MIB/SIB and Scheduling
It seems there is pretty big difference in terms of design concept between LTE and LTE-NB MIB/SIBs. To me, LTE-NB design concept seems closer to WCDMA MIB/SIB logic.
Overall operation of MIB/SIB for LTE-NB is described in 36.300 7.4 as summarized below.
- MIB-NB and SystemInformationBlockType1-NB uses fixed scheduling (Same as legacy LTE)
- The periodicity of MIB-NB is 640 ms (The periodicity of MIB in legacy LTE is 40 ms)
- The periodicity of SIB1-NB is 2560 ms (The periodicity of SIB1 in legacy LTE is 80 ms)
- MIB-NB contains all the information required to aquire SIB1 (In legacy LTE, SIB1 decoding information is configured by DCI 1A, not by MIB)
- SIB1-NB contains all the information to aquire other SIBs (In legacy LTE, SIB1 carries only periodicity information of other SIBs, all other information required to decode other SIBs are carried by DCI 1A, not by SIB1)
- BCCH and other logical channel cannot be transmitted in the same subframe (Different from Legacy LTE)
- UE is not required to detect SIB changes in RRC_CONNECTED state (Different from legacy LTE. So, if network wants the UE to aquire the changed SIB, it may trigger RRC Release to put UE into IDLE mode and detect the changed SIBs.)
Followings are the topics with the details.
When we think of MIB/SIB decoding, we usually think of following factors
- i) In what order each of the SIB is decoded ?
- ii) What kind of configuration information UE need to get to decode SIBs
- iii) How a UE get those configuration information (by DCI ? or Higher layer signaling message ? )
The answer to all of these questions may be answered (hopefully) by a single illustration shown below. First, just take a look at this figure and see if you can make your own story to explain the process to others. (This kind of practice would be very helpful for you to learn anything new)
As you see, in terms of sequence of decoding SIB LTE-NB has no special differences from the legacy LTE or LTE-BL/CE(M1). It goes as MIB decoding --> SIB1 --> SIB2 and others.
In terms of SIB1 decoding, LTE-NB(M2) take a similar approach to LTE-M1 which is a little different from the legacy LTE. In LTE-NB, a parameter in MIB (as shown in (2)) determines the exact transmission timing and periodicity and PHY/MAC configuration. This is similar concept to LTE BL/CE(M1). It is a little bit different from legacy LTE in which SIB1 decoding information is predefined by 3GPP specification and DCI.
In terms of SIB2 and other SIB decoding, all the information that is required to decode these SIBs are informed to UE via SIB 1 parameters as shown in (3). DCI is not used here.
The most outstanding difference between LTE-NB(M2) and the legacy LTE SIB decoding is that DCI is not used in LTE-NB SIB decoding. All the information (even PHY/MAC) that is required to decode SIBs are notified to UE over MIB or SIB1 as illustrated above.
In normal LTE, MIB carries very simple set of information. However, in LTE-NB MIB carries relatively large set of information. It carries following high level information.
-
i) System Timing : SFN(Partial data), HyperSFN(Partial data)
-
ii) Scheduling Information for SIB1-NB
-
iii) Access Barring
-
iv) Operation Mode Information for LTE-NB
Followings are from 36.331 5.2.1.2a Scheduling for NB-IoT MIB scheduling.
- Uses a fixed schedule with a periodicity of 640 ms and repetitions made within 640 ms.
- The first transmission of the MIB-NB is scheduled in subframe #0 of radio frames for which the SFN mod 64 = 0
- Repetitions are scheduled in subframe #0 of all other radio frames.
- The transmissions are arranged in 8 independently decodable blocks of 80 ms duration
MasterInformationBlock-NB ::= SEQUENCE {
systemFrameNumber-MSB-r13 BIT STRING (SIZE (4)),
hyperSFN-LSB-r13 BIT STRING (SIZE (2)),
schedulingInfoSIB1-r13 INTEGER (0..15),
systemInfoValueTag-r13 INTEGER (0..31),
ab-Enabled-r13 BOOLEAN,
operationModeInfo-r13 CHOICE {
inband-SamePCI-r13 Inband-SamePCI-NB-r13,
inband-DifferentPCI-r13 Inband-DifferentPCI-NB-r13,
guardband-r13 Guardband-NB-r13,
standalone-r13 Standalone-NB-r13
},
spare BIT STRING (SIZE (11))
}
ChannelRasterOffset-NB-r13 ::= ENUMERATED {khz-7dot5, khz-2dot5, khz2dot5, khz7dot5}
Guardband-NB-r13 ::= SEQUENCE {
rasterOffset-r13 ChannelRasterOffset-NB-r13,
spare BIT STRING (SIZE (3))
}
Inband-SamePCI-NB-r13 ::= SEQUENCE {
eutra-CRS-SequenceInfo-r13 INTEGER (0..31)
}
Inband-DifferentPCI-NB-r13 ::= SEQUENCE {
eutra-NumCRS-Ports-r13 ENUMERATED {same, four},
rasterOffset-r13 ChannelRasterOffset-NB-r13,
spare BIT STRING (SIZE (2))
}
Standalone-NB-r13 ::= SEQUENCE {
spare BIT STRING (SIZE (5))
}
ab-Enabled : It stands for "access barring Enabled". If this IE is enabled, UE shall wait for SystemInformationBlockType14-NB before initiating RRC connection establishment or resume
operationModeInfo : This IE indicates the operation mode of the LTE-NB. There are four different types of Operation Mode as listed below.
