一种基于快跳频技术的多载波CDMA系统

为进一步提高多载波CDMA系统的频带效率与抗干扰能力,提出了一种跳频多址技术结合多载波调制的传输方案,利用跳频技术将部分子载波传输与随机交织引入到多载波传输系统中,给出了系统实现的模型,并对该传输方案的系统带宽和误码性能进行了分析。理论分析与仿真结果表明：与以往的多载波CDMA系统相比,所建议系统的结构简单,性能优异,消除了已有系统中峰均功率比高和远近效应等问题,具有较强的抗多址干扰与窄带干扰的能力,并能有效地抗信道中突发错误的能力。     

LTE-A中逼近最优性能的峰值对消峰均比抑制算法

最优化限幅滤波法(OICF)是一种最优化的限幅类技术,它可以在满足峰均比(PAPR)要求下实现信号矢量误差的最小化,但其需要进行最优化求解,其计算复杂度与信号的子载波总数的立方成正比.针对OICF复杂度高的缺点,考虑LTE-Advanced多载波信号,提出了一种基于峰值对消降低PAPR的方法(PC-PAPR).PC-PAPR在峰值对消前,将对消脉冲通过一个零相位滤波器,滤除带外泄漏的同时,保证对消脉冲的相位不发生改变.理论分析表明,PC-PAPR计算复杂度降至与信号的子载波总数成正比,数字仿真结果表明PC-PAPR降低PAPR的性能与OICF性能差异小于0.06dB.     

OFDM Link with a Better Performance Using Artificial Neural Network

In this paper, a scheme for reducing the peak-to-average power ratio (PAPR) primarily and bit error rate simultaneously in orthogonal frequency division multiplexing using feed forward artificial neural network is proposed and analyzed. The proposed scheme switches one or more null-carriers with data subcarriers to offer minimum PAPR and requires no channel side information during transmission. To reduce high computational complexity, a multilayer neural network with Levenberg–Marquardt training algorithm is used. The proposed scheme thus suits to supplement some of other PAPR-reduction methods with low rate hit and complexity.     

OFDM系统中降低峰均比的联合算法

正交频分复用（OFDM）系统中,有很多降低峰均比（PAPR）的方法,联合算法是其中的一个大类。系统研究了峰均功率比（PAPR）较高的原因,着重比较几种联合算法的降低峰均比的效果,并给予仿真说明比较。在现有PARR降低算法的基础上,深入研究了算法之间的最佳联合方法。通过理论对比和实际仿真,总结出较易实现和简便的联合算法。     

Optimization of Peak to Average Power Reduction in OFDM

Orthogonal frequency division multiplexing (OFDM) a multicarrier system [1, 2] provides base for all advanced wireless communication system. The performance of OFDM is degraded by peak-to-averagepower ratio (PAPR). High PAPR requires high power amplifiers (HPAs). The nonlinearity of the HPA exhibits amplitude and section distortions, that cause loss of orthogonality among the subcarriers, and hence, intercarrier interference (ICI) is introduced inside the transmitted signal. Not only that, high PAPR put together lands up in in-band distortion and out-of-band radiation. Rather than using HPA’s, the only way to improve performance of OFDM system is to reduce PAPR. The PAPR reduction of OFDM system gives fair reduction in PAPR under partial transmits sequence (PTS) and DCT-SLM techniques. Here in this paper we proposed a combination of PTS and DCT-SLM and an algorithm to cut back the PAPR. This hybrid combined technique reduces PAPR effectively and minimizes the complexity of PTS technique.     

一种OFDM系统中PAPR的抑制算法

为降低正交频分复用(OFDM)系统中发射信号的峰值功率,提出了在一个OFDM符号内使用两种信号星座图对二进制数据进行编码,通过在各个子载波处选用合理的信号星座图来实现对峰值均值功率比(PAPR)的抑制。由于算法不改变现有OFDM系统的实现结构,在不影响OFDM中其它信号处理性能的条件下,仿真表明算法能有效地降低系统的峰值均值功率比。     

预编码⁃TR联合峰均比抑制算法研究

OFDM架构的雷达干扰一体化波形是近年来研究的热点,该类波形将探测子载波与干扰子载波分开,具有探测子载波稳定、干扰子载波灵活的结构特点,能够同时保证波形的探测性能和干扰性能,同时也具有波形峰均比较大的波形特点。本文针对OFDM架构的雷达干扰一体化波形子载波的调制特点,提出了一种预编码?TR联合峰均比抑制算法。该算法结合预编码峰均比抑制算法和TR峰均比抑制算法原理,能够在保持一体化波形探测干扰子载波能量分配方式不变的前提条件下对波形峰均比进行有效抑制。理论和仿真试验表明：本文所提出的预编码?TR联合峰均比抑制算法对一体化波形具有不失真、峰均比抑制能力强、效率高以及性能稳定的性能优点。     

