4th GENERATION OF WIRELESS NETWORKS (LTE)

i

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

1. INTRODUCTION…………………………………………………………………………………2

2. WIRELESS EVOLUTION………………………………………………………………...............3

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

1. Introduction………………………………………………………………………………….17

2. Features and capabilities………………………………………………………………….….20

3. 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

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

ii

ABBREVIATION

4G 4th Generation

ACK Acknowledgement

ARQ Automatic Repeat Request

BCCH Broadcast Control Channel

BCH Broadcast Channel

CAPEX Capital Expenditures

CCCH Common Control Channel

CCDF Complementary Cumulative Density Function

CCO Cell Change Order

CDD Cyclic Delay Diversity

CP Cyclic Prefix

C-plane Control Plane

CQI Channel Quality Indicator

CRC Cyclic Redundancy Check

C-RNTI Cell Radio Network Temporary Identifier

CS Circuit Switched

DCCH Dedicated Control Channel

DCI Downlink Control Information

DFT Discrete Fourier Transform

DL Downlink

DL-SCH Downlink Shared Channel

DRS Demodulation Reference Signal

DRX Discontinuous Reception

DTCH Dedicated Traffic Channel

DTX Discontinuous Transmission

DVB Digital Video Broadcast

DwPTS Downlink Pilot Timeslot

eNB E-UTRAN NodeB

EDGE Enhanced Data Rates for GSM Evolution

EPC Evolved Packet Core

E-UTRA Evolved UMTS Terrestrial Radio Access

E-UTRAN Evolved UMTS Terrestrial Radio Access Network

FDD Frequency Division Duplex

FFT Fast Fourier Transform

GERAN GSM EDGE Radio Access Network

GP Guard Period

GSM Global System for Mobile communication

HARQ Hybrid Automatic Repeat Request

HRPD High Rate Packet Data

HSDPA High Speed Downlink Packet Access

HSPA High Speed Packet Access

HSUPA High Speed Uplink Packet Access

IFFT Inverse Fast Fourier Transformation

IP Internet Protocol

LCID Logical channel identifier

LTE Long Term Evolution

MAC Medium Access Control


iii

MBMS Multimedia Broadcast Multicast Service

MIMO Multiple Input Multiple Output

MME Mobility Management Entity

MU-MIMO Multi User MIMO

NACK Negative Acknowledgement

NAS Non Access Stratum

OFDM Orthogonal Frequency Division Multiplexing

OFDMA Orthogonal Frequency Division Multiple Access

OPEX Operational Expenditures

PAPR Peak-to-Average Power Ratio

PBCH Physical Broadcast Channel

PCCH Paging Control Channel

PCFICH Physical Control Format Indicator Channel

PCH Paging Channel

PDCCH Physical Downlink Control Channel

PDCP Packet Data Convergence Protocol

PDN Packet Data Network

PDSCH Physical Downlink Shared Channel

PDU Protocol Data Unit

PHICH Physical Hybrid ARQ Indicator Channel

P-GW PDN Gateway

PHY Physical Layer

PMI Precoding Matrix Indicator

PRACH Physical Random Access Channel

PS Packet Switched

PUCCH Physical Uplink Control Channel

PUSCH Physical Uplink Shared Channel

QAM Quadrature Amplitude Modulation

QoS Quality of Service

QPSK Quadrature Phase Shift Keying

RACH Random Access Channel

RAN Radio Access Network

RA-RNTI Random Access Radio Network Temporary Identifier

RAT Radio Access Technology

RB Radio Bearer

RF Radio Frequency

RI Rank Indicator

RIV Resource Indication Value

RLC Radio Link Control

ROHC Robust Header Compression

RRC Radio Resource Control

RRM Radio Resource Management

RTT Radio Transmission Technology

S1 Interface between eNB and EPC

SAE System Architecture Evolution

SC-FDMA Single Carrier – Frequency Division Multiple Access

SDMA Spatial Division Multiple Access

SDU Service Data Unit

SFBC Space Frequency Block Coding


iv

SISO Single Input Single Output

S-GW Serving Gateway

SR Scheduling Request

SRS Sounding Reference Signal

SU-MIMO Single User MIMO

TDD Time Division Duplex

TD-SCDMA Time Division-Synchronous Code Division Multiple Access

TPC Transmit Power Control

TS Technical Specification

TTI Transmission Time Interval

UCI Uplink Control Information

UE User Equipment

UL Uplink

UL-SCH Uplink Shared Channel

UMTS Universal Mobile Telecommunications System

U-plane User plane

UpPTS Uplink Pilot Timeslot

UTRA UMTS Terrestrial Radio Access

UTRAN UMTS Terrestrial Radio Access Network

VoIP Voice over IP

WCDMA Wideband Code Division Multiple Access

W LAN Wireless Local Area Network

X2 Interface between eNBs


v

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


vi

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


1

