Principles of communication
To analyze a signal, it must be represented. This representation in communication systems is of two types -
- Frequency domain representation and
- Time domain representation
Consider two signals with frequencies of 1 kHz and 2 kHz. Both are represented in the time and frequency domain as shown in the following figure.
Time domain analysis, gives the behavior of the signal over a certain period of time. In the frequency domain, the signal is analyzed as a mathematical function with respect to the frequency.
A representation of the frequency domain is needed where signal processing such as filtering, amplification and mixing is performed.
For example, if a signal such as the following is considered, it is heard that there is noise there.
The frequency of the original signal can be of 1 kHz, but the noise of a certain frequency, which corrupts this signal is unknown. However, whenthat the same signal is represented in the frequency domain, using a spectrum analyzer, it is plotted as shown in the following figure.
Here we can observe some harmonics, which represent noise introduced into the original signal. Therefore, signal representation helps in analyzing the signals.
Frequency domain analysis helps to create the desired wave patterns. For example, binary bit patterns in a computer, Lissajous patterns in a CRO, etc. Time domain analysis helps to understand these bit patterns.