METHODS AND APPARATUS FOR DATA TRANSMISSION IN NEW RADIO (NR) INACTIVE STATE

Apparatus and methods are provided for initiating INACTIVE small data transmission (ISDT). In one novel aspect, the UE verifies one or more sets of conditions to select an ISDT initiation procedure. The UE first verifies that a set of ISDT conditions are met and selects an ISDT initiation procedure based on one or more sets of selection conditions, otherwise, the UE goes to the CONNECTED state. In one embodiment, the ISDT conditions comprises a data volume is smaller than or equal to a preconfigured ISDT data volume threshold, the UE has a valid Inactive AS context, no fallback indication has been received, and ISDT is supported by the wireless network. In another embodiment, the ISDT condition further includes the RSRP is greater than or equal to a preconfigured RSRP threshold. In one embodiment, the ISDT initiation procedures comprises: RRC-based RA procedure, RRC-less RA procedure, RRC-based CG, and RRC-less CG procedure.

TECHNICAL FIELD

The disclosed embodiments relate generally to wireless communication, and, more particularly, to initiate small data transmission in new radio (NR) INACTIVE state.

BACKGROUND

The fifth generation (5G) radio access technology (RAT) will be a key component of the modern access network. It will address high traffic growth, energy efficiency and increasing demand for high-bandwidth connectivity. It will also support massive numbers of connected devices and meet the real-time, high-reliability communication needs of mission-critical applications. The 5G network introduces RRC INACTIVE state to reduce control plane and user plane latency. In the RRC INACTIVE state, the UE is always connected from the core network (CN) aspect so that the transition from the INACTIVE state to the CONNECTED state is more efficiency than from the IDLE state to the CONNECTED. However, the UE needs to perform state transition from INACTIVE to CONNECTED state and completes connection resume procedures first for any DL and UL data. The data transmission and reception are performed in the CONNECTED state. Connection setup and subsequently release to INACTIVE state happens for each data transmission. The transition comprises extensive signaling sequence between the UE and the network. When the amount of data that wireless devices exchange with the network is small and the data transmission is usually not urgent enough to justify the high battery consumption required to handle all the signaling involved in the legacy INACTIVE-to-CONNECTED transition. The initiation procedure for the small data transmission in the UE INACTIVE state is a new challenge to enable the more efficient small data transmission in the INACTIVE state.

Improvements are required to define initiation of small data transmission in the UE INACTIVE state more efficiently.

SUMMARY

Apparatus and methods are provided for initiating INACTIVE small data transmission (ISDT) in the wireless network. In one novel aspect, the UE verifies one or more sets of conditions to select an ISDT initiation procedure and initiates ISDT with the selected procedure. The UE first verifies that a set of ISDT conditions are met to select an ISDT initiation procedure, otherwise, the UE goes to the CONNECTED state for the data transmission. In one embodiment, the ISDT conditions comprises, a data volume is smaller than or equal to a preconfigured data volume threshold, the UE has a valid Inactive AS context, no fallback indication has been received, and ISDT is supported by the wireless network. In another embodiment, the ISDT condition further includes the RSRP is greater than or equal to a preconfigured RSRP threshold. Different sets of conditions are defined for different procedures. RRC-less CG conditions include UE has valid CG configuration; UE has valid time alignment value; Data volume is smaller than or equal to the value configured for CG; No need of security update; and No need of reconfiguration. RRC-based CG procedure condition include UE has valid CG configuration; UE has valid time alignment value; and Data volume is smaller than or equal to the value configured for CG. RRC-less RA conditions include the data volume is smaller than or equal to the value configured for ISDT; no need of security update; no need of reconfiguration; and RRC-less ISDT is supported. RRC-based RA conditions include the data volume is smaller than or equal to the value configured for ISDT; and the ISDT is supported. In one embodiment, when UE initiates ISDT, it further verifies the following conditions: the upper layer requests data transmission for the RBs configured with ISDT; UE has valid UE Inactive AS context; and no fallback indication has been received from lower layers. In yet another embodiment, the ISDT condition further includes the RSRP is greater than or equal to a preconfigured RSRP threshold.

This summary does not purport to define the invention. The invention is defined by the claims.

