DATA COMMUNICATION PRINCIPLES Baseband Passband Modulations Baseband Passband
DATA COMMUNICATION PRINCIPLES : Baseband Passband Modulations
Baseband Passband Modulations If the frequency spectrum of a signal is close to zero Hz, such a signal is called a baseband signal. An example of a baseband signal is the electrical speech signal. If we use Fourier analysis to find the frequency spectrum of such a signal, the spectrum vanishes at a frequency values greater than 4 k. Hz. We say that the bandwidth of speech signal is 4 k. Hz (meaning that the frequencies in it range between 0 and 4000 Hz 4). A data representation in the form of baseband signal is called baseband modulation. Baseband signal usually cannot be transmitted to relatively longer distances. To transmit a baseband signal to a long distance, it is modulated with a highfrequency signal, with much higher frequency than the highest frequency component of the baseband signal. The resulting modulated signal is called the passband signal. The passband modulation and the baseband modulations exist for analog and digital signals. Example of a digital baseband signal is a voltage pulse similar to the gate function discussed in a section above. Figure 3 -7 shows what happens to the spectrum of a baseband signal when it is modulated with high frequency sinusoid - called as a carrier signal.
REFERENCES • Ahmad A. - Data Communication Principles. For Fixed and Wireless Networks • Cornelius T. Leondes - Database and Data Communication Network Systems, Three-Volume Set_. . -Academic Press
- Slides: 3