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PSS vs SSS in LTE


This tutorial section on LTE basics covers following sub topics:
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  Hotspot  router 


This page describes Primary Synchronization Signal(P-SS) and Secondary Synchronization Signal(S-SS) sequences used in LTE system.It provides comparison between P-SS and S-SS as per 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 6th symbol of slot 0 and slot10 of each radio frame on 72 subcarriers centered around DC.


LTE PSS vs SSS or primary SCH secondary SCH

Secondary Synchronization Signal (S-SS) Sequences

•  SSC1 and SSC2 are two codes 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 5th symbol of slot 0 and slot10 of each radio frame on 72 subcarriers centered around DC.

PSS carries physical layer identity (NID)(2)
SSS carries physical layer cell identity group (NID)(1)
Cell identity is computed using (NID)cell = 3*NID(1) + NID (2) ,
Where (NID)(1) = 0,1,.....,167 and (NID)(2) = 0,1,2


Signal Full
Form
Direction Position Modulation/
Coding scheme
Function
P-SS Primary
Synchro-
nization
Signal
Downlink 6th symbol of slot 0 and
slot 10(time exis)
mapped on 72 subcarriers
centered around DC(frequency axis)
Zadoff Chu sequence of
length 63
UE first finds the
primary synchronization signal (PSS)
which is located in the
last OFDM symbol of first
time slot of the first and
5th sub-frames This enables UE to be
synchronized on sub-frame level
Primary Synchronization Signal
helps for Slot Timing
Detection and Physical Layer ID
(0,1,2) detection
S-SS Secondary
Synchro-
nization
Signal
Downlink 5th symbol of slot 0 and
slot 10(time exis)
mapped on 72 subcarriers
centered around DC(frequency axis)
BPSK modulated length-31 M sequence From SSS, UE is able to obtain
physical layer cell
identity group number (0 to 167)
It helps for
Radio Frame Timing detection, find Physical
Layer Cell ID, cyclic prefix
length detection, FDD or TDD detection

P-SS constellation diagram

Primary Synchronization Signal PSS constellation

As shown in the figure P-SS constellation plots frequency domain view of zadoff chu sequences.

S-SS constellation diagram

Secondary Synchronization Signal SSS constellation

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

LTE Tutorial related links

What is LTE?  Terminology  3GPP ref   LTE tutorial  LTE Features  UE categories  LTE Bands  EARFCN vs frequency   LTE frame  FDD vs TDD   PHY  protocol stack  throughput  VoLTE  CA
UE cell search  UE network entry  Timers  PSS vs SSS  LTE RS DMRS SRS  LTE Channels  BW vs FS vs RB  Zadoff chu sequence  LTE Advanced   eNodeB Measurements  UE Measurements  SC-FDMA Vs OFDMA   LTE Security  

RF and Wireless Terminologies


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