by Dinesh Thakur Category: Switching

As we know, for transmitting a bit, it must transmit a particular signal to recognize if its value is equal to 0 or 1. The technical baseband sub crenellated is not reliable when the distance exceeds a few hundreds of meters. For a signal that we can recover properly, it must be given a special shape the modulating.

We distinguish three broad categories of modulation:

• Amplitude modulation or ASK (Amplitude-Shift Keying);

• Phase modulation or PSK (Phase-Shift Keying);

• Frequency modulation or FSK (Frequency Shift Keying).

An intermediate material, modem (modulator-demodulator), is required to modulating the signal in a sinusoidal form. The modem receives a baseband signal of base and the module, that is to say assigns a sinusoidal analog form. The fact of having more rising edges or descendants protects much better signal degradations caused by the distance traveled by the signal in the cable because the signal is continuous rather than discrete.

Once a terminal situated at a somewhat large distance to be achieved, a modem is required so that the error rate is acceptable. The distance depends strongly on the cable used and the baud rate. Typically, from a few hundred meters to very high speeds and a few kilometers to the lower rates, it is necessary to use a modem.

The Amplitude Modulation

In amplitude modulation, the distinction between the 0 and 1 is obtained by a difference in amplitude of the signal, as shown in Figure.

  Amplitude modulation

The Modulation Phase

For phase modulation, the distinction between 0 and 1 is performed by a signal begins at different locations of the sinusoid, called phases. In the figure, the values 0 and 1 are represented by the respective phases of 0 ° and 180 °.

  Phase Modulation

The Modulation Frequency

In frequency modulation, the issuer has the option to change the frequency for sending signals according to the bit to be sent is 0 or 1, as illustrated in Figure.

  modulation Frequency

In previous presentations modulation techniques, the physical quantity used for amplitude, phase or frequency is only two possible states. If we manage to transmit and detect the arrival more than two states of the same quantity, we can give a meaning to each state to encode 2 or more bits. For example, using four frequencies, phases 4 and 4 amplitudes, it may encode 2 bits for each state. The figure illustrates a possibility to encode two bits in phase modulation.

  Phase modulation to four times

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About Dinesh Thakur

Dinesh ThakurDinesh Thakur holds an B.SC (Computer Science), MCSE, MCDBA, CCNA, CCNP, A+, SCJP certifications. Dinesh authors the hugely popular blog. Where he writes how-to guides around Computer fundamental , computer software, Computer programming, and web apps. For any type of query or something that you think is missing, please feel free to Contact us.



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