NR-Primary Synchronization Signal (PSS)

NR-Primary Synchronization Signal (PSS)

5G-NR Primary Synchronization Signal (PSS) is Physical Layer specific signal and help UE to get Radio Frame Boundary. It is type of an m-Sequence which is a special type of LFSR (Linear Feedback Shift Register) sequence provides the longest non-repeating sequence.

NR-PSS has following characteristics

• NR-PSS a m-Sequence made up of 127 Values
• PSS is mapped to 127 active sub carriers around the lower end of the system bandwidth
• It is used by UE for Downlink Frame Synchronization and provides Radio Frame Boundary i.e. Position of 1^st Symbol in a Radio frame
• It is a critical factors determining Physical Layer Cell ID and provides N ⁽²⁾ _ID value for calculation

PSS Sequence Generation:
As per the 3GPP TS 38.211 PSS Sequence is represented by d _PSS ⁽ⁿ⁾ and it is determined by N ⁽²⁾ _ID. It can be generated using following equation.

Following depiction explains it’s each field which help to determines the sequence

NR PSS and LTE PSS Comparison:

While comparing the NR PSS sequence with LTE PSS sequence, the major difference is the type of sequence used for generation. LTE PSS is use Zadoff-Chu sequence while NR PSS use m-Sequence. Below is the comparison for both NR PSS and LTE PSS generation equation.

Another difference is the LTE PSS is mapped to center 72 sub-carriers whereas NR PSS is mapped to 127 active sub-carriers.