Apparatus and method for resuming radio connection in communication network

Abstract

The present invention provides a method in a base station for resuming a connection with a user equipment (UE), the method comprising: transmitting, by processing hardware, a message with the UE according to a format corresponding to a first RAT using a radio connection over a radio interface conforming to a second RAT; transmitting, by the processing hardware, a command to release the radio connection to the UE; after the transmission, receiving, by the processing hardware, an indication from the UE that the connection has been recovered; and decoding, by the processing hardware, the indication according to a format corresponding to the first RAT.

Description

[0001] This case is a divisional application of the invention patent application with the application date of February 13, 2020, application number 202080028919.5, and invention name "Restoring Radio Connections in Communication Networks". Technical Field

[0002] The present disclosure relates generally to wireless communications and, more particularly, to procedures for restoring a radio connection. Background Art

[0003] According to some types of network architectures, a base station communicates with a user equipment (UE) using a specific radio access technology (RAT) and is connected to a higher-level core network (CN) to provide the UE with functions of the higher-level CN.

[0004] For example, the next generation evolved Node B eNB (ng-eNB) supports Evolved Universal Terrestrial Radio Access (EUTRA) and is connected to the 5G Core (5GC). In this case, the physical layer (PHY) of EUTRA provides a transport channel to the media access control (MAC) sublayer, the MAC sublayer in turn provides a logical channel to the radio link control (RLC) sublayer, and the RLC sublayer in turn provides an RLC channel to the packet data convergence protocol (PDCP) sublayer. To support connection with 5GC, the EUTRA PDCP sublayer provides a signaling radio bearer (SRB) to the radio resource control (RRC) sublayer, and the new radio (NR) PDCP sublayer provides a data radio bearer (DRB) to the service data adaptation protocol (SDAP) and provides SRB to the RRC sublayer.

[0005] At the RRC sublayer, the 4G and 5G standards support different functions in some cases. For example, the 4G-LTE RRC protocol specifies the RRC_IDLE state when the UE does not have an active radio connection with a base station and the RRC_CONNECTED state when the UE has an active radio connection with a base station. The 5G protocol introduces an intermediate state RRC_INACTIVE to allow the UE to transition back to the RRC_CONNECTED state more quickly.

[0006] When the UE is in the RRC_INACTIVE state, the UE must transition to the RRC_CONNECTED state in order to start transmitting data in the uplink direction. To do this, the UE must perform an RRC recovery procedure, which requires the UE to transmit an RRCConnectionResumeRequest message to the base station, receive an RRCConnectionResume command in response from the base station, and transmit an RRCConnectionResumeComplete message to the base station to confirm that the state transition is complete. In some cases, after the UE transmits an RRCConnectionResumeRequest message to the base station, the base station follows the fallback procedure and transmits an RRCConnectionSetup command in response to the RRCConnectionResumeRequest message, and the UE transmits an RRCConnectionSetupComplete message to the base station to confirm that the state transition is complete.

[0007] Several specifications related to cellular communications provide protocols according to which the UE can transition between RRC states in the above-mentioned types of networks (e.g., 3GPP TS 36.331v 15.3.0, TS 36.323v 15.1.0, TS 38.323v15.3.0, TS 38.331v15.3.0, and TS 36.300v 15.3.0), but there is still an abnormal situation in which the UE still cannot transmit or receive data when it transitions from the RRC_INACTIVE state to the RRC_CONNECTED state.

[0008] In one such scenario, the UE operates in the RRC_CONNECTED state and communicates with the ng-eNB over EUTRA to exchange NR PDCP protocol data units (PDUs) with the RRC entity of the ng-eNB. For example, after transitioning to the RRC_INACTIVE state, the UE attempts to resume the connection at some point to transmit uplink data. To this end, the UE transmits an RRCConnectionResumeRequest message and receives an RRCConnectionSetup message in response. The UE then releases all radio resources including the NR PDCP entity and transmits an RRCConnectionSetupComplete message and includes the message in the EUTRA PDCP PDU.

[0009] As a result, the UE remains in the RRC_CONNECTED state but may not transmit or receive any data. Summary of the invention

[0010] In general, the techniques of this disclosure allow a UE and a base station to correctly decode messages related to an RRC resumption procedure when a PDCP entity that previously released a connection corresponds to a RAT that is different from the RAT used by the base station to communicate with the UE.

[0011] According to one technique, the UE transmits an RRC message (RRCConnectionSetupComplete message) to the ng-eNB reporting that the connection has been successfully restored using the same underlying protocol (e.g., NR PDCP) as used before releasing the connection. In one example embodiment, the UE retains the same entity (e.g., NR PDCP entity) as that which formats and transmits the RRC message. In another example embodiment, the UE initiates a new entity to format and transmit the RRC message. In either case, after the UE successfully restores the RRC connection, the UE performs subsequent procedures (e.g., security mode, DL information, UL information, RRC reconfiguration, etc.) using the same format or protocol as that used to restore the RRC connection.

[0012] According to another technique, the base station decodes the data unit carrying the RRC message (the received RRCConnectionSetupComplete message) reporting that the UE has restored the connection according to the protocol corresponding to the RAT used by the base station to communicate with the UE (e.g., EUTRA PDCP) by default. Therefore, regardless of the format of any previous PDCP PDU exchange, the UE transmits the RRC message (RRCConnectionSetupComplete message) reporting that the connection has been successfully restored to the ng-eNB using the protocol corresponding to the RAT. The UE performs subsequent procedures (e.g., security mode, DL information, UL information, RRC reconfiguration, etc.) using the same format or protocol as that used to restore the RRC connection.

[0013] According to yet another technique, similar to the above method, the base station decodes a data unit carrying an RRC message (a received RRCConnectionSetupComplete message) reporting that the UE has resumed the connection according to a protocol corresponding to the RAT used by the base station to communicate with the UE (e.g., EUTRA PDCP). However, the UE then performs subsequent procedures (e.g., security mode, DL information, UL information, RRC reconfiguration, etc.) using the same format (e.g., NR PDCP) as used before releasing the RRC connection.

[0014] An example embodiment of the techniques is a method in a UE for resuming a connection with a base station. The method may be performed by processing hardware and includes communicating a message with the base station according to a format corresponding to a first RAT over a radio interface conforming to a second RAT using a radio connection. The method also includes suspending the radio connection and, after suspending, transmitting to the base station an indication that the radio connection has been restored according to a format corresponding to the first RAT.

[0015] Another example embodiment of the techniques is a method in a UE for resuming a connection with a base station. The method may be performed by processing hardware and includes communicating a first message with the base station according to a first format corresponding to a first RAT over a radio interface conforming to a second RAT using a radio connection. The method also includes suspending the radio connection and, after suspending, transmitting to the base station a radio connection resumed indication according to a second format corresponding to the second RAT, and communicating a second message related to a process for controlling radio resources according to the first format or the second format.

[0016] Yet another example embodiment of the techniques is a UE comprising processing hardware configured to perform one of the methods described above.

[0017] Another example embodiment of the techniques is a method in a base station for resuming a connection with a UE. The method includes using a radio connection over a radio interface conforming to a second RAT to communicate a message with the UE according to a format corresponding to a first RAT. The method also includes transmitting a command to the UE to suspend the radio connection; after the transmission, receiving an indication from the UE that the connection has been resumed, and decoding the indication according to a format corresponding to the first RAT.

