3GPP Long Term Evolution A Technical Study

1
3GPP Long Term Evolution A Technical Study

• EEL 6936 Advanced Topics in Wireless
  Communications
• Spring 2009
• Advised by Dr. Hüseyin Arslan
• Presented by Divya Ramamoorthy

2
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

3
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

4
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

5
LTE Network Architecture

• 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

6
LTE Network Architecture
7
LTE Frame Structure

• LTE Frame Structure
• Type I (FDD)
• LTE Frame Structure
• Type II (TDD)

8
Concept of Resource Blocks (RB)

• Downlink Resource Grid
  Reference Signals for MIMO

9
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!!!

11
Subcarrier Mapping Schemes

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

12
Frequency and Time Domain Representation

• Frequency Time

13
Time domain signals of LFDMA, DFDMA and IFDMA20
14
PAPR characteristics of an SC-FDMA signal 20

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

15
Effect of roll-off factor, alpha on the PAPR20
16
Why does SC-FDMA have a low PAPR?

• OFDMA
• Parallel Transmission
• Multi carrier structure
• Increase in M gt
• 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

17
SC-FDMA in comparison with OFDMA and DS-CDMA/FDE

• DS-CDMA/FDE

18
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)

19
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

20
Cognitive Features to enhance RRM in LTE
21
Enhanced context acquisition mechanism
architecture for cognitive intra-cell RRM
22
Simulation Results27

• Success Probability slowly increases with time
  and
• mean response time decreases as more and more
• familiar contexts are encountered. Cognitive RRM
• with the context matching techniques understands
• and learns from previous interactions

23
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

24
LTE Advanced

• LTE doesnt 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 gtgt20 MHz)
• An LTE-Advanced capable network must appear as a
  LTE network for the LTE UEs

26
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
• CoMP

Carrier aggregation and
Spectrum aggregation
27
(Extra Slides)
28
LTE Physical Layer

• Enables exchange of data control info between
  eNB and UE and also transport of data to and from
  higher layers
• Functions performed include error detection, FEC,
  MIMO antenna processing, synchronization, etc.
• It consists of Physical Signals and Physical
  Channels
• Physical Signals are used for system
  synchronization, cell identification and channel
  estimation.
• Physical Channels for transporting control,
  scheduling and user payload from the higher
  layers
• OFDMA in the DL, SC-FDMA in the UL
• LTE supports FDD and TDD modes of operation

29
LTE Physical Signals in DL and UL
30
LTE Physical Channels in DL and UL
31
Modulation

• QPSK, 16 QAM and 64 QAM used for the payload
  channels (spectrally efficient)
• BPSK and QPSK used for the control channels
  (Reliability and coverage)
• Adaptive modulation and coding

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CDS algorithms -Localized FDMA
Rk average data rate of user k Ich,k chunk
set of user k Pk transmit power of user k

• Marginal utility is defined by
• -gt
• This is computed for each chunk n and each user
  k
• N best users for each chunk become candidates for
  that chunk
• Find the chunk n with highest marginal utility
  and for each of the N users obtained above, find
  the user k who gives the max improvement in
  utility and assign n to k
• Remove n from the set of available chunks and
  repeat for the remaining chunks

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Interleaved FDMA
Rk average data rate of user k Nch,k no. of
chunks for user k

• Marginal utility is defined by -gt
• For each user, the utility is found when the
  chunk is assigned to the user and the utility
  when there is no chunk allocation at all. N best
  users are the candidate for chunk allocation.
• Now it is required to find the number of chunks
  to give to each of these above users The Greedy
  alloc computes this figure

34

• Localized FDMA CDS much better than IFDMA CDS
  due to frequency selective scheduling

35
Channel Dependent Scheduling

• No CDS gt IFDMA is better
• With CDS gt LFDMA is better
• Algorithms for Localized FDMA
• FME First Maximum Expansion
• RME Recursive Maximum Expansion

36
Figures for explanation of FME and RME

• 
  

37
Packet Scheduling using buffer and channel status

• UE buffer status and
• channel status (CQI)
• must be considered
• UE sends CQI and BSR
• to the eNB CQI used in PHY and MAC
• (eNB Scheduler) layers for transmission and
• scheduling decisions

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CABA Scheduling Algorithm

• Channel adapted factor
• Denominator ensures fairness
• Buffer Aware factor
• of user i
• Priority Function
• involves BSR, CQI
• and RT/NRT

Buffi (Lbuff Ncurr)/Lbuff, for
i1,2,,M
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Impact of feedback delay in CDS

