WO2017074042A1

WO2017074042A1 - Method and apparatus for indicating system information change for low complexity user equipments in wireless communication system

Info

Publication number: WO2017074042A1
Application number: PCT/KR2016/012124
Authority: WO
Inventors: Jaewook Lee; Youngdae Lee; Sunghoon Jung
Original assignee: Lg Electronics Inc.
Priority date: 2015-10-27
Filing date: 2016-10-27
Publication date: 2017-05-04

Abstract

A method and apparatus for receiving an indication of system information change in a wireless communication system is provided. An indication of system information change per system information category is proposed. A user equipment (UE) receives an indication of system information change for a specific system information category which related to a specific usage of system information from a network, and verifies whether the specific system information category has changed according to the indication of system information change for the specific system information category. If verified, the UE receives updated system information included in the specific system information category from the network.

Description

METHOD AND APPARATUS FOR INDICATING SYSTEM INFORMATION CHANGE FOR LOW COMPLEXITY USER EQUIPMENTS IN WIRELESS COMMUNICATION SYSTEM

The present invention relates to wireless communications, and more particularly, to a method and apparatus for indicating a system information change for low complexity user equipments (UEs) in a wireless communication system.

3rd generation partnership project (3GPP) long-term evolution (LTE) is a technology for enabling high-speed packet communications. Many schemes have been proposed for the LTE objective including those that aim to reduce user and provider costs, improve service quality, and expand and improve coverage and system capacity. The 3GPP LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement.

In the future versions of the LTE-A, it has been considered to configure low-cost/low-end (or, low-complexity) user equipments (UEs) focusing on the data communication, such as meter reading, water level measurement, use of security camera, vending machine inventory report, etc. For convenience, these UEs may be called machine type communication (MTC) UEs. Since MTC UEs have small amount of transmission data and have occasional uplink data transmission/downlink data reception, it is efficient to reduce the cost and battery consumption of the UE according to a low data rate. Specifically, the cost and battery consumption of the UE may be reduced by decreasing radio frequency (RF)/baseband complexity of the MTC UE significantly by making the operating frequency bandwidth of the MTC UE smaller.

System information is one of key aspects of air interface. It consists of master information block (MIB) and a number of system information blocks (SIBs). The MIB is broadcast on the physical broadcast channel (PBCH), while SIBs are sent on the physical downlink shared channel (PDSCH).　The MIB carries physical layer information of LTE cell which in turn help receive further SIBs. SIBs carry relevant information for the UE, which helps　UE to access　a cell, perform　cell re-selection, information related to intra-frequency, inter-frequency and inter-radio access technology (RAT) cell selections. When system information changes, it is indicated to the UE.

For the MTC UE, a method for indicating system information change more efficiently may be required.

The present invention provides a method and apparatus for indicating a system information change for low complexity user equipments (UEs) in a wireless communication system. The present invention provides a method and apparatus for indicating a system information change per system information block (SIB) category for low complexity UE, e.g. a bandwidth reduced low complexity (BL) UE, a UE in enhanced coverage, etc.

In an aspect, a method for receiving an indication of system information change by a user equipment (UE) in a wireless communication system is provided. The method includes receiving an indication of system information change for a specific system information category which related to a specific usage of system information from a network, verifying whether the specific system information category has changed according to the indication of system information change for the specific system information category, and if it is verified that the specific system information category has changed, receiving updated system information included in the specific system information category from the network.

In another aspect, a user equipment (UE) in a wireless communication system is provided. The UE includes a memory, a transceiver, a processor, coupled to the memory and the transceiver, that controls the transceiver to receive an indication of system information change for a specific system information category which related to a specific usage of system information from a network, verifies whether the specific system information category has changed according to the indication of system information change for the specific system information category, and if it is verified that the specific system information category has changed, controls the transceiver to receive updated system information included in the specific system information category from the network.

System information change can be indicated efficiently.

FIG. 1 shows LTE system architecture.

FIG. 2 shows a block diagram of architecture of a typical E-UTRAN and a typical EPC.

FIG. 3 shows a block diagram of a user plane protocol stack of an LTE system.

FIG. 4 shows a block diagram of a control plane protocol stack of an LTE system.

FIG. 5 shows an example of a physical channel structure.

FIG. 6 shows an example of change of system information.

FIG. 7 shows a method for receiving an indication of system information change by a UE according to an embodiment of the present invention.

FIG. 8 shows a wireless communication system to implement an embodiment of the present invention.

