共查询到20条相似文献,搜索用时 46 毫秒
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一种OFDM系统同步参数盲估计方法 总被引:2,自引:0,他引:2
首先提出一种扩大周期平稳信号循环周期的方法,然后在此基础上提出一种基于信号周期平稳特性的盲同步参数快速估计算法,最后通过分析算法获得一种可以估计非整数倍样点周期时延和扩大频偏估计范围的方法,从而实现整个OFDM基带带宽范围内的频偏估计。理论分析和仿真结果表明,该算法仅用很少的OFDM符号就可以实现同步参数的估计、有好的抗噪特性、衰落信道适应性和高的估计精度。 相似文献
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Jing Zheng Suping Peng Guowei Zhu Huaixiu Wang 《Wireless Personal Communications》2013,69(4):1207-1222
A joint synchronization and channel estimation scheme is proposed for orthogonal frequency division multiplexing (OFDM) system. In the proposed scheme, the integer frequency offset, fine timing offset and channel estimation are estimated based on the characteristics of the chirp signals. The main contributions of the paper are: the more robust ability to find the actual first path instead of the strongest path on the assumption of repeated chirp waveforms in the timing synchronization approach, and the lower computational complexity with high performance in the channel estimation approach. Moreover, we analyze the performance of the proposed method and check it via Monte Carlo simulations. The simulation results show that the proposed method can achieve good performance for both synchronization and channel estimation in frequency selective channels. 相似文献
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Joint carrier frequency synchronization and channel estimation for OFDM systems via the EM algorithm 总被引:6,自引:0,他引:6
Jong-Ho Lee Jae Choong Han Seong-Cheol Kim 《Vehicular Technology, IEEE Transactions on》2006,55(1):167-172
A joint carrier frequency synchronization and channel estimation scheme is proposed for orthogonal frequency-division multiplexing (OFDM) system. In the proposed scheme, carrier frequency synchronization and channel estimation are performed iteratively via the expectation-maximization (EM) algorithm using an OFDM preamble symbol. Moreover, we analytically investigate the effect of frequency offset error on the mean square error (MSE) performance of channel estimator. Simulation results present that the proposed scheme achieves almost ideal performance for both channel and frequency offset estimation. 相似文献
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该文首先提出一种基于信号周期平稳特性的OFDM系统时延和频偏的盲估计算法,然后分析算法,获得一种可以估计非整数倍样点周期的时延和扩大频偏估计范围,实现整个OFDM系统带宽范围内的频偏估计的方法,并指出本算法可以在信道未知的情况下获得好的估计性能,最后给出相应的仿真结果。理论分析和仿真结果表明,本算法有很好的抗噪特性、强的变化信道适应性,与同类方法比较,具有更高的估计精度、估计非整数倍样点周期时延和扩大频偏估计范围的能力。 相似文献
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Inamori M. Bostamam A.M. Sanada Y. Minami H. 《Wireless Communications, IEEE Transactions on》2009,8(5):2214-2220
A direct conversion architecture reduces the cost and power consumption of a receiver. However, a direct conversion receiver may suffer from direct current (DC) offset, frequency offset, and IQ imbalance. This paper presents an IQ imbalance estimation scheme for orthogonal frequency division multiplexing (OFDM) direct conversion receivers. The proposed IQ imbalance estimation scheme operates in the presence of dynamic DC offset and frequency offset. The proposed scheme calculates IQ imbalance from a simple equation. It employs the knowledge of the preamble symbols of the IEEE 802.11 a/g standards, while it does not require the impulse response of the channel. Numerical results obtained through computer simulation show that the bit error rate (BER) performance for the proposed IQ imbalance estimation scheme has a degradation of about 4dB with a large DC offset, frequency offset, and IQ imbalance. 相似文献
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We provide expressions for the bit error rate of various transmit and receive diversity schemes for orthogonal frequency division multiplexing (OFDM) systems in the presence of frequency offset, phase noise, and channel estimation errors. The derivations are also applicable for a general multiplicative distortion of the received signal. Our results show that with perfect channel estimates, practical values of the phase noise do not significantly degrade the performance of the various diversity methods for binary phase-shift keying modulation. In contrast, the transmit diversity schemes for OFDM are much more sensitive to channel estimation errors than maximal ratio combining receive diversity. 相似文献
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《中国邮电高校学报(英文版)》2014,21(6):30-36
The orthogonal frequency division multiplexing (OFDM) is currently used in long term evolution (LTE) system. The time offset estimation (TOE) and frequency offset estimation (FOE) of OFDM is essential in mobile communication base. According to the conventional cross correlation TOE and FOE algorithms, a new cross correlation computation was proposed to estimate the time offset and frequency offset for LTE uplink system, so that the time offset and frequency offset can be estimated simultaneously with low complexity. Compared with the conventional TOE and FOE algorithms, the simulation show that the proposed can reduce complexity and improve performance for FOE with good performance for TOE in additive white Gaussian noise (AWGN) and multipath channel. 相似文献
