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Technology for reduction of the high Peak-to-Average-Power-Ratio
Tianqing Su, 21.01.2015
21.01.2015 | Paula Becker | Sensitivity of OFDM performance to Doppler shift | 2/24
Gliederung
1. Introduction
2. OFDM
3. The Peak-to-Average-Power-Radio Problem
4. PAPR Reduction Techniques
5. Comparison of PAPR Reduction Performances
6. Conclusion
1. Introduction
2. OFDM
3. The Peak-to-Average-Power-Radio Problem
4. PAPR Reduction Techniques
5. Comparison of PAPR Reduction Performances
6. Conclusion
21.01.2015 | Paula Becker | Sensitivity of OFDM performance to Doppler shift | 3/24
The Evolution of Mobile Technologies
source: http:// androidauthority.com
21.01.2015 | Paula Becker | Sensitivity of OFDM performance to Doppler shift | 4/24
Gliederung
1. Introduction
2. OFDM
3. The Peak-to-Average-Power-Radio Problem
4. PAPR Reduction Techniques
5. Comparison of PAPR Reduction Performances
6. Conclusion
21.01.2015 | Paula Becker | Sensitivity of OFDM performance to Doppler shift | 5/24
Orthogonal Frequency Division Multiplexing(OFDM)
OFDM is a Multi-Carrier Modulation technique, which has been known since 1966
Basic idea: a single high rate data-stream is divided into multiple low rate data streams and is modulated using sub-carriers which are orthogonal to each other
Multicarrier Transmission Technique with orthogonal subcarriers, source: http://lightwaveonline.com
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OFDM Transceiver Structure
OFDM Transceiver Block Diagram, source: http://cp.literature.agilent.com
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Advantages and Drawbacks of OFDM Advantages:
Robustness against frequency selective fading and time dispersion Transmission rates close to capacity can be achieved Low computational complexity implementation (FFT)
Drawbacks: Sensitivity to frequency offset Sensitivity to nonlinear amplification
High power amplifiers source: http://alibaba.comNonlinearity of HPA source: MilastMagazine, February, 2013
21.01.2015 | Paula Becker | Sensitivity of OFDM performance to Doppler shift | 8/24
Gliederung
1. Introduction
2. OFDM
3. The Peak-to-Average-Power-Radio Problem
4. PAPR Reduction Techniques
5. Comparison of PAPR Reduction Performances
6. Conclusion
21.01.2015 | Paula Becker | Sensitivity of OFDM performance to Doppler shift | 9/24
The Peak-to-Average-Power-Radio Problem
Peak-to-Average Power Ratio (PAPR) is defined as the maximum power to the average
power of the OFDM transmission
The OFDM symbol s(t) is ,
∆f =1/T: the subcarrier spacing
Xk : complex baseband data modulating the k-th subcarrier for s(t)
The peak instantaneous power of the OFDM symbol sequence is:
The average power of the OFDM symbol sequence is:
Therefore, the PAPR of the OFDM symbol s(t) can be expressed as:
21.01.2015 | Paula Becker | Sensitivity of OFDM performance to Doppler shift | 10/24
Effect of PAPR
The high PAPR : introduces inter-modulation distortion and out-of-band radiation because of the nonlinearity
of the HPA increases BER and adjacent channel interference requires a large range of dynamic linearity from the analog circuits which usually results in
expensive devices and high power consumption
It is desirable to reduce the PAPR of an OFDM signal.