The technology described below can be used in various wireless communication systems such as code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), etc. The CDMA can be implemented with a radio technology such as universal terrestrial radio access (UTRA) or CDMA-2000. The TDMA can be implemented with a radio technology such as global system for mobile communications (GSM)/general packet ratio service (GPRS)/enhanced data rate for GSM evolution (EDGE). The OFDMA can be implemented with a radio technology such as institute of electrical and electronics engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), etc. IEEE 802.16m is an evolution of IEEE 802.16e, and provides backward compatibility with an IEEE 802.16-based system. The UTRA is a part of a universal mobile telecommunication system (UMTS). 3rd generation partnership project (3GPP) long term evolution (LTE) is a part of an evolved UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE uses the OFDMA in downlink and uses the SC-FDMA in uplink. LTE-advance (LTE-A) is an evolution of the 3GPP LTE.

For clarity, the following description will focus on the LTE-A. However, technical features of the present invention are not limited thereto.

FIG. 1 shows LTE system architecture. The communication network is widely deployed to provide a variety of communication services such as voice over internet protocol (VoIP) through IMS and packet data.

Referring to FIG. 1, the LTE system architecture includes one or more user equipment (UE; 10), an evolved-UMTS terrestrial radio access network (E-UTRAN) and an evolved packet core (EPC). The UE 10 refers to a communication equipment carried by a user. The UE 10 may be fixed or mobile, and may be referred to as another terminology, such as a mobile station (MS), a user terminal (UT), a subscriber station (SS), a wireless device, etc.

The E-UTRAN includes one or more evolved node-B (eNB) 20, and a plurality of UEs may be located in one cell. The eNB 20 provides an end point of a control plane and a user plane to the UE 10. The eNB 20 is generally a fixed station that communicates with the UE 10 and may be referred to as another terminology, such as a base station (BS), an access point, etc. One eNB 20 may be deployed per cell.

Hereinafter, a downlink (DL) denotes communication from the eNB 20 to the UE 10, and an uplink (UL) denotes communication from the UE 10 to the eNB 20. In the DL, a transmitter may be a part of the eNB 20, and a receiver may be a part of the UE 10. In the UL, the transmitter may be a part of the UE 10, and the receiver may be a part of the eNB 20.

The EPC includes a mobility management entity (MME) and a system architecture evolution (SAE) gateway (S-GW). The MME/S-GW 30 may be positioned at the end of the network and connected to an external network. For clarity, MME/S-GW 30 will be referred to herein simply as a "gateway," but it is understood that this entity includes both the MME and S-GW.

The MME provides various functions including non-access stratum (NAS) signaling to eNBs 20, NAS signaling security, access stratum (AS) security control, inter core network (CN) node signaling for mobility between 3GPP access networks, idle mode UE reachability (including control and execution of paging retransmission), tracking area list management (for UE in idle and active mode), packet data network (PDN) gateway (P-GW) and S-GW selection, MME selection for handovers with MME change, serving GPRS support node (SGSN) selection for handovers to 2G or 3G 3GPP access networks, roaming, authentication, bearer management functions including dedicated bearer establishment, support for public warning system (PWS) (which includes earthquake and tsunami warning system (ETWS) and commercial mobile alert system (CMAS)) message transmission. The S-GW host provides assorted functions including per-user based packet filtering (by e.g., deep packet inspection), lawful interception, UE Internet protocol (IP) address allocation, transport level packet marking in the DL, UL and DL service level charging, gating and rate enforcement, DL rate enforcement based on access point name aggregate maximum bit rate (APN-AMBR).

Interfaces for transmitting user traffic or control traffic may be used. The UE 10 is connected to the eNB 20 via a Uu interface. The eNBs 20 are connected to each other via an X2 interface. Neighboring eNBs may have a meshed network structure that has the X2 interface. A plurality of nodes may be connected between the eNB 20 and the gateway 30 via an S1 interface.

FIG. 2 shows a block diagram of architecture of a typical E-UTRAN and a typical EPC. Referring to FIG. 2, the eNB 20 may perform functions of selection for gateway 30, routing toward the gateway 30 during a radio resource control (RRC) activation, scheduling and transmitting of paging messages, scheduling and transmitting of broadcast channel (BCH) information, dynamic allocation of resources to the UEs 10 in both UL and DL, configuration and provisioning of eNB measurements, radio bearer control, radio admission control (RAC), and connection mobility control in LTE_ACTIVE state. In the EPC, and as noted above, gateway 30 may perform functions of paging origination, LTE_IDLE state management, ciphering of the user plane, SAE bearer control, and ciphering and integrity protection of NAS signaling.

FIG. 3 shows a block diagram of a user plane protocol stack of an LTE system. FIG. 4 shows a block diagram of a control plane protocol stack of an LTE system. Layers of a radio interface protocol between the UE and the E-UTRAN may be classified into a first layer (L1), a second layer (L2), and a third layer (L3) based on the lower three layers of the open system interconnection (OSI) model that is well-known in the communication system.

