共查询到20条相似文献,搜索用时 15 毫秒
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利用循环前缀(CP)引入的信息冗余,在利用接受信号的二阶统计特性实现正交频分复用(OFDM)系统信道盲估计的子空间算法基础上,采用矩阵变换的方法,改善信息序列的非周期相关函数,推导出信道估计的新算法。 相似文献
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We propose a new space‐time block coding (STBC) for asynchronous cooperative systems in full‐duplex mode. The orthogonal frequency division multiplexing (OFDM) transmission technique is used to combat the timing errors from the relay nodes. At the relay nodes, only one OFDM time slot is required to delay for a pair‐wise symbol swap operation. The decoding complexity is lower for this new STBC than for the traditional quasi‐orthogonal STBC. Simulation results show that the proposed scheme achieves excellent performances. 相似文献
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Jun Li Da Chen Daiming Qu Tao Jiang 《Wireless Communications and Mobile Computing》2016,16(17):2975-2990
Offset quadrature amplitude modulation‐based orthogonal frequency division multiplexing (OFDM) systems cannot be directly combined with the Alamouti code because of the intrinsic imaginary interference. In this paper, we propose a block‐wise space‐frequency block coding (SFBC) scheme and a block‐wise space‐time block coding (STBC) scheme for offset quadrature amplitude modulation‐based OFDM systems, which achieve bit error rate performances that are close to OFDM systems. The proposed schemes satisfy the orthogonality condition of the Alamouti code in the complex field with guard band/intervals. To improve the spectral efficiency of the block‐wise SFBC scheme, we also consider the case without the guard band. It is observed that only the two innermost subcarriers do not satisfy the complex orthogonality condition when the guard band is removed. Then, a simple equalization scheme is proposed to independently equalize the two innermost subcarriers. Simulation results show that the block‐wise SFBC scheme works well under channels with mild‐to‐moderate frequency selectivity, and the block‐wise (STBC ) scheme suffers less than 1 dB loss under severe frequency selective channels at the bit error rate of 10 − 3, when only a simple one tap zero‐forcing equalizer is employed. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Wen‐Long Chin 《Wireless Communications and Mobile Computing》2014,14(2):200-209
In this work, a channel‐power profile estimation for orthogonal frequency‐division multiplexing systems, based on the cyclic prefix (CP), is introduced. By knowing the delay of each path, the time‐dispersion information can be derived. The proposed method, considering long intersymbol interference (ISI) fading channels, requires only the coarse symbol timing information. More specifically, quasi‐stationary fading channels are considered. The basic contribution is to obtain the maximum‐likelihood estimation of the correlation coefficient based on the CP. Subsequently, the relationship between the correlation coefficient and the channel‐tap powers is explored. With the estimate of correlation coefficient, the least‐square solution of the channel‐tap powers can be determined. The proposed method is suitable for both short and long ISI channels. Furthermore, the Cramér–Rao lower bound of the channel‐power profile estimation is analyzed, and simulations confirm the advantages of the proposed estimator. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Haixia Zhang Dongfeng Yuan Matthias Ptzold Yi Wu Van Duc Nguyen 《Wireless Communications and Mobile Computing》2010,10(6):758-771
In this paper, we extend the geometrical one‐ring multiple‐input multiple‐output (MIMO) channel model with respect to frequency selectivity. Our approach enables the design of efficient and accurate simulation models for wideband space‐time MIMO channels under isotropic scattering conditions. Two methods will be provided to compute the parameters of the simulation model. Especially, the temporal, frequency and spatial correlation properties of the proposed wideband space‐time MIMO channel simulator are studied analytically. It is shown that any given specified or measured discrete power delay profile (PDP) can be incorporated into the simulation model. The high accuracy of the simulation model is demonstrated by comparing its statistical properties with those of the underlying reference model with specified correlation properties in the time, frequency and spatial domain. As an application example of the new MIMO frequency‐selective fading channel model, we study the influence of various channel model parameters on the system performance of a space‐time coded orthogonal frequency division multiplexing (OFDM) system. For example, we investigate the influence of the antenna element spacings of the base station (BS) antenna as well as the mobile station (MS) antenna. It turns out that an increasing of the antenna element spacing at the BS side results in a higher diversity gain than an increasing of the antenna element spacing at the MS side. Furthermore, the diversity gain brought in by space‐time block coding schemes is investigated by simulation. Our results show that transmitter diversity can significantly reduce the symbol error rate (SER) of multiple antenna systems. Finally, the influence of the Doppler effect and the impact of imperfect channel state information (CSI) on the system performance is also investigated. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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基于训练序列的信道估计方法在慢衰落信道中呈现出较好的性能,但是这种方法不适用于快衰落环境,为了能够及时跟踪信道的变化,通常采用基于导频符号的信道估计方法。将针对采用连续传输方式的MIMO—OFDM系统,讨论基于导频符号的信道估计方法并进行了计算机仿真。 相似文献
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介绍MIMO-OFDM系统中几种基于导频的信道估计方法。首先研究了单天线OFDM系统的信道估计算法。一方面重点关注三种估计准则的原理,仿真表明LMMSE准则具有最佳的性能;另一方面介绍了几种插值的方法用来恢复非导频处的信道信息。 相似文献
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MIMO-OFDM channel estimation method utilizing correlation in time domain for B3G-TDD uplink 总被引:3,自引:0,他引:3
ZHOU Ming-yu LI Li-hua JIANG Jun ZHONG Ming-hua TAO Xiao-feng Wireless Technologies Innovation Institute Beijing University of Posts Telecommunications Beijing China 《中国邮电高校学报(英文版)》2007,14(2):23-27
