Patent Description:
<NPL>) discussed the make-before-break solution for the mobility event of SCG change in dual connectivity, analyzed the standard impact for the solution of RACH-less handover and the solution of maintaining source eNB connection during handover from RAN3's point of view, and provided some proposals.

Advantageous, optional features of the invention are then set out in the accompanying dependent claims.

To the accomplishment of the foregoing and related ends, the one or more aspects include the features hereinafter fully described and particularly pointed out in the claims.

The base stations <NUM> may include macro cells (e.g., high power cellular base stations) and/or small cells (e.g., low power cellular base stations).

A network that includes both small cells and macro cells may be known as a heterogeneous network. The base stations <NUM> / UEs <NUM> may use spectrum up to Y MHz (e.g., <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) bandwidth per carrier allocated in a carrier aggregation of up to a total of Yx MHz (x component carriers) used for transmission in each direction. Allocation of carriers may be asymmetric with respect to DL and UL (e.g., more or less carriers may be allocated for DL than for UL).

The mmW base station (gNB <NUM>) may utilize beamforming <NUM> with the UE <NUM> to compensate for the extremely high path loss and short range.

The base station may also be referred to as a gNB, Node B, evolved Node B (eNB), an access point, a base transceiver station, a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS), an extended service set (ESS), or some other suitable terminology. The base station <NUM> provides an access point to the EPC <NUM> for a UE <NUM>. Examples of UEs <NUM> include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal digital assistant (PDA), a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (e.g., MP3 player), a camera, a game console, a tablet, a smart device, a wearable device, a vehicle, an electric meter, a gas pump, a large or small kitchen appliance, a healthcare device, an implant, a display, or any other similar functioning device.

Referring again to <FIG>, in certain aspects, the UE <NUM> may be configured to receive a pre-allocation resource for a target cell via a handover command, transmit a physical layer acknowledgment based on a target cell downlink packet, receive an indication for a communication with the target cell in response to the physical layer acknowledgement, and access the target cell using the pre-allocated resource based on the indication for the communication with the target cell (<NUM>). The pre-allocation resource for the target cell may be a resource for communication with the target cell that is allocated for a communication from the UE <NUM> and the target resource before use.

<FIG> is a diagram <NUM> illustrating an example of a DL subframe within a <NUM>/NR frame structure. <FIG> is a diagram <NUM> illustrating an example of channels within a DL subframe. <FIG> is a diagram <NUM> illustrating an example of an UL subframe within a <NUM>/NR frame structure. <FIG> is a diagram <NUM> illustrating an example of channels within an UL subframe. In the examples provided by <FIG>, the <NUM>/NR frame structure is assumed to be TDD, with subframe <NUM> a DL subframe and subframe <NUM> an UL subframe. While subframe <NUM> is illustrated as providing just DL and subframe <NUM> is illustrated as providing just UL, any particular subframe may be split into different subsets that provide both UL and DL. Note that the description infra applies also to a <NUM>/NR frame structure that is FDD.

For slot configuration <NUM>, different numerologies <NUM> to <NUM> allow for <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> slots, respectively, per subframe. The subcarrier spacing may be equal to <NUM>µ * <NUM> kKz, where µ is the numerology <NUM>-<NUM>. <FIG> provide an example of slot configuration <NUM> with <NUM> symbols per slot and numerology <NUM> with <NUM> slots per subframe.

As illustrated in <FIG>, some of the REs carry reference (pilot) signals (RS) for the UE (indicated as R). The RS may include demodulation RS (DM-RS) and channel state information reference signals (CSI-RS) for channel estimation at the UE.

<FIG> illustrates an example of various channels within a DL subframe of a frame. The physical control format indicator channel (PCFICH) is within symbol <NUM> of slot <NUM>, and carries a control format indicator (CFI) that indicates whether the physical downlink control channel (PDCCH) occupies <NUM>, <NUM>, or <NUM> symbols (<FIG> illustrates a PDCCH that occupies <NUM> symbols). The PDCCH carries downlink control information (DCI) within one or more control channel elements (CCEs), each CCE including nine RE groups (REGs), each REG including four consecutive REs in an OFDM symbol. A UE may be configured with a UE-specific enhanced PDCCH (ePDCCH) that also carries DCI. The ePDCCH may have <NUM>, <NUM>, or <NUM> RB pairs (<FIG> shows two RB pairs, each subset including one RB pair). The physical hybrid automatic repeat request (ARQ) (HARQ) indicator channel (PHICH) is also within symbol <NUM> of slot <NUM> and carries the HARQ indicator (HI) that indicates HARQ acknowledgement (ACK) / negative ACK (NACK) feedback based on the physical uplink shared channel (PUSCH). The primary synchronization channel (PSCH) may be within symbol <NUM> of slot <NUM> within subframes <NUM> and <NUM> of a frame. The PSCH carries a primary synchronization signal (PSS) that is used by a UE <NUM> to determine subframe/symbol timing and a physical layer identity. The secondary synchronization channel (SSCH) may be within symbol <NUM> of slot <NUM> within subframes <NUM> and <NUM> of a frame. The SSCH carries a secondary synchronization signal (SSS) that is used by a UE to determine a physical layer cell identity group number and radio frame timing. Based on the PCI, the UE can determine the locations of the aforementioned DL-RS. The physical broadcast channel (PBCH) which carries a master information block (MIB), may be logically grouped with the PSCH and SSCH to form a synchronization signal (SS)/PBCH block. The MIB provides a number of RBs in the DL system bandwidth, a PHICH configuration, and a system frame number (SFN).

As illustrated in <FIG>, some of the REs carry demodulation reference signals (DM-RS) for channel estimation at the base station. The UE may additionally transmit sounding reference signals (SRS) in the last symbol of a subframe.

<FIG> illustrates an example of various channels within an UL subframe of a frame. A physical random access channel (PRACH) may be within one or more subframes within a frame based on the PRACH configuration. The PRACH may include six consecutive RB pairs within a subframe. The PRACH allows the UE to perform initial system access and achieve UL synchronization. A physical uplink control channel (PUCCH) may be located on edges of the UL system bandwidth.

At the UE <NUM>, each receiver 354RX receives a signal through the receiver's respective antenna <NUM>.

Each receiver 318RX receives a signal through the receiver's 318RX respective antenna <NUM>.

<FIG> is a diagram of a device-to-device (D2D) communications system <NUM>. The D2D communications system <NUM> includes a plurality of UEs <NUM>, <NUM>, <NUM>, <NUM>. The D2D communications system <NUM> may overlap with a cellular communications system, such as for example, a WWAN. Some of the UEs <NUM>, <NUM>, <NUM>, <NUM> may communicate together in D2D communication using the downlink/uplink WWAN spectrum, some may communicate with the base station <NUM>, and some may do both. For example, as shown in <FIG>, the UEs <NUM>, <NUM> are in D2D communication and the UEs <NUM>, <NUM> are in D2D communication. The UEs <NUM>, <NUM> are also communicating with the base station <NUM>. The D2D communication may be through one or more sidelink channels, such as a physical sidelink broadcast channel (PSBCH), a physical sidelink discovery channel (PSDCH), a physical sidelink shared channel (PSSCH), and a physical sidelink control channel (PSCCH).

