Relationship

How can I find a relation between the input and output of the overall system?
How do you find the relationship between the input and output of a function?What is the relationship between inputs and outputs?What is the relations...
How to explain this BER vs SNR behaviour?
What is the relationship between SNR and BER?Which SNR is relevant for BER? What is the relationship between SNR and BER?SNR is logarithmic ratio of...