Diffusion Based Channel Gains Estimation in WSN Using Fractional Order Strategies

In this study,it is proposed that the diffusion least mean square(LMS)algorithm can be improved by applying the fractional order signal processing methodologies.Application of Caputo’s fractional derivatives are considered in the optimization of cost function.It is suggested to derive a fractional order variant of the diffusion LMS algorithm.The applicability is tested for the estimation of channel parameters in a distributed environment consisting of randomly distributed sensors communicating through wireless medium.The topology of the network is selected such that a smaller number of nodes are informed.In the network,a random sleep strategy is followed to conserve the transmission power at the nodes.The proposed fractional ordermodified diffusionLMS algorithms are applied in the two configurations of combine-then-adapt and adapt-then-combine.The average squared error performance of the proposed algorithms along with its traditional counterparts are evaluated for the estimation of the Rayleigh channel parameters.Amathematical proof of convergence is provided showing that the addition of the nonlinear term resulting from fractional derivatives helps adjusts the autocorrelation matrix in such a way that the spread of its eigenvalues decreases.This increases the convergence as well as the steady state response even for the larger step sizes.Experimental results are shown for different number of nodes and fractional orders.The simulation results establish that the accuracy of the proposed scheme is far better than its classical counterparts,therefore,helps better solves the channel gains estimation problem in a distributed wireless environment.The algorithm has the potential to be applied in other applications related to learning and adaptation.

Effect of the fluctuant acoustic channel on the gain of a linear array in the ocean waveguide

The inhomogenous ocean waveguide, which leads the amplitude and phase of the signal arriving at a hydrophone array to fluctuate, is one of the causes that make the array gain deviate from its ideal value. The relationship between the array gain and the fluctuant acoustic channel is studied theoretically. The analytical expression of the array gain is derived via an acoustic channel transfer function on the assumption that the ambient noise field is isotropic. The expression is expanded via the Euler formula to give an insight into the effect of the fluctuant acoustic channel on the array gain. The result demonstrates that the amplitude fluctuation of the acoustic channel transfer functions has a slight effect on the array gain; however, the uniformity of the phase difference between the weighting coefficient and the channel transfer function on all the hydrophones in the array is a major factor that leads the array gain to further deviate from its ideal value. The numerical verification is conducted in the downslope waveguide, in which the gain of a horizontal uniform linear array(HLA) with a wide-aperture operating in the continental slope area is considered. Numerical result is consistent with the theoretical analysis.

柔性直流光纤电流互感器阶跃响应特性研究

传统直流光纤电流互感器无法满足柔性直流输电工程的高速响应需求,因此需要研究直流光纤电流互感器的阶跃响应特性及其动态性能改善方法。文中结合直流光纤电流互感器的离散数学模型,对其动态特性进行了全面的仿真、计算和实验研究,结果表明:影响直流光纤电流互感器阶跃响应特性的关键参数是渡越时间、前向通道增益、滤波器阶数和通讯延迟。搭建了直流光纤电流互感器阶跃响应测试平台,经参数优化后的直流光纤电流互感器的阶跃响应上升时间小于50μs,满足相关应用要求。

Energy efficiency enhancement of two-way amplifier forward relaying with channel estimation error

In order to save energy consumption of two-way amplifier forward(AF) relaying with channel estimation error, an energy efficiency enhancement scheme is proposed in this work. Firstly, through the analysis of two-way AF relaying mode with channel estimation error, the resultant instantaneous SNRs at end nodes is obtained. Then, by using a high SNR approximation, outage possibility is acquired and its simple closed-form expression is represented. Specially, for using the energy resource more efficiently, a low-complexity power allocation and transmission mode selection policy is proposed to enhance the energy efficiency of two-way AF relay system. Finally, relay priority region is identified in which cooperative diversity energy gain can be achieved. The computer simulations are presented to verify our analytical results, indicating that the proposed policy outperforms direct transmission by an energy gain of 3 dB at the relative channel estimation error less than 0.001. The results also show that the two-way AF relaying transmission loses the two-way AF relaying transmission loses its superiority to direct transmission in terms of energy efficiency when channel estimation error reaches 0.03.