• CSI becomes obsolete
• Throughput degradation
• Fast UEs get affected more

40
Impact of delay and mobile speed
41
Hybrid Subcarrier Mapping

• LFDMA is best in maximizing throughput when CDS
  is used but is highly sensitive for large mobile
  speeds so low mobility is best for LFDMA
• For high mobility, Distributed mapping of IFDMA
  with static scheduling is preferred
• Using both subcarrier mappings at once is
  preferable but can conflict exclusive allocation
  requirement
• Hybrid subcarrier mapping uses direct sequence
  spread spectrum technique prior to SC-FDMA
  modulation

42
Single carrier code-frequency division multiple
access (SC-CFDMA)
43
Spatial Multiplexing in SC-FDMA(UL)

44
Simulation Conclusions 20

• Averaging and Quantization leads to performance
  loss
• Feedback delay affects high speed users
• PAPR of the MIMO case increases due to precoding
  compared to single antenna transmission

45
Efficient feedback of precoder matrix

• SVD of averaged channel matrix
• Channel correlation matrix R
• Jacobi matrix J can also be used to
• diagonalize R it can be used as the
  precoder matrix
• At instant n, J(n) is obtained
• At instant n1, instead of sending
• J(n1), J is sent
• Transmitter can compute the new
• J(n1) using J(n) and J
• Scheme works only for low speeds
• and less feed back delays
• To prevent error propagation
• and accumulation, combined differential and
  non-differential feed back is employed

46
Transmit Antenna Selection Mode in SC-FDMA Systems
47
Spatial Multiplexing in DL using SIC

• Data vector corresponding to each transmit
  antenna
• The complete data vector, on subcarrier l
• The received vector
• Frequency domain samples at the receiver, after
  DFT
• In a SIC MMSE receiver, a weight vector is
  applied to the received vector
• A new received data vector is got by removing the
  effect of the previously detected symbol from the
  current received vector
• Data symbol with max SNR can be detected first to
  help improve SNR of future iterations

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Relation of DS-CDMA and IFDMA
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Conclusion

• 3GPP Long Term Evolution has a large amount of
  potential to become the technology of the future
  whose success will definitely guarantee that 3GPP
  has a significant edge over all its competitors.
• With LTEAdvanced also adopting SC-FDMA as the
  uplink technology, SC-FDMA seems to be an
  important future technology and it is expected
  that the future would see a lot of research
  activity in this field.
• LTE and LTE Advanced together seem to be very
  promising in fulfilling all the requirements set
  forth by ITU for IMT Advanced

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References

• http//www.3gpp.com/article/lte
• http//www.3gpp.com/article/lte-advanced.
• http//en.wikipedia.org/wiki/LTE_Advanced
• UTRA-UTRAN Long Term Evolution (LTE) and 3GPP
  System Architecture Evolution (SAE) - Technical
  paper from http//www.3gpp.com/article/lte
• Overview of the 3GPP Long Term Evolution Physical
  Layer White paper by Jim Zyren, freescale
  semiconductor, Document Number 3GPPEVOLUTIONWP
  http//www.freescale.com/files/wireless_comm/doc/w
  hite_paper/3GPPEVOLUTIONWP.pdf
• 3GPP TR 25.913 V8.0.0 (2008-12), Requirements
  for Evolved UTRA (E-UTRA) and Evolved UTRAN
  (E-UTRAN) (Release 8)
• 3GPP TS 36.300 v8.7.0, E-UTRA and E-UTRAN
  Overall Description Stage 2
• 3GPP TS 36.401 V8.4.0 (2008-12), Evolved
  Universal Terrestrial Radio Access Network
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• 3GPP TS 36.410 V8.1.0 (2008-12), Evolved
  Universal Terrestrial Radio Access Network
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  (Release 8)
• 3GPP TS 36.420 V8.1.0 (2008-12), Evolved
  Universal Terrestrial Radio Access Network
  (E-UTRAN) X2 general aspects and principles
  (Release 8)
• 3GPP TS 36.201 V8.2.0 (2008-12), Evolved
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• 3GPP Long-Term Evolution (LTE) Qualcomm
  Incorporated, January 2008 http//www.qualcomm.co
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• Technical Overview of 3GPP LTE Hyung G. Myung
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  w
• LTE Overview NEC Corporation By K. Jay
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• Agilent 3GPP Long Term Evolution System
  Overview, Product Development, and Test
  Challenges http//cp.literature.agilent.com/litwe
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• Ekstrom, H. Furuskar, A. Karlsson, J. Meyer,
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• http//wiki.hsc.com/LTE
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• 3GPP LTE Introducing Single - Carrier FDMA By
  Moray Rumney, Agilent Technologies
  http//cp.literature.agilent.com/litweb/pdf/5989-7
  898EN.pdf

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• Thank You !