共查询到20条相似文献,搜索用时 15 毫秒
1.
As an alternative to the traditional pilot‐aided orthogonal frequency division multiplexing (OFDM), the time‐domain pseudonoise (PN)‐padded OFDM provides a higher spectral efficiency. However, the carrier frequency offset (CFO) attenuates peaks of the conventional PN correlation output, which limits the CFO estimation range of the OFDM synchronizer. An improved correlation is proposed in this letter to remove the CFO‐induced amplitude attenuation of correlation peaks. For a synchronizer adopting the designed correlator, a larger range of CFO acquisition is obtained through using wider correlation windows with a smaller interval between them. The proposed method of CFO acquisition is verified in a digital terrestrial multimedia broadcast receiver, in which the synchronizer is able to acquire CFOs up to ±320 kHz in the DVB‐T F1 channel. Furthermore, the acquisition range can be expanded in more favorable channels. 相似文献
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This article proposes a new algorithm of joint channel and carrier frequency-offset OCCFO) estimation for multi-user multi-input and multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. A least square (LS) channel estimation and a carrier frequency offset (CFO) correlation estimation are combined in this contribution. CFOs are generally estimated using training sequences in a special synchronization timeslot. In this contribution, CFO estimation is further improved by taking advantages of channel estimation based on pilot symbols in traffic timeslots. The CFOs can be first obtained from the primary channel estimation. And then, with the knowledge of the CFOs estimated, channel estimation can be enhanced greatly. Computer simulation results indicate that the proposed JCCFO scheme is of good performance. Besides, the computational complexity is low. 相似文献
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《Vehicular Technology, IEEE Transactions on》2006,55(5):1677-1690
An accurate estimation of carrier frequency offset (CFO) is a crucial task for orthogonal frequency-division multiplexing (OFDM) systems but should be performed with affordable computational complexity for practicality. In this paper, the authors derive two new estimation algorithms (one for the integer part and the other for the fractional part of CFO), each of which utilizes only one OFDM block with null subcarriers but offers improved accuracy and reduced complexity. The proposed estimator for fractional CFOs operates iteratively and is insensitive to the initial CFO. The other proposed estimator for integer CFOs employs a pseudonoise binary random sequence to assist in subcarrier arrangement and accurate estimation of the integer CFO. To demonstrate the efficiency of the proposed methods, numerical results are provided from computer simulation and analysis, and comparisons are made with other existing methods in the literature. 相似文献
4.
In this paper, we propose a novel carrier frequency offset (CFO) tracking algorithm for orthogonal frequency division multiplexing (OFDM) systems by exploiting scattered pilot carriers and virtual carriers embedded in the existing OFDM standards. Assuming that the channel remains constant during two consecutive OFDM blocks and perfect timing, a CFO tracking algorithm is proposed using the limited number of pilot carriers in each OFDM block. Identifiability of this pilot based algorithm is fully discussed under the noise free environment, and a constellation rotation strategy is proposed to eliminate the c-ambiguity for arbitrary constellations. A weighted algorithm is then proposed by considering both scattered pilots and virtual carriers. We find that, the pilots increase the performance accuracy of the algorithm, while the virtual carriers reduce the chance of CFO outlier. Therefore, the proposed tracking algorithm is able to achieve full range CFO estimation, can be used before channel estimation, and could provide improved performance compared to existing algorithms. The asymptotic mean square error (MSE) of the proposed algorithm is derived and simulation results agree with the theoretical analysis. 相似文献
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Xiaoli Ma Mi-Kyung Oh Giannakis G.B. Dong-Jo Park 《Communications, IEEE Transactions on》2005,53(1):162-172
We design pilot-symbol-assisted modulation for carrier frequency offset (CFO) and channel estimation in orthogonal frequency-division multiplexing transmissions over multi-input multi-output frequency-selective fading channels. The CFO and channel-estimation tasks rely on -subcarrier and nonzero pilot symbols that we insert and hop from block to block. Because we separate CFO and channel estimation from symbol detection, the novel training patterns lead to further decoupled CFO and channel estimators. The performance of our algorithms is investigated analytically, and then compared with an existing approach by simulations. 相似文献
7.
Channel impulse response of a multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) channel contains a smaller number of nonzero components. In addition, locations of nonzero taps coincide in delay domain. So channel impulse responses can be modeled into an approximately group sparse signals. In this work we use extended sparse Bayesian learning (ESBL), a new method for multichannel compressive sensing for channel estimation in MIMO-OFDM. In joint extended sparse Bayesian learning (JESBL), both pilot and data subcarriers are utilized for channel estimation. These methods can reduce the number of pilot subcarriers in OFDM and improve the spectral efficiency of the MIMO-OFDM system. 相似文献
8.
《Wireless Communications, IEEE Transactions on》2008,7(8):2988-2999
Carrier frequency synchronization is critical to the quality of signal reception in OFDM systems. This paper presents an approximate maximum-likelihood (ML) carrier frequency offset (CFO) estimation scheme based on time-domain channel estimates which retain the CFO information in the form of phase rotation. The proposed ML CFO estimate is investigated under static as well as time-varying fading channels. Statistical properties of the estimator are examined and Cramer-Rao lower bound (CRLB) is derived. Theoretical analysis and numerical simulations show that the proposed CFO estimator renders excellent performance with lower computational complexity. The proposed CFO estimate also has an advantage of allowing for more flexible pilot patterns 相似文献
9.
