Baud rate = Symbol rate?
David P. FOK
May I ask if the statement "Baud rate = Symbol rate" is correct?
Someone told me that the bandwidth for the phone system is about
3kHz, so the baud rate (which equals to
bit_rate/#_of_bits_per_symbol -by his definition)
could never attain the number like 19,200.
I was doubted as this is not what I've learnt and consulted many
text-books to make a proof of the difference between the
definitions. But the gentleman said that the books are wrong. He
said that NO baud rate numbers are given in the V.32, V.34 specs.
and baud rate can only be calculated when the #_of_bits_per_symbol
is known.
Any comment on this?
Thanks in advance.
-david
Ed Hall
: Dear experts,
V.34 has symbol rates of 2400, 3000, and 3200 mandatory, 2743, 2800, and
3429 optional. You can call them "baud" if you want, although its sort
of an old term, and tends to be misused for the bit rate. In V.34 even
term "symbol rate" is a bit misleading, since two successive symbols are
often combined into what the standard calls a "4D symbol." It's another
case of technology outstripping terminology...
The particualar symbol rate used in V.34 depends upon the bandwidth
available, which is usually better than 3kHz by several hundred Hz. The
standard includes sophisticated methods for probing the line's frequency
response and compensating for it, as well as compensating for other line
defects, such as non-linear quantization. V.34 performs pretty close to
the theoretical maximum stated by Shannon's law relating bandwidth and
channel noise to bit rate.
-Ed Hall
edh...@rand.org
wer...@ns.net
This is correct. The baud rate is simply defined as "symbols per second".
I am not sure, but I think that 14.4 modems (not sure about V.34) are
actually 2400 baud modems.
Mike Werstlein
wer...@ns.net
Squeegee
> Dear experts,
>
> May I ask if the statement "Baud rate = Symbol rate" is correct?
>
It is correct.
> Someone told me that the bandwidth for the phone system is about
> 3kHz, so the baud rate (which equals to
> bit_rate/#_of_bits_per_symbol -by his definition)
> could never attain the number like 19,200.
Bit rate = baud rate * bits/symbol
The advances in modems over the past several years have been in
pushing up bits/symbol. The baud rate could not attain a value like
19,200. It's limited to something near 3000 baud (shorthand for symbols
per second).
>
> I was doubted as this is not what I've learnt and consulted many
> text-books to make a proof of the difference between the
> definitions. But the gentleman said that the books are wrong. He
> said that NO baud rate numbers are given in the V.32, V.34 specs.
> and baud rate can only be calculated when the #_of_bits_per_symbol
> is known.
Whether it is spec'd or not, my understanding is that the signaling
scheme for V.32 and V.32bis involves 2400 symbols per second (2400 baud)
and 4 or 6 bits per symbol. I'm pretty sure V.34 follows this same
pattern.
It's for this reason that high speed modems are sold as e.g., "14,400
bps" (bits per second) modems. Not as 14,400 baud modems.
>
> Any comment on this?
> Thanks in advance.
>
> -david
--Steve
--
Stephen C. Gilardi
SQ Software
sque...@cris.com
Steven Chamberlin
writes:
Baud stands for bits per second. With 8 n 1 ( 1 start bit, 8
data bits, no parity, and 1 stop bit, 10 bits per character),
theoretically, baud rate/10(bits per second)= #of characters per second.
In other words, 19200 baud = 1920 cps. that is the way I understand
it. I am however open to correction.
Steve.
Wessel Ganzevoort
> data bits, no parity, and 1 stop bit, 10 bits per character),
> theoretically, baud rate/10(bits per second)= #of characters per second.
> In other words, 19200 baud = 1920 cps. that is the way I understand
> it. I am however open to correction.
> Steve.
This is correct!
Wessel Ganzevoort.
Wessel Ganzevoort
> data bits, no parity, and 1 stop bit, 10 bits per character),
> theoretically, baud rate/10(bits per second)= #of characters per second.
> In other words, 19200 baud = 1920 cps. that is the way I understand
> it. I am however open to correction.
> Steve.
This ic correct!
Wessel Ganzevoort
Bob Myers
> Baud stands for bits per second. With 8 n 1 ( 1 start bit, 8
No, it doesn't. And what's even more disturbing is that you posted this
little bit of misinformation following a very lengthy excerpt from an
earlier posting which DID contain the correct information!
Bob Myers KC0EW Hewlett-Packard Co. |Opinions expressed here are not
Workstations Systems Div.|those of my employer or any other
my...@fc.hp.com Fort Collins, Colorado |sentient life-form on this planet.
