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基于多天线正交频分复用(MIMO- OFDM)系统提出了一种根据信道状态信息进行自适应比特交织的混合自动重传请求(HARQ)方案,它充分利用信道的状态信息对每次重传的比特进行交织来获得频率分集增益和平均各个比特间的可靠性.仿真结果表明,在Type III HARQ类型(包括Chase合并和部分冗余递增)下,该方案可以有效降低系统的误码率性能. 相似文献
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本文采用TURBO码为纠错码,在分析传统的反馈重传方式的基础上,将分块传输系统和码合并技术相结合,提出了一种新型HARQ系统,并为其设计了新型交织器。新型HARQ系统将每帧数据多次重传合并,转化为在一帧的多个分块之间合并,不需要重传。该系统大幅度降低了重传次数、交织的时延和平均迭代次数,实现了数据的实时通信;译码器接收的数据在解扩之前充分合并,更加有效地利用了软信息;该系统还省去了常用Ⅰ型HARQ系统中必须使用的收发端复杂的反馈重传控制和庞大的存储器;新型HARQ系统巾TURBO码的最小距离增加为原来的许多倍。通过理论分析和仿真比较了新型HARQ系统和Ⅰ型HARQ系统的性能,结果证明了新型HARQ系统性能的优越性。新型HARQ系统为第三代无线通信技术提供了一种较好地选择。 相似文献
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基于正交频分复用(OFDM)系统提出一种自适应混合自动重传请求(HARQ)方案,它充分利用发送端获得的信道状态信息对每次重传数据符号进行重组并且采用星座重组方案平均调制符号内各比特间的可靠性差异。仿真分析表明,自适应HARQ方案与星座重组方案相结合大大提高了系统通过率。 相似文献
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为了克服无线信道时变和多径衰落对信号传输的影响,全球微波互联接入(WiMAX)系统采用混合自动重传请求(HARQ)技术以提高数据传输的可靠性,确保服务质量。传统的非合并HARQ算法处理比较简单,内存需求较少,但是重传次数多,系统吞吐量低;合并译码HARQ算法能够有效减少重传次数,提高系统吞吐量,但是运算复杂度和内存需求较大。针对已有算法存在的不足,提出了一种基于大数逻辑判决(MLD)和信道冲激响应功率(CSI)的HARQ合并译码算法—MLD-CSI。该算法综合运用择多判决法则和择优选择法则,在接收端对多次重传的接收信号进行合并译码。分析和仿真结果表明,在时变和多径信道环境下,所提算法与MRC合并算法相比,几乎不损失系统的误码率和吞吐量性能,且运算复杂度和内存需求显著降低,非常适用于实际系统。 相似文献
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HARQ合并是具有高度鲁棒性的4G通信系统所必备的重要功能。针对LTE上行PUSCH数据传输信道,本文提出一种新的接收机模型,该模型对HARQ合并算法进行了改进。通过与传统的接收机模型的对比分析,可知:该模型能在不影响传输速率的情况下,极大降低每次重传数据的误码率、平均重传次数,从而进一步提高系统的传输性能。最后,通过不同信道环境下的仿真实验,验证了新型接收机的理论有效性及实际开发应用的可行性。 相似文献
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This article investigates transmitter design in Rayleigh fading multiple input multiple output (MIMO) channels with spatial correlation when there are channel uncertainties caused by a combined effect of channel estimation error and limited feedback. To overcome the high computational complexity of the optimal transmit power allocation, a simple and suboptimal allocation is proposed by exploiting the transmission constraint and differentiating a bound based on Jensen inequality on the channel capacity. The simulation results show that the mutual information corresponding to the proposed power allocation closely approaches the channel capacity corresponding to the optimal one and meanwhile the computational complexity is greatly reduced. 相似文献
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该文利用信道的特征矢量,将MIMO高斯信道转化成混合信道,结合功率分配给出了自适应调制方案,使系统容量在发射功率和服务质量约束下达到最大。发射端所需的波束成形和功率分配等信息利用有限的比特反馈到发射端。仿真结果表明:在小信噪比的情况下,该自适应调制方案对系统容量有明显改善。 相似文献
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On the information throughput and optimized power allocation for MIMO wireless systems with imperfect channel estimation 总被引:1,自引:0,他引:1
In this paper, we focus on the throughput analysis, outage evaluation and optimized power allocation for Multiple-Input Multiple-Output (MIMO) pilot-based wireless systems subject to short-term constraints on the radiated power and equipped with a feedback-path for communicating back to the transmitter the imperfect MIMO channel estimates available at the receiver. The case of the ergodic throughput for Gaussian distributed input signals is analyzed, and the conditions for the (asymptotical) achievement of the Shannon capacity are pointed out. The main contributions of this work may be so summarized. First, we develop closed-form analytical expressions for the computation of the ergodic information throughput conveyed by the considered MIMO system for the case of ideal feedback link. Second, we present an iterative algorithm for the optimized power allocation over the transmit antennas that explicitly accounts for the imperfect MIMO channel estimates available at the receiver. Third, after relaxing the assumption of ideal feedback link, we test the sensitivity of the proposed power allocation algorithm on errors possibly introduced by the feedback channel, and then, we numerically evaluate the resulting throughput loss. Finally, we develop closed-form upper and lower bounds on the outage probability that are asymptotically tight. 相似文献
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Song Fei Tong Xiaobing Wu Qihui Wang Jinlong 《电子科学学刊(英文版)》2008,25(1):53-58
A multi-Cyclic Redundancy Check (CRC) selective Hybrid Automatic-Repeat-reQuest (HARQ) scheme for improving the throughput efficiency of Multiple Input Multiple Output (MIMO) systems is proposed in this paper. According to different feedback information from the receiver, the proposed HARQ scheme employs two strategies, referred to as retransmission frame selection and space diversity. These two strategies decrease the successive frame errors upon retransmission. Theoretic analysis and computer simulation results show that this HARQ scheme achieves higher throughput than the existing HARQ schemes even in poor conditions of low Signal-to-Noise Ratio (SNR). 相似文献
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In this paper, a novel multiple antenna system framework, which combines smart antennas (SA) with multiple-input-multiple-output (MIMO) at the transmitter, is proposed. The downlink capacity of the single-user SA-MIMO wireless systems is investigated. The joint optimization problem corresponding to the capacity is deduced. After that, upper bounds of the capacity are given in general case and in the case of equal power allocation, respectively. Furthermore, in the case of equal power allocation and the same direction of departure from one transmit smart antenna to all antenna arrays at the receiver the closed-form expression of the capacity is obtained. Some numerical results are given to show that smart antennas can bring significant capacity gain for the MIMO systems due to the smart antennas gain, without additional spatial degrees of freedom, especially at high SNR with strong correlation among the MIMO channel links or at low SNR. 相似文献
