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1.
该文提出了一种适用于OFDM系统的联合符号和采样钟同步校正方法,其中同步校正是在数字域通过改变对接收过采样信号的插值(interpolation)和抽取(decimation)实现的.这种方法在发送端相邻载波间采用差分QPSK调制,在接收端利用QPSK的差分解调信号获得同步误差信号,从而获得关于OFDM符号同步和采样钟同步调整的算法,其特点是无需专门的同步导频信号.所提出算法的同步性能在高斯白噪声信道和多径衰落信道均得到验证.  相似文献   

2.
On the synchronization techniques for wireless OFDM systems   总被引:3,自引:0,他引:3  
The latest research works on the synchronization scheme for either continuous transmission mode or burst packet transmission mode for the wireless OFDM communications are overviewed in this paper. The typical algorithms dealing with the symbol timing synchronization, the carrier frequency synchronization as well as the sampling clock synchronization are briefly introduced and analyzed. Three improved methods for the fine symbol timing synchronization in frequency domain are also proposed, with several key issues on the synchronization for the OFDM systems discussed.  相似文献   

3.
In this paper, we present a novel joint algorithm to estimate the symbol timing and carrier frequency offsets of wireless orthogonal frequency division multiplexing (OFDM) signals. To jointly estimate synchronization parameters using the maximum likelihood (ML) criterion, researchers have derived conventional models only from additive white Gaussian noise (AWGN) or single-path fading channels. We develop a general ML estimation algorithm that can accurately calculate symbol timing and carrier frequency offsets over a fast time-varying multipath channel. To reduce overall estimation complexity, the proposed scheme consists of two estimation stages: coarse and fine synchronizations. A low complexity coarse synchronization based on the least-squares (LS) method can rapidly estimate the rough symbol timing and carrier frequency offsets over a fast time-varying multipath channel. The subsequent ML fine synchronization can then obtain accurate final results based on the previous coarse synchronization. Simulations demonstrate that the coarse-to-fine method provides a good tradeoff between estimation accuracy and computational complexity.  相似文献   

4.
This paper calculates the performance of an orthogonal frequency division multiplexing (OFDM) system confronted with Rayleigh fading channels in terms of sync detection probability. We adopted a timing synchronization scheme employing simple repeated constant amplitude zero auto-correlation (CAZAC) training symbol with relevant correlation techniques, and analyzed the effect of imperfect noise estimation. Some probability expressions of OFDM timing synchronization for system measurement are evaluated.  相似文献   

5.
In this paper, we propose three symbol synchronization schemes for Orthogonal Frequency Division Multiplex (OFDM) systems. The cyclic extension preceding OFDM symbols is of decisive importance for these schemes. The first scheme uses the phase‐differential coding of the received OFDM signal. The second and the third schemes use the length of the received OFDM signal. All three schemes make symbol synchronization possible, even though there is a frequency offset in the system. Simulation results show that these schemes can be used to synchronize an OFDM system over AWGN and multi‐path fading channels.  相似文献   

6.
In this paper we consider the design of a robust timing synchronization algorithm for pilot-aided OFDM systems in high-mobility fading environments. We first analyze the impact of both mobility and timing errors on the performance of a pilot-aided OFDM system for frequency selective fading channels, by deriving an expression for channel estimation error variance. The analysis will show that, even for high levels of mobility, a pilot-aided channel estimator is considerably sensitive to timing errors, due to the impact of rotations in different bases. We then show how this sensitivity can be utilized to design a robust timing synchronization algorithm for mobile OFDM systems, without relying on synchronization training information. Theoretical results are then confirmed by simulating the performance of an OFDM system in high delay and Doppler spread fading environments. Finally, we show how the proposed mathematical framework and algorithm can be used to address timing synchronization in the presence of a frequency offset as well. The analysis of this paper is the extension of the derivations of Part I [8], the accompanying paper on the design of a robust timing synchronizer for low-mobility OFDM systems.  相似文献   

