一种改进了的OFDM信道估计算法

有较长持续时间的正交频分复用符号对频率选择性衰落有更强的承受能力,但是对于时间选择性衰落则较为敏感,因此信道估计在正交频分复用系统中占有重要的地位.文中对正交频分复用的特点进行了概述,并根据正交频分复用本身的特性、WiMAX帧结构,提出了一种基于导频的信道估计的算法.并在SUI1-SUI6信道环境下,用MATLAB对其性能进行了仿真.仿真结果表明,该算法的抗衰落性能有所提高,且具有一定的灵活性.     

OFDM/OQAM系统中联合迭代信道估计和信号检测

与基于复数域空间正交条件的传统正交频分复用系统(OFDM with Cyclic Prefix, CP-OFDM)有所不同,基于交错正交调制的正交频分复用系统(OFDM/Offset QAM, OFDM/OQAM)满足实数域空间严格正交条件。因此在多径衰落信道条件下,CP-OFDM系统中的信道估计方法会导致OFDM/OQAM系统严重的字符间干扰和载波间干扰。该文结合OFDM/OQAM系统结构特点,提出了一种基于迭代信道估计和信号检测算法。该算法通过信道估计器和接收到的信号互相交换信息,消除导频序列中的字符间干扰和载波间干扰,提高信道估计和信号检测的准确度。仿真分析结果表明,经过一定次数迭代处理后,OFDM/OQAM迭代信道估计性能趋近于理想信道估计性能。     

SFBC-OFDM系统在时频双选信道下的迭代接收算法

基于广义最小信道估计算法,结合迫零均衡原则,针对空频块码正交频分复用系统,提出了一种迭代的均衡广义最小接收算法.该方法推导了两发两收空频块码正交频分复用系统的迫零频域均衡算法,以便消除信道频率选择性衰落所引起的系统相邻子载波间信道系数的差异,从而保证了空频块码的正交性,使得接收算法能够有效抑制差错传播、明显加快迭代的收敛速度并改善系统的比特误码性能.数值仿真结果表明:当归一化多普勒较大时,采用该接收算法的空频块码正交频分复用系统能够较快地收敛,并较基于期望最大化的空频块码正交频分复用系统与基于时域卡尔曼的空烦块码正交频分复用系统分别获得8 dB和14,dB的增益.     

移动OFDM系统中子信道干扰及其均衡算法

移动衰落信道中正交频分复用(OFDM)系统的子信道干扰(ICI)是引起系统性能下降的主要因素。本文分析了ICI对系统性能的影响,结果表明子信道干扰取决于信号能量E_s,子信道数N,和多普勒频移f_d,与信号星座无关。为了消除ICI,我们提出一种基于Jacobi迭代方法的均衡算法。考虑到子信道干扰主要影响相邻子信道的实际情况,兼顾系统性能和算法复杂性,进一步提出改进算法。文章最后给出16QAM调制的OFDM系统性能的仿真结果。     

BICM-OFDM系统中基于叠加导频的迭代信道估计

传统叠加导频算法应用在正交频分复用系统中存在信道估计精度差的缺点。针对比特交织编码调制（BICM）联合正交频分复用（OFDM）的系统（BICM—OFDM）,提出一种利用叠加导频的迭代信道估计算法。该算法充分利用了均衡器的反馈信息,分两步进行。首先,导频信号叠加在发送信号上,接收端采用一阶统计量进行初始信道估计;然后利用均衡器的硬判决反馈信息,在信道估计与均衡之间进行信息交换,通过迭代的方式提高信道估计精度。在短波宽带信道下的仿真结果表明,与传统叠加导频算法相比,新算法经过二次迭代可有效提高信道估计精度和系统误码率性能。     

一种改进的正交频分复用信道同步估计算法

针对当前正交频分复用系统的同步算法检测正确率低、计算复杂度高的难题,提出一种改进正交频分复用信道同步估计算法。首先对正交频分复用的工作原理进行分析,并构建加权的横幅零自相关特性序列,然后分别对OFDM系统定时和频偏同步进行估计,最后采用具体实例对算法的性能进行测试。测试结果表明,相对于当前经典同步算法,本文算法降低了定时同步估计误差,提高了检测正确率,提高了系统的通信性能。     

