Analytical determination of flow resistance characteristic for combination channel inside hydraulic manifold block

Computational fluid dynamics （CFD） was used in conjunction with BP neural network to study the flow resistance characteristic of the combination-channel inside hydraulic manifold block （HMB）. The input parameters of the combination-channel model were confirmed to have effect on the pressure-drop by the numerical method, and a BP neural network model was accordingly constructed to predict the channel pressure-drops. The flow resistance characteristic curves of various channels were achieved, and a performance parameter was given to evaluate the through-flow characteristic of the channel according to the curves. The predictions are in agreement with the numerical computation, indicating that the method can be utilized to accurately determine the flow characteristic of the combination channel with high efficiency.     

星地链路雨衰信道动态特性的HIL仿真

为进一步研究自适应传输、功率控制和分集等毫米波频段星地链路的抗雨衰措施,提出了一种雨衰信道硬件在环路HIL(Hardware-in-the-loop)仿真系统的原理与实现方案.讨论了U.C.Fiebig等人提出的基于时间序列发生器原理的雨衰信道动态预测模型,设计并实现了基于MATLAB/SIMULINK软件与FPGA硬件相结合的雨衰信道硬件在环路实时仿真器.在此基础上,对不同降雨衰减条件下的MPSK/MQAM自适应调制抗雨衰措施及误码率性能进行了分析和比较,HIL仿真结果与理论上的预测分析是一致的.这种HIL雨衰信道仿真器可以用于检验卫星通信系统抗雨衰措施的有效性.     

一种基于信道感知和预测的多址接入方法

为了实现认知无线电系统中机会式的频谱接入、主动避免对主用户的干扰,提出了一种基于信道感知和预测的多址接入方法。考虑主用户对信道的占用过程具有一定的突发性和相关性,将主用户的活动规律建模为半马尔可夫过程。新算法充分利用信道感知结果和主用户的活动规律预测下一个时刻主用户的状态及剩余状态持续时间,并采用递归预测误差法进行参数估计。仿真结果表明,与传统的载波侦听多址接入算法相比,新算法能够在保证主用户阻塞概率约束的前提下,较大地提高频谱利用率,非常适用于认知无线电。     

基于平面拼装的Ad Hoc网络抗毁性研究及其信道分配

提出一种基于平面拼装方法解决Ad Hoc网络抗毁性及其信道分配问题. 在1 000×1 000单位区域内用若干个半径均为100的圆构建Ad Hoc网络, 当相交部分不小于5%时, 得到与6个圆的正六边形相交拼接效果, 用45个圆可以完全覆盖全部区域, 选择3个通信信道即可完全进行数据交换; 当相交部分不小于18%时, 得到与4个圆的正方形相交拼接效果, 用64个圆可以完全覆盖全部区域, 选择2个通信信道即可完全进行数据交换. 实验结果表明, 该方法对各种蜂窝移动通信网组网具有指导意义.     

一种新的TD-SCDMA信道估计改进方法

提出了一种用于TD-SCDMA(时分双工同步CDMA)移动通信系统的信道估计改进方法.TD-SCDMA系统中采用Steiner信道估计器,这种估计器实质上是基于最小二乘的估计,忽视了信道噪声的影响,而信道的噪声对估计精度有很大影响.利用TD-SCDMA在相邻帧为慢变信道的特征,提出一种基于时延相关信道估计改进方法,同时对Steiner估计器进行门限滤波,滤除了大部分噪声抽头.仿真结果表明,改进的信道估计使系统的性能获得较大的改善与提高,甚至在高速移动传播环境下可以达到2 dB的增益.     

基于隐含导频的长距离IM/DD DFT-S-OFDM无源光网络的实验系统研究

基于隐含导频、超奈奎斯特镜像混叠和直接检测,首次在IM/DD光通信系统中使用基于隐含导频（ST）的信道估计和均衡方式,通过实验实现了速率为20 Gb/s的正交相移键控（QPSK）离散傅里叶变换扩展正交频分复用（DFT-S-OFDM）信号传输832 km的光通信系统.使用隐含导频信道估计（ST-CE）方法来均衡信道的线性损伤,关键是把隐含导频（ST）算术叠加在数据信号上,而不占用单独的时隙. 通过对接收到的信号进行1阶统计分析估计出精确的信道. 为了增加传输距离,根据超奈奎斯特镜像混叠的方法增加接收机带宽来补偿色散引起的功率衰落. 结果显示,在长距离强度调制/直接检测（IM/DD）DFT-S-OFDM无源光网络（PON）系统中,采用ST-CE能得到更高的频谱效率,且其信道估计性能与TA-CE相当. 该方法节省了带宽,提高了频谱利用率.     

