How do UE read modified SI by NW

Below are the steps how do UE read when there is a modification of sib from NW side.

This we can get from below test case according 3GPP spec TS-36.523-1
8.1.1.2 RRC / Paging for notification of BCCH modification in idle mode


According the Test Case Below is the steps included for the Test case,


Main Steps in this test cases are 1,5,6,7 and 7a.

Step 1 verifies whether the UE is able respond to paging or not after the attach which is without any SI modification. In-fact this during this attach whatever SI has been transmitted are the scale to determine about the SI changes done by NW.

Step 5 NW transmits a paging like below,

Air Message: AIR_MSG_TYPE_PCCH
        paging Paging
          systemInfoModification PagingsystemInfoModification_true
          pagingRecordList_exist         0
          systemInfoModification_exist 1
          etws_Indication_exist                 0
          nonCriticalExtension_exist         0
As this is applicable to all the UE on that eNB so this kind of Paging doesn't include any UE identity.

Step 6 ensures that UE receive's the changed system information.
         This will be done by in this test scenario,
          First UE will go and read SIB1 - which will have SystemInfoValueTag as 1 in this case.
          Then UE will go and read SIB2 according scheduling Info provided by the new SIB1.
           This test case includes only PRACH CONFIG INDEX changed in SIB2 as below,

Previously:
prach_ConfigIndex 3
Now:
prach_ConfigIndex 10


Step 7  and 7a is just for checking whether UE is able to setup RRC Connection with NW or not?
         This steps will not be happening in case of live NW.
          Here NW pages (Step 7) UE with Paging message as below with S-Tmsi and UE establishes Rrc Connection Successfully (Step 7a).

Air Message: AIR_MSG_TYPE_PCCH

 

          pagingRecordList_exist         1

          systemInfoModification_exist 0

          etws_Indication_exist                 0

          nonCriticalExtension_exist         0

        pagingRecordList[0] PagingRecord

            ue_Identity PagingUE_Identity_

              s_TMSI S_TMSI

                mmec MMEC

                  buff[0..0] 01 

                TMSI S_TMSIm_TMSI

                  buff[0..3] c2 34 56 78 

       

St	Procedure	Message Sequence		TP	Verdict
		U - S	Message
1	The SS transmits a Paging message including a matched identity.	<--	Paging	-	-
2	Check: Does the UE transmit an RRCConnectionRequest message?	-->	RRCConnectionRequest	1	P
3	The SS transmits an RRCConnectionSetup message.	<--	RRCConnectionSetup	-	-
3A	The UE transmits an RRCConnectionSetupComplete message. This message includes a SERVICE REQUEST message.	-->	RRCConnectionSetupComplete	-	-
3B	The SS transmits a SecurityModeCommand message.	<--	SecurityModeCommand	-	-
3C	The UE transmits a SecurityModeComplete message.	-->	SecurityModeComplete	-	-
3D	The SS transmits an RRCConnectionReconfiguration message.	<--	RRCConnectionReconfiguration	-	-
3E	The UE transmits an RRCConnectionReconfigurationComplete message.	-->	RRCConnectionReconfigurationComplete	-	-
3F	The SS transmits an RRCConnectionRelease message.	<--	RRCConnectionRelease	-	-
3G	Wait for 5 s for the UE to enter E-UTRA RRC_IDLE state.	-	-	-	-
4	The SS changes the prach-ConfigIndex in the system information	-	-	-	-
5	The SS transmits a Paging message including a systemInfoModification.	<--	Paging	-	-
6	Wait for 15s for the UE to receive system information.	-	-	-	-
7	The SS transmits a Paging message including a matched identity.	<--	Paging	-	-
7A	Check: Does the UE re-transmit a random access using prach-ConfigIndex given in step 4?	-	-	1	P
8	The UE transmit an RRCConnectionRequest message.	-->	RRCConnectionRequest	-	-
9	The SS transmits an RRCConnectionSetup message.	<--	RRCConnectionSetup	-	-
9A	The UE transmits an RRCConnectionSetupComplete message. This message includes a SERVICE REQUEST message.	-->	RRCConnectionSetupComplete	-	-
9B	The SS transmits a SecurityModeCommand message.	<--	SecurityModeCommand	-	-
9C	The UE transmits a SecurityModeComplete message.	-->	SecurityModeComplete	-	-
9D	The SS transmits an RRCConnectionReconfiguration message.	<--	RRCConnectionReconfiguration	-	-
9E	The UE transmits an RRCConnectionReconfigurationComplete message.	-->	RRCConnectionReconfigurationComplete	-	-
9F	The SS transmits an RRCConnectionRelease message.	<--	RRCConnectionRelease	-	-
9G	Wait for 5 s for the UE to enter E-UTRA RRC_IDLE state.	-	-	-	-
10	Check: Does the test result of generic test procedure in TS 36.508 subclause 6.4.2.2 indicate that the UE is in E-UTRA RRC_IDLE state on Cell 1?	-	-	1	-

