1. The University of Texas at Austin
EE 381V Wireless Communications Lab Graduate Course Project PAPR Reduction Techniques in OFDM Systems
Nachiappan Valliappan & Rajaganesh Ganesh
The University of Texas at Austin

2. Objectives Understand the effects of high PAPR in multicarrier systems
Investigate performance of available PAPR reduction techniques
Identify criterion for PAPR reduction technique selection

3. Instrument Specs NI 5660 – RF Signal Analyzer
Input power +30 to -130 dBm (provides up to 50 dB of input attenuation)
Digitizer 64MS/s
NI 5670 – RF Vector Signal Generator
Output average power -145dBm to +13dBm
Maximum allowable peak envelope power +17dBm
1dB Gain Compression point dependent on temperature, frequency etc.

4. Instrument Specs
NI 5670 – RF Vector Signal Generator
Table 1 [1]

5. System Design Symbol rates supported
1Msps, 2Msps,5Msps,10Msps,12.5Msps
Channel coding
Rate 2/3 convolutional code
Modulation schemes supported
BPSK, 4-QAM, 16-QAM
Pulse Shaping
Raised cosine pulse shape with roll-off 0.5

6. System Design Passband Bandwidth 1MHz, 2MHz, 5MHz, 10MHz, 12.5MHz
Number of subcarriers N (= FFT Size) 64
Length of Cyclic Prefix Lc 16
PAPR Oversample Factor 4

7. System Design Symbol Timing Extraction
Max Energy, Early-Late Gate Method
Frame Timing & Frequency Offset Estimation Schmidl-Cox Algorithm
Channel Estimation & Equalization
IEEE a training sequence

8. PAPR Reduction Techniques
Interleaving
Amplitude Clipping & Filtering (RCF)
Selection Level Mapping (SLM)
Partial Transmit Sequence (PTS)
Active Constellation Exchange (ACE)
Tone Injection

9. Experiment I PAPR Measurement for unusually high PAPR Signals

10. Loop back Tx-Rx by an RF cable
Procedure
Loop back Tx-Rx by an RF cable
Send a sequence of all ones (1’s) so that the max. theoretical PAPR is reached
(N – Number of subcarriers)
Oversample the Rx signal & calculate PAPR
Compare observed PAPR with theoretical results for the different schemes
Max. PAPR = 10*log10(N)

11. System Setup for Expt. I Data: All 1’s sequence Symbol Rate: 1 Msps
Modulation scheme: 4-QAM
N=64, Lc=16
No channel coding
Tx average power level = - 2.2dBm
PEP is just below 17dBm!
Rx reference level = 20dBm

12. Experiment I Results

13. Effect of PA saturation
In-band distortion
1dB compression point 2.7G, 2G
@2GHz @2.7GHz

14. No PAPR scheme

15. RCF

16. Interleaving

17. SLM

18. PTS

19. ACE

20. Experiment II PAPR Measurement of a typical OFDM signal Complementary CDF (CCDF) comparison

21. Procedure
Loop back Tx-Rx. by an RF cable
Send a sequence of random bits
Oversample the Rx signal & calculate PAPR for the different schemes
Plot the CCDF at Tx & Rx
Observe reduction in PAPR
Observe changes to Tx constellation

22. System Setup for Expt. II
Data: Random bits
Symbol Rate: 1 Msps
Modulation scheme: 4-QAM
N=64, Lc=16
No channel coding
Tx average power level = -40dBm
Rx reference level = -20dBm

23. Experiment II Results

24. RCF

25. Effect of Tx Power Spectrum
Before RCF After RCF

26. Effect on Tx Constellation

27. Interleaving

28. SLM

29. PTS

30. ACE

31. Effect on Tx Constellation

32. Tone Injection

33. Effect on Tx Constellation

34. Experiment III A typical OFDM system with PAPR reduction

35. Procedure Transmit random bits over the wireless channel
Perform synchronization, offset, channel estimation & equalization
Find the BER for uncoded transmissions
Observe the impact of in-band distortion (esp. in RCF!) on BER

36. Experiment III Results

37. 5MHz Bandwidth

38. 10MHz Bandwidth

39. 12MHz Bandwidth

40. BER vs SNR - Uncoded 4-QAM

41. PAPR Techniques - A Comparative Study

42. Tradeoff Table 2 [7] Technique Distortionless Power Increase
Data rate loss
RCF No
Interleaving
Yes
SLM
PTS
Tone Injection
ACE
Table 2 [7]

43. Table 2 [6] Technique Processing at Tx & Rx RCF
Tx: Amplitude clipping, filtering
Rx: None
Interleaving
Tx: K IDFTs, (K – 1) interleavings
Rx: Side information extraction, inverse interleaving
SLM
Tx: U IDFTs
Rx: Side information extraction, inverse SLM
PTS
Tx: M IDFTs, WM–1 complex vector sums
Rx: Side information extraction, inverse PTS
Tone Injection
Tx: IDFTs, search for maximum point in time, tones to be modified, value of p and q
Rx: Modulo-D operation
ACE
Tx: IDFTs, projection onto “shaded area”
Table 2 [6]
Table 3 [7]

44. References
[1] National Instruments, NI RF Signal Generator: NI PXI-5670/5671 Specifications, Retrieved December 3, 2010 from [2] National Instruments, 2.7 GHz RF Vector Signal Analyzer, Retrieved December 2, 2005 from pdf [3] National Instruments, NI RF Signal Generator: Getting Started Guide, Retrieved December 1, 2005 from [4] National Instruments, NI 5670 RF Vector Signal Generator User Manual, Retrieved December 1, 2005 from _um.pdf [5] National Instruments, 2.7 GHz RF Vector Signal Analyzer, Retrieved December 2, 2005 from

45. References
[6] National Instruments, NI RF Signal Analyzer: Getting Started Guide, Retrieved December 2, 2005 from [7] Jae Hong Lee and Seung Hee Han. An overview of peak-to-average power ratio reduction techniques for multicarrier transmission Wireless Communications. IEEE Wireless Communications Magazine, Vol. 12:pp 56-65, April 2005.