Mobile terminal and method

Abstract

To allow a mobile terminal to more quickly perform handover from a source base station to a target base station.SOLUTION: A target base station performs a process including receiving, from a source base station, a handover request message including information regarding capability of a mobile terminal that communicates over at least a configured first bandwidth part and a configured second bandwidth part, configuring at least the first bandwidth part and the second bandwidth part for the mobile terminal upon receiving the handover request message, and transmitting a handover request response confirmation message to the source base station. The handover request response confirmation message includes information regarding the at least first bandwidth part and second bandwidth part that are configured.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a mobile terminal performing a handover procedure from a source base station to a target base station in a wireless communication system. [Background technology]

[0002] Currently, the 3rd Generation Partnership Project (3GPP®) is focused on the next release (Release 15) of technical specifications for the next generation of cellular technology, also known as the fifth generation (5G).

[0003] At 3GPP's Technical Specification Group (TSG) Radio Access Network (RAN) Meeting #71 (March 2016, Gothenburg), the first study item for 5G, "Study on New Radio Access Technology," involving RAN1, RAN2, RAN3, and RAN4, was approved, laying the foundation for the Release 15 work item (WI) that will define the first 5G standards.

[0004] 5G new radio (NR) provides a single technical framework that addresses all usage scenarios, requirements, and deployment scenarios defined in 3GPP TS 2013-01-01 11:15 AM (available at www.3gpp.org), including at least enhanced mobile broadband (eMBB), ultra-reliable low-latency communications (URLLC), and massive machine type communication (mMTC).

[0005] For example, deployment scenarios for eMBB may include indoor hotspots, dense urban areas, suburban areas, urban areas, and high-speed areas. Deployment scenarios for URLLC may include industrial control systems, mobile health management (remote monitoring, diagnosis, and treatment), real-time control of vehicles, and wide-area monitoring and control systems for smart grids. Deployment scenarios for mMTC may include scenarios using a large number of devices with low-latency data transmission, such as smart wearables and sensor networks.

[0006] 5G also offers forward compatibility for future use cases / deployment scenarios. Backward compatibility to Long Term Evolution (LTE) is not required, which facilitates the introduction of entirely new system designs and / or novel features.

[0007] As summarized in one of the technical reports of the NR (New Radio) study items (Non-Patent Document 2), the basic signal waveform of the physical layer is based on Orthogonal Frequency Division Multiplexing (OFDM). Waveforms based on OFDM with Cyclic Prefix (CP-OFDM) are supported in both the downlink and uplink. At least for the uplink of eMBB up to 40 GHz, waveforms based on Discrete Fourier Transformation (DFT) spread OFDM (DFT-S-OFDM) are also supported as a supplement to the CP-OFDM waveform.

[0008] One of the design goals of NR is to minimize interruptions to ongoing traffic, if any, while simultaneously enhancing user mobility without increasing user equipment power consumption. In RAN#78, RAN2 was tasked with investigating how the IMT-2020 requirement for a 0 ms handover interruption time can be addressed by LTE and NR within the Rel-15 timeframe. In a first step, the handover procedure in LTE is being discussed as a baseline design for NR. Discussions are underway in 3GPP working groups regarding what functionality needs to be added or modified to enhance NR mobility.

[0009] The term "downlink" refers to communication from a higher-level node to a lower-level node (e.g., from a base station to a relay node, from a base station to a UE, from a relay node to a UE, etc.). The term "uplink" refers to communication from a lower-level node to a higher-level node (e.g., from a UE to a relay node, from a UE to a base station, from a relay node to a base station, etc.). The term "sidelink" refers to communication between nodes at the same level (e.g., between two UEs, between two relay nodes, or between two base stations). [Prior art documents] [Non-patent literature]

[0010] [Non-Patent Document 1] 3GPP TSG RAN TR 38.913 v14.1.0,“Study on Scenarios and Requirements for Next Generation Access Technologies”,Dec.2016 [Non-patent document 2] 3GPP TSG TR 38.801 v2.0.0,“Study on New Radio Access Technology;Radio Access Architecture and Interfaces”,March 2017 Summary of the Invention [Means for solving the problem]

[0011] One non-limiting exemplary embodiment allows a mobile terminal to more quickly handover from a source base station to a target base station. If the target base station already configures multiple bandwidth portions for the mobile terminal during handover and signals the same configuration to the mobile terminal, the mobile terminal can immediately (re)start communication with the target base station with the appropriate bandwidth portion configuration during handover. Additional reconfiguration attempts can be avoided after handover.

[0012] In one embodiment, the technology disclosed herein features a mobile terminal for performing a handover procedure from a source base station to a target base station in a mobile communication system. The target base station is configured for the mobile terminal with at least a first bandwidth portion and a different second bandwidth portion within its cell bandwidth. The mobile terminal includes: a transceiver that, in operation, receives a handover command message from the source base station, the handover command message including information regarding the configured at least first and second bandwidth portions; and processing circuitry, such as a processor, that, in operation and upon receipt of the handover command message, controls the transceiver to activate at least a pre-selected one of the configured at least first or second bandwidth portions and to communicate with the target base station over the activated at least one of the configured at least first or second bandwidth portions as part of the handover procedure.

[0013] In another general aspect, the technology disclosed herein features a mobile terminal for performing a handover procedure from a source base station to a target base station in a mobile communication system. The target base station is configured for the mobile terminal with at least a first bandwidth portion and a different second bandwidth portion within its cell bandwidth. The mobile terminal includes: a transceiver that, in operation, receives a handover command message from the source base station, the handover command message including information about the configured at least first bandwidth portion and the second bandwidth portion; and a processor that, in operation and upon receipt of the handover command message, controls the transceiver to select and activate at least one of the configured at least first bandwidth portion or the second bandwidth portion and to communicate with the target base station over the selected and activated at least one of the configured at least first bandwidth portion or the second bandwidth portion as part of the handover procedure.

[0014] In a further general aspect, the technology disclosed herein features a target base station for performing a handover procedure for a mobile terminal from a source base station in a mobile communication system. The target base station is capable of communicating with the mobile terminal over at least a first bandwidth portion and a different second bandwidth portion within its cell bandwidth. The target base station includes: a transceiver that, in operation, receives a handover request message from the source base station, the handover request message including information regarding the mobile terminal's ability to communicate over at least the first bandwidth portion and the second bandwidth portion; and a processor that, in operation and upon receiving the handover request message, controls the transceiver to configure at least the first bandwidth portion and the second bandwidth portion for the mobile terminal and to transmit a handover request response confirmation message to the source base station, the handover request response confirmation message including information regarding the configured at least the first bandwidth portion and the second bandwidth portion.

[0015] In yet another general aspect, the technology disclosed herein features a method for performing a handover procedure of a mobile terminal from a source base station to a target base station in a mobile communication system, the target base station being configured for the mobile terminal with at least a first bandwidth portion and a different second bandwidth portion within its cell bandwidth, the method including: receiving a handover command message from the source base station, the handover command message including information regarding the configured at least first bandwidth portion and the second bandwidth portion; and, upon receipt of the handover command message, activating at least a pre-selected one of the configured at least first bandwidth portion or the second bandwidth portion, and communicating with the target base station on the activated at least one of the configured at least first bandwidth portion or the second bandwidth portion as part of the handover procedure.

[0016] In a further general aspect, the technology disclosed herein features another method for performing a handover procedure of a mobile terminal from a source base station to a target base station in a mobile communication system. The target base station is configured with at least a first bandwidth portion and a different second bandwidth portion within its cell bandwidth for the mobile terminal. The method includes receiving a handover command message from the source base station, the handover command message including information about the configured at least first bandwidth portion and the second bandwidth portion; and, upon receiving the handover command message, selecting and activating at least one of the configured at least first bandwidth portion or the second bandwidth portion, and communicating with the target base station on the selected and activated at least one of the configured at least first bandwidth portion or the second bandwidth portion as part of the handover procedure.

[0017] In yet another general aspect, the technology disclosed herein features a further method for a target base station to perform a handover procedure for a mobile terminal from a source base station in a mobile communication system. The target base station is capable of communicating with the mobile terminal over at least a first bandwidth portion and a different second bandwidth portion within its cell bandwidth. The method includes receiving a handover request message from the source base station, the handover request message including information regarding the mobile terminal's ability to communicate over at least the first bandwidth portion and the second bandwidth portion; and, upon receiving the handover request message, configuring at least the first bandwidth portion and the second bandwidth portion for the mobile terminal and transmitting a handover request response confirmation message to the source base station, the handover request response confirmation message including information regarding the configured at least the first bandwidth portion and the second bandwidth portion.

[0018] It should be noted that the general or specific embodiments may be implemented as a system, a method, an integrated circuit, a computer program, a storage medium, or any combination thereof.

