Contention-Based Nonorthogonal Massive Access with Massive MIMO

The sporadic communication character of massive machine-type communication systems provides natural advantages to utilize the principle of compressive sensing(CS).However,due to the high computational complexity of CS algorithms,CS-based contention-free access schemes have limited scalability and high computational complexity for massive access with user-specific pilots.To address these problems,in this paper,we propose a new contention-based scheme for CSbased massive access,which can support the sporadic access of massive devices(more than one million devices)with limited resources.Furthermore,an advanced receiver algorithm is designed to solve the optimal solutions for the proposed scheme,which utilizes various prior information to enhance the performance.In specific,the joint sparsity between the channel and data is used to improve the accuracy of pilot detection,and the information of modulation and cyclic redundancy check is exploited for channel correction to improve the performance of data recovery.The simulation results show that the proposed scheme can achieve improved active user detection performance and data recovery accuracy than existing methods.

Hierarchical Content Caching in Fog Radio Access Networks:Ergodic Rate and Transmit Latency

In order to alleviate capacity constraints on the fronthaul and decrease the transmit latency, a hierarchical content caching paradigm is applied in the fog radio access networks(F-RANs). In particular, a specific cluster of remote radio heads is formed through a common centralized cloud at the baseband unit pool, while the local content is directly delivered at fog access points with edge cache and distributed radio signal processing capability. Focusing on a downlink F-RAN, the explicit expressions of ergodic rate for the hierarchical paradigm is derived. Meanwhile, both the waiting delay and latency ratio for users requiring a single content are exploited. According to the evaluation results of ergodic rate on waiting delay, the transmit latency can be effectively reduced through improving the capacity of both fronthaul and radio access links. Moreover, to fully explore the potential of hierarchical content caching, the transmit latency for users requiring multiple content objects is optimized as well in three content transmission cases with different radio access links. The simulation results verify the accuracy of the analysis, further show the latency decreases significantly due to the hierarchical paradigm.

Eliminating Explicit Contention from Channel Access in Distributed Wireless Networks

Emerging techniques such as WiFi direct makes the objective of always-on be true. People can easily chat and share files with nearby friends even without AP(Access Point) or cellular coverage. In this paper, we focus on the channel efficiency issue of APfree Wi-Fi networks, which can be easily constructed in the subway, in a high-speed railway, or when camping in the wild. Today IEEE 802.11 DCF is the most commonly used MAC protocol for Wi-Fi networks, however, due to the control messages and backoff time, channel efficiency in high data rate networks can be extremely low. To solve this, we propose CD-MAC, which allows control messages to be transmitted with data packets concurrently, and thus eliminates the overheads of backoff and explicit contention. To maintain the reception reliability, we redesign the control messages and use signal detection in PHY instead of bits decoding to detect them. In MAC layer, CD-MAC is built upon our Correlation Detection based PHY. We have implemented and evaluated CD-MAC using USRP N210. Evaluation results show that CD-MAC can achieve over 95.5% channel efficiency and provide throughput gains of up to 80%, 60%, and 29.1% compared with DCF, 802.11 ec, and back2F, respectively.

移动边缘计算中的无人机三维部署和内容缓存优化方法

随着无线网络中的移动数据流量爆炸式增长,支持高速缓存的无人机被应用于移动计算领域充当边缘服务器,为网络中的用户提供按需服务。为了在满足其他资源约束的条件下,给用户带来更好的体验,通过联合优化无人机部署、缓存放置和用户关联以实现最小化所有用户的内容访问时延,并为用户提供质量不同的内容缓存服务。针对多无人机和地面基站协同提供缓存服务的场景,提出了一种基于迭代优化的联合优化算法。该算法通过迭代求解由目标问题分解得到的三个子问题的方式来获得具有收敛性保证的次优解决方案。首先,采用基于连续凸近似的算法求解无人机部署子问题;其次,采用基于贪心的算法求解内容缓存子问题;然后,利用基于罚函数的连续凸近似算法求解用户关联子问题;最后,对上述过程重复迭代,得到目标问题的一个次优解。多次仿真实验验证了所提算法的有效性和可行性。仿真结果表明,与基准算法相比,所提联合优化算法在平均内容访问时延、缓存命中率两方面均具有更好的性能。

《Access数据库应用技术》实验内容设置的问题分析及改进

结合学校的实际情况,对《Access数据库应用技术》课程实验内容设置存在的问题进行了分析,同时给出了改进的建议。

通信网络中的数据库缓存策略与性能优化

在通信网络中,数据库的性能优化至关重要,以确保高并发访问和实时数据需求的满足。针对通信网络数据库面临的大规模、高并发访问的特殊需求和挑战,深入研究了数据库缓存策略与性能优化。通过基于内容的缓存策略和基于访问模式的缓存策略的优化方法,结合数据存储引擎的选择、数据分区与分片、缓存与持久性的平衡以及数据压缩与编码等关键策略,提出了一套完整的性能提升解决方案,以满足通信网络数据库在实时响应、高并发访问方面的需求。

