The unguided transmission of information using electromagnetic waves at radio frequency (RF) is often referred to as wireless communications, the first demonstration of which took place at the end of the 19th cen- tury and is attributed to Hertz. The technology was, shortly thereafter, commercialised by, amongst others, Marconi in one of the first wire- less communication systems, i.e., wireless telegraphy. In the first Half of the 20th century the technology was developed further to enable more than the mere transmission of Morse code. This first resulted in uni- directional radio broadcasting and several years later also in television broadcasting.
標(biāo)簽： Imperfections RF
上傳時間： 2020-06-01
上傳用戶：shancjb
When 3GPP started standardizing the IMS a few years ago, most analysts expected the number of IMS deploymentsto grow dramatically as soon the initial IMS specifications were ready (3GPP Release 5 was functionallyfrozenin the first Half of 2002and completedshortly after that). While those predictions have proven to be too aggressive owing to a number of upheavals hitting the ICT (Information and Communications Technologies) sector, we are now seeing more and more commercial IMS-based service offerings in the market. At the time of writing (May 2008), there are over 30 commercial IMS networks running live traffic, addingup to over10million IMS users aroundthe world; the IMS is beingdeployedglobally. In addition, there are plenty of ongoing market activities; it is estimated that over 130 IMS contracts have been awarded to all IMS manufacturers. The number of IMS users will grow substantially as these awarded contracts are launched commercially. At the same time, the number of IMS users in presently deployed networks is steadily increasing as new services are introduced and operators running these networks migrate their non-IMS users to their IMS networks.
標(biāo)簽： Multimedia Subsystem The IMS 3G IP
上傳時間： 2020-06-01
上傳用戶：shancjb
The continuing explosive growth in mobile communication is demanding more spectrally efficient radio access technologies than the prevalent second generation (2G) systems such as GSM to handle just the voice traffic. We are already witnessing high levels of mobile penetration exceeding 70% in some countries. It is anticipated that by 2010 more than Half of all communications will be carried out by mobile cellular networks. On the other hand, the information revolution and changing life habits are bringing the requirement of commu- nicating on a multimedia level to the mobile environment. But the data handling capabilities and flexibility of the 2G cellular systems are limited.
標(biāo)簽： Planning Network UMTS
上傳時間： 2020-06-01
上傳用戶：shancjb
I can remember buying my first electronic calculator. I was teaching a graduate level statistics course and I had to have a calculator with a square root function. Back in the late 1960s, that was a pretty high-end requirement for a calculator. I managed to purchase one at the “educational discount price” of $149.95! Now, I look down at my desk at an ATmega2560 that is Half the size for less than a quarter of the cost and think of all the possibilities built into that piece of hardware. I am amazed by what has happened to everything from toasters to car engines. Who-da-thunk-it 40 years ago?
標(biāo)簽： Beginning Arduino for
上傳時間： 2020-06-09
上傳用戶：shancjb
? LLC series-resonant Half-bridge: operationand significant waveforms? Simplified model (FHA approach)? 300W design example
上傳時間： 2021-11-22
上傳用戶：
This Section covers the design of power transformers used in buck-derived topologies: forward converter, bridge, Half-bridge, and full-wave centertap. Flyback transformers (actually coupled inductors) are covered in a later Section. For more specialized applications, the principles discussed herein will generally apply.
上傳時間： 2021-12-16
上傳用戶：fliang
通過采用無橋PFC和半橋LLC諧振變換器作為數(shù)字開關(guān)電源的主變換拓?fù)?基于STM32系列微控制器的全數(shù)字控制PFC和DC-DC變換器,首先對數(shù)字化開關(guān)電源方案進(jìn)行對比,然后闡述了200W數(shù)字開關(guān)電源整體方案,并對數(shù)字開關(guān)電源的無橋PFC和半橋LLC變換器進(jìn)行系統(tǒng)研究。By using a bridgeless PFC and a Half-bridge LLC resonant converter as the main conversion topology of the digital switching power supply,the all-digital control PFC and DC-DC converter based on the STM32 series of microcontrollers,firstly the digital switching power supply scheme is compared,and then the overall scheme of 200 W digital switching power supply is expounded, and the bridgeless PFC and Half-bridge LLC converter of digital switching power supply are systematically studied.
