How can a communication system operating at a 1 GigaHertz rate of signal changes achieve a 10 Gbps data transfer rate?

Answer

By successfully encoding 10 bits per transmitted signal element (symbol).

High data rates are achieved not just by how fast signals change, but by using complex modulation schemes to reliably encode multiple bits onto each individual signal element or symbol.

How can a communication system operating at a 1 GigaHertz rate of signal changes achieve a 10 Gbps data transfer rate?
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