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1.
A pilot-aided coherent uplink transmission scheme is proposed for mobile satellite communications at L-band. The scheme is designed to enhance link performance as compared to coded noncoherent M-ary orthogonal modulation, while maintaining small envelope fluctuations and low complexity. A rigorous analysis is performed for the proposed technique, when used in conjunction with a direct-sequence code-division multiple-access convolutionally encoded binary phase shift keying link, in a Rice-fading channel with satellite diversity. The pilot-aided scheme has been extensively simulated, accounting for finite interleaving in slow fading and nonideal carrier frequency recovery. The results show a significant performance gain with respect to noncoherent schemes designed for similar links, which goes up to 1.8 dB for 9.6 kb/s services with slow moving users exploiting dual-satellite diversity 相似文献
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《Broadcasting, IEEE Transactions on》2009,55(1):84-94
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从理论上分析了激光器相位偏移对相干光正交频分复用(CO-OFDM)系统传输性能影响,并指出相位噪声是相干光OFDM主要噪声源。在传统无线OFDM信道估计基础上,提出了一种基于导频子载波的相位噪声估计和补偿方法,在OptiSystem中建立CO-OFDM系统仿真模型,通过仿真证明了该方法可以有效地改善CO-OFDM系统传输性能。 相似文献
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在时变信道下正交频分复用(OFDM)系统中,通过导频辅助,提出基于可变遗忘因子RLS(VFF-RLS)的载波频偏(CFO)估计改进算法。针对传统RLS(CFF-RLS)算法中遗忘因子无法同时满足CFO估计收敛速度和收敛精度的缺陷,本文设计了线性变化遗忘因子(LFF)和非线性变化遗忘因子(NLFF) 两种可变遗忘因子方案来提升CFO估计性能。仿真结果显示:在低信噪比的情形下,基于VFF-RLS算法的CFO估计性能明显优于基于CFF-RLS算法的CFO估计性能。 相似文献
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在多径分量数确定的前提下,MIMO-OFDM系统采用传统的基于导频辅助和盲信道估计算法能获得较好性能。实际无线环境中,多径分量数目与幅度都是时变的,则传统信道估计方法不再适用。该文采用随机集理论建模MIMO-OFDM系统信道多径分量数的变化和MIMO信道。基于此模型提出了集中粒子空间重采样方法(CRS),在保留大概率粒子抽样样本的同时主动抛弃小概率抽样样本,以获得更为准确的真实样本逼近。并提出了基于集中重采样Rao-Blackwellised粒子滤波的信道估计方法(RBPFC)。仿真结果表明:所提出的RBPFC方法信道估计性能最好,基本Rao-Blackwellised粒子滤波方法次之但优于基本粒子滤波算法,卡尔曼滤波的信道估计方法性能最差。 相似文献
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A pilot-aided Orthogonal Frequency Division Multiplexing (OFDM) frequency offset estimator designed for satellite communication system is proposed in the paper. The estimator focuses on the acquisition of the integer part of carrier frequency offset and the acquisition range is as large as the whole signal bandwidth. Making full use of the phase difference between received pilot and local referential pilot, a fast estimation is obtained. Compared with existing method, our method can also work well even in SNR as low as 0dB. Simulations verify the good performance of our method. 相似文献
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在诸如卫星通信、深空通信和无人机通信等领域中,收发端通常工作在低信噪比、功率和频谱双重受限的条件下。因此,串行级联CPM(包括GMSK调制)方案得到了广泛的关注和应用。针对串行级联CPM中非相干解调算法存在的较大性能损失,提出了一种导频辅助的准相干解调算法。该算法的基本原理是将编码后的序列分成若干组,在每组数据块中分插导频符号后送入调制器,解调时在相邻导频块之间采用状态初始化后的BCJR算法。仿真结果表明:非联合迭代方案下,利用少量导频辅助的准相干解调串行级联CPM系统可以获得接近于相干解调的性能;联合迭代方案下,仅利用2个导频的准相干软输入软输出串行级联CPM系统能够得到将近2 dB的性能增益。此外,设计的串行级联CPM系统还具有一定的抗突发错误能力。 相似文献
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改进的相位展开算法及其在瞬时频率估计中的应用 总被引:5,自引:1,他引:4
研究了一种改进的相位展开算法及其在瞬时频率估计中的应用.首先讨论了噪声对相位展开的影响,发现当每个周期内的样本数为2个样本时相位展开具有最佳的性能;接着利用这个性质得到一种简单的相位展开算法,可以在较低信噪比条件下估计出信号的瞬时相位;随后把相位展开算法应用于正弦波频率估计,得到了改进的相位平均法,利用它可以在较低信噪比条件下得到宽带信号的瞬时频率曲线;最后通过MATLAB仿真对算法进行验证. 相似文献
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Cyclic delay diversity (CDD) is a low-complexity standard-conformable transmit diversity scheme for coded orthogonal frequency division multiplexing (OFDM) systems. However, it makes channel estimation more challenging due to the increased frequency-selectivity of the equivalent single-input single-ouput channel. In this paper, we propose a novel CDD-OFDM scheme with pilot-aided channel estimation for any number of transmit antennas. By alternating and optimizing the cyclic delay parameter over adjacent OFDM symbols, we design a simple yet efficient channel estimation scheme and illustrate its excellent performance for the DVB-T application. 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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In this paper, we investigate the problem of carrier frequency-offset (CFO) synchronization and channel estimation in multiple-input multiple-output orthogonal frequency-division multiplexing systems operating over unknown frequency-selective fading channels. We first propose a novel joint CFO and channel estimator, assuming time-domain training blocks are available. The proposed joint estimator consists of two recursive least-square (RLS) algorithms which iterate their estimated CFO and CIR values. We then derive a more precise pilot-aided RLS algorithm to estimate the residual frequency synchronization errors or track small CFO changes. With this, the accuracy of channel estimation is also enhanced. The analysis and simulation results show that, the proposed estimation and tracking scheme which is fully compatible with the existing standards is able to attain fast convergence, high stability, and ideal performances as compared with relevant Cramer–Rao bounds in all ranges of signal-to-noise ratio. Moreover, it can work well for wide tracking range up to ±0.5 of the subcarrier spacing. 相似文献