[0019] Further benefits and advantages of the disclosed embodiments will become apparent from the specification and drawings. These benefits and / or advantages may be obtained individually by the various embodiments and features of the specification and drawings, although not all of these features need be present to obtain one or more of such benefits and / or advantages. [Brief explanation of the drawings]

[0020] [Figure 1A] 1 shows a sequence diagram of an exemplary handover procedure. [Figure 1B] 1 illustrates a scenario illustrating bandwidth throttling over time. [Figure 2A] 1 illustrates an example scenario involving the configuration of bandwidth portions in a source cell and a target cell before and after a handover. [Figure 2B]1 illustrates an example scenario involving the configuration of bandwidth portions in a source cell and a target cell before and after a handover. [Figure 3] FIG. 2 is a block diagram illustrating the structures of a mobile terminal, a source base station, and a target base station. [Figure 4] FIG. 1 shows a sequence diagram of a handover procedure according to an exemplary implementation of the first embodiment in a 3GPP NR deployment scenario. [Figure 5] 1A-1C show sequence diagrams of handover procedures according to different exemplary implementations of the first embodiment in a 3GPP NR deployment scenario; [Figure 6] FIG. 10 shows a sequence diagram of a handover procedure according to an exemplary implementation of the second embodiment in a 3GPP NR deployment scenario. [Figure 7] 7 shows an association table for the handover procedure according to FIG. [Figure 8] 10A-10C show sequence diagrams of handover procedures according to different exemplary implementations of the second embodiment in a 3GPP NR deployment scenario. [Figure 9] 9 shows another association table for the handover procedure according to FIG. 8; DETAILED DESCRIPTION OF THE INVENTION

[0021] 3GPP NR introduces a new feature: bandwidth part (BWP) operation. A BWP of a group of contiguous physical resource blocks (PRBs) defines the UE's operating bandwidth within the cell's operating bandwidth. Furthermore, the bandwidth of the BWP is less than or equal to the maximum bandwidth capability supported by the UE.

[0022] In each UE-specific serving cell, one or more downlink BWPs and one or more uplink BWPs may be configured for the UE by dedicated radio resource control (RRC) signaling. The BWP configuration may include characteristics of numerology, frequency location (e.g., center frequency), and bandwidth (e.g., number of PRBs), where numerology refers to subcarrier spacing and cyclic prefix.

[0023] However, in Release-15, for a UE, there is at most one active downlink BWP and at most one active uplink BWP for the serving cell at a given time. The UE only expects communication to / from the gNB via the active BWP, i.e., the UE may monitor the PDCCH and possible PDSCH only on the active downlink BWP and may transmit the PUSCH / PUCCH only on the active uplink BWP.

[0024] NR supports the case where a single scheduling DCI (Downlink Control Information) can switch the UE's active BWP from one BWP configured for the UE to another, which is called (dynamic) BWP adjustment.

[0025] Bandwidth adjustment is described in the 3GPP technical specifications for New Radio (NR) and Next Generation (NG) radio access networks (RAN) (3GPP TSG TS 38.300 V.2.0.0, “NR; NR and NG-RAN Overall Description”, December 2017) as follows:

[0026] In Bandwidth Adaptation (BA), the UE's receive and transmit bandwidth need not be as large as the cell's bandwidth and can be adjusted, the width can be ordered to vary (e.g., shrink to save power during periods of low activity), the location can be moved in the frequency domain (e.g., to increase scheduling flexibility), and the subcarrier spacing can be ordered to vary (e.g., to accommodate different services). A subset of the cell's total cell bandwidth is called a Bandwidth Partition (BWP), and BA is achieved by configuring the UE with a BWP and informing the UE which of the configured BWPs is the currently active BWP.

[0027] As shown in Figure 1B, three different BWPs each with the same or different center frequencies, different (band) widths and / or different subcarrier spacings. - BWP1 with a width of 40 MHz and a subcarrier spacing of 15 kHz, - BWP2 with a width of 10 MHz and a subcarrier spacing of 15 kHz, and - BWP3 with a width of 20 MHz and subcarrier spacing of 60 kHz It is possible to imagine a scenario in which

[0028] A general description of network-controlled mobility is given in the 3GPP Technical Specification for New Radio NR and Next Generation NG Radio Access Network RAN (3GPP TSG TS 38.300 V.2.0.0, “NR; NR and NG-RAN Overall Description”, December 2017). Network-controlled mobility applies to UEs that are RRC_CONNECTED and is categorized into two types of mobility: cell-level mobility and beam-level mobility.

[0029] Cell-level mobility requires explicit RRC signaling to be triggered, e.g., handover. For inter-gNB handover, the signaling procedure includes at least the following element components shown in Figure 9.2.3.1-1, which for consistency reasons is reproduced herein as Figure 1A: Apart from that, beam-level mobility does not require explicit RRC signaling to be triggered, is handled at lower layers, and does not require the RRC to know which beam is being used at a given time.

[0030] As shown in Figure 1A, RRC-driven mobility is responsible for cell-level mobility, e.g., handover. The handover signaling procedure adopts the same principles as in Rel-13 LTE. For inter-gNB handover, the signaling procedure consists of at least the following element components:

[0031] 1. The source gNB initiates the handover and issues a handover request over the Xn interface.

[0032] 2. The target gNB performs admission control and provides RRC configuration as part of the handover response confirmation.

[0033] 3. The source gNB provides the UE with RRC configuration in a handover command. The handover command message includes at least a cell ID and information necessary to access the target cell, so that the UE can access the target cell without reading system information. In some cases, information necessary for contention-based and contention-free random access may be included in the handover command message. The access information to the target cell may include beam-specific information, if any.

[0034] 4. The UE moves the RRC connection to the target gNB and returns handover completion.

[0035] The RRC-triggered handover mechanism requires the UE to reset at least the MAC entity and re-establish RLC. Both RRC-managed handovers with and without PDCP entity re-establishment are supported. For DRBs using RLC AM mode, PDCP may be re-established with a security key change or initiate a data recovery procedure without a key change. For DRBs and SRBs using RLC UM mode, PDCP may be re-established with a security key change or remain unchanged.

[0036] When the target gNB uses the same DRB configuration and QoS flow-to-DRB mapping as the source gNB, data forwarding, in-order delivery, and duplicate avoidance during handover can be facilitated. In NR, a timer-based handover failure procedure is supported. For recovery from handover failure, the RRC connection re-establishment procedure is used.

[0037] It should be mentioned that the element components shown in Figure 1A not only characterize an inter-gNB handover, but are also part of an intra-NR RAN handover. For brevity, reference is made to Figure 9.2.3.2.1-1, which discloses a specific aspect of an intra-AMF / UPF handover. In this figure, the handover request is in message 3, the handover (request) response confirmation is in message 5, the handover command is part of communication 6, and the handover completion is part of communication 8.

[0038] Importantly, currently known handover components do not support the concept of bandwidth adjustment. Recognizing these shortcomings, the present disclosure seeks to improve handover procedures.

[0039] Non-limiting exemplary embodiments facilitate a mobile terminal to more quickly handover from a source base station to a target base station, minimize interruptions to ongoing data transmission (if any), and avoid increased power consumption of the mobile terminal.

[0040] If the target base station already configured multiple bandwidth portions for the mobile terminal during handover and signaled the same configuration to the mobile terminal, the mobile terminal may immediately (re)start communicating with the target base station with the appropriate bandwidth portion configuration during handover. After handover, no additional reconfiguration or bandwidth portion adjustment attempts may be necessary.

[0041] It should be mentioned that the Xn interface for inter-gNB message exchange is chosen for the purpose of illustration of the present disclosure, which should not be considered as a limitation of the present disclosure, which can be directly applied to the case of inter-AMF / UPF handover, where information regarding the usage of bandwidth portions mentioned in the present disclosure is exchanged via the interface between the gNB and the core network.

[0042] For a more comprehensive discussion of the advantages provided by the present disclosure, two different scenarios will be described in more detail, from which it will become apparent that there are further synergies that can be achieved when considering bandwidth adjustments during handover.

[0043] Referring to FIG. 2A, an exemplary scenario is shown in which a mobile terminal is configured with multiple bandwidth portions in a source cell and a target cell, for example, before or after a handover.

[0044] This exemplary scenario illustrates a situation in which a mobile terminal performs a handover from a source base station (particularly from a source cell served by the source base station) to a target base station (particularly a target cell served by the target base station), where in both the source cell and the target cell the mobile terminal is configured with multiple bandwidth portions, e.g., first and second bandwidth portions with corresponding indexes #0 and #1.

[0045] In particular, the configuration (e.g., location and bandwidth) of a first bandwidth portion (referred to as BWP with index #0) and a second bandwidth portion (referred to as BWP with index #1) are indicated in the source cell and the target cell, e.g., with respect to a synchronization signal SS block of a carrier bandwidth in the frequency domain. The indicated first and second bandwidth portions both correspond to downlink bandwidth portions of the mobile terminal, since they are included in the same carrier bandwidth that is also occupied by the SS block. However, further description equally applies to the uplink bandwidth portion, and therefore specific distinctions are omitted for brevity.

[0046] In the source cell, the first and second bandwidth portions are both centered (in the frequency domain) with one (e.g., lower) SS block, and in the target cell, the first and second bandwidth portions are both centered (in the frequency domain) with another (e.g., upper) SS block. In other words, in this exemplary scenario, the multiple bandwidth portions are located at different parts of the carrier frequency.

[0047] Thus, when a mobile terminal is triggered to perform a handover from a source cell to a target cell, it receives radio resources from different parts of the carrier bandwidth, which is beneficial for load balancing purposes in the target cell.

[0048] However, adjusting the reception behavior at the mobile terminal involves (re)tuning to the different center frequencies at which the respective bandwidth portions are located, and adjusting the filtering bandwidth to the corresponding widths of the bandwidth portions.

