Rapid growth of wireless communication services in recent decades has created a huge demand of radio spectrum. Spectrum scarcity and utilization inefficiency limit the development of wireless networks. Cognitive radio is a promising tech- nology that allows secondary users to reuse the underutilized licensed spectrum of primary users. The major challenge for spectrum sharing is to achieve high spectrum efficiency while making non-intrusive access to the licensed bands. This requires in- formation of availability and quality of channel resources at secondary transmitters, however, is difficult to be obtained perfectly in practice.
标签： Opportunistic Spectrum Sharing
上传时间： 2020-05-31
上传用户：shancjb
Since the advent of optical communications, a great technological effort has been devoted to the exploitation of the huge bandwidth of optical fibers. Start- ing from a few Mb/s single channel systems, a fast and constant technological development has led to the actual 10 Gb/s per channel dense wavelength di- vision multiplexing (DWDM) systems, with dozens of channels on a single fiber. Transmitters and receivers are now ready for 40 Gb/s, whereas hundreds of channels can be simultaneously amplified by optical amplifiers.
标签： Communication Techniques Optical Theory and
上传时间： 2020-05-31
上传用户：shancjb
A wireless communication network can be viewed as a collection of nodes, located in some domain, which can in turn be transmitters or receivers (depending on the network considered, nodes may be mobile users, base stations in a cellular network, access points of a WiFi mesh etc.). At a given time, several nodes transmit simultaneously, each toward its own receiver. Each transmitter–receiver pair requires its own wireless link. The signal received from the link transmitter may be jammed by the signals received from the other transmitters. Even in the simplest model where the signal power radiated from a point decays in an isotropic way with Euclidean distance, the geometry of the locations of the nodes plays a key role since it determines the signal to interference and noise ratio (SINR) at each receiver and hence the possibility of establishing simultaneously this collection of links at a given bit rate. The interference seen by a receiver is the sum of the signal powers received from all transmitters, except its own transmitter.
标签： Stochastic Geometry Networks Wireless Volume and II
上传时间： 2020-06-01
上传用户：shancjb
T his book covers basic communications theory and practical imple- mentation of transmitters and receivers. In so doing, I focus on dig- ital modulation, demodulation methods, probabilities, detection of digital signals, and spread spectrum system design and analysis. This book was written for those who want a good understanding of the basic prin- ciples of digital wireless communication systems, including spread spec- trum techniques. This book also provides a good intuitive and practical approach to digital communications. Therefore it is a valuable resource for anyoneinvolvedinwirelesscommunicationsandtransceiverdesignfordig- ital communications. The reader will gain a broad understanding of basic communication principles for transceiver design, digital communications, and spread spectrum, along with examples of many types of commercial and military data link systems.
