Method and apparatus for requesting SIB in wireless communication system

This application is areissue of U.S. Pat. No. 10,771,931, which issued Sep. 8, 2020 from U.S. patent application Ser. No. 16/300,216, filed Nov. 9, 2018, which is aNational Stage filing under 35 U.S.C. 371 of International No. PCT/KR2017/004792, filed on May 10, 2017, which claims the benefit of U.S. Provisional Applications No. 62/334,418, filed May 10, 2016, No. 62/334,427 filed on May 10, 2016, No. 62/334,443 filed on May 10, 2016, and No. 62/366,643 filed on Jul. 26, 2016, the contents of which are all hereby incorporated by reference herein in their entirety.

The present invention relates to a wireless communication system and, more particularly, to a method for a user equipment (UE) to request a missing system information block (SIB) in a wireless communication system, and an apparatus for supporting the same.

In order to meet the demand for wireless data traffic soring since the 4th generation (4G) communication system came to the market, there are ongoing efforts to develop enhanced 5th generation (5G) communication systems or pre-5G communication systems. For the reasons, the 5G communication system or pre-5G communication system is called the beyond 4G network communication system or post long-term evolution (LTE) system.

In order to accomplish a higher data transfer rate, the 5G communication system considers implementation at a super-high frequency (mmWave) band (e.g., such as a 60 GHz band). In order to obviate a path loss of a radio wave and increase a delivery distance of a radio wave at the super-high frequency band, various techniques such as a beamforming, a massive MIMO, a full dimensional MIMO (FD-MIMO), an array antenna, an analog beam-forming, and a large scale antenna are discussed in the 5G communication system.

Additionally, for an improvement in network of the 5G communication system, technical developments are made in an advanced small cell, a cloud radio access network (cloud RAN), an ultra-dense network, a device to device (D2D) communication, a wireless backhaul, a moving network, a cooperative communication, coordinated multi-points (CoMP), a reception interference cancellation, and the like.

Besides, in the 5G communication system, a hybrid FSK and QAM modulation (FQAM) and a sliding window superposition coding (SWSC) are developed as advanced coding modulation (ACM) schemes, and a filter bank multi carrier (FBMC), a non orthogonal multiple access (NOMA), and a sparse code multiple access (SCMA) are also developed as advanced access techniques.

System information refers to essential information for communication between a terminal and a base station. In 3GPP LTE, the system information is divided into an MIB (Master Information Block) and an SIB (System Information Block). The MIB is the most essential information. The SIB is subdivided into SIB-x forms according to its importance or cycle. The MIB is transmitted through a PBCH (Physical Broadcast Channel) which is a physical channel. The SIB is common control information and is transmitted through a PDCCH differently from the MIB.

Meanwhile, the number of system information blocks is continuously increasing, and radio resources are required to broadcast a system information block. Thus, as the number of system information blocks increases, the quantity of radio resources required to broadcast a system information block also inevitably increases. To transmit continuously increasing system information to a user equipment (UE), it is necessary to propose a method for acquiring system information that efficiently utilizes radio resources.

According to an embodiment, there is provided a method for requesting, by a user equipment (UE), a system information block (SIB) in a wireless communication system. The method may include: receiving an SIB list including one or more SIBs supported by a cell from a radio access network (RAN); receiving, from the RAN, SIB broadcast information indicating whether an SIB supported by the cell is broadcast in a broadcast control channel (BCCH) period; detecting a missing SIB based on the SIB list and the SIB broadcast information; and requesting the missing SIB from the RAN.

The missing SIB may be an SIB that is not broadcasted in the BCCH period among the SIBs included in the SIB list. The BCCH period may be a current BCCH period or a next BCCH period.

The BCCH period may be one of a BCCH modification period or a BCCH repetition period.

The missing SIB may be an SIB that the UE needs to receive from the RAN in order to perform a particular service. The particular service may include at least one of a multimedia broadcast/multicast service (MBMS) service, a device-to-device (D2D) service, a vehicle-to-everything (V2X) service, or wireless local area network (WLAN) interworking.

The missing SIB may be requested from the RAN by indicating a service associated with the missing SIB.

The SIB list and the SIB broadcast information may be received by the UE via particular system information. The particular system information may be system information that is always broadcast by the RAN.

The method may further include receiving a probability factor from the RAN, wherein when a random number drawn by the UE is less than or equal to the probability factor, the missing SIB may be requested from the RAN.

The method may further include receiving, from the RAN, a value tag indicating system information to be requested from the RAN, wherein when the missing SIB is system information indicated by the value tag, the missing SIB may be requested from the RAN.