[0018] An example embodiment of these techniques is a method in a base station for restoring a connection with a user equipment (UE), the method comprising: transmitting, by processing hardware, a message with the UE according to a format corresponding to a first RAT using a radio connection over a radio interface conforming to a second RAT; transmitting, by processing hardware, a command to release the radio connection to the UE; after the transmission, receiving, by processing hardware, an indication from the UE that the connection has been restored; and decoding, by processing hardware, the indication according to a format corresponding to the first RAT.

[0019] Another example embodiment of the techniques is a base station comprising processing hardware configured to perform one of the methods described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a block diagram of an example wireless communication network in which a UE and a base station correctly decode messages related to a procedure for restoring a radio connection using the techniques of the present disclosure;

[0021] Figure 2AIt is a block diagram of the user plane protocol stack. Figure 1 The UE and the base station can communicate according to this user plane protocol stack;

[0022] Figure 2B This is a block diagram of the control plane protocol stack. Figure 1 The UE and the base station can communicate according to this control plane protocol stack;

[0023] Figure 3 is a messaging diagram for an example scenario in which, in the RRC_CONNECTED state, the UE exchanges NR PDCP PDUs with the ng-eNB and, upon subsequent transition from the RRC_INACTIVE state to the RRC_CONNECTED state, uses the NR PDCP PDUs to transmit an RRCConnectionSetupComplete message;

[0024] Figure 4 is with Figure 3 Schematic diagram of message reception and transmission in a similar situation to the situation described above. In this situation, the UE restarts the NR PDCP entity after transitioning back to the RRC_CONNECTED state.

[0025] Figure 5 is a message transmission diagram of an example case, in which, in the RRC_CONNECTED state, the UE exchanges NR PDCP PDUs with the ng-eNB, and the ng-eNB subsequently decodes the RRCConnectionSetupComplete message from the UE according to the EUTRA PDCP format;

[0026] Figure 6 is a message transmission diagram of an example case, in which in the RRC_CONNECTED state, the UE exchanges NR PDCP PDUs with the ng-eNB, transmits an RRCConnectionSetupComplete message in EUTRA PDCP format to the ng-eNB, and exchanges EUTRA PDCP PDUs with the ng-eNB to perform another RRC procedure;

[0027] Figure 7 is a flow chart of an example method in a user equipment for transmitting an indication that a radio connection has been restored, which example method may be used in Figure 1 implementation in the system;

[0028] Figure 8 is a flow chart of another example method in a user equipment for transmitting an indication that a radio connection has been restored, which example method may be used in Figure 1 Implementation in the system; and

[0029] Fig. 9 is a flow chart of an example method in a base station for decoding an indication that a radio connection has been restored, which example method may be used in Figure 1 implemented in the system. DETAILED DESCRIPTION

[0030] Figure 1 An example wireless communication network 100 is depicted in which an example UE 102 communicates with a base station (ng-eNB 104) of an evolved long term evolution (eLTE) network. The UE 102 and the ng-eNB 104 communicate via the EUTRA RAT in a cell 110. The ng-eNB 104 in turn communicates with the 5GC 108 via a next generation (NG) interface. Thus, the UE 102 can access functionality of the 5GC 108, including an access management function (AMF) 112. The eLTE network may also include an ng-eNB 106.

[0031] According to the techniques of the present disclosure, UE 102 and ng-eNB 104 exchange RRC messages using NR PDCP format and / or EUTRA PDCP format in a manner that allows both devices to decode the RRC messages. Although these techniques are discussed below with reference to examples of EUTRA, NR, and 5GC, generally similar techniques can be applied to other radio access and / or core network technologies.

[0032] like Figure 1 As shown, the UE 102 is equipped with processing hardware 120, which may include one or more general-purpose processors (such as central processing units (CPUs)) and non-transitory computer-readable memory storing machine-readable instructions that can be executed on one or more general-purpose processors and / or special-purpose processing units. The processing hardware 120 in the example embodiment includes an RRC controller 122, which can instantiate, release, and otherwise interact with the EUTRA PDCP entity 124 and the NRPDCP entity 126.

[0033] The ng-eNB 104 is equipped with processing hardware 130, which may also include one or more general-purpose processors (such as a CPU) and non-transitory computer-readable memory storing machine-readable instructions executable on one or more general-purpose processors and / or special-purpose processing units. The processing hardware 130 includes an RRC controller 132 that can interact with an EUTRA PDCP entity 134 and an NR PDCP entity 136, similar to the RRC controller 122 of the UE 102.

[0034] In some embodiments, the RRC controller 132 may operate in another component of the eLTE network external to the ng-eNB 104. However, for convenience, the following discussion refers to the RRC controller 132 operating in the ng-eNB 104. When the RRC controller 132 operates external to the ng-eNB 104, the interactions between the RRC controller 132, the EUTRA PDCP entity 134, the NR PDCP entity 136, and the components of the UE 102 are similar to those discussed below.

[0035] In some cases, UE 102 and ng-eNB 104 exchange data according to the NR PDCP format, and, for example, after a period of inactivity, UE 102 transitions to the RRC_INACTIVE state. When UE 102 transitions from the RRC_INACTIVE state to the RRC_CONNECTED state, UE 102 may transmit an RRCConnectionSetupComplete message using the EUTRA PDCP format or the NR PDCP format, and ng-eNB 104 may decode the message using the EUTRA PDCP entity 134 or the NR PDCP entity 136, respectively. UE 102 and ng-eNB 104 may also perform another RRC procedure using the EUTRA PDCP entity 124, the EUTRA PDCP entity 134, or the NR PDCP entity 126, the NR PDCP entity 136.

[0036] For clarity, in reference Figure 3-6 Before discussing these situations in more detail, refer to Figure 2A Discuss an example user plane protocol stack according to which UE 102 and ng-eNB 104 may communicate, and refer to Figure 2B Discuss the control plane protocol stack.

[0037] First reference Figure 2A , the processing hardware 120 of the UE 102 and the processing hardware 130 of the ng-eNB 104 may support a PHY sublayer 202, a MAC sublayer 204 layered above the PHY sublayer 202, and an RLC sublayer 206 layered above the MAC sublayer 204. The NR PDCP entity 126 and the NR PDCP entity 136 may layer an NR PDCP data unit at a sublayer 208 above the RLC sublayer 206. For example, the NR PDCP data unit may carry information at the SDAP sublayer 210.

[0038] like Figure 2BAs shown, the processing hardware 120 and the processing hardware 130 similarly use sublayers 202, 204, and 206 to support communications on the control plane. The RLC sublayer 206 can support both the NR PDCP sublayer 208 and the EUTRA PDCP sublayer 218. Therefore, the NR PDCP entity 126, the NR PDCP entity 136 and the EUTRA PDCP entity 124, the EUTRA PDCP entity 134 can layer data units on top of the RLC sublayer 206.

[0039] like Figure 2B As further shown, the UE 102 and the ng-eNB 104 can transmit RRC messages at sublayer 220 on the NR PDCP sublayer 208 or the EUTRA PDCP sublayer 218. In addition, the UE 102 can exchange non-access stratum (NAS) information with the AMF 112 at the NAS sublayer 230.

[0040] Next, Figure 3 An example scenario is shown in which the UE 102 initially exchanges NR PDCP PDUs (302) with the ng-eNB 104 in the RRC_CONNECTED state 301. For example, the NR PDCP entity 126 may transmit NR PDCP PDU 1 (303) to the NR PDCP entity 136 and receive NR PDCP PDU 2 (304) from the NR PDCP entity 136. Each of the NR PDCP PDUs 303, 304, etc. may include, for example, an Internet Protocol (IP) packet, a NAS message, or an RRC message.