This article proposes a simple pilot-aided channel estimation method based on correlation in time domain for multiple-input and multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. Pilot symbols in all transmit antennas are generated from different circular shifting of a certain sequence. Through once correlation, the receiver can obtain time-domain pulse responses for channel fading from all transmit antennas to a certain receive antenna, from which channel estimation in frequency domain can be obtained. Beyond 3G time-division duplex (B3G-TDD) uplink is introduced, and the channel estimation method is used in it. Theoretical analysis and simulation are both carried out. Mean square error (MSE) performance shows that the method can exhibit precise estimation. Complexity analysis proves it requires very low complexity. System simulation result shows that it guarantees the performance of B3G-TDD uplink very well. 相似文献
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We propose two schemes for asynchronous multi‐relay two‐way relay (MR‐TWR) systems in which neither the users nor the relays know the channel state information. In an MR‐TWR system, two users exchange their messages with the help of NR relays. Most of the existing works on MR‐TWR systems based on differential modulation assume perfect symbol‐level synchronization between all communicating nodes. However, this assumption is not valid in many practical systems, which makes the design of differentially modulated schemes more challenging. Therefore, we design differential modulation schemes that can tolerate timing misalignment under frequency‐selective fading. We investigate the performance of the proposed schemes in terms of either probability of bit error or pairwise error probability. Through numerical examples, we show that the proposed schemes outperform existing competing solutions in the literature, especially for high signal‐to‐noise ratio values. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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In this paper, we discuss the design problem and the robustness of space‐frequency trellis codes (SFTCs) for multiple input multiple output, orthogonal frequency division multiplexing (MIMO‐OFDM) systems. We find that the channel constructed by the consecutive subcarriers of an OFDM block is a correlated fading channel with the regular correlation function of the number and time delay of the multipaths. By introducing the first‐order auto‐regressive model, we decompose the correlated fading channel into two independent components: a slow fading channel and a fast fading channel. Therefore, the design problem of SFTCs is converted into the joint design in both slow fading and fast fading channels. We present an improved design criterion for SFTCs. We also show that the SFTCs designed according to our criterion are robust against the multipath time delays. Simulation results are provided to confirm our theoretic analysis. 相似文献
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In this paper, we investigate the analytical performance of the multiple‐input multiple‐output system (MIMO) with orthogonal space‐time block codes (STBCs) subject to Weibull fading channels (WFC). Space‐time block code technique provides an efficient pattern for wireless transmission over various fading channels using multiple transmit antennas. Two approximating methods of the sum of independent Weibull random variables are studied. For each approach, we derive accurate approximate expressions for several performance metrics of MIMO‐STBC system operating under independent and nonidentical WFC. The proposed approximations are expressed in terms of 2 generalized hypergeometric functions, namely, Fox's H and Meijer's G functions. All the derived approximate expressions prove high accuracy, while compared with the simulation results established via Monte Carlo method and Kolmogorov‐Smirnov test as well. Although the 2 approaches have approximately the same accuracy, the second method approximate expressions are much less complex than those of the first method. 相似文献
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针对STBC-OFDM信号盲识别中存在着识别所需样本数多、对频偏敏感和不适用于单接收天线等问题,提出一种基于FOLP(Fourth Order Lag Product)的识别方法.根据不同空时分组码元素的相关性,推导了接收信号的FOLP,构造了基于FOLP的峰值检测算法.推导和仿真结果表明,该算法能够在单接收天线下运行,且不需要知道信道信息、噪声信息、调制信息以及OFDM块的起始位置;且该算法不受调制方式的影响,对时延、相位噪声和频率偏移鲁棒性能好,能够应用于认知无线电、频谱监控等工程领域中. 相似文献
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Xihua Dong Xiaochen Li Dapeng Wu 《Wireless Communications and Mobile Computing》2013,13(11):1014-1026
A recursive maximum likelihood carrier frequency offset (CFO) estimator is proposed in this work, where redundancy information contained in the cyclic prefix of multiple consecutive orthogonal frequency‐division multiplexing (OFDM) symbols is exploited in an efficient recursive fashion. Because the estimator is based on multiple OFDM symbols, the time‐varying CFO must be considered. We investigate the effect of time‐varying CFO on the performance of the estimator and the trade‐off between fast tracking ability and low estimation variance. We show that, without channel noise, the mean squared error (MSE) of estimation due to CFO estimation variation increases approximately quadratically with n, where n is the number of OFDM symbols used for CFO estimation (estimation window size), whereas the MSE due to channel noise decreases proportionally to 1/n (approximately) if the CFO is constant. A closed‐form expression of the optimal estimation window size (approximately) is derived by minimizing the MSE caused by both time‐varying CFO and channel noise. For wireless systems with time‐varying rate of change for CFO, the proposed estimator can be implemented adaptively. In addition, typical optimal estimation window sizes for WiMAX, DVB‐SH and MediaFLO systems are evaluated as an example. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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与传统的正交频分复用(OFDM)频域信道估计方法不同,提出了一种循环前缀为PN序列的OFDM信道估计方法:在时域OFDM符号中不插入传统意义上的循环前缀,而是插入PN序列作为训练序列,将PN序列与对应的接收序列作圆周相关处理获得信道频率响应估计;而由于PN序列周期性出现,它也起到了循环前缀的作用。仿真结果表明:在多径瑞利衰落信道中,在相同信噪比和相同信道利用率的条件下,提出的算法比频域梳状导频插入的时域滤波算法具有更高的信道估计精度。 相似文献