DETAILED DESCRIPTION

FIG.1is a schematic system diagram illustrating an exemplary wireless communication network100that supports initiating ISDT and performing small data transmission in INACTIVE state. Wireless communication network100includes one or more fixed base infrastructure units forming a network distributed over a geographical region. The base unit may also be referred to as an access point, an access terminal, a base station, a Node-B, an eNode-B (eNB), a gNB, or by other terminology used in the art. As an example, base stations serve a number of mobile stations within a serving area, for example, a cell, or within a cell sector. In some systems, one or more base stations are coupled to a controller forming an access network that is coupled to one or more core networks. gNB106, gNB107and gNB108are base stations in the wireless network, the serving area of which may or may not overlap with each other. As an example, user equipment (UE)101or mobile station101is in the serving area covered by gNB106and gNB107. As an example, UE101or mobile station101is only in the service area of gNB106and connected with gNB106. UE102or mobile station102is only in the service area of gNB107and connected with gNB107. gNB106is connected with gNB107via Xn interface121. gNB106is connected with gNB108via Xn interface122. A 5G network entity109connects with gNB106,107, and108via NG connection131,132, and133, respectively. In one embodiment, UE101is configured to be able to transmit data in the INACTIVE state without the transition to CONNECTED state.

In one novel aspect, the UE initiates data transmission and/or reception in the INACTIVE state. In one embodiment, the data transmission is INACTIVE small-data transmission (ISDT) as data bursts shown in a block110. The NR network supports many services with infrequent and small-data packets. For example, traffic from instant messaging (IM) services, heartbeat/keep-alive traffic from IM/email clients and other apps and push notifications from various applications are the typical use cases of smart phone applications. For non-smartphone applications, traffic from wearables, sensors and smart meters/smart meter networks sending periodic meter readings are the typical use cases. For these small data shown in the block110, the data transmission and/or reception are initiated in the INACTIVE state.

FIG.1further illustrates simplified block diagrams of a base station and a mobile device/UE for data transmission and reception in the INACTIVE state.FIG.1includes simplified block diagrams of a UE, such as UE101. The UE has an antenna165, which transmits and receives radio signals. An RF transceiver circuit163, coupled with the antenna, receives RF signals from antenna165, converts them to baseband signals, and sends them to a processor162. In one embodiment, the RF transceiver163may comprise two RF modules (not shown). A first RF module is used for High Frequency (HF) transmitting and receiving, and the other RF module is used for different frequency bands transmitting and receiving which is different from the HF transceiver. RF transceiver163also converts received baseband signals from processor162, converts them to RF signals, and sends out to antenna165. Processor162processes the received baseband signals and invokes different functional modules to perform features in UE101. Memory161stores program instructions and data164to control the operations of UE101. The memory161also stores UE INACTIVE Access Stratum (AS) CONTEXT, which includes the current KgNB and KRRCint keys, the robust header compression (ROHC) state, the stored QoS flow to dedicated radio bearer (DRB) mapping rules, the cell radio network temporary identifier (C-RNTI) used in the source primary cell (PCell), the cellIdentity and the physical cell identity of the source PCell, and/or some other parameters. In one embodiment, the UE INACTIVE AS CONTEXT also has another set of parameters configured for data transmission in the INACTIVE state, which includes the configurations for physical layer and MAC layer. In one embodiment, the physical layer configuration includes pre-configured UL resources, which can be used for UL data transmission in the INACTIVE state. In one embodiment, the physical layer configuration includes an MAC configuration, e.g., MAC-CellGroupConfig. Antenna165sends uplink transmission and receives downlink transmissions to/from antenna156of gNB106.

The UE also includes a set of control modules that carry out functional tasks. These control modules can be implemented by circuits, software, firmware, or a combination of them. An ISDT verification module191verifies a set of preconfigured ISDT conditions in the wireless network, wherein the UE is configured to perform small data transmission in a UE INACTIVE state when the set of preconfigured ISDT conditions is met. A selection module192selects an ISDT initiation procedure based on one or more sets of selection conditions, wherein the one or more sets of selection conditions comprise a set of selection conditions for a radio resource control (RRC) procedure and a set of selection conditions for a uplink (UL) resource obtaining procedure, and wherein the RRC procedure is one selecting from an RRC-based procedure and an RRC-less procedure, and the UL resource obtaining procedure is one selecting from a random access (RA) procedure and a configured grant (CG) procedure. An initiation module193initiates small data transmission in the UE INACTIVE state following the selected ISDT initiation procedure. An ISDT module194performs one or more small data transmissions in the UE INACTIVE state.

