Orthogonal Frequency-Division Multiplexing (OFDM)
OFDM is a frequency-division multiplexing (FDM) method developed by Bell Labs’ Robert W. Chang in 1966. To convey data in parallel, OFDM uses several closely spaced orthogonal subcarrier signals with overlapping spectra. Fast Fourier transform algorithms are used in demodulation.
What is ODFM? :
OFDM stands for Orthogonal Frequency Division Multiplexing, which separates a high data rate modulating stream into numerous slowly modulated narrowband close-spaced subcarriers, making it less susceptible to frequency selective fading.
How it works:
The basic premise of OFDM is to divide a high-rate datastream into a number of lower-rate streams that are sent over a number of subcarriers at the same time. As evidenced by its presence or absence in the output spectrum, each subcarrier sends one bit of information (total N bits). To create an orthogonal signal set, the frequency of each subcarrier is chosen. For signal recovery, these frequencies are also known at the receiver.
OFDM is a widely used wideband digital communication technique, with applications including digital television and audio broadcasting, DSL internet access, wireless networks, power line networks, and 4G/5G mobile communications.
In comparison to other double sideband modulation methods, spread spectrum, and so on, this scheme has a high spectral efficiency. Without the need for complicated time-domain equalisation, it can rapidly adapt to harsh channel circumstances.Co-channel interference in narrow bands is not a problem. Intersymbol interference (ISI) and fading produced by multipath propagation are not a problem. The use of the fast Fourier transform allows for a more efficient implementation. Time synchronisation faults have a low sensitivity. It is not necessary to use tuned sub-channel receiver filters (unlike conventional FDM).
Doppler shift sensitivity Sensitive to problems with frequency synchronisation. High peak-to-average-power-ratio (PAPR) necessitates linear transmitter circuitry, which is inefficient in terms of power. The cyclic prefix/guard interval causes a loss of efficiency.