1. PAPR Reduction Method for OFDM Systems without Side Information
Pornpawit Boonsrimuang, Pisit Boonsrimuang
Kazuo Mori, Tawil Paungma and Hideo Kobayashi

2. Contents Research Topic Objective of Research Conventional Methods
Proposal of PAPR Reduction Method
Performance Evaluation
Conclusions

3. Proposal of PAPR Reduction Method
Research Topic
Proposal of PAPR Reduction Method
for OFDM Signal without Side Information
OFDM: Orthogonal Frequency Division Multiplexing

4. Target of Research Field Next Generation of Wireless LAN
Outdoor
100Mbit
Indoor
Gigabit
Next Generation of Wireless LAN

5. WiMAX(Worldwide Interoperability for Microwave Access)
Advantages of OFDM
Enable the higher data rate transmission
Robustness to multi-path fading
Efficient usage of frequency bandwidth
The OFDM has already been adopted as the standard transmission techniques in
ADSL (Asynchronous Digital Subscriber Line)
Terrestrial Digital TV
WiMAX(Worldwide Interoperability for Microwave Access)
Wireless LAN(Wireless Local Area Network)
Candidate transmission technique for the next generation of wireless LAN systems

6. Structure of OFDM System
System Overview
(a) OFDM spectrum
s(t)
Serial to Parallel (S/P)
...
...
Parallel to Serial (P/S)
Mod
IFFT
Add GI
AMP
Transmitter
vs.
(b) conventional FDM spectrum
Fading Channel
H(w)
Channel
Noise n(t)
Receiver
r(t)
Parallel to Serial (P/S)
...
...
Serial to Parallel (S/P)
Equalization
Remove GI
Demod
FFT
Channel estimation

7. Disadvantage of OFDM Larger peak to averaged power ratio (PAPR)
Larger PAPR will cause the degradation of BER performance and expansion of spectrum
re-growth in the non-linear channel
PAPR: Peak to Averaged Power Ratio

8. Comparison of OFDM Signal with Single Carrier Signal2 2
1.5
1.5
Amplitude of OFDM Time Domain Signal 1
Amplitude of OFDM Time Domain Signal 1
0.5
0.5
100
200
300
400
500
100
200
300
400
500
Sample Number
Sample Number
(a) OFDM signals in time domain
(b) Single carrier signal in time domain
Amplitude of OFDM time domain signal is fluctuated much larger than that for single carrier signal

9. Operation of OFDM Signal at Lower IBO in Non-Linear Channel
-10 -8 -6 -4 -2 2 4
Input Power (dB)
Output Power (dB)
r=2
r=4
r=30
r=6
Linear
where F[ ] represent the AM/AM conversion characteristics of non-linear amplifier

10. Operation of OFDM Signal at Higher IBO in Non-Linear Channel
Inter-modulation Noise
-10 -8 -6 -4 -2 2 4
Input Power (dB)
Output Power (dB)
r=2
r=4
r=30
r=6
Linear
where F[ ] represent the AM/AM conversion characteristics of non-linear amplifier

11. Inter-Modulation Noise Occurred at Non-Linear Amplifier
Transmitter structure of conventional OFDM
...
Parallel to Serial (P/S)
Mod
Serial to Parallel (S/P)
s(t)
Add GI
IFFT
AMP
AMP
Non-Linear
(a) Input of power amplifier
(b) Output of power amplifier

12. Disadvantage of OFDM Technique
OFDM with N sub carriers has PAPR ratio of 10log N [dB]
N sub Carriers
Larger PAPR
Required Low Input Back-Off
Inefficient Usage of Power Amplifier

13. Several methods have been proposed to reduce the PAPR of OFDM signal
Improvement of PAPR
Several methods have been proposed to reduce the PAPR of OFDM signal
Data coding technique
The main disadvantage of this method is to degrade
transmission efficiency
Clipping technique
BER performance
Phase alignment technique
The main disadvantage of this method is required to transmit
side information which leads the degradation of transmission
efficiency

14. Conventional PAPR Reduction Methods Based on Phase Alignment Technique
The Selected Mapping (SLM) and Partial Transmission Sequence (PTS) methods which control the phase of data sub-carrier
SLM and PTS are required to inform the phase information to the receiver as the side information (SI) for the correct demodulation
Although the conventional method could improve the PAPR performance relatively,
the transmission efficiency and system complexity would be degraded because of the necessity of transmission of side information

15. Objective of Research
Improve PAPR and BER performances without
degradation of transmission efficiency
Proposal of PAPR Reduction Method for OFDM Signal
Based on Phase Alignment Technique which Requires No Side Information

16. Proposal of PAPR Reduction Method
for OFDM Signal without Side Information
Use the common weighting factor over one frame including the preamble symbols
The time-frequency domain swapping algorithm is employed in the determination of common weighting factor
The common weighting factor can be estimated together with the channel frequency response by using preamble symbols
The common weighting factor can be removed from the received data symbols by using the frequency domain equalization
Proposed method could improve the PAPR performance
without Side Information

