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From: Tony Hwang on 9 Jan 2010 00:20
species8350 wrote:
> On Jan 7, 5:19 pm, Jeff Liebermann<je...(a)cruzio.com> wrote:
>> On Thu, 7 Jan 2010 03:58:50 -0800 (PST), species8350
>>
>> <not_here.5.species8...(a)xoxy.net> wrote:
>>> I know that the wifi signal is modulated.
>>
>> Yep.
>>
>>> Firstly, why does the signal need to be modulated.
>>
>> Because it's the modulation that carries the information (data). No
>> modulation, no data.
>>
>>> Secondly regarding g: why are ther so many coding systems used.
>>
>> The modulation method varies with the speed of transmission. Slow
>> speeds have greater range because they have a higher signal to noise
>> ratio for a given signal level. Higher speeds have progressively
>> lower signal to noise ratios for the same signal level. 802.11g will
>> try to negotiate and establish a modulation method that produces the
>> highest data rate, without having the signal to noise ratio become so
>> low that all that is being received are errors and garbage. More
>> simply, the different modulation methods trade transmission speed for
>> error rate. If the errors increase for some reason, the access point
>> will slow things down until the error rate returns to a reasonable
>> value.
>>
>> I guess you haven't looked at 802.11n, which as 77 modulation coding
>> schemes.
>> <http://www.airmagnet.com/assets/whitepaper/WP-802.11nPrimer.pdf>
>> The faster you go, the more complexicated the mess.
>>
>> --
>> Jeff Liebermann je...(a)cruzio.com
>> 150 Felker St #D http://www.LearnByDestroying.com
>> Santa Cruz CA 95060http://802.11junk.com
>> Skype: JeffLiebermann AE6KS 831-336-2558
>
> Thanks for the response.
>
> Is this a way of looking at modulation.
>
> The data has to be transmitted, so it is converted into a wave. That
> wave is the modulation.
>
> So, at transmission point, the wave is created. At receiver point, it
> is demodulated, that is, converted back into data.
>
> The problem with this model is that it doesn't explain how the coding
> schemes will vary, depending upon data rate and errors.
>
> Thanks.
Hmmm,
What is your back? For a starter do you listen to AM radio? Or FM radio?

From: species8350 on 9 Jan 2010 11:38
On Jan 9, 5:20 am, Tony Hwang <drago...(a)shaw.ca> wrote:
> species8350 wrote:
> > On Jan 7, 5:19 pm, Jeff Liebermann<je...(a)cruzio.com>  wrote:
> >> On Thu, 7 Jan 2010 03:58:50 -0800 (PST), species8350
>
> >> <not_here.5.species8...(a)xoxy.net>  wrote:
> >>> I know that the wifi signal is modulated.
>
> >> Yep.
>
> >>> Firstly, why does the signal need to be modulated.
>
> >> Because it's the modulation that carries the information (data).  No
> >> modulation, no data.
>
> >>> Secondly regarding g: why are ther so many coding systems used.
>
> >> The modulation method varies with the speed of transmission.  Slow
> >> speeds have greater range because they have a higher signal to noise
> >> ratio for a given signal level.  Higher speeds have progressively
> >> lower signal to noise ratios for the same signal level.  802.11g will
> >> try to negotiate and establish a modulation method that produces the
> >> highest data rate, without having the signal to noise ratio become so
> >> low that all that is being received are errors and garbage.  More
> >> simply, the different modulation methods trade transmission speed for
> >> error rate.  If the errors increase for some reason, the access point
> >> will slow things down until the error rate returns to a reasonable
> >> value.
>
> >> I guess you haven't looked at 802.11n, which as 77 modulation coding
> >> schemes.
> >> <http://www.airmagnet.com/assets/whitepaper/WP-802.11nPrimer.pdf>
> >> The faster you go, the more complexicated the mess.
>
> >> --
> >> Jeff Liebermann     je...(a)cruzio.com
> >> 150 Felker St #D    http://www.LearnByDestroying.com
> >> Santa Cruz CA 95060http://802.11junk.com
> >> Skype: JeffLiebermann     AE6KS    831-336-2558
>
> > Thanks for the response.
>
> > Is this a way of looking at modulation.
>
> > The data has to be transmitted, so it is converted into a wave. That
> > wave is the modulation.
>
> > So, at transmission point, the wave is created. At receiver point, it
> > is demodulated, that is, converted back into data.
>
> > The problem with this model is that it doesn't explain how the coding
> > schemes will vary, depending upon data rate and errors.
>
> > Thanks.
>
> Hmmm,
> What is your back? For a starter do you listen to AM radio? Or FM radio?- Hide quoted text -
>
> - Show quoted text -