A physical (PHY) layer belongs to the L1. The PHY layer provides a higher layer with an information transfer service through a physical channel. The PHY layer is connected to a medium access control (MAC) layer, which is a higher layer of the PHY layer, through a transport channel. A physical channel is mapped to the transport channel. Data between the MAC layer and the PHY layer is transferred through the transport channel. Between different PHY layers, i.e., between a PHY layer of a transmission side and a PHY layer of a reception side, data is transferred via the physical channel.

A MAC layer, a radio link control (RLC) layer, and a packet data convergence protocol (PDCP) layer belong to the L2. The MAC layer provides services to the RLC layer, which is a higher layer of the MAC layer, via a logical channel. The MAC layer provides data transfer services on logical channels. The RLC layer supports the transmission of data with reliability. Meanwhile, a function of the RLC layer may be implemented with a functional block inside the MAC layer. In this case, the RLC layer may not exist. The PDCP layer provides a function of header compression function that reduces unnecessary control information such that data being transmitted by employing IP packets, such as IPv4 or Ipv6, can be efficiently transmitted over a radio interface that has a relatively small bandwidth.

A radio resource control (RRC) layer belongs to the L3. The RLC layer is located at the lowest portion of the L3, and is only defined in the control plane. The RRC layer controls logical channels, transport channels, and physical channels in relation to the configuration, reconfiguration, and release of radio bearers (RBs). The RB signifies a service provided the L2 for data transmission between the UE and E-UTRAN.

Referring to FIG. 3, the RLC and MAC layers (terminated in the eNB on the network side) may perform functions such as scheduling, automatic repeat request (ARQ), and hybrid ARQ (HARQ). The PDCP layer (terminated in the eNB on the network side) may perform the user plane functions such as header compression, integrity protection, and ciphering.

Referring to FIG. 4, the RLC and MAC layers (terminated in the eNB on the network side) may perform the same functions for the control plane. The RRC layer (terminated in the eNB on the network side) may perform functions such as broadcasting, paging, RRC connection management, RB control, mobility functions, and UE measurement reporting and controlling. The NAS control protocol (terminated in the MME of gateway on the network side) may perform functions such as a SAE bearer management, authentication, LTE_IDLE mobility handling, paging origination in LTE_IDLE, and security control for the signaling between the gateway and UE.

FIG. 5 shows an example of a physical channel structure. A physical channel transfers signaling and data between PHY layer of the UE and eNB with a radio resource. A physical channel consists of a plurality of subframes in time domain and a plurality of subcarriers in frequency domain. One subframe, which is 1ms, consists of a plurality of symbols in the time domain. Specific symbol(s) of the subframe, such as the first symbol of the subframe, may be used for a physical downlink control channel (PDCCH). The PDCCH carries dynamic allocated resources, such as a physical resource block (PRB) and modulation and coding scheme (MCS).

A DL transport channel includes a broadcast channel (BCH) used for transmitting system information, a paging channel (PCH) used for paging a UE, a downlink shared channel (DL-SCH) used for transmitting user traffic or control signals, a multicast channel (MCH) used for multicast or broadcast service transmission. The DL-SCH supports HARQ, dynamic link adaptation by varying the modulation, coding and transmit power, and both dynamic and semi-static resource allocation. The DL-SCH also may enable broadcast in the entire cell and the use of beamforming.

A UL transport channel includes a random access channel (RACH) normally used for initial access to a cell, an uplink shared channel (UL-SCH) for transmitting user traffic or control signals, etc. The UL-SCH supports HARQ and dynamic link adaptation by varying the transmit power and potentially modulation and coding. The UL-SCH also may enable the use of beamforming.

The logical channels are classified into control channels for transferring control plane information and traffic channels for transferring user plane information, according to a type of transmitted information. That is, a set of logical channel types is defined for different data transfer services offered by the MAC layer.

The control channels are used for transfer of control plane information only. The control channels provided by the MAC layer include a broadcast control channel (BCCH), a paging control channel (PCCH), a common control channel (CCCH), a multicast control channel (MCCH) and a dedicated control channel (DCCH). The BCCH is a downlink channel for broadcasting system control information. The PCCH is a downlink channel that transfers paging information and is used when the network does not know the location cell of a UE. The CCCH is used by UEs having no RRC connection with the network. The MCCH is a point-to-multipoint downlink channel used for transmitting multimedia broadcast multicast services　(MBMS) control information from the network to a UE. The DCCH is a point-to-point bi-directional channel used by UEs having an RRC connection that transmits dedicated control information between a UE and the network.

Traffic channels are used for the transfer of user plane information only. The traffic channels provided by the MAC layer include a dedicated traffic channel (DTCH) and a multicast traffic channel (MTCH). The DTCH is a point-to-point channel, dedicated to one UE for the transfer of user information and can exist in both uplink and downlink. The MTCH is a point-to-multipoint downlink channel for transmitting traffic data from the network to the UE.

