- What is digital communication?
Digital communication is a mode of communication where the information or the thought is encoded digitally as discreet signals and electronically transferred to the recipients. Digital communication is one of the most commonly used mode of communication in the current scenario.
- Types of modulation techniques:
Digital communication systems also employ modulation techniques, some of which include:
- Amplitude Shift Keying(ASK):
The most basic (binary) form of ASK involves the process of switching the carrier either on or off, in correspondence to a sequence of digital pulses that constitute the information signal. One binary digit is represented by the presence of a carrier; the other binary digit is represented by the absence of a carrier. Frequency remains fixed.
Figure 1.ASK
- Frequency Shift Keying(FSK):
The most basic (binary) form of FSK involves the process of varying the frequency of a carrier wave by choosing one of two frequencies (binary FSK) in correspondence to a sequence of digital pulses that constitute the information signal. Two binary digits are represented by two frequencies around the carrier frequency. Amplitude remains fixed.
Figure 2.FSK
- Phase Shift Keying(PSK):
Phase-shift keying (PSK) is a method of digital communication in which the phase of a transmitted signal is varied to convey information. There are several methods that can be used to accomplish PSK.
- Basic digital communication system:
Figure 3. Basic Digital Communication System
- MODEMS:
- Modems are devices used to enable the transfer of data over the public switched telephone network (PSTN).
- The name modem comes from the name Modulator- Demodulator which describes the function the modem performs to transfer digital information over an analog network
- The goal is to produce a signal that can be transmitted easily and decoded ton reproduce the original digital data.
- Primarily used to communicate via telephone lines, modems can be used over any means of transmitting analog signals
- There are many kinds of modems available today:
–Internal modem: A modem card in your computer that is integrated within the system. Less expensive than external modems. Disadvantage is that you need to access inside the computer to replace then modem
–External modem: A device that connects externally to your computer through a serial portn External power supply does not drain power from the computer. Modem activity can easily be observed. More expensive than an internal modem
- DSL (Digital Subscriber Line): A high-speed data service that works over conventional telephone linesn and is typically offered by telephone companies. It does not occupy the phone line-you can still talk on the phone. Speed is much higher than regular modem
- Cable modem: A device that connects to the existing cable feed and to an Ethernet network card in the PC (also called a NIC for Network Interface Card) is different than a common dial up modem. Supports higher speeds. Typically offered by cable companies.
- Modems are the most popular means of Internet access, UCLAn 2001 study of American Internet users shows that 81.3% of them use telephone modem, and 11.5% cable modem