Technical field
[0001]
　The present disclosure relates to wireless communication systems, in particular to contention-based random access.
Background technology
[0002]
　The 3rd Generation Partnership Project (3GPP) is working on standardization of the 5th generation mobile communication system (5G) for introduction after 2020. As used herein, the 5th generation mobile communication system is referred to as a 5G system, or Next Generation (NextGen) System (NG System). The new Radio Access Technology (RAT) for the 5G System is called New Radio (NR), 5G RAT, or NG RAT. The new Radio Access Network (RAN) for the 5G System is called NextGen RAN (NG-RAN, or 5G-RAN. The new base station (NG-RAN node) in NG-RAN is. , GNodeB or gNB. The new core network for the 5G System is called the 5G Core Network (5GC) or NextGen Core (NG Core). The radio terminal (User Equipment (UE)) connected to the 5G System is Called 5G UE, NextGen UE (NG-UE) or simply UE.
[0003]
　The main components of 5GC are Access and Mobility Management function (AMF), Session Management function (SMF), and User plane function (UPF). AMF can, for example, manage UE connections and mobility, terminate NG-RAN control planes (CPs) (eg, exchange CP information with NG-RAN nodes, and terminate NAS layers (eg NAS messages with UEs). SMF, for example, terminates the session management (SM), the session management part of the NAS message. UPF is the anchor point of Intra-RAT and Inter-RAT mobility (eg handover). Yes, manage the QoS flow (eg DL reflective QoS marking).
[0004]
　The term "LTE" as used herein includes improvements and developments of LTE and LTE-Advanced to enable interworking with the 5G System, unless otherwise noted. The improvements and developments of LTE and LTE-Advanced for interworking with the 5G System are called LTE-Advanced Pro, LTE +, or enhanced LTE (eLTE). For example, an eLTE eNB that functions as an NG-RAN node is also called an ng-eNB. In addition, the “Evolved Packet Core (EPC)”, “Mobility Management Entity (MME)”, “Serving Gateway (S-GW)”, and “Packet Data Network (PDN) Gateway (P-GW)” used herein. Terms relating to LTE networks or logical entities, such as ")", include these improvements and developments to enable interworking with the 5G System, unless otherwise noted. The improved EPC, MME, S-GW, and P-GW are, for example, enhanced EPC (eEPC), enhanced MME (eMME), enhanced S-GW (eS-GW), and enhanced P-GW (eP-GW). ).
[0005]
　Non-Patent Documents 1, 2 and 3 disclose 2-step contention based random access (CBRA). LTE CBRA, as is well known, uses a 4-step CBRA procedure. In the standardization of 5G NR, a 2-step CBRA procedure is being considered in addition to the 4-step CBRA procedure.
[0006]
　For example, in a 4-step CBRA for initial access from Radio Resource Control (RRC) _IDLE, the UE first sends a first message (Msg1), a random access preamble, via the Physical Random Access Channel (PRACH). The network (ie, gNB) then sends a second message (Msg2), a random access response, using the Physical Downlink Control Channel (PDCCH) and Physical Downlink Shared Channel (PDSCH). Specifically, the network sends Downlink Control Information (DCI), which indicates the PDSCH resource for which Msg2 is scheduled, on the PDCCH and Msg2 on the PDSCH. Subsequently, the UE sends a third message (Msg3) on the Physical Uplink Shared Channel (PUSCH). For initial access, Msg3 includes a Medium Access Control Protocol Data Unit (MAC PDU) that carries the Common Control Channel (CCCH) data (Service Data Unit (SDU)) of the RRC layer. CCCH data (CCCH SDU) carries, for example, an RRC Setup Request. The Msg3 MAC PDU (including CCCH SDU) is at least the UE identifier (eg, eg, used for contention resolution). Includes Cell Radio Network Temporary Identifier (C-RNTI), System Architecture Evolution (SAE) Temporary Mobile Subscriber Identity (S-TMSI), or random value). Finally, the network sends a fourth message (Msg4) for contention resolution using PDCCH and PDSCH. Specifically, the network sends a DCI on the PDCCH indicating the PDSCH resource to which Msg4 is scheduled, and sends Msg4 on PDSCH. Msg4 includes a MAC PDU (or MAC subPDU) that carries a UE Contention Resolution Identity MAC Control Element (CE).
[0007]
　On the other hand, according to the basic principle of 2-step CBRA, the UE sends the first message (Msg1) and the third message (Msg3) of the 4-step CBRA together, and the network (ie, gNB) of the 4-step CBRA. The second message (Msg2) and the fourth message (Msg4) are transmitted together. In other words, the first message of the 2-step CBRA (hereinafter referred to as Msg1 *) corresponds to the first message (Msg1) and the third message (Msg3) of the 4-step CBRA, and the second message of the 2-step CBRA (hereinafter referred to as Msg3). (Called Msg2 *) corresponds to the second message (Msg2) and the fourth message (Msg4) of the 4-step CBRA. However, the 2-step CBRA Msg1 * does not have to contain exactly the same content as the 4-step CBRA Msg1 and Msg3. Similarly, Msg2 * in 2-step CBRA need not contain exactly the same content as Msg2 and Msg4 in 4-step CBRA.
[0008]
　Further, a fallback from 2-step CBRA to 4-step CBRA has been investigated (see Non-Patent Documents 2 and 3). The fallback involves switching to a 4-step CBRA procedure in the middle of a 2-step CBRA procedure. In Non-Patent Document 2, if the 4-step CBRA Msg1 and Msg3 were transmitted in the first step of the 2-step CBRA procedure, but the network successfully received only the 4-step CBRA Msg1, the network would be 4 It discloses that Msg4 of step CBRA cannot be sent but Msg2 can be sent. Further, Non-Patent Document 2 therefore, the UE receives a message corresponding to Msg2 of 4-step CBRA or a message corresponding to Msg4 after transmitting a message corresponding to Msg1 and Msg3 of 4-step CBRA in the 2-step CBRA procedure. It discloses that you may expect to do it. That is, in Non-Patent Document 2, in the first step of the 2-step CBRA procedure, a message corresponding to Msg1 and Msg3 of 4-step CBRA was transmitted, but only a message corresponding to Msg1 of 4-step CBRA was successfully received by the network. It discloses that the network and the UE will fall back to the 4-step CBRA procedure if done.
[0009]
　Non-Patent Document 3 discloses that gNB can detect a preamble, but may not be able to receive a message other than the preamble in the first message of the two-step CBRA. Further, in Non-Patent Document 3, in this case, gNB transmits a random access response (Random Access Response (RAR)) using 4-step RA-RNTI calculation, and UE responds to the reception of the RAR. It discloses that it can fall back to the 4-step CBRA procedure. As is well known, RA-RNTI (ie, Random Access Radio Network Temporary Identifier) ​​addresses a PDSCH carrying Msg2 in a 4-step CBRA. Specifically, in a 4-step CBRA, the UE monitors the PDCCH using RA-RNTI to decode the DCI indicating the PDSCH-scheduled resource carrying Msg2. RA-RNTI is associated with the PRACH in which Msg1 (ie, random access preamble) was transmitted and is calculated based on the time-frequency slot index in which Msg1 was transmitted.
Prior art literature
Non-patent literature
[0010]
Non-Patent Document 1: MediaTek Inc., “2-step CBRA procedure”, 3GPP R2-1812342, 3GPP TSG-RAN WG2 Meeting # 103, Gothenburg, Sweden, 20-24 August 2018
Non-Patent Document 2: LG Electronics Inc., “Considerations on 2-Step CBRA procedure for NR-U SA”, 3GPP R2-1812832, 3GPP TSG-RAN WG2 Meeting # 103, Gothenburg, Sweden, 20-24 August 2018
Non-Patent Document 3: Intel Corporation, “Considerations of 2” -step CBRA for NR licensed and unlicensed operation ”, 3GPP R2-1811664, 3GPP TSG-RAN WG2 Meeting # 103, Gothenburg, Sweden, 20-24 August 2018
Outline of the invention
Problems to be solved by the invention
[0011]
　The inventor examined the fallback from 2-step CBRA to 4-step CBRA and switching between 2-step CBRA and 4-step CBRA, and found various problems. For example, Non-Patent Document 2 describes how the UE receives Msg2 or Msg4 after transmitting the first message (Msg1 *) of 2-step CBRA, for example, Msg1 and Msg3 equivalents of 4-step CBRA. Not specifically disclosed. Non-Patent Document 3 also shows how the UE receives a RAR containing a preamble using 4-step RA-RNTI calculation after sending the first message (Msg1 *) of 2-step CBRA. Is not specifically disclosed.
[0012]
　If the UE is forced to receive the second message of the 4-step CBRA (Msg2) in addition to the second message of the 2-step CBRA (Msg2 *), the load of the UE's PDCCH / DCI blind decoding May increase. In one example, the UE may or may not have succeeded in PDCCH / DCI blind decoding for receiving the second message (Msg2 *) of the two-step CBRA after sending the first message of the two-step CBRA. PDCCH / DCI blind decoding must be performed to receive the second message (Msg2) of the 4-step CBRA. Such behavior can lead to increased load on the UE, increased complexity, or increased battery consumption.
[0013]
　Furthermore, the RAR window for receiving the second message (Msg2 *) of the 2-step CBRA may be different from the RAR window for receiving the second message (Msg2) of the 4-step CBRA. If the RAR window of the 4-step CBRA expires after the RAR window of the 2-step CBRA, the UE will spend more time trying to receive the RAR. Therefore, if the UE cannot receive either RAR and restarts random access from the first step, the start of the restart may be delayed.
[0014]
　One of the objectives to be achieved by the embodiments disclosed herein is to provide devices, methods, and programs that contribute to reducing the load on the UE to support fallback from 2-step CBRA to 4-step CBRA. It is to be. It should be noted that this object is only one of the purposes that the embodiments disclosed herein seek to achieve. Other objectives or issues and novel features will be apparent from the description or accompanying drawings herein.
Means to solve problems
[0015]
　In the first aspect, the wireless terminal comprises at least one memory and at least one processor coupled to said at least one memory. The at least one processor is configured to send the first message of the two-step random access procedure, send the first message, and then attempt to receive the second message of the two-step random access procedure. .. The at least one processor also succeeds in receiving the second message of the two-step random access procedure, and the second message explicitly or implicitly indicates a fallback to the four-step random access procedure. In response to the determination, an attempt is made to receive a control message including an uplink grant indicating an uplink resource that can be used to send the third message of the four-step random access procedure.
[0016]
　In the second aspect, the radio access network node comprises at least one memory and at least one processor coupled to said at least one memory. The at least one processor is configured to receive the first message of the two-step random access procedure, receive the first message, and then transmit the second message of the two-step random access procedure. Here, the second message succeeds in receiving the control message including the uplink grant indicating the uplink resource that can be used for transmitting the third message in the 4-step random access procedure. The fallback to the 4-step random access procedure is shown explicitly or implicitly to require the radio terminal to try afterwards.
[0017]
　In the third aspect, the method in the wireless terminal is to (a) transmit the first message of the two-step random access procedure, and (b) after transmitting the first message, the two-step random access procedure. Attempt to receive the second message, and (c) succeed in receiving the second message of the two-step random access procedure, and the second message explicitly falls back to the four-step random access procedure. Alternatively, in response to determining that it is implied, an attempt is made to receive a control message including an uplink grant indicating an uplink resource that can be used to send the third message of the 4-step random access procedure. Be prepared.
[0018]
　In a fourth aspect, the method at the radio access network node is to receive the first message of the two-step random access procedure, and after receiving the first message, the second message of the two-step random access procedure. Be prepared to send. Here, the second message succeeds in receiving the control message including the uplink grant indicating the uplink resource that can be used for transmitting the third message in the 4-step random access procedure. The fallback to the 4-step random access procedure is shown explicitly or implicitly to require the wireless terminal to try afterwards.
[0019]
　In the fifth aspect, the program includes an instruction group (software code) for causing the computer to perform the method according to the third or fourth aspect described above when the program is read by the computer.
The invention's effect
[0020]
　According to the above aspects, it is possible to provide an apparatus, a method, and a program that contribute to reducing the load of the UE that supports the fallback from the 2-step CBRA to the 4-step CBRA.
A brief description of the drawing
[0021]
FIG. 1 is a diagram showing a configuration example of a wireless communication network according to some embodiments.
FIG. 2 is a sequence diagram showing an example of a successful case of the CBRA procedure according to the first embodiment.
FIG. 3 is a sequence diagram showing an example of a failure case of the CBRA procedure according to the first embodiment.
FIG. 4 is a flowchart showing an example of the operation of the wireless terminal according to the first embodiment.
FIG. 5 is a flowchart showing an example of the operation of the radio access network node according to the first embodiment.
FIG. 6 is a sequence diagram showing an example of the operation of the radio access network node and the radio terminal according to the third embodiment.
FIG. 7 is a flowchart showing an example of the operation of the wireless terminal according to the third embodiment.
FIG. 8 is a sequence diagram showing an example of the operation of the wireless terminal according to the fourth embodiment.
FIG. 9 is a sequence diagram showing an example of the operation of the wireless terminal according to the fourth embodiment.
FIG. 10 is a sequence diagram showing an example of the operation of the wireless terminal according to the fifth embodiment.
FIG. 11 is a sequence diagram showing an example of the operation of the radio access network node and the radio terminal according to the sixth embodiment.
FIG. 12 is a sequence diagram showing an example of the operation of the wireless terminal according to the sixth embodiment.
FIG. 13 is a sequence diagram showing an example of the operation of the radio access network node and the radio terminal according to the seventh embodiment.
FIG. 14 is a sequence diagram showing an example of the operation of the radio access network node and the radio terminal according to the eighth embodiment.
FIG. 15 is a flowchart showing an example of the operation of the wireless terminal according to the eighth embodiment.
FIG. 16 is a flowchart showing an example of the operation of the radio access network node according to the eighth embodiment.
FIG. 17 is a block diagram showing a configuration example of a radio access network node according to some embodiments.
FIG. 18 is a block diagram showing a configuration example of a wireless terminal according to some embodiments.
Embodiment for carrying out the invention
[0022]
　Hereinafter, specific embodiments will be described in detail with reference to the drawings. In each drawing, the same or corresponding elements are designated by the same reference numerals, and duplicate explanations are omitted as necessary for the sake of clarity of explanation.
[0023]
　The plurality of embodiments described below may be implemented independently or in combination as appropriate. These plurality of embodiments have novel features that differ from each other. Therefore, these plurality of embodiments contribute to solving different purposes or problems, and contribute to different effects.
[0024]
　The plurality of embodiments shown below are described with the 3GPP 5G system as the main subject. However, these embodiments may be applied to other wireless communication systems.
[0025]

