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In this paper a novel technique for timing and carrier frequency offset (CFO) estimation for orthogonal frequency division multiplexing (OFDM) systems is presented. This technique is a modification of extended cyclic prefix for correlation sequence (ECPCS) based technique, called as selective extended cyclic prefix for correlation sequence (SECPCS) based technique. In cyclic prefix (CP) based technique, magnitude of timing metric near the exact starting point of CP is quite similar which causes problem in timing estimation. SECPCS is utilized in order to increase the difference between magnitudes of timing metric at the exact starting point of time of CP and its adjacent timing instants. In SECPCS technique, first of all correlation length of CP is extended using available CP samples and then those sequences which enlarge the difference in the magnitude of timing metric is selected. In the proposed technique the difference between magnitude of timing metric at exact starting point and its adjacent timing instants is significantly large compared to the previous techniques. The performance of different techniques is evaluated in terms of mean square error (MSE) in estimation of timing and CFO estimate. Further signal-to-interference-plus-noise ratio (SINR) loss of different techniques in different channel conditions is also estimated. From the simulation results it is observed that under different channel conditions, performance of the proposed SECPCS based technique is significantly better than previous techniques. 相似文献
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基于循环前缀的OFDM系统定时同步估计算法 总被引:1,自引:1,他引:0
正交频分复用(OFDM)是一种多载波高效调制技术,由于能够有效地对抗无线环境中多径信道引起的码间干扰(ISI),近些年来受到越来越广泛的关注.同步是一切数字通信系统能够有效工作的基础.由于OFDM相对于单载波通信系统对同步误差更加敏感,因此同步技术更是OFDM系统中最关键技术之一.文中定量分析了符号定时同步误差对系统性能的影响,并详细给出了基于循环前缀的符号定时同步估计算法及其性能分析.通过仿真对各基于循环前缀同步估计算法进行了比较,给出了算法的应用场三合. 相似文献
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We consider half-duplex amplify-and-forward (AF) relaying for increasing network coverage and spectrum efficiency of an OFDM-based cellular system. Due to the fact that OFDM symbols are transmitted over two serial multipath channels (i.e., the source-relay link and the relay-destination link) via AF relaying, the time spread of the received signal at destination nodes is introduced by both source-relay and relay-destination channels. Consequently, cyclic prefix (CP) added at the source node should have a much longer length than that of one-hop OFDM transmission to avoid inter-symbol interference. However, the increased CP length leads to the reduced spectrum efficiency of OFDM communications. In this paper, we propose a novel CP update scheme for achieving efficient and reliable multi-hop transmission in OFDM-based AF relay systems. By enabling the additional CP discarding and CP re-adding functionalities to relay nodes, the proposed scheme significantly reduces the required CP length without causing extra loss in the bit error rate performance, and therefore improves achievable end-to-end throughput and spectrum utilization efficiency. Simulation results confirm the theoretical analysis and illustrate the effectiveness of the proposed scheme. 相似文献
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循环前缀在OFDM系统中的应用 总被引:1,自引:0,他引:1
本文详细论述了OFDM系统中循环前缀在削弱符号间干扰(ISI)、载波间干扰(ICI)以及在实现时频同步中的应用。在OFDM符号间插入循环前缀,可以减小ISI和ICI,并为实时时频偏移估计提供足够信息,使得系统同步结构简单且工作高效。 相似文献
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近年来,正交频分复用(OFDM)技术已被越来越多的人所关注,并且在IEEE 802.11无线局域网中得到实际应用.在经典的OFDM系统中,接收端恢复信号时,只是对去掉循环前缀(CP)的信号进行处理,而没有考虑循环前缀中的部分有用信息.文章提出了一种基于LS(Least Squares)准则,利用循环前缀恢复发送信号的方法,并给出这种方法的仿真结果.结果表明,当循环前缀长度较大时,文章方法得到的误码率明显低于传统方法. 相似文献
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针对正交频分复用(OFDM)监测系统无法预先得知循环前缀(CP)长度的问题,提出了一种基于循环相关处理技术的CP参数估计方法,该方法充分利用了OFDM信号的时域准周期性,实现了FFT时间长度、保护间隔周期和符号同步时刻等参数的精确估计。对该方法的信号参数适应能力进行了理论分析和计算机仿真,结果表明新方法无需任何先验信息,运算量小、精度高,适于硬件实现。 相似文献
