PSS stands for Primary synchronization Signal and the purpose of PSS is for slot synchronization.

The PSS serves as a reference signal that is embedded in the LTE frame structure. When the UE detects the PSS in the time domain, it extracts the timing information embedded within the signal. This timing information includes the frame number, subframe number, and slot number. The UE device then uses this information to align its internal clock with the base station’s clock, ensuring that it is ready to receive the next downlink transmission at the expected time.

Slot synchronization is particularly important in TDD (Time Division Duplexing) mode, where the uplink and downlink transmissions share the same frequency band. By synchronizing with the base station’s slot timing, the UE can avoid interference between its uplink and downlink transmissions.

Periodicity – 5ms (shown below in Grid)

Position of PSS in FDD and TDD frame structure:

• In Frequency Division Duplex (FDD), the Primary Synchronisation Signal (PSS) undergoes dual broadcasts within each radio frame, specifically during time slots 0 and 10. This broadcast utilizes the central 62 subcarriers located in the final symbol of both time slots 0 and 10.
• Contrastingly, in Time Division Duplex (TDD), the PSS is transmitted using the central 62 subcarriers associated with the third symbol of time slot 2 (subframe 1) and also the third symbol of time slot 12 (subframe 6).

Information Elements of PSS (Primary Synchronisation Signal):

• Number of PSS recorded: Total PSS results while scanning
• PSS Indices (0,1,2): 0,1,2 value will be used in formula to calculate the proper PCI.
• PSS peak Value: Based on good RSSI it will give the list with reference to energy in dB

In below grid PSS position is been marked

LTE Resource Grid for FDD

LTE Resource Grid for FDD

Mapping of PSS

The Primary Synchronization Signal (PSS) is a sequence of 62 consecutive symbols that is used to synchronize the receiver with the transmitter in an LTE (Long Term Evolution) system. The PSS is mapped into the first 31 subcarriers either side of the DC subcarrier, which means that it occupies six resource blocks with five reserved subcarriers each side. This is shown in the figure below.

The PSS is a known sequence of symbols that is easy for the receiver to detect. By correlating the received signal with the PSS, the receiver can determine the frequency offset and timing of the transmitter. This allows the receiver to demodulate the data symbols and decode the received data.

The use of the PSS is an important part of the LTE synchronization process. Without the PSS, the receiver would not be able to synchronize with the transmitter and demodulate the received data.

Generation of PSS:

• The PSS is based on a frequency-domain Zadoff-Chu sequence, which is a type of spreading sequence that has good autocorrelation properties.
• This means that the PSS can be easily detected by the receiver, even in the presence of noise.
• Zadoff-Chu sequences are a type of Frank-Zadoff sequence that was defined by D.C. Chu in 1972.
• These sequences have the useful property of having zero cyclic autocorrelation at all nonzero lags.
• This means that when the sequence is correlated with itself, the correlation is zero at all lags except for zero.
• This property makes Zadoff-Chu sequences ideal for use as synchronization signals, as they can be easily detected even in the presence of noise.
• The PSS is a sequence of 62 consecutive symbols that is mapped into the first 31 subcarriers either side of the DC subcarrier.