All-Pass Filters as a Low-Complexity PAPR Reduction Scheme for SC-FDMA System

This paper presents a low-complexity peak-to-average power ratio (PAPR) reduction scheme for single-carrier frequency division multiple access (SC-FDMA) system that is based on all-pass filters (APFs). The basic idea of the APF scheme is that it allows a flat magnitude response with a non-linear phase response. This means that this type of filters passes all frequency content of the input signal, while the phase is severely or intentionally degraded. This idea is well-exploited in this paper for generating random phase sequences that can be treated as multiple versions of an input sequence for the SC-FDMA system. The heart of traditional PAPR reduction techniques such as the conventional selective mapping and blind selective mapping schemes is the generation of multiple random phase sequences for the proper selection of the sequence that achieves the minimum PAPR. This can be accomplished through multiple inverse fast Fourier transform (IFFT) operations, which add more complexity to the system performance. In contrary, with the proposed APF scheme, we generate the signals with different phases through passing the original signal through multiple APFs with different phase responses, which reduces the system complexity.

     

OFDM系统中峰平功率比减小技术的研究

主要对减小OFDM系统中的峰值平均值功率比(PAPR)问题进行了研究。利用Golay互补序列和Reed-Muller码的关系,研究了一种把输入信息序列编成Golay互补序列的分组编码算法,并利用该编码算法对一个16子载波的OFDM系统的PAPR特性进行仿真。理论研究和仿真结果均表明,采用该编码方案后的OFDM信号的PAPR不超过3dB。     

降低可见光DCO-OFDM系统峰均比的DCT-GCS方法

为了克服现有降低OFDM峰值平均功率比的方法在可见光通信中效果不好的问题,通过分析发现DCO-OFDM系统输入序列的共轭对称形式增强了序列的相关性,使传统方法的PAPR抑制性能有明显下降,所以提出了离散余弦变换(DCT)与分组循环移位(GCS)结合的降低系统PAPR的方法。该方法中的分组循环移位能够在DCT的基础上降低输入序列的相关性,使系统输出信号具有更低的PAPR。仿真结果表明:提出的方法比仅采用DCT或者GCS能够更好地抑制系统的PAPR。在CCDF=10-4时,DCT-GCS方法使系统的PAPR下降了5.4dB。DCT-GCS具有较低的PAPR,且计算复杂度要远远低于PTS和SLM方法。      

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.

     

基于功放效率的OFDM信号幅度的最佳分布——峰均比抑制

星座图扩展（ACE）技术可以无损地降低OFDM信号的峰均比,本文的论述指出仅追求低峰均比对应的功放效率和效能并不是最好.笔者提出了OFDM信号的最佳互补累积分布函数（OCCDF）峰均比抑制方法,即考虑OFDM信号的幅度分布及出现概率,整体地评估其对放大器失真的影响,以OFDM信号放大器的效率为评估峰均比优劣的标准,在算法上以限定MER条件下得到尽可能低的功放输入功率回退（IBO）为迭代收敛目标,预见了应该存在最高功放效率意义匹配的所谓OFDM信号的最佳幅度分布.实验证实：相比原始OFDM系统,在放大基于OCCDF准则优化后的OFDM信号时,放大器获得了3.15dB的IBO性能改善,对比同等条件下单载波系统仅差0.05dB.     

The New Peak-to-Average Power Reduction Algorithm in the OFDM System

In this paper, we proposed a new peak-to-average power reduction (PAPR) algorithm of orthogonal frequency division multiplexing (OFDM) system using block coding scheme and discrete cosine transform (DCT). We are using DCT to concentrate the energy of the original signal into a few coefficients. After the DCT data were fed into the IDFT, the output of signal of OFDM appeared to have uniform distribution. With the newly proposed schemes, that we founded those three important properties, the first property is the PAPR used be reduced by 9.4419 dB for BPSK mapper. The second property is the OFDM signals have capability of noise immunity and of error correction. And the third property is the effect of PAPR reduced can be implement by cascaded different method.     

