共查询到20条相似文献,搜索用时 156 毫秒
1.
研究了基于放大转发(AF)的协作传输系统的中断概率性能.考虑了源节点到目的节点的直通链路,建立了适用于中继随机分布的非对称和对称信道下协作传输系统的数学模型,给出了协作传输系统节点信道和位置多种状况下接收端的瞬时信噪比的概率密度函数表达式,针对不同的状况给出了系统中断概率的精确表达式,并对于各中继信道具有不同信道状态参数的情形,提出了系统中断概率的一种近似表达式. 相似文献
2.
为提高认知无线电网络中主用户和次用户的通信质量,并可简单有效地利用中继节点来控制主用户和次用户之间的相互干扰,提出了一种基于公共中继的最佳中继选择和功率分配方案.首先,在认知无线电网络中建立了基于公共DF中继的无线通信模型;然后,根据无线通信理论推导出要优化的目标函数;最后,在保证主用户中断概率低于目标值的前提下,利用凸优化理论得出了模型中的最佳中继选择和功率分配方案.仿真实验结果表明,与常见的直接传输方案和功率平均分配的中继方案相比,本文提出的中继选择和功率分配方案提高了次用户的通信距离和速率,并且降低了主用户的中断概率,为更好地解决认知无线电网络中主用户和次用户的相互干扰问题提供了新的思路. 相似文献
3.
MC-CDMA技术是正交频分复用和码分多址技术相结合的综合技术,兼有OFDM和CDMA的优点。在水声通信中,由于海洋信道的复杂性,尤其在浅海信道中,存在严重的多途干扰和海洋环境噪声以及严重的时变和空变特性,因此水声信号的衰落很严重。为了在条件恶劣的水下声信道中实现高速可靠通信,将MC-CDMA技术应用于水声通信。该研究分析了MC-CDMA技术的基本原理,并通过仿真MC-CDMA系统和OFDM系统,以及两个系统的水池实验,验证了在水声通信中MC-CDMA系统具有比OFDM系统更好的性能。 相似文献
4.
采用多输入多输出(MIMO)结构和空时编码可以使水声通信系统获得分集增益,改善系统性能。针对水声信道中的频率选择性衰落,研究了一种用于MIMO水声通信系统的空时分组扩展编码方案(STBSC),利用正交扩频编码克服了水声信道中多径干扰对空时分组编码(STBC)信号正交性的破坏。给出了方案的系统模型和实现框图,采用MIMO水声模型对方案的性能进行了仿真。仿真结果表明,STBSC方案在多径水声信道中可以得到完全发射分集。最后介绍了方案的水库试验,试验结果表明了方案的有效性。 相似文献
5.
6.
为实现高速水下通信,提出了一种基于VBLAST(贝尔实验室垂直分层空时)编码的水声MIMO(多输入多输出)通信技术。该技术通过在发射端和接收端同时采用多个阵元进行多发多收,借助空间复用,可有效解决水下通信系统带宽资源缺乏的难题,使系统在不增加带宽的条件下成倍提高数据传输速率。在水声MIMO通信系统的接收端,提出采用带有二阶数字锁相环、基于自适应空时判决反馈均衡的相干解调技术。该技术可有效克服水声MIMO信道中的多径干扰及同频干扰,且能自适应跟踪信道变化。仿真及湖试结果证明了所提水声MIMO高速通信技术的良好性能。 相似文献
7.
对于正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)水声通信系统,最小二乘(Least Squares,LS)信道估计方法受噪声影响较大,并且使用的导频数量较多,影响通信效率。而基于压缩感知理论的正交匹配追踪(Orthogonal Matching Pursuit,OMP)信道估计方法可以充分利用水声信道的稀疏特性,同时能够有效地抑制系统噪声,但控制迭代运算次数的相关参数(稀疏度或误差容忍值)是OMP算法的关键条件。针对上述问题,提出了利用少量导频随机分布的LS和OMP联合的信道估计方法,该方法首先利用少量导频采用LS方法估计出OMP算法的误差容忍值,再利用OMP算法恢复数据子载波的信道信息。理论分析和仿真结果同时表明,与传统的LS算法或OMP算法相比,新算法能够在数据恢复的同时有效抑制系统噪声,应用稀疏特性及较少量的导频,进一步提高了系统的频谱效率,对时变稀疏水声信道具有更好的适应性。 相似文献
8.
