[digitalradio] Re: OFDM data is Emission Designator D1D
OFDM squeezes more carriers into the same space by making the carriers orthogonal to their next door neighbors. Its not only the next door neighbors but ALL the carriers. If you look at the the ofdm signal with a correctly timed FFT with exactly a symbol time length, there is NO overlap of the carriers. That is how domodualtion is done. But if you look at the the ofdm signal with an fft of incorrect length, or not proprly timed (including phase-change symbol boundaries) the carriers will overlap quite a bit ! Your waterfall display is such a randomly timed fft of incorrect lenght. The advantage of this system ? each subcarrier can change it's phase (and amplitude) much faster than a carrier of limited bandwidth could do, but during symbol integration time there is no carrier overlap, the orthogonality remains perfect. One example of a bandwidth limited subcarrier system is RDFT. in contrast OFDM does NOT limit the subcarrier bandwidth !
Re: [digitalradio] Re: OFDM data is Emission Designator D1D
I'm aware of the definition of orthogonality. The document originally referenced that defined Pactor-3 made it obvious that the sidebands overlapped. My email was to make the point that the Pactor-3 subcarriers have to be orthogonal to make it work and therefore Pactor-3 must be OFDM -- something that others disputed. 73, John KD6OZH - Original Message - From: Rick Karlquist To: digitalradio@yahoogroups.com Cc: digitalradio@yahoogroups.com Sent: Sunday, November 26, 2006 07:28 UTC Subject: Re: [digitalradio] Re: OFDM data is Emission Designator D1D You are still confused about the definition of orthogonal. Before Orthogonal Frequency Domain Multiplex (OFDM), there are (Non-orthogonal) Frequency Domain Multiplex (FDM). It too used each sub carrier to send an independent stream of bits. The sub carriers were NOT orthogonal. They didn't need to be because their sidebands did not overlap. OFDM squeezes more carriers into the same space by making the carriers and their modulation orthogonal to their next door neighbors. This allows some overlap. The subcarriers in Pactor-3 may indeed be orthogonal (I don't know) but that cannot be deduced from the fact that they carry independent streams of bits. Rick N6RK John B. Stephensen wrote: I should have said that the subcarriers must be orthogonal because Pactor-3 uses each subcarrier to send an independent stream of bits. In someone else's email they verified that the subcarriers are indeed orthogonal. 73, John KD6OZH - Original Message - From: Rick Karlquist To: digitalradio@yahoogroups.com Cc: digitalradio@yahoogroups.com Sent: Wednesday, November 22, 2006 19:49 UTC Subject: Re: [digitalradio] Re: OFDM data is Emission Designator D1D John B. Stephensen wrote: its orthogonal because the state of each subcarrier is independent of the state of the others. John KD6OZH That is NOT the definition of orthogonal. Rick N6RK
Re: [digitalradio] Re: OFDM data is Emission Designator D1D
I should have said that the subcarriers must be orthogonal because Pactor-3 uses each subcarrier to send an independent stream of bits. In someone else's email they verified that the subcarriers are indeed orthogonal. 73, John KD6OZH - Original Message - From: Rick Karlquist To: digitalradio@yahoogroups.com Cc: digitalradio@yahoogroups.com Sent: Wednesday, November 22, 2006 19:49 UTC Subject: Re: [digitalradio] Re: OFDM data is Emission Designator D1D John B. Stephensen wrote: its orthogonal because the state of each subcarrier is independent of the state of the others. John KD6OZH That is NOT the definition of orthogonal. Rick N6RK
Re: [digitalradio] Re: OFDM data is Emission Designator D1D
You are still confused about the definition of orthogonal. Before Orthogonal Frequency Domain Multiplex (OFDM), there are (Non-orthogonal) Frequency Domain Multiplex (FDM). It too used each sub carrier to send an independent stream of bits. The sub carriers were NOT orthogonal. They didn't need to be because their sidebands did not overlap. OFDM squeezes more carriers into the same space by making the carriers and their modulation orthogonal to their next door neighbors. This allows some overlap. The subcarriers in Pactor-3 may indeed be orthogonal (I don't know) but that cannot be deduced from the fact that they carry independent streams of bits. Rick N6RK John B. Stephensen wrote: I should have said that the subcarriers must be orthogonal because Pactor-3 uses each subcarrier to send an independent stream of bits. In someone else's email they verified that the subcarriers are indeed orthogonal. 73, John KD6OZH - Original Message - From: Rick Karlquist To: digitalradio@yahoogroups.com Cc: digitalradio@yahoogroups.com Sent: Wednesday, November 22, 2006 19:49 UTC Subject: Re: [digitalradio] Re: OFDM data is Emission Designator D1D John B. Stephensen wrote: its orthogonal because the state of each subcarrier is independent of the state of the others. John KD6OZH That is NOT the definition of orthogonal. Rick N6RK
[digitalradio] Re: OFDM data is Emission Designator D1D
relevant to its classification to OFDM. Which it is NOT. The carriers are on 120 Hz centers and the baud times are 100 Hz. Because the baud time is not commensurate with angular frequency of the carriers, the dot products are not zero and therefore, they are NOT orthogonal in PACTOR-III. I do not agree. 100 baud means 10ms/symbol, of which 8.33ms symbol time, 1.66ms guard interval. Carrier spacing is 1000ms/8.33ms = 120hz. The carrier spacing is orthogonal to the integration time, and not to integration time + guard intervall. It's exacly like all the other ofdm systems.
Re: [digitalradio] Re: OFDM data is Emission Designator D1D
Thank you for the note. If it is designed the way you say (and this is not contraindicated by the document I provided a link to) then the bauds in the detector will be orthogonal. 73's Bob N4HY cesco12342000 wrote: relevant to its classification to OFDM. Which it is NOT. The carriers are on 120 Hz centers and the baud times are 100 Hz. Because the baud time is not commensurate with angular frequency of the carriers, the dot products are not zero and therefore, they are NOT orthogonal in PACTOR-III. I do not agree. 100 baud means 10ms/symbol, of which 8.33ms symbol time, 1.66ms guard interval. Carrier spacing is 1000ms/8.33ms = 120hz. The carrier spacing is orthogonal to the integration time, and not to integration time + guard intervall. It's exacly like all the other ofdm systems. Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Yahoo! Groups Links -- AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. ARRL SDR WG Chair If you board the wrong train, it is no use running along the corridor in the other direction. - Dietrich Bonhoffer
