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Concept
Orthogonal frequency-division multiplexing
Summary
In telecommunications, orthogonal frequency-division multiplexing (OFDM) is a type of digital transmission used in digital modulation for encoding digital (binary) data on multiple carrier frequencies. 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/5G mobile communications.
OFDM is a frequency-division multiplexing (FDM) scheme that was introduced by Robert W. Chang of Bell Labs in 1966. In OFDM, the incoming bitstream representing the data to be sent is divided into multiple streams. Multiple closely spaced orthogonal subcarrier signals with overlapping spectra are transmitted, with each carrier modulated with bits from the incoming stream so multiple bits are being transmitted in parallel. Demodulation is based on fast Fourier transform algorithms. 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. Each subcarrier (signal) is modulated with a conventional modulation scheme (such as quadrature amplitude modulation or phase-shift keying) at a low symbol rate. This maintains total data rates similar to conventional single-carrier modulation schemes in the same bandwidth.
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 the need for complex equalization filters. Channel equalization is simplified because OFDM may be viewed as using many slowly modulated narrowband signals rather than one rapidly modulated wideband signal. The low symbol rate makes the use of a guard interval between symbols affordable, making it possible to eliminate intersymbol interference (ISI) and use echoes and time-spreading (in analog television visible as ghosting and blurring, respectively) to achieve a diversity gain, i.
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An All-Digital 1.25 Mbps 5-Subcarrier OFDM Backscatter Uplink with Delta-Sigma Modulation for Improved Spurious-Free Dynamic Range
This paper describes an all-digital backscatter modulation approach leveraging delta-sigma modulation (DSM) to improve the in-channel spectral characteristics of orthogonal frequency division multiple
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Orthogonal frequency-division multiplexing
In telecommunications, orthogonal frequency-division multiplexing (OFDM) is a type of digital transmission used in digital modulation for encoding digital (binary) data on multiple carrier frequencies. 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/5G mobile communications. OFDM is a frequency-division multiplexing (FDM) scheme that was introduced by Robert W.
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Related lectures (146)
OFDM: Orthogonal Frequency Division Multiplexing
Explores OFDM, a crucial technology in high throughput mobile networks, simplifying channel estimation and utilizing multiple sub-carrier frequencies.
OFDM: Orthogonal Frequency Division Multiplexing
Covers the importance and implementation of OFDM in modern communication systems, focusing on synchronization, interference reduction, and packet detection.
OFDM Basics: Channel Estimation and Frequency Offset Correction
Explores OFDM basics, channel estimation, and frequency offset correction, along with MAC protocols and CDMA applications.