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Why PSS and SSS are placed adjacent in FDD but not in TDD?

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Why PSS and SSS are placed adjacent in FDD but not in TDD?
posted Apr 24, 2016 by Bhaskar Kalaria

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Why these two are placed side by side within "first time slot" of 0th and 5th sub frame of a radio frame ?
Is it due to any mathematical calculation or something else ?

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I know PSS and SSS will occupy last and penultimate symbol simultaneously in slot#0 and slot#10. How can we ensure they are occupying that positions only? And what is the reason behind those particular positions?

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I understand that according to the standard a 64 FFT is used by the UE for cell search for all Bandwidth configurations(see section 2.2.1 page 7 in the below document). Suppose we are transmitting at 20 MHz which means we do a 2048 FFT on the transmitter side for the whole resource grid, including the 6th and 7th symbols corresponding to PSS and SSS in Subframe 0 and 5. In this case how is it possible for UE to do cell search using 64-FFT. Although PSS and SSS use only the central 62 subcarriers, shouldn't the UE use the same FFT length used in the transmitter side ? Also, how is the DL resource grid processed by the UE ?Does the UE extract Symbols 6,7 of Subframes 0,5 and process it separately with 64-FFT(after low pass filtering) while using 2048 FFT for the rest of the symbols ?

http://cdn.rohde-schwarz.com/dl_downloads/dl_application/application_notes/1ma150/1MA150_0E_cell_searchselection_in_LTE.pdf

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