　FIG. 1 shows a configuration example of a wireless communication network according to some embodiments including the present embodiment. In the example of FIG. 1, the radio communication network includes a radio access network (RAN) node (ie, gNB) 1 and a radio terminal (ie, UE) 2. The gNB 1 is a RAN (ie, NG-RAN). ). The gNB1 may be a gNB Central Unit (gNB-CU) or a gNB Distributed Unit (gNB-DU) in a cloud RAN (C-RAN) deployment. UE2 Is connected to the gNB1 via the air interface 101. The UE2 is a plurality of base stations (ie, Master gNB (MgNB) and Secondary gNB (SgNB), or Master Node (MN)) for dual connectivity. And Secondary Node (SN)) may be connected at the same time.
[0026]
　FIG. 2 shows an example of the CBRA procedure according to the present embodiment. More specifically, FIG. 2 shows an example of a successful case with a fallback from a 2-step CBRA to a 4-step CBRA procedure. In step 201, UE2 transmits the first message (Msg1 *) of the two-step CBRA procedure. The Msg1 * may carry, for example, preambles and MAC PDUs. The preamble in Msg1 * may be referred to as a random access (RA) preamble, a random access channel (RACH) preamble, or the like. The MAC PDU may include, for example, CCCH data (CCCH SDU). CCCH data (CCCH SDU) carries, for example, RRC Setup Request, RRC Re-establishment Request, or RRC Resume Request. Further or instead, the MAC PDU may include a terminal identifier (eg, C-RNTI, S-TMSI, or random value) used for contention resolution. The terminal identifier may be included in the MAC control information (Control Element (CE)) in the MAC PDU. Further or instead, the MAC PDU may include control information for other MAC layers specified for 2-step CBRA.
[0027]
　In step 202, gNB1 transmits a second message (Msg2 *) of the two-step CBRA procedure. In response to the reception of Msg1 *, gNB1 determines whether or not all of Msg1 * have been successfully received. For example, if the preamble in Msg1 * (ie, the equivalent of Msg1 in 4-step CBRA) was successfully received, but the MAC PDU in Msg1 * was not received, gNB1 would be the second message in 2-step CBRA (Msg2). *) May include a fallback notification. The fallback notification indicates the fallback to the 4-step CBRA procedure, either explicitly or implicitly.
[0028]
　Msg2 * may include MAC control information (CE) that is defined as a 2-step CBRA random access response (RAR) and is different from the 4-step CBRA RAR. Alternatively, Msg2 * may include another information element (or field) that corresponds to the random access response (RAR) of the two-step CBRA. In addition, Msg2 * provides the MAC PDU in Msg1 * with information elements (eg, Timing Advance Command) and terminal identifiers (eg, Temporary C-RNTI) related to the uplink transmission timing associated with the successfully received preamble. It may be included regardless of the success or failure of reception. In other words, gNB1 is Msg2 * (ie, downlink MAC subPDU) that includes the Timing Advance Command for the target (ie, UE) to be notified of fallback, and the information necessary to complete the two-step CBRA (ie, downlink MAC subPDU). You may send Msg2 * (ie, downlink MAC subPDU) that includes the Timing Advance Command for the target (ie, UE) to which you want to send eg, RRC messages or UE Contention Resolution Identity MAC CE (ie, UE). These two types of Msg2 * may be contained in the same downlink MAC PDU or have different radio resources (eg, eg, It may be included in different downlink MAC PDUs transmitted in time or frequency). Successful reception of the preamble in Msg1 * may mean that the preamble was detected correctly or that the preamble portion was successfully decoded. The fallback notification can be thought of as a notification that only the preamble in Msg1 * was successfully received. Hereinafter, it will be described as a fallback notification (or a fallback notification) as an example.
[0029]
　When the UE successfully receives the second message (Msg2 *) of the 2-step CBRA, it determines whether the Msg2 * indicates (explicitly or implicitly) a fallback to the 4-step CBRA procedure. do. In response to determining that the Msg2 * indicates a fallback to the 4-step CBRA procedure, UE2 falls back to the 4-step CBRA procedure (step 203). Then, UE2 starts the operation for transmitting the third message (Msg3) of the 4-step CBRA procedure. That is, UE2 expects a fallback to the 4-step CBRA procedure only if it successfully decodes the fallback notification from Msg2 * (or detects the fallback notification). In other words, UE2 does not have to anticipate or prepare for a fallback to the 4-step CBRA procedure unless it has successfully decoded the fallback notification from Msg2 * (or has not detected a fallback notification). ..
[0030]
　UE2 performs steps 204-206 in response to determining that Msg2 * in step 202 indicates an explicit or implied fallback to the 4-step CBRA. In step 204, UE2 provides an uplink resource (ie, PUSCH resource) available for transmission of the third message (Msg3) of the 4-step CBRA procedure in response to receiving the fallback notification in step 202. Attempts to receive a control message containing the indicated uplink grant.
[0031]
　In some implementations, the control message may be downlink control information (ie, uplink scheduling DCI) transmitted over the PDCCH and including uplink grants. In this case, the scheduled DCI may be sent to the Temporary C-RNTI (ie scrambled by the Temporary C-RNTI), and UE2 may use the Temporary C-RNTI to decode the scheduled DCI. May be monitored. The Temporary C-RNTI may be associated with the RA preamble detected by gNB1 and included in Msg2 * in step 202. That is, UE2 may use the Temporary C-RNTI associated with the preamble transmitted by itself. The Temporary C-RNTI may be included in Msg2 * of step 202, for example, as MAC CE.
[0032]
　In some other implementations, the control message may be a 4-step CBRA second message (Msg2), i.e. a random access response (RAR) message. In this case, UE2 attempts to receive the PDCCH containing the downlink control information (ie, downlink scheduling DCI) indicating the downlink resource (ie, PDSCH resource) for which the random access response message is scheduled using RA-RNTI. , Msg2 (ie, random access response message) may be received in response to the successful reception of this downlink control information. The RA-RNTI value may be different from the RA-RNTI value used in step 202 to receive the second message (Msg2 *) of the 2-step CBRA.
[0033]
　For example, the RA-RNTI (for 4-step CBRA) may be calculated using the same formula as the RA-RNTI for 2-step CBRA. However, in this case, the value entered in at least one variable of the formula for the calculation of the RA-RNTI (for the 4-step CBRA) is the value at the time of the calculation of the RA-RNTI for the 2-step CBRA. It may be different. At least one variable in the formula may be an index indicating the radio resource (eg, time-frequency slot) of the first message (ie, RA preamble). Specifically, instead of the index of the time-frequency slot actually used for transmitting the first message (Msg1 *) of the 2-step CBRA, 4 at the same timing as the Msg1 * or subsequent (for example, immediately after). The index of time-frequency slots available at the timing of the first message (Msg1) of step CBRA may be used. More specifically, the index may include a first (sub) index indicating a time slot and a second (sub) index indicating a frequency slot. To calculate the RA-RNTI (for 4-step CBRA), UE2 uses a second (sub) index indicating the frequency slot actually used for Msg1 * transmission of 2-step CBRA. While using a first (sub) index indicating the time slots available for Msg1 in 4-step CBRA.
[0034]
　Instead, the RA-RNTI (for 4-step CBRA) is different from that for RA-RNTI for 2-step CBRA due to the reception of the second message (Msg2) of 4-step CBRA. It may be calculated according to the calculation formula. These RA-RNTI calculations are performed on both UE2 and gNB1 based on the same rules. For example, a radio resource for which UE2 has transmitted Msg1 * is understood to be a radio resource for which gNB1 has received Msg1 *.
[0035]
　Steps 205 and 206 may be similar to the third and fourth steps of the well-known 4-step CBRA. That is, in step 205, UE2 transmits the third message (Msg3) of the 4-step CBRA in the PUSCH resource indicated by the uplink grant received in step 204. The Msg3 may carry a MAC PDU containing a terminal identifier (eg, C-RNTI, S-TMSI, or random value) used for contention resolution. The MAC PDU may further include CCCH data (CCCH SDU). CCCH data (CCCH SDU) carries messages such as RRC Setup Request, RRC Re-establishment Request, or RRC Resume Request. In step 206, gNB1 transmits a fourth message (Msg4) for contention resolution using PDCCH and PDSCH. Specifically, gNB1 transmits DCI indicating the PDSCH resource scheduled by Msg4 on PDCCH, and transmits Msg4 on PDSCH. Msg4 includes a MAC PDU that carries a UE Contention Resolution Identity MAC Control Element (CE). In addition, Msg4 may include messages such as RRC Setup, RRC Re-establishment, or RRC Resume.
[0036]
　According to such an operation, the UE 2 successfully receives the second message (Msg2 *) of the 2-step CBRA, and the Msg2 * explicitly or implicitly indicates a fallback to the 4-step CBRA. It is only necessary to try to receive the control message (step 204) for continuing the 4-step CBRA. In other words, UE2 does not have to anticipate or prepare for a fallback to the 4-step CBRA procedure unless it has successfully decoded (or detected) the fallback notification from Msg2 *. Therefore, this can contribute to reducing the load on the UE, reducing complexity, or reducing battery consumption.
[0037]
　FIG. 3 shows another example of the CBRA procedure according to this embodiment. More specifically, FIG. 3 shows an example of a random access failure case. The operations of gNB1 and UE2 in steps 301 and 302 are similar to those in steps 201 and 202 of FIG. However, in the example of FIG. 3, the second message (step 302) of the 2-step CBRA may not include the fallback notification. In other words, the second message of the 2-step CBRA (step 302) may not indicate a fallback to the 4-step CBRA.
[0038]
　Further, in the example of FIG. 3, UE2 fails to receive the second message (Msg2 *) of the 2-step CBRA. Specifically, when the RAR window has expired and the UE2 cannot receive the second message containing the preamble identifier matching the index of the RA preamble transmitted in step 301, the UE2 can receive the second message. It is considered that the reception was not successful (step 303). Then, in response to the failure to receive the second message, UE2 performs the two-step CBRA procedure from the transmission of the first message without attempting to receive the control message for the four-step CBRA (step 204). Restart (step 304). In other words, the second message (Msg2 *) of the 2-step CBRA according to the present embodiment receives the control message for the 4-step CBRA (step) in response to the failure to receive the second message to UE2. 204) Requests (or causes) to restart the two-step CBRA procedure from sending the first message without attempting.
[0039]
　According to such an operation, even if UE2 fails to receive the second message (Msg2 *) of the 2-step CBRA, it is not necessary to anticipate or prepare for a fallback to the 4-step CBRA procedure, so that the 2-step CBRA procedure is performed. There is a possibility that the CBRA procedure can be restarted promptly.
[0040]
　FIG. 4 is a flowchart showing an example of the operation of UE2 of the present embodiment. In step 401, UE2 transmits the first message (Msg1 *) of the two-step CBRA. In step 402, UE2 attempts to receive the second message (Msg2 *) of the two-step CBRA. In step 403, UE2 determines whether the second message (Msg2 *) has been successfully received. Specifically, when UE2 can receive the second message containing the preamble identifier matching the index of the RA preamble transmitted in step 401 in the RAR window, the second message (Msg2 *). Is considered successful (step 403). That is, here, the successful reception of the second message (Msg2 *) means that the UE2 can confirm that the RA preamble transmitted by the UE2 itself has been successfully received (or detected). .. In step 404, UE2 determines whether the second message (Msg2 *) indicates a fallback.
[0041]
　If the second message (Msg2 *) is successfully received and the second message (Msg2 *) indicates a fallback, UE2 falls back to the 4-step CBRA (step 405). Specifically, UE2 may perform the operation of steps 204 to 205 of FIG.
[0042]
　If the second message (Msg2 *) is successfully received and the second message (Msg2 *) does not show fallback, UE2 continues the two-step CBRA (step 406). In other words, UE2 considers that the RA preamble it sent was successfully received (or detected) (that is, succeeded in preamble transmission) based on the content of the second message (Msg2 *), and further CBRA. Judge whether or not the content was successful. Specifically, UE2 considers that the two-step CBRA procedure was successfully completed in response to determining the success of contention resolution based on the successfully received second message (Msg2 *). (Consider) is also good.
[0043]
　If the second message (Msg2 *) is not successfully received, UE2 restarts the two-step CBRA procedure (step 407). Specifically, UE2 may perform the operation of step 304 in FIG.
[0044]
　FIG. 5 is a flowchart showing an example of the operation of gNB1 of the present embodiment. In step 501, gNB1 receives the first message (Msg1 *) of the two-step CBRA. In step 502, gNB1 fails back if the RA preamble in MSG1 * is successfully received but the MAC PDU (eg, RRC message containing UE identifier) ​​in Msg1 * is not successfully received. The second message (Msg2 *) of the two-step CBRA shown is transmitted. For example, gNB1 may include a fallback notification in the second message (Msg2 *) of the 2-step CBRA. The second message (Msg2 *) or the fallback notification receives a control message including an uplink grant indicating an uplink resource available for transmission of the third message (Msg3) of the 4-step CBRA. Requests (or causes) UE2 to try after successfully receiving *.
[0045]
　In step 503, gNB1 transmits a control message including an uplink grant indicating an uplink resource available for transmission of the third message (Msg3) of the 4-step CBRA.
[0046]
　Subsequently, a specific example of the fallback notification will be described below. The fallback notification may explicitly or implicitly indicate a fallback to the 4-step CBRA. In other words, the second message of the 2-step CBRA (Msg2 *) may explicitly or implicitly indicate a fallback to the 4-step CBRA. The second message (Msg2 *) of the 2-step CBRA may include information that explicitly indicates the fallback to the 4-step CBRA, or may include information that implies.
[0047]
　For example, the fallback notification may indicate that only the preamble in Msg1 * could be received. The fact that the preamble can be received here may mean, for example, that the preamble could be detected or that the preamble portion could be correctly decoded.
[0048]
　Alternatively, the second message (Msg2 *) of the two-step CBRA may include a field representing a flag bit indicating whether or not a fallback should occur. The field may be included in the MAC subheader in the MAC PDU or in the MAC payload (MAC SDU).
[0049]
　Instead, the second message of the 2-step CBRA (Msg2 *) is the MAC subheader associated with the fallback when a fallback to the 4-step CBRA is required. May include. The format of the MAC subheader may be newly defined for explicit fallback notification. The MAC subheader may include, for example, a field indicating that it is the MAC subheader, a Random Access Preamble Identifier (RAPID) field and some reserved bits.
[0050]
　Alternatively, the second message of the two-step CBRA (Msg2 *) may imply a fallback due to the lack of certain information from the message. The information missing to imply fallback may be information for contention resolution. For example, the information may be UE Contention Resolution Identity MAC CE. That is, if the preamble and other information in Msg1 * (eg, MAC PDU) can be successfully received, gNB1 will send the UE Contention Resolution Identity MAC CE associated with the preamble to Msg2 * (ie, downlink). Included in MAC subPDU or downlink MAC PDU). On the other hand, if only the preamble can be successfully received and falls back to the 4-step CBRA, gNB1 sets the UE Contention Resolution Identity MAC CE associated with the preamble to Msg2 * (ie, downlink MAC subPDU or downlink MAC PDU). ) Not included. Strictly speaking, gNB1 cannot successfully include UE Contention Resolution Identity MAC CE in Msg2 * because it has not successfully received information in other Msg1 *. If only the preamble was successfully received but did not fall back to the 4-step CBRA, gNB1 does not even include the index corresponding to the preamble in the downlink MAC subPDU (or downlink MAC PDU). In other words, if only the preamble in the first message (Msg1 *) of the 2-step CBRA was successfully received but does not fall back to the 4-step CBRA, gNB1 responds to the first message (Msg1 *). Do not send the second message (Msg2 *) of.
[0051]
　It should be noted that the second message of the 2-step CBRA (Msg2 *) may contain additional information such as the Temporary C-RNTI or Timing Advance Command or both, even if this indicates a fallback to the 4-step CBRA.
[0052]