[0041] After a period of data inactivity by UE 102, ng-eNB 104 (or another component of the eLTE network in which ng-eNB 104 operates) determines that the RRC (or radio) connection between UE 102 and ng-eNB 104 should be suspended. Then, ng-eNB 104 initiates a connection release procedure 310 to suspend the RRC (or radio) connection. Specifically, RRC controller 132 provides an RRCConnectionRelease message (312) to NR PDCP entity 136, and NR PDCP entity 136 transmits the RRCConnectionRelease message (314) in NR PDCP PDU 3 over the EUTRA radio interface to suspend the RRC (or radio) connection.

[0042] The NR PDCP entity 126 of the UE 102 receives the NR PDCP PDU 3, extracts the RRCConnectionRelease message, and provides the RRCConnectionRelease message to the RRC controller 122. In response, the RRC controller 122 transitions to the RRC_INACTIVE state 318 (i.e., suspends the RRC (or radio) connection).

[0043] Later, RRC controller 122 initiates an RRC connection resumption procedure (320). For example, RRC controller 122 may receive an indication from a higher layer (e.g., SDAP sublayer 210) that UE 102 needs to transmit data to ng-eNB 104. RRC controller 122 transmits an RRCConnectionResumeRequest message (322) to the eLTE network in which ng-eNB 104 operates. In this example case, RRC controller 122 transmits the RRCConnectionResumeRequest message to ng-eNB 104, but in other cases, RRC controller 122 may transmit the message to ng-eNB 106. In response, RRC controller 132 transmits an RRCConnectionSetup message (324) to UE 102.

[0044] exist Figure 3In the case where the UE 102, after transitioning from the RRC_INACTIVE state to the RRC_CONNECTED state, continues to communicate with the ng-eNB 104 using the same NR PDCP entity 126 that the UE 102 used for the exchange 302. More specifically, the UE 102 may establish the NR PDCP entity 126 for the SRB (e.g., SRB1) before or at the time of the exchange 302 with the NR PDCP entity 136. After the UE 102 receives the RRCConnectionRelease message (324) from the ng-eNB 104, the UE 102 does not release the NR PDCP entity 126. Therefore, after the UE 102 receives the RRCConnectionSetup message (324) from the ng-eNB 104 (or ng-eNB 106), the UE 102 does not establish a new NR PDCP entity. UE 102 transmits an RRCConnectionSetupComplete message (352) to ng-eNB 104 (or ng-eNB 106) using the previously established NR PDCP entity 126. However, in other embodiments discussed below, UE 102 may release or suspend NR PDCP entity 126 in certain circumstances and, in response to certain events, create a new NR PDCP entity or resume a suspended NR PDCP entity 126. UE 102 may re-establish NR PDCP entity 126 before receiving the RRCConnectionSetup message or before transmitting the RRCConnectionSetupComplete message.

[0045] Similarly, the ng-eNB 104 may use the previously established NR PDCP entity 136 to receive the RRCConnectionSetupComplete message (352) from the UE 102. However, in other embodiments discussed below, the ng-eNB 104 may release or suspend the NR PDCP entity 136 in certain circumstances and, in response to certain events, create a new NR PDCP entity or resume the suspended NR PDCP entity 136. In the case of using the NR PDCP entity 136, the ng-eNB 104 may re-establish the NR PDCP entity 136 before receiving the RRCConnectionSetupComplete message. In the case of releasing the NR PDCP entity 136, the ng-eNB 106 establishes a new instance of the NR PDCP entity 136 to receive the RRCConnectionSetupComplete message.

[0046] The RRC controller 122 transitions to the RRC_CONNECTED state (330). In this example, before releasing the RRC connection, the RRC controller 122 continues to utilize the NR PDCP entity 126 (340) that exchanges NR PDCP PDUs with the NR PDCP entity 136 or uses the new NR PDCP entity of the ng-eNB 104 (or the new NR PDCP entity of the ng-eNB 106). Specifically, the RRC controller 122 provides the NR PDCP entity 126 with an RRCConnectionSetupComplete message (350), and then the NR PDCP entity 126 includes the RRCConnectionSetupComplete message in the NR PDCP PDU 4 and transmits the NR PDCP PDU to the NR PDCP entity 136 or the new NR PDCP entity of the ng-eNB 104 (or the new NR PDCP entity of the ng-eNB 106) (352). In some embodiments, the UE 102 releases the radio resources configured by the ng-eNB 104 before receiving the RRCConnectionRelease message. The radio resources may include the EUTRA RLC entity, the NR SDAP entity (if configured), and other NR PDCP entities (except the NR PDCP entity 126).

[0047] Continue to refer Figure 3 , the NR PDCP entity 136 decodes the NR PDCP PDU 4 using the format of the NR PDCP to extract the RRCConnectionSetupComplete message (354). Therefore, in the present embodiment, both the UE 102 and the ng-eNB 104 (or ng-eNB 106) use the NR PDCP format to transmit the RRCConnectionSetupComplete message. In the present embodiment, even if the UE 102 and the ng-eNB 104 (or ng-eNB 106) communicate via EUTRA, the UE 102 does not utilize the EUTRA PDCP entity 124 to restore the RRC connection (or perform subsequent RRC procedures as described below).

[0048] and Figure 3In contrast to the technology of the prior art, the existing ng-eNB may try to decode the NR PDCP PDU 4 using the format of EUTRA PDCP (because the PDU arrives over the EUTRA interface), and the decoding fails in this case because, for example, the PDCP SN according to the EUTRA PDCP PDU format includes 5 bits and the PDCP SN according to the NR PDCP PDU format has 12 bits. Moreover, after the existing ng-eNB fails to decode the RRCConnectionSetupComplete message, the ng-eNB transmits an RRCConnectionRelease message in the NR PDCP PDU to the UE. Because the UE expects the EUTRA PDCP PDU, the UE also fails to decode the message. Therefore, the UE does not know that the ng-eNB has released the RRC connection.

[0049] After NR PDCP entity 136 extracts the RRCConnectionSetupComplete message, NR PDCP entity 136 provides the RRCConnectionSetupComplete message to RRC controller 132 (356), and RRC controller 132 decodes the content of the RRC message (360).

[0050] like Figure 3 As further shown, UE 102 and ng-eNB 104 may perform subsequent RRC procedures using the NR PDCP format to transmit and receive RRC messages (370). For example, UE 102 and ng-eNB 104 may perform one or more of an RRC security mode procedure, a downlink (DL) information procedure, an uplink (UL) information procedure, an RRC reconfiguration procedure, or a measurement report procedure.

[0051] More specifically, when performing the security mode procedure, the ng-eNB 104 transmits a security mode command message to the UE 102, and receives a security mode complete message from the UE 102. During the DL information procedure, the ng-eNB 104 transmits a DL information message to the UE 102. On the other hand, during the UL information procedure, the UE 102 transmits a UL information message to the ng-eNB 104. During the RRC connection reconfiguration procedure, the ng-eNB 104 transmits an RRC connection reconfiguration message to the UE 102, and receives an RRC connection reconfiguration complete message from the UE 102. Finally, as part of the measurement report procedure, the UE 102 transmits a measurement report message to the ng-eNB 104.

