When you separate the collected signals, each car’s channel must attenuate the other cars’ signals at least by 20 dB.
A speaker will be able to generate a sound which contains 3 different frequency values of sine waves. And also the amplitudes of the sine waves will be tunable, so that at each instant;
A(f1) = 0 (meaning does not exist at that time)
A(f2) = above_threshold ( higher amplitude w.r.t f3 )
A(f3) = below_threshold
Note: The f1,f2,f3 will be change their states for different scenarios. A means amplitude, f_i correspondes to the sine wave at that frequency.
Then a microphone(seperated by 10 cm from the speaker) should be able to collect this sound, distinguish different frequency components by also indicating their relative amplitudes, because "which of frequency components has higher amplitude which one has lower amplitude and which one is non-existing" is an important information that should be obtained.
This information will be used in a next step of decison mechanism, so I will need DC converted signal levels. To achieve that I plan to amplify signals and then full wave rectify them.
So, relating this part, there is a requirement which is quoted above. Please notice that car's signal means one of the three different frequencies.