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How Synchronization Channel Works in LTE?

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After the power on, the UE knows: 

  • the UE category and capability.
  • the preferred PLMN.
    the carriers.

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:

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  • 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.
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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.

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