Patent Description:
Wireless communications systems are widely deployed to provide various telecommunications services such as telephony, video, data, messaging, and broadcasts. Typical wireless communications systems may employ multiple-access technologies capable of supporting communications with multiple users by sharing available system resources (e.g., bandwidth, transmit power, and/or the like). Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency-division multiple access (FDMA) systems, orthogonal frequency-division multiple access (OFDMA) systems, single-carrier frequency-division multiple access (SC-FDMA) systems, time division synchronous code division multiple access (TD-SCDMA) systems, and long term evolution (LTE). LTE/LTE-Advanced is a set of enhancements to the universal mobile telecommunications system (UMTS) mobile standard promulgated by the Third Generation Partnership Project (3GPP). Narrowband (NB)-Internet of things (IoT) and enhanced machine-type communications (eMTC) are a set of enhancements to LTE for machine type communications.

A wireless communications network may include a number of base stations (BSs) that can support communications for a number of user equipment (UEs). The downlink (or forward link) refers to the communications link from the BS to the UE, and the uplink (or reverse link) refers to the communications link from the UE to the BS. As will be described in more detail, a BS may be referred to as a Node B, an evolved Node B (eNB), a gNB, an access point (AP), a radio head, a transmit and receive point (TRP), a new radio (NR) BS, a <NUM> Node B, and/or the like.

The above multiple access technologies have been adopted in various telecommunications standards to provide a common protocol that enables different user equipment to communicate on a municipal, national, regional, and even global level.

3GPP contribution "<NPL>, discusses aspects of SCG suspension including signaling. <CIT> relates to receiving packets over aggregated connections in a wireless communication system. <CIT> relates to applying of common discontinuous reception configuration.

In one aspect of the present disclosure, a method for wireless communication in a split bearer system performed by a user equipment, UE, as according to claim <NUM> is provided.

Another aspect of the present disclosure is directed to a UE as according to claim <NUM>.

In one aspect of the present disclosure, a method performed by a first base station as according to claim <NUM> is provided.

Another aspect of the present disclosure is directed to a first base station associated with a first RAT for a split bearer system, as according to claim <NUM>.

Aspects generally include methods and apparatuses as substantially described with reference to and as illustrated by the accompanying drawings and specification.

Additional features and advantages will be described. Characteristics of the concepts disclosed, both their organization and method of operation, together with associated advantages will be better understood from the following description when considered in connection with the accompanying figures.

So that features of the present disclosure can be understood in detail, a particular description may be had by reference to aspects, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only certain aspects of this disclosure and are therefore not to be considered limiting of its scope, for the description may admit to other equally effective aspects.

Various aspects of the disclosure are described more fully below with reference to the accompanying drawings.

Several aspects of telecommunications systems will now be presented with reference to various apparatuses and techniques.

It should be noted that while aspects may be described using terminology commonly associated with <NUM> and later wireless technologies, aspects of the present disclosure can be applied in other generation-based communications systems, such as and including <NUM> and/or <NUM> technologies.

In some deployment scenarios, a base station associated with a first radio access technology (RAT), such as a <NUM> new radio (NR) base station, may be deployed as a supplementary node (e.g., secondary node (SN)) to another base station associated with a second RAT, such as long-term evolution (LTE) base station. In such deployment scenarios, the base station associated with the second RAT may be deployed as a master node (MN). This type of deployment may also be referred to as a non-standalone (NSA) deployment using dual connectivity with inter-RAT base stations, such as LTE and <NUM> NR base stations. For ease of explanation, <NUM> NR may be referred to as NR. Different bearer types may be used for a non-standalone deployment, such as, a master cell group (MCG) bearer, secondary cell group (SCG) bearer, and split bearer, as according to the invention. For the split bearer, traffic, such as user plane traffic, is split between the base station associated with the first RAT (e.g., LTE) and the base station associated with the second RAT (e.g., NR).

In some cases, a user equipment (UE) may measure network latency based on a round trip time of a data packet. When using a split bearer, the round trip time may be the difference in time from transmitting a packet via an uplink channel associated with the first RAT and receiving a response via a downlink channel associated with the second RAT. In some examples, round trip time may be tested via a cross-radio access network (RAN) ping latency test. In conventional systems, a latency associated with a split bearer is larger in comparison to a latency associated with a standalone deployment. The increase in latency may be based on a delay of a connected mode discontinuous reception (CDRX) cycle, such as an NR CDRX cycle. Aspects of the present disclosure are directed to reducing latency of traffic across the split bearer.

