Method and device for fallback action of small data transmission in wireless communication system

Abstract

The present invention provides a method and apparatus for fallback action of small data transmission in a wireless communication system. In one embodiment, the method includes a user equipment initiating a 2-step random access procedure including uplink data in an RRC_INACTIVE state. The method also includes the user equipment switching from the 2-step random access procedure to a 4-step random access procedure not including uplink data in response to a condition.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 62 / 976,017, filed on February 13, 2020, the entire disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure relates generally to wireless communication networks, and more particularly, to methods and apparatus for backoff actions for small data transmissions in wireless communication systems. Background Art

[0004] With the rapid growth of the communication demand for large amounts of data to and from mobile communication devices, traditional mobile voice communication networks have evolved into networks that communicate with Internet Protocol (IP) data packets. Such IP data packet communications can provide IP-bearing voice, multimedia, multicast and on-demand communication services to users of mobile communication devices.

[0005] An exemplary network structure is an Evolved Universal Terrestrial Radio Access Network (E-UTRAN). The E-UTRAN system can provide high data throughput to enable the above-mentioned IP-borne voice and multimedia services. Currently, the 3rd Generation Partnership Project (3GPP) standards organization is discussing new next-generation (e.g., 5G) radio technologies. Therefore, changes to the current body of 3GPP standards are currently being submitted and considered to evolve and complete the 3GPP standards. Summary of the invention

[0006] A method and apparatus are disclosed from the perspective of a user equipment (UE). In one embodiment, the method includes the UE initiating a 2-step random access (RA) procedure including uplink (UL) data in an RRC_INACTIVE state. The method also includes the UE switching from the 2-step RA procedure to a 4-step RA procedure not including UL data in response to a condition. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 A drawing showing a wireless communication system according to an exemplary embodiment;

[0008] Figure 2 is a block diagram of a transmitter system (also referred to as an access network) and a receiver system (also referred to as a user equipment or UE) according to an exemplary embodiment;

[0009] Figure 3 is a functional block diagram of a communication system according to an exemplary embodiment;

[0010] Figure 4 According to an exemplary embodiment Figure 3 Functional block diagram of the program code;

[0011] Figure 5 It is a reproduction of Table 5.1.4-1 of 3GPP TS 36.321 V15.8.0;

[0012] Figure 6 is a flow chart of a 2-step random access procedure with small data according to an exemplary embodiment;

[0013] Figure 7 is a flow chart of a 4-step random access procedure with small data according to an exemplary embodiment;

[0014] Figure 8 is a flow chart according to an exemplary embodiment;

[0015] Fig. 9 is a flow chart according to an exemplary embodiment;

[0016] Fig.10 is a flow chart according to an exemplary embodiment. DETAILED DESCRIPTION

[0017] The exemplary wireless communication systems and devices described below employ wireless communication systems that support broadcast services. Wireless communication systems are widely deployed to provide various types of communications, such as voice, data, etc. These systems can be based on code division multiple access (CDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), 3GPP Long Term Evolution (LTE) radio access, 3GPP Long Term Evolution Advanced (LTE-A or LTE-Advanced), 3GPP2 Ultra Mobile Broadband (UMB), WiMax, 3GPP New Radio (NR), or some other modulation technology.

[0018] Specifically, the exemplary wireless communication system apparatus described below can be designed to support one or more standards, for example, standards provided by an association named "3rd Generation Partnership Project" (referred to herein as 3GPP), including: TS 38.321V15.8.0, "NR, Medium Access Control (MAC) Protocol Specification"; R2-1914798, "Operation MAC CR for 2-step RACH", ZTE Corporation, ZTE Microelectronics; R2-1915889, "Phase 2 Operation CR for 2-step RACH" Nokia, Nokia Shanghai Bell; 3GPP TS 38.331V15.8.0, "NR, Radio Resource Control (RRC) Protocol Specification"; TS 36.300V15.8.0, "E-UTRA and E-UTRAN; Overall Specification; Stage 2"; TS 36.321V15.8.0, "E-UTRA; Medium Access Control (MAC) Protocol Specification"; TS 36.331V15.8.0, "E-UTRA, Radio Resource Control (RRC)" protocol specification; RP-193252, "Work items on NR small data transmission in INACTIVE state", ZTE Corporation; and RP-193238, "New SID for NR devices supporting reduced capacity", Ericsson. The standards and documents listed above are expressly incorporated by reference in their entirety.

[0019] Figure 1 A multiple access wireless communication system according to an embodiment of the present invention is shown. Access network 100 (AN) includes multiple antenna groups, one antenna group includes antennas 104 and 106, another antenna group includes antennas 108 and 110, and another antenna group includes antennas 112 and 114. Figure 1In the figure, only two antennas are shown for each antenna group, however, each antenna group may utilize more or fewer antennas. Access terminal 116 (AT) communicates with antennas 112 and 114, where antennas 112 and 114 transmit information to access terminal 116 via forward link 120 and receive information from access terminal 116 via reverse link 118. Access terminal (AT) 122 communicates with antennas 106 and 108, where antennas 106 and 108 transmit information to access terminal (AT) 122 via forward link 126 and receive information from access terminal (AT) 122 via reverse link 124. In an FDD system, communication links 118, 120, 124, and 126 may use different frequencies for communication. For example, forward link 120 may use a different frequency than the frequency used by reverse link 118.

[0020] Each antenna group and / or the area in which the antenna group is designed to communicate is often referred to as a sector of the access network. In an embodiment, the antenna groups are each designed to communicate with access terminals in a sector of the area covered by the access network 100.

[0021] In communicating over forward links 120 and 126, the transmit antennas of access network 100 may utilize beamforming in order to improve the signal-to-noise ratio of the forward links for the different access terminals 116 and 122. Also, an access network that uses beamforming to transmit to access terminals that are randomly dispersed throughout the coverage area of ​​the access network may generate less interference to access terminals in neighboring cells than an access network that transmits to all of its access terminals via a single antenna.

[0022] An access network (AN) may be a fixed station or base station for communicating with a terminal, and may also be referred to as an access point, Node B, base station, enhanced base station, evolved Node B (eNB), network node, network, or some other term. An access terminal (AT) may also be referred to as a user equipment (UE), a wireless communication device, a terminal, an access terminal, or some other term.

[0023] Figure 2 2 is a simplified block diagram of an embodiment of a transmitter system 210 (also referred to as an access network) and a receiver system 250 (also referred to as an access terminal (AT) or user equipment (UE)) in a MIMO system 200. At the transmitter system 210, traffic data for a number of data streams is provided from a data source 212 to a transmit (TX) data processor 214.

[0024] In one embodiment, each data stream is transmitted via a respective transmit antenna.TX data processor 214 formats, codes, and interleaves the traffic data for each data stream based on a particular coding scheme selected for that data stream to provide coded data.

[0025] The decoded data for each data stream may be multiplexed with pilot data using OFDM techniques. The pilot data is typically a known data pattern that is processed in a known manner and may be used at the receiver system to estimate the channel response. The multiplexed pilot and decoded data for each data stream is then modulated (i.e., symbol mapped) based on a particular modulation scheme (e.g., BPSK, QPSK, M-PSK, or M-QAM) selected for that data stream to provide modulation symbols. The data rate, coding, and modulation for each data stream may be determined by execution of instructions in memory 232 by processor 230.

[0026] The modulation symbols for all data streams are then provided to a TX MIMO processor 220, which may further process the modulation symbols (e.g., for OFDM). The TX MIMO processor 220 then converts the N T The modulation symbol stream is provided to N T transmitters (TMTR) 222a through 222t. In certain embodiments, TX MIMO processor 220 applies beamforming weights to the symbols of the data streams and to the antenna from which the symbol is being transmitted.

[0027] Each transmitter 222 receives and processes a respective symbol stream to provide one or more analog signals, and further conditions (e.g., amplifies, filters, and upconverts) the analog signals to provide a modulated signal suitable for transmission over the MIMO channel. T The antennas 224a to 224t transmit N signals from the transmitters 222a to 222t. T a modulated signal.

[0028] At the receiver system 250, N R The transmitted modulated signals are received by each antenna 252a through 252r and the received signal from each antenna 252 is provided to a respective receiver (RCVR) 254a through 254r. Each receiver 254 conditions (e.g., filters, amplifies, and downconverts) a respective received signal, digitizes the modulated signal to provide samples, and further processes the samples to provide a corresponding “received” symbol stream.

[0029] RX data processor 260 then extracts the N R The receiver 254 receives and processes N R received symbol streams to provide NT The RX data processor 260 then demodulates, deinterleaves, and decodes each detected symbol stream to recover the traffic data for the data stream. The processing by the RX data processor 260 is complementary to the processing performed by the TX MIMO processor 220 and the TX data processor 214 at the transmitter system 210.

[0030] Processor 270 executes instructions in memory 232 to periodically determine which pre-coding matrix to use (discussed below). Processor 270 formulates a reverse link message comprising a matrix index portion and a rank value portion.

[0031] The reverse link message includes various types of information about the communication link and / or the received data stream. The reverse link message is then processed by the TX data processor 238 (which also receives traffic data for a number of data streams from the data source 236), modulated by the modulator 280, conditioned by the transmitters 254a to 254r, and transmitted back to the transmitter system 210.

[0032] At the transmitter system 210, the modulated signal from the receiver system 250 is received by the antenna 224, conditioned by the receiver 222, demodulated by the demodulator 240, and processed by the RX data processor 242 to extract the reverse link message transmitted by the receiver system 250. The processor 230 then determines which precoding matrix to use to determine the beamforming weights and then processes the extracted message.

[0033] See instead Figure 3 , this figure shows an alternative simplified functional block diagram of a communication device according to one embodiment of the present invention. Figure 3 As shown, the communication device 300 in the wireless communication system can be used to implement Figure 1 UE (or AT) 116 and 122 in or Figure 1The base station (or AN) 100 in the wireless communication system is preferably an NR system. The communication device 300 may include an input device 302, an output device 304, a control circuit 306, a central processing unit (CPU) 308, a memory 310, a program code 312, and a transceiver 314. The control circuit 306 executes the program code 312 in the memory 310 through the CPU 308, thereby controlling the operation of the communication device 300. The communication device 300 can receive signals input by the user through the input device 302 (such as a keyboard or a keypad), and can output images and sounds through the output device 304 (such as a monitor or a speaker). The transceiver 314 is used to receive and transmit wireless signals, pass the received signals to the control circuit 306, and wirelessly output the signals generated by the control circuit 306. The communication device 300 in the wireless communication system can also be used to implement Figure 1 AN 100 in.

[0034] Figure 4 According to one embodiment of the present invention Figure 3 4. In this embodiment, program code 312 includes application layer 400, layer 3 portion 402, and layer 2 portion 404, and is coupled to layer 1 portion 406. Layer 3 portion 402 generally performs radio resource control. Layer 2 portion 404 generally performs link control. Layer 1 portion 406 generally performs physical connectivity.

[0035] In NR, the RA procedure is specified in 3GPP TS 38.321 with operation CR R2-1914798 as follows:

[0036] 5.1 Random Access Procedure

[0037] 5.1.1 Random Access Procedure Initialization

[0038] According to TS 38.300 [2], the random access procedure described in this section is initiated by a PDCCH command, the MAC entity itself, or an RRC event. In the MAC entity, there is only one ongoing random access procedure at any point in time. The random access procedure on the SCell will only be initiated by a PDCCH command where the ra-PreambleIndex is different from 0b000000.

[0039] NOTE 1: If a new random access procedure is triggered while another random access procedure is already in progress in the MAC entity, it will depend on the UE implementation whether to continue the ongoing procedure or start a new procedure (e.g. for SI request).

[0040] RRC configures the following parameters for the random access procedure:

[0041] Editor's note: RRC parameters for 2-step random access will be added here (power control related parameters required for RAN1 input etc.) The names of the IEs listed below are also for further study and may be revisited later.

[0042] -prach-ConfigurationIndex: a set of available PRACH opportunities for transmitting random access preambles;

[0043] -preambleReceivedTargetPower: initial random access preamble power;

[0044] -rsrp-ThresholdSSB: RSRP threshold for selecting SSB; if a random access procedure is initiated for beam failure recovery, the rsrp-ThresholdSSB used to select SSB in candidateBeamRSList refers to the rsrp-ThresholdSSB in BeamFailureRecoveryConfig IE;

[0045] -rsrp-ThresholdCSI-RS: RSRP threshold for selecting CSI-RS. If a random access procedure is initiated for beam failure recovery, rsrp-ThresholdCSI-RS is equal to rsrp-ThresholdSSB in the BeamFailureRecoveryConfig IE;

[0046] -rsrp-ThresholdSSB-SUL: RSRP threshold for selecting between NUL carrier and SUL carrier;

[0047] -rsrp-ThresholdSSB-2stepCBRA: RSRP threshold for selecting 2-step random access

[0048] - candidateBeamRSList: A list of reference signals (CSI-RS and / or SSB) identifying candidate beams for recovery and associated random access parameters

[0049] -recoverySearchSpaceId: the search space identifier used to monitor the response to the beam failure recovery request;

[0050] -powerRampingStep: power boost factor;

[0051] -powerRampingStepHighPriority: power boost factor in case of prioritized random access procedure;

[0052] -scalingFactorBI: scaling factor for prioritized random access procedures;

[0053] -ra-PreambleIndex: random access preamble;

[0054] -ra-ssb-OccasionMaskIndex: defines the PRACH occasions associated with the SSB where the MAC entity may transmit the random access preamble (see clause 7.4);

[0055] -ra-OccasionList: defines the PRACH occasions associated with the CSI-RS, where the MAC entity can transmit the random access preamble;

[0056] -ra-PreambleStartIndex: the start index of the random access preamble for on-demand SI request;

[0057] -preambleTransMax: Maximum number of random access preamble transmissions;

[0058] -ssb-perRACH-OccasionAndCB-PreamblesPerSSB: defines the number of SSBs mapped to each PRACH opportunity and the number of contention-based random access preambles mapped to each SSB;

[0059] - If groupBconfigured is configured, random access preamble group B is configured.

[0060] - Among the contention-based random access preambles (as defined in TS 38.213 [6]) associated with an SSB, the first numberOfRA-PreamblesGroupA random access preambles belong to random access preamble group A. The remaining random access preambles associated with an SSB belong to random access preamble group B (if configured).

[0061] NOTE 2: If random access preamble group B is supported by the cell, then for each SSB, random access preamble group B is included.