Uplink connections between logical channels and transport channels include the DCCH that can be mapped to the UL-SCH, the DTCH that can be mapped to the UL-SCH and the CCCH that can be mapped to the UL-SCH. Downlink connections between logical channels and transport channels include the BCCH that can be mapped to the BCH or DL-SCH, the PCCH that can be mapped to the PCH, the DCCH that can be mapped to the DL-SCH, and the DTCH that can be mapped to the DL-SCH, the MCCH that can be mapped to the MCH, and the MTCH that can be mapped to the MCH.

An RRC state indicates whether an RRC layer of the UE is logically connected to an RRC layer of the E-UTRAN. The RRC state may be divided into two different states such as an RRC idle state (RRC_IDLE) and an RRC connected state (RRC_CONNECTED). In RRC_IDLE, the UE may receive broadcasts of system information and paging information while the UE specifies a discontinuous reception (DRX) configured by NAS, and the UE has been allocated an identification (ID) which uniquely identifies the UE in a tracking area and may perform public land mobile network (PLMN) selection and cell re-selection. Also, in RRC_IDLE, no RRC context is stored in the eNB.

In RRC_CONNECTED, the UE has an E-UTRAN RRC connection and a context in the E-UTRAN, such that transmitting and/or receiving data to/from the eNB becomes possible. Also, the UE can report channel quality information and feedback information to the eNB. In RRC_CONNECTED, the E-UTRAN knows the cell to which the UE belongs. Therefore, the network can transmit and/or receive data to/from UE, the network can control mobility (handover and inter-radio access technologies (RAT) cell change order to GSM EDGE radio access network (GERAN) with network assisted cell change (NACC)) of the UE, and the network can perform cell measurements for a neighboring cell.

In RRC_IDLE, the UE specifies the paging DRX cycle. Specifically, the UE monitors a paging signal at a specific paging occasion of every UE specific paging DRX cycle. The paging occasion is a time interval during which a paging signal is transmitted. The UE has its own paging occasion. A paging message is transmitted over all cells belonging to the same tracking area. If the UE moves from one tracking area (TA) to another TA, the UE will send a tracking area update (TAU) message to the network to update its location.

System information (SI) is described. It may be referred to Section 5.2.1 of 3GPP TS 36.331 V12.6.0 (2015-06). System information is divided into the MasterInformationBlock (MIB) and a number of SystemInformationBlocks (SIBs). The MIB includes a limited number of most essential and most frequently transmitted parameters that are needed to acquire other information from the cell, and is transmitted on BCH. SIBs other than SystemInformationBlockType1 are carried in SystemInformation (SI) messages and mapping of SIBs to SI messages is flexibly configurable by schedulingInfoList included in SystemInformationBlockType1, with restrictions that: each SIB is contained only in a single SI message, and at most once in that message. Only SIBs having the same scheduling requirement (periodicity) can be mapped to the same SI message. SystemInformationBlockType2 is always mapped to the SI message that corresponds to the first entry in the list of SI messages in schedulingInfoList. There may be multiple SI messages transmitted with the same periodicity. SystemInformationBlockType1 and all SI messages are transmitted on DL-SCH.

In addition to broadcasting, E-UTRAN may provide SystemInformationBlockType1, including the same parameter values, via dedicated signaling i.e., within an RRCConnectionReconfiguration message.

The UE applies the system information acquisition and change monitoring procedures for the primary cell (PCell). For a secondary cell (SCell), E-UTRAN provides, via dedicated signaling, all system information relevant for operation in RRC_CONNECTED when adding the SCell. However, a UE that is configured with dual connectivity (DC) shall acquire the MasterInformationBlock of the primary SCell (PSCell) but use it only to determine the system frame number (SFN) timing of the secondary cell group (SCG), which may be different from the master cell group (MCG). Upon change of the relevant system information of a configured SCell, E-UTRAN releases and subsequently adds the concerned SCell, which may be done with a single RRCConnectionReconfiguration message. If the UE is receiving or interested to receive an MBMS service in a cell, the UE shall apply the system information acquisition and change monitoring procedure to acquire parameters relevant for MBMS operation and apply the parameters acquired from system information only for MBMS operation for this cell.

The MIB uses a fixed schedule with a periodicity of 40ms and repetitions made within 40ms. The first transmission of the MIB is scheduled in subframe #0 of radio frames for which the SFN mod 4 = 0, and repetitions are scheduled in subframe #0 of all other radio frames.

The SystemInformationBlockType1 uses a fixed schedule with a periodicity of 80ms and repetitions made within 80ms. The first transmission of SystemInformationBlockType1 is scheduled in subframe #5 of radio frames for which the SFN mod 8 = 0, and repetitions are scheduled in subframe #5 of all other radio frames for which SFN mod 2 = 0.

