The concept of frequency grid is introduced in 5G, that is, the cell center frequency point and the frequency domain position of the SSB cannot be arbitrarily configured, and must meet certain rules. The main purpose is for the UE to quickly search for the cell; the three most important concepts are Channel raster, synchronization raster and pointA;
1、Channel raster
It can be understood as the optional position of the center frequency of the carrier;
generally the frequency value is expressed indirectly by the value of NR-ARFCN (NR absolute radio frequency channel number), that is, the Nref in the following table, which is generally transmitted in the RRC message If you need to know the specific frequency value of this channel number, refer to the calculation of frequency Fref in the following formula:
ΔFGlobal global frequency grid interval (granularity of the global frequency raster), the values of different frequency ranges are shown in the table below.
Fref RF reference frequencies, that is, the specific frequency value
The value range of NR-ARFCN (NR Absolute Radio Frequency Channel Number) is 0…2016666, and FR2 is 2016667 – 3279165. The relationship with RF reference frequency Fref is shown in the following formula.
FREF = FREF-Offs + ΔFGlobal (NREF – NREF-Offs)
Channel raster is a subset of R F reference frequencies. For each band, the center frequency cannot be selected at will. It needs to be selected according to a certain starting point and step length. The specific available ones are shown in the table below.
ΔFRaster is the interval granularity, which is greater than or equal to ΔFGlobal.
For example, for n41, if the step size is 3, the corresponding frequency step size is 3 Fglobal=3× 5=15Khz; if the step size is 6, the corresponding frequency step size is 6 Fglobal=6× 5= 30Khz, there are two ΔFRaster , according to I is determined. How to determine if I was not found .
Table 5.4.2.3-1: Applicable NR-ARFCN per operating band
| NR operating band |
ΔFRaster (kHz) |
Uplink Range of NREF (First – <Step size> – Last) |
Downlink Range of NREF (First – <Step size> – Last) |
| n1 |
100 |
384000 – <20> – 396000 |
422000 – <20> – 434000 |
| n28 |
100 |
140600 – <20> – 149600 |
151600 – <20> – 160600 |
| n41 |
15 |
499200 – <3> – 537999 |
499200 – <3> – 537999 |
| 30 |
499200 – <6> – 537996 |
499200 – <6> – 537996 |
|
| n77 |
15 |
620000 – <1> – 680000 |
620000 – <1> – 680000 |
| 30 |
620000 – <2> – 680000 |
620000 – <2> – 680000 |
|
| n78 |
15 |
620000 – <1> – 653333 |
620000 – <1> – 653333 |
| 30 |
620000 – <2> – 653332 |
620000 – <2> – 653332 |
|
| n79 |
15 |
693334 – <1> – 733333 |
693334 – <1> – 733333 |
| 30 |
693334 – <2> – 733332 |
693334 – <2> – 733332 |
The center frequency channel raster position of the entire carrier is related to the total number of RBs. When the number of RBs is an even number, it represents subcarrier 0 of Nprb, and when the number of RBs is a base number, it represents subcarrier 6 of Nprb. That is, it is shifted upward by half a subcarrier from the absolute center of the cell frequency.
2、synchronization raster
Synchronization raster can be understood as the optional location of the center frequency of the SSB block; it is also for the UE to find the SSB more quickly; the center of the SSB in 5G does not need to coincide with the center of the carrier;
see the table below, the center frequency of the SSB is in the table below SSref; is also stepped according to a certain rule;
the center frequency of SSB is generally expressed indirectly by the number value of GSCN, which is convenient for message transmission;
GSCN Global Synchronization Channel Number, the global synchronization channel number, is the channel number used to mark the SSB.
Each GSCN corresponds to the frequency domain position SSREF of an SSB (the starting frequency of the 0th subcarrier of RB10 of the SSB), and the GSCN is numbered in increasing order of the frequency domain.
Table 5.4.3.1-1: GSCN parameters for the global frequency raster
| Frequency range |
SS Block frequency position SSREF |
GSCN |
Range of GSCN |
| 0 – 3000 MHz |
N * 1200kHz + M * 50 kHz, N=1:2499, M ϵ {1,3,5} (Note 1) |
3N + (M-3) / 2 |
2 – 7498 |
| 3000 – 24250 MHz |
3000 MHz + N * 1.44 MHz N = 0:14756 |
7499 + N |
7499 – 22255 |
| NOTE 1: The default value for operating bands with which only support SCS spaced channel raster(s) is M=3. |
|||
Table 5.4.3.1-1: GSCN parameters for the global frequency raster
| Frequency range |
SS block frequency position SSREF |
GSCN |
Range of GSCN |
| 24250 – 100000 MHz |
24250.08 MHz + N * 17.28 MHz, N = 0:4383 |
22256 + N |
22256 – 26639 |
Synchronization raster is not the absolute center (1/2) of the SSB block. The SSB block has 20 RBs, a total of 20*12=240 subcarriers; absoluteFrequencySSB corresponds to the 0th sub-carrier of the 10th RB (numbered from 0) The center of the carrier, that is , is offset from the absolute center by half a subcarrier ;
Table 5.4.3.2-1: Synchronization raster to SS block resource element mapping
| Resource element index k |
0 |
| Physical resource block number nPRB of the SS block |
n PRB = 10 |
3, PointA
According to the definition of the public reference point absoluteFrequencyPointA , this reference point is the center point of the 0th subcarrier of the 0th RB (RB0); note that it is not an edge. Many online articles understand it as edge;
Absolute frequency position of the reference resource block (Common RB 0). Its lowest subcarrier is also known as Point A. Note that the lower edge of the actual carrier is not defined by this field but rather in the scs-SpecificCarrierList. Corresponds to L1 parameter 'offset-ref-low-scs-ref-PRB' (see 38.211, section FFS_Section)
参见38.211 定义
absoluteFrequencyPointA for all other cases where absoluteFrequencyPointA represents the frequency-location of point A expressed as in ARFCN
The center（中心） of subcarrier 0 of common resource block 0 for subcarrier spacing configuration μ coincides with ‘point A’.
