Section 3 - Sync Signals

Question 1

What are the goals of the synchronization signals?

Answer 1

Establish and maintain time-frequency synchronization on the DL. Provide support for beam sweeping/beamforming. Act as reference signals for RSRP measurements

Question 2

How many types of synchronization signals does NR has?

Answer 2

Two, PSS and SSS

Question 3

How are the possible locations of the SSB determined?

Answer 3

There is a predefined raster which establishes the possible locations of the SSB resources

Question 4

Is the SSB in NR more flexible than LTE?

Answer 4

Yes, in LTE it was always located on the center of the bandwidth, while in NR it can be located more flexible

Question 5

How is the sync raster distributed depending on the frequency range?

Answer 5

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

Question 6

How many resources does the SSB has?

Answer 6

It has 4 OFDM symbols and 20 RBs (240 subcarriers). In LTE it was only 6 RBs

Question 7

How is the PSS located within the SSB?

Answer 7

The PSS occupies 127 subcarriers at the center of the SSB frequency block, and one OFDM symbol

Question 8

What is the structure of SSB?

Answer 8

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

Question 9

Where is the cell-defining SSB located?

Answer 9

At the synchronization raster

Question 10

How is the location of SSB defined in SIB1?

Answer 10

SIB1 states the point A marking the start of the bandwidth and the offset from point A to the first usable PRB

Question 11

Can the nework define an additional offset for the SSB?

Answer 11

Yes

Question 12

What are the maximum number of SSB per burst set by frequency band?

Answer 12

For f<3GHz is 4, for 3GHz<f<6GHz is 6, and 64 for higher frequencies

Question 13

What is the maximum time duration of the SSB in ms?

Answer 13

5ms

Question 14

What is the SSB periodicity for idle and connected UEs?

Answer 14

10ms

Question 15

What is the SSB periodicity for initial acquisition?

Answer 15

20ms

Question 16

What is the time range in which the SSB periodicity can be configured?

Answer 16

5 to 160ms

Question 17

What information is included in the PBCH?

Answer 17

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

Question 18

What information in on the PBCH payload?

Answer 18

The PBCH is self decodable, contains the MIB, physical bits and 3 bits from DMRS scrambling sequences

Question 19

What mechanism is implemented to facilitate the UE decoding the MIB?

Answer 19

Identical MIB is transmitted four times in 80ms to allow the UE to apply soft-combining for easier decoding

Question 20

How is the system information (SI) distributed?

Answer 20

The SI is divided into MIB and several SIB

Question 21

What are the differences between the SI in LTE and NR?

Answer 21

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

Question 22

How does the SI acquisition happen in NSA?

Answer 22

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.

Question 23

How does the SI acquisition happen in SA?

Answer 23

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

Question 24

Are both RMSI and OSI broadcast?

Answer 24

RMSI is broadcast in SA or signaled via LTE RRC in NSA. OSI is broadcasted or provided on UE request