No background in communications
From: Bob on 10 Jan 2010 05:43
On 09/01/2010 16:38, species8350 wrote:
> On Jan 9, 5:20 am, Tony Hwang<drago...(a)shaw.ca> wrote:
>> species8350 wrote:
>>> On Jan 7, 5:19 pm, Jeff Liebermann<je...(a)cruzio.com> wrote:
>>>> On Thu, 7 Jan 2010 03:58:50 -0800 (PST), species8350
>>
>>>> <not_here.5.species8...(a)xoxy.net> wrote:
>>>>> I know that the wifi signal is modulated.
>>
>>>> Yep.
>>
>>>>> Firstly, why does the signal need to be modulated.
>>
>>>> Because it's the modulation that carries the information (data). No
>>>> modulation, no data.
>>
>>>>> Secondly regarding g: why are ther so many coding systems used.
>>
>>>> The modulation method varies with the speed of transmission. Slow
>>>> speeds have greater range because they have a higher signal to noise
>>>> ratio for a given signal level. Higher speeds have progressively
>>>> lower signal to noise ratios for the same signal level. 802.11g will
>>>> try to negotiate and establish a modulation method that produces the
>>>> highest data rate, without having the signal to noise ratio become so
>>>> low that all that is being received are errors and garbage. More
>>>> simply, the different modulation methods trade transmission speed for
>>>> error rate. If the errors increase for some reason, the access point
>>>> will slow things down until the error rate returns to a reasonable
>>>> value.
>>
>>>> I guess you haven't looked at 802.11n, which as 77 modulation coding
>>>> schemes.
>>>> <http://www.airmagnet.com/assets/whitepaper/WP-802.11nPrimer.pdf>
>>>> The faster you go, the more complexicated the mess.
>>
>>>> --
>>>> Jeff Liebermann je...(a)cruzio.com
>>>> 150 Felker St #D http://www.LearnByDestroying.com
>>>> Santa Cruz CA 95060http://802.11junk.com
>>>> Skype: JeffLiebermann AE6KS 831-336-2558
>>
>>> Thanks for the response.
>>
>>> Is this a way of looking at modulation.
>>
>>> The data has to be transmitted, so it is converted into a wave. That
>>> wave is the modulation.
>>
>>> So, at transmission point, the wave is created. At receiver point, it
>>> is demodulated, that is, converted back into data.
>>
>>> The problem with this model is that it doesn't explain how the coding
>>> schemes will vary, depending upon data rate and errors.
>>
>>> Thanks.
>>
>> Hmmm,
>> What is your back? For a starter do you listen to AM radio? Or FM radio?- Hide quoted text -
>>
>> - Show quoted text -
>
> No background in communications
Have a look at this for starters:-
<http://www.veriwave.com/pdf/07/80211_Tutorial.pdf>
From: species8350 on 10 Jan 2010 20:24
On Jan 10, 10:43 am, Bob <b...(a)invalid.invalid> wrote:
> On 09/01/2010 16:38, species8350 wrote:
>
>
>
> > On Jan 9, 5:20 am, Tony Hwang<drago...(a)shaw.ca>  wrote:
> >> species8350 wrote:
> >>> On Jan 7, 5:19 pm, Jeff Liebermann<je...(a)cruzio.com>    wrote:
> >>>> On Thu, 7 Jan 2010 03:58:50 -0800 (PST), species8350
>
> >>>> <not_here.5.species8...(a)xoxy.net>    wrote:
> >>>>> I know that the wifi signal is modulated.
>
> >>>> Yep.
>
> >>>>> Firstly, why does the signal need to be modulated.
>
> >>>> Because it's the modulation that carries the information (data).  No
> >>>> modulation, no data.
>
> >>>>> Secondly regarding g: why are ther so many coding systems used.
>
> >>>> The modulation method varies with the speed of transmission.  Slow
> >>>> speeds have greater range because they have a higher signal to noise
> >>>> ratio for a given signal level.  Higher speeds have progressively
> >>>> lower signal to noise ratios for the same signal level.  802.11g will
> >>>> try to negotiate and establish a modulation method that produces the
> >>>> highest data rate, without having the signal to noise ratio become so
> >>>> low that all that is being received are errors and garbage.  More
> >>>> simply, the different modulation methods trade transmission speed for
> >>>> error rate.  If the errors increase for some reason, the access point
> >>>> will slow things down until the error rate returns to a reasonable
> >>>> value.
>
> >>>> I guess you haven't looked at 802.11n, which as 77 modulation coding
> >>>> schemes.
> >>>> <http://www.airmagnet.com/assets/whitepaper/WP-802.11nPrimer.pdf>
> >>>> The faster you go, the more complexicated the mess.
>
> >>>> --
> >>>> Jeff Liebermann     je...(a)cruzio.com
> >>>> 150 Felker St #D    http://www.LearnByDestroying.com
> >>>> Santa Cruz CA 95060http://802.11junk.com
> >>>> Skype: JeffLiebermann     AE6KS    831-336-2558
>
> >>> Thanks for the response.
>
> >>> Is this a way of looking at modulation.
>
> >>> The data has to be transmitted, so it is converted into a wave. That
> >>> wave is the modulation.
>
> >>> So, at transmission point, the wave is created. At receiver point, it
> >>> is demodulated, that is, converted back into data.
>
> >>> The problem with this model is that it doesn't explain how the coding
> >>> schemes will vary, depending upon data rate and errors.
>
> >>> Thanks.
>
> >> Hmmm,
> >> What is your back? For a starter do you listen to AM radio? Or FM radio?- Hide quoted text -
>
> >> - Show quoted text -
>
> > No background in communications
>
> Have a look at this for starters:-
> <http://www.veriwave.com/pdf/07/80211_Tutorial.pdf>- Hide quoted text -
>
> - Show quoted text -