Deep Learning Based Signal Detector for OFDM Systems

In this paper,we propose a novel deep learning(DL)-based receiver design for orthogonal frequency division multiplexing(OFDM)systems.The entire process of channel estimation,equalization,and signal detection is replaced by a neural network(NN),and hence,the detector is called a NN detector(N^(2)D).First,an OFDM signal model is established.We analyze both temporal and spectral characteristics of OFDM signals,which are the motivation for DL.Then,the generated data based on the simulation of channel statistics is used for offline training of bi-directional long short-term memory(Bi-LSTM)NN.Especially,a discriminator(F)is added to the input of Bi-LSTM NN to look for subcarrier transmission data with optimal channel gain(OCG),which can greatly improve the performance of the detector.Finally,the trained N^(2)D is used for online recovery of OFDM symbols.The performance of the proposed N^(2)D is analyzed theoretically in terms of bit error rate(BER)by Monte Carlo simulation under different parameter scenarios.The simulation results demonstrate that the BER of N^(2)D is obviously lower than other algorithms,especially at high signal-to-noise ratios(SNRs).Meanwhile,the proposed N^(2)D is robust to the fluctuation of parameter values.

Effect of asymmetrical channel chirping on field intensity patterns of supermodes and modal discrimination in index guided laser arrays

The effect of channel-width chirping on near- and far-field intensity patterns of the six supermodes was investigated. The supermode discrimination was evaluated in various channel-chirped index guided laser arrays. The results show that the linearly channel-chirped laser array has very good supermode discrimination which is better than that of a uniform laser array, the V channel-chirped laser array has the smallest radiation angle of the fundamental supermode among the calculated arrays, and the asymmetrically V channel-chirped array has a very small radiation angle of the fundamental supermode, which is smaller than that of the uniform array and also allows for very good fundamental supermode discrimination against the higher-order supermodes, which is better than that of the V channel-chirped laser array.

自由空间光通信网络拓扑自适应控制方法研究

自由空间光通信网络拓扑优化控制可以降低网络传输延迟,提高通信速率,提出基于平均辐射光功率调节的自由空间光通信网络拓扑自适应控制方法。构建自由空间光通信网络的光传输和信道模型,结合光学度量的方法分析光通信网络的辐射功率、辐射通量以及光通量参数,采用光谱光视度量的方法,进行自由空间光通信网络脉冲幅度调制,采用强度调制和直接检测的方法,实现自由空间光通信的平均辐射光功率调节。根据反馈调节和前置补偿的方法,构建等效自由空间光通信网络拓扑结构模型,实现光通信网络的信道均衡控制和视距链路自适应增益调节。测试表明,该方法提高了信道增益,安全传输速率较高。

Short Baseline Positioning with an Improved Time Reversal Technique in a Multi-path Channel

在水下面的一条多路径隧道的存在极大地减少放系统的短基线的精确性。在这份报纸，到放系统的短基线的一面时间颠倒镜子的申请被调查。时间颠倒镜子技术允许声学的信号更好集中在未知环境，它有效地减少了多路径的扩大声学的信号象一样改进了集中的信号。时间颠倒操作员的 signal-to-noise 比率(SNR ) 极大地增加了并且能被 ensonifying 获得水。这种技术被环境并且因此少些影响对复杂的浅水环境更适用。数字模拟和水池实验被用来表明这种技术的效率。

基于细粒度极化的隐蔽密钥分发方案

针对现有密钥分发协议在水声信道环境下的信息泄露问题,提出了一种基于细粒度极化的隐蔽密钥分发(Covert Secret-key distribution based on Fine-grained Polarization,CSFP)方案.首先,采用一致最大功效检验方法建立敌手模型,并给出隐蔽密钥分发方案的形式化定义.考虑到水声信道的非对称性和衰落效应,根据注水原理推导出信息传输速率达到香农极限时最优码字符号分布对应的带宽以及信道容量,并利用莱布尼兹积分法则和黎曼积分的保号性推导出信道容量与信道增益的函数关系,通过计算水声信道增益对极化子信道的容量进行排序实现极化码的码字构造,确保信息传输速率达到香农极限.其次,对信息比特索引集合进行细粒度极化,采用链式结构将多个消息块依次链接实现信息比特索引序列的对齐,设计出多轮通信下隐蔽密钥分发的编码和解码算法,利用合法发送方和接收方共享的随机种子对首轮传输的消息块进行初始化,并从当前生成的密钥中提取出随机种子对后续消息块进行随机化,确保密钥分发过程的隐蔽性.最后,通过信息理论证明了CSFP方案的可靠性、随机性、保密性和隐蔽性,利用最大熵原理推导出水声信道环境下隐蔽性约束的可达性条件和隐蔽密钥生成速率.仿真结果表明,与现有方案相比,CSFP方案的隐蔽密钥生成速率平均提高了18.78%,隐蔽概率平均提高了38.29%.此外,CSFP方案生成的密钥成功通过了SP 800-22测试平台的随机性检测.