Other optional control modules can be configured for the UE, include a RRC state control module181, a DRB control module182, an AS context control module183, and a protocol control module184. The RRC state control module181controls UE RRC state according to network's command and UE conditions. UE RRC supports the following states, RRC_IDLE, RRC_CONNECTED and RRC_INACTIVE. In one embodiment, UE is configured to transmit UL data in INACTIVE with one or multiple shots to a network. In one embodiment, UL data transmission in INACTIVE is configured per DRB. UE can initiate data transmission for those DRBs when the total data amount for those DRBs arrives in the buffer is less than a threshold. In one embodiment, the network configures the threshold of data amount through system information or dedicated RRC signaling. The DRB control module182suspends or resumes the DRBs. In one embodiment, one or multiple particular DRBs are configured by network, whose data packets can be transmitted in INACTIVE. In one embodiment, the DRB is resumed when a burst of data is to be transmitted; the DRB is suspended when the transmission of data burst is finished. The INACTIVE AS CONTEXT control module183manages to store, restore, or release the UE INACTIVE AS CONTEXT. In one embodiment, the UE INACTIVE AS CONTEXT controller decides which parameters, or which set of parameters are restored according to whether UE initiate data transmission or not in INACTIVE state. In one embodiment, UE restores all the stored parameters including MAC configuration and physical layer configuration. The protocol control module184controls the establishment, re-establishment, release, reset, reconfiguration of the user plane protocols including packet data convergence protocol (PDCP), radio link control (RLC) and media access control (MAC). In one embodiment, the SDAP layer is optionally configured.

FIG.1further includes simplified block diagrams of a gNB, such as gNB106. gNB106has an antenna156, which transmits and receives radio signals. An RF transceiver circuit153, coupled with the antenna156, receives RF signals from antenna156, converts them to baseband signals, and sends them to a processor152. RF transceiver153also converts received baseband signals from processor152, converts them to RF signals, and sends out to antenna156. Processor152processes the received baseband signals and invokes different functional modules to perform features in gNB106. Memory151stores program instructions and data to control the operations of gNB2. The memory151also stores UE INACTIVE AS CONTEXT. In one embodiment, the UE INACTIVE AS CONTEXT also has another set of parameters configured supporting data transmission in INACTIVE, which includes the configurations for physical layer and MAC layer. The gNB106also includes a set of control modules155that carry out functional tasks to communicate with mobile stations. The set of control modules155includes a RRC state controller, a DRB controller, an INACTIVE AS CONTEXT controller, and a protocol controller. The RRC state controller controls UE RRC state by sending command to UE or providing configuration for the conditions. The DRB controller suspends or resumes the DRBs of a UE. In one embodiment, the DRB is resumed when a burst of data is to be transmitted; the DRB is suspended when the transmission of data burst is finished. The INACTIVE AS CONTEXT controller manages to store, restore, or release the UE INACTIVE AS CONTEXT. The protocol controller controls the establishment, re-establishment, release, reset, configuration of the user plane protocols including PDCP, RLC and MAC. In one embodiment, the SDAP layer is optionally configured. The gNB also includes multiple function modules. A random access (RA) module, which performs random access for a UE. It supports 2-step RA procedure and 4-step RA procedure. A Configured Grant (CG) module, which receives data on the pre-configured PUSCH resources. An RRC-based module, which receives ISDT from UE with RRC messages/procedures, i.e., RRCResumeRequest. An RRC-less module, which receives ISDT from UE without RRC messages.

FIG.2illustrates an exemplary NR wireless system with centralized upper layers of the NR radio interface stacks and UE protocol stacks with multicast protocols and unicast protocols. Different protocol split options between central unit (CU) and distributed unit (DU) of gNB may be possible. The functional split between the CU and DU of gNB may depend on transport layer. Low performance transport between the CU and DU of gNB can enable higher protocol layers of the NR radio stacks to be supported in the CU, since the higher protocol layers have lower performance requirements on the transport layer in terms of bandwidth, delay, synchronization, and jitter. In one embodiment, SDAP and PDCP layers are located in the CU, while RLC, MAC and PHY layers are located in the DU. A core unit201is connected with a central unit211with gNB upper layer252. In one embodiment250, gNB upper layer252includes the PDCP layer and optionally the SDAP layer. Central unit211connects with distributed units221,222, and221. Distributed units221,222, and223each corresponds to a cell231,232, and233, respectively. The DUs, such as221,222and223includes gNB lower layers251. In one embodiment, gNB lower layers251include the PHY, MAC and the RLC layers. In another embodiment260, each gNB has a protocol stack261including SDAP, PDCP, RLC, MAC and PHY layers.