William C.M. Leung
>
>No, it doesn't. And what's even more disturbing is that you posted this
>little bit of misinformation following a very lengthy excerpt from an
>earlier posting which DID contain the correct information!
TRUE! In fact symbols != characters either.
BAUD RATE != CHARACTER RATE or BIT RATE.
I've got no information of the 19200 bps modem :-( but I've got
information of the V.32 (9600 bps) & V.33 (14400 bps) modems.
The modulation technique of V.32 is 32-ary QAM. Every 5 binary bits
are grouped to form a 32-ary symbol (log2(32) = 5) so the SYMBOL RATE
is 9600/5 = 1920 baud. The CHARACTER RATE should be 9600/10 = 960 cps
though.
V.33 uses 128-ary QAM, so the baud rate should be 14400/log2(128) =
14400/7 = 2057 baud.
If the 19200 bps modem also uses 128-level signalling, the baud rate
should be 19200/7 = 2743 baud.
These are rough estimates only. They do not take error-control coding
into account, which may require greater symbol rate.
>
>
>Bob Myers KC0EW Hewlett-Packard Co. |Opinions expressed here are not
> Workstations Systems Div.|those of my employer or any other
>my...@fc.hp.com Fort Collins, Colorado |sentient life-form on this planet.
--
William - Have a good time all the time :-)
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For information about myself and LaTeX2e Chinese typesetting CJK
package, my URL is http://club.eng.cam.ac.uk/~92cml
Steve Harmon
: > Baud stands for bits per second. With 8 n 1 ( 1 start bit, 8
Actually, baud doesn't mean bits per second. However, when talking about
serial ports they are equal and modem manufacturers have come to equate baud
with bits per second (abbreviated bps). If you're talking about modems and
their symbol rate then baud has a very different meaning (i.e. a 2400 baud
modem does not produce 2400 symbol transitions per second ;^)...
--
| Steve Harmon @ AT&T Tridom Marietta, Georgia.
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BabySocks
stuff.
The term "baud" originated from the early age of telecommunication, and
was named after the French inventor, Emile Baudot.
The correct meaning of the term is 'Number of signal changes per second',
quite similar to 'frequency'. And since analog telephone lines provide
only 3000Hz of bandwidth before extreme attenuation occurs, the maximum
baud rate for this medium is 2400baud. Any and all modems that have high
bps rates such as 9.6, 14.4, 28.8, etc. use a data compression algorithm
to achieve these speeds, but the truth of the matter is they are all still
2400baud modems.
Hope this will shed light on this fascinating subject. Your welcome....
baby...@aol.com
Norman W Cramer
: It seems there is somewhat of a misunderstanding about all this "baud"
: stuff.
: The term "baud" originated from the early age of telecommunication, and
: was named after the French inventor, Emile Baudot.
: The correct meaning of the term is 'Number of signal changes per second',
: quite similar to 'frequency'. And since analog telephone lines provide
: only 3000Hz of bandwidth before extreme attenuation occurs, the maximum
: baud rate for this medium is 2400baud.
Correct.
: Any and all modems that have high
: bps rates such as 9.6, 14.4, 28.8, etc. use a data compression algorithm
: to achieve these speeds, but the truth of the matter is they are all still
: 2400baud modems.
Almost correct. Yes some do use data compression in the traditonal sense but
most use a scheme that encodes more than one bit to a signal event (this is
sort of like compression but all bits are sent). For example, a carrier
frequency can be phase shifted 0 deg to represent the "dibit" 00, shifted
90 deg to represent 01, shifted 180 deg to represent 11, and shifted 270 deg
to represent 10. With this scheme (QAM) 2 bits can be sent every signal event.
The baud is still 2400 but the bps is now 4800. There are many more schemes
that achive more than 1 bit per signal event.
For more info see "The Green Handbook of Telecomunications"
David Hough
baby...@aol.com (BabySocks) writes:
>
> The correct meaning of the term is 'Number of signal changes per second',
> quite similar to 'frequency'. And since analog telephone lines provide
> only 3000Hz of bandwidth before extreme attenuation occurs, the maximum
> baud rate for this medium is 2400baud. Any and all modems that have high
> bps rates such as 9.6, 14.4, 28.8, etc. use a data compression algorithm
> to achieve these speeds, but the truth of the matter is they are all still
> 2400baud modems.
I think you will find that the V34 standard uses a higher baud rate.
Unfortunately I can't remember what it is offhand :-(
Dave
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Tel +44 1285 655 766
Fax +44 1285 655 595
Michael Schwingen
DH>I think you will find that the V34 standard uses a higher baud rate.
DH>Unfortunately I can't remember what it is offhand :-(
It's somewhere areound 3000 baud.
cu
Michael
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