Modulation vs Demodulation
Modulation is a method of transferring information by adding that information into a carrier signal. Demodulation is the process of filtering out the actual transferred information from the received signal. In general, at the transmission side of a telecommunication link a radio carrier is generated. A single carrier frequency does not transfer useful information via a radio link unless, a modulation method is used to implant useful information into the carrier signal. Also, this carrier signal needs to be demodulated at the receiver end, to complete the transfer of useful information from one end to another.
Modulation is the process of putting the information that we need to transfer into a carrier signal. IEEE defines modulation as “a process whereby certain characteristics of a wave,often called the carrier, are varied or selected in accordance with a modulation function.”There are a number of methods that can be used to achieve this purpose such as Amplitude Modulation (AM), which varies the carrier amplitude as per the information signal, Frequency Modulation (FM), which changes the carrier frequency as per the information signal, and Phase Modulation (PM), which changes the carrier phase according to the information signal.When it comes to digital signal transmission, the basic modulation schemes are Amplitude Shift Keying (ASK), which uses tone on and off conditions as digital binary states, Frequency Shift Keying (FSK) uses two frequencies as binary 1 and 0, while Phase Shift Keying (PSK) uses two phases of a signal to represent binary states. Modulation of a sine waveform is used to transform a baseband message signal into a passband signal; for example, low-frequency audio signal into a radio-frequency signal (RF signal). In radio broadcasting and voice communication this concept is highly utilized to shift baseband voice signal into a passband channel.
Demodulation is the process of extracting information signal from the carrier signal. Demodulation process should be exactly compatible with the modulation method otherwise, the destination end will not be able to extract the original information signal from the carrier signal. Therefore, initial handshake should take place in a proper mechanism to negotiate the modulation and demodulation methods in advance, for a dynamic environment. For an example, in mobile communications, modulation methods could change on the fly, therefore handshaking takes place before shifting from one method to another or uses special algorithms at the destination end to extract the information by identifying the original modulation method. All the modulation methods, such as AM, FM , PM etc. have their own demodulation methods to recover the original signal at the destination end.
Difference Between Modulation and Demodulation
Modulation is the process of impinging useful information on the carrier, while demodulation is the recovery of original information from the carrier at the distant end, near the destination user. Equipment that does both modulation and demodulation is called a modem. Modulation and demodulation processes mainly aims to achieve transfer of information with the minimum distortion or corruption, minimum loss to the carrier signal, and efficient use of the spectrum. Even though there are a number of methods or schemes for modulation and demodulation process, they have their own advantages and disadvantages as well. For an example, AM is used in short wave and medium wave radio broadcasting, FM is used in Very High Frequency (VHF) radio broadcasting, and PM is popular with the digital signal modulation.
Both modulation and demodulation processes are equally important to transfer an information signal in a given channel using a carrier signal. Therefore, the modulation method we use at the transmitter must be exactly compatible with the demodulation method at the receiver end to achieve proper transfer of information from one location to another.