The exemplary methods and apparatuses discussed infra are applicable to any of a variety of wireless D2D communications systems, such as for example, a wireless device-to-device communication system based on FlashLinQ, WiMedia, Bluetooth, ZigBee, or Wi-Fi based on the IEEE <NUM> standard. To simplify the discussion, the exemplary methods and apparatus are discussed within the context of LTE. However, one of ordinary skill in the art would understand that the exemplary methods and apparatuses are applicable more generally to a variety of other wireless device-to-device communication systems.

Mobility interruption time may be defined as the shortest time duration supported by a system during which a user terminal, e.g., a UE, is unable to exchange user plane packets with any base station, e.g., a gNB, during a transition from one base station to another base station.

Some applications may be delay sensitive. Examples of delay sensitive applications may include remote control vehicles or remote driving vehicles. Other examples of delay sensitive applications may include augmented reality applications, e.g., in smart glasses, other specific machine communications requiring low latency, or other time sensitive communications.

The 3rd Generation Partnership Project (3GPP) is a collaboration between groups of telecommunications associations. 3GPP has promulgated lists of performance indexes for fifth generation mobile networks (<NUM>). Mobility interruption time reduction is one performance index for <NUM>. Mobility interruption time reduction may be required to support delay sensitive applications. The target for mobility interruption time may be zero milliseconds. Some embodiments described herein may decrease mobility interruption time relative to the mobility interruption time of pre-<NUM> communications systems. For example, some embodiments described herein may decrease mobility interruption time to zero milliseconds or something close to zero.

Some proposed solutions for decreasing mobility interruption time are based on UE capability enhancements. The UE capability enhancements may enable simultaneous intra-frequency target base station 102b (e.g., target cell) PUSCH transmission. Simultaneous intra-frequency target base station 102b PUSCH transmission may be used to send a handover complete message to a target. The UE capability enhancements may also enable source base station 102a downlink PDCCH packet reception for downlink data non-interruption (e.g., a lack of a mobility interruption) and/or PDSCH packet reception for downlink data non-interruption. The proposed solutions, however, may require changes in UE capability and, accordingly, may not be cost effective and/or backward compatible. Some aspects herein for decreasing mobility interruption time relate to a downlink data coordination procedure by which a network may receive an indication that a UE is synchronized to a target cell (e.g., to a target base station 102b in the target cell) and the UE is ready to transmit to or receive from the target base station 102b directly without performing a Random Access Chanel (RACH) procedure at the target base station 102b. A downlink data coordination procedure that does not perform the RACH procedure at the target base station 102b may avoid the increased UE capability requirements of the other proposed solutions discussed above. Some aspects proposed herein may provide a more complete solution. In other words, some examples proposed herein may achieve zero millisecond mobility interruption during handover. Additionally, aspects may be associated with an intra-frequency handover.

An example of a handover is discussed with respect to <FIG> and <FIG>. The example handover may be a fourth generation mobile network (<NUM>) handover procedure. In a <NUM> network, a mobility interruption may lead to a break down in data communication for delay sensitive applications. For example, mobility interruptions in <NUM> may, in some cases be too long for one or more of the delay sensitive applications discussed above (or other delay sensitive applications).

<FIG> is a diagram illustrating a handover signaling procedure <NUM>. The diagram illustrates signaling between the UE <NUM>, the source base station 102a, the target base station 102b, the MME <NUM>, and the serving gateway <NUM>. As illustrated in the diagram, when the UE <NUM> and the source base station 102a are in communication, e.g., prior to a handover, packet data may be transmitted and received between the UE <NUM> and the source base station 102a. Packet data may also be transmitted and received between the source base station 102a and the serving gateway <NUM>. The packet data may be, for example, user data from or to the UE.

A downlink allocation may be transmitted from the source base station to the UE <NUM>. The downlink allocation may be via level <NUM> or level <NUM> signaling, e.g., signaling data link level (level <NUM>) or signaling link level (level <NUM>). The downlink allocation may be a downlink resource allocation, such as an indication of a handover to a another base station, e.g., the target base station 102b. Additionally, at <NUM>, the source base station 102a may transmit a RRC connection reconfiguration message that includes mobility control information. The RRC connection reconfiguration message may be transmitted using level <NUM> signaling, e.g., signaling at the network level. Additionally, the RRC connection reconfiguration message may include information related to the handover to the new base station, e.g., the target base station 102b. Accordingly, the UE <NUM> may detach from the old cell (e.g., source base station 102a) and synchronize to the new cell (e.g., target base station 102b) at <NUM>. Additionally, the source base station 102a may deliver buffered and in-transit packets to the target base station 102b at <NUM>.

At <NUM>, the source base station 102a may transmit a serial number (SN) status transfer message to the target base station 102b. The SN status transfer message may be used to transfer received status information of the uplink data sent by the UE <NUM> as part of the handover. The SN status transfer message may be sent using level <NUM> signaling. Data, e.g., user data, may also be forwarded from the source base station 102a to the target base station 102b. The target base station 102b may buffer packets from the source base station 102a at <NUM>.

At <NUM>, the UE <NUM> may synchronize to the target base station 102b. Synchronization of the UE <NUM> with the target base station 102b may be performed using level <NUM> or level <NUM> signaling. For example, timing information may be transmitted between the UE <NUM> and the base station 102b over level <NUM> or level <NUM> so that the timing of the UE <NUM> may be synchronized with the timing at the base station <NUM>. At <NUM>, e.g., in a non-intra-frequency handover, the target base station 102b may allocate an uplink frequency for use to send data from the UE <NUM> to the target and a timing advance (TA) for the UE <NUM>. (In an intra-frequency handover the frequency may be unchanged. ) The TA may be used to make timing adjustments between the UE <NUM> and the target base station 102b. For example, because different UEs <NUM> in a cell may be located at different locations, the UEs <NUM> may need to initiate transmissions at different times in order for the UEs <NUM> transmissions to arrive at a base station <NUM> at the same time. The TA may be used for the timing adjustments. The target base station 102b uplink allocation and the TA for the UE <NUM> may be transmitted over level <NUM> or level <NUM> signaling.