The SI messages are transmitted within periodically occurring time domain windows (referred to as SI-windows) using dynamic scheduling. Each SI message is associated with a SI-window and the SI-windows of different SI messages do not overlap. That is, within one SI-window only the corresponding SI is transmitted. The length of the SI-window is common for all SI messages, and is configurable. Within the SI-window, the corresponding SI message can be transmitted a number of times in any subframe other than multicast-broadcast single-frequency network (MBSFN) subframes, UL subframes in TDD, and subframe #5 of radio frames for which SFN mod 2 = 0. The UE acquires the detailed time-domain scheduling (and other information, e.g. frequency-domain scheduling, used transport format) from decoding system information radio network temporary identifier (SI-RNTI) on PDCCH.

A single SI-RNTI is used to address SystemInformationBlockType1 as well as all SI messages.

SystemInformationBlockType1 configures the SI-window length and the transmission periodicity for the SI messages.

System information validity and notification of changes is described. Change of system information (other than for earthquake and tsunami warning system (ETWS), commercial mobile alert system (CMAS) and extended access barring (EAB) parameters) only occurs at specific radio frames, i.e. the concept of a modification period is used. System information may be transmitted a number of times with the same content within a modification period, as defined by its scheduling. The modification period boundaries are defined by SFN values for which SFN mod m=0, where m is the number of radio frames comprising the modification period. The modification period is configured by system information.

FIG. 6 shows an example of change of system information. 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. Referring to FIG. 6, different pattern indicate different system information. Upon receiving a change notification, the UE acquires the new system information immediately from the start of the next modification period. The UE applies the previously acquired system information until the UE acquires the new system information.

The Paging message is used to inform UEs in RRC_IDLE and UEs in RRC_CONNECTED about a system information change. If the UE receives a Paging message including the systemInfoModification, it knows that the system information will change at the next modification period boundary. Although the UE may be informed about changes in system information, no further details are provided e.g. regarding which system information will change.

SystemInformationBlockType1 includes a value tag, systemInfoValueTag, that indicates 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. Additionally, the UE considers stored system information to be invalid after 3 hours from the moment it was successfully confirmed as valid, unless specified otherwise.

E-UTRAN may not update systemInfoValueTag upon change of some system information e.g. ETWS information, CMAS information, regularly changing parameters like time information (SystemInformationBlockType8, SystemInformationBlockType16), EAB parameters. Similarly, E-UTRAN may not include the systemInfoModification within the Paging message upon change of some system information.

The UE verifies that stored system information remains valid by either checking systemInfoValueTag in SystemInformationBlockType1 after the modification period boundary, or attempting to find the systemInfoModification indication at least modificationPeriodCoeff times during the modification period in case no paging is received, in every modification period. If no paging message is received by the UE during a modification period, the UE may assume that no change of system information will occur at the next modification period boundary. If UE in RRC_CONNECTED, during a modification period, receives one paging message, it may deduce from the presence/absence of systemInfoModification whether a change of system information other than ETWS information, CMAS information and EAB parameters will occur in the next modification period or not.

Low complexity UEs are targeted to low-end (e.g. low average revenue per user, low data rate, delay tolerant) applications, e.g. some machine-type communications (MTC). A low complexity UE indicates UE category 0 and has reduced Tx and Rx capabilities compared to other UE of different categories. A low complexity UE may access a cell only if system information block type 1 (SIB1) indicates that access of low complexity UEs is supported. If the cell does not support low complexity UEs, a low complexity UE considers the cell as barred.

For one type of low complexity UEs, a bandwidth reduced low complexity (BL) UE can operate in any LTE system bandwidth but with a limited channel bandwidth of 6 PRBs (corresponding to the maximum channel bandwidth available in a 1.4MHz LTE system) in DL and UL. A BL UE may access a cell only if master information block (MIB) indicates that access of BL UEs is supported. The UE considers the cell as barred if the cell does not support BL UEs. A BL UE receives a separate occurrence of system information blocks (sent using different time/frequency resources). A BL UE has a transport block (TB) size limited to 1000 bit for broadcast and unicast. The SIB transmission occasions within an SI-window are provided in the SIB1 specific for BL UEs. The UE determines the TBS of SIB1 specific for BL UEs based on information in MIB. The BCCH modification period for BL UEs is a multiple of the BCCH modification period provided in SIB2. A BL UE can acquire SI messages across SI windows. A BL UE is not required to detect SIB change when in RRC_CONNECTED.