[0049] Referring to FIG. 2B, another exemplary scenario is shown in which a mobile terminal is (again) configured with multiple bandwidth portions in the source and target cells, eg, before and after handover.

[0050] Here, in both the source and target cells, the first and second bandwidth portions are no longer configured centered (in the frequency domain) with one or another SS block, but are instead more flexibly distributed across the carrier bandwidth. It is important that the mobile terminal is configured with first bandwidth portions of the same width (e.g. number of physical resource blocks PRB) at the same location in the source and target cells.

[0051] Therefore, when the mobile terminal is triggered to perform a handover from the first bandwidth portion (BWP#0) of the source cell to the first bandwidth portion (BWP#0) of the target cell, it does not have to receive radio resources from a different portion of the carrier bandwidth, instead the reception behavior at the mobile terminal may remain the same.

[0052] This other exemplary scenario does not require (re)tuning and filter adjustment to be performed, thus avoiding interruption of ongoing traffic due to frequency retuning during handover.

[0053] However, it will be appreciated that in this other exemplary scenario, the mobile terminal is configured with a first bandwidth portion (BWP#0) and a second bandwidth portion (BWP#1) that is not centered (in the frequency domain) in the source and target cells, respectively. When changing between different bandwidth portions, the mobile terminal receives radio resources from different portions of the carrier bandwidth.

[0054] In other words, changing between the first and second bandwidth portions in each of the source and target cells requires both (re)tuning and filter adjustment to be performed, which delays the change (increases latency), but this can be compensated for by the increased bandwidth available to the mobile terminal in the second bandwidth portion (BWP#1) of the source and target cells.

[0055] In summary, two different exemplary scenarios are discussed, the latter (shown in Figure 2B) having the advantage of enabling seamless handover between at least the first bandwidth portion of the source and target cells, while the former can achieve load balancing (shown in Figure 2A).

[0056] These considerations are not limited to the downlink bandwidth portion, but also apply to the uplink bandwidth portion of the source or target cell, for which the location and width are crucial for the transmission behavior at the mobile terminal. The mobile terminal may need to perform uplink transmissions on different frequency resources, which also typically requires (re)tuning and filter adjustment.

[0057] Therefore, the advantages / disadvantages described above apply equally to the downlink and uplink bandwidth portions.

[0058] 3 shows a block diagram of a mobile communication system including a mobile terminal 100 (also referred to as user equipment, UE), a source base station 200-a (also referred to as source gNodeB, GNB), and a target base station 200-b (also referred to as target gNodeB, gNB). This block diagram serves the purpose of illustrating the mobile terminal in a situation where it is performing a handover from the source base station 200-a to the target base station 200-b.

[0059] Generally, there are several events that can cause the source base station 200-a to trigger a handover of the mobile terminal 100. For example, the source base station 200-a can trigger a handover due to a poor coverage situation for the mobile terminal 100. The coverage is measured by the mobile terminal 100 in the form of measurements and (then) reported to the source base station 200-a. Alternatively, the source base station 200-a can also trigger a handover of the mobile terminal 100 for load balancing reasons at the source base station 200-a.

[0060] Regardless of the cause, the processor 230-a of the source base station 200-a triggers a handover to the target base station 200-b by causing its transceiver 220-a to send a handover request message (see message 1 in FIG. 1) to the target base station 200-b.

[0061] This message and other messages may be sent over wireless or wired interfaces connecting base stations to each other. For example, the handover request message may be sent over the Xn interface defined as part of the Next Generation NG radio access network (RAN), or over the Next Generation NG interface via an entity providing the access and mobility management function (AMF) and / or the user plane function (UPF). If the handover involves different 5G core networks, it may also be necessary to transfer the same message between different AMF / PDF entities.

[0062] Transceiver 220-b of target base station 200-b receives a handover request message from source base station 200-a. In particular, this message contains (among other things) information regarding the capability of mobile terminal 100 to communicate in at least two different bandwidth portions, e.g., a first bandwidth portion BWP#0 and a second bandwidth portion BWP#1, on the uplink and downlink. This information helps target base station 200-b determine the number of bandwidth portions it is expected to configure for mobile terminal 100.

[0063] For purposes of example, assume that mobile terminal 100 can communicate over only one bandwidth portion, not multiple, then target base station 200-b will not configure multiple bandwidth portions for mobile terminal 100. Regardless of this possibility, this disclosure focuses on mobile terminal 100 that can communicate over multiple bandwidth portions, thus facilitating target base station 200-b configuring all of the multiple bandwidth portions for the mobile terminal.

[0064] The above limitations on bandwidth portion capacity may be understood to apply equally to the uplink and downlink in a frequency division duplex FDD mode of operation, and to the uplink and downlink in a time division duplex TDD mode of operation.

[0065] In other words, when a mobile terminal is said to be capable of communicating over one bandwidth portion in an FDD mode of operation, this may be understood to imply a configuration with at most one bandwidth portion in the downlink and a separate bandwidth portion in the uplink. When a mobile terminal is said to be capable of communicating over one bandwidth portion in a TDD mode of operation, this may be understood to imply a joint configuration with (again) at most one bandwidth portion in the downlink and one bandwidth portion in the uplink (as a pair).

[0066] For this reason, the present disclosure will be described with reference to the term "bandwidth portion," knowing that it could equally well be referred to as the term "uplink and downlink bandwidth portion" or "uplink and downlink bandwidth portion pair." Either case merely emphasizes that separate bandwidth portions, e.g., in the uplink and downlink, are necessarily configured. Therefore, in FDD and TDD operation, it is essential to simultaneously configure the first or second uplink and downlink bandwidth portions.

[0067] When the target base station 200-b receives a handover request message indicating that the mobile terminal 100 can communicate in at least two bandwidth portions, e.g., first and second bandwidth portions, on the uplink and downlink, the processor 230-b controls the transceiver 220-b to configure at least both the first bandwidth portion and the second bandwidth portion for the mobile terminal.

[0068] The processor 230-b of the target base station 200-b also controls the transceiver 220-b to send a handover (request) response confirmation message (see message 2 in FIG. 1) to the source base station 200-a, the handover (request) response confirmation message including information regarding at least both the configured first and second bandwidth portions of the uplink and downlink.

[0069] For example, this information includes numerology indicating the location (e.g., center frequency), bandwidth (e.g., number of physical resource blocks PRB), subcarrier spacing and cyclic prefix for each of the uplink and downlink bandwidth portions, as well as an index associated with this bandwidth.

[0070] Instead of a position, the information may include an offset from a (given) position of the downlink bandwidth portion, or an offset that indirectly identifies the position of the uplink bandwidth portion by specifying an offset from a known reference position, e.g., the first PRB of the DL carrier bandwidth. It may be mentioned that some parameters for the configuration of the bandwidth portion, e.g., position and bandwidth, may be coded together to become one parameter in the configuration.

[0071] Again, this handover (request) response confirmation message may be sent over the Xn interface, which connects the base stations directly to each other, or over the NG interface, which connects the base stations to the core network.

[0072] The source base station 200-a then forwards the information from this handover (request) response confirmation message to the mobile terminal 100. This information is conveyed in the form of a handover command message (see message 3 in FIG. 1). In other words, information about at least the first and second bandwidth portions configured at least in the target base station 200-b is (also) included in the handover command message to the mobile terminal 100.

[0073] Transceiver 120 of mobile terminal 100 receives a handover command message from source base station 200-a, which includes, among other things, information regarding the configured bandwidth portions (described above). Upon receiving this handover command message, processor 130 may process the included information in this disclosure in two different mechanisms, discussed below as a first embodiment and a second embodiment.

[0074] Apart from the details, it is important to understand that in both embodiments, the processor 130 of the mobile terminal 100 has successfully activated one of the bandwidth portions configured (especially) for this mobile terminal 100 and can already perform the handover on this configured bandwidth portion. Therefore, the mobile communication system is not limited to performing the handover on a common configuration of bandwidth portions that is broadcast to all mobile terminals, for example via a system information message. The method of the present disclosure can avoid congestion on the common configured bandwidth portion.

[0075] In the first embodiment, the mobile terminal 100 processes the information of the handover command such that the processor 130 activates at least one preselected one of the configured at least first and second bandwidth portions in the uplink and downlink in the transceiver 120. For example, the mobile terminal 100 activates (exactly) one preselected bandwidth portion in the uplink and one preselected bandwidth portion in the downlink. However, this should not be understood as limiting in any way. Rather, the mobile terminal 100 may activate two or more preselected bandwidth portions in the uplink and downlink. In the future, to support simultaneous multiple numerology processing, it may be beneficial for the mobile terminal to simultaneously activate two bandwidth portions of different numerologies in the uplink and downlink carrier bandwidth. Therefore, it can be said that the mobile terminal 100 activates at least one preselected one of the configured bandwidth portions.

[0076] In the context of this disclosure, the term "preselected" shall be understood to emphasize that the selection is not made by the mobile terminal itself. The selection may be defined by the specification as a bandwidth portion at a particular index (e.g., index #0) or a special bandwidth portion such as an initial bandwidth portion or a default bandwidth portion, and the selection is made by the target base station and then instructed to the mobile terminal.

