Configure the modulation scheme and the data of any of the eight subcarriers shown below. Click the Reset button to select an OFDM symbol duration that will make the subcarriers orthogonal. Toggle the data bits or click on the New Bits button to generate new bits.
Each subcarrier is modulated with a given MCS and the corresponding data bits. Any modulation symbol is then represented by the I and Q values.
Each modulated subcarrier is represented by a complex number X[k] = I + jQ, where I (in-phase) and Q (quadrature) are the coordinates of the constellation point selected by the bit mapping.
In OFDM all N subcarriers are assembled into a frequency-domain vector X = [X[0], X[1], …, X[N−1]], where each index k corresponds to one subcarrier frequency fk = k/Ts. Subcarrier bins not assigned to any signal are set to zero. The IFFT of X then produces the composite time-domain OFDM symbol that is actually transmitted.
The real and imaginary parts of the IFFT need to be sent to the receiver. In an actual system, the real and imaginary values would be sent by carrying out IQ modulation of a carrier. This carrier would have a frequency given by the band the system is intended to operate in and sent over the air. In this simplified demo, these values will just be assumed to arrive at the receiver with the presence of added noise.