[0062] - If random access preamble group B is configured, then:

[0063] -ra-Msg3SizeGroupA: determines the threshold of the group of random access preamble codes;

[0064] -msg3-DeltaPreamble: Delta in TS 38.213 [6] PREAMBLE_Msg3 ;

[0065] -messagePowerOffsetGroupB: power offset for preamble selection;

[0066] -numberOfRA-PreamblesGroupA: defines the number of random access preambles in random access preamble group A used for each SSB.

[0067] Editor's note: Configuration of Group B preamble for 2-step RACH etc needs to be added above.

[0068] - A set of random access preambles and / or PRACH opportunities (if any) used for SI request;

[0069] - A set of random access preambles and / or PRACH opportunities (if any) for beam failure recovery request;

[0070] - A set of random access preambles and / or PRACH opportunities (if any) for synchronization reconfiguration;

[0071] -ra-ResponseWindow: Time window for monitoring RA response (SpCell only);

[0072] -ra-ContentionResolutionTimer: Contention resolution timer (SpCell only).

[0073] Furthermore, it is assumed that the following information of the relevant serving cell is available to the UE:

[0074] - If random access preamble group B is configured, then:

[0075] - If the serving cell for the random access procedure is configured with a supplementary uplink as specified in TS 38.331 [5] and the SUL carrier is selected for performing the random access procedure, then:

[0076] - PCMAX,f,c of the SUL carrier as specified in TS 38.101-1

[14] , TS 38.101-2

[15] and TS 38.101-3

[16] .

[0077] -otherwise:

[0078] - P for NUL carriers as specified in TS 38.101-1

[14] , TS 38.101-2

[15] and TS 38.101-3

[16] CMAX,f,c .

[0079] The following UE variables are used for the random access procedure:

[0080] Editor's note: Add variables for 2-step random access here

[0081] -PREAMBLE_INDEX;

[0082] -PREAMBLE_TRANSMISSION_COUNTER;

[0083] -PREAMBLE_POWER_RAMPING_COUNTER;

[0084] -PREAMBLE_POWER_RAMPING_STEP;

[0085] -PREAMBLE_RECEIVED_TARGET_POWER;

[0086] -PREAMBLE_BACKOFF;

[0087] -PCMAX;

[0088] -SCALING_FACTOR_BI;

[0089] -TEMPORARY_C-RNTI.

[0090] -RA_TYPE.

[0091] When a random access procedure is initiated on a serving cell, the MAC entity shall:

[0092] 1> Clear the Msg3 buffer;

[0093] 1> Clear the MSGA buffer;

[0094] 1> Set PREAMBLE_TRANSMISSION_COUNTER to 1;

[0095] 1> Set PREAMBLE_POWER_RAMPING_COUNTER to 1;

[0096] 1> Set PREAMBLE_BACKOFF to 0ms;

[0097] 1> If the carrier to be used for the random access procedure is explicitly signalled, then:

[0098] 2> Select the transmitted signal carrier for performing the random access procedure;

[0099] 2> Set PCMAX to the P value of the transmitted carrier. CMAX,f,c .

[0100] 1> otherwise, if the carrier to be used for the random access procedure is not explicitly signalled; and

[0101] 1> if the serving cell for the random access procedure is configured with a supplementary uplink as specified in TS 38.331 [5]; and

[0102] 1> If the RSRP referenced by the downlink path loss is less than rsrp-ThresholdSSB-SUL, then:

[0103] 2> Select the SUL carrier to perform a random access procedure;

[0104] 2> Set PCMAX to the P of the SUL carrier CMAX,f,c .

[0105] 1> Otherwise:

[0106] 2> Select NUL carrier to perform random access procedure;

[0107] 2> Set PCMAX to the P of NUL carrier CMAX,f,c .

[0108] 1>Perform the BWP operation as specified in clause 5.15;

[0109] Editor's note: How to select RA_TYPE in case of configuring 4-step CFRA (for BFR or for HO) is for further study. After agreement on 4-step CFRA for BFR / HO, the following logic for selecting RA_TYPE needs to be updated (and may also be simplified).

[0110] 1> if the random access procedure is initiated by a PDCCH command and if the ra-PreambleIndex explicitly provided by the PDCCH is not 0b000000; or

[0111] 1> If the random access procedure is initiated for an SI request (as specified in TS 38.331 [5]) and the random access resources for the SI request have been explicitly provided by RRC:

[0112] 2> Set RA_TYPE to 4-stepRA;

[0113] 1> Otherwise, if rsrp-ThresholdSSB-2stepCBRA is configured and the RSRP referenced by the downlink path loss is higher than the configured rsrp-ThresholdSSB-2stepCBRA; or

[0114] 1> If the BWP selected for the random access procedure is configured with only 2-step random access resources (i.e., 4-step RACH resources are not configured):

[0115] 2> Set RA_TYPE to 2-stepRA;

[0116] 1> Otherwise:

[0117] 2> Set RA_TYPE to 4-stepRA;

[0118] 1> If RA_TYPE is set to 2-stepRA:

[0119] 2> Set PREAMBLE_POWER_RAMPING_STEP to powerRampingStep;

[0120] 2> Set SCALING_FACTOR_BI to 1;

[0121] 2> if a random access procedure is initiated for beam failure recovery (as specified in clause 5.17); and

[0122] 2> If beamFailureRecoveryConfig is configured as the active UL BWP for the selected carrier, then:

[0123] 3> If powerRampingStepHighPriority is configured in beamFailureRecoveryConfig, then:

[0124] 4>Set PREAMBLE_POWER_RAMPING_STEP to powerRampingStepHighPriority.

[0125] 3>If scalingFactorBI is configured in beamFailureRecoveryConfig, then:

[0126] 4>Set SCALING_FACTOR_BI to scalingFactorBI.

[0127] 2> Otherwise, if a random access procedure is initiated for handover; and

[0128] 2> If rach-ConfigDedicated is configured for the selected carrier, then:

[0129] 3> If powerRampingStepHighPriority is configured in rach-ConfigDedicated, then:

[0130] 4>Set PREAMBLE_POWER_RAMPING_STEP to powerRampingStepHighPriority.

[0131] 3>If scalingFactorBI is configured in rach-ConfigDedicated, then:

[0132] 4>Set SCALING_FACTOR_BI to scalingFactorBI.

[0133] Editor's note: The above configuration names are for further study. Whether these variables are the same between 2-step and 4-step RACH is also for further study. We will need to update the variable names and parameter names based on the final decision on whether the configuration parameters are common for 2-step and 4-step RACH (e.g., based on the RRC parameters email discussion).

[0134] 2> Perform the random access resource selection procedure for 2-step random access (see Section 5.1.2a).

[0135] 1> Otherwise: (i.e., set RA_TYPE to 4-stepRA)

[0136] 2> Set PREAMBLE_POWER_RAMPING_STEP to powerRampingStep;

[0137] 2> Set SCALING_FACTOR_BI to 1;

[0138] 2> if a random access procedure is initiated for beam failure recovery (as specified in clause 5.17); and

[0139] 2> If beamFailureRecoveryConfig is configured as the active UL BWP for the selected carrier, then:

[0140] 3>If configured, start beamFailureRecoveryTimer;

[0141] 3> Apply the parameters powerRampingStep, preambleReceivedTargetPower and preambleTransMax configured in beamFailureRecoveryConfig;

[0142] 3> If powerRampingStepHighPriority is configured in beamFailureRecoveryConfig, then:

[0143] 4>Set PREAMBLE_POWER_RAMPING_STEP to powerRampingStepHighPriority.

[0144] 3>If scalingFactorBI is configured in beamFailureRecoveryConfig, then:

[0145] 4>Set SCALING_FACTOR_BI to scalingFactorBI.

[0146] 2> Otherwise, if a random access procedure is initiated for handover; and

[0147] 2> If rach-ConfigDedicated is configured for the selected carrier, then:

[0148] 3> If powerRampingStepHighPriority is configured in rach-ConfigDedicated, then:

[0149] 4>Set PREAMBLE_POWER_RAMPING_STEP to powerRampingStepHighPriority.

[0150] 3>If scalingFactorBI is configured in rach-ConfigDedicated, then:

[0151] 4>Set SCALING_FACTOR_BI to scalingFactorBI.

[0152] 2> Perform the random access resource selection procedure (see clause 5.1.2).

[0153] 5.1.2 Random Access Resource Selection

[0154] The MAC entity will:

[0155] 1> if a random access procedure is initiated for beam failure recovery (as specified in clause 5.17); and

[0156] 1> if beamFailureRecoveryTimer (Section 5.17) is running or not configured; and

[0157] 1> if contention-free random access resources for beam failure recovery request associated with any of the SSB and / or CSI-RS have been explicitly provided by RRC; and

[0158] 1> If at least one of an SSB with an SS-RSRP higher than rsrp-ThresholdSSB among the SSBs in candidateBeamRSList or a CSI-RS with a CSI-RSRP higher than rsrp-ThresholdCSI-RS among the CSI-RSs in candidateBeamRSList is available, then:

[0159] 2> Select an SSB with an SS-RSRP higher than rsrp-ThresholdSSB among the SSBs in candidateBeamRSList or a CSI-RS with a CSI-RSRP higher than rsrp-ThresholdCSI-RS among the CSI-RSs in candidateBeamRSList;

[0160] 2> If CSI-RS is selected and there is no ra-PreambleIndex associated with the selected CSI-RS, then:

[0161] 3> Set PREAMBLE_INDEX to the ra-PreambleIndex corresponding to the SSB in candidateBeamRSList, which is quasi-colocated with the selected CSI-RS, as specified in TS 38.214 [7].

[0162] 2> Otherwise:

[0163] 3> Set PREAMBLE_INDEX to the ra-PreambleIndex corresponding to the SSB or CSI-RS selected from a set of random access preambles for beam failure recovery request.

[0164] 1> Otherwise, if ra-PreambleIndex has been explicitly provided via PDCCH; and

[0165] 1> If ra-PreambleIndex is not 0b000000, then:

[0166] 2> Set PREAMBLE_INDEX to the transmitted signal ra-PreambleIndex;

[0167] 2> Select the SSB signaled via PDCCH.

[0168] 1> Otherwise, if the contention-free random access resource associated with the SSB has been explicitly provided in rach-ConfigDedicated, and at least one SSB among the associated SSBs with an SS-RSRP higher than rsrp-ThresholdSSB is available, then:

[0169] 2> Select the SSB with SS-RSRP higher than rsrp-ThresholdSSB among the associated SSBs;

[0170] 2> Set PREAMBLE_INDEX to the ra-PreambleIndex corresponding to the selected SSB.

[0171] 1> Otherwise, if the contention-free random access resource associated with the CSI-RS has been explicitly provided in rach-ConfigDedicated, and at least one CSI-RS with a CSI-RSRP higher than rsrp-ThresholdCSI-RS among the associated CSI-RS is available, then:

[0172] 2> Select a CSI-RS with a CSI-RSRP higher than rsrp-ThresholdCSI-RS among the associated CSI-RS;

[0173] 2> Set PREAMBLE_INDEX to the ra-PreambleIndex corresponding to the selected CSI-RS.

[0174] 1> Otherwise, if a random access procedure is initiated for an SI request (as specified in TS 38.331 [5]); and

[0175] 1> If the random access resources for SI request have been explicitly provided by RRC:

[0176] 2> If at least one of the SSBs with SS-RSRP higher than rsrp-ThresholdSSB is available, then:

[0177] 3> Select an SSB with SS-RSRP higher than rsrp-ThresholdSSB.

[0178] 2> Otherwise:

[0179] 3>Select Any SSB.

[0180] 2> Select the random access preamble corresponding to the selected SSB from the random access preambles determined according to ra-PreambleStartIndex as specified in TS 38.331 [5];

[0181] 2> Set PREAMBLE_INDEX to the selected random access preamble.

[0182] 1> Otherwise (i.e., for contention-based random access preamble selection):

[0183] 2> If at least one of the SSBs with SS-RSRP higher than rsrp-ThresholdSSB is available, then:

[0184] 3> Select an SSB with SS-RSRP higher than rsrp-ThresholdSSB.

[0185] 2> Otherwise:

[0186] 3>Select Any SSB.

[0187] 2> If the Msg3 buffer is not empty:

[0188] 3> If random access preamble group B is configured, then:

[0189] 4> If the potential Msg3 size (e.g., UL data available for transmission plus MAC header and MAC CE if required) is greater than ra-Msg3SizeGroupA and the path loss is less than PCMAX-preambleReceivedTargetPower-msg3-DeltaPreamble-messagePowerOffsetGroupB (of the serving cell performing the random access procedure); or

[0190] 4> If a random access procedure is initiated for the CCCH logical channel and the CCCH SDU size plus the MAC subheader is greater than ra-Msg3SizeGroupA, then:

[0191] 5> Select random access preamble group B.

[0192] 4> Otherwise:

[0193] 5> Select random access preamble group A.

[0194] 3> Otherwise:

[0195] 4> Select random access preamble group A.

[0196] 2> Otherwise (that is, Msg3 is retransmitted):

[0197] 3> Select the same random access preamble group as the random access preamble transmission attempt used for the first transmission corresponding to Msg3.

[0198] 2> Randomly select a random access preamble from the random access preambles associated with the selected SSB and the selected random access preamble group with equal probability.

[0199] 2> Set PREAMBLE_INDEX to the selected random access preamble.

[0200] 1> Otherwise, if a random access procedure is initiated for an SI request (as specified in TS 38.331 [5]); and

[0201] 1> If ra-AssociationPeriodIndex and si-RequestPeriod are configured, then:

[0202] 2> Determine the next available PRACH opportunity from the PRACH opportunity corresponding to the selected SSB in the association period given by ra-AssociationPeriodIndex in si-RequestPeriod permitted by the restrictions given by ra-ssb-OccasionMaskIndex (if configured) (the MAC entity shall randomly select the PRACH opportunity among consecutive PRACH opportunities with equal probability according to clause 8.1 of TS 38.213 [6] corresponding to the selected SSB).

[0203] 1> Otherwise, if SSB is selected as above, then:

[0204] 2> Determine the next available PRACH opportunity based on the PRACH opportunity corresponding to the selected SSB given by ra-ssb-OccasionMaskIndex (if configured) or permitted by the restriction indicated by PDCCH (the MAC entity shall randomly select the PRACH opportunity among the consecutive PRACH opportunities corresponding to the selected SSB with the same probability according to clause 8.1 of TS38.213[6]; the MAC entity may consider the possible occurrence of measurement gaps when determining the next available PRACH opportunity corresponding to the selected SSB).

