Patent Description:
A user equipment (UE) may establish a connection to at least one of multiple different networks or types of networks. The UE may establish this connection by connecting to a base station (e.g., large cell, small cell, access point, etc.) of a network. As a UE moves, the UE may have to switch from a first base station to a second base station to maintain the connection to the network. This switching from a first base station to a second base station is referred to as a handover, e.g., the first base station is handing the UE over to the second base station.

<NUM> and <NUM> of the 3GPP standards handovers are controlled based on Radio Resource Control (RRC) signaling between the base stations and the UE. Those skilled in the art will understand that the RRC protocol is an Internet Protocol (IP) level layer or a Layer <NUM> protocol. Further background information can be found in the following documents:.

The exemplary embodiments may be further understood with reference to the following description and the related appended drawings, wherein like elements are provided with the same reference numerals. The exemplary embodiments relate to a handover for a UE from a first base station to a second base station using lower layer (e.g., layer <NUM> and/or <NUM>) signaling.

The exemplary embodiments are described with regard to a UE. However, reference to a UE is merely provided for illustrative purposes. The exemplary embodiments may be utilized with any electronic component that may establish a connection to a network and is configured with the hardware, software, and/or firmware to exchange information and data with the network. Therefore, the UE as described herein is used to represent any electronic component.

The exemplary embodiments are also described with regard to <NUM> new radio (NR) radio access technology (RAT). However, it should be understood that <NUM> NR is being used for illustrative purposes and the exemplary embodiments may be applied to any network that exhibits the characteristics and functionalities described below for the <NUM> NR network.

The exemplary embodiments relate to using lower layer (e.g., layer <NUM> and/or <NUM> "L1/L2") signaling for the handover procedure. Using the lower layers for handover may reduce the latency and signaling overhead associated with the handover procedure. In general, the exemplary embodiments start the handover procedure using L1/L2 signaling from a base station. The UE receives the corresponding signaling and then synchronizes to the target cell. The exemplary embodiments address the issues of the signaling details for the L1/L2 signaling and the UE behavior to synchronize to the target cell. The exemplary embodiments will be described in detail below.

<FIG> shows an exemplary network arrangement <NUM> according to various exemplary embodiments. The exemplary network arrangement <NUM> includes a UE <NUM>. Those skilled in the art will understand that the UE <NUM> may be any type of electronic component that is configured to communicate via a network, e.g., mobile phones, tablet computers, desktop computers, smartphones, phablets, embedded devices, wearables, Internet of Things (IoT) devices, etc. It should also be understood that an actual network arrangement may include any number of UEs being used by any number of users. Thus, the example of a single UE <NUM> is merely provided for illustrative purposes.

The UE <NUM> may be configured to communicate with one or more networks. In the example of the network configuration <NUM>, the networks with which the UE <NUM> may wirelessly communicate are a <NUM> New Radio (NR) radio access network (<NUM> NR-RAN) <NUM>, an LTE radio access network (LTE-RAN) <NUM> and a wireless local access network (WLAN) <NUM>. However, it should be understood that the UE <NUM> may also communicate with other types of networks and the UE <NUM> may also communicate with networks over a wired connection. Therefore, the UE <NUM> may include a <NUM> NR chipset to communicate with the <NUM> NR-RAN <NUM>, an LTE chipset to communicate with the LTE-RAN <NUM> and an ISM chipset to communicate with the WLAN <NUM>.

The <NUM> NR-RAN <NUM> and the LTE-RAN <NUM> may be portions of cellular networks that may be deployed by cellular providers (e.g., Verizon, AT&T, Sprint, T-Mobile, etc.). These networks <NUM>, <NUM> may include, for example, cells or base stations (Node Bs, eNodeBs, HeNBs, eNBS, gNBs, gNodeBs, macrocells, microcells, small cells, femtocells, etc.) that are configured to send and receive traffic from UEs that are equipped with the appropriate cellular chip set. The WLAN <NUM> may include any type of wireless local area network (WiFi, Hot Spot, IEEE <NUM>. 11x networks, etc.).