FIG.3illustrates an exemplary top-level flow diagram for initiation of ISDT. UE initiates data transmission in the INACTIVE state. At step301, the UE verifies whether a preconfigured set of ISDT conditions is met to decide whether to initiate the ISDT or go to the CONNECTED state for the data transmission. At step302, if step301verifies the set of preconfigured ISDT conditions is met, the UE selects an ISDT initiation procedure. The UE selects the ISDT initiation procedure based on one or more sets of selection conditions. According to an embodiment320, the sets of selection conditions comprise a set of selection conditions for a radio resource control (RRC) procedure321and a set of selection conditions for an uplink (UL) resource obtaining procedure322. Selection321selects an RRC procedure from an RRC-based procedure and an RRC-less procedure. Selection322selects an UL resource obtaining procedure is one selecting from a random access (RA) procedure and a configured grant (CG) procedure. The ISDT initiation procedure is one selecting from an RRC-based RA procedure, an RRC-based CG procedure, an RRC-less RA procedure, and an RRC-less CG procedure. Upon initiating the ISDT using the selected ISDT initiation procedure, at step303, the UE performs ISDT.

FIG.4illustrates exemplary flow diagrams for ISDT initiation procedure options including RRC-based procedure, RRC-less procedure, RA procedure, and CG procedure. Upon determining the ISDT is selected, the UE401, communicates with gNB402, selects an initiation procedure for the ISDT. UE401selects a RRC procedure481including an RRC-based procedure410and an RRC-less procedure420. The UE401also selects a resource obtaining procedure482, which includes an RA procedure483and a CG procedure450. RA procedure483includes a 4-step RA procedure430and a 2-step RA procedure440.

In RRC-based procedure410, the upper layer requests the resume of a suspended RRC connection when there is UL data for the RBs configured with ISDT. UE transmits UL data during the RRC Resume procedure. In one embodiment, UE401, at step411, transmits UL data with RRCResumeRequest message. At step412, the UE receives RRCRelease message with suspendConfig. Subsequently, UE401goes to INACTIVE state after data transmission completion. In another embodiment, the upper layer requests direct data transmission without resume of a suspended RRC connection when there is UL data for the RBs configured with ISDT. In RRC-less procedure420, UE401, at step421, transmits UL data directly without any RRC message. At step422, UE401receives a L1 or L2 acknowledgement as the response.

The UE also selects an initiation procedure for UL resources including an RA procedure and a CG procedure. If UL data is transmitted through RA procedure, the UL data is transmitted by Msg3 (in 4-step RA)/MsgA (in 2-step RA). If UL data is transmitted through CG procedure, the UL data is transmitted through configured UL grant. The UL grant is provided by a dedicated configuration through an RRC message by the network. In 4-step RA procedure430, UE401, at step431, sends MSG1. At step432, UE401receives MSG2 from gNB402. At step433, UE401sends MSG3 with data to gNB402. At step434, UE401receives MSG4 from gNB402. In 2-step procedure440, UE401sends MSGA with data to gNB402at step441. At step442, UE401receives MSGB from gNB402. In CG procedure450, at step451, UE401sends UL data through the resource provided by the UL grant.

