What is 5G NR SS Block | SS Burst vs SS Block
This page mentions 5G NR SS Block basics including function of SS Block. It mentions contents or fields of SS block and its position in the 5G NR frame. The difference between SS Burst and SS Block in 5G NR is also mentioned.
As shown in the figure-1, a frame in 5G NR consists of 10 ms duration. A frame consists of 10 subframes with each having 1ms duration similar to LTE. Each subframe consists of 2μ slots. Each slot can have either 14 (normal CP) or 12 (extended CP) OFDM symbols. All the subcarrier spacing options have 14 OFDM symbols. 60 KHz spacing supports both normal and extended CP types.
For μ = 0 there are 1 slots per subframe , for μ = 1 there are 2 slots per subframe, for μ = 2 there are 4 slots per subframe and so on. Number of slots per frame is ten times of number of slots per sub frame. Hence for μ = 2, there are 40 slots/frame. 5G NR uses 4096 FFT points which consists of 3300 data subcarriers for maximum bandwidth of 400 MHz.
5G NR SS Block contents, position and function
In the 5G NR downlink frame, SS blocks are transmitted towards UEs at regular intervals based on periodicity set (i.e. 5/10/20/40/80/160 ms).
Multiple SS blocks are carried in a SS burst. A single SS block spans 4 OFDM symbols on time axis and 240 subcarriers on
frequency axis. SS block carry PSS (Primary Synchronization Signal), SSS (Secondary Synchronization Signal)
and PBCH with DMRS. The SS blocks are grouped into first 5 ms of the SS burst.
The maximum number (L) of SS blocks in single burst
is frequency dependant.
There can be about 64 blocks per burst at frequencies above 6 GHz (i.e. mmwave frequencies).
Following are the possible candidate SSB locations (L) within SS Burst set.
• L =4 for Up to 3 GHz
• L = 8 from 3 GHz to 6 GHz
• L = 64 from 6 GHz to 52.6 GHz
Here DMRS (Demodulation Reference Signal) associated with PBCH channel is used to estimate RSRP (Reference signal received power) is calculated from the received SS blocks at the UE.
The figure depicts periodic transmission of SS burst (carrying SS blocks) from gNB to UE at every 20 ms interval. In 5G NR system SS blocks are transmitted using directional beams unlike LTE. In LTE, downlink frame is transmitted omnidirectionally which carries PSS and SSS signals. UE is aware of their location in control channel.
SS block contains are as follows.
• 1 Symbol PSS
• 1 Symbol SSS
• 2 Symbols PBCH
• Each SS Bursts carry one or multiple SS blocks.
• SS Burst set consists of one or multiple SS bursts.
• Transmission is periodic (20 ms by default).
• The transmission of SSBs within SS burst set is confined within a 5 ms window.
5G NR Numerology | 5G NR Terminology
5G NR Control channels | 5G NR Traffic Channels | 5G NR Reference Signals and sequences
5G TECHNOLOGY RELATED LINKS
This 5G tutorial also covers following sub topics on the 5G technology:
5G basic tutorial
5G Frequency Bands
5G millimeter wave tutorial
5G mm wave frame
5G millimeter wave channel sounding
Difference between 4G and 5G
5G testing and test equipments
5G network architecture
5G NR Physical layer
5G NR MAC layer
5G NR RLC layer
5G NR PDCP layer
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