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高速无线数据服务的需求的增长,要求下一代无线网络显著提高其吞吐量。文章研究了自动重发请求(ARQ)机制,来满足这些新的要求。针对基于速率兼容纠错码的速率自适应I类混合ARQ机制和增量冗余重传II类混合ARQ机制,提出了一种系统框架,并对其在无线瑞利衰落信道上的性能进行了分析。数值结果表明,增量冗余重传(IRR)II类HARQ机制与速率自适应(RA)I类HARQ机制相比,有较高的吞吐量,而RAI类HARQ机制的延迟较小。 相似文献
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链路性能预测的核心是根据即时信道状态信息,准确地预测通信系统未来的传输差错概率.现有的LTE系统链路性能预测算法没有考虑速率匹配和自适应HARQ过程,因此其实用性受到限制.针对这一现状,本文以具有速率匹配和自适应HARQ通信模块的LTE系统为研究对象,提出了一种基于平均比特互信息的链路性能预测算法.该算法首先充分考虑速率匹配过程中比特重复对互信息的影响,利用符号重复率得到重复比特的解码增益;在此基础上,利用合并重传码块的平均比特互信息计算模型,得到整个系统中的信道编码码块比特平均互信息;最后利用加性高斯白噪声AWGN信道的仿真映射关系得到链路的误块率.仿真结果表明该算法均具有较高的准确性. 相似文献
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介绍多载波系统中,采用Turbo码的混合自动重传请求(HARQ)的差错控制方案,并从易于实现的角度提出了两种基于OFDM的自适应HARQ机制.仿真分析表明,其中基于数据帧全部重传的机制可以提高系统稳健性,而基于数据帧部分重传的机制可以提高系统吞吐率. 相似文献
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基于信道状况提出自适应的混合自动重传请求(HARQ)方案。充分利用发送端获得的上次成功传输时重传的冗余信息次数和信道估计的信息,判断当前的信道状况,由此确定当前发送的数据帧被成功接收可能需要重传的次数K,将初传信息和K次增量冗余信息一起发送给接收端译码,最大可能地一次性将数据发送成功,减少传输出错再启动重传协议发送增量冗余信息的次数。仿真表明,新的方案在吞吐率基本不变的情况下,传输延时降低,易于实现。 相似文献
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针对预重传GBN-ARQ方案在误码率低的情况下吞吐率与时延大大下降的问题, 结合重传编码合并技术, 提出了一种基于TDD上行CSI的自适应预重传GBN-HARQ方案。首先, 发送端将数据进行前向纠错编码得到不同冗余版本; 然后, 根据上行CSI信息对重传分组自适应地选择冗余版本数, 在信道状况较差时一次性传输多个冗余版本以保证预重传的可靠性, 减小由预重传错误所带来的时延性能下降, 在信道状况较好时采用较少冗余以保证较高的吞吐率; 最后, 分析比较了传统GBN-ARQ方案、预重传GBN-ARQ方案和自适应预重传GBN-HARQ方案在不同情况下的吞吐率性能。理论和仿真分析表明, 在误码率大于10-1时自适应预重传GBN-HARQ方案的吞吐率比传统GBN-ARQ方案提升了0. 1左右, 比预重传GBN-ARQ方案提升了0. 05左右, 在误码率较大的情况下, 基于编码合并技术的自适应预重传GBN-HARQ方案能够更好地保证预重传的可靠性。 相似文献
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多用户多输入多输出(MIMO)系统中,用户可以通过反馈的方式把信道状态信息(CSI)传递给基站,基站利用该CSI进行预编码或者用户调度,可以有效地提取复用增益。但是传统的反馈方式,反馈量太大,占用过多上行资源。针对收发都是多天线条件的多用户MIMO系统,提出一种基于Grassmannian码本的有限反馈预编码方法,通过对用户信道矩阵进行量化,每个用户仅仅需要反馈一个序号而不是信道矩阵,从而大大减少了反馈量。通过对系统误码率(BER)和吞吐率的仿真,表明了该方法能保证系统性能。同时,由于信道估计存在误差,量化过程存在误差,所以,分析了信道矩阵误差对于新方法性能的影响,得到了系统吞吐率同信道矩阵误差的方差,以及基站发射功率三者的关系,并通过仿真进行验证,从而为评估信道估计和量化过程的优劣提供了理论依据。 相似文献
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多输入多输出技术可以增加分集阶数或系统自由度,以往研究多侧重于最大化其中一种增益,不能充
分利用多天线系统的性能.针对上述问题,本文提出了一种新的基于链路自适应技术的分集复用折中方法.该方法
以误比特率为判决准则,依据实时信道状态信息进行自适应码率、功率分配,并通过少量比特信息反馈到发送端来
确定系统的工作方式.同时,为降低计算量,通过对不同工作方式下接收端信噪比边界值的近似,给出了低复杂度
的次优判决准则.本文所提算法可充分利用分集、复用增益,提高系统可靠性的同时保证了较高的传输速率,具有
较小的计算量,抗扰动性强.仿真结果表明,与传统方法相比本文提出的折中方法具有较好的性能,满足了无线通
信系统实时性、快速性的要求. 相似文献
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This paper presents a mathematical model that analyzes the throughput of the IEEE 802.11b distributed coordination function (DCF) with the collision aware rate adaptation (CARA) algorithm. IEEE 802.11 WLANs provide multiple transmission rates to improve system throughput by adapting the transmission rate to the current channel conditions. The system throughput is determined by some stations using low transmission rates due to bad channel conditions. CARA algorithm does not disturb the existing IEEE 802.11b formats and it can be easily incorporated into the commercial wireless local area networks (WLAN) devices. Finally, we verify our findings with simulation. 相似文献
