Forums

Multicarrier modulation scheme vs FSK

Started by koolguyuf January 14, 2007
Hey,

What is the difference between multicarrier modulation and FSK
(Frequency Shift  Keying)?

Can OFDM considered to be a hybrid of the two?

Thanks
TD

On Sun, 14 Jan 2007 21:56:23 -0000, koolguyuf <tdgoswami@gmail.com> wrote:
> Hey, > > What is the difference between multicarrier modulation and FSK > (Frequency Shift Keying)?
FSK modulates the carrier frequency according to the digital data to be transmitted (so a "0" might correspond to 10kHz, and a "1" might correspond to 11kHz, for instance). Multicarrier modulation means a scheme that uses multiple carrier frequencies simultaneously; each carrier is modulated by an independent symbol-stream.
> Can OFDM considered to be a hybrid of the two?
No. OFDM is a form of multi-carrier modulation, but isn't (normally) based on FSK. -- Oli
Oli Charlesworth wrote:
> On Sun, 14 Jan 2007 21:56:23 -0000, koolguyuf <tdgoswami@gmail.com> wrote: > > Hey, > > > > What is the difference between multicarrier modulation and FSK > > (Frequency Shift Keying)? > > FSK modulates the carrier frequency according to the digital data to be > transmitted (so a "0" might correspond to 10kHz, and a "1" might > correspond to 11kHz, for instance). > > Multicarrier modulation means a scheme that uses multiple carrier > frequencies simultaneously; each carrier is modulated by an independent > symbol-stream. > > > > Can OFDM considered to be a hybrid of the two? > > No. OFDM is a form of multi-carrier modulation, but isn't (normally) > based on FSK. > > > -- > Oli
What do you mean by the statement " each carrier is modulated by an independent symbol-stream." ? -- Td
Since each of the OFDM sub-carriers are orthogonal, they can carry data
without interference (at least in theory), with each other. You can
consider them to be parallel channels. Hence each sub-carrier can carry
a data stream.

Sudhir


koolguyuf wrote:
> Oli Charlesworth wrote: > > On Sun, 14 Jan 2007 21:56:23 -0000, koolguyuf <tdgoswami@gmail.com> wrote: > > > Hey, > > > > > > What is the difference between multicarrier modulation and FSK > > > (Frequency Shift Keying)? > > > > FSK modulates the carrier frequency according to the digital data to be > > transmitted (so a "0" might correspond to 10kHz, and a "1" might > > correspond to 11kHz, for instance). > > > > Multicarrier modulation means a scheme that uses multiple carrier > > frequencies simultaneously; each carrier is modulated by an independent > > symbol-stream. > > > > > > > Can OFDM considered to be a hybrid of the two? > > > > No. OFDM is a form of multi-carrier modulation, but isn't (normally) > > based on FSK. > > > > > > -- > > Oli > > > > What do you mean by the statement " each carrier is modulated by an > independent > symbol-stream." ? > -- > Td
I guess I had a follow-up question to this. I always thought:
FSK + MCM = OFDM
However, Now I'm not convinced that to be true.

I have a RF transceiver that support 2-level FSK as the 
modulation scheme. What do I need to do to generate OFDM 
signals. Consequently, I would like to use OFDMA as my 
multiple access scheme as well. Any thoughts on how I 
can go about doing that?

