共查询到19条相似文献,搜索用时 156 毫秒
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针对混沌通信系统的非线性信道干扰问题,基于混沌信号重构理论和函数型连接神经网络理论,提出了一种横向滤波器与函数型连接神经网络组合(combination of transversal filter and functional link neural network,CFFLNN)的自适应非线性信道均衡器,并给出基于低复杂度归一化最小均方(NLMS)的自适应算法,并对该均衡器的稳定性以及收敛条件进行了分析.该非线性自适应均衡器充分利用了横向滤波器的快速收敛,以及函数型连接神经网络通过增大输入空间提高非线性逼近能力的特点,进一步提高均衡器的收敛速度和降低稳态误差.仿真研究表明:所提出的非线性自适应均衡器能够有效地消除线性和非线性信道干扰,均衡器输出信号能反映出混沌信号的特性,具有良好的抗干扰性能;且该均衡器的结构简单,收敛稳定性较好,易于工程实现.
关键词:
非线性信道
自适应均衡器
混沌吸引子
神经网络 相似文献
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针对高空平台不稳定性以及大气湍流对平台光通信性能的影响,提出利用空间分集技术改善高空平台光通信链路性能。在系统采用开关键控(OOK)调制条件下,利用矩母函数特性分别得到采用协作分集技术和多输入多输出(MIMO)技术的高空平台光链路误码率表达式,并求解协作通信系统中继平台的最优位置。仿真结果表明:协作分集技术与光MIMO技术对高空平台光链路性能的改善效果受到跟瞄误差的限制。采用发射选择分集的光MIMO技术对光链路的误码率性能最好。与采用重复码的MIMO方法相比,协作分集技术更适用于跟瞄误差大的通信系统。中继平台的最优位置与中继策略以及跟瞄误差无关。在中继平台最优位置附近,采用协作分集的光链路性能优于采用重复码MIMO光通信链路。 相似文献
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水声信道的典型特点为多普勒频移严重、可利用带宽窄以及强多径干扰。空间分集均衡技术是相干水声通信中克服信道多径干扰,消除码间干扰的一种有效手段。为了极大化地输出阵增益,结合无源相位共轭方法和多通道均衡算法,本文设计了组合信噪干比的全新信道评价方法。利用改进的Sigmoid函数对各通道接收信号的幅度进行加权处理;采用二阶锁相环跟踪各通道信号的相位变化,实现各通道信号同相累加。将各通道低通滤波后的信号能量归一化,采用了分数阶-判决反馈分集均衡器,加入各通道权重系数实现了水声通信系统的分集均衡接收。仿真结果和湖试数据处理结果均表明,优化的幅相加权分集均衡接收算法能抵消多径和噪声的干扰,性能优于等增益合并接收算法。湖试数据处理结果误码率降低了1.8%。 相似文献
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提出了一种基于神经网络的多输入多输出(MIMO)均衡器,并在大容量模分-波分复用通信系统中进行了实验验证。该系统基于6模掺铒光纤放大器实现了16通道波分复用双极化48 Gbaud 16阶正交振幅调制(16QAM),在LP01、LP02、LP11a、LP11b、LP21a、LP21b六种模式上传输了100 km少模光纤(FMF)。为降低非线性的影响,在接收端数字信号处理中,采用基于多标签技术的MIMO神经网络均衡器,能够显著提升系统性能。实验结果表明,经100 km的FMF传输,MIMO神经网络均衡器的强大性能使得系统的比特误码率能满足15%软判决前项纠错阈值要求。 相似文献
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自组织型模糊类神经网络(SCFNN)可依据一定的法则自我构建神经网络的组织结构,从而适用于当前控制对象;多层神经元是传统的类神经网络,广泛应用于各个领域;倒传递学习法与最陡坡降法相结合,可使以上两种类神经网络进行有效的融合;目前,信道均衡器上的系统架构种类非常多,各种类神经网络应用于信道均衡器也颇为普遍;在研究SCFNN的基础上,将其应用于通道均衡器确实可行,效果良好;比较了SCFNN与MLP在通道均衡器的成效;仿真表明,在相同通道环境下,SCFNN的训练收敛速度、位错误率与系统敏感度优于MLP,完成结构学习后SCFNN的结构也颇为精简。 相似文献
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The UWA channel is characterized as a time-dispersive rapidly fading channel,which in addition exhibits Doppler instabilities and limited bandwidth. To eliminate intersymbol interference caused by multipath propagation, spatial diversity equalization is the main technical means. The paper combines the passive phase conjugation and spatial processing to maximize the output array gain. It uses signal-to-noise-plus-interference to evaluate the quality of signals received at different channels. The amplitude of signal is weighted using Sigmoid function. Second order PLL can trace the phase variation caused by channel, so the signal can be accumulated in the same phase. The signals received at different channels need to be normalized. It adopts fractional-decision feedback diversity equalizer(FDFDE) and achieves diversity equalization by using different channel weighted coefficients. The simulation and lake trial data processing results show that, the optimized diversity receiving equalization algorithm can improve communication system's ability in tracking the change of underwater acoustic channel,offset the impact of multipath and noise and improve the performance of communication system.The performance of the communication receiving system is better than that of the equal gain combination. At the same time, the bit error rate(BER) reduces 1.8%. 相似文献