For other type of low complexity UEs, a UE in enhanced coverage is a UE that requires the use of coverage enhancement techniques to access the cell. A UE may access a cell using enhanced coverage techniques only if MIB indicates that access of UEs in enhanced coverage is supported. A UE in enhanced coverage receives a separate occurrence of system information blocks (sent using different time/frequency resources). The separate occurrence of SIB1 for UEs in enhanced coverage is identical to the separate occurrence of SIB1 for BL UEs. A UE in enhanced coverage has a TB size limited to 1000 bit for broadcast and unicast. The SIB transmission occasions within an SI-window are provided in the SIB1 specific for UEs in enhanced coverage. The BCCH modification period used for UEs in enhanced coverage is a multiple of the BCCH modification period provided in SIB2. A UE in enhanced coverage can acquire SI messages across SI windows. A UE capable of enhanced coverage acquires, if needed, and uses legacy system information when operating in normal coverage if it is not a BL UE. A UE capable of enhanced coverage acquires, if needed, and uses system information specific for UEs operating in enhanced coverage. A UE in enhanced coverage is not required to detect SIB change when in RRC_CONNECTED.

As described above, SystemInformationBlockType1 includes the systemInfoValueTag that indicates if a change has occurred in the SI messages. Although the UE may be informed about changes in system information by the systemInfoValueTag, which system information will change are not provided. If one system information block in the SI message changes, the UE should read all updated SI message. That is, since indication of system information change is provided per SI message, the flexible mapping of SIBs into SI message is restricted.

Meanwhile, for low complexity UEs, e.g. BL UEs or UEs in enhanced coverage, which SIB(s) actually changes may be indicated, in addition to the legacy systemInfoValueTag. That is, indication of system information change may be provided per SIB. However, if indication of system information change is provided per SIB, many bits are necessary for indicating system information change. This is not preferable considering a lot of repetitions for coverage enhancement.

In order to solve the problem described above, a method for indicating system information change per system information category (i.e. SIB category) may be proposed according to an embodiment of the present invention. According to an embodiment of the present invention, the SIBs may be classified into each category according to the usage of system information. The usage of system information may include e.g. radio resource configuration, intra-LTE reselection, inter-RAT reselection, public warning, MBMS, MTC, sidelink, etc. The followings are examples of category of SIBs according to an embodiment of the present invention. The following examples are only exemplary, and other category classifications may also be possible.

- SIB(s) for radio resource configuration: SIB2

- SIB(s) for intra-LTE reselection: SIB3/4/5

- SIB(s) for Inter-RAT reselection: SIB6/7/8

- SIB(s) for public warning message: SIB10/11/12

- SIB(s) for MBMS related: SIB13/15

- SIB(s) for MTC related: SIB14

- SIB(s) for other purposes: SIB9/17/18/19 (or SIB(s) for home eNB (HeNB): SIB9, SIB(s) for wireless local area network (WLAN): SIB17, SIB(s) for sidelink: SIB18/19)

- SIB(s) for radio resource configuration: SIB2

- SIB(s) for common reselection: SIB3

- SIB(s) for Intra-LTE reselection: SIB4/5

- SIB(s) for Inter-RAT reselection: SIB6/7/8

- SIB(s) for public warning message: SIB10/11/12

- SIB(s) for MBMS related: SIB13/15

- SIB(s) for MTC related: SIB14

- SIB(s) for other purposes: SIB9/17

- SIB(s) for sidelink: SIB18/19

After classifying SIBs into a specific system information category, the network may broadcast indications of system information change per system information category. The indications may be included in MIB or system information block type 1, i.e. SIB1. The mapping between indication and SIB(s) may be fixed or configured by system information. Further, in the above examples, indications of system information change for only SIB2~SIB8 may be indicated. Or, one indication of system information change for other SIBs (SIB9/13/15/17/18/19) may be indicated.

A size of the indication of system information change per SIB category may be 5 bits. That is, the range of indication of system information change per SIB category may be 0 to 31, which is similar as to the legacy systemInfoValueTag. In this case, if there is the legacy systemInfoValueTag, the UE may verify whether the stored system information remains valid by checking the legacy systemInfoValueTag in SystemInformationBlockType1 after the modification period boundary. If there is no change in value of the legacy systemInfoValueTag, the UE may consider the stored system information valid. If there is a change in value of the legacy systemInfoValueTag, the UE may additionally verify which SIB category remains valid by checking the indications of system information change per SIB category. If there is no change in value of the indication of system information change for a specific SIB category, the UE may consider the associated stored system information in the specific SIB category valid. Otherwise, the UE may consider the associated stored system information in the specific SIB category invalid. Accordingly, the UE may read the associated system information included in the specific SIB category again.

When the range of indication of system information change per SIB category is 0 to 31, which is similar as to the legacy systemInfoValueTag, and if there is not the legacy systemInfoValueTag, the UE may verify whether the stored system information remains valid by checking the indications of system information change per SIB category. The UE may check the indications of system information change per SIB category after the modification period boundary. If there is no change in value of the indication of system information change for a specific SIB category, the UE may consider the associated stored system information in the specific SIB category valid. Otherwise, the UE may consider the associated stored system information in the specific SIB category invalid. Accordingly, the UE may read the associated system information included in the specific SIB category again.