[0077] Upon activating the at least one preselected bandwidth portion, the processor 130 of the mobile terminal 100 controls the transceiver 120 to communicate with the target base station 200-b as part of the handover over the activated at least one preselected bandwidth portion.

[0078] Since the target base station 200-b also knows which of the at least two configured bandwidth portions is the pre-selected one to be activated by the mobile terminal, the target base station 200-b can also proceed with activating the same pre-selected at least one bandwidth portion that the mobile terminal is expected to activate after sending the handover (request) response confirmation message.

[0079] In a first embodiment, the mobile terminal 100 is provided with information about the at least two configured bandwidth portions. This information is signaled to the mobile terminal 100, even though (only) one of the at least two bandwidth portions has already been pre-selected. Despite (being added to) the payload to the handover command, this information advantageously increases flexibility during handover, i.e. allows switching between the at least two configured bandwidth portions during handover.

[0080] Conversely, in the second embodiment, the mobile terminal 100 processes the information in the handover command such that the processor 130 first (actively) selects and then activates at least one of the at least two configured bandwidth portions for the uplink and downlink in the transceiver 120. For example, again, the mobile terminal 100 selects and activates (exactly) one of the at least two bandwidth portions.

[0081] Again, this should not be understood as limiting in any way. Rather, the mobile terminal 100 may select and activate two or more of the at least two configured bandwidth portions for the uplink and downlink. This again serves the purpose of simultaneously processing multiple numerologies or alleviating congestion among available radio resources, for example, when simultaneously selecting and activating two non-adjacent bandwidth portions of different numerologies.

[0082] Upon selecting and activating at least one of the at least two configured bandwidth portions for the uplink and downlink, the processor 130 of the mobile terminal 100 controls the transceiver 120 to communicate with the target base station 200-b as part of the handover on the selected and activated bandwidth portion.

[0083] Here, the target base station 200-b does not know (exactly) which of the at least two configured bandwidth portions has been selected and activated by the mobile terminal 100. Nevertheless, because both of the at least two bandwidth portions are configured for selection and activation (among other things) for the mobile terminal, the target base station 200-b may proceed with activating all of the at least two configured bandwidth portions, eliminating this uncertainty at the earliest phase of communicating with the mobile terminal.

[0084] Thereafter, at a later stage, the mobile terminal may signal the selection of the first activated bandwidth to the target base station by way of RACH resource or PUSCH resource differentiation, as will be described in more detail below.

[0085] As a result, the target base station 200-b may detect which of the configured bandwidth portions is actually being used for communication from further communication with the mobile terminal 100. This may allow the target base station 200-b to (retroactively) obtain information about which of the configured bandwidth portions the mobile terminal has selected and activated.

[0086] Again, it is important to note that in the second embodiment, the mobile terminal 100 is provided with information regarding at least two configured bandwidth portions. This information (along with other information detailed below) is signaled to the mobile terminal 100 to enable it to make a selection and subsequently indicate the selection to the target base station.

[0087] Despite being (added to) the payload to the handover command, this information advantageously increases flexibility during handover, i.e. allows switching between at least two bandwidth portions (already) configured during handover.

[0088] 4 shows a sequence diagram of a handover procedure according to an exemplary implementation of the first embodiment in a 3GPP NR deployment scenario, in particular a user equipment (UE) when performing a handover from a source gNodeB, gNB, to a target gNB.

[0089] In preparation for the handover, the source gNB sends a handover request message (see message 1 in Figure 4) to the target gNB. The handover request message is typically sent over the Xn interface, which establishes communication between gNBs in the Next Generation Radio Access Network (RAN). This handover request message provides sufficient details for the target gNB to prepare for the handover of the UE, e.g., to perform admission control.

[0090] Through this handover request message, the target gNB receives information about the UE's ability to communicate in at least two bandwidth portions in the uplink and downlink. This allows the target gNB to configure an appropriate number of bandwidth portions for the UE, e.g., matching the UE's capabilities. For example, if the UE can communicate in two bandwidth portions, a narrow bandwidth portion and a wide bandwidth portion, the target gNB will configure two bandwidth portions for the UE as well.

[0091] Once the appropriate number of bandwidth portions has been configured in the uplink and downlink, the target gNB includes this information in a handover (request) response acknowledgment message (see message 2 in Figure 4), which is sent from the target gNB to the source gNB. The handover (request) response acknowledgment message is also typically sent over the Xn interface between the gNBs, if available.

[0092] The source gNB then relays this information to the UE in a handover command message (see message 3 in Figure 4). As a result, information regarding the appropriate number of configured bandwidth portions is received by the UE. As discussed with respect to 3GPP NR, the handover command message contains a number of details for the UE to perform the handover to the target gNB.

[0093] Importantly, with information about the (appropriate number of) configured bandwidth portions, the UE is in a position to perform a handover to the target gNB using the bandwidth portions that have been configured for the UE in a UE-specific manner, in other words, the UE is not limited to performing a handover with a (common) initial bandwidth portion that is shared among multiple UEs at once.

[0094] Thus, the knowledge about the configured bandwidth portions reduces the effects of congestion during handover, while at the same time, this information eliminates the need to configure the bandwidth portions at a later point in time. These advantages are achieved despite a fixed handover sequence in which a limited number of messages are exchanged.

[0095] Advantageously, in a random access channel (RACH) based handover, the UE can already perform random access message transmission with the target gNB on a UE-specific configured bandwidth portion without having to rely solely on the (common) initial bandwidth portion.

[0096] In particular, the UE-specific configured bandwidth portion allows for less congestion for RACH message 1 and more flexible scheduling for RACH message 2.

[0097] The UE completes the handover by sending a handover complete message (see Figure 4, message 4) to the target gNB.

[0098] While various configurations of bandwidth portions for the UE have been detailed, there has been no discussion so far about which of the multiple bandwidth portions are activated. This is an important point to mention, because activating more bandwidth would increase power consumption and processing complexity, so neither the UE nor the target gNB will (likely) activate all configured bandwidth portions in the uplink and one bandwidth portion in the downlink. For this reason, in Release-15 it is agreed that an NR mobile terminal will always activate one downlink bandwidth portion and one uplink bandwidth portion.

[0099] Therefore, during handover, the UE and the target gNB activate only one of the configured bandwidth portions in the uplink and one bandwidth portion in the downlink. It is therefore necessary to establish a common understanding between the target gNB and the UE as to which of the two configured bandwidth portions in both the uplink and the downlink should be activated.

[0100] In this exemplary implementation, it is assumed that among the information about configured bandwidth portions, there is (always) one pre-selected bandwidth portion activated for the uplink and downlink.

[0101] For example, assuming that the information about the configured bandwidth portions has a particular sequence, both the UE and the target gNB may (always) activate the first or last bandwidth portion of the particular sequence. If there are more than two configured bandwidth portions in the sequence, both the UE and the target gNB may also (always) activate other bandwidth portions of the particular sequence, such as the second bandwidth portion, the third bandwidth portion, etc.

[0102] As another example, the preselected bandwidth portion may be some special bandwidth portion, such as an initial BWP or a default BWP. By providing a new configuration of such a special BWP at the target gNB, the load balancing of the target cell may also be adjusted.

[0103] In summary, the mere fact that information about the configured bandwidth portions is provided in a particular sequence is sufficient to establish a common understanding between the UE and the target gNB as to which of this sequence should be activated.

[0104] However, this requires that the sequence of information about the configured bandwidth portions be the same in both the handover (request) response acknowledgment message and the handover command. In other words, the source gNB relaying this information preserves the sequence of information when generating the handover command from the handover (request) response acknowledgment message.

[0105] In an exemplary extension of this implementation, the handover (request) response acknowledgement message as well as the handover command also includes random access transmission parameters such as a preamble sequence or time and frequency resources to be used during the RACH-based handover.

[0106] Importantly, the included random access transmission parameters need to be associated with at least a pre-selected one of the configured bandwidth portions, so the UE will perform the random access message transmission (e.g., RACH message 1) using the random access transmission parameters associated (among other things) with the pre-selected bandwidth portion to be activated.

[0107] The freedom to define random access transmission parameters in association with only a preselected one of the configured bandwidth portions may improve RACH resource utilization. In such a case, the target gNB does not need to reserve RACH resources corresponding to other configured bandwidth portions than the preselected bandwidth portion for the UE performing handover. As a result, more free RACH resources become available for other UEs in the target cell.

[0108] In a further exemplary extension of this implementation, the handover request message further includes information regarding the status of the activated bandwidth portion of the source gNB. Alternatively or additionally, the handover request message includes data traffic information predicted by the source gNB, for example, information regarding the data traffic expected after the handover.

[0109] For example, the status of the activated bandwidth portion may include, for example, a narrowband or wideband descriptor, or a reference to the (bandwidth) width (e.g., in physical resource blocks) of the bandwidth portion activated at the source gNB before the handover. Also, for example, the traffic information predicted by the source gNB may include an index to the buffer size level of the downlink buffer status, or information from a buffer status report from the uplink UE before the handover.

[0110] In either case, once the source gNB forwards this information to the target gNB in the handover request message, the target gNB may (actively) select which of the configured bandwidth portions is best suited to become the pre-selected one of the configured bandwidth portions.