A novel CVM precoding scheme for PAPR reduction in OFDM transmissions

High peak-to-average power ratio (PAPR) is still one of the major problems in orthogonal frequency division multiplexing (OFDM). In this article, a new precoding method is proposed and analyzed based on complex Vandermonde matrix (CVM). The reduction in PAPR of the OFDM signal is obtained using the decorrelation property of CVM which removes any redundancy from the input sequence and can be a very effective for PAPR reduction. Also, the phase-rotation property of CVM takes an advantage of the fact that the PAPR is very sensitive to phase-shifts of the signal. It is shown that the proposed precoding outperforms most of the powerful precoding techniques and can achieve a PAPR gain up to 6.5 and 7.4 dB for IEEE 802.11a and DVB-T OFDM systems respectively. Moreover, CVM precoding does not change power spectral levels or error performances when compared with the normal OFDM systems, also it does not increase the computational complexity when compared with the existing precoding methods. It is shown that the performance of the proposed precoding is independent of modulation schemes and the number of subcarriers. The proposed CVM precoding also takes advantage of the frequency variations of the communication channel and can provide considerable performance gain in fading-multipath channels.     

Peak-to-average power reduction using partial transmit sequences: a suboptimal approach based on dual layered phase sequencing

A high peak-to-average power ratio (PAPR) is a major shortcoming in multicarrier systems, as it causes nonlinearity in the transmitter, degrading the performance of the system significantly. Partial transmit sequences (PTS) is one of the best methods in reducing PAPR, in which the information-bearing subcarriers are divided into M disjoint subblocks, each controlled by a phase rotation factor which brings PAPR down. Though PAPR reduction by PTS is more effective with more subblocks, there is a corresponding exponential increase in complexity. In this paper, a novel implementation of PTS is presented, in which a dual-layered approach is employed to reduce the complexity.     

A New PAPR Reduction Technique in OFDM Systems Using Linear Predictive Coding

High peak-to-average power ratio (PAPR) has always been as a major problem in orthogonal frequency division multiplexing (OFDM) that leads to a severe nonlinear distortion in practical hardware implementations of high power amplifier. In this article, a new PAPR reduction method is proposed based on linear predictive coding (LPC). This method proposes the use of signal whitening property of LPC as a preprocessing step in OFDM systems. Error filtering of the proposed method removes the predictable content of stationary stochastic processes which can reduce the autocorrelation of input data sequences and is shown to be very effective solution for PAPR problem in OFDM transmissions. It is shown that the proposed method can achieve a significant reduction in PAPR without degrading the power spectral level, error performance or computational complexity of the systems. It is also shown that the proposed method is independent of modulation schemes and can be applied to any number of subcarriers under both additive white gaussian noise and wireless Rayleigh fading channel.     

PAPR Reduction in OFDM Systems Based on Autoregressive Filtering

Orthogonal frequency division multiplexing (OFDM) has a very high peak-to-average power ratio (PAPR) that causes a severe nonlinear distortion in practical hardware implementation of high power amplifiers (HPA). In this article, a new PAPR reduction method is proposed based on autoregressive (AR) error filtering. This method proposes the use of signal whitening property of error filtering as a preprocessing step to remove the predictable content of stationary stochastic processes which can reduce the autocorrelation of input data sequences and is shown to be a very effective solution for the PAPR problem in OFDM systems. It is shown that the proposed method can achieve a significant reduction in PAPR without degrading the error performance or power spectral levels. It is also shown that the proposed method is applicable to any modulation scheme and can work for any number of subcarriers under both additive white Gaussian noise and wireless Rayleigh fading channel.     