　The configuration example of the wireless communication network according to the present embodiment is the same as the example shown in FIG. The gNB1 of the present embodiment notifies the fallback and the third message of the 4-step CBRA (Msg3) when the first message (Msg1 *) of the 2-step CBRA is not successfully received and falls back to the 4-step CBRA. ) Include an uplink grant indicating the uplink resources available for transmission in the second message (Msg2 *) of the 2-step CBRA. The fallback notification indicates explicit or implied fallback to the 4-step CBRA procedure. Further, this may be performed by the same method as in the first embodiment. For example, the fallback notification may indicate that only the preamble in Msg1 * could be detected (or received) in association with the identifier of the preamble (eg, flag bit with detected preamble index). The fallback notification may be a predetermined field or bit contained in the MAC sub-header in the downlink MAC PDU. That is, the fact that the predetermined field or bit is included in Msg2 * and the corresponding MAC subPDU is included may be regarded as a fallback notification.
[0053]
　The Msg2 * may be defined as a 2-step CBRA random access response (RAR). The random access response (RAR) if Msg1 * was successfully received, and another random access response if Msg1 * was not successfully received but the preamble was successfully received, are the same down. It may be included in a linked MAC PDU or may be transmitted in different downlink MAC PDUs transmitted by different radio resources (eg, time or frequency). In addition, Msg2 * sets the information element (eg, Timing Advance Command) and terminal identifier (eg, Temporary C-RNTI) related to the uplink transmission timing associated with the successfully received preamble to the MAC PDU in Msg1 *. It may be included regardless of the success or failure of reception.
[0054]
　When UE2 of the present embodiment receives the Msg2 * of the 2-step CBRA including the notification of the fallback and the uplink grant, the UE2 of the present embodiment transmits the Msg3 of the 4-step CBRA according to the uplink grant.
[0055]

　The configuration example of the wireless communication network according to the present embodiment is the same as the example shown in FIG. The gNB1 of this embodiment is configured to transmit system information indicating activation of fallback to a 4-step CBRA. gNB1 may broadcast the system information so that UE2 of RRC_IDLE can receive the system information (eg, in System Information Block Type 1 (SIB1)). The system information is the reception of the second message (Msg2 *) of the two-step CBRA and the reception of the second message (Msg2) of the four-step CBRA after transmitting the first message (Msg1 *) of the two-step CBRA to UE2. Encourage them to try both at the same time.
[0056]
　When UE2 of the present embodiment receives the system information from the network (ie, gNB1), it transmits the first message (Msg1 *) of the two-step CBRA and then the second message (Msg2 *) of the two-step CBRA. Attempt both reception and reception of the second message (Msg2) of the 4-step CBRA.
[0057]
　An attempt to receive the second message (Msg2 *) of the two-step CBRA is to receive the second message (Msg2 *) of the two-step CBRA in the first time window (eg, RAR window) associated with the two-step CBRA. May include trying. Similarly, an attempt to receive the second message (Msg2) of the 4-step CBRA is the second message (Msg2) of the 4-step CBRA in the second time window (eg, RAR window) associated with the 4-step CBRA. It may include attempting reception. At this time, the reception of Msg2 * and the reception of Msg2 by the UE are performed simultaneously (that is, in parallel) in a predetermined period, but the reception of Msg2 * and the reception of Msg2 are exactly at the same timing (eg, subframe, OFDM symbol). , or TTI), UE2 may try to receive only one of them (eg, Msg2 *).
[0058]
　More specifically, an attempt to receive the second message of the two-step CBRA (Msg2 *) is to decode the DCI indicating the downlink resource for which the second message of the two-step CBRA (Msg2 *) is scheduled. It may include monitoring the PDCCH using the first RA-RNTI associated with the two-step CBRA in the first time window (eg, RAR window). Similarly, an attempt to receive the second message (Msg2) of the 4-step CBRA is a second time window to decode the DCI indicating the scheduled downlink resource for the second message (Msg2) of the 4-step CBRA. (Eg, RAR window) may include monitoring the PDCCH using the second RA-RNTI associated with the 4-step CBRA.
[0059]
　The first RA-RNTI is associated with the first message (Msg1 *) of the 2-step CBRA transmitted by the UE and is calculated based on the index of the radio resource (eg, time-frequency slot) transmitted by the Msg1 *. Will be done. On the other hand, the second RA-RNTI is assigned for the first message (Msg1) of the 4-step CBRA that is simultaneous with or subsequent (for example, immediately after) the first message (Msg1 *) of the 2-step CBRA transmitted by the UE. It may be calculated based on at least a part of the index of the radio resource (eg, time-frequency slot). More specifically, the index may include a first (sub) index indicating a time slot and a second (sub) index indicating a frequency slot. To calculate the second RA-RNTI, UE2 uses a second (sub) index indicating the frequency slot actually used for Msg1 * transmission of the 2-step CBRA, while using the 4-step CBRA. A first (sub) index indicating the available time slots for Msg1 may be used. Alternatively, the second RA-RNTI may be calculated according to a calculation formula different from that of the first RA-RNTI. These RA-RNTI calculations are performed on both UE2 and gNB1 based on the same rules. For example, a radio resource for which UE2 has transmitted Msg1 * is understood to be a radio resource for which gNB1 has received Msg1 *.
[0060]
　FIG. 6 shows an example of the operation of gNB1 and UE2 according to the present embodiment. In step 601, gNB1 transmits system information indicating activation of fallback to 4-step CBRA.
[0061]
　FIG. 7 is a flowchart showing an example of the operation of UE2 according to the present embodiment. In step 701, UE2 transmits the first message (Msg1 *) of the two-step CBRA. In step 702, if system information indicating that fallback is enabled is received, both the reception of the second message (Msg2 *) of the 2-step CBRA and the reception of the second message (Msg2) of the 4-step CBRA are tried at the same time. do.
[0062]
　Instead of the system information described above, gNB1 may include information indicating activation of fallback in the second message (Msg2 *) of the two-step CBRA. At this time, when UE2 receives the second message (Msg2 *) of the 2-step CBRA, successfully decodes the Msg2 *, and detects information indicating the activation of the fallback, the UE2 has four steps. You may try to receive the second message (Msg2) of CBRA.
[0063]
　According to such an operation, UE2 may try to receive the second message (Msg2) of the 4-step CBRA only when the network has instructed to enable fallback. Therefore, this can contribute to reducing the load on the UE, reducing complexity, or reducing battery consumption.
[0064]

