This page describes difference between FDM and OFDM techniques.
FDM stands for Frequency Division Multiplexing and OFDM stands for Orthogonal Frequency Division Multiplexing.
As shown in the figure in FDM systems carriers are far apart with respect to each other and in OFDM systems carriers are densely packed and are orthogonal to the other carriers. Orthogonal means peak of one carrier occurs at null of the other. Hence OFDM system is bandwidth efficient compare to FDM system. In FDM system carriers are not orthogonal.
OFDM system usually will have more Peak to Average Power ration i.e. PAPR compare to FDM system. PAPR can be reduced by use of scrambler module and other techniques in OFDM systems.
OFDM system provides higher data rate compare to FDM system in the same bandwidth usage.
FDM systems are used in radio, satellite communications requiring good amount of guard bands between adjacent frequency bands. OFDM systems are used in wimax-16d/16e, wlan-11g/11n and LTE technologies requiring higher data rate and mainly used for broadband internet service.
In OFDM systems multipath interference is more compare to FDM systems but can be avoided/reduced using high end algorithms such as cyclic prefix insertion etc.
In FDM case entire bandwidth is used by user/subscriber, while in OFDM bandwidth is divided into many narrow band channels and each is allocated to user/subscriber. Hence OFDM supports more subscribers/channels compare to FDM.
If one wants to understand difference between FDM and OFDM, it requires wast knowledge on carrier multiplexing techniques for optimal utilization of scarce frequency resoures.
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