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In this work, we propose an efficient selective retransmission method for multiple‐input and multiple‐output (MIMO) wireless systems under orthogonal frequency‐division multiplexing (OFDM) signaling. A typical received OFDM frame may have some symbols in error, which results in a retransmission of the entire frame. Such a retransmission is often unnecessary, and to avoid this, we propose a method to selectively retransmit symbols that correspond to poor‐quality subcarriers. We use the condition numbers of the subcarrier channel matrices of the MIMO‐OFDM system as a quality measure. The proposed scheme is embedded in the modulation layer and is independent of conventional hybrid automatic repeat request (HARQ) methods. The receiver integrates the original OFDM and the punctured retransmitted OFDM signals for more reliable detection. The targeted retransmission results in fewer negative acknowledgements from conventional HARQ algorithms, which results in increasing bandwidth and power efficiency. We investigate the efficacy of the proposed method for optimal and suboptimal receivers. The simulation results demonstrate the efficacy of the proposed method on throughput for MIMO‐OFDM systems. 相似文献
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Aiming at the problem of resource allocation in multiuser multi-input multi-output (MIMO) systems, a new power allocation algorithm based on dual waterfilling is proposed. Block diagonalization is adopted to cancel the inter-user interference, and then the complete diagonalization method is employed to derive the spatial sub-channels for each user. The overall power of the system is divided among users based on each user's large scale fading; then the power of each user is further allocated to its spatial sub-channels based on the small scale fading. Simulation results show that compared with the existing resource allocation strategies, the proposed algorithm can provide more ergodic capacity for multi-user MIMO systems. When the total transmit power is 100w, it has 15% capacity advantage over the traditional waterfilling method. 相似文献
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Tharaka A. Lamahewa Rodney A. Kennedy Thushara D. Abhayapala Van K. Nguyen 《Wireless Personal Communications》2007,43(2):777-799
In realistic channel environments the performance of space–time coded multiple-input multiple output (MIMO) systems is significantly
reduced due to non-ideal antenna placement and non-isotropic scattering. In this paper, by exploiting the spatial dimension
of a MIMO channel we introduce the novel idea of linear spatial precoding (or power-loading) based on fixed and known parameters
of MIMO channels to ameliorate the effects of non-ideal antenna placement on the performance of coherent (channel is known
at the receiver) and non-coherent (channel is un-known at the receiver) space–time codes. Antenna spacing and antenna placement
(geometry) are considered as fixed parameters of MIMO channels, which are readily known at the transmitter. With this design,
the precoder is fixed for fixed antenna placement and the transmitter does not require any feedback of channel state information
(partial or full) from the receiver. We also derive precoding schemes to exploit non-isotropic scattering distribution parameters
of the scattering channel to improve the performance of space–time codes applied on MIMO systems. However, these schemes require
the receiver to estimate the non-isotropic parameters and feed them back to the transmitter. Closed form solutions for precoding
schemes are presented for systems with up to three receive antennas. A generalized method is proposed for more than three
receive antennas. 相似文献
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Love D.J. Heath R.W. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2005,51(8):2967-2976
Multiple-input multiple-output (MIMO) wireless systems use antenna arrays at both the transmitter and receiver to provide communication links with substantial diversity and capacity. Spatial multiplexing is a common space-time modulation technique for MIMO communication systems where independent information streams are sent over different transmit antennas. Unfortunately, spatial multiplexing is sensitive to ill-conditioning of the channel matrix. Precoding can improve the resilience of spatial multiplexing at the expense of full channel knowledge at the transmitter-which is often not realistic. This correspondence proposes a quantized precoding system where the optimal precoder is chosen from a finite codebook known to both receiver and transmitter. The index of the optimal precoder is conveyed from the receiver to the transmitter over a low-delay feedback link. Criteria are presented for selecting the optimal precoding matrix based on the error rate and mutual information for different receiver designs. Codebook design criteria are proposed for each selection criterion by minimizing a bound on the average distortion assuming a Rayleigh-fading matrix channel. The design criteria are shown to be equivalent to packing subspaces in the Grassmann manifold using the projection two-norm and Fubini-Study distances. Simulation results show that the proposed system outperforms antenna subset selection and performs close to optimal unitary precoding with a minimal amount of feedback. 相似文献