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《声学学报:英文版》2016,(4)
A direct-adaptation based bidirectional turbo equalizer for underwater acoustic communications is proposed.Abandoning the channel estimation process,the direct-adaptation based turbo equalizer embedded with digital phase-locked loop is adopted to track time-varying channel.The fast self-optimized algorithm is used to adjust the step size,thus a good tradeoff between the convergence speed and performance has been made.Furthermore,by minimizing the mean squared error,an optimal weighting factor is derived to exploit bidirectional diversity gain.The forward turbo equalizer is combined with the backward turbo equalizer to eliminate error propagation effect.Simulated and experimental results demonstrate that the bidirectional turbo equalizer outperforms the single directional one.It can be seen from the experimental results that,compared with the channel estimation based algorithm,the direct-adaptation based algorithm is less sensitive to the time-varying channel and has a lower bit error rate. 相似文献
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针对稀疏水声信道的长时延扩展及梯度下降的权值迭代方案导致的神经网络均衡器收敛速度慢的问题,提出了近似L0范数约束的BP神经网络均衡器。首先在传统BP网络均衡器基础上增加判决反馈项,然后在代价函数中对均衡器输入层到隐含层的权值增加L0范数约束,构造新的代价函数,利用高斯族函数近似L0范数约束,并根据不同隐层神经元节点输出权值的L2范数设定近似参数。仿真结果表明,稀疏信道条件下,本方法相比传统的BP网络均衡器收敛速度更快,误码率更低,可以有效提升神经网络均衡器的性能。 相似文献
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提出了一种水声通信系统中直接自适应双向turbo均衡算法。摒弃了信道估计步骤,采用基于直接自适应的turbo均衡器,并利用内嵌数字锁相环的判决反馈均衡器结构跟踪时变信道,采用最速优化算法自适应调整迭代步长,使得收敛速度和算法性能得到很好折中。此外,利用最小均方误差准则,得到最优权重因子,对正向与反向turbo均衡结果加权求和,消除误差传播效应。仿真和湖上实验验证了方法的正确性,双向均衡的性能优于单向均衡。湖上实验结果表明,基于直接自适应算法相比于基于信道估计的算法,对时变信道不敏感,能获得更低的误比特率。 相似文献
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针对盲均衡算法收敛速度较慢的问题,提出一种结合改进支持向量机和常数模算法的水声信道盲均衡算法。该算法首先利用具有优异小样本学习能力的支持向量机进行盲均衡器权系数初始化,在完成初始化后切换至运算量较小的常数模算法。考虑到支持向量机本身非自适应运算的限制,在时变水声信道条件下利用经典支持向量机获得的均衡器初始权向量与切换后的信道仍然存在失配。因此,本文导出时变条件下的改进支持向量机用于盲均衡器初始化,改善算法切换时的权系数失配,并结合分数间隔结构和内嵌数字锁相环进一步提高盲均衡算法性能。仿真和湖试实验结果表明:在时变水声信道条件下,本文算法的收敛性能优于经典支持向量机盲均衡算法。 相似文献
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蛟龙号的水声通信机实现了世界上首次7000 m深度的潜器与母船间的图像、语音、数据和文字的水声通信传输。研究了适用于载人潜水器的水声通信信号处理。(1)它有4种通信功能:1)相干水声通信,传输速率为5~15 kbps,用于传输图像;2)非相干水声通信,传输速率300 bps,传输文字、指令和数据;3)扩频水声通信,传输速率16 bps,传输指令;4)水声语音通信,采用单边带调制技术传输语音。(2)相干水声通信信号处理方法主要是自适应多普勒补偿的多通道自优化判决反馈自适应均衡器,它与Turbo码级联工作,同时采用定长编码的小波图像压缩方法。(3)声呐线阵吊放至水中一定深度,实现空间分集合并技术。(4)太平洋水域试验表明,水声通信机的作用距离几乎覆盖了所有地球海洋的深度,7s或14s传输一幅光图或声图。 相似文献
