CO-OFDM传输系统相位噪声估计

从理论上分析了激光器相位偏移对相干光正交频分复用(CO-OFDM)系统传输性能影响,并指出相位噪声是相干光OFDM主要噪声源。在传统无线OFDM信道估计基础上,提出了一种基于导频子载波的相位噪声估计和补偿方法,在OptiSystem中建立CO-OFDM系统仿真模型,通过仿真证明了该方法可以有效地改善CO-OFDM系统传输性能。     

CO-OFDM系统中一种基于空载波间隔的新相位噪声补偿算法

针对激光器的相位噪声会严重影响相干光正交频分复用(CO-OFDM)系统的性能问题,基于空载波间隔提出了一种适用于CO-OFDM系统的新相位噪声补偿算法,通过空载波来间隔信息子载波,从而有效降低载波间干扰并提高有效信息干扰比.仿真结果表明:与最小平方准则-公共相位误差(LS-CPE)算法相比,该补偿算法能有效地改善系统的误码性能,降低系统对激光器线宽的要求.     

基于DCT正交基的相位噪声均衡法

相位噪声是困扰OFDM通信系统的问题之一，它会破坏系统子载波之间的正交性，从而引起载波间干扰（ICI），降低系统性能。为此，提出一种时域的相位噪声均衡算法。仿真结果表明它具有良好的性能。     

概率整形相位共轭孪生波OFDM WDM系统IQ不平衡研究

为探究IQ不平衡产生机理，结合偏振复用（PDM）、16进制正交幅度调制（QAM）、相位共轭孪生波（PCTW）、正交频分复用（OFDM）、波分复用（WDM）等技术，采用Opti System软件搭建了PCTW-OFDM-WDM系统，分析了概率整形、串扰、统计相关噪声引起IQ不平衡的机理。理论分析和仿真结果表明：IQ不平衡是由多种因素造成的，只有过大的IQ不平衡才会对系统性能产生较为明显的影响；几何整形方案对系统IQ不平衡和性能改善的作用有限；在时隙和子载波PCTW模式下，适当地改变共轭分量的分布位置可有效改善IQ不平衡，并获得比相邻结构更好的传输性能表现。     

零前缀OFDM中智能反射表面环境下干扰抑制算法研究

在智能反射表面(RIS)场景下的零前缀正交频分复用(ZP-OFDM)系统中由于反射元件系数转换引起的等效信道时变,其破坏了正交频分复用(OFDM)系统的正交性并产生严重的子载波间干扰(ICI)。该文通过构建该场景下的系统传输模型,通过分析ICI功率和对反射元件系数转换时变特性进行建模,利用构建子载波间干扰抑制矩阵对ICI进行补偿,抑制由于反射系数变化造成的等效时变信道对系统性能的影响。仿真结果表明,子载波间干扰得到了有效抑制,该文提出的干扰抑制算法对于系统的传输性能有较明显的提升。     

快衰落信道下OFDM系统的信道估计简化算法

在快衰落时变信道中，正交频分复用（OFDM：Orthogonal Frequency Division Multiplexing）系统子载波间的正交性会遭到破坏，由此引起的载波间干扰（ici：Inter-Carrier Interferellce）会对系统性能带来很大的影响。本文提出了一种利用时域线性模型的信道估计算法，利用随时间线性变化的模型描述信道。仿真结果表明，本算法能够有效地消除载波间干扰，降低系统的BER。与类似算法相比，当系统的BER性能相同时，算法复杂度大大的降低。     

针对DTMB-A系统的相位噪声消除算法

相位噪声会破坏OFDM (Orthogonal Frequency Division Multiplex) 符号内频域子载波的正交性,产生公共相位误差（CPE, Common Phase Error）和子载波间干扰（ICI, Inter-Carrier Interference）,对系统性能造成严重影响。针对数字电视地面广播传输标准演进方案（DTMB-A）的相位噪声问题,本文提出了一种两步结合的相位噪声估计和消除算法。首先,利用相邻两帧的帧头符号中所包含的PN（Pseudo Noise）序列,对帧体符号内的公共相位误差进行粗估计;随后,对帧体数据子载波进行标记,选取合适的子载波集合用于估计公共相位误差和子载波间干扰的精确结果。由此获得相位噪声频域估计结果后,通过快速傅立叶变换（FFT, Fast Fourier Transform）得到时域估计结果并进行消除。和现有基于判决反馈的相位噪声估计算法对比,本文所提算法的创新性在于采用了粗估计和精确估计结合的方法,同时利用子载波标记的方法有效降低了由于错误判决导致的误码扩散。仿真结果表明在现有算法已经不能正常工作的情况下,本文所提算法还可以有效的抑制相位噪声对系统性能的影响。      

