Conventional Selected Mapping Research Articles

Cached SLM to reduce the PAPR of OFDM signal

Selected mapping (SLM) is one of the most well-known peak-to-average power ratio (PAPR) reduction techniques proposed for the orthogonal frequency-division multiplexing (OFDM) systems. The main drawback of the conventional SLM scheme is high computational complexity because of numerous inverse fast fourier transform (IFFT) operations when transmitting one OFDM signal, which may hinder its wide application in certain systems. The aim of this paper is to propose a post-IFFT PAPR reduction scheme based on a cache structure. in the proposed scheme, several candidates are created through combining two of time-domain signal vectors in cache and the one with the lowest PAPR is transmitted. Because the generation of candidates is implemented after the IFFT, one OFDM signal only requires one complex IFFT operation when using the proposed cache scheme. simulation results show that the new proposed scheme has promising PAPR performance while it decreases the complexity compared with the conventional SLM scheme. In addition, the cache scheme has the ability to be combined with other scheme such as SLM to further reduce the PAPR at the cost of a moderate increase of the complexity. Copyright © 2012 John Wiley & Sons, Ltd.

REDUCING PAPR OF OFDM BASED WIRELESS SYSTEMS USING COMPANDING WITH CONVOLUTIONAL CODES

OFDM is a promising broadband technique. However, the implementation disadvantage of OFDM is Peak-to-Average Power Ratio (PAPR) which outweighs all the potential benefits of OFDM. In this paper, a new scheme will be introduced, that combines selective mapping and companding technique to reduce PAPR. However, companding technique is a distortion technique but by using convolutional codes with companding also improves BER performance of the OFDM system. It also removes the disadvantage of SLM technique of extra side information i.e. this technique does not require any side information unlike in conventional SLM. By considering the example of OFDM with BPSK modulation, it is shown in simulation results that the proposed scheme performs well in both reducing PAPR and improving BER performance without the need of any side information. It has been calculated that PAPR of OFDM signal can be reduced by 5dB over the original system with the proposed scheme.

Joint Reduction of Peak-to-Average Power Ratio, Cubic Metric, and Block Error Rate in OFDM Systems Using Network Coding

The reductions of peak-to-average power ratio (PAPR) and block error rate (BLER) are two challenges in wireless systems employing orthogonal frequency-division multiplexing (OFDM)/orthogonal frequency-division multiple access. High BLER renders the system unreliable, and high PAPR is associated with power inefficiency and nonlinearity of the system. These two issues have separately been studied in the literature, but few works have studied simultaneous reductions of PAPR and BLER. In this paper, we propose a new scheme to jointly reduce and tradeoff PAPR and BLER in OFDM systems using random network coding (NC). In our proposed scheme, different representations of the input information block are generated using a special form of NC matrices, for which we prove it achieves the minimum BLER. We then propose an additional step to our proposed scheme to tradeoff a further improvement in PAPR against degradation in BLER using encoded block puncturing. Simulation results show that the proposed scheme achieves the same PAPR as conventional selective mapping (C-SLM) schemes while achieving the minimum BLER. We also show through simulations the PAPR gains achieved by our proposed additional step over C-SLM and the tradeoff of this gain against BLER degradation. Simulations finally show that our proposed scheme achieves the same results for the recently developed cubic metric.

A low complexity selected mapping scheme for peak to average power ratio reduction with digital predistortion in OFDM systems

SUMMARYOne of the effective methods used for reducing peak‐to‐average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems is selected mapping (SLM). In this paper, a new SLM scheme called DSI‐SLM, which is a combination of dummy sequence insertion (DSI) and conventional selected mapping (C‐SLM) is proposed. Previous techniques have had some drawbacks. In DSI, increasing the number of dummy sequences to have better PAPR degrades transmission efficiency, and in C‐SLM, the complexity rises dramatically when the number of sub‐blocks increases. The proposed DSI‐SLM scheme significantly reduces the complexity because of the reduction in the number of sub‐blocks compared with the C‐SLM technique while its PAPR performance is even better. To enhance the efficiency of the OFDM system and suppress the out‐of‐band distortion from the power amplifier nonlinearity, a digital predistortion technique is applied to the DSI‐SLM scheme. Simulations are carried out with the actual power amplifier model and the OFDM signal based on the worldwide interoperability for microwave access standard and quadrature phase‐shift keying modulation. The simulation results show improvement in PAPR reduction and complexity, whereas the BER performance is slightly worse. Copyright © 2011 John Wiley & Sons, Ltd.

