共查询到19条相似文献,搜索用时 140 毫秒
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OFDM系统中的盲信道估计 总被引:1,自引:0,他引:1
本文从OFDM信号的矩阵表示出发,分析比较了OFDM系统中现有的各种盲信道估计方法。OFDM盲信道估计方法分为两类,一类是统计型方法,它利用了发送信号和接收信号的统计特性;另一类是确定型方法,它利用了发送调制信号的固有特性。一般而言,统计型方法的计算量较小,但是估计精度不高且估计的实时性不好;而确定型方法的估计精度较高,实时性较好,但是其计算量较大。计算机仿真表明,这些盲信道估计方法的性能受信道参数尤其是多普勒频率影响很大,盲信道估计的实用化有待进一步研究。 相似文献
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OFDM系统中的盲信道估计对能否正确恢复信号起决定性作用,现有的算法存在计算复杂度高、精度低的缺点.本文提出将传统的盲信道辨识算法,即线性预报法应用于SIMOOFDM系统中.该算法利用二阶统计量信息,其计算复杂度明显降低,本算法对信道阶数的估计更具有鲁棒性,可获得较高的估计精度.仿真表明,本文算法的性能优于子空间算法. 相似文献
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基于OFDM信号周期平稳特性的盲信道估计算法 总被引:2,自引:1,他引:1
该文提出一种基于信号周期平稳特性的盲信道估计算法,用于频率选择性衰落环境下的正交频分复用(OFDM)系统。该算法利用OFDM信号本身具有的周期平稳特性以及其周期自相关函数值的能量分布规律,确定信道阶数,并通过确定信道零点的方法间接获得信道冲激响应。理论和仿真结果表明,与其它的盲信道估计算法相比,该算法不仅可以较准确地获得信道阶数,而且降低了信道估计的均方误差。 相似文献
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该文提出一种基于矩阵开方(computing Roots of Matrices, RM)的盲信道估计算法和一种自适应矩阵开方(Adaptive computing Roots of Matrices, ARM)盲信道估计算法。RM算法利用信息符号的有限字符集特性,在时域上通过对一个Toeplitz下三角矩阵开方进行信道解卷积,得到信道估计的闭合解。该运算复杂度远低于现有的盲信道估计搜索算法,并且适用于信道阶数较大、搜索算法不能处理的情况。仿真结果表明RM信道估计性能接近于搜索算法的最佳性能,而ARM通过最陡下降迭代将代价函数最小化,可以进一步提高信道估计的准确性。 相似文献
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基于信号子空间的改进OFDM系统信道半盲估计 总被引:1,自引:0,他引:1
本文改进了一种基于信号子空间的OFDM系统半盲信道估计算法.该算法利用基于梯度变化的变遗忘因子递归最小二乘算法(GVFF-RLS)计算接收信号的自相关矩阵.通过同时对角化接收信号中的信息信号和噪声信号的全局协方差矩阵,推导出噪声信号子空间,无需对噪声信号的统计特性进行任何先验假定.本算法弥补了原始算法在慢衰落信道下收敛慢以及只限于加性白噪声的不足,实现了色噪声背景下高效半盲信道估计.仿真结果表明本文提出的算法具有良好的性能. 相似文献
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Video broadcasting is one of the feasible solutions to implement a large-scale video-on-demand (VoD) system. Nevertheless, it is still an open issue for the provision of continuous VCR functions in a delay insensitive broadcast VoD system. In this paper, we propose to jointly optimize an active buffer management scheme with contingency channels to support the VCR functions in an efficient protocol called partitioned broadcasting. We develop a greedy channel management scheme by exploiting the property of the broadcasting protocol such that the system bandwidth capacity can be fully utilized. Incorporating the channel management scheme with the partitioned video broadcast, the VoD system not only provides delay insensitive services but also handles all the interactive requests. Extensive simulation results demonstrate that the partitioned broadcasting system outperforms the traditional system based on the staggered broadcasting protocols. It is found that 20 broadcasting channels and 10 contingency channels are sufficient to support on average 720 customers for a single video with less that one second start-up delay and all types of VCR functions. 相似文献
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By exploiting the wireless multiple-input multiple-output (MIMO) channel structure, a brand new space-time code design criterion is derived. Based on the new criterion, we propose one low-complexity channel-adapted space-time (CAST) coding scheme, where trade-offs among codeword error rate, data throughput, and computational complexity are very flexible. Simulation results confirm that, in the frequency-selective MIMO channels, the CAST coding scheme can perform significantly better than the existing space-time codes, e.g., Alamouti space-time orthogonal code. 相似文献
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A MIMO channel spatial decorrelation scheme based on semi‐definite programming is introduced. As a particular application example, the paper addresses the potential gain of using multiple antennas and MIMO–OFDM techniques in order to increase the bandwidth efficiency in satellite communication systems. In particular, we consider the increase in channel capacity that is possible by exploiting satellite and polarization diversity. A fundamental case is studied with three satellite branches, and where each transmit/receive antenna unit consists of six elemental electric and magnetic dipoles yielding six distinguishable parallel polarization channels per frequency. The numerical examples show that capacity increases linearly on a logarithmic signal‐to‐noise ratio scale where the constant of proportionality is the number of active parallel channels. In this respect, the simultaneous use of triple electric and triple magnetic dipoles has the potential to triple the capacity of an antenna system based on antenna units of single dipoles. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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In this paper, we consider a new channel sounding scheme for opportunistic scheduling with the use of reduced channel information
in the uplink of orthogonal frequency division multiplexing (OFDM)-based wireless systems. To reduce signaling overhead for
the sounding, we propose a two step channel sounding process considering the correlation characteristic in the time and frequency
domain; called pre-sounding and main-sounding. Signal-to-noise power ratio (SNR) of each subchannel is first estimated through
the pre-sounding process. Then, a main-sounding signal is sent over subchannels having high SNR but not highly correlated
to each other. Since it is possible to extract the whole channel information from partial one by exploiting the channel correlation,
the proposed scheme can significantly reduce the sounding signaling overhead without noticeable performance degradation compared