[0111] For example, when the UE has low or no traffic demand, it would be better to activate a narrower bandwidth portion during and after handover so as not to waste the UE's power, while when the UE has high traffic demand, it would be a wise decision to activate a wider bandwidth portion of the configured bandwidth portion even during handover.

[0112] Then, after handover, the UE's data can be immediately served on the wider bandwidth portion (at full capacity) without the need for additional bandwidth portion switching (thus avoiding the delay introduced by bandwidth portion switching).

[0113] During handover, it can be said that there is only a small amount of traffic to communicate between the UE and the target base station, for example, for random access. Therefore, during handover, the UE can operate in a narrower bandwidth portion. Then, after random access is completed, the target gNB can instruct the UE by DCI to switch to a wider BWP if necessary. However, the following drawbacks are observed:

[0114] The BWP switching transition time is still under discussion, but it is likely that at least one slot (of 15 kHz SCS) will be required. Thus, if a BWP switching DCI is sent in slot n and the UE then performs a BWP switch in slot n+1 (since BWP switching DCI with null data scheduling is not supported, the UE must still receive the PDSCH in slot n in a narrow BWP), the first opportunity to schedule UE data to a wide BWP is slot n+2. In cases where UE traffic demand is high, data delivery latency will suffer.

[0115] Furthermore, the channel state information (CSI) is also delayed. Since the CSI is measured within the active BWP, the CSI for the wide BWP is not available until the wide BWP is activated. Thus, in the above example where the wide BWP is activated in slot n+2, the gNB has to use conservative scheduling decisions for at least slot n+2 (and possibly also for slot n+3 if the UE is not able to feedback CSI in the same slot), resulting in additional latency.

[0116] There is a risk that the UE will miss the DCI for BWP switching. This concerns the general DCI error case, but it is more reasonable to avoid unnecessary BWP switching by consistently setting BWP during and after handover.

[0117] To communicate this preselected bandwidth portion selection to the UE, the target gNB then (re)arranges the information about the configured bandwidth portions in a specific sequence. For example, the target gNB may (re)arrange the optimal one of the configured bandwidth portions to be the first or last bandwidth portion of the configured bandwidth portions in the specific sequence included in the handover (request) response confirmation message. Then, when the UE is expected to (always) activate the first or last bandwidth portion of the specific sequence of bandwidth portions as the preselected bandwidth portion, the target gNB (automatically) activates the optimal bandwidth portion.

[0118] Figure 5 shows a sequence diagram of a handover procedure according to a different exemplary implementation of the first embodiment in a 3GPP NR deployment scenario. This different exemplary implementation is closely related to the previous exemplary implementation shown in Figure 4, so the following discussion will focus only on the differences.

[0119] As before, here too, the information about the (appropriate number of) configured bandwidth portions puts the UE in a position to perform a handover to the target gNB utilizing the bandwidth portions configured for the UE, thus achieving the same or similar advantages.

[0120] Unlike the above, there is an index (or bandwidth portion index) that is additionally included in the handover (request) response acknowledgement message from the target gNB to the source gNB (see message 2 in Figure 5) and in the handover command message from the source gNB to the UE (see message 3 in Figure 5). This index indicates which of the bandwidth portions consisting of uplink and downlink should be activated.

[0121] For example, both messages may include an index for the uplink and downlink, e.g., BWP#1, to clearly indicate which of the configured bandwidth portions should be activated. Thus, the index may also allow the target gNB to pre-select the corresponding bandwidth portion to be activated.

[0122] Considering that both messages contain information about the first and second configured bandwidth portions, then an index indicating the first or second configured bandwidth portion to which the information is transmitted enables the UE to activate the corresponding preselected one of the two bandwidth portions.

[0123] This avoids the need to provide information about the configured bandwidth portions in a particular sequence, and the information can be arranged in ascending order, e.g., so that the (narrowest) bandwidth portion is arranged first, followed by the (larger) bandwidth portions.

[0124] Similarly in a further exemplary extension, the request message may further include information regarding the status of the bandwidth portion activated at the source gNB or information regarding the data traffic predicted by the source gNB, e.g., information regarding the data traffic expected after the handover.

[0125] In either case, once the source gNB forwards this information to the target gNB in the handover request message, the target gNB may again (actively) select which of the configured bandwidth portions is best suited to become the pre-selected one of the configured bandwidth portions. To communicate this pre-selected bandwidth portion selection to the UE, the target gNB then includes an index corresponding to the information regarding the configured bandwidth portions in the message, as described above.

[0126] 6 shows a sequence diagram of a handover procedure according to an exemplary implementation of the second embodiment in a 3GPP NR deployment scenario, in particular showing a user equipment UE when performing a handover from a source gNB to a target gNB.

[0127] In preparation for the handover, the source gNB sends a handover request message (see message 1 in Figure 6) to the target gNB. The handover request message is again typically sent over the Xn interface (if such a link is available) that establishes communication between gNBs of the Next Generation Radio Access Network (RAN); otherwise, the message is sent via the core network. This handover request message provides sufficient details for the target gNB to prepare for the handover of the UE, e.g., to perform admission control.

[0128] Through this handover request message, the target gNB receives information about the UE's ability to communicate in at least two bandwidth portions in the uplink and downlink. This allows the target gNB to configure an appropriate number of bandwidth portions for the UE, e.g., matching the UE's capabilities. For example, if the UE can communicate in two bandwidth portions, a narrow bandwidth portion and a wide bandwidth portion, the target gNB will configure two bandwidth portions for the UE as well.

[0129] Once the appropriate number of bandwidth portions in the uplink and downlink have been configured, the target gNB includes this information in a Handover (Request) Response Acknowledgement message (see message 2 in Figure 6), which is sent from the target gNB to the source gNB. The Handover (Request) Response Acknowledgement message is also typically sent over the Xn interface, if available.

[0130] Unlike the above, the target gNB also includes in the handover (request) response confirmation message an association table that associates each of the two configured bandwidth portions with various random access transmission parameters.

[0131] An example of such an association table is shown in Figure 7. This example assumes that at least two bandwidth portions are configured in the uplink and downlink, identified as UL BWP#0 and UL BWP#1 or DL BWP#0 and DL BWP#1, respectively. The extra column containing three dots indicates that further configured bandwidth portions may be included.

[0132] From this table it can be seen that each configured bandwidth portion of the uplink as well as the downlink is associated with different transmission parameters.

[0133] For example, a configured UL BWP#0 is associated with some random access transmission parameters, i.e., RACH#0 or RACH#2, and a further configured UL BWP#1 is associated with different random access transmission parameters, i.e., RACH#1 or RACH#3. Similarly, configured DL BWP#0 and BWP#1 are also associated with different random access transmission parameters.

[0134] It will be appreciated that each of the configured bandwidth portions of the uplink and downlink, individually (as described above), will be associated with different random access parameters, and also in combination will be associated with different random access parameters.

[0135] In other words, here each combination of configured bandwidth portions of the uplink and downlink is also associated with different random access transmission parameters, e.g., a combination of DL BWP#0 and UL BWP#0 is associated with parameter RACH#0, while a different combination of DL BWP#0 and UL BWP#1 is associated with parameter RACH#1.

[0136] However, although this is beneficial, it is not necessary to achieve the advantageous effects, as will become apparent below.

[0137] The source gNB then relays this information to the UE in a handover command message (see message 3 in Figure 6). As a result, information about the appropriate number of configured bandwidth portions is received by the UE. Similar to the case described in Figure 4, the information about the configured bandwidth portions reduces the impact of congestion on the (common) initial bandwidth portion during handover, while avoiding the need to configure bandwidth portions at a later point in time.

[0138] The source gNB also relays an association table in the handover command message to the UE, which enables the UE to perform a random access channel (RACH)-based handover to the target gNB. Both contention-based and contention-free random access can be performed, depending on whether the target gNB decides to include contention-based or contention-free RACH resources in its association table.

[0139] In a RACH-based handover, the UE may transmit random access messages to the target gNB over the configured bandwidth portion without having to rely solely on the (common) initial bandwidth portion.

[0140] In particular, the configured bandwidth portions allow for less congestion of RACH message 1 in the uplink and more flexible scheduling of RACH message 2 in the downlink.

[0141] The UE completes the handover by sending a handover complete message (see Figure 6, message 6) to the target gNB.

[0142] Having detailed the various configurations of bandwidth portions for the UE, it is also necessary to establish a common understanding between the target gNB and the UE as to which of the two configured bandwidth portions should be activated in both the uplink and downlink.

[0143] In this exemplary implementation, it is assumed that the UE (actively) selects the configured bandwidth portion to be activated, in other words, the UE is now free to (freely) select any of the configured bandwidth portions over which information is relayed from the target gNB, without being constrained by any pre-selection performed by the target gNB.

[0144] Advantageously, the UE is usually best able to know and predict its uplink traffic. Although buffer status reports are signaled from the UE to the source gNB, this is not necessarily accounted for at the target gNB during handover. Furthermore, buffer status reports may become outdated due to the time gap between when the buffer status is reported and when the handover command is received by the UE. Therefore, by the UE (actively) selecting the configured bandwidth portions to be activated, it can be ensured that the activation, at least in the uplink, best suits the UE's demands during and after handover.

