共查询到20条相似文献,搜索用时 15 毫秒
1.
QIANG Jian-feng ZHANG PingDepartment of Telecommunications Engineering Beijing University of Posts Telecommunications Beijing P.R. China 《中国邮电高校学报(英文版)》2005,12(4)
1IntroductionOrthogonal Frequency Division Multiplexing(OFDM) hasgained strong position in the next generation widebandwireless systems for its advantages over frequency-selec-tive fading channels . The principal weakness of OFDMis its sensitivity to Carrier Frequency Offset ( CFO)caused by Doppler drifts and/or oscillator instabili-ties[1 ~3]. Many frequency synchronization algorithmsfor OFDM have been proposed, which can be dividedinto three main categories .First groupis based on s… 相似文献
2.
It is well known that orthogonal frequency division multiplexing (OFDM) is sensitive to carrier frequency offset (CFO) and suffers from a high peak‐to‐average ratio. In addition, the performance of OFDM is severely affected by strong co‐channel interference and strong narrowband interference. To mitigate the limitations of OFDM, we propose a new multi‐carrier transceiver based on frequency‐shift filter. A frequency‐shift filter can separate spectrally overlapping sub‐carrier signals by exploiting the spectral correlation inherent in the cyclostationary modulated signals. To increase spectral efficiency, we increase the percentage of spectral overlap between two adjacent sub‐channels. We derive an upper bound and a lower bound on the bit error rate performance of the proposed multi‐carrier transceiver in additive white Gaussian noise channel and frequency‐nonselective Rayleigh fading channel, respectively. Compared with OFDM, our simulation results show that the proposed multi‐carrier transceiver is much less sensitive to CFO and has a lower peak‐to‐average ratio; moreover, without any additional interference suppression technique, the proposed transceiver has the advantage of being able to mitigate strong co‐channel interference with CFO from the intended multi‐carrier signal and mitigate strong narrowband interference in additive white Gaussian noise channel and in Rayleigh fading channel in which a large CFO between the transmitted signal and the received signal often occurs. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
3.
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
4.
Qingfeng Jing Weizhi Zhong Yuping Lu Xiaoju Yan 《Radioelectronics and Communications Systems》2013,56(1):29-35
Carrier frequency offset (CFO) due to Doppler frequency shift or frequency mismatch between the transmitter’s and receiver’s oscillators can introduce severe inter-symbol and inter-carrier interference into OFDM systems. A simplified OFDM system model is considered to analyze effects of CFO in theory and simulation. The article briefly reviews some traditional CFO estimation algorithms. Relying on relatively good correlation characteristic of pseudo-noise (PN) sequence, the PN preamble based algorithm of CFO estimation is developed. Performance characteristics of traditional and the new improved algorithms are simulated under different conditions. Results indicate that the PN preamble based algorithm of CFO estimation is more accurate, resource-saving and robust even under poor communications channel condition, such as low SNR and big normalized CFO. 相似文献
5.
Orthogonal frequency division multiplexing (OFDM) systems with direct-conversion receiver (DCR) are vulnerable to carrier frequency offset (CFO), dc offset (DCO) and in-phase/quadrature (I/Q) imbalance. In this paper, we propose blind estimator for joint estimation of CFO, DCO and I/Q imbalance in OFDM systems with DCR. Simulation results show that performance of proposed estimator approaches Cramér-Rao lower bound (CRLB) asymptotically, which demonstrates its effectiveness. 相似文献
6.
Robust Frame Synchronization for Chinese DTTB System 总被引:3,自引:0,他引:3
Shigang Tang Kewu Peng Ke Gong Jian Song Changyong Pan Zhixing Yang 《Broadcasting, IEEE Transactions on》2008,54(1):152-158
Digital terrestrial multimedia/television broadcasting (DTMB), which is the recently released Chinese digital television terrestrial broadcasting (DTTB) standard, uses guard intervals padded with known pseudo-noise (PN) sequences for multi-carrier or single-carrier block transmission. Well designed synchronization algorithms are a prerequisite for achieving high-quality multimedia transmission. In this paper, a novel frame synchronization technique, which is robust to carrier frequency offset (CFO), is proposed for DTMB systems. This technique is derived through segmenting the local PN sequence into M contiguous blocks and performing multiple cross-correlations with the received signal. The metric for peak detection is defined as the non-coherent summation of the M cross-correlation magnitude outputs. Moreover, a low-complexity frame synchronizer based on segment-based full correlation for PN420 mode in DTMB system is proposed. It is shown through computer simulation that the proposed techniques generally outperform the conventional ones when CFO occurs, over both AWGN and frequency-selective fading channels. For a DTMB system using PN420 mode, the maximal allowed CFO to keep system still working normally of our proposed schemes are more than 3 times larger than that of the conventional method. 相似文献
7.