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Shaodan Ma Xinyue Pan Guang-Hua Yang Tung-Sang Ng 《Vehicular Technology, IEEE Transactions on》2009,58(4):1746-1751
In this paper, a blind symbol synchronization algorithm is presented for orthogonal frequency-division multiplexing (OFDM) systems, and a new timing function based on the redundancy of the cyclic prefix (CP) is introduced. It proves that the maximum of this function necessarily points to the correct timing offset, irrespective of channel conditions when the signal-to-noise ratio is high. Using the timing function, the timing offset is estimated through a searching algorithm. Channel power profile and channel length information are unnecessary. Simulation results show that the proposed algorithm is robust and outperforms the existing CP-based algorithms, particularly in frequency-selective fading channels. 相似文献
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文章对几种常用的基于循环前缀(CP)的最大似然同步算法进行了分析,并对其频偏估计方差进行了比较;同时针对基于CP的同步算法在多径衰落信道下性能较差的情况,提出了一种改进的CP同步算法并进行了仿真,结果表明相比于原ML算法,文中算法在多径信道下可有效提高频偏估计性能. 相似文献
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当正交频分复用(OFDM)通信系统的循环保护前缀(CP)长度小于信道冲激响应长度时,常采用时域均衡方法消除符号间干扰(ISI)和子载波间干扰(ICI)。但时域均衡器结构复杂,且收敛速度较慢。为此,利用OFDM系统的零子载波信息,设计了一种频域均衡器。该均衡器具有稀疏矩阵结构,因此计算量小。理论分析和计算机仿真表明:它能有效消除由于循环前缀不足引起的符号间干扰和子载波间干扰,从而较好地恢复传输信号。 相似文献
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利用CAZAC序列的OFDM频率同步方法 总被引:1,自引:0,他引:1
频率偏移估计是OFDM (Orthogonal Frequency Division Multiplexing)的关键技术。该文提出了在一个OFDM符号内利用两个重复的CAZAC (Constant Amplitude Zero Auto Correlation)序列进行频率偏移估计的新方法,估计范围可达整个OFDM带宽。用于同步的训练序列还可用于信道估计和均衡,这将提高系统的数据传输效率。此算法同步精度达到了Schmidl提出的Cramer-Rao bound,有效性在AWGN和Rayleigh多径信道下得到了验证。 相似文献
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《Broadcasting, IEEE Transactions on》2005,51(3):305-314
The intercarrier interference (ICI) matrix for the orthogonal frequency division multiplexing (OFDM) systems usually has a fairly large dimension. The traditional least-square solution based on the pseudo-inverse operation, therefore, has its limitation. In addition, the provision of a sufficiently long training sequence to estimate the complete ICI matrix is not feasible, since it will result in severe throughput reduction. In this paper, we derive a lower bound for the mean-square estimation error among the least-square ICI matrix estimators using different training sequences and prove that the minimum mean-square error (MMSE) optimality is attained when the training sequences in different OFDM blocks are orthogonal to each other, regardless of the sequence length. We also prove that the asymptotical mean-square estimation error using the maximal-length shift-register sequences ($m$ -sequences) as in the existing communication standards is 3 dB larger than that using the perfectly orthogonal sequences for ICI matrix estimation. Thus, we propose to employ the training sequences based on the Hadamard matrix to achieve a highly efficient and optimal ICI matrix estimator with minimum mean-square estimation error among all least-square ICI matrix estimators. Meanwhile, our new scheme involves only square computational complexity, while other existing least-square methods require the complexity proportional to the cube of the ICI matrix size. Analytical and experimental comparisons between our new scheme using Hadamard sequences and the existing method using$m$ -sequences (pseudo-random sequences) show the significant advantages of our new ICI matrix estimator. The proposed method is most suitable for OFDM systems with large amount of subcarriers, using high order of subcarrier modulation, and designed for high-end of RF frequency band, where accurate ICI estimation is crucial. 相似文献
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本文提出了一种新的适合于OFDM系统的符号定时估计算法。该算法利用经过特殊处理的前后两段信息序列的内在相关性进行准确的符号定时估计。理论分析和仿真表明,该算法能在大频偏低信噪比的条件下完成定时捕获的任务,并且无需专门的训练符号,从而大大提高了系统传输的效率。 相似文献
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OFDM符号是由多个子载波信号叠加而成,为确保各子载波之间的正交性,就对载波间的同步有很严格的要求,否则将造成信道间干扰和符号间干扰,严重影响OFDM系统的性能。提出一种新的基于循环前缀的OFDM时频同步算法,通过仿真,将新算法和传统的ML算法及集相关算法相比较。仿真结果表明,新算法具有更好的频偏和定时估计性能。 相似文献