The UE <NUM> may connect to the <NUM> NR-RAN <NUM> via the gNB 120A or the gNB 120B. The gNBs 120A and 120B may be configured with the necessary hardware, software and/or firmware to perform massive multiple in multiple out (MIMO) functionality. Massive MIMO may refer to a base station that is configured to generate a plurality of beams for a plurality of UEs. As will be described in greater detail below, the exemplary embodiments will provide manners of handing over the UE <NUM> from the gNB 120A to the gNB 120B, or vice versa. Reference to two gNBs 120A, 120B is merely for illustrative purposes. The exemplary embodiments may apply to any appropriate number of gNBs. Further, the UE <NUM> may communicate with the eNB 122A of the LTE-RAN <NUM> or an access point of the WLAN <NUM>.

Those skilled in the art will understand that any association procedure may be performed for the UE <NUM> to connect to the <NUM> NR-RAN <NUM>. For example, as discussed above, the <NUM> NR-RAN <NUM> may be associated with a particular cellular provider where the UE <NUM> and/or the user thereof has a contract and credential information (e.g., stored on a SIM card). Upon detecting the presence of the <NUM> NR-RAN <NUM>, the UE <NUM> may transmit the corresponding credential information to associate with the <NUM> NR-RAN <NUM>. More specifically, the UE <NUM> may associate with a specific base station (e.g., the gNB 120A of the <NUM> NR-RAN <NUM>).

In addition to the networks <NUM>, <NUM> and <NUM> the network arrangement <NUM> also includes a cellular core network <NUM>, the Internet <NUM>, an IP Multimedia Subsystem (IMS) <NUM>, and a network services backbone <NUM>. The cellular core network <NUM> may be considered to be the interconnected set of components that manages the operation and traffic of the cellular network. The cellular core network <NUM> also manages the traffic that flows between the cellular network and the Internet <NUM>. The IMS <NUM> may be generally described as an architecture for delivering multimedia services to the UE <NUM> using the IP protocol. The IMS <NUM> may communicate with the cellular core network <NUM> and the Internet <NUM> to provide the multimedia services to the UE <NUM>. The network services backbone <NUM> is in communication either directly or indirectly with the Internet <NUM> and the cellular core network <NUM>. The network services backbone <NUM> may be generally described as a set of components (e.g., servers, network storage arrangements, etc.) that implement a suite of services that may be used to extend the functionalities of the UE <NUM> in communication with the various networks.

<FIG> shows an exemplary UE <NUM> according to various exemplary embodiments. The UE <NUM> will be described with regard to the network arrangement <NUM> of <FIG>. The UE <NUM> may represent any electronic device and may include a processor <NUM>, a memory arrangement <NUM>, a display device <NUM>, an input/output (I/O) device <NUM>, a transceiver <NUM> and other components <NUM>. The other components <NUM> may include, for example, an audio input device, an audio output device, a battery that provides a limited power supply, a data acquisition device, ports to electrically connect the UE <NUM> to other electronic devices, one or more antenna panels, etc..

The processor <NUM> may be configured to execute a plurality of engines of the UE <NUM>. For example, the engines may include a handover engine <NUM>. The handover engine <NUM> may be configured to manage the operation of the UE <NUM> during a handover procedure from the gNB 120A to the gNB 120B. The specific operations will be described in greater detail below.

The above referenced engine being an application (e.g., a program) executed by the processor <NUM> is only exemplary. The functionality associated with the engines may also be represented as a separate incorporated component of the UE <NUM> or may be a modular component coupled to the UE <NUM>, e.g., an integrated circuit with or without firmware. For example, the integrated circuit may include input circuitry to receive signals and processing circuitry to process the signals and other information. The engines may also be embodied as one application or separate applications. In addition, in some UEs, the functionality described for the processor <NUM> is split among two or more processors such as a baseband processor and an applications processor. The exemplary embodiments may be implemented in any of these or other configurations of a UE.

The memory arrangement <NUM> may be a hardware component configured to store data related to operations performed by the UE <NUM>. The display device <NUM> may be a hardware component configured to show data to a user while the I/O device <NUM> may be a hardware component that enables the user to enter inputs. The display device <NUM> and the I/O device <NUM> may be separate components or integrated together such as a touchscreen. The transceiver <NUM> may be a hardware component configured to establish a connection with the <NUM> NR-RAN <NUM>, the LTE-RAN <NUM>, the WLAN <NUM>, etc. Accordingly, the transceiver <NUM> may operate on a variety of different frequencies or channels (e.g., set of consecutive frequencies).

