The remote control transmits pulse of infrared light that carry coded instruction to a receiver. Exists four methods of infrared transmission



· Broadband optical telepoint



· Line of sight



· Reflective infrared



· Scatter infrared





Infrared transmission is limited to within 100 feet but bandwidth is 10 Mbps. Infrared is insensitive to radio frequency interference, but it is sensitive to rain or fog when bandwidth falls down or is not possible connection. Infrared transmission is commonly used for LAN transmission



Laser transmission: is similar as infrared transmission but laser can transmit signal for several thousand of yards when line of sight is possible.



Narrow band radio transmission: transmissions occur as a single radio frequency. The range of narrow-band radio is greater than that of infrared.It is not neccessary to have a line of sight connection because signal can bounce of walls, buildings or athmosphere. But heavy steel walls can block signal.









Spread-Spectrum Radio Transmission: uses multiple frequencies to transmit messages. Uses two techniques to transmit signal

· frequency hoping 250 kbps – 2Mbps

· direct sequence modulation. 2 – 6 Mbps



Microwave transmission: can take two forms: terrestrial link

Satelitte link





Figure 5.2



Terrestrial transmission : employs earth-based transmitters and receivers. The frequencies used are in the low gigahertz range, 4–6GHz and 21–23GHz, which limits all communications to line-of-sight.

· typically uses a parabolic antenas to transfer signal

· transmitter and receiver must be highly focused!

· terrestrial microwave uses licensed frequencies.

· highly susceptible to atmospheric interference

· transfer rate from 1 Mbps to 10 Mbps







Satellite transmission: relay transmissions through communication satellites that operate in geosynchronous orbits 22,300 miles above the earth.