Orthogonal frequency-division multiplexing

OFDMCOFDMOFDM system comparison tableorthogonal frequency division multiplexingdiscrete multitone modulationdiscrete multi-toneDiscrete multi-tone modulationDMTDiscrete multitoneOrthogonal frequency division modulation
In telecommunications, orthogonal frequency-division multiplexing (OFDM) is a method of encoding digital data on multiple carrier frequencies.wikipedia
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Orthogonal frequency-division multiple access

OFDMAOrthogonal Frequency Division Multiple AccessOFDM
Sprint purchased the carrier in 2006 and decided to deploy the mobile version of WiMAX, which is based on Scalable Orthogonal Frequency Division Multiple Access (SOFDMA) technology.
Orthogonal frequency-division multiple access (OFDMA) is a multi-user version of the popular orthogonal frequency-division multiplexing (OFDM) digital modulation scheme.

IEEE 802.11a-1999

a802.11aIEEE 802.11a
IEEE 802.11a-1999 or 802.11a was an amendment to the IEEE 802.11 wireless local network specifications that defined requirements for an orthogonal frequency division multiplexing (OFDM) communication system.

G.hn

G.9960G.9961G.hn/G.9960
The ITU-T G.hn standard, which provides high-speed local area networking over existing home wiring (power lines, phone lines and coaxial cables) is based on a PHY layer that specifies OFDM with adaptive modulation and a Low-Density Parity-Check (LDPC) FEC code.
G.hn specifies a single physical layer based on fast Fourier transform (FFT) orthogonal frequency-division multiplexing (OFDM) modulation and low-density parity-check code (LDPC) forward error correction (FEC) code.

Symbol rate

symbolbaud rateSR
Each subcarrier (signal) is modulated with a conventional modulation scheme (such as quadrature amplitude modulation or phase-shift keying) at a low symbol rate.
The maximum baud rate for a passband for common modulation methods such as QAM, PSK and OFDM is approximately equal to the passband bandwidth.

4G

4G LTE3G evolution4-G
OFDM has developed into a popular scheme for wideband digital communication, used in applications such as digital television and audio broadcasting, DSL internet access, wireless networks, power line networks, and 4G mobile communications.
The physical radio interface was at an early stage named High Speed OFDM Packet Access (HSOPA), now named Evolved UMTS Terrestrial Radio Access (E-UTRA).

DVB-T

Digitalterrestrialdigital broadcasting
The time to compute the inverse-FFT or FFT transform has to take less than the time for each symbol, which for example for DVB-T (FFT 8k) means the computation has to be done in 896 µs or less. Much of Europe and Asia has adopted OFDM for terrestrial broadcasting of digital television (DVB-T, DVB-H and T-DMB) and radio (EUREKA 147 DAB, Digital Radio Mondiale, HD Radio and T-DMB).
This system transmits compressed digital audio, digital video and other data in an MPEG transport stream, using coded orthogonal frequency-division multiplexing (COFDM or OFDM) modulation.

HD Radio

HDHD2HD-2
Much of Europe and Asia has adopted OFDM for terrestrial broadcasting of digital television (DVB-T, DVB-H and T-DMB) and radio (EUREKA 147 DAB, Digital Radio Mondiale, HD Radio and T-DMB).
Digital information is transmitted using OFDM with an audio compression algorithm called HDC (High-Definition Coding).

Bell Labs

Bell LaboratoriesBell Telephone LaboratoriesAT&T Bell Laboratories
OFDM was introduced by Chang of Bell Labs in 1966.
In 1966, Orthogonal frequency-division multiplexing (OFDM), a key technology in wireless services, was developed and patented by R. W. Chang.

WiMedia Alliance

WiMedia
This UWB specification is advocated by the WiMedia Alliance (formerly by both the Multiband OFDM Alliance [MBOA] and the WiMedia Alliance, but the two have now merged), and is one of the competing UWB radio interfaces.
The WiMedia ultra-wideband (UWB) common radio platform incorporated MAC layer and PHY layer specifications based on multi-band orthogonal frequency-division multiplexing (MB-OFDM).

Wireless network

wireless networkingwireless networkswireless
OFDM has developed into a popular scheme for wideband digital communication, used in applications such as digital television and audio broadcasting, DSL internet access, wireless networks, power line networks, and 4G mobile communications.
The use of spread-spectrum or OFDM technologies may allow users to move around within a local coverage area, and still remain connected to the network.

