802.15.4规范的增强型保障时隙通信协议的研究

针对IEEE 802.15.4-2006标准的保障通信时隙(GTS)分配机制存在系统容量低和传输时延大的不足,提出了增强型的GTS方案。该方案设计了新的GTS分配算法,以支持端设备之间的直接端对端通信;将原标准中的单信道分配算法扩展为多信道分配算法,以充分利用物理层规范提供的多信道资源;设计了GTS通信维护算法,以增强系统的可靠性。理论分析和仿真结果均表明,该方案可将相邻端对端设备之间的平均传输时延减少到原标准的1/3,系统容量最大可以扩展2N倍(N为系统数据信道数),且增加的网络开销可接受。     

基于遗传算法的图关联着色算法

图的着色算法是一种典型的NP-完全问题。给出了一种用于图的关联着色的遗传算法。遗传算法用于进行全局搜索,从而有效的查找解空间。文中对关联色数为6的一个图进行了仿真实验,给出了该图的关联色数以及4种6-关联着色。用本文提出的算法,得到了完全图、完全多部图的关联色数。实验结果表明,本文设计的遗传算法可以很好的对关联着色猜想进行求解,获得问题的高质量的解。     

无线传感器网络的流量自适应分簇算法协议

在分析LEACH路由协议算法的缺点的基础上,提出了一种用于无线传感器网络的基于流量自适应的TDMA分簇算法协议.该协议根据当前节点数据流量的变化,自适应地调整该节点在其簇内通信的时隙长度,减少节点空闲时消耗的能量和节点从睡眠到活跃状态来回切换的能量.仿真实验结果表明,与LEACH协议簇内时隙分配算法相比,运用这种新的时隙分配算法,可以节省节点的能量,提高网络的生存时间,改善网络性能.     

基于3E均衡的CDM GDP机场时隙分配

为了科学合理利用机场时隙资源、降低航班延误损失,本文研究适合我国的CDM GDP时隙分配机制与方法。提出按工效分配的原则,给出了一种有效性、工效性和公平性均衡的CDM GDP时隙分配优化模型;并引入具体的评价指标量化分析航空公司之间延误分配的公平性。模型采用遗传算法予以实现。实例仿真结果表明,模型的工效性和公平性均比RBS算法有所提高,从而验证了其有效性。     

基于智能天线的动态时隙指派技术研究

针对TDMA/TDD公众蜂窝移动通信系统的特征，运用了一种智能天线的解决方案，研究并提出一种动态时隙指派的算法。目的是让无线资源指派根据空时最佳特性进行量化评估并优选，然后把最优载波和时隙分配给需要的移动终端。系统级仿真表明，本算法和传统时隙分配算法相比，移动通信网络的综合性能指标得到的显著的改善。     

基于二元指数后退的电子标签防碰撞算法

为解决目前现有电子标签防碰撞算法在电子标签数量较大时,读取效率低且耗时较长的问题,提出了一种基于二元指数后退的时隙选择算法,当碰撞发生时,改进算法以二进制指数方式进行时隙的增加,并随机选择时隙发送数据,重复这个过程直到所有标签被正确读出。仿真试验表明,在电子标签数量急剧增加时,改进算法的读取效率较高,电子标签读取所需时隙基本不增加。     

基体PP分子量及分散相含量对分散相形态的影响

采用凝胶渗透色谱仪(GPC)、扫描电子显微镜(SEM)、转矩流变仪研究了基体分子量和分散相含量对聚丙烯(PP)/乙烯-辛烯共聚物(POE)共混体系分散相形态的影响。研究表明,当固定分散相POE含量时,随着基体PP分子量的降低,基体黏度降低,POE/PP的两相黏度比变大,导致分散相粒径大小和分布宽度增加。当固定基体分子量(M-w=148021),POE/PP两相黏度比不变时,增加分散相POE含量,分散相粒径大小及分布宽度均随其含量的增加先增大后趋于平台区。     

汽车零部件平准化拣配作业优化研究

针对汽车零部件拣配作业工作效率低、工作负荷不均衡及配送车辆装载率低的问题,以作业人员工作负荷均衡化和配送车辆装载率最大化为目标,建立汽车零部件平准化拣配作业优化模型.模型求解过程分为两级:运用启发式算法确定动态作业人员分配方案;在作业人员合理分配基础上利用遗传算法确定换装顺序及车辆装载计划.实例分析结果显示,与原拣配作业方案相比,该模型使车辆装载率提高了18.4%,作业总工时减少了26 h.     