>Since each of the OFDM sub-carriers are orthogonal, they can carry data >without interference (at least in theory), with each other. You can >consider them to be parallel channels. Hence each sub-carrier can carry >a data stream. > >Sudhir > > >koolguyuf wrote: >> Oli Charlesworth wrote: >> > On Sun, 14 Jan 2007 21:56:23 -0000, koolguyuf <tdgoswami@gmail.com>
wrote:
>> > > Hey, >> > > >> > > What is the difference between multicarrier modulation and FSK >> > > (Frequency Shift Keying)? >> > >> > FSK modulates the carrier frequency according to the digital data to
be
>> > transmitted (so a "0" might correspond to 10kHz, and a "1" might >> > correspond to 11kHz, for instance). >> > >> > Multicarrier modulation means a scheme that uses multiple carrier >> > frequencies simultaneously; each carrier is modulated by an
independent
>> > symbol-stream. >> > >> > >> > > Can OFDM considered to be a hybrid of the two? >> > >> > No. OFDM is a form of multi-carrier modulation, but isn't
(normally)
>> > based on FSK. >> > >> > >> > -- >> > Oli >> >> >> >> What do you mean by the statement " each carrier is modulated by an >> independent >> symbol-stream." ? >> -- >> Td > >
>I guess I had a follow-up question to this. I always thought: >FSK + MCM = OFDM >However, Now I'm not convinced that to be true. > >I have a RF transceiver that support 2-level FSK as the >modulation scheme. What do I need to do to generate OFDM >signals. Consequently, I would like to use OFDMA as my >multiple access scheme as well. Any thoughts on how I >can go about doing that? > >>Since each of the OFDM sub-carriers are orthogonal, they can carry data >>without interference (at least in theory), with each other. You can >>consider them to be parallel channels. Hence each sub-carrier can carry >>a data stream. >> >>Sudhir >> >> >>koolguyuf wrote: >>> Oli Charlesworth wrote: >>> > On Sun, 14 Jan 2007 21:56:23 -0000, koolguyuf <tdgoswami@gmail.com> >wrote: >>> > > Hey, >>> > > >>> > > What is the difference between multicarrier modulation and FSK >>> > > (Frequency Shift Keying)? >>> > >>> > FSK modulates the carrier frequency according to the digital data
to
>be >>> > transmitted (so a "0" might correspond to 10kHz, and a "1" might >>> > correspond to 11kHz, for instance). >>> > >>> > Multicarrier modulation means a scheme that uses multiple carrier >>> > frequencies simultaneously; each carrier is modulated by an >independent >>> > symbol-stream. >>> > >>> > >>> > > Can OFDM considered to be a hybrid of the two? >>> > >>> > No. OFDM is a form of multi-carrier modulation, but isn't >(normally) >>> > based on FSK. >>> > >>> > >>> > -- >>> > Oli >>> >>> >>> >>> What do you mean by the statement " each carrier is modulated by an >>> independent >>> symbol-stream." ? >>> -- >>> Td >> >> > > >
FSK + MCM = OFDM (without guard interval) iff the frequency difference between two adjacent tones is the inverse of the symbol duration. LBB
On Jun 22, 6:59 am, "asgt97" <asg...@hotmail.com> wrote:
> I guess I had a follow-up question to this. I always thought: > FSK + MCM = OFDM > However, Now I'm not convinced that to be true. > > I have a RF transceiver that support 2-level FSK as the > modulation scheme. What do I need to do to generate OFDM > signals. Consequently, I would like to use OFDMA as my > multiple access scheme as well. Any thoughts on how I > can go about doing that? >
I'd guess that you can't do it with that equipment. John
I've realized that I cant do it. But I'm trying to come up with  
a formal reasoning for why that is the case? the general question 
would be if I can use FSK and then divide the channel into orthogonal
sub-carriers. 

What would be a textbook answer to this question.

>On Jun 22, 6:59 am, "asgt97" <asg...@hotmail.com> wrote: >> I guess I had a follow-up question to this. I always thought: >> FSK + MCM = OFDM >> However, Now I'm not convinced that to be true. >> >> I have a RF transceiver that support 2-level FSK as the >> modulation scheme. What do I need to do to generate OFDM >> signals. Consequently, I would like to use OFDMA as my >> multiple access scheme as well. Any thoughts on how I >> can go about doing that? >> > >I'd guess that you can't do it with that equipment. > >John > >
On Jun 25, 12:48 pm, "asgt97" <asg...@hotmail.com> wrote:
> I've realized that I cant do it. But I'm trying to come up with > a formal reasoning for why that is the case? the general question > would be if I can use FSK and then divide the channel into orthogonal > sub-carriers. >
When you say "RF transceiver for 2-level FSK", what exactly did you mean? What input does it accept (digital, analog, what format) and what output does it produce? It may be possible to do what you want, depending on how restricted the input-output relationship is. Julius
On Jun 25, 1:48 pm, "asgt97" <asg...@hotmail.com> wrote:
> I've realized that I cant do it. But I'm trying to come up with > a formal reasoning for why that is the case? the general question > would be if I can use FSK and then divide the channel into orthogonal > sub-carriers. > > What would be a textbook answer to this question. > >
The FSK transmitter outputs a single tone at a time. OFDM is a whole bunch of simultaneous tones. Totally different hardware. John