[0145] Upon selecting one of the configured bandwidth portions, the UE performs a RACH-based handover by first activating the selected bandwidth portion and then performing a random access message transmission using parameters associated with the selected and activated bandwidth portion.

[0146] The random access message transmission is performed in the selected and activated bandwidth portion as well as using the associated parameters. Thus, there is a clear association between the parameters of the transmission and the bandwidth portion in which the transmission is performed. This provides the following advantages:

[0147] For example, if a UE selects and activates UL BWP#1, the association table in Figure 7 requires the UE to use parameters RACH#1 or RACH#3. In any case, when the UE performs a random access message transmission with parameters RACH#1 or RACH#3, the target gNB can reconfirm that the random access transmission occurred on the (correct) UL BWP#1.

[0148] This level of reconfirmation is beneficial because random access transmissions do not occupy a complete uplink bandwidth portion, and therefore it becomes difficult for the target gNB to distinguish between different uplink bandwidth portions, especially if, for example, two configured uplink bandwidth portions are centered on each other or configured with a large overlap.

[0149] The association table therefore prevents a situation where the target gNB receives a random access message transmission but is unable to determine which uplink bandwidth portion has been used, and therefore selected and activated, by the UE.

[0150] In addition, the parameters of the association table in Figure 7 also convey information about the selected and activated downlink part: for example, when the UE performs a random access message transmission with parameters RACH#1, the target gNB knows that not only UL BWP#1 but also DL BWP#0 has been selected.

[0151] The association table therefore helps the UE and the gNB to reach a common understanding of which of the bandwidth portions, consisting of uplink and downlink, the UE has selected and activated for use in communications that are (already) part of the handover procedure.

[0152] Referring now to RACH-based handover in more detail, based on the information in the handover command, the UE selects and activates one of the bandwidth portions consisting of uplink and downlink bandwidth portions to be used in the subsequent handover procedure.

[0153] The UE transmits a random access preamble message (see FIG. 6, message 4) to the target gNB using the preamble sequence and / or time and frequency resources from the association table corresponding to the selected and activated bandwidth.

[0154] This random access preamble message is received by the target gNB and responded to with a random access response message (see message 5 in Figure 6), which is sent from the target gNB to the UE. The target gNB uses the corresponding bandwidth portion of the downlink for the transmission of this message.

[0155] Returning to the example where the random access transmission parameter is RACH#1, the target gNB uses downlink bandwidth portion DL BWP#0 for the transmission of the random access response message. Here again, it can be seen that the association table achieves a common understanding between the UE and the target gNB of which of the configured bandwidth portions should be used during and after the handover.

[0156] However, there are situations in which this level of autonomy in the UE is undesirable or even disadvantageous.

[0157] Thus, in an exemplary extension of this implementation, the handover (request) response acknowledgment includes a bandwidth portion index transferred to the UE in the handover command, which limits the UE's freedom to select a bandwidth portion. Thus, the UE receives information about the configured bandwidth portions, but can only select from them the one that corresponds to the index. This restriction can also be imposed by the source gNB in the handover command. In such a case, the bandwidth portion index is determined by the source gNB.

[0158] A particularly advantageous effect is achieved when this index indexes a particular downlink bandwidth portion to be used while at the same time preserving the freedom for the UE to (actively) select its uplink bandwidth portion for handover, where the index indexes a subset of bandwidth portion combinations, i.e., the uplink bandwidth portion for the particular downlink bandwidth portion corresponding to the bandwidth portion index.

[0159] Such definition of the bandwidth portion index restricts the UE to select and activate a bandwidth portion from a subset of all configured bandwidth portions for which information is included in the handover command, this subset including all configured uplink bandwidth portions but not the configured downlink bandwidth portions since the downlink bandwidth portions are pre-selected by the index.

[0160] An advantageous effect arises from the observation that the UE is typically best able to know and predict its own uplink traffic, while the source or target gNB may be best able to predict downlink traffic. In other words, this index stands between two extremes: one where the target gNB pre-selects all bandwidth portions, and the other where the UE selects all bandwidth portions.

[0161] This exemplary extension with indexes provides additional benefits when combined with the following modifications.

[0162] In a further exemplary extension of this implementation, the handover request message further includes information regarding the status of the activated bandwidth portions of the source gNB. Alternatively or additionally, the handover request message includes information regarding data traffic predicted by the source gNB, for example, information regarding data traffic expected after the handover.

[0163] In either case, when the source gNB forwards this information to the target gNB in the handover request message, it may (actively) select which of the configured bandwidth portions is best suited to become the pre-selected downlink bandwidth portion, without restricting the UE's freedom to (actively) select an uplink bandwidth portion from the configured bandwidth portions.

[0164] To communicate this pre-selected downlink bandwidth portion selection to the UE, the target gNB includes a corresponding index (bandwidth portion index) in a handover (request) response acknowledgement message relayed by the source gNB to the UE in the form of a handover command.

[0165] Then, when the UE is expected to select and activate a configured bandwidth portion, it is restricted to do so from the subset of all configured bandwidth portions for which information is included in the handover command, which not only prevents the UE from (actively) selecting the best uplink bandwidth portion, but also prevents the UE from receiving guidance in selecting the best downlink bandwidth portion.

[0166] Of course, the association table provides the target gNB with a level of reassurance as to which of the configured uplink bandwidth portions has been selected and activated by the UE.

[0167] In another exemplary extension of this implementation, the bandwidth portion index included in the handover (request) response acknowledgement message and the handover command indexes one bandwidth portion in the uplink as well as the downlink, thereby depriving the UE of the freedom to select any one of the configured bandwidth portions in either the downlink or the uplink.

[0168] Returning to a more general discussion of the exemplary implementation, it must be mentioned that the target gNB does not know that the UE has pre-selected one of the configured bandwidth portions until the UE first contacts the target gNB by sending RACH message 1. In other words, the UE is truly given the freedom to select and (simultaneously) activate (the best) one of the configured bandwidth portions (at least for the uplink).

[0169] Since the random access transmission message (see message 4 in Figure 6) is already transmitted on the uplink bandwidth portion selected by the UE, the target gNB must arrange to receive this message regardless of the selection. This uncertainty leaves the target gNB in a situation where it cannot predict which uplink bandwidth portion will be used.

[0170] For this reason, the target gNB activates not just one but all of the configured bandwidth portions, e.g., all uplink bandwidth portions for which information was included in the handover (request) response acknowledgement and handover command messages. In other words, unlike previous implementations, the target gNB must monitor all configured uplink bandwidth portions, not just one.

[0171] Nevertheless, once it becomes clear via the association table which of the configured bandwidth portions has been selected, the uncertainty is removed from the target gNB, and the target gNB may proceed with the deactivation of all non-selected bandwidth portions.

[0172] Returning to the example where the UE has selected RACH#1 for use in the random access preamble transmission (message 4 in Figure 6), due to the uncertainty, the target gNB must activate UL BWP#0 and UL BWP#1, which were previously configured and indicated to the UE in the form of additional information. Only then will the target gNB ensure that it receives the message regardless of the selection.

[0173] Upon receiving this random access preamble transmission on RACH#1, the target gNB is provided with knowledge of the outcome of the UE's selection, e.g., that the UE has selected DL BWP#0 and UL BWP#1 as shown in Figure 7. The target gNB may immediately proceed with deactivation of the remaining configured but unselected BWPs.

[0174] Figure 8 shows a sequence diagram of a handover procedure according to a different exemplary implementation of the second embodiment in a 3GPP NR deployment scenario. This different exemplary implementation is closely related to the previous exemplary implementation shown in Figure 6, so the following discussion will focus only on the differences.

[0175] As a starting point, this implementation is based on the understanding that handover does not necessarily require RACH transmission (called RACH-based handover) and that handover is also possible in a RACH-less manner (called RACH-less handover).

[0176] Such a RACH-less handover is expected, for example, in a mobile communication system where time synchronization exists between multiple gNBs or the UE performing the handover already knows the time advance for the neighboring cell (e.g., when a secondary cell (SCell) is changed to a primary cell (PCell)). In such a case, the UE does not need to perform a random access procedure to re-establish time synchronization when performing a handover from a source cell to a target cell.

[0177] For example, the UE will reuse the same timing advance command when communicating with the source gNB or with the target gNB in such a RACH-less handover. When there is no uncertainty in the timing of the target gNB, there is no need to perform any random access transmission, e.g., a random access preamble transmission.

[0178] With this understanding, it is immediately apparent that an association table associating configured bandwidth portions with various random access transmission parameters is unnecessary. Rather, in this exemplary implementation, there is an association table associating configured bandwidth portions with various uplink shared channel transmission parameters, as shown in Figure 9.

[0179] For example, the various uplink shared channel transmission parameters may include time and frequency of radio channel resources that may be used by the UE when transmitting the handover complete message (see FIG. 8, message 4). In other words, the uplink shared channel transmission parameters may be considered as uplink grants to various radio resources of the physical uplink shared channel of the target base station.

[0180] Other than this fundamental difference, the handover procedure only differs with respect to the information contained in the Handover (Request) Response Acknowledgement message (see Figure 8, Message 2) and the Handover Command message (see Figure 8, Message 3), sent from the target gNB via the source gNB to the UE.

[0181] These messages do not include association tables that associate configured bandwidth portions with various random access transmission parameters, but instead include association tables that associate configured bandwidth portions with various uplink shared channel transmission parameters.