FIG.5illustrates an exemplary flow diagram for the ISDT initiation procedure selection. At step501, UE determines whether to initiate ISDT procedure or resume RRC connection with legacy procedure, i.e., transfer to CONNECTED state for data transmission based on a set of predefined ISDT conditions510. The ISDT conditions510include UL data for the RBs configured with ISDT, a data volume is smaller than or equal to a preconfigured ISDT data volume threshold, the UE has a valid Inactive AS context, no fallback indication has been received, and ISDT is supported by the wireless network. In other embodiment, the ISDT conditions further include a reference signal received power (RSRP) is greater than or equal to a preconfigured RSRP threshold. The set of preconfigured ISDT conditions is also called the ISDT common conditions, which applies to all ISDT initiation procedures. If step501determines the set of predefined ISDT conditions is met, UE initiates ISDT. Otherwise, at step511, UE resumes RRC connection and transfers to RRC_CONNECTED for data transmission. If step501determines to initiate ISDT, the UE determines whether to use RRC-less or RRC-based procedure at step502, and whether to use CG or RA procedure at step503. The sequence of step502and step503is interchangeable. At step502, the UE determines whether an RRC-less procedure is to be used based on selection conditions520. Selection conditions520include RRC-less for ISDT is supported by the network, no security update is needed, and no reconfiguration is needed. According to some embodiments, security update comprises security configuration (for example, security key and algorithm) update. If step502determines RRC-less procedure is selected, the UE determines whether to use CG or RA procedure at step504. If step502determines RRC-based procedure is selected, at step503, the UE determines whether to carry ISDT through RA or CG based on selection conditions530, including valid preconfigured UL resources, valid time alignment, and a data volume is smaller than or equal to a preconfigured CG data volume threshold. If step503determines “yes”, the UE selects RRC-based CG procedure for ISDT initiation at step531. Otherwise, the UE selects RRC-based RA procedure for the ISDT initiation at step532. Similarly, if step504determines “yes” according to selection conditions530, the UE selects RRC-less CG procedure for ISDT initiation at step521. If step504determines “no” according to selection conditions530, the UE selects RRC-less RA procedure for ISDT initiation at step522. In one embodiment, the UE further determines whether a 2-step or 4-step RA is to be used when the UE selects the RA procedure for ISDT initiation, such as steps522and532. The UE selects the 2-step RA procedure for the ISDT initiation when a RSRP is larger than a preconfigured two-step RSRP threshold.

The order of steps502and503can be changed, i.e., UE selects between RA and CG first and then selects between RRC-based and RRC-less schemes. In one embodiment, the preconfigured ISDT data volume threshold for ISDT initiation and the preconfigured CG data volume threshold for transmission by CG is the same. In another embodiment, the preconfigured CG data volume threshold for transmission by CG is a value of TB size. UE compares between the sum of TB size for the total data volume and the maximum TB size configured by the network. After the two steps of selection, UE initiates ISDT with the combination of the two selections including RRC-based RA procedure, RRC-less RA procedure, RRC-based CG procedure, and RRC-less CG procedure.

FIG.6illustrates an exemplary flow diagram for the ISDT initiation procedure selection when the RRC-less is not supported for ISDT. In one embodiment, ISDT with RRC message is always required, and the selection between RRC-based and RRC-less initiation is not needed. The ISDT initiation procedure is selected from the RRC-based RA procedure and the RRC-based CG procedure when the RRC-less procedure for ISDT is not supported by the wireless network. At step601, the UE determines whether to initiate ISDT procedure or transfer to CONNECTED state for data transmission based on a set of predefined ISDT conditions610. The ISDT conditions610include UL data for the RBs configured with ISDT, a data volume is smaller than or equal to a preconfigured ISDT data volume threshold, the UE has a valid Inactive AS context, no fallback indication has been received, and ISDT is supported by the wireless network. In other embodiment, the ISDT conditions610further include a reference signal received power (RSRP) is greater than or equal to a preconfigured RSRP threshold. The set of preconfigured ISDT conditions is also called the ISDT common conditions, which applies to all ISDT initiation procedures. If step601determines the set of predefined ISDT conditions is met, UE initiates ISDT. Otherwise, at step611, UE resumes RRC connection and transfers to RRC_CONNECTED for data transmission. Since the RRC-less ISDT is not support, upon determined ISDT is to be used, the UE selects either a CG or a RA procedure for ISDT initiation. At step602, the UE determines whether a preconfigured set of CG conditions620is met. CG conditions620include valid preconfigured UL resources, valid time alignment, and a data volume is smaller than or equal to a preconfigured CG data volume threshold. If step602determines “yes”, the UE selects the RRC-based CG procedure for the ISDT initiation. If step602determines “no”, the UE selects the RRC-based RA procedure for the ISDT initiation. In one embodiment, the UE further determines whether a 2-step RA or a 4-step RA procedure is to be used at step604based on a preconfigured 2-step RA condition630, which includes a RSRP is larger than a preconfigured two-step RSRP threshold. If step604determines “yes”, the UE selects the RRC-based 2-step RA for the ISDT initiation, otherwise, the RRC-based 4-step RA for the ISDT initiation is selected.

