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

# Multicarrier modulation scheme vs FSK

Started by ●January 14, 2007

Reply by ●January 14, 20072007-01-14

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

Reply by ●January 14, 20072007-01-14

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. > > > -- > OliWhat do you mean by the statement " each carrier is modulated by an independent symbol-stream." ? -- Td

Reply by ●January 15, 20072007-01-15

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

Reply by ●June 22, 20072007-06-22

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 tobe>> > 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 anindependent>> > 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 > >

Reply by ●June 22, 20072007-06-22

>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 datato>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

Reply by ●June 22, 20072007-06-22

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

Reply by ●June 25, 20072007-06-25

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 > >

Reply by ●June 25, 20072007-06-25

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

Reply by ●June 25, 20072007-06-25

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