Hi all, I started working on FEC for burst FSK system over multipath channel. I want to ask the community here about what type of FEC would be best for such system. Which type of FEC is being used in existing FSK systems? Any pointers to literature and implementation work would be welcomed. -- Sam --------------------------------------- Posted through http://www.DSPRelated.com
FEC for Burst FSK
Started by ●May 20, 2015
Reply by ●May 20, 20152015-05-20
On Wed, 20 May 2015 13:58:47 -0500, "mite_learner" <94814@DSPRelated> wrote:>Hi all, > >I started working on FEC for burst FSK system over multipath channel. I >want to ask the community here about what type of FEC would be best for >such system. Which type of FEC is being used in existing FSK systems? Any >pointers to literature and implementation work would be welcomed.How long is the data block? What is the expected raw error rate and error distribution? Is there a channel interleaver? What is the order of the FSK modulation? All of these things matter, probably plus other stuff I'm not thinking of right now. Eric Jacobsen Anchor Hill Communications http://www.anchorhill.com
Reply by ●May 21, 20152015-05-21
>On Wed, 20 May 2015 13:58:47 -0500, "mite_learner" <94814@DSPRelated> >wrote: > >>Hi all, >> >>I started working on FEC for burst FSK system over multipath channel. >I >>want to ask the community here about what type of FEC would be best >for >>such system. Which type of FEC is being used in existing FSK systems? >Any >>pointers to literature and implementation work would be welcomed. > >How long is the data block? What is the expected raw error rate and >error distribution? Is there a channel interleaver? What is the >order of the FSK modulation? > >All of these things matter, probably plus other stuff I'm not thinking >of right now. > > >Eric Jacobsen >Anchor Hill Communications >http://www.anchorhill.comHi thanks for the response, below are the answers to your questions: data block length is 220 symbols with 4-FSK. there is no channel interleaver yet. I have not calculated the raw error rate yet but it correspondes to around 7dB SNR. --------------------------------------- Posted through http://www.DSPRelated.com
Reply by ●May 21, 20152015-05-21
On Thursday, May 21, 2015 at 3:19:23 AM UTC-4, mite_learner wrote:> >On Wed, 20 May 2015 13:58:47 -0500, "mite_learner" <94814@DSPRelated> > >wrote: > > > >>Hi all, > >> > >>I started working on FEC for burst FSK system over multipath channel. > >I > >>want to ask the community here about what type of FEC would be best > >for > >>such system. Which type of FEC is being used in existing FSK systems? > >Any > >>pointers to literature and implementation work would be welcomed. > > > >How long is the data block? What is the expected raw error rate and > >error distribution? Is there a channel interleaver? What is the > >order of the FSK modulation? > > > >All of these things matter, probably plus other stuff I'm not thinking > >of right now. > > > > > >Eric Jacobsen > >Anchor Hill Communications > >http://www.anchorhill.com > > Hi thanks for the response, below are the answers to your questions: > > data block length is 220 symbols with 4-FSK. there is no channel > interleaver yet. I have not calculated the raw error rate yet but it > correspondes to around 7dB SNR. > --------------------------------------- > Posted through http://www.DSPRelated.comOk, I'm going to ask a question here... If the effectice SNR is 7 dB and it is mostly AWGN, then I understand that you would want an FEC to help. BUT If the effective SNR is 7 dB and that is due mostly to multipath which causes ISI, then is FEC really the correct approach? Would not an equalizer be more appropriate. Mark
Reply by ●May 21, 20152015-05-21
On Thu, 21 May 2015 05:56:22 -0700 (PDT), makolber@yahoo.com wrote:>On Thursday, May 21, 2015 at 3:19:23 AM UTC-4, mite_learner wrote: >> >On Wed, 20 May 2015 13:58:47 -0500, "mite_learner" <94814@DSPRelated> >> >wrote: >> > >> >>Hi all, >> >> >> >>I started working on FEC for burst FSK system over multipath channel. >> >I >> >>want to ask the community here about what type of FEC would be best >> >for >> >>such system. Which type of FEC is being used in existing FSK systems? >> >Any >> >>pointers to literature and implementation work would be welcomed. >> > >> >How long is the data block? What is the expected raw error rate and >> >error distribution? Is there a channel interleaver? What is the >> >order of the FSK modulation? >> > >> >All of these things matter, probably plus other stuff I'm not thinking >> >of right now. >> > >> > >> >Eric Jacobsen >> >Anchor Hill Communications >> >http://www.anchorhill.com >> >> Hi thanks for the response, below are the answers to your questions: >> >> data block length is 220 symbols with 4-FSK. there is no channel >> interleaver yet. I have not calculated the raw error rate yet but it >> correspondes to around 7dB SNR. >> --------------------------------------- >> Posted through http://www.DSPRelated.com > >Ok, I'm going to ask a question here... > >If the effectice SNR is 7 dB and it is mostly AWGN, then I understand that you would want an FEC to help. > >BUT > >If the effective SNR is 7 dB and that is due mostly to multipath which causes ISI, then is FEC really the correct approach? Would not an equalizer be more appropriate. > >Mark >Ooh, you're gonna make him define SNR, aren't you? ;) Eric Jacobsen Anchor Hill Communications http://www.anchorhill.com
Reply by ●May 21, 20152015-05-21
