Digital Modulation in Data Communicaion

Topics: Modulation, Local area network, Computer network Pages: 4 (1275 words) Published: December 11, 2012
The Universal Seven-Part Circuit of Data Communications System

Seven-Part Circuit of Data Communications System
- A universally accepted standard designed to send data from a source to a remote destination.

The Universal Seven-Part Circuit of Data Communications System 1.The Data Terminal Equipment (DTE) at point A.
2.The interface between the DTE and the Data Circuit-Terminating Equipment (DCE or often called Data Communications Equipment) at point A. 3.The DCE at point A.
4.The transmission channel between points A and B.
5.The DCE at point B.
6.The DCE - DTE interface at point B.
7.The DTE at point B.

Phase Shift Keying
-One of the simplest forms of digital modulation is binary or Bi-Phase Shift Keying (BPSK). One application where this is used is for deep space telemetry. The phase of a constant amplitude carrier signal moves between zero and 180 degrees. On an I and Q diagram, the I state has two different values. There are two possible locations in the state diagram, so a binary one or zero can be sent. The symbol rate is one bit per symbol. A more common type of phase modulation is Quadrature Phase Shift Keying (QPSK). It is used extensively in applications including CDMA (Code Division Multiple Access) cellular service, wireless local loop, Iridium (a voice/data satellite system) and DVB-S (Digital Video Broadcasting — Satellite).

Frequency Shift Keying
Frequency modulation and phase modulation are closely related. A static frequency shift of +1 Hz means that the phase is constantly advancing at the rate of 360 degrees per second (2 π rad/sec), relative to the phase of the unshifted signal. FSK (Frequency Shift Keying) is used in many applications including cordless and paging systems. Some of the cordless systems include DECT (Digital Enhanced Cordless Telephone) and CT2 (Cordless Telephone 2).In FSK, the frequency of the carrier is changed as a function of the modulating signal (data) being transmitted....
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