正交频分复用(OFDM)可以有效地将频率选择性衰落信道转化成多个并行平坦衰落信道,从而大大提高传输效率。多输入多输出正交频分复用(MIMO-OFDM)技术可以大幅度地提高无线通信系统的信道容量与传输速率,其信道估计精度对系统性能有着直接的影响。研究了基于导频插入的SISO-OFDM和MIMO-OFDM最小二乘法估计(LS)信道估计方法。采用广义平稳非相关散射下的多径时变瑞利信道模型,对各个算法进行了仿真试验,得出不同算法下信道估计的误比特曲线,比较了各个算法的性能。仿真结果表明:MIMO-OFDMLS算法在误码率性能上优于SISO-OFDM。 相似文献
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《Broadcasting, IEEE Transactions on》2009,55(1):84-94
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正交频分复用(OFDM)技术能有效克服多径带来的不利影响,提高频谱利用率;多输入多输出(MI-MO)技术,可以在不增加系统带宽和发射功率的前提下,成倍提高系统容量和带宽利用率。将两者结合的MIMO-OFDM系统是近年来的研究热点,信道估计在提高该系统性能方面发挥着重要作用。基于此,主要介绍MIMO-OFDM系统结构,在此基础上介绍基于导频的信道估计、半盲信道估计和盲信道估计。 相似文献
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MIMO-OFDM系统能在宽带无线信道中达到很高的速率。文章建立了MIMO-OFDM信道识别的条件并实现了基于子空间方法的盲信道估计技术。该方法将现存的在SISO-OFDM系统中的基于子空间的盲信道估计进行统一,并且推广到MIMO-OFDM系统中。特别是该方法可以获得信道的精确估计,且能快速收敛。仿真实验的结果显示了该方法的均方误差性能。 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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在多输入多输出(MIMO)-正交频分复用(OFDM) 系统中,怎样在较高频谱利用率的情况下对快时变信道进行较为准确的估计是一个具有挑战性的课题。该文在利用压缩感知理论可提高系统频谱利用率的基础上,提出了一种适合于快时变环境下MIMO-OFDM 系统的稀疏自适应信道估计方法。该方法不再受到奈奎斯特采样频率条件约束,避免了传统导频辅助信道估计方法频谱利用率低的缺点。该文方法通过构建多天线群时频结构特征稀疏基,利用多天线间和群时变OFDM符号内信道冲激响应具有更强稀疏性的特点,对MIMO-OFDM快衰落信道进行稀疏变换。由于实际MIMO-OFDM快衰落信道往往处于频率选择性、时变性和多种干扰并存的复杂环境,受到干扰的信道参数对系统而言是未知,采用该方法克服了现有基于压缩感知理论的信道估计方法需要预先知道信道冲激响应稀疏度才能重构信道参数的不足,在信道稀疏度未知道的情况下,运用稀疏自适应的方法来对不同时频结构特征的信道参数进行估计。仿真结果表明所提估计方法具有对快时变信道参数估计的鲁棒性和较高频谱利用率,且均方误差小。 相似文献
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《Signal Processing, IEEE Transactions on》2006,54(8):3125-3135
In this paper, we address the problem of blind carrier frequency offset (CFO) estimation in orthogonal frequency-division multiplexing (OFDM) systems in the case of frequency-selective channels. CFO destroys the orthogonality between the carriers leading to nondiagonal signal covariance matrices in frequency domain. The proposed blind method enforces a diagonal structure by minimizing the power of nondiagonal elements. Hence, the orthogonality property inherent to OFDM transmission with cyclic prefix is restored. The method is blind since it does not require a priori knowledge of the transmitted data or the channel, and does not need any virtual subcarriers. A closed-form solution is derived, which leads to accurate and computationally efficient CFO estimation in multipath fading environments. Consistency of the estimator is proved and the convergence rate as a function of the sample size is analyzed as well. To assess the large sample performance, we derive the CramÉr–Rao bound (CRB) for the blind CFO estimation problem. The CRB is derived assuming a general Gaussian model for the OFDM signal, which may be applied to both circular and noncircular modulations. Finally, simulation results on CFO estimation are reported using a realistic channel model. 相似文献
18.
This paper studies the joint estimation technique of carrier frequency offset (CFO) and channel information for a distributed decode‐and‐forward (DF) cooperative space‐time block‐coded (STBC) orthogonal frequency division multiplexing (OFDM) system. For the considered relay system, we provide theoretical analysis of the effects upon the output signal‐to‐noise ratio (SNR), which is caused by the CFO/channel estimation error. Based on the provided analytical results, a joint CFO/channel estimation scheme is then developed, where the CFO estimate is achieved by a multiple‐dimensional linear search algorithm. Furthermore, we propose an alternative estimation solution with iteration approach being designed for the CFO estimation prior to the channel estimation. In contrast to the former estimator, the iterative method enjoys the advantage of the substantially reduced implementation complexity without sacrificing the estimate performance. The conducted computer simulation results verify the effectiveness of the proposed schemes. 相似文献
19.
Xiaoli Ma 《Communications, IEEE Transactions on》2005,53(12):2129-2138
Carrier frequency offset (CFO) estimation for orthogonal frequency-division multiplexing (OFDM) has caught attention as OFDM systems have become widely adopted in recent years. In this paper, we design a novel double-differential (DD) codec with low computational complexity. Our design bypasses CFO and channel estimation, and is easy to implement at both transmitter and receiver. It also guarantees full multipath diversity, and reduces the peak-to-average power ratio from the number of subcarriers to the channel order. In addition, it is robust to CFO drifting. The closed form of the performance for our design is derived for OFDM transmissions over frequency-selective channels with CFO. Thorough simulation results corroborate our claims. 相似文献