[0052] Returning to event 352, the UE 102 in some embodiments sets the sequence number (SN) in the PDCP header of the NR PDCP PDU 4 to zero.

[0053] In other embodiments, the UE 102 assigns an initial value (e.g., zero) to the transmission count variable (TX_COUNT) in response to a subsequent communication event of an NR PDCP PDU that is conceptually separate from the exchange 302. This event may be, for example, receiving an RRCConnectionRelease message, initiating an RRC connection recovery procedure, transmitting an RRCConnectionResumeRequest message to the ng-eNB 104, or receiving an RRCConnectionSetup message. The UE 102 then uses the TX_COUNT to transmit the NR PDCP PDU including the RRC message.

[0054] In some embodiments, if integrity protection is configured in the RRCConnectionSetup message, the UE 102 uses TX_COUNT to generate a message authentication code for the integrity (MAC-I) of the RRC PDU including the RRCConnectionSetupComplete message. If encryption is configured in the RRCConnectionSetup message, the UE 102 may use TX_COUNT to encrypt the PDCP service data unit (SDU) including the RRC PDU and the message authentication code for the MAC-I of the RRC PDU. The UE 102 in this embodiment includes the encrypted PDCP SDU in the NR PDCP PDU 4 and sets the SN in the PDCP PDU header of the NR PDCP PDU 4 to a specific number (X) of least significant bits (LSBs) of TX_COUNT. For example, the value of X may be the length of the SN. Then, after encrypting the PDCP SDU or generating the NR PDCP PDU 4, the UE 102 increases the TX_COUNT value by 1. In other embodiments, if neither integrity protection nor encryption is configured in the RRCConnectionSetup message, the UE 102 still generates a MAC-I for the RRCPDU including the RRCConnectionSetupComplete message, and sets the MAC-I to a default value (e.g., 0). The UE 102 in this embodiment generates a PDCP SDU to include the RRC PDU and the MAC-I, includes the PDCP SDU in the NR PDCP PDU 4, and sets the SN in the PDCP PDU header of the NR PDCP PDU 4 to a specific number (X) of least significant bits (LSBs) of a specific TX_COUNT.

[0055] In addition, when the UE 102 needs to transmit the first RRC message after transmitting the RRCConnectionSetupComplete message or after receiving the SecurityModeCommand message from the ng-eNB 104 (or ng-eNB 106), the UE 102 in one embodiment uses TX_COUNT to encrypt the PDCP SDU including the RRC PDU, wherein the RRC PDU includes the first RRC message and the MAC-I including the RRC PDU. Then, the UE 102 includes the encrypted PDCP SDU in the NR PDCP PDU 5. Then, the UE 102 sets the SN in the PDCP PDU header of the NR PDCP PDU 5 to a specific number of LSBs of TX_COUNT. The UE 102 transmits the NR PDCP PDU 5 to the ng-eNB 104 (or ng-eNB 106). After encrypting the PDCP SDU or generating the NR PDCP PDU 5, the UE 102 also increases the TX_COUNT by 1. UE 102 may transmit each subsequent RRC message in a similar manner.

[0056] In addition, in response to the same or similar events as discussed above with reference to TX_COUNT, the UE 102 in some embodiments assigns an initial value (e.g., zero) to a receive count variable (RX_COUNT). The UE 102 then uses the RX_COUNT to process NR PDCP PDUs received from the ng-eNB 104 (or ng-eNB 106). For example, the UE uses the RX_COUNT to decrypt NR PDCP SDUs in the received NR PDCP PDUs and / or to perform integrity checks on RRC PDUs in the NR PDCP SDUs. The UE 102 in some embodiments increases the RX_COUNT value by 1 after processing each NR PDCP PDU. In an example case, each NR PDCP PDU is a PDCP data PDU.

[0057] Reference now Figure 4 , the RRC controller 122 or other suitable component of the UE 102 in this case, after transitioning to the RRC_CONNECTED state, establishes a new instance of the NR PDCP entity 126 so that the different instances of the NR PDCP entity 126 participate in the exchange 302 and transmission of the RRCConnectionSetupComplete message (and subsequent RRC messages).

[0058] In this case, UE 102 is initially in RRC_CONNECTED state 401, and ng-eNB 104 exchanges NRPDCP PDUs (402), similar to exchange 302 discussed above. ng-eNB 104 then performs a connection release procedure 410, which is similar to procedure 310. UE 102 then transitions to RRC_INACTIVE state (418), subsequently initiates an RRC connection resumption procedure (420), transmits an RRCConnectionResumeRequest message (422) to the eLTE network in which ng-eNB 104 (or ng-eNB 106) operates, receives an RRCConnectionSetup message (424), and transitions to RRC_CONNECTED state (430) (similar to events 318, 320, 322, and 324 discussed above).

[0059] like Figure 4 As shown, the RRC controller 122 releases the NR PDCP entity 126 (432) and establishes a new instance of the NR PDCP entity 126 (434) before transmitting an RRCConnectionSetupComplete message (452) to the ng-eNB 104. The UE 102 may apply the default NR PDCP configuration to the NR PDCP entity 126 when creating an instance of the NR PDCP entity 126 or when transmitting the RRCConnectionSetupComplete message (452). In some embodiments, the UE 102 releases the radio resources configured by the ng-eNB 104 (e.g., all established RBs except SRB0) before receiving the RRCConnectionRelease message. The radio resources may include EUTRA RLC entities, NR SDAP entities (if configured), and other NR PDCP entities.

[0060] The new instance of NR PDCP entity 126 transmits NR PDCP PDU (452) including RRCConnectionSetupComplete message to ng-eNB 104. Subsequent events 454, 456, 460, and 470 are similar to events 354, 356, 360, and 370 discussed above.

[0061] General reference Figure 3 and Figure 4 In response to different events, the RRC controller 122 in other embodiments may establish, re-establish (i.e., apply new configuration), and release instances of the NR PDCP entity 126.

[0062] For example, the UE 102 may establish the NR PDCP entity 126 before or in response to receiving the RRCConnectionRelease message (312) from the ng-eNB 104. When the UE 102 establishes the NR PDCP entity 126 before receiving the RRCConnectionRelease message (312), the UE 102 receives the NR PDCP PDU 3 (314) and extracts the RRCConnectionRelease message from the NR PDCP PDU 3 using the NR PDCP entity 126. UE 102 may apply a default NR PDCP configuration for NR PDCP entity 126 (reference NR PDCP entity 126 or a new instance of NR PDCP entity 126 described above) in response to an RRCConnectionRelease message or prior to transmitting an RRCConnectionSetupComplete message (352, 452) to ng-eNB 104 (or ng-eNB 106). UE 102 may then re-establish NR PDCP entity 126, for example, in response to an RRCConnectionRelease message (event 314), in response to initiating an RRC connection recovery procedure (320, 420), in response to an RRCConnectionSetup message (event 324, event 424), or in response to transmitting an RRCConnectionSetupComplete message (352, 452) to ng-eNB 104 (or ng-eNB 106), prior to transmitting the RRCConnectionSetupComplete message (352, 452).

[0063] In some cases, if the RRCConnectionSetup message includes an NR PDCP configuration (e.g., a PDCP-Config information element) for SRB1 used by the UE 102 to transmit the RRCConnectionSetupComplete message, the UE 102 applies the NR PDCP configuration to the NR PDCP entity 126. For example, the RRCConnectionSetup message includes an SRB-ToAddMod information element for SRB1, and the SRB-ToAddMod information element includes the NR PDCP configuration. In another example, the RRCConnectionSetup message does not include the NR PDCP configuration.