“随机信号分析”课程教学内容与教学方法研究

“随机信号分析”课程是电子信息类专业的核心基础课之一,在课程体系中处于承前启后的位置。要解决学生在该课程学习过程中知识点孤立、动手计算较少、对知识点外延了解不够的问题,须进行基于知识点类比和知识点构图等的教学内容改革。针对该课程概念抽象、理论性强的特点,引入并结合实例介绍了随机通达教学和BOPPPS教学。授之以渔,为数字中国建设培养创新型、应用型、复合型人才,为构筑国家竞争新优势提供强有力的人才支撑。

无人机位置、缓存与用户接入联合优化方法

无人机作为空中基站,不仅可为地面用户提供移动通信服务,还可预先存储热点内容,有效提升了边缘通信能力。对无人机位置部署、无人机缓存配置与用户接入进行联合优化可大幅提升网络性能,然而传统优化方法计算量庞大且收敛速度慢。为解决上述问题,将该联合优化问题分解成无人机编队部署子问题和缓存接入子问题,设计了一种集中式和分布式相结合的快速资源分配优化方法。针对部署子问题,分阶段进行集中式一致博弈建模和分布式势能博弈建模,提出了一种基于较优响应的分阶段部署算法;针对缓存接入子问题,构建“用户-内容”虚拟体,将缓存与接入的联合问题建模为虚拟体与无人机缓存空间的匹配问题,提出了一种基于匹配的虚拟体接入算法。仿真结果表明,所提方法和传统分布式较优响应方法相比,具有更快的收敛速度和更高的全局性能。

Influence of Heavy Fuel Oil on the Thermo-Physical and Erodibility Properties of Earthen Materials

This study focuses on the use of heavy fuel oil in construction material in Burkina Faso. Its mixture with silty or clayey soil is used as a coating to reinforce the walls of raw earth constructions which are very sensitive to water. The interest of this study is to determine erodibility, water content, while highlighting the influence of the porosity accessible by water on thermal diffusion in construction material containing heavy fuel oil. The heavy fuel oil was mixed with a silty-clayey soil, in different proportions, and water to make bricks samples on which tests were carried out. At the end of the experimental tests, it appears that the water content increases gradually, but not significantly with the addition of heavy fuel oil, which causes a slight increase in the speed of heat propagation through the material with reduced porosity, particularly those containing higher quantities of heavy fuel oil. Conversely, we note a good performance of heavy fuel oil in terms of water resistance properties such as porosity accessible by water and erodibility. This allows us to conclude that the mixture of heavy fuel oil and silty-clayey soil used as a coating material could greatly reduce water infiltration into the walls of housing constructions with raw earthen materials.

Neighbor-Aware Multiple Access Protocol for 5G m MTC Applications

In order to support massive Machine Type Communication(mMTC) applications in future Fifth Generation(5G) systems,a key technical challenge is to design a highly effective multiple access protocol for massive connection requests and huge traffic load from all kinds of smart devices,e.g.bike,watch,phone,ring,glasses,shoes,etc..To solve this hard problem in distributed scenarios with massive competing devices,this paper proposes and evaluates a Neighbor-Aware Multiple Access(NAMA) protocol,which is scalable and adaptive to different connectivity size and traffic load.By exploiting acknowledgement signals broadcasted from the neighboring devices with successful packet transmissions,NAMA is able to turn itself from a contention-based random access protocol to become a contention-free deterministic access protocol with particular transmission schedules for all neighboring devices after a short transition period.The performance of NAMA is fully evaluated from random state to deterministic state through extensive computer simulations under different network sizes and Contention Window(CW)settings.Compared with traditional IEEE802.11 Distributed Coordination Function(DCF),for a crowded network with 50 devices,NAMA can greatly improve system throughput and energy efficiency by more than 110%and210%,respectively,while reducing average access delay by 53%in the deterministic state.

Priority access for QoS support in distributed wireless networks

Guaranteed quality of service(QoS) support has been an open issue of distributed wireless networks for years. The IEEE802.11 e provides a valuable method for this purpose. However, it could only provide service differentiation, rather than service guarantee, for multi-priority traffic. Many studies have tried to improve its QoS ability, but still leave some problems. This paper investigates these problems and proposes a scheme called the priority access based on busy tone(PABT) to improve the Qo S performance. To guarantee the priority channel access, this scheme uses an in-band busy tone to limit the transmission of lower-priority traffic when higher-priority traffic has packets to send. Based on that, it also optimizes the contention window tuning according to the flows number of each traffic type individually, in order to improve the throughput as well as the traffic capacity. Simulation results show that the proposed scheme significantly improves the real-time traffic capacity, throughput, delay, fairness and packet loss rate.