[0205] 1> Otherwise, if CSI-RS is selected as above, then:

[0206] 2> If there is no contention-free random access resource associated with the selected CSI-RS, then:

[0207] 3> Determine the next available PRACH opportunity according to the PRACH opportunity corresponding to the SSB in candidateBeamRSList that is quasi-co-located with the selected CSI-RS as specified in TS 38.214 [7], as permitted by the restrictions given by ra-ssb-OccasionMaskIndex (if configured) (the MAC entity shall randomly select a PRACH opportunity among consecutive PRACH opportunities corresponding to the SSB that is quasi-co-located with the selected CSI-RS with equal probability according to clause 8.1 of TS 38.213 [6]; the MAC entity may consider the possible occurrence of measurement gaps when determining the next available PRACH opportunity corresponding to the SSB that is quasi-co-located with the selected CSI-RS).

[0208] 2> Otherwise:

[0209] 3> Determine the next available PRACH opportunity based on the PRACH opportunity corresponding to the selected CSI-RS in the ra-OccasionList (the MAC entity will randomly select a PRACH opportunity from the PRACH opportunities corresponding to the selected CSI-RS that appear simultaneously but on different subcarriers with equal probability; the MAC entity may consider the possible occurrence of measurement gaps when determining the next available PRACH opportunity corresponding to the selected CSI-RS).

[0210] 1> Perform the random access preamble transmission procedure (see clause 5.1.3).

[0211] Note: When the UE determines whether there is an SSB with SS-RSRP higher than rsrp-ThresholdSSB or a CSI-RS with CSI-RSRP higher than srp-ThresholdCSI-RS, the UE uses the latest unfiltered L1-RSRP measurement.

[0212] 5.1.2a Random Access Resource Selection for 2-Step Random Access

[0213] The MAC entity will:

[0214] 1> If at least one of the SSBs with SS-RSRP higher than rsrp-ThresholdSSB is available, then:

[0215] 2> Select an SSB with SS-RSRP higher than rsrp-ThresholdSSB.

[0216] 1> Otherwise:

[0217] 2>Select Any SSB.

[0218] 1> If MSGA has not been transmitted:

[0219] 2> If random access preamble group B for 2-step RA is configured:

[0220] 3> if the potential MSGA payload size (UL data available for transmission plus MAC header and MAC CE if required) is greater than [ra-MsgASizeGroupA] and the path loss is less than PCMAX-[preambleReceivedTargetPower]-[msgA-DeltaPreamble]-[messagePowerOffsetGroupB] (of the serving cell performing the random access procedure); or

[0221] 3> If a random access procedure is initiated for the CCCH logical channel and the CCCH SDU size plus the MAC subheader is greater than [ra-MsgASizeGroupA], then:

[0222] 4> Select random access preamble group B.

[0223] 3> Otherwise:

[0224] 4> Select random access preamble group A.

[0225] 2> Otherwise:

[0226] 3> Select random access preamble group A.

[0227] 1> Otherwise (i.e., MSGA is retransmitted):

[0228] 2> Select the same random access preamble group as the random access preamble transmission attempt used for the first transmission corresponding to the MSGA.

[0229] Editor's Note: The above variable names and whether these variable names are the same as or different from the corresponding variables in the 4-step RACH are subject to further study.

[0230] 1> randomly select a random access preamble from the 2-step random access preambles associated with the selected SSB and the selected random access preamble group with equal probability;

[0231] 1> Set PREAMBLE_INDEX to the selected random access preamble;

[0232] 1> Determine the next available PRACH opportunity based on the PRACH opportunity corresponding to the selected SSB (the MAC entity shall randomly select a PRACH opportunity with equal probability among the consecutive PRACH opportunities allocated for 2-step random access corresponding to the selected SSB according to section 8.1 of TS38.213[6]; the MAC entity may consider the possible occurrence of measurement gaps when determining the next available PRACH opportunity corresponding to the selected SSB).

[0233] 1> Determine the UL grant of PUSCH resources for the MSGA associated with the selected preamble and PRACH opportunity and the associated HARQ information according to section x of TS 38.213 [6];

[0234] 1> passing the UL grant and associated HARQ information to the HARQ entity;

[0235] Editor's Note: Aspects regarding the selection of PUSCH resources and payload size of MSGA are for further study (pending RAN1 input). Therefore, the above sentence may be changed based on further discussions in RAN2 and RAN1.

[0236] 1>Execute the MSGA transfer process (see Section 5.1.3a).

[0237] NOTE: To determine if there is an SSB with SS-RSRP above rsrp-ThresholdSSB, the UE uses the latest unfiltered L1-RSRP measurement.

[0238] 5.1.3 Random Access Preamble Transmission

[0239] For each random access preamble, the MAC entity shall:

[0240] 1> If PREAMBLE_TRANSMISSION_COUNTER is greater than one; and

[0241] 1> If the notification to suspend the power ramp counter has not been received from the lower layer; and

[0242] 1> If the selected SSB or CSI-RS has not changed since the selection in the last random access preamble transmission, then:

[0243] 2>Increase PREAMBLE_POWER_RAMPING_COUNTER by 1.

[0244] 1> Select the value of DELTA_PREAMBLE according to clause 7.3;

[0245] 1>Set PREAMBLE_RECEIVED_TARGET_POWER to preambleReceivedTargetPower+DELTA_PREAMBLE+(PREAMBLE_POWER_RAMPING_COUNT ER-1)×PREAMBLE_POWER_RAMPING_STEP;

[0246] 1> Calculate the RA-RNTI associated with the PRACH opportunity in which the random access preamble is transmitted, except for the contention-free random access preamble used for beam failure recovery request;

[0247] 1> Instructs the physical layer to transmit the random access preamble using the selected PRACH opportunity, the corresponding RA-RNTI (if available), PREAMBLE_INDEX and PREAMBLE_RECEIVED_TARGET_POWER.

[0248] The RA-RNTI associated with the PRACH opportunity in which the random access preamble is transmitted is calculated as:

[0249] RA-RNTI=1+s_id+14×t_id+14×80×f_id+14×80×8×ul_carrier_id

[0250] where s_id is the index of the first OFDM symbol of the PRACH opportunity (0≤s_id<14), t_id is the index of the first time slot of the PRACH opportunity in the system frame (0≤t_id<80), where the subcarrier spacing determining t_id is based on the value of μ specified in clause 5.3.2 of TS38.211 [8], f_id is the index of the PRACH opportunity in the frequency domain (0≤f_id<8), and ul_carrier_id is the UL carrier used for random access preamble transmission (0 for NUL carrier and 1 for SUL carrier).

[0251] 5.1.3a MSGA Transfer

[0252] Editor's note: The handling of the counters in this section is now for further study. The description below is for information and will be updated based on input from RAN1 on how to handle the power ramp counters. Also, the calculation of RA-RNTI will also be updated based on further agreements (in RAN1 and RAN2 on whether to use a new RNTI, etc.), so this is also for information only.

[0253] The MAC entity shall, for each MSGA:

[0254] 1> If PREAMBLE_TRANSMISSION_COUNTER is greater than one; and

[0255] 1> If the notification to suspend the power ramp counter has not been received from the lower layer; and

[0256] 1> If the selected SSB has not changed since the selection in the last random access preamble transmission, then:

[0257] 2>Increase PREAMBLE_POWER_RAMPING_COUNTER by 1.

[0258] 1> Select the value of DELTA_PREAMBLE according to clause 7.3;

[0259] 1>Set PREAMBLE_RECEIVED_TARGET_POWER to preambleReceivedTargetPower+DELTA_PREAMBLE+(PREAMBLE_POWER_RAMPING_COU NTER-1)×PREAMBLE_POWER_RAMPING_STEP;

[0260] 1> If this is the first MSGA transmission within this random access procedure:

[0261] 2> If no transmission is performed for the CCCH logical channel, then:

[0262] 3> Indicate to the multiplexing and combining entity to include the C-RNTI MAC CE in subsequent uplink transmissions.

[0263] 2> Get the MAC PDU to transmit from the multiplexing and combining entity and store it in the MSGA buffer.

[0264] 1> Calculate the MSGB-RNTI associated with the PRACH opportunity in which the random access preamble is transmitted;

[0265] 1> Instruct the physical layer to use the selected PRACH opportunity and associated PUSCH resources, and use the corresponding RA-RNTI, MSGB-RNTI, PREAMBLE_INDEX, and PREAMBLE_RECEIVED_TARGET_POWER to transmit MSGA.

[0266] NOTE: The MSGA transmission includes the PRACH preamble and the transmission of the contents of the MSGA buffer in the PUSCH resource corresponding to the selected PRACH opportunity and PREAMBLE_INDEX (see TS 38.213 [6]).

[0267] The MSGB-RNTI associated with the PRACH opportunity in which the random access preamble is transmitted is calculated as:

[0268] Further research is needed

[0269] Editor's Note: The format and details of MSGB-RNTI are subject to further study.

[0270] 5.1.4 Random Access Response Reception

[0271] Once the random access preamble is transmitted, then regardless of whether measurement gaps may occur, the MAC entity shall:

[0272] 1> If the contention-free random access preamble for beam failure recovery request is transmitted by the MAC entity, then:

[0273] 2> Starting from the end of the random access preamble transmission, the ra-ResponseWindow configured in BeamFailureRecoveryConfig is started at the first PDCCH opportunity as specified in TS 38.213 [6];

[0274] 2> When ra-ResponseWindow is in operation, monitor the PDCCH transmission on the search space indicated by recoverySearchSpaceId of the SpCell identified by C-RNTI.

[0275] 1> Otherwise:

[0276] 2> Starting from the end of the random access preamble transmission, the ra-ResponseWindow configured in RACH-ConfigCommon starts at the first PDCCH opportunity as specified in TS 38.213 [6];

[0277] 2> When ra-ResponseWindow is in operation, monitor the PDCCH of the SpCell of the random access response identified by RA-RNTI.

[0278] 1> If a notification of a PDCCH transmission is received on the search space indicated by recoverySearchSpaceId is received from a lower layer on the serving cell transmitting the preamble; and

[0279] 1> if the PDCCH transmission is addressed to the C-RNTI; and

[0280] 1> If the contention-free random access preamble for beam failure recovery request is transmitted by the MAC entity, then:

[0281] 2> The random access procedure is considered to be completed successfully.

[0282] 1> Otherwise, if a downlink assignment has been received on the PDCCH for RA-RNTI and the received TB was successfully decoded:

[0283] 2> If the random access response contains a MAC sub-PDU with a backoff indicator, then:

[0284] 3> Using Table 7.2-1, set PREAMBLE_BACKOFF to the value of the BI field of the MAC sub-PDU multiplied by SCALING_FACTOR_BI.

[0285] 2> Otherwise:

[0286] 3> Set PREAMBLE_BACKOFF to 0ms.

[0287] 2> If the Random Access Response contains a MAC sub-PDU with a Random Access Preamble identifier corresponding to the transmitted PREAMBLE_INDEX (see clause 5.1.3), then:

[0288] 3> This random access response is considered to be received successfully.

[0289] 2> If the random access response is considered to be received successfully, then:

[0290] 3> If the Random Access Response contains a MAC sub-PDU with only RAPID, then:

[0291] 4> The random access procedure is considered to be successfully completed;

[0292] 4>Indicate to the upper layer that a response to the SI request has been received.

[0293] 3> Otherwise:

[0294] 4> Apply the following actions for the serving cell in which the random access preamble is transmitted:

[0295] 5> Process the received timing advance command (see clause 5.2);

[0296] 5> Indicate to the lower layer the preambleReceivedTargetPower and the amount of power ramp-up applied to the latest random access preamble transmission (i.e. (PREAMBLE_POWER_RAMPING_COUNTER-1)×PREAMBLE_POWER_RAMPING_STEP);

[0297] 5> If the serving cell used for the random access procedure is an SRS-only SCell, then:

[0298] 6> Ignore the received UL grant.

[0299] 5> Otherwise:

[0300] 6> Process the received UL grant value and indicate the value to the lower layers.

[0301] 4> If the MAC entity does not select a random access preamble among the contention-based random access preambles, then:

[0302] 5> The random access procedure is considered to be completed successfully.

[0303] 4> Otherwise:

[0304] 5> Set TEMPORARY_C-RNTI to the value received in the random access response;

[0305] 5> If this is the first successfully received Random Access Response within this Random Access procedure:

[0306] 6> If no transmission is performed for the CCCH logical channel, then:

[0307] 7> Indicate to the multiplexing and combining entity to include the C-RNTI MAC CE in subsequent uplink transmissions.

[0308] 6> Get the MAC PDU for transmission from the multiplexing and combining entity and store it in the Msg3 buffer.

[0309] NOTE: If within the random access procedure, the uplink grant provided in the random access response for the same group of contention based random access preamble has a different size than the first uplink grant allocated during the random access procedure, the UE behavior is not defined.

[0310] 1> if the ra-ResponseWindow configured in BeamFailureRecoveryConfig expires and if a PDCCH transmission on the search space indicated by recoverySearchSpaceId addressed to the C-RNTI has not been received on the serving cell that transmitted the preamble; or

[0311] 1> If the ra-ResponseWindow configured in RACH-ConfigCommon expires and if a Random Access Response containing a Random Access Preamble identifier matching the transmitted PREAMBLE_INDEX has not been received, then:

[0312] 2> The random access response reception is considered unsuccessful;

[0313] 2>Increment PREAMBLE_TRANSMISSION_COUNTER by 1;

[0314] 2>If PREAMBLE_TRANSMISSION_COUNTER=preambleTransMax+1:

[0315] 3> If the random access preamble is transmitted on the SpCell, then:

[0316] 4>Indicate random access problem to upper layer;

[0317] 4> If the random access procedure is triggered for an SI request, then:

[0318] 5> The random access procedure is considered to have not been completed successfully.

[0319] 3> Otherwise, if the random access preamble is transmitted on the SCell, then:

[0320] 4> The random access procedure is considered to have not been completed successfully.

[0321] 2> If the random access procedure is not completed, then:

[0322] 3> Select a random backoff time based on a uniform distribution between 0 and PREAMBLE_BACKOFF;

[0323] 3> If the criteria for selecting a contention-free random access resource (as defined in clause 5.1.2) are met during the back-off time, then:

[0324] 4>Perform the random access resource selection procedure (see clause 5.1.2);

[0325] 3> Otherwise:

[0326] 4> Perform the random access resource selection procedure after the backoff time (see clause 5.1.2).