The network <NUM> may be a <NUM> or NR network or some other wireless network, such as an LTE network. A BS is an entity that communicates with user equipment (UEs) and may also be referred to as a base station, an NR BS, a Node B, a gNB, a <NUM> node B (NB), an access point, a transmit and receive point (TRP), and/or the like. Each BS may provide communications coverage for a particular geographic area.

A BS may provide communications coverage for a macro cell, a pico cell, a femto cell, and/or another type of cell. The terms "eNB," "base station," "NR BS," "gNB," "TRP," "AP," "node B," "<NUM> NB," and "cell" may be used interchangeably.

In the example shown in <FIG>, a relay station 110d may communicate with macro BS 110a and a UE 120d in order to facilitate communications between the BS 110a and UE 120d.

The wireless network <NUM> may be a heterogeneous network that includes BSs of different types, e.g., macro BSs, pico BSs, femto BSs, relay BSs, and/or the like. These different types of BSs may have different transmit power levels, different coverage areas, and different impact on interference in the wireless network <NUM>.

As an example, the BSs <NUM> (shown as BS 110a, BS 110b, BS 110c, and BS 110d) and the core network <NUM> may exchange communications via backhaul links <NUM> (e.g., S1, etc.). Base stations <NUM> may communicate with one another over other backhaul links (e.g., X2, etc.) either directly or indirectly (e.g., through core network <NUM>).

The core network <NUM> may be an evolved packet core (EPC), which may include at least one mobility management entity (MME), at least one serving gateway (S-GW), and at least one packet data network (PDN) gateway (P-GW). The MME may be the control node that processes the signaling between the UEs <NUM> and the EPC. All user IP packets may be transferred through the S-GW, which itself may be connected to the P-GW. The P-GW may be connected to the network operator's IP services. The operator's IP services may include the Internet, the Intranet, an IP multimedia subsystem (IMS), and a packet-switched (PS) streaming service.

The core network <NUM> may provide user authentication, access authorization, tracking, IP connectivity, and other access, routing, or mobility functions. One or more of the base stations <NUM> or access node controllers (ANCs) may interface with the core network <NUM> through backhaul links <NUM> (e.g., S1, S2, etc.) and may perform radio configuration and scheduling for communications with the UEs <NUM>.

UEs <NUM> (e.g., 120a, 120b, 120c) may be dispersed throughout the wireless network <NUM>, and each UE may be stationary or mobile. A UE may be a cellular phone (e.g., a smart phone), a personal digital assistant (PDA), a wireless modem, a wireless communications device, a handheld device, a laptop computer, a cordless phone, a wireless local loop (WLL) station, a tablet, a camera, a gaming device, a netbook, a smartbook, an ultrabook, a medical device or equipment, biometric sensors/devices, wearable devices (smart watches, smart clothing, smart glasses, smart wrist bands, smart jewelry (e.g., smart ring, smart bracelet)), an entertainment device (e.g., a music or video device, or a satellite radio), a vehicular component or sensor, smart meters/sensors, industrial manufacturing equipment, a global positioning system device, or any other suitable device that is configured to communicate via a wireless or wired medium.

One or more UEs <NUM> may establish a protocol data unit (PDU) session for a network slice. In some cases, the UE <NUM> may select a network slice based on an application or subscription service. By having different network slices serving different applications or subscriptions, the UE <NUM> may improve its resource utilization in the wireless network <NUM>, while also satisfying performance specifications of individual applications of the UE <NUM>. In some cases, the network slices used by UE <NUM> may be served by an AMF (not shown in <FIG>) associated with one or both of the base station <NUM> or core network <NUM>. In addition, session management of the network slices may be performed by an access and mobility management function (AMF).

The UEs <NUM> may include a latency test module <NUM>. For brevity, only one UE 120d is shown as including the latency test module <NUM>. The latency test module <NUM> may transmits an uplink message to a first base station <NUM>. The first base station <NUM> may be associated with a first radio access technology (RAT). The latency test module <NUM> also transmits a scheduling request to a second base station <NUM> associated with a second RAT to trigger an extended connected mode discontinuous reception (CDRX) ON period. The first RAT may be LTE or NR, and the second RAT may be NR. The latency test module <NUM> also receives a downlink message from the second base station <NUM> during the extended CDRX ON period in response to transmitting the uplink message to the first base station <NUM>.