电力线OFDM/OQAM通信系统信道相位预处理均衡算法

针对电力线通信（PLC）正交频分复用（OFDM）系统存在频率掩码和频谱资源利用率低等问题,提出将正交频分复用/偏移正交幅度调制（OFDM/OQAM）技术应用到PLC系统中。该技术通过选用频率选择性较好的滤波器来抑制带外干扰,且不需要循环前缀,但是OFDM/OQAM系统在PLC频域复数信道下会产生严重的自干扰,传统的均衡算法并不能有效地消除OFDM/OQAM系统的固有干扰。针对这种情况提出了一种基于信道相位预处理的均衡算法。该算法的思想是让接收信号乘以一个信道相位调整因子,使等效信道的虚部尽量小,以此来减小接收信号中的干扰分量。仿真结果表明,与传统的均衡算法相比,所提算法在误比特率为1.0×10－6时可以获得0.5dB的性能提升。     

OFDM中基于导频的加窗FFT信道估计

正交频分复用（OFDM）是一种正交的多载波复用技术,分析了OFDM系统中基于导频的信道估计模型;基于导频的信道估计需要进行插值,为了降低插值算法的复杂度,研究了基于导频的FFT信道估计算法。由于直接FFT信道估计算法存在能量频谱泄露问题,提出了基于汉明窗函数的优化型加窗FFT信道估计的算法。实验仿真表明：在多径衰落信道下,该算法能够有效地提高OFDM系统的信道估计性能。     

基于PIC的多载波系统联合检测译码算法

针对多入多出—正交频分复用（MIMO-OFDM）信号检测问题,基于并行干扰抵消技术提出了一种编码MIMO-OFDM系统联合检测与译码算法,通过在干扰抵消检测器和信道译码器之间传递判决信息提高系统的误比特率性能。计算机仿真表明,该算法获得的误码率性能较传统的迫零检测以及V-BLAST检测算法有了较大的提升。     

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。     

Semidefinite programming detection for OvHDM signal

Non-orthogonal time-frequency division multiplexing （NTFDM） transmission scheme has been proposed to further improve the bandwidth efficiency and overcome the drawbacks of the conventional orthogonal frequency division multiplexing （OFDM） method. Based on such approach, the fast signal detection algorithm, semidefinite programming （SDP） detection, has been studied. As the coefficient matrix tends to be ill conditioned, the modified SDP algorithm combined with successive interference cancellation （SIC） has been developed. The improved algorithm is a good tradeoff between performance and detection complexity. Simulation results show that the proposed algorithm can achieve better performance than cutting plane aided SDP method.     

正交频分复用系统中抗线性调频干扰算法研究

针对基于离散傅立叶变换的正交频分复用系统(OFDM),提出了一种新的线性调频(LFM)干扰抑制算法。该算法分为两部分:干扰估计和干扰重构抑制。干扰估计时,首先采用离散傅立叶变换进行粗略估计,然后采用离散匹配傅立叶变换进行精确估计,整个过程均可共用傅立叶变换单元,有效地节省了系统资源。实验结果表明:该算法的干扰抑制性能良好;与现有的抗线性调频干扰算法相比,其运算复杂度大为降低,具有很好的工程实用性。     

Effects of Phase Noise on OFDM Systems With and Without PLL: Characterization and Compensation

In this paper, we propose an algorithm for suppressing intercarrier interference due to phase noise in coded orthogonal frequency division multiplexing (OFDM) systems. The algorithm approximates the phase-noise waveform by using a Fourier series approximation for the current phase-noise realization. Thereby, it cancels the effects of the phase noise beyond the standard common phase error correction used in contemporary OFDM standards. The algorithm requires that the correlation properties of the intercarrier interference are known. We calculate these properties in terms of the phase-noise spectral correlation matrix for both Wiener and Ornstein-Uhlenbeck phase-noise models, respectively. This modeling corresponds to a free-running oscillator, as well as a phase-locked loop realization of the local oscillator in orthogonal frequency division multiplexing transceivers. For both transceiver configurations, we investigate the performance of the proposed algorithm. It is demonstrated that the new algorithm achieves as much as one order of magnitude better performance in terms of packet/bit error rate when compared to a receiver with only the common phase error suppression.     

非正交频分复用系统的无干扰分离算法

针对现有的非正交频分复用信号分离算法复杂度高这一问题,提出了对多路非正交频分复用信号可以实现无干扰分离的简化算法,通过建立系统模型和理论推导,使用傅里叶变换降低了非正交频分复用信号接收机的复杂度.系统仿真结果表明,使用非正交频分复用技术可以在更小的带宽内传输与OFDM相同速率的信号;在传输速率相同的情况下,由于传输带宽的减小,引入传输系统的噪声功率得到了降低,最终使得接收机处的误码率变小.     

