Hi I have a question regarding primary sync signal in LTE.

It is generated in frequency domain and its length is 63. How to convert this signals frim frequency to time domain. Should I use IFFT? what is the length of IFFT and the signal in time domain?



The PSS signal is generated based on Zadoff-Chu sequence and is mapped to the central 62 sub-carriers apart from DC sub-carrier as explained here. If you want to view the PSS alone, leaving aside other subcarriers in the PSS containing OFDM symbols then yes, you'll have to do a 64 IFFT on the length 63 Zadoff-Chu + DC symbols. It is worth nothing that on the receiver side, synchronization is achieved by locking on to the central 63 subcarriers using a 64 point FFT.

  • $\begingroup$ Thanks for the answer. I have several more questions. Hope smb will help me. 1) For example I have a BW=20MHz, why the sampling rate is 30.7MHz? why not 40MHz? 2) How can I detect what type of cyclic prefix is used? normal or extended? Where in signal this info is? Without knowing the type of prefix I cannot discard it before FFT. 3) Ok. I found the PSS signal. I would help me to detect the symbol boundaries, rigth? Rigth now I have several peaks on my plot. How to detect the fractional frequency offset? Many thanks in advance -Marcus $\endgroup$ – dcs Jun 3 '15 at 13:21
  • $\begingroup$ @dcs 1) It is because OFDM uses complex signals which does't exhibit conjugate symmetry in the frequency domain unlike real signals. The discussion in this thread should answer your question. 2) The length of the cyclic prefix is determined when the UE scans for PSS and SSS. From the symbol length determined from PSS and SSS it can determine whether normal or extended CP is used. $\endgroup$ – Naveen Jun 3 '15 at 21:17
  • $\begingroup$ continued.. 3) I'm not sure if a specific FFO estimation scheme is specified in the 3GPP spec. One way to do it is by utilizing the CP along with the PSS. Look into this paper for details. $\endgroup$ – Naveen Jun 3 '15 at 21:17
  • $\begingroup$ @dcs Does the above answer your questions? $\endgroup$ – Naveen Jun 4 '15 at 14:58

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