Paging in LTE

The purpose of this procedure is:
- to transmit paging information to a UE in RRC_IDLE and/ or;
- to inform UEs in RRC_IDLE and UEs in RRC_CONNECTED about a system information change and/ or;
- to inform about an ETWS primary notification and/ or ETWS secondary notification and/ or;
- to inform about a CMAS notification.
The paging information is provided to upper layers, which in response may initiate RRC connection establishment, e.g.
to receive an incoming call.

Discontinuous Reception for paging

The UE may use Discontinuous Reception (DRX) in idle mode in order to reduce power consumption.
One Paging Occasion (PO) is a subframe where there may be P-RNTI transmitted on PDCCH addressing the paging message.
One Paging Frame (PF) is one Radio Frame, which may contain one or multiple Paging Occasion(s). When DRX is used the UE needs only to monitor one PO per DRX cycle.

PF and PO is determined by following formulae using the DRX parameters provided in System Information:
PF is given by following equation:
SFN mod T= (T div N)*(UE_ID mod N)

Index i_s pointing to PO from subframe pattern , will be derived from following calculation:
i_s = floor(UE_ID/N) mod Ns

System Information DRX parameters stored in the UE shall be updated locally in the UE whenever the DRX parameter
values are changed in SI. If the UE has no IMSI, for instance when making an emergency call without USIM, the UE
shall use as default identity UE_ID = 0 in the PF and i_s formulas above.

The following Parameters are used for the calculation of the PF and i_s:
- T: DRX cycle of the UE. T is determined by the shortest of the UE specific DRX value, if allocated by upper
layers, and a default DRX value broadcast in system information. If UE specific DRX is not configured by upper
layers, the default value is applied.
- nB: 4T, 2T, T, T/2, T/4, T/8, T/16, T/32.
- N: min(T,nB)
- Ns: max(1,nB/T)
- UE_ID: IMSI mod 1024.

IMSI is given as sequence of digits of type Integer (0..9), IMSI shall in the formulae above be interpreted as a decimal
integer number, where the first digit given in the sequence represents the highest order digit.
For example:
IMSI = 12 (digit1=1, digit2=2)
In the calculations, this shall be interpreted as the decimal integer "12", not "1x16+2 = 18".

FDD Sub-frame Patterns

TDD Sub-frame Patterns

Ref: http://www.etsi.org/deliver/etsi_ts/136300_136399/136304/12.02.00_60/ts_136304v120200p.pdf




Upon receiving the Paging message, the UE shall:

1> if in RRC_IDLE, for each of the PagingRecord, if any, included in the Paging message:
2> if the ue-Identity included in the PagingRecord matches one of the UE identities allocated by upper layers:
3> forward the ue-Identity and the cn-Domain to the upper layers;
1> if the systemInfoModification is included:
2> re-acquire the required system information using the system information acquisition procedure as specified in
5.2.2.
1> if the etws-Indication is included and the UE is ETWS capable:
2> re-acquire SystemInformationBlockType1 immediately, i.e., without waiting until the next system information
modification period boundary;
2> if the schedulingInfoList indicates that SystemInformationBlockType10 is present:
3> acquire SystemInformationBlockType10;
2> if the schedulingInfoList indicates that SystemInformationBlockType11 is present:
3> acquire SystemInformationBlockType11;
1> if the cmas-Indication is included and the UE is CMAS capable:
2> re-acquire SystemInformationBlockType1 immediately, i.e., without waiting until the next system information modification period boundary as specified in 5.2.1.5;
2> if the schedulingInfoList indicates that SystemInformationBlockType12 is present:
3> acquire SystemInformationBlockType12;



