数据链路多径传输模型的物理映射方法研究

根据无人机数据链路的多径传输要求,针对在传输中电磁波衰落,为保证精度,在微波暗室中建立与之相关的分析模型,采用仿真手段有助于提高无人机数据链的有效性。通过对数据链路的实际传输场景(散射点属性等)以及信道传输模型的多径参数(时延、衰落、多普勒频移)分析,解算出该场景下接收点处的合成功率,并在微波暗室中,依据仪表的衰落仿真机理和暗室环境中求得的合成功率。用两种方法对场景进行仿真,可从中选取一种精度更好的方法进行仿真验证有效性,实现了多径传输链路在微波暗室的准确物理映射。     

移动通信中宽带接收系统信号电平特性的研究

首先建立了一个包括直达波和非直达波的无线电波的传播模型,然后得到宽带接收系统中接收信号的电平表达式,再通过MATLAB仿真得到宽带接收系统中信号的电平变化和分布的特性。根据仿真结果,可知宽带接收系统的信号电平变化约为10dB,信号电平的分布受到传播模式中的接收带宽、达波数、路径差的影响。     

正交频分复用技术系统仿真及其应用

正交频分复用（OFDM）技术能够有效地克服频率选择性衰落,因此目前在宽带无线通信中被广泛地应用。该文首先介绍了正交频分复用技术的基本原理,分别对其发射机和接收机的具体结构进行了详细描述。通过对正交频分系统结构的分析,建立了正交频分复用全系统的数学仿真模型,并采用Matlab对系统进行了计算机仿真运算,分析了该系统在不同的信道条件和调制体制下,系统的误码率对比特性,并以具体图像作为实例,以更加直观的角度,反映出正交频分复用系统在不同条件下的性能差异。     

基于ARMA的无线传感器网络流量预测模型的研究

无线传感器网络(WSN)的流量预测研究对于WSN管理具有至关重要的意义。基于WSN的特点,结合自回归滑动平均(ARMA)模型,该文提出了一个面向WSN的流量预测算法。仿真结果表明,该算法具有较高的预测精度;利用本算法对WSN的多路径路由机制进行改进后,可进一步提高WSN的生存期。     

The BMLA/LS technique and its application in A mobile satellite communication channel

The burst mode link analyser with least squares algorithm (BMLA/LS) is a real-time impulse or frequency response extraction (IRE/FRE) technique of a satellite communication channel, originated and explored by the author. This paper summarizes some key technical points of the BMLA/LS and presents its novel simulation results and applications in a land-mobile DBPSK/DQPSK satellite channel at K_a-band, including the channel additive white Gaussian noise (AWGN) effect on IRE/FRE by BMLA/LS, and the instantaneous IRE/FRE in a Rician channel with multi-path reflection, in a shadowed channel by trees and in a combinational fading channel, and their comparisons and conclusions.     

O<Superscript>3</Superscript>BPSK-based Linear Decorrelating Detector for Asynchronous DS/CDMA Systems over Frequency-Selective Rayleigh Fading Channels

In this paper, a convenient signaling scheme, called orthogonal on–off BPSK (O³BPSK), along with a simple one-shot linear decorrelating detector (LDD) and a whitening Rake bank, is proposed for near–far resistant detection in asynchronous DS/CDMA systems. Based on the maximum multi-path spreading delay, a minimum duration of “off” is suggested, during which the temporally adjacent bits (TABs) that contain multi-user interference (MUI) and inter-symbol interference (ISI) from different users at the receiver are decoupled. The O³BPSK signaling scheme is combined with the whitening Rake receiver to preserve multi-path diversity gain in multi-path fading CDMA channels. The scheme offers low complexity, no detection delay, near–far resistance, and compensation for fading channels.

Multi-path connected network for medical image segmentation

In recent years, deep learning has been successfully applied to medical image segmentation. However, as the network extends deeper, the consecutive downsampling operations will lead to more loss of spatial information. In addition, the limited data and diverse targets increase the difficulty for medical image segmentation. To address these issues, we propose a multi-path connected network (MCNet) for medical segmentation problems. It integrates multiple paths generated by pyramid pooling into the encoding phase to preserve semantic information and spatial details. We utilize multi-scale feature extractor block (MFE block) in the encoder to obtain large and multi-scale receptive fields. We evaluated MCNet on three medical datasets with different image modalities. The experimental results show that our method achieves better performance than the state-of-the-art approaches. Our model has strong feature learning ability and is robust to capture different scale targets. It can achieve satisfactory results while using only 0.98 million (M) parameters.     

基于DHT的消息转发防御机制研究

DHT（Distributed Hash Tables）是结构化P2P（Peer to Peer）系统实现资源高效组织和定位的关键技术。对DTH系统中消息转发过程中的安全威胁及其解决方法进行了分析。以多路径算法为基础,对消息转发效率和安全性进行优化,提出了一种混合路由防御机制。首先结合迭代路由与递归路由的优点,设计了混合路由方式,保证了消息的转发效率并降低消息开销。然后改进了消息转发过程中的可靠性和消息源鉴别机制。最后,在四川大学校园网内进行了测试。仿真试验结果表明,采用混合路由下的防御机制在减少消息数量的同时提高了查询成功率,对于消息转发过程中的攻击有着较好的防御效果。     

基于交替投影的DOA估计方法及其在米波雷达中的应用

由于低仰角目标回波中存在多径信号,使得米波雷达难以对低仰角目标进行高度测量,为此该文提出一种适用于多径信号情况下的波达方向估计的迭代方法。该方法将回波信号的相关矩阵,在各个信号子空间中交替投影,该方法可以同时对直达波和反射波进行精确的波达方向估计,并可以有效地对米波雷达中的低仰角低空目标进行高度测量。计算机仿真和某米波雷达实测数据的处理结果证实了该方法的有效性。Monte-Carlo试验结果表明在低仰角低空测高时,该方法具有比时空级联最大似然方法更好的性能。     

一种新的用于无线Ad hoc网络中视频传输的多路径包调度算法

该文提出了一种新的在无线Ad hoc网络中进行视频传输的多路径包调度算法(MPPA)。该算法充分考虑到视频流传输的特殊QoS要求,针对视频流中的每个数据包进行操作,通过计算将其指定在某条路径上传输。避免了传统多路径传输中的接收端数据包乱序和重新排序的问题,有效地减小了接收端的启动延时和缓冲区需求。同时仿真结果验证了上述理论的正确性。