Does anyone know about or can refer to me any work/papers related to TDoA (Time Differential of Arrival) of OFDM signals?. I would like to learn more about current and new algorithms for TDoA estimation that take advantage of the multi-carrier structure of OFDM. Thanks in advance...

# TDoA in OFDM

Started by ●February 13, 2007

Reply by ●May 8, 20072007-05-08

So maybe TDoA estimation of OFDM signals is a trivial problem no one is interested in?? Is this topic already covered or maybe applying CDMA methods (i.e. Generalized Correlation Methods) is good enough? I have searched about TDoA of OFDM signals and can hardly find anything. I can tell from what I have read that OFDM physical characteristics (multicarrier) may allow implementation of more efficient and accurrate TDoA estimation algorithms using GCC method and/or Bispectral methods but my mathematics knowledge on these topics are slowing me down. Any papers, references or books that have related information would be great and appreciated. _____________________________________ Do you know a company who employs DSP engineers? Is it already listed at http://dsprelated.com/employers.php ?

Reply by ●May 9, 20072007-05-09

On May 8, 9:54 pm, "ryujin_ssdt" <hsan...@gmail.com> wrote:> So maybe TDoA estimation of OFDM signals is a trivial problem no one is > interested in?? Is this topic already covered or maybe applying CDMA > methods (i.e. Generalized Correlation Methods) is good enough? > > I have searched about TDoA of OFDM signals and can hardly find anything. I > can tell from what I have read that OFDM physical characteristics > (multicarrier) may allow implementation of more efficient and accurrate > TDoA estimation algorithms using GCC method and/or Bispectral methods but > my mathematics knowledge on these topics are slowing me down. > > Any papers, references or books that have related information would be > great and appreciated. >The mean-square error of the best linear unbiased estimator of signal delay is inversely proportional to the bandwidth of the signal. Can you make a guess as to why using OFDM may be an issue here? Julius

Reply by ●May 9, 20072007-05-09

>On May 8, 9:54 pm, "ryujin_ssdt" <hsan...@gmail.com> wrote: >> So maybe TDoA estimation of OFDM signals is a trivial problem no oneis>> interested in?? Is this topic already covered or maybe applying CDMA >> methods (i.e. Generalized Correlation Methods) is good enough? >> >> I have searched about TDoA of OFDM signals and can hardly findanything. I>> can tell from what I have read that OFDM physical characteristics >> (multicarrier) may allow implementation of more efficient andaccurrate>> TDoA estimation algorithms using GCC method and/or Bispectral methodsbut>> my mathematics knowledge on these topics are slowing me down. >> >> Any papers, references or books that have related information would be >> great and appreciated. >> > >The mean-square error of the best linear unbiased estimator >of signal delay is inversely proportional to the bandwidth >of the signal. Can you make a guess as to why using OFDM >may be an issue here? > >Julius > >My guess is that since OFDM is spectral efficient it can transmit a lot of data using a small bandwidth. This translates to less accurrate estimation ot delays. Does this mean that OFDM cannot be used for localization purposes?? _____________________________________ Do you know a company who employs DSP engineers? Is it already listed at http://dsprelated.com/employers.php ?

Reply by ●May 9, 20072007-05-09

On May 9, 8:18 am, "ryujin_ssdt" <hsan...@gmail.com> wrote:> My guess is that since OFDM is spectral efficient it can transmit a lot of > data using a small bandwidth. This translates to less accurrate estimation > ot delays. > > Does this mean that OFDM cannot be used for localization purposes??Let's be clear here: OFDM is a communication scheme, not a localization scheme. It is simply a signaling format. Now let's go back to how people do delay estimation in a typical single-carrier, narrowband communication system. When the modulation symbols are known, the answer is straightforward: it's based on finding the maximum of the correlation in the time domain. Of course, an equivalent operation can be done in the frequency domain. And as I said, the quality is better when the bandwidth is wider. When the modulation symbols are not known exactly, either they are first decoded and then used to estimate the delay (or iteratively, a la expectation- maximization), or they are considered to be a nuisance parameter. Most of what I think is the good research in the area try to solve this problem, or side step it by finding a good "training sequence of symbols" to use to get good estimation performance. There's a bunch of really good papers by Georghiades et al. Suppose now you want to do the same for OFDM. OK, that is fine. But in order to get quality proportional to your *overall* bandwidth, you have to consider all the tones all at once. And I said above that correlation can be computed either in time or frequency domain. There is no advantage to using OFDM. Think of it as if you were *designing* a signal that you wish to send to get the best time delay estimate. It is already known that the best signal is the one with the most narrow autocorrelation. So what does it matter if the signal were an OFDM signal or not? Hope this clarifies things a bit. Julius

Reply by ●May 9, 20072007-05-09

ryujin_ssdt wrote:> So maybe TDoA estimation of OFDM signals is a trivial problem no one is > interested in?? Is this topic already covered or maybe applying CDMA > methods (i.e. Generalized Correlation Methods) is good enough?OFDM is a sort of modulation. OFDM allows building simple yet efficient receivers for the wideband signals; that's the only advantage of it. The task of estimating TDoA is unrelated to the modulation. The main parameter is the autocorrelation function of the signal. For TDoA estimation, it would be good to have the zonde signal with the constant envelope. The OFDM signal is very inconvenient for that purpose.> I have searched about TDoA of OFDM signals and can hardly find anything. I > can tell from what I have read that OFDM physical characteristics > (multicarrier) may allow implementation of more efficient and accurrate > TDoA estimation algorithms using GCC method and/or Bispectral methods but > my mathematics knowledge on these topics are slowing me down.You can compute the autocorrelation in time domain or in frequency domain. It is a matter of preference. The width of the peak of ACF is determined by the bandwidth of the signal. It does not matter if the signal is formed by OFDM or by any other method. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com