At <NUM>, the UE <NUM> may send a RRC connection reconfiguration complete message indicating that the handover is complete. The UE <NUM> is in the cell of the target base station 102b, e.g., in a connected mode with the target base station 102b. In other words, the target base station 102b is now the serving cell of the UE <NUM>. The RRC connection reconfiguration complete message may be sent using level <NUM> signaling. After the UE <NUM> sends a RRC connection reconfiguration complete message indicating that the handover is complete, packet data, e.g., user data, may be sent and received between the UE <NUM>, the target base station 102b (now the new source base station of the new serving cell), and the serving gateway <NUM>. As illustrated in the diagram, when the UE <NUM> and the target base station 102b are in communication, e.g., after a handover, packet data may be transmitted and received between the UE <NUM> and the target base station 102b. Packet data may also be transmitted and received between the target base station 102b and the serving gateway <NUM>.

<FIG> is a diagram <NUM> illustrating four phases (e.g., Phase I, Phase II, Phase III, and Phase IV) in a handover of the UE <NUM> from the source base station 102a to the target base station 102b. The handover procedure discussed with respect to <FIG> may be divided into four phases. In Phase I, the UE <NUM> may send a measurement report to the source base station 102a. The UE <NUM> may send the measurement report to the source base station 102a before the UE <NUM> receives a handover command, e.g., a RRC connection reconfiguration message from the source base station 102a. The source base station 102a may transmit a handover request to the target base station 102b and receive a handover request acknowledge from the target base station 102b before transmitting the handover command, e.g., the RRC connection reconfiguration message, to the UE <NUM>.

In Phase II, e.g., from the end of Phase I to when the UE <NUM> performs a RACH procedure with the target base station 102b, the source base station 102a may send the SN status transfer to the target base station 102b.

In Phase III, e.g., from the end of Phase II to when the UE <NUM> sends the RRC reconfiguration complete message to target base station 102b, the target base station 102b sends a random access response (RAR) to the UE <NUM>. The UE <NUM> may then send the RRC reconfiguration complete message to the target base station 102b.

In Phase IV, e.g., after the RRC reconfiguration complete message, a path switch request path switch acknowledge may be transmitted by the target base station 102b to the MME <NUM>. Additionally, a UE context release message may be transmitted from the source base station 102a to the target base station 102b.

The four phases illustrated in <FIG> may be used in conjunction with a <NUM> system as part of a handover from one base station <NUM> (e.g., the source base station 102a) to another base station (e.g., the target base station 102b). As discussed above, mobility interruption time may be defined as the shortest time duration supported by a system during which a user terminal, e.g., a UE, is unable to exchange user plane packets with any base station, e.g., a base station, during a transition from one base station to another base station. As illustrated in <FIG>, the mobility interruption happens in Phase II and Phase III. Table <NUM> (below) may be referred to for mobility interruption analysis. Table <NUM> lists example delays for various operations in the example handover illustrated in <FIG>.

The mobility interruption components may be grouped into four parts. Mobility interruption part <NUM> is handover message handling. Handover message handling may introduce a mobility interruption of <NUM> in the illustrated example of handover described herein. The handover message handling is also referred to as <NUM>. The handover message handling includes the RRC procedure delay. The RRC procedure delay includes RRC connection reconfiguration and mobility control information as well as related reconfiguration information, such as information related to changing from one base station 102a to another base station 102b. The RRC procedure delay may also include resetting the MAC layer, reconfiguring the PDCP, reconfiguring the RLC layer, and reconfiguring L3.

Mobility interruption part <NUM> is target base station 102b synchronization. The target base station 102b synchronization in the illustrated example may introduce a mobility interruption of <NUM>. The target base station 102b synchronization includes a mobility interruption time based on delays introduced by <NUM> and at <NUM>. Accordingly, the target base station 102b synchronization related mobility interruption includes time for a target base station 102b search, a UE processing time for RF/baseband retuning, time for a derive target base station specific keys, and a configure security algorithm related interruption time, The configuration security algorithm may be used in a target base station 102b and may increase the mobility interruption time. The target base station 102b synchronization related mobility interruption includes the RACH procedure. The RACH procedure may include an uncertainty delay to acquire a RACH opportunity followed by a PRACH preamble transmission.

The mobility interruption part <NUM> may include a PRACH procedure. In the illustrated example, the mobility interruption part <NUM> has a mobility interruption time that is <NUM>. The mobility interruption time includes at <NUM>, a delay of <NUM> to acquire first available PRACH, at <NUM>, a delay of <NUM> for a PRACH Transmission, and at <NUM> a delay of <NUM> for an uplink Allocation + TA for UE.

The mobility interruption part <NUM> may include transmission of a RRC reconfigure complete message. The mobility interruption time due to the RRC configuration is <NUM>. The mobility interruption time for part <NUM> in the illustrated example includes at <NUM> a UE <NUM> sending a RRC connection reconfiguration message. The mobility interruption time for a UE <NUM> sending the RRC connection reconfiguration message in the illustrated example is <NUM>.

The examples described herein include techniques for mobility interruption reduction in each part, e.g., parts <NUM>, <NUM>, <NUM>, and <NUM>. The examples for parts <NUM>, <NUM>, <NUM>, or <NUM> may be used alone or in combination. Furthermore, in some examples, subsets of one or more of the proposals for each part, e.g., parts <NUM>, <NUM>, <NUM>, or <NUM>, may be used to reduce a mobility interruption.

In an example for mobility interruption reduction for part <NUM>, e.g., handover message handling in <NUM>, the mobility interruption may include UE <NUM> RRC procedure delay. For example, in part <NUM>, the UE <NUM> receives the RRC connection reconfiguration message. The RRC connection reconfiguration message may include parameters for a handover (HO). The UE <NUM> may be commanded by the source base station 102a to perform the handover (HO). The part <NUM> mobility interruption reduction may be from both the network side, e.g., the base stations <NUM>, and the UE <NUM> side.

<FIG> is a signaling diagram <NUM> related to packet bi-casting. Bi-casting is transmitting to both a source base station 102a and a target base station 102b. Bi-casting may be used in conjunction with other aspects described herein to decrease mobility interruption time. In an example, the network side may bi-cast a received packet and an enhanced Packet Data Convergence Protocol (PDCP) SN update. With packet bi-casting, a source new radio access network (RAN), e.g., within a coverage area <NUM>, node X2 communication link (or S1 interfaces) may start to transmit downlink packets to both the source base station 102a and the target base station. Transmitting DL packets to both the source base station 102a and the target base station 102b differs from other handover data forwarding, which only forwards a received packet to the target base station 102b with no copy of the received packet retained at the source base station 102a. Packet bi-casting may be defined as not only sending a copy of a received packet to the target base station 102b, e.g., a base station in a coverage area <NUM>, but also storing the packet or continuing to store the packet at the source base station 102a, e.g., after transmission is complete. For example, the UE <NUM>, a RAN node, or both may bi-cast to both the base station 102a and the base station 102b. In some examples, data transmissions, e.g., from the RAN, may continue for a while after the RRC connection reconfiguration including mobility control is sent to the UE <NUM>. In some examples, receiving in the source RAN node may also continue for a while after the RRC connection reconfiguration including mobility control is sent to the UE <NUM>.

