Communication system and method

Abstract

To enable a mobile terminal to more quickly perform handover from a source base station to a target base station.SOLUTION: A target base station performs steps of: receiving from a source base station a handover request message including information regarding the capability of a mobile terminal to communicate over at least a first configured bandwidth part and a second configured bandwidth part; and upon reception of the handover request message, configuring for the mobile terminal at least the first bandwidth part and the second bandwidth part; and transmitting to the source base station a handover request acknowledge message. The handover request acknowledge message includes information regarding the at least first bandwidth part and second bandwidth part configured.SELECTED DRAWING: Figure 4

Description

Technical Field

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

Background Art

[0002] Currently, the 3rd Generation Partnership Project (3GPP) is focusing on the next release (Release 15) of the technical specifications of the next-generation cellular technology (also referred to as the 5th generation (5G)).

[0003] At the 71st meeting of the Radio Access Network (RAN) of the Technical Specification Group (TSG) of 3GPP (Gothenburg, March 2016), the first study item of 5G, "Study on New Radio Access Technology", in which RAN1, RAN2, RAN3, and RAN4 are involved, was approved, and this study forms the basis of the work item (WI) of Release 15 that defines the first standard specification of 5G.

[0004] 5G New Radio (NR) addresses all usage scenarios, requirements, and deployment scenarios defined in Non-Patent Document 1 (available at www.3gpp.org) and provides a single technical framework that includes at least enhanced mobile broadband (eMBB), ultra-reliable low-latency communications (URLLC), and massive machine type communication (mMTC).

[0005] For example, eMBB deployment scenarios may include indoor hotspots, dense urban areas, suburbs, urban areas, and highways. URLLC deployment scenarios may include industrial control systems, mobile health management (remote monitoring, diagnosis, and treatment), real-time vehicle control, and wide-area monitoring and control systems for smart grids. mMTC may include scenarios that use a large number of devices for data transmission with little impact of latency, such as smart wearables and sensor networks.

[0006] In 5G, forward compatibility for future use cases / deployment scenarios is also provided. Backward compatibility with Long Term Evolution (LTE) is not required, which promotes a completely new system design and / or the introduction of new features.

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

[0008] One of the design goals of NR is to minimize the interruption of ongoing traffic and improve the user's mobility without increasing the power consumption of the user equipment at the same time. In RAN#78, it was tasked to RAN2 to investigate how the requirement of 0ms handover interruption time of IMT-2020 can be addressed in LTE and NR within the time frame of Rel-15. In the first step, the handover procedure in LTE is being discussed as the baseline design of NR. Discussions are ongoing in the 3GPP working group regarding what functionality needs to be added or modified for the improvement of NR mobility.

[0009] The term "downlink" means 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" means 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" means 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 Documents

[0010]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Means for Solving the Problem

[0011] One non-limiting exemplary embodiment enables a mobile terminal to perform a handover from a source base station to a target base station more quickly. If the target base station has already configured a plurality of bandwidth parts for the mobile terminal during the handover and signals the same configuration to the mobile terminal, the mobile terminal can immediately (again) start communicating with the target base station with the appropriate bandwidth part configuration during the handover. After the handover, additional reconfiguration attempts can be avoided.

[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 composed of at least a first bandwidth part and a different second bandwidth part within its cell bandwidth for the mobile terminal. The mobile terminal includes a transceiver that receives a handover command message including information regarding at least a first bandwidth part and a second bandwidth part configured from the source base station during operation, and a processing circuit such as a processor that, during operation and upon receiving the handover command message, activates at least one preselected one of the configured at least first bandwidth part or second bandwidth part in the transceiver and controls the transceiver to communicate with the target base station as part of the handover procedure with at least one of the activated at least first bandwidth part or second bandwidth part configured.

[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 composed of at least a first bandwidth portion and a different second bandwidth portion within its cell bandwidth for the mobile terminal. The mobile terminal includes a transceiver that receives a handover command message including information regarding at least the first bandwidth portion and the second bandwidth portion configured from the source base station during operation, and a processor that, during operation and upon receiving the handover command message, selects and activates at least one of the configured at least the first bandwidth portion or the second bandwidth portion in the transceiver, and controls the transceiver to communicate with the target base station as part of the handover procedure using at least one of the selected and activated at least the first bandwidth portion or the second bandwidth portion configured.

