DSP analysis for DMT signal

My project is to design a DMT visible light comm. test bed. I have sent a DMT signal through the wireless channel and after photodetection, I have found the signal to be buried in noise.I have to apply a power and bit-loading algorithm based on the SNR of each subcarrier in the received signal. The sampled data of received signal can be obtained from the oscilloscope. Performing an FFT yields frequency spectrum of the received time domain signal. How can I get SNR of each individual subcarrier? Can anyone provide me with good references on this topic?