RFID读写器防冲突问题的混沌神经网络建模与求解

针对密集读写器环境下的RFID读写器冲突情况,提出了一种通过中央计算机集中控制读写器分时操作来避免读写器冲突的方法,并设计了基于退火策略的混沌神经网络算法进行读写器时隙分配的求解.首先,根据平面图着色问题与读写器防冲突问题的相似性,确定四时隙分时操作的防冲突原理;然后采用二维Hopfield神经网络建立四时隙分配问题模型,并构造了满足冲突约束条件的神经网络能量函数;最后,通过引入混沌机制和模拟退火策略进行问题求解以使得算法具有较好的搜索能力和收敛速度.与现有的分布式防冲突算法相比,该方法能够保证读写器具有更多的扫描标签时间和更高的标签扫描频度.仿真实验结果表明用该算法求解读写器防冲突问题是可靠的、高效的.     

基于边缘计算与区块链的车载计算资源智能调度研究

随着车联网(IoV)的快速发展及部署,用户对网络服务质量的要求也随之提高。车联网数据计算作为网络服务的重要内容之一,越来越受到关注。移动边缘计算(MEC)作为一种允许车辆将计算任务卸载到车联网系统边缘服务器的技术,能够有效降低计算时延,提升数据处理效率。然而,车联网的数据流量日益增加,导致边缘计算设备的需求量大幅提高且存在数据安全可靠性问题。对此,本文面向车联网中移动车辆计算卸载的场景,提出一种基于区块链的停放车辆辅助计算的系统模型。通过联合考虑服务器计算资源、车辆机动性等条件,利用深度强化学习(DRL)对计算卸载和资源分配策略进行优化,减少系统能耗和数据传输时延,并提高区块链系统的交易吞吐量。仿真结果表明,本文所提优化方法可以有效提升系统性能,同时具有良好的收敛性能和稳定性。     

A pinwheel packet scheduling scheme for broadband wireless networks

Abstract

A frame‐based packet scheduling scheme, the pinwheel scheduling (PWS) scheme, is proposed and investigated at the medium access control (MAC) layer in broadband wireless networks. The objective of the proposed scheduling scheme is to provide low delay and low jitter for real‐time traffic. We have demonstrated in this paper that the proposed PWS scheme not only satisfies the packet‐level QoS requirements but also has low implementation cost. The PWS scheme gives the highest priority to CBR connections in a service cycle to minimize their delay and jitter. For ABR traffic, a number of slots are allocated to fit their MCR. The remaining time slots are then allocated to VBR traffic according to their PCR. Thus, the VBR traffic may suffer large delay and jitter when the number of CBR connections increases. The PWS with modular strategy (PWS/MS) is proposed to improve the performance of the VBR traffic. We also introduce three different slot‐reuse strategies named real‐time traffic first (RTF), non‐real‐time traffic first (NRTF) and longest queue first (LQF), respectively, to improve resource utilization. In order to demonstrate the performance of the PWS and PWS/MS schemes, comparisons are made with existing schemes such as the round‐robin (RR) and weighted‐round‐robin (WRR) by using OPNET software. Simulation results show that the proposed schemes are capable of maintaining the lowest delay and jitter for VBR and CBR traffic while not sacrificing the available bit rate (ABR) traffic.     

Cluster-Based Stable BSM Dissemination System for Safe Autonomous Platooning

Recently, the importance of vehicle safety supporting system has been highlighted as autonomous driving and platooning has attracted the researchers. To ensure driving safety, each vehicle must broadcast a basic safety message (BSM) every 100 ms. However, stable BSM exchange is difficult because of the changing environment and limited bandwidth of vehicular wireless communication. The increasing number of vehicles on the road increases the competition to access wireless networks for BSM exchange; this increases the packet collision rate. An increased packet collision rate impairs the transmission and reception of BSM information, which can easily cause a traffic accident. We propose a solution, the vehicular safety support system (V3S), which exchanges BSMs reliably even when many vehicles are on the road. The V3S uses a clustering scheme to decrease network traffic by reducing the amount of data exchanged between a vehicle and the roadside unit (RSU). In addition, the V3S reduces the collision rate of wireless network packets by broadcasting the vehicle's BSM in an allocated timeslot using the time division multiple access (TDMA) MAC protocol. The V3S also deals with insufficient bandwidth for dedicated short-range communications (DSRC) by changing DSRC channels according to traffic flow. In evaluating the packet error rate for stable BSM packet delivery, the V3S demonstrates an excellent packet error rate of less than 1%, compared to the 802.11p with its packet error rate of 82%.     