　The configuration example of the wireless communication network according to the present embodiment is the same as the example shown in FIG. UE2 of this embodiment provides RRC layer 21 and MAC layer 22. MAC layer 22 can also be paraphrased as MAC sublayer or MAC entity.
[0065]
　FIG. 8 shows an example of the operation of the RRC layer 21 and the MAC layer 22. In step 801 the MAC layer 22 informs the RRC layer 21 of the fallback when it falls back from the 2-step CBRA to the 4-step CBRA. The MAC layer 22 may transmit the fallback display to the RRC layer 21. The RRC layer 21 may generate Msg3 content (eg, CCCH SDU) corresponding to the 4-step CBRA in response to receiving the fallback display. Further or instead, the RRC layer 21 updates at least one of the parameters for the random access procedure to the 4-step CBRA setting in response to receiving the fallback display. (That is, to switch from the 2-step setting to the 4-step setting), this may be transmitted to the MAC layer 22.
[0066]
　When falling back from 2-step CBRA to 4-step CBRA, the MAC layer 22 flushes the transmit buffer (eg Tx buffer) for holding the content transmitted by Msg1 * of 2-step CBRA. The content transmitted by Msg3 of 4-step CBRA may be stored in this. This transmission buffer may be the Msg3 Buffer conventionally used in the 4-step CBRA. Instead of this, UE2 (MAC layer 22) may newly provide Msg1 Buffer for Msg1 * of 2-step CBRA, and may use the Msg1 Buffer and Msg3 Buffer for Msg3 of 4-step CBRA properly.
[0067]
　When falling back from a 2-step CBRA to a 4-step CBRA, a predetermined timer (eg, T3xy) associated with the procedure that triggers the CBRA may be continued or restarted. In order to restart the predetermined timer, the UE 2 (RRC layer 21) may, for example, temporarily stop and reset the predetermined timer that is already being measured, and start the measurement again from the initial value. The timer restarts, for example, the timer used for the RRC Setup procedure for establishing an RRC connection (ie T300), the timer used for the RRC Re-establishment procedure for reestablishing an RRC connection (ie T301), or the RRC connection. It may be a timer (ie T319) used in the RRC Resume procedure for the purpose, or it may be a timer of another RRC layer.
[0068]
　When falling back from 2-step CBRA to 4-step CBRA, UE2 (MAC layer 22) may continue the counter (ie PREAMBLE_TRANSMISSION_COUNTER) that measures the number of times the RA preamble is transmitted, or may restart it. ..
[0069]
　Further, the MAC layer 22 may notify the RRC layer 21 when returning from the 4-step CBRA to the 2-step CBRA (when ending the fallback). That is, as shown in FIG. 9, the MAC layer 22 may notify the RRC layer 21 of the change from the 2-step CBRA to the 4-step CBRA and vice versa (step 901). As in the case of the fallback from the 2-step CBRA to the 4-step CBRA described above (but in the opposite direction), the MAC layer 22 may control the transmit buffer, timer, or counter.
[0070]
　According to such an operation, the RRC layer 21 of UE2 is a process (eg, Msg1 * content generation, Msg3 content) adapted to the CBRA procedure (that is, 2-step CBRA or 4-step CBRA) selected by MAC layer 22. It can be generated or updated with random access related parameters).
[0071]

　The configuration example of the wireless communication network according to the present embodiment is the same as the example shown in FIG. UE2 of the present embodiment has a 2-step CBRA and a 2-step CBRA in order to restart the random access when the fallback from the 2-step CBRA to the 4-step CBRA is performed but the random access is not completed successfully. Choose between 4-step CBRA.
[0072]
　FIG. 10 is a flowchart showing an example of the operation of UE2 of the present embodiment. In step 1001, UE2 falls back to 4-step CBRA in the middle of the 2-step CBRA procedure. The fallback may be performed in the same manner as, for example, the procedure described in the first embodiment (eg, FIG. 2) or the procedure described in the second embodiment, but is not limited thereto. That is, the fallback may be performed according to another procedure different from the procedure described in the first or second embodiment. For example, UE2 may start from the beginning of the 4-step CBRA, i.e., the transmission of the first message (Msg1), when falling back to the 4-step CBRA in the middle of the 2-step CBRA procedure.
[0073]
　In step 1002, UE2 determines that a fallback to the 4-step CBRA has taken place but the random access has not been successfully completed. UE2 may consider that the random access was not completed in response to the failure to resolve the contention (consider). More specifically, UE2 received the PDCCH (DCI) addressed to its Temporary C-RNTI and successfully decoded the MAC PDU of the 4th message (Msg4), but the UE contained in the MAC PDU. If the Contention Resolution Identity MAC CE does not match the CCCH SDU (ie, UE identifier (eg, S-TMSI or random value) sent in the third message (Msg3), it is considered that the random access was not completed (consider). Alternatively, the UE 2 may consider that the random access was not completed when the transmission of the third message (Msg3) fails or the reception of the fourth message (Msg4) fails (consider). Alternatively, if UE2 sends a third message (Msg3) containing C-RNTI, but cannot successfully receive the PDCCH (DCI) addressed to that C-RNTI, it is considered that the random access was not completed. (Consider) is also good.
[0074]
　In step 1003, UE2 chooses between 2-step CBRA and 4-step CBRA to restart random access. In other words, UE2 selects (or determines) whether 2-step CBRA or 4-step CBRA is used to restart random access.
[0075]
　In some implementations, UE2 may restart random access by following one of the two-step CBRA and four-step CBRA steps where the next available preamble transmission opportunity (ie, PRACH occasion) arrives earlier. good. Such an operation allows UE2 to restart random access promptly.
[0076]
　Further or instead, UE2 restarts random access according to one of the two-step CBRA and the four-step CBRA, which has the shorter cycle or interval of multiple available preamble transmission opportunities (ie, PRACH occasions). You may. Such an operation allows UE2 to restart random access promptly. In particular, such an operation is effective when the preamble needs to be retransmitted.
[0077]
　Further or instead, the UE 2 may independently count the number of trials (or the number of preamble transmissions) of the 2-step CBRA and the number of trials (or the number of preamble transmissions) of the 4-step CBRA. Specifically, UE2 may use PREAMBLE_TRANSMISSION_COUNTER for counting the number of preamble transmissions of the 2-step CBRA in addition to PREAMBLE_TRANSMISSION_COUNTER for counting the number of preamble transmissions of the 4-step CBRA. In this case, UE2 may choose whether 2-step CBRA or 4-step CBRA is used to restart random access based on the values ​​of these two counters. For example, UE2 may select a CBRA procedure associated with a counter with a smaller count value for restart. Alternatively, the maximum value of the 2-step CBRA PREAMBLE_TRANSMISSION_COUNTER may be set smaller than the maximum value of the 4-step CBRA PREAMBLE_TRANSMISSION_COUNTER. In this case, UE2 may preferentially select 2-step CBRA for restart until PREAMBLE_TRANSMISSION_COUNTER of 2-step CBRA equals its maximum value. The maximum value of these counters may be included in the system information block (eg, SIB1) message described above or later and notified from gNB1 to UE2.
[0078]

　The configuration example of the wireless communication network according to the present embodiment is the same as the example shown in FIG. FIG. 11 shows an example of the operation of gNB1 and UE2 of the present embodiment. In step 1101, gNB1 associates one or more of the events that trigger the initiation of random access with the two-step CBRA (ie, the use of the two-step CBRA is permitted, or the two-step CBRA. Is specified to be used) to send a setting to UE2. The setting is common to a plurality of UEs and may be broadcast to a plurality of UEs. That is, the setting may be included in the system information block message and transmitted. Alternatively, the setting may be created for each UE and supplied to UE2 by individual signaling (eg, RRC signaling).
[0079]
　FIG. 12 is a flowchart showing an example of the operation of UE2 of the present embodiment. In step 1201, UE2 receives from the network (eg, gNB1) a setting indicating that one or more of the events that trigger the start of random access are associated with the two-step CBRA. In step 1202, UE2 performs a two-step CBRA procedure when initiating random access for these one or more events and a four-step CBRA procedure when initiating random access for other events. conduct.
[0080] [0080]
　Multiple trigger events for random access include, for example:
--Initial access from RRC_IDLE; --RRC
Connection Re-establishment procedure;
--Handover ; --DL
or UL data arrival during RRC_CONNECTED when UL synchronisation status is "non-synchronised" --UL
data arrival during RRC_CONNECTED when there are no PUCCH resources for SR available;
--Transition from RRC_INACTIVE; --To
establish time alignment at SCell addition; --Request
for Other SI; and
-Beam failure recovery.
[0081]
　According to such an operation, gNB1 can control the selection of the random access procedure by UE2. For example, the size of the L2 / L3 message (eg, CCCH SDU) carried by the UL MAC PDU for one trigger event is different from that for another trigger event. The larger the size of the L2 / L3 message (eg, CCCH SDU), the higher the probability that the first message (Msg1 *) of the 2-step CBRA will fail to be transmitted. Therefore, gNB1 sets 4 trigger events in which the size of the L2 / L3 message (eg, CCCH SDU) is larger than the threshold value when the collision probability is high or the cell-to-cell interference with the adjacent cell is strong. A trigger event that is associated with step CBRA and whose L2 / L3 message (eg, CCCH SDU) size is smaller than the threshold may be associated with 2-step CBRA.
[0082]
　The present embodiment may be modified as follows. gNB1 sends to UE2 a setting indicating that at least one of the RRC establishment, RRC reestablishment, and RRC resume causes is associated with a two-step random access procedure. UE2 performs a two-step CBRA procedure when initiating random access for an RRC establishment, RRC reestablishment, or RRC resume based on these factors, and for an RRC establishment, RRC reestablishment, or RRC resume based on other factors. Perform the 4-step CBRA procedure when starting random access to.
[0083]
　Even by such an operation, gNB1 can control the selection of the random access procedure by UE2.
[0084]