- Inband-SamePCI : indicates an in-band deployment and that the NB-IoT and LTE cell share the same physical cell id and have the same number of NRS and CRS ports.
- Inband-DifferentPCI : indicates an in-band deployment and that the NB-IoT and LTE cell have different physical cell id.
- guardband : indicates a guard-band deployment.
- standalone : indicates a standalone deployment
schedulingInfoSIB1 : This IE indicates the index of the following table. The IE value itself is indicates I_TBS for SIB1-NB transmission and for each I_TBS different number of repetition occurs as mapped in the second column (Number of NPDSCH repetitions).
< 36.213 Table 16.4.1.3-3: Number of repetitions for NPDSCH carrying SystemInformationBlockType1-NB >
< 36.213 Table 16.4.1.5.2-1:Transport block size (TBS) table for NPDSCH carrying SystemInformationBlockType1-NB >
systemFrameNumber-MSB : We need 10 bits to represents SFN(0~1023). This IE represents 4 MSB of SFN and 6 remaining bits are derived implicitely from PBCH decoding process.
Example 1 >
BCCH-BCH-Message-NB
message
systemFrameNumber-MSB-r13: 00 [bit length 4, 4 LSB pad bits, 0000 .... decimal value 0]
hyperSFN-LSB-r13: 00 [bit length 2, 6 LSB pad bits, 00.. .... decimal value 0]
schedulingInfoSIB1-r13: 4 NPDSCH repetitions - TBS 208 bits (0)
systemInfoValueTag-r13: 0
.... ...0 ab-Enabled-r13: False
operationModeInfo-r13: standalone-r13 (3)
standalone-r13
spare: 00 [bit length 5, 3 LSB pad bits, 0000 0... decimal value 0]
spare: 0000 [bit length 11, 5 LSB pad bits, 0000 0000 000. .... decimal value 0]
Like in normal (Legacy) LTE, SIB1-NB also carries the information as follows :
- i) Cell Access Related Information - PLMN Identity List, PLMN Identity, TA Code, Cell identity & Cell Status
- ii) Cell Selection Information - Minimum Receiver Level
- iii) Scheduling Information (Scheduling Information for other SIBs) - SI message type & Periodicity, SIB mapping Info, SI Window length
In terms of transmission schedule, SIB1-NB is transmitted as follows (based on 36.331 5.2.1.2a Scheduling for NB-IoT MIB scheduling)
- Transmitted at a fixed schedule with a periodicity of 2560 ms (256 Radio Frames)
- Transmitted in subframe #4 of every other frame in 16 continuous frames
- The starting frame for the first transmission of the SIB1-NB is derived from the cell PCID and the number of repetitions within the 2560 ms period and repetitions are made, equally spaced, within the 2560 ms period
- TBS for SystemInformationBlockType1-NB and the repetitions made within the 2560 ms are indicated by schedulingInfoSIB1 field in the MIB-NB
As mentioned above, SIB1 periodicity is predefined to be same in all eNB, but the offset (Starting subframe = the subframe where the first SIB1 is transmitted) gets different depending on schedulingInfoSIB1 in MIB based on following tables.
Following is ASN structure of SIB1 defined in 3GPP 36.331.