正交频分复用在高速水声通信中的应用越来越广泛.水声信道是多径、高噪声的衰落信道.由于信道条件差,容易产生码间干扰,信道均衡技术是提高通信系统性能的重要技术.提出了线性最小均方估计在水声通信系统中应用的方案,研究了实际通信中利用调频信号如何确定信号的平均多径时延、最大多径时延,比较了不同调频信号测量信道的性能.该方案基于导频辅助均衡方法,利用调频信号测量信道,获得的信道统计信息,计算信道的自相关矩阵.从而根据线性最小均方误差算法进行信道均衡.通过仿真和湖试进行验证,结果表明该方案效果较好,对系统性能改善比较明显. 相似文献
9.
10.
近年来,以深度学习为代表的机器学习技术飞速发展,凭借其出色的学习能力,在复杂环境条件下的建模问题中展现出了独特的优势。当前,基于机器学习的水声通信技术研究方兴未艾,在信道估计及均衡、典型通信系统应用等方面取得了一定的进展,但是针对实际水声环境约束条件下的研究较少。为此,文章围绕信道估计这一水声通信关键技术,针对水声信道估计中存在的样本不足,标签标定困难以及水声环境时空变导致的源域、目标域失配等问题,讨论了水声信道估计与数据增强、无标签学习、少样本学习等模型和方法交叉研究的发展思路,并给出了初步的仿真和试验结果。文章是对水声通信中的信道估计与机器学习交叉领域研究重难点问题的初步探索,为水下各类平台自主智能化的通信技术发展提供了参考。 相似文献
11.
12.
近年来,深水探测中水下通讯节点的小型化、低功耗成为设计的难点。在水声通信中,普遍使用正弦脉宽调制(Sinusoidal Pulse Width Modulation, SPWM)信号驱动功率放大器进行工作。传统SPWM产生系统电路复杂度高,针对SPWM生成原理和电路实现,提出基于脉冲采样的SPWM生成方法,并进行性能分析;基于数字处理器设计了高能效SPWM发生系统,在保证SPWM信息损失较小的同时,减小硬件电路面积。实验结果表明,提出的高能效脉冲采样法与SPWM发生系统可以满足工程应用。 相似文献
13.
The authors consider a dual-hop multi-relay cooperative relay system in this study. Both decode-and-forward (DF) and amplify-and-forward (AF) protocols are considered. Under different relay selection strategies, the authors derive closed-form outage probability expressions. With the second-order channel statistics, the authors propose to jointly optimise power allocation (PA) and relay positions in order to minimise the system outage probability. Simulation results show that the proposed adaptive allocation algorithms significantly outperform fixed allocation algorithms. With the proposed joint optimisation algorithm, AF relaying outperforms DF relaying when multiple relays are selected to help. When only the best relay is selected to help, DF relaying is shown to have better performance. 相似文献
14.
Manimekalai Thirunavukkarasu Romera Joan Sparjan Laxmikandan Thangavelu 《计算机、材料和连续体(英文)》2020,63(2):1043-1064
Future wireless networks demand high spectral efficiency, energy efficiency
and reliability. Cooperative non-orthogonal multiple access (NOMA) with simultaneous
wireless information and power transfer (SWIPT) is considered as one of the novel
techniques to meet this demand. In this work, an adaptive power allocation scheme called
SWIPT based adaptive power allocation (SWIPT-APA-NOMA) is proposed for a power
domain NOMA network. The proposed scheme considers the receiver sensitivity of the
end users while calculating the power allocation coefficients in order to prevent wastage
of power allocated to user in outage and by offering priority to any one of the users to use
maximum harvested power. A detailed analysis on the bit error rate (BER) performance
of the proposed scheme is done and closed form expression is obtained. Simulations have
been carried out with various parameters that influence the receiver sensitivity and the
results show that the network achieves better outage and BER performance using the
proposed scheme. It is found that the proposed scheme leads to a ten-fold decrease in
transmit power for the same error performance of a fixed power allocation scheme.