A Novel Constellation Reshaping Method for PAPR Reduction of OFDM Signals

In this paper, we propose a constellation reshaping method for peak-to-average power ratio (PAPR) reduction in orthogonal frequency division multiplexing (OFDM) systems. The key idea of the proposed method is to generate a reshaped quadrature amplitude modulation (R-QAM) constellation, in which the minimum distance of the R-QAM is the same as that of the traditional QAM constellation. When the novel R-QAM constellation is employed with the traditional partial transmit sequence (PTS) and selected mapping (SLM) methods in OFDM systems, called as the R-PTS and R-SLM methods in this paper, respectively, the mean square errors between the constellations of the received data and each R-QAM rotated by different phase rotation factors are calculated at the receiver, and the phase rotation factor with the minimum mean square error is selected to recover the original data without side information. Therefore, the flexibility in phase rotation choice and the ability to avoid data rate loss make the R-PTS and R-SLM methods more suitable for good bit-error-rate performance in OFDM systems. Theoretical analysis and simulation results show that the R-PTS and R-SLM methods could provide the same PAPR reduction and bit-error-rate as those of the conventional PTS and SLM methods with perfect side information, respectively.

Fountain Codes With PAPR Constraint for Multicast Communications

The Forward Link Only (FLO) merit of fountain codes is utilized to avoid excessive retransmission requests for multicast communications. Two important and basic classes of fountain codes, Random Linear (RL) codes and Luby Transform (LT) codes, are considered in this paper as application layer Forward Error Correction (FEC) codes. High Peak-to-Average Power Ratio (PAPR) is a notorious physical layer problem in OFDM systems. We take the PAPR constraint into account in the encoding of fountain codes for OFDM multicast communications. We propose a selective mapping (SLM) technique that selects the best P candidates among the QP candidates. This SLM technique performs significant better than the conventional SLM technique that selects the best candidate among the Q candidates. Mathematical analysis and computer simulation verify the excellence of our designs.

A Novel SLM Scheme for PAPR Reduction in OFDM Systems

Orthogonal frequency-division multiplexing (OFDM) is an attractive transmission technique for high-bit-rate communication systems. One major drawback of OFDM is the high peak-to-average power ratio (PAPR) of the transmitter's output signal. A novel selected mapping (SLM) scheme is proposed, which employs matrix transformation, cyclically shifting, and linear combining algorithm to generate new candidates. The novel scheme requires only one IFFT and gets more candidate transmission signals throughout the entire process. The complexity analysis and simulation results show that this algorithm can dramatically reduce computational complexity comparing with the conventional SLM scheme as in Hill et al., 2000; Yang et al., 2009; Wang and Ouyang, 2005; Li et al., 2010; and Heo et al., 2007 under the similar PAPR reduction performance.

Peak-to-Average Power Ratio Reduction in OFDM Systems Using All-Pass Filters

A low-complexity peak-to-average power ratio (PAPR) reduction scheme for orthogonal frequency division multiplexing (OFDM) systems is proposed. The proposed scheme produces OFDM sequences by rotating the symbol phase using multiple all-pass filters, whereas the phase rotation of conventional selected mapping (SLM) scheme is performed with multiple complex multiplication modules in conjunction with inverse fast Fourier transform (IFFT) modules. As such, the proposed scheme does not require multiple IFFT modules that incur a heavy computational burden. Analysis results show that the proposed PAPR reduction scheme can significantly decrease computational complexity over the SLM scheme, though the reduction is achieved at the cost of slightly worse PAPR reduction performance. As an instance, the proposed scheme with eight first order all-pass filters for 2048 subcarriers reduces the number of required multiplications by 69.2% and additions by 63.1% at a sacrifice of only 0.25 dB PAPR increase over the conventional SLM scheme with eight IFFT modules.

