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INTRODUCTION Orthogonal frequency division multiplexing (OFDM) is now a popular technique for high data rate wireless communication. Due to its simple imple-mentation and attractive performance against fre-quency-selective wireless fading channels, it has been adopted in several wireless standards such as digital audio broadcasting (DAB), digital video broadcasting (DVB), IEEE 802.11a local area network (LAN), IEEE 802.16a metropolitan area network (MAN) and asymmetric digital s… 相似文献
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在采用导频的正交频分复用(OFDM)系统中,常采用离散傅里叶变换(DFT)插值的方法来实现信道估计。针对DFT算法中虚子载波的缺失而导致冲激响应有频谱泄漏的现象,对DFT算法进行了两种改进,一是采用维纳滤波插入法重建虚子载波的信道信息,二是通过优化有效导频的LS信道估计来减小噪声的影响,并提高系统的性能。通过仿真证明,改进算法明显优于传统DFT算法。 相似文献
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针对接收IQ不平衡的OFDM系统,设计了横跨2个OFDM符号的特殊训练结构.提出了一种高效的时域最小二乘(TD-LS)信道估计和一种低复杂度的频域高斯消元补偿算法来消除IQ失真.前者与传统的频域LS算法相比,信道估计噪声的影响降低了N/(L+1)倍,其中N为子载波总数,L+1为循环前缀长度;后者实现复杂度低,每个OFDM符号仅需要2N次复数乘法.仿真结果表明:由于充分挖掘了信道参数的时域特性,提出的TD-LS信道估计算法与传统的FD-LS算法相比获得了可观的信噪比增益;提出的低复杂度的GE补偿算法能够获得与基于LS的频域补偿方案几乎相同的误码性能. 相似文献
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This paper deals with design and analysis of user scheduling and power allocation for multi-antenna OFDM systems with DPC, ZF-DPC, ZF-BF and TDMA transmit strategies. We consider the general multi-user downlink scheduling problem and power minimization with multi-user rate constraints. According to the channel state, it is shown that there is a power optimal policy which selects a subset of users in each scheduling interval. We present user selection algorithms for DPC, ZF-DPC, ZF-BF and TDMA for multi-antenna OFDM system in broadcast channels, and we also present the practical water-filling solution in this paper. By the selected users with the consideration of fairness, we derive the power optimization algorithm with multi-user rate constraints. We also analyze the power duality of uplink-downlink for the transmit strategies of DPC, ZF-DPC and ZF-BF. Simulation results show that the present user-scheduling algorithm and power minimization algorithm can achieve good power performance, and that the scheduling algorithm can guarantee fairness. 相似文献
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提出了一种新的构造LDPC码的方法, 并把用该方法产生的LDPC码应用到编码正交频分复用(OFDM)系统中进行了研究. 该方法拓展了单位阵移位构造的LDPC码, 它利用简单的不等式可确保在置换单位阵构造中不会产生Tanner图中的短圈, 使得产生的LDPC码的Tanner图最小圈长为8. 由于该类码是准循环码以及其校验矩阵所固有的分层结构, 编码器和解码器都易于实现, 它们分别是线性可编和线性可译的. 所提出的LDPC码码率范围较大, 可以灵活选取. 利用迭代解码进行计算机仿真, 发现新的LDPC码比其他的规则LDPC码在编码OFDM系统中具有更好的性能. 相似文献
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孟琳君 《绵阳师范学院学报》2007,26(11):28-31
提出了OFDM系统中一种新的基于软信息迭代处理的信道估计算法。该算法将面向判决最小二乘估计算法和盲估计算法相结合,在估计器中构造了一种新的置信度量函数,根据解码和软映射重构的反馈信号置信度大小在两种估计算法中自适应选择,这样估计的信道频响可以有效提高软信息迭代接收性能,大大降低信道估计训练开销。仿真结果表明,该文提出的算法能有效跟踪信道时变,限制传统面向判决估计的错误传播,达到好的系统性能。 相似文献
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Peak-power reduction by the lattice-reduction-aided closest point search for MIMO broadcast channels
In this letter, we present a modified vector-perturbation precoding scheme for the multiple-input multiple-output broadcast channel, where a perturbation vector is chosen to take into account both the instantaneous power and the instantaneous peak power of the transmitted signal. This perturbation vector is obtained by using the closest point search, with the aid of the lattice-reduction algorithm. Simulation results show that the proposed scheme yields a tradeoff among power efficiency, peak-to-average power ratio reduction, and complexity. 相似文献
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As one of the most important components of the wideband wireless access technique, orthogonal frequency division multiplexing (OFDM) has a high usage rate of spectrum and combats inter-symbol interference (ISI) in multi-path fading channel. However, when there are frequency offsets during the signal transmission, the inter-carrier interference (ICI) is introduced, which significantly degrades the performance. The existing ICI self-cancellation schemes such as PCC-OFDM are not optimum to minimize the interference considering both noise and ICI. In this paper, a new metric named S1NR (signal-to-interference- and-noise ratio) is proposed. We discuss the optimization issue when a constant frequency offset exists and in time-varying channels. The optimum weighting-coefficient-pair (OWCP) is obtained, which maximizes SINR theoretically through the alternant iteration algorithm. Simulations show that the performance of OWCP-OFDM is better than that of PCC-OFDM, especially when the frequency offset is large. Although the ICI self-cancellation scheme suffers bandwidth inefficiency, from the simulation results we can also see that the performance of OWCP-OFDM is much better than that of the standard OFDM systems with the same bandwidth efficiency when a frequency offset exists. Moreover, since the redundant modulation provides the capability to suppress ICI as well as a receiving SNR gain, it can be considered as exchanging the bandwidth for SNR. 相似文献