Additionally, one or more base stations <NUM>, such as a first base station <NUM> may include a latency test module <NUM> for receiving, from a second base station <NUM> of a second RAT, an uplink message transmitted by a UE <NUM>. The latency test module <NUM> may also receive, during a CDRX ON period of the UE <NUM>, a scheduling request from the UE <NUM>. The CDRX ON period may be activated after a first scheduled CDRX ON period and prior to a second scheduled CDRX ON period scheduled according to a CDRX cycle of the first RAT. The latency test module <NUM> also transmits, during an extension of the CDRX ON period of the UE <NUM>, a downlink message in response to the uplink message.

Some UEs may be considered machine-type communications (MTC) or evolved or enhanced machine-type communications (eMTC) UEs. A wireless node may provide, for example, connectivity for or to a network (e.g., a wide area network such as Internet or a cellular network) via a wired or wireless communications link. Some UEs may be considered a customer premises equipment (CPE).

In this case, the UE <NUM> may perform scheduling operations, resource selection operations, and/or other operations described elsewhere as being performed by the base station <NUM>. For example, the base station <NUM> may configure a UE <NUM> via downlink control information (DCI), radio resource control (RRC) signaling, a media access control-control element (MAC-CE) or via system information (e.g., a system information block (SIB).

<FIG> shows a block diagram of a design <NUM> of the base station <NUM> and UE <NUM>, which may be one of the base stations and one of the UEs in <FIG>. The base station <NUM> may be equipped with T antennas 234a through 234t, and UE <NUM> may be equipped with R antennas 252a through 252r, where in general T ≥ <NUM> and R ≥ <NUM>.

At the base station <NUM>, a transmit processor <NUM> may receive data from a data source <NUM> for one or more UEs, select one or more modulation and coding schemes (MCS) for each UE based at least in part on channel quality indicators (CQIs) received from the UE, process (e.g., encode and modulate) the data for each UE based at least in part on the MCS(s) selected for the UE, and provide data symbols for all UEs. Decreasing the MCS lowers throughput but increases reliability of the transmission. The transmit processor <NUM> may also process system information (e.g., for semi-static resource partitioning information (SRPI) and/or the like) and control information (e.g., CQI requests, grants, upper layer signaling, and/or the like) and provide overhead symbols and control symbols. The transmit processor <NUM> may also generate reference symbols for reference signals (e.g., the cell-specific reference signal (CRS)) and synchronization signals (e.g., the primary synchronization signal (PSS) and secondary synchronization signal (SSS)).

At the UE <NUM>, antennas 252a through 252r may receive the downlink signals from the base station <NUM> and/or other base stations and may provide received signals to demodulators (DEMODs) 254a through 254r, respectively. A receive processor <NUM> may process (e.g., demodulate and decode) the detected symbols, provide decoded data for the UE <NUM> to a data sink <NUM>, and provide decoded control information and system information to a controller/processor <NUM>. In some aspects, one or more components of the UE <NUM> may be included in a housing.

On the uplink, at the UE <NUM>, a transmit processor <NUM> may receive and process data from a data source <NUM> and control information (e.g., for reports comprising RSRP, RSSI, RSRQ, CQI, and/or the like) from the controller/processor <NUM>. The symbols from the transmit processor <NUM> may be precoded by a TX MIMO processor <NUM> if applicable, further processed by modulators 254a through 254r (e.g., for DFT-s-OFDM, CP-OFDM, and/or the like), and transmitted to the base station <NUM>. At the base station <NUM>, the uplink signals from the UE <NUM> and other UEs may be received by the antennas <NUM>, processed by the demodulators <NUM>, detected by a MIMO detector <NUM> if applicable, and further processed by a receive processor <NUM> to obtain decoded data and control information sent by the UE <NUM>. The receive processor <NUM> may provide the decoded data to a data sink <NUM> and the decoded control information to a controller/processor <NUM>. The base station <NUM> may include communications unit <NUM> and communicate to the core network <NUM> via the communications unit <NUM>. The core network <NUM> may include a communications unit <NUM>, a controller/processor <NUM>, and a memory <NUM>.

