基于DHT的光OFDM系统PAPR抑制算法

针对光OFDM系统存在高峰均功率比(PAPR),提出了一种基于离散哈特利变换(DHT)的选择映射抑制算法。采用快速哈特利逆变换(IFHT)代替传统的快速傅立叶逆变换(IFFT)和Hermi t i an对称算法,并结合非对称限幅法产生满足光OFDM系统要求的正、实值信号送入光纤信道。     

降低OFDM系统峰均比的改进方法

正交频分复用（OFDM）系统最主要的一个缺点就是峰值平均功率（PAPR）比过高,选择性映射（SLM）虽然能无失真地降低OFDM信号峰均比PAPR,但不能完全避免OFDM系统高峰值的出现。提出一种新的算法,将SLM法与迭代限幅滤波算法结合,通过迭代限幅滤波（RCF）来进一步提高系统的性能。仿真结果表明,该方法可以在不增加系统误码率性能的基础上,在降低OFDM信号峰均比方面,比限幅法、迭代限幅滤波法和SLM法均有很大的提高。     

基于星座映射降低OFDM系统峰均功率比的新方法

降低峰均功率比(PAPR)是正交频分复用(OFDM)技术所要解决的关键问题之一,为此,提出了一种新的降低PAPR的方法——星座映射法。在发送端,对经IFFT变换后的超过最大允许范围的数据样值进行软限幅,提高了发射系统的输出功率。在接收端,根据不同调制方式所具有的不同星座分布特性,恢复出被限幅的数据样值,从而减小了由于限幅而造成的信号畸变。理论分析和仿真结果表明,新方法能够有效降低OFDM系统的峰均功率比,同时使系统获得较好的误码性能。     

基于DSP的正交频分复用的实现

在理论上推导了采用快速傅里叶逆变换/傅里叶变换(IFFT/FFT)实现正交频分复用(OFDM)调制解调的可行性,分析了采用IFFT/FFT实现OFDM调制解调比传统方法更具优势;然后在数字信号处理器(DSP)硬件平台上对采用IFFT/FFT实现OFDM调制解调进行了验证。实验结果表明:采用IFFT/FFT不仅能正确实现OFDM信号的调制解调,而且还大大简化了OFDM系统结构,降低了系统实现难度,节约了成本。     

基于FPGA技术实现的OFDM基带调制系统

OFDM基带调制的目的是将高速的串行数据流转换成并行的低速数据流,再调制到频谱是正交重叠的子载波上进行传输,以便于提高频谱利用率。OFDM可以采用IFFT/FFT实现调制解调,在本设计中采用FPGA技术可以比较容易地实现OFDM通信系统的的调制器部分。整个系统包括RS编码、交织、QAM星座映射,IFFT和插入CP等模块,经过仿真验证:提高了系统的处理速度,具有较高的应用价值。     

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。      

基于DHT和PTS的光OFDM系统PAPR抑制算法

提出了一种基于离散哈特利变换(DHT)和部分传送序列(PTS)的PAPR抑制算法。在每个子块中,通过利用快速哈特利逆变换(IFHT)代替传统的快速傅里叶逆变换(IFFT),并结合非对称限幅技术,对子载波信号进行调制。该方法 PAPR抑制效果好,且不需要Hermitian对称,运算复杂度低。     

面向5G三大应用场景的F-OFDM系统PAPR抑制算法研究

曾作为5G候选波形技术的基于子带滤波的正交频分复用(Filtered-Orthogonal Frequency Division Multiplexing,F-OFDM)是基于正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)发展而来的,和OFDM一样存在峰值平均功率比(Peak to Average Power Ratio,PAPR)的问题。高PAPR的信号在发送时对系统功率放大器的性能要求很高,容易发生信号失真,并且会直接影响整个系统的运行成本和效率。为了提高F-OFDM系统在5G三大应用场景中的PAPR抑制性能,引入一种基于迭代限幅滤波的次优PTS抑制算法。该算法主要分为两个过程,先对F-OFDM系统的各子带的高PAPR值信号进行线性抑制,然后待各子带的信号经过各自的数字子带滤波器合并后再进行迭代限幅滤波处理,从而完成对F-OFDM信号PAPR的抑制。仿真表明,该算法相对于单独使用次优PTS算法或迭代限幅滤波算法,能提高F-OFDM系统的PAPR抑制性能。     