Will look at the pdf.

Thanks
From: Rich Johnson on 17 Jan 2010 22:25
On 1/8/2010 4:04 AM, species8350 wrote:
> On Jan 7, 5:19 pm, Jeff Liebermann<je...(a)cruzio.com> wrote:
>> On Thu, 7 Jan 2010 03:58:50 -0800 (PST), species8350
>>
>> <not_here.5.species8...(a)xoxy.net> wrote:
>>> I know that the wifi signal is modulated.
>>
>> Yep.
>>
>>> Firstly, why does the signal need to be modulated.
>>
>> Because it's the modulation that carries the information (data). No
>> modulation, no data.
>>
>>> Secondly regarding g: why are ther so many coding systems used.
>>
>> The modulation method varies with the speed of transmission. Slow
>> speeds have greater range because they have a higher signal to noise
>> ratio for a given signal level. Higher speeds have progressively
>> lower signal to noise ratios for the same signal level. 802.11g will
>> try to negotiate and establish a modulation method that produces the
>> highest data rate, without having the signal to noise ratio become so
>> low that all that is being received are errors and garbage. More
>> simply, the different modulation methods trade transmission speed for
>> error rate. If the errors increase for some reason, the access point
>> will slow things down until the error rate returns to a reasonable
>> value.
>>
>> I guess you haven't looked at 802.11n, which as 77 modulation coding
>> schemes.
>> <http://www.airmagnet.com/assets/whitepaper/WP-802.11nPrimer.pdf>
>> The faster you go, the more complexicated the mess.
>>
>> --
>> Jeff Liebermann je...(a)cruzio.com
>> 150 Felker St #D http://www.LearnByDestroying.com
>> Santa Cruz CA 95060http://802.11junk.com
>> Skype: JeffLiebermann AE6KS 831-336-2558
>
> Thanks for the response.
>
> Is this a way of looking at modulation.
>
> The data has to be transmitted, so it is converted into a wave. That
> wave is the modulation.
>
> So, at transmission point, the wave is created. At receiver point, it
> is demodulated, that is, converted back into data.
>
> The problem with this model is that it doesn't explain how the coding
> schemes will vary, depending upon data rate and errors.
>
> Thanks.

Modulation:

Baseband information is converted into electrical information. That
electrical information is then used to change a "carrier" in some way to
convey the information.

So, if you were using morse code, with it's dits and dahs. You could
simply turn the carrier on and off following the duration of the dit or
the dah.

This is the first way we conveyed information. In essence, we varied
the amplitude of the carrier. Once we wanted to carry sound, we
converted it into an electrical signals and used it to directly affect
the amplitude of a carrier wave signal. This was called Amplitude
Modulation. (AM)

Another component of a carrier wave is frequency. We could also vary it
in accordance with an electrically converted audio information. This is
called Frequency Modulation. (FM)

Video signals, (in the USA) were impressed on to a carrier using AM.
(Vestigal side band AM, but still AM). Later schemes allowed the color
information to be modulated onto a 3.58 MHz subcarrier, using the
combination of phase (something a carrier also has) and AM.

This is also how we have moved in data carriers. Using a phase of a
carrier and the amplitude of the carrier we can set up a scheme that
allows multiple bits to be conveyed with a single phase/amplitude change.

This is modulation. Pure and simple. Once we can convey
information/data, we have other opportunities to set protocols for the
transmission of data. Here is where error correction and validation
come into play. In essence here we can control what a "packet" of data
looks like and can use math to be sure the data is valid. Also, we can
sequence the data with it.

Each thing is simple, put together very powerful.


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