Particle filter with ant colony optimization for frequency offset estimation in OFDM systems with unknown noise distribution 总被引:2,自引:0,他引:2
Orthogonal frequency division multiplexing (OFDM) is sensitive to carrier frequency offset (CFO) that causes inter-carrier interference (ICI). In this paper, a particle filter (PF) method augmented with ant colony optimization (ACO) is developed to estimate the CFO. The ACO for continuous domains is incorporated into PF to optimize the sampling process. Unlike the standard PF, resampling is not required in the method. Moreover, it does not require the noise distribution. Simulation results show that the proposed method is effective when estimating the CFO and can effectively combat the effect of ICI in OFDM systems. 相似文献
8.
Orthogonal frequency division multiplexing (OFDM) systems are known to be sensitive to carrier frequency offset (CFO). This
paper is concerned with the CFO estimation for multiple input multiple output (MIMO) systems employing OFDM waveforms. We
present two approaches to derive maximum likelihood (ML) pilot-assisted frequency estimators that use either two or multiple
identical training symbols. It is shown that the resulting ML frequency estimators are similar to maximum ratio combining
versions of Moose estimator and Yu–Su solution, respectively. Numerical examples demonstrate that the proposed frequency estimators
are robust against spatial Signal-to-noise ratio (SNR) variation and they yield performance superior to that of the corresponding
single-antenna system. 相似文献
9.
J. Y. Hua Z. J. Xu L. M. Meng G. Li 《International Journal of Communication Systems》2010,23(8):1041-1056
We put forward a novel frequency offset estimator for burst orthogonal frequency division multiplexing (OFDM) systems under double selective fading channels. With the help of pilot bits and channel estimates in frequency domain, we calculate the delay power spectrum (DPS) of multi‐path channels and estimate the integer carrier frequency offset (CFO), in which the FFT‐realized (Fast Fourier Transform) algorithm is computation effective. Additionally, the pseudo noise (PN) sequence is proposed to act as a pilot signal to extend the estimation range. Yet the algorithm uses pilots instead of preambles, resulting in higher spectrum efficiency than conventional methods. Simulations show high accuracy and robustness in a wide range of terminal velocities (time‐selectivity) and signal‐to‐noise ratios (SNRs). Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
10.
Orthogonal frequency division multiplexing (OFDM) systems are more sensitive to carrier frequency offset (CFO) compared to
the conventional single carrier systems. CFO destroys the orthogonality among subcarriers, resulting in inter-carrier interference
(ICI) and degrading system performance. To mitigate the effect of the CFO, it has to be estimated and compensated before the
demodulation. The CFO can be divided into an integer part and a fractional part. In this paper, we investigate a maximum-likelihood
estimator (MLE) for estimating the integer part of the CFO in OFDM systems, which requires only one OFDM block as the pilot
symbols. To reduce the computational complexity of the MLE and improve the bandwidth efficiency, a suboptimum estimator (Sub
MLE) is studied. Based on the hypothesis testing method, a threshold Sub MLE (T-Sub MLE) is proposed to further reduce the
computational complexity. The performance analysis of the proposed T-Sub MLE is obtained and the analytical results match
the simulation results well. Numerical results show that the proposed estimators are effective and reliable in both additive
white Gaussian noise (AWGN) and frequency-selective fading channels in OFDM systems.
相似文献
Feng YangEmail: |
11.
Carrier frequency offset (CFO) in OFDM systems results in loss of channel orthogonality and hence degrades the system's performance. In this paper, we propose a new method for joint CFO/channel estimation for OFDM systems with two receive antennas. Our method avoids the complexity of full search methods in one or two dimensions. Using one training OFDM symbol and utilizing the knowledge of the structure of the inter‐channel interference that results from CFO, we develop a two‐stage estimation procedure. The first stage derives an initial CFO/channel estimate based on a one shot minimization step. The second stage refines this joint estimate by conducting a small CFO search in the vicinity of the initial estimate. This procedure provides CFO estimates over a full range of −N /2–N /2, (N : number of subcarriers), as well as the channel estimates. Computer simulations show an excellent performance that is very close to the Cramer–Rao lower bound and superior to some existing methods. The effect of antenna correlation on performance is also investigated through computer simulations, showing small performance degradation even at medium correlation coefficients (0.3–0.6). Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
12.