The controller/processor <NUM> of the base station <NUM>, the controller/processor <NUM> of the UE <NUM>, and/or any other component(s) of <FIG> may perform one or more techniques associated with reducing round trip time (RTT) latency for cross-RAN latency testing as described in more detail elsewhere. For example, the controller/processor <NUM> of the base station <NUM>, the controller/processor <NUM> of the UE <NUM>, and/or any other component(s) of <FIG> may perform or direct operations of, for example, the process of <FIG> and/or other processes as described. Memories <NUM> and <NUM> may store data and program codes for the base station <NUM> and UE <NUM>, respectively.

In some aspects helpful for understanding the invention, the UE <NUM> may include means for transmitting an uplink message to a first base station associated with a first RAT; means for transmitting one or more scheduling requests to a second base station associated with a second RAT to trigger an extended CDRX ON period; and means for receiving a downlink message from the second base station during the extended CDRX ON period in response to transmitting the uplink message to the first base station.

In some aspects helpful for understanding the invention, the base station <NUM> may include means for receiving, from a second base station of a second RAT, an uplink message transmitted by a UE; means for receiving, during a connected mode discontinuous reception (CDRX) ON period of the UE, one or more scheduling requests from the UE; and means for transmitting, during an extension of the CDRX ON period of the UE, a downlink message in response to the uplink message.

Such means may include one or more components of the UE <NUM> or base station <NUM> described in connection with <FIG>.

In some deployment scenarios, a base station associated with a first radio access technology (RAT), such as a <NUM> new radio (NR) base station, may be deployed as a supplementary node (e.g., secondary node (SN)) to another base station associated with a second RAT, such as long-term evolution (LTE) base station. In such deployment scenarios, the base station associated with the second RAT may be deployed as a master node (MN). This type of deployment may also be referred to as a non-standalone (NSA) deployment using dual connectivity with inter-RAT base stations, such as LTE and <NUM> NR base stations. Different bearer types may be used for a non-standalone deployment, such as, a master cell group (MCG) bearer, secondary cell group (SCG) bearer, and split bearer, as according to the claimed invention. For the split bearer, traffic, such as user plane traffic, is split between the base station associated with the first RAT (e.g., LTE) and the base station associated with the second RAT (e.g., NR).

As described, a UE may measure network latency based on a round trip time of a data packet. For a split bearer, the round trip time may be the difference in time from transmitting a packet via an uplink channel associated with the first RAT and receiving a response via a downlink channel associated with the second RAT. In some examples, round trip time may be tested via a cross-RAN ping latency test.

In some examples, network latency may increase when the split bearer is employed in a non-standalone access (NSA) deployment. That is, network throughput may decrease when a UE transmits uplink traffic to an LTE base station and receives downlink traffic from an NR base station. In conventional systems, a round trip time (RTT) of a packet for a split bearer is greater than the RTT of a packet in a standalone NR deployment (e.g., non-split bearer deployment). That is, a latency of a split bearer deployment is higher than a latency of a standalone NR deployment. The increase in latency may be based on a delay of a connected mode discontinuous reception (CDRX) cycle, such as an NR CDRX cycle. Aspects of the present disclosure are directed to reducing latency of traffic across the split bearer.

<FIG> is a diagram illustrating an example of a cross-RAN ping latency test, and may be helpful for understanding the invention. As shown in <FIG>, a UE <NUM> may transmit an uplink packet <NUM> to a first base station <NUM>, at time t1. At time t2, the first base station <NUM> forwards the uplink packet <NUM> to the core network <NUM>. The core network <NUM> may be an example of the core network <NUM> described with reference to <FIG>. At time t3, the core network <NUM> transmits a response <NUM> to the uplink packet <NUM>. As shown in <FIG>, the response <NUM> is transmitted to the first base station <NUM>. At time t4, the first base station <NUM> forwards the response <NUM> to the second base station <NUM> via a backhaul connection <NUM>, such as an X2 interface. The backhaul connection <NUM> may be a split bearer. At time t5, the second base station <NUM> transmits the response <NUM>, as a downlink packet <NUM>, to the UE <NUM>. In this example, the round trip time is the difference between time t1 and time t5.

