Kashif Sultan, Hazrat Ali, Zhongshan Zhang
Presentation by
Dr. Hazrat Ali
COMSATS Institute of Information Technology
Joint SLM and Modified
Clipping Technique
for PAPR Reduction
14 Jan, 2016 IBCAST 2016 1
Orthogonal Frequency Division Multiplexing
Peak-to-Average Power Ratio
Effect on Power Amplifier
PAPR Reduction Techniques
Selective Mapping
Conventional Clipping
Proposed Scheme
Modified Clipping
Joint SLM and Modified Clipping
Contents
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OFDM forms the basis for 4G (fourth generation wireless communication)
It is revolutionary technology in wireless communication
Long Term Evoultion (LTE) โ the 4G cellular standard
LTE is based on two key technologies OFDM
WiMax
OFDM is a key broadband wireless technology which supports data rates in excess of 100 Mbps
WLAN standard 802.11a/g/n are also based on OFDM.
Orthogonal Frequency Division
Multiplexing (OFDM)
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OFDM
Block Diagram of an OFDM system
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The peaks in an OFDM signal cause challenges as they create non-uniform envelope
Due to high peaks in a signal, the power amplifier goes to its non-linear region resulting in non-linear distortion and spectral spreading
๐๐ด๐๐ ๐ฅ ๐ = max0โค๐โค๐โ1
๐ฅ ๐ 2
๐ธ ๐ฅ ๐ 2
Peak-to-Average Power Ratio (PAPR)
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Ideally, one would prefer a high number of sub-carriers for an OFDM system
However, PAPR increases if the number of sub-carriers is increased
PAPR in OFDM System
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Effect of PAPR on Power Amplifier
High PAPR in OFDM signal results in amplifier saturation.
Loss of orthogonality
Leads to Inter Carrier Interference
Distortion
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PAPR Reduction Techniques
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PAPR Reduction Techniques
Signal Distortion Techniques
Multiple Signaling and Probabilistic Techniques
Coding Technique
Hybrid Techniques
Y. Rahmatallah and S. Mohan, โPeak-To-Average Power Ratio Reduction in OFDM Systems : A
Survey And Taxonomy,โ IEEE Comun. Surv. Tutorials, vol. 15, no. 4, pp. 1567โ1592, 2013.14 Jan, 2016 IBCAST 2016 9
PAPR Reduction Techniques
Signal Distortion Techniques
Clipping and Filtering
Peak Windowing
CompandingTechniques
Peak Cancellation
Multiple Signaling and Probabilistic Techniques
Selective Mapping
Partial Transmit Sequence
Tone Injection
Active Constellation Extension
Coding Technique
Linear Block Coding
Golay Sequence
Turbo Coding
Hybrid Techniques
Joint PTS-QC Scheme
Joint Clipping and CompandingJoint Clipping and ACE
Y. Rahmatallah and S. Mohan, โPeak-To-Average Power Ratio Reduction in OFDM Systems : A
Survey And Taxonomy,โ IEEE Comun. Surv. Tutorials, vol. 15, no. 4, pp. 1567โ1592, 2013.14 Jan, 2016 IBCAST 2016 10
PAPR Reduction Techniques
Signal Distortion Techniques
Clipping and Filtering
Peak Windowing
CompandingTechniques
Peak Cancellation
Multiple Signaling and Probabilistic Techniques
Selective Mapping
Partial Transmit Sequence
Tone Injection
Active Constellation Extension
Coding Technique
Linear Block Coding
Golay Sequence
Turbo Coding
Hybrid Techniques
Joint PTS-QC Scheme
Joint Clipping and CompandingJoint Clipping and ACE
Y. Rahmatallah and S. Mohan, โPeak-To-Average Power Ratio Reduction in OFDM Systems : A
Survey And Taxonomy,โ IEEE Comun. Surv. Tutorials, vol. 15, no. 4, pp. 1567โ1592, 2013.14 Jan, 2016 IBCAST 2016 11
Selective Mapping
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Selective Mapping
Multiple copies of OFDM symbol
Transmit the one with minimum PAPR
Multiplying original data block with different phase factors โ prior to IFFT operation
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Conventional Clipping
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Conventional Clipping
The expression for conventional clipping can be written as,
๐ฅ ๐ก = ๐ฅ ๐ก ๐ฅ ๐ก < ๐ถ๐ฟ
๐ถ๐ฟ๐๐โ ๐ก ๐ฅ ๐ก > ๐ถ๐ฟ
Where ๐ฅ ๐ก is transmitted signal and โCLโ is the clipping level
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Conventional Clipping
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PAPR for Conventional Clipping
โข PAPR performance for conventional clipping approach
โข Simplest to implement
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Joint SLM and modified
Clipping
(Proposed Approach)
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Joint SLM and modified Clipping
Firstly, the conventional SLM technique is applied.
SLM improves the PAPR and control BER
The application of modified clipping further improves the PAPR
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Input DataSLM
techniqueModified Clipping
Transmit Data
Modified Clipping
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Modified Clipping
Mathematical representation for proposed clipping scheme
๐ฅ ๐ก =
๐ถ๐ฟ๐ป๐๐โ (๐ก) ๐ฅ ๐ก > ๐ถ๐ฟ๐ป ๐ฅ ๐ก ๐ถ๐ฟ๐ฟ < ๐ฅ ๐ก < ๐ถ๐ฟ๐ป
๐ถ๐ฟ๐ฟ๐๐โ ๐ก ๐ฅ ๐ก < ๐ถ๐ฟ๐ฟ
Where โฒ ๐ฅ ๐ก โฒ is input signal, โCLHโ is higher threshold level and โCLLโ is lower threshold level
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Joint SLM and modified Clipping
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PAPR for Modified Clipping
โข PAPR performance improves for modified clipping (with 2 levels of threshold)
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PAPR for Joint SLM and Modified Clipping
โข Joint SLM and Modified Clipping scheme further improves the PAPR performance
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Conclusion
PAPR is a key challenge in OFDM Systems
A simple modified clipping approach has been presented which brings improvement in PAPR performance
Combining it with Selective Mapping further improves the performance
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Thank you
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