Combining discrete cosine transform with clipping for PAPR reduction in intensity-modulated OFDM systems

In this paper, the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signal is reduced by combining the discrete cosine transform (DCT) with clipping in optical intensity-modulated direct-detection (IM/DD) OFDM systems. First, the data are transformed into new modified data by DCT. Second, the proposed scheme utilizes the clipping technique to further reduce the PAPR of OFDM signal. We experimentally demonstrate that the optical OFDM transmission system with this proposed scheme can achieve significant performance improvement in terms of PAPR and bit error rate (BER) compared with the original optical OFDM systems.     

A post-coding scheme for peak-to-average power ratio reduction in intensity modulated optical OFDM systems

An efficient post-coding strategy is proposed in this letter to reduce the peak-to-average power ratio （PAPR） of orthogonal frequency division multiplexing （OFDM） signals for optical intensity modulated direct detection （IM/DD） systems. The post-coding scheme based on discrete cgsine transform （DCT） is employed after the inverse fast Fourier transform （IFFT） in the transmitter to reduce the PAPR of OFDM signals. This method is different from the conventional pre-coding scheme which is employed before IFFT operation. Numerical simulations demonstrate that the new DCT post-coding strategy can significantly reduce the PAPR than the conventional pre-coding scheme. Meantime, the bit error rate （BER） performance of the proposed post-coding system can be improved compared with the conventional pre-coding scheme.     

Experimental evaluation of the BER performance in optical OFDM system based on discrete Hartley transform precoding

We experimentally assess the bit error rate （BER） performance of an intensity modulation/direct detection （IM/DD） optical orthogonal frequency division multiplexing （OFDM） system based on discrete Hartley transform （DHT） precoding in single-mode fiber （SMF） link for 2.5 Gbit/s quadrature phase shift keying （QPSK） OFDM symbol rate. The experimental results show that for the optical OFDM system based on DHT-precoding, the receiver sensitivity at the BER of 10-4 after 100 km SMF transmission is about 1.5 dBm better than that of the original QPSK OFDM signal, and the DHT-precoded OFDM QPSK signal can achieve approximately 1.3 dB of peak-to-average power ratio （PAPR） reduction.     

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.     

Hartley变换OFDM调制的可见光通信研究

针对正交频分复用(OFDM)可见光通信系统中存在高峰均功率比的问题，将预编码与迭代限幅滤波技术相结合应用于Hartley变换OFDM调制的可见光通信系统中，并对传统的采用FFT/IFFT限幅滤波的OFDM系统进行改进。根据建立的FHT的可见光OFDM系统模型，分别比较了不同方案下系统的频谱利用率、PAPR和误码率等性能，并分析了离散余弦变换和Hadamard矩阵预编码对PAPR的抑制作用以及FFT/IFFT、DCT/IDCT和FHT/IFHT三种不同变换方案的滤波性能。结果表明:FHT的可见光OFDM系统比FFT的OFDM系统的计算复杂度低、频谱利用率高；DCT预编码技术在克服系统PAPR及提升系统误码性能上更具优势；FHT/IFHT迭代限幅滤波的误码性能优于FFT/IFFT和DCT/IDCT。      

Novel multi-band DFT-spread OFDM-PON systems based on intensity modulation and direct detection for cloud computing

Passive optical network (PON) has become a preferable access technique for cloud computing due to its elastic bandwidth capacity and transmission stability. In particular, the orthogonal frequency division multiplexing PON based on intensity modulation and direct detection (IM/DD OFDM-PON) has gained extensive attention since it is a cost- and spectral-efficient system, while for the traditional IM/DD OFDM-PON, the use of OFDM could lead to the high peak-to-average power ratio (PAPR), and it is impossible to satisfy the different QoS degrees required by ONUs under a cloud environment. Thus in this paper, we design a novel multi-band discrete Fourier transform (DFT)-spread IM/DD OFDM-PON. The DFT-spread is utilized to reduce the PAPR; meanwhile, a multi-band power allocation and bit loading are achieved to satisfy the different degrees of QoS requirement owned by ONUs. The simulation results show that our system has the better performance of PAPR reduction compared with the traditional IM/DD OFDM-PON; meanwhile, the different QoS degrees of all ONUs are guaranteed.     

