Secondary synchronization signal SSS 5G NR

Secondary synchronization signal NR

After the UE has detected PSS and acquired symbol timing and initial frequency synchronization, it detects SSS which carries the physical cell identity.

Secondary synchronization Signal

SSS signal

  • 336 different sequences called Physical-Layer Cell-Identity groups (0-335)
  • Ν1(ID)in 3GPP  PhysicalLayerCellIdGroup
  • Secondary synchronization signal is based on maximum length sequences (Gold-sequences)
  • The NR-SSS carries the information including the radio frame timing and the cell ID group
    SS/PBCH
  • The NR-SSS detection is done based on the relative position between the NR-PSS and the NR-SSS.
  • Since the SSS is located on the same frequency location as PSS and one OFDM symbol apart, the UE may perform either non-coherent or coherent detection using channel estimates based on PSS.
  • Furthermore, since there are 1008 NR cell IDs and 3 NR PSSs, we need a set of 1008 NR SSS sequences that can be divided into 3 sub-sets, each with 1008/3 = 336 NR SSS sequences associated to one of the three NR PSS sequences.

Sequence generation:

The sequence dsss(n)  for the secondary synchronization signal is defined below.

Sequence generation

where 𝑥0(𝑘) and 𝑥1(𝑘) (𝑘=0, 1, ⋅ ⋅ ⋅ , 126) are two length-127 (binary) m-sequences and 𝑚0 and 𝑚1 are their corresponding cyclic shift values determined by the cell ID.

The sequence of symbols dsss(0) . . . dsss(126) containing the secondary synchronization signal is scaled by a factor of βSSS and is mapped to resource elements (k,l)  in increasing order of k where k and l represent the frequency and time indices,

 

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