Construction of block orthogonal golay sequences and application to channel estimation of mimo-ofdm systems

In this paper, we construct a family of block orthogonal Golay sequences that have low peak-to-mean envelope power ratio (PMEPR) as well as block wise orthogonal properties. We then present an application of the sequences to channel estimation of multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. We compare the performance of the proposed algorithm with that of a frequency division multiplexing (FDM) piloting algorithm, and investigate the effect of co-channel interference (CCI) on the channel estimation performance.     

时频双选信道OFDM系统的ICI消除与均衡

在正交频分复用（OFDM）系统中,因高速移动造成的多普勒效应导致子载波间正交性的破坏并产生载波间干扰（ICI）。为了消除ICI,本文通过分析ICI分布特性及带状矩阵特性,提出了低复杂度的迭代干扰抵消算法和基于最小均方误差准则的排序串行干扰抵消(MMSE-OSIC)算法。仿真结果表明,与传统子载波间干扰频域均衡算法相比,新算法在计算复杂度和性能之间取得了良好的平衡,且MMSE-OSIC算法可以利用时变信道的时间分集特性在高信噪比情况下有效地消除“地板效应”。      

Orthogonal spectral precoder for minimizing adjacent channel leakage ratio in OFDM based cognitive radio

One of the major drawback of an orthogonal frequency division multiplexing based cognitive radio is high out‐of‐band leakage that can severely affect primary users operating in adjacent bands. The paper aims to design a new spectral precoding scheme that minimizes Adjacent Channel Leakage Ratio (ACLR) while retaining the orthogonality among data symbols. The problem is formulated as trace ratio minimization subjected to unitary constraint that can be effectively solved using iterative methods. The proposed precoder's error performance is similar to uncoded orthogonal frequency division multiplexing system due to orthogonal multiplexing. Also, it is practically realizable due to lower complexity. The scheme also extends for distinct ACLR requirements in upper and lower adjacent bands. A relative important factor is introduced so as to flexibly control the interference leakage in upper and lower adjacent channels. An algorithm is suggested for choosing suitable values of this factor. Simulation results display the superiority of proposed scheme over existing techniques in terms of ACLR and throughput. Copyright © 2016 John Wiley & Sons, Ltd.     

Application of jacobi algorithm for ISI channels

Here, the Jacobi iterative algorithm is applied to combat intersymbol interference (ISI) caused by frequency-selective channels. The performance bound of the equaliser is analysed in order to gain an insight into its asymptotic behaviour. Because of the error propagation problem, the potential of this algorithm is not reached in an uncoded system. However, its extension to a coded system with the application of the turboprocessing principle results in a new turbo equalisation algorithm, which demonstrates comparable performance with reduced complexity compared with some existing filter-based turbo equalisation schemes; and superior performance compared with some frequency domain solutions, such as orthogonal frequency division multiplexing and single-carrier frequency domain equalisation.     

基于EBSBL-BO算法的L-DACS系统干扰抑制方法

L频段数字航空通信系统（L-band digital aviation communication system,L-DACS） 是未来面向航路阶段的空地数据链路,其工作频段部署在两个测距仪（distance measure equipment,DME）工作频段之间,为了消除测距仪产生的高功率脉冲信号对L-DACS系统前向链路正交频分复用接收机的干扰,本文提出基于扩展稀疏贝叶斯-边界优化（extended block sparse Bayesian learning-boundary optimization,EBSBL-BO）算法的高功率DME脉冲干扰抑制方法。首先,利用L-DACS系统正交频分复用接收机的空子载波建立DME干扰信号压缩感知模型;然后,基于EBSBL-BO算法对DME信号进行重构;最后将高功率DME脉冲信号在时域消除。仿真结果显示:本文算法与其他稀疏贝叶斯重构算法相比,本文算法DME脉冲信号重构精度更高,正交频分复用接收机误码率更低,可有效改善L-DACS系统正交频分复用接收性能。      

Parallel interference cancellation for carrier frequency offset in OFDM assisted with recursive least squares algorithm

Parallel interference cancellation (PIC) assisted with recursive least squares (RLS) algorithm is proposed to cancel the interference due to the carrier frequency offset (CFO) in orthogonal frequency division multiplexing (OFDM) system. The proposed algorithm is composed of two stages, which are RLS scheme and PIC scheme. RLS scheme is selected to compensate the frequency offset in the time domain in the first stage, and the interference induced by residual frequency offset is canceled by the PIC scheme in the frequency domain in the second stage. The result of bit error rate (BER) shows that its performance is robust for cancellation as comparison criteria, even though the frequency offset is 0.45. The 16QAM constellation is also simulated to observe the improvements from the proposed suppression schemes.