PAPR 감소와 효과적 채널 추정을 위한 SC-FDMA 통신 시스템의 파이럿 배치 방법

SC-FDMA(Single Carrier-Frequency Division Multiple Access) 통신 시스템에서 채널 추정을 위한 파일럿은 CAZAC 시퀀스를 이용하여 OFDM(Orthogonal Frequency Division Multiplexing) 신호의 높은 PAPR(Peak-to-Average Power Ratio)을 낮추는 방식을 사용한다. 그런데, 채널 추정을 위한 파일럿이 블록 타입으로 전송되므로, 수신단에서 파일럿 블록 사이의 여러 OFDM 심볼들은 시간 영역에서의 보간법을 시용하여 채널 추정하여야 하므로 매우 복잡하고 처리 시간이 길어질 수 있다. 또한 심한 fast fading 채널에서는 이러한 문제점이 더욱 커진다. 한편, 효과적인 고속 채널 추정을 위하여 OFDM 심벌 단위로, 주파수 영역에서 보간법을 수행하는 comb 타입의 파일럿을 사용하게 되면 OFDM 신호의 PAPR이 다시 높아지는 문제가 발생한다. 본 논문에서는 PAPR 감소와 효과적 채널 추정이 가능한 comb 타입의 파일럿을 배치 방법을 연구하였다. 이를 위하여 CAZAC 행렬 변환된 OFDM 신호에 comb 타입의 파일럿을 배치하고, 추가로 SLM 기법을 사용하였다. 그러나 기본적인 SLM(Selected Mapping) 기법은 위상 회전에 관한 부가 정보 전송이 필요하기 때문에 대역폭의 손실을 가져온다는 단점이 있다. 따라서, 본 연구에서는 파일럿은 SLM 위상 시퀀스와 곱해지지 않으며, SLM 위상 회전 시퀀스에 따라 서로 다른 파일럿을 신호에 삽입하여, 부가 정보를 사용하지 않고 대역폭의 손실이 없는 개선형 SLM 기법을 연구하였다. 시뮬레이션 결과, 4개의 위상 회전 시퀀스를 갖는 SLM을 사용하였을 때, 파일럿 삽입으로 인해 높아진 신호의 PAPR을 원래 수준과 비슷한 성능으로 감소되는 것을 알 수 있다. PAPR of the pilot symbols can be reduced down by the CAZAC sequence in the SC-FDMA communication system. However, it is very complicated and takes quite a long time to compute the interpolation between the OFDM information symbols for the channel estimation because the pilot data are trasmitted in the block type. Furthermore, situation will be much more serious in the severe fading channel. Actually the pilot insertion of the comb type is much efficient and convenient for the channel estimation since the calculation of the interpolation can be made in the frequency domain symbol by symbol. But, the PAPR will be regrown when the pilot data are inserted with the information data in the comb type. So, in this paper, we like to study the PAPR reduction and comb type pilot assignment for the efficient channel estimation. Unlike the conventional SLM(selected mapping) method requiring the side information, our improved SLM method is to use the phase rotation sequence into information data without rotating phase of pilot. We use different pilot data according to the different phase rotation sequence. From the simulation result, it can be confirmed that when SLM method of 4 phase rotation sequence is used, PAPR is almost same to the block type method without pilot.

Reduction PAPR of OFDM Signals by Combining SLM with DCT Transform

One of main disadvantage of OFDM is high peak-to-average power ratio (PAPR). In this paper, two effective PAPR reduction schemes are proposed. These techniques combine DCT and SLM techniques. The scheme 1 is composed of the DCT followed by SLM technique, and the DCT is used followed by conventional SLM in proposed scheme 2. Simulation results show that the proposed schemes can obtain significant PAPR reduction performance with that of ordinary SLM techniques.

SLM-based OFDM system without side information for data recovery

An effective selected mapping (SLM) based method without requiring side information for orthogonal frequency division multiplexing (OFDM) systems is presented. For the proposed method, a specific set of phase sequences is designed. Simulation results show that the proposed method provides almost the same peak-to-average power ratio reduction performance, compared to the conventional SLM method requiring side information.

Performance of peak-to-average power ratio reduction in single- and multi-antenna OFDM via directed selected mapping

Selected mapping (SLM) is a popular scheme for peak power reduction in orthogonal frequency-division multiplexing (OFDM) systems. In this letter, the performance of various versions of SLM, among them ordinary and directed SLM, in single- and multi-antenna point-to-point OFDM systems is assessed. Analytic expressions for the distribution of the PAR are derived. Numerical results cover that significant gains over conventional SLM can be achieved by directed SLM.

Bit-Based SLM Schemes for PAPR Reduction in QAM Modulated OFDM Signals

In this paper, we propose two bit-based selected mapping (SLM) schemes for reducing peak to average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals with quadrature amplitude modulation (QAM), called bitwise SLM (BSLM) and partial bit inverted SLM (PBISLM). Contrary to the conventional SLM which rotates the phases of QAM symbols in the frequency domain, the proposed schemes change the magnitudes as well as the phases of QAM symbols by applying binary phase sequences to the binary data sequence before mapped to QAM symbols. Simulation results show that the proposed schemes have better PAPR reduction performance with shaping gain than the conventional SLM scheme for the QAM modulated OFDM signals, especially for the small number of subcarriers.

