共查询到20条相似文献,搜索用时 15 毫秒
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Hsiao-Chun Wu Xiaozhou Huang Dongxin Xu 《Broadcasting, IEEE Transactions on》2006,52(2):211-218
Intercarrier interference is deemed as one of the crucial problems in the wireless orthogonal frequency division multiplexing (OFDM) systems. The conventional ICI mitigation schemes involve the frequency-domain channel estimation or the additional coding, both of which require the spectral overhead and hence lead to the significant throughput reduction. Besides, the OFDM receivers using the ICI estimation rely on a large-dimensional matrix inverter with high computational complexity especially for many subcarriers such as digital video broadcasting (DVB) systems and wireless metropolitan-area networks (WMAN). To the best of our knowledge, no semi-blind ICI equalization has been addressed in the existing literature. Thus, in this paper, we propose a novel semi-blind ICI equalization scheme using the joint multiple matrix diagonalization (JMMD) algorithm to greatly reduce the intercarrier interference in OFDM. However, the well-known phase and permutation indeterminacies emerge in all blind equalization schemes. Hence we also design a few OFDM pilot blocks and propose an iterative identification method to determine the corresponding phase and permutation variants in our semi-blind scheme. Our semi-blind ICI equalization algorithm integrating the JMMD with the additional pilot-based iterative identification is very promising for the future high-throughput OFDM systems. Through Monte Carlo simulations, the QPSK-OFDM system with our proposed semi-blind ICI equalizer can achieve significantly better performance with symbol error rate reduction in several orders-of-magnitude. For the 16QAM-OFDM system, our scheme can also improve the performance over the plain OFDM system to some extent. 相似文献
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针对传输正交幅度调制信号的多输入多输出频率选择性衰落无线通信系统中的信号间干扰与信号内部的码间干扰问题, 提出了一种改进的软决策算法.该方法精确地利用了正交振幅调制(Quadrature Amplitude Modulation, QAM)信号星座图信息, 避免了经典恒模算法、多模算法中存在的误调问题, 提高了均衡性能.对代价函数采用梯度牛顿法进行优化, 与常用的梯度类算法相比, 其具有更快的收敛速度.通过均方误差和最大信道扭曲分析和验证了该算法的可靠性和有效性. 相似文献
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This paper details a new orthogonal-frequency-division-multiplexing (OFDM) modulator based on the use of a pseudorandom postfix (PRP)-OFDM and discusses low-complexity equalization and channel estimation/tracking architectures. The main property of this new modulation scheme is the ability to estimate and track the channel variations semi-blindly using order-one statistics of the received signal. Compared with known cyclic prefix OFDM (CP-OFDM) pilot-symbol-assisted modulation (PSAM) schemes, the pilot overhead is avoided: The channel estimation is performed based on the exploitation of pseudorandomly weighted postfix sequences replacing the guard interval contents of CP-OFDM. PRP-OFDM is shown to be of advantage if the target application requires 1) a minimum pilot overhead, 2) low-complexity channel tracking (e.g., high mobility context), and 3) adjustable receiver complexity/performance trade-offs (available due to the similarities of PRP-OFDM to the zero-padded OFDM (ZP-OFDM) modulation scheme) without requiring any feedback loop to the transmitter. 相似文献
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XuChangqing ZhangXiaobo SongWentao 《电子科学学刊(英文版)》2004,21(1):78-82
The Bit Error Rate (BER) caused by Inter Carrier Interference (ICI) increases greatly with the increase of frequency offset in Orthogonal Frequency Division Multiplexing (OFDM) systems.According to a typical OFDM signal model,this letter proves that the coefficient matrix of ICI is a unitary matrix whose inverse matrix is much easier to get,and then proposes a new ICI cancellation method with less computation complexity by sending typical pilot symbols.Compared with two existing ICI cancellation methods,self-cancellation and windowing cancellation,it is shown that the proposed algorithm can cancel ICI better and overcome the limitation of the two traditional methods. 相似文献
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在OFDM系统中,时域均衡器用来抵消因循环前缀长度不足而引起的码间串扰。本文提出了一种新的时域均衡器的设计方法,该方法同时考虑了码间串扰和噪声对传输速率的影响。最佳均衡器的系数通过快速傅立叶变换在频域进行计算,并可通过求取矩阵的特,征向量来获得。仿真结果表明所提出来的方法能有效地提高系统传输速率。 相似文献
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频率选择性衰落OFDM的半盲信道估计算法研究 总被引:4,自引:4,他引:0
从系统性能分析和设计的角度详细地研究了基于无线HIPERLAN2通信协议的OFDM(orthogonal frequency division multiplexing,正交频分多路复用技术)系统信道估计与均衡的一种半盲算法,提出了结合直接法和Cholesky分解法的切换盲算法。这种半盲算法综合了全盲算法得到的信息与已知导频符号,充分利用了原发信号的统计特性和OFDM帧结构中插入的导频符号,克服了全盲和导频训练序列存在的问题^[6,7],且不需额外的带宽。仿真结果表明,在误比特率和收敛性方面,该算法比现有的主要三种全盲算法有更好的收敛和抗干扰特性。 相似文献
