SC-FDMA and LTE Uplink Physical Layer Design SC-FDMA and LTE Uplink Physical Layer Design Seminar LTE: Der Mobilfunk der Zukunft Seminar LTE: Der Mobilfunk der Zukunft Burcu Hanta University Erlangen-Nürnberg Chair of Mobile Communications November 18, 2009
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SC-FDMA and LTE Uplink Physical Layer DesignSC-FDMA and LTE Uplink Physical Layer Design
Seminar LTE: Der Mobilfunk der ZukunftSeminar LTE: Der Mobilfunk der Zukunft
Burcu Hanta
University Erlangen-Nürnberg
Chair of Mobile Communications
November 18, 2009
OutlineOutline
1 Introduction
Structure of SC-FDMA vs. OFDMA
Why SC-FDMA?
2 Uplink Time and Frequency Structure
3 Uplink Physical Channel
4 SC-FDMA Transmission
Localized and Distributed Mode
Comparison Criteria for Different Carrier Modes
Transmitter Structure
Receiver Structure
5 Conclusion
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design1 /331 /33
IntroductionIntroduction
IntroductionIntroduction
Remark on Orthogonal Frequency Division Multiple Access
(OFDMA):
A multiple access scheme which provides multiple
channels for different users
Used in many applications including the downlink of LTE.
Robust to time delays especially in multiple fading
channels
If orthogonality of subcarriers cannot be ensured, high
performance degradation is observed.
Important problem: Peak-to-average power ratio (PAPR)
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design2 /332 /33
IntroductionIntroduction
Peak-to-Average Power Ratio Problem in OFDMAPeak-to-Average Power Ratio Problem in OFDMA
PAPR =Ppeak
Pavg(1)
The OFDM transmitter performs a linear transform over a
large number of i.i.d. QAM-modulated complex symbols.
The time domain OFDM symbol can be approximated as a
Gaussian waveform from the central limit theorem [1].
⇒High PAPR in the OFDM signal.
High PAPR causes:
Either non-linear operation or high power consumption in
power amplifiers due to clipping.
A brand new system is introduced for the uplink: Single
Carrier FDMA.
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design3 /333 /33
IntroductionIntroduction Structure of SC-FDMA vs. OFDMAStructure of SC-FDMA vs. OFDMA
Structure of SC-FDMA vs. OFDMAStructure of SC-FDMA vs. OFDMA
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Figure: Transmitter and receiver structure of OFDMA [2].
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design4 /334 /33
IntroductionIntroduction Structure of SC-FDMA vs. OFDMAStructure of SC-FDMA vs. OFDMA
Structure of SC-FDMA vs. OFDMAStructure of SC-FDMA vs. OFDMA
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Figure: Transmitter and receiver structure of SC-FDMA [2].
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design4 /334 /33
IntroductionIntroduction Why SC-FDMA?Why SC-FDMA?
Why SC-FDMA?Why SC-FDMA?
The subcarriers are transmitted sequentially instead of in
parallel as in OFDM.
⇒ The transmitted waveform is no longer a Gaussian
waveform which is probable to have high peak variations.
This helps to reduce the PAPR.
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design5 /335 /33
Uplink Time and Frequency StructureUplink Time and Frequency Structure
SC-FDMA Frame StructureSC-FDMA Frame Structure
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Figure: Type 1 Frame structure [3].
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design6 /336 /33
Uplink Time and Frequency StructureUplink Time and Frequency Structure
Resource GridResource Grid
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Figure: Uplink resource grid for one slot [3].
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design7 /337 /33
Uplink Physical ChannelUplink Physical Channel
Physical Channel IPhysical Channel I
ScramblingModulation
mapper
Transform
precoder
Resource
element mapper
SC-FDMA
signal gen.
Figure: Uplink physical channel [4].
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design8 /338 /33
Uplink Physical ChannelUplink Physical Channel
Physical Channel IIPhysical Channel II
Scrambler: scrambles the coded bits in order to
randomize the interference and thus ensure that the
processing gain provided by the channel code can be fully
used.