　The configuration example of the wireless communication network according to the present embodiment is the same as the example shown in FIG. FIG. 13 shows an example of the operation of gNB1 and UE2 of the present embodiment. In step 1301, gNB1 sends to UE2 a setting indicating the maximum number of restarts for the two-step CBRA procedure. The setting is common to a plurality of UEs and may be broadcast to a plurality of UEs. That is, the setting may be included in the system information block message and transmitted. Alternatively, the setting may be created for each UE and supplied to UE2 by individual signaling (eg, RRC signaling). Alternatively, the setting may be sent from gNB1 to UE2 using the second message (Msg2 *) of the 2-step CBRA.
[0085]
　UE2 may restart random access according to the 2-step CBRA until the number of restarts of the 2-step CBRA reaches the maximum number. Then, UE2 may fall back to the 4-step CBRA after the number of restarts of the 2-step CBRA reaches the maximum number. The maximum number of restarts of the 2-step CBRA procedure may be the maximum value of PREAMBLE_TRANSMISSION_COUNTER of the 2-step CBRA described above. gNB1 includes a notification in the second message (Msg2 *) of the 2-step CBRA indicating that this control (ie, fallback to the 4-step CBRA based on the maximum number of restarts of the 2-step CBRA procedure) is enabled. May be good. The notification may be, for example, a flag bit or a predetermined MAC subheader. UE2 may execute this control only when the notification is received (detected).
[0086]
　According to such an operation, gNB1 can control the selection of the random access procedure by UE2. In addition, instead of the maximum number of restarts of the 2-step CBRA procedure, the maximum number of starts of the 2-step CBRA procedure may be used.
[0087]

　The configuration example of the wireless communication network according to the present embodiment is the same as the example shown in FIG. FIG. 14 shows an example of a contention-free random access (CFRA) procedure according to this embodiment. More specifically, FIG. 14 shows an example of a successful case with a fallback from a two-step CFRA to a three-step CFRA-based access. First, the three-step CFRA-based access mentioned here is the preamble (Msg1), random access response (RAR) of random access in the existing two-step CFRA, and the first uplink transmission (eg, eg, after successful CFRA. UL data transmission, UL RRC message). On the other hand, in the two-step CFRA of the present embodiment, the first message (Msg1 *) includes the preamble and the first uplink data of the three-step CFRA-based access or the MAC PDU corresponding to the message, and the second message (Msg2 *). ) Includes a response to the first message (Msg1 *). As a result, the two-step CFRA of the present embodiment can reduce the delay until the first uplink transmission.
[0088]
　In step 1401, UE2 transmits the first message (Msg1 *) of the two-step CFRA procedure. The Msg1 * may carry, for example, preambles and MAC PDUs. The preamble in Msg1 * may be referred to as a random access (RA) preamble, a random access channel (RACH) preamble, or the like. The MAC PDU may include, for example, the same as or equivalent to the first uplink transmission in the conventional 3-step CFRA-based access. For example, a MAC PDU can be uplink user data in resume of uplink data transmission, an RRC message (eg, handover confirmation, or reconfiguration-with-sync completion) indicating the completion of the handover at the time of handover, or Dual. It may be an RRC message (eg, RRC Reconfiuration Complete) indicating the completion of the modification of the secondary cell group (SCG) setting of Connectivity or the change of the secondary base station (eg, SgNB). Further or instead, the MAC PDU may include control information for other MAC layers specified for 2-step CBRA.
[0089]
　In step 1402, gNB1 transmits a second message (Msg2 *) of the two-step CFRA procedure. In response to the reception of Msg1 *, gNB1 determines whether or not all of Msg1 * have been successfully received. For example, if the preamble in Msg1 * (ie, the equivalent of Msg1 for 3-step CFRA-based access) was successfully received, but the MAC PDU in Msg1 * was not received, gNB1 would be the second in 2-step CFRA. The message (Msg2 *) may include a fallback notification. The fallback notification indicates an explicit or implied fallback to the 3-step CFRA-based access procedure.
[0090]
　Msg2 * may contain MAC control information (CE) that is defined as a 2-step CFRA random access response (RAR) and is different from the 3-step CFRA-based access RAR. Alternatively, Msg2 * may include another information element (or field) that corresponds to the random access response (RAR) of the two-step CFRA. In addition, Msg2 * provides the MAC PDU in Msg1 * with information elements (eg, Timing Advance Command) and terminal identifiers (eg, Temporary C-RNTI) related to the uplink transmission timing associated with the successfully received preamble. It may be included regardless of the success or failure of reception. In other words, gNB1 is Msg2 * (ie, downlink MAC subPDU) that includes the Timing Advance Command for the target (ie, UE) to be notified of fallback, and the information necessary to complete the two-step CBRA (ie, downlink MAC subPDU). You may send Msg2 * (ie, downlink MAC subPDU) that includes the Timing Advance Command for the target (ie, UE) to which you want to send eg, RRC messages or UE Contention Resolution Identity MAC CE (ie, UE). Also, these two types of Msg2 * may be contained in the same downlink MAC PDU, or different radio resources (eg, eg, It may be included in different downlink MAC PDUs transmitted in time or frequency). Successful reception of the preamble in Msg1 * may mean that the preamble was detected correctly or that the preamble portion was successfully decoded. The fallback notification can be thought of as a notification that only the preamble in Msg1 * was successfully received. Hereinafter, it will be described as a fallback notification (or a fallback notification) as an example.
[0091]
　Whether the UE (explicitly or implicitly) indicates a fallback to the 3-step CFRA-based access procedure if the UE successfully receives the second message (Msg2 *) of the 2-step CFRA. Is determined. In response to determining that the Msg2 * indicates a fallback to the 3-step CFRA-based access procedure, UE2 falls back to the 3-step CFRA-based access procedure (step 1403). Then, UE2 starts the operation for transmitting the third message (Msg3) of the three-step CBFA-based access procedure. That is, UE2 expects a fallback to the 3-step CFRA-based access procedure only if it successfully decodes the fallback notification from Msg2 * (or detects the fallback notification). In other words, if UE2 has not successfully decoded the fallback notification from Msg2 * (or has not detected the fallback notification), it does not anticipate or prepare for a fallback to the 3-step CFRA-based access procedure. You may.
[0092]
　UE2 performs step 1404 in response to determining that Msg2 * in step 1402 indicates a fallback to the 3-step CFRA-based access, either explicitly or implicitly. In step 1404, UE2 sends a third message (Msg3) (ie, the first uplink data or message) of the 3-step CFRA-based access procedure in response to receiving the fallback notification in step 1402. I do. The information of the radio resource (uplink grant) that can be used to transmit the Msg3 may be specified by the MAC PDU of Msg2 *, or may be specified by PDCCH / DCI after Msg2 *. In the latter case, UE2 may attempt to receive the uplink grant by receiving the PDCCH / DCI in response to the determination that Msg2 * indicates fallback.
[0093]
　FIG. 15 is a flowchart showing an example of the operation of UE2 of the present embodiment. In step 1501, UE2 transmits the first message (Msg1 *) of the two-step CFRA. In step 1502, UE2 attempts to receive the second message (Msg2 *) of the two-step CFRA. In step 1503, UE2 determines whether the second message (Msg2 *) has been successfully received. Specifically, when UE2 can receive the second message containing the preamble identifier matching the index of the RA preamble transmitted in step 1501 in the RAR window, the second message (Msg2 *). Is considered successful (step 1503). That is, here, the successful reception of the second message (Msg2 *) means that the UE2 can confirm that the RA preamble transmitted by the UE2 itself has been successfully received (or detected). .. In step 1504, UE2 determines whether or not the second message (Msg2 *) indicates a fallback.
[0094]
　If the second message (Msg2 *) is successfully received and the second message (Msg2 *) indicates a fallback, UE2 falls back to a 3-step CFRA-based access (step 1505). Specifically, UE2 may perform the operations of steps 1403 and 1404 of FIG.
[0095]
　If the second message (Msg2 *) is successfully received and the second message (Msg2 *) does not show fallback, UE2 considers the two-step CFRA procedure to be successfully completed (step 1506). ). In other words, UE2 considers that the RA preamble that it sent based on the content of the second message (Msg2 *) was successfully received (or detected) (that is, the preamble was successfully sent), and two more steps. If it can be confirmed that the information required for the CFRA procedure is included in the Msg2 *, it is considered that the 2-step CFRA procedure has been completed successfully.
[0096]
　If the second message (Msg2 *) is not successfully received, UE2 restarts the 2-step CFRA procedure (step 1507).
[0097]
　FIG. 16 is a flowchart showing an example of the operation of gNB1 of the present embodiment. In step 1601, gNB1 receives the first message (Msg1 *) of the two-step CFRA. In step 1602, gNB1 fails back if the RA preamble in Msg1 * is successfully received but the MAC PDU (RRC message containing eg, UE identifier) ​​in Msg1 * is not successfully received. The second message (Msg2 *) of the two-step CBRA shown is transmitted. For example, gNB1 may include a fallback notification in the second message (Msg2 *) of the 2-step CFRA. The second message (Msg2 *) or the fallback notification requires UE2 to send the third message (Msg3) (ie, the first uplink data or message) of the 3-step CFRA-based access procedure. (Or cause). The information of the radio resource (uplink grant) that can be used to transmit the Msg3 may be specified by the MAC PDU of Msg2 *, or may be specified by PDCCH / DCI after Msg2 *. In the latter case, in step 1603, gNB1 sends a control message comprising an uplink grant indicating the uplink resources available for sending the third message (Msg3) of the three-step CFRA-based access. That is, when UE2 receives Msg2 * and determines that it has been notified of the fallback to the 3-step CFRA-based access, it receives the subsequent PDCCH / DCI to receive the Msg3 uplink grant. You may try.
