How Synchronization Channel Works in LTE?
After the power on, the UE knows:
- the UE category and capability.
- the preferred PLMN.
The UE needs to know:
- The frame synchronization to be able to decode the DL radio frame.
- The cell parameters to be able request a connection.
The UE can use:
- The PSS: Primary Synchronization Signal.
- The SSS: Secondary Synchronization Signal.
- The BCH, the broadcast channel.
The synchronization signals provide the cell id to the UE.
LTE supports 510 different cell identities.
- They are divided into 170 cell id groups and there are 3 cell ids per group.
- Cell id = 3* Cell_Group_id(0 to 169 Provided by the SSS) + Cell_id_in_group(0 to 2 Provided by the PSS )
The Primary Synchronization Signal (PSS):
- is used for the slot synchronization.
- is on the last OFDM symbol of slots 0 & 10 in the 1st & 6th sub-frames of each frame.
- carries one of the 3 cell id in group sequence.
The Secondary Synchronization Signal (SSS):
- is used for the frame synchronization.
- is on the same slot as PSS.
- is on the next to last OFDM symbol of slots 0 & 10 in the 1st & 6th sub-frames of each frame.
- carries one of the 170 unique cell group identifiers.
The PSS, the SSS and the BCH are carried over 6 Resource Blocks (RB) whatever the bandwidth
6 RBs = 6 * 12 Sub-ca = 72 Sub-carriers
By this way, these signals are independent from the bandwidth and can decode this signal without knowing it.