4. The relationship between the parameters
offsetToPointA : Represents the frequency domain offset between the lowest subcarrier of the lowest RB of the SSB and point A, in RB. Note that the frequency domain offset is not calculated with the actual subcarrier spacing, but for FR1 hypothesis The carrier spacing is 15kHz, and for FR2, the subcarrier spacing is assumed to be 60kHz.
offsetToPointA for a PCell downlink where offsetToPointA represents the frequency offset between point A and the lowest subcarrier of the lowest resource block, which has the subcarrier spacing provided by the higher-layer parameter subCarrierSpacingCommon and overlaps with the SS/PBCH block used by the UE for initial cell selection, expressed in units of resource blocks assuming 15 kHz subcarrier spacing for FR1 and 60 kHz subcarrier spacing for FR2;
Kssb: The number of RBs that differ between poin A and SSB's No. 0 RB0 sub-carrier may not be exactly an integer number of RBs, and there may be a few sub-carriers; Kssb means that there are still a few sub-carriers; here it is also assumed that the sub-carrier spacing is fixed The value FR1 is 15kHz and FR2 is 60kHz. The lower 4 bits of Kssb are given by the high-level parameter ssb-SubcarrierOffset. For SS/PBCH block type B (μ∈{3,4}), kSSB∈{0,1,2,...,11}, 4 bits are sufficient; while SS/PBCH block type A (μ ∈ {0,1} is kSSB∈ {0,1,2, ..., 23} , indicates that 5 bits, the protocol used in the payload of PBCH to indicate
a high bit bit.
Therefore, the frequency difference between poin A and subcarrier 0 of RB0 of SSB is equal to offsetToPointA*15*12+Kssb*15;
And the frequency difference between absoluteFrequencySSB and SSB's RB0 subcarrier 0 is equal to 10×12×subCarrierSpacingCommon (the number of RBs in SSB is 20)
offsetToCarrier: Frequency domain offset betweenPoint A (the lowest subcarrier of CRB0 ) and the lowest available subcarrier, in PRB.
Offset in frequency domain between Point A (lowest subcarrier of common RB 0) and the lowest usable subcarrier on this carrier in number of PRBs (using the subcarrierSpacing defined for this carrier). The maximum value corresponds to 275*8-1. Corresponds to L1 parameter 'offset-pointA-low-scs' (see 38.211, section 4.4.2)
For below 3GHz
ΔFGlobal = 5
absoluteFrequencyPointA × ΔFGlobal + offsetToPointA×15×12+Kssb×15 = SSREF - 10×12×subCarrierSpacingCommon
SSREF = absoluteFrequencySSB * ΔFGlobal = absoluteFrequencySSB × 5
Yasui:
absoluteFrequencyPointA + offsetToPointA×15×12/5 + Kssb ×15/5 = absoluteFrequencySSB - 10×12×subCarrierSpacingCommon/5
Carrier Center NR-ARFCN:
NREF = 载波中心NR-ARFCN= absoluteFrequencyPointA + N_CRB×12/2× subcarrierSpacing/5 + offsetToCarrier × 12 × subcarrierSpacing/5
5. NSA configuration
In NSA, the base station will notify the UE about frequency information through the RRC reconfiguration message to help the UE quickly search for the target cell;
NR=band 41, which is a band less than 3Ghz, and the parameters in the first column corresponding to the above table 5.4.2.1-1 can be applied;
carrierBandwidth=273, which means that there are 273 RBs in the carrier, 273RB * 12 * 30Khz = 98.280Mhz, which does not completely occupy the 100Mhz bandwidth, because guard bands need to be reserved on both sides.
