In FDM system, signals from multiple transmitters are transmitted simultaneously (at the same time slot) over multiple frequencies. Each frequency range (sub-carrier) is modulated separately by different data stream and a spacing (guard band) is placed between sub-carriers to avoid signal overlap.
OFDM is a multiplexing technique that divides the bandwidth into multiple frequency sub carriers. OFDM also uses multiple sub-carriers but the sub-carriers are closely spaced to each other without causing interference, removing guard bands between adjacent sub-carriers. Here all the sub carriers are orthogonal to each other. Two periodic signals are orthogonal when the integral of their product, over one period, is equal to zero. The use of OFDM results in bandwidth saving as seen in the figure:
Figure given below shows example of Orthogonal sub carriers:
OFDM is a multiplexing technique that divides the bandwidth into multiple frequency sub carriers. OFDM also uses multiple sub-carriers but the sub-carriers are closely spaced to each other without causing interference, removing guard bands between adjacent sub-carriers. Here all the sub carriers are orthogonal to each other. Two periodic signals are orthogonal when the integral of their product, over one period, is equal to zero. The use of OFDM results in bandwidth saving as seen in the figure:
Figure given below shows example of Orthogonal sub carriers:
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