3GPP TSG-RAN2#99bis
`Pargue, Czech Republic, 9th – 13th, October 2017
`
`10.4.1.6.4
`Agenda Item:
`OPPO
`Source:
`Discussion on NR SI Modification
`Title:
`Document for: Discussion and Decision
`
` R2-1710181
`
`1 Introduction
`In NR system, the SI messages are divided into two groups, one is named as Minimum SI which is
`periodically broadcast and comprises of basic information required for initial access and information for ther SI
`scheduling. The other one is named as Other SI which includes everything not broadcast in the Minimum SI
`and may either be broadcast or triggered upon network or the request from the UE [1].
`However, in previous meeting, what’s the behavior of network and UE has not been discussed when the SI is
`changed. Therefore, in this contribution, we discuss both Minimums SI modification and Other SI modification
`respectively, and subsequently provide our proposals.
`
`2 Discussion
`2.1 Modification Period
`In LTE, when the network changes (some of the) system information, it first notifies the UEs about this
`change, i.e. this may be done throughout a modification period. In the next modification period, the network
`transmits the updated system information as indicated in Figure 1. This general principle is applied to almost
`all SI message in LTE.
`
`Change notification
`
`Updated information
`
`BCCH modification period (n)
`
`BCCH modification period (n+1)
`
`
`
`Figure 1. Change of System Information
`In NR, the SI message including both Minimum SI and Other SI can still follow the same LTE principle, which
`is that the change notification will be sent through modification period n, while the new system information will
`be updated in modification period n+1, because both types of SI require the UE who are interested in the
`information getting the notification before the system information really changes.
`Proposal 1 NR can take the modification period concept in LTE as the baseline for NR SI Change.
`2.2 Change Notification
`In LTE, the systemInfoModification included in the Paging message is used to notify the UE in RRC_IDLE and
`UEs in RRC_CONNECTED about the system information change. When the UE gets the change notification
`i.e. systemInfoModification in Paging message, it will understand that there is some modification on the stored
`system information without knowing exactly which one is changed. In this case, the UE has to either update all
`the system information, or at least acquire the MIB information to determine whether to update the system
`information accordingly if the UE is eMTC or NB-IoT UE. Obviously, this is not efficient from UE power
`consumption perspective.
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`In NR, the Minimum SI will be defined as two parts, i.e. Minimum SI transmitted in PBCH (i.e. MSI defined in
`RAN1, and similar like MIB in LTE) as well as Minimum SI transmitted via PDSCH (i.e. RMSI defined in
`RAN1, and similar like SIB1 and SIB2 in LTE).
`The Minimum SI contained in PBCH will be always transmitted with using specific resource defined by
`physical layer, and based on previous discussions and agreements about the contents of PBCH in RAN1 [2],
`the information contained in PBCH including the configuration of RMSI scheduling information may be quite
`static, therefore, there is no change notification needed for the Minimum SI contained in PBCH.
`Proposal 2 No need to add change notification in Paging message for Minimum SI contained in
`PBCH.
`The Minimum SI contained in PDSCH i.e. SIB1 (and SIB2 if defined) discussed in RAN2 will contain rest of
`the Minimum SI related to initial access and Other SI scheduling. The information here will change more
`frequent than that contained in PBCH. If UE could know exactly whether the Minimum SI contained in PDSCH
`is changed or not, the UE power as well as the SI acquisition time could be optimized, therefore,
`Proposal 3 The change notification for the Minimum SI contained in PDSCH i.e. SIB1 (and SIB2 if
`defined) should be added in Paging message.
`For Other SI message, since they are interested by specific UEs, it’s better for the UE to understand well
`which Other SI is changed, in this case, those UEs who are not interested in the SI message could skip the SI
`update, therefore, the UE power consumption could be saved.
`Proposal 4 For Other SI, the SI specific/per-SIB change notification should be introduced in Paging
`message.
`2.3 Value Tag
`In current LTE system, in addition to the change notification provided in Paging, a value tag i.e.
`systemInfoValueTag is also included in SIB1 to indicate if a change has occurred in the SI messages. UEs
`may use systemInfoValueTag, e.g. upon return from out of coverage, to verify if the previously stored SI
`messages are still valid. And in LTE enhancements for eMTC and NB-IoT, the value tag has been enhanced
`to identify specific SI changed. Moreover, in LTE, the SIBs other than MIB,SIB1, SIB10/11/12/14 share the
`same SystemInfoValueTag. We think this may not be suitable for NR because Other SIs may be
`independently broadcasted. If all the SIs in Other SI shares just one SystemInfoValueTag, then each SIB
`change will cause the UE to acquire all the SIBs. Considering all the above aspects, we propose that in
`stage-3 work, RAN2 could define SystemInfoValueTag per SIB, or per SI message or per SIB group. Here,
`SIB group means certain SIBs which may appear together which may be relevant for one function like cell
`selection reselection or one service like V2X, D2D etc.
`Proposal 5 For NR, RAN2 should discuss whether value tag can be per-SIB or per-SI message or
`per-SIB group.
`For per-SIB value tag, as the change notification discussed in Section 2.2, the per-SIB value tag for RMSI and
`Other SI should be supported.
`Proposal 6 The per-SIB value tag for RMSI (at least SIB2 is RAN2 agrees RMSI contains SIB1 and
`SIB2) and Other SI can be supported.
`In the last meeting discussion, it was agreed that no value tag/area related info will be included in MIB.
`Therefore, the value tag will be included in SIB1 which is aligned with LTE.
`Proposal 7 The value tag should be included in SIB1.
`2.4 Behavior of Network and UE when SI is changed
`When the one SI is changed, including the Minimum SI contained in PDSCH and Other SI, the UE will receive
`the paging message with change notification for that SI. After the reception of the notification, the UE will
`understand which SI is changed. If the UE is interested in that SI, the UE will update the SI with the
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`scheduling information stored; while if the UE is not interested in that SI, the UE will just skip the change
`notification.
`No matter the updated SI belongs to Minimum SI or Other SI, no request is supposed to be transmitted from
`UE. The network should transmitted the updated SI message after the modification boundary at least for a
`defined period.
`Proposal 8 When the SI is changed, no SI request needs to be sent from UE, and network will send
`the updated SI after the modification boundary at least for a period defined.
`
`3 Conclusions:
`In this contribution, we discuss both Minimums SI modification and Other SI modification respectively, and
`subsequently provide our proposals as follows:
`Proposal 1 NR can take the modification period concept in LTE as the baseline for NR SI Change.
`Proposal 2 No need to add change notification in Paging message for Minimum SI contained in
`PBCH.
`Proposal 3 The change notification for the Minimum SI contained in PDSCH i.e. SIB1 (and SIB2 if
`defined) should be added in Paging message.
`Proposal 4 For Other SI, the SI specific change notification should be introduced in Paging
`message.
`Proposal 5 For NR, RAN2 should discuss whether SystemValueTag can be per-SIB or per-SI
`message or per-SIB group.
`Proposal 6 The per-SIB value tag for RMSI (at least SIB2 is RAN2 agrees RMSI contains SIB1 and
`SIB2) and Other SI can be supported.
`Proposal 7 The value tag should be included in SIB1.
`Proposal 8 When the SI is changed, no SI request needs to be sent from UE, and network will send
`the updated SI after the modification boundary at least for a period defined.
`
`4 References:
`[1]. TS 38.300, NR and NG-RAN Overall Description, Stage 2;
`[2]. R2-1706304, LS on NR-PBCH content (R1-1709789; contact: Ericsson), RAN1.
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