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.
![](images/ppt26image1.JPG)
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 its destination. Since
the signal s(t) is weak(low frequency) it cant 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 its best to
reproduce the original signal.
The received message is passed to the information sink that some how
makes use of the message.
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