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Nachiappan Valliappan & Rajaganesh Ganesh 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. Objectives. Understand the effects of high PAPR in multicarrier systems

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Nachiappan Valliappan & Rajaganesh Ganesh The University of Texas at Austin

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  1. EE 381VWireless Communications LabGraduate Course ProjectPAPR Reduction Techniques in OFDM Systems NachiappanValliappan & RajaganeshGanesh 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 802.11a 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 IPAPR Measurement for unusually high PAPR Signals

  10. 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 13dBm @ 2.7G, 16dBm @ 2G • @2GHz @2.7GHz

  14. No PAPR scheme

  15. RCF

  16. Interleaving

  17. SLM

  18. PTS

  19. ACE

  20. Experiment IIPAPR Measurement of a typical OFDM signalComplementary 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 TxConstellation

  27. Interleaving

  28. SLM

  29. PTS

  30. ACE

  31. Effect on Tx Constellation

  32. Tone Injection

  33. Effect on Tx Constellation

  34. Experiment IIIA 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. BERvsSNR - Uncoded 4-QAM

  41. PAPR Techniques- A Comparative Study

  42. Tradeoff Table 2 [7]

  43. 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 http://www.ni.com/pdf/manuals/371355c.pdf [2] National Instruments, 2.7 GHz RF Vector Signal Analyzer, Retrieved December 2, 2005 from http://www.ni.com/pdf/products/us/4mi469-471.pdf [3] National Instruments, NI RF Signal Generator: Getting Started Guide, Retrieved December 1, 2005 from http://www.ni.com/pdf/manuals/371356b.pdf [4] National Instruments, NI 5670 RF Vector Signal Generator User Manual, Retrieved December 1, 2005 from http://www.ni.com/pdf/manuals/rfsg _um.pdf [5] National Instruments, 2.7 GHz RF Vector Signal Analyzer, Retrieved December 2, 2005 from http://www.ni.com/pdf/products/us/4mi469-471.pdf

  45. References [6] National Instruments, NI RF Signal Analyzer: Getting Started Guide, Retrieved December 2, 2005 from http://www.ni.com/pdf/manuals/371237a.pdf [7] Jae Hong Lee and SeungHee 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.

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