission
on the radio interface, e.g. to VoIP, video streaming, file transfer and control plane
communications.
The MAC sublayer [11] controls access to the physical medium. It performs the
mapping among logical and transport channels, and the multiplexing/demultiplexing of
these channels. It also performs radio resource allocation, priority handling and HARQbased error corrections.
The RLC (Radio Link Control) [12] controls links on the radio interface, performs
traffic control, segmentation and reassembly of data packets and error correction based
on ARQ (Automatic Repeat reQuest). It provides different modes of operation suitable
for different radio bearers.
The PDCP (Packet Data Convergence Protocol) [13] converts the PDUs of the
higher layers into a format suitable for transfer over the radio interface. It provides insequence delivery of PDUs and security mechanisms, and performs header compression
of network-layer PDUs.
The RRC (Radio Resource Protocol) [14] is a network layer protocol of the
control plane that handles signalization.

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It supports the transmission of broadcast system information and dedicated control
information, establishes and maintains services, and controls the QoS.

Figure 30 : Link layer structure for the downlink

E. Evolution Of Applications And Services
The success of the evolution in mobile communications and the improvement of
user experience will mostly depend on:


sufficient network capabilities to provide high data rates and low latencies;



sufficient radio signal quality and coverage to ensure availability of
services over entire cell area;



efficient means for creating and maintaining connections and quality of
services;



independence of services from different access networks;



Competitive prices with various flat-rate fees and unified cost control
dependent on the service and not on the access network.

While voice transmissions will remain the primary application for the majority of
users, new services in LTE will be mainly focused on data and multimedia
communications (Fig. 31). The following trends are expected [15], [16]:


Converged services independent of means of Internet access will replace
separate fixed and mobile services.


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

Mobile Web 2.0 applications will enable user participation in various
communities. Mobile users will be able to create multimedia content and
interact in virtual worlds.



Increasing popularity of streaming services, such as video on demand and
mobile television.



Real-time and interactive games will become important also in mobile
world. The game industry already has a turnover of tens of millions of
dollars per year.



The quadruple play (voice, mobile television, Internet, mobile services)
will blur the fixed-mobile divide.



Mobile offices with smart phones, portable computers, mobile broadband
access and advanced security solutions will free business users from their
desks.

Figure 31 : Mobile applications with technical requirements and growth drivers

1. New Primary Internet Connection
When data rates reach and exceed those of fixed networks, user experience will be
the same in fixed and in mobile networks. Users will be able to browse the Web, send
and receive e-mails with large attachments, share files on the same servers and play
network games anywhere and anytime. Mobile broadband connection could become a


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primary network connection in portable computers, providing an alternative to DSL
(Digital Subscriber Line) technologies.
2.

Various Degrees of Services

The support for quality of service in LTE enables operators to offer various
mobile broadband services for different prices and needs. While service bundles with
high data rates and low latencies will suit the needs of companies, those for more
affordable prices will increase penetration of mobile broadband services among
population.
3.

Audio and Video on Demand

Higher data rates could also enable service providers to offer high quality audio
and video on demand. Users will be able to access rich multimedia content more quickly.
For example, it would take only a few minutes to download a movie in VGA quality.
4.

Mobile Web 2.0

With the increasing popularity of Web 2.0 applications, such as blogging and
social networking, more and more users share their own photos, music and videos. Fast
uplink connection will enable faster transfer of such multimedia content.
5.

Consumer Electronics

LTE will also enable service providers to better support consumer electronic
devices, such as portable multimedia players, video game consoles and digital cameras.
Currently, the majority of portable multimedia players uses a cable connection to a
desktop computer to download desired multimedia content. Although there are some
devices with wireless network interfaces on the market, the coverage of wireless
networks is limited. With mobile broadband connection game players could play
multiplayer tournaments anywhere and anytime. Multiplayer games usually require realtime interaction among participants that could be easily achieved with LTE.
An important field is also consumer electronics in cars. Navigation and mapping
systems could be updated anywhere and anytime as also car computer software. The car
will become an Internet terminal with interfaces that will provide passengers with access
to applications and data.


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Business Applications

The LTE„s capabilities will allow operators to offer services dedicated to business
users. An example of such a service is a videoconference in which the employees could
participate regardless of their location; they could be in their office or in the field.
7.

Instantaneous Synchronization

Instantaneous synchronization of data in different devices distributed around the
globe will also be possible. For example, documents or multimedia that will be created or
modified with a device supporting LTE will be automatically synchronized with the
user's home computer and accessible with the cell phone.


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4th GENERATION OF WIRELESS NETWORKS (LTE)

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