PAPR Reduction of OFDM Signals using Hybrid Clipping-Companding Scheme with Sigmoid Functions. Orthogonal Frequency Division-Multiplexing

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1 International Conference on pplied Electronics Pilsen, Czech E 20 PPR Reduction of OFDM Signals using Hbrid Clipping-Companding Scheme with Sigmoid Functions Victor Cuteanu, leandru Isar Orthogonal Frequenc Division-Multipleing popular technologies used in broadband wireless communication sstems like WiMX, DVB-T or DB. is a form of multi-carrier modulation, where spectra overlap but signals are orthogonal. 2/3/20 Eugen Victor Cuteanu, leandru Isar - Pilsen, Czech - E20 2

2 Block Diagram of Base-band OFDM Transmitter Data Pilot Insertion Guard Insertion MOD S/P IFFT P/S Cclic Prefi D/ LPF Nonlin. Comp. HP channel 2/3/20 Eugen Victor Cuteanu, leandru Isar - Pilsen, Czech - E20 3 High Power mplifier (HP) The HP nonlinearit ( Saleh Memor-less Model ) The amplitude and phase are influenced. Saturation threshold should not be eceeded. α u + β u a [] 2 u Φ ϕ [] u 2 a α u 2 + β u ϕ HP 2/3/20 Eugen Victor Cuteanu, leandru Isar - Pilsen, Czech - E20 4 2

3 OFDM & PPR Important drawback of OFDM communication sstem is PPR. Peak to verage Power Ratio (PPR) is given b: ma PPR E N () t N n 0 2 ( () t ) 2 () t [ ] X n e j2πfnt where the sub-carriers are chosen to be orthogonal: n Δf f n Δf /T 2/3/20 Eugen Victor Cuteanu, leandru Isar - Pilsen, Czech - E20 5 PPR Reduction Techniques For the PPR Reduction Problem, different solutions proposed: Nonlinear methods: Clipping Compression / Companding ( -law, eponential, ) Linear methods: Selective Mapping / Partial Transmit Sequence Multiple Signal Representations ( Constellation derivatives ) Tone Reservation: One Tone One Peak (OTOP) One-b-One iteration. The PPR of a given OFDM signal is evaluated with the complementar cumulative distribution function (CCDF): ( Y ) Pr( PPR > Y ) Pr( PPR Y ) CCDF < 2/3/20 Eugen Victor Cuteanu, leandru Isar - Pilsen, Czech - E20 6 3

4 Proposed Hbrid Technique for PPR Reduction The proposed PPR reduction technique: Represents a combination of two standard methods: Clipping (with filtering); Companding (@T) with Epanding (@R). Performs nonlinear and quasi-nonlinear signal processing. Data Zero Padding MOD S/P IFFT P/S Clipping Frequenc Domain Filtering Companding (Compression) HP channel 2/3/20 Eugen Victor Cuteanu, leandru Isar - Pilsen, Czech - E20 7 Clipping with Filtering B clipping, time domain signal amplitude is limited to a given threshold. The clipping ratio is defined as the clipping level divided b the rootmean-square power σ of the unclipped base-band signal. The input vector is padded b inserting N(p-) zeros in its middle, resulting time domain signal trigonometric interpolation. Filtering can also cause peak re-growth, but less than before clipping. a 0,,a N/2- N(p-) zeroes a N/2,,a N- Inverse DFT Non-linear processing (Clipping) 20log CR 0 σ Forward DFT Signal Zero Padding Inverse DFT Frequenc domain filtering 2/3/20 Eugen Victor Cuteanu, leandru Isar - Pilsen, Czech - E20 8 4

5 Zero Padding in the Frequenc Domain OFDM zero-padded signal after epanding (in frequenc domain). Signal s noise level is affected (slightl increased) 2/3/20 Eugen Victor Cuteanu, leandru Isar - Pilsen, Czech - E20 9 Effects in Time Domain Signal processing b clipping and filtering (before & after). Signal peaks level decreased > smaller PPR 2/3/20 Eugen Victor Cuteanu, leandru Isar - Pilsen, Czech - E20 0 5

6 6 2/3/20 Eugen Victor Cuteanu, leandru Isar - Pilsen, Czech - E20 Companding/Epanding Signal is amplified/attenuated with a factor which depends b signal level. Different conversion laws are considered: ln ep ) ( ) ( ln ln sign sign μ μ μ μ b sign e sign b log ) ( + + a c d b d c b a μ-law eponential proposed + c d d c simplified 2/3/20 Eugen Victor Cuteanu, leandru Isar - Pilsen, Czech - E20 2 Comparison in Time Domain Companding functions changes signal s mean value > new PPR.

