5G/NR  -  SSS

  

 

 

 

SSS (Secondary Synchronization Signal)

 

SSS is a specific physical layer signal that is used for radio frame synchronization. It has characterstics as listed below.

  • Mapped to 127 active sub carriers around the center of SSB block located at subcarrier 56~182 (Refer to the structure of SSB)
  • Placed at the third OFDM symbol (symbol 2) within a SSB Burst
  • Made up of 127 m-Sequence Values
  • Used for Downlink Frame Synchronization
  • One of the critical factors determining Physical Cell ID

 

 

Comparision to LTE PSS

 

Following is the PSS sequence generation formula for NR PSS and LTE SSS. Even though the details of LTE sequence generation is not shown here, fundamental nature of NR SSS and LTE SSS is similar. They are both based on m-sequence. However, if you get into the details of the sequence generation process, you will notice that LTE SSS generation is much more complicated than NR. LTE SSS sequence gets different depending on which subframe it is transmitted, whereas NR SSS does not vary with the subframe at which it is transmitted.

 

 

Sequence Generation Algorithm

 

NR SSS sequence is generated by the following formula. Unless you are the one who need to implement this, you may not need to understand every details of this formula. But at least it would be good to know of the major factors to determine the sequence. Followings are some highlights about this sequence.

  • The sequence is determined by both NID(1) and NID(2). In LTE, only NID(1) gets involved in SSS generation.

 

Reference

 

[1] 38.211 NR;Physical channels and modulation(Release 15)