[0327] Upon successful receipt of a Random Access Response containing a Random Access Preamble identifier matching the transmitted PREAMBLE_INDEX, the MAC entity may stop the ra-ResponseWindow (and therefore stop monitoring for Random Access Responses).

[0328] HARQ operation is not applicable for random access response reception.

[0329] 5.1.4a MSGB Reception and Contention Resolution for 2-Step Random Access

[0330] Editor's note: The handling of counters and other RAN1 related parameters for power control may be updated following other information from RAN1. The names of the variables are also for further study and may change later.

[0331] Once the MSGA is transmitted, regardless of the possibility of measurement gaps occurring, the MAC entity shall:

[0332] 1> Start msgB-ResponseWindow at the first PDCCH opportunity from the end of MSGA transmission, as specified in TS38.213 [6];

[0333] 1>While msgB-ResponseWindow is running, monitor the PDCCH of SpCell to see if there is a random access response identified by MSGB-RNTI;

[0334] 1> If the C-RNTI MAC CE is included in the MSGA:

[0335] 2>While msgB-ResponseWindow is running, monitor the PDCCH of SpCell to see if there is a random access response identified by C-RNTI;

[0336] 1> If a notification of receiving a PDCCH transmission of SpCell is received from a lower layer:

[0337] 2> If the C-RNTI MAC CE is included in the MSGA:

[0338] 3> If the random access procedure is initiated for beam failure recovery (as specified in clause 5.17) and the PDCCH transmission is addressed to the C-RNTI:

[0339] 4> This random access response is considered to be received successfully;

[0340] 4> This random access procedure is considered to be completed successfully.

[0341] Editor's note: The above text for BFR requires RAN2's approval. We do not agree to any new conditions for BFR. However, given that the intention is not to have a separate search space for BFR response reception, it seems that the companies are willing to leave the handling of any false positives to the network implementation. Therefore, the above text essentially implements the minimum required per Rel-15 BFR procedures.

[0342] 3> If the timeAlignmentTimer associated with PTAG is running:

[0343] 4> If the PDCCH transmission is addressed to the C-RNTI and contains an UL grant for a new transmission:

[0344] 5> This random access response is considered to be received successfully;

[0345] 5> This random access procedure is considered to be completed successfully.

[0346] 3> Otherwise:

[0347] 4> If a downlink assignment has been received on the PDCCH of the C-RNTI and the received TB is successfully decoded, then:

[0348] 5> If the MAC PDU contains the absolute timing advance command MAC CE:

[0349] 6> This random access response is considered to be received successfully;

[0350] 6> This random access procedure is considered to be completed successfully.

[0351] 2> If a downlink assignment has been received on the PDCCH for MSGB-RNTI and the received TB is successfully decoded, then:

[0352] 3> If the MSGB contains a MAC sub-PDU with a fallback indicator:

[0353] 4> Use Table 7.2-1 to set PREAMBLE_BACKOFF to the value of the BI field of the MAC sub-PDU.

[0354] 3> Otherwise:

[0355] 4> Set PREAMBLE_BACKOFF to 0ms.

[0356] 3> If the MSGB contains the fallbackRAR MAC sub-PDU; and

[0357] 3> If the random access preamble identifier in the MAC sub-PDU matches the transmitted PREAMBLE_INDEX (see subsection 5.1.3a):

[0358] 4> This random access response is considered to be received successfully;

[0359] 4> Apply the following actions to SpCell:

[0360] 5> Process the received timing advance command (see clause 5.2);

[0361] 5> Set TEMPORARY_C-RNTI to the value received in fallbackRAR;

[0362] 5> Indicate to the lower layer the preambleReceivedTargetPower and the amount of power ramp-up applied to the latest random access preamble transmission (i.e. (PREAMBLE_POWER_RAMPING_COUNTER-1)×PREAMBLE_POWER_RAMPING_STEP);

[0363] Editor's note: Whether MAC should provide the above power control related parameters to the physical layer is for further study.

[0364] 5> If the Msg3 buffer is empty:

[0365] 6> Get MAC PDU to transmit from MSGA buffer and store it in Msg3 buffer;

[0366] 5> Process the received UL grant value and indicate it to the lower layer and continue with Msg3 transmission;

[0367] NOTE: If within the 2-step random access procedure the uplink grant provided in the fallback RAR has a different size than the MSGA payload, the UE behavior is undefined.

[0368] 3> Otherwise if the MSGB contains a successRAR MAC sub-PDU; and

[0369] 3> If the CCCH SDU is included in the MSGA and the UE contention resolution identity in the MAC sub-PDU matches the CCCH SDU:

[0370] 4> If this random access procedure is initiated for an SI request, then:

[0371] 5>Indicate to the upper layer that a response to the SI request has been received.

[0372] 4> Otherwise:

[0373] 5> Set C-RNTI to the value received in successRAR;

[0374] 5> Apply the following actions to SpCell:

[0375] 6> Process the received timing advance command (see section 5.2);

[0376] 6> Indicate to the lower layer the preambleReceivedTargetPower and the amount of power ramping applied to the latest random access preamble transmission (i.e. (PREAMBLE_POWER_RAMPING_COUNTER-1)×PREAMBLE_POWER_RAMPING_STEP);

[0377] Editor's note: Whether MAC should provide the above power control related parameters to the physical layer is for further study.

[0378] 4> This random access response is considered to be received successfully;

[0379] 4> The random access procedure is considered to be successfully completed;

[0380] 4>Complete the disassembly and demultiplexing of MAC PDU.

[0381] 1> If msgB-ResponseWindow expires and random access response reception has not been considered successful based on the above description:

[0382] 2>Increment PREAMBLE_TRANSMISSION_COUNTER by 1;

[0383] 2>If PREAMBLE_TRANSMISSION_COUNTER=preambleTransMax+1:

[0384] 3>Indicate random access problems to upper layers;

[0385] 3> If the random access procedure is triggered for an SI request, then:

[0386] 4> This random access procedure is considered to have not been completed successfully.

[0387] 2> If the random access procedure is not completed, then:

[0388] 3> Select a random backoff time based on a uniform distribution between 0 and PREAMBLE_BACKOFF;

[0389] 3> If msgATransMax is configured and PREAMBLE_TRANSMISSION_COUNTER = msgATransMax + 1:

[0390] 4> Set RA_TYPE to 4-stepRA;

[0391] 4> If the Msg3 buffer is empty:

[0392] 5> Get MAC PDU to transmit from MSGA buffer and store it in Msg3 buffer;

[0393] 4> Clear the HARQ buffer in the MSGA buffer used to transmit MAC PDU.

[0394] 4> Perform the random access resource selection procedure as specified in Section 5.1.2.

[0395] 3> Otherwise:

[0396] 4> Perform the random access resource selection procedure for 2-step random access after the backoff time (see subsection 5.1.2a).

[0397] The MAC entity may stop the msgB-ResponseWindow once random access response reception is deemed successful

[0398] Editor's Note: Feedback for successful reception of MSGB on RAN1 input is for further study

[0399] 5.1.5 Contention Resolution

[0400] Once Msg3 is transmitted, the MAC entity shall:

[0401] 1> For each HARQ retransmission in the first symbol after the end of Msg3 transmission, start ra-ContentionResolutionTimer and restart ra-ContentionResolutionTimer;

[0402] 1> Regardless of whether measurement gaps may occur, PDCCH is monitored when ra-ContentionResolutionTimer is running;

[0403] 1> If a notification of receiving a PDCCH transmission of SpCell is received from a lower layer:

[0404] 2> If C-RNTI MAC CE is included in Msg3:

[0405] 3> if the random access procedure is initiated for beam failure recovery (as specified in clause 5.17) and the PDCCH transmission is addressed to the C-RNTI; or

[0406] 3> If the random access procedure is initiated by a PDCCH command and the PDCCH transmission is addressed to the C-RNTI;

[0407] or

[0408] 3> If the random access procedure is initiated by the MAC sublayer itself or by the RRC sublayer and the PDCCH transmission is addressed to the C-RNTI and contains an UL grant for a new transmission:

[0409] 4> The contention is considered to be resolved successfully;

[0410] 4>Stop ra-ContentionResolutionTimer;

[0411] 4> discard TEMPORARY_C-RNTI;

[0412] 4> This random access procedure is considered to be completed successfully.

[0413] 2> Otherwise, if the CCCH SDU is contained in Msg3 and the PDCCH transmission is addressed to its TEMPORARY_C-RNTI, then:

[0414] 3> If the MAC PDU is decoded successfully, then:

[0415] 4>Stop ra-ContentionResolutionTimer;

[0416] 4> If the MAC PDU contains the UE contention resolution identity MAC CE; and

[0417] 4> If the UE contention resolution indicator in the MAC CE matches the CCCH SDU transmitted in Msg3, then:

[0418] 5> The contention resolution is considered successful and the decomposition and demultiplexing of MAC PDU is terminated;

[0419] 5> If this random access procedure is initiated for an SI request, then:

[0420] 6>Indicate to the upper layer that a response to the SI request has been received.

[0421] 5> Otherwise:

[0422] 6> Set C-RNTI to the value of TEMPORARY_C-RNTI;

[0423] 5> discard TEMPORARY_C-RNTI;

[0424] 5> This random access procedure is considered to be completed successfully.

[0425] 4> Otherwise:

[0426] 5> discard TEMPORARY_C-RNTI;

[0427] 5> Consider this contention resolution unsuccessful and discard the successfully decoded MAC PDU.

[0428] 1> If ra-ContentionResolutionTimer expires:

[0429] 2> discard TEMPORARY_C-RNTI;

[0430] 2>Consider contention resolution unsuccessful.

[0431] 1> If contention resolution is deemed unsuccessful, then:

[0432] 2> Clear the HARQ buffer area in the Msg3 buffer used to transmit MAC PDU;

[0433] 2>Increment PREAMBLE_TRANSMISSION_COUNTER by 1;

[0434] 2>If PREAMBLE_TRANSMISSION_COUNTER=preambleTransMax+1:

[0435] Editor's Note: The above conditions apply to both the fallback case of 4-step RACH and 2-step RACH. This needs to be checked after the final decision on the disposition of the counter.

[0436] 3>Indicate random access problems to upper layers.

[0437] 3> If the random access procedure is triggered for an SI request, then:

[0438] 4> The random access procedure is considered to have not been completed successfully.

[0439] 2> If the random access procedure is not completed, then:

[0440] 3> Select a random backoff time based on a uniform distribution between 0 and PREAMBLE_BACKOFF;

[0441] 3> If the criteria for selecting a contention-free random access resource (as defined in clause 5.1.2) are met during the back-off time, then:

[0442] 4>Perform the random access resource selection procedure (see clause 5.1.2);

[0443] 3> Otherwise, if RA_TYPE is set to 2-stepRA:

[0444] 4> If msgATransMax is configured and PREAMBLE_TRANSMISSION_COUNTER = msgATransMax + 1:

[0445] 5> Set RA_TYPE to 4-stepRA;

[0446] 5> Clear the HARQ buffer in the MSGA buffer used to transmit MAC PDU.

[0447] 5> Perform random access resource selection as specified in subsection 5.1.2.

[0448] 4> Otherwise:

[0449] 5> Perform random access resource selection for the 2-step random access procedure after the backoff time (see clause 5.1.2a).

[0450] 3> Otherwise:

[0451] 4> Perform random access resource selection as specified in subsection 5.1.2 after the backoff time.

[0452] In LTE, the random access (RA) procedure with early data transfer (EDT) in the RRC_IDLE state is specified in 3GPP TS 36.321 as follows:

[0453] 5.1.4 Random Access Response Reception

[0454] Upon transmission of a random access preamble and regardless of the possible occurrence of measurement gaps or sidelink discovery gaps for transmission or sidelink discovery gaps for reception, and regardless of the prioritization of V2X sidelink communications as described in clause 5.14.1.2.2, the MAC entity shall monitor the PDCCH of the SpCell for a random access response identified by the RA-RNTI defined below in a RA response window starting at the subframe containing the end of the preamble transmission as specified in TS 36.211 [7] plus three subframes and having a length of ra-ResponseWindowSize. If the UE is a BL UE or a UE in enhanced coverage, the RA response window starts at the subframe containing the end of the last preamble repetition plus three subframes and has a length of ra-ResponseWindowSize for the corresponding enhanced coverage level. If the UE is a NB-IoT UE, the RA response window starts at the subframe containing the end of the last preamble repetition plus X subframes and has a length of ra-ResponseWindowSize for the corresponding enhanced coverage layer, where the value X is determined from Table 5.1.4-1 based on the preamble format used and the number of NPRACH repetitions.

[0455] [Table 5.1.4-1 of 3GPP TS 36.321 V15.8.0 entitled "Subframes between preamble transmission and RA response window in NB-IoT" is reproduced as Figure 5 ]

[0456] The RA-RNTI associated with the PRACH in which the random access preamble is transmitted is calculated as:

[0457] RA-RNTI=1+t_id+10*f_id

[0458] Where t_id is the index of the first subframe of the specified PRACH (0≤t_id<10), and f_id is the index of the specified PRACH within the subframe, in ascending order in the frequency domain (0≤f_id<6) except for NB-IoT UEs, BL UEs, or UEs in enhanced coverage. If the PRACH resource is on a TDD carrier, then f_id is set to f RA , where fRA is defined in clause 5.7.1 of TS 36.211 [7].

[0459] For BL UEs and UEs in enhanced coverage, the RA-RNTI associated with the PRACH in which the random access preamble is transmitted is calculated as:

[0460] RA-RNTI=1+t_id+10*f_id+60*(SFN_id mod(Wmax / 10))

[0461] Where t_id is the index of the first subframe of the specified PRACH (0≤t_id<10), f_id is the index of the specified PRACH within the subframe, in ascending order in the frequency domain (0≤f_id<6), SFN_id is the index of the first radio frame of the specified PRACH, and Wmax is 400, which is the maximum possible RAR window size in the subframe for BL UEs or UEs in enhanced coverage. If the PRACH resource is on a TDD carrier, then f_id is set to f RA , where f RA Defined in clause 5.7.1 of TS 36.211 [7].

[0462] For NB-IoT UEs, the RA-RNTI associated with the PRACH in which the random access preamble is transmitted is calculated as:

[0463] RA-RNTI=1+floor(SFN_id / 4)+256*carrier_id

[0464] Where SFN_id is the index of the first radio frame of the specified PRACH, and carrier_id is the index of the UL carrier associated with the specified PRACH. The carrier_id of the anchor carrier is 0.