An example device may receive a pre-allocation resource for a target cell via a handover command and determine a handover message handling period. The device may also bi-cast downlink date to a source base station and a target base station during the handover message handling period.

<FIG> graphically illustrates four options for the timing of packet bi-casting, option A, option B, option C, and Option D. With option A, a device, e.g., the source base station 102a, may start packet bi-casting immediately after sending a handover command to UE <NUM>. As illustrated in <FIG>, by the letter "A," packet bi-casting starts immediately after sending the handover command, e.g., the RRC connection reconfiguration message including mobility control information, to UE <NUM>.

With option B, a device, e.g., the source base station 102a, may start packet bi-casting within the time duration when the UE <NUM> is processing the handover (HO) message. For example, as illustrated in <FIG>, by the letter "B," the source base station 102a starts packet bi-casting within the time duration when the UE <NUM> is processing the handover (HO) message.

With option C, a device, e.g., the source base station 102a, may start packet bi-casting within the time duration when the UE <NUM> is RF baseband re-tuning to the target base station frequency, e.g., at <NUM>. The RF-retuning procedure may be skipped when the network is synchronized and the UE <NUM> is in an intra-frequency handover. For example, as illustrated in <FIG>, by the letter "C," the source base station 102a, starts packet bi-casting within the time duration when the UE <NUM> is RF baseband re-tuning to the target base station frequency. When the network is synchronized and the UE <NUM> is in an intra-frequency handover the packet bi-casting may be started in advance (e.g., option B, C). For example, the RF-retuning procedure may be skipped for an intra-frequency handover (HO).

With option D, a device, e.g., the source base station 102a, may start data bi-casting within the time duration when the UE <NUM> is performing a RACH procedure <NUM>. For example, as illustrated in <FIG>, by the letter "D," the source base station 102a may start data bi-casting within a time duration that may be needed by the UE <NUM> to perform the RACH procedure <NUM>. The RACH procedure is highlighted by the dashed line rectangle. The RACH procedure <NUM> is optional in some cases. When the RACH procedure <NUM> is used, however, the packet bi-casting may need to be started in advance (e.g., options A, B, C).

The timing of bi-casting may be determined based on a consideration of a series of factors. The time to start packet bi-casting should not be too early or too late, e.g., with respect to a particular handover (HO), as defined by a consideration of the factors described herein, as well as other factors known to a person of skill in the art. The earlier the data packet bi-casting to a target, e.g., the base station 102b, starts, the more data the target node may have to buffer. Conversely, the later the packet bi-casting begins, the greater the risk that a source node, e.g., a source base station 102a, signal may degrade before the UE <NUM> receives the packet. When a source node, base station 102a, signal degrades before the UE <NUM> receives the packet, the packet may not be receivable by the UE <NUM>, and packet loss may occur.

The time to start packet bi-casting may consider the following factors, (<NUM>) target node buffer requirements (e.g., large buffer size, medium buffer size, or low buffer size), (<NUM>) the Xn backhaul (a backhaul communication link)(ideal or non-ideal backhaul) (whether the UE <NUM> needs to downlink synchronize to the target may determine whether <NUM> is needed or not. ), (<NUM>) whether RACH procedure <NUM> is needed or not. (at <NUM> ~<NUM>), and/or (<NUM>) the UE <NUM> capability (simultaneous or concurrent Rx/Tx with target and Rx/TX with source). Various different implementations may select different timing of packet bi-casting after consideration the above parameters.

Some aspects may perform a PDCP SN Update. A SN status transfer procedure may also be enhanced to support the mobility interruption reduction. In <NUM>, the source base station 102a stops downlink data transmission and downlink PDCP SN allocation when the source base station 102a sends a RRC handover command to the UE <NUM>. The source base station 102a sends a SN status Transfer to a target base station 102b after the source base station 102a stops downlink PDCP SN allocation. The SN status transfer may indicate the PDCP SN to allocate to packets that do not have a PDCP SN. The source base station 102a may also indicate hyper frame number (HFN) values for both an uplink and a downlink. The parameter in the SN status transfer may be input to the target base station 102b for downlink and uplink data encryption and decryption in the target base station 102b.

In an aspect, to achieve low or zero millisecond mobility interruption during handover, the source node base station <NUM> may continue packet reception and packet transmission and downlink PDCP SN allocation after the source node base station <NUM> sends the handover command to the UE <NUM>. Accordingly, the SN status transfer does not use the PDCP SN to allocate packets. The base station <NUM> may already have allocated resources for the forwarded PDCP.

For a downlink PDCP SN update, when a target base station <NUM> starts a downlink transmission, the target base station 102b may update the "real" downlink PDCP SN according to the downlink PDCP SN and the Hyper-Frame Number (HFN) in the SN Status transfer message and the downlink packet count. For an uplink PDCP SN update, when the UE <NUM> starts to access a target base station 102b, e.g., starts a connection procedure to the base station <NUM>, the update uplink SN may be reported from the source base station 102a to the target base station 102b via Xn backhaul, as discussed with respect to the downlink data coordination procedure. When the UE <NUM> accesses a target base station 102b, duplicate downlink PDCPs status reports may have already been received by the UE <NUM> from the source base station 102a. According to a UE PDCP status report, when the UE <NUM> accesses the target node base station <NUM>, the target node base station <NUM> may remove the duplicated packets, for example, the target base station 102b may remove the duplicates based on a status report that include which packets have been received by the UE <NUM> such that the target base station 102b removes the duplicates from the transmit buffer. In an example, the target base station 102b may otherwise not send the duplicates to the UE <NUM>.

<FIG> is a diagram <NUM> illustrating a UE <NUM> with a dual stack that may be used to a decrease mobility interruption time during handover. In <NUM>, for example, the UE <NUM> stops transmitting and receiving packets after a handover command is received. To achieve a lower or zero millisecond mobility interruption during handover, the UE <NUM> maintains transmission and reception of packets from the source base station 102a after the source base station 102a receives a handover command (at <NUM>), e.g., the UE <NUM> maintains a temporary dual stack, such as a TCP/IP protocol dual stack, one stack for the source base station 102a and one stack for the target base station 102b.

At <NUM>, when the UE <NUM> receives a handover command from the source base station 102a, the UE <NUM> does not stop downlink packet reception and uplink packet transmission via a source protocol stack associated with the source base station 102a while preparing the layer <NUM> and layer <NUM> protocol configuration for the target base station. At <NUM>, the UE <NUM> may need to re-tune the UE's <NUM> RF chain for target base station 102b downlink synchronization. During the re-tuning and synchronization time, the uplink packet transmission from the UE <NUM> to the target base station 102b may also be transmitted using the source protocol stack and the downlink transmission from the target base station 102b to the UE <NUM> may be received in the source protocol stack. Accordingly, continuous packet transmissions may occur. The RACH, starting at <NUM> and ending during <NUM>, may be skipped in aspects that do not need the RACH, as described herein.