The method may further include receiving, from the RAN, a number of a type of an SIB to be requested from the RAN, wherein when the missing SIB matches the number of the type of the SIB to be requested, the missing SIB may be requested from the RAN.

The method may further include receiving, from the RAN, a set of SIBs to be requested from the RAN, wherein when the missing SIB is included in the set of SIBs to be requested, the missing SIB may be requested from the RAN.

The method may further include receiving the missing SIB from the RAN in response to the request.

According to another embodiment, there is provided a UE for requesting an SIB in a wireless communication system. The UE may include: a memory; a transceiver; and a processor to connect the memory and the transceiver, wherein the processor may be configured to: control the transceiver to receive an SIB list including one or more SIBs supported by a cell from an RAN; control the transceiver to receive, from the RAN, SIB broadcast information indicating whether an SIB supported by the cell is broadcast in a broadcast control channel (BCCH) period; detect a missing SIB based on the SIB list and the SIB broadcast information; and control the transceiver to request the missing SIB from the RAN.

A UE may receive a missing SIB.

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 evolved from IEEE 802.16e, and provides backward compatibility with a system based on the IEEE 802.16e. 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 a downlink and uses the SC-FDMA in an uplink. LTE-advanced (LTE-A) is an evolution of the LTE. 5G is an evolution of the LTE-A.

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

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, the LTE system architecture includes one or more user equipment (UE;), an evolved-UMTS terrestrial radio access network (E-UTRAN) and an evolved packet core (EPC). The UErefers to a communication equipment carried by a user. The UEmay 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), and a plurality of UEs may be located in one cell. The eNBprovides an end point of a control plane and a user plane to the UE. The eNBis generally a fixed station that communicates with the UEand may be referred to as another terminology, such as a base station (BS), a base transceiver system (BTS), an access point, etc. One eNBmay be deployed per cell. There are one or more cells within the coverage of the eNB. A single cell is configured to have one of bandwidths selected from 1.25, 2.5, 5, 10, and 20 MHz, etc., and provides downlink or uplink transmission services to several UEs. In this case, different cells can be configured to provide different bandwidths.

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

The EPC includes a mobility management entity (MME) which is in charge of control plane functions, and a system architecture evolution (SAE) gateway (S-GW) which is in charge of user plane functions. The MME/S-GWmay be positioned at the end of the network and connected to an external network. The MME has UE access information or UE capability information, and such information may be primarily used in UE mobility management. The S-GW is a gateway of which an endpoint is an E-UTRAN. The MME/S-GWprovides an end point of a session and mobility management function for the UE. The EPC may further include a packet data network (PDN) gateway (PDN-GW). The PDN-GW is a gateway of which an endpoint is a PDN.

The MME provides various functions including non-access stratum (NAS) signaling to eNBs, 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), 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 APN-AMBR. For clarity MME/S-GWwill be referred to herein simply as a “gateway,” but it is understood that this entity includes both the MME and S-GW.

Interfaces for transmitting user traffic or control traffic may be used. The UEand the eNBare connected by means of a Uu interface. The eNBsare interconnected by means of an X2 interface. Neighboring eNBs may have a meshed network structure that has the X2 interface. The eNBsare connected to the EPC by means of an S1 interface. The eNBsare connected to the MME by means of an S1-MME interface, and are connected to the S-GW by means of S1-U interface. The S1 interface supports a many-to-many relation between the eNBand the MME/S-GW.

The eNBmay perform functions of selection for gateway, routing toward the gatewayduring 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 UEsin 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, gatewaymay 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.

shows a control plane of a radio interface protocol of an LTE system.shows a user plane of a radio interface protocol 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. The radio interface protocol between the UE and the E-UTRAN may be horizontally divided into a physical layer, a data link layer, and a network layer, and may be vertically divided into a control plane (C-plane) which is a protocol stack for control signal transmission and a user plane (U-plane) which is a protocol stack for data information transmission. The layers of the radio interface protocol exist in pairs at the UE and the E-UTRAN, and are in charge of data transmission of the Uu interface.

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 is transferred between the MAC layer and the PHY layer through the transport channel. Between different PHY layers, i.e., a PHY layer of a transmitter and a PHY layer of a receiver, data is transferred through the physical channel using radio resources. The physical channel is modulated using an orthogonal frequency division multiplexing (OFDM) scheme, and utilizes time and frequency as a radio resource.