基于改进蚁群算法和共用航段的搜索救援通道规划

针对战斗搜救任务场景中,空中搜索救援等待区至跳伞区之间的往返路径规划问题,提出一种基于改进蚁群算法和共用航段的搜索救援通道规划方法。首先,针对基本蚁群算法易出现局部极值及收敛速度慢等缺点,对启发函数、状态转移策略、信息素更新策略进行了改进。然后,针对单起点多目标点的路径规划问题,提出了设置分航点以生成共用航段的搜索救援通道规划方法,并以总路径长度表征任务准备负荷量与分别规划航路进行对比。实验结果表明,在本文测试环境下,改进蚁群算法规划的路径长度分别缩减15.4%和14.2%,搜索救援通道的任务准备负荷量减少25.4%。所提出的搜索救援通道规划方法有一定的理论和应用价值。     

基于改进信息熵和LSTM网络的轴承故障诊断

针对传统的时频域故障诊断方法无法对故障实现自适应识别和分类,且准确率较低的问题,提出一种基于改进信息熵(improved information entropy, IIE)的长短时记忆网络(long-short time memory network, LSTM)方法。首先对原始信号分别进行集合经验模态分解(ensemble empirical mode decomposition, EEMD)和变分模态分解(variational mode decomposition, VMD);将包含故障信息的所有本征模式分量(intrinsic mode functions, IMF)进行信息熵的求取;通过信息熵反映IMF的信息量和峭度指标对描述冲击成分的优势改进信息熵,构成特征向量;最后结合LSTM处理非线性数据的优势,利用组合特征训练LSTM网络建立诊断模型。实验结果表明：该方法能准确、高效地识别多种故障,准确率要比单一的EEMD-LSTM、VMD-LSTM、人工神经网络等传统方法更高。     

Two-Level Cross-Talked Admission Control Mechanism for QoS Guarantee in 802.11e EDCA

This paper describes a two-level cross-talked admission control mechanism that guarantees quality of service （QoS） requirements for multimedia applications over wireless local area networks （WLANs）. An enhanced distributed channel access analytical model is used to compute the maximum number of admitted users according to the QoS requirements and the packet arrival characters. Then, some channel resources are reserved for handoff calls based on the maximum number of admitted users and the call-level traffic model. The channel utilization ratio is also measured to reflect the current system traffic load. The maximum number of admitted users and the channel utilization ratio are used for admission control for applications with QoS requirements in the call level and for rate control of best effort applications in the packet level using the p-nonacknowledgement scheme. Thus, the QoS requirements are statistically guaranteed while the system is efficiently utilized. Simulations validate the effectiveness of this mechanism to guarantee the QoS and bandwidth utilization.     

Multiuser MIMO Downlink Transmission Schemes over Time-Varying Channels

The performance of multiuser multiple-input-multiple-output （MIMO） downlink systems with block diagonalization （BD） depends on the accuracy of the channel state information （CSI） available at the trans- mitter and the receiver. In time-varying channels, the CSI available at the transmitter （CSIT） is always out-dated due to an inherent time delay between the uplink channel estimation and the downlink data transmission in time division duplexing （TDD） systems. This leads to a drastic degradation of system capacity. This paper first analyzes the effect of the outdated CSIT on multiuser MIMO downlink systems using the BD method and then proposes two linear processing methods, BD precoding with user selection and scheduling at the transmitter and total minimum mean squared error （MMSE） decoding at the receiver （TBDUSS-RTMMSE） and BD preceding at the transmitter with partial MMSE decoding at the receiver （TBD-RPMMSE）, to mitigate the interference among data streams and users. Analysis and simulation results show that these methods can effectively reduce the impairment of the outdated CSIT to increase the system sum capacity in a suitable time delay region of the CSIT.