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 mobile-

radio 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.

Chapter 01: Wireless Evolution towards 4thG


2

1. 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 one-

tenth 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.



3

2. 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 re-

entered 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,



4

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 low-

band 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



5

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.



6

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.



7

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 Circuit-

Switched 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



8

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



9

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.



10

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



11

1. 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 high-

speed 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.



12

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 one-

tenth 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.



13

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-to-

average 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.



14

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 high-

performance 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.



15

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.

1. 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.

2. 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.

3. 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.

4. 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.

5. Technique used in 4G:

o OFDM

o UWB(Ultra Wide Band)

o Millimeter wireless.

o Smart Antennas



16

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.

Chapter 2: 4GLTE


17

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.

Chapter 2: 4GLTE


18

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

Chapter 2: 4GLTE


19

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 1xEV-

DO) 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.

Chapter 2: 4GLTE


20

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) Uplink (20 MHz)

Unit Mbps bps/Hz Unit Mbps Bps/Hz

Requirement 100 5 Requirement 50 2.5

2x2 MIMO 172.8 8.6 16QAM 57.6 2.9

4x4 MIMO 326.4 16.3 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

Chapter 2: 4GLTE


21

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

Chapter 2: 4GLTE


22

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

Chapter 2: 4GLTE


23

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.

Chapter 2: 4GLTE


24

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

Downlink to Uplink

Switch point periodicity Subframe number

0 1 2 3 4 5 6 7 8 9

0 5 ms D S U U U D S U U U

1 5 ms D S U U D D S U U D

2 5 ms D S U D D D S U D D

3 10 ms D S U U U D D D D D

4 10 ms D S U U D D D D D D

5 10 ms D S U D D D D D D D

6 5 ms D S U U U D S U U D

Chapter 2: 4GLTE


25

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

Special

Subframe

Config.

Normal cyclic prefix in downlink Extended cyclic prefix downlink

DwPTS

Guard

Period

UpPTS

DwPTS

Guard

Period

UpPTS

Normal

Cyclic

prefix

Extended

Cyclic

prefix

Normal

Cyclic

Prefix

In uplink

Extended

Cyclic

Prefix

In uplink

0 3 10

1

1

3 8

1

1 1 9 4 8 3

2 10 3 9 2

3 11 2 10 1

4 12 1 3 7

2

2 5 3 9

2

2

8 2

6 9 3 9 1

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.

Chapter 2: 4GLTE


26

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.

Chapter 2: 4GLTE


27

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

Configuration

Resource

Block size

Number

Of

Symbols

Cyclic prefix

Length in

samples

Cyclic prefix length

in µs

Normal cyclic prefix

12

7

160 for first symbol

144 for other symbols

5.2 µs for first symbols

4.7 µs for other symbols Ext cyclic prefix

12 6 512 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.

Chapter 2: 4GLTE


28

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 time-

frequency 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.

Chapter 2: 4GLTE


29

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

Chapter 2: 4GLTE


30

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.