In one configuration, the first base station <NUM> is a long-term evolution (LTE) base station (e.g., eNB) and the second base station <NUM> is a new radio (NR) base station (e.g., gNB). In another configuration, the first base station <NUM> and the second base station <NUM> are NR base stations. In this configuration, the first base station <NUM> may operate within a first frequency range (FR1), such as a sub-<NUM> frequency range, and the second base station <NUM> may operate within a second frequency range (FR2), such as a millimeter wave (mmW) frequency range. Alternatively, the first base station <NUM> may operate within FR2 and the second base station <NUM> may operate within FR1.

At the UE <NUM>, when using the split bearer, an NR packet data convergence protocol (PDCP) module (not shown) may separate PDCP protocol data units (PDUs) for processing by a first radio link control (RLC) module (not shown) for a first RAT (e.g., LTE or NR) and a second RLC module (not shown) for a second RAT (e.g., NR) for respective transmission. In the current example, uplink transmissions are directed to the first RLC module.

A latency test based on the round trip time may be performed when connected mode discontinuous reception (CDRX) is enabled at the UE for both a radio associated with a first RAT, such as an LTE radio, and a radio associated with a second RAT, such as an NR radio. As described above, the increased round trip time may be due to a length of a CDRX cycle, such as an NR CDRX cycle. <FIG>, which is helpful for understanding the invention, is a timing diagram illustrating an example of cross-radio access network (RAN) latency testing. For exemplary purposes, the cross-RAN latency test shown in <FIG> is directed to a cross-RAN ping latency test. Still, as described, the latency test is not limited to a ping test. The latency test may be performed by measuring a round trip time between transmitting a first data packet to the first RAT (e.g., LTE) and receiving a second data packet from the second RAT (e.g., NR) in response to the first data packet. For example, the latency test may be performed when data is transmitted and received for a video game or web-browsing application. Additionally, as described, the first RAT is not limited to an LTE RAT. The first RAT and the second RAT may be NR RATs, where the first RAT and the second RAT operate in different NR frequency ranges (e.g., FR1 and FR2).

In the example of <FIG>, CDRX is enabled for an LTE radio <NUM> and an NR radio <NUM> of a UE <NUM>, such as the UE <NUM> described with reference to <FIG>. At time t1a, the NR radio <NUM> enters a first scheduled CDRX ON period. Additionally, at time t2, the LTE radio <NUM> enters a CDRX ON period. The LTE radio <NUM> and NR radio <NUM> CDRX ON periods may overlap. At time t1b, the NR radio <NUM> transitions to a CDRX OFF period. In the example of <FIG>, the LTE radio <NUM> transmits a ping request, at time t3, over an LTE uplink, to an LTE base station <NUM>. In this example, the ping request falls within the CDRX OFF period of the NR radio <NUM>. In conventional systems, an NR base station <NUM> (e.g., gNB) waits until the second scheduled CDRX ON period, at time t4a, to send the corresponding ping response on an NR downlink, at time t4b. The first and second scheduled CDRX ON periods may be scheduled based on a configuration of the CDRX cycle for the NR radio <NUM> (e.g., NR CDRX cycle). A CDRX period for the NR radio <NUM> may be referred to as an NR CDRX period. Also, a CDRX period for the LTE radio <NUM> may be referred to as an LTE CDRX period.

As shown in <FIG>, the NR CDRX cycle is <NUM>. Thus, the NR base station <NUM> waits <NUM> until the next configured NR CDRX ON period (e.g., second scheduled CDRX ON period), at time t4a. In a best-case scenario, for a <NUM> NR CDRX cycle, when the ping request is transmitted at the end of the first scheduled CDRX cycle (e.g., time t1b), the delay may be <NUM>. In other scenarios, such as when the ping request is transmitted during an NR CDRX ON period, the delay may be greater than <NUM>. As shown in <FIG>, the LTE CDRX cycle is <NUM>. The CDRX cycle refers to a period between CDRX ON periods. A CDRX ON period may also be referred to as a CDRX awake period. Also, a CDRX OFF period may be referred to as a CDRX sleep period.

As described with respect to the example of <FIG>, for a split bearer system, the round trip time delay may be due to a length of the NR CDRX cycle. As previously described, a round trip time for a standalone test is less than the round trip time for the cross-RAN test.