标签： Transceiver System Design
上传时间： 2020-06-01
上传用户：shancjb
Wavelength division multiplexing (WDM) refers to a multiplexing and transmission scheme in optical telecommunications fibers where different wavelengths, typically emitted by several lasers, are modulated independently (i.e., they carry independent information from the transmitters to the receivers). These wavelengths are then multiplexed in the transmitter by means of passive WDM filters, and likewise they are separated or demultiplexed in the receiver by means of the same filters or coherent detection that usually involves a tunable local oscillator (laser).
标签： Multiplexing Wavelength Division
上传时间： 2020-06-01
上传用户：shancjb
随着汽车行业的飞速发展，汽车市场的不断升温，与之相关的电子技术也得到时了迅速发展及广泛应用，汽车技术的成熟使得汽车销售及使用不断壮大，现代汽车的行驶速度也随着路况的提高，汽车性能的提高而不断提升。而由于突发性道路交通事故的频繁发生，人们对汽车安全的关注度也日益提高。在汽车的高速行驶过程中，轮胎故障是驾驶人员最为担心和最难预防的，也是突发性交通事故发生的重要原因。据统计，在高速公路上发生的交通事故有70%-80%是由于爆胎引起的，怎样防止爆胎已成为汽车安全的第一大重要课题。权威的研究结果表明，保持标准的轮胎气压和及时发现轮胎故障是防止爆胎的关键，这就使对轮胎充气压力实行监测显得非常重要。本文设计了一种汽车轮胎压力监测系统（Tire Pressure Monitoring System）TPMS及气压调节系统的结合使用，该系统能够对轮胎的参数进行实时监测，当发轮胎压力参数异常时，及时采取报警措施并进行实时的汽压调节，从而避免交通事故的发生。论文在对当前存在的各种TPMS系统结构形式进行分析和比较后，选用一种现行直接式TPMS结合气压调节系统，实现轮胎压力实时的监测和调节的一种新型系统。提出一种基于直接式TPMS系统的，引入调节功能的新型设计。设计本身解决原有直接式TPMS的电池供电影响系统寿命的瓶颈，保证了监测系统的的稳定性。气压调节系统将解决汽车轮胎压力偏差的问题，在监测到气压偏高或者偏低时，对驾驶人员作出警报提醒并实时启动气压调节系统进行胎压调节，在数他钟内调节气压到标准值，保证行驶的畅顺。本文对系统的电源部分，气压调节部分进行了分析设计，解决系统供电，信号采集，信号处理及执行调节，RFLF通信通等关键技术问题。对硬件进行测试。结果表明，该系统切实可行，成本，通信距离及可靠性方面均达到没计指标。
标签： 汽车胎压监测
上传时间： 2022-06-19
上传用户：kingwide
根据美国国家交通安全管理局估计每年大约有23000交通事故与500起致事故都是由于轮胎的压力不足引起的。保持适合的轮胎压力能降低油耗，如果压力高于标准的10%或低于标准的30%。如果压力过高，摩擦力减小而油耗增加。此外，轮胎状态与温度有直接联系，温度越高轮胎力量减弱，而且变化时很大的。通常情况下，温度不能超过80，如果达到95是很危险的，而且每升高1轮胎损耗增加2%，速度增加两倍轮胎寿命为原来的一半。标准胎压状态的概率有利于减少事故威胁生命，车轮爆胎时，增进燃料效益、延长使用寿命，提高轮胎的驾驶执照及车辆的安全性能。智能轮胎安全型设计了系统可以帮助司机掌握汽车轮胎的精确，也可以为泄漏，超压型或低压和异常温度条件，确保车辆驾驶稳定性，避免严重事故由于突然当车辆车轮爆胎时，高速运转。
上传时间： 2022-06-19
上传用户：
本文主要提出了基于新型无线技术-ZigBee的胎压监测系统（TPMS）的设计方案。鉴于ZigBee低成本、低功耗、小范围、低复杂度的个人局域网特点，所以设计将这项技术用于车用胎压监测系统。保证标准的胎压是车辆在日常维护以及行驶时防止爆胎的关键所在，于是胎压监测系统（TPMS）应运而生。本次设计正是使用了完美支持最新版本ZigBee技术的第二代片上系统CC2530芯片实现胎压监测示警功能。本文主要介绍轮胎压力监测系统的应用设计和实现，利用压力传感器无线节点组成ZigBee无线网络，实现轮胎内部温度和压力数据的自动采集和传输。由于使用了ZigBee技术，大大降低了系统的成本和功耗，保证了系统的长使用寿命。经试验，胎压监测系统能够对轮胎内的气压和温度进行实时地自动监测，通过ZigBee无线方式将胎压的信息传送给车内显示模块，并显示在液晶显示屏上，同时在轮胎出现危险征兆时及时给驾驶员报警，确保行车安全。【关键词】ZigBee；胎压监测系统；压力传感器；显示屏；报警
上传时间： 2022-06-20
上传用户：wangshoupeng199
1引言汽车在高速行驶过程中，轮胎气压不足易导致爆胎。爆胎是引起交通事故的主要原因。轮胎压力检测系统（TPMS）的作用是在汽车行驶过程中对轮胎气压进行实时检测，并对轮胎漏气和低气压等情况进行报警，确保行车安全。目前，TPMS主要分为直接式和间接式。直接式系统通过安装在轮胎内部的压力传感器直接检测胎内压力和温度状态：间接式是通过安装在转轴上的转速传感器推算出胎内压力。直接式TPMS具有实时、准确等特点，得到了市场的广泛关注。本文介绍基于英飞凌（Infineon）压力传感器SP30的直接式TPMS系统，并将本系统接入汽车的高速局域通信网络一CAN总线网络及辅助通信网络-LIN的总线设计。2胎压检测系统总体方案直接式TPMS系统结构如图1，主要包括轮胎发射模块、RF接收模块、显示报警控制模块、低频唤醒模块、CAN总线及LIN总线。
上传时间： 2022-06-20
上传用户：1208020161
功能Function： 1.振动触发、运动检测，倾斜感应，等触发唤醒功能。 2.传感器是完全被动的，无需任何信号调节，至少具备50nA的电流即可运作，其耗电量取决于应用电路的单一电阻限制电流。 3.产品通过内部滚珠的接触来侦测环境动作，并使接触点间的接触电阻所产生的由高到低或由低到高的变化（建议在应该设计软件时要考虑的是高到低电平、低到高电平的转换变化而不是打开的开关信号，通过电路或软件的延时设置可对自身产品灵敏度的要求来做调试、即可提升产品的准确性和实用性）。 应用ApplicaTIon： 产品广泛适应于：振动感应系统、智能防盗装置，汽车电子/GPRS跟踪器，胎压监测（TPMS），RFID电子标签，智能穿戴，智能蓝牙，智能家居电子，自动步枪/手枪电子装置，微型发射器感应装置/接收器，无线智能数码电子，自动化装置及各类智能系统的振动感应或运动检测而设定应用下的触发唤醒功能。
上传时间： 2022-06-20
上传用户：zhanglei193
