WirelessTransmission：无线传输

Wireless Transmission The Electromagnetic Spectrum Radio Transmission Microwave Transmission Infrared and Millimeter Waves Lightwave Transmission The Electromagnetic SpectrumThe 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 SpectrumThe ISM bands in the United States. Lightwave TransmissionConvection 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 SatellitesCommunication 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.