<FIG>, which is helpful for understanding the invention, is a timing diagram illustrating an example of standalone NR latency testing. As shown in <FIG>, a UE <NUM> enters a first scheduled CDRX ON period, at time t1, and then enters a CDRX OFF period, at time t2. As described, the NR CDRX cycle is <NUM>. Based on the NR CDRX cycle, the second scheduled CDRX ON period is at time t9. Still, in the example of <FIG>, when a UE <NUM> enters the CDRX OFF period (time t2), the UE <NUM> may enter a CDRX ON period earlier than a scheduled CDRX ON period to transmit a ping request. That is, as shown in the example of <FIG>, the UE <NUM> enters a CDRX ON period (time t3a) to transmit a scheduling request to a base station <NUM>, at time t3b. The scheduling request (time t3b) may be transmitted to receive an uplink grant for transmitting a ping request. The CDRX ON period may be extended in response to transmitting a scheduling request and receiving an uplink grant. A time period between entering the CDRX OFF period, at time t2, and entering the CDRX ON period, at time t3a, may be less than the CDRX cycle. For example, the time period between entering the CDRX OFF period, at time t2, and entering the CDRX ON period, at time t3a, may be <NUM>.

As shown in <FIG>, the UE <NUM> receives an uplink (UL) grant from the base station <NUM>, at time t4, in response to transmitting the scheduling request, at time t3a. As described, the CDRX ON period is extended in response to transmitting the scheduling request, at time t3b. The CDRX ON period may be extended by extending a CDRX inactivity timer in response to receiving an uplink grant at time t4. In the example of <FIG>, the UE <NUM> extends the CDRX inactivity timer, at time t5, and transmits a ping request to the base station <NUM>, at time t6. The timing of the ping request is not limited to time t6. Transmission of a ping request may occur prior to extending the CDRX inactivity timer (e.g., before time t5), at a time when the CDRX inactivity timer is extended (e.g., at time t5), or during a period of the CDRX inactivity timer (e.g., between times t5 and t8). In response to transmitting the ping request, at time t6, the UE <NUM> may receive a ping response from the base station <NUM>, at time t7. The UE <NUM> may enter a CDRX OFF period, at time t8, upon expiration of the inactivity timer. Additionally, as shown in the example of <FIG>, the UE <NUM> may enter a second scheduled CDRX ON period, at time t9. In the example of <FIG>, the round trip time (RTT) is a time difference between sending the ping request, at time t6, and receiving the ping response, at time t7. In the example of <FIG>, the RTT is not delayed due to the CDRX cycle.

According to aspects of the present disclosure, during a cross-RAN performance test with CDRX enabled, such as NR CDRX, a UE transmits a scheduling request on an uplink associated with a first RAT, such as an NR RAT, before and/or after transmitting a ping request on an uplink associated with a second RAT, such as an LTE RAT. The UE enters a CDRX ON period earlier than scheduled in response to transmitting the scheduling request. Accordingly, the ping response is received earlier due to the earlier CDRX ON period.

<FIG> is a timing diagram illustrating an example of cross-radio access network (RAN) latency testing, in accordance with aspects of the present disclosure. In the example of <FIG>, connected mode discontinuous reception (CDRX) is enabled for an LTE radio <NUM> and an NR radio <NUM> of a UE <NUM>, such as the UE <NUM> described with reference to <FIG> and <FIG>. Additionally, in <FIG>, the LTE base station and the NR base station may each be an example of a base station <NUM> described with reference to <FIG> and <FIG>. Furthermore, <FIG> uses LTE and NR as examples of different RATs, aspects of the present disclosure are not limited to LTE and NR. For example, as discussed, the first RAT is not limited to an LTE RAT. The first RAT and the second RAT may be NR RATs, where the first RAT and the second RAT operate in different NR frequency ranges (e.g., FR1 and FR2). In the example of <FIG>, at time t1a, the NR radio <NUM> enters a first scheduled CDRX ON period. Additionally, at time t2, the LTE radio <NUM> enters a CDRX ON period. The LTE radio <NUM> and NR radio <NUM> CDRX ON periods may overlap. At time t1b, the NR radio <NUM> enters a CDRX OFF period. In the example of <FIG>, the LTE radio <NUM> transmits an uplink message to the LTE base station <NUM>, at time t3, over an LTE uplink and L2 interface. In this example, the uplink message falls within a CDRX OFF period. The uplink message may include a ping request, a data message, or control signaling. In one configuration, to reduce a round trip time between transmitting the uplink message (time t3) and receiving a corresponding downlink message, the UE <NUM> enters a CDRX ON period earlier than scheduled to transmit a scheduling request. In some examples helpful for understanding the invention, the scheduling request may be transmitted during a CDRX OFF period and transmission of the scheduling request may trigger the UE <NUM> to wake from the CDRX OFF period prior to a second scheduled CDRX ON period, at time t9, according to the CDRX cycle. In some examples, the uplink message and the corresponding downlink message may both include a data transfer.