MIMO-OFDM系统中相噪公共相位误差的分析与抑制

随着无线通信频段的不断提高,非理想载波所引入的相位噪声对多输入多输出正交频分复用(MIMO-OFDM)系统性能的影响也越来越突出,不仅影响OFDM系统载波的正交性,同时导致多天线预编码性能急剧下降。相位噪声对MIMO-OFDM系统的影响可分为公共相位误差(CPE)和载波间干扰(ICI)两部分。本文对CPE影响MIMO-OFDM系统的性能进行深入分析,提出一系列基于频域正交导频设计的CPE估计算法,以实现对CPE的有效抑制;最后,在多个场景下进行链路仿真,充分验证了提出算法的有效性和可靠性。     

OFDM中联合IQ不平衡和相位噪声估计补偿新算法

正交频分复用(OFDM)系统中的非理想特性对系统性能影响很大,针对非理想特性中的两个主要部分:同相支路和正交支路(IQ)间的不平衡及相位噪声,提出了一种新的相位噪声和IQ不平衡联合估计算法。该算法首先由一个训练符号利用简单的最小二乘(LS)准则在频域估计出IQ不平衡和相位噪声的复合参数,并从中分离得到IQ不平衡估计值,然后利用估计出的IQ不平衡参数在时域对数据符号做IQ不平衡补偿,最后对IQ不平衡补偿后的数据在频域做相位噪声公共相位误差(CPE)和子载波间干扰(ICI)的估计和补偿。理论分析和仿真结果表明,该算法能简单有效的补偿IQ不平衡和相位噪声带来的性能损失。     

载波频偏对OFDM系统的影响分析及仿真

正交频分复用(OFDM)是4G通信中的关健技术之一,主要依靠各子载波之间的正交性实现高速传输。但OFDM对载波频偏(CFO,Carrier Frequency Offset)非常敏感,很小的频偏就会引起信道间的干扰(ICI)。从理论上分析了载波频偏产生信道间干扰的过程,重点研究了CFO对OFDM性能的影响,并对相关结论进行了仿真验证。     

Analysis of ICI cancellation scheme in OFDM systems with phase noise

Phase noise in orthogonal frequency division multiplexing (OFDM) systems destroys the orthogonality of the subcarriers and inter-carrier interference (ICI) is caused. In this paper, the ICI self-cancellation scheme is adopted to combat the ICI caused by phase noise in OFDM systems. Moreover, the error coefficients are defined and the theoretical expressions of carrier to interference ratio (C/I) with and without the ICI self-cancellation scheme are separately derived. From the simulation results, it is verified that the ICI self-cancellation scheme obviously decreases the amount of the ICI caused by phase noise and the improvement of C/I could reach 10 dB when the normalized 3 dB bandwidth of phase noise is 0.4. However, the convolutional coding OFDM (COFDM) system could supply more performance gain at the expense of increasing decoder complexity compared to OFDM system with the ICI self-cancellation scheme in the frequency-selective channel.     

A phase noise suppression algorithm for OFDM-based WLANs

Orthogonal frequency-division multiplexing (OFDM) has been specified by the IEEE 802.11a standard as the transmission technique for high-rate wireless local area networks (WLANs). The performance of an OFDM system, however, is heavily degraded by random Wiener phase noise, which causes both common phase error (CPE) and inter-carrier interference (ICI). To mitigate this problem, a new phase noise suppression (PNS) algorithm is proposed to efficiently eliminate the effect of phase noise on OFDM-based WLANs. Numerical results are presented to illustrate the effectiveness of the proposed algorithm.     

Theoretical analysis of ICI self-cancellation in OFDM systems over Rayleigh flat-fading channels

Orthogonal frequency division multiplexing (OFDM) has been widely used for its robustness against multipath fading and low-complexity implementation. However, OFDM system, especially with large number of subcarriers and high modulation order, is severely affected by the phase noise of oscillators and carrier frequency offset (CFO). On the other hand, self-cancellation schemes have received a lot of attention due to their simple implementation and high efficiency to suppress inter-carrier interference (ICI) in OFDM systems. Among those ICI self-cancellation methods, symmetric conjugate symbol repetition (SCSR) has been proven to have the best bit error ratio (BER) performance for phase noise suppression. In this paper, the performance of OFDM systems with SCSR ICI self-cancellation in the presence of both phase noise (PHN) and CFO are investigated, and analytical expressions are derived to calculate error probability evaluated by symbol error ratio (SER) over additive white Gaussian noise (AWGN) and Rayleigh flat fading channels. An approach of second order approximation of PHN/CFO has been performed to estimate the residual ICI, which could provide more accurate results. Simulation results show perfect agreement with those obtained by theoretical analysis, which could be used to estimate OFDM system error probability, facilitating the design of the overall system.     