<FIG> will describe signaling associated with two examples of a lower layer based handover command and synchronization procedure. Prior to describing the signaling of <FIG>, it is noted that throughout this description it will be considered that the UE <NUM> is currently connected to the gNB 120A and the handover procedure is being performed to handover the UE to the gNB 120B. Thus, the gNB 120A will be considered the "source gNB" and the gNB 120B will be considered the "target gNB. " It should be understood that this is only for illustrative purposes and any gNB may be a source gNB or a target gNB and perform the operations described herein for each of these components.

<FIG> shows a first exemplary signaling diagram <NUM> for a lower layer based handover command and synchronization procedure according to various exemplary embodiments. The signaling diagram <NUM> may be considered a Random Access Channel (RACH) procedure based handover.

In <NUM>, the source gNB 120A sends a L1/L2 based handover command to the UE <NUM>. The L1/L2 based handover command will be described in greater detail below. In <NUM>, the UE <NUM> sends an ACK for the L1/L2 handover command to the source gNB 120A. While not shown in the signaling diagram <NUM>, the UE <NUM> may also send the ACK for the L1/L2 handover command to the target gNB 120B. In <NUM>, the UE <NUM> and the target gNB 120B perform the RACH procedure to complete the handover from the source gNB 120A to the target gNB 120B. The details of the L1/L2 based handover command and the RACH procedure will be described in greater detail below.

<FIG> shows a second exemplary signaling diagram <NUM> for a lower layer based handover command and synchronization procedure according to various exemplary embodiments. The signaling diagram <NUM> may be considered a RACH-less based handover.

In <NUM>, the source gNB 120A sends a L1/L2 based handover command to the UE <NUM>. In <NUM>, the UE <NUM> sends an ACK for the L1/L2 handover command to the source gNB 120A. In <NUM>, the UE <NUM> and the target gNB 120B exchange handover messages on a configured Physical Uplink Shared Channel (PUSCH) to complete the handover from the source gNB 120A to the target gNB 120B. The details of the L1/L2 based handover command and the PUSCH messaging will be described in greater detail below.

<FIG> shows a diagram of the UE <NUM> being handed over from a source gNB 120A to a target gNB 120B according to the claimed embodiment. As described above, in <NUM> and <NUM>, the source gNB 120A will send a L1/L2 based handover command to the UE <NUM> to initiate the handover procedure. The following describes an exemplary L1/L2 based handover command that will be described with reference to <FIG>.

The gNB to which the UE is currently connected (e.g., gNB 120A) may provide a downlink beam indication based on a Transmission and Configuration Indication (TCI). The TCI may be used to indicate the quasi-co-location (QCL) source reference signal for a downlink channel (PDSCH, PDCCH). Two antenna ports are considered to be quasi-co-located if properties of the channel over which a symbol on one antenna port is conveyed can be inferred from the channel over which a symbol on the other antenna port is conveyed. The UE <NUM> may be configured with a number (S) of TCI state sets. Within each TCI state set, a number (N) of TCI states may be configured. Each TCI state set may correspond to a serving cell. For example, in <FIG>, it may be considered that TCI state x corresponds to a TCI state set for the source gNB 120A and TCI state y corresponds to a TCI state set for the target gNB 120B. This correspondence may be based on a physical cell ID (PCI) that is configured for each of the TCI state sets or each TCI state. This correspondence allows for implicit association, e.g. gNB can configure different PCIs in different TCI states, and the TCI states that share the same PCI may be considered to belong to the same set.

The L1/L2 based handover command may be based on a TCI update command that is sent from the source gNB 120A to the UE <NUM>. For example, as described in the above example, the source gNB 120A is associated with the TCI state x and the target gNB 120B is associated with the TCI state y. Thus, in the L1/L2 based handover command, the source gNB 120A may send a TCI update command that indicates the TCI state y. Since the UE <NUM> is configured with information indicating that the TCI state y is associated with the target gNB 120B, the UE <NUM> will understand that the source gNB 120A is signaling that a handover operation should be performed to the handover to the target gNB 120B.

