Sheng-Ju Ku

Novel conversion matrices for simplifying the IFFT computation of an SLM-based PAPR reduction scheme for OFDM systems

There have been a set of conversion matrices proposed recently by Wang and Ouyang to simplify the inverse fast Fourier transform (IFFT) computation involved in the selected mapping (SLM) scheme for reduction of the peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. As compared to the conventional SLM scheme, the modified approach achieves close PAPR reduction with much lower complexity but degraded bit error rate (BER) performance. In this paper, we propose a new set of conversion matrices for the SLM scheme such that the complexity can be reduced without sacrificing the BER performance. It is shown that the improved SLM method has better BER performance and lower complexity than the previous work by Wang and Ouyang, at the cost of a slight PAPR reduction loss.

A Reduced-Complexity PTS-Based PAPR Reduction Scheme for OFDM Systems

In this paper, a reduced-complexity partial transmit sequences (PTS) scheme is proposed to resolve the intrinsic high peak-to-average power ratio (PAPR) problem of orthogonal frequency division multiplexing (OFDM) systems. In the proposed PTS scheme, a cost function Qn is generated by summing the power of the time-domain samples at time n in each subblock. Only those samples with Qn greater than or equal to a preset threshold are used for peak power calculation during the process of selecting a candidate signal with the lowest PAPR for transmission. As compared to the conventional PTS scheme, the proposed one achieves almost the same PAPR reduction performance with much lower computational complexity.

A Low-Complexity PAPR Estimation Scheme for OFDM Signals and Its Application to SLM-Based PAPR Reduction

Peak-to-average power ratio (PAPR) reduction methods for orthogonal frequency division multiplexing (OFDM) systems commonly use four times oversampling for the discrete-time OFDM signal to approximate the peak of the continuous-time OFDM signal. However, the four times oversampling process increases the computational complexity. In this paper, we propose a new low-complexity method to efficiently estimate the PAPR value of the OFDM signal. The proposed scheme uses an interpolator to find the peak of the four times oversampled OFDM signal around some searched samples of the original discrete-time OFDM signal using oversampling with a factor lower than four. Some criteria are derived to determine the interpolation filter length and the threshold of sample power for the search process. As compared to the method with four times oversampling, the proposed PAPR estimation scheme achieves close performance with only about half of the computational complexity. It is also shown that the proposed approach can easily be combined with the selected mapping method for PAPR reduction, where the complexity is significantly reduced but the performance is degraded only slightly.

Low-Complexity PTS-Based Schemes for PAPR Reduction in SFBC MIMO-OFDM Systems

Multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) is an attractive technique for high-data-rate transmission. However, MIMO-OFDM systems have an inherent drawback in that the transmitted signals may suffer from a high peak-to-average power ratio (PAPR). The conventional partial transmit sequences (PTS) scheme can be applied to each transmitting antenna directly to reduce the PAPR of MIMO-OFDM systems, but it has high computational complexity. In this paper, two types of low-complexity PTS schemes are proposed to reduce the PAPR for MIMO-OFDM systems that use space-frequency block coding (SFBC). The two proposed PTS schemes use the sample powers of subblocks to generate cost functions for selecting samples to estimate the peak power of each candidate signal, thus reducing the computational complexity. In addition, for one of the proposed PTS schemes, the similarity of the input signals from the various transmitting antennas is used to further reduce the computational complexity. Simulation results show that, as compared with other related works, the proposed PTS schemes can achieve a reduced PAPR performance and a bit error rate performance close to that of SFBC MIMO-OFDM systems, but at much lower computational cost.

A Low-Complexity Companding Transform for Peak-To-Average Power Ratio Reduction in OFDM Systems

The high peak-to-average power ratio (PAPR) feature is one main drawback associated with orthogonal frequency division multiplexing (OFDM) systems. To overcome this problem, many approaches have been presented in the literature, such as the selected mapping technique, the partial transmit sequence technique, the linear nonsymmetrical transform (LNST), and the exponential companding transform (Exp-CT). However, most of them involve high computational complexity. In this paper, we propose a new low-complexity companding transform scheme for PAPR reduction. From computer simulations, the proposed low-complexity scheme can successfully reduce the PAPR value with a lower bit error rate than the Exp-CT scheme and smaller spectrum side-lobe generation than the LNST and Exp-CT schemes. It is useful for physical realization of an OFDM system.

A Low-Complexity Constellation Extension Scheme for PAPR Reduction of OFDM Signals

Modulation constellation extension (CE) schemes provide good peak-to-average power ratio (PAPR) reduction performance for orthogonal frequency division multiplexing (OFDM) signals. However, they usually require a complicated algorithm to find the optimal signal for transmission. In this paper, we propose a low-complexity CE scheme to reduce the PAPR of OFDM signals, in which some low-complexity conversion matrices are used to generate multiple candidate signals for selection. Also, we develop a mechanism to limit the increase in the average transmitted power that results from the constellation extension to an acceptable level. As compared to the related work using the CE technique, the proposed CE scheme can achieve close PAPR reduction performance with much lower computational complexity and lower transmitted power.

A new side-information free PTS scheme for PAPR reduction in OFDM systems

Partial transmit sequences (PTS) is an efficient technique to reduce the peak-to-average power ratio (PAPR) for orthogonal frequency division multiplexing (OFDM) systems. One main drawback of the conventional PTS method is the need of side information. When the side information is lost, the received data cannot be decoded correctly by the receiver. In this paper, we propose a new side-information free PTS scheme, where a difference vector along with an input data block is generated by using an extended constellation. After dividing the difference vector into some disjoint subblocks, the inverse fast Fourier transform of the input data block and that of each subblock of the difference vector are combined optimally to form a low-PAPR OFDM signal for transmission. Simulation results show that the proposed PTS scheme can achieve better PAPR reduction performance than the conventional PTS scheme, but it has lower computational complexity and does not need side information.

A Low-Complexity PTS Scheme for PAPR Reduction in SFBC MIMO-OFDM Systems

Multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) is an attractive technique for high-data-rate wireless communications because of its high spectral efficiency and robustness with respect to multipath fading channels. However, MIMO-OFDM systems have an inherent drawback in that the transmitted signals of various antennas may have a high peak-to-average power ratio (PAPR). In this paper, a low-complexity partial transmit sequences (PTS) scheme is proposed to reduce the PAPR for MIMO-OFDM systems with space- frequency block coding (SFBC). In the proposed PTS scheme, we use the sample powers of subblocks derived from the input data blocks to generate a set of cost functions. We then use the cost functions and the similarity among the subblocks to develop a new method to jointly select the samples to estimate the peak power of candidate signals for various transmitting antennas. Simulation results show that, in SFBC MIMO-OFDM systems, the proposed PTS scheme can achieve a PAPR reduction performance close to that of the conventional PTS scheme, but with much lower computational complexity.

An improved low-complexity PTS scheme for PAPR reduction in OFDM systems

In this paper, an improved low-complexity partial transmit sequences (PTS) scheme is proposed to reduce the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) systems. In the proposed PTS scheme, a set of cost functions derived from the power of the time-domain samples of each subblock is used to select the samples for peak power estimation. Furthermore, we develop a new two-stage algorithm to reduce the computational complexity of the optimization process of the PTS scheme. Compared to related works, the proposed PTS scheme can achieve similar PAPR reduction performance, but with much lower computational complexity.