共查询到17条相似文献,搜索用时 93 毫秒
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为了克服正交频分复用(Orthogonal Frequency Division Multip lexing,OFDM)系统中时间和频率漂移,提出了一种基于pilot的定时跟踪算法。与基于循环前缀的频偏估计方法向结合,提出了一种适合工程实现的OFDM时频同步环路结构。环路完全利用数据符号中的冗余信息实现时偏和频偏的跟踪,降低了对OFDM同步符号的需求,提高了系统效率。在FPGA上实现了该同步环路,实测曲线证明该方法能够有效的补偿时偏和频偏。 相似文献
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正交频分复用(OFDM)因其在抗频率选择性衰落和窄带干扰方面具有良好的性能而被广泛应用,但是OFDM系统比单载波系统对定时和频偏更加敏感。提出了一种简单有效的帧同步与频率跟踪算法,与传统的最大似然估计算法相比,实现更加容易,而且能保证精确的帧和频率同步。 相似文献
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宽带OFDM系统中的频率同步算法与FPGA实现 总被引:3,自引:0,他引:3
频率同步是宽带OFDM系统中的关键技术,IEEE 802.11a 采用OFDM技术,利用其前导序列的重复结构,提出了一种分步的粗细频偏捕获与校正算法,同时为了补偿时域同步后的残余相差和适应信道的时变特性,还提出了一种基于频域导频的相位跟踪方案.通过仿真对算法性能进行了分析,并通过FPGA实现验证了算法在宽带OFDM无线接入系统中应用的有效性.结果表明,算法可以对±2个子载波频率间隔内的载波频偏实施快速捕获与跟踪,估计精度达10-3,满足突发分组传输OFDM系统的快速同步要求. 相似文献
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同步是OFDM系统的基本技术。介绍了时域相关获得突发及符号同步的方法,以及频域差分调制快速估计整数频偏和小数频偏的方法。依据估计结果对频偏进行补偿,可保证采用廉价晶振所实现系统的解调性能。同步捕获后则通过锁相环技术跟踪长突发的同步变化。 相似文献
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针对正交频分复用(OFDM)系统对同步错误率和频率偏移敏感的问题,提出了一种叠加共轭对称训练序列的OFDM系统时间和频率同步方法。该同步方法将快速傅里叶逆变换(IFFT)调制后的序列构成具有共轭对称特性的训练序列,并叠加到OFDM数据符号上;在接收端,利用叠加训练序列和融合循环前缀信息来获取OFDM系统同步信息。理论分析和仿真表明:在信噪比为5 dB时,该同步算法定时同步正确概率已接近100%;在信噪比为4 dB时,频偏估计精度可以达到10-4;该同步算法不仅具有更好的同步性能,而且节省系统的有效带宽以及降低系统的计算法复杂度。 相似文献
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同步技术是MIMO—OFDM系统中的重要技术之一。本文简要介绍了MIMO—OFDM系统的基本原理,讨论了同步误差对系统的影响和系统同步的任务,并总结了MIMO—OFDM系统的同步方法。 相似文献
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OFDM系统的实现还存在着一些方面问题,如:同步问题尤其是频偏,峰值功率与平均功率比值过高,器件的非线性化等。OFDM系统对同步偏差敏感是本文讨论的重点,尤其是频偏。因此怎样获得准确的符号定时和载波频偏估计对OFDM系统性能至关重要。本文围绕OFDM同步过程中的符号定时和载波频率偏差问题进行描述,在分别介绍同步过程中捕获和跟踪两个阶段各自一些典型算法基础上,对一种基于保护间隔/循环前缀(PI/CP)的联合实现符号定时和载波同步最大似然估计(MLE)算法进行叙述并仿真。 相似文献
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Broadband MIMO-OFDM wireless communications 总被引:48,自引:0,他引:48
Stuber G.L. Barry J.R. McLaughlin S.W. Ye Li Ingram M.A. Pratt T.G. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》2004,92(2):271-294
Orthogonal frequency division multiplexing (OFDM) is a popular method for high data rate wireless transmission. OFDM may be combined with antenna arrays at the transmitter and receiver to increase the diversity gain and/or to enhance the system capacity on time-varying and frequency-selective channels, resulting in a multiple-input multiple-output (MIMO) configuration. The paper explores various physical layer research challenges in MIMO-OFDM system design, including physical channel measurements and modeling, analog beam forming techniques using adaptive antenna arrays, space-time techniques for MIMO-OFDM, error control coding techniques, OFDM preamble and packet design, and signal processing algorithms used to perform time and frequency synchronization, channel estimation, and channel tracking in MIMO-OFDM systems. Finally, the paper considers a software radio implementation of MIMO-OFDM. 相似文献
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通过对无人机正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)系统时频同步方法分析,对最大似然准则、最大相关准则和基于循环移位的最大相关算法等3种同步算法进行了研究。针对无人机数据链OFDM系统同步传输的特性,提出了一种采用粗同步和细同步相结合的时频联合同步方法。通过仿真结果可以得出,该时频联合同步方法能够达到系统同步范围和同步精度的统一。 相似文献
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Zhongshan Zhang Ming Zhao Haiyan Zhou Yuanan Liu Jinchun Gao 《Communications Letters, IEEE》2004,8(3):171-173
A new carrier frequency offset estimation scheme in orthogonal frequency-division multiplexing (OFDM) system is proposed. The carrier frequency offset estimation includes acquisition and tracking, and the acquisition range is as large as one half of overall signal bandwidth. The proposed tracking estimator is a maximum-likelihood estimator, and in AWGN channel, the Cramer-Rao lower bound is met at high signal-to-noise ratio (SNR); in multipath channel, the tracking algorithm works well at moderate SNR. Timing synchronization can be also performed during the course of acquisition. 相似文献
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Implementation of a MIMO OFDM-based wireless LAN system 总被引:11,自引:0,他引:11
The combination of multiple-input multiple-output (MIMO) signal processing with orthogonal frequency division multiplexing (OFDM) is regarded as a promising solution for enhancing the data rates of next-generation wireless communication systems operating in frequency-selective fading environments. To realize this extension of OFDM with MIMO, a number of changes are required in the baseband signal processing. An overview is given of the necessary changes, including time and frequency synchronization, channel estimation, synchronization tracking, and MIMO detection. As a test case, the OFDM-based wireless local area network (WLAN) standard IEEE 802.11a is considered, but the results are applicable more generally. The complete MIMO OFDM processing is implemented in a system with three transmit and three receive antennas, and its performance is evaluated with both simulations and experimental test results. Results from measurements with this MIMO OFDM system in a typical office environment show, on average, a doubling of the system throughput, compared with a single antenna OFDM system. An average expected tripling of the throughput was most likely not achieved due to coupling between the transmitter and receiver branches. 相似文献