Alternatively, a size of the indication of system information change per SIB category may be 1 bit. That is, the range of indication of system information change per SIB category may be 0 to 1 (or, true/false). In this case, if there is the legacy systemInfoValueTag, the UE may verify whether the stored system information remains valid by checking the legacy systemInfoValueTag in SystemInformationBlockType1 after the modification period boundary. If there is no change in value of the legacy systemInfoValueTag, the UE may consider the stored system information valid. If there is a change in value of the legacy systemInfoValueTag, the UE may additionally verify which SIB category remains valid by checking the indications of system information change per SIB category. If there is no change in value of the indication of system information change for a specific SIB category, the UE may consider the associated stored system information in the specific SIB category valid. Otherwise, the UE may consider the associated stored system information in the specific SIB category invalid. Accordingly, the UE may read the associated system information included in the specific SIB category again.

Table 1 shows an example of update of system information based on the legacy systemInfoValueTag and the indication of system information change per SIB category according to an embodiment of the present invention. It is assumed that the indication is 1 bit in the following example.

Instant of time	SI value tag	New change indication
t₀	x	Same as before	UE₁and UE₂ check the legacy systemInfoValueTag and, if the value is different from the previous one, UE₁and UE₂acquire all the common SI.
t₁	x+1	Different	UE₁and UE₂ check the legacy systemInfoValueTag and, as the value is different from the previous one, UE₁and UE₂acquire all the common SI.
t₂	x+1	Same as before	UE₁and UE₂ check the legacy systemInfoValueTag and, as the value is the same as the previous one, UE₁and UE₂continue using previous SI.
t₃	x+2	SI_y = 1	Case 1) UE₁checks the legacy systemInfoValueTag and, as the value is different from the previous one, but UE₁only acquires the SI message that changes, i.e. SI_y.Case 2) For some reasons, UE₂ misses the change on the legacy systemInfoValueTag.
t₄	x+3	SI_z = 1	Case 1) UE₁checks the legacy systemInfoValueTag and, as the value is different from the previous one, but UE₁only acquires the SI message that changes, i.e. SI_zCase 2) UE₂checks the legacy systemInfoValueTag and, as the value is different by more than one from the previous one, UE₂ realized that it missed previous change and behaves as legacy (i.e. UE₂ acquires all SI messages)

1) At time t₀, the value of the legacy systemInfoValueTag is x and the indication of system information change per SIB category is the same as before. If the value of the legacy systemInfoValueTag is different from the previous one, UE1 and UE2 acquired all common SI messages.

2) At time t₁, the value of the legacy systemInfoValueTag is x+1, which is different from the previous one (i.e. x at time t₁) and the indication of system information change per SIB category is also different from the previous one. Accordingly, UE1 and UE2 acquire all common SI messages.

3) At time t₂, the value of the legacy systemInfoValueTag is x+1, which is the same as the previous one (i.e. x+1 at time t₁) and the indication of system information change per SIB category is also the same as the previous one. Accordingly, UE1 and UE2 continue using previous SI messages.

4) At time t₃, the value of the legacy systemInfoValueTag is x+2, which is different from the previous one (i.e. x+1 at time t₂) and the indication of system information change for a first specific SIB category is 1 (i.e. SI_y=1). Accordingly, UE1 may only acquire SI message that changes, i.e. system information included in SI_y. But, for some reasons, UE2 may miss change of the legacy systemInfoValueTag.

5) At time t₄, the value of the legacy systemInfoValueTag is x+3, which is different from the previous one (i.e. x+2 at time t₃) and the indication of system information change for a second specific SIB category is 1 (i.e. SI_z=1). Accordingly, UE1 may only acquires SI message that changes, i.e. system information included in SI_z. Meanwhile, UE2 checks the legacy systemInfoValueTag and since the current value (x+3) of the legacy systemInfoValueTag is different more than one from the previous one (x+1), UE2 may realize that it has missed previous system information change. Accordingly, UE2 may behave as legacy and acquire all SI messages hereafter.

FIG. 7 shows a method for receiving an indication of system information change by a UE according to an embodiment of the present invention. The above description for the present invention may be applied to this embodiment of the present invention. The UE may be a low complexity UE, which includes at least one of a BL UE or a UE in enhanced coverage.

In step S100, the UE receives an indication of system information change for a specific system information category which related to a specific usage of system information from a network. The specific usage of system information may include at least one of radio resource configuration, common reselection, intra-LTE reselection, inter-RAT reselection, public warning message, MBMS, MTC, or sidelink. The indication of system information change for the specific system information category may be received via MIB or SIB1. Mapping between the indication of system information change for the specific system information category and each system information may be fixed or configured by the network. A size of the indication of system information change for the specific system information category may be 5 bits or 1 bit.