17. Structure of Proposed PAPR Reduction Method
Weighting Factors for Reducing PAPR
1st Preamble Symbol
2nd Preamble Symbols
Common weighting factor over one frame
1st Data Symbol
One Frame
Lth Data Symbol 1 2
N-1
Number of sub-carriers
Common weighting factor will be assigned for each sub-carrier over one frame

18. Amplitude (Time Domain) Amplitude (Time Domain)
Determination of Weighting Factor by Using Time-Frequency Domains Swapping Algorithm
Predetermined threshold level (S)
Amplitude (Time Domain)
FFT
Amplitude (Time Domain)
Time domain
Frequency domain
Basic concept of Time-Frequency Swapping Algorithm

19. Flowchart of Time-Frequency Domains Swapping Algorithm3
Calculation of
Time-domain Signal 2 S
mi (t) 1
Threshold level(S)
N-1
N-FFT
Calculation of Error Signal 2
FFT
ei (t) 1
N-1
N-FFT
Determined Phase (weighting factor)

20. Basic Concept of Proposed Algorithm
N-1 1 2 3 4 5 6
N-2
N-1
Frequency Domain
IFFT 10 20 30 40 50 60 -1 1 2
Sampling time
Amplitude S
Threshold Level
Time Domain

21. Basic Concept of Proposed Algorithm
N-1 1 2 3 4 5 6
N-2
N-1
Frequency Domain
FFT 10 20 30 40 50 60 -1 1 2
Sampling time
Amplitude
Time Domain

22. Basic Concept of Proposed Algorithm
N-1 1 2 3 4 5 6
N-2
N-1
Frequency Domain
FFT 10 20 30 40 50 60 -1 1 2
Sampling time
Amplitude
Time Domain

23. Basic Concept of Proposed Algorithm
N-1 1 2 3 4 5 6
N-2
N-1
Frequency Domain
FFT 10 20 30 40 50 60 -1 1 2
Sampling time
Amplitude
Time Domain

24. Basic Concept of Proposed Algorithm
N-1 1 2 3 4 5 6
N-2
N-1
Frequency Domain
IFFT 10 20 30 40 50 60 -1 1 2
Sampling time
Amplitude
Time Domain

25. Basic Concept of Proposed Algorithm
N-1 1 2 3 4 5 6
N-2
N-1
Frequency Domain
FFT 10 20 30 40 50 60 -1 1 2
Sampling time
Amplitude S
Time Domain

26. Amplitude of OFDM signal in the time domain1 3 2
120 80 60 40 20
100
Time Sample Number
(a) Before T-F Swapping Algorithm
Amplitude 1
0.5
1.5
120 80 60 40 20
100
Time Sample Number
(b) After T-F Swapping Algorithm
Amplitude

27. Determination of Weighting Factor
Error signal in frequency domain
OFDM signal in frequency domain
Determined weighting factor
Average for the weighting factors obtained for all symbols
Common weighting factor over one frame

28. (a) Original OFDM Signal (b) Phase Rotation due to weighting factor
Scatter Diagram of Preamble and Data Symbols -1 1
(a) 1 -1
(b)
(a) Original OFDM Signal (b) Phase Rotation due to weighting factor

29. Structure of Transmitter for Proposal Method/ P
MOD Xn
Data
&
Preamble N - 1 I F T + GI
SSPA D A U C yk X i
Number of
predetermined iteration
or PAPR
<
Target No
Yes
Calculate error
signal
FFT
Determination of
common weighting factor

30. Structure of Receiver for Proposed Method/ C
& A
Estimation
Preamble X
DEMOD
DATA - GI S P
FFT 1 ˆ n H
Received Data
Frequency Domain Equlization
Estimated Channel
Response
Demodulated Data
: Weighting Factor at n-th Sub-Carrier

31. in Performance Evaluation Multi-path fading model
List of Parameters
in Performance Evaluation
Modulation
64QAM
Demodulation
Coherent
Allocated bandwidth
5MHz
Number of FFT points
256
Number of sub-carriers 64
Symbol duration
12.8 s
Guard interval
1.28 s
Non-linear amplifier
SSPA
Non-linear parameter of SSPA
r =2
Number of data symbols in one frame 12
Number of preamble symbols in one frame 2
Multi-path fading model
Power delay profile
Exponential
Number of delay paths 16
Decay constant
-1 dB

32. PAPR Performance
Modulation Method =64QAM
Conventional
Proposed

33. PAPR Performance vs. Number of Iterations
Modulation Method =64QAM
Conventional
Proposed

34. BER Performance
Modulation Method =16QAM
Conventional
Ideal
Proposed

35. BER Performance
Modulation Method =64QAM
Conventional
Ideal
Proposed

36. Conclusions Proposed the PAPR reduction method for OFDM
signal without side information
Use the common weighting factor over one frame including the preamble symbols
The time-frequency domain swapping algorithm is employed in the determination of common weighting factor
The common weighting factor can be removed from the received data symbols by using the frequency domain equalization
The common weighting factor can be estimated together with the channel frequency response by using preamble symbols

37. Conclusions
The proposed technique can achieve the better PAPR performance and better BER performance than the conventional OFDM in the channel of non-linear amplifier and multi-path fading