Adaptive spread-spectrum multicarrier multiple-access over wirelines

In this paper, we investigate the dynamic resource allocation adapted to spread-spectrum multicarrier multiple-access (SS-MC-MA) systems in a multiuser power line communication (PLC) context. The developed adaptive system is valid for uplink, downlink, as well as for indoor and outdoor communications. The studied SS-MC-MA system is based on classical multicarrier modulation like digital multitone (DMT), combined with a spread-spectrum (SS) component used to multiplex several information symbols of a given user over the same subcarriers. The multiple-access task is carried out using a frequency-division multiple-access (FDMA) approach so that each user is assigned one or more subcarrier sets. The number of subcarriers in each set is given by the spreading code length as in classical SS-MC-MA systems usually studied in the wireless context. We derive herein a new loading algorithm that dynamically handles the system configuration in order to maximize the data throughput. The algorithm consists in an adaptive subcarrier, code, bit, and energy assignment algorithm. Power-spectral density constraint due to spectral mask specifications is considered, as well as finite-order modulations. In that case, it is shown that SS-MC-MA combined with the proposed loading algorithm achieves higher throughput than DMT in a multiuser PLC context. Because of the finite granularity of the modulations, some residual energy is indeed wasted on each subcarrier of the DMT spectrum. The combining of a spreading component with DMT allows to merge these amounts of energy so that one or more additional bits can be transmitted in each subcarrier subset leading to significant throughput gain. Simulations have been run over measured PLC channel responses and highlight that the proposed system is all the more interesting than the signal-to-noise ratio is low.     

A study on the PAPRs in multicarrier modulation systems with different orthogonal bases

This paper studies the peak‐to‐average power ratios (PAPRs) in multicarrier modulation (MCM) systems with seven different orthogonal bases, one Fourier base and six wavelet bases. It is shown by simulation results that the PAPRs of the Fourier‐based MCM system are lower than those of all wavelet‐based MCM (WMCM) systems. A novel threshold‐based PAPR reduction method is then proposed to reduce the PAPRs in WMCM systems. Both numerical and simulation results indicate that the proposed PAPR reduction method works very effectively in WMCM systems. Copyright © 2006 John Wiley & Sons, Ltd.     

A Hybrid Clustering Approach Based Q-Leach in TDMA to Optimize QOS-Parameters

An Orthogonal frequency part multiplexing suffers from a considerable challenge due to a high peak to average power ratio (PAPR). Hence, an effective method such as partial transmits sequence (PTS) can avert this defiance by limit the design of PAPR. Therefore, an improving PAPR reduction performance via a novel approach is proposed by detaching each subblock into two parts furthermore exchanges the first sample with the final selection in each portion of the subblock to generate a new partitioning scheme. Several typical traditional segmentation schemes are used to analyze and apply the presented algorithm, such as adjacent, interleaving, and pseudo-random schemes. Besides, two scenarios are adopted based on simulation software in which the number of subcarriers is set to 128 and 256. Based on the results, a superior PAPR reduction performance is achieved based on the improved segmentation schemes regarding traditional strategies in both systems. Moreover, the enhanced adjusted PTS scheme poses a low computational complexity compared with that of the conventional schemes.

     

光OFDM系统中一种改进的SLM峰均比抑制方案

针对光正交频分复用(O-OFDM)系统中峰值平均功 率比(PAPR)较高的缺点,对PAPR抑制技术的选择性 映射法(SLM) 进行了深入研究。基于低复杂度SLM方案的深入研究,提出了一种改进的次PAP R选择的思 想与低复杂度SLM相结合的PAPR抑制方案。改 进的SLM方案能够成倍降低传统SLM方案的计算复杂 度。仿真分析表明,改进的SLM方案在载波数为256的O-OFDM系统中,计算复杂度能降低50%以上,并 且随着子载波数的增加,其复杂度降低程度更为高效;同时,该改进的SLM方案又能使其PAPR抑制性能优于传统的SLM方案,从而进一步提升了低复杂度SLM 方案的实用价值。     

SAP算法降低OFDM系统PAPR

为了降低OFDM系统峰均功率比(PAPR),提出一种基于改型选择性映射(SLM)与凸集映射星座扩展算法(ACEPOCS)的SAP算法.新算法采用并行组合方式,通过两种算法的分组联合,以较低的复杂度实现了对PAPR抑制能力的优化.在16QAM调制的OFDM系统模型中对新算法的PAPR、复杂度及误码率(BER)性能进行仿真和分析,结果表明,与传统SLM算法和ACE-POCS算法相比,相同条件下,新算法具有更快的收敛速度,更强的PAPR抑制能力,且不增加计算复杂度,具有优异的综合性能.     