[0064] If the RRCConnectionSetup message includes the RLC configuration (e.g., RLC-Config information element) for SRB1, the UE 102 may establish a EUTRA RLC entity (or referred to as an RLC bearer) according to the RLC configuration, and associate the EUTRA RLC entity with the NR PDCP entity 126. Then, the NR PDCP entity 126 transmits the NR PDCP PDU 4 via the EUTRA RLC entity (354, 454).

[0065] The ng-eNB 104 (or ng-eNB 106) may apply the default NR PDCP configuration to the NR PDCP entity 136 (refer to the NR PDCP entity 136 or the new instance of the NR PDCP entity 136 described above) before receiving the RRCConnectionSetupComplete message. The default NR PDCP configuration applied by the UE and the ng-eNB 104 (or ng-eNB 106) may be the same or different. In one example, the ng-eNB 104 (or ng-eNB 106) may include the NR PDCP configuration (e.g., PDCP-Config information element) for SRB1 in the RRCConnectionSetup message. The ng-eNB 104 (or ng-eNB 106) may apply the NR PDCP configuration to the NR PDCP entity 136. For example, ng-eNB 104 (or ng-eNB 106) includes the NR PDCP configuration in the SRB-ToAddMod information element for SRB1 and includes it in the RRCConnectionSetup message. In another example, ng-eNB 104 (or ng-eNB 106) does not include the NR PDCP configuration in the RRCConnectionSetup message.

[0066] The ng-eNB 104 (or ng-eNB 106) may include the RLC configuration (e.g., RLC-Config information element) for SRB1 in the RRCConnectionSetup message. The ng-eNB 104 (or ng-eNB 106) may establish a EUTRA RLC entity (or RLC bearer) based on the RLC configuration and associate the EUTRA RLC entity with the NR PDCP entity 136. The PDCP entity 136 receives NR PDCP PDU 4 (354, 454) via the EUTRA RLC entity. Alternatively, although the ng-eNB 104 (or ng-eNB 106) includes the RLC configuration in the RRCConnectionSetup message, the ng-eNB 104 (or ng-eNB 106) may establish a EUTRA RLC entity (or RLC bearer) based on a default RLC configuration that is different from the RLC configuration. The NR PDCP entity 136 then receives the NR PDCP PDU 4 via the EUTRA RLC entity (354, 454).

[0067] As another example, the RRC controller 122 establishes the NR PDCP entity 126 before receiving the RRCConnectionRelease message (314) from the ng-eNB 104. The UE 102 receives the NR PDCP PDU 3 and uses the NR PDCP entity 126 to extract the RRCConnectionRelease message from the NR PDCP PDU 3. In response to the RRCConnectionRelease message, the RRC controller 122 in this embodiment releases the NR PDCP entity 126.

[0068] On the eLTE network side (e.g., at the ng-eNB 104), the RRC controller 132 or other suitable component of the eLTE network may also use the same instance of the NR PDCP entity 136 for SRBs to transmit RRC messages or, when resuming an RRC connection, reestablish the NR PDCP entity 136. In a manner generally similar to the RRC controller 122 operating in the UE 102, the RRC controller 132 may release and establish instances of the NR PDCP entity 136 in response to various events, such as messages received from or transmitted to the UE 102.

[0069] For example, the RRC controller 132 may establish the NR PDCP entity 136 for the SRB (e.g., SRB1) prior to receiving the NR PDCP PDU 4 (352, 452). The ng-eNB 104 may then extract the RRCConnectionSetupComplete message from the NR PDCP PDU 4 using the NR PDCP entity 136. In one example embodiment, the RRC controller 132 establishes the NR PDCP entity 136 in response to receiving the RRCConnectionResumeRequest message (322, 422) from the UE 102. In another example embodiment, the RRC controller 132 establishes the NR PDCP entity 136 in response to transmitting the RRCConnectionSetup message (324) to the UE 102. The RRC controller 136 may apply the default NR PDCP configuration to the NR PDCP entity 136 when establishing the NR PDCP entity 136 or prior to receiving the RRCConnectionSetupComplete message (352) from the UE 102.

[0070] As another example, the RRC controller 132 (or another suitable component of the eLTE network) may establish the NR PDCP entity 136 to exchange RRC messages with the UE 102 before transmitting the RRCConnectionRelease message (312) to the UE 102. The RRC controller 132 may apply the default NR PDCP configuration to the NR PDCP entity 136 in response to transmitting the RRCConnectionRelease message (312) to the UE 102 or before receiving the RRCConnectionSetupComplete message (352, 452) from the UE 102. The RRC controller 132 may re-establish the NR PDCP entity 136, e.g., in response to transmitting the RRCConnectionRelease message (312) to the UE 102, in response to receiving the RRCConnectionResumeRequest message (322, 422), or in response to transmitting the RRCConnectionSetup message (324, 424) before receiving the RRCConnectionSetupComplete message (352).

[0071] Reference above Figure 3 and Figure 4In the discussed embodiments, UE 102 and ng-eNB 104 (or ng-eNB 106) utilize NR PDCP format to transmit the RRCConnectionSetupComplete message and messages related to one or more subsequent RRC procedures. Alternatively, UE 102 and ng-eNB 104 (or ng-eNB 106) may apply EUTRA PDCP format to the RRCConnectionSetupComplete message, messages related to one or more subsequent RRC procedures, or both.

[0072] refer to Figure 5 , events or states 501, 502, 510, 518, 520, 522, 524, and 520 are similar to events or states 301 / 401, 302 / 402, 310 / 410, 318 / 418, 320 / 420, 322 / 422, 324 / 424, and 330 / 430. However, in this case, the RRC controller 122 releases all radio resources including the NR PDCP entity 126 (538). The RRC controller 122 then provides an RRCConnectionSetupComplete message (550) to the EUTRA PDCP entity 124, which includes the RRC message in EUTRA PDCP PDU 1 and transmits EUTRA PDCP PDU 1 to the ng-eNB 104 (or ng-eNB 106) (552).

[0073] ng-eNB 104 receives EUTRA PDCP PDU 1 and extracts the RRCConnectionSetupComplete message from the PDU according to the EUTRA PDCP format using EUTRA PDCP entity 134 (554). Figure 3 In contrast to the techniques of , an existing ng-eNB may try to extract the RRCConnectionSetupComplete message using the NR PDCP entity and accordingly using the NR PDCP format. This decoding fails for the reasons described above.

[0074] The EUTRA PDCP entity 134 then provides an RRCConnectionSetupComplete message to the RRC controller 132 (556), and the RRC controller 132 decodes the RRC message (560). Thus, in this case, the UE 102 transmits the RRCConnectionSetupComplete message by using the same format (i.e., the EUTRA PDCP format), and the ng-eNB 104 decodes the RRCConnectionSetupComplete message.

[0075] exist Figure 5 After UE 102 has restored the RRC connection, UE 102 and ng-eNB 104 may perform one or more subsequent procedures (e.g., security mode, DL information, UL information, RRC reconfiguration) (570) using the EUTRA PDCP format to transmit RRC messages and decode received RRC messages. Therefore, UE 102 may continue to use EUTRA PDCP entity 124 and ng-eNB 104 may continue to use EUTRA PDCP entity 134.

[0076] Similar to Figure 3 In some embodiments, the UE 102 sets the SN in the PDCP header of EUTRA PDCP PDU 1 to zero.