In <NUM>, at <NUM> the UE <NUM> may send handover complete packets to the target base station 102b. The handover complete packets may be packets that indicate that a handover is completed. Using the downlink data coordination method described herein, <NUM> may be skipped by a target base station 102b. The target base station 102b may obtain an indication that the UE <NUM> is ready to access the target base station's 102b downlink and uplink directly, e.g., the UE <NUM> may communicate directly with the target base station 102b, without sending a handover complete to the target base station 102b. In some systems, on receipt of the handover complete packets at the source base station 102a from the UE <NUM>, a gateway may send one, or more, dummy packets. The source base station 102a may forward the dummy packets to the target base station 102b. The target base station 102b may then start sending fresh data when the base station 102b receives the dummy packets from the source base station 102a. The handover complete packets may not need to be sent in each aspect. For example, when packets are simultaneously sent from both the source base station 102a and the target base station 102b a handover complete packet may not be needed. The handover complete packet may not be needed because the handover may be completed by source base station 102a and then source base station <NUM> may discontinuing the sending of packets to the UE <NUM>. When the source base station 102a discontinues sending packets to the UE <NUM>, the target base station 102b may already be sending packets to the UE <NUM>. Duplicate packet sending may allow for overlap between the transmissions until the handover is known to be complete at the base station 102a.

In the downlink data coordination procedure, the downlink data may be jointly scheduled, for example, by the base station 102a and the base station 102b. The source base station 102a and the target base station 102b may simultaneously transmit a downlink data transmission. The downlink data transmission by the source base station 102a and/or target base station 102b may be transparent to the UE <NUM>. The UE <NUM> may use the source base station 102a protocol stack to receive downlink data and transmit uplink data. The UE <NUM> may receive both target and source packets using the source stack. For example, both target and source packets may be stored to the source stack and retrieved from the source stack. In an aspect, a memory may be used to store data received as part of a target packet. The memory may also be used to store data received as part of a source packet. The data stored in the memory (e. , data received as part of a target packet and/or data received as part of a source packet) may be read from memory when the data later needs to be received.

After the UE <NUM> is ready to access a target base station control channel (the control channel may be determined by the target base station 102b according to an uplinkACK of a pre-configured PUCCH of target base station 102b or by an action time which is received by the UE <NUM> from the source MAC CE), the UE <NUM> may access the target base station 102b downlink and uplink using the target base station protocol stack. For example, the UE <NUM> may prepare the target base station protocol stack according to a handover command configuration while continuing UL/DL data transmission with the source base station.

The UE <NUM> may need to downlink synchronize with the target base station 102b before the UE <NUM> may access the target base station 102b. Additionally, the UE <NUM> may need to read the target base station 102b PSS and SSS. In another example, in order to achieve a lower or zero mobility interruption during a handover, the UE <NUM> may have an enhanced capability of simultaneous Rx from two intra-frequency cells (target cell: receive PSS/SSS/CRS and source cell: receive PDCCH/PDSCH) and transmission to source base station 102a PUCCH/PUSCH. The UE <NUM> enhanced capability may be defined as the UE <NUM> supporting simultaneous Rx from two intra-frequency cells ( receive PSS/SSS/CRS from target base station and receive PDCCH/PDSCH from source base station) while transmitting to source base station 102a PUCCH/PUSCH, e.g., while transmitting PUCCH/PUSCH to the source base station 102a.

In, for example, in a <NUM> handover procedure, the UE <NUM> may perform a RACH procedure with a target base station 102b after a target base station 102b downlink synchronization. In the RACH procedure, the UE <NUM> may acquire target base station 102b uplink time alignment, perform power ramping, and obtain an uplink grant to transmit the RRC reconfiguration complete message to the target base station 102b. After transmitting the RRC reconfiguration complete message to the target base station 102b, the target base station 102b knows the UE <NUM> is ready to receive downlink transmissions from the target base station 102b and transmit uplink transmissions to the target base station 102b.

As discussed above, however, the RACH procedure may be avoided at least in some aspects without introducing any new time alignment control or estimation mechanism. The RACH procedure may be avoided because the network knows when the timing alignment is the same for both the source base station 102a and the target base station 102b, for example, during a small cell handover. In a small cell handover, "RACH-less" operation may be enabled by setting the timing advance to zero, TA = <NUM>. TA is a time offset for various UEs. The TA may be used to cause an offset of timing in a UE, e.g., UE <NUM>. In other words, the TA may change the timing of events at the UE <NUM> so that transmissions to a base station <NUM> may arrive at the base station <NUM> at an appropriate time based on timing at that base station <NUM>. Different TA values may be used based on distance of the UE <NUM> from a base station <NUM>. In a small cell handover, TA may be set to zero because the distances from a UE <NUM> or UEs <NUM> and a base station may be small. Furthermore, the TA may be <NUM> because in a small cell handover (HO) the distance from the UE <NUM> to the source base station 102a and to the target base station 102b is about the same hence timing alignment is the same.

In another example, for an intra-base station handover (e.g., when a network transmission site is collocated), the RACH-less operation reusing the current TA value may be applicable. The same, e.g., non-zero TA value, may be used for collocated base stations <NUM> because the distance from the base stations <NUM> to the UE <NUM> will generally be the same or nearly equal.

In an aspect, for general handover scenarios which are neither a small cell handover nor an intra-base station handover, the target base station 102b TA may be acquired without the RACH procedure through a UE <NUM> based method or network based method. For example, for a UE-based TA calculation, a new Uplink TA of the target base station 102b may be formulated as: <MAT> where TA is the Time Alignment, NTA,UE is a downlink subframe boundary difference between the source base station 102a and the target base station 102b, depending on the particular UE implementation and where NTA,new is based on the old base station time alignment (NTA,old) and the TA difference between source base station and target base station.

In an example, the TA value of (NTA,UE) may be calculated by the UE <NUM> based on the downlink subframe boundary difference between the source base station 102a and the target base station 102b. For example, a same downlink subframe boundary at the source base station 102a and the target base station 102b may be used and the offset in the boundary may be the offset. In another example, the TA value may be up to the UE implementation.

For the network based TA calculation, a target base station 102b may measure a UE <NUM> uplink signal at a certain Xn coordinated transmission time interval (TTI). The target base station 102b may compare the timing of the Xn coordinated TTI relative to a desired timing for such a UE uplink signal and base the TA value on a difference between the two. The uplink signal may or may not be uplink timing alignment specific (chirp, SRS). The target base station 102b may measure the relative TA and forward the relative TA to the source base station 102a and to the UE <NUM> as described below.