An efficient joint algorithm for reducing PAPR of SC-FDMA system in cognitive radio networks

Cognitive radio (CR) has been proposed as a solution for the spectrum scarcity problem. This paper investigates single-carrier frequency division multiple access (SC-FDMA) for cognitive radios. Recently, SC-FDMA has been suggested as a candidate for multicarrier based CR systems. In this paper, we propose enhanced techniques to reduce the peak to average power ratio (PAPR) in SC-FDMA for Cognitive Radio Network (CRN). We start by showing the effect of two standard PAPR reduction techniques (interleaver based and selective mapping) to reduce the PAPR in SC-FDMA based CR. Then, a proposed joint algorithm interleaver with selective mapping in a way that is suitable for SC-FDMA based CR will be proposed that results in a lower PAPR than using them individually. Simulation results show that the SC-FDMA with proposed techniques has a lower PAPR when compared with the conventional SC-FDMA system for CRN, while the complexity of the system slightly increases. Results also reveal that the no. of interleavers and SLM sequences must be chosen carefully in order to limit the PAPR with slightly increases in the complexity of the system.

     

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.     

宽带系统中有记忆大功率功放的数字预失真器研究

针对高峰均比的宽带输入信号,提出了一套联合峰均比抑制技术和基带自适应预失真技术的数字预失真器设计方案,并仿真了峰值抵消算法和自适应预失真算法.结果表明对于峰均比为8.4 dB的输入信号,经过1.5 dB的削峰处理后,预失真器改善带外频谱抑制27 dB,非常有效地补偿了功放的非线性失真,提高了功放效率,对发射机功放线性化技术有一定的实用价值.     

降低TDCS峰均功率比算法及性能分析

针对变换域通信系统出现的高峰均功率比的问题,提出了一种降低TDCS系统峰均功率比的算法。该算法通过对随机相位进行选择,生成一定数量的基函数,并在此基础上,寻找到峰均功率比较低的基函数来传输数据,从而得到改进的TDCS框图。仿真结果表明,改进算法能在不影响TDCS的误码率性能的情况下有效降低PAPR,在CCDF为10-3时,改进算法的PA0较原始TDCS降低了6.1 dB。     

A computationally efficient selected mapping technique for reducing PAPR of OFDM

In orthogonal frequency division multiplexing (OFDM) system, high value of peak-to-average power ratio (PAPR) is an operational problem that may cause non-linear distortion resulting in high bit error rate. Selected mapping (SLM) is a well known technique that shows good PAPR reduction capability but inflicts added computational overhead. In this paper, using Riemann sequence based SLM method, we applied reverse searching technique to find out low PAPR yielding phase sequences with significant reduction in computational complexity. Additionally, we explored side-information free transmission that achieves higher throughput but sacrifices PAPR reduction. Finally, to overcome this loss in PAPR reduction, we proposed application of Square-rooting companding technique over the output OFDM transmitted signal. Simulation results show that the proposed method is able to compensate the sacrifice in PAPR and achieved PAPR reduction of 8.9 dB with very low computational overhead.     

Reduction of peak factor in orthogonal multicarrier modulation byamplitude limiting and coding

A main disadvantage of orthogonal multicarrier modulation is that it exhibits a high peak-to-average-power ratio (PAPR). Because of this, all circuits between the output of the modulator and the input of the demodulator must be linear within a large dynamic range to avoid distortions and spectral spreading. It is therefore desirable to limit the PAPR of the multicarrier signal. A method based on amplitude limiting and forward error correcting (AL-FEC) coding is proposed for reduction of the PAPR. The performance of the AL-FEC is compared to two methods, based on block coding, specially constructed to reduce the PAPR. The AL-FEC is superior as compared to the existing methods. Moreover, its practical realization is very simple for any number of carriers     