Channel Pre-emphasis Equalization for a 270km 40×40 Gbit/s WDM System with Cascaded EDFAs/Raman Amplifiers

Optical channel pre-emphasis equalization is experimentally researched for a 270 km 40×40 Gbit/s wavelength division multiplexing (WDM) transmission system with three Erbium-doped fiber amplifiers (EDFAs) and Raman amplifiers concatenated as booster amplifier. The channel imbalance of the overall system changes with different sets of power launched into EDFAs. By appropriately choosing the power input to concatenated EDFAs, the output spectrum of 40 channel signal can be equalized to the most extent. The merit of benefit can be around 5.5 dB by this pre-emphasis equalization. The requirement for the gain equalizer is therefore greatly released. Then the gain imbalance of the overall system and the power imbalance of 40 channels are compared and the two almost matches, but the significant difference lies on some channels. Finally, the pump power into Raman amplifier is also optimized, and another 1.3 dB improvement of channel equalization can be further achieved.

Ku波段高增益8通道T/R组件设计与实现

利用低温共烧陶瓷(LTCC)高集成化设计优势,设计并实现了一款Ku波段高增益8通道T/R组件。该组件通过双向放大器的合理运用,有效提高了组件的收发增益,同时利用液态金属材料的特性,将硅铝壳体与铝合金散热齿进行有机结合,大大提高了组件在连续波发射工作模式下的热量传导能力,保证了组件小体积下工作的可靠性。最终设计实现的Ku波段高增益8通道T/R组件,体积仅84 mm×48 mm×6 mm,质量约60 g,发射功率增益大于45 dB,发射输出功率大于1 W,接收增益大于29 dB,接收噪声系数小于3.5 dB。该组件8个通道收发性能一致性好,性能稳定,具有良好的工程实用价值。

一种多通道声呐接收机设计与实现

介绍一种用于图像声呐的多通道接收机设计与实现方法,详细介绍该接收机的设计原则,阐述接收机的组成和各模块的设计原理,优化接收机的电路拓扑结构,降低接收机通道的本底噪声,提高各通道的相位一致性。通过对本底噪声、增益控制、幅度一致性和相位一致性等关键性能指标的测试和数据分析,给出实际测试结果,验证了该多通道接收机满足该种类声呐的实际使用需求。

高精度模数转换器通道之间的时间误差校准算法研究

为避免模数转换器数字输出信号出现明显的滞后现象,实现对信号传输误差的有效弥补,提出了高精度模数转换器通道之间的时间误差校准算法。基于增益误差、失配误差、采样误差等3个指标,分析高精度模数转换器通道之间的主要时间误差参量。根据过零点数量,求解增益失配系数,确定动态校准指标数值,进而完成对时间误差参量的实时校准。对比实验结果表明,与TIADC时间误差校准算法相比,高精度模数转换器通道之间的时间误差校准算法能够实现对信号传输误差的有效补偿。

基于惯量估计的工业机器人关节伺服系统变增益自抗扰控制

针对工业机器人关节伺服系统存在时变负载和模型不确定性问题,提出了基于惯量估计的变增益自抗扰控制策略。首先,建立了关节伺服系统数学模型,并通过频域分析,得到了关节伺服系统二阶状态方程。为了削弱扰动和不确定参数的影响,设计了线性扩张状态观测器,利用自适应的方法估计惯量,同时结合鲁棒和滑模控制以保持系统稳定性,并对该控制策略进行了仿真和实验研究。实验结果表明,在该控制策略下,电机端正弦信号跟踪误差小于0.2 rad,在负载扰动下位置误差小于0.03 rad,较之单一自抗扰控制误差大约减小了40%,具有较强的抗扰动性,提高了关节伺服系统的控制精度和动态性能。

