5G
NR system information in general is discussed in detail in the post 5G NR:System Information. This
post discusses SIB9 in detail.
SIB9 contains
information related to GPS time and Coordinated Universal Time (UTC). The UE
may use the parameters provided in SIB9 to obtain the UTC, the GPS and
the local time.
The UE may use the time information for numerous
purposes, possibly involving upper layers e.g. to assist GPS initialisation, to
synchronise the UE clock etc.
General Information
SIB9
is mapped to BCCH logical channel and is either broadcast
periodically on DL-SCH or broadcast on-demand on DL-SCH (i.e. upon request from
UEs in RRC_IDLE or RRC_INACTIVE) or sent in a dedicated manner on DL-SCH to UEs
in RRC_CONNECTED.
SIB9
is carried in SystemInformation (SI) messages,
which are transmitted on the DL-SCH. SIB1 contains scheduling
information for SI-message carrying SIB9. For more information about
scheduling of SI-messages, refer to 5G NR: System Information.
SIB9
can be configured to be cell specific or area specific, using an indication in SIB1.
The cell specific SIB is applicable only within a cell that provides the
SIB while the area specific SIB is applicable within an area
referred to as SI area, which consists of one or several cells and is
identified by systemInformationAreaID.
Contests of SIB9
Overview
of SIB9 contents presented below.
| SIB9 | |
| timeInfo | |
| timeInfoUTC | INTEGER (0 … 549755813887) |
| dayLightSavingTime | BIT STRING ( SIZE (2) ) |
| leapSeconds | INTEGER (-127 … 128) |
| localTimeOffset | INTEGER (-63 … 64) |
timeInfo
timeInfoUTC
is Coordinated Universal Time corresponding to the SFN boundary at or
immediately after the ending boundary of the SI-window in which SIB9 is
transmitted. The field counts the number of UTC seconds in 10 ms units
since 00:00:00 on Gregorian calendar date 1 January, 1900 (midnight between
Sunday, December 31, 1899 and Monday, January 1, 1900).
-
The
UE may use this field together with the leapSeconds field
to obtain GPS time as follows: GPS Time (in seconds) = timeInfoUTC (in seconds) - 2,524,953,600
(seconds) + leapSeconds, where 2,524,953,600 is the number of
seconds between 00:00:00 on Gregorian calendar date 1 January, 1900 and
00:00:00 on Gregorian calendar date 6 January, 1980 (start of GPS time).
This field is excluded when
determining changes in system information, i.e. changes of timeInfoUTC should
neither result in system information change notifications nor in a modification
of valueTag in SIB1.
dayLightSavingTime
indicates if and how daylight-saving time (DST) is
applied to obtain the local time. The semantics are the same as the semantics
of the Daylight-Saving Time IE in 24.008. The first/leftmost bit of the bit
string contains the b2 of octet 3 and the second bit of the bit string contains
b1 of octet 3 in the value part of the Daylight-Saving Time IE in 24.008 (as
shown below);
First/Left Most bit value
|
Second bit value
|
DST
|
0
|
0
|
No adjustment for Daylight Saving Time |
0
|
1
|
+1 hour adjustment for Daylight Saving Time |
1
|
0
|
+2 hours adjustment for Daylight Saving Time |
1
|
1
|
Reserved |
leapSeconds
is the number of leap seconds offset between GPS Time
and UTC. UTC and GPS time are related i.e. GPS time -leapSeconds = UTC time.
localTimeOffset
is the offset between UTC and local time in units of 15 minutes. Actual value = field value * 15
minutes. Local time of the day is calculated as UTC time + localTimeOffset.
Reference: 3GPP TS 38.331 and 24.008
