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Q: data comms(what is the significance of frequency domain concept in data transmi) ( Answered,   0 Comments )
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Subject: data comms(what is the significance of frequency domain concept in data transmi)
Category: Computers > Operating Systems
Asked by: nanosumaila-ga
List Price: $6.00
Posted: 28 Aug 2003 04:19 PDT
Expires: 27 Sep 2003 04:19 PDT
Question ID: 249581
what is the significance of frequency domain concept in data transmission
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Subject: Re: data comms(what is the significance of frequency domain concept in data transmi)
Answered By: reeteshv-ga on 28 Aug 2003 05:30 PDT
 
Dear nanosumaila-ga,

Good day!

In a communications system, information (data, voice, image, video) is
propagated from one point to another by means of electromagnetic
signals. Signals are the electromagnetic representations of data.
Transmission refers to data communication by the propagation and
processing of signals.

While the signal is a function of time, it can also be expressed as a
function of frequency, i.e., the signal consists of components of
different frequencies. This frequency-domain concept is more important
in understanding data transmission.

Time-domain concept
-------------------
With respect to time, a signal can be either continuous or discrete.
In a continuous signal, the signal intensity varies smoothly over a
period of time, i.e., there are no breaks in the signal, e.g., human
speech. The familiar sine wave (y = sin(x)) is an example of a
continuous signal. On the other hand, in a discrete signal, the signal
intensity is maintained at a constant level for some period of time
and then changes to another constant level, e.g., binary 1 and 0.

Frequency-domain concept
------------------------
Practically speaking, an electromagnetic signal is made up of many
frequencies, for example, the human speech uses a frequency range
between 20 Hz – 200,000 Hz. This frequency range is called as the
spectrum of the signal.

Other concepts
--------------
Depending on the transmission media and the communications
environment, either analog or digital signals can be used. An analog
signal is a continuously varying electromagnetic wave that can be
propagated over a variety of media. A digital signal is a sequence of
voltage pulses that may be transmitted over a wire medium. For
example, a constant positive voltage level may represent binary 1, and
a constant negative voltage level may represent binary 0. Multiplexing
allows the simultaneous transmission of multiple signals across a
single data like much as a large water pipe is used to carry water to
several separate houses simultaneously.

Frequency Division Multiplexing
-------------------------------
Frequency-division multiplexing (FDM) is a familiar and widely used
form of multiplexing wherein the transmission facility is divided into
channels by splitting the total frequency band (of the carrier) into
narrow bands, each allotted to an individual signal (sub-channeling).
Cable TV systems, carrying multiple video channels on a single cable,
are a common example of FDM.

In FDM, a multiplexer accepts the input from each individual end user,
and generates a signal on a different frequency for each of the
inputs. At the destination, the individual signals are separated out
by a demultiplexer and routed to the proper end users. Therefore, FDM
also requires a multiplexer/demultiplexer at each end of the carrier
to support two-way communication.

The biggest advantage of FDM is its speed, as each input signal is
sent and received at maximum speed at all times. This makes it more
efficient than digital systems (that work on Time Division
Multiplexing (TDM) principles) in terms of bandwidth utilization.
However, FDM can only be used with analog signals. A digital signal
must first be converted into an analog signal before it can be
transmitted using FDM technique.

For many years, FDM was the mainstay of telephone transmission. The
problem is that noise is amplified along with the voice signal. This
fact, and the great decrease in the cost of digital electronics has
led to the widespread displacement of FDM systems by TDM systems in
telephone networks. FDM is still widely used for television
distribution systems, including broadcast and cable TV.

I hope that this information satisfactorily answers your query :)

Thanks & regards,
reeteshv-ga
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