Paging in LTE
   1. For MT Call(PS/CS)
   2. For SI (System Information) modification
   3. For ETWS (Earthquake and Tsunami Warning System)


Example for Type 1: PS Call
As this is for a specific UE , it includes a paging record list.
Paging record list is an array, so this might include more than UE if needed.

Air Message: AIR_MSG_TYPE_PCCH

 

          pagingRecordList_exist         1

          systemInfoModification_exist 0

          etws_Indication_exist                 0

          nonCriticalExtension_exist         0

        pagingRecordList[0] PagingRecord

            ue_Identity PagingUE_Identity_

              s_TMSI S_TMSI

                mmec MMEC

                  buff[0..0] 01

                TMSI S_TMSIm_TMSI

                  buff[0..3] c2 34 56 78

Example for Type 2: SI Modification 
as it is applicable for all the UE's under that eNB so it doesn't need any UE identifier.


Air Message: AIR_MSG_TYPE_PCCH
        paging Paging
          systemInfoModification PagingsystemInfoModification_true
          pagingRecordList_exist         0
          systemInfoModification_exist 1
          etws_Indication_exist                 0
          nonCriticalExtension_exist         0

Example for Type 3: For ETWS 
as it is applicable for all the UE's under that eNB so it doesn't need any UE identifier.

Air Message: AIR_MSG_TYPE_PCCH
        paging Paging
          systemInfoModification PagingsystemInfoModification_true
          pagingRecordList_exist         0
          systemInfoModification_exist 0
          etws_Indication_exist                 1
          nonCriticalExtension_exist         0



SIB2 Caries Configuration for PCCH - Paging Control Channel

Sib2 contains , RadioResourceConfigCommonSIB

Under PCCH-Config

PCCH-Config ::= SEQUENCE {
defaultPagingCycle ENUMERATED {
rf32, rf64, rf128, rf256},
nB ENUMERATED {
fourT, twoT, oneT, halfT, quarterT, oneEighthT,
oneSixteenthT, oneThirtySecondT}
}

defaultPagingCycle
Default paging cycle, used to derive "T" in TS 36.304 [4]. Value rf32 corresponds to 32 radio frames, rf64 corresponds to 64 radio frames and so on.

nB
Parameter: nB is used as one of parameters to derive the Paging Frame and Paging Occasion according to TS 36.304 [4]. Value in multiples of 'T' as defined in TS 36.304 [4]. A value of fourT corresponds to 4 * T, a value of twoT corresponds to 2 * T and so on.



Either SIB2 configuration or UE upper-layer configuration is considered for nB.

There is concept of paging occasion and paging frame to help UE saving it's power further on DRX mode.

Paging Occasion: Paging Frame:

Cell Acqusition in LTE

This is one of the confusing and most beautiful thing in LTE.

To understand Cell Acquisition in LTE we will need help of 3gpp Spec 36.211 and 36.331 sometime.

36.211 : Physical Channel
36.331 : Radio Resource Control

1. From the primary synchronization signal(PSS), it discovers the symbol timing and gets some incomplete information about the physical cell identity.
2. From the secondary synchronization signal(SSS), it discovers the frame timing, the physical cell identity, the transmission mode(FDD or TDD) and the cyclic prefix duration (normal or extended).