For the target base station 102b uplink grant, in <NUM>, first the uplink grant from target base station 102b may be used for the handover UE <NUM> to send the RRC reconfiguration complete message to target base station 102b. The RRC reconfiguration complete message indicates to the target that the UE <NUM> has access to the target base station 102b and the UE <NUM> may start downlink and uplink packet scheduling.

A "target base station pre-allocated periodic uplink grant" may be used for a RACH-less solution. In certain cases, a RACH-less procedure for handovers may employ a target base station 102b uplink grant. The target base station 102b may use a pre-allocated periodic uplink grant. For example, the target base station 102b PUSCH may be pre-allocated to the UE <NUM> via a handover command as an semi-persistent scheduling (SPS)-like interval (e.g., an interval with the same periodicity, as well as having other similar attributes such as the particular resources used for the SPS) with the indication of a sub-frame location. But a "target base station pre-allocated periodic uplink grant" solution requires a UE <NUM> capability enhancement to achieve a low or non-interruption handover, e.g.. , the UE <NUM> may need additional capability to support simultaneous intra-frequency target base station 102b PUSCH transmission and source base station 102a downlink PDCCH/PDSCH packet reception.

Some aspects described herein may include a downlink data coordination method which may have no additional UE capability requirement to achieve a lower or non-interruption handover. The downlink data coordination method may include a target base station 102b pre-allocation of an uplink/downlink resource to the UE <NUM> via a handover command. The handover command may have an SPS-like interval. In other words, the handover command may have, for example, the same periodicity as the SPS.

In the downlink data coordination method, the downlink data coordination procedure may be triggered. The downlink data coordination procedure may be triggered at the UE <NUM> based on receiving a UE physical layer ACK feedback, i.e., feedback from a network in response to the UE physical layer ACK. The UE physical layer ACK feedback may be in a target base station 102b downlink packet. The target base station 102b downlink packet may be transmitted from the base station 102b to the UE <NUM>. The source radio access network (RAN) node may instruct the UE to direct uplink transmissions to the target base station 102b and/or direct downlink transmissions from the target base station 102b in a next pre-allocated Transmission Time Interval (TTI) on the pre-allocated resource. For example, the UE <NUM> may direct uplink transmissions to the target base station 102b. The UE may signal the network to direct downlink transmissions from the target base station 102b in a next pre-allocated TTI on the pre-allocated resource.

The UE <NUM> may access a target base station 102b directly for UP data transmission without the RACH procedure or the RRC reconfiguration complete message being sent to the target base station 102b. In an aspect, there may be no additional capability requirement for the UE <NUM> to support simultaneous or concurrent intra-frequency target base station 102b PUSCH transmission and source base station 102a downlink PDCCH/PDSCH packet reception.

<FIG> is a diagram <NUM> illustrating X2/Xn downlink data coordination. In <NUM>-<NUM>, during handover preparation, as shown in <FIG>, eMob capability may be negotiated between the UE <NUM> and the target base station 102b via the source base station 102a. The term "eMob" refers to the capability to support zero mobility handover functionality including dual stack (UE side) and the downlink data coordination procedure (UE side and network side). When the target base station 102b acknowledges support of the eMob feature, then the source base station 102a may send the RRC reconfiguration message with handoverControlIn (an indication that may be carried in the RRC reconfiguration message) for an indication of eMob activation that eMob has been activated.

In a handover execution stage <NUM> (e.g., during <NUM>-<NUM> of <FIG>), when the UE <NUM> receives a handover command from the source base station 102a, the UE <NUM> starts to setup a dual protocol stack (i.e. dual stack establishment). The UE <NUM> may also reconfigure the UE's <NUM> layer <NUM> and layer <NUM> parameters, while continuing to receive downlink packets and transmit uplink packets via the source protocol stack. The target base station 102b may start to measure the UE's SRS in order to adjust the UE uplink time alignment and send the uplink grant. At <NUM>, the source gNB 102a may start downlink PDCP data bi-casting, e.g., transmission of packets to multiple devices, e.g., to the target base station 102b and/or the UE <NUM> via Xn (copy downlink data to target) and Uu. At <NUM>, the UE <NUM> may synchronize to the target base station 102b (e.g., a base station that is in a target cell). The UE <NUM> may simultaneously or concurrently receive from two intra-frequency cells (target cell: receive PSS/SSS/CRS and source base station 102a: receive PDCCH/PDSCH) and transmit to source base station 102a PUCCH/PUSCH.

In handover execution stage <NUM> (e.g., <NUM> - <NUM> of <FIG>), at <NUM>-<NUM>, there may be Xn downlink data coordination between the source base station 102a and the target base station 102b. The Xn may be useful for providing the downlink data coordination. However, Xn messages are not required because downlink data coordination is not required. Xn messages and downlink data coordination are not required because the latency requirement of Xn may not be very strict. For example, in some aspects, the Xn transmission latency may be more loose than carrier aggregation (CA).

At <NUM>, the source base station 102a may schedule a downlink data transmission on both the source base station 102a and the target base station 102b using at least two codewords. The two codewords may contain the information needed to schedule a downlink data transmission on both the source base station 102a and the target base station 102b. At <NUM>, the target base station 102b sends a downlink packet together with a measured TA and the pre-allocated uplink grant (e.g., may be a SPS like grant) in the MAC control element (CE) to the UE <NUM>. At <NUM>, if an ACK to the target gNB 102b transmission is received by the source base station 102a, the source base station 102a may know that the target base station 102b signal situation is suitable for direct access to the target base station 102b by the UE <NUM>. If a NACK is received, e.g., from the UE <NUM>, e.g., in response to the sent downlink packet, <NUM>-<NUM> may be repeated until the UE <NUM> can correctly receive downlink data from the target base station 102b, e.g., when the UE <NUM> receives data from the target base station 102b that may be verified as valid and correct data using data verification techniques such as check sums or other data detection or data correction methods.

In the Handover Execution Stage <NUM> (e.g., <NUM> - <NUM> of <FIG>), for <NUM>-<NUM>, the source base station 102a notifies the UE <NUM> to access the target base station 102b directly at target base station 102b pre-allocated subframe X. The pre-allocated subframe X may be a semi-persistent resource allocation which may be provided to the UE <NUM> in a handover command. The source base station 102a may also notify the target base station 102b via an X2/Xn message of the SN Status update for the last uplink packet and the SN the source base station 102a received. The source base station 102a may also notify the target base station 102b via an X2/Xn message of the pre-allocated subframe x at which the UE <NUM> may appear to the target.