基于信管专业在就业指导下“Access数据库应用”课程教学实践与内容设计

"Access数据库应用"是一门实用技术课程,应用范围很广。论文结合信管专业的课程体系及培养目标,立足主流数据库应用技术发展方向,设计教学内容,突出该门课程的实践性和应用性,以现实增强学生理论联系实际及综合就业能力的目标。

Authentication and Access Control in RFID Based Logistics-customs Clearance Service Platform

The content security requirements of a radio frequency identification （RFID） based logistics-customs clearance service platform （LCCSP） are analysed in this paper. Then, both the unified identity authentication and the access control modules are designed according to those analyses. Finally, the unified identity authentication and the access control on the business level are implemented separately. In the unified identity authentication module, based on an improved Kerberos-based authentication approach, a new control transfer method is proposed to solve the sharing problem of tickets among different servers of different departments. In the access control module, the functions of access controls are divided into different granularities to make the access control management more flexible. Moreover, the access control module has significant reference value for user management in similar systems.

窗视野:建筑采光分析中的重要方面

建筑天然光环境分析应包含三个主要方面:1)天然光利用率、2)视觉舒适度、3)窗视野。良好窗视野可提升房间环境品质,对于房间使用者的身心均有益处,但目前窗视野尚缺少具体评价指导建筑设计。本论文系统介绍窗视野分析所涉及的内容及其指标和规定,并以LEED v4.1和EN 17037建筑评价体系为例,介绍窗视野评价体系并作案例分析;最后提取窗视野评价的重要特征及设计策略,为建筑师提供将窗视野评价融入建筑设计过程的具体建议。

大豆核心种质籽粒铁、锌含量精准鉴定及相关性分析

【目的】针对中国居民因铁、锌等微量元素摄取不足引发的营养不良问题,开展大豆核心种质籽粒铁、锌含量的精准鉴定。【方法】以国内外来源不同的163份大豆核心种质为材料,2019—2020年种植于华南农业大学试验教学基地,采用火焰原子吸收光谱仪测定籽粒铁和锌的含量,并进行相关性分析。【结果】大豆种质籽粒铁、锌含量在年份间存在显著差异(P<0.05);籽粒铁质量分数为71.02~159.92 mg·kg^(-1),平均为107.09 mg·kg^(-1);籽粒锌质量分数为36.32~53.11 mg·kg^(-1),平均为42.80 mg·kg^(-1)。相关性分析发现,不同年份间籽粒铁与锌含量存在正相关关系,说明这2个元素在大豆籽粒吸收中存在较强的相互促进关系。利用概率分级法将163份大豆种质籽粒铁、锌元素含量分为5级(即极低、低、中、高和极高),综合分析筛选出4份高铁含量、4份高锌含量、5份低铁含量、6份低锌含量和2份铁锌含量双高的大豆种质。【结论】鉴定出多份不同来源的高/低铁、锌含量的大豆种质,可用于富铁、锌大豆新品种的选育和种质创新,同时也为营养功能型新品种遗传基础解析提供基础材料,加快推动大豆核心种质在华南地区的开发与利用。

面向缓存网络内容分发的非正交传输策略研究

面向无线缓存网络的内容分发场景,设计了一种两阶段自适应非正交/正交多址接入传输方案。针对该方案,提出了一种高可靠性用户调度策略,并通过理论分析得出了中断概率的解析表达式及其高信噪比下渐近表达式。分析结果表明,该策略可获得满空间分集增益。仿真结果表明,与基于瞬时信道状态信息的调度策略、随机调度策略以及传统的正交多址接入传输策略相比,所提策略可通过获取空间分集增益,实现优于现有策略的内容分发可靠性。

试论高校图书馆员的继续教育

通过分析高校图书馆的发展趋势及馆员现状 。

有效提高吞吐量的UPMA++协议

本文提出了基于有效竞争接入、高效无冲突传输的多址接入协议—UPMA ++.该协议采用了有效的冲突分解策略和及时重获信道资源的方法,克服了UPMA(根据用户数目妥善安排传输的多址接入)协议中的开销;通过自适应调整竞争接入周期长度和限制无冲突服务周期长度的方法,很好地解决了激活节点快速接入信道和传输节点尽快传输分组之间的矛盾,从而提高了协议的吞吐量.本文还应用排队论的方法对UPMA ++协议的性能进行了理论分析,计算结果与仿真结果基本一致.

Web信息系统的内容易用性规范

根据 W3C规范文件 ,介绍了 Web环境下包括数字图书馆系统在内的信息系统内容易用性的意义、要求、级别、易用性准则和相应检验点。

基于IEEE802.11e EDCA的下行信道动态无竞争接入机制

为了改善无线局域网络服务质量,IEEE工作组形成了增补标准IEEE802.11e,但是其增强的接入机制仍然不能完全满足IPTV、视频点播等类似场景的应用。为此提出了针对这一类应用场景的一种新的简单易行的下行信道动态无竞争接入机制,该机制基于MAC层队列长度信息动态调整下行信道接入参数,能有效地保护下行流媒体数据的传输,通过仿真结果验证了该机制有效并且实用。