EIS Whitepaper LTE Advanced Future of Mobile Broadband 09 2009

7/28/2019 EIS Whitepaper LTE Advanced Future of Mobile Broadband 09 2009

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Third Generation Partnership Project (3GPP) a group of

telecommunication associations working towards the

development and maintenance of a Global System for

Mobile communication (GSM) including evolved radio

access technologies, has started working on Long-Term

Evolution advanced (LTE-Advanced) in order to achieve

the requirements of next generation technology. The

key goals for this evolution are increased data rate,

improved spectrum efficiency, improved coverage andreduced latency. The end results of these goals are

significantly improving service provisioning and

reduction of operator costs for different traffic scenarios.

The requirements for LTE-Advanced are agreed and the

radio interface techniques are currently under

discussion.

One of the most important requirements for LTE-

Advanced is to support LTE and enhancement in the

frequency spectrum. Layered OFDMA radio access is

used to attain higher level requirements such as system

performance and full backward compatibility.

Moreover, key radio access technologies such as fast

inter-cell radio resource management, multi-antenna

transmissions with more antennas for coverage, and

enhanced techniques are employed to achieve a high

level of cell-edge spectrum efficiency.

LTE-Advanced: Future ofMobile Broadband


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LTE-Advanced: Future of Mobile Broadband

About the Authors

K. N Shantha Kumar

K. N Shantha Kumar, who has a masters degree in VLSI design andembedded system, has over 9 years of experience in design and

development of hardware, software and system integration.

Madhu Kata

Madhu Kata with Masters Degree in VLSI, has over three years of

experience in design and development of Linux Device Drivers,

development of protocol stacks in Layer1 (L1) and Layer2 (L2) for

WCDMA and LTE.

Paruchuri Chaitanya

Paruchuri Chaitanya with Masters Degree in Electronics, has over

two years of experience in design & development of wireless

Medical devices and development of LTE Layer1 (L1) layer.

Dinesh Mukkollu

Dinesh Mukkollu with Masters Degree in Digital Communication,

has over two years of experience in development of protocol stacksin Wimax and LTE.


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Table of Contents

1. Third Generation Wireless Systems 3

2. Radio Interface Concepts of LTE 3

3. Evolution of LTE-Advanced 7

4. Advantages and key features of LTE- Advanced 11

5. Comparision between LTE and LTE-Advanced 12

6. Conclusion 13

7. Reference 13


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Third Generation Wireless Systems

Radio Interface Concepts Of LTE

Third generation (3G) wireless systems partnership project Long Term Evolution (LTE), based on radio access

technology is taking momentum and continuing to grow at an accelerated pace. However, it is necessary to further

develop the future demands for mobile broadband services through higher data rates, shorter delays, and evengreater capacity. In parallel to these activities related to the evolution of current 3G wireless technologies, there is also

an increased research effort on future radio access, referred to as fourth-generation (4G) radio access. Such future

radio access is anticipated to take the performance and service provisioning of wireless systems a step further,

providing data rates up to 100 Mbps with wide-area coverage and up to 1 Gbps with local-area coverage, fulfilling the

requirements for Beyond IMT-2000 systems [1][2]. To meet the challenges of major enhancements to LTE-Advanced

which will be introduced in release 10, 3GPP has initiated the study item on LTE-A, aiming at achieving additional

substantial leaps in terms of service provisioning and cost reduction[3][4].

Figure 1 : Evolution of Radio Access Technologies

In this paper, we first address some of the radio interface concepts of Release 8 LTE and then provide the majordifferences between LTE and LTE-A. Later we will discuss some of the advantages and key features of LTE-advanced.

The ability to provide a high bit rate is a key measure for LTE. LTE is designed to meet the requirements of peak data

rate up to 150 Mbps in down-link, 75 Mbps at up-link. The characteristics of LTE will be cellular coverage, mobility,

scalable bandwidth of 1.3, 3, 5, 10, 15, 20 MHz, FDD (Frequency Division Duplexing) and TDD (Time Division

Duplexing).