[0014] In a further general aspect, the technology disclosed herein features 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 can communicate with the mobile terminal in each of at least a first bandwidth portion and a different second bandwidth portion within its cell bandwidth. The target base station includes a transceiver that receives a handover request message including information regarding the capabilities of the mobile terminal that communicates in at least the first bandwidth portion and the second bandwidth portion from the source base station during operation, and a processor that, during 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 controls the transceiver to transmit a handover request response confirmation message to the source base station, where the handover request response confirmation message includes 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 is composed of at least a first bandwidth portion and a different second bandwidth portion within its cell bandwidth for the mobile terminal. This method includes receiving, from the source base station, a handover command message including information regarding the at least first bandwidth portion and the second bandwidth portion thus configured; and at the time of receiving the handover command message, activating at least one preselected one of the at least first bandwidth portion or the second bandwidth portion thus configured, and communicating with the target base station as part of the handover procedure using at least one of the at least first bandwidth portion or the second bandwidth portion thus configured that has been activated.

[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 composed of at least a first bandwidth portion and a different second bandwidth portion within its cell bandwidth for the mobile terminal. This method includes receiving, from the source base station, a handover command message including information regarding the at least first bandwidth portion and the second bandwidth portion thus configured; and at the time of receiving the handover command message, selecting and activating at least one of the at least first bandwidth portion or the second bandwidth portion thus configured, and communicating with the target base station as part of the handover procedure using at least one of the at least first bandwidth portion or the second bandwidth portion thus configured that has been selected and activated.

[0017] In yet another general aspect, the techniques disclosed herein feature a further method for a target base station to perform a handover procedure of a mobile terminal from a source base station in a mobile communication system. The target base station can communicate with the mobile terminal in at least a first bandwidth portion and a different second bandwidth portion within its cell bandwidth. The method includes receiving a handover request message including information regarding the capabilities of the mobile terminal to communicate in at least the first bandwidth portion and the second bandwidth portion from the source base station, and at the time of 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, wherein the handover request response confirmation message includes information regarding the configured at least the first bandwidth portion and the second bandwidth portion.

[0018] Note that a general embodiment or a specific embodiment can be implemented as a system, a method, an integrated circuit, a computer program, a storage medium, or any optional combination thereof.

[0019] Further benefits and advantages of the disclosed embodiments will become apparent from the specification and the drawings. These benefits and / or advantages can be obtained individually by the various embodiments and features of the specification and the drawings, provided that not all of these features are required to obtain one or more of such benefits and / or advantages.

Brief Description of the Drawings

[0020]

Figure 1A

Figure 1B

Figure 2A

Figure 2B

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

DETAILED DESCRIPTION OF THE INVENTION

[0021] In 3GPP NR, bandwidth part (BWP) operation is introduced as a new feature. The BWP of a group of adjacent physical resource blocks (PRBs) defines the operating bandwidth of the UE within the operating bandwidth of the cell. Furthermore, the bandwidth of the BWP is below the maximum bandwidth capability supported by the UE.

[0022] In the serving cell specific to each UE, one or more downlink BWPs and one or more uplink BWPs can be configured by dedicated radio resource control (RRC) signaling for the UE. The configuration of the BWP may include characteristics of numerology, frequency position (e.g., center frequency), and bandwidth (e.g., number of PRBs), where numerology means 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 a given serving cell at a given time. The UE only expects communication to / from the gNB via the active BWP, i.e., the UE can monitor the PDCCH and the possible PDSCH only with the active downlink BWP, and can transmit the PUSCH / PUCCH only with 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 among the BWPs configured for the UE to another. This is called (dynamic) BWP adjustment.

[0025] Bandwidth adjustment is described as follows in the 3GPP technical specification of the new radio (NR) and the 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).

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

[0027] As shown in Figure 1B, three different BWPs 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 a subcarrier spacing of 60 kHz can be considered.

[0028] A general description of network-controlled mobility is described 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 is applicable to UEs in the RRC_CONNECTED state and is classified into two types of mobility: cell-level mobility and beam-level mobility.