[0077] In other embodiments, the UE 102 assigns an initial value (e.g., zero) to the transmission hyperframe number (TX_HFN) and assigns another initial value (which may also be zero) to the next PDCP transmission variable (Next_PDCP_TX_SN) in response to an event. Similar to the TX_COUNT variable discussed above, the event may be, for example, receiving an RRCConnectionRelease message, initiating an RRC connection recovery procedure, transmitting an RRCConnectionResumeRequest message to the ng-eNB 104, or receiving an RRCConnectionSetup message. The UE 102 then uses TX_HFN and Next_PDCP_TX_SN to transmit EUTRA PDCP PDU 1 and subsequent EUTRA PDCP PDUs.

[0078] In addition, if integrity protection is configured in the RRCConnectionSetup message, the UE 102 in some embodiments uses TX_HFN and Next_PDCP_TX_SN to generate a MAC-I of the RRC PDU including the RRCConnectionSetupComplete message. If encryption is configured in the RRCConnectionSetup message, the UE can encrypt the PDCP SDU including the MAC-I of the RRC PDU and the RRC PDU message. The UE 102 includes the encrypted PDCP SDU in EUTRA PDCP PDU1. The UE 102 sets the SN in the PDCP PDU header of EUTRA PDCP PDU 1 to Next_PDCP_TX_SN. Then, the UE 102 increases the Next_PDCP_TX_SN by 1 after encrypting the PDCP SDU or generating EUTRA PDCP PDU1. In other embodiments, if neither integrity protection nor encryption is configured in the RRCConnectionSetup message, the UE 102 still generates a MAC-I of the RRC PDU including the RRCConnectionSetupComplete message, and sets the MAC-I to a default value (e.g., 0). The UE 102 in this embodiment generates a PDCP SDU to include the RRC PDU and the MAC-I, includes the PDCP SDU in the NR PDCP PDU 4, and sets the SN in the PDCP PDU header of the NR PDCP PDU 4 to Next_PDCP_TX_SN.

[0079] When the UE 102 needs to transmit the first RRC message after transmitting the RRCConnectionSetupComplete message (552) or after receiving the SecurityModeCommand message from the ng-eNB 104 (or ng-eNB 106), the UE 102 in some embodiments uses TX_HFN and Next_PDCP_TX_SN to encrypt the PDCP SDU including the MAC-I with the first RRC message RRC PDU and the RRC PDU. The UE 102 includes the encrypted PDCP SDU in the EUTRA PDCP PDU 2. The UE 102 sets the SN in the PDCP PDU header of the EUTRA PDCP PDU 2 to Next_PDCP_TX_SN. After encrypting the PDCP SDU or generating the EUTRA PDCP PDU 2, the UE 102 increases the Next_PDCP_TX_SN by 1. Then, the UE 102 transmits the EUTRA PDCP PDU 2 to the ng-eNB 104 (or ng-eNB 106). UE 102 may transmit each subsequent RRC message in a similar manner.

[0080] In addition, in response to events similar to those described above with reference to the RX_COUNT variable, the UE 102 in some embodiments assigns an initial value (e.g., zero) to a receive count variable HFN (RX_HFN) and a next PDCP receive SN (Next_PDCP_RX_SN). The UE 102 then uses RX_HFN and Next_PDCP_RX_SN to process the received EUTRA PDCP PDU (e.g., for decrypting the EUTRA PDCP SDU in the received EUTRA PDCP PDU and / or for performing an integrity check on the RRC PDU in the EUTRA PDCP SDU). The UE 102 increases the RX_COUNT value by 1 after processing each EUTRA PDCP PDU (the EUTRA PDCP PDU may be, for example, a data PDU).

[0081] exist Figure 5In a corresponding embodiment, for example, the RRC controller 122 may establish the NR PDCP entity 126 for the SRB (e.g., SRB1) before receiving the RRCConnectionSetup message (524). In one embodiment, the RRC controller 122 establishes the NR PDCP entity 126 in response to initiating an RRC connection resumption procedure or transmitting an RRCConnectionResumeRequest message (522) to the ng-eNB 104. The UE 102 may release the NR PDCP entity 126 in response to the RRCConnectionSetup message.

[0082] In another example implementation, during process 510, the UE 102 establishes the NR PDCP entity 126 before receiving the RRCConnectionRelease message from the ng-eNB. More specifically, the UE 102 may receive the NR PDCP PDU 3, extract the RRCConnectionRelease message from the NR PDCP PDU 3 using the NR PDCP entity 126, and release the NR PDCP entity 126 in response to the RRCConnectionRelease message.

[0083] For another example, the RRC controller 122 may establish the NR PDCP entity 126 in response to receiving the RRCConnectionRelease message from the ng-eNB 104. The RRC controller 122 in this case may release the NR PDCP entity 126 in response to receiving the RRCConnectionSetup message (524).

[0084] In some implementations, the RRC controller 122 establishes the EUTRA PDCP entity 124 while releasing the NR PDCP entity 126. Specifically, the RRC controller 122 may establish the EUTRA PDCP entity 124 in response to receiving the RRCConnectionSetup message (524).

[0085] Reference now Figure 6 In this case, UE 102 and ng-eNB 104 (or ng-eNB 106) transmit the RRCConnectionSetupComplete message using the EUTRA PDCP format, similar to Figure 5 However, here, during one or more subsequent processes, UE 102 and ng-eNB 104 (or ng-eNB 106) transmit RRC messages using the NR PDCP format.

[0086] More specifically, events or states 601, 602, 610, 618, 620, 622, 624, 620, and 630 are similar to events or states 301 / 401 / 501, 302 / 402 / 502, 310 / 410 / 510, 318 / 418 / 518, 320 / 420 / 520, 322 / 422 / 522, 324 / 424 / 524, and 330 / 430 / 530. After the RRC controller 122 transitions to the RRC_CONNECTED state (630), the RRC controller 122 establishes a new instance of the NR PDCP entity 126 (639).

[0087] The RRC controller 122 then provides an RRCConnectionSetupComplete message (650) to the EUTRA PDCP entity 124. Depending on the implementation, the RRC controller 122 may establish the EUTRA PDCP entity 124 after receiving the RRCConnectionSetup message (624), or the RRC controller 122 may continue to utilize an instance of the EUTRA PDCP entity 124 established earlier (e.g., before the exchange 602). The EUTRA PDCP entity 124 includes the RRCConnectionSetup message in the EUTRAPDCP PDU 1 and transmits the EUTRA PDCP PDU 1 to the ng-eNB 104 (652). Then, ng-eNB 104 receives EUTRA PDCP PDU 1, extracts the RRCConnectionSetupComplete message from the PDU using EUTRA PDCP entity 134 according to the EUTRA PDCP format (654), and provides the RRCConnectionSetupComplete message to RRC controller 132 (656), which in turn decodes the RRC message (660). Figure 5 In the case of the above, UE 102 transmits an RRCConnectionSetupComplete message by using the EUTRA PDCP format, and ng-eNB 104 (or ng-eNB 106) decodes the RRCConnectionSetupComplete message.