[0098]
　Subsequently, a configuration example of gNB1 and UE2 according to the above-mentioned plurality of embodiments will be described below. FIG. 17 is a block diagram showing a configuration example of gNB1 according to the above-described embodiment. Referring to FIG. 17, gNB1 includes a Radio Frequency transceiver 1701, a network interface 1703, a processor 1704, and a memory 1705. RF transceiver 1701 performs analog RF signal processing to communicate with NG UEs including UE2. The RF transceiver 1701 may include a plurality of transceivers. The RF transceiver 1701 is coupled with the antenna array 1702 and the processor 1704. The RF transceiver 1701 receives the modulation symbol data from the processor 1704, generates a transmit RF signal, and supplies the transmit RF signal to the antenna array 1702. Further, the RF transceiver 1701 generates a baseband reception signal based on the received RF signal received by the antenna array 1702, and supplies the baseband reception signal to the processor 1704. The RF transceiver 1701 may include an analog beamformer circuit for beamforming. The analog beamformer circuit includes, for example, a plurality of phase shifters and a plurality of power amplifiers.
[0099]
　Network interface 1703 is used to communicate with network nodes (eg, 5G Core control and transfer nodes). The network interface 1703 may include, for example, an IEEE 802.3 series compliant network interface card (NIC).
[0100]
　The processor 1704 performs digital baseband signal processing (data plane processing) and control plane processing for wireless communication. The processor 1704 may include a plurality of processors. For example, the processor 1704 may include a modem processor (eg, Digital Signal Processor (DSP)) that performs digital baseband signal processing and a protocol stack processor (eg, Central Processing Unit (CPU) or Micro Processing Unit (eg, Central Processing Unit (CPU)) that performs control plane processing. MPU)) may be included. Processor 1704 may include a digital beamformer module for beamforming. The digital beamformer module may include a Multiple Input Multiple Output (MIMO) encoder and precoder.
[0101]
　The memory 1705 is composed of a combination of a volatile memory and a non-volatile memory. Volatile memory is, for example, Static Random Access Memory (SRAM) or Dynamic RAM (DRAM) or a combination thereof. Non-volatile memory can be masked Read Only Memory (MROM), Electrically Erasable Programmable ROM (EEPROM), flash memory, or hard disk drive, or any combination thereof. The memory 1705 may include storage located away from the processor 1704. In this case, processor 1704 may access memory 1705 via network interface 1703 or an I / O interface (not shown).
[0102]
　The memory 1705 may store one or more software modules (computer programs) 1706 containing instructions and data for performing processing by gNB1 described in the plurality of embodiments described above. In some implementations, the processor 1704 may be configured to read the software module 1706 from memory 1705 and execute it to perform the processing of gNB1 described in the embodiments described above.
[0103]
　When gNB1 is gNB-CU, gNB1 may not include the RF transceiver 1701 (and the antenna array 1702).
[0104]
　FIG. 18 is a block diagram showing a configuration example of UE2. Radio Frequency (RF) transceiver 1801 performs analog RF signal processing to communicate with gNB1. The RF transceiver 1801 may include a plurality of transceivers. The analog RF signal processing performed by the RF transceiver 1801 includes frequency up-conversion, frequency down-conversion, and amplification. The RF transceiver 1801 is coupled with the antenna array 1802 and the baseband processor 1803. The RF transceiver 1801 receives modulation symbol data (or OFDM symbol data) from the baseband processor 1803, generates a transmit RF signal, and supplies the transmit RF signal to the antenna array 1802. Further, the RF transceiver 1801 generates a baseband reception signal based on the received RF signal received by the antenna array 1802, and supplies the baseband reception signal to the baseband processor 1803. The RF transceiver 1801 may include an analog beamformer circuit for beamforming. The analog beamformer circuit includes, for example, a plurality of phase shifters and a plurality of power amplifiers.
[0105]
　The baseband processor 1803 performs digital baseband signal processing (data plane processing) and control plane processing for wireless communication. Digital baseband signal processing includes (a) data compression / restoration, (b) data segmentation / concatenation, (c) transmission format (transmission frame) generation / decomposition, and (d) transmission path coding / decoding. , (E) Modulation (symbol mapping) / demodulation, and (f) Generation of OFDM symbol data (baseband OFDM signal) by Inverse Fast Fourier Transform (IFFT). On the other hand, the control plane processing includes layer 1 (eg, transmission power control), layer 2 (eg, radio resource management, and hybrid automatic repeat request (HARQ) processing), and layer 3 (eg, attach, mobility, and call management). Includes communication management (signaling regarding).
[0106]
　For example, digital baseband signal processing by the baseband processor 1803 includes signal processing for the Service Data Adaptation Protocol (SDAP) layer, Packet Data Convergence Protocol (PDCP) layer, Radio Link Control (RLC) layer, MAC layer, and PHY layer. It may be included. Further, the control plane processing by the baseband processor 1803 may include the processing of the Non-Access Stratum (NAS) protocol, the RRC protocol, and the MAC CE.
[0107]
　Baseband processor 1803 may perform MIMO encoding and precoding for beamforming.
[0108]
　Baseband processor 1803 may include a modem processor (eg, DSP) for digital baseband signal processing and a protocol stack processor (eg, CPU or MPU) for control plane processing. In this case, the protocol stack processor that performs the control plane processing may be shared with the application processor 1804 described later.
[0109]
　The application processor 1804 is also referred to as a CPU, MPU, microprocessor, or processor core. The application processor 1804 may include a plurality of processors (a plurality of processor cores). The application processor 1804 is a system software program (Operating System (OS)) read from memory 1806 or a memory (not shown) and various application programs (eg, call application, web browser, mailer, camera operation application, music playback). By executing the application), various functions of UE2 are realized.
[0110]
　In some implementations, the baseband processor 1803 and the application processor 1804 may be integrated on one chip, as shown by the dashed line (1805) in FIG. In other words, the baseband processor 1803 and application processor 1804 may be implemented as one System on Chip (SoC) device 1805. SoC devices are sometimes referred to as system Large Scale Integration (LSI) or chipsets.
[0111]
　The memory 1806 is a volatile memory, a non-volatile memory, or a combination thereof. The memory 1806 may include a plurality of physically independent memory devices. Volatile memory is, for example, SRAM or DRAM or a combination thereof. Non-volatile memory can be MROM, EEPROM, flash memory, or a hard disk drive, or any combination thereof. For example, the memory 1806 may include an external memory device accessible from the baseband processor 1803, the application processor 1804, and the SoC 1805. The memory 1806 may include an internal memory device integrated in the baseband processor 1803, in the application processor 1804, or in the SoC 1805. Further, the memory 1806 may include a memory in a Universal Integrated Circuit Card (UICC).
[0112]
　The memory 1806 may store one or more software modules (computer programs) 1807 that include instructions and data for performing processing by UE2 described in the plurality of embodiments described above. In some implementations, the baseband processor 1803 or application processor 1804 is configured to read the software module 1807 from memory 1806 and execute it to perform the processing of UE2 described with reference to the drawings in the above embodiments. May be done.
[0113]
　It should be noted that the control plane processing and operation performed by UE2 described in the above-described embodiment is performed by other elements other than the RF transceiver 1801 and the antenna array 1802, that is, at least one of the baseband processor 1803 and the application processor 1804, and the software module 1807. It can be realized by the memory 1806 that stores the software.
[0114]
　As described with reference to FIGS. 17 and 18, each of the processors included in gNB1 and UE2 according to the above embodiment includes one or a set of instructions for causing the computer to perform the algorithm described with reference to the drawings. Run multiple programs. This program can be stored and supplied to a computer using various types of non-transitory computer readable medium. Non-temporary computer-readable media include various types of tangible storage media. Examples of non-temporary computer readable media are magnetic recording media (eg flexible disks, magnetic tapes, hard disk drives), optomagnetic recording media (eg optomagnetic disks), Compact Disc Read Only Memory (CD-ROM), CD- Includes R, CD-R / W, semiconductor memory (eg, mask ROM, Programmable ROM (PROM), Erasable PROM (EPROM), flash ROM, Random Access Memory (RAM)). The program may also be supplied to the computer by various types of transient computer readable medium. Examples of temporary computer-readable media include electrical, optical, and electromagnetic waves. The temporary computer-readable medium can supply the program to the computer via a wired communication path such as an electric wire and an optical fiber, or a wireless communication path.
[0115]