[0465] For a NB-IoT UE operating in TDD mode, the RA-RNTI associated with the PRACH in which the random access preamble is transmitted is calculated as:

[0466] RA-RNTI=1+floor(SFN_id / 4)+256*(H-SFN mod 2)

[0467] Where SFN_id is the index of the first radio frame specifying the PRACH and H-SFN is the index of the first superframe specifying the PRACH. The PDCCH transmission and the PRACH resources are on the same carrier.

[0468] After successfully receiving a random access response containing a random access preamble identifier that matches the transmitted random access preamble, the MAC entity may stop monitoring the random access response.

[0469] - If a downlink assignment for this TTI has been received on the PDCCH for the RA-RNTI and the received TB was successfully decoded, the MAC entity shall, regardless of the possible occurrence of measurement gaps or sidelink discovery gaps for transmission or sidelink discovery gaps for reception and regardless of the prioritization of V2X sidelink communications described in clause 5.14.1.2.2:

[0470] - If the Random Access Response contains a Backoff Indicator subheader, then:

[0471] - Except for NB-IoT where the values ​​of Table 7.2-2 are used, the fallback parameter values ​​are set as indicated by the BI field of the Fallback Indicator subheader and Table 7.2-1.

[0472] - Otherwise, set the backoff parameter value to 0ms.

[0473] - If the Random Access Response contains a Random Access Preamble Identifier corresponding to the transmitted Random Access Preamble (see subsection 5.1.3), the MAC entity shall:

[0474] - The random access response is considered to be received successfully and the following actions are applied to the serving cell that transmitted the random access preamble:

[0475] - Processing of received timing advance commands (see clause 5.2);

[0476] - Indicates to lower layers the preambleInitialReceivedTargetPower and the amount of power ramping to apply to the latest preamble transmission (i.e., PREAMBLE_TRANSMISSION_COUNTER-1)*powerRampingStep);

[0477] - If the SCell is configured with ul-Configuration-r14, ignore the received UL grant, otherwise process the received UL grant value and indicate it to the lower layer;

[0478] - If, except for NB-IoT, ra-PreambleIndex is explicitly sent and it is not 000000 (i.e. not selected by MAC), then:

[0479] - The random access procedure is considered to have been completed successfully.

[0480] - Otherwise, if the UE is a NB-IoT UE, ra-PreambleIndex is explicitly signaled and is not 000000 (i.e. not selected by the MAC), and ra-CFRA-Config is configured, then:

[0481] - The random access procedure is considered to have been completed successfully.

[0482] - The UL grant provided in the Random Access Response message is only valid for the configured carrier (ie the UL carrier used before this random access procedure).

[0483] -otherwise:

[0484] - If the random access preamble is selected by the MAC entity; or

[0485] - If the UE is a NB-IoT UE, ra-PreambleIndex is explicitly signalled and is not 000000, and ra-CFRA-Config is not configured, then:

[0486] - no later than the time corresponding to the first transmission of the UL grant provided in the random access response message, setting the temporary C-RNTI to the value received in the random access response message;

[0487] - If a random access preamble associated with EDT has been transmitted and the UL grant provided in the random access response message is not for EDT, then:

[0488] - Indicate to the upper layer that EDT is cancelled because UL grant is not used for EDT;

[0489] - For CP-EDT, clear the Msg3 buffer.

[0490] -For UP-EDT, the MAC PDU in the Msg3 buffer is updated according to the uplink grant received in the random access response.

[0491] - If a Random Access Preamble associated with EDT is transmitted, a UL Grant is received in a Random Access Response for EDT, and there is a MAC PDU in the Msg3 buffer, then:

[0492] - If the TB size does not match the size of the MAC PDU in the Msg3 buffer according to edt-SmallTBS-Enabled and as described in clauses 8.6.2 and 16.3.3 of TS 36.213 [2], then:

[0493] -MAC entity will update the MAC PDU in Msg3 buffer according to the TB size.

[0494] - if this is the first successfully received Random Access Response within this Random Access procedure; or

[0495] - If CP-EDT is cancelled because the UL grant provided in the Random Access Response message is not for EDT, then:

[0496] - if the transmission is not for the CCCH logical channel, instruct the multiplexing and combining entity to include the C-RNTI MAC control element in the subsequent uplink transmission;

[0497] - Get the MAC PDU for transmission from the "Multiplexing and Combining" entity and store it in the Msg3 buffer.

[0498] NOTE 1: When uplink transmission is required, e.g. for contention resolution, the eNB SHOULD NOT provide a grant smaller than 56 bits (or 88 bits for NB-IoT) in the Random Access Response.

[0499] NOTE 2: If within the random access procedure, the uplink grant provided in the random access response for the same group of random access preambles has a different size than the first uplink grant allocated during the random access procedure, the UE behavior is not defined (except for EDT).

[0500] If there is no random access response or no PDCCH scheduled random access response is received within the RA response window for a NB-IoT UE, BL UE or UE in enhanced coverage for mode B operation, or if all received random access responses do not contain a random access preamble identifier corresponding to the transmitted random access preamble, then the random access response reception is deemed unsuccessful and the MAC entity shall:

[0501] - If a power boost suspend notification has not been received from the lower layer, then:

[0502] -Increment PREAMBLE_TRANSMISSION_COUNTER by 1;

[0503] - If the UE is a NB-IoT UE, a BL UE or a UE in enhanced coverage:

[0504] - If PREAMBLE_TRANSMISSION_COUNTER = preambleTransMax - CE + 1, then:

[0505] - If a random access preamble is transmitted on the SpCell, then:

[0506] - indicate random access problems to upper layers;

[0507] -If NB-IoT:

[0508] - The random access procedure is considered to have not been successfully completed;

[0509] -otherwise:

[0510] -If PREAMBLE_TRANSMISSION_COUNTER=preambleTransMax+1:

[0511] - If a random access preamble is transmitted on the SpCell, then:

[0512] - Indicate random access issues to upper layers;

[0513] - If the random access preamble is transmitted on the SCell, then:

[0514] - The random access procedure is considered to have not been completed successfully.

[0515] - If the random access preamble is selected by the MAC in this random access procedure, then:

[0516] - Based on the backoff parameter, a random backoff time is selected according to a consistent distribution between 0 and the backoff parameter value;

[0517] - Delaying subsequent random access transmissions by the backoff time;

[0518] - Otherwise if the SCell in which the random access preamble is transmitted is configured with ul-Configuration-r14:

[0519] - Delay subsequent random access transmissions until the random access procedure is initiated by a PDCCH command with the same ra-PreambleIndex and ra-PRACH-MaskIndex;

[0520] - If the UE is a NB-IoT UE, a BL UE or a UE in enhanced coverage:

[0521] -Increment PREAMBLE_TRANSMISSION_COUNTER_CE by one;

[0522] - If PREAMBLE_TRANSMISSION_COUNTER_CE = maxNumPreambleAttemptCE + 1 for the corresponding enhanced coverage layer:

[0523] - reset PREAMBLE_TRANSMISSION_COUNTER_CE;

[0524] - If supported by the serving cell and the UE, then considered to be in the next enhanced coverage layer, otherwise remain in the current enhanced coverage layer;

[0525] - If the UE is a NB-IoT UE:

[0526] - If the random access procedure is initiated by a PDCCH order, then:

[0527] - Selecting a PRACH resource from the list of UL carriers, providing PRACH resources for the selected enhanced coverage layer with a carrier index equal to ((carrier indication from the PDCCH command) modulo (number of PRACH resources in the selected enhanced coverage));

[0528] - The selected PRACH resources are considered to be explicitly signaled;

[0529] - Proceed to the selection of random access resources (see clause 5.1.2).

[0530] The work item for small data transmission in RRC_INACTIVE state in NR was approved in NR plenary #86 meeting. The description of the work item is specified in 3GPP RP-193252 as follows:

[0531] 3 Adjustment

[0532] NR supports the RRC_INACTIVE state, and UEs with infrequent (periodic and / or aperiodic) data transfers are generally maintained by the network in the RRC_INACTIVE state. Until Rel-16, the RRC_INACTIVE state did not support data transfers. Therefore, the UE must recover the connection (i.e., move to the RRC_CONNECTED state) for any DL (MT) and UL (MO) data. Each data transfer establishes a connection and then releases to the INACTIVE state, but the data packets are small and rare. This results in unnecessary power consumption and signaling overhead.

[0533] Specific examples of smaller and infrequent data traffic include the following use cases:

[0534] -Smartphone App:

[0535] ○Instant messaging service traffic (WhatsApp, QQ, WeChat, etc.)

[0536] ○ Heartbeat / keep-alive traffic from IM / email clients and other applications

[0537] ○Push notifications from various apps

[0538] - Non-smartphone applications:

[0539] ○Traffic from wearable devices (periodic positioning information, etc.)

[0540] ○ Sensors (industrial wireless sensor networks transmit temperature, pressure readings periodically or in an event-triggered manner, etc.)

[0541] ○Smart meters and smart meter networks that send periodic meter readings

[0542] As mentioned in 3GPP TS 22.891, the NR system will:

[0543] - Efficient and flexible for short data bursts with low throughput

[0544] - Support efficient signaling mechanisms (e.g., signaling is smaller than payload)

[0545] - Overall reduction in signaling overhead

[0546] The signaling overhead of small packets from UEs in INACTIVE state is a common problem and will become a critical issue with more UEs in NR, not only for network performance and efficiency, but also for UE battery performance. In general, any device with intermittent small packets in INACTIVE state will benefit from enabling small data transmission in INACTIVE.

[0547] The key enablers for small data transmission in NR, namely, INACTIVE state, 2-step, 4-step RACH and configured grant type 1 have been specified as part of Rel-15 and Rel-16. Hence, this work builds on these building blocks to enable small data transmission in NR in INACTIVE state.

[0548] 4. Goals

[0549] 4.1 Objectives of SI or core WI or test WI

[0550] This work item enables small data transfer in the RRC_INACTIVE state as follows:

[0551] -For RRC_INACTIVE state:

[0552] ○ UL small data transmission based on RACH scheme (i.e., 2-step and 4-step RACH):

[0553] ■ Generic procedure to enable UP data transfer of small packets from the INACTIVE state (e.g. using MSGA or MSG3) [RAN2]

[0554] ■ Enable flexible payload sizes for MSGA and MSG3 that are larger than the current Rel-16 CCCH message size that may be used for INACTIVE state to support UP data transfer in UL (actual payload size is up to network configuration) [RAN2]

[0555] ■ Context acquisition and data forwarding in INACTIVE state for RACH based solutions (with or without anchor relocation) [RAN2, RAN3]

[0556] NOTE 1: The security aspects of the above solution should be checked using SA3

[0557] o Transmission of UL data on pre-configured PUSCH resources (i.e., reusing configured grant type 1) - when TA is valid

[0558] ■General procedure for small data transfer from INACTIVE state via configured grant type 1 [RAN2]

[0559] ■ Configuration of configured grant type 1 resources for small data transfer in UL in INACTIVE state [RAN2]

[0560] No new RRC states should be introduced in this WID. Small data transmission in UL, subsequent transmission of small data in UL and DL, and state transition decisions should be under network control.

[0561] The focus of WID should be on licensed operators and these solutions can be repurposed for NR-U if applicable.

[0562] NOTE 2: Any relevant specification work required in RAN1 to support the above set of objectives should be initiated by RAN2 via LS.

[0563] The UE transmits data in the RRC_CONNECTED state and may transition to the RRC_INACTIVE state to save power when there is no data to transfer. When data arrives while the UE is in the RRC_INACTIVE state, the UE may resume the radio resource control (RRC) connection and transition from the RRC_INACTIVE state to the RRC_CONNECTED state. However, the RRC connection establishment and subsequent release to the RRC_INACTIVE state for each small and infrequent data results in power consumption and signaling overhead. Therefore, small data transmission in the RRC_INACTIVE state without establishing a connection (as discussed in 3GPP RP-193252) should be studied.

[0564] In order to achieve UL data transmission in the RRC_INACTIVE state, a method based on a random access channel (RACH) and / or a method based on pre-configured physical uplink shared channel (PUSCH) resources may be considered. The RACH-based method may include a 2-step random access (RA) and / or a 4-step RA. When some UL data (e.g., small data) is available for transmission when the UE is in the RRC_INACTIVE state, the UE may initiate an RRC recovery procedure in the RRC_INACTIVE state, which triggers an RA procedure for small data transmission.

[0565] For 2-step RA (e.g., with small data), the UE may perform random access resource selection and then send message A (MSGA) containing the RA preamble and PUSCH payload. The PUSCH payload may contain an RRC recovery request and UL data (e.g., small data). In response to receiving MSGA, the network (NW) may send message B (MSGB) to notify the UE that the RA procedure is completed, and may transmit an RRC release message to keep the UE in the RRC_INACTIVE state. If the NW receives the RA preamble but fails to receive the PUSCH payload, the NW may send MSGB to inform the UE to fall back to Msg3. The UE may transmit Msg3 using the UL grant in MSGB. Msg3 may contain an RRC recovery request and UL data (e.g., small data). In response to receiving Msg3, the NW may send Msg4 to notify the UE that the RA procedure is completed, and may transmit an RRC release message to keep the UE in the RRC_INACTIVE state.

[0566] For a 4-step RA (e.g., with small data), the UE may perform random access resource selection and then send a RA preamble. The NW may receive the RA preamble and send a RAR. In response to receiving the RAR, the UE may use the UL grant in the RAR to transmit a Msg3 that may contain an RRC recovery request and UL data (e.g., small data). In response to receiving Msg3, the NW may send a Msg4 to notify the UE that the RA procedure is completed, and transmit an RRC release message to keep the UE in the RRC_INACTIVE state.

[0567] For RACH-based methods (e.g., 2-step RA, 4-step RA), the goal is to achieve a flexible payload size that is larger than the Rel-16 CCCH message size to support small data transmission (as discussed in 3GPP RP-193252). It can be expected that the data size of MSGA (or Msg3) with small data will be larger than the case without small data. It can also be expected that MSGA transmission (or Msg3 transmission) with small data will be more difficult under the same radio conditions compared to MSGA transmission (or Msg3 transmission) without small data. After the initiation of small data transmission (e.g., via 2-step RA, 4-step RA or pre-configured PUSCH resources), radio conditions may change from time to time during the procedure of small data transmission. If the radio conditions become bad or are bad, so that the UE cannot successfully transmit small data in the RRC_INACTIVE state (e.g., via MSGA, Msg3 or pre-configured PUSCH resources), it may be better to handle the failure quickly rather than repeat the transmission failure.