[0088] However, the NR PDCP entity 126 of the UE 102 may then exchange RRC messages related to subsequent RRC procedures (e.g., security mode, DL information, UL information, RRC reconfiguration) with the NR PDCP entity 136 of the ng-eNB 104 (or ng-eNB 106) using the NR PDCP format (670). Thus, in this embodiment, the UE 102 and the ng-eNB 104 (or ng-eNB 106) initially exchange PDCP PDUs using the NR PDCP format, restore the RRC connection using the EUTRA PDCP format, and continue to use the NR PDCP format for subsequent RRC procedures. As previously described, the UE 102 may apply the default NR PDCP configuration to the NR PDCP entity 126. As previously described, if the RRCConnectionSetup message includes the NR PDCP configuration, the UE 102 may apply the NR PDCP configuration to the NR PDCP entity 126. As previously described, the ng-eNB 104 (or ng-eNB 106) may apply the default NR PDCP configuration to the NR PDCP entity 136. As previously described, if the RRCConnectionSetup message includes the NR PDCP configuration, the ng-eNB 104 (or ng-eNB 106) may apply the NR PDCP configuration to the NR PDCP entity 136.

[0089] To manage the PDU count, the UE 102 in this embodiment may use the above reference Figure 3 The TX_COUNT technique discussed above is referenced Figure 5 104. In some embodiments, the UE 102 may utilize the TX_COUNT technique discussed above to process received NR PDUs. In some embodiments, the UE 102 may utilize the TX_HFN and Next_PDCP_TX_SN techniques discussed above. More specifically, the UE 102 may apply the TX_COUNT technique to outgoing NR PDCP PDUs and the TX_HFN / Next_PDCP_TX_SN technique to outgoing EUTRA PDCP PDUs. The UE 102 may also utilize the RX_COUNT technique discussed above to process received NR PDUs. Because in this case, the UE 102 does not receive EUTRA PDCP PDUs from the ng-eNB 104, the UE 102 does not need to implement the RX_COUNT technique for EUTRA PDCP PDUs.

[0090] General reference Figure 3-6 The eLTE network in which the UE 102 and the ng-eNB 104 operate may communicate the PDCP PDUs discussed above to each other using the EUTRA RLC PDUs. Figure 2BAs shown, on the control plane, the EUTRA PDCP sublayer 218 and the NR PDCP sublayer 208 are layered above the RLC sublayer 206. In some embodiments, in response to the RRCConnectionSetup message, in response to initiating the RRC connection recovery process, or in response to transmitting the RRCConnectionResumeRequest message, the UE102 establishes an EUTRA RLC entity for the SRB (e.g., SRB1) (not shown in any figure to avoid confusion). Similarly, for example, the ng-eNB 104 can establish an EUTRA RLC entity for the SRB in response to receiving the RRCConnectionResumeRequest message (also omitted in the above figures to avoid confusion). The EUTRA RLC entity of the UE 102 and the EUTRA RLC entity of the ng-eNB104 can use the EUTRA RLC PDU to transmit and receive NR PDCP PDUs and / or EUTRA PDCP PDUs.

[0091] Figure 7 is a flow chart of an example method 700 for transmitting an indication that a radio connection has been restored. The method 700 may be implemented in a UE 102 and is discussed below with reference to the UE 102. However, the method 700 may generally be implemented in any suitable device.

[0092] At block 702, UE 102 communicates messages with a base station (such as ng-eNB 104) according to a format corresponding to a first RAT. For example, the first RAT may be NR and the messages may conform to an NR PDCP format. UE 102 communicates these messages at block 702 over a radio interface conforming to a different second RAT using a radio connection (e.g., an RRC connection). For example, the second RAT may be EUTRA. Examples of communicating messages according to the NR format over the EUTRA radio interface include exchange 302, exchange 402, exchange 502, and exchange 604. UE 102 at block 702 may be in an RRC_CONNECTED state (see Figure 3 Status 301 in Figure 4 Status 401, Figure 5 Status 501 and Figure 6 Operate in state 601).

[0093] At block 704, UE 102 may suspend the radio connection. For example, UE 102 may transition to the RRC_INACTIVE state ( Figure 3 Event 318 in Figure 4 Event 418 in Figure 5 Event 518 and Figure 6The suspension may be due to receiving an RRCConnectionRelease message (e.g., Figure 3 Event 312 in ), which in turn may be due to data inactivity at UE 102 for a certain period of time.

[0094] Next, at block 706, UE 102 may restore the radio connection (eg, Figure 3 Event 320 in Figure 4 Event 420 in Figure 5 Event 520 and Figure 6 For example, RRC controller 122 may receive an indication that outgoing data is available for transmission to ng-eNB 104 or another base station.

[0095] At block 708, UE 102 transmits an indication that the radio connection has been restored (e.g., Figure 3 Event 352 and Figure 4 Event 452 in ). The indication may be an RRCConnectionSetupComplete message. UE 102 uses a format corresponding to the first RAT. To continue with the above example, the format corresponding to the first RAT may be NR PDCP. As described above, ng-eNB 104 may use an NR PDCP entity to decode the RRC message.

[0096] Optionally, the UE 102 at block 710 may perform at least one subsequent RRC procedure (eg, Figure 3 Event 370 and Figure 4 470 in the event).

[0097] Figure 8 8 is a flow chart of another example method 800 for transmitting an indication that a radio connection has been restored. The method 800 may also be implemented in the UE 102 and is discussed below with reference to the example of the UE 102.

[0098] Blocks 802, 804, and 806 of method 800 are similar to blocks 702, 704, and 706 of method 700. However, at block 810, UE 102 transmits an indication that the radio connection has been restored (e.g., Figure 5 Event 552 and Figure 6652 in method 700). The indication may be an RRCConnectionSetupComplete message, similar to method 700, but according to the present method, UE 102 uses a format corresponding to the second RAT. To continue with the above example, the format corresponding to the second RAT may be EUTRA PDCP. As described above, ng-eNB 104 may use the EUTRA PDCP entity to decode the RRC message.

[0099] The method 800 may include optional block 812 or optional block 814. At block 812, the UE 102 performs a subsequent RRC procedure according to a format corresponding to the second RAT, which in the above example is EUTRA (e.g., Figure 5 On the other hand, at block 814, UE 102 performs a subsequent RRC procedure according to a format corresponding to the first RAT, which in the above example is NR (e.g., Figure 6 670 in the event).

[0100] Next, Fig. 9 An example method 900 for decoding an indication that a radio connection has been restored is shown. The method 900 may be implemented in any suitable base station and is discussed below with reference to the example of the ng-eNB 104.

[0101] At block 902, ng-eNB 104 communicates messages with a UE, such as UE 102, according to a format corresponding to a first RAT. For example, the first RAT may be NR, and the messages may conform to an NR PDCP format. ng-eNB 104 communicates the messages at block 902 over a radio interface conforming to a different second RAT using a radio connection (e.g., an RRC connection). For example, the second RAT may be EUTRA. Examples of communicating messages according to an NR PDCP format over an EUTRA radio interface include exchanges 302, 402, 502, and 604.

[0102] At block 904, ng-eNB 104 may transmit a command to UE 102 to suspend a radio connection, such as an RRC connection (e.g., Figure 3 For example, the ng-eNB 104 may transmit the command in response to detecting a period of inactivity.

[0103] At block 906, the ng-eNB 104 may receive an indication that the radio connection has been restored. Examples of this indication include Figure 3-6 Event 352, event 422, event 522 and event 622.

[0104] At block 908, in accordance with the method 900, the ng-eNB 104 decodes the indication (e.g., Figure 5 Event 554 and Figure 6 More specifically, the ng-eNB 104 may use a PDCP entity corresponding to the second RAT and process the PDU according to the format of the second RAT.

