LTE PSS vs SSS: Primary and Secondary Synchronization Signals

This tutorial section on LTE basics covers the following subtopics: Main page features, terminologies, Frame TDD FDD, Channel types, PHY stack, throughput, VoLTE CA, cell search, network entry, Timers, PSS vs SSS, Security, LTE Bands, EARFCN, and Hotspot router.

This page describes Primary Synchronization Signal (P-SS) and Secondary Synchronization Signal (S-SS) sequences used in the LTE system. It provides a comparison between P-SS and S-SS as per the LTE standard.

Primary Synchronization Signal (P-SS) Sequences

• Three PSS sequences are used in LTE, corresponding to the three physical layer identities within each group of cells.
• The PSS is constructed from a frequency-domain ZC sequence of length 63.
• Transmitted on the 6th symbol of slot 0 and slot 10 of each radio frame on 72 subcarriers centered around DC.

Secondary Synchronization Signal (S-SS) Sequences

• SSC1 and SSC2 are two codes that are two different cyclic shifts of a single length-31 M sequence.
• Each SSS sequence is constructed by interleaving, in the frequency-domain, two length-31 BPSK-modulated secondary synchronization codes.
• Two codes are alternated between the first and second SSS transmissions in each radio frame.
• This enables the UE to determine the 10 ms radio frame timing from a single observation of a SSS.
• Transmitted on the 5th symbol of slot 0 and slot 10 of each radio frame on 72 subcarriers centered around DC.

PSS carries physical layer identity $(N_{ID}^{(2)})$. SSS carries physical layer cell identity group $(N_{ID}^{(1)})$.

Cell identity is computed using:

$N_{ID}^{cell} = 3 * N_{ID}^{(1)} + N_{ID}^{(2)}$,

Where $N_{ID}^{(1)} = 0, 1, ..., 167$ and $N_{ID}^{(2)} = 0, 1, 2$

P-SS constellation diagram

As shown in the figure, the P-SS constellation plots the frequency domain view of Zadoff Chu sequences.

S-SS constellation diagram

As shown in the figure, the S-SS constellation plots BPSK M sequence signals.