[0568] To solve the problem, if the UE detects that it may be difficult to successfully deliver UL data (e.g., small data) and / or the current procedure of continuing small data transmission is not suitable (e.g., due to poor radio conditions, resource congestion, etc.), then the UE can perform a fallback action (e.g., it can save UE power, alleviate the current problematic situation and / or change to another procedure that is more likely to succeed). The UE can perform one or more of the following actions under one or more of the following conditions. Different alternatives can be considered in combination or individually.

[0569] The actions may include one or more of the following techniques:

[0570] - Stop the ongoing process of small data transfer

[0571] The UE may stop (terminate, cancel or suspend) an ongoing procedure for small data transmission. The procedure may be a 2-step RA. The procedure may be a 4-step RA. The procedure may be an UL transmission using pre-configured PUSCH resources.

[0572] The UE may clear the HARQ buffer used for transmission of small data (or UL data). The UE may initiate another random access procedure. The UE may indicate a problem. The UE may reset the Media Access Control (MAC).

[0573] - Switch to transfer without user data, e.g. recovery program

[0574] The UE may switch from a procedure for small data transmission (e.g., 2-step RA, 4-step RA, preconfigured PUSCH transmission, procedure containing UL data) to a recovery procedure that does not carry user data (or UL data). The type of transmission may remain the same during the switch (e.g., from 2-step RA with small data transmission to 2-step RA for recovery without small data, from 4-step RA with small data transmission to 4-step RA for recovery without small data). The type of transmission may change during the switch (e.g., from 2-step RA to 4-step RA, from preconfigured PUSCH transmission to 2-step RA, from preconfigured PUSCH transmission to 4-step RA). The type of transmission may include 2-step RA, 4-step RA and / or preconfigured PUSCH transmission.

[0575] The UE may initiate a recovery procedure to recover the RRC connection. The recovery procedure may not carry user data (e.g., small data). User data (e.g., small data) may be transmitted after the connection is recovered (e.g., after the UE enters the connected mode).

[0576] During the recovery procedure, the UE may transmit a recovery request. The recovery request may be an RRC message. The UE may transmit the recovery request using a 2-step RA procedure. The UE may transmit the recovery request using a 4-step RA procedure.

[0577] The UE may instruct the multiplexing and combining entity to reconstruct the data in the MSGA (or Msg3) buffer to exclude small data. The UE may stop the RA procedure and / or re-initiate the RA procedure to recover.

[0578] As discussed in 3GPP TS 36.321, if the UL grant received in the RAR provided by the NW is not for EDT, the UE cancels EDT. In the present invention, the UE can cancel the small data transmission when the radio condition measured by the UE is below a threshold. The UE can cancel the small data transmission at different timings (e.g., before MSGA or Msg3 transmission, after failing to receive MSGB or Msg4) without an indication from the NW. The UE can then transmit small data in the RRC_CONNECTED state with more flexibility and effectiveness.

[0579] - Switch the type of small data transmission or random access procedure

[0580] The UE may transmit small data using different types of transmissions. The UE may switch from a first type of transmission to a second type of transmission. The type of transmission (e.g., first type of transmission, second type of transmission) may include 2-step RA, 4-step RA, and / or pre-configured PUSCH transmission. The UE may switch from a 2-step RA procedure to a 4-step RA procedure. The UE may switch from a 2-step RA with small data transmission to a 4-step RA with small data transmission. The UE may switch from a pre-configured PUSCH transmission to a 2-step RA with small data transmission. The UE may switch from a pre-configured PUSCH transmission to a 4-step RA with small data transmission.

[0581] The switching may be one-shot, for example, switching back to the first type of transmission after switching to the second type of transmission and transmission failure.For example, if the UE fails to receive Msg4 in response to Msg3 during a 4-step RA, the UE may fall back and transmit MSGA.

[0582] The switch may be permanent, for example, retrying the second type of transmission after switching to the second type of transmission and failing.For example, if the UE fails to receive Msg4 in response to Msg3 during a 4-step RA, the UE may back off and transmit the RA preamble (Msg1).

[0583] - Back

[0584] The UE may perform a backoff during the ongoing procedure. For example, the UE selects a random backoff time to wait, and / or returns to the random access resource selection procedure after the backoff. The UE may reselect the RA preamble and PRACH resources, and / or the beam used to transmit the preamble.

[0585] As discussed in 3GPP TS 38.321 with operating CR R2-1914798, the UE backs off when it fails to receive Msg3 or MSGB. In the present invention, the UE can back off before transmitting the MSGA when the UE expects that the MSGA transmission will fail. The UE can reselect RA resources without attempting to transmit a failed MSGA.

[0586] - wait

[0587] For example, the UE waits for a certain period of time, for example, waiting for radio conditions to become better. If the UE spends too much time waiting, the UE may resume, back off and / or continue the RA procedure.

[0588] Instead of transmitting MSGA in bad radio conditions and then re-selecting RA resources, the UE may suspend the RA procedure for a while. MSGA may have a chance to be transmitted in better radio conditions.

[0589] Conditions can include one or more of the following:

[0590] - Radio conditions become bad or poor, e.g., become below a threshold

[0591] If the UE detects that the current radio conditions are not good enough, the UE may take action. The radio conditions may be below a configured threshold. The radio conditions may be a differential lower than the radio conditions that initiated the procedure.

[0592] For example, before MSGA transmission (with small data), the UE may measure and / or derive current radio conditions and compare them with a threshold. If the radio conditions are above the threshold, the UE transmits MSGA with small data. If the radio conditions are below the threshold, the UE may cancel the small data transmission, may fall back to random access resource selection, may wait for a certain time period, and / or may continue the RA procedure.

[0593] For example, before Msg3 transmission (with small data), the UE may measure and / or derive the current radio conditions and compare them with a threshold. If the radio conditions are above the threshold, the UE transmits Msg3 with small data. If the radio conditions are below the threshold, the UE cancels the small data transmission.

[0594] - Failed to receive MSGB in response to small data transfer

[0595] If the UE fails to receive the MSGB in response to the MSGA containing small data, the UE may take action. If the UE does not successfully receive the MSGB during a certain time period (e.g., response window) after the MSGA transmission, the UE may consider that the MSGB reception has failed. If the UE does not successfully receive the MSGB (or cannot continue the current procedure) during a certain time period (e.g., response window) after a certain number of preamble transmissions (e.g., preambleTransMax), the UE may consider that the MSGB reception has failed.

[0596] - Failed to receive Msg4 in response to small data transfer

[0597] If the UE fails to receive Msg4 in response to Msg3 containing small data, the UE can take action. If the UE does not successfully receive Msg4 during a certain time period after Msg3 transmission (for example, when the contention resolution timer is running), the UE can consider that Msg4 reception has failed. If the UE does not successfully receive Msg4 during a certain time period after a certain number of preamble code transmissions (for example, preambleTransMax) (for example, when the contention resolution timer is running) (or cannot continue the current procedure such contention resolution failure), the UE can consider that Msg4 reception has failed.

[0598] - Receiving network signaling

[0599] The UE may take action in response to receipt of network signaling. The details are specified in the following description.

[0600] To solve the problem, if the network node (or NW) detects that it may be difficult to continue the current procedure of small data transmission (for example, due to poor radio conditions, resource congestion, etc.), the network node can transmit signaling to the UE. The signaling can trigger the UE to perform a fallback action. In response to the reception of the signaling, the UE can take one or more of the following actions. Different signaling can be used to instruct (or trigger) the UE to perform different actions. For example, the first signaling is used to instruct the UE to perform a first action. And the second signaling is used to instruct the UE to perform a second action. The signaling can be used to indicate which action the UE is to perform (for example, the first action or the second action).

[0601] The (fallback) actions (e.g., the first action and / or the second action) may include one or more of the following techniques:

[0602] - Switching to 4-step RA with small data transfer

[0603] The NW may instruct the UE to switch to a 4-step RA with or without UL grant. The UE may have an ongoing 2-step RA procedure with small data transmission. The UE may switch the RA type, for example, from 2-step to 4-step. The UE may perform a 4-step RA procedure. The 4-step RA procedure may have small data transmission. The UE may transmit Msg3 with small data using the UL grant provided by the NW. The switch may be a one-shot, for example, switching back to the first type of transmission after switching to the second type of transmission and the transmission fails.

[0604] For example, if the UE fails to receive Msg4 in response to Msg3 during a 4-step RA, the UE may fall back and transmit MSGA. The switch may be permanent, e.g., retrying the second type of transmission after switching to the second type of transmission and failing to transmit. For example, if the UE fails to receive Msg4 in response to Msg3 during a 4-step RA, the UE may fall back and transmit the RA preamble (Msg1).

[0605] As described in CN110583093A (titled "Random Access Method, Reception Method, Apparatus, Device and Medium"), when the SS / PBCH block (SSB) meets the target condition, for example, the signal quality of all SSBs does not reach the measurement threshold, the UE can switch from 2-step RA to 4-step RA. In the present invention, when the radio conditions are not qualified for the UE to transmit small data, the NW can switch from 2-step RA to 4-step RA. The measurement of the NW is based on a UL reference (e.g., a sounding reference signal) that can more appropriately represent the UL radio conditions. And the NW can fully know the radio conditions of the UE.

[0606] - Switch to 2-step RA without small data transfer

[0607] For example, the NW instructs the UE to cancel a small data transmission with or without UL grant. The UE cancels the small data transmission. The UE may instruct the multiplexing and combining entity to reconstruct the data in the MSGA buffer to exclude the small data. The UE may transmit an MSGA without small data using the UL grant provided by the NW. The UE may fall back to the random access resource selection procedure and transmit a RA preamble. The UE may stop the RA procedure and instruct the upper layers to re-initiate the 2-step RA procedure to recover. The UE may then transmit small data in the RRC_CONNECTED state with more robustness.

[0608] - 4 Steps to Switch to RA without Small Data Transfer

[0609] For example, the NW instructs the UE to switch to a 4-step RA and / or cancel small data transmission with or without UL grant. The UE switches the RA type and / or cancels small data transmission. The UE may instruct the multiplexing and combining entity to reconstruct data in the MSGA buffer to exclude small data. The UE may transmit Msg3 without small data using the UL grant provided by the NW. The UE may fall back to the random access resource selection procedure and transmit the RA preamble. The UE may stop the RA procedure and instruct the upper layer to re-initiate the 4-step RA procedure to recover. The switch may be single-trigger, for example, switching back to the first type of transmission after switching to the second type of transmission and the transmission fails. For example, if the UE fails to receive Msg4 in response to Msg3 during the 4-step RA, the UE may fall back and transmit MSGA.

[0610] The switch may be permanent, for example, retrying the second type of transmission after switching to the second type of transmission and failing.For example, if the UE fails to receive Msg4 in response to Msg3 during a 4-step RA, the UE may back off and transmit the RA preamble (Msg1).

[0611] If the NW instructs the UE to switch from 2-step RA with small data to 4-step RA without small data, small data can be transmitted in RRC_CONNECTED state after recovery. When the UE is in extremely bad radio conditions, small data transmission can be completed earlier and with more robustness.

[0612] - Extended response window (e.g., msgB-ResponseWindow, ra-ResponseWindow)

[0613] For example, the NW instructs the UE to extend the response window, for example, to wait for the radio conditions to improve. The UE extends the msgB-ResponseWindow or ra-ResponseWindow and waits for the MSG B or Msg3. If the waiting time is too long, the NW may instruct the UE to switch to 4-step RA, resume, and / or continue the RA procedure.

[0614] The NW can suspend the RA procedure for a while. Instead of the UE transmitting Msg3 (with small data) in bad radio conditions and then re-doing RA resource selection, the small data can have a chance to be successfully transmitted in better radio conditions.

[0615] - recover

[0616] For example, the NW instructs the UE to cancel the small data transmission. The UE cancels the small data transmission. The UE can instruct the multiplexing and combining entity to reconstruct the data in the MSGA (or Msg3) buffer to exclude the small data. The UE can stop the RA procedure and instruct the upper layer to re-initiate the RA procedure to recover.

[0617] As discussed in 3GPP TS 36.321, if the NW transmits a RAR with an UL grant not for EDT, the UE cancels EDT. In the present invention, when Msg3 transmission fails and the radio conditions measured by the NW are below a threshold, the NW can instruct the UE to cancel the small data transmission. When failure does occur, the NW can instruct the UE to cancel the small data transmission.

[0618] Signaling can be or contain one or more of the following constructs:

[0619] -( 2 Steps to RA Instructions can be included in the fallbackRAR for example. Instructions can also be included in the subheader. Instructions can be included in other payloads.

[0620] -( 4 Steps to RA of) RAR - For example, the indication is included in a subheader. The indication may also be included in a reserved bit of the RAR payload. The indication may be included in a UL grant of the RAR payload.

[0621] - In response to a message with small data, MSGA and / or Msg3

[0622] - Downlink Control Information (DCI)

[0623] -MAC Control Element (CE)

[0624] -RRC Message

[0625] The network may determine to transmit signaling to the UE due to the following techniques:

[0626] - Radio conditions become poor detection

[0627] For example, before MSGB transmission with UL grant for small data (e.g., fallbackRAR), the NW may measure and / or derive current radio conditions. If the radio conditions are qualified for the UE to transmit small data, the NW may transmit the MSGB. If the radio conditions are bad, the NW may instruct the UE to switch to 4-step RA, extend the msgB-ResponseWindow, and / or cancel the small data. The NW may continue the RA procedure.

[0628] For example, before RAR transmission with UL grant for small data, NW may measure and / or derive current radio conditions. If radio conditions are qualified for UE to transmit small data, NW may transmit RAR. If radio conditions are bad, NW may instruct UE to extend RA-ResponseWindow, and / or cancel small data. NW may continue RA procedure.

[0629] - Too much packet loss

[0630] For example, after the NW fails to respond to MSGB and receives Msg3 with small data, the NW can measure and / or derive the current radio conditions. If the radio conditions are qualified for the UE to transmit small data, the NW can request retransmission. If the radio conditions are bad, the NW can instruct the UE to cancel the small data transmission and / or switch to 4-step RA.

[0631] For example, after the NW fails to receive Msg3 with small data in response to RAR, the NW can measure and / or derive the current radio conditions. If the radio conditions are qualified for the UE to transmit small data, the NW can request retransmission. If the radio conditions are bad, the NW can instruct the UE to cancel the small data transmission.