FIG.7illustrates an exemplary ISDT initiation procedure selection flow chart with RRC-less supported or without RRC-less supported. At step701, the UE selects one ISDT initiation procedure. At step702, the UE initiates ISDT with the selected initiation procedure. In selecting the ISDT initiation procedure, the UE determines whether RRC-less ISDT is supported by the network at step711. If RRC-less ISDT is supported by the network, the UE selects from list of ISDT initiation procedures721including the RRC-less CG procedure, the RRC-less RA procedure, the RRC-based CG procedure, and the RRC-based RA procedure. If RRC-less ISDT is not supported by the network, the UE selects from list of ISDT initiation procedures722including the RRC-based CG procedure and the RRC-based RA procedure.

FIG.8illustrates exemplary flowcharts for ISDT initiation procedures including the RRC-less CG procedure, the RRC-based CG procedure, the RRC-less RA procedure, and the RRC-based RA procedure. UE801in a wireless network with a gNB802, selects an ISDT initiation procedure including the RRC-less CG procedure810, the RRC-based CG procedure820, the RRC-less RA procedure830, which includes a 4-step procedure8301, and a 2-step procedure8302, and the RRC-based RA procedure840, which includes a 4-step procedure8401, and a 2-step procedure8402.

For RRC-less CG procedure810, UE801, at step811, transmits UL data directly without any RRC message. At step812, UE801receives a L1 or L2 acknowledgement as the response from gNB802. The UL data is transmitted based on the configured UL grant. The UL grant is provided through a dedicated configuration and RRC message by the network. For RRC-based CG procedure820, the upper layer requests the resume of a suspended RRC connection when there is UL data for the RBs configured with ISDT. UE801transmits UL data during the RRC Resume procedure. In one embodiment, at step821, UE801transmits UL data with RRCResumeRequest message through the configured UL resources. In one embodiment, at step822, UE801receives RRCRelease message with suspendConfig later, which sends UE801to INACTIVE state after data transmission completion. In one embodiment, UE801receives a L1/L2 ACK as the response to the RRCResumeRequest, which sends UE801to INACTIVE state.

In RRC-less RA procedure830, UE801transmits UL data directly without any RRC message. In one embodiment, the upper layer requests direct data transmission without resume of a suspended RRC connection when there is UL data for the RBs configured with ISDT. UE transmits the UL data in Msg3 (in 4-step RA)/MsgA (in 2-step RA). For the RRC-less 4-step RA procedure8301, UE801, at step831, transmits MSG1 to gNB802. At step832, UE801receives MGS2 from gNB802. At step833, UE801sends MSG 3 with data to gNB802. At step834, UE801receives MSG4 from gNB802. For the RRC-less 2-step RA procedure8302, at step836, UE801sends MSGA with data to gNB802. At step837, UE801receives MSGB from gNB802.

In RRC-based RA procedure840, the upper layer requests the resume of a suspended RRC connection when there is UL data for the RBs configured with ISDT. UE801transmits UL data during the RRC Resume procedure. In one embodiment, UE transmits UL data with RRCResumeRequest message in Msg3 (in 4-step RA)/MsgA (in 2-step RA). In one embodiment, UE receives RRCRelease message with suspendConfig in Msg4 (in 4-step RA)/MsgB (in 2-step RA), which sends UE to INACTIVE state after data transmission completion. For RRC-based 4-step RA procedure8401, at step841, UE801transmits MSG1 to gNB802. At step842, UE801receives MGS2 from gNB802. At step843, UE801sends MSG 3 with RRC Resume Request and data to gNB802. At step844, UE801receives MSG4 with RRC release message from gNB802. For the RRC-less 2-step RA procedure8402, at step846, UE801sends MSGA with RRC Resume Request and data to gNB802. At step847, UE801receives MSGB with RRC Release from gNB802. When the ISDT conditions are not met, the UE may transfer to the CONNECTED state to transmit the data packets. The upper layer requests the resume of a suspended RRC connection. The UE performs RRC connection resume procedure through RA procedure and transfers to CONNECTED. After that, UE starts UL data transmission. After completion of data transmission, RRCRelease message is received.

