AQPSK调制系统中一种自动频偏纠正算法

在移动通信系统中,移动台(mobile station,MS)需要与基站(base station,BS)保持频率同步,因此在移动台接收机中通常都会采用自动频偏补偿机制(automatic frequency compensation,AFC)。通常情况下,AFC会根据本机晶振和频偏估计(frequency offset estimation)结果来直接调整频偏补偿值。但是,在某些信道条件恶劣的特殊场景下,FOE的结果可能存在很大错误,这种错误会导致AFC系统崩溃。本文提出一种新的自动频偏补偿算法,可以改进AFC环路控制,以抵抗恶劣信道对接收机的影响。     

一种Inmarsat卫星通信系统下行链路初始同步方法

同步技术是Inmarsat卫星通信系统的关键技术,下行链路初始同步是MES与卫星系统之间建立联系的重要一步。为实现MES快速稳定入网,提出了一种下行链路初始同步的方法。该同步方法已经在移动卫星通信终端上实现,并已商业化应用。应用结果表明,该方法稳定可靠,终端能快速注册入网,可为我国自主研制的卫星系统终端的设计和研究提供参考。     

OFDM系统上行链路的一种载波偏差估计算法

通过分析OFDM信号的特点,该文给出了OFDM系统上行链路的一种基于高倍钟采样的载波偏差估计算法.与采用循环前缀的载波偏差估计算法相比,该算法实现复杂度低,算法精度高,受用户子载波数目影响较小,适宜于多用户OFDM系统.计箅机仿真表明该算法具有优良的性能,优于采用循环前缀的载波偏差估计算法.     

一种抗频偏的定时同步方法及其性能分析

针对长序列互相关定时同步性能受频偏影响的问题,提出了一种分段频偏补偿的定时同步算法.该算法在分段互相关的基础上,使用频偏补偿替代传统的绝对值操作,在减少载波频偏对同步峰值影响的同时不增加噪声均值.理论分析和仿真结果表明,改进方法定时同步性能优于传统分段方法,适用于低信噪比大频偏的无线通信系统.     

一种基于自相关矩阵的OFDM信号同步参数盲估计算法

该文提出了利用自相关矩阵实现OFDM信号符号定时参数和频偏估计算法。该算法不需要数据辅助,通过使得接收信号自相关矩阵非对角线元素的模值之和达到最小实现分数倍频偏的跟踪,通过判断对角线元素位置发生的移动可以准确地估计整数倍频偏,同时通过使得对角线上对应虚载波位置的元素的模值之和最小实现符号同步。文中给出了算法的推导过程和具体应用的步骤。仿真结果表明该算法具有较大的估计范围以及良好的估计精度。     

LTE中小区初始搜索与主同步算法的研究

3GPPLTE系统的同步信号包括主同步信号PSS与辅同步信号SSS,用于小区搜索。时频同步是LTE系统小区搜索的基本需求,文章简单介绍了LTEFDD系统主同步序列与辅同步序列的产生、小区初始搜索流程,总结了探测LTE主同步信号PSS的几种不同方法,针对当系统频偏较大时同步性能较差这个问题,对一种改进的M．partN]步算法的性能进行仿真。仿真和实验结果表明,M-part同步算法具有良好的同步性能,能够满足LTE系统对同步性能的要求。     

一种TD-SCDMA载波频偏与信道联合估计算法

通过分析时分同步码分多址(TD-SCDMA)系统的载波频偏和信道特性,提出一种频偏与信道联合估计算法。该算法通过对训练序列部分相关,然后做差分将频偏和信道特性解耦,并通过逐次迭代最终精确估计出频偏和信道参数。仿真结果表明,算法频偏估计性能接近Cramr-Rao界,准确度较高;全链路仿真误码率性能优越,信道估计准确。算法复杂度不高,实用性强,同样适用于其它的TDD模式的CDMA系统。     

一种改进的LTE系统下行同步算法

LTE(Long Term Evolution)系统中,作为小区搜索的第一步,符号定时算法需要具备很强的鲁棒性。为了进一步增强现有符号同步算法的抗频偏性能,提出了一种优化的符号同步算法。该算法一方面保持已有分段相关同步算法的优点,同时考虑结合预频偏处理来进行符号定时与粗频偏的联合估计,再将多个相关运算集做叠加处理。理论分析和仿真实验结果表明,在多径信道下,所提算法在完成符号定时和粗频偏估计的同时,大大提高了系统抗频偏性能。     