[0632] The UE may switch from a first type of transmission to a second type of transmission. The first type of transmission may have small data. The first type of transmission may be without small data. The second type of transmission may have small data. The second type of transmission may be without small data. The first type of transmission may be a 2-step RA. The first type of transmission may be a 4-step RA. The first type of transmission may be a pre-configured PUSCH transmission. The second type of transmission may be a 2-step RA. The second type of transmission may be a 4-step RA. The second type of transmission may be a pre-configured PUSCH transmission.

[0633] The switching may be one-shot, for example, switching back to the first type of transmission after switching to the second type of transmission and transmission failure.For example, if the UE fails to receive Msg4 in response to Msg3 during a 4-step RA, the UE may fall back and transmit MSGA.

[0634] The switch may be permanent, for example, retrying the second type of transmission after switching to the second type of transmission and failing.For example, if the UE fails to receive Msg4 in response to Msg3 during a 4-step RA, the UE may back off and transmit the RA preamble (Msg1).

[0635] Radio conditions may be measured and / or derived by the UE. Radio conditions may be derived from one or more measurements from the UE. Radio conditions and / or measurements may be relative to a path loss reference, an average of a set of path loss references, and / or a reference signal (e.g., SSB, CSI-RS) of a beam. Radio conditions and / or measurements may be based on a cell group, a serving cell, a carrier, a bandwidth part (BWP), and / or a beam. Radio conditions may be represented by a reference signal received power (RSRP), a reference signal received quality (RSRQ), and / or a signal to interference and noise ratio (SINR).

[0636] The radio conditions may be measured and / or derived by the NW. The radio conditions may be derived from one or more measurement results from the NW. The radio conditions and / or the measurement results may be relative to a sounding reference signal and / or an average of a set of sounding reference signals. The radio conditions may be represented by RSRP, RSRQ, and / or SINR.

[0637] Small data transmission based on RACH can be a 2-step RA, such as Figure 6As shown in FIG. 1 , the figure is a flow chart of a 2-step random access procedure with small data according to an exemplary embodiment. Small data transmission based on RACH can also be a 4-step RA, such as Figure 7 , which is a flow chart of a 4-step random access procedure with small data according to an exemplary embodiment. When the UE is in the RRC_INACTIVE state, RACH-based small data transmission is applicable. RACH-based small data transmission can be contention-based. RACH-based small data transmission can be contention-free. RSRP thresholds can be provided in the RACH configuration on each BWP to determine the RA type (e.g., 2-step RA, 4-step RA), as discussed in 3GPP R2-1915889. RACH-based small data transmission in the RRC_INACTIVE state can be contention-based and / or contention-free, or based on configuration and / or radio conditions from the NW.

[0638] When (or in response to) the upper layer indicates the RRC recovery process for small data transmission, for example, when UL data arrives and / or with a period, a small data transmission process based on RACH can be initiated. If both the NW and the UE support small data transmission and / or the relevant configuration is configured on the UE, a small data transmission process based on RACH can be initiated. In addition, if the size of the small data is less than or equal to the TB size indicated in the relevant configuration, system information, dedicated RRC signaling and / or DCI, a small data transmission procedure based on RACH can be initiated. One or more of the above conditions can be applied together.

[0639] If the radio condition measured by the UE is below a threshold, it may imply that the small data transmission in the RA procedure cannot succeed. The UE may cancel the small data transmission in the RA procedure, for example, to process the recovery procedure. The UE may fall back to the random access resource selection procedure. The UE may wait for a certain time period, for example, for better radio conditions. The UE may continue the RA procedure. Some examples are provided below.

[0640] In one example, the UE may cancel the small data transmission and initiate (or fall back to or continue with) the RA procedure for recovery. The RA procedure may be a 2-step RA or a 4-step RA. The UE may reconstruct the MSGA (or Msg3) to exclude the small data. The UE transmits the MSGA (or Msg3) containing the RRC recovery request without the small data. The small data may be transmitted in the RRC_CONNECTED state. The radio conditions may be measured at each time before the UE transmits the MSGA with small data. The radio conditions may be measured at each time before the UE transmits the Msg3 with small data. The radio conditions may be measured at each time after the UE fails to receive the MSGB in response to the small data transmission. The radio conditions may be measured at each time after the UE fails to receive the Msg4 in response to the small data transmission.

[0641] In one example, the UE may fall back to a random access resource selection procedure. The UE may use the reselected RA resources to transmit small data in the MSGA. The radio conditions may be measured every time before the UE transmits the MSGA with small data.

[0642] In one example, the UE may wait for a while and then measure the radio conditions again. If the radio conditions are above a threshold, the UE may transmit a MSGA with small data. If the radio conditions are below a threshold, the UE may continue to wait. If the UE spends too much time waiting, the UE may cancel the small data transmission and initiate (or fall back to or continue with) a RA procedure to recover. The RA procedure may be a 2-step RA or a 4-step RA. The UE may reconstruct the MSGA or Msg3 to exclude small data. The UE may transmit a MSGA containing an RRC recovery request without small data. Small data may be transmitted in the RRC_CONNECTED state. Radio conditions may be measured at each time before the UE transmits a MSGA with small data.

[0643] In one example, the UE may wait for a while and then measure the radio conditions again. If the radio conditions are above a threshold, the UE may transmit a MSGA with small data. If the radio conditions are below a threshold, the UE may continue to wait. If the UE spends too much time waiting, the UE may fall back to the random access resource selection procedure. The UE may use the reselected RA resources to transmit small data in the MSGA. The radio conditions may be measured at each time before the UE transmits a MSGA with small data.

[0644] In one example, the UE may wait for a while and then measure the radio conditions again. If the radio conditions are above a threshold, the UE may transmit a MSGA with small data. If the radio conditions are below a threshold, the UE may continue to wait. If the UE spends too much time waiting, the UE may continue the RA procedure and transmit a MSGA with small data regardless of the radio conditions. If the transmission of small data fails, the UE may fall back to the random access resource selection procedure and transmit small data in the MSGA. The radio conditions may be measured at each time before the UE transmits a MSGA with small data.

[0645] If the radio conditions measured by the NW are not qualified for small data transmission in the RA procedure, the NW may instruct the UE to switch to 4-step RA. The NW may instruct the UE to cancel the small data transmission in the RA procedure and process the recovery procedure. The NW may instruct the UE to wait for a certain time period, for example, until the radio conditions become better. The NW may continue the RA procedure. Some examples are shown below.

[0646] In one example, the NW may instruct the UE to switch to a 4-step RA. The UE may switch the RA type to a 4-step. The UE may transmit small data in Msg3 with UL grant in the MSGB provided by the NW. The UE may reselect RA resources and transmit an RA preamble (Msg1), and then transmit small data in Msg3 with UL grant in the RAR provided by the NW. If the UE fails to receive Msg4 in response to Msg3, the UE may fall back and transmit MSGA. If the UE fails to receive Msg4 in response to Msg3, the UE may fall back and transmit the RA preamble. The NW may instruct the UE via MSGB. The NW may instruct the UE via MAC CE. The NW may instruct the UE via an RRC message. The NW may instruct the UE via DCI. Radio conditions may be measured at each time before the NW transmits an MSGB with UL grant for small data (e.g., with fallbackRAR). The radio condition may be measured every time when the NW fails to receive Msg3 with small data and the NW has transmitted MSGB with UL grant for small data (eg, with fallbackRAR).

[0647] In one example, the NW may instruct the UE to cancel the small data transmission and initiate (or fall back to or continue) the RA procedure for recovery. The RA procedure may be a 2-step RA or a 4-step RA. The UE may reconstruct the MSGA or Msg3 to exclude small data. The UE may transmit an MSGA (or Msg3) containing an RRC recovery request without small data. Small data may be transmitted in the RRC_CONNECTED state. The NW may instruct the UE via a MAC CE. The NW may instruct the UE via an RRC message. The NW may instruct the UE via a DCI. The radio conditions are measured at each time after the NW fails to receive the Msg3 with small data. The NW may have transmitted a MSGB with UL grant for small data (e.g., with fallbackRAR). The NW may have transmitted a RAR with UL grant for small data.

[0648] In one example, the NW may wait for a while and may then measure the radio conditions again. If the radio conditions are above a threshold, the NW may transmit a MSGB (or RAR) with an UL grant for small data. If the radio conditions are below a threshold, the NW may continue to wait. If the radio conditions are below a threshold, the NW may instruct the UE to extend the response window (e.g., msgB-ResponseWindow, ra-ResponseWindow).

[0649] The UE may extend the response window (e.g., msgB-ResponseWindow, ra-ResponseWindow) and may wait for a MSGB (or RAR) with UL grant for small data; then transmit the small data in Msg3. If the NW spends too much time waiting, it may instruct the UE to cancel the small data transmission and initiate (or fall back to or continue with) the RA procedure to recover. The RA procedure may be a 2-step RA or a 4-step RA. The UE may reconstruct the MSGA or Msg3 to exclude small data. The UE may transmit an MSGA (or Msg3) containing an RRC recovery request without small data. Small data may be transmitted in the RRC_CONNECTED state. The NW may instruct the UE via the MSGB (or RAR).

[0650] The NW may indicate the UE via MAC CE. The NW may inform the UE via RRC message. The NW may indicate the UE via DCI. The radio condition may be measured each time before the NW transmits a MSGB with UL grant for small data (e.g., with fallback RAR). The radio condition may be measured each time before the NW transmits a RAR with UL grant for small data.

[0651] In one example, the NW may wait for a while, and then measure the radio conditions again. If the radio conditions are higher than the threshold, the NW may transmit a MSGB (or RAR) with UL grant for small data. If the radio conditions are lower than the threshold, the NW may continue to wait. If the radio conditions are lower than the threshold, the NW may instruct the UE to extend the response window (e.g., msgB-ResponseWindow, ra-ResponseWindow). The UE may extend the response window (e.g., msgB-ResponseWindow, ra-ResponseWindow), and may wait for a MSGB (or RAR) with UL grant for small data, and may subsequently transmit small data in Msg3.

[0652] If the NW spends too much time waiting, it can continue the RA procedure and transmit a MSGB (or RAR) with UL grant for small data regardless of the radio conditions. If the small data transmission fails, the UE can fall back to the random access resource selection procedure and transmit the small data in Msg3. The NW can indicate the UE through the MSGB (or RAR). The NW can indicate the UE through the MACCE. The NW can indicate the UE through the RRC message. The NW can indicate the UE through the DCI. The radio conditions can be measured every time before the NW transmits a MSGB (e.g., with fallbackRAR) with UL grant for small data. The radio conditions can be measured every time before the NW transmits a RAR with UL grant for small data.

[0653] In one example, the NW may wait for a while and then measure the radio conditions again. If the radio conditions are above a threshold, the NW may transmit a MSG B with UL grant for small data. If the radio conditions are below a threshold, the NW may continue to wait. If the radio conditions are below a threshold, the NW may instruct the UE to extend the response window (e.g., msgB-ResponseWindow). The UE may extend the response window (e.g., msgB-ResponseWindow) and wait for a MSG B with UL grant for small data, and may subsequently transmit small data in Msg3. If the NW spends too much time waiting, it may instruct the UE to switch to a 4-step RA.

[0654] The UE may switch the RA type to 4-step. The UE may transmit small data in Msg3 with UL grant in MSGB provided by the NW. The UE may reselect RA resources and transmit RA preamble (Msg1), and then transmit small data in Msg3 with UL grant in RAR provided by the NW. If the UE fails to receive Msg4 in response to Msg3, the UE may fall back and transmit MSGA. If the UE fails to receive Msg4 in response to Msg3, the UE may fall back and transmit RA preamble.

[0655] The NW may indicate the UE via MSGB. The NW may indicate the UE via MAC CE. The NW may indicate the UE via RRC message. The NW may indicate the UE via DCI. The radio conditions may be measured at each time before the NW transmits a MSGB with UL grant for small data (e.g., with fallback RAR).

[0656] When the upper layer indicates a small data transmission and the RSRP is below a threshold (e.g., rsrp-Threshold-msgA), the UE may initiate a 4-step RA to transmit the small data. The UE may transmit an RA preamble. If the UE receives a RAR in response to an RA preamble with an UL grant not for small data, the UE may cancel the small data transmission and / or continue the RA procedure to recover.

[0657] The UE may initiate a 2-step RA (without small data) when the RSRP is above a threshold (e.g., rsrp-Threshold-msgA). If the UE detects an RSRP below a threshold (e.g., rsrp-Threshold-msgA) during the RA procedure (e.g., it may be difficult to successfully deliver UL data), the UE may continue with the 2-step RA procedure (without small data).

[0658] The UE may initiate a 2-step RA (no small data) when RSRP is above a threshold (e.g., rsrp-Threshold-msgA). The UE may transmit an MSGA and then receive a fallback message (e.g., fallbackRAR) in response to the MSGA. In response to the fallback message, the UE may transmit Msg3 with UL grant in the fallback message. If the UE fails to receive Msg4 in response to Msg3, the UE may fall back and / or transmit an MSGA.

[0659] The UE may have an ongoing 2-step RA procedure. The UE may have an ongoing 4-step RA procedure. The UE may have pre-configured PUSCH resources. The UE may have an ongoing procedure for small data transmission. The UE may be in RRC_INACTIVE state, RRC_IDLE state, or RRC_CONNECTED state.

[0660] The UE may receive some configurations related to the radio conditions and the RA procedure for small data transmission provided by the NW. For example, the configuration (i.e., the relevant configuration) may include a threshold for determining the small data transmission. For example, the relevant configuration may include a timer, a counter, a window and / or other parameters to wait before the small data transmission. The relevant configuration may be provided in the system information, the RRC signaling and / or the MAC CE.

[0661] The UE may be referred to as a UE, a MAC entity of the UE, or a multiplexing and combining entity of the UE. The UE may be a new RAT / radio (NR) device. The UE may be a NR light device as discussed in 3GPP RP193238. The UE may be a reduced capability device as discussed in 3GPP RP193238. The UE may be a mobile phone, a wearable device, a sensor, or a fixed device.

[0662] NW can be a base station, access point, eNB or gNB.

[0663] If the upper layer indicates small data transmission, the RA procedure may be used for small data transmission. If the upper layer requests to resume the suspended RRC connection to transmit small data in the RRC_INACTIVE state, the RA procedure may be used for small data transmission.

