Most advanced microwave link gives 250Mbps on 28MHz channel, using 2048QAM modulation.
ipasolink.PNG
If you use XPIC (like our "MIMO"), you may get 500Mbps.
Of course you need totally clean spectrum, what you can only achieve by using licensed bands (or moving to North Pole).
Actually, most used modulation are QAM (Quadrature Amplitude Modulation). Each time you add a symbol, modulation index doubles. For example, in 64QAM signal can represent 64 differents simultaneous symbols.
modulation.png
In order to get 1Gbps on 28MHz channel, you'll need 37 bits / Hz (assuming perfect efficiency and no guard interval)
This means... 137438953472QAM. I'm afraid we will never see something like that.
To get higher datarates, you need to use wider channels.
Regards
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