The L1/L2 based handover command, e.g., the TCI update command including the TCI state indication may be included in a Medium Access Control (MAC) Control Element (CE), e.g., a layer <NUM> message, or in a Downlink Control Information (DCI) message, e.g., a layer <NUM> message. The UE <NUM> stores various RRC parameters sets associated with different TCI state sets that are used for handover. Examples of this stored information will be provided below. The exemplary L1/L2 based handover command may be used in operation <NUM> or <NUM> for either the RACH based handover or the RACH-less based handover.

The following provides additional information that may be used for the RACH based handover procedure as was described above with respect to <FIG>. For example, since a RACH procedure is being used and the candidate beam for the target cell 120B has been identified, e.g., the TCI state y, the source gNB 120A may also provide Physical RACH (PRACH) resources to UE <NUM> to reduce additional latency for beam measurement. A PRACH resource may indicate the preamble index and a time/frequency resource for a PRACH transmission. The UE <NUM> may derive the pathloss for PRACH power control based on the synchronization signal blocks (SSB)/ Channel State Indication - Reference Signal (CSI-RS) configured in the TCI state.

In a first exemplary embodiment, for each TCI state, the source gNB 120A may configure a PRACH resource from the target cell 120B by RRC signaling. The RRC signaling described in this example is RRC signaling that occurs prior to the start of the handover procedure, e.g., during the normal course of RRC signaling that occurs while the UE <NUM> is connected to the gNB 120A. As described above, the UE <NUM> may store various RRC parameters sets associated with different TCI state sets. For example, as part of the TCI state information that is signaled to the UE <NUM>, the source GNB 120A may include an indication of a PRACH resource for a TCI state. When the UE <NUM> receives the L1/L2 based handover command that includes a TCI state, the UE <NUM> can retrieve the information associated with the TCI state that includes the PRACH resource.

The UE <NUM> may then start the RACH procedure (e.g., operation <NUM> of <FIG>) based on the configured PRACH resource. The initial attempt at the RACH procedure <NUM> may be a contention-free based RACH procedure. The UE <NUM> may monitor for a response after transmitting the PRACH, and, if after a given time window, the UE <NUM> does not receive any response, the UE may then fallback to use a contention-based RACH procedure. Completion of the RACH procedure <NUM> will complete the handover from the source gNB 120A to the target gNB 120B.

<FIG> shows a block diagram <NUM> of a relationship between a TCI state <NUM>, a SSBs <NUM>, <NUM> and PRACH resources <NUM> for a RACH based handover according to various exemplary embodiments. In a second exemplary embodiment of the RACH based handover, in each TCI state, the source gNB 120A may configure a SSB or CSI-RS that is QCLed with a SSB. In this example, it may be considered that the TCI state <NUM><NUM> is associated with the target gNB 120B. The SSB <NUM> is associated with the TCI <NUM> state <NUM> and the PRACH resources <NUM>-<NUM>. The association between the PRACH resources <NUM>-<NUM> and the SSB <NUM> from the target cell 120B may again be configured by RRC signaling in a similar manner as was described above with reference to the TCI state information.

In this exemplary embodiment, the UE <NUM> may randomly select one of associated PRACH resources (e.g., PRACH resource <NUM>) based on the SSB <NUM> associated with the TCI <NUM> state <NUM> of the target gNB 120B and perform a contention-based RACH procedure in <NUM>. For example, in some embodiments, the radio network temporary ID (RNTI) of the UE <NUM> in the target cell may be configured for each TCI state. The UE <NUM> may transmit a Msg3 to the target gNB 120B that includes the RNTI. In other embodiments, the target gNB 120B may not provide the UE <NUM> with the new RNTI. In this case, the UE <NUM> may transmit a Msg3 with the initial UE-ID for collision handling.

The following provides additional information that may be used for the RACH-less based handover procedure as was described above with respect to <FIG>. <FIG> shows a scheduling diagram <NUM> for a RACH-less handover according to various exemplary embodiments. The operations described with reference to scheduling diagram <NUM> are related to the PUSCH signaling <NUM> described above with reference to <FIG>.