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Cai Xuelian Li Jiandong Li Changle Chen Chen 《电子科学学刊(英文版)》2005,22(6):569-574
One of the principal disadvantages of Orthogonal Frequency Division Multiplexing (OFDM) is very sensitive to carrier frequency offset. The integer frequency offset has no effect on the orthogonality among the subcarriers, but it causes a circular shift and phase rotation of the received data symbols sequence, resulting in a Bit Error Rate(BER) of 0.5. In this paper, a novel integer frequency offset estimator for OFDM is derived based on maximum likelihood estimation technique and exploration of the differential relation between two consecutive OFDM data symbol sequences in frequency domain. Its performance is compared with the conventional method by computer simulations for the additive white Gaussian noise channel and a multipath fading channel. Simulation results show that the performance of the proposed estimator is better than the conventional estimator. 相似文献
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OFDM系统中定时偏移的估计技术 总被引:1,自引:0,他引:1
在T.M.Schmidl和D.C.Cox提出的解决正交频分多路复用(OFDM)系统定时同步的基础上,给出了两种改进算法。在加性高斯白噪声信道(AWGN)和存在符号间干扰(ISI)的两种信道中,分别对估值进行比较,这两种改进算法得到估值的方差要小得多。 相似文献
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Orthogonal frequency division multiplexing (OFDM) is a multi-carrier modulation scheme, which has been adopted for several
wireless standards. In order to fully exploit the benefits of an OFDM system, estimation of the channel state information
must be performed. Moreover a well-known problem of OFDM is its sensitivity to frequency offset between the transmitted and
received carrier frequencies. This frequency offset introduces inter-carrier interference in the OFDM signal. In this paper
we address the problem of jointly tracking the channel and frequency offset based on a Sequential Monte Carlo filtering approach.
The proposed algorithm works in a decision-directed way, thus does not require the use of pilot symbols, providing a worth-mentioned
increase in the useful data rate. Through simulations we demonstrate the efficiency of this approach against a similar approach
where the Extended Kalman Filter is used. Moreover our method is compared with two recently proposed pilot-based methods. 相似文献
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One of the challenges in designing orthogonal frequency-division multiplexing (OFDM) systems is their inherent sensitivity to any frequency shift in the signal. A frequency offset between the local oscillators at the transmitter and receiver causes a single frequency shift in the signal, while a time-varying channel can cause a spread of frequency shifts known as the Doppler spread. Frequency shifts ruin the orthogonality of OFDM subcarriers and cause intercarrier interference (ICI); therefore, quickly diminishing the performance of the system. ICI self-cancellation schemes have been proposed to reduce the sensitivity of OFDM systems to frequency shifts. These schemes use signal processing and frequency domain coding to reduce the amount of ICI generated as a result of frequency shifts, with little additional computational complexity. These methods can be used as an alternative to the fine frequency-offset estimation methods to battle oscillator frequency offset or simply be used as an ICI mitigation technique when the system is operating over time-varying channels. We propose a general ICI self-cancellation scheme that can be implemented through windowing at the transmitter and receiver. We show that the previously proposed self-cancellation schemes are equivalent to special cases of this method. Through theoretical analysis of the signal-to-interference ratio and bit-error rate and the use of Monte Carlo simulations, we demonstrate that the proposed system considerably outperforms the existing systems in the presence of frequency offset or time variations in the channel. We consider both coherent and noncoherent systems. 相似文献
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Zhongshan Zhang Weiyu Jiang Haiyan Zhou Yuanan Liu Jinchun Gao 《Wireless Communications, IEEE Transactions on》2005,4(1):228-237
A new carrier frequency offset estimation scheme in orthogonal frequency-division multiplexing (OFDM) systems is proposed in this paper. Both the carrier frequency offset acquisition and tracking are based on a fixed-length training-symbol-block, which consists of multiple small identical training symbols. When each training symbol is shortened, the number of training symbols in the training-symbol-block should be increased accordingly to keep the total training-symbol-block length fixed. The proposed scheme extends Moose's estimator, where the estimation error is only dependent on total training symbol energy and cannot be reduced any more, once the total training symbol energy is determined. The proposed scheme can shorten each training symbol in a training-symbol block and select an appropriate estimator simultaneously, which can lead to further reduction of estimation error and increase of acquisition range, even with the total training-symbol-block energy being fixed. Performance analyzes for the proposed scheme in both the additive white Gaussian noise channel (AWGN) and the multipath channel are also presented in this paper. All estimators in the proposed scheme are conditionally unbiased, and simulation results demonstrate that they can work well both in the multipath channel and in the AWGN channel. 相似文献