[0664] Figure 8 800 is a flow chart according to an exemplary embodiment from the perspective of a UE. In step 805, the UE initiates a 2-step RA procedure including UL data in the RRC_INACTIVE state. In step 810, the UE switches from the 2-step RA procedure to the 4-step RA procedure without UL data in response to conditions.

[0665] In one embodiment, the condition may be that the UE receives network signaling. The network signaling may be an indication in a random access response.

[0666] In one embodiment, the condition may be that the UE cannot successfully complete the 2-step RA procedure after a number of preamble transmissions. The number of preamble transmissions may exceed a configured threshold.

[0667] In one embodiment, the condition may be that the radio condition of the UE becomes or falls below a radio condition threshold. The radio condition of the UE may be RSRP of a path loss reference.

[0668] In one embodiment, the UE may perform a handover by stopping the 2-step RA procedure and initiating the 4-step RA procedure. In addition, the UE may transmit uplink (UL) data after entering the RRC_CONNECTED state. The 2-step RA procedure may be initiated in response to an upper layer request.

[0669] Return to reference Figure 3 and Figure 4 In one exemplary embodiment of the UE, the UE 300 includes program code 312 stored in the memory 310. The CPU 308 may execute the program code 312 to enable the UE to: (i) initiate a 2-step RA procedure including UL data in the RRC_INACTIVE state, and (ii) switch from the 2-step RA procedure to a 4-step RA procedure not including UL data in response to a condition. In addition, the CPU 308 may execute the program code 312 to perform all of the above actions and steps or other actions and steps described herein.

[0670] Fig. 9 900 is a flow chart according to an exemplary embodiment from the perspective of a UE. In step 905, the UE initiates a procedure for transmitting UL data when the UE is in the RRC_INACTIVE state. In step 910, if a condition is met, the UE performs a fallback action.

[0671] In one embodiment, (all or at least part of) the UL data (ie, small data) may be transmitted in MSGA, Msg3 and / or pre-configured physical uplink shared channel (PUSCH) resources.

[0672] In one embodiment, the condition may be that the UE receives network signaling. The condition may also be that the UE fails to receive MSGB in response to the small data transmission. In addition, the condition may be that the UE fails to receive Msg4 in response to the small data transmission.

[0673] In one embodiment, the condition may be that the radio condition becomes or is poor (e.g., below or less than a radio condition threshold). The radio condition may be measured and / or derived by the UE. The radio condition may be relative to a path loss reference, an average of a set of path loss references, and / or a reference signal (e.g., SSB and / or CSI-RS) of a beam. The radio condition may be based on a cell group, a serving cell, a carrier, a BWP, and / or a beam.

[0674] In one embodiment, the fallback action may be (i) stopping (ongoing) small data transmission, (ii) canceling small data transmission, (iii) switching transmission type, (iv) falling back to RA resource selection procedure, and / or (v) waiting for a certain time period. If the UE stops (ongoing) small data transmission, the UE may clear the HARQ buffer used for transmission of small data, re-initiate the random access procedure, and / or reset the MAC. If the UE cancels the small data transmission, the UE may initiate a recovery procedure, stop the ongoing RA procedure and re-initiate the RA procedure to recover, and / or reconstruct the data in the MSGA (or Msg3) buffer to exclude the small data.

[0675] If the UE switches transmission type, the UE may switch from 2-step RA to 4-step RA, from pre-configured PUSCH to 2-step RA, and / or from pre-configured PUSCH to 4-step RA. In addition, if the UE switches transmission type, the switching may be one-shot and / or permanent.

[0676] If the UE spends too much time waiting (eg, greater than a parameter for the waiting time), the UE may cancel the small data transmission, fall back to the RA resource selection procedure, and / or continue the small data transmission.

[0677] In one embodiment, the UE may receive relevant configurations related to small data transmission provided by the NW (eg, radio condition thresholds and / or parameters for waiting time). The UE may also receive network signaling.

[0678] In one embodiment, relevant configurations may be provided in system information, RRC signaling and / or MAC CE. Network signaling may be MSGB, random access response (RAR), MAC CE, RRC message and / or downlink control information (DCI).

[0679] In one embodiment, the UE may be a NR device and / or a NR light device. The UE may also be a reduced capability device and / or a fixed device. In addition, the UE may be a mobile phone, a wearable device and / or a sensor. The UE may have mobility capabilities and / or may not have mobility capabilities.

[0680] Return to reference Figure 3 and Figure 4In one exemplary embodiment of the UE, the UE 300 includes a program code 312 stored in the memory 310. The CPU 308 may execute the program code 312 to enable the UE to: (i) initiate a procedure for transmitting UL data when the UE is in the RRC_INACTIVE state, and (ii) perform a fallback action if a condition is met. In addition, the CPU 308 may execute the program code 312 to perform all of the above actions and steps or other actions and steps described herein.

[0681] Fig.10 1000 is a flow chart according to an exemplary embodiment from the perspective of the NW. In step 1005, the NW detects that the UE has initiated a procedure for transmitting UL data when the UE is in the RRC_INACTIVE state. In step 1010, the UE transmits signaling to the UE, wherein the signaling triggers the UE to perform a fallback action.

[0682] In one embodiment, (all or at least part of) the UL data (ie, small data) may be received from MSG A, Msg3 and / or pre-configured PUSCH resources.

[0683] In one embodiment, the condition may be that the radio condition becomes or is bad (e.g., below / less than a radio condition threshold). The condition may also be that the NW detects too many packet losses (e.g., the NW fails to receive Msg3 with small data in response to MSGB and / or RAR). The radio condition may be measured and / or derived by the NW. The radio condition may be relative to a sounding reference signal and / or an average of a set of sounding reference signals.

[0684] In one embodiment, the fallback action may be (i) switching to a 4-step RA with small data transmission, (ii) switching to a 2-step RA without small data transmission, (iii) switching to a 4-step RA without small data transmission, (iv) extending the response window (e.g., msgB-ResponseWindow, ra-ResponseWindow), and / or (v) resuming to the RRC_CONNECT state. If the UE extends the response window too long, the NW may trigger (or instruct) the UE to cancel the small data transmission, switch to the 4-step RA, and / or continue the small data transmission. The NW may trigger (or instruct) the UE by sending MSGB, RAR, MAC CE, RRC message, and / or DCI. The NW may transmit an RRC release message after the RA procedure with small data is completed to keep the UE in the RRC_INACTIVE state.

[0685] In one embodiment, the NW may send relevant configurations related to small data transmission (e.g., radio condition thresholds and / or parameters for waiting time) to the UE. The relevant configurations may be provided in system information, dedicated RRC signaling, and / or MAC CE. The NW may be a base station, access point, eNB, and / or gNB.

[0686] In one embodiment, the small data transmission may be a 2-step RA, a 4-step RA and / or a pre-configured PUSCH. RA may be contention-based and / or contention-free.

[0687] In one embodiment, when the upper layer indicates the RRC recovery procedure for small data transmission, small data transmission can be initiated. When the upper layer requests to resume the suspended RRC connection to transmit small data under the RRC_INACTIVE state, small data transmission can also be initiated. In addition, if UE and NW all support small data transmission, or if relevant configuration is configured on UE, small data transmission can be initiated so. In addition, if the uplink data size is less than or equal to the TB size indicated in relevant configuration, system information, dedicated RRC signaling and / or DCI, small data transmission can be initiated so.

[0688] In one embodiment, the radio conditions may be represented by RSRP, RSRQ and / or SINR.

[0689] Return to reference Figure 3 and Figure 4 In one exemplary embodiment of the network, the network 300 includes program code 312 stored in the memory 310. The CPU 308 can execute the program code 312 to enable the network to: (i) detect that the UE has initiated a procedure for transmitting UL data when the UE is in the RRC_INACTIVE state, and (ii) transmit signaling to the UE, wherein the signaling triggers the UE to perform a fallback action. In addition, the CPU 308 can execute the program code 312 to perform all of the above actions and steps or other actions and steps described herein.

[0690] Various aspects of the present disclosure have been described above. It should be understood that the teachings herein can be implemented in a wide variety of forms, and any specific structure, function, or both disclosed herein are only representative. Based on the teachings herein, it should be understood by those skilled in the art that the aspects disclosed herein can be implemented independently of any other aspects, and two or more of these aspects can be combined in various ways. For example, any number of aspects described herein can be used to implement a device or practice method. In addition, by using other structures, functionality, or structures and functionality other than one or more of the aspects described herein or different from one or more of the aspects described herein, this device can be implemented or this method can be practiced. As an example of some of the above concepts, in some aspects, parallel channels can be established based on pulse repetition frequency. In some aspects, parallel channels can be established based on pulse position or offset. In some aspects, parallel channels can be established based on hopping sequences. In some aspects, parallel channels can be established based on pulse repetition frequency, pulse position or offset, and time hopping sequence.

[0691] Those skilled in the art will understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltage, current, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0692] Those skilled in the art will further appreciate that the various illustrative logical blocks, modules, processors, components, circuits, and algorithm steps described in conjunction with the aspects disclosed herein may be implemented as electronic hardware (e.g., a digital implementation, an analog implementation, or a combination of both, which may be designed using source decoding or some other technique), various forms of program or design code incorporating instructions (which may be referred to herein for convenience as "software" or "software modules"), or a combination of both. To clearly illustrate this interchangeability of hardware and software, the above has been generally described in terms of the functionality of various illustrative components, blocks, modules, circuits, and steps. Whether such functionality is implemented as hardware or software depends on the specific application and the design constraints imposed on the overall system. Those skilled in the art may implement the described functionality in different ways for each specific application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

[0693] In addition, the various illustrative logical blocks, modules, and circuits described in conjunction with the aspects disclosed herein may be implemented within or performed by an integrated circuit ("IC"), an access terminal, or an access point. An IC may include a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, electrical components, optical components, mechanical components, or any combination thereof designed to perform the functions described herein, and may execute code or instructions residing within the IC, outside the IC, or both. A general purpose processor may be a microprocessor; however, in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

[0694] It should be understood that any specific order or hierarchy of steps in any disclosed process is an example of a sample approach. It should be understood that based on design preferences, the specific order or hierarchy of steps in a process can be rearranged while remaining within the scope of the present disclosure. The accompanying method claims present elements of the various steps in a sample order, and are not intended to be limited to the specific order or hierarchy presented.

[0695] The steps of the method or algorithm described in conjunction with the aspects disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. Software modules (e.g., containing executable instructions and associated data) and other data may reside in a data memory, such as a RAM memory, a flash memory, a ROM memory, an EPROM memory, an EEPROM memory, a register, a hard disk, a removable disk, a CD-ROM, or any other form of computer-readable storage medium known in the art. A sample storage medium may be coupled to a machine such as a computer / processor (for convenience, the machine may be referred to herein as a "processor") so that the processor can read information (e.g., code) from the storage medium and write information to the storage medium. A sample storage medium may be integrated with a processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user device. In an alternative, the processor and the storage medium may reside in a user device as discrete components. In addition, in some aspects, any suitable computer program product may include a computer-readable medium including code related to one or more aspects of the present disclosure. In some aspects, a computer program product may include packaging materials.

[0696] Although the present invention has been described in conjunction with various aspects, it will be appreciated that the present invention is capable of further modifications. This application is intended to cover any variation, use or adaptation of the present invention, which generally follows the principles of the present invention and includes such deviations from the present disclosure, which are within the scope of known and customary practice in the technical field to which the present invention belongs.

Claims

1. A method for a user device, characterized in that: include: Initiating a first procedure of small data transmission (SDT) using 2-step random access based on a reference signal received power (RSRP) of the user equipment being higher than an RSRP threshold, wherein the SDT is used to transmit data in an RRC_INACTIVE state; In response to the user equipment being unable to successfully complete the first procedure: Stopping the first program of random access using the 2 steps; resetting a media access control (MAC) of the user equipment; Clearing a HARQ buffer for the data transmission; as well as Based on at least the RSRP of the user equipment being lower than the RSRP threshold, a second procedure not used for the SDT using 4-step random access is initiated, the second procedure not used for transmitting the data in the RRC_INACTIVE state.

2. The method according to claim 1, characterized in that The stopping of the first procedure for the SDT does not receive network signaling.

3. The method according to claim 1, characterized in that The situation is that the user equipment cannot successfully complete the 2-step random access after a certain number of preamble transmissions.

4. The method according to claim 3, characterized in that The number of times the preamble is transmitted exceeds a configured threshold.

5. The method according to claim 1, characterized in that The situation is that a radio condition of the user equipment becomes below a radio condition threshold.

6. The method according to claim 5, characterized in that The radio condition of the user equipment is a reference signal received power of a path loss reference.

7. The method according to claim 1, characterized in that Also includes: The data is transmitted after entering the RRC_CONNECTED state.

8. The method according to claim 1, characterized in that The first procedure for the SDT is initiated in response to an upper layer request.

9. A user equipment, characterized in that: include: Control circuit; a processor installed in the control circuit; as well as a memory installed in the control circuit and operatively coupled to the processor; wherein the processor is configured to execute program code stored in the memory to: Initiating a first procedure of small data transmission (SDT) using 2-step random access based on a reference signal received power (RSRP) of the user equipment being higher than an RSRP threshold, wherein the SDT is used to transmit data in an RRC_INACTIVE state; In response to the user equipment being unable to successfully complete the first procedure: Stopping the first program of random access using the 2 steps; resetting a media access control (MAC) of the user equipment; Clearing a HARQ buffer for the data transmission; as well as Based on at least the RSRP of the user equipment being lower than the RSRP threshold, a second procedure not used for the SDT using 4-step random access is initiated, the second procedure not used for transmitting the data in the RRC_INACTIVE state.

10. The user equipment according to claim 9, characterized in that The stopping of the first procedure for the SDT does not receive network signaling.

11. The user equipment according to claim 9, characterized in that The situation is that the user equipment cannot successfully complete the 2-step random access after a certain number of preamble transmissions.

12. The user equipment according to claim 11, characterized in that The number of times the preamble is transmitted exceeds a configured threshold.

13. The user equipment according to claim 9, characterized in that The situation is that a radio condition of the user equipment becomes below a radio condition threshold.

14. The user equipment according to claim 13, characterized in that The radio condition of the user equipment is a reference signal received power of a path loss reference.

15. The user equipment according to claim 9, characterized in that The processor is configured to execute program code stored in the memory to: The data is transmitted after entering the RRC_CONNECTED state.

16. The user equipment according to claim 9, characterized in that The first procedure for the SDT is initiated in response to an upper layer request.

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