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From: Daku on 7 Aug 2010 23:57
Thanks to all for your answers. However, I am a bit confused. In a
very simple situation where e.g., a
clock (1 - 0 - 1 - 0 ....) may I know where the bits/
symbol concept is coming in - I am transferring
some bits. Thanks in advance.

On Aug 7, 10:30 pm, Gareth <m...(a)privacy.net> wrote:
> On 05/08/2010 16:04, Daku wrote:
>
> > I understand that they are different domains (Hz - analog and bits/sec
> > - digital), how would one convert e.g., 1Gbit/s to corresponding Hertz
> > frequency ?
>
> According to the Shannon-Hartley theorem, the highest possible data rate is:
>
> C = B*log2(1 + S/N)
>
> Where C is the channel capacity in bits per second
>
> B is the channel bandwidth in Hz
>
> Log2 is base 2 logarithm
>
> and S/N is the signal to noise power ratio (as a linear ratio not in dB)
>
> In practice you will always get less than this, though some modulation
> schemes can get quite close.
>
> --
> -----------------------------------------------------------------------
> To reply to me directly:
>
> Replace privacy.net with: totalise DOT co DOT uk and replace me with
> gareth.harris

From: Grant on 8 Aug 2010 00:29
On Sat, 7 Aug 2010 20:57:07 -0700 (PDT), Daku <dakupoto(a)gmail.com> wrote:

>Thanks to all for your answers. However, I am a bit confused. In a
>very simple situation where e.g., a
>clock (1 - 0 - 1 - 0 ....) may I know where the bits/
>symbol concept is coming in - I am transferring
>some bits. Thanks in advance.

depends how you do the data framing too, how do you tell if a bit is a
one or zero?

Grant.
From: Daku on 8 Aug 2010 12:00
Bit values may be inferred from the specified voltage levels,
as in stabdard CMOS - analogous to a timing diagram.

On Aug 8, 9:29 am, Grant <o...(a)grrr.id.au> wrote:
>
> depends how you do the data framing too, how do you tell if a bit is a
> one or zero?
>
> Grant.

From: Gareth on 8 Aug 2010 12:27

On 08/08/2010 17:00, Daku wrote:
> Bit values may be inferred from the specified voltage levels,
> as in stabdard CMOS - analogous to a timing diagram.
>

What exactly are you trying to do here? a bit of background may help
answer your question. E.g. are you trying to send data down a cable? if
so will it be synchronous or asynchronous? Is it just one way
communication between two devices?

Gareth.

PS top posting, that's posting your reply above the relevant text, can
make threads difficult to follow. it is usually clearer to put your
reply below the relevant text in the post you are replying to.

From: Tim Wescott on 8 Aug 2010 13:17
On 08/06/2010 03:42 AM, Daku wrote:
(top posting fixed)
> On Aug 6, 3:25 am, "k...(a)att.bizzzzzzzzzzzz"<k...(a)att.bizzzzzzzzzzzz>
> wrote:
>> On Fri, 06 Aug 2010 06:49:33 +1000, Grant<o...(a)grrr.id.au> wrote:
>>> On Thu, 5 Aug 2010 16:19:00 -0400, "Tom Biasi"<tombi...(a)optonline.net> wrote:
>>
>>>> "Daku"<dakup...(a)gmail.com> wrote in message
>>>> news:1f08b0d9-9d6a-4cf3-93cc-19803e81b278(a)y32g2000prc.googlegroups.com...
>>>>> I understand that they are different domains (Hz - analog and bits/sec
>>>>> - digital), how would one
>>>>> convert e.g., 1Gbit/s to corresponding Hertz
>>>>> frequency ?
>>
>>>> Hi,
>>>> Tim is quite knowledgeable on these subjects and gave some usefull info but
>>>> maybe your question is not quite so deep.
>>>> Hertz is used to describe cycles/second (cycles per second). If you allow it
>>>> to mean events per second then a bit can be an event.
>>>> So 1Gb/sec is 10^9bits / sec or 1 Ghz.
>>>> This is for mental clarity and the actual units may vary.
>>
>>> Yes, Tim touches on the old baud rate (symbol rate) vs frequency that
>>> you're suggesting as the simple answer.
>>
>>> Both are not incorrect (double negative only to show grey area).
>>
>>> For example 100Mbps network link bangs four symbols on each of 1/25MHz
>>> to get the speed, and Gbps copper network links don't run at 1GHz, they
>>> run slower speed, using a couple pairs in each direction.
>>
>>> So, in this case, context matters.
>>
>>> Where I said symbols, Tim said constellation, Tim is more accurate :)
>>
>> Not really. Symbols are the stars in a constellation of stars. The symbol is
>> the basic unit of information transferred. A constellation is a
>> representation of the possible physical values (voltage, frequency, phase,
>> whatever).
>>
>> A little more specifically, a symbol may be a specific value in the
>> constellation or a transition from the current point to another.
>
> Thanks to all for your feedback. I had thought
> about the baud rate idea that Tim elaborated
> on, but the context in which I asked this question
> was Ethernet bits going from the MAC layer
> to the PHY layer at say 1 Gb/s or more (for the
> newer standards).

GB Ethernet uses 5-level signaling on four pairs of wires. I can't find
a reference that gives the symbol rate; without forward error correction
(FEC) it could be as low as 110MBaud. I don't believe this at all-- I'm
sure there's at least some coding to keep the average voltage at 0 for
transformer coupling, for error detection, and maybe even for error
correction.

But surfing on Wikipedia for a few moments didn't tell me -- you'll have
to dig up the appropriate standard and take a look for yourself!

http://en.wikipedia.org/wiki/Ethernet_over_twisted_pair has a
discussion, and a link to IEEE 803.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html
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