A power-constrained design strategy for CMOS tuned low noise amplifiers

This paper presents a design methodology for tuned low noise amplifiers (LNAs), based on the minimization of the noise figure for a given power consumption. Our proposed design strategy is demonstrated through the design of a 2.4 GHz LNA. Simulation results show that the amplifier draws 5 mA from a 3.3 V supply voltage and features a 1.7 dB noise figure, while keeping the input/output impedance matched to 50 Ω. The circuit achieves a gain of 11dB and a 1dB compression point of about −5 dB m. Custom ESD structures that do not degrade excessively the LNA performance are used for protection. The chip area (excluding the bonding pads) is approximately 0.3 × 0.3 mm².     

A PAPR reduction technique using Hadamard transform combined with clipping and filtering based on DCT/IDCT for IM/DD optical OFDM systems

In Intensity Modulator/Direct Detection (IM/DD) optical OFDM systems, the high peak-to-power average ratio (PAPR) will cause signal impairments through the nonlinearity of modulator and fiber. In this paper, a joint PAPR reduction technique based on Hadamard transformation and clipping and filtering using DCT/IDCT transform has been proposed for mitigating the impairments in IM/DD optical OFDM system. We then experimentally evaluated the effect of PAPR reduction on the bit error rate (BER) performance and the results show the effectiveness of the proposed technique. At a bit error rate (BER) of 1 × 10⁻³, the receiver sensitivity of the proposed 2.5 Gb/s IM/DD optical OFDM system after 100-km standard single-mode fiber transmission has been improved by 0.8 dB, 1.3 dB and 3.1 dB for a launch power of 6.4 dBm, 8 dBm and 10 dBm respectively when compared with the classical system.     

基于复制理论降低MIMO-OFDM系统中的峰均比

到目前为止,降低MIMO-OFDM系统中所产生的较大PAPR的技术大致可以被分为三类：第一类是限幅类技术,包括限幅、峰值加窗或者峰值消除等操作;第二类是编码类技术,主要是使用补偿码,但是,以一定的开销为代价;第三类技术就是概率类技术,它利用不同的加扰序列对OFDM符号进行加权处理,从而选择PAPR较小的OFDM符号来传输。由于直接应用这些方法解决PAPR问题时,会带来很大的不便。鉴于此,文中提出一种新的理论-信号生成理论,融合在传统的编码类当中。从仿真结果来看,该方法不仅更好地保持了编码类方法原来的优势,而且极大地提高了编码效率和频谱利用率。     

Dynamic spreading code selection method for PAPR reduction inOFDM-CDMA systems with 4-QAM modulation

We present a new dynamic spreading code selection technique to obtain low peak-to-average-power ratio (PAPR) of an orthogonal frequency-division multiplexing code-division multiple-access (OFDM-CDMA) system with 4-QAM modulation for the down-link in mobile communication. In this method, initially, each user is assigned a low and a high PAPR spreading code, which allows selecting one when the system is operating. The spreading code of each user is dynamically selected so that total PAPR level of the whole user group present in the system is minimized. With the proposed technique, the PAPR level of a system with 10 users and 64 sub-carriers using 64 chip Walsh-Hadamard (WH) codes, can be limited to 15 dB while the worst case theoretical maximum could go up to 28.1 dB. Although 64 chip WH codes are employed to evaluate the performance it can be generalized to all other sets of spreading codes     

Peak to Average Power Ratio Reduction in ECMA-368 Ultra wideband Communication Systems Using Active Constellation Extension

Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) is an efficient approach for The ECMA-368 Ultra Wideband (UWB) wireless communication Standard. However, the high Peak to Average Power Ratio (PAPR) of MB-OFDM UWB signals, limits the power efficiency of the High Power Amplifier (HPA) due to nonlinear distortion. Hence the need to reduce the PAPR of MB-OFDM UWB signals. In this paper, the efficiency of some recently proposed methods including the Active Constellation Extension Approximate Gradient-Project technique (ACE-AGP) is evaluated in real ECMA-368 communication system, with the use of typical HPA models and the UWB channel models defined in IEEE 802.15.3a standard. The PAPR measure and the bit error rate (BER) are used as performance measures in this evaluation.The results indicate that the ACE-AGP algorithm introduces a significant reduction of PAPR about 6.7 dB and reduces the BER degradation in all UWB channel models with different data rates.     

