Secondary Synchronization Signal, is a crucial component of LTE’s synchronization process, along with the Primary Synchronization Signal (PSS).
SSS provides more precise timing information and aids in cell identification, ensuring accurate frame synchronization between the User Equipment (UE) and the eNodeB.
Periodicity – 5ms (shown below in Grid)
Position of PSS in FDD and TDD frame structure:
In FDD: SSS is broadcast using the central 62 subcarriers belonging to the second to last symbol of time slots 0 and 10.
In TDD: SSS is broadcast using the central 62 subcarriers belonging to the last symbol of time slots 1 and 12.
Information Elements of SSS (Secondary Synchronisation Signal):
- Frame Boundary Info: Frame boundary information refers to the starting and ending points of an LTE frame. This information is crucial for synchronizing the UE with eNodeB.
- EARFCN: It is a unique identifier for a carrier frequency in LTE before calculating PCI.
CP (Cyclic Prefix): Cyclic Prefix, is a portion of the LTE frame that is inserted at the beginning of each symbol. It is used to mitigate the effects of inter-symbol
Generation of SSS:
- SSS Generation from m-Sequences
- The Secondary Synchronization Signal (SSS) is generated using three maximum length sequences (m-sequences), each of length 31.
- An m-sequence is a pseudorandom binary sequence that can be generated by cycling through every possible state of a shift register of length m.
- This results in a sequence of length 2m–1.
- To generate the SSS, the three m-sequences are combined using a scrambling code. The scrambling code is different for each cell, which allows the UE to identify the cell it is attempting to connect to.
In below grid SSS position is been marked
LTE Resource Grid for FDD
LTE Resource Grid for TDD
Finally, the PCI will be decoded based on PSS and SSS decoding.