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Chapter 2 Wireless Communication Technology (Part Two in textbook)

Chapter 2 Wireless Communication Technology (Part Two in textbook). Outline. 2.1Antennas and Propagation( 天线与传输 ) 2.2 Signal Encoding Techniques( 信号编码技术 ) 2.3 Spread Spectrum( 扩频 ) 2.4 Coding and Error Control( 差错控制 ). 2.1Antennas and Propagation.

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Chapter 2 Wireless Communication Technology (Part Two in textbook)

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  1. Chapter 2 Wireless Communication Technology(Part Two in textbook)

  2. Outline • 2.1Antennas and Propagation(天线与传输) • 2.2 Signal Encoding Techniques(信号编码技术) • 2.3 Spread Spectrum(扩频) • 2.4 Coding and Error Control(差错控制)

  3. 2.1Antennas and Propagation Reading material: [1]Antenna Tutorial[2]Chapter 5 in textbook

  4. 2.1.1 Classifications of Transmission Media (2.4 in textbook) • Transmission Medium(传输媒介) • Physical path between transmitter and receiver • Guided Media(导波介质) • Waves are guided along a solid medium • E.g., copper twisted pair, copper coaxial cable, optical fiber • Unguided Media • Provides means of transmission but does not guide electromagnetic signals • Usually referred to as wireless transmission • E.g., atmosphere, outer space

  5. Unguided Media • Transmission and reception are achieved by means of an antenna • Configurations for wireless transmission • Directional • Omnidirectional

  6. 无线电波波长与频率

  7. General Frequency Ranges • Microwave frequency range • 1 GHz to 40 GHz • Directional beams possible • Suitable for point-to-point transmission • Used for satellite communications • Radio frequency range • 30 MHz to 1 GHz • Suitable for omnidirectional applications • Infrared frequency range • Roughly, 3x1011 to 2x1014 Hz • Useful in local point-to-point multipoint applications within confined areas

  8. 无线频谱的分配

  9. ISM

  10. 无线电(1)

  11. 无线电(2)

  12. 无线电(3)

  13. 无线电先驱—长波 • 波段--LF (Low Frequency) • 传播特性--白天靠地波，夜晚靠天波 • 无线电先驱许多无线电通讯的先驱，都是在长波进行试验的。工作频率越高，越不管用 。 • 应用广泛标帜台或导航电台，标时台 ，地标导航 ，长波广播 ，军事用途 • 阅读材料：长波及其应用

  14. Broadcast Radio • Description of broadcast radio antennas • Omnidirectional • Antennas not required to be dish-shaped • Antennas need not be rigidly mounted to a precise alignment • Applications • Broadcast radio • VHF and part of the UHF band; 30 MHZ to 1GHz • Covers FM radio and UHF and VHF television

  15. Microwave

  16. Microwave System

  17. Terrestrial Microwave • Description of common microwave antenna • Parabolic "dish", 3 m in diameter • Fixed rigidly and focuses a narrow beam • Achieves line-of-sight transmission to receiving antenna • Located at substantial heights above ground level • Applications • Long haul telecommunications service • Short point-to-point links between buildings

  18. Satellite Microwave • Description of communication satellite • Microwave relay station • Used to link two or more ground-based microwave transmitter/receivers • Receives transmissions on one frequency band (uplink), amplifies or repeats the signal, and transmits it on another frequency (downlink) • Applications • Television distribution • Long-distance telephone transmission • Private business networks

  19. 红外线

  20. 多路复用技术(Multiplexing)(1)

  21. 多路复用技术(2)

  22. 多路复用技术(3)

  23. 多路复用技术(4)

  24. 多路复用技术(5)

  25. 多路复用技术(6)

  26. 2.1.2 Introduction to Antennas • 天线可以看作一条电子导线和导线系统(An antenna is an electrical conductor or system of conductors) • Transmission - radiates electromagnetic energy into space • Reception - collects electromagnetic energy from space • 在双向通信中同一天线既可用于接收也可以用于发送(In two-way communication, the same antenna can be used for transmission and reception)

  27. 辐射模式(Radiation Patterns) • 天线辐射出的功率是全方位的，但各方位上的功率不一定相等。描述天线性能特性的常用方法是辐射模式。 • 辐射模式（Radiation pattern）： • 天线的辐射属性的图形化表示 • 一般被描绘为三维模式的一个二维剽面(cross section) • 常见的理想化的辐射模式： 各向同性天线（全向天线）、有向天线 • 接收模式(Reception pattern) • Receiving antenna’s equivalent to radiation pattern

  28. 辐射模式(Radiation Patterns) 各向同性天线（全向天线） 有向天线

  29. 天线类型(Types of Antennas) • 等方向性的天线 (idealized) • Radiates power equally in all directions • 偶极天线（Dipole antennas） • 半波偶极天线(or 赫兹天线) • 1/4波垂直天线 (or 马可尼天线)：汽车无线和便携无线中最常见的天线类型 • 抛物反射天线

  30. 偶极天线（Dipole antennas） • 在一个维上具有一致的或全向的辐射模式。另两个维上具有8字形的辐射模式。 天线的长度是可最有效传输信号波长的一半。

  31. 偶极天线（Dipole antennas） • 汽车无线和便携无线中 最常见的天线类型 • 汽车为什么不能使用长波？

  32. 抛物反射天线(parabolic reflective) • 抛物反射天线 :一种重要的天线类型，常用于地面微波和卫星。 • 抛物线是由到一固定直线和不在该直线上的某一固定点的距离相等的点的轨迹。固定点叫焦点(focus)，固定直线叫准线（directrix）

  33. 天线实例—华硕WL-ANT150全向天线 产品图

  34. 天线实例—华硕WL-ANT150全向天线 辐射范围

  35. 天线实例—华硕WL-ANT168定向天线 产品图案

  36. 天线实例—华硕WL-ANT168定向天线 产品应用示例

  37. 天线实例—抛物天线

  38. 天线增益（Antenna Gain） • 天线增益是天线定向性的度量 • 天线增益是定义在一特定方向上的功率输出。 • 在某一特定方向上增加功率是以降低其它方向功率为代价的。 • 天线增益并不是为了获得比输入功率更高的输出功率，而主要目的是为了定向。 • 有效面积Effective area • Related to physical size and shape of antenna

  39. 天线增益（Antenna Gain） • 天线增益和有效面积 • G = antenna gain • Ae= effective area • f = carrier frequency • c = speed of light (» 3 ´ 108 m/s) •  = carrier wavelength

  40. 天线增益（Antenna Gain） • 例：一个直径为2m的抛物反射天线，工作频率是12GHz，它的有效面积和天线增益是多少？ • 提示：有效面积为0.56A，A为抛物天线口面积。 • 答： • A=pi, Ae =0.56A, 波长=0.025m • G=7*pi/(0.025*0.025)=35186 • Gdb=l0lg35186=45.46db

  41. 2.1.3 Propagation Modes • Ground-wave propagation • Sky-wave propagation • Line-of-sight propagation

  42. Ground Wave Propagation

  43. Ground Wave Propagation • Follows contour of the earth • Can Propagate considerable distances • Frequencies up to 2 MHz • Example • AM radio

  44. Sky Wave Propagation

  45. Sky Wave Propagation • Signal reflected from ionized layer of atmosphere back down to earth • Signal can travel a number of hops, back and forth between ionosphere and earth’s surface • Reflection effect caused by refraction • Examples • Amateur radio • CB radio

  46. Line-of-Sight Propagation

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