Convert demodulation I/Q to soft Data

[Davy]

I found the signal after demodulation module are Data_I[q:0] and
Data_Q[q:0].
How to convert Data_I[q:0] and Data_Q[q:0] to soft information
Data[q:0]?
May you please recommend some references?

Any suggestions will be appreciated!

Best regards,
Davy