to the full sounding scheme. Simulation results show that the proposed scheme provides significant performance improvement
over conventional schemes especially when the channel is highly correlated in the time and frequency domain. 相似文献
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《Solid-State Circuits, IEEE Journal of》2008,43(11):2381-2389
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Long-Lived TCP Connections Via Satellite: Cross-Layer Bandwidth Allocation, Pricing, and Adaptive Control 总被引:1,自引:0,他引:1
《Networking, IEEE/ACM Transactions on》2006,14(5):1019-1030
The paper focuses on the assignment of a common bandwidth resource to TCP connections over a satellite channel. The connections are grouped according to their source–destination pairs, which correspond to the up- and down-link channels traversed, and each group may experience different fading conditions. By exploiting the tradeoff between bandwidth and channel redundancy (as determined by bit and coding rates) in the maximization of TCP goodput, an overall optimization problem is constructed, which can be solved by numerical techniques. Different relations between goodput maximization and fairness of the allocations are investigated, and a possible pricing scheme is proposed. The allocation strategies are tested and compared in a fading environment, first under static conditions, and then in a real dynamic scenario. The goodput-fairness optimization allows significant gains over bandwidth allocations only aimed at keeping the channel bit error rate below a given threshold in all fading conditions. 相似文献
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The wireless mesh network is a new emerging broadband technology providing the last-mile Internet access for mobile users by exploiting the advantage of multiple radios and multiple channels. The throughput improvement of the network relies heavily on the utilizing the orthogonal channels. However, an improper channel assignment scheme may lead to network partition or links failure. In this paper we consider the assignment strategy with topology preservation by organizing the mesh nodes with available channels, and aim at minimizing the co-channel interference in the network. The channel assignment with the topology preservation is proved to be NP-hard and to find the optimized solution in polynomial time is impossible. We have formulated a channel assignment algorithm named as DPSO-CA which is based on the discrete particle swarm optimization and can be used to find the approximate optimized solution. We have shown that our algorithm can be easily extended to the case with uneven traffic load in the network. The impact of radio utilization during the channel assignment process is discussed too. Extensive simulation results have demonstrated that our algorithm has good performance in both dense and sparse networks compared with related works. 相似文献
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We present a new scheme that addresses the call handoff problem in mobile cellular networks. Efficiently solving the handoff problem is important for guaranteeing quality of service to already admitted calls in the network. Our scheme is based on a new approach called channel carrying: when a mobile user moves from one cell to another, render certain mobility conditions, the user is allowed to carry its current channel into the new cell. We propose a new channel assignment scheme to ensure that this movement of channels will not lead to any extra co-channel interference or channel locking. In our scheme, the mobility of channels relies entirely on localized information, and no global coordination is required. Therefore, the scheme is simple and easy to implement. We further develop a hybrid channel carrying scheme that allows us to maximize performance under various constraints 相似文献
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Lai L. Liu K. El Gamal H. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2006,52(3):805-828
We consider a wireless network composed of three nodes and limited by the half-duplex and total power constraints. This formulation encompasses many of the special cases studied in the literature and allows for capturing the common features shared by them. Here, we focus on three special cases, namely, 1) relay channel, 2) multicast channel, and 3) three-way channel. These special cases are judicially chosen to reflect varying degrees of complexity while highlighting the common ground shared by the different variants of the three-node wireless network. For the relay channel, we propose a new cooperation scheme that exploits the wireless feedback gain. This scheme combines the benefits of the decode-and-forward (DF) and compress-and-forward (CF) strategies and avoids the noiseless feedback assumption adopted in earlier works. Our analysis of the achievable rate of this scheme reveals the diminishing feedback gain in both the low and high signal-to-noise ratio (SNR) regimes. Inspired by the proposed feedback strategy, we identify a greedy cooperation framework applicable to both the multicast and three-way channels. Our performance analysis reveals the asymptotic optimality of the proposed greedy approach and the central role of list source-channel decoding in exploiting the receiver side information in the wireless network setting. 相似文献