Low

Speed

MedSpeed

HighSpeed

Mobility

AMPSETACS, ITACS

CDMA/GSM/TDMA

CDMA2000 EV-DO/DV W-CDMA/HSDPA

LTE

LTE-Adv

Data Rates~14.4 Kbps ~400 Kbps ~40 Mbps 150 Mbps 500 Mbps

1 G

2 G

3 G

3.x G

4 G


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The down-link by OFDMA (Orthogonal Frequency Division Multiplexing Access), up-link by SCFDMA (Single Carrier

Frequency Division Multiplexing Access), MIMO (Multiple Input Multiple Output), and modulations by 16 QAM, 64

QAM technologies are used by LTE for meeting the data rate requirements mentioned above.

A .Down-link OFDMA

OFDMA is a multi-user version of a digital modulation scheme called Orthogonal Frequency-Division Multiplexing

(OFDM). In OFDM the signal is first split into independent sub-carriers and these closely-spaced orthogonal sub-

carriers are used to carry the data. The data is divided into several parallel data streams or channels, one for each sub-

carrier. Each sub-carrier is modulated with a conventional modulation scheme (such as quadrature amplitude

modulation or phase shift keying) at a low symbol rate, maintaining total data rates similar to conventional single-

carrier modulation schemes of the same bandwidth.

A general analogy for OFDM can be of many small lamps in a hall rather than a single big lamp. The advantage is that

light will be distributed across the hall equally as compared to a single lamp and increase redundancya defect in

one lamp will not affect the light in the hall.

The primary advantage of OFDM over single-carrier scheme is its ability to cope with severe channel conditions

without complex equalization filters. For example, attenuation of high frequencies in a long copper wire, narrowband

interference, and frequency-selective fading due to multipath.

Figure 2 : Multi Path Fading

With the help of OFDM, channel equalization is simplified as OFDM may be viewed as using many slowly-modulated

narrowband signals rather than one rapidly-modulated wideband signal. With the duration of each symbol being

long, it is feasible to insert a guard interval between the OFDM, making it possible to handle time-spreading and

eliminate inter-symbol interference (ISI). This mechanism also facilitates the design of single-frequency networks,

where several adjacent transmitters send the same signal simultaneously at the same frequency. As the signals from

multiple distant transmitters may be combined constructively, rather than interfering as would typically occur in a

traditional single-carrier system.

ReflectedwaveDiffractedwave



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In an OFDM symbol the cyclic prefix, transmitted during the guard interval, consists of the end of the OFDM symbol as

shown in the following figure. The guard interval is used so that the receiver will integrate over an integer number of

sinusoid cycles for each of the multipath when it performs OFDM demodulation with the FFT.

Figure 3: OFDM Symbol with Cyclic Prefix

In OFDM, the available bandwidth is divided into a large number of smaller bandwidths using Fast Fourier Transforms

(FFTs) that are mathematically orthogonal. Reconstruction of the band is performed by the Inverse Fast Fourier

Transform (IFFT). FFTs and IFFTs are well-defined algorithms that can be implemented very efficiently when sized as

powers of 2. Typical FFT sizes for OFDM systems are 512, 1024, and 2048. For example, a 10-MHz bandwidth allocation

may be divided into 1,024 smaller bands, whereas a 5-MHz allocation would be divided into 512 smaller bands. These

smaller bands are referred to as subcarriers and are typically on the order of 10 KHz.

The multiple access techniques selected for LTE are OFDMA in down-link and SC-FDMA in up-link. In OFDMA, the data

is transmitted over a large number of orthogonal narrow band channels. By inserting the cyclic prefix, the received

signal, even after undergoing multipath propagation, can be detected by a low complexity single tap equalizer in the

UE. OFDMA provides easy bandwidth scalability by configuration of the number of the subcarriers. This allows the

base station to dynamically adjust the bandwidth usage according to the system requirements.

In addition, because each user consumes only a portion of the total bandwidth, the signal power of each user can also

be modulated according to the current system requirements. Quality of service (QoS) is another feature that can be

adapted for different users depending on their specific application, such as voice, streaming video, or Internet access.

The drawback of OFDMA is the relatively large peak to average power ratio (PAPR), which tends to reduce the

efficiency of the radio frequency (RF) power amplifier [10].

