OFDM (orthogonal frequency division multiplexing)

A technique for increasing the amount of information that can be carried over a wireless network.

In frequency-division multiplexing, multiple signals, or carriers, are sent simultaneously over different frequencies between two points. However, FDM has an inherent problem: Wireless signals can travel multiple paths from transmitter to receiver (by bouncing off buildings, mountains and even passing airplanes); receivers can have trouble sorting all the resulting data out.

Orthogonal FDM deals with this multipath problem by splitting carriers into smaller subcarriers, and then broadcasting those simultaneously. This reduces multipath distortion and reduces RF interference (a mathematical formula is used to ensure the subcarriers' specific frequencies are "orthogonal," or non-interfering, to each other), allowing for greater throughput.

OFDM is at the heart of 802.11a wireless-LAN technology, which can offer throughput of up to 54M bit/sec (the 802.11a specification calls for up to 52 subcarriers). It is also used in ADSL over copper telephone wires.

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OFDM

Orthogonal frequency-division multiplexing, or OFDM, is a process of digital modulation that is used in computer technology today. Essentially, OFDM is configured to split a communication signal in several different channels. Each of these channels is formatted into a narrow bandwidth modulation, with each channel operating at a different frequency. The process of OFDM makes it possible for multiple channels to operate within close frequency levels without impacting the integrity of any of the data transmitted in any one channel.

The history of OFDM goes back to the 1960’s. At the time, there was a need to make more efficient use of bandwidth transmissions without creating situations where signals would be subject to a phenomenon referred to as crosstalk. Essentially, crosstalk occurs when two audio sources are broadcasting at the same time. The end result is that the message of each broadcast is partially obscured for anyone attempting to listen to either of the messages. Crosstalk can be compared to two people choosing to speak while another individual is already speaking.

Generally, the process of OFDM is focused on preventing the occurrence of crosstalk, or any other type of outside interference with the quality of the transmission. However, the method does have some limited capability to attempt to enhance the quality of the transmission proper. For example, it is sometimes possible to make use of OFDM in order to minimize background noise that is resident in the transmission, or to boost the volume level if the transmission has weak sound clarity.

The use of OFDM is common worldwide. Many radio networks around the globe make use of OFDM to service their broadcast ranges. Some amateur radio systems also employ elements of OFDM for sending out signals as well. There are some applications of OFDM that lend well to the audio component of digital television, and it is also possible to make use of OFDM to boost the speed of an Internet connection over a standard telephone line. With the emergence of more wireless methods of communication, OFDM is also finding a place in local wireless networks.