[0105] The method 900 may include optional block 910 or optional block 912. At block 912, the ng-eNB 104 performs a subsequent RRC procedure according to a format corresponding to the second RAT, which in the above example is EUTRA (e.g., Figure 5 On the other hand, at block 912, the ng-eNB 104 performs a subsequent RRC procedure according to a format corresponding to the first RAT, which in the above example is NR (e.g., Figure 6 670 in the example above).

[0106] The following additional considerations apply to the above discussion.

[0107] The user equipment (e.g., UE 102) in which the technology of the present disclosure may be implemented may be any suitable device capable of wireless communication, such as a smart phone, tablet computer, laptop computer, mobile game console, point of sale (POS) terminal, health monitoring device, drone, camera, streaming media dongle or other personal media device, wearable device (such as smart watch), wireless hotspot, femtocell or broadband router. In addition, in some cases, the user equipment may be embedded in an electronic system, such as a head unit of a vehicle or an advanced driver assistance system (ADAS). In addition, the user equipment may be operated as an Internet of Things (IoT) device or a mobile Internet device (MID). Depending on the type, the user equipment may include one or more general purpose processors, a computer readable memory, a user interface, one or more network interfaces, one or more sensors, etc.

[0108] Certain embodiments are described in the present disclosure as including logic or multiple components or modules. A module may be a software module (e.g., a code or machine-readable instruction stored on a non-transitory machine-readable medium) or a hardware module. A hardware module is a tangible unit that is capable of performing a specific operation and may be configured or arranged in a specific manner. A hardware module may include dedicated circuits or logic that are permanently configured (e.g., as a dedicated processor, such as a field programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), a digital signal processor (DSP), etc.) to perform a specific operation. A hardware module may also include programmable logic or circuits (e.g., contained within a general-purpose processor or other programmable processor) that are temporarily configured by software to perform a specific operation. The decision to implement a hardware module in a dedicated and permanently configured circuit or in a temporarily configured circuit (e.g., configured by software) may be based on cost and time considerations.

[0109] When implemented in software, the technology may be provided as part of an operating system, a library used by multiple applications, a specific software application, etc. The software may be executed by one or more general-purpose processors or one or more special-purpose processors.

[0110] After reading this disclosure, those skilled in the art will understand other and alternative structural and functional designs for restoring RRC connections through the principles disclosed herein. Therefore, although specific embodiments and applications have been shown and described, it should be understood that the disclosed embodiments are not limited to the precise configurations and components disclosed herein. It is obvious to those of ordinary skill in the art that various modifications, changes and variations may be made to the arrangement, operation and details of the methods and devices disclosed herein without departing from the spirit and scope defined in the appended claims.

[0111] The following listing of aspects reflects various embodiments expressly contemplated by the present disclosure.

[0112] Aspect 1. A method in a user equipment (UE) for restoring a connection with a base station, which can be performed by processing hardware. The method includes: using a radio connection on a radio interface conforming to a second RAT, transmitting a first message with the base station according to a first format corresponding to a first RAT. The method also includes: suspending the radio connection; and after the suspension: (i) transmitting an indication to the base station that the radio connection has been restored according to a second format corresponding to the second RAT, and (ii) transmitting a second message for a process of controlling radio resources according to the first format or the second format.

[0113] Aspect 2. The method according to aspect 1 comprises: transmitting a second message according to the first format.

[0114] Aspect 3. The method according to aspect 1 comprises: transmitting a second message according to a second format.

[0115] Aspect 4. The method according to Aspect 1 further includes: establishing a first entity for communicating with a base station using a first format; and when the radio connection has been restored: (i) releasing the first entity, and (ii) establishing a second entity for communicating with the base station using a second format.

[0116] Aspect 5. A method according to any one of aspects 1-4, wherein the first format is NR PDCP and the second format is EUTRA PDCP.

[0117] Aspect 6. The method according to any one of aspects 1-5, wherein transmitting the indication that the radio connection has been restored includes transmitting an RRC message.

[0118] Aspect 7. A method according to any one of Aspects 1-6, wherein the process is one of the following: (i) a security mode process for activating access stratum security, (ii) a downlink (DL) information process, (iii) an uplink (UL) information process, (iv) a connection reconfiguration process, or (v) a measurement reporting process.

[0119] Aspect 8. A method according to any one of aspects 1-7, wherein the transmission indication includes: setting a count in a header of a data unit including the indication to zero.

[0120] Aspect 9: A UE comprising processing hardware configured to implement the method described in any one of the above aspects.

[0121] Aspect 10. A method in a base station for restoring a connection with a UE, which can be executed by processing hardware and includes: transmitting a message with the UE using a radio connection on a radio interface conforming to a second RAT according to a format corresponding to a first RAT; transmitting a command to release the radio connection to the UE; after the transmission, the processing hardware receiving an indication from the UE that the connection has been restored; and, according to the format corresponding to the first RAT, decoding the indication.

[0122] Aspect 11. The method according to aspect 10, wherein the format is a first format, and the method further comprises, after receiving the indication: transmitting a message of a process related to controlling radio resources according to a second format corresponding to a second RAT.

[0123] Aspect 12: The method according to aspect 10 further comprises, after receiving the indication: transmitting, by processing hardware, a message for controlling a process of radio resources with the UE according to a format corresponding to the first RAT.

[0124] Aspect 13. A method according to Aspect 10 or Aspect 11, wherein the process is one of the following: (i) a security mode process for activating access layer security, (ii) a downlink (DL) information process, (iii) an uplink (UL) information process, (iv) a connection reconfiguration process, or (v) a measurement reporting process.

[0125] Aspect 14. The method according to aspect 10, wherein the format is associated with a first protocol sublayer that provides a radio bearer to a second protocol sublayer, wherein the UE and the base station transmit messages related to controlling radio resources at the second protocol sublayer.

[0126] Aspect 15. The method according to aspect 14, wherein the first protocol sublayer is a PDCP protocol, and wherein the second protocol sublayer is an RRC protocol.

[0127] Aspect 16. A base station comprising processing hardware configured to perform the method according to any one of aspects 10-15.

Claims

1. A method in a base station for restoring a connection with a user equipment (UE), the method comprising: communicating, by processing hardware, a message with the UE according to a format corresponding to the first RAT using a radio connection over a radio interface conforming to the second RAT; transmitting, by processing hardware, to the UE a command to release the radio connection; After the transmission, receiving, by the processing hardware, an indication from the UE that the connection has been restored; and The indication is decoded by processing hardware according to a format corresponding to the first RAT.

2. The method according to claim 1, wherein: The format is associated with a first protocol sublayer providing a radio bearer to a second protocol sublayer at which the UE and the base station communicate messages related to controlling radio resources.

3. The method according to claim 2, wherein: The first protocol sublayer is a Packet Data Convergence Protocol (PDCP) protocol, and wherein the second protocol sublayer is a Radio Resource Control (RRC) protocol.

4. The method of claim 1 , further comprising, after receiving the indication: A message related to a process of controlling radio resources is transmitted to the UE by processing hardware according to a format corresponding to the first RAT.

5. The method according to claim 4, wherein: The process is one of the following: (i) Activate the security mode process of access layer security, (ii) Downlink (DL) information process, (iii) Uplink (UL) information procedure, (iv) a connection reconfiguration process, or (v) Measurement reporting process.

6. A base station, configured to implement the method according to any one of claims 1 to 5.

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