Modeling and performance analysis of VI‐CRA: A congestion control algorithm for vehicular networks

This study proposes a Vehicle ID‐based CAM Rate Adaptation (VI‐CRA) algorithm for beacon messages in the vehicular network. Foremost, an improved vehicle ID–based analytical model is proposed at the MAC layer of vehicular network. The model weighs the random back‐off number chosen by vehicles participating in the back‐off process, with the vehicle ID incorporated in their respective CAMs. This eventually leads to the selection of a vehicle ID–based random back‐off number, minimizing the probability of collision due to same back‐off number selection. It is worth noting that the improved analytical model outperforms the existing works in terms of average packet delay since only one fourth of the contention window size is used throughout the simulation. To enhance the performance of the analytical model, the paper incorporates a congestion control algorithm, by adapting the rate of CAM broadcast over the control channel. The algorithm is designed considering a wide range of scenarios, ranging from nonsaturated to extremely saturated network (in terms of collision probability) and sparsely distributed to teemed network (in terms of vehicular density). For better analyses of simulation results, the algorithm is applied over different vehicle ID–based back‐off numbers. Simulation results for all the back‐off numbers show that vehicle ID–based CAM rate adaptation algorithm performs better than the traditional fixed CAM rate IEEE 802.11p, even at high vehicular density.     

Reliable M2M/IoT data delivery from FANETs via satellite

The use of unmanned aerial vehicles (UAVs) is rising in several application fields. This work deals with the communication challenges in UAV swarms, or flying ad hoc network (FANET), when taking into account non–line‐of‐sight scenarios. The use of satellites is a necessity in such operating conditions; thus, this work provides architectural considerations and performance assessments when several (FANETs) share an uplink random access satellite channel, fed with M2M/IoT traffic generated from on‐board sensors, to be reliably delivered to a remote ground destination.     

Design and Analysis of an Efficient Communication Strategy for Hierarchical and Highly Changing Ad-hoc Mobile Networks

In this work we introduce two practical and interesting models of ad-hoc mobile networks: (a) hierarchical ad-hoc networks, comprised of dense subnetworks of mobile users interconnected by a very fast yet limited backbone infrastructure, (b) highly changing ad-hoc networks, where the deployment area changes in a highly dynamic way and is unknown to the protocol. In such networks, we study the problem of basic communication, i.e., sending messages from a sender node to a receiver node. For highly changing networks, we investigate an efficient communication protocol exploiting the coordinated motion of a small part of an ad-hoc mobile network (the runners support) to achieve fast communication. This protocol instead of using a fixed sized support for the whole duration of the protocol, employs a support of some initial (small) size which adapts (given some time which can be made fast enough) to the actual levels of traffic and the (unknown and possibly rapidly changing) network area, by changing its size in order to converge to an optimal size, thus satisfying certain Quality of Service criteria. Using random walks theory, we show that such an adaptive approach is, for this class of ad-hoc mobile networks, significantly more efficient than a simple non-adaptive implementation of the basic runners support idea, introduced in [9,10]. For hierarchical ad-hoc networks, we establish communication by using a runners support in each lower level of the hierarchy (i.e., in each dense subnetwork), while the fast backbone provides interconnections at the upper level (i.e., between the various subnetworks). We analyze the time efficiency of this hierarchical approach. This analysis indicates that the hierarchical implementation of the support approach significantly outperforms a simple implementation of it in hierarchical ad-hoc networks. Finally, we discuss a possible combination of the two approaches above (the hierarchical and the adaptive ones) that can be useful in ad-hoc networks that are both hierarchical and highly changing. Indeed, in such cases the hierarchical nature of these networks further supports the possibility of adaptation.     

一种基于混沌的真随机源电路

提出了一种基于混沌的随机源电路,通过利用电容上电荷的再分配,实现了一个离散混沌系统.该电路在0 .8μm CMOS工艺下流片成功,核心面积小于4 2 0 0 μm2 ,功耗小于1m W,优于目前已有的几种实现方法.     