On Thu, 21 May 2015 02:19:20 -0500, "mite_learner" <94814@DSPRelated> wrote:>>On Wed, 20 May 2015 13:58:47 -0500, "mite_learner" <94814@DSPRelated> >>wrote: >> >>>Hi all, >>> >>>I started working on FEC for burst FSK system over multipath channel. >>I >>>want to ask the community here about what type of FEC would be best >>for >>>such system. Which type of FEC is being used in existing FSK systems? >>Any >>>pointers to literature and implementation work would be welcomed. >> >>How long is the data block? What is the expected raw error rate and >>error distribution? Is there a channel interleaver? What is the >>order of the FSK modulation? >> >>All of these things matter, probably plus other stuff I'm not thinking >>of right now. >> >> >>Eric Jacobsen >>Anchor Hill Communications >>http://www.anchorhill.com > >Hi thanks for the response, below are the answers to your questions: > >data block length is 220 symbols with 4-FSK. there is no channel >interleaver yet. I have not calculated the raw error rate yet but it >correspondes to around 7dB SNR.How much of the 440 bits needs to be payload? i.e., how much overhead can you afford for parity? Or are you saying there's 55 bytes of payload? Similar question, though, how long can you afford the coded packet to be? Another way to ask that, perhaps, is how much gain do you need from the FEC? 440 bits is pretty small. As the block size decreases it's harder to get really good gain due to decreasing bit diversity. Hint: I'm just gonna keep asking questions until it becomes clear that there's no easy answer to your question. We haven't even started on how much complexity or latency you can afford yet. Eric Jacobsen Anchor Hill Communications http://www.anchorhill.com
Reply by ●May 21, 20152015-05-21
Eric Jacobsen <eric.jacobsen@ieee.org> wrote:>440 bits is pretty small. As the block size decreases it's harder to >get really good gain due to decreasing bit diversity.I'm not sure what is meant by bit diversity in this context. Polarra et. al, 1998 formulated an expression for channel capacity vs. block size using a sphere-packing bound. There is a JPL technical report on the topic, readilys" googlable. Yes, by the time you have a block length as short as a few hundred bits, capacity is noticably less than longer blocks (say a few thousand bits). But you're still in the range where either turbo or LDPC codes perform close to capacity. Steve
Reply by ●May 21, 20152015-05-21
On Thu, 21 May 2015 17:40:34 +0000 (UTC), spope33@speedymail.org (Steve Pope) wrote:>Eric Jacobsen <eric.jacobsen@ieee.org> wrote: > >>440 bits is pretty small. As the block size decreases it's harder to >>get really good gain due to decreasing bit diversity. > >I'm not sure what is meant by bit diversity in this context. > >Polarra et. al, 1998 formulated an expression for channel >capacity vs. block size using a sphere-packing bound. There >is a JPL technical report on the topic, readilys" googlable. > >Yes, by the time you have a block length as short as a few >hundred bits, capacity is noticably less than longer blocks >(say a few thousand bits). But you're still in the range >where either turbo or LDPC codes perform close to capacity. > >SteveIt's tough to achieve. When we did the LDPC codes for 802.16 and 802.11n, we only defined codes down to a certain block size because the existing, plain Convolutional Code with a single-pass Viterbi decoder would do just as well at that size or smaller blocks. It was counter-productive to use the LDPC for smaller blocks. The drop in capacity, and practical performance, is due to the reduction in mutual information as the number of bits decreases. This is what is meant by "bit diversity". If there aren't enough bits to get mutual information from, you just can't do as good of a job with error correction. Eric Jacobsen Anchor Hill Communications http://www.anchorhill.com
Reply by ●May 21, 20152015-05-21
Eric Jacobsen <eric.jacobsen@ieee.org> wrote:>(Steve Pope) wrote:>>Eric Jacobsen <eric.jacobsen@ieee.org> wrote:>>Polarra et. al, 1998 formulated an expression for channel >>capacity vs. block size using a sphere-packing bound. There >>is a JPL technical report on the topic, readilys" googlable.>>Yes, by the time you have a block length as short as a few >>hundred bits, capacity is noticably less than longer blocks >>(say a few thousand bits). But you're still in the range >>where either turbo or LDPC codes perform close to capacity.>It's tough to achieve. When we did the LDPC codes for 802.16 and >802.11n, we only defined codes down to a certain block size because >the existing, plain Convolutional Code with a single-pass Viterbi >decoder would do just as well at that size or smaller blocks. It was >counter-productive to use the LDPC for smaller blocks.Hmm. Did you evaluate turbo codes? According to the Polarra result they should outperform convolutional codes at a bit length of 440 by a couple dB. See Figure 11 in "TMO Progress Report 42-133", which is on the JPL website. Usually LDPC codes and turbo codes work approximately equally well, but it's possible there are block size, code rate, and demodulator distance metric combinations where one underperforms the other. In parallel-tone modems (as I prefer calling them) the tone interleaver figures in as well. Steve
Reply by ●May 21, 20152015-05-21
Am 20.05.2015 um 20:58 schrieb mite_learner:> Hi all, > > I started working on FEC for burst FSK system over multipath channel. I > want to ask the community here about what type of FEC would be best for > such system. Which type of FEC is being used in existing FSK systems? Any > pointers to literature and implementation work would be welcomed. > > -- > Sam > --------------------------------------- > Posted through http://www.DSPRelated.com >Interesting question I am not an expert here but I wonder if the modulation scheme matters at all for the choice of the FEC. Things that matter are: - Channel model / conditions - Bandwidth - Target Bitrate - Framing / Interleaving But I can not think of a reason why one would use a different FEC for FSK than for QPSK, but maybe one of the experts in the groups know better. Greetz, Sebastian
