5G PSS, SSS, and ESS: Understanding the Differences

This article clarifies the differences between Primary Synchronization Signal (PSS), Secondary Synchronization Signal (SSS), and Extended Synchronization Signal (ESS) in the context of 5G technology.

5G Frame Structure Basics

In 5G-TF, a radio frame has a duration of 10ms. This frame is divided into 100 slots or 50 subframes. Each subframe contains two consecutive slots. With a normal cyclic prefix, each slot comprises 7 OFDM symbols.

• Resource Block: Consists of 12 subcarriers and 7 symbols.
• Resource Grid: The transmitted signal in each slot is represented by one or more resource grids with (N_RB)^DL * (N_SC)^RB = 1200 subcarriers and (N_Symb)^DL = 7 OFDM symbols.
• Resource Element: Each element within the resource grid for antenna port-p is called a resource element. It’s uniquely identified by the index pair (k,l) within a slot, where:
  • k = 0, …, (N_RB)^DL * (N_SC)^RB -1 (frequency domain index)
  • l = 0, …, (N_Symb)^DL -1 (time domain index)

Primary Synchronization Signal (PSS) in 5G

• Constructed using 62 subcarriers based on a Zadoff-Chu sequence.
• Transmitted on all OFDM symbols, unlike LTE where it’s transmitted on only one.
• Used to acquire symbol timing of a downlink frame.
• Transmitted in symbols 0 to 13 in subframes number 0 and 25, and on antenna ports p = 300 to 313.

Secondary Synchronization Signal (SSS) in 5G

• Constructed using 62 data bits as per a “Gold Sequence” and occupies 62 subcarriers.
• Similar to PSS, it’s also used for radio frame synchronization.
• Transmitted in symbols 0 to 13 in subframes number 0 and 25, and on antenna ports p = 300 to 313.

Extended Synchronization Signal (ESS) in 5G

• ESS is a new type of synchronization signal, not present in LTE.
• Used to identify the OFDM symbol index.
• Transmitted in symbols 0 to 13 in subframes 0 and 25 on antenna ports 300 to 313.
• The sequence used to generate ESS is a length 63 Zadoff-Chu sequence, defined as: d(n) = e^{-j*{(25πn*(n+1))/63}}, where n = 0,1,…,62.

Reference: TS V5G.211 V1.7