Different criteria for "broad" have
been applied in different contexts and at different times. Its origin is in
physics, acoustics, and radio systems engineering, where it had been used with
a meaning similar to "wideband".[1][2] Later, with the advent of digital
telecommunications, the term was mainly used for transmission over multiple
channels. Whereas a passband signal is also modulated so that it occupies
higher frequencies (compared to a baseband signal which is bound to the lowest
end of the spectrum, see line coding), it is still occupying a single channel.
The key difference is that what is typically considered a broadband signal in
this sense is a signal that occupies multiple (non-masking, orthogonal)
passbands, thus allowing for much higher throughput over a single medium but
with additional complexity in the transmitter/receiver circuitry.
The term became popularized through the 1990s as
a marketing term for Internet access that was faster than dialup access, the
original Internet access technology, which was limited to 56 kbit/s. This
meaning is only distantly related to its original technical meaning.
In telecommunications, a broadband signaling
method is one that handles a wide band of frequencies. "Broadband" is
a relative term, understood according to its context. The wider (or broader)
the bandwidth of a channel, the greater the information-carrying capacity,
given the same channel quality.
In radio, for example, a very narrow band will
carry Morse code, a broader band will carry speech, and a still broader band
will carry music without losing the high audio frequencies required for
realistic sound reproduction. This broad band is often divided into channels or
"frequency bins" using passband techniques to allow frequency-division
multiplexing instead of sending a higher-quality signal.
A television antenna may be described as
"broadband" because it is capable of receiving a wide range of
channels, while a single-frequency or Lo-VHF antenna is "narrowband"
since it receives only 1 to 5 channels. The U.S. federal standard FS-1037C
defines "broadband" as a synonym for wideband.[3]
In data communications a 56k modem will transmit
a data rate of 56 kilobits per second (kbit/s) over a 4-kilohertz-wide
telephone line (narrowband or voiceband). The various forms of digital
subscriber line (DSL) services are broadband in the sense that digital
information is sent over multiple channels. Each channel is at higher frequency
than the baseband voice channel, so it can support plain old telephone service
on a single pair of wires at the same time.[4]
भिडियो हेर्न तलको बक्स भित्र क्लिक गर्नुहोस
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