For example, as shown in <FIG>, the UE <NUM> transmits a scheduling request to the NR base station <NUM>, at time t4a, and enters an earlier CDRX ON period, at time t4b, based on transmitting the scheduling request. According to the invention, the UE first enters the CDRX ON period and then transmits the scheduling request. At time t5, the NR radio <NUM> receives a UL grant from the NR base station <NUM> in response to the scheduling request transmitted at time t4b. Transmitting the scheduling request, at time t4b, and receiving the UL grant, at time t5, extends the inactivity timer, at time t6, such that the earlier CDRX ON period is extended. The NR radio <NUM> receives a downlink message from the NR base station <NUM>, at time t7. The round trip time may be determined based on a time difference between transmitting the uplink message, at time t3, and receiving the downlink message, at time t7. In the example of <FIG>, the round trip time is not delayed due to the CDRX cycle. The UE <NUM> may enter a CDRX OFF period, at time t8, upon expiration of the inactivity timer.

In the example of <FIG>, the LTE scheduling request (time t4a) is transmitted after the UE <NUM> transmits the uplink message (time t3) on the LTE uplink. Aspects of the present disclosure are not limited to transmitting the scheduling request after transmitting the uplink message (e.g., ping request). In one configuration, the NR scheduling request is transmitted before the UE <NUM> transmits the uplink message via the LTE uplink. That is, the scheduling request may be transmitted before time t3. In some examples, the scheduling request may be transmitted before and after time t3. In another configuration, the NR scheduling request is scheduled based on a network delay, a scheduling request delay, and an inactivity timer duration. For example, a time for scheduling transmission of the scheduling request may be determined as: network delay (e.g., NW_DELAY_MARGIN) - (scheduling request delay (e.g., SR_Delay_time) + inactivity timer duration (e.g., inactivity_timer_duration)).

Additionally, as described, the UE <NUM> is not limited to calculating the round trip time based on a ping latency test. The round trip time may be determined based on the time difference between transmitting data via the LTE uplink and receiving a response to the data transmission on the NR downlink.

In some cases, depending on a duration of the inactivity timer, the UE <NUM> may issue multiple scheduling requests if the UE <NUM> did not receive the ping response on the NR downlink in response to the ping request transmitted on the LTE uplink. In one configuration, the UE <NUM> may continue extending the CDRX ON period until the ping response is received on the NR downlink.

<FIG>, which is helpful for understanding the invention, is a flow diagram illustrating an example process <NUM> performed, for example, by a user equipment (UE) (e, in accordance with various aspects of the present disclosure. The UE may be an example of a UE <NUM> or <NUM> as described in <FIG>, <FIG>, and <FIG>, respectively. The example process <NUM> is an example of improving split bearer RTT latency.

As shown in <FIG>, in some aspects, the process <NUM> may include transmitting an uplink message to a first base station associated with a first radio access technology (RAT) (block <NUM>). For example, the UE (e.g., using the antenna <NUM>, DEMOD/MOD <NUM>, TX MIMO <NUM>, transmit processor <NUM>, controller/processor <NUM>, and/or memory <NUM>) can transmit an uplink message to a first base station (e.g., base station <NUM> or base station <NUM>) associated with a first RAT, such as LTE or NR. In some aspects, the process <NUM> may include transmitting a scheduling request to a second base station associated with a second RAT to trigger a connected mode discontinuous reception (CDRX) ON period (block <NUM>). For example, the UE (e.g., using the antenna <NUM>, DEMOD/MOD <NUM>, TX MIMO <NUM>, transmit processor <NUM>, controller/processor <NUM>, and/or memory <NUM>) can transmit one or more scheduling requests to a second base station (e.g., base station <NUM> or base station <NUM>) associated with a second RAT, such as NR. The one or more scheduling requests may be transmitted before and/or after the uplink message.