面向多媒体业务的无线ATM多址接入协议

基于MDR-TDMA（Multi-service Dynamic Reservation-TDMA）的无线ATM多址接入控制协议包括两个主要的过程，即请求报文的信息时隙的分配过程，对于前者，通过基于帧的自适应伪贝叶斯ALOHA算法，在保证请求报文最优吞吐率的条件下，实现了不同优先级的请求报文接入。对于后者，着重分析了以视频会议为模型的VBR业务的带宽分配，提出了一种新的带宽分配方法-Minmax算法，并将它的仿真结果与线性比例算法进行比较。     

A Physical Layer Algorithm for Estimation of Number of Tags in UHF RFID Anti-Collision Design

A priori knowledge of the number of tags is crucial for anti-collision protocols in slotted UHF RFID systems. The number of tags is used to decide optimal frame length in dynamic frame slotted ALOHA (DFSA) and to adjust access probability in random access protocols. Conventional researches estimate the number of tags in MAC layer based on statistics of empty slots, collided slots and successful slots. Usually, a collision detection algorithm is employed to determine types of time slots. Only three types are distinguished because of lack of ability to detect the number of tags in single time slot. In this paper, a physical layer algorithm is proposed to detect the number of tags in a collided slot. Mean shift algorithm is utilized, and some properties of backscatter signals are investigated. Simulation results verify the effectiveness of the proposed solution in terms of low estimation error with a high SNR range, outperforming the existing MAC layer approaches.     

基于服务曲线的TDMA无线网络上行信道时隙调度算法

研究了采用TDMA接入方式的无线分组网络上行信道时隙分配策略,基于移动台的QoS要求,提出了一种自适应时隙分配算法。利用服务曲线对移动台的QoS要求进行了建模。算法的目标是在尽量满足所有移动台Qos要求的基础上提高系统的上行吞吐量。在无法满足所有移动台QoS要求的情况下,使得移动台实际发送的数据与满足服务曲线要求之间的偏差最小。仿真结果表明：该算法能够在系统吞吐量和系统偏差之间进行折衷,从而有效地平衡上述两个目标。     

A Dynamic Multi-ary Query Tree Protocol for Passive RFID Anti-collision

In this paper, a dynamic multi-ary query tree (DMQT) anti-collision protocol for Radio Frequency Identification (RFID) systems is proposed for large scale passive RFID tag identification. The proposed DMQT protocol is based on an iterative process between the reader and tags which identifies the position of collision bits through map commands and dynamically encodes them to optimize slots allocation through query commands. In this way, the DMQT completely eliminates empty slots and greatly reduces collision slots, which in turn reduces the identification time and energy costs. In addition and differently to other known protocols, the DMQT does not need to estimate the number of tags, reducing the protocol implementation complexity and eliminating the uncertainty caused by the estimation algorithm. A numerical analysis shows that DMQT has better performance than other algorithms for a number of tags larger than 300. Meanwhile, when the number of tags is 2000 and the tag identity (ID) length is 128 bits, the total identification time is 2.58 s and the average energy cost for a tag identification is 1.2 mJ, which are 16.9% and 10.4% less than those of state-of-the-art algorithms, respectively. In addition, a DMQT extension based on ACK command has also been presented to deal with capture effect and avoid missing identification.

     

客户偏好约束下的网络零售配送时隙分配优化

在B2C环境下,提高配送时隙运营效率,降低运营成本,尽力通过高效的资源利用率来降低成本,从而产生良好的经济效益,成为网络零售商提高竞争力的关键所在。本文规避单目标研究不能够较为全面反映配送的实际问题,拟考虑从多目标角度对问题进行优化,建立了基于客户偏好的时隙偏差最小和时隙配送成本最小的综合优化模型。最后通过算例分析,模拟几种不同情况,综合优化模型在时间和成本水平下都较传统单目标更优,能使配送时隙综合效用最大。     

Separation control on a thick airfoil with multiple slots blowing at small speeds

Summary Using multiple slots blowing at small speeds to efficiently control boundary-layer separation on a thick airfoil is studied. The method of numerically solving the Reynolds averaged Navier-Stokes equations was used for the study. The following results were obtained. For multiple slots blowing at small speeds, the wall jet from each slot does not decay very fast (unlike the single slot blowing at the same momentum rate, the wall jet of which has much larger speed) and the near-wall momentum is continuously reinforced by the blowing slots sequentially located on the airfoil upper surface; as a result, under the same momentum blowing rate, multiple slots blowing at small speeds control the boundary layer separation more effectively than single slot blowing at large speed. Moreover, the power expenditure of multiple slots blowing at small speeds is much smaller than that of single slot case. Therefore, using multiple slots blowing at small speeds, high lift and high efficiency (as measured by equivalent lift-drag ratio) can be achieved at the same time. For the multi-slotted thick airfoil (40 percent thickness, 10 slots) considered in this paper, with the blowing total pressure the same as the free-stream total pressure, high lift (C _L =2.3) and large equivalent lift-drag ratio (almost 40) were realized; with a slightly larger blowing total pressure, even higher lift (C _L =3.2) but slightly smaller equivalent lift-drag ratio (about 36) were obtained.