SystemInformationBlockType1-NB ::= SEQUENCE {
hyperSFN-MSB-r13 BIT STRING (SIZE (8)),
cellAccessRelatedInfo-r13 SEQUENCE {
plmn-IdentityList-r13 PLMN-IdentityList-NB-r13,
trackingAreaCode-r13 TrackingAreaCode,
cellIdentity-r13 CellIdentity,
cellBarred-r13 ENUMERATED {barred, notBarred},
intraFreqReselection-r13 ENUMERATED {allowed, notAllowed}
},
cellSelectionInfo-r13 SEQUENCE {
q-RxLevMin-r13 Q-RxLevMin,
q-QualMin-r13 Q-QualMin-r9
},
p-Max-r13 P-Max OPTIONAL, -- Need OP
freqBandIndicator-r13 FreqBandIndicator-NB-r13,
freqBandInfo-r13 NS-PmaxList-NB-r13 OPTIONAL, -- Need OR
multiBandInfoList-r13 MultiBandInfoList-NB-r13 OPTIONAL, -- Need OR
downlinkBitmap-r13 DL-Bitmap-NB-r13 OPTIONAL, -- Need OP,
eutraControlRegionSize-r13 ENUMERATED {n1, n2, n3} OPTIONAL, -- Cond inband
nrs-CRS-PowerOffset-r13 ENUMERATED {dB-6, dB-4dot77, dB-3,
dB-1dot77, dB0, dB1,
dB1dot23, dB2, dB3,
dB4, dB4dot23, dB5,
dB6, dB7, dB8,
dB9} OPTIONAL, -- Cond inband-SamePCI
schedulingInfoList-r13 SchedulingInfoList-NB-r13,
si-WindowLength-r13 ENUMERATED {ms160, ms320, ms480, ms640,
ms960, ms1280, ms1600, spare1},
si-RadioFrameOffset-r13 INTEGER (1..15) OPTIONAL, -- Need OP
systemInfoValueTagList-r13 SystemInfoValueTagList-NB-r13 OPTIONAL, -- Need OR
lateNonCriticalExtension OCTET STRING OPTIONAL,
nonCriticalExtension SEQUENCE {} OPTIONAL
}
PLMN-IdentityList-NB-r13 ::= SEQUENCE (SIZE (1..maxPLMN-r11)) OF PLMN-IdentityInfo-NB-r13
PLMN-IdentityInfo-NB-r13 ::= SEQUENCE {
plmn-Identity-r13 PLMN-Identity,
cellReservedForOperatorUse-r13 ENUMERATED {reserved, notReserved},
attachWithoutPDN-Connectivity-r13 ENUMERATED {true} OPTIONAL -- Need OP
}
SchedulingInfoList-NB-r13 ::= SEQUENCE (SIZE (1..maxSI-Message-NB-r13)) OF SchedulingInfo-NB-r13
SchedulingInfo-NB-r13::= SEQUENCE {
si-Periodicity-r13 ENUMERATED {rf64, rf128, rf256, rf512,
rf1024, rf2048, rf4096, spare},
si-RepetitionPattern-r13 ENUMERATED {every2ndRF, every4thRF,
every8thRF, every16thRF},
sib-MappingInfo-r13 SIB-MappingInfo-NB-r13,
si-TB-r13 ENUMERATED {b56, b120, b208, b256, b328, b440, b552, b680}
}
SystemInfoValueTagList-NB-r13 ::= SEQUENCE (SIZE (1.. maxSI-Message-NB-r13)) OF
SystemInfoValueTagSI-r13
SIB-MappingInfo-NB-r13 ::= SEQUENCE (SIZE (0..maxSIB-1)) OF SIB-Type-NB-r13
SIB-Type-NB-r13 ::= ENUMERATED {
sibType3-NB-r13, sibType4-NB-r13, sibType5-NB-r13,
sibType14-NB-r13, sibType16-NB-r13, spare3, spare2, spare1}
downlinkBitmap : This indicate which subframe can be used for downlink transmission. If this IE is missing, it is assumed that any subframe except NPSS/NSSS/NPBCH/SIB1-NB subframe can be used for downlink transmission.
eutraControlRegionSize : This applies only to in-band Operation mode. It indicates how many OFDM symbols are used for control region.
si-RadioFrameOffset : This indicates the Offset to calculate the start of the SI window in the unit of radio frames. If the field is absent, no offset is applied.
si-Periodicity : This sepcifies periodicity of SI message (SIB message other than SIB1) in the unit of radio frames.
si-WindowLength : This specifies the SI window size for all SI messages (SIB message other than SIB1) in the unit of ms.
si-RepetitionPattern : This Indicates the starting radio frames within the SI window used for SI message transmission.
si-TB : This specifies the transport block size for all SI messages (SIB message other than SIB1) in the unit of bits.