subcarrierSpacing; representative subcarrier spacing is 30Khz; each RB has 12 subcarriers
absoluteFrequencyPointA=503172: Represents public reference point A; 503172 *5Khz = 2515860Khz
absoluteFrequencySSB=504990 represents the center frequency of the SSB block; 504990*5Khz = 2524950Khz, that is, the center of the SSB is at 2524950Khz;
offsetToCarrier = 0
NREF = 载波中心ARFCN = absoluteFrequencyPointA + N_CRB×12/2× subcarrierSpacing/5 + offsetToCarrier × 12 × subcarrierSpacing/5
Carrier Center NR-ARFCN = 503172 + 273*12/2* subcarrierSpacing / 5 + 0 = 503172 + 9828 = 513000
The frequency is 513000 × 5 = 2565000kHz
absoluteFrequencyPointA + offsetToPointA×15×12/5 + Kssb ×15/5 = absoluteFrequencySSB - 10×12×subCarrierSpacingCommon/5
503172 + offsetToPointA×15×12/5 + Kssb ×15/5 = 504990 - 10 ×12 × 30 / 5
offsetToPointA × 36 + Kssb ×3 = 1098
Obtain offsetToPointA = 30, Kssb = 6
SSB GSCN = 6312，N = 2104，M = 3
The relationship of each variable is shown in the figure below:
6, SA placement
You can see that sb-SubcarrierOffset = 6, offsetToPointA = 30, and offsetToCarrier =0 configured in the MIB .
7. Restrictions
1. Minimum guard interval
The minimum guard interval is defined in 38.101,
Table 5.3.3-1: Minimum guardband for each UE channel bandwidth and SCS (kHz)
| SCS (kHz) |
5 MHz |
10 MHz |
15 MHz |
20 MHz |
25 MHz |
30 MHz |
40 MHz |
50 MHz |
60 MHz |
70 MHz |
80 MHz |
90 MHz |
100 MHz |
| 15 |
242.5 |
312.5 |
382.5 |
452.5 |
522.5 |
592.5 |
552.5 |
692.5 |
N/A |
N/A |
N/A |
N/A |
N/A |
| 30 |
505 |
665 |
645 |
805 |
785 |
945 |
905 |
1045 |
825 |
965 |
925 |
885 |
845 |
| 60 |
N/A |
1010 |
990 |
1330 |
1310 |
1290 |
1610 |
1570 |
1530 |
1490 |
1450 |
1410 |
1370 |
Table 5.3.3-1: Minimum guardband for each UE channel bandwidth and SCS (kHz)
| SCS (kHz) |
50 MHz |
100 MHz |
200 MHz |
400 MHz |
| 60 |
1210 |
2450 |
4930 |
N. A |
| 120 |
1900 |
2420 |
4900 |
9860 |
NOTE: The minimum guardbands have been calculated using the following equation: (BWChannel x 1000 (kHz) - NRB x SCS x 12) / 2 - SCS/2, where NRB are from Table 5.3.2-1.
The number of RBs configured in any channel bandwidth shall ensure that the minimum guardband specified in this clause is met.
Figure 5.3.3-2: UE PRB utilization
2. The bandwidth supported by the UE in different frequency bands
Table 5.3.5-1 Channel bandwidths for each NR band
|
|
|
NR band / SCS / UE Channel bandwidth |
|||||||||||||
| NR band |
SCS kHz |
5 MHz |
101,2 MHz |
152 MHz |
202 MHz |
252 MHz |
30 MHz |
40 MHz |
50 MHz |
60 MHz |
70 MHz |
80 MHz |
90 MHz |
100 MHz |
|
| n1 |
15 |
Yes |
Yes |
Yes |
Yes |
|
|
|
|||||||
| 30 |
|
Yes |
Yes |
Yes |
|
|
|
||||||||
| 60 |
|
Yes |
Yes |
Yes |
|
|
|
||||||||
| n28 |
15 |
Yes |
Yes |
Yes |
Yes7 |
|
|
|
|
|
|
|
|
|
|
| 30 |
|
Yes |
Yes |
Yes7 |
|
|
|
|
|
|
|
|
|
||
| 60 |
|
|
|
|
|
|
|
|
|
|
|
|
|
||
| n41 |
15 |
|
Yes |
Yes |
Yes |
|
Yes |
Yes |
Yes |
|
|
|
|
|
|
| 30 |
|
Yes |
Yes |
Yes |
|
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
|||
| 60 |
|
Yes |
Yes |
Yes |
|
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
|||
| n77 |
15 |
|
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
|
|
|
|
||
| 30 |
|
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes4 |
Yes |
Yes4 |
Yes |
||
| 60 |
|
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes4 |
Yes |
Yes4 |
Yes |
||
| n78 |
15 |
|
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
|
|
|
|
|
|
| 30 |
|
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes4 |
Yes |
Yes |
Yes |
||
| 60 |
|
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes4 |
Yes |
Yes |
Yes |
||
| n79 |
15 |
|
|
|
|
|
|
Yes |
Yes |
|
|
|
|
|
|
| 30 |
|
|
|
|
|
|
Yes |
Yes |
Yes |
Yes |
|
Yes |
|||
| 60 |
|
|
|
|
|
|
Yes |
Yes |
Yes |
Yes |
|
Yes |
|||