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针对传统的无味卡尔曼相位展开算法效率和精度之间存在矛盾的问题,提出一种快速局部频率估计算法与量化质量图跟踪策略相结合的无味卡尔曼滤波(UKF)高效算法。快速局部频率估计算法首先利用二维傅里叶变换粗略计算出局部窗口内的复相位频谱的谱峰位置;然后,以谱峰为中心利用二维离散时间傅里叶变换快速算法计算出谱峰的精确位置,进而精确地获取局部频率值,得到UKF 相位展开系统模型所需的相位梯度估计值;最后,将UKF 算法与量化质量图跟踪策略相结合,利用量化质量图引导UKF 相位展开,进一步提高展开的效率。仿真实验验证了方法的有效性。 相似文献
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Phase Estimation for Coherent Optical OFDM 总被引:5,自引:0,他引:5
Phase estimation is one of the enabling functionalities in coherent optical orthogonal frequency-division-multiplexing (CO-OFDM) receivers. In this letter, we compare pilot-aided and data-aided phase estimation methods for a CO-OFDM transmission experiment at 8 Gb/s over 1000-km standard single-mode fiber without optical dispersion compensation. We also show that as few as five subcarriers are sufficient for pilot-aided phase estimation 相似文献
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In this paper we are interested in designing a robust timing synchronization algorithm for OFDM systems that utilize pilot-aided channel estimation. We first characterize the impact of timing errors on the performance of a pilot-aided OFDM system. We derive analytical expressions for average channel estimation error variance in the presence of timing errors in high delay spread fading environments. The derived expressions show that pilot-aided channel estimators are considerably sensitive to timing synchronization errors due to the impact of rotations in different bases. We then show how to utilize this sensitivity to design a robust timing synchronization algorithm, without training overhead. The proposed algorithm is a cross-block design that uses channel estimation information to improve timing synchronization. We confirm our analytical results by simulating the proposed algorithm in high delay spread fading environments. In this paper, i.e. part I, we focus on timing synchronization for low-mobility cases. The analysis and results are then extended to high-mobility applications in part II. 相似文献
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A new joint frame synchronization and carrier frequency offset estimation scheme in orthogonal frequency division multiplexing (OFDM) systems is proposed in this paper, where both frame synchronization and carrier frequency offset estimation can be performed by using only ONE training symbol. Frame synchronization and carrier frequency offset acquisition are performed simultaneously in the proposed scheme. Reliable frame synchronization is obtained in the proposed scheme even in low SNR. The maximum carrier frequency offset acquisition range of the proposed scheme can be up to one half of the total signal bandwidth. The same training symbol can also be utilized to carrier frequency offset Fine Adjustment, which estimates the remaining carrier frequency offset after acquisition with higher accuracy. The performance comparison of the proposed Fine Adjustment algorithm and Schmidl's algorithm by using computer simulation illustrates and verify the superior performance of the proposed algorithm with regard to estimation accuracy. 相似文献
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A simple channel estimation (CE) scheme, which is pilot-aided with just a little number of pilots inserted in the first half part of the subcarriers, is proposed and simulated for resisting the fiber dispersion in optical orthogonal frequency division multiplexing (OFDM) systems. The simulation results verify that the receiver sensitivity is improved by 2-3 dBm for bit error rate (BER) of 10-3 with the proposed CE algorithm than that with other kinds of CE algorithms based on linear square principle. The good constellation performance for a 40 Gbit/s transmission system can be also obtained by the proposed scheme. 相似文献
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Low-complexity pilot-aided compensation for carrier frequency offset and I/Q imbalance 总被引:1,自引:0,他引:1
We propose a novel pilot-aided compensation scheme for carrier frequency offset (CFO) and I/Q imbalance. The proposed scheme comprises a generalized periodic pilot and a low-complexity acquisition algorithm, where the CFO and the coefficients for I/Q imbalance compensation can be obtained in explicit closed-form. 相似文献