nachiappan valliappan & rajaganesh ganesh the university of texas at austin
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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 - PowerPoint PPT PresentationTRANSCRIPT
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EE 381V Wireless Communications Lab
Graduate Course Project
PAPR Reduction Techniques in OFDM Systems
Nachiappan Valliappan & Rajaganesh Ganesh
The University of Texas at Austin
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Objectives
Understand the effects of high PAPR in multicarrier systems
Investigate performance of available PAPR reduction techniques
Identify criterion for PAPR reduction technique selection
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Instrument SpecsNI 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.
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Instrument SpecsNI 5670 – RF Vector Signal
Generator
Table 1 [1]
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System DesignSymbol rates supported
1Msps, 2Msps,5Msps,10Msps,12.5Msps
Channel codingRate 2/3 convolutional code
Modulation schemes supportedBPSK, 4-QAM, 16-QAM
Pulse ShapingRaised cosine pulse shape with roll-off 0.5
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System DesignPassband Bandwidth
1MHz, 2MHz, 5MHz, 10MHz, 12.5MHz
Number of subcarriers N (= FFT Size)64
Length of Cyclic Prefix Lc
16
PAPR Oversample Factor4
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System DesignSymbol Timing Extraction
Max Energy, Early-Late Gate Method
Frame Timing & Frequency Offset Estimation Schmidl-Cox Algorithm
Channel Estimation & Equalization IEEE 802.11a training sequence
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PAPR Reduction TechniquesInterleaving
Amplitude Clipping & Filtering (RCF)
Selection Level Mapping (SLM)
Partial Transmit Sequence (PTS)
Active Constellation Exchange (ACE)
Tone Injection
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Experiment I
PAPR Measurement for unusually high PAPR Signals
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Procedure
Loop back Tx-Rx by an RF cableSend a sequence of all ones (1’s) so that
the max. theoretical PAPR is reached
(N – Number of subcarriers)Oversample the Rx signal & calculate
PAPRCompare observed PAPR with theoretical
results for the different schemes
Max. PAPR = 10*log10(N)
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System Setup for Expt. IData: All 1’s sequenceSymbol Rate: 1 MspsModulation scheme: 4-QAM N=64, Lc=16No channel coding
Tx average power level = - 2.2dBmPEP is just below 17dBm!
Rx reference level = 20dBm
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Experiment I
Results
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Effect of PA saturation In-band distortion1dB compression point 13dBm @ 2.7G, 16dBm @ 2G
@2GHz @2.7GHz
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No PAPR scheme
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RCF
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Interleaving
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SLM
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PTS
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ACE
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Experiment II
PAPR Measurement of a typical OFDM signal
Complementary CDF (CCDF) comparison
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Procedure
Loop back Tx-Rx. by an RF cableSend a sequence of random bitsOversample the Rx signal & calculate
PAPR for the different schemesPlot the CCDF at Tx & RxObserve reduction in PAPRObserve changes to Tx constellation
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System Setup for Expt. IIData: Random bitsSymbol Rate: 1 MspsModulation scheme: 4-QAM N=64, Lc=16No channel coding
Tx average power level = -40dBm
Rx reference level = -20dBm
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Experiment II
Results
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RCF
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Effect of Tx Power Spectrum
Before RCF After RCF
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Effect on Tx Constellation
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Interleaving
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SLM
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PTS
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ACE
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Effect on Tx Constellation
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Tone Injection
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Effect on Tx Constellation
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Experiment III
A typical OFDM system with PAPR reduction
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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
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Experiment III Results
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5MHz Bandwidth
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10MHz Bandwidth
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12MHz Bandwidth
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BER vs SNR - Uncoded 4-QAM
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PAPR Techniques
- A Comparative Study
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Table 2 [7]
Technique Distortionless
Power Increase
Data rate loss
RCF No No NoInterleaving Yes No YesSLM Yes No YesPTS Yes No YesTone Injection Yes Yes NoACE Yes Yes No
Tradeoff
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Table 2 [6]
Technique Processing at Tx & RxRCF Tx: Amplitude clipping, filtering
Rx: None
Interleaving Tx: K IDFTs, (K – 1) interleavingsRx: Side information extraction, inverse interleaving
SLM Tx: U IDFTsRx: Side information extraction, inverse SLM
PTS Tx: M IDFTs, WM–1 complex vector sumsRx: Side information extraction, inverse PTS
Tone Injection Tx: IDFTs, search for maximum point in time, tones to be modified, value of p and qRx: Modulo-D operation
ACE Tx: IDFTs, projection onto “shaded area”Rx: None
Table 3 [7]
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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
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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 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.