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The accuracy of channel state information (CSI) available at a base station (BS) has a direct impact on the performance of precoding in wideband multi-user multiple input, multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) systems and depends on many factors, including: the delay between estimation and beamforming at the BS (also called the CSI delay), Doppler spread, the channel estimation method used, the average transmit power of pilot symbols, and the average number of pilot symbols that must be estimated per channel parameter. In this paper, the coefficient of CSI error needed to adapt to fading channels is modeled as a function of Doppler spread, CSI delay, and signal-to-noise ratio (SNR). In terms of the Gaussian-Markov CSI error model, an adaptive robust maximum signal-to-leakage-and-noise ratio (Max- SLNR) precoder is designed to track the statistical parameters of CSI error. The Doppler spread and SNR can be obtained through real-time estimation based on orthogonal pilot patterns. Simulation results show that, compared to non-adaptive robust and non-robust precoders of Max-SLNR, the proposed adaptive robust Max- SLNR precoder performs much better in terms of bit error rate (BER). Moreover, as either the average number of training symbols per channel parameter or the average transmit power increases, the BER performance of the proposed precoder approaches that of a precoder with ideal CSI. 相似文献
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Dawei GongAuthor Vitae Miao ZhaoAuthor VitaeYuanyuan Yang 《Journal of Parallel and Distributed Computing》2014
As the latest IEEE 802.11 standard, 802.11n applies several new technologies, such as multiple input multiple output (MIMO), channel bonding, and frame aggregation to greatly improve the rate, range and reliability of wireless local area networks (WLANs). In 802.11n WLANs, access points (APs) are often densely deployed to provide satisfactory coverage. Thus nearby APs should operate at non-overlapping channels to avoid mutual interference. It is challenging to assign channels in legacy 802.11a/b/g WLANs due to the limited number of channels. Channel assignment becomes more complex in 802.11n WLANs, as the channel bonding in 802.11n allows WLAN stations (APs and clients) to combine two adjacent, non-overlapping 20MHz channels together for transmission. On the other hand, IEEE 802.11n is backward compatible, such that 802.11n clients will coexist with legacy clients in 802.11n WLANs. Legacy clients may affect the performance of nearby 802.11n clients, and reduce the effectiveness of channel bonding. Based on these observations, in this paper, we study channel assignment in 802.11n WLANs with heterogeneous clients. We first present the network model, interference model, and throughput estimation model to estimate the throughput of each client. We then formulate the channel assignment problem into an optimization problem, with the objective of maximizing overall network throughput. Since the problem is NP-hard, we give a distributed channel assignment algorithm based on the throughput estimation model. We then present another channel assignment algorithm with lower complexity, and aim at minimizing interference experienced by high-rate, 802.11n clients. We have carried out extensive simulations to evaluate the proposed algorithms. Simulation results show that our algorithms can significantly improve the network throughput of 802.11n WLANs, compared with other channel assignment algorithms. 相似文献
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虚拟MIMO是一种克服无线多媒体传感器网络信道多径衰落和降低节点能耗的有效方法,但现有文献均假设信道状态信息未知或仅知道信道的统计特性,源节点则无法根据信道的实时信息动态调整传输策略。针对WMSNs信道特点,提出一种适用于WMSNs传输机制的信道盲估计方法以获得节点间信道信息进而确定传输策略,通过构造权值衰减联合决策函数,将节点间的信道盲估计问题转化为一个无约束优化问题,在此基础上设计了一种快速收敛的迭代算法以降低运算代价。该方法仅依赖小数据量就可正确估计出节点间信道,具有对抗信道时变特性的能力;理论推导与仿真表明该算法的收敛速度和运算量均能符合降低节点能耗的要求。 相似文献