7 Implementation Variet of companding (and corresponding epanding) functions has been proposed. Their nonlinearit ma be static (constant) or dnamicall (variable) from an OFDM frame to another Variable parameters impl additional information to be sent to receiver. The computational effort depends b the mathematical compleit of the respective formula: Logarithms, Eponentials, Polnomial ratios. Due to necessar operation of signal amplitude epanding, noise level increases. 2/3/20 Eugen Victor Cuteanu, leandru Isar - Pilsen, Czech - E20 3 Companding Eamples Signal is amplified with a factor which depends b signal level. 2/3/20 Eugen Victor Cuteanu, leandru Isar - Pilsen, Czech - E20 4 7

8 Epanding eamples Signal is attenuated with a factor which depends b signal level. 2/3/20 Eugen Victor Cuteanu, leandru Isar - Pilsen, Czech - E20 5 Simulation Scenario Data T M-QM M-PSK OFDM block Clipping & Filtering Companding (Compression) BER(SNR) Evaluation parameters PPR Evaluator Data R M-QM M-PSK Epanding (Decompression) WGN CCDF Evaluator 2/3/20 Eugen Victor Cuteanu, leandru Isar - Pilsen, Czech - E20 6 8

9 Numerical Results. 6 QM The CCDF of PPR for a 6-QM based OFDM, 28 data carriers. Different compression laws applied (after clipping). 2/3/20 Eugen Victor Cuteanu, leandru Isar - Pilsen, Czech - E20 7 Distortions The BER(SNR) for a 6-QM based OFDM, 28 data carriers, WGN channel. Different compression laws applied (after clipping). 2/3/20 Eugen Victor Cuteanu, leandru Isar - Pilsen, Czech - E20 8 9

10 Numerical Results. 6 PSK The CCDF of PPR for a 6-PSK based OFDM, 28 data carriers. Different compression laws applied (after clipping). 2/3/20 Eugen Victor Cuteanu, leandru Isar - Pilsen, Czech - E20 9 Distortions The BER(SNR) for a 6-PSK based OFDM, 28 data carriers, WGN channel. Different compression laws applied (after clipping). 2/3/20 Eugen Victor Cuteanu, leandru Isar - Pilsen, Czech - E

11 Conclusions Characteristics of the new PPR Reduction technique: Is a combination of two methods: Clipping (with filtering); Companding (Compression). Overall provides advantages of less nonlinearit (companding) and reduced computation compleit (from Clipping). Performance of the new PPR Reduction technique: Better PPR reduction; Slight BER(SNR) degradation at low SNR; Improved BER(SNR) at higher SNR. Variations of the new PPR Reduction technique: Different companding functions; Provide different PPR/BER(SNR) performances. 2/3/20 Eugen Victor Cuteanu, leandru Isar - Pilsen, Czech - E20 2 Bibliograph J. rmstrong, New OFDM Peak-to-verage Power Reduction Scheme, IEEE VTC'200 Ma 200, Rhodes, Greece. Xiao Huang, Jianhua Lu, Junli Zheng, Jun Gu, "Piecewise-scales transform for the reduction of PPR of OFDM signals", IEEE Global Telecommunications Conference, GLOBECOM '02 C. Tellambura, Coding Technique For Reducing Peak-To-verage Power Ration in OFDM, IEEE, 998. Seung Hee Han and Jae Hong Lee, "Reduction of PPR of an OFDM Signal b Partial Transmit Sequence Technique with Reduced Compleit", IEEE Global Telecommunications Conference, GLOBECOM '03. X. Wang, T. T. Yjhung, and C. S. Ng, Reduction of peak-to-average power ratio of OFDM sstem using a companding technique, IEEE Trans. Broadcast., vol. 45, no. 9, pp , Sept M. Malkin, T. Magesacher, J. M. Cioffi, "Dnamic llocation of Reserved Tones for PR Reduction," in OFDM Workshop, ug 2008, Hamburg, German. Brian Scott Krongold and Douglas L. Jones, "PR Reduction in OFDM via ctive Constellation Etension", IEEE Transactions On Broadcasting, Vol. 49, No. 3, September 2003 X. Wang, T. T. Tjhung, C. S. Ng and.. Kassim, On the SER nalsis of -Law Companded OFDM Sstem, in Proc. IEEE GLOBECOM 00, vol.2, pp , Jiao, Y.Z., Liu, X.J., Wang, X.., " Novel Tone Reservation Scheme with Fast Convergence for PPR Reduction in OFDM Sstems", Consumer Communications and Networking Conference, Marc Deumal, Carles Vilella, Joan Lluis Pijoan, Pau Bergadà, Partiall Clipping (PC) Method For The Peak-To- verage Power Ratio (PPR) Reduction In OFDM, Personal, Indoor and Mobile Radio Communications, PIMRC Jaewoon Kim and Yoan Shin, "n Effective Clipped Companding Scheme for PPR Reduction of OFDM Signals", IEEE International Conference on Communications, ICC '08. Taleb Moazzeni, Henr Selvaraj, Yingtao Jiang, " novel Multi-Eponential Function-based Companding Technique for Uniform Signal Compression over Channels with Limited Dnamic Range", Intl. Journal of Electronics and Telecommunications, Vol. 56, No.2, pp , 200 Tao Jiang, Yang Yang, and Yong-Hua Song, "Companding Technique for PPR Reduction in OFDM Sstems Based on n Eponential Function", IEEE Global Telecommunications Conference, GLOBECOM '05. S. H. Muller and J. B. Huber, Novel Peak Power Reduction scheme for OFDM, Proc. of IEEE PIMPC 97, Helsinki, Finland, pp , Sep /3/20 Eugen Victor Cuteanu, leandru Isar - Pilsen, Czech - E20 22

12 Thank You Ver Much for Your ttention! 2/3/20 Eugen Victor Cuteanu, leandru Isar - Pilsen, Czech - E