System Specification

• Actually, one cannot define the properties of a system in the form of first principles as they vary from system to system used in different areas of applications.

• For example, the properties of man-to-machine communication systems may be different from those of man-to-man and machine-to-man communication systems.

Hence, our area of focus is a general communication system.
• LINEARITY :- In general, we would expect the systems to be linear in order to produce effects such as amplification and attenuation.

• STABILITY :- for any bounded input, we would expect a bounded output in the field of communication.

• INVERTIBILITY :- A communication system has to be invertible because it is ridiculous to transmit a signal in such a way that no one can recover the original signal.

• MEMORY :- As far as man-to-man communication is considered, the system should be memoryless . But in case of man-to-machine communication systems like speaker verification systems(security systems) ,it should have memory because the identity of the speaker has to be verified from the stored data.

• CAUSALITY :- In our day-to-day life, we can consider communication to be causal since the system does not look into future.

• TIME-INVARIANCE :-Clearly ,if we delay the input signal ,the output signal would also be delayed by the same amount.



• In general, a communication system works as seen above.
• The source generates a signal such as speech, which is a time-domain signal.
• The transmitter is a system designed in such a way that the original signal can be transmitted through the channel and reach it’s destination. Since the signal s(t) is weak(low frequency) it can’t be transmitted as such, it has to be modulated with a carrier wave first .
• Channel is the medium through which the signal is transmitted. One cannot avoid the channel though the signal being transmitted will be corrupted by noise, distorted and attenuated.
• The receiver would serve as the inverse system to the transmitter. However, because of the channel, the receiver must do it’s best to reproduce the original signal.
• The received message is passed to the information sink that some how makes use of the message.