Equalization without a training sequence
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From: Steve Pope on 16 May 2010 21:11 Randy Yates <yates(a)ieee.org> wrote: >HardySpicer <gyansorova(a)gmail.com> writes: >> I have seen many IEEE papers on what is now called Blind Equalization >> where a PBRS sequence is not needed for training. This is for muliple- >> channel (multivariable) problems. A colleague of mine says this is >> just academic rubbish and not used in practice. true or false and if >> true would there be any advantage? >For old-style single-carrier systems like QPSK, QAM, etc., it is NOT >rubbish at all. John Treichler was a "codiscoverer" of the >constant-modulus algorithm and it was (is?) used extensively in the comm >systems developed there at Applied Signal Technology, and I'm sure many >other places as well. Of course, but I think the question had to do with multiple-channel systems. There are plenty of single-channel systems doing blind equalization -- V.x telephone modems, single-carrier modes of 802.11/11b ... almost any single-carrier single-channel system has a tracking equalizer although some rely on pilots and are therefore not "blind". The question, I think, if I project correctly how HardySpicer may be paraphrasing his friend, is if you have MIMO or similar do you give up on trying to track it. The 802.3 examples referenced upthread may be an example of cases where you do in fact do this, on a multichannel system. Steve
From: Randy Yates on 16 May 2010 21:19 spope33(a)speedymail.org (Steve Pope) writes: > Randy Yates <yates(a)ieee.org> wrote: > >>HardySpicer <gyansorova(a)gmail.com> writes: > >>> I have seen many IEEE papers on what is now called Blind Equalization >>> where a PBRS sequence is not needed for training. This is for muliple- >>> channel (multivariable) problems. A colleague of mine says this is >>> just academic rubbish and not used in practice. true or false and if >>> true would there be any advantage? > >>For old-style single-carrier systems like QPSK, QAM, etc., it is NOT >>rubbish at all. John Treichler was a "codiscoverer" of the >>constant-modulus algorithm and it was (is?) used extensively in the comm >>systems developed there at Applied Signal Technology, and I'm sure many >>other places as well. > > Of course, but I think the question had to do with multiple-channel > systems. There are plenty of single-channel systems doing blind > equalization -- V.x telephone modems, single-carrier modes of > 802.11/11b ... almost any single-carrier single-channel system > has a tracking equalizer although some rely on pilots and are > therefore not "blind". > > The question, I think, if I project correctly how HardySpicer may > be paraphrasing his friend, is if you have MIMO or similar do > you give up on trying to track it. The problem being computational complexity? Otherwise couldn't you just do single-channel blind on each of the channels? > The 802.3 examples referenced upthread may be an example of > cases where you do in fact do this, on a multichannel system. What, give up? -- Randy Yates % "Watching all the days go by... Digital Signal Labs % Who are you and who am I?" mailto://yates(a)ieee.org % 'Mission (A World Record)', http://www.digitalsignallabs.com % *A New World Record*, ELO
From: Eric Jacobsen on 17 May 2010 10:06 On 5/16/2010 6:19 PM, Randy Yates wrote: > spope33(a)speedymail.org (Steve Pope) writes: > >> Randy Yates<yates(a)ieee.org> wrote: >> >>> HardySpicer<gyansorova(a)gmail.com> writes: >> >>>> I have seen many IEEE papers on what is now called Blind Equalization >>>> where a PBRS sequence is not needed for training. This is for muliple- >>>> channel (multivariable) problems. A colleague of mine says this is >>>> just academic rubbish and not used in practice. true or false and if >>>> true would there be any advantage? >> >>> For old-style single-carrier systems like QPSK, QAM, etc., it is NOT >>> rubbish at all. John Treichler was a "codiscoverer" of the >>> constant-modulus algorithm and it was (is?) used extensively in the comm >>> systems developed there at Applied Signal Technology, and I'm sure many >>> other places as well. >> >> Of course, but I think the question had to do with multiple-channel >> systems. There are plenty of single-channel systems doing blind >> equalization -- V.x telephone modems, single-carrier modes of >> 802.11/11b ... almost any single-carrier single-channel system >> has a tracking equalizer although some rely on pilots and are >> therefore not "blind". >> >> The question, I think, if I project correctly how HardySpicer may >> be paraphrasing his friend, is if you have MIMO or similar do >> you give up on trying to track it. > > The problem being computational complexity? Otherwise couldn't > you just do single-channel blind on each of the channels? > >> The 802.3 examples referenced upthread may be an example of >> cases where you do in fact do this, on a multichannel system. > > What, give up? I don't have citations handy, but there've been some papers on what is essentially blind equalization for multi-carrier, done as you suggest using slicer error on non-pilot subcarriers. One issue is complexity, since a multi-tap EQ on a subcarrier in a multi-carrier system generally defeats the purpose of a multi-carrier system. If a multi-carrier system is being used as expected such that each subcarrier is flat-faded then the trick is just to sort out the gain constant for each subcarrier. If there's no AM in the signal this can be done without too much trouble, e.g., if the subcarriers are modulated with something like BPSK or QPSK. It's not that hard to run an independent AGC on each subcarrier if the signal is constant modulus. If there's AM, though, like with QAM, it's tough to tell gain deviations due to the channel from AM modulation. So I don't think it would be impossible to build a blind multi-carrier system if the modulation were restricted to something like QPSK. I don't think it'd necessarily be easy, especially if the coherence time of the channel is short. -- Eric Jacobsen Minister of Algorithms Abineau Communications http://www.abineau.com
From: Alexander Petrov on 17 May 2010 10:58 For example, a blind criterion can easily be used in the FMT multi-carrier modulation for subcarrier equalization or multiple inputs channel estimation.
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