一种基于滤波多音系统的半盲同步算法

该文在研究滤波多音(Filtered MultiTone,FMT)调制性质的基础上,给出了一种新的FMT系统定时同步算法。该算法将FMT符号的相关性和PN序列强自相关性结合,在保证算法性能的同时,大大缩短了构造同步符号所需训练序列的长度。此外,该文还提出了一种简单有效的整数倍子载波间隔频偏的估计算法。仿真结果表明,这两种算法在加性高斯噪声信道中性能优良,结合分集技术在多普勒频移的瑞利信道下也获得良好的估计性能。     

GSM系统频率同步的实现

在GSM系统中提出一种简单的频率同步算法,利用系统频率校正信道(FCCH)的信号特征估计接收信号的频率偏移,并通过频率补偿实现系统频率同步.仿真结果表明,该算法丢包率低,信噪比为8 dB时就可完全检测到FCCH;频偏估计和补偿效果好,降低了系统误码率.与传统的基于频域FCCH检测算法和最大似然匹配检测算法相比,所提算法基于时域信号处理,不需进行频域分析,其性能好且简单实用.     

A robust timing and frequency synchronization for OFDM systems

A robust symbol-timing and carrier-frequency synchronization scheme applicable to orthogonal frequency-division-multiplexing systems is presented. The proposed method is based on a training symbol specifically designed to have a steep rolloff timing metric. The proposed timing metric also provides a robust sync detection capability. Both time domain training and frequency domain (FD) training are investigated. For FD training, maintaining a low peak-to-average power ratio of the training symbol was taken into consideration. The channel estimation scheme based on the designed training symbol was also incorporated in the system in order to give both fine-timing and frequency-offset estimates. For fine frequency estimation, two approaches are presented. The first one is based on the suppression of the interference introduced in the frequency estimation process by the training symbol pattern in the context of multipath dispersive channels. The second one is based on the maximum likelihood principle and does not suffer from any interference. A new performance measure is introduced for timing estimation, which is based on the plot of signal to timing-error-induced average interference power ratio against the timing estimate shift. A simple approach for finding the optimal setting of the timing estimator is presented. Finally, the sync detection, timing estimation, frequency estimation, and bit-error-rate performance of the proposed method are presented in a multipath Rayleigh fading channel.     

一种用于MP3文件版权保护的鲁棒水印算法

在详细分析MP3音频数据流结构的基础上,利用数字水印技术,提出一种版权保护的鲁棒音频水印算法。首先,选择MP3编码长窗中的中频对应的比例因子作为嵌入位置,保证了水印的不可感知性;其次,将二值图像水印进行混沌加密,提高了水印信息的安全性;并且实现了版权水印的盲提取。仿真实验证明,该算法不仅具有较好的透明性,而且对诸如噪声、滤波、采样、回声、剪切、压缩等攻击均具有较好的鲁棒性。     

A robust blind watermarking algorithm for depth-image-based rendering 3D images

The protection of 3D contents from illegal distribution has attracted considerable attention and depth-image-based rendering (DIBR) is proved to be a promising technology for 3D image and video displaying. In this paper, we propose a new digital watermarking scheme for DIBR 3D images based on feature regions and ridgelet transform (RT). In this scheme, the center view and the depth map are made available at the content provider side. After selecting the reference points of the center view, we construct the feature regions for watermark embedding. Considering the sparse image representation and directional sensitivity of the RT, the watermark bits are embedded into the amplitudes of the ridgelet coefficients of the most energetic direction. The virtual left and virtual right views are generated from the watermarked center view and the associated depth map at the content consumer side. The watermarked view has good perceptual quality under both the objective and subjective image quality evaluations. The embedded watermark can be detected blindly with low bit error rate (BER) from the watermarked center view, the synthesized left and right views even when the views are distorted and distributed separately. The experimental results demonstrate that the proposed scheme exhibits good performance in terms of robustness against various image processing attacks. Meanwhile, our method can be robust to common DIBR processing, such as depth image variation, baseline distance adjustment and different rendering conditions. Furthermore, compared with other related and state-of-the-art methods, the proposed algorithm shows higher accuracy in watermark extraction.     