7.
Orthogonal frequency division multiplexing (OFDM) is a popular modulation technique that can combat impulsive noise, is robust to multipath fading, is spectrally efficient, and can allow flexible allocation of spectrum. It has become a key standard in cognitive radio systems as well as an enabling technology for mobile data access systems. An OFDM receiver’s performance is heavily impacted by the accuracy of its symbol timing offset (STO) and carrier frequency offset (CFO) estimation. This paper proposes a novel OFDM synchronization method that combines robust performance with computational efficiency. FPGA prototyping is used to explore the trade-off between the number of computations to be performed and computation word length with respect to both synchronization performance and power consumption. Through simulation, the proposed method is shown to provide accurate fractional CFO estimation as well as STO estimation in a range of channels. In particular, it can yield excellent synchronization performance in the face of a CFO that is larger than many state-of-the-art synchronization implementations can handle. The system implementation demonstrates efficient resource usage and reduced power consumption compared with existing methods, and this is explored as a fine-grained trade-off between performance and power consumption. The result is a robust method suitable for use in low-power radios, enabling less precise analog front ends to be used.  相似文献   

8.
OFDM has the advantage over the conventional single-carrier modulation schemes in the presence of frequency-selective fadings. Nevertheless, intercarrier-interference (ICI) due to Doppler frequency drift, phase offset, local oscillator frequency drift, and sampling clock offset will be a severe problem in the wireless OFDM systems. Previous ICI self-cancellation coding schemes can greatly reduce the ICI, but they are very sensitive to the phase ambiguity, which is due to the composite effect of the phase offset, the multipath fading and the local oscillator frequency drift. In this paper, a novel receiver which combines the current ICI self-cancellation coding techniques with a new pilot-free joint phase/amplitude estimation and symbol detection scheme is proposed. Based on the energy modulation or the irregular symbol constellation, our new technique does not have any requirement of pilot symbols and it can operate on all kinds of phase error ranges. The proposed scheme is promising in comparison with other existing methods at different noise levels through OFDM simulations.  相似文献   

9.
In this paper, a super-imposed scheme for timing and frequency synchronization is proposed for orthogonal frequency division multiplexing (OFDM) systems. The proposed architecture includes a pre-defined pseudo-noise (PN) sequence, which is added to both the OFDM symbol and the cyclic prefix (CP) in time domain. In contrast to existing synchronization schemes, the proposed architecture has the advantage of better bandwidth utilization since it does not require extra pilot symbols. The peak-to-average power ratio (PAPR) is also significantly decreased. Both the timing and frequency offset estimators are derived using the maximum likelihood (ML) criterion. Efficiencies of the estimators are analyzed mathematically in AWGN channels. Simulation experiments are also conducted in frequency selective fading channels. Moreover, the optimal power allocation factor of the PN sequence is determined by minimizing the bit error rate using simulation experiments  相似文献   

10.
Joint Frequency and Symbol Synchronization Schemes for an OFDM System   总被引:8,自引:0,他引:8  
This paper proposes two multi-stage joint symbol timing and carrier frequency synchronization schemes for an orthogonal frequency division multiplex (OFDM) system. Simultaneous estimation of symbol timing and frequency offset is derived from the maximum likelihood (ML) principle, assuming a cyclic prefix (guard interval) is inserted in each OFDM symbol. One of the proposed algorithms derives an initial frequency estimate in the first stage that reduces the frequency uncertainty to only two or three sub-carrier spacings. The timing information and a finer frequency estimate that has a resolution of a sub-carrier spacing are obtained in the second stage. The third stage provides an estimation for the residual fractional frequency error. The other algorithm bypasses the first stage for one can use the second stage alone to search for the timing and frequency offsets. However, the computing complexity of the second stage is higher than that of the first stage, thus the three-stage algorithm is a preferred choice unless the frequency uncertainty is small. Simulation results show that both algorithms yield excellent performance not only in white Gaussian channels but also in multipath fading channels.  相似文献   

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