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5G NR – Primary Synchronization Signal(PSS)

Main pillar of the NR is a Synchronization Signal and PBCH block (SS/PBCH block).

SSB Block contains

  1. PSS 2 SSS PBCH

In this article , I am going to discuss about PSS.

Lets see the PCI formula below.

Lets first understand LTE PSS location in sub frame.

For FDD frame, PSS is allocated on symbol 6 (last symbol) of slot 0 (subframe 0) and slot 10 (subframe 5) of each radio frame.

And, for TDD frame, PSS is allocated on symbol 2 of slot 2, subframe1 and slot 12 subframe 6 of each radio frame.

NR PSS is also same like LTE PSS, where we use as Physical layer reference signal, this we use to get radio frame boundary for device & to detect the cell ID sector N(2,ID)

Instead of using Zadoff-Chu sequences as in LTE,

NR adopted a frequency domain based BPSK M-sequence. M-sequence was selected because of not having time offset – frequency offset ambiguity present with Zadoff-Chu sequences.

LTE PSS consist of one of three 62 symbols zadoff chu sequence and is mapped to the central 72 subcarriers with a guard band of 10 subcarriers.

5G NR PSS Consist of one of three 127 symbols m-sequence
5G NR PSS is allocated on the first symbol of each SSB

Similar to LTE, NR also have 3 PSS sequence ,

The 3 possible m-sequences for the PSS are defined as follows

Mapping of PSS within an SS/PBCH block

The UE shall assume the sequence of symbols dpss(0) …………….dpss(126) constituting the primary synchronization signal to be scaled by a factor  to conform to the Bpss power allocation and mapped to resource elements(k,l) in increasing order of k where K & L and which represent the frequency and time indices, respectively, within one SS/PBCH block.

3GPP 38.211- Table 7.4.3.1-1: Resources within an SS/PBCH block for PSS, SSS, PBCH, and DM-RS for PBCH
PSS sequence mapping to the resource elements

Comments

  • satya
    July 28, 2020

    Please correct me if I am wrong ?
    In the diagram if we take either SCS=15KHZ or 30KHz, number of symbols in subframe is always 14 in all NR numerologies. But in first diagram mentioned as 7 symbols for slot.

  • satya
    July 28, 2020

    sorry .. please ignore above comment as above diagram for LTE and not for NR.

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