Chapter 2: 4GLTE


31

5. 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

Number of HARQ processes for normal

HARQ operation

Number of HARQ processes for

subframe bundling operation

0 7 3

1 4 2

2 2 N/A

3 3 N/A

4 2 N/A

5 1 N/A

6 6 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

Chapter 2: 4GLTE


32

B. 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.

Chapter 2: 4GLTE


33

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.

Chapter 2: 4GLTE


34

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 7 160 for 1st symbol

144 for other symbols

5.2 µs for 1st symbol

4.7 µs for other symbols Ext. cyclic prefix 6 512 16.7 µs

Chapter 2: 4GLTE


35

3. 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 2 3 4 5 6 8 9 10 12

15 16 18 20 24 25 27 30 32 36

40 45 48 50 54 60 64 72 75 80

81 90 96 100

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.

Chapter 2: 4GLTE


36

Table 9 : Contents of DCI format 0 carried on PDCCH

Information type Number of bits on

PDCCH

Purpose

Flag for format 0/ format1A

Differentiation

1 Indicates DCI format to UE

Hopping flag 1 Indicates whether uplink frequency

hopping is used or not

Resource block assignment

and hopping resource

allocation

Depending on

resource block

allocation type

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

Modulation and coding

scheme and redundancy

version

5 Indicates modulation scheme and,

together with the number of allocated

physical resource blocks, the transport

block size indicates redundancy version

to use

New date indicator 1 Indicates whether a new transmission

shall be sent

TPC command for scheduled

PUSCH

2 Transmit power control (TPC) for

adapting the transmit power on the

Physical Uplink Shared Channel

(PUSCH)

Cyclic shift for

demodulation reference

signal

3 Indicates the cyclic shift to use for

deriving the uplink demodulation

reference signal from the base sequence

Uplink index (TDD only) 2 Indicates the uplink subframe where the

scheduling grant has to be applied

CQI request 1 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.

Chapter 2: 4GLTE


37

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.

Chapter 2: 4GLTE


38

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 4th

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.

Chapter 2: 4GLTE


39

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.

Chapter 2: 4GLTE


40

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 / SU-

MIMO) 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.

Chapter 2: 4GLTE


41

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 de-

correlated, 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

Chapter 2: 4GLTE


42

of data transmission especially in fading scenarios. Typically an additional antenna-

specific 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 Description TM1 Single Antenna transmission (SISO) TM2 Transmit Diversity TM3 Open-loop spatial multiplexing, no UE feedback (PMI) on MIMO

transmission provided TM4 Closed-loop spatial multiplexing, UE provides feedback on MIMO

transmission TM5 Multi-user MIMO(more than one UE is assigned to the same resource

block) TM6 Closed-loop precoding for rank=1(i.e. no spatial multiplexing, but

precoding is used) TM7 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.

Chapter 2: 4GLTE


43

Table 11 : Precoding codebook for 2 transmit antenna case

Codebook index Number of layers v

1 2

0

[ ]

[

]

1

[ ]

[

]

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

Chapter 2: 4GLTE


44

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.

Chapter 2: 4GLTE


45

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)

Chapter 2: 4GLTE


46

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 HARQ-

based 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 in-

sequence 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.

Chapter 2: 4GLTE


47

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.

Chapter 2: 4GLTE


48

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

Chapter 2: 4GLTE


49

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 real-

time 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.

Chapter 2: 4GLTE


50

6. 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.

Chapter 2: 4GLTE


51

4. CONCLUSION

The LTE evolved radio access network and simplified network architecture offer

higher data rates and better network responsiveness compared to existing 3G mobile

systems. These improvements enable applications and services that were previously only

available in fixed networks to enter the mobile world as well.

The enhanced mobile network will bring benefits to users, mobile operators and

service providers. Users will benefit from improvements in existing services and from the

introduction of new ones, and the user experience will also improve. Operators and

service providers will be able to maintain their level of profitability despite the

continuously falling prices of transferred data.