Example 1 >
systemInformationBlockType1-r13
hyperSFN-MSB-r13: 00 [bit length 8, 0000 0000 decimal value 0]
cellAccessRelatedInfo-r13
plmn-IdentityList-r13: 1 item
Item 0
PLMN-IdentityInfo-NB-r13
plmn-Identity-r13
mcc: 3 items
Item 0
MCC-MNC-Digit: 0
Item 1
MCC-MNC-Digit: 0
Item 2
MCC-MNC-Digit: 1
mnc: 2 items
Item 0
MCC-MNC-Digit: 0
Item 1
MCC-MNC-Digit: 1
cellReservedForOperatorUse-r13: notReserved (1)
attachWithoutPDN-Connectivity-r13: true (0)
trackingAreaCode-r13: 0001 [bit length 16, 0000 0000 0000 0001 decimal value 1]
cellIdentity-r13: 00000010
cellBarred-r13: notBarred (1)
intraFreqReselection-r13: allowed (0)
cellSelectionInfo-r13
q-RxLevMin-r13: -140dBm (-70)
q-QualMin-r13: -34dB
p-Max-r13: -30dBm
freqBandIndicator-r13: 2
eutraControlRegionSize-r13: n2 (1)
nrs-CRS-PowerOffset-r13: dB6 (12)
schedulingInfoList-r13: 1 item
Item 0
SchedulingInfo-NB-r13
si-Periodicity-r13: rf64 (0)
si-RepetitionPattern-r13: every4thRF (1)
sib-MappingInfo-r13: 1 item
Item 0
SIB-Type-NB-r13: sibType3-NB-r13 (0)
si-TB-r13: b256 (3)
si-WindowLength-r13: ms160 (0)
SystemInformationBlockType2-NB-r13 ::= SEQUENCE {
radioResourceConfigCommon-r13 RadioResourceConfigCommonSIB-NB-r13,
ue-TimersAndConstants-r13 UE-TimersAndConstants-NB-r13,
freqInfo-r13 SEQUENCE {
ul-CarrierFreq-r13 CarrierFreq-NB-r13
additionalSpectrumEmission-r13 AdditionalSpectrumEmission
},
timeAlignmentTimerCommon-r13 TimeAlignmentTimer,
multiBandInfoList-r13 SEQUENCE (SIZE (1..maxMultiBands)) OF AdditionalSpectrumEmission
lateNonCriticalExtension OCTET STRING
...
}
RadioResourceConfigCommonSIB-NB-r13 ::= SEQUENCE {
rach-ConfigCommon-r13 RACH-ConfigCommon-NB-r13,
bcch-Config-r13 BCCH-Config-NB-r13,
pcch-Config-r13 PCCH-Config-NB-r13,
nprach-Config-r13 NPRACH-ConfigSIB-NB-r13,
npdsch-ConfigCommon-r13 NPDSCH-ConfigCommon-NB-r13,
npusch-ConfigCommon-r13 NPUSCH-ConfigCommon-NB-r13,
dl-Gap-r13 DL-GapConfig-NB-r13
uplinkPowerControlCommon-r13 UplinkPowerControlCommon-NB-r13,
...
}
RACH-ConfigCommon-NB-r13 ::= SEQUENCE {
preambleTransMax-CE-r13 PreambleTransMax,
powerRampingParameters-r13 PowerRampingParameters,
rach-InfoList-r13 RACH-InfoList-NB-r13,
connEstFailOffset-r13 INTEGER (0..15) OPTIONAL, -- Need OP
...
