Compilation of important modulation method
In this article, I will explain compilation of important modulation method. In this I have explained different modulation methods used to transmit the signal in detail. I also illustrated the classification using block diagrams.
The transmission of signals is an extensive scope of telecommunications. If different signals on the same transmission or transmission medium can be sent simultaneously, the separation of the individual information at the receiver is without a previous signal processing usually no longer possible. It is easy to see that a voice and a musical message that is sent via a line at the feed superimposed additively. This produces a sum signal from the receiver, the original message can no longer recover. He both, mutually interfering receives information simultaneously.
The frequency range of speech and music in the audio band covers 20 Hz to 20 kHz. If this bandwidth is transmitted by radio signal as an electromagnetic wave, it can not happen in this the baseband. The wavelength of a 1 kHz tone is = 300 km. The radio antenna as ?/4-Dipol would be 75 km or high. Television picture signals in the higher frequency band is by a factor of 15 and may also be unmodulated not radiated as electromagnetic waves via an antenna practically useful proportions.The purpose of the modulation
1) It is used in frequency adaptation to a transmission channel used with different passports. For radio signals band-pass filters are used as resonant circuits with a fixed bandwidth.
2) By modulating a multiple use of a transmission medium is possible. In frequency-division multiplexing method, various signals are converted in staggered adjacent frequency ranges. In the receiver, signals can be filtered out separately. An example is the radio and television stations are to call on the radio and cable network.
In time-division multiplexing a plurality of pulse beams are interlaced. The receiver performs the temporal separation by the respective individual message. The telephone traffic and the stereo broadcast work by this method.
3) Modulation method can improve noise immunity. This is particularly true in the pulse modulation. It reaches a wider bandwidth at a high level of security against foreign interference.The modulation method
In modulating one or more signal parameters, such as amplitude, frequency or phase of a carrier signal will be altered or modulated by the information signal. The carrier is in this case the information signal, which is also referred to as a modulation signal is impressed. After this process, the information signal having a different shape and is located in a new frequency band. Each type of signal can serve as a carrier signal. Of practical importance are harmonic sinusoidal carrier signals, the carrier and the continuous-time periodic square-wave pulses as a time-discrete carrier.
The modulation is described mathematically by the multiplication of the carrier with the information. This new frequencies occur in the output signal, which are not included in the initial signals and frequencies it may disappear altogether. In contrast to the additive superposition of signal components with a linear characteristic, such as a resistor matrix, the modulation is held to a non-linear characteristic, such as a diode or an input path of a transistor.
In a continuous-time carrier signal is called modulation. Depending on the combination results in various ways, of which the most important ones are mentioned below:
The following modulation types offer the possibility to represent an analog signal by a digital signal. These methods are therefore not always understood as a modulation in the classical sense.
Modulation method can also be used combined with each other, such as AM modulation with angular, quadrature amplitude modulation of 16 QAM, 32 QAM, 64 QAM and 4 quadrature phase shift keying PSK, 8PSK, 16 PSK).