3GPP – Long Term Evolution – A Technical Study

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Mr. Vishal PawarMITSOT

Main Topics • Introduction to LTE• LTE Network Architecture• LTE Physical Layer • SC-FDMA• Channel Dependent Scheduling • Cognitive Radio for LTE RRM• Multiple antenna schemes in LTE • LTE-Advanced• Conclusion

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Introduction to LTE

• 3GPP Long Term Evolution - the next generation of wireless cellular technology beyond 3G

• Initiative taken by the 3rd Generation Partnership Project in 2004

• Introduced in Release 8 of 3GPP

• Mobile systems likely to be deployed by 2010

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Requirements to be met by LTEFast, Efficient, Cheap, Simple

• Peak Data Rates• Spectrum efficiency• Reduced Latency• Mobility• Spectrum flexibility• Coverage• Low complexity and cost• Interoperability• Simple packet-oriented E-UTRAN architecture

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LTE Network Architecture

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• Simple Architecture• Flat IP-Based Architecture• Reduction in latency and cost• Split between EPC and E-UTRAN• Compatibility with 3GPP and

non-3GPP technologies• eNB-radio interface-related

functions• MME-manages mobility, UE

identity and security parameters

• S-GW-node that terminates the interface towards E-UTRAN

eNB

MME / S-GW MME / S-GW

eNB

eNB

S1

S1

X2 E-UTRAN

LTE Network Architecture

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LTE Frame Structure

• LTE Frame Structure Type I (FDD)

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LTE Frame Structure Type II (TDD)

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Single-Carrier Frequency Division Multiple Access (SC-FDMA)

• Motivation for SC-FDMA

• SC-FDMA utilizes single carrier modulation at the transmitter and frequency domain equalization at the receiver.

• It has the best of both worlds - the low PAPR of single carrier systems and the multipath resistance and channel dependent subcarrier allocation features of OFDM.

• Same complexity and performance as OFDMA

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The “SC”-”FDMA” System

DFT-Spread OFDMA – Mapping of spread symbols , not original symbols to subcarriers!!!

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Subcarrier Mapping Schemes

• Localized (LFDMA)• Distributed (DFDMA)• Interleaved (IFDMA)

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Frequency and Time Domain Representation

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Frequency Time

Time domain signals of LFDMA, DFDMA and IFDMA[20]

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PAPR characteristics of an SC-FDMA signal [20]

Comparison of the CCDF of PAPR for LFDMA, DFDMA, IFDMA and OFDMA

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Effect of roll-off factor, alpha on the PAPR[20]

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Why does SC-FDMA have a low PAPR?

• OFDMA • Parallel Transmission • Multi carrier structure• Increase in M => high PAPR• SC-FDMA • Serial Transmission• Each symbol represented by a wide signal – DFT spreads symbols over all subcarriers• PAPR not affected by increase in M

Both occupy the same bandwidth with same symbol durations

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SC-FDMA in comparison with OFDMA and DS-CDMA/FDE

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DS-CDMA/FDE

Channel Dependent Scheduling

• Channel is highly frequency selective

• Resources in deep fade for one user could be excellent for another user

• Frequency selectivity of the channel can be exploited by using CDS to maximize throughput

• LFDMA – frequency selective diversity

• IFDMA – Multi user diversity (inherently frequency diversity is obtained)

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Cognitive RRM in LTE

• Link adaptation possible as network segments in LTE adapt to the environmental changes

• System can learn from solutions that were provided in the past

• Faster response, improved performance, intelligent system

• Decisions reg. apt BW,DSA,APA and AM

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Cognitive Features to enhance RRM in LTE

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Enhanced context acquisition mechanism architecture for cognitive intra-cell RRM

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Multiple Antenna Schemes in LTE

• In DL : Tx diversity, Rx diversity, Spatial multiplexing (2x2,4x2 configurations – SU-MIMO and MU-MIMO) supported

• In UL : Only 1 Transmitter (antenna selection Tx diversity ), MU-MIMO possible, Rx diversity with 2 or 4 antennas at eNB supported

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LTE Advanced• LTE doesn’t fulfill the requirements of IMT-Advanced

• 3GPP has also started work on LTE-Advanced, an evolution of LTE, as a proposal to ITU-R for the development of IMT Advanced.

• LTE Advanced is envisioned to be the “first true 4G technology”.

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Requirements of LTE Advanced

• Peak data rates – 1Gbps in DL and 500 Mbps in UL• Cell edge user data rates twice as high and average user throughput

thrice as high as in LTE• Peak spectrum efficiency DL: 30 bps/Hz, UL: 15 bps/Hz• Operate in flexible spectrum allocations up to 100 MHz and support

spectrum aggregation (as BW in DL >>20 MHz)• An LTE-Advanced capable network must appear as a LTE network

for the LTE UEs

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Technological proposals for LTE Advanced

• Larger BW can be used for high date rates and more coverage at cell edges

• Advanced repeater structures• Relaying for adaptive coding

based on link quality

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Carrier aggregation and Spectrum aggregation

Thank You !

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