標(biāo)簽： 數(shù)字開關(guān)電源
上傳時間： 2022-04-02
上傳用戶：qingfengchizhu
該步進(jìn)電機(jī)驅(qū)動器又稱為EasyDriver，EasyDriver能夠?yàn)閮杉壊竭M(jìn)電機(jī)提供大約每相750mA（兩極一共1.5A）的驅(qū)動。它默認(rèn)設(shè)置為8步細(xì)分模式（所以如果你的電機(jī)是每圈200步，你使用EasyDriver時默認(rèn)為每圈1600步），更多細(xì)分模式可以通過將MS1或MS2兩個接腳接地進(jìn)行設(shè)置。這是一種基于Allegro A3967驅(qū)動芯片的細(xì)分?jǐn)嗦菲鳌τ诖嗽O(shè)計的完整規(guī)格，請查閱A3967的參數(shù)表。它的最大每相電流從150mA到750mA?？梢圆捎玫淖畲篁?qū)動電壓大概是30V，其中包括板載5V的調(diào)壓器，所以只需要一個電源。質(zhì)優(yōu)價廉，這玩意兒只要十幾美元，比你自己制作電路板更便宜。步進(jìn)電機(jī)驅(qū)動器設(shè)計特色：· A3967 Microstepping Driver· MS1 and MS2 pins broken out to change microstepping resolution to full, Half, quarter and eighth steps (defaults to eighth)· Compatible with 4, 6, and 8 wire stepper motors of any voltage· Adjustable current control from 150mA/phase to 700mA/phase· Power supply range from 6V to 30V. The higher the voltage, the higher the torque at high speeds
標(biāo)簽： 步進(jìn)電機(jī) 驅(qū)動器 pcb 驅(qū)動
上傳時間： 2022-04-27
上傳用戶：
PrefaceDuring the past years, there has been a quickly rising interest in radio access technologies for providingmobile as well as nomadic and fixed services for voice, video, and data. The difference indesign, implementation, and use between telecom and datacom technologies is also becoming moreblurred. One example is cellular technologies from the telecom world being used for broadband dataand wireless LAN from the datacom world being used for voice-over IP.Today, the most widespread radio access technology for mobile communication is digital cellular,with the number of users passing 5 billion by 2010, which is more than Half of the world’s population.It has emerged from early deployments of an expensive voice service for a few car-borne users,to today’s widespread use of mobile-communication devices that provide a range of mobile servicesand often include camera, MP3 player, and PDA functions. With this widespread use and increasinginterest in mobile communication, a continuing evolution ahead is foreseen.This book describes LTE, developed in 3GPP (Third Generation Partnership Project) and providingtrue 4G broadband mobile access, starting from the first version in release 8 and through the continuingevolution to release 10, the latest version of LTE. Release 10, also known as LTE-Advanced,is of particular interest as it is the major technology approved by the ITU as fulfilling the IMTAdvancedrequirements. The description in this book is based on LTE release 10 and thus provides acomplete description of the LTE-Advanced radio access from the bottom up.Chapter 1 gives the background to LTE and its evolution, looking also at the different standardsbodies and organizations involved in the process of defining 4G. It also gives a discussion of the reasonsand driving forces behind the evolution.Chapters 2–6 provide a deeper insight into some of the technologies that are part of LTE and itsevolution. Because of its generic nature, these chapters can be used as a background not only for LTEas described in this book, but also for readers who want to understand the technology behind othersystems, such as WCDMA/HSPA, WiMAX, and CDMA2000.Chapters 7–17 constitute the main part of the book. As a start, an introductory technical overviewof LTE is given, where the most important technology components are introduced based onthe generic technologies described in previous chapters. The following chapters provide a detaileddescription of the protocol structure, the downlink and uplink transmission schemes, and the associatedmechanisms for scheduling, retransmission and interference handling. Broadcast operation andrelaying are also described. This is followed by a discussion of the spectrum flexibility and the associated
上傳時間： 2022-07-08
上傳用戶：
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