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We investigate underwater acoustic (UWA) channel equalization and introduce hierarchical and adaptive nonlinear (piecewise linear) channel equalization algorithms that are highly efficient and provide significantly improved bit error rate (BER) performance. Due to the high complexity of conventional nonlinear equalizers and poor performance of linear ones, to equalize highly difficult underwater acoustic channels, we employ piecewise linear equalizers. However, in order to achieve the performance of the best piecewise linear model, we use a tree structure to hierarchically partition the space of the received signal. Furthermore, the equalization algorithm should be completely adaptive, since due to the highly non-stationary nature of the underwater medium, the optimal mean squared error (MSE) equalizer as well as the best piecewise linear equalizer changes in time. To this end, we introduce an adaptive piecewise linear equalization algorithm that not only adapts the linear equalizer at each region but also learns the complete hierarchical structure with a computational complexity only polynomial in the number of nodes of the tree. Furthermore, our algorithm is constructed to directly minimize the final squared error without introducing any ad-hoc parameters. We demonstrate the performance of our algorithms through highly realistic experiments performed on practical field data as well as accurately simulated underwater acoustic channels. 相似文献
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Passive time reversal exploits underwater acoustic channels’ spatial and temporal diversity. It can refocus multipath propagated signal at the receiver and can be realized simply by the passive phase conjugation (PPC) method. By the temporal focusing, time delay spread caused by multipath propagation is mitigated for spectral efficient coherent communications. However, the PPC method is unable to eliminate multipath and is limited by channel variations. An adaptive equalizer is therefore needed to compensate residual multipath after refocusing and to track channel temporal variations. Spatial diversity is obtained by using a vertical receiving array. In this paper we used 4-hydrophone array and demonstrated that the adaptive decision feedback equalization in conjunction with PPC significantly decreased the bit error rate. 相似文献
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Song HC 《The Journal of the Acoustical Society of America》2012,131(4):EL342-EL347
The bidirectional decision feedback equalizer (BiDFE) that combines the outputs of a conventional decision feedback equalizer (DFE) and backward DFE can improve the performance of the conventional DFE by up to 1-2 dB based on simulations. In this letter, the BiDFE concept is extended to multichannel time reversal communications involving a DFE as a post-processor. Experimental data collected in shallow water (10-20 kHz) show that the performance can be enhanced by 0.4-1.8 dB in terms of output signal-to-noise ratio. In particular, a larger improvement (e.g., 1.8 dB) is achieved for time-varying channels where the channel diversity in opposite directions is more profound. 相似文献