What Type of Wireless Transmission Is Limited to Line-Of-Sight Communications?

by Elizabeth Mott, studioD

When you stand too far away from someone who tries to talk to you, you can't hear what she says because the sound waves she emits don't reach your ears. Wireless line-of-sight communications technologies face similar limitations. When transmission and reception are set too far apart for signals to reach from one to the other, the communication path breaks off and the information -- a control, data or message signal -- misses its target.


Most infrared sources transmit using an LED or laser. The infrared technology that underlies most remote controls only works across a straight, short, unobstructed path between the remote and the device. Likewise, if you try to control an infrared-equipped printer from your computer while someone walks between you and the receiving device, nothing happens because the intervening individual blocks the signal. Although infrared transmission broadens out in a cone shape from the transmitter, you have little margin for error in aiming at a receiving device's small reception window. Bright light also interferes with infrared reception.


Microwave-based communications can connect buildings in a commercial park or on a school campus using paired transceivers and roof-mounted antennas. As with other forms of line-of-sight signal transmission and reception, the two sets of equipment must face each other with no intervening obstructions. Microwave communications also underlie satellite-based signal systems that can provide TV entertainment and Internet access in areas that lack wired connections. The line-of-sight aspect of these systems requires precisely aimed dish-shaped antennas that point skyward without intervening trees or buildings. Rain and snow can create temporary line-of-sight interference that stops signal reception.

Radio Frequency

Walkie-talkies and handheld two-way radios rely on signals that travel in a straight line. The exception to their line-of-sight communication restriction lies in the fact that intervening surfaces can reflect their output, overcoming obstacles as a result. They work over limited distances, however, and lack the relative privacy of communications carried over telephone connections. Higher signal power increases signal distance, but it also drains batteries more quickly. Lower-frequency VHF signals tend to travel longer distances than higher-frequency UHF signals because VHF signals reflect off obstacles that block UHF emissions.

Other Considerations

Overcoming line-of-sight limitations can mean choosing an alternate way of connecting two points that lack a clear signal path. For example, if you need a wireless connection between your computer and a peripheral device such as a printer but the two operate in adjacent rooms with no line of sight between them, you can use a Bluetooth connection to overcome the signal-reach problem. Walkie-talkies can offer convenience as a short-range communication technology, but once you exceed their signal range, you need a cellular signal and a telephone instead.

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