双基地高频地波SIAR通道幅相误差的自校准方法

该文针对多载频阵列发射、单天线接收的双基地高频地波SIAR,分析了通道幅相误差对空时二维超分辨的影响,研究了发射通道幅相误差的自校准方法。该方法利用直达波信号,将传统自校正算法中误差参数与目标参数的联合估计,转化为先估计误差参数再超分辨估计目标参数的级联处理,大大降低了计算量和时间损耗,操作简单且易于实现。该文对影响误差参数估计的因素及因应措施也作了讨论。计算机仿真验证了所提方法的有效性。

基于chirp信号的传输功率控制超短波渔船通信系统

针对超短波信道快衰落、远近效应、多径效应等特点,针对现有渔船超短波通信系统噪声高、通信距离下降的问题,提出一种适用于渔船超短波通信系统的前端功率控制算法:利用双chirp前导信号实现发送端信号功率控制和接收端自动增益控制,先通过一次检测chirp波相关峰值,获得信道的增益初估计,反馈调整AD前端的自动增益放大器,使信号达到合适的处理增益;通过检测第2个chirp波相关峰值,获得第2次增益估计;最后通过AR模型实现增益的精确估计与调整。仿真结果表明,该算法对接收端可以实现40 d B以上的增益调整,发送端可以节省30%以上的功耗。该算法的应用,可以降低超短波信道的背景噪声,改善渔业超短波信道环境,网络性能可得到提高。

矢量传感器增益校正与补偿

矢量传感器与每个通道的接收功率与信号的到达方向和极化状态有关,但信号的到达方向和极化状态很难精确控制,原有的基于全向天线估计通道增益的方法不适用于矢量传感器的情况。提出了估计矢量传感器通道增益的方法,并从电磁波特点出发导出了各通道增益的计算公式。数值仿真结果证明了该方法是有效的。

多径条件下基于辅助阵元的阵列幅相误差自校正

针对多径环境中均匀线阵(uniform linear array,ULA)的幅相误差的校正问题,在不破坏阵列幅相误差矩阵的前提下,提出了一种多径条件下基于辅助阵元的波达方向(direction of arrival,DOA)估计及幅相误差自校正算法。利用阵列平移的方法对相干信号进行解相干预处理,再利用辅助阵元依据子空间原理构建代阶函数实现相干信源的方位估计,进而对阵列幅相误差进行估计。计算机仿真结果表明,该算法对多径环境下的相干信源具有准确的方位估计与幅相误差自校正性能。

认知网络中基于中继的频谱资源分配

根据无线认知中继网络上、下行链路子载波的信道特性,研究认知网络的频谱资源分配,提出一种上、下行链路子载波联合优化的分配算法。该算法根据子信道增益差值因子的大小分配下行链路子载波,以源节点和中继节点功率最小化为优化目标配对上行链路子载波,以用户的实时需求分配子载波的比特和功率,有效降低了系统的发射功率,提高了系统吞吐量。仿真结果表明,与启发—集中式和分布式辅助反馈传输功率分配算法比较,该联合优化算法的单位比特功耗降低了1.5~3 dBμW,误比特率性能提高了1个数量级左右。

基于信道相关性的物理层安全性能分析

针对物理层安全研究中主窃信道具有相关性的场景,研究了主窃信道间的相关性对系统安全性能产生的影响,推导得到了遍历保密容量及中断概率的精确计算式,以及主窃信道的信道状态差异较大和较小这2种场景下的渐近计算式,并通过仿真验证了理论分析的正确性。研究结果表明,信道相关性会造成遍历保密容量的损失,但信道相关性强并不一定表明通信中断概率大。当目标速率设置合理时,信道相关性的影响与接收端平均信噪比有关,在高信噪比区域,强相关性会降低中断概率;在低信噪比区域,强相关性会增大中断概率;在中信噪比区域内,相关性几乎不影响系统的中断概率。基于上述结论,可以根据接收端信噪比、信道增益比、相关性等条件合理地设置系统参数,维护系统的安全性能。