Phase Noise Correction Based on TPS Symbols for the Chinese DTTB System

In orthogonal frequency division multiplexing (OFDM) system, phase noise (PHN) from oscillator can severely reduce the performance by causing: common phase error (CPE) and inter-carrier interference (ICI). The impact of PHN on received signal can be characterized by the circular convolution of the transmitted signal and the discrete Fourier transform (DFT) of PHN signal in frequency domain. Digital television/terrestrial multimedia broadcasting (DTMB), announced as the Chinese digital television terrestrial broadcasting (DTTB) standard, adopted the time-domain synchronous OFDM system (TDS-OFDM) system which has 36 continuous transmission parameter signaling (TPS) symbols in frequency domain which be used for PHN suppression. Based on a linearized parametric model for PHN, least squared (LS) estimation and fast Fourier transform (FFT) approaching method for PHN correction are proposed in this paper. The effects of the PHN on channel estimation in both TDS-OFDM system and conventional cyclic prefix OFDM (CP-OFDM) are also investigated. Simulations show that the proposed algorithm can effectively reduce the PHN and improve the symbol error rata (SER) of TDS-OFDM systems over both additive white Gaussian noise (AWGN) and broadcasting multipath channel. In practice, the FFT-approaching method can be applied to the DTMB receiver-chip design directly with low implementation cost.      

一种针对双衰落信道OFDM的新均衡算法

在OFDM系统中，子载波间的正交性是保证OFDM性能的重要保障。针对双选择性衰落信道下的OFDM系统，该文在分析载波间干扰（ICI）的基础上，提出了一种采用频域迭代消除ICI的均衡算法。分析和仿真结果表明此方法能有效地保证载波间的正交性和改善了OFDM系统的误码率（BER）性能。     

一种适用于快衰落信道的ICI抑制方案

针对高速移动环境下多普勒频偏造成信道的快衰落和正交频分复用(OFDM)系统中子载波间干扰(ICI)的问题,提出了一种适合快衰落环境的OFDM系统子载波间干扰抑制算法。此算法用线性变化模型来近似一个OFDM符号周期内的信道冲激响应,并以此为基础采用迭代MMSE均衡方法抑制载波间干扰。分析和仿真结果表明,此方法能有效地保证载波间的正交性,从而改善了OFDM系统的误码率(BER)性能。     

Improved Nyquist-I Pulses to Enhance the Performance of OFDM-Based Systems

Wireless Personal Communications - Pulse shaping is used in orthogonal frequency division multiplexing (OFDM) based systems to reduce inter-carrier interference (ICI) power and peak-to-average...     

基于预编码设计的载频间干扰抑制

针对正交频分复用(OFDM)系统中归一化频偏所引起的载频间干扰(ICI)系数分布特点,设计了一种通用的OFDM预编码传输方案.可将ICI系数更好地集中在较少的子载波位置上,使接收端的干扰矩阵成为稀疏的矩阵,简化信号检测.从理论分析与系统仿真这2方面对这一算法进行了研究.与已有的基于均衡的ICI抑制算法相比,所建议的算法具有更低的计算复杂度;与ICI自身干扰抑制算法相比,具有更高的频带利用率.     

Analysis and Solutions for Amplitude Distortions in an OFDM Signal at Communication Receivers

This paper presents an analysis of amplitude distortions happening in an orthogonal frequency division multiplexing (OFDM) signal at communication receivers. It is shown in this paper that the amplitude distortion causes inter-carrier interference (ICI) in an OFDM system. Simple but efficient solutions are proposed for combating different amplitude distortions and subsequent ICI cancellation. Simulation results in typical urban channel and Gaussian channel show that extra gains are obtained by introducing these techniques into an existing OFDM receiver system.      

Particle filter with ant colony optimization for frequency offset estimation in OFDM systems with unknown noise distribution

Orthogonal frequency division multiplexing (OFDM) is sensitive to carrier frequency offset (CFO) that causes inter-carrier interference (ICI). In this paper, a particle filter (PF) method augmented with ant colony optimization (ACO) is developed to estimate the CFO. The ACO for continuous domains is incorporated into PF to optimize the sampling process. Unlike the standard PF, resampling is not required in the method. Moreover, it does not require the noise distribution. Simulation results show that the proposed method is effective when estimating the CFO and can effectively combat the effect of ICI in OFDM systems.