Section 3 - Sync Signals Flashcards
What are the goals of the synchronization signals?
Establish and maintain time-frequency synchronization on the DL. Provide support for beam sweeping/beamforming. Act as reference signals for RSRP measurements
How many types of synchronization signals does NR has?
Two, PSS and SSS
How are the possible locations of the SSB determined?
There is a predefined raster which establishes the possible locations of the SSB resources
Is the SSB in NR more flexible than LTE?
Yes, in LTE it was always located on the center of the bandwidth, while in NR it can be located more flexible
How is the sync raster distributed depending on the frequency range?
For f<3GHz the sync raster is located in multiples of 1.2MHz + the offset factor, for 3GHz < f < 24250 is multiples of 1.44 MHz and for higher frequencies is multiples of 17.82 MHz
How many resources does the SSB has?
It has 4 OFDM symbols and 20 RBs (240 subcarriers). In LTE it was only 6 RBs
How is the PSS located within the SSB?
The PSS occupies 127 subcarriers at the center of the SSB frequency block, and one OFDM symbol
What is the structure of SSB?
The first symbols has the PSS with 127 subcarriers occupied. The Second symbol has PBCH and DMRS occupying the full bandwidth. The third symbol has the SSS occupying the same bandwidth as the PSS surrounded by 9 and 8 SCs without data up and down respectively, and 48 SCs with PBCH and DMRS in each side. The fourth symbol is similar to the second
Where is the cell-defining SSB located?
At the synchronization raster
How is the location of SSB defined in SIB1?
SIB1 states the point A marking the start of the bandwidth and the offset from point A to the first usable PRB
Can the nework define an additional offset for the SSB?
Yes
What are the maximum number of SSB per burst set by frequency band?
For f<3GHz is 4, for 3GHz<f<6GHz is 6, and 64 for higher frequencies
What is the maximum time duration of the SSB in ms?
5ms
What is the SSB periodicity for idle and connected UEs?
10ms
What is the SSB periodicity for initial acquisition?
20ms
What is the time range in which the SSB periodicity can be configured?
5 to 160ms
What information is included in the PBCH?
It contains essential system information to enable cell acquisition. Contains the Master Information Blocks which has downlink timing information, the 6 MSB of the 10 bit SFN (rest are on the PBCH). The PBCH also has information about the scheduling of the RMSI
What information in on the PBCH payload?
The PBCH is self decodable, contains the MIB, physical bits and 3 bits from DMRS scrambling sequences
What mechanism is implemented to facilitate the UE decoding the MIB?
Identical MIB is transmitted four times in 80ms to allow the UE to apply soft-combining for easier decoding
How is the system information (SI) distributed?
The SI is divided into MIB and several SIB
What are the differences between the SI in LTE and NR?
NR introduces the option to broadcast only part of the SI, and send the rest only upon request, while in LTE, the SI is always broadcast. Only the MIB is broadcasted in NR. NR supports SI beam sweeping
How does the SI acquisition happen in NSA?
After the UE enters in LTE RRC Connected mode and the master eNodeB configures the NR measurement, the UE reads the SSB from which extracts the NR MIB. Then it reports the cell ID and RSRP to LTE eNodeB. The eNodB then does an RRC connection reconfiguration to add NR as SCG and sends NR RMSI and NR other system information (OSI) to UE.
How does the SI acquisition happen in SA?
The UE reads the MIB containing SIB1 from the SSB. From there it extracts the scheduling of OSI or reads indication if that OSI is available for request. Then it reads the OSI on PDCCH or PDSCH wit or without UE request
Are both RMSI and OSI broadcast?
RMSI is broadcast in SA or signaled via LTE RRC in NSA. OSI is broadcasted or provided on UE request