[0182] The different uplink shared channel transmission parameters again provide the target gNB with a beneficial level of reassurance: because the handover complete transmission does not occupy the full uplink bandwidth portion, the target gNB may find it difficult to distinguish between different uplink bandwidth portions, especially if, for example, two configured uplink bandwidth portions are centered or configured with a large overlap.

[0183] Thus, again, the association table advantageously prevents a situation where the target gNB receives an uplink shared channel transmission but is unable to determine which uplink bandwidth portion has been used, and therefore selected and activated, by the UE. For the remaining details, please refer to the above description of Figure 6, which can be understood to describe the procedure as well as the advantages in an analogous manner.

[0184] It should be mentioned that in the case of carrier aggregation where multiple component carriers are configured for a UE, the bandwidth portion configuration and activation method of the present disclosure is for each component carrier. In other words, each component carrier has an independent bandwidth portion configuration. During handover, the PCell of the UE is changed. However, the SCell configuration of the UE can be released or still maintained according to a handover response confirmation received by the UE. Similarly, a new bandwidth portion configuration can be provided accordingly.

[0185] To put it in its most general terms, the present disclosure can be summarized as providing a mechanism that enables cooperative bandwidth portion configuration during handover, thereby minimizing interruption time and reducing power consumption during handover. Figuratively speaking, if the utilization level of the target base station allows, the bandwidth portions can be configured identically in the source and target cells, as discussed with respect to FIG. 2B.

[0186] This is particularly the case when the handover request message (see Figures 4, 5, 6 and 8 message 1) further includes information on the configured at least third and a different fourth bandwidth portion of the source base station and / or information on activated ones of the configured at least third and fourth bandwidth portions of the source base station.

[0187] In this case, the target base station may configure, at the transceiver, the first and second bandwidth portions for the mobile terminal based on the third and fourth bandwidth portions, respectively. In particular, the target base station may configure the first bandwidth portion to be the same as (or similar to) the third bandwidth portion and the second bandwidth portion to be the same as (or similar to) the fourth bandwidth portion.

[0188] In this way, cooperative bandwidth portion configuration is achieved during handover, realizing many of the advantages discussed above.

[0189] Finally, by having information about the most recently activated bandwidth portion at the source base station readily available at the target base station, the target base station can not only cooperatively configure a bandwidth portion for the mobile terminal, but also transmit a handover (request) response confirmation message including a bandwidth portion index that indexes the same bandwidth portion as the previously activated one among the configured bandwidth portions at the source base station.

[0190] The present disclosure can be implemented by software, hardware, or software cooperating with hardware. Each functional block used in the above-described embodiments can be implemented in part or in whole by an LSI such as an integrated circuit, and each process described in each embodiment can be controlled in part or in whole by the same LSI or a combination of LSIs. The LSI can be formed as an individual chip, or a single chip can be formed to include some or all of the functional blocks. The LSI can include a data input / output unit coupled to it. Depending on the degree of integration, the LSI can also be referred to as an IC, system LSI, super LSI, or ultra LSI.

[0191] However, the technology for implementing an integrated circuit is not limited to LSI, and can be implemented using dedicated circuits, general-purpose processors, or dedicated processors. Furthermore, FPGAs (field programmable gate arrays), which can be programmed after LSI fabrication, and reconfigurable processors, which can reconfigure the connections and settings of circuit cells located within LSI, can also be used. The present disclosure can be implemented as digital or analog processing. If LSI is replaced by future integrated circuit technology as a result of advances in semiconductor technology or other derivative technologies, functional blocks can be integrated using that future integrated circuit technology. Biotechnology can also be applied.

[0192] According to a first aspect, a mobile terminal for performing a handover procedure from a source base station to a target base station in a mobile communication system is proposed, the target base station being configured for the mobile terminal with at least a first bandwidth portion and a different second bandwidth portion within its cell bandwidth, the mobile terminal including: a transceiver configured to receive a handover command message from the source base station in operation, the handover command message including information about the configured at least first and second bandwidth portions, and a processor configured to control the transceiver in operation and upon receipt of the handover command message to activate at least a pre-selected one of the configured at least first or second bandwidth portions and to communicate with the target base station in the activated at least one of the configured at least first or second bandwidth portions as part of the handover procedure.

[0193] According to a second aspect that can be combined with the first aspect, the information about the configured at least first and second bandwidth portions has a specific sequence, and in operation the processor activates the first or last bandwidth portion of the specific sequence, or a specific other bandwidth portion if more bandwidth portions than at least the first and second bandwidth portions are configured, as a pre-selected one of the bandwidth portions.

[0194] According to a third aspect that can be combined with the first aspect, the received handover command message further includes a bandwidth portion index, and the processor activates a preselected one of the configured at least the first bandwidth portion or the second bandwidth portion that corresponds to the bandwidth portion index.

[0195] According to a fourth aspect which can be combined with the first to third aspects, the processor controls the transceiver to perform at least a random access message transmission to the target base station as part of the handover procedure.

[0196] According to a fifth aspect which can be combined with the first to fourth aspects, if the received handover command message further includes a plurality of different random access transmission parameters associated with at least a pre-selected one of the configured at least first bandwidth portion and the second bandwidth portion, the processor controls the transceiver to perform a random access message transmission to at least the target base station using the random access transmission parameters associated with the activated pre-selected one of the configured at least first bandwidth portion or the second bandwidth portion.

[0197] According to a sixth aspect, a mobile terminal for performing a handover procedure from a source base station to a target base station in a mobile communication system is proposed. The target base station is configured for the mobile terminal with at least a first bandwidth portion and a different second bandwidth portion within its cell bandwidth. The mobile terminal includes: a transceiver that, in operation, receives a handover command message from the source base station, the handover command message including information about the configured at least first bandwidth portion and the second bandwidth portion; and a processor that, in operation and upon receipt of the handover command message, controls the transceiver to select and activate at least one of the configured at least first bandwidth portion or the second bandwidth portion and to communicate with the target base station on the selected and activated at least one of the configured at least first bandwidth portion or the second bandwidth portion as part of the handover procedure.

[0198] According to a seventh aspect that can be combined with the sixth aspect, the received handover command message further includes a bandwidth portion index, and the processor, in operation, selects and activates, in the transceiver, one of a subset of at least the configured first bandwidth portion or second bandwidth portion that corresponds to the bandwidth portion index.

[0199] According to an eighth aspect that can be combined with the sixth aspect, the bandwidth portion index indexes a subset of uplink bandwidth portions for a particular downlink bandwidth portion, and the processor, in operation, selects and activates, in the transceiver, a subset of at least the configured first or second bandwidth portions that corresponds to the bandwidth portion index.

[0200] According to a ninth aspect which can be combined with the sixth to eighth aspects, the received handover command message further includes a plurality of different random access transmission parameters associated with each or a subset of the configured at least first bandwidth portion and second bandwidth portion, and the processor, in operation, controls the transceiver to perform at least the random access message transmission using the random access transmission parameters associated with the selected and activated one of the configured at least first bandwidth portion or second bandwidth portion.

[0201] According to a tenth aspect which can be combined with the ninth aspect, the plurality of random access transmission parameters include at least one or more of a random access preamble sequence to be transmitted together with the random access message, and a time and a frequency of radio channel resources to be used by the mobile terminal when transmitting the random access message to the target base station.

[0202] According to an eleventh aspect, there is proposed a target base station for performing a handover procedure of a mobile terminal from a source base station in a mobile communication system. The target base station is capable of communicating with the mobile terminal over at least a first bandwidth portion and a different second bandwidth portion within its cell bandwidth. The target base station includes: a transceiver that, in operation, receives a handover request message from the source base station, the handover request message including information regarding the mobile terminal's ability to communicate over at least the first bandwidth portion and the second bandwidth portion; and a processor that, in operation and upon receiving the handover request message, controls the transceiver to configure at least the first bandwidth portion and the second bandwidth portion for the mobile terminal and to transmit a handover request response confirmation message to the source base station, the handover request response confirmation message including information regarding the configured at least first bandwidth portion and second bandwidth portion.

[0203] According to a twelfth aspect which can be combined with the eleventh aspect, the processor, upon operation and after controlling the transceiver to transmit a handover request response confirmation message, activates in the transceiver the same pre-selected one of the configured at least first bandwidth portion or second bandwidth portion that the mobile terminal is expected to activate.

[0204] According to a thirteenth aspect which can be combined with the twelfth aspect, the information about the configured at least first and second bandwidth portions has a specific sequence, and in operation the processor activates the first or last bandwidth portion of the specific sequence, or a specific other bandwidth portion if more bandwidth portions than at least the first and second bandwidth portions are configured, as a preselected one of the bandwidth portions.

[0205] According to a fourteenth aspect that can be combined with the twelfth aspect, the handover request response confirmation message further includes a bandwidth portion index, and the processor, upon operation, activates a preselected one of the configured at least the first bandwidth portion or the second bandwidth portion that corresponds to the bandwidth portion index.

[0206] According to a 15th aspect which can be combined with the 11th to 14th aspects, the handover request message further includes information on the status of the activated bandwidth portions or predicted traffic information, and the processor controls the transceiver, in operation and upon receipt of the handover request message, to select and activate at least one of the at least first and second bandwidth portions which the mobile terminal is expected to activate as a pre-selected bandwidth portion as part of the handover procedure.

