EE 381 V Wireless Communications Lab Graduate Course

EE 381 V 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 d. Bm (provides up to 50 d. B of input attenuation) � Digitizer 64 MS/s �NI • • • 5670 – RF Vector Signal Generator Output average power -145 d. Bm to +13 d. Bm Maximum allowable peak envelope power +17 d. Bm 1 d. B Gain Compression point dependent on temperature, frequency etc.

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

System Design �Symbol rates supported 1 Msps, 2 Msps, 5 Msps, 10 Msps, 12. 5 Msps �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 1 MHz, 2 MHz, 5 MHz, 10 MHz, 12. 5 MHz �Number of subcarriers N (= FFT Size) 64 �Length of Cyclic Prefix Lc 16 �PAPR 4 Oversample Factor

System Design �Symbol Timing Extraction Max Energy, Early-Late Gate Method �Frame Timing & Frequency Offset Estimation Schmidl-Cox Algorithm �Channel Estimation & Equalization IEEE 802. 11 a training sequence

PAPR Reduction Techniques �Interleaving �Amplitude �Selection Clipping & Filtering (RCF) 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*log 10(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. 2 d. Bm PEP is just below 17 d. Bm! �Rx reference level = 20 d. Bm

Experiment I Results

Effect of PA saturation � In-band distortion � 1 d. B compression point 13 d. Bm @ 2. 7 G, 16 d. Bm @ 2 G @2 GHz @2. 7 GHz

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 = -40 d. Bm �Rx reference level = -20 d. Bm

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

5 MHz Bandwidth

10 MHz Bandwidth

12 MHz 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 No ACE 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/371355 c. pdf [2] National Instruments, 2. 7 GHz RF Vector Signal Analyzer, Retrieved December 2, 2005 from http: //www. ni. com/pdf/products/us/4 mi 469 -471. pdf [3] National Instruments, NI RF Signal Generator: Getting Started Guide, Retrieved December 1, 2005 from http: //www. ni. com/pdf/manuals/371356 b. 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/4 mi 469 -471. pdf

References [6] National Instruments, NI RF Signal Analyzer: Getting Started Guide, Retrieved December 2, 2005 from http: //www. ni. com/pdf/manuals/371237 a. 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 5665, April 2005.