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 Blind SLM Scheme for Reduction of PAPR in OFDM Systems

In this paper we propose a blind algorithm for peakto-average power ratio (PAPR) reduction in OFDM systems, based on selected mapping (SLM) algorithm as a distortionless method. The main drawback of the conventional SLM technique is the need for transmission of several side information bits, for each data block, which results in loss in data rate transmission. In the proposed method some special number of carriers in the OFDM frame is reserved to be rotated with one of the possible phases according to the number of phase sequence blocks in SLM algorithm. Reserving some limited number of carriers wont effect the reduction in PAPR of OFDM signal. Simulation results show using ML criteria at the receiver will lead to the same system-performance as the conventional SLM algorithm, while there is no need to send any side information to the receiver. Keywords— Orthogonal Frequency Division Multiplexing (OFDM), Peak-to-Average Power Ratio (PAPR), Selected Mapping (SLM), Blind SLM (BSLM).

A Low Complexity Selected Mapping Scheme by Use of Time Domain Sequence Superposition Technique for PAPR Reduction in OFDM System

By using the time domain sequence superposition (TDSS) technique, in this paper, we propose a low complexity selected mapping (LC-SLM) scheme for the peak-to-average power ratio (PAPR) reduction of the orthogonal frequency division multiplexing (OFDM) system. Unlike the conventional selected mapping (SLM) scheme which needs several inverse fast Fourier transform (IFFT) operations for an OFDM signal, the proposed scheme requires to implement two IFFT operations only. Thus, it can remarkably reduce the computational complexity. Simulation results show that the proposed scheme can achieve similar PAPR performance as the conventional SLM scheme.

Novel SLM Scheme with Low-Complexity for PAPR Reduction in OFDM System

Orthogonal frequency-division multiplexing (OFDM) is an attractive transmission technique for high-bit-rate communication systems. One major drawback of OFDM is the high peak-to-average power ratio (PAPR) of the transmitted signal. This study introduces a low-complexity selected mapping (SLM) OFDM scheme based on discrete Fourier transform (DFT) constellation-shaping. The DFT-based constellation-shaping algorithm applied with conventional SLM scheme usually requires a bank of DFT-shaping matrices to generate low-correlation constellation sequences and a bank of inverse fast Fourier transforms (IFFTs) to generate a set of candidate transmission signals, and this process usually results in high computational complexity. Therefore, a sparse matrix algorithm with low-complexity is proposed to replace the IFFT blocks and the DFT-shaping blocks in the proposed DFT constellation-shaping SLM scheme. By using the proposed sparse matrix, the candidate transmission signal with the lowest PAPR can be achieved with lower complexity than that of the conventional SLM scheme. The complexity analysis of the proposed algorithm shows great an improvement in the reduction of the number of multiplications. Moreover, this new low-complexity technique offers a PAPR that is significantly lower than that of the conventional SLM without any loss in terms of energy and spectral efficiency.

A Partitioned-SLM with Low Complexity for OFDM PAPR Reduction

We propose the P-SLM (Partitioned-Selected Mapping) scheme with low complexity for PAPR reduction of OFDM signals. In the proposed scheme, a symbol sequence in the frequency domain is partitioned into several sub-blocks which are multiplied by different orthogonal phase sequences whose length and number are shorter and smaller than those used in the conventional SLM. Then, among various sequences in the time domain generated after the IFFT for the SLM sub-blocks, the sub-block combination with the lowest PAPR is selected and transmitted. Simulation results show that the proposed P-SLM scheme significantly reduces the number of IFFT calculation and multiplication than the conventional SLM without loss of PAPR reduction performance.

An Adaptive SLM Scheme Based on Peak Observation for PAPR Reduction of OFDM Signals

We propose an adaptive SLM scheme based on peak observation for PAPR reduction of OFDM signals. The proposed scheme is composed of three steps: peak scaling, sequence selection, and SLM procedures. In the first step, the peak signal samples in the IFFT outputs of the original input sequence are scaled down. In the second step, the sub-carrier positions where the power difference between the original input sequence and the FFT output of the scaled signal is large, are identified. Then, the phase sequences having the maximum number of phase-reversed sequence words only for these positions are selected. Finally, the generic SLM procedure is performed by using only the selected phase sequences for the original input sequence. Simulation results show that the proposed scheme significantly reduce the complexity in terms of IFFT and PAPR calculation than the conventional SLM, while maintaining the PAPR reduction performance.

Turbo Coded OFDM for Reducing PAPR and Error Rates

A selective-mapping (SLM) scheme which does not require the transmission of side information and can reduce the peak to average power ratio (PAPR) in turbo coded orthogonal frequency-division multiplexing (OFDM) systems is proposed. The candidates of the proposed SLM are respectively generated by a turbo encoder using various interleavers. The waiver of side information can avoid the degradation of error rate performance which results from the incorrect recovery of side information at receiver in the conventional SLM OFDM system.