Hadamard precoding for PAPR reduction in optical direct detection OFDM systems

The high peak-to-average power ration (PAPR) values of optical orthogond frequency division multiplexing (OFDM) signal limit the system nonlinear tolerance (NLT). In this paper, a novel method based on Hadamard precoding is proposed to reduce the peak-to-average power ratio in optical direct detection OFDM system. The proposed scheme is successfully applied to an experimental system of optical direct-detection OFDM signal transmission through fiber. In this experiment, the 2.5 Gbit/s binary phase shift keying (BPSK) optical OFDM signals with Hadamard precoding are generated and transmitted though a single mode fiber. The experimental results show that the proposed scheme can reduce PAPR by almost 1.5 dB. Meantime the received sensitivity is improved by 2 dB with 100 km fiber transmission compared with that of an ordinary optical direct detection OFDM system.     

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.     

Peak‐to‐average power ratio reduction in space–time coded MIMO‐OFDM via preprocessing

In this paper, we propose a trellis exploration algorithm based preprocessing strategy to lower the peak‐to‐average power ratio (PAPR) of precoded MIMO‐OFDM. We first illustrate the degradation in PAPR due to optimal linear precoding in MIMO‐OFDM systems. Then we propose two forms of multi‐layer precoding (MLP) schemes to reduce PAPR. In both schemes, the inner‐layer precoder is designed to optimize system capacity/BER performance. In the first MLP scheme (MLP‐I), a common outer‐layer polyphase precoding matrix is employed. In the second MLP scheme (MLP‐II), data stream corresponding to every transmit antenna is precoded with a different outer‐layer polyphase precoding matrix. Both outer‐layer precoders are custom designed using the trellis exploration algorithm by applying the aperiodic autocorrelation of OFDM data symbols as the metric to minimize. Simulation results indicate that both MLP schemes show superior PAPR performance over conventional MIMO‐OFDM with and without precoding. In addition, MLP better exploits frequency diversity resulting in BER performance gains in multi‐path environments. Copyright © 2010 John Wiley & Sons, Ltd.     

VLM Precoded SLM Technique for PAPR Reduction in OFDM Systems

Orthogonal frequency division multiplexing (OFDM) is perhaps the most spectrally efficient, robust transmission technique discovered so far for communication systems, and it also mitigates the problem of multipath environment. High peak-to-average power ratio (PAPR) has always been a major drawback of the OFDM systems. In this article, a new precoding technique has been proposed based on Vandermonde-like matrix (VLM) and selective mapping (SLM) to reduce PAPR in OFDM systems. VLM precoding reduces the autocorrelation of the input sequences while SLM takes an advantage of the fact that the PAPR is very sensitive to phase shifts of the signal. The main advantage of this proposed scheme is to achieve a significant reduction in PAPR without increasing the system complexity. Computer simulations show that, the proposed method outperforms the existing precoding techniques without degrading the error performance of the system.     

Hybrid Zadoff‐Chu and multilateral piecewise exponential companding transform–based PAPR reduction technique in OFDM systems

The orthogonal frequency‐division multiplexing (OFDM) is a multicarrier modulation system that is used to transmit the large volume of data to the receiver. Reducing the peak‐to‐average power ratio (PAPR) in OFDM system is one of the demanding and crucial task in recent days. For this reason, various precoding and companding mechanisms are developed in the traditional works, but it remains with the limitations of increased complexity, reduced performance, and nonlinear distortion. The reduction of PAPR is achieved by minimizing the companding distortion with the enhancement of the bit error rate (BER) performance significantly. Then, in order to avoid clipping in OFDM, a multilateral piecewise exponential companding transform (MPECT) method has been utilized rather than using piecewise exponential companding transform (PEC) where PAPR is getting reduced. The OFDM is very sensitive to synchronizing error. To overcome this sensitivity, employ the Zadoff‐Chu sequence to carrier frequency offsets. Zadoff‐Chu matrix transform (ZCMT) has numerous merits among the other ODFM systems such as the improvement in the performance of the channels that are fading away and provides an ideal periodic autocorrelation and a constant magnitude periodic cross correlation. Both of these techniques provide improvement in the ODFM systems. To get more efficiency, this paper aims to develop a hybrid technique by integrating the ZCMT and MPECT techniques for reducing the PAPR in OFDM systems. Further, convolutional encoding is applied for better BER and PAPR. The simulation results of the proposed ZCMT‐MPECT technique are evaluated and compared with the conventional OFDM and other precoding methods.     