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A particle filter is proposed to perform joint estimation of the carrier frequency offset (CFO) and the channel in multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) wireless communication systems. It marginalizes out the channel parameters from the sampling space in sequential importance sampling (SIS), and propagates them with the Kalman filter. Then the importance weights of the CFO particles are evaluated according to the imaginary part of the error between measurement and estimation. The varieties of particles are maintained by sequential importance resampling (SIR). Simulation results demonstrate this algorithm can estimate the CFO and the channel parameters with high accuracy. At the same time, some robustness is kept when the channel model has small variations. 相似文献
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A simplified minimum mean square error (MMSE) detector is proposed for joint detection and decoding of multiple-input multiple-output (MIMO) systems. The matrix inversion lemma and the singular value decomposition (SVD) of the channel matrix are used to simplify the computation of the coefficient of the MMSE filter. Compared to the original MMSE detector, the proposed detector has a much lower computational complexity with only a marginal performance loss. The proposed detector can also be applied to MIMO systems with high order modulations. 相似文献
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为了克服现有通信技术中在低信噪比情况下计算复杂度高、误码性能差的缺陷,提出了一种改进型的OFDM通信系统,在Simulink仿真平台中设计了完整的通信系统模型,模拟了多径瑞利衰落信道与加性高斯白噪声信道的OFDM通信完整过程,实验结果表明,改进型的OFDM通信系统对信噪比要求不高,降低了OFDM通信系统中所存在的高峰均比问题,能有效地消除信号多径传播所造成符号干扰并且误码率较低。 相似文献
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1 Introduction Space-ti me coding (STC)[1-4]is an emerging tech-nique in communications . Multi-input multi-output(MIMO) signals are encoded in both spatial and tem-poral domains .As a result ,diversity and coding gainsare achieved . Most works to date on this subject arebased on two fundamental assumptions . One is thatthe transmitter does not knowthe channel state infor-mation (CSI) ,i.e.,openloop .The otheris that fad-ing from each base station antenna to any mobile an-tenna is indepen… 相似文献
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1 Introduction Space-ti me coding (STC)[1-4]is an emerging tech-nique in communications . Multi-input multi-output(MIMO) signals are encoded in both spatial and tem-poral domains .As a result ,diversity and coding gainsare achieved . Most works to date on this subject arebased on two fundamental assumptions . One is thatthe transmitter does not knowthe channel state infor-mation (CSI) ,i.e.,openloop .The otheris that fad-ing from each base station antenna to any mobile an-tenna is indepen… 相似文献
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莫文辉 《十堰职业技术学院学报》2013,26(1):97-99
随机因素对振动的影响不可忽略。本文将质量刚度、阻尼系数看作随机变量,研究了单自由度强迫振动的共振频率的可靠性。对随机变量进行计算机模拟,产生大量样本。应用Monte Carlo模拟研究了振动位移的可靠性。模拟次数越多,求得的可靠度精度越高。算例表明本文方法是正确的。 相似文献
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We present novel vector permutation and branch reduction methods to minimize the number of execution cycles for bit reversal algorithms. The new methods are applied to single instruction multiple data (SIMD) parallel implementation of complex data floating-point fast Fourier transform (FFT). The number of operational clock cycles can be reduced by an average factor of 3.5 by using our vector permutation methods and by 1.1 by using our branch reduction methods, compared with conventional implementations. Experiments on MPC7448 (a well-known SIMD reduced instruction set computing processor) demonstrate that our optimal bit-reversal algorithm consistently takes fewer than two cycles per element in complex array operations. 相似文献