3. Once PSS and SSS is acquired, the mobile starts reception of the cell specific reference signals. These provides an amplitude and phase reference for the channel estimation process, which are essential for everything that follows.
4. The mobile then receives the physical broadcast channel and reads the master information block.
5. By doing so, it discovers the number of transmit antennas at the base station, the downlink bandwidth, the system frame number and a quantity called the PHICH configuration that describes the physical hybrid ARQ indicator channel.
6. The mobile can now start reception of the physical control format indicator channel (PCFICH), so as to read the control format indicators. These indicate how many symbols are reserved at the start of each downlink subframe for the physical control channels and
   how many are available for data transmissions.
7. Finally, the mobile can start reception of the physical downlink control channel (PDCCH).
8. This allows the mobile to read the remaining system information blocks (SIBs), which are sent on the physical downlink shared channel (PDSCH).
9. By doing this, it discovers all the remaining details about how the cell is configured, such as the identities of the networks that it belongs to.

Steps in the cell acquisition procedure
1	Receive PSS	Symbol Timing
		Cell Identity within Group
2	Receive SSS	Frame Timing
		Physical Cell Identity
		Transmission Mode (FDD/TDD)
		Cyclic Prefix Duration (Normal/Extended)
3	Receive RS	Amplitude and phase reference for demodulation
		Power reference for channel quality estimation
4	Read MIB from PBCH	Number Of Transmit Antennas
		Downlink bandwidth
		System frame number
		PHICH configuration
5	Start Reception Of PCFICH	Number of control symbols per subframe
6	Read SIB’s from PDSCH	System information

Frame Structure in LTE

FDD Down-link Frame Structure in LTE

Source: http://www.sharetechnote.com/image/36_211_Fig4_1_1_FDD_DL_FrameStructure.PNG


1 Frame = 1 ms
1 Frame = 10 Sub-frame

1 Slot = 0.5 ms
2 Slot = 2*0.5 ms = 1 ms
2 Slot = 1 Sub-frame

1 Frame = 10 (Sub-frame) * 2  slots = 20 Slots





Source: http://www.sharetechnote.com/image/FDD_DL_FrameStructure_Symbols.PNG


1 Slot = 7 Symbols
(In case of Normal Cyclic Prefix, 6 in case of Extended Cyclic Prefix)

1 Symbol = 0.5(Duration of 1 slot) / 7 (Number of Symbol per slot) ms =  ~71.4 us
1 Symbol =  Cyclic Prefix + Data

First OFDM symbol is longer than the rest of the OFDM symbol in that slot.

First Symbol = 71.9 us  = 5.2 us+ 66.7 us
Rest Symbol = 71.3 us  = 4.7 us + 66.6 us

First Symbol (time) + 6*Rest Symbol (time) = 71.9 us  + 6*71.3 us = 71.9 us + 427.8 us = 499.7 us = ~500 us = 0.5 ms

The Number of sample we see here in below illustration is based on the sampling rate is 30.072 M Samples/Sec and 2048 bins/IFFT(N_ifft). Since real sampling rate and N_ifft varies depending on system BW, we need to scale this number according to a specific BW.




Source: http://www.sharetechnote.com/image/FDD_DL_FrameStructure_Subframe_01.PNG












Source :http://www.sharetechnote.com/image/PHY_CH_DL.PNG













Source: http://www.sharetechnote.com/image/LTE_DL_FrameStructure_01.png

NEED ON/OR/OP in RRC

Abbreviation Meaning

Cond conditionTag (Used in downlink only) 
Conditionally present An information element for which the need is specified by means of conditions. For each conditionTag, the need is specified in a tabular form following the ASN.1 segment. In case, according to the conditions, a field is not present, the UE takes no action and where applicable shall continue to use the existing value (and/ or the associated functionality) unless explicitly stated otherwise in the description of the field itself.

Need OP (Used in downlink only)
 Optionally present An information element that is optional to signal. For downlink messages, the UE is not required to take any special action on absence of the IE beyond what is specified in the procedural text or the field description table following the ASN.1 segment. The UE behaviour on absence should be captured either in the procedural text or in the field description.

Need ON (Used in downlink only) 
Optionally present, No action An information element that is optional to signal. If the message is received by the UE, and in case the information element is absent, the UE takes no action and where applicable shall continue to use the existing value (and/ or the associated functionality).

Need OR (Used in downlink only)
 Optionally present, Release An information element that is optional to signal. If the message is received by the UE, and in case the information element is absent, the UE shall discontinue/ stop using/ delete any existing value (and/ or the associated functionality).