Given the multiple parallel channels, what is the actual modulation process?
The serial digital data stream to be transmitted is split into multiple slower data streams, and each is modulated onto a separate carrier in the allotted spectrum. These carriers are called subcarriers or tones. The modulation can be any form of modulation used with digital data, but the most common are binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), and quadrature amplitude modulation (QAM). The outputs of all the modulators are linearly summed, and the result is the signal to be transmitted. It could be upconverted and amplified if needed.
