I am working on developing a communication protocol using Multicarrier OFDM. I have the code running and the simulation is good. My next task is to validate my simulation by transmitting an image or text string over the air using sdrsharp and recieving with an sdrplay. I have done this and captured the over the air image signal.

Now I am trying to decode and reconstruct the transmitted image back.

I plotted the fftshift(fft(Y)); where Y is the recieved signal. In the plot, there is an offset of the carrier frequency of the recieved signal from the 0 Hz. I am using 64-points FFT, BW= 20MHz upsampling factor =4. How do I estimate the offset value that I will need to use to generate the complex exponential that I will multiply with my signal to carry out the coarse frequency synchronization.