21.01.2015 | Paula Becker | Sensitivity of OFDM performance to Doppler shift | 11/24
Gliederung
1. Introduction
2. OFDM
3. The Peak-to-Average-Power-Radio Problem
4. PAPR Reduction Techniques
5. Comparison of PAPR Reduction Performances
6. Conclusion
21.01.2015 | Paula Becker | Sensitivity of OFDM performance to Doppler shift | 12/24
PAPR Reduction Techniques
PAPR Reduction techniques are dependent on PAPR Spectral efficiency, reduction capacity, complexity of computation, etc., which are divided into three categories: Signal Distortion Techniques
Signal Clipping Peak Windowing Companding …
Signal Scrambling Techniques Selected Mapping Method (SLM) Partial Transmit Sequence (PTS) Interleaving
… Coding Techniques
Block Coding Schemes Sub Block Coding Schemes Block Coding with Error Correction
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Clipping
X source: http:// rfmw.em.keysight.com
The simplest way to reduce the PAPR
The peak amplitude becomes limited to some desired level
the clipped signal will then go through a low-pass filter to reduce the high frequency signals which correspond to the sharp corners in the clipped signal
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Performance of Clipping and Filtering
source: nternational Journal of Electrical & Computer Sciences IJECS-IJENS Vol:10 No:05
By distorting the OFDM signal amplitude, a kind of self-interference is introduced
Nonlinear distortion increases out-of-band radiation
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Peak Windowing
To remedy the out-of-band problem of clipping Large signal peak is multiplied with a certain window, such as Gaussian shaped window to
minimize the out-of-band interference The window should be narrowband and not be too long in the time domain
source: http://rfmw.em.keysight.com
21.01.2015 | Paula Becker | Sensitivity of OFDM performance to Doppler shift | 16/24
Selected Mapping Method (SLM)
In SLM, several candidate data blocks are generated from the original data block and the one with lowest PAPR is transmitted
No distortion is introduced ⌈log_2 bits of side information per OFDM symbol is required𝑀 ⌉ Computational complexity is increased to ensure a better performance
source: Study of Peak-to-Average Power Ratio Reduction Techniques for OFDM Signals by Chhavi Choudhary S.S. Rattan
21.01.2015 | Paula Becker | Sensitivity of OFDM performance to Doppler shift | 17/24
Partial Transmit Sequence (PTS)
The original data block is partitioned into V disjoint subblocks in PTS system. The subcarriers in each subblock are rotated by the same phase factor such the PAPR of the combination is minimized
source: Study of Peak-to-Average Power Ratio Reduction Techniques for OFDM Signals by Chhavi Choudhary S.S. Rattan
21.01.2015 | Paula Becker | Sensitivity of OFDM performance to Doppler shift | 18/24
Performance of PTS
PAPR performance improves as the number sub-blocks increases
source: Study of Peak-to-Average Power Ratio Reduction Techniques for OFDM Signals by Chhavi Choudhary S.S. Rattan
21.01.2015 | Paula Becker | Sensitivity of OFDM performance to Doppler shift | 19/24
Comparison of SLM and PTS
SLM produce multiple independent signals, however PTS signals are interdependent. The complexity in PTS is reduced compared to SLM method
PTS method also provides a better PAPR reduction performance
source: Comparative study between Selection Mapping Technique (SLM) and Partial Transmission sequence (PTS) for PAPR reduction in OFDM signals by Md. Kislu Noman
21.01.2015 | Paula Becker | Sensitivity of OFDM performance to Doppler shift | 20/24
Coding Techniques
Basic idea: Coding schemes utilize the complementary bits that are added to the original information bits to reduce the probability of the peak signals occurrence
Block codes with a generator matrix G and parity check matrix H provide also error correction capability
Advantages: the inherent error control capability and simplicity of implementation Dawbacks: reduction of the transmission rate, the number of subcarriers is limited
source: PAPR Reduction in OFDM systems using Quasi Cyclic LDPC Codes by S.P Vimal
21.01.2015 | Paula Becker | Sensitivity of OFDM performance to Doppler shift | 21/24
Gliederung
1. Introduction
2. OFDM
3. The Peak-to-Average-Power-Radio Problem
4. PAPR Reduction Techniques
5. Comparison of PAPR Reduction Performances
6. Conclusion
21.01.2015 | Paula Becker | Sensitivity of OFDM performance to Doppler shift | 22/24
Comparison of PAPR Reduction Performances
Type Powerincrease
ImplementationComplexity
Bandwidthexpansion
Data rate loss
Clipping & Filtering
No Low No No
PTS No High Yes Yes
SLM No High Yes Yes
Coding No Low Yes Yes
Basic requirement of practical PAPR reduction techniques include the compatibility with the existing modulation schemes high spectral efficiency low complexity
No specific PAPR reduction technique is the best solution for all multi-carrier transmission
21.01.2015 | Paula Becker | Sensitivity of OFDM performance to Doppler shift | 23/24
Gliederung
1. Introduction
2. OFDM
3. The Peak-to-Average-Power-Radio Problem
4. PAPR Reduction Techniques
5. Comparison of PAPR Reduction Performances
6. Conclusion
21.01.2015 | Paula Becker | Sensitivity of OFDM performance to Doppler shift | 24/24
Summery
OFDM is a digital multi-carrier modulation method where a large number of closely spaced
orthogonal sub-carriers to support high bit rate transmission
The high PAPR is the main obstacle which causes non-linearity at the transmitter end
PAPR reduction techniques are roughly divided into three categories:
Signal Scrambling Techniques
Signal Distortion Techniques
Coding Techniques
PAPR reduction capacity, Power increase, data rate, computational complexity, BER
increase at the receiver, etc. should be considered before a specific PAPR reduction
technique is chosen
source: http:// itpro.co.uk
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Thank you for your attention.
Tianqing [email protected]