Evolution of the 4th Generation Mobile Communication Network

Evolution of the 4th Generation Mobile Communication Network: LTE-

Advanced

Khondokar Fida Hasan Md. Morshedul Islam

Lecturer, Department of Information and Communication Technology

Department of Computer Science and Engineering

Comilla University, Comilla, Bangladesh

Bangladesh University of Engineering and Technology (BUET), Dhaka, Bangladesh

E-Mail: [email protected] E-Mail: [email protected]

ABSTRACT

Mobile communication network experiences

dramatic advances and changes over the last two

decades. With the growing demand, the development of

the design and optimization of radio access technologies

and a further evolution of the existing system, the Third

Generation Partnership Project (3GPP) had laid down

the foundation of the future Long Term Evolution (LTE)

advanced standards as the 3GPP candidates for 4G. This

research work provides a high-level technical overview

of LTE Release-10, also known as LTE-Advanced. This

article covers a quick overview of LTE-Advanced

technology and its predecessor technologies. It also

describes all the technological enhancements introduced

to LTE-Advanced. Thus, this paper can steer all those

learners and researchers who desire to have a

foundation for further research and study in the field of

next generation mobile communication system.

Keywords: LTE, LTE-Advanced, 4G network, Carrier

Aggregation, Relaying, Spectrum Utilization.

I. INTRODUCTION

In recent years, the demand for mobile internet

access has grown significantly. The number of pages

viewed on the mobile Web browser Opera grew from 1.8

billion pages in January 2008 to 51.5 billion pages in

February 2011 where 7.3 petabytes of operator data were

compressed for 89.8 million Opera Mini users [1].

Nevertheless, the current technology is not widely

successful to serve and to satisfy the users because of its

low transmission rate and high service costs.

Consequently, research is going and new concepts toward

evolution are subjected to verify for implementation

throughout the world. Based on the requirements of high

speed mobile wireless access services, wireless systems

can be broadly classified as into two groups; Cellular

system based on IMT 2000 (WCDMA, HSDPA, HSUPA,

HSPA+, LTE/LTE-Advanced by 3GPP, CDMA2000 1X)

and Extension of fixed wireless systems incorporate

mobile functions i.e. WiMAX (IEEE 802.16e) & IEEE

802.16m. The overall evolution of cellular technology is

diagrammatically shown in Figure-1[2]. LTE Advanced

is a broadband mobile communication standard. It is

being standardized by the 3rd Generation Partnership

Project (3GPP) as a major enhancement of the pre-4G

3GPP Long Term Evolution (LTE) standard, which

verified to be insufficient to satisfy market’s demand [3].

The 3GPP group has been working on different aspects to

improve LTE performance, using for this purpose the

framework provided by LTE Advanced, which includes

some advanced features. Figure 2 shows a typical

migration scenario toward LTE-Advanced. The

horizontal axis explains the performance which includes

capacity, throughput, latency and cost, etc. LTE

(Release-8) area will be overlaid firstly with

3G area and expanded gradually according to the

customer’s demand. Since LTE-Advanced is based on the

Md.Morshedul Islam et al, Int. J. Comp. Tech. Appl., Vol 2 (4), 1092-1098

IJCTA | JULY-AUGUST 2011 Available [email protected]

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2G 3G

4G

IMT-Advanced Converged OFDMA

based standard

1994 2002 2006 2009

IS95A cdma 1X 1x EV-DO IS 956 DO Rev A DO Rev B

Flash-OFDM Rev 0 &

UMB

GSM GPRS EDG

UMT

HSDPA HSUPA LTE

802.11 b/g WiFi

802.16d WiMAX-e WiMAX-m

3GPP2

3GPP

IEEE

OFDMA based physical layer

LTE Rel. 8 and supported with full backward

compatibility with LTE Rel. 8, LTE-Advanced UE can

be shared with LTE of previous release in the same

frequency and area

Thus, the migration from LTE toward LTE-

Advanced is very smooth, e.g. support of CA with new

frequency to improve the capacity and throughput. In

other words, LTE operators can easily upgrade to the

LTE-Advanced according to the market demands and

new frequency allocation [4].

Figure: 1. Evolutionary path of cellular technology.

In this research work, it has been presented a

detail review on the LTE-Advanced mobile broad band

communication systems and outlines some features

that are still in progress.

Figure: 2. Migration scenario toward LTE-Advanced.

LTE-Advanced requirements:

Based on the ITU requirements for IMT-Advanced

systems, 3GPP created a technical report summarizing

LTE-Advanced requirements in [3-5].

In wards the prime requirements are:

• A high degree of commonality of functionality

worldwide while retaining the flexibility to support a

wide range of services and applications in a cost

efficient manner;

• Compatibility of services within IMT and with fixed

networks;

• Capability of interworking with other radio access

systems;

• High quality mobile services;

• User equipment suitable for worldwide use;

• User-friendly applications, services and equipment;

• Worldwide roaming capability; and Enhanced peak

data rates to support advanced services and

applications (100 Mbps for high and 1 Gbps for low

mobility were established as targets for Research).