[0029] Cell-level mobility requires explicit RRC signaling to be triggered, for example, handover. In handover between gNBs, the signaling procedure includes at least the following element components shown in Figure 9.2.3.1-1, which is reproduced as Figure 1A in this specification for reasons of consistency. Separately, beam-level mobility does not require explicit RRC signaling to be triggered, is processed at a lower layer, and RRC does not need 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, such as handover. The handover signaling procedure adopts the same principle as Rel-13 LTE. In handover between gNBs, the signaling procedure consists of at least the following element components.

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

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

[0033] 3. The source gNB provides the UE with an RRC configuration in the handover command. The handover command message includes at least the cell ID and the information necessary to access the target cell, so that the UE can access the target cell without reading the system information. In some cases, the information required 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 a handover completion.

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

[0036] When the target gNB uses the same DRB configuration and mapping from QoS flows to DRBs as the source gNB, data transfer, sequential delivery, and duplicate avoidance during handover can be facilitated. In NR, timer - based handover failure procedures are supported. For recovery from handover failure, RRC connection re - establishment procedures are used.

[0037] It should be noted that the element components shown in Figure 1A not only characterize handovers between gNBs but are also part of handovers within the NR RAN. For brevity, refer to Figure 9.2.3.2.1 - 1 which discloses specific aspects of handovers within the AMF / UPF. 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 complete is part of communication 8.

[0038] It is important that the currently known element components of handovers do not support the concept of bandwidth adjustment. Recognizing these drawbacks, the present disclosure aims to improve handover procedures.

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

[0040] If the target base station already configures multiple bandwidth parts for the mobile terminal during handover and signals the same configuration to the mobile terminal, the mobile terminal can immediately (again) start communicating with the target base station with the appropriate bandwidth part configuration during handover. After handover, additional reconfiguration or attempts to adjust the bandwidth part may not be necessary.

[0041] It should be noted that the Xn interface for gNB - to - gNB message exchange is chosen for illustrative purposes of this disclosure. This should not be regarded as a limitation of this disclosure, and this disclosure can be directly applied to the case of handover between AMF / UPF where information regarding the use of the bandwidth parts mentioned in this disclosure is exchanged via the interface between the gNB and the core network.

[0042] For a more comprehensive discussion of the advantages provided by this disclosure, two different scenarios are described in more detail. From this description, it will become apparent that there are additional synergistic effects that can be achieved when considering bandwidth adjustment during handover.

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

[0044] This exemplary scenario shows a situation where the mobile terminal performs a handover from a source base station (especially from a source cell served by the source base station) to a target base station (especially a target cell served by the target base station). In both the source cell and the target cell, the mobile terminal is configured with multiple bandwidth parts, for example, a first and a second bandwidth part corresponding to indices #0 and #1.

[0045] In particular, in the source cell and the target cell, for example, with respect to the synchronization signal SS block of the carrier bandwidth in the frequency domain, the configuration (e.g., position and bandwidth) of the first bandwidth part (referred to as the BWP with index #0) and the second bandwidth part (referred to as the BWP with index #1) is shown. Since the indicated first and second bandwidth parts are included in the same carrier bandwidth also occupied by the SS block, they both correspond to the downlink bandwidth part of the mobile terminal. However, the further explanation also equally applies to the uplink bandwidth part, and thus the specific distinction is omitted for the sake of brevity.

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

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

[0048] However, the adjustment of the reception operation in the mobile terminal includes (re)tuning to the different center frequencies where the respective bandwidth parts are located, and adjusting the filtering bandwidth to the corresponding (band)width of the bandwidth part.

[0049] Referring to FIG. 2B, another exemplary scenario is shown in which the mobile terminal is (re)configured with a plurality of bandwidth parts in the source cell and the target cell, for example, before and after the handover.

[0050] Here, neither the source cell nor the target cell has the first and second bandwidth portions configured to be centered with one or another SS block (in the frequency domain). Instead, they are more flexibly distributed across the carrier bandwidth. It is important that the mobile terminal is composed of the first bandwidth portions of the same (band)width (e.g., the number of physical resource blocks PRBs) at the same positions in the source cell and the target cell.

[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 need to receive radio resources from different portions of the carrier bandwidth. Instead, the receiving operation at the mobile terminal may remain the same.

[0052] This other exemplary scenario avoids interruption of ongoing traffic due to retuning of frequencies during handover because (re)tuning and filter adjustment are not required to be performed.

