R
Ratish Kumar Srivastava
- Jan 1, 1970
- 0
Can any body explain difference between Bit and baud rate with an example?
Best Regards,
Ratish
Best Regards,
Ratish
Best Regards,
Ratish
Bob said:Can any body explain difference between Bit and baud rate with an
example?
Best Regards,
Ratish
When digital information is transmitted it is sometimes more efficient to
encode the bits in a way such as to reduce the total bandwidth necessary
for that transmission.
If you use only two different values of a signal's characteristic (let say
its amplitude) to encode a binary signal then the bandwidth required to
send that signal is fairly high.
If, on the other hand, you use more than two different values of that
signal to encode a binary signal then the same bitrate can be transmitted
using a lower-bandwidth channel.
For example, a two-level voltage signal's spectral content is easily
calculated using the Fourier transform of the time-domain signal. Use a
1-0-1-0-1-0... data pattern with a given rise/fall time to see the highest
needed bandwidth of the channel (and get the signal through with minimal
time-domain distortion).
Now, try using four levels to encode the bitstream. Each pair of bits can
be encoded with a single voltage level. Do the same Fourier transform and
see its reduced spectral width. Note that this type of encoding requires
the bitstream to be scrambled such that if you have each pair of bits
repeat themselves (over and over) you always get some voltage level
changes (which is necessary to recover the level-change boundary
information [aka, clock recovery]).
A baud is the symbol rate (per second). With encoding, you send more than
one bit/second (bps) per baud.
If you send 1M bit per second, but encode 16 bits per symbol, then the
baud rate is 62.5K baud. This could be done (for example) by using 4
voltage levels per symbol or by using 4 different phases per symbol.
If I recall correctly, fast dial-up modems (say 38.4Kbps and 56Kbps) are
all 2400 baud. This high bps per baud encoding is required because dial-up
lines only have about 3KHz of bandwidth (they're all digitally sampled at
8Ksps).
By the way, if this is a homework question then I hope (at least) you
force yourself to really understand this. If my explanation doesn't click
with you, then do some research. Please don't just copy this text and
paste it. Please.
Hope this helps.
Bob
PeteS said:Bit rate : The actual data rate in bits per second that is to be
transmitted
Baud rate : The maximum number of line signaling symbols per second
PeteS said:In addition to what Bob said, the most basic definition, when
considering communications systems, of course:
Bit rate : The actual data rate in bits per second that is to be
transmitted
Baud rate : The maximum number of line signaling symbols per second
when transmitting the above data in the transmission medium. (Sometimes
we refer to line transitions, but that gets a little sticky for FSK,
but the principle holds)
We encode data so there are multiple bits per line transition, usually
for bandwidth reasons (there's a correlation between encoding and S/S+N
degradation). The Baud rate is sometimes also known as **the Symbol
Rate**, the imply the number of symbols, not the original data rate.
Just to aid with the homework, some encoding techniques that are common
(not line coding, but multi-level codes) are:
QAM
PAM
PSK
QPSK
DQAM
DQPSK
DPSK
There's a lot more - I suggest some light reading
Cheers
PeteS
Roger said:Baud has been misused a lot, as a fancier word for bps. Especially when
talking about modems you see that Baud is often used incorrectly.
"Data speed used to be specified in terms of baud, which is a measure
of the number of times a digital signal changes state in one second.
Baud, sometimes called the "baud rate," is almost always a lower figure
than bps for a given digital signal because some signal modulation
techniques allow more than one data bit to be transmitted per change
state."
The advertising departments of modem manufacturers wanted to tell the
users about the higher number, the bps, but they also wanted to use the
fancier word Baud, so they often used Baud in place of bps.
From http://www.essaysample.com/essay/001633.html
"While taking about modems, the transmission speed is the source of a
lot of confusion. The root of the problem is the fact that the terms
"baud" and "bits per second" are used interchangeably. This is a result
of the fact that it's easier to say "baud" than "bits per second,"
though misinformation has a hand in it, too. A baud is "A change in
signal from positive to negative or vice-versa that is used as a
measure of transmission speed" and bits per second is a measure of the
number of data bits (digital 0's and 1's) transmitted each second in a
communications channel. This is sometimes referred to as "bit rate."
Individual characters (letters, numbers, spaces, etc.), also referred
to as bytes, are composed of 8 bits. Technically, baud is the number of
times per second that the carrier signal shifts value, for example a
1200 bit-per-second modem actually runs at 300 baud, but it moves 4
bits per baud (4 x 300 = 1200 bits per second)."
Yeah - you missed BTFSPLK ;-)In addition to what Bob said, the most basic definition, when
considering communications systems, of course:
Bit rate : The actual data rate in bits per second that is to be
transmitted
Baud rate : The maximum number of line signaling symbols per second
when transmitting the above data in the transmission medium. (Sometimes
we refer to line transitions, but that gets a little sticky for FSK,
but the principle holds)
We encode data so there are multiple bits per line transition, usually
for bandwidth reasons (there's a correlation between encoding and S/S+N
degradation). The Baud rate is sometimes also known as **the Symbol
Rate**, the imply the number of symbols, not the original data rate.
Just to aid with the homework, some encoding techniques that are common
(not line coding, but multi-level codes) are:
QAM
PAM
PSK
QPSK
DQAM
DQPSK
DPSK
There's a lot more - I suggest some light reading