As shown in <FIG>, in some aspects, the process <NUM> may include receiving a downlink message from the second base station during the CDRX ON period in response to transmitting the uplink message to the first base station (block <NUM>). For example, the UE (e.g., using the antenna <NUM>, DEMOD/MOD <NUM>, MIMO detector <NUM>, receive processor <NUM>, controller/processor <NUM>, and/or memory <NUM>) can receive a downlink message from the second base station (e.g., base station <NUM> or base station <NUM>) associated with the second RAT, such as NR. In some examples, the downlink message may include a data transfer. Additionally, the uplink message may also include a data transfer.

<FIG> which is helpful for understanding the invention, is a flow diagram illustrating an example process <NUM> performed, for example, by a base station of a first RAT, such as NR, in accordance with various aspects of the present disclosure. The base station may be an example of the base station <NUM> or <NUM> as described in <FIG>, <FIG>, and <FIG>, respectively. The example process <NUM> is an example of improving NR split bearer RTT latency.

As shown in <FIG>, in some aspects, the process <NUM> may include receiving, from a second base station of a second RAT, an uplink message transmitted by a UE (block <NUM>). For example, a first base station of the first RAT (e.g., using the antenna <NUM>, MOD/DEMOD <NUM>, MIMO detector <NUM>, receive processor <NUM>, controller/processor <NUM>, and/or memory <NUM>) can receive, from a second base station associated with second RAT, an uplink message transmitted by a UE. In some aspects, the process <NUM> may include receiving, during a connected mode discontinuous reception (CDRX) OFF period of the UE, one or more scheduling requests from the UE (block <NUM>). The one or more scheduling requests may be transmitted by the UE before and/or after the uplink message. A CDRX ON period may be triggered at the UE based on the UE transmitting the one or more scheduling requests. The CDRX ON period may be activated after a first scheduled CDRX ON period and prior to a second scheduled CDRX ON period scheduled according to a CDRX cycle of the first RAT For example, the first base station (e.g., using the antenna <NUM>, MOD/DEMOD <NUM>, MIMO detector <NUM>, receive processor <NUM>, controller/processor <NUM>, and/or memory <NUM>) can receive a scheduling request from the UE (e.g., UE <NUM> or UE <NUM>).

As shown in <FIG>, in some aspects, the process <NUM> may include transmitting, during a CDRX ON period of the UE, a downlink message in response to the uplink message (block <NUM>). For example, the first base station (e.g., using the antenna <NUM>, MOD/DEMOD <NUM>, TX MIMO processor <NUM>, transmit processor <NUM>, controller/processor <NUM>, and/or memory <NUM>) can transmit a downlink message. In some examples, the downlink message may include a data transfer. Additionally, the uplink message may also include a data transfer.

As used, the term "component" is intended to be broadly construed as hardware, firmware, and/or a combination of hardware and software. As used, a processor is implemented in hardware, firmware, and/or a combination of hardware and software.

Some aspects are described in connection with thresholds. As used, satisfying a threshold may, depending on the context, refer to a value being greater than the threshold, greater than or equal to the threshold, less than the threshold, less than or equal to the threshold, equal to the threshold, not equal to the threshold, and/or the like.

It will be apparent that systems and/or methods described may be implemented in different forms of hardware, firmware, and/or a combination of hardware and software. Thus, the operation and behavior of the systems and/or methods were described without reference to specific software code-it being understood that software and hardware can be designed to implement the systems and/or methods based, at least in part, on the description.

Claim 1:
A method for wireless communication in a split bearer system performed by a user equipment, UE, comprising:
transmitting (<NUM>) an uplink message to a first base station associated with a first radio access technology, RAT;
entering a connected mode discontinuous reception, CDRX, ON period to transmit one or more scheduling requests, SRs, to a second base station associated with a second RAT;
transmitting the one or more SRs to the second base station associated with the second RAT during the CDRX ON period; and
receiving (<NUM>) a downlink message from the second base station during the CDRX ON period in response to transmitting the uplink message to the first base station.