MIMO信道中衰落信号的空域相关性评估

将MIMO(多输入多输出)信道建立为Nakagami衰落信道,进一步推导单元天线接收多径衰落信号的空域相关系数的通用解析式,并在均匀分布、余弦分布、高斯分布和拉式分布的来波功率角谱下分别进一步评估接收信号的空域相关性,分析各参数对相关系数的影响,比较各种来波功率角谱下相关性的数值结果,这些对于准确分析MIMO系统性能与设计MIMO多天线系统是十分必要的.     

一种具有不可预测性的随机延时引信延迟时间的总体分布

构造了一种变组合分布作为随机延时引信延迟时间的总体分布 ,并利用 BP网络对其与其它总体分布产生的随机延迟时间序列进行预测性分析比较 ,证明按该法产生的随机时间序列具有不可预测性     

Spreading Codes Generator for Wireless CDMA Networks

The prime characteristic of spread spectrum modulated signals is that their bandwidth is greater than the information rate. In this way a redundancy is introduced that allows the severe levels of inteference inherent in the transmission of digital information over radio and satellite links to be overcome. Current spread spectrum applications are primarily in military communications; nevertheless, there is growing interest in this technique for third generation mobile radio networks (UMTS, FPLTS, etc.) with open discussion regarding the practicality of using a multiple access system based on spread spectrum techniques (CDMA). However, in order to support as many users in the same bandwidth as other multiple access techniques such as TDMA or FDMA, it is important how to generate large families of sequences that present low cross-correlation. The aim of this paper is to describe a spreading codes generator that can produce a large number of PN sequences with good properties of auto- and cross-correlation. Moreover, the codes generated shows high unpredictability and good statistical behaviour. This also allows the implementation of some features that are common on military networks such as message privacy (increasingly important in commercial networks) without additional cost. The structure presented shows itself to be advantageous for high speed generation of codes at a low cost, low power consumption (allowing longer life for batteries), small size and simplicity of implementation, essential ingredients for commercial equipment. Another attractive feature is its structural parallelism, useful in VLSI implementations. All of these features render it potentially suitable for the implementation of channel bandwidth sharing systems in future wireless personal communications networks.     

二维随机粗糙面的fBm模拟及其统计特性

数值模拟在物理建模中具有相当重要的地位。本文基于对二维分形布朗运动（ｆＢｍ）的研究，根据ｆＢｍ的特征，阐述了用二维ｆＢｍ函数模拟随机粗糙面的方法。由于很多电磁散射问题与粗糙面的各阶矩有很大的关系，我们导出了二维随机粗糙面的统计参量与分维Ｄ的关系。基于对二维ｆＢｍ的小波分析，提出了在时－频相空间估计分维Ｄ的方法。这种方法比较简单而切实可行，不但适合于粗糙面整体分维的计算，更适合于局部分数维的计算。所     

车载控制台结构设计与仿真分析

某控制台位于空间紧凑的轻型高机动底盘车内,控制台的结构紧凑、重量轻、多功能操控、操控舒适度高等需求是设计中的难点和重点。针对控制台内装设备的结构特点,提出了控制台的轻量化和集成化设计方案,满足结构的美观性和可靠性要求。基于控制台的车载使用环境条件,采用有限元软件构建控制台的力学分析模型,分析了控制台的模态计算结果,同时探讨了不同方向的随机振动对控制台强度和刚度的影响。仿真结果和试验验证表明,控制台的强度和刚度满足设计要求。控制台结构设计合理可行,满足整车系统的使用要求。     

一种基于随机投影的贝叶斯时间差分算法

在强化学习方法中,大部分的算法都是基于值函数评估的算法.高斯过程时间差分算法利用贝叶斯方法来评估值函数,通过贝尔曼公式和贝叶斯规则,建立立即奖赏与值函数之间的概率生成模型.在状态空间中,通过在线核稀疏化并利用最小二乘方法来求解新样本的近似线性逼近,以提高算法的执行速度,但时间复杂度依然较高.针对在状态空间中近似状态的选择问题,在高斯过程框架下提出一种基于随机投影的贝叶斯时间差分算法,该算法利用哈希函数把字典状态集合中的元素映射成哈希值,根据哈希值进行分组,进而减少状态之间的比较.实验结果表明,该方法不仅能够提高算法的执行速度,而且较好地平衡了评估状态值函数精度和算法执行时间.