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 ratio reduction of a hidden training sequence‐aided precoding scheme for MIMO‐OFDM

We analyze a peak‐to‐average power ratio (PAPR) reduction property based on a hidden training sequence‐aided precoding scheme for MIMO‐OFDM systems. In addition to the benefits of a hidden training sequence‐aided precoding scheme such as improvement in bandwidth efficiency and frequency diversity gain, we address that power amplifier efficiency can be improved without any additional complexity burden. By mathematically analyzing PAPR of the precoded MIMO‐OFDM signal with a hidden training sequence, we demonstrate that PAPR reduction can be obtained by varying the allocated power to the hidden training sequence. Because of the low PAPR property of this scheme, it is possible to utilize a low‐cost power amplifier, resulting in the reduction in the total cost for hardware implementation. Copyright © 2014 John Wiley & Sons, Ltd.     

电力线通信中降低峰均比的有效方法

针对应用于低压电力线通信的OFDM系统具有较高的峰均比的特点,本文通过比较已有的降低峰均比的技术,提出了一种预编码与压扩技术相结合的改进方案,给出了其实现方法,并通过建立的电力线信道仿真平台,对其进行了仿真.仿真结果表明所提算法能够改善信号的峰均比,减小误码率.     

A Modified SLM Scheme With Low Complexity for PAPR Reduction of OFDM Systems

In this paper, we propose a new peak-to-average power ratio (PAPR) reduction scheme of orthogonal frequency division multiplexing (OFDM) system, called a modified selected mapping (SLM) scheme, which considerably reduces the computational complexity with keeping the similar PAPR reduction performance compared with the conventional SLM scheme. The proposed scheme is analytically and numerically evaluated for the OFDM system specified in the IEEE 802.16 standard. For the OFDM system with 2048 subcarriers, the proposed scheme with 4 binary phase sequences can reduce the complex multiplications by 63.5% with the similar PAPR reduction compared with the SLM scheme with 16 binary phase sequences.     

单载波大规模MIMO频域预均衡与波束成型的联合设计

本文考虑了单载波频域预处理技术作为多用户大规模MIMO下行链路通信的传输方案。首先,根据系统模型推导出宽带多用户大规模MIMO下行链路预编码的形式,其中包括匹配滤波(MF)和迫零(ZF)预编码方案。随后,通过理论推导和仿真验证得到两种预编码方案下OFDM与SC-FDP的用户和速率表达式,结果显示SC-FDP在大规模MIMO场景下拥有与OFDM相似的用户和速率。然后,通过仿真实验对比OFDM与SC-FDP的峰均比(PAPR),结果表明在用户数目较少的情况下,SC-FDP相对于OFDM具有更小的PAPR,随着用户数增加,两者之间差异逐渐减小。最后,对多用户MIMO下行链路中OFDM与SC-FDP的运算复杂度进行比较,二者系统复杂度相当,而SC-FDP主要运算任务在基站端完成。基于以上比较分析,SC-FDP在宽带多用户大规模MIMO下行链路中是一种很有潜力的传输方案。      

Selective Time-Domain Filtering for Reduced-Complexity PAPR Reduction in OFDM

A new selective time-domain filtering scheme for reducing the peak-to-average power ratio (PAPR) in orthogonal frequency-division multiplexing (OFDM) systems is proposed. The proposed scheme not only relies on conventional pilot symbol channel estimation and demodulation techniques to recover the data in OFDM systems but also uses additional pilot symbols. The proposed scheme has greatly reduced complexity compared with the selective mapping (SLM) scheme and only slightly poorer performance than the SLM scheme. The new scheme achieves significant PAPR reduction at a cost of typically 0.1–0.75 dB in signal-to-noise ratio (SNR) relative to pilot symbol OFDM not having PAPR reduction.      

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。     

Analytical Performance Evaluation of a STBC Coded OFDM FSO Communication System over Turbulent Atmospheric Channel

Journal of Communications Technology and Electronics - An analytical approach is presented for an optical IM/DD system with STBC coded OFDM RF subcarrier modulation over a free space optical...     

A ZCMT Precoding Based Multicarrier OFDM System to Minimize the High PAPR

This paper presents a Zadoff-Chu matrix transform (ZCMT) precoding based multicarrier orthogonal-frequency-division-multiplexing (OFDM) system to minimize the high peak-to-average power ratio (PAPR). In the proposed system, ZCMT kernel is applied to the constellation symbols which not only reduces PAPR but also improves bit-error-rate (BER) performance. The ZCMT precoded OFDM signals allow the radio-frequency high-power-amplifier (HPA) to operate near its saturation level, thus maximize the power efficiency. Extensive computer simulations have been performed to analyze the PAPR, BER and power-spectral-density (PSD). Simulation results show that the proposed system has excellent PAPR gain and BER performance with no spectral distortion.