In step S110, the UE verifies whether the specific system information category has changed according to the indication of system information change for the specific system information category. If it is verified that the specific system information category has changed, in step S120, the UE receives updated system information included in the specific system information category from the network. It may be verified that the specific system information category has changed if a value of the indication of system information change for the specific system information category has changed. If it is verified that the specific system information category has changed, stored system information included in the specific system information category may be considered invalid.

An eNB 800 may include a processor 810, a memory 820 and a transceiver 830. The processor 810 may be configured to implement proposed functions, procedures and/or methods described in this description. Layers of the radio interface protocol may be implemented in the processor 810. The memory 820 is operatively coupled with the processor 810 and stores a variety of information to operate the processor 810. The transceiver 830 is operatively coupled with the processor 810, and transmits and/or receives a radio signal.

A UE 900 may include a processor 910, a memory 920 and a transceiver 930. The processor 910 may be configured to implement proposed functions, procedures and/or methods described in this description. Layers of the radio interface protocol may be implemented in the processor 910. The memory 920 is operatively coupled with the processor 910 and stores a variety of information to operate the processor 910. The transceiver 930 is operatively coupled with the processor 910, and transmits and/or receives a radio signal.

The

processors

810, 910 may include application-specific integrated circuit (ASIC), other chipset, logic circuit and/or data processing device. The

memories

820, 920 may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium and/or other storage device. The

transceivers

830, 930 may include baseband circuitry to process radio frequency signals. When the embodiments are implemented in software, the techniques described herein can be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The modules can be stored in

memories

820, 920 and executed by

processors

810, 910. The

memories

820, 920 can be implemented within the

processors

810, 910 or external to the

processors

810, 910 in which case those can be communicatively coupled to the

processors

810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies that may be implemented in accordance with the disclosed subject matter have been described with reference to several flow diagrams. While for purposed of simplicity, the methodologies are shown and described as a series of steps or blocks, it is to be understood and appreciated that the claimed subject matter is not limited by the order of the steps or blocks, as some steps may occur in different orders or concurrently with other steps from what is depicted and described herein. Moreover, one skilled in the art would understand that the steps illustrated in the flow diagram are not exclusive and other steps may be included or one or more of the steps in the example flow diagram may be deleted without affecting the scope and spirit of the present disclosure.

Claims

A method for receiving an indication of system information change by a user equipment (UE) in a wireless communication system, the method comprising:

receiving an indication of system information change for a specific system information category which related to a specific usage of system information from a network;

verifying whether the specific system information category has changed according to the indication of system information change for the specific system information category; and

if it is verified that the specific system information category has changed, receiving updated system information included in the specific system information category from the network.
The method of claim 1, wherein the specific usage of system information includes at least one of radio resource configuration, common reselection, intra-long term evolution (LTE) reselection, inter-radio access technology (RAT) reselection, public warning message, multimedia broadcast multicast services　(MBMS), machine-type communication (MTC), or sidelink.
The method of claim 1, wherein the indication of system information change for the specific system information category is received via a master information block (MIB) or a system information block type 1 (SIB1).
The method of claim 1, wherein mapping between the indication of system information change for the specific system information category and each system information is fixed or configured by the network.
The method of claim 1, wherein a size of the indication of system information change for the specific system information category is 5 bits or 1 bit.
The method of claim 1, wherein it is verified that the specific system information category has changed if a value of the indication of system information change for the specific system information category has changed.
The method of claim 1, wherein if it is verified that the specific system information category has changed, stored system information included in the specific system information category is considered invalid.
The method of claim 1, wherein the UE is a low complexity UE, which includes at least one of a low complexity bandwidth reduced UE (BL UE) or a UE in enhanced coverage.
A user equipment (UE) in a wireless communication system, the UE comprising:

a memory;

a transceiver; and

a processor, coupled to the memory and the transceiver, that:

controls the transceiver to receive an indication of system information change for a specific system information category which related to a specific usage of system information from a network,

verifies whether the specific system information category has changed according to the indication of system information change for the specific system information category, and

if it is verified that the specific system information category has changed, controls the transceiver to receive updated system information included in the specific system information category from the network.
The method of claim 1, wherein the specific usage of system information includes at least one of radio resource configuration, common reselection, intra-long term evolution (LTE) reselection, inter-radio access technology (RAT) reselection, public warning message, multimedia broadcast multicast services　(MBMS), machine-type communication (MTC), or sidelink.
The UE of claim 9, wherein the indication of system information change for the specific system information category is received via a master information block (MIB) or a system information block type 1 (SIB1).
The UE of claim 9, wherein mapping between the indication of system information change for the specific system information category and each system information is fixed or configured by the network.
The UE of claim 9, wherein a size of the indication of system information change for the specific system information category is 5 bits or 1 bit.
The UE of claim 9, wherein it is verified that the specific system information category has changed if a value of the indication of system information change for the specific system information category has changed.
The UE of claim 9, wherein if it is verified that the specific system information category has changed, stored system information included in the specific system information category is considered invalid.