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Debarati Sen Saswat Chakrabarti R. V. Raja Kumar 《Circuits, Systems, and Signal Processing》2009,28(6):993-1016
This paper presents a highly accurate frequency offset estimation algorithm for multi-band orthogonal frequency division multiplexing
(MB-OFDM) systems effective for realistic ultra-wideband (UWB) environment. The proposed algorithm derives its estimates based
on phase differences in the received subcarrier signals of several successive OFDM symbols in the preamble. We consider different
carrier frequency offsets and different channel responses in different bands to keep the analysis and simulation compatible
for practical multi-band UWB scenario. Performance of the proposed algorithm is studied by means of bit error rate (BER) performance
of MB-OFDM system. In order to compare the variance of the synchronizer to that of the theoretical optimum, we derive the
Cramer–Rao lower bound (CRLB) of the estimation error variance and compare it with the simulated error variance both in additive
white Gaussian noise and UWB channel model (CM) environments, CM1–CM4. Next, we modify the estimation algorithm by proposing
a multi-band averaging frequency offset synchronization (MBAFS) scheme. We establish superior BER performance with MBAFS compared
to our first scheme. We calculate modified CRLB for MBAFS and compare it with simulation results for CM1–CM4. Both analysis
and simulation show that MBAFS algorithm can estimate the carrier frequency offset effectively and precisely in UWB fading
channels for MB-OFDM applications. We also analyze the computational complexity of both the proposed algorithms in order to
verify their feasibility of implementation in practical UWB receiver design. 相似文献
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CAO Xue-hong Department of Information Engineering Nanjing University of Posts Telecommunications Nanjing P.R. China 《中国邮电高校学报(英文版)》2005,12(2)
1Introduction Orthogonal Frequency Division Multiplexing(OFDM) has become a popular technique for transmis-sion of signals over wireless channels . OFDMhas beenadoptedinseveral wireless standards such as Digital Au-dio Broadcasting ( DAB) , Digital Video Broadcasting(DVB-T) ,the IEEE 802 .11a[1]Local Area Network(LAN) standard and high performance LAN type 2(HIPERLAN/2)[2]standard. OFDMis also being pur-sued for Dedicated Short-Range Communications(DSRC) for road side to … 相似文献
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Robust channel estimation and ISI cancellation for OFDM systems with suppressed features 总被引:5,自引:0,他引:5
A feature-suppressed orthogonal frequency-division multiplexing (OFDM) system and the corresponding channel estimation and intersymbol interference (ISI) mitigation techniques are investigated in this paper. Cyclic prefix (CP) and pilot tones, which are commonly used in civilian OFDM systems for ISI mitigation and channel estimation, create distinctive waveform features that can be easily used for synchronization and channel estimation purposes by intercepting receivers. As a result, CP and pilot tones are eliminated in the proposed feature suppressed OFDM system to reduce the interception probability. Instead, a set of specially designed OFDM symbols, driven by different pseudorandom sequences, are employed as preambles to avoid unique spectral signature. These preambles are inserted into the OFDM data symbol stream periodically and in a round-robin manner. In addition, a random frequency offset is introduced to each preamble to further mask the multicarrier signature. New challenges arising from these feature suppression efforts are studied, including robust channel estimation and demodulation techniques in the presence of frequency offset and severe interference. Based on our interference analysis, an iterative ISI and intercarrier interference (ICI) estimation-cancellation-based technique is proposed for both channel estimation and OFDM data demodulation. Our channel estimator performs joint frequency offset and channel impulse response estimation based on the maximum-likelihood (ML) principle. To reduce its complexity, we employ a number of techniques, which include approximation of the ML metrics, as well as fast Fourier transform pruning. The performances and feasibility of the proposed feature suppressed OFDM system and the channel estimator are analyzed and verified through numerical simulations. 相似文献