Adaptive PAPR Reduction Scheme for OFDM Using SLM with the Fusion of Proposed Clipping and Filtering Technique in Order to Diminish PAPR and Signal Distortion

One of the main disadvantages of multicarrier transmission is the high peak-to-average power ratio (PAPR) of the transmitted signal. If the highest transmitted power is confined by the application restrictions or regulatory, the result is to decrease the average power permitted under multicarrier transmission. Selected mapping (SLM) is a standard PAPR reduction scheme that is appropriate for orthogonal frequency division multiplexing (OFDM) scheme as it realizes the performance of PAPR reduction without signal distortion. This paper proposes a method in order to handle the difficulties of high PAPR in OFDM scheme. The offered system is an arrangement of two distinguished methods, such as clipping and SLM. Compared to other hybrid methods, where the individual methods are implemented sequentially, this paper integrates the clipping method in the SLM procedure. This produces a supplementary PAPR reduction associated to the serial arrangement. Simulation results specify that the offered scheme acquires the performance of appropriate PAPR reduction with low computational complexity. The PAPR reduction at different number of subcarriers is analyzed and compared with the existing research work. The performance of relative energy efficiency has also been focused on this paper.

     

A hybrid technique for the PAPR reduction of NOMA waveform

Non-orthogonal multiple access (NOMA) is a great contender for future cellular modulation due to its desirable properties like massive connectivity, high data rate transmission, and high spectral efficiency. However, its peak-to-average power ratio (PAPR) is significant, which becomes a significant disadvantage for the efficient operability of the NOMA waveform compared to current techniques. Several PAPR reduction algorithms like selective mapping (SLM), partial transmission sequence (PTS), and companding techniques have been proposed to lower the PAPR of multicarrier waveforms (MCWs). PTS reduces the PAPR but has high complexity. On the other hand, SLM has a less complex framework, but its PAPR performance is not as efficient as PTS. Companding methods reduce the PAPR by compressing the signals at the transmitter, which unfortunately reduces the dynamic range of the signal. In this work, we propose a hybrid algorithm (SLM + PTS) with a companding method for the first time for the NOMA waveform, which efficiently reduces the PAPR with low computational complexity. Furthermore, we compare the performances of a host of candidate algorithms like SLM, PTS, hybrid (SLM + PTS), hybrid + A law (SLM–PTS–A law), and hybrid + Mu law (SLM–PTS–Mu law). The results of the experiments show that the hybrid + Mu law did a better job than the existing PAPR reduction algorithms.     

Security aware hybrid precoding based peak‐to‐average power ratio reduction Approaches for telecommunication systems

In wireless telecommunication, one of the modulation approaches used is the orthogonal frequency division multiplexing (OFDM). Moreover, the high peak‐to‐average power ratio (PAPR) is the one notorious demerit in OFDM systems. Hence, the high power amplifier (HPA) is used in its linear region. Otherwise, the bit error rate (BER) will be increased. Several approaches are proposed in the wireless communications for reducing the PAPR issue. In this paper, we propose a hybrid Discrete Hartley Matrix Transform (DHMT) precoding using both selected mapping (SLM) and partial transmit sequence (PTS) PAPR reduction strategies. For the multicarrier modulation process, instead of Inverse Fast Fourier transform (IFFT) operation, the DHMT operation is used because of its low computational complexity. Based on multi‐chaotic, the time‐frequency domain encryption (TFDE) approach is adopted for physical layer security to confirm the security in data transmission. For enhancing the physical layer security, the proposed encryption system generates chaotic sequences based on Logistic maps and Lozi in the frequency and time domains together. In this study, the implementation of the DHMT‐based OFDM system is processed to reduce the maximum PAPR. Implementation is performed on the MATLAB platform, and the performances are calculated using complementary cumulative distribution function (CCDF), BER regards to signal‐to‐noise ratio (SNR), and the outputs are compared based on the computation time. However, compared with the existing models, the proposed model produced better PAPR minimization regarding SNR.     

Joint channel estimation and turbo equalisation for MIMO-OFDM-IM systems

Multiple-Input Multiple-Output (MIMO) communications are frequently employed to improve the transmitted data rate and the link quality. Index modulated orthogonal frequency division multiplexing (OFDM-IM) improves the error rate performance and the peak-to-average power ratio (PAPR) compared with those of the conventional OFDM system due to the activation of partial subcarriers. The MIMO OFDM-IM can transmit additional information bits via the indices of active subcarriers. Also, in order to reduce the transmission power of the OFDM system, the MIMO OFDM-IM scheme can be employed to approach the demanded data transmission rate and the error rate performance. Multiple-input multiple-output orthogonal frequency division multiplexing index modulation (MIMO-OFDM-IM) is an effective multicarrier transmission scheme and can be proposed as an alternative to conventional MIMO-OFDM system. In this scheme, OFDM-IM is combined with MIMO transmission to take the benefits of these two techniques. In this paper, we propose a joint channel estimation and turbo equalisation receiver for MIMO-OFDM-IM system. Some simulation examples are given to demonstrate the effectiveness of the proposed receiver.