At <NUM>, at subframe x, the UE <NUM> may tune the UE's <NUM> receiver to the frequency of the target base station 102b to receive PDCCH, PDSCH from the target base station 102b. In an aspect, a notification from the source base station 102a to the target base station 102b about the subframe X when the UE <NUM> is available may not be sent. Rather, the target base station 102b may monitor the target base station 102b's semi pre-allocated uplink resource PUCCH to the UE. If the UE feedback is an ACK via the target base station 102b PUCCH, the target base station 102b determines that the UE <NUM> is in the connected mode with the target base station 102b and that the UE <NUM> may be scheduled by the target base station 102b.

At <NUM>, at a same subframe, e.g., subframe "x," the UE <NUM> may send an RRC configuration message and a PDCP status report to the target base station 102b (gNB, next generation eNB) <NUM>. The target base station 102b may remove the received duplicated packets, e.g., from a stream of data the target base station <NUM> is receiving by comparing packets to already received packets and start to schedule the remaining packets to the UE. At <NUM>-<NUM>, the path used to route packets to the UE <NUM> may switch from the source base station 102a to the target base station 102b. In other words, the UE <NUM> may begin using the target base station 102b as the base station <NUM> that the UE <NUM> is connected to.

Various aspects described herein may be used in combination to reduce user plane mobility interruption and may achieve a zero millisecond Mob or reduced user plane mobility interruption during handover. Aspects may use network bi-casting of downlink data to a source node and to a target node during handover message handling period. The time when packet bi-casting starts may vary depending on the implementation (e.g., target node buffer size, Xn backhaul reliability, UE capability, RACH-less access to the target base station 102b, as well as other considerations).

In some aspects, the uplink PDCP SN update procedure may, after a UE <NUM> starts to access target, update an uplink SN. The uplink SN may be reported from the source base station 102a to the target base station 102b via the Xn backhaul. In some aspects employing a downlink data coordination method, the target base station 102b may pre-allocate an uplink and/or downlink resource (e.g., time, frequency, and/or time/frequency resources) to a UE <NUM> via a handover command with mobility control information that may include an SPS-like interval (e.g., periodicity).

A source base station 102a may start a downlink data coordination when an ACK for the target base station transmission is received by the source base station 102a via the source base station 102a's PUCCH resources, e.g., the pre-[allocated resource referred to above. The source base station 102a may know that the target base station 102b signal situation is suitable for the UE <NUM> to access the target base station 102b directly. For example, that the target cell (base station 102b) signal strength at the UE <NUM> allows reliable reception at the UE <NUM>, or that the UE <NUM> is in connected mode with the target base station 102b. The source base station 102a may order the UE <NUM> to directly access the target in a next pre-allocated transmission time interval (TTI) on the pre-allocated resource.

In an alternative solution a notification from the source base station 102a to the target base station 102b about the subframe X backhaul is not sent when the UE <NUM> is available, but instead may depend on the target base station 102b to monitor the target base station 102b's semi pre-allocated uplink resource PUCCH to the UE. For example, a UE <NUM> may receive from a target base station a semi pre-allocated uplink resource PUCCH, e.g., a pre-allocated UL PUCCH or a pre-allocated resource on a UL PUCCH. When the UE feedback ACK is received by the target base station 102b on the PUCCH, the target base station 102b may determine that the UE <NUM> is present in the target cell (e.g., is connected to the target base station 102b). The procedures described herein may allow the UE <NUM> to connect to the target base station 102b and bypass other connection procedures. Accordingly, the UE <NUM> may be scheduled by target base station 102b itself.

In an aspect, the UE <NUM> may access the target base station 102b directly for UL data transmission without performing a RACH procedure with the target base station 102b. Compared with other eMob solutions, the downlink data coordination may not require additional UE capability to support simultaneous intra-frequency target base station 102b PUSCH transmission and source base station 102a downlink PDCCH/PDSCH packet reception to achieve a lower or zero mobility interruption during handover.

<FIG> is a flowchart <NUM> of a method of wireless communication. The method may be performed by a UE (e.g., the UE <NUM>). At <NUM>, the UE receives a pre-allocation resource for a target cell via a handover command. For example, the UE <NUM> may receive a pre-allocation resource for a target cell (e.g., from the target base station 102b) via a handover command.

At <NUM>, the UE transmits a physical layer acknowledgment based on a target cell downlink packet. For example, the UE <NUM> may transmit a physical layer acknowledgment based on a target cell downlink packet. The UE may receive the target cell downlink packet from a base station (e.g. target base station 102b) and send an acknowledgment, e.g., to the target base station 102b. In another example, a MAC layer acknowledgement may also be applied here. The acknowledgment, which may be based on a target cell downlink packet, may be sent on the frequency resources of the target cell, e.g., target base station 102b.

At <NUM>, the UE receives an indication for a communication with the target cell in response to the physical layer acknowledgement. For example, the UE <NUM> may receive an indication for a communication with the target cell in response to the physical layer acknowledgement. For example, a network (e.g., a base station of the network) may send an indication for the communication with the target cell in response to the physical layer acknowledgment. The network may transmit signals that provide the indication for the communication with the target cell. In an aspect, the indication may be transmitted via level one (L1) signaling. In another aspect, the indication may be transmitted via level two (L2) using at least one of MAC, RLC, and/or PDCP extension header or control signaling command.

At <NUM>, the UE accesses the target cell using the pre-allocated resource, e.g., signaled in the indication, based on the indication for the communication with the target cell. For example, the UE <NUM> may access the target cell using the pre-allocated resource based on the indication for the communication with the target cell. The received indication may include data that indicates a pre-allocated resource. The pre-allocated resource may include some combination of time and frequency or time/frequency resources that are pre-assigned and enable the UE to establish communication with the target base station using the resource.

At <NUM>, the UE maintains, e.g., using a buffer or protocol stack, transmitted and received packets for both the source cell (e.g., source base station 102a) and the target cell based on reception of the handover command received in <NUM>. For example, buffers and/or a protocol stack may be setup in response to the handover command. The UE <NUM> may place entire packets into the buffer or protocol stack (or some subset of the data in the packets) that may be needed during the handover, until the handover is complete, or as needed after the handover is complete. For example, referring to <FIG>, the UE <NUM> may maintain transmitted and received packets for both the source cell and the target cell based on reception of the handover command.

At <NUM>, the UE synchronizes to the target cell by simultaneously receiving from the target cell and a source cell. The simultaneously received signals that are received from the target cell and the source cell may provide an indication of the timing at each of the cells. Accordingly, timing between the two cells may be determined and the UE may synchronize based on the trimming differences and/or the timing information gained from the simultaneously received signals. For example, the UE <NUM> may synchronize to the target cell by simultaneously receiving from the target cell and a source cell.