At <NUM>, the UE <NUM> sends a PUSCH message to the target gNB 120B. The PUSCH resource that is used by the UE <NUM> to communicate with the target gNB 120B may be configured in various manners. In some exemplary embodiments, a PUSCH resource can be configured for each TCI state. Again, this information may be stored by the UE <NUM> based on RRC signaling from the source gNB 120A. The PUSCH configuration may include, a Modulation and Coding Scheme (MCS), an allocated bandwidth, time resources, DMRS port index, power control parameters, etc. The UE <NUM> may use the same beam to transmit the PUSCH as that to receive the SSB/CSI-RS configured in the TCI state. In addition, the UE <NUM> may derive the pathloss for PUSCH power control based on the SSB/CSI-RS configured in the TCI state.

In other exemplary embodiments, the PUSCH resource may be triggered by a PDCCH or MAC CE from the source gNB 120A. In one example, an indicator in the DCI may indicate whether the PDCCH is to trigger a PUSCH to the source gNB 120A or the target gNB 120B. In another example, the PUSCH resource may be indicated by the L1/L2 handover command from the source gNB 120A.

The initial scrambler of the PUSCH at <NUM> may be determined based on any of the configured RNTI from the source gNB 120A, an index of random access preambles or a virtual cell ID for the target gNB 120B.

The UE <NUM> may also derive a timing advance (TA) for the PUSCH transmission <NUM>. There may be various options for deriving the TA. In a first example, the TA may be assumed to be <NUM>. In a second example, the TA may be configured by the source gNB 120A. For example, the TA may be configured per TCI state set or per TCI state.

In a third example, the TA may be based on measurements of a CSI-RS configured in the TCI state. To improve the TA measurement accuracy, the CSI-RS may be configured based on one or more of the following rules. The CSI-RS may be <NUM>-port. The frequency density for the CSI-RS may be at least x resource elements/resource block (REs/RB), e.g. x=<NUM>. The minimal bandwidth for the CSI-RS may be min{N_RB_max, N1}, where N_RB_max indicates the maximum number of RBs for the bandwidth part and N1 is a predefined value, e.g. N1=<NUM>, or based on the capability of the UE.

At <NUM>, the target gNB 120B responds to the PUSCH message from the UE <NUM>. The target gNB 120B response may be based on a PDCCH. As part of the response in <NUM>, the target gNB 120B may schedule an uplink (UL) transmission with a scheduling offset K. The scheduling offset K may be determined as K2+delta, where K2 is the minimal scheduling offset and delta is the additional scheduling offset, which is predefined based on the subcarrier spacing of the PUSCH.

At <NUM>, the UE <NUM> may then perform the UL transmission to the target gNB 120B. Once this is completed, the handover procedure is complete and the UE <NUM> is connected to the target gNB 120B.

Those skilled in the art will understand that the above-described exemplary embodiments may be implemented in any suitable software or hardware configuration or combination thereof. An exemplary hardware platform for implementing the exemplary embodiments may include, for example, an Intel x86 based platform with compatible operating system, a Windows OS, a Mac platform and MAC OS, a mobile device having an operating system such as iOS, Android, etc. In a further example, the exemplary embodiments of the above described method may be embodied as a program containing lines of code stored on a non-transitory computer readable storage medium that, when compiled, may be executed on a processor or microprocessor.

Claim 1:
A user equipment, UE (<NUM>), comprising:
a transceiver (<NUM>) configured to connect to a first next generation Node B, gNB, of a <NUM> new radio, NR, network;
a baseband processor configured to:
receive a handover command from the first gNB (120A) via one of a Layer <NUM> signaling or Layer <NUM> signaling that instructs the UE (<NUM>) to perform a handover procedure to handover to a second gNB (120B), wherein the handover command comprises an identification of a Transmission and Configuration Indication, TCI, state that is associated with the second gNB (120B); and
wherein the UE is configured to store a relationship between the second gNB (120B) and the identified TCI state and further store relationships between the identified TCI state and parameters to perform the handover procedure;
and conduct the handover procedure with the second gNB (120B) for the UE (<NUM>) to connect to the second gNB (120B) using said parameters.