OFDM系统中多导频的FFT信道估计算法

论文提出了OFDM系统中基于FFT的信道估计方法,包括基于时域插值及变换域插值方法。时域插值算法的理论基础是利用FFT频域采样定理,可由频域有限频点的采样值经过IFFT／FFT得到整个频域传输函数的估计值,而不发生混叠。变换域插值算法的理论基础是利用FFT时域抽样定理,利用OFDM信号特点和信道特性,经过FFT／IFFT将信号和噪声分离,并在此基础上进行加窗改进算法,以减小插值中的频谱泄漏,提高估计效果。仿真结果说明,加窗的基于FFT变换域的方法性能有了很大改善。     

降低OFDM系统PAPR的低复杂度ACE-C算法

针对现有凸集映射星座扩展算法(ACE-POCS)在OFDM信号峰均功率比(PAPR)抑制过程中存在收敛速度慢、复杂度高等问题,提出一种基于ACE-POCS算法与限幅算法(Clipping)的ACE-C算法。新算法通过对输入数据序列进行分组处理,使得在运算过程中只进行低点数的IFFT和FFT变换,有效降低了运算复杂度。在4QAM调制的OFDM系统模型中对新算法的PAPR、复杂度及误码率(BER)性能进行研究分析,结果表明,与ACE-POCS算法相比,ACE-C算法的复杂度减小了1/2以上,收敛速度也得到了一定的提高,且不需要传送边带信息,实现了在PAPR抑制效率、复杂度、误码率三方面性能的折中。     

Grouped DCT precoding for PAPR reduction in optical direct detection OFDM systems

A new grouped precoding technique based on discrete cosine transform (DCT) is presented for peak to average power ratio (PAPR) reduction of optical intensity modulated/direct detection (IM/DD) orthogonal frequency division multiplexing (OFDM) system. The computational complexity of the scheme is reduced by at least about 15% compared with that of the ordinary DCT precoding scheme when the number of groups is 2. The PAPR with this method can be reduced by about 0.8 dB. Meantime, compared with original OFDM, the bit error rate (BER) performance of system is improved. So the proposed scheme for reducing PAPR is very effective in optical IM/DD 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.     

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.     

基于分数阶Fourier变换减小OFDM系统PAPR的研究

介绍了基于分数阶Fourier变换的OFDM系统,给出了这种系统中经过变换后的信号的表达形式,探讨了该系统在不同的调制方式下（QAM调制和QPSK调制）使用Clipping算法降低系统PAPR的情况,并使用Matlab对不同阶数的CCDF进行了仿真。仿真结果表明,QAM调制下基于分数阶Fourier变换的Clipping算法性能不如基于傅立叶变换的Clipping算法好,而在QPSK调制方式下基于分数阶Fourier变换的OFDM系统PAPR性能比基于傅立叶变换的OFDM系统性能有了显著的提高。     

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.     

PAPR reduction for OFDM‐based visible light communication systems using proposed hybrid technique

Orthogonal Frequency Division Multiplexing (OFDM) is utilized with visible light communication (VLC) systems to decrease the impacts of inter‐symbol interference and to achieve communication with high speed of data transmission and huge bandwidth. In any case, the main problem in OFDM‐based VLC systems is high peak‐to‐average power ratios (PAPRs). This paper proposes a hybrid PAPR reduction technique based on signal transformation combined with clipping. The Hadamard transform is used in the proposed technique to reduce the PAPR without affecting the bit error rate (BER) of the VLC systems. The optimum clipping threshold at which the PAPR is reduced simultaneously with the improvement the BER of the VLC systems is also determined. The performance of the proposed system is assessed in terms of complementary cumulative distribution function and the BER. The obtained results demonstrate that the proposed procedure can simultaneously decrease the PAPR and achieve good BER performance compared to the OFDM‐based VLC system.     

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.     

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.