New signal processing approaches to peak-to-average power ratio reduction in multicarrier systems

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Title: New signal processing approaches to peak-to-average power ratio reduction in multicarrier systems
Author: Bae, Ki-taek
Abstract: Multi -carrier systems based on orthogonal frequency division multiplexing (OFDM ) are efficient technologies for the implementation of broadband wireless communication systems . OFDM is widely used and has been adopted for current mobile broadband wireless communication systems such as IEEE 802 .a /g wireless LANs , WiMAX , 3GPP LTE , and DVB -T /H digital video broadcasting systems . Despite their many advantages , however , OFDM -based systems suffer from potentially high peak -to -average power ratio (PAR ) . Since communication systems typically include nonlinear devices such as RF power amplifiers (PA ) and digital -to -analog converters (DAC ) , high PAR results in increased symbol error rates and spectral radiation . To mitigate these nonlinear effects and to avoid nonlinear saturation effects of the PA , the operating point of a signal with high peak power must be backed off into the linear region of the PA . This so -called output backoff (OBO ) results in a reduced power conversion efficiency which limits the battery life for mobile applications , reduces the coverage range , and increases both the cost of the PA and power consumption in the cellular base station . With the increasing demand for high energy efficiency , low power consumption , and greenhouse gas emission reduction , PAR reduction is a key technique in the design of practical OFDM systems . Motivated by the PAR reduction problem associated with multi -carrier systems , such as OFDM , this research explores the state of the art of PAR reduction techniques and develops new signal processing techniques that can achieve a minimum PAR for given system parameters and that are compatible with the appropriate standards . The following are the three principal contributions of this dissertation research . First , we present and derive the semi -analytical results for the output of asymptotic iterative clipping and filtering . This work provides expressions and analytical techniques for estimating the attenuation factor , error vector magnitude , and bit -error -rate (BER ) , using a noise enhancement factor that is obtained by simulation . With these semi -analytical results , we obtain a relationship between the BER and the target clipping level for asymptotic iterative clipping and filtering . These results serve as a performance benchmark for designing PAR reduction techniques using iterative clipping and filtering in OFDM systems . Second , we analyze the impact of the selected mapping (SLM ) technique on BER performance of OFDM systems in an additive white Gaussian noise channel in the presence of nonlinearity . We first derive a closed -form expression for the envelope power distribution in an OFDM system with SLM . Then , using this derived envelope power distribution , we investigate the BER performance and the total degradation (TD ) of OFDM systems with SLM under the existence of nonlinearity . As a result , we obtain the TD -minimizing peak backoff (PBO ) and clipping ratio as functions of the number of candidate signals in SLM . Third , we propose an adaptive clipping control algorithm and pilotaided algorithm to address a fundamental issue associated with two lowcomplexity PAR reduction techniques , namely , tone reservation (TR ) and active constellation extension (ACE ) . Specifically , we discovered that the existing low -complexity algorithms have a low clipping ratio problem in that they can not achieve the minimum PAR when the target clipping level is set below the initially unknown optimum value . Using our proposed algorithms , we overcome this problem and demonstrate that additional PAR reduction is obtained for any low value of the initial target clipping ratio .
URI: http : / /hdl .handle .net /2152 /ETD -UT -2010 -08 -1649
Date: 2010-12-06


New signal processing approaches to peak-to-average power ratio reduction in multicarrier systems. Doctoral dissertation, University of Texas at Austin. Available electronically from http : / /hdl .handle .net /2152 /ETD -UT -2010 -08 -1649 .

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