[0207] According to a sixteenth aspect which may be combined with the eleventh aspect, the processor, upon operation and after controlling the transceiver to transmit a handover request response confirmation message, activates all of at least the configured first bandwidth portion or second bandwidth portion in the transceiver.

[0208] According to a 17th aspect that can be combined with the 11th aspect, the handover request response confirmation message further includes a plurality of different uplink shared channel transmission parameters each associated with a different one of the configured at least first bandwidth portion and the configured at least second bandwidth portion, and the processor, in operation, controls the transceiver to schedule candidates for handover complete message transmission using all of the plurality of uplink shared channel transmission parameters associated with the configured at least first bandwidth portion or the configured at least second bandwidth portion.

[0209] According to an 18th aspect which can be combined with the 17th aspect, the plurality of uplink shared channel transmission parameters include a time and a frequency of radio channel resources to be used by the mobile terminal when transmitting a handover complete message to the target base station.

[0210] According to a 19th aspect which may be combined with the 17th or 18th aspect, if the handover request response confirmation message further includes a plurality of uplink shared channel transmission parameters each associated with a different one of the configured at least first bandwidth portion and second bandwidth portion, the transceiver, in operation, further receives a handover complete message transmission from the mobile terminal using one of the plurality of uplink shared channel transmission parameters associated with the one of the configured at least first bandwidth portion or second bandwidth portion selected and activated by the mobile terminal, and the processor, in operation, deactivates the remainder of the configured at least first bandwidth portion and second bandwidth portion that have not been selected and activated by the mobile terminal.

[0211] According to a twentieth aspect that can be combined with the eleventh aspect, the handover request response confirmation message further includes a plurality of different random access transmission parameters each associated with a different one of the configured at least first bandwidth portion and the configured at least second bandwidth portion, and the processor controls the transceiver to reserve the random access message transmission using all of the plurality of random access transmission parameters associated with the configured at least first bandwidth portion or the configured at least second bandwidth portion.

[0212] According to a 21st aspect which can be combined with the 20th aspect, the plurality of random access transmission parameters include at least one or more of a random access preamble sequence to be transmitted together with the random access message, and a time and frequency of radio channel resources to be used by the mobile terminal when transmitting the random access message to the target base station.

[0213] According to a 22nd aspect that can be combined with the 21st aspect, if the handover request response confirmation message further includes a plurality of different random access transmission parameters each associated with a different one of the configured at least first bandwidth portion and second bandwidth portion, the transceiver, in operation, further receives a random access message transmission from the mobile terminal using one of the plurality of random access transmission parameters associated with the one of the configured at least first bandwidth portion or second bandwidth portion selected and activated by the mobile terminal, and the processor, in operation, deactivates the remainder of the configured at least first bandwidth portion and second bandwidth portion that have not been selected and activated by the mobile terminal.

[0214] According to a 23rd aspect which may be combined with the 11th aspect, the handover request message further includes information on at least a third bandwidth portion and a different fourth bandwidth portion configured for the mobile terminal at the source base station.

[0215] According to a 24th aspect that can be combined with the 23rd aspect, the handover request message further includes information regarding an activated one of at least a third bandwidth portion and a fourth bandwidth portion configured in the source base station.

[0216] According to a 25th aspect which may be combined with the 24th aspect, the processor, when operating, configures, in the transceiver, for a mobile terminal, a first bandwidth portion and a second bandwidth portion based on the third bandwidth portion and the fourth bandwidth portion, respectively.

[0217] According to a 26th aspect that may be combined with the 25th aspect, the processor, in operation, controls the transceiver to transmit a handover request response confirmation message including a bandwidth portion index, the bandwidth portion index indicating the same bandwidth portion as previously activated among at least a third bandwidth portion and a fourth bandwidth portion configured of the source base station.

[0218] According to a 27th aspect, there is proposed a method for performing a handover procedure of a mobile terminal from a source base station to a target base station in a mobile communication system, the target base station being configured for the mobile terminal with at least a first bandwidth portion and a different second bandwidth portion within its cell bandwidth, the method comprising the steps of: receiving from the source base station a handover command message including information about the configured at least first bandwidth portion and the second bandwidth portion; and, upon receipt of the handover command message, activating at least a pre-selected one of the configured at least first bandwidth portion or the second bandwidth portion, and communicating with the target base station on the activated at least one of the configured at least first bandwidth portion or the second bandwidth portion as part of the handover procedure.

[0219] According to a 28th aspect, there is proposed a method for performing a handover procedure of a mobile terminal from a source base station to a target base station in a mobile communication system, the target base station being configured with at least a first bandwidth portion and a different second bandwidth portion within its cell bandwidth for the mobile terminal, the method comprising the steps of: receiving from the source base station a handover command message including information about the configured at least first bandwidth portion and the second bandwidth portion; and, upon receipt of the handover command message, selecting and activating at least one of the configured at least first bandwidth portion or the second bandwidth portion, and communicating with the target base station on the selected and activated at least one of the configured at least first bandwidth portion or the second bandwidth portion as part of the handover procedure.

[0220] According to a 29th aspect, there is proposed a method for a target base station to perform a handover procedure for a mobile terminal from a source base station in a mobile communication system, wherein the target base station is capable of communicating with the mobile terminal over at least a first bandwidth portion and a different second bandwidth portion within its cell bandwidth, the method comprising the steps of: receiving a handover request message from the source base station, the handover request message including information on the capability of the mobile terminal to communicate over at least the first bandwidth portion and the second bandwidth portion; and, upon receiving the handover request message, configuring at least the first bandwidth portion and the second bandwidth portion for the mobile terminal and sending a handover request response confirmation message to the source base station, the handover request response confirmation message including information on the configured at least first bandwidth portion and second bandwidth portion.

Claims

1. a transceiver for receiving a handover command message from a source base station, the handover command message including information regarding at least a configured first bandwidth portion and a configured second bandwidth portion; a processor configured to, upon receipt of the handover command message, activate a pre-selected one of the configured at least first or second bandwidth portions in the transceiver and control the transceiver to communicate with a target base station as part of a handover procedure over the activated one of the configured at least first or second bandwidth portions; Including, the handover command message includes information of a specific sequence, and a bandwidth portion index for activating the first bandwidth portion or the second bandwidth portion is included at a specific position within the specific sequence; Mobile terminal.

2. the processor activates the first or last bandwidth portion of the particular sequence, or a particular other bandwidth portion if more bandwidth portions than the at least first bandwidth portion and the second bandwidth portion are configured, as the preselected one of the bandwidth portions; the processor activates the preselected one of the configured at least first bandwidth portion or the second bandwidth portion corresponding to the bandwidth portion index. The mobile terminal of claim 1 .

3. the processor controls the transceiver to perform at least a random access message transmission to the target base station as part of the handover procedure; and / or and if the received handover command message further includes a plurality of different random access transmission parameters associated with at least the pre-selected one of the configured at least first bandwidth portion and second bandwidth portion, the processor controls the transceiver to perform a random access message transmission to at least the target base station using the random access transmission parameters associated with the activated selected one of the configured at least first bandwidth portion or the second bandwidth portion. The mobile terminal of claim 1 .

4. a transceiver for receiving a handover command message from a source base station, the handover command message including information regarding at least a configured first bandwidth portion and a configured second bandwidth portion; a processor that, in operation and upon receipt of the handover command message, controls the transceiver to select and activate at least one of the configured at least first bandwidth portion or the second bandwidth portion and to communicate with a target base station as part of a handover procedure on the selected and activated at least one of the configured at least first bandwidth portion or the second bandwidth portion; A mobile terminal including:

5. The received handover command message further includes a bandwidth portion index, and the processor selects and activates, at the transceiver, one of the configured at least first bandwidth portion or a subset of the second bandwidth portion that corresponds to the bandwidth portion index; or the bandwidth portion index indexes a subset of uplink bandwidth portions for a particular downlink bandwidth portion, and the processor selects and activates, at the transceiver, the subset of the configured at least first bandwidth portion or the second bandwidth portion that corresponds to the bandwidth portion index; the received handover command message further includes a plurality of different random access transmission parameters associated with each or a subset of the configured at least first and second bandwidth portions; the processor controls the transceiver to transmit at least a random access message using the random access transmission parameters associated with the selected and activated one of the configured at least first bandwidth portion or the second bandwidth portion; The plurality of random access transmission parameters are: a random access preamble sequence transmitted together with said random access message; and the time and frequency of radio channel resources used by the mobile terminal when transmitting the random access message to the target base station; including at least one or more of: The mobile terminal of claim 4.

6. 1. A method for performing a handover procedure for a mobile terminal, comprising: receiving a handover command message from a source base station, the handover command message including information about at least a configured first bandwidth portion and a configured second bandwidth portion; upon receipt of the handover command message, selecting and activating one of the configured at least first bandwidth portion or the second bandwidth portion, and communicating with a target base station on the selected and activated one of the configured at least first bandwidth portion or the second bandwidth portion as part of a handover procedure; Including, the handover command message includes information of a specific sequence, and a bandwidth portion index for activating the first bandwidth portion or the second bandwidth portion is included at a specific position within the specific sequence; method.

Images