Figure 4 : OFDMA sub carriers


Data 1 Data 2CP CP

Cyclic Prefix Cyclic Prefix

Frequency

ReferenceSub carriers

User 1

User 2

User 3

User 4


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Figure 5 : Bandwidth allocation OFDM Vs OFDMA

B. Uplink Single-Carrier FDMA with Dynamic Bandwidth

To improve the RF transmission power efficiency in the UE, Single Carrier Frequency Division Multiple Access (SC-

FDMA) is used. SC-FDMA has similar performance and essentially the same overall structure as those of an OFDMA

system. One prominent advantage of SC-FDMA over OFDMA is that the SC-FDMA signal has lower peak-to-average

power ratio (PAPR). In the up-link communications low PAPR greatly benefits the User Equipment (UE) in terms of

transmit power efficiency.

Guard intervals with cyclic repetition are introduced between blocks of symbols as in OFDM explained earlier. In

OFDM, FFT is applied on the receiver side on each block of symbols, and IFFT on the transmitter side. In SC-FDMA,

both FFT and IFFT are applied on the transmitter side, and also on the receiver side. However SC-FDMA requires

transmissions in consecutive bands, and thus introduces restrictions on the frequency domain packet scheduling for

individual users compared to OFDMA.

C. Multi-Antenna Solutions

Multiple Input Multiple Output (MIMO) is the major feature used to improve the performance of the LTE system, it

allows in improving the spectral efficiency and data throughput. MIMO consists of multiple antennas on the receiverand transmitter to utilize the multipath effects. This reduces the interference and leads to high throughputs.

Multipath occurs when the different signals arrive at the receiver at various times intervals. MIMO divides a data

stream into multiple unique streams, transmits data streams in the same radio channel at the same time. The

receiving end uses an algorithm or employs special signal processing to generate one signal that was originally

transmitted from the multiple signals [7].


Carriers

Carriers

Time Time

-----

User 1 User 2 User 3 User 4


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Figure 6: MIMO Block

In LTE, the MIMO concepts vary from down-link to up-link to keep the terminal (UE) cost low.

The base station either consists of two or four transmitting antennas and two receiving antennas on the terminal (UE)

side for the down-link, and UE employs MU-MIMO (Multi User MIMO) for the up-link. With this scheme UE only haveone transmit antenna which reduces the cost of the equipment. Interference due to transmission of data in the same

channel by multiple mobile terminals is reduced by using mutually orthogonal pilot patterns.

Figure 7 : MIMO Tx and Rx Schemes LTE (4 X 2 MIMO)

LTE-A should be real broadband wireless network that provides peak data rates equal to or greater than those for

wired networks, i.e., FTTH (Fiber To The Home), while providing better QoS. The major high-level requirements of LTE-

A are reduced network cost (cost per bit), better service provisioning and compatibility with 3GPP systems [8]. LTE-A

being an evolution from LTE is backward compatible.

Some of the major technology proposals of LTE-A are [8]:

A. Asymmetric transmission bandwidth

Access such as Frequency Division Duplex (FDD) and Time Division Duplex (TDD) are the two most prevalentduplexing schemes used in fixed broadband wireless networks. FDD uses two distinct radio channels and supports

Evolution of LTE-ADVANCED

7


Transmitter Receiver

Data Streams Data Streams

4G

4G

Base Station Base Station

UE

UE

A: DL Direction B: UL Direction


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two-way radio communication and TDD uses a single frequency to transmit signals in both the downstream and

upstream directions.

Symmetric transmission results when the data in down-link and in the up-link are transmitted at the same data rate.

This is one of the cases in voice transmission which transmits the same amount of data in both directions. However,

for internet connections or broadcast data (for example, streaming video), it is likely that more data will be sent from

the server to the UE (the down-ink).

Based on the current and future traffic demands in cellular networks the required bandwidth in up-link will be

narrower than that in down-link. So asymmetric transmission bandwidth will be a better solution for efficient

utilization of the bandwidth.

Figure 8: Support of Asymmetric Bandwidths for LTE Advanced

B. Layered OFDMA

In layered structure, the entire system bandwidth comprises multiple basic frequency blocks. The bandwidth of basic

frequency block is, 1520 MHz. Layered OFDMA radio access scheme in LTE-A will have layered transmission

bandwidth, support of layered environments and control signal formats.

The support of layered environments helps in achieving high data rate (user throughput), QoS, or widest coverageaccording to respective radio environments such as macro, micro, indoor, and hotspot cells.

