### A Novel Algorithm for peak to Average Ratio Reduction in Wireless OFDM Systems

"... Abstract: In OFDM systems, the major obstacle is that the multiplex signal exhibits a very high peak-to-average power ratio (PAR) In this paper propose a new novel method to reduce the PAR.A simple and attractive technique is Active cancellation extension used. However, we observe it cannot achieve ..."

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Abstract: In OFDM systems, the major obstacle is that the multiplex signal exhibits a very high peak-to-average power ratio (PAR) In this paper propose a new novel method to reduce the PAR.A simple and attractive technique is Active cancellation extension used. However, we observe it cannot achieve the minimum PAR when the target clipping level is set below an initially unknown optimum value. A low clipping ratio is the problem in OFDM system to overcome this AEC algorithm with adaptive clipping control. However the simulation results shows our algorithm can reach the minimum Peak to Average for several clipping ratios, and also in AWGN channel we calculate the tradeoff between PAR and the loss in

### A low-complexity PAR reduction method for WFMT System r

"... Abstract:- This paper discusses a simple method of Peak to Average Power Ratio (PAR) reduction developed for system with WFMT modulation. The novel Wavelet based Filtered Multi-Tone (WFMT) modulation was proposed as an alternative of the Discrete Multi-tone line code for xDSL system and represents f ..."

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Abstract:- This paper discusses a simple method of Peak to Average Power Ratio (PAR) reduction developed for system with WFMT modulation. The novel Wavelet based Filtered Multi-Tone (WFMT) modulation was proposed as an alternative of the Discrete Multi-tone line code for xDSL system and represents future extending of OFDM / DMT technologies. Because of multicarrier nature of WFMT modulation, it is well suited to carry high-speed data over a wide frequency band. As it is well known, the major drawback of the multicarrier system is the large PAR of the transmit signal, which renders a straightforward implementation costly and inefficient. In this paper, we describe a new PAR reduction technique based on an overlapping structure of a WFMT signal. We examine the WFMT PAR characteristics by SIMULINK Model of a Cable TV Broadcast System, described in [1]. The results illustrate a significant PAR reduction of the WFMT transmit signal when the proposed method is used.

### for OFDM

"... Abstract — New peak-to-average power-ratio reduction (PAPR) algorithms for orthogonal frequency-division multiplexing systems are investigated in a probabilistic framework. Specifically, two de-randomization algorithms for PAPR reduction are developed by applying the so-called conditional probabilit ..."

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Abstract — New peak-to-average power-ratio reduction (PAPR) algorithms for orthogonal frequency-division multiplexing systems are investigated in a probabilistic framework. Specifically, two de-randomization algorithms for PAPR reduction are developed by applying the so-called conditional probability method. Our simulations demonstrate that the proposed algorithms outperform several existing algorithms and the computational complexity of the proposed algorithms is found to be significantly less than that of existing algorithms. I.

### 1 A New Peak-to-Average Power-Ratio Reduction Algorithm for OFDM Systems via Constellation Extension

"... Abstract — Peak-to-average power-ratio (PAPR) reduction for OFDM systems is investigated in a probabilistic framework. A new constellation extension technique is developed whereby the data for each subcarrier are represented either by points in the original constellation or by extended points. An op ..."

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Abstract — Peak-to-average power-ratio (PAPR) reduction for OFDM systems is investigated in a probabilistic framework. A new constellation extension technique is developed whereby the data for each subcarrier are represented either by points in the original constellation or by extended points. An optimal representation of the OFDM signal is achieved by using a de-randomization algorithm where the conditional probability involved is handled by using the Chernoff bound and the evaluation of the many hyperbolic cosine functions involved is replaced by a tight upper bound for these functions. The proposed algorithm can be used by itself or be combined with a selective rotation technique described in the paper and with other known algorithms such as the coordinate descent optimization and selective mapping algorithms to achieve further performance enhancements at the cost of a slight increase in the computational complexity. When compared with other existing PAPR-reduction algorithms, the enhanced algorithm offers improved PAPRreduction performance and improved computational complexity although the transmit power is increased somewhat. Index Terms — OFDM, peak-to-average power-ratio reduction, constellation extension, de-randomization.

### DSA Networks

, 2007

"... With the advent of new high data rate wireless applications, as well as growth of existing wireless services, demand for additional bandwidth is rapidly increasing. Existing “command-and-control ” spectrum allocations defined by government regulatory agencies, such as federal communications commissi ..."

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With the advent of new high data rate wireless applications, as well as growth of existing wireless services, demand for additional bandwidth is rapidly increasing. Existing “command-and-control ” spectrum allocations defined by government regulatory agencies, such as federal communications commission (FCC), prohibit unlicensed access to licensed spectrum, constraining them instead to several heavily populated, interference-prone frequency bands. However, it has been shown that the spectrum is not utilized efficiently across time and frequency. Therefore, FCC is currently working on the concept of unlicensed users “borrowing ” spectrum from incumbent license holders temporarily to improve the spectrum utilization. This concept is called dynamic spectrum access (DSA). Cognitive radios offer versatile, powerful, and portable wireless transceivers enabling DSA. This dissertation investigates physical layer techniques to enhance a cognitive radio performance. Multi-carrier techniques, such as orthogonal frequency division multiplexing (OFDM), support huge data rates that are robust to channel impairments. However, with a growing

### Clipping Versus Symbol Switching for PAPR Reduction in Coded OFDM

"... In multicarrier systems, the transmitted time-domain signal exhibits large amplitude peaks. This peak-toaverage power ratio (PAPR) problem complicates the practical use of multicarrier systems: the amplifier used to transmit the signal saturates because of the large peaks and causes non-linear dist ..."