LTE standardization has come to a point where changes in specifications are

limited to minor corrections and bug fixes.

The first LTE networks were deployed in the beginning of 2010; however, the

evolution of mobile networks continues even beyond LTE. LTE-Advanced [17], a

successor to LTE, is already in the specification phase and is already considered a true

4G technology.

General Conclusion


52

IV. GENERAL CONCLUSION

This paper reported the 4G system objectives including potential applications and

system requirements, technical challenges, and related standardization activities. Through

the discussion, it has been revealed that the major feature of the 4G system capability

should be its ultra-high speed IP packet transmission with reduced delay to meet a variety

of requirements derived from the two-way enhanced reality communications such as 3D-

audio, 3D-video, and biological information media world.

It was also described that our technical challenges in radio communication fields

are likely to provide breakthrough candidates to realize the above features. The local and

international standardization activities indicate a global strong support toward this 4G

direction.


53

V. REFERENCES

[1] ITU-R, “Requirements, Evaluation Criteria and Submission Templates for the

Development of IMT-Advanced”, REPORT ITU-R M.2133, 2008.

[2] ITU-R, “Requirements Related to Technical Performance for IMT-Advanced

Radio Interface(s)”, REPORT ITU-R M.2134, 2008.

[3] 1MA205; HSPA+ Technology Introduction Whitepaper, February2012

[4] 3GPP, “Requirements for Evolved UTRA (E-UTRA) and Evolved UTRAN (E-

UTRAN) (Release 8)”, TR 25.913V8.0.0, December 2008.

[5] Rohde & Schwarz, “UMTS Long Term Evolution (LTE) Technology

Introduction“, Application Note 1MA111, January 2008.

[6] J. Zyren, W. McCoy, “Overview of the 3GPP LTE Physical Layer“, Free scale

Semiconductor, July 2007.

[7] 3GPP, “Evolved Universal Terrestrial Radio Access (E-UTRA); Services

provided by the physical layer (Release 8)”, TS 36.302 V8.1.0, March 2009.

[8] H.G. Myung, L. Junsung, and D.J. Goodman, “Single Carrier FDMA for Uplink

Wireless Transmission“, IEEE Vehicular Technology Magazine, Vol. 1, No. 3,September

2006, pp. 30-38.

[9] S.M. Alamouti (October1998)."A simple transmit diversity technique for

wireless communications", IEEE Journal on Selected Areas in Communications, Vol. 16,

No. 8

[10] 3GPP, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved

Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2

(Release 8)”, TS 36.300 V8.8.0, March 2009.

[11] 3GPP, “Evolved Universal Terrestrial Radio Access (E-UTRA) Medium Access

Control (MAC) protocol specification (Release 8)”, TS 36.321 V8.5.0, March 2009.

[12] 3GPP, “Evolved Universal Terrestrial Radio Access (E-UTRA) Radio Link

Control (RLC) protocol specification (Release 8)”, TS 36.322 V8.5.0, March 2009.

[13] 3GPP, “Packet Data Convergence Protocol (PDCP) specification (Release 8)”, TS

36.323 V8.5.0, March 2009.

[14] 3GPP, “Evolved Universal Terrestrial Radio Access (E-UTRA) Radio Resource

Control (RRC); Protocol specification (Release 8)”, TS 36.331 V8.5.0, March 2009.


54

[15] Nokia Siemens Networks, “Charting the Course for Mobile Broadband: Heading

Towards High-Performance All-IP with LTE/SAE”, 2007.

[16] Qualcomm, “UMB/LTE Applications and Services”, December 2007.

[17] 3GPP, “Requirements for Further Advancements for Evolved Universal

Terrestrial Radio Access (E-UTRA) (LTE-Advanced) (Release 8)”, TR 36.913 V8.0.1,

March 2009.

Education

4th GENERATION OF WIRELESS NETWORKS (LTE)