Modulation mapper: performs the 4QAM or 16QAM
modulation on data blocks.
Transform precoder: supports multi-layer transmission in
MIMO systems.
Resource element mapper: assignment of the data blocks
to the suitable physical resource blocks.
SC-FDMA signal generation: will be detailed investigated
in the subsequent part.
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design9 /339 /33
SC-FDMA TransmissionSC-FDMA Transmission
SC-FDMA TransmissionSC-FDMA Transmission
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Figure: SC-FDMA transmission chain [2].
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design10 /3310 /33
SC-FDMA TransmissionSC-FDMA Transmission
Subcarrier Allocation Methods ISubcarrier Allocation Methods I
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Mapping
N-point
IFFTAdd cyclic
prefix
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Mapping
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x(M - 1,n)
Serial toParallelConverter
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Bit toConstellationMapping
-
Transmission
circuitry
Figure: SC-FDMA transmitter for localized and distributed subcarrier
mappings [1].
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design11 /3311 /33
SC-FDMA TransmissionSC-FDMA Transmission
Subcarrier Allocation Methods IISubcarrier Allocation Methods II
Terminal 1
Terminal 2
Terminal 3SubcarrierSubcarrier
Distributed Mode Localized Mode
Figure: Subcarrier allocation methods for multiple users (3 users, 12
subcarriers, and 4 subcarriers per user) [5].
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design12 /3312 /33
SC-FDMA TransmissionSC-FDMA Transmission Localized and Distributed ModeLocalized and Distributed Mode
Localized and Distributed ModeLocalized and Distributed Mode
Localized Mode
Each terminal uses a set of adjacent subcarriers to
transmit its symbols.
Along with channel dependent scheduling (CDS), it offers
high multi-user diversity.
Distributed Mode
The subcarriers used by a single terminal are distributed
over the whole frequency band.
Since the subcarriers are spread over the different parts
of the frequency band, the subcarrier data transmitted
over different channels are subject to different fading.
This provides high frequency diversity.
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design13 /3313 /33
SC-FDMA TransmissionSC-FDMA Transmission Comparison Criteria for Different Carrier ModesComparison Criteria for Different Carrier Modes
Comparison Criteria for Different Carrier ModesComparison Criteria for Different Carrier Modes
Comparison criteria:
System throughput
PAPR
Problem: trade-off between these criteria.
Solution: find the optimum mode for the system by
testing.
The localized carrier transmission mode is used in LTE uplink
since it offers much better performance with the arrangement
of pulse-shaping filter.
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design14 /3314 /33
SC-FDMA TransmissionSC-FDMA Transmission Comparison Criteria for Different Carrier ModesComparison Criteria for Different Carrier Modes
Effect of CDS on System PerformanceEffect of CDS on System Performance
Key question:
“How to allocate time and frequency resources among
users while achieving multi-user diversity and frequency
diversity?” [6].
Aim:
Maximize the user utility in each transmission time
interval.
All in all, CDS improves the throughput of the system for
localized mode much more than the distributed mode where
the throughput measure is the Shannon’s channel capacity
formula, C = BW log (1 + SNR).
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design15 /3315 /33
SC-FDMA TransmissionSC-FDMA Transmission Comparison Criteria for Different Carrier ModesComparison Criteria for Different Carrier Modes
Effect of Pulse Shaping IEffect of Pulse Shaping I
Aim:
Mitigate the out-of-band signal energy.
Problem:
Pulse shaping increases the PAPR, especially too much for
localized FDMA.
However, the PAPR of SC-FDMA signals is still lower than
OFDMA signals and in terms of system throughput, localized
FDMA with CDS is much better than distributed FDMA.
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design16 /3316 /33
SC-FDMA TransmissionSC-FDMA Transmission Comparison Criteria for Different Carrier ModesComparison Criteria for Different Carrier Modes
Effect of Pulse Shaping IIEffect of Pulse Shaping II