一种卫星SCMA系统接收机同步算法

SCMA技术通过资源过载能够实现大规模用户的并发接入,非常适合物联网应用,但是SCMA解调性能受定时误差和载波频差影响较大。对此,文中通过基于导频的两阶段频差估计算法和ML相位偏差估计算法,实现大频差下的高精度频、相偏估计;通过SCMA和LDPC联合迭代,利用发送数据实现高精度定时误差估计。仿真结果表明,在AWGN信道下,载波同步算法采用优化的帧结构后可以获得距理想性能不到0.25dB的优异性能,定时同步算法在1次迭代下获得了距理想性能仅0.2dB的性能,在3次迭代下获得了与理想性能一致的优异性能,能适应大频差、高动态的卫星信道环境。     

A SFH spread spectrum synchronization algorithm for databroadcasting

In this paper, a practical slow frequency hopping (SFH) spread spectrum discrete synchronization algorithm suitable for data broadcasting is proposed. This algorithm uses additional sync bits in the binary stream of the slow frequency hopping signals for both initial synchronization and tracking purposes. A complete hop period or a complete time slot in every frame is used to carry these additional sync bits. These sync bits are changed at each frame and are used to control the startup condition of the pseudo-random number (PN) generator. As a result, a robust algorithm with fast synchronization time is obtained. The security measure is enhanced while at the same time using simpler hardware, requiring only one detector. It can also be used in systems with any number of hop channels, whether large or small, and may operate with several broadcasters simultaneously in a cell to improve the spectra usage     

一种单载波MIMO系统的同步算法

单载波系统由于具有峰均功率比低,对频率偏差不敏感等特点一直以来受到关注,但现有公开的文献中还没有对与MIMO结合的单载波系统给出比较完整的解决方案。提出了一种适用于单载波MIMO系统的帧结构和同步算法,结合了迭代估计和分集合并的优点,仿真结果表明该算法在低SNR条件下可以解决单载波MIMO系统的同步问题。     

一种鲁棒性的抖动视频稳像算法

设计了一种适用于移动摄像设备获取的视频序列的基于特征匹配的鲁棒性不稳定视频稳像算法,算法首先将亮度自适应模型融入传统的KLT方法中以实现鲁棒性的特征匹配,而后基于特征误差分析和运动一致性原则对特征集合进行有效性验证以提高特征的可靠性,并提出一种基于运动往复特性的抖动检测方法以避免视频无抖动时的稳像误差,最后根据匹配的特征区域间的对应关系采用Affine运动模型进行图像稳定.实验结果表明,算法对于前景物体运动和外界光线突变具有较好的鲁棒性.     

A robust sequential detection algorithm for cardiac arrhythmiaclassification

In ibid., vol. 37, no. 9, p. 837-43 (1990) and Proc. IEEE 9th Annu. Conf. Eng. Med. Biol. Soc., p. 918-19 (1988) N.V. Thakor et al. describe a sequential probability ratio test (SPRT) based on threshold crossing intervals (TCI) for the discrimination of ventricular fibrillation (VF) from ventricular tachycardia (VT). However, in applying their algorithm to data from the MIT-BIH malignant arrhythmia database, the authors observed some overlap in the distributions of TCI for VF and VT resulting in 16% overall error rate for the discrimination. In this communication, the authors describe a modified SPRT algorithm, using a new feature dubbed blanking variability (BV) as the basis for discrimination. Using the MIT-BIH database, the preliminary results showed that the proposed method decreases the overall error rate to 5%     

一种鲁棒的彩色图像多功能水印算法

首先转换彩色图像的颜色空间抽取相应的灰度图像,再对灰度图像进行提升小波分解,在分解过程中利用图像压缩操作,引起近半数的小波系数增大,另一半系数减小,基于系数增减特征实现版权水印和消费者数字指纹的同时嵌入,从而获得版权认证和盗版追踪的双重功能。仿真实验表明该算法具有良好的鲁棒性和不可感知性。     

A robust eye localization algorithm for face recognition

The accuracy of face alignment affects greatly the performance of a face recognition system. Since the face alignment is usually conducted using eye positions, the algorithm for accurate eye localization is essential for the accurate face recognition. In this paper, an algorithm is proposed for eye localization. First, the proper AdaBoost detection is adaptively trained to segment the region based on the special gray distribution in the region. After that, a fast radial symmetry operator is used to precisely locate the center of eyes. Experimental results show that the method can accurately locate the eyes, and it is robust to the variations of face poses, illuminations, expressions, and accessories.