Further, it offers 96.06% improvement in the capacity for a cumulative noise figure and
fading margin of 10 dB. 相似文献
15.
Yinghua Zhang Jian Liu Yunfeng Peng Yanfang Dong Guozhong Sun Hao Huang Changming Zhao 《计算机、材料和连续体(英文)》2020,63(1):197-212
This paper proposes a hybrid spectrum accessing mechanism by using NOMA-based cooperative transmission and beam-forming technology. In this mechanism, the secondary user employs spectrum-sensing technology to detect the existence of the primary user. If the primary user does not exist, the secondary source user directly transmits data to the destination user. If the primary user exists, the secondary source user finds the optimal relay according to certain selection principle before transmitting data to the destination user through the chosen relay node. For the signal receiving stage, the secondary user takes use of beam-forming technology to receive the signal from both the secondary source and the secondary relay node. Meanwhile the interference from the primary user is cancelled out in the stage. Furthermore, the outage probability for secondary user in the proposed mechanism is theoretically derived. Finally, the simulation results show that compared with the traditional mechanism, the proposed system model can not only guarantee the continuity of secondary transmission, but also significantly reduce the outage probability of secondary transmission. 相似文献
16.
Yinghua Zhang Yanfang Dong Lei Wang Jian Liu Yunfeng Peng Jim Feng 《计算机、材料和连续体(英文)》2019,60(1):379-397
In this paper, we propose a downlink cognitive non-orthogonal multiple access (NOMA) network, where the secondary users (SUs) operate in underlay mode. In the network, secondary transmitter employs NOMA signaling for downlink transmission, and the primary user (PU) is interfered by the transmission from SU. The expressions for the outage probabilities are derived in closed-form for both primary and secondary users in the presence of channel estimation error. Numerical simulation results show that the channel estimation error and the inter-network interference cause degradation of the downlink outage performance. Also the power allocation and the location have a significant impact on the outage probability. The numerical experiments demonstrate that the analytic expressions of the outage probabilities match with the simulation results. 相似文献
17.
18.
Choi J. Tran T. Kwon J. Thomas R. Mount T. Billinton R. 《Generation, Transmission & Distribution, IET》2008,2(1):32-42
A nodal probabilistic production cost simulation method is described for power system long-term expansion planning considering unavailability and delivery limitation constraints of the transmission system. This new nodal production cost simulation model includes capacity constraints and unavailabilities of generators as well as transmission lines. This simulation methodology comes from the nodal composite power system equivalent load duration curve (CMELDC), based on a new effective load model at load points developed by the authors. The nodal CMELDC can be obtained from convolution integral processing of the outage capacity probability distribution function of the fictitious generator and the original LDC. It is expected that the new simulation model based on the nodal CMELDC proposed here will provide solutions to many problems based on nodal and decentralised operation and control of electric power systems under a competition environment. The nodal CMELDC based on the new model at load points can extend application areas of nodal probabilistic production cost simulation, probabilistic congestion cost assessment, analytical outage cost assessment and nodal reliability evaluation and so on at load points. The characteristics and effectiveness of this new proposed methodology are illustrated by a small system case study using a network flow and enumeration method. 相似文献
19.
20.
以某地铁钢轨探伤车为研究对象,利用多体动力学软件UM建立车辆-轨道耦合动力学模型,分析探伤车在直线、曲线两种工况下的运行平稳性、安全性和曲线通过能力,为后续悬挂参数多目标优化提供原始数据支撑。基于MATLAB编程建立UM-ISight 联合仿真平台,在ISight 中以转向架一、二系悬挂刚度、阻尼等为目标参数,通过最优拉丁超立方法进行参数组合样本设计,并在此基础上构建符合精度要求的径向基函数神经网络(RBF-NN)近似模型,最后通过多目标优化算法NSGA-Ⅱ对近似模型进行寻优计算,得到最优的转向架悬挂参数组合。结果表明,所建近似模型具有较高的拟合精度,优化后车辆平稳性指标都得到明显改善,最多可降低35.39 %,且车辆的脱轨系数、轮轨横向力、轮轴横向力、轮重减载率等曲线通过性能指标也有不同程度好转。 相似文献