[0053] However, in this other exemplary scenario, it goes without saying that the mobile terminal is composed of the first bandwidth portion (BWP#0) and the second bandwidth portion (BWP#1) that is not centered (in the frequency domain) in the source cell and the target cell, respectively. When changing between different bandwidth portions, the mobile terminal receives radio resources from different portions of the carrier bandwidth.

[0054] In other words, for the change between the first bandwidth portion and the second bandwidth portion within each of the source cell and the target cell, both (re)tuning and filter adjustment need to be performed, so the change is delayed (the latency increases). However, this can be compensated for by the increased bandwidth available to the mobile terminal in the second bandwidth portion (BWP#1) of the source cell and the target cell.

[0055] In summary, two different exemplary scenarios are discussed, with the latter (shown in FIG. 2B) having the advantage of enabling seamless handover at least between the first bandwidth portions of the source cell and the target cell, and the former being able to achieve load distribution (shown in FIG. 2A).

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

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

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

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

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

[0061] This message and other messages can be sent via a wireless or wired interface that connects the base stations to each other. For example, the handover request message can be sent via an Xn interface defined as part of a next-generation NG radio access network RAN, or via a next-generation NG interface via an entity that provides an access and mobility management function AMF and / or a 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] The transceiver 220-b of the target base station 200-b receives the handover request message from the source base station 200-a. In particular, this message includes information regarding the capabilities of the mobile terminal 100 to communicate in at least two different bandwidth parts, for example, a first bandwidth part BWP#0 and a second bandwidth part BWP#1, in the uplink and downlink, among others. This information helps the target base station 200-b determine the number of bandwidth parts it is expected to configure for the mobile terminal 100.

[0063] For example, assuming that the mobile terminal 100 can communicate in only one bandwidth part rather than multiple bandwidth parts, the target base station 200-b will not configure multiple bandwidth parts for the mobile terminal 100. Despite this possibility, the present disclosure focuses on the mobile terminal 100 that can communicate in multiple bandwidth parts and thus facilitates the target base station 200-b to configure all of the multiple bandwidth parts for the mobile terminal.

[0064] The above limitations on the capabilities of the bandwidth part are understood to apply equally to the uplink and downlink in the frequency division duplexing (FDD) operation mode, as well as to the uplink and downlink in the time division duplexing (TDD) operation mode.

[0065] In other words, when it is said that a mobile terminal can communicate in one bandwidth part in the FDD operation mode, this can be understood to imply a configuration having at most one bandwidth part for the downlink and a separate one bandwidth part for the uplink. When it is said that a mobile terminal can communicate in one bandwidth part in the TDD operation mode, this can be understood to imply a joint configuration having (similarly) at most one bandwidth part for the downlink and one bandwidth part for the uplink (as a pair).

[0066] For this reason, while the present disclosure may equally refer to the terms "uplink and downlink bandwidth parts" or "uplink and downlink bandwidth part pair", it is described with reference to the term "bandwidth part". In either case, it only emphasizes that separate bandwidth parts are necessarily configured for the uplink and downlink, for example. Thus, in FDD and TDD operations, it is essential to configure at least a first or second uplink and downlink bandwidth part simultaneously.

[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, for example, a first and a second bandwidth part, in the uplink and downlink, the processor 230-b controls the transceiver 220-b to configure at least both the first bandwidth part and the second bandwidth part for the mobile terminal.

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

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

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

[0071] Here too, this handover (request) response confirmation message can be transmitted via the Xn interface directly connecting the base stations to each other or the NG interface connecting the base stations to the core network.

[0072] Next, the source base station 200-a transfers the information from this handover (request) response confirmation message to the mobile terminal 100. This information is transmitted in the form of a handover command message (refer to message 3 in FIG. 1). In other words, information regarding 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] The transceiver 120 of the mobile terminal 100 receives a handover command message from the source base station 200-a that particularly includes information regarding the configured bandwidth portion (described above). Upon receiving this handover command message, the processor 130 can process the information included in the present disclosure in two different mechanisms that will be discussed below as the first embodiment and the second embodiment.

[0074] Apart from the details, in both embodiments, it is important to understand that the processor 130 of the mobile terminal 100 successfully activates one of the bandwidth portions specifically configured for this mobile