The PHY layer uses several physical control channels. A physical downlink control channel (PDCCH) reports to a UE about resource allocation of a paging channel (PCH) and a downlink shared channel (DL-SCH), and hybrid automatic repeat request (HARQ) information related to the DL-SCH. The PDCCH may carry a UL grant for reporting to the UE about resource allocation of UL transmission. A physical control format indicator channel (PCFICH) reports the number of 01-DM symbols used for PDCCHs to the UE, and is transmitted in every subframe. A physical hybrid ARQ indicator channel (PHICH) carries an HARQ acknowledgement (ACK)/non-acknowledgement (NACK) signal in response to UL transmission. A physical uplink control channel (PUCCH) carries UL control information such as HARQ ACK/NACK for DL transmission, scheduling request, and CQI. A physical uplink shared channel (PUSCH) carries a UL-uplink shared channel (SCH).

A physical channel consists of a plurality of subframes in time domain and a plurality of subcarriers in frequency domain. One subframe consists of a plurality of symbols in the time domain. One subframe consists of a plurality of resource blocks (RBs). One RB consists of a plurality of symbols and a plurality of subcarriers. In addition, each subframe may use specific subcarriers of specific symbols of a corresponding subframe for a PDCCH. For example, a first symbol of the subframe may be used for the PDCCH. The PDCCH carries dynamic allocated resources, such as a physical resource block (PRB) and modulation and coding scheme (MCS). A transmission time interval (TTI) which is a unit time for data transmission may be equal to a length of one subframe. The length of one subframe may be 1 ms.

The transport channel is classified into a common transport channel and a dedicated transport channel according to whether the channel is shared or not. A DL transport channel for transmitting data from the network to the UE includes a broadcast channel (BCH) for transmitting system information, a paging channel (PCH) for transmitting a paging message, a DL-SCH for transmitting user traffic or control signals, etc. 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. The system information carries one or more system information blocks. All system information blocks may be transmitted with the same periodicity. Traffic or control signals of a multimedia broadcast/multicast service (MBMS) may be transmitted through the DL-SCH or a multicast channel (MCH).

A UL transport channel for transmitting data from the UE to the network includes a random access channel (RACH) for transmitting an initial control message, a 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 RACH is normally used for initial access to a cell.

A MAC layer belongs to the L2. The MAC layer provides services to a radio link control (RLC) layer, which is a higher layer of the MAC layer, via a logical channel. The MAC layer provides a function of mapping multiple logical channels to multiple transport channels. The MAC layer also provides a function of logical channel multiplexing by mapping multiple logical channels to a single transport channel A MAC sublayer provides data transfer services on logical channels.

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 logical channels are located above the transport channel, and are mapped to the transport channels.

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 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 RLC layer belongs to the L2. The RLC layer provides a function of adjusting a size of data, so as to be suitable for a lower layer to transmit the data, by concatenating and segmenting the data received from an upper layer in a radio section. In addition, to ensure a variety of quality of service (QoS) required by a radio bearer (RB), the RLC layer provides three operation modes, i.e., a transparent mode (TM), an unacknowledged mode (UM), and an acknowledged mode (AM). The AM RLC provides a retransmission function through an automatic repeat request (ARQ) for reliable data transmission. 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.

A packet data convergence protocol (PDCP) layer belongs to the L2. 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. The header compression increases transmission efficiency in the radio section by transmitting only necessary information in a header of the data. In addition, the PDCP layer provides a function of security. The function of security includes ciphering which prevents inspection of third parties, and integrity protection which prevents data manipulation of third parties.

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 takes a role of controlling a radio resource between the UE and the network. For this, the UE and the network exchange an RRC message through the RRC layer. The RRC layer controls logical channels, transport channels, and physical channels in relation to the configuration, reconfiguration, and release of RBs. An RB is a logical path provided by the L1 and L2 for data delivery between the UE and the network. That is, the RB signifies a service provided the L2 for data transmission between the UE and E-UTRAN. The configuration of the RB implies a process for specifying a radio protocol layer and channel properties to provide a particular service and for determining respective detailed parameters and operations. The RB is classified into two types, i.e., a signaling RB (SRB) and a data RB (DRB). The SRB is used as a path for transmitting an RRC message in the control plane. The DRB is used as a path for transmitting user data in the user plane.

A Non-Access Stratum (NAS) layer placed over the RRC layer performs functions, such as session management and mobility management.

Referring to, 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 automatic repeat request (HARQ). 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.

Referring to, the RLC and MAC layers (terminated in the eNB on the network side) may perform the same functions for the control plane. 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.

Hereinafter, system information will be described.