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This paper presents a general framework for space-time codes (STCs) that encompasses a number of previously proposed STC schemes as special cases. The STCs considered are block codes that employ arbitrary redundant linear precoding of a given data sequence together with embedded training symbols, if any. The redundancy introduced by the linear precoding imposes structure on the received data that under certain conditions can be exploited for blind or semi-blind estimation of the transmitted sequence, a linear receiver that recovers the sequence, or both simultaneously. Algorithms based on this observation are developed for the single-user flat-fading case and then extended to handle multiple users, frequency-selective fading, as well as situations where the channel is rank deficient, or there are fewer receive than transmit antennas. 相似文献
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Channel identification techniques that do not require the use of a training sequence (blind methods), or that can operate with very short training sequence (semiblind methods) are a topic of major concern for modern communication applications. This paper presents a review of channel identification methods that are applicable in this context, with a strong emphasis on second-order subspace-based and maximum likelihood (Ml) estimation schemes. The main focus of the paper is on: (i) providing a clear picture of the principle and theory associated with subspace-based methods in the blind and semi-blind contexts; (ii) describing algorithmic solutions, sometimes based on novel results, that are suitable for carrying out the delicate likelihood optimization task associated withMl estimation. 相似文献
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Orthogonal frequency division multiplexing (OFDM) has been widely used for its robustness against multipath fading and low-complexity implementation. However, OFDM system, especially with large number of subcarriers and high modulation order, is severely affected by the phase noise of oscillators and carrier frequency offset (CFO). On the other hand, self-cancellation schemes have received a lot of attention due to their simple implementation and high efficiency to suppress inter-carrier interference (ICI) in OFDM systems. Among those ICI self-cancellation methods, symmetric conjugate symbol repetition (SCSR) has been proven to have the best bit error ratio (BER) performance for phase noise suppression. In this paper, the performance of OFDM systems with SCSR ICI self-cancellation in the presence of both phase noise (PHN) and CFO are investigated, and analytical expressions are derived to calculate error probability evaluated by symbol error ratio (SER) over additive white Gaussian noise (AWGN) and Rayleigh flat fading channels. An approach of second order approximation of PHN/CFO has been performed to estimate the residual ICI, which could provide more accurate results. Simulation results show perfect agreement with those obtained by theoretical analysis, which could be used to estimate OFDM system error probability, facilitating the design of the overall system. 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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Per-tone equalization for MIMO OFDM systems 总被引:5,自引:0,他引:5
This paper focuses on multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems with channel order larger than the cyclic prefix (CP) length. Writing the demodulating fast Fourier transform (FFT) as a sliding FFT followed by a downsampling operation, we show in this paper that by swapping the filtering operations of the MIMO channel and the sliding FFT, the data model for the temporally smoothened received signal of each individual tone of the MIMO OFDM system is very similar to the data model for the temporally smoothened received signal of a MIMO single-carrier (SC) system. As a result, to recover the data symbol vectors, the conventional equalization approach for MIMO SC systems can be applied to each individual tone of the MIMO OFDM system. This so-called per-tone equalization (PTEQ) approach for MIMO OFDM systems is an attractive alternative to the recently developed time-domain equalization (TEQ) approach for MIMO OFDM systems. In the second part of this paper, we focus on direct per-tone equalizer design and adapt an existing semi-blind equalizer design method for space-time block coding (STBC) SC systems to the corresponding semi-blind per-tone equalizer design method for STBC OFDM systems. 相似文献