FIG.9illustrates exemplary diagrams for one-step selection of the ISDT initiation procedure based on a set of selection conditions corresponding to the possible ISDT initiation procedures. In order to initiate ISDT, the upper layer requests data transmission for the RBs configured with ISDT. UE checks the different set of conditions to determine to utilize which procedure to initiate ISDT. At step9001, the UE determines if ISDT common conditions900are met. ISDT common conditions900include a data volume is smaller than or equal to a preconfigured data volume threshold, the UE has a valid Inactive AS context, no fallback indication has been received, and ISDT is supported by the wireless network. In another embodiment, ISDT common conditions900further comprises the RSRP is greater than or equal to a preconfigured RSRP threshold. At step901, RRC-less CG procedure911is selected when ISDT conditions are met, and RRC-less CG conditions910are met. RRC-less CG conditions910include valid preconfigured UL resources, valid time alignment, a data volume is smaller than or equal to a preconfigured CG data volume threshold, and RRC-less ISDT is supported. At step902, RRC-based CG procedure921is selected when ISDT conditions are met, and RRC-based CG conditions920are met. RRC-based CG conditions920include valid preconfigured UL resources, valid time alignment, and a data volume is smaller than or equal to a preconfigured CG data volume threshold. At step903, an RRC-less RA procedure931is selected when ISDT conditions are met, and RRC-less RA conditions930are met. RRC-less RA conditions930include no security update is needed, and no reconfiguration is needed, and RRC-less ISDT is supported. At step904, the RRC-based RA procedure941is selected when the ISDT conditions are met, and RRC-based RA conditions940are met. At step905, UE goes to the CONNECTED state when the CONNECTED state transmission conditions950are met. CONNECTED state transmission conditions950include the data volume is greater than the preconfigured ISDT data volume threshold, and the ISDT is not supported by the network. Steps901through905can be performed in the exemplary order. The exemplary order gives RRC-less CG the highest priority. Any other orders of selection are available. The UE may be preconfigured with different preferences or priorities for the available ISDT initiation procedures. The preferences/priorities of the ISDT initiation procedures can be dynamically configured and changed as well.

FIG.10illustrates an exemplary data volume calculation for the ISDT initiation procedure selection. At a first step1001, the UE determines the data volume calculation for consideration of ISDT initiation procedure selection. In one embodiment1010, the data volume calculation considers both signalling radio bearers (SRB) and dedicated radio bearers (DRBs). In one embodiment1020, the data volume calculation only considers the DRBs. In one embodiment1030, the data volume calculation only considers the DRBs configured for ISDT. For each RB, from PDCP1050aspect, the data volume considers: the PDCP SDUs for which no PDCP Data PDUs have been constructed1051, the PDCP Data PDUs that have not been submitted to lower layers1052, the PDCP Control PDUs1053, for acknowledged mode (AM) DRBs, the PDCP SDUs to be retransmitted1054, for AM DRBs, the PDCP Data PDUs to be retransmitted1055. From the RLC1060aspect, the data volume considers RLC SDUs and RLC SDU segments that have not yet been included in an RLC data PDU1061, RLC data PDUs that are pending for initial transmission1062, and RLC data PDUs that are pending for retransmission (RLC AM)1063.

FIG.11illustrates an exemplary flow chart for the selection of the ISDT initiation procedure. At step1101, the UE verifies a set of preconfigured inactive small data transmission (ISDT) conditions in a wireless network, wherein the UE is configured to perform small data transmission in a UE INACTIVE state when the set of preconfigured ISDT conditions are met. At step1102, the UE selects an ISDT initiation procedure based on one or more sets of selection conditions, wherein the one or more sets of selection conditions comprise a set of selection conditions for a radio resource control (RRC) procedure and a set of selection conditions for a uplink (UL) resource obtaining procedure, and wherein the RRC procedure is one selecting from an RRC-based procedure and an RRC-less procedure, and the UL resource obtaining procedure is one selecting from a random access (RA) procedure and a configured grant (CG) procedure. At step1103, the UE initiates small data transmission in the UE INACTIVE state following the selected ISDT initiation procedure. At step1104, the UE performs one or more data transmissions in the UE INACTIVE state.