OFDM (Orthogonal Frequency Division Multiplexing) **4G technology**

In the next few WotD’s we’ll take a look at the principal technologies that comprise 4G…

OFDM (Orthogonal Frequency Division Multiplexing): A modulation technique for wireless communications, OFDM was patented by Bell Labs in 1970, and initially was used in a naval communications system dubbed ‘Catherine’. Much like DMT (Discrete MultiTone), OFDM splits the datastream into multiple RF (Radio Frequency) channels, each of which is sent over a subcarrier frequency. DMT and other more conventional techniques encode data symbols for a given data stream onto one radio frequency. In an OFDM system, however, each tone (i.e., frequency) is orthogonal (i.e., independent or unrelated) to the other tones; multiple data symbols are encoded concurrently onto multiple tones in a parallel fashion. The signal-to-noise ratio of each of those very precisely defined frequencies is carefully monitored to ensure maximum performance. OFDM eliminates the requirement for guard bands to separate the frequencies and, thereby, avoid interference from adjacent RF channels. Guard bands are required only around the edges of a set of tones, i.e., RF channels. This yields greater spectral efficiency, as virtually all of the allocated RF spectrum can be used for data transmission.

OFDM is used by the HomePlug Powerline alliance to avoid line noise in a residential power-line network. How it works:

1. Broadband content from cable modem, DSL or satellite is fed to home gateway
2. By plugging gateway into any electrical outlet, content is bridged to any HomePlug-enabled device
3. OFDM takes multiple signals of different frequencies and combines them to form one signal to avoid line “noise”
4. HomePlug network monitors power lines for “noise”.

For more on HomePlug visit their website: http://www.homeplug.org/home

If noise occurs on a particular frequency, OFDM engine shifts transmission to another frequency. OFDM also is used in the IEEE 802.16 WLL specification, also known as WiMax.