Fading

shadowingfading channelfrequency-selective fading
The main advantage of OFDM over single-carrier schemes is its ability to cope with severe channel conditions (for example, attenuation of high frequencies in a long copper wire, narrowband interference and frequency-selective fading due to multipath) without complex equalization filters.
Certain modulation schemes such as orthogonal frequency-division multiplexing (OFDM) and code division multiple access (CDMA) are well-suited to employing frequency diversity to provide robustness to fading.

Guard interval

guard periodtime of cyclic prefix protection
OFDM was improved by Weinstein and Ebert in 1971 with the introduction of a guard interval, providing better orthogonality in transmission channels affected by multipath propagation.
These transmissions may belong to different users (as in TDMA) or to the same user (as in OFDM).

Mobile television

mobile TVMobile DTVmobile digital TV
The defunct MediaFLO used COFDM broadcast on UHF TV channel 55.

IEEE 802.11ah

Wi-Fi HaLow802.11ahah
2 MHz channel uses an FFT of 64, of which: 56 OFDM subcarriers, 52 are for data and 4 are pilot tones with a carrier separation of 31.25 kHz (2 MHz/64) (32 µs).

Interference (communication)

interferenceInterferencesinterfere
The main advantage of OFDM over single-carrier schemes is its ability to cope with severe channel conditions (for example, attenuation of high frequencies in a long copper wire, narrowband interference and frequency-selective fading due to multipath) without complex equalization filters.

Digital multimedia broadcasting

DMBT-DMBDigital Multimedia Broadcast
Much of Europe and Asia has adopted OFDM for terrestrial broadcasting of digital television (DVB-T, DVB-H and T-DMB) and radio (EUREKA 147 DAB, Digital Radio Mondiale, HD Radio and T-DMB).
In order to diminish the channel effects such as fading and shadowing, the DMB modem uses OFDM-DQPSK modulation.

Power-line communication

power line communicationpower linespowerline networking
OFDM has developed into a popular scheme for wideband digital communication, used in applications such as digital television and audio broadcasting, DSL internet access, wireless networks, power line networks, and 4G mobile communications.
As delivered, the physical layer is OFDM, sampled at 250 kHz, with 512 differential phase shift keying channels from 42–89 kHz.

Digital radio

digitaldigital transmissionradio
Transmissions use orthogonal frequency-division multiplexing, a technique which is also used for European terrestrial digital TV broadcast (DVB-T).

Ultra-wideband

Ultra WidebandUWBultrawideband
In some standards such as Ultrawideband, in the interest of transmitted power, cyclic prefix is skipped and nothing is sent during the guard interval.
Thus, pulse-based systems—where each transmitted pulse occupies the UWB bandwidth (or an aggregate of at least 500 MHz of narrow-band carrier; for example, orthogonal frequency-division multiplexing (OFDM))—can access the UWB spectrum under the rules.

Digital subscriber line

DSLxDSLDigital Subscriber Line (DSL)
OFDM has developed into a popular scheme for wideband digital communication, used in applications such as digital television and audio broadcasting, DSL internet access, wireless networks, power line networks, and 4G mobile communications.

MediaFLO

FLOTVFLO TVTV broadcasting for mobile devices
Some systems that have implemented these codes have concatenated them with either Reed-Solomon (for example on the MediaFLO system) or BCH codes (on the DVB-S2 system) to improve upon an error floor inherent to these codes at high signal-to-noise ratios.
The transmission was an encrypted OFDM set of QAM signals sent on a 5.55 MHz channel from 716-722 MHz (former UHF TV channel 55).

Frequency-division multiplexing

frequency division multiplexingFDMfrequency division multiplex
OFDM is a frequency-division multiplexing (FDM) scheme used as a digital multi-carrier modulation method.
Since the late 20th century digital subscriber lines (DSL) have used a Discrete multitone (DMT) system to divide their spectrum into frequency channels.

Crest factor

peak-to-average power ratiopeak-to-average ratioPAPR
Many crest factor reduction techniques have been developed.

Multi-carrier code-division multiple access

multi-carrier code division multiple accessMC-CDMAmulti-carrier
In multi-carrier code division multiple access (MC-CDMA), also known as OFDM-CDMA, OFDM is combined with CDMA spread spectrum communication for coding separation of the users.
Multi-carrier code-division multiple access (MC-CDMA) is a multiple access scheme used in OFDM-based telecommunication systems, allowing the system to support multiple users at the same time over same frequency band.