按一下以編輯母片標題樣式,按一下以編輯母片,第二層,第三層,第四層,第五層,*,Wireless Transmission,The Electromagnetic Spectrum,Radio Transmission,Microwave Transmission,Infrared and Millimeter Waves,Lightwave,Transmission,The Electromagnetic Spectrum,The electromagnetic spectrum and its uses for communication.,Radio Transmission,(,a),In the VLF,LF,and MF bands,radio waves follow the curvature of the earth.,(b),In the HF band,they bounce off the ionosphere.,Politics of the Electromagnetic Spectrum,The ISM bands in the United States.,Lightwave Transmission,Convection currents can interfere with laser communication systems.,A bidirectional system with two lasers is pictured here.,Lightwave Transmission,Communication Satellites,Geostationary,Satellites,Medium-Earth Orbit Satellites,Low-Earth Orbit Satellites,Satellites versus Fiber,Communication Satellites,Communication satellites and some of their properties,including altitude above the earth,round-trip delay time and number of satellites needed for global coverage.,Communication Satellites(2),The principal satellite bands.,Communication Satellites(3),VSATs using a hub.,Low-Earth Orbit SatellitesIridium,(,a),The Iridium satellites from six necklaces around the earth.,(b),1628 moving cells cover the earth.,Globalstar,(,a),Relaying in space.,(b),Relaying on the ground.,