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Robust multiuser multiple-input-multiple-output (MIMO) scheduling algorithms are proposed in this paper.With imperfect channel state information (CSI),traditional scheduling algorithms for the multiuser MIMO system based on the zero forcing precoding scheme will lose some performance due to the multi-user interference (MUI).In order to improve the system average throughput,we study the robust multiuser MIMO scheduling problem with imperfect CSI.From the average capacity formula,we derive a robust factor which can transform the robust multiuser MIMO scheduling problem into the traditional one,thus most existing non-robust scheduling algorithms can be robust if this factor is adopted.Simulation results show that compared with the traditional algorithms,the proposed robust algorithms can improve the system average throughput significantly under the CSI error environment. 相似文献
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This paper deals with the superposition coding (SPC) scheme in multiple-input multiple-output two-way relay channels subject to imperfect channel estimation. In this scenario, two multiple antenna terminals, which are unable to communicate directly, exchange information with each other via a multiple antenna relay. We determine the impact of the channel estimation error degradation on the achievable rate region for two main SPC techniques: (a) SPC without channel state information (CSI) at the users, (b) SPC with an imperfect CSI at the users where a waterfilling power allocation is employed. We demonstrate that imperfect CSI significantly improves the achievable rate at low signal-to-noise ratios (SNRs) while it becomes less critical at high SNRs. In addition, a SPC power allocation technique that incorporates the average channel statistics and does not require any instantaneous CSI is also investigated. We show how the available power is split between the two bi-directional (superimposed) data flows in order to maximize the system performance and to support fairness as well as to maximize the achievable sum-rate. 相似文献
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We investigate the problem of resource allocation in a downlink orthogonal frequency-division multiple access (OFDMA) broadband network with an eavesdropper under the condition that both legitimate users and the eavesdropper are with imperfect channel state information (CSI). We consider three kinds of imperfect CSI: (1) noise and channel estimation errors, (2) feedback delay and channel prediction, and (3) limited feedback channel capacity, where quantized CSI is studied using rate-distortion theory because it can be used to establish an informationtheoretic lower bound on the capacity of the feedback channel. The problem is formulated as joint power and subcarrier allocation to optimize the maximum-minimum (max-min) fairness criterion over the users’ secrecy rate. The problem considered is a mixed integer nonlinear programming problem. To reduce the complexity, we propose a two-step suboptimal algorithm that separately performs power and subcarrier allocation. For a given subcarrier assignment, optimal power allocation is achieved by developing an algorithm of polynomial computational complexity. Numerical results show that our proposed algorithm can approximate the optimal solution. 相似文献