　The above-described embodiments may be implemented independently, or the whole embodiment or a part thereof may be combined as appropriate. For example, the second to sixth embodiments do not require the details of the fallback operation described in the first embodiment. In other words, the second to sixth embodiments can be implemented independently of the first embodiment. Further, the second to sixth embodiments can be implemented independently, which contributes to solving different purposes or problems and contributes to different effects.
[0116]
　The above embodiments have been described primarily assuming a 5G system. A 5G system is a beam-based system in which many beams are used in one cell. For example, if the synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) is transmitted by multiple beams (eg 8 beams), UE2 will be tied to the most strongly detected SSB (beam). Select one from the pool of random access preambles attached. In addition, UE2 is transmitted from gNB using the downlink beam associated with the (uplink) beam to which the preamble was transmitted, or the downlink beam corresponding to the most strongly detected SSB beam. Receive a random access response. In the above embodiments, different beams (sets) may be used for the two-step CBRA (or CFRA) and the four-step CBRA (or three-step CFRA-based access).
[0117]
　The above embodiment can also be applied when the first message (Msg1 *) of the two-step CBRA and CFRA contains a signal or information other than the preamble. The signal or information that replaces the preamble may be, for example, a reference signal (eg, Demodulation RS (DM-RS)) for demodulating the information (eg, MAC PDU) contained in Msg1 *. In the case of CBRA, UE2 randomly selects one candidate from a plurality of candidates of the reference signal (series) or according to a predetermined criterion, and transmits it by Msg1 *. Among the reference signals included in Msg1 *, gNB1 was detected to have a high reception level (eg, autocorrelation value is equal to or higher than a predetermined threshold value), but the information of Msg1 * (eg, autocorrelation value is equal to or higher than a predetermined threshold value) is detected. If eg, MAC PDU) is not successfully received, it may be decided to fall back. When fallback is performed, the identifier (eg, RS index) of the reference signal may be used instead of the index of the preamble in the above-described embodiment.
[0118]
　The above embodiments can be applied to random access in the Dual Connectivity Master Cell Group (MCG) and / or Secondary Cell Group (SCG). Here, the Dual Connectivity may be EUTRA-NR DC (EN-DC) between LTE eNB and NR gNB. Alternatively, the Dual Connectivity may be Dual Connectivity (NR-DC) between two gNBs connecting to 5GC or Multi-RAT Dual Connectivity (MR-DC) between NG-RAN nodes of different RATs. There may be. The NR-DC and the MR-DC described above may be collectively defined as Multi-Radio Dual Connectivity (MR-DC).
[0119]
　The above-described embodiment can be applied to cellular communication in the licensed spectrum, and cellular communication in the unlicensed spectrum (for example, LTE-Unlicensed (LTE-U) and NR). -Unlicensed (NR-U)) can also be applied. This may be Licensed Assisted Access (LAA), which communicates in the unlicensed spectrum in cooperation with communication in the licensed spectrum, or Standalone (SA), which communicates independently in the unlicensed spectrum. Moreover, SA operations in the unlicensed spectrum are not limited to cellular communications.
[0120]
　A user terminal (User Equipment (UE)) in the present specification is an entity connected to a network via a wireless interface. The UE of the present specification is not limited to the dedicated communication device, and may be any device as follows having the communication function of the UE described in the present specification.
[0121]
　"User equipment (UE)" (as a word used in 3GPP), "mobile station", "mobile terminal", "mobile device", and "mobile device" The terms "wireless device" are generally intended to be synonymous with each other. The UE may be a stand-alone mobile station such as a terminal, mobile phone, smartphone, tablet, cellular IoT terminal, IoT device, and the like. The terms "UE" and "wireless terminal" also include devices that are stationary for extended periods of time.
[0122]
　UE is, for example, production equipment / manufacturing equipment and / or energy related machinery (for example, boilers, engines, turbines, solar panels, wind power generators, hydroelectric generators, thermal power generators, nuclear power generators, storage batteries, nuclear systems, etc. Nuclear-related equipment, heavy electrical equipment, pumps including vacuum pumps, compressors, fans, blowers, hydraulic equipment, pneumatic equipment, metal processing machines, manipulators, robots, robot application systems, transport equipment, lifting equipment, cargo handling equipment, etc. Textile machinery, sewing machinery, printing machinery, printing-related machinery, paperworking machinery, chemical machinery, mining machinery, mining-related machinery, construction machinery, construction-related machinery, agricultural machinery and / or equipment, forestry machinery and / or equipment, fishing Machines and / or equipment, safety and / or environmental protection equipment, tractors, power transmissions, and / or application systems of any equipment or machine mentioned above).
[0123]
　UE is, for example, transportation equipment (for example, vehicles, automobiles, two-wheeled vehicles, bicycles, trains, buses, rearcars, rickshaws, ships and other watercraft, airplanes, rockets, artificial satellites, drones, balloons, etc.) There may be.
[0124]
　The UE may be, for example, an information communication device (for example, a computer and related devices, a communication device and related devices, electronic components, etc.).
[0125]
　UEs are, for example, commercial and service equipment, vending machines, automatic service machines, office machinery and equipment, consumer electrical and electronic machinery (eg audio equipment, speakers, radios, video equipment, televisions, etc.). You may.
[0126]
　The UE may be, for example, an electronic application system or an electronic application device (for example, an X-ray device, a particle accelerator, a radioactive material application device, a sound wave application device, an electromagnetic application device, a power application device, etc.).
[0127]
　UEs are, for example, light bulbs, lighting, weighing machines, analyzers, testing machines and measuring machines (for example, smoke alarms, personal alarm sensors, motion sensors, wireless tags, etc.), watches or clocks, physics and chemistry machines, etc. It may be an optical machine, a medical device and / or a medical system, a weapon, a clockwork tool, or a hand tool.
[0128]
　The UE is, for example, a personal digital assistant or device with wireless communication capabilities (for example, an electronic device (eg, a personal computer, electronic measuring instrument, etc.) configured to install or insert a wireless card, wireless module, etc.). ) May be.
[0129]
　The UE may be, for example, a device or part thereof that provides the following applications, services, and solutions in the "Internet of Things (IoT)" using wired or wireless communication technology. IoT devices (or things) include suitable electronic devices, software, sensors, network connections, etc. that allow devices to collect and exchange data with each other and with other communication devices. The IoT device may be an automated device that complies with software directives stored in internal memory. IoT devices may operate without the need for human supervision or response. The IoT device may remain inactive for a long period of time and / or for a long period of time. IoT devices can be implemented as part of a stationary device. IoT devices can be embedded in non-stationary devices (eg vehicles) or attached to animals or people that are monitored / tracked. IoT technology can be implemented on any communication device that can be connected to a communication network that sends and receives data regardless of human input control or software instructions stored in memory. IoT devices are sometimes referred to as Machine Type Communication (MTC) devices, or Machine to Machine (M2M) communication devices, Narrow Band-IoT (NB-IoT) UEs.
[0130]
　The UE may support one or more IoT or MTC applications.
[0131]
　Some examples of MTC applications are listed in the list presented in 3GPP TS22.368 V13.2.0 (2017-01-13) Annex B, the contents of which are incorporated herein by reference. This list is not exhaustive and shows an example MTC application. In this list, the Service Areas for MTC applications are Security, Tracking & Tracing, Payment, Health, Remote Maintenance / Control, Includes Metering and Consumer Devices.
[0132]
　Examples of security MTC applications are Surveillance systems, Landline Backup for landline, Control of physical access (eg to buildings), and vehicles. / Includes Car / driver security.
[0133]
　Examples of MTC applications for tracking and tracing are Fleet Management, Order Management, Telematics Insurance: Pay as you drive (PAYD), Asset Tracking, Navigation. Includes Navigation, Traffic information, Road tolling, and Road traffic optimisation / steering.
[0134]
　Examples of MTC applications for payments include point of sale (POS), vending machines, and Gaming machines.
[0135]
　Examples of health MTC applications are Monitoring vital signs, Supporting the aged or handicapped, Web Access Telemedicine points, and Remote diagnostics. including.
[0136]
　Examples of MTC applications for remote maintenance / control are Sensors, Lighting, Pumps, Valves, Elevator control, Vending machine control, and vehicles. Includes Vehicle diagnostics.
[0137]
　Examples of MTC applications for weighing include Power, Gas
, Water, Heating, Grid control, and Industrial metering.
[0138]
　Examples of MTC applications for consumer devices include digital photo frames, digital cameras, and ebooks.
[0139]
　Applications, services, and solutions include, for example, MVNO (Mobile Virtual Network Operator) services / systems, disaster prevention wireless services / systems, and on-site wireless telephone (PBX (Private Branch eXchange)) services. / System, PHS / Digital Cordless Telephone Service / System, Point of sales (POS) System, Advertisement Transmission Service / System, Multimedia Broadcast and Multicast Service (MBMS) Service / System, V2X (Vehicle to Everything: Vehicle-to-Vehicle Communication) And road-to-vehicle / pedestrian communication) services / systems, in-train mobile wireless services / systems, location information-related services / systems, disaster / emergency wireless communication services / systems, IoT (Internet of Things) services / systems , Community service / system, video distribution service / system, Femto cell application service / system, VoLTE (Voice over LTE) service / system, wireless tag service / system, billing service / system, radio on-demand service / system, roaming service / System, user behavior monitoring service / system, communication carrier / communication NW selection service / system, function restriction service / system, PoC (Proof of Concept) service / system, personal information management service / system for terminals, display / video for terminals It may be a service / system, a non-communication service / system for terminals, an ad hoc NW / DTN (Delay Tolerant Networking) service / system, or the like.
[0140]
　The UE category described above is merely an application of the technical ideas and embodiments described herein. The UEs herein are not limited to these examples, and one of ordinary skill in the art may make various modifications to them.
[0141]
　Furthermore, the above-described embodiment is merely an example relating to the application of the technical idea obtained by the inventor of the present invention. That is, the technical idea is not limited to the above-described embodiment, and it goes without saying that various changes can be made.
[0142]
　For example, some or all of the above embodiments may be described as, but not limited to, the following appendixes.
[0143]
(Appendix 1) It comprises at least one
　memory and
　at least one processor coupled to the at least one memory, wherein the at
　least one processor falls back from a two-step random access procedure to a four-step random access procedure. In response to receiving system information indicating activation from the network, the first message of the two-step random access procedure is transmitted, and then the second message of the two-step random access procedure is received. And a
wireless terminal configured to simultaneously attempt to receive the second message of the four-step random access procedure .
[0144]
(Appendix 2)
　The attempt to receive the second message of the two-step random access procedure is the first of the two-step random access procedures in the first time window associated with the two-step random access procedure. The attempt to receive the second message in the
　four-step random access procedure comprises attempting to receive the two messages in the second time window associated with the four-step random access procedure.
The wireless terminal according to Appendix 1, wherein the second message of the random access procedure is attempted to be received .
[0145]
(Appendix 3)
　The attempt to receive the second message in the two-step random access procedure decodes the downlink control information indicating the downlink resource to which the second message in the two-step random access procedure is scheduled. In order to use the first RA-RNTI associated with the two-step random access procedure in the first time window, the
　four-step procedure comprises monitoring the Physical Downlink Control Channel (PDCCH). The attempt to receive the second message in the random access procedure is the second time in order to decode the downlink control information indicating the downlink resource to which the second message in the four-step random access procedure is scheduled.
The wireless terminal according to Appendix 2, comprising monitoring the PDCCH using a second RA-RNTI associated with the 4-step random access procedure in a window .
[0146]
(Appendix 4) The memory comprises at least one
　memory and
　at least one processor coupled to the at least one memory, the at least one
　processor providing a Radio Resource Control (RRC) layer and a Medium Access Control (MAC) layer. The MAC layer is configured
　to notify the RRC layer of the fallback when it falls back from a two-step random access procedure to a four-step random access procedure
.
[0147]
(Appendix 5) The memory comprises at least one
　memory and
　at least one processor coupled to the at least one memory, the at least one
　processor providing a Radio Resource Control (RRC) layer and a Medium Access Control (MAC) layer. The MAC layer is configured
　to notify the RRC layer of a change from a 2-step random access procedure to a 4-step random access procedure and vice versa
.
[0148]
(Appendix 6)
　The memory comprises at least one memory and
　at least one processor coupled to the at least one memory, wherein the at
　least one processor falls back from a two-step random access procedure to a four-step random access procedure. Is performed, but if the random access is not completed successfully, it is configured to select between the two-step random access procedure and the four-step random access procedure in order to restart the random access. Random
terminal.
[0149]
(Appendix 7)
　The at least one processor performs the random access according to one of the two-step random access procedure and the four-step random access procedure in which the next available preamble transmission opportunity arrives earlier.
The wireless terminal according to Appendix 6, which is configured to restart .
[0150]
(Appendix 8)
　The at least one processor follows the random one of the two-step random access procedure and the four-step random access procedure, one of which has a shorter cycle or interval of a plurality of available preamble transmission opportunities.
The wireless terminal according to Appendix 6, which is configured to restart access .
[0151]
(Appendix 9)
　The at least one processor has the two-step random access procedure and the four-step random access procedure based on the number of trials of each of the two-step random access procedure and the four-step random access procedure. The
wireless terminal according to Appendix 6, which is configured to be selected between .
[0152]
(Appendix 10)
　The memory comprises at least one memory and
　at least one processor coupled to the at least one memory, wherein the at
　least one of
　the plurality of events triggering the start of random access has two steps. • If the network is configured to receive a setting indicating that it is associated with a random access procedure and
　initiates random access for the at least one event, then perform the two-step random access procedure and the at least one event. A wireless terminal
configured to perform a 4-step random access procedure when initiating random access for an event other than .
[0153]
(Appendix 11)
　The memory comprises at least one memory and
　at least one processor coupled to the at least one memory, wherein the at
　least one processor is a plurality of
　Radio Resource Control (RRC) establishment, RRC reestablishment, and RRC resume.
　For an RRC establishment, RRC reestablishment, or RRC resume that is configured to receive from the network a setting indicating that at least one of the causes is associated with a two-step random access procedure. Perform the two-step random access procedure when initiating random access, and four-step random when initiating random access for an RRC establishment, RRC reestablishment, or RRC resume based on factors other than the at least one factor. A wireless terminal
configured to perform access procedures .
[0154]
(Appendix 12)
　The at least one memory and the
　at least one processor coupled to the at least one memory are provided, and the
　at least one processor is
　set to indicate the maximum number of restarts of the two-step random access procedure. A wireless terminal configured to receive from
　, and to fall back to a 4-step random access procedure after the number of restarts of the 2-step random access procedure reaches the maximum .
[0155]
(Appendix 13) It comprises at least one
　memory and
　at least one processor coupled to the at least one memory, wherein the at
　least one processor falls back from a two-step random access procedure to a four-step random access procedure. The system information is configured to transmit system information indicating activation of
　the two-step random access procedure, after transmitting the first message of the two-step random access procedure to the wireless terminal. A
RAN node that prompts both the reception of the second message and the reception of the second message of the 4-step random access procedure at the same time .
[0156]
(Appendix 14)
　The attempt to receive the second message of the two-step random access procedure is the first of the two-step random access procedures in the first time window associated with the two-step random access procedure. The attempt to receive the second message in the
　four-step random access procedure comprises attempting to receive the two messages in the second time window associated with the four-step random access procedure.
The RAN node according to Appendix 13, comprising attempting to receive the second message of the random access procedure .
[0157]
(Appendix 15)
　The attempt to receive the second message in the two-step random access procedure decodes the downlink control information indicating the downlink resource to which the second message in the two-step random access procedure is scheduled. In order to use the first RA-RNTI associated with the two-step random access procedure in the first time window, the
　four-step procedure comprises monitoring the Physical Downlink Control Channel (PDCCH). The attempt to receive the second message in the random access procedure is the second time in order to decode the downlink control information indicating the downlink resource to which the second message in the four-step random access procedure is scheduled.
RAN node according to Appendix 14, comprising monitoring the PDCCH using a second RA-RNTI associated with the 4-step random access procedure in a window .
[0158]
　This application claims priority on the basis of Japanese application Japanese Patent Application No. 2018-20276 filed on October 26, 2018 and incorporates all of its disclosures herein.
Description of the sign
[0159]
1 gNB
2 UE
101 Air Interface
1704 Processor
1705 Memory
1803 Baseband Processor
1804 Application Processor
1806 Memory
The scope of the claims
[Claim 1]
　It comprises at least one memory and
　at least one processor coupled to the at least one memory, the at least one
　processor transmitting a first message of a
　two-step random access procedure and transmitting
　the first message. Later, an attempt was made to receive the second message of the two-step random access procedure, the second message of the
　two-step random access procedure was successfully received, and the second message was sent to the four-step random access procedure. A control message comprising an uplink grant indicating an uplink resource available for sending the third message of the four-step random access procedure in response to determining that it indicates fallback explicitly or implicitly. A
wireless terminal that is configured to try to receive .
[Claim 2]
　The at least one processor responds to the failure to receive the second message of the two-step random access procedure without attempting to receive the control message for the four-step random access procedure.
The wireless terminal according to claim 1 , wherein the two-step random access procedure is configured to restart from the transmission of the first message .
[Claim 3]
　The at least one processor is configured to send the third message in response to the successful receipt of the control message and attempt to receive the fourth message of the four-step random access procedure.
The wireless terminal according to claim 1 or 2.
[Claim 4]
　The at least one processor has succeeded in receiving the second message, determined that the second message does not show the fallback, and determined that the contention resolution was successful based on the second message.
The wireless terminal according to any one of claims 1 to 3, which is configured to respond and consider that the two-step random access procedure has been successfully completed .
[Claim 5]