The symbiotic FM radio data system(SRDS)is a radio data system that a specially designed OFDM signal co-lives with FM signal,which enables a significantly higher data rate than existing radio data systems.The cyclic prefix of the OFDM symbol has the same length as the OFDM body,which enables the analytic separation of the co-channel OFDM and FM signal at receiver side,utilizing the fact that the OFDM body and prefix is equal.In this work,we show that the OFDM body and prefix cannot be viewed as equal when there is sufficient carrier frequency offset(CFO).Thus,we propose a two-step CFO estimation algorithm for FM and SRDS hybrid signal.The first step estimates the coarse CFO by exploring the characteristics of the FM signal.Once the coarse CFO is removed,the residual CFO is small enough for FM and OFDM separation.The second step fine estimates CFO from the OFDM-only signal using its repeated PN structure after the separation.Detailed mathematical equations are formulated and simulation results are given.The results show that the proposed algorithm works fine with the simulation setup and has a final residual CFO less than 3.9Hz. 相似文献
13.
Blind carrier frequency synchronization for orthogonal frequency division multiplexing (OFDM) systems with receive diversity is proposed in this paper. This method utilizes the fact that different receive branches contain uncorrelated observations about the same information bits. Due to receive diversity, our synchronizer can perform well without virtual subcarriers when channel state information (CSI) is known. In addition, we shall analyze the effects of CSI errors on the carrier frequency offset (CFO) estimation and show that the proposed algorithm is robust to CSI error. In particular, we derive the Cramer-Rao bound (CRB) from the mean square error (MSE) of the carrier frequency synchronizer. Computer simulation results show the performance improvement of our synchronizer to the single antenna systems and to the existing method. 相似文献
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15.
为了提高船舶自动识别系统(AIS)的容量,提出了基于正交频分复用技术(OFDM)的新型AIS系统设计方案.新系统设计主要包括系统参数设计、系统帧结构设计.新系统链路容量和信道传输速率均较传统AIS系统提高了6倍,实现了频域资源的有效利用.该系统对符号定时偏差和载波频率偏差特别敏感,因此对接收信号的同步处理必不可少,在设计的新系统基础之上提出了一种新的盲估计算法,利用包含在循环前缀内的冗余信息,在多径信道信息未知的情况下,直接通过对接收信号做相关构造一个归一化的相关特性函数,通过此函数可得到符号时延位置和多径信道长度,进而得到载波频率偏差.仿真结果表明在多径信道下该算法也具有较好的性能. 相似文献
16.
Khaled Ramadan Khalil F. Ramadan Ahmed S. Fiky Hasna Alam Moawad I. Dessouky Fathi E. Abd El‐Samie 《International Journal of Communication Systems》2020,33(3)
Frequency synchronization has a great importance in preserving the performance of the underwater acoustic (UWA) orthogonal frequency division multiplexing (OFDM) systems. The carrier frequency offset (CFO) estimation can be blind or data‐aided. In this paper, the Zadoff‐Chu (ZC) sequences are used for OFDM synchronization in UWA communications, and they are compared with different data‐aided algorithms. We propose a low‐complexity algorithm for CFO estimation based on ZC sequences. Also, a joint equalization and CFO compensation scheme for UWA‐OFDM communication systems is presented. Simulation results demonstrate that the proposed CFO estimation algorithm allows estimation of the CFO accurately with a simple implementation in comparison with the traditional schemes. Also, the performance of the UWA‐OFDM system can be preserved in the presence of frequency offsets. 相似文献
17.
《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》2008,16(12):1620-1630
18.
Li Jun Liao Guisheng Wu Yuntao 《电子科学学刊(英文版)》2006,23(1):121-123
Most of the blind Orthogonal Frequency Division Multiplexing (OFDM) Carrier Frequency Offset (CFO) estimators necessitate large number of samples to ensure the estimation accuracy. However, the number of samples can not be selected too large because of the carrier offset drift. In this letter, a new closed form algorithm for blind OFDM CFO estimation in frequency-selective channel is proposed. This method utilizes the propagator obtained from data matrix and the diagonal loading technique, thus it has better performance even only using one or two OFDM blocks. Furthermore, the range of the CFO estimation which can be handled is overall transmission spectral. Simulation results confirm its effectiveness. 相似文献
19.