}
RACH-InfoList-NB-r13 ::= SEQUENCE (SIZE (1.. maxNPRACH-Resources-NB-r13)) OF RACH-Info-NB-r13
RACH-Info-NB-r13 ::= SEQUENCE {
ra-ResponseWindowSize-r13 ENUMERATED {
pp2, pp3, pp4, pp5, pp6, pp7, pp8, pp10},
mac-ContentionResolutionTimer-r13 ENUMERATED {
pp1, pp2, pp3, pp4, pp8, pp16, pp32, pp64}
}
NPRACH-ConfigSIB-NB-r13 ::= SEQUENCE {
nprach-CP-Length-r13 ENUMERATED {us66dot7, us266dot7},
rsrp-ThresholdsPrachInfoList-r13 RSRP-ThresholdsNPRACH-InfoList-NB-r13
nprach-ParametersList-r13 NPRACH-ParametersList-NB-r13
}
NPRACH-ParametersList-NB-r13 ::= SEQUENCE (SIZE (1.. maxNPRACH-Resources-NB-r13))
NPRACH-Parameters-NB-r13::= SEQUENCE {
nprach-Periodicity-r13 ENUMERATED {ms40, ms80, ms160, ms240,
ms320, ms640, ms1280, ms2560},
nprach-StartTime-r13 ENUMERATED {ms8, ms16, ms32, ms64,
ms128, ms256, ms512, ms1024},
nprach-SubcarrierOffset-r13 ENUMERATED {n0, n12, n24, n36, n2, n18, n34, spare1},
nprach-NumSubcarriers-r13 ENUMERATED {n12, n24, n36, n48},
nprach-SubcarrierMSG3-RangeStart-r13 ENUMERATED {zero, oneThird, twoThird, one},
maxNumPreambleAttemptCE-r13 ENUMERATED {n3, n4, n5, n6, n7, n8, n10, spare1},
numRepetitionsPerPreambleAttempt-r13 ENUMERATED {n1, n2, n4, n8, n16, n32, n64, n128},
npdcch-NumRepetitions-RA-r13 ENUMERATED {r1, r2, r4, r8, r16, r32, r64, r128,
r256, r512, r1024, r2048,
spare4, spare3, spare2, spare1},
npdcch-StartSF-CSS-RA-r13 ENUMERATED {v1dot5, v2, v4, v8, v16, v32, v48, v64},
npdcch-Offset-RA-r13 ENUMERATED {zero, oneEighth, oneFourth, threeEighth}
}
RSRP-ThresholdsNPRACH-InfoList-NB-r13 ::= SEQUENCE (SIZE(1..2)) OF RSRP-Range
Example >
sib2-r13
radioResourceConfigCommon-r13
rach-ConfigCommon-r13
preambleTransMax-CE-r13: n20 (7)
powerRampingParameters-r13
powerRampingStep: dB4 (2)
preambleInitialReceivedTargetPower: dBm-92 (14)
rach-InfoList-r13: 1 item
Item 0
RACH-Info-NB-r13
ra-ResponseWindowSize-r13: pp10 (7)
mac-ContentionResolutionTimer-r13: pp8 (4)
bcch-Config-r13
modificationPeriodCoeff-r13: n16 (0)
pcch-Config-r13
defaultPagingCycle-r13: rf128 (0)
nB-r13: fourT (0)
npdcch-NumRepetitionPaging-r13: r1 (0)
nprach-Config-r13
nprach-CP-Length-r13: us66dot7 (0)
nprach-ParametersList-r13: 1 item
Item 0
NPRACH-Parameters-NB-r13
nprach-Periodicity-r13: ms640 (5)
nprach-StartTime-r13: ms8 (0)
nprach-SubcarrierOffset-r13: n12 (1)
nprach-NumSubcarriers-r13: n12 (0)
nprach-SubcarrierMSG3-RangeStart-r13: one (3)
maxNumPreambleAttemptCE-r13: n10 (6)
numRepetitionsPerPreambleAttempt-r13: n1 (0)
npdcch-NumRepetitions-RA-r13: r16 (4)
npdcch-StartSF-CSS-RA-r13: v4 (2)
npdcch-Offset-RA-r13: zero (0)
npdsch-ConfigCommon-r13
nrs-Power-r13: 1dBm
npusch-ConfigCommon-r13
ack-NACK-NumRepetitions-Msg4-r13: 1 item
Item 0
ACK-NACK-NumRepetitions-NB-r13: r1 (0)
dmrs-Config-r13
threeTone-BaseSequence-r13: 0
threeTone-CyclicShift-r13: 0
sixTone-CyclicShift-r13: 0
ul-ReferenceSignalsNPUSCH-r13
.... 0... groupHoppingEnabled-r13: False
groupAssignmentNPUSCH-r13: 0
uplinkPowerControlCommon-r13
p0-NominalNPUSCH-r13: -92dBm
alpha-r13: al1 (7)
deltaPreambleMsg3-r13: -2dB (-1)
ue-TimersAndConstants-r13
t300-r13: ms2500 (0)
t301-r13: ms2500 (0)
t310-r13: ms0 (0)
n310-r13: n1 (0)
t311-r13: ms1000 (0)
n311-r13: n1 (0)
freqInfo-r13
additionalSpectrumEmission-r13: 1
timeAlignmentTimerCommon-r13: infinity (7)
sib-TypeAndInfo-r13 item: sib3-r13 (1)
Reference :
[1] 3GPP TS 36.331
[2] NB-IoT : A SUSTAINABLE TECHNOLOGY FOR CONNECTING BILLIONS OF DEVICES (Ericsson)
[3] LTE evolution for IoT connectivity