The wireless terminal according to any one of claims 1 to 4, 　wherein the control message is transmitted via the Physical Downlink Control Channel (PDCCH) and is the first downlink control information including the uplink grant. ..
[Claim 6]

The wireless terminal according to any one of claims 1 to 4, 　wherein the control message is a random access response message transmitted via the Physical Downlink Shared Channel (PDSCH) .
[Claim 7]
　The at least one processor attempts to receive a second downlink control information indicating a downlink resource for which the random access response message is scheduled using the Random Access Radio Network Temporary Identifier (RA-RNTI).
The wireless terminal according to claim 6, which is configured to receive the random access response message in response to the successful reception of the downlink control information of 2 .
[Claim 8]

The wireless terminal according to any one of claims 1 to 7, 　wherein the first message of the two-step random access procedure includes at least a terminal identifier used for contention resolution .
[Claim 9]

The wireless terminal according to any one of claims 1 to 8 　, wherein the second message of the two-step random access procedure includes a flag indicating whether or not the fallback should be performed .
[Claim 10]

The second message of the two-step random access procedure is any of claims 1-8, 　comprising a Medium Access Control (MAC) subheader associated with the fallback if the fallback is required . The wireless terminal according to item 1.
[Claim 11]

The wireless terminal according to any one of claims 1 to 8, 　wherein the second message of the two-step random access procedure implies the fallback due to a lack of specific information from the second message .
[Claim 12]

The wireless terminal according to claim 11, 　wherein the specific information is a UE Contention Resolution Identity MAC Control Element (CE) .
[Claim 13]

The wireless terminal according to any one of claims 1 to 8, 　wherein the second message of the two-step random access procedure implies the fallback by adding specific information to the second message .
[Claim 14]
　The first of the two-step random access procedures, said at least one processor, in response to receiving system information from the network indicating the activation of the fallback to the four-step random access procedure. Claims
1 to 1, wherein after transmitting one message, both the reception of the second message of the two-step random access procedure and the reception of the second message of the four-step random access procedure are tried at the same time . 13. The wireless terminal according to any one of 13.
[Claim 15]
　The attempt to receive the second message of the two-step random access procedure is to receive the second message of the two-step random access procedure in the first time window associated with the two-step random access procedure. The attempt to
　receive the second message of the four-step random access procedure comprises the trial of the two-step random access procedure in the second time window associated with the four-step random access procedure.
14. The wireless terminal according to claim 14, comprising attempting to receive the second message of the above .
[Claim 16]
　The attempt to receive the second message in the two-step random access procedure is said to decode the downlink control information indicating the downlink resource to which the second message in the two-step random access procedure is scheduled. In the first time window, the first RA-RNTI associated with the two-step random access procedure is used to monitor the Physical Downlink Control Channel (PDCCH) of the
　four-step random access procedure. The attempt to receive the second message is described in the second time window in order to decode the downlink control information indicating the downlink resource to which the second message of the four-step random access procedure is scheduled.
15. The wireless terminal of claim 15, comprising monitoring the PDCCH using a second RA-RNTI associated with a 4-step random access procedure .
[Claim 17]
　The at least one processor is configured to provide a Radio Resource Control (RRC) layer and a Medium Access Control (MAC) layer, which
　may fall back to the 4-step random access procedure.
The wireless terminal according to any one of claims 1 to 16, which is configured to notify the back to the RRC layer .
[Claim 18]
　The at least one processor is configured to provide a Radio Resource Control (RRC) layer and a Medium Access Control (MAC) layer, the
　MAC layer from the two-step random access procedure to the four-step random access procedure. The
wireless terminal according to any one of claims 1 to 16, which is configured to notify the RRC layer of the change and vice versa .
[Claim 19]
　The at least one processor restarts the random access if a fallback from the two-step random access procedure to the four-step random access procedure is performed but the random access is not successfully completed.
The wireless terminal according to any one of claims 1 to 18, configured to select between the two-step random access procedure and the four-step random access procedure .
[Claim 20]
　The at least one processor is to restart the random access according to one of the two-step random access procedure and the four-step random access procedure in which the next available preamble transmission opportunity arrives earlier. The wireless terminal according to
claim 19.
[Claim 21]
　The at least one processor restarts the random access according to one of the two-step random access procedure and the four-step random access procedure, one of which has a shorter cycle or interval of a plurality of available preamble transmission opportunities. 19. The wireless terminal according to
claim 19.
[Claim 22]
　The at least one processor is selected between the two-step random access procedure and the four-step random access procedure based on the number of trials of each of the two-step random access procedure and the four-step random access procedure. 19. The wireless terminal according to
claim 19.
[Claim 23]
　The at least one processor is
　configured to receive from the network a setting indicating that at least one of the plurality of events triggering the initiation of random access is associated with the two-step random access procedure
　. The two-step random access procedure is performed when starting random access for the purpose, and the four-step random access procedure is performed when the random
access is started for an event other than the at least one event. The wireless terminal according to any one of
claims 1 to 22.
[Claim 24]
　The at least one processor is
　configured from the network to indicate that at least one of the Radio Resource Control (RRC) establishment, RRC reestablishment, and RRC resume causes is associated with the two-step random access procedure. Perform the two-step random access procedure when initiating random access for an RRC establishment, RRC reestablishment, or RRC resume that is configured to receive
　and is based on the at least one factor, and factors other than the at least one factor. The radio according to any one of claims 1 to 22,
configured to perform the four-step random access procedure when initiating random access for RRC establishment, RRC reestablishment, or RRC resume based on.
Terminal.
[Claim 25]
　The at least one processor is
　configured to receive a setting from the network indicating the maximum number of restarts of the
　two-step random access procedure, and the number of restarts of the two-step random access procedure reaches the maximum number.
The wireless terminal according to any one of claims 1 to 24, which is configured to fall back to the four-step random access procedure .
[Claim 26]
　A wireless access network (RAN) node comprising at least one
　memory and
　at least one processor coupled to the at least one memory,
　wherein the at least one processor is
　the first message of a two-step random access procedure. Is received
　, and after receiving the first message, the second message of the two-step random access procedure is transmitted, and
the
　second message is the transmission of the third message of the four-step random access procedure. The four-step random access procedure for requesting a wireless terminal to attempt to receive a control message comprising an uplink grant indicating an uplink resource available to the radio terminal after successfully receiving the second message. A
RAN node that explicitly or implicitly indicates a fallback to .
[Claim 27]
　The second message is the second message to the wireless terminal without attempting to receive the control message for the four-step random access procedure when the wireless terminal fails to receive the second message.
The RAN node according to claim 26, which prompts the restart of the step random access procedure from the transmission of the first message .
[Claim 28]

The RAN node according to claim 26 or 27, 　wherein the at least one processor is configured to transmit the control message after the transmission of the second message .
[Claim 29]
　13
. The described RAN node.
[Claim 30]

The RAN node according to any one of claims 26 to 29, 　wherein the control message is transmitted via the Physical Downlink Control Channel (PDCCH) and is the first downlink control information including the uplink grant. ..
[Claim 31]

The RAN node according to any one of claims 26 to 30, 　wherein the control message is a random access response message transmitted via the Physical Downlink Shared Channel (PDSCH) .
[Claim 32]
　The second message attempts to receive the second downlink control information indicating the downlink resource for which the random access response message is scheduled to the wireless terminal by using the Random Access Radio Network Temporary Identifier (RA-RNTI).
31. The RAN node according to claim 31, which prompts the user to receive the random access response message in response to the successful reception of the second downlink control information .
[Claim 33]

The RAN node according to any one of claims 26 to 32, 　wherein the first message of the two-step random access procedure includes at least a terminal identifier used for contention resolution .
[Claim 34]

The RAN node according to any one of claims 26 to 33 　, wherein the second message of the two-step random access procedure includes a flag indicating whether or not the fallback should be performed .
[Claim 35]

The second message of the two-step random access procedure is any of claims 　26-33, comprising a Medium Access Control (MAC) subheader associated with the fallback if the fallback is required . The RAN node described in item 1.
[Claim 36]

The RAN node according to any one of claims 26 to 33, 　wherein the second message of the two-step random access procedure implies said fallback due to a lack of specific information from the second message .
[Claim 37]

36. The RAN node of claim 36, 　wherein the particular information is a UE Contention Resolution Identity MAC Control Element (CE) .
[Claim 38]

The RAN node according to any one of claims 26 to 33, 　wherein the second message of the two-step random access procedure implies said fallback by adding specific information to the second message .
[Claim 39]
　The at least one processor is configured to transmit system information indicating activation of the fallback to the four-step random access procedure, and the system information is delivered to the
　wireless terminal in the two steps. After transmitting the first message of the random access procedure, it is urged to try both the reception of the second message of the two-step random access procedure and the reception of the second message of the four-step random access procedure at the same time. ,
The RAN node according to any one of claims 26 to 38.
[Claim 40]
　The attempt to receive the second message of the two-step random access procedure is to receive the second message of the two-step random access procedure in the first time window associated with the two-step random access procedure. The attempt to
　receive the second message of the four-step random access procedure comprises the trial of the two-step random access procedure in the second time window associated with the four-step random access procedure.
39. The RAN node of claim 39, comprising attempting to receive said second message .
[Claim 41]
　The attempt to receive the second message of the two-step random access procedure is said to decode the downlink control information indicating the downlink resource to which the second message of the two-step random access procedure is scheduled. In the first time window, the first RA-RNTI associated with the two-step random access procedure is used to monitor the Physical Downlink Control Channel (PDCCH) of the
　four-step random access procedure. The attempt to receive the second message is described in the second time window in order to decode the downlink control information indicating the downlink resource to which the second message is scheduled in the four-step random access procedure.
40. The RAN node of claim 40, comprising monitoring the PDCCH using a second RA-RNTI associated with a 4-step random access procedure .
[Claim 42]
　A method in a wireless terminal, in which
　the first message of the two-step random access procedure
　is transmitted, and after the first message is transmitted, the second message of the two-step random access procedure is attempted to be received. And
　in response to determining that the second message of the two-step random access procedure was successfully received and that the second message explicitly or implicitly indicates a fallback to the four-step random access procedure. , A method comprising attempting to receive a control message comprising an uplink grant indicating an uplink resource available for transmission of the third message of the four-step random access procedure
.
[Claim 43]
　A method in a radio access network (RAN) node
　that receives the first message of the two-step random access procedure, and
　after receiving the first message, the second message of the two-step random access procedure. 　The second message comprises receiving a control message comprising an uplink grant indicating an uplink resource available for transmission of the third message in a four-step random access procedure
. A method
of explicitly or implicitly indicating a fallback to the four-step random access procedure to require a radio terminal to attempt after successfully receiving a message
.
[Claim 44]
　A non-temporary computer-readable medium containing a program for causing a computer to perform a method in a wireless terminal,
　wherein the method is
　to send a first message of a two-step random access procedure, the first
　message. After transmission, an attempt is made to receive the second message of the two-step random access procedure, and the second message of the
　two-step random access procedure is successfully received and the second message is four-step random. In response to determining that it indicates a fallback to the access procedure, either explicitly or implicitly, an uplink grant indicating the uplink resources available for sending the third message of the four-step random access procedure. A
non-temporary computer-readable medium , comprising attempting to receive a containing control message .
[Claim 45]
　A non-temporary computer-readable medium containing a program for causing a computer to perform a method at a wireless access network (RAN) node,
　wherein the method
　receives the first message of a two-step random access procedure. And
　, after receiving the first message, the second message of the two-step random access procedure is transmitted,
and
　the second message can be used for transmitting the third message of the four-step random access procedure. Fall to the 4-step random access procedure to require the wireless terminal to attempt to receive a control message containing an uplink grant indicating an uplink resource after successfully receiving the second message. A
non-temporary computer-readable medium that indicates the back, either explicitly or implicitly .