The control signal formats are a straightforward extensions of L1/L2 control signal formats of LTE to LTE-A.

Independent control channel structure is used for each component carrier. Control channel supports only shared

channel belonging to the same component carrier.

C. Advanced Multi-cell Transmission/Reception Techniques

In a multi-user multi-cell environment employing multi-transmission/reception antenna devices for each cell have

multiple first units and a second units in wireless communication.

The first units consists of a predetermined antenna and the second unit consists of the following sub units:

LTE

Bandwidth

Symmentric BW

Asymmetric BW

LTE DL BW(20 MHz)

LTE Advanced Max BW

100 MHz

LTEAdvanced

UL BW(10 MHz)

LTE UL BW(20 MHz)

LTE AdvancedDL BW

(20 MHz)


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lEstimation unit: Estimates channel information on signals from the individual first units and estimates

information of noise and interference signals from adjacent cells.

lCalculation unit: Calculates the sum of transfer rates for each user group having at least one first unit using the

information estimated by the estimation unit.

lDetermination unit: Determines one user group by comparing the sum of the transfer rates of each user group

calculated by the calculation unit.

lFeedback unit: Information on the user group determined by the determination unit is fed back to the first units

of the corresponding cell.

In LTE-A, the advanced multi-cell transmission/reception processes (also called as coordinated multipoint

transmission/reception) helps in increasing frequency efficiency and cell edge user throughput. Faster handovers

among different inter-cell sites are achieved by employing Inter-Cell Interference (ICI) management (that is, inter-cell

interference coordination (ICIC) aiming at inter-cell orthogonalization).

D. Enhanced Multi-antenna Transmission Techniques

Mobile traffic in wireless communications has been increasing multi folds over the years, which amplifies therequirement of higher-order MIMO channel transmissions and higher peak frequency efficiency than LTE.

In LTE-A, the MIMO scheme has to be further improved in the area of spectrum efficiency, average cell through put

and cell edge performances. With multipoint transmission/reception, where antennas of multiple cell sites are

utilized in such a way that the transmitting/receiving antennas of the serving cell and the neighboring cells can

improve quality of the received signal at the UE/eNodeB and reduces the co-channel interferences from neighboring

cells. Peak spectrum efficiency is directly proportional to the number of antennas used. In LTE-A the antenna

configurations of 8x8 in DL and 4x4 in UL are planned.

Figure 9 : MIMO Tx & Rx Schemes LTE-A (8 X 4 MIMO)

E. Enhanced Techniques to Extend Coverage Area

Remote Radio Requirements (RREs) using optical fiber should be used in LTE-A as effective technique to extend cell

coverage. Layer 1 relays with non-regenerative transmission, that is, repeaters can also be used for improving

coverage in existing cell areas. Layer 2 and Layer 3 relays can achieve wide coverage extension through an increase in

Signal to Noise Ratio (SNR).

4G

4G

Base Station Base Station

UE

UE

Fig a: DL Direction Fig b: UL Direction


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Figure 10 : RRE using optical fibers

F. Support of Larger Bandwidth in LTE-Advanced

Peak data rates up to 1Gbps are expected from bandwidths of 100MHz. OFDM adds additional sub-carrier to increase

bandwidth. The available bandwidth may not be continuous as a result of fragmented spectrum. To ensure backward

compatibility to the current LTE, the control channels such as synchronization, broadcast, or PDCCH/PUCCH might

be needed for every 20 MHz.

Figure 11: Support of larger Bandwidths

The above described technology proposals of LTE-A will help us to:

lLower the total cost of network ownership

lEasily deploy the network

lIncrease user throughput for fully multi-media feature services

lAchieve spectrum flexibilitysupport scalable bandwidth and spectrum aggregation

lAchieve backward compatibility and inter-working with LTE with 3GPP legacy systems

lEnable extended multi-antenna deployments and denser infrastructure in a cost-efficient way

10


4G

4G

Dire

ctConn

ectio

ntoB

S

IndirectConnectiontoBS

OpticalFiber

Base Station

RREUE

UE

(20 MHz)

LTE

100 MHz


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Advantages and Key Features Of LTE- Advanced

A. Advantages

Some advantages that are applicable to the 4th Generation mobile communications are also applicable to LTE-A.

