One of the challenging issues for Orthogonal Frequency Division Multiplexing (OFDM) system is its high Peak-to-Average Power Ratio (PAPR). In this paper, we review and analysis different OFDM PAPR reduction techniques, based on computational complexity, bandwidth expansion, spectral spillage and performance. We also discuss some methods of PAPR reduction for multiuser OFDM broadband communication systems.

https://engold.ui.ac.ir/~sabahi/Advanced%20digital%20communication/An%20Overview%20Peak-to-Average%20Power%20Ratio%20Reduction%20Reduction%20Techniques%20for%20OFDM%20Signals.pdf

An Overview: Peak-to-Average Power Ratio Reduction Techniques for OFDM Signals

Orthogonal-frequency-division-multiplexing (OFDM) techniques allow the transmission of high data rates over broadband radio channels subject to multipath fading without the need for powerful channel equalization. However, they are very sensitive to nonlinear effects due to the high peak-to-average power ratio (PAPR) owned by their transmitted signals. This paper proposes an efficient technique for reducing the PAPR of OFDM signals. The proposed technique is data-independent and, thus, does not require new processing and optimization for each transmitted OFDM block. The reduction in PAPR of the OFDM signal is obtained through a proper selection of a precoding scheme that distributes the power of each modulated symbol over the OFDM block. The obtained results show that this precoding scheme is an attractive solution to the PAPR problem of OFDM signals. It is shown, through computer simulations, that the PAPR of precoded OFDM signals approaches that of single-carrier signals. The good improvement in PAPR given by the present technique permits the reduction of the complexity and cost of the transmitter significantly. The precoding schemes also take advantage of the frequency variations of the communication channel and can provide considerable performance gain in fading-multipath channels

Reducing the Peak-to-Average Power Ratio of OFDM Signals Through Precoding

Orthogonal frequency division multiplexing (OFDM) is an efficient multi-carrier modulation technique for wireless communication. However, one of the main drawbacks encountered in implementing it is its resultant high peak-to-average power ratio (PAPR). Many techniques have been proposed in the literature to substantially decrease the peaks in the OFDM signal. The problem with these, however, is that their effects on other parameters are not always positive. These effects include a decrease in the bit error rate (BER), an increase in complexity, or a reduction in the bit rate. The objective of this paper is to describe the PAPR problem in a bid to reduce the peaks in the OFDM signal. The paper proposes a classification, performance evaluation and optimization of PAPR reduction techniques for commercial, public safety, and tactical applications. In the taxonomy proposed herein, we also include a new category, namely, hybrid techniques. Furthermore, we compare the principal characteristics through a complementary cumulative distribution function and BER evaluation, and conclude on the importance of hybrid techniques, when the goal is to both improve the BER and reduce the PAPR.

Hybrid Peak-to-Average Power Ratio Reduction Techniques: Review and Performance Comparison

Methods and systems are provided that enable an OFDM transmitter to be used for transmitting conventional OFDM or a form of transformed OFDM. A technique is provided for transforming a coded and modulated sequence of samples prior to an IFFT that enables the transformed sequence of samples to be transmitted using conventional OFDM or transformed OFDM. The selection of a transform function for transforming the coded and modulated sequence of samples may be based on optimizing the transform function for particular operating conditions between the transmitter and receiver. In some embodiments of the invention OFDM and time transformed OFDM are multiplexed in time and/or frequency in a transmission frame. In some embodiments of the invention a pilot pattern is provided in which the pilot are sent using OFDM and data is sent using OFDM and/or transformed OFDM.

Method and system for combining ofdm and transformed ofdm

Fast and accurate frequency estimation of a complex sinusoidal plays an important role in many applications, including communications, radar, and sonar. This paper presents two methods for the frequency estimation of a complex sinusoidal in noisy environments. The proposed methods interpolate on shifted DFT coefficients to acquire the frequency estimates iteratively. The first method interpolates on the $q$ -shifted DFT coefficients of the signal, whose optimum iteration number is found to be a logarithmic function of the signal length. Furthermore, we also show that by appropriately selecting the value of the shift $q$ , the proposed method becomes asymptotically efficient. In the second method, we use hybrid half-shifted and $q$ -shifted DFT interpolators together, which converges in only two iterations. It is shown that both of the estimators are asymptotically unbiased with their mean square errors performing on the Cramer–Rao lower bound. Theoretical results are validated by extensive computer simulations.

Fast and Efficient Sinusoidal Frequency Estimation by Using the DFT Coefficients

The synchronization method using the available constant envelop preamble is analyzed, and a new preamble weighted by pseudo-noise sequence is proposed, with which a novel timing and frequency offset estimation method is presented for orthogonal frequency division multiplexing (OFDM) systems in this paper. By the proposed method, the accuracy of the timing offset estimator is significantly improved, and the estimate range of the frequency offset estimator is greatly enlarged with no loss in accuracy. The performance of the proposed method is demonstrated by simulations.

Synchronization method based on a new constant envelop preamble for OFDM systems

A novel transform technique is proposed for reducing the peak-to-average ratio (PAPR) of an orthogonal frequency division multiplexing (OFDM) signal. Large OFDM signals are replaced by small complementary signals according to the proposed method. It has a low SNR loss in bit error rate while achieving a significant reduction of PAPR. It is shown by computer simulations that the proposed method can outperform the well-known clipping filtering scheme and /spl mu/-law companding technique substantially.

A complementary clipping transform technique for the reduction of peak-to-average power ratio of OFDM system

Signal-to-noise ratio (SNR) measurement is required in many receivers and systems of communications. In this brief, we derive a new SNR's estimator based on the second and fourth-order moments of the complex signals of quadrature phase-shift keying modulations. The mean square error of the estimated SNR by the proposed algorithm is smaller than that by other methods for a low SNR with limited samples.

A new SNR's estimator for QPSK Modulations in an AWGN channel

An efficient frequency offset estimation method is proposed for wireless orthogonal frequency-division multiplexing (OFDM) systems. In the proposed method, the received samples of the training symbol are processed by a novel envelop equalized processing method, and the estimation of the frequency offset in the OFDM systems turns out to be the frequency estimation of a complex tone. A novel frequency estimation method is employed to estimate the frequency offset. The estimation range of the proposed method is as large as the bandwidth of the OFDM signal, and the performance of the proposed method is independent of the structure of the training symbol.

An Efficient Frequency Offset Estimation Method With a Large Range for Wireless OFDM Systems

A novel scheme for space-time block coding with a variable transmit diversity gain is proposed for OFDM systems in the paper. The OFDM symbols are divided into two groups of orthogonal sub-symbols with each group coded in Alamouli STBC in the coding, and the new scheme for STBC is constructed by differently combining the coded data of each group with the different transmit diversity gain to be achieved by linear processing and correspondingly combining the received data on the sub-carriers. The proposed scheme is feasible to be used in video transmission and a new unequal error protection applied to MPEG-4 video transmission is discussed. The results of computer simulation show that the proposed scheme has double diversity gain and quadruple diversity gain. The new unequal error protection scheme has a gain more than 8 dB and higher efficiency than the UEP based on the RCPC codes.

Hui Zhang

Papers

Synchronization method based on a new constant envelop preamble for OFDM systems

A complementary clipping transform technique for the reduction of peak-to-average power ratio of OFDM system

A new SNR's estimator for QPSK Modulations in an AWGN channel

An Efficient Frequency Offset Estimation Method With a Large Range for Wireless OFDM Systems

A novel scheme for space-time block coding with a variable transmit diversity gain in OFDM systems