NR-Secondary Synchronization Signal (SSS)

NR-Secondary Synchronization Signal (SSS)

NR-Secondary Synchronization Signal:
5G-NR Secondary Synchronization Signal (SSS) is Physical Layer specific signal and help UE to get subframe boundary. It is similar to PSS, as it is also an m-Sequence.

NR-SSS has following characteristics

• NR-SSS a m-Sequence made up of 127 Values
• SSS 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 Subframe Boundary i.e. Position of 1^st Symbol in a Subframe
• It is a critical factors determining Physical Layer Cell ID and provides N ⁽¹⁾ _ID value for calculation

SSS Sequence Generation:
As per the 3GPP TS 38.211 SSS Sequence is represented by d_SSS ⁽ⁿ⁾ and it is determined with the help of N ⁽¹⁾ _ID and N ⁽²⁾_ID.  It can be generated using following equation.

NR SSS and LTE SSS Comparison:

NR SSS and LTE SSS are very much similar as both are generated using m-Sequence, however when compares sequence generation formula for each, we could notice the LTE SSS generation is much complicated than NR SSS. Reason behind LTE SSS complexity is because LTE SSS gets different sequence depending on the subframe in which it is being transmitted, whereas NR SSS sequence does not depend on the subframe. Below equations show the generation of sequence for both.

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