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In multicarrier systems, the transmitted time-domain signal exhibits large amplitude peaks. This peak-toaverage power ratio (PAPR) problem complicates the practical use of multicarrier systems: the amplifier used to transmit the signal saturates because of the large peaks and causes non-linear distortion. As this non-linear distortion frustrates severely the detection of the multicarrier signal, the average power of the multicarrier signal must be reduced such that the system operates in the linear part of the amplifier. However, this power reduction comes at the cost of a reduced capacity of the multicarrier system. Hence, several techniques were investigated to reduce the PAPR. In this paper, we compare two PAPR reduction techniques for coded OFDM using an iterative decoder, i.e. clipping and symbol switching. Clipping outperforms the symbol switching technique as for given PAPR reduction, a lower BER degradation is obtained. However, the clipping technique causes out-of-band radiation whereas the spectrum is not changed when using the symbol switching technique.

### PEAK-TO-AVERAGE POWER RATIO REDUCTION IN AN FDM BROADCAST SYSTEM

"... Digital predistortion is a technique used to reduce the signal dynamic range in a multichannel system in order to improve power amplifier (PA) efficiency. These techniques have been developed for orthogonal frequency-division multiplexing (OFDM) systems, but are not directly applicable to general fr ..."

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Digital predistortion is a technique used to reduce the signal dynamic range in a multichannel system in order to improve power amplifier (PA) efficiency. These techniques have been developed for orthogonal frequency-division multiplexing (OFDM) systems, but are not directly applicable to general frequency-division multiplexing (FDM) systems such as those used in broadcast. A modification to the tone injection approach allows constellation translations to be directly applied at the digital intermediate frequency (IF) domain and provides redundancy in lowering peak-toaverage ratio (PAR). Simulation of a 24-channel 256-QAM FDM cable television transmission system shows a 3.3 dB PAR reduction at 10-6 clipping probability. Index Terms — multichannel systems, power amplifiers, peak-to-average ratio, digital predistortion, tone injection. 1.

### IMPROVING THE PERFORMANCE OF BICM-OFDM SYSTEMS IN PRESENCE OF HPA NONLINEARITIES BY EFFICIENT BIT AND POWER LOADING

"... The usage of Orthogonal Frequency Division Multiplexing (OFDM) allows to adapt the available time-frequency grid to the current channel conditions. To exploit the offered degrees of freedom many bit and power loading algorithms were introduced. However, they do not include channel coding in the opti ..."

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The usage of Orthogonal Frequency Division Multiplexing (OFDM) allows to adapt the available time-frequency grid to the current channel conditions. To exploit the offered degrees of freedom many bit and power loading algorithms were introduced. However, they do not include channel coding in the optimization. Similar to conventional multicarrier schemes in such link adaptation scenarios the peak-to-average powerratio (PAPR) problem occurs. The combination of active constellation extension (ACE) with additional tone reservation (TR) is a promising approach to reduce this ratio without sacrificing the bit error rate (BER). Hence, in this contribution we propose an extended bisection method for coded bit and power loading in combination with ACE/TR techniques to jointly improve the BER and PAPR performance in high-rate OFDM systems. Results indicate that in presence of a memoryless nonlinear high power amplifier (HPA) device the BER can be lowered compared to existing loading algorithms. 1.

### A ZCMT Pre-coding based PTS Technique for PAPR Reduction in OFDM System

"... Orthogonal frequency division multiplexing (OFDM) has been considered as a promising technique to achieve high data rate transmission in mobile environment. However, they are very sensitive to nonlinear effects due to high peak to average power ratio (PAPR). This paper proposes an efficient techniqu ..."

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Orthogonal frequency division multiplexing (OFDM) has been considered as a promising technique to achieve high data rate transmission in mobile environment. However, they are very sensitive to nonlinear effects due to high peak to average power ratio (PAPR). This paper proposes an efficient technique for reducing the PAPR of OFDM signals. The reduction in PAPR of the OFDM signal is obtained through Zadoff-Chu matrix transform (ZCMT) precoding based partial transmit sequence (PTS).The obtained results show that this precoding scheme is an attractive solution of the PAPR problem of OFDM signals.

### Peak to Average Power Reduction using Radix-2 Decimation in Frequency Fast Fourier Transform in OFDM System

"... Orthogonal Frequency Division Multiplexing (OFDM) is used for wideband data communications over ..."

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Orthogonal Frequency Division Multiplexing (OFDM) is used for wideband data communications over