Transforming the Statistical Distribution of Wireless OFDM Signal for PAPR Reduction

To reduce the high peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signal, a novel nonlinear companding transform (CT) scheme is proposed in this paper. This scheme can reallocate both the amplitude/power as well as statistical distribution of the companded signal more reasonably and flexibly than existing CT methods with low computational complexity. By choosing an appropriate companding parameter, it can provide more effective PAPR reduction but at the price of a minimal amount of bit-error-rate (BER) performance degradation caused by the companding distortion. The closed-form expressions including the achievable PAPR gain, signal attenuation factor, and corresponding selection criteria for the companding parameter were derived. Computer simulations demonstrate that the scheme significantly improves the overall performances of OFDM system in terms of PAPR, BER and bandwidth efficiency under the multipath fading channel or with the high power amplifier.

     

Performance Analysis of Parallel Concatenation of LDPC Coded SISO-GFDM System for Distinctive Pulse Shaping Filters using USRP 2901 Device and its Application to WiMAX

The increasing demand for high data rates requires channel error control codes for the upcoming fifth generation. This article presents an investigation of the parallel concatenation of low-density parity-check codes (PC-LDPC) in the fifth generation proposed waveform candidate called generalized frequency division multiplexing (GFDM). PC-LDPC codes are obtained by dividing the long and high complexity single LDPC codes into small two lower complexity codes, and these designed codes are applied to the 5G-GFDM waveform. Since the GFDM signal transmits data in both the time and frequency domain, these PC-LDPC codes can deal with two-dimensional errors. This channel coded GFDM system is integrated into Universal software radio peripheral (USRP) device for real-time implementation. The Attainment of the proposed transceiver is verified by computation of BER under distinctive channel coding techniques like convolutional, Golay, Bose-Chaudhuri-Hochquenghem (BCH), extended length single LDPC code. The different pulse shaping filters such as Raised Cosine (RC), Root Raised Cosine (RRC), Gaussian, and Xia 4th order filter are applied to the GFDM under the Gaussian noise and Rayleigh fading channel to compute Out of band (OOB) power. The PC-LDPC coded GFDM outperforms LDPC by 6.5 dB in the RRC filter for roll-off factor rate 0.5 under the Rayleigh fading channel. PC-LDPC code outperforms LDPC code with a coding gain of 2 dB was observed in IEEE 802.16 Transceiver.

     

Energy efficient VLSI decoder chip with reduced PAPR in FECG monitoring

ABSTRACT

Medical data transmission is a major challenge in wireless communication to preserve their integrity and coherence. Orthogonal frequency division multiplexing (OFDM) has emerged as a modulation scheme that can achieve high data rates over frequency selective fading channel by multipath effects. As the foetal ECG (FECG) signal is large to process, the dimensionality of the data is reduced by linear discriminant analysis (LDA) and is then sent through the space time block coded (STBC) multiple input multiple output (MIMO) upon using cockroach swarm pptimisation algorithm as a classifier to demarcate the FECG signal from noise. This paper also proposes decoder design for STBC transmission over frequency-selective time-variant channels with data recovery at the receiver by using proposed error prediction and correction adders (EPD) to achieve reduced peak to average power ration (PAPR). The simulation results prove that the PAPR reduces by 1.3 dB and the sensitivity of classifier is 96.4%. The implementations are carried out over 200 data sets taken from MIT-BIH arrhythmia using simulation tools such as MATLAB 2013b, ModelSim 10.0b and Cadence Virtuoso under 65 nm. The finally fabricated and tested decoder chip consumes an average power of 0.64 µW.