<FIG> is a conceptual data flow diagram <NUM> illustrating the data flow between different means/components in an exemplary apparatus <NUM>. The apparatus may be a UE. The apparatus includes a reception component <NUM> that receives a pre-allocation resource for a target cell via a handover command 1152a, e.g., from a base station <NUM>, and receives an indication 1152b for a communication with the target cell in response to the physical layer acknowledgement. The allocation resource via handover command 1154a, may be passed to the received pre-allocation resource for a target cell component <NUM> (1154a). The indication 1152b may be passed to the received indication for a communication with the target cell component <NUM> (1154b).

The apparatus includes a transmission component <NUM> that may be controlled (<NUM>) by a physical layer acknowledge component <NUM> to transmit a physical layer acknowledgment <NUM> based on a target cell downlink packet <NUM>, e.g., to base station <NUM>. The apparatus includes an accessing component <NUM> that controls (<NUM>) accesses the target cell using the pre-allocated resource based on the indication for the communication (<NUM>) with the target cell. The apparatus includes a synchronization component <NUM> that may synchronize the UE to the target cell as part of concurrently receiving from the target cell and a source cell and an access component <NUM> that may provide for accessing the target cell using the pre-allocated resource based on the indication for the communication with the target cell. The apparatus includes a maintain component <NUM> that maintains, e.g., using a buffer of or protocol stack, transmitted packets (<NUM>) and received packets (<NUM>) for both the source cell (e.g., source base station 102a) and the target cell based on reception of the handover command.

The apparatus <NUM> may include additional components that perform each of the blocks of the algorithm in the aforementioned flowchart of <FIG>.

<FIG> is a diagram <NUM> illustrating an example of a hardware implementation for an apparatus <NUM>' employing a processing system <NUM>. The processing system <NUM> may be implemented with a bus architecture, represented generally by the bus <NUM>. The bus <NUM> may include any number of interconnecting buses and bridges depending on the specific application of the processing system <NUM> and the overall design constraints. The bus <NUM> links together various circuits including one or more processors and/or hardware components, represented by the processor <NUM>, the components <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> (and/or components <NUM>, <NUM> of <FIG>), and the computer-readable medium / memory <NUM>. The bus <NUM> may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further.

The processing system <NUM> may be coupled to a transceiver <NUM>. The transceiver <NUM> is coupled to one or more antennas <NUM>. The transceiver <NUM> provides a means for communicating with various other apparatus over a transmission medium. The transceiver <NUM> receives a signal from the one or more antennas <NUM>, extracts information from the received signal, and provides the extracted information to the processing system <NUM>, specifically the reception component <NUM> (not shown). In addition, the transceiver <NUM> receives information from the processing system <NUM>, specifically the transmission component <NUM> (not shown), and based on the received information, generates a signal to be applied to the one or more antennas <NUM>. The processing system <NUM> includes a processor <NUM> coupled to a computer-readable medium / memory <NUM>. The processor <NUM> is responsible for general processing, including the execution of software stored on the computer-readable medium / memory <NUM>. The software, when executed by the processor <NUM>, causes the processing system <NUM> to perform the various functions described supra for any particular apparatus. The computer-readable medium / memory <NUM> may also be used for storing data that is manipulated by the processor <NUM> when executing software. The processing system <NUM> further includes at least one of the components <NUM>, <NUM>, <NUM>. The components may be software components running in the processor <NUM>, resident/stored in the computer readable medium / memory <NUM>, one or more hardware components coupled to the processor <NUM>, or some combination thereof. The processing system <NUM> may be a component of the UE <NUM> and may include the memory <NUM> and/or at least one of the TX processor <NUM>, the RX processor <NUM>, and the controller/processor <NUM>.

In one configuration, the apparatus <NUM>/<NUM>' for wireless communication includes means for receiving a pre-allocation resource for a target cell via a handover command, means for transmitting a physical layer acknowledgment based on a target cell downlink packet (<NUM>), means for receiving an indication for a communication with the target cell in response to the physical layer acknowledgement (<NUM>), and means for accessing the target cell using the pre-allocated resource based on the indication for the communication with the target cell (<NUM>). The means for accessing the target cell may select the pre-allocated resource and cause a communication with the target cell using the pre-allocated resource.

The apparatus <NUM>/<NUM>' for wireless communication may also include means for maintaining transmitted and received packets for both a source cell and the target cell based on reception of the handover command (<NUM>), means for synchronizing to the target cell by concurrently receiving from the target cell and a source cell (<NUM>), means for causing a receiver to tune to receive a physical downlink control channel (PDCCH) from the target cell, and/or means for causing a receiver to tune to receive a physical downlink shared channel (PDSCH) from the target cell (<NUM>).

The means for maintaining transmitted and received packets for both a source cell and the target cell may receive packets and store packets to maintain the information in the packets. The means for synchronizing to the target cell by concurrently receiving from the target cell and a source cell may receive information and modify timing based on the received information. The means for causing a receiver to tune to receive a PDCCH may cause a receiver to be active and set a tuning of the receiver. The means for causing a receiver to tune to receive a PDSCH may also cause a receiver to be active and set a tuning of the receiver.

In an aspect, an apparatus for wireless communication may include a memory and at least one processor coupled to the memory. The at least one processor may be configured to negotiate with a source node based on a user equipment (UE) eMob capability to start a low mobility interruption time handover, determine a UE uplink time alignment, determine a semi pre-allocated uplink resource, transmit downlink data according to a source cell coordination request, monitor a source cell semi pre-allocated uplink resource physical uplink control channel (PUCCH) allocated to the UE, and determine UE successfully access via physical layer acknowledgement.

In an aspect, the processor may be further configured to perform an SRA measurement. The semi pre-allocation uplink resource may be determined based on the SRA measurement.

In an aspect, the semi pre-allocation uplink resource may be determined the semi-pre-allocation resource for the UE via a handover command message.

In an aspect, the low interruption handover comprises a zero interruption handover.

Claim 1:
A method (<NUM>) for wireless communication performed by a user equipment, UE, the UE configured with a dual protocol stack, comprising:
receiving (<NUM>, <NUM>.) a pre-allocation resource for a target cell via a handover command for handover from a source cell to the target cell;
in response to receipt of the handover command, establishing the dual protocol stack as a temporary dual stack that comprises a first stack for the source cell and a second stack for the target cell, and continuing to receive downlink packets from and transmit uplink packets to the source cell via the first stack;
synchronizing (<NUM>.) to the target cell, while concurrently receiving from the target cell and the source cell;
receiving (11a.) from the target cell, a target cell downlink packet together with a MAC control element, CE, that includes a measured timing advance, TA, and a pre-allocated uplink grant;
transmitting (<NUM>, <NUM>.), to the source cell, a physical layer acknowledgment based on the target cell downlink packet;
receiving (<NUM>, <NUM>.), from the source cell, an indication for communication with the target cell, in response to the physical layer acknowledgement; and
accessing (<NUM>, <NUM>.) the target cell using the pre-allocated resource to complete the handover, based on the indication for communication with the target cell.