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Another important requirement for LTE-Advanced is

to reduce the cost in the radio interface network. As

LTE advanced (Release-10 and beyond) is the next

phase of LTE (Release-8), it has been shown a brief

comparison of the performance target of LTE and

LTE-Advanced technological demands in Table-1 [3],

[5], [6].

II. TECHNOLOGY COMPONENTS OF

LTE-ADVANCED

To satisfy the requirements for the next generation

broadband wireless technology, LTE-Advanced focused

on five technical topics also called technology

components. Which are: wider bandwidths with carrier

aggregation, uplink transmission scheme including

spatial multiplexing, MIMO (Multiple Input Multiple

Output) enhancements, coordinated multiple point

transmission and reception (CoMP) and relaying

functionality.

Features LTE LTE-Advanced Uplink Downlink Uplink Downlink

Peak Spectrum usage efficiency (b/s/cell) >2.5 >5 15 30

Average spectrum usage efficiency (b/s/cell)

With respect to antenna configuration. 1ˣ2 2ˣ4 2ˣ2 4ˣ4 1ˣ2 2ˣ4 2ˣ2 4ˣ4

0.66 1.0 1.6 2.1 1.2 2.0 2.4 3.7 Cell-edge spectrum usage efficiency

(b/s/user) 0.02 0.03 0.04 0.06 0.04 0.07 0.07 0.12

Operating bandwidth (MHz) 1.4-2.0 Up to 100 User Plane delay (Unidirectional)

(ms) <5 <5

Connection setup delay (ms) <100 <50

Mobility

Optimized for low speeds(<15km/hr)

High performance at speed up to 120km/hr

Maintain links at speeds up to 350km/hr

Same as that in LTE

Coverage Full performance up to 5km

a) Same as LTE requirements. b) Should be optimized or deployments in local areas/micro cell environments

Capacity 200 active users per cell in 5 MHz 3 times higher than that in LTE

Table: 1. Comparison of the performance target of LTE and LTE-Advanced.

1. BAND AGGREGATION FOR WIDEBAND

TRANSMISSION AND SPECTRUM

UTILIZATION

One of the salient targets of LTE-Advanced is to

evolve technology that will support to significantly

increase the pick data rate up to 1Gbits/s in the downlink

and 500Mbits/s in the uplink [7]. An effective and slim

strategy to reach high data rates requirements is to

aggregate multiple LTE carriers. Two or more

component carriers are aggregated in order to support wider

transmission bandwidths up to 100MHz [8].

Figure: 3. Carrier aggregation of five contiguous carriers.

100



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Here several smaller contiguous and noncontiguous

carriers can be aggregated while maintaining the

backward compatibility with the legacy user. Five

20MHz component carriers can be aggregated to form

100 MHz system as shown in Figure-3. Initially, LTE-

Advanced (3GPP Release 10) deployments will likely be

limited to the use of maximum two component carrier,

i.e. the maximum DL/UL bandwidth will be 40MHz for

FDD. This will not preclude higher number of

aggregated carriers been specified in 3GPP Release 11

and/or higher [8].

Considering frequency location of component

carriers, carrier aggregation can be represented into three

categories (as shown in figure: 4); intra-band aggregation

with contiguous carriers (e.g., aggregation of #2 and #3

in Fig. 2), inter-band aggregation (#1and #4), and intra-

band aggregation with non-contiguous carriers (#1 and

#2) [9].

Figure: 4. Carrier Aggregation in LTE-Advanced

(Release-10)

2. ENHANCED MULTIPLE ANTENNA

TECHNOLOGIES

Multiple Input/Multiple Output (MIMO) increases

peak throughput by transmitting and receiving multiple

streams of information within the same spectrum.

Together MIMO and OFDMA (Orthogonal Frequency

Division Multiple Access) improves the spectral efficiency

and capacity of the wireless network, and proves a very

valuable asset in maximizing usage of scarce spectrum

typically controlled by regulatory bodies. Thus MIMO

(Multiple Input Multiple Output) is probably the most

important feature of LTE-Advanced for improving the data

bit rates and the spectral efficiency [10]. LTE-Advanced

extends the MIMO capabilities and now supporting eight

downlink antennas and four uplink antennas where as LTE

support maximum four downlink antennas and one uplink

antennas.

In order to support downlink peak spectrum efficiency

of 30 bps/Hz and uplink peak spectrum efficiency of

15 bps/Hz according to LTE-Advanced requirement [13],

the spatial multiplexing with antenna configuration of 8×8

for downlink transmission and 4×4 for uplink transmission

is being investigated. Here N×N denotes a configuration of

N transmit antennas and N receive antennas. In addition to

meeting the peak spectrum efficiency, further improvement

of the average cell throughput as well as the cell edge

performance is also an important aspect of the LTE-

advanced study [8].

3. ENHANCED UPLINK TRANSMISSION

SCHEME

The uplink transmission scheme of LTE-Advanced is

based on SC-FDMA, a powerful technology that combines

many parts of OFDM with the low peak to average power

ratio of a single carrier system. SC-FDMA is a discrete

Fourier transformed (DFT) pre-coded orthogonal frequency

division multiple access scheme [3].

Figure-5 shows a block diagram for the enhanced uplink

multiple access (clustered SC-FDMA) process. It has one

transport block and one hybrid ARQ entity per scheduled

component carrier. Each transport block is mapped to a

single component carrier, and a UE may be scheduled over

multiple component carriers simultaneously using carrier

aggregation, as described in the previous section.



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Figure: 5. Block diagram of clustered SC-FDMA in

uplink LTE-Advanced.

4. CO-ORDINATE MULTIPLE POINT

TRANSMISSION AND RECEPTION

Coordinated multi-point (CoMP)

transmission/reception is a candidate technology

considered for LTE-Advanced as a tool to improve the

coverage of high data rates, the cell-edge throughput and

to increase system throughput [6]. It has been

demonstrated that Spectrum efficiency can be improved

with multiple antenna technologies (4 or more antennas)

using spatial interference coordination methods. Thus the

multiple access schemes, enhanced multiple-input

multiple-output (MIMO) channel transmission

techniques and widespread coordination among

multiple cell sites called coordinated multipoint (CoMP)

transmission/reception were accepted as the key

techniques for LTE Advanced at the Technical

Specification Group- Radio Access Network (TSG-RAN)

Working Group 1 (WG1) meeting in the 3GPP [11].

CoMP improves the received signal of the user terminal.

Both the serving and the neighbor cells are used in a way

that the co-channel interference from neighboring cells is

reduced. It implies dynamic coordination between

geographically separated transmission points in the

downlink and reception at separated points in the uplink.

This mechanism will improve the coverage of high data

rates and will increase the system bit rate [12]. The

application of coordinated multipoint transmission is

illustrated in Figure-6 for a downlink transmission

scenario. An example scheme is to form a beam to the

scheduled UE by using the transmit antennas of the cells 1,

2, and 3, where each cell transmits the same data to the

scheduled UE and the UE-specific reference signal is used

for support of demodulation at the UE.

Figure: 6. Coordinate multipoint transmission in the

downlink

For the cells 1, 2, and 3 to jointly form the transmit

signal matching to the composite channel experienced by

the UE, it may be necessary to provide feedback

representing the downlink spatial channel of each cell

without any presumption on operation at the eNodeB

transmitter and the UE receiver. The feedback for explicit

representation of the spatial channel of each cell may

naturally require much larger overhead than the feedback

defined in LTE.

5. RELAYING

In the evolution process of next generation mobile

communication system, relaying is a technological

milestone to improve the coverage of high data rates, group

mobility, temporary network deployment, the cell-edge

throughput and/or to provide coverage in new areas. With

relaying, the mobile terminal communicates with the

network via a relay node that is wirelessly connected to the

rest of the part of the radio-access network. The relay

node (RN) is wirelessly connected to a donor cell of a donor

eNB via the Un interface, and UEs connect to the RN via

the Uu interface as shown in figure: 7 [14]



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Figure: 7. Relays

The doner-cell/relay link is based on the LTE radio-

interface technology and may operate on the same

frequency as the relay/terminal link (“inband relaying”)

or on a different frequency (“outband relaying”) as

shown in figure: 8.

Figure: 8. Inband-Outband Relaying

Relay stations can be classified into different ways.

Based on the amount of protocol knowledge a relay station

may be distinguished into three layers. The first layer is the

simplest one, Layer 1 relay station (repeater), which simply

receives the donor eNodeB signal and amplifies it into its

own coverage area. A Layer 2 relay station will have

medium access control (MAC) layer functionality. A layer 3

relay station would include functionality like mobility

management, session set-up and handover and as such acts

as a full service (sub-) eNodeB.

Table: 2. Classification of Relays

Another important classification is used in 3GPP

standardization and distinguishes between Type 1 and

Type 2 relay stations. A Type 1 relay effectively

creates its own cell, i.e. transmits its own identity

number (Cell_ID) and own synchronization and

reference signals. The UE receives scheduling

information and HARQ feedback directly from and

sends its own control channels to the relay station.

From an UE perspective this Type1 relay station looks

like a eNodeB. On the other hand, a Type 2 relay

station will not have its own Cell_ID and thus would

not create any new cell(s). Consequently the UE will

not be able to distinguish between transmitted signals

form the eNodeB and the relay station. In such a

scenario it would be possible to transmit control

information from the eNodeB and data via the relay

station. [8], [14].

III. CONCLUSION The performance requirements of LTE-Advanced are

set by ITU-R for IMT-Advanced and it is an evolution of

existing LTE standard. This paper addressed all the LTE-

Advanced features comparing with existing LTE network,

as the commercial launch for LTE single mode has

already been piloted in Northern Europe. Therefore this

paper covers all the new concepts to power LTE-

Advanced, towards next generation networks.

Relay Station

Protocol Based Transparency

Layer-1 Layer-2 Layer-3 Type-1 Type-2



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http://www.rohde-schwarz.com/�

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Evolution of the 4th Generation Mobile Communication Network

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