With average download speeds of 400 Kbps to 700 Kbps, the network offers enough bandwidth to enable cell phoneusers to surf and download data from the Internet.

LTE-A should significantly lower the bit-cost for the end-users and the total cost of ownership for the operators. At the

same time, LTE-A should meet new emerging challenges such as energy-efficient Radio Access Network (RAN)

design, increase the flexibilities of network deployments, and off load networks from localized user communications.

Regardless of the actual technology, the forthcoming technology will also be able to allow the complete

interoperability among heterogeneous networks and associated technologies, thus providing clear advantages in

terms of:

lCoverage: The user gets best QoS and widespread network coverage as there is network availability at any giventime.

lBandwidth: Sharing the resources among the various networks will reduce the problems of spectrum limitations

of the third generation.

B. Key Features

1. Friendliness and Personalization: User friendliness exemplifies and minimizes the interaction between

applications and the user. Thanks to a well designed transparency that allows the person and the machine to

interact naturally (for example, the integration of new speech interface is a great step to achieve this goal).

2. Heterogeneous Services: Services that are heterogeneous in nature (for example, different types of services such

as audio, video etc.) such as quality and accessibility may not be the same due to the heterogeneity of thenetwork. For instance, a user in proximity of the shopping mall but out of the coverage of a WLAN can still receive

pop-up advertisements using the multi-hop ad hoc network setup in his surrounding. Therefore the dynamics of

the network environment can change the number of users, terminals, topology, etc.


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Comparision between LTE and LTE-advanced

Comparison of performance requirements of LTE with some of the current agreements of LTE Advanced [8] are:

Table 1: Difference between LTE and LTE-A

Technology

Peak data rate Down Link( DL)

Peak data rate Up Link (UL)

Transmission bandwidthDL

Transmission bandwidthUL

Mobility

Coverage

Scalable Band Widths

Capacity

LTE

150 Mbps

75 Mbps

20MHz

20MHz

Optimized for low speeds(


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Conclusion

References

LTE-A helps in integrating the existing networks, new networks, services and terminals to suit the escalating user

demands. The technical features of LTE-A may be summarized with the word integration. LTE-Advanced will be

standardized in the 3GPP specification Release 10 (Release 10 LTE-A) and will be designed to meet the 4Grequirements as defined by ITU. LTE-A as a system needs to take many features into considerations due to

optimizations at each level which involves lots of complexity and challenging implementation. Numerous changes

on the physical layer can be expected to support larger bandwidths with more flexible allocations and to make use of

further enhanced antenna technologies. Coordinated base stations, scheduling, MIMO, interference management

and suppression will also require changes on the network architecture.

[1] S. Parkvall et al. Evolving 3G Mobile SystemsBroadband and Broadcast Services in WCDMA, IEEE

Communications Magazine, February 2006.

[2] 3GPP, RP-040461,Proposed Study Item on Evolved UTRA and UTRAN, www.3gpp.org.

[3] D. Astely et al., A Future-Radio-Access Framework, Journal on Selected Areas in Communications, Special

Issue on 4G Wireless Systems, to appear

[4] E. Mino Diaz, et al., The WINNER project: Research for new Radio Interfaces for better Mobile Services, IEICE

Transactions, Japan, Vol. E87-A, No. 10, October 2004

[5] X. Yu, G. Chen, M. Chen, and X. Gao, Toward Beyond 3G: The FuTURE Project in China, IEEE Communications

Magazine, pp 70-75, January 2005

[6] 3GPP, TR 36.201, Evolved Universal Terrestrial Radio Access (E-UTRA); Long Term Evolution (LTE) physical layer;General description, www.3gpp.org.

[7] H. Ekstrm et al., Technical Solutions for the 3G Long-term Evolution, IEEE Communications Magazine, March

2006.

[8] 3GPP, TR 36.913, Requirements for further advancements for E-UTRA (LTE-Advanced), www.3gpp.org.

[9] Progress on LTE Advanced - the new 4G standard Eiko Seidel, Chief Technical Officer

Nomor Research GmbH, Munich, Germany.

[10] IEEE Communications Magazine. April 2008.


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EIS Whitepaper LTE Advanced Future of Mobile Broadband 09 2009