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I am quite new to OFDM modulation. I am reading this from a tutorial. In one of its parts, for showing amplitude variation of the OFDM signals, there is a graph that has used 8 sub-carriers and BPSK modulation as below:

enter image description here

Now I have faced to this question, that we are using OFDM modulation here, so why we have used BPSK modulation? Do we double modulate the signal? I cannot understand the use of BPSK in this example. Any help?

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OFDM isn't a modulation technique. It stands for "Orthogonal frequency-division multiplexing" and is a way of splitting the spectrum into discrete channels for sending data. Each of those channels, which is just a single frequency carrier in its own right, requires the data to be modulated onto it. In this example BPSK is used.

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    \$\begingroup\$ Yes. Another minor point is that BPSK and OFDM work very well together spectrally. Your BPSK bit rate is equal to the frequency between the subcarriers and in theory you get zero interference between them. \$\endgroup\$ – Michael Fox Oct 26 '14 at 19:07
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    \$\begingroup\$ @MichaelFox: That's not just true of BPSK, though. Any single-carrier modulation scheme with zero-ISI will achieve the same property when combined with OFDM. \$\endgroup\$ – Oliver Charlesworth Oct 26 '14 at 20:08

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