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

Investigate performance of available PAPR
reduction techniques

Identify criterion for PAPR reduction technique
selection
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.

•
•
Instrument Specs

NI 5670 – RF Vector Signal Generator
Table 1 [1]
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
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
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
PAPR Reduction Techniques

Interleaving

Amplitude Clipping & Filtering (RCF)

Selection Level Mapping (SLM)

Partial Transmit Sequence (PTS)

Active Constellation Exchange (ACE)

Tone Injection
Experiment I
PAPR Measurement for unusually
high PAPR Signals
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

Max. PAPR = 10*log10(N)
(N – Number of subcarriers)
 Oversample the Rx signal & calculate PAPR
 Compare observed PAPR with theoretical results
for the different schemes
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
Experiment I
Results
Effect of PA saturation


In-band distortion
1dB compression point 13dBm @ 2.7G, 16dBm @ 2G
@2GHz
@2.7GHz
No PAPR scheme
RCF
Interleaving
SLM
PTS
ACE
Experiment II
PAPR Measurement of a typical
OFDM signal
Complementary CDF (CCDF)
comparison
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
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




Experiment II
Results
RCF
Effect of Tx Power Spectrum
Before RCF
After RCF
Effect on Tx Constellation
Interleaving
SLM
PTS
ACE
Effect on Tx Constellation
Tone Injection
Effect on Tx Constellation
Experiment III
A typical OFDM system with PAPR
reduction
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
Experiment III
Results
5MHz Bandwidth
10MHz Bandwidth
12MHz Bandwidth
BER vs SNR - Uncoded 4-QAM
PAPR Techniques
- A Comparative Study
Tradeoff
Technique
Distortionless
Power Increase
Data rate loss
RCF
No
No
No
Interleaving
Yes
No
Yes
SLM
Yes
No
Yes
PTS
Yes
No
Yes
Tone Injection
Yes
Yes
No
ACE
Yes
Yes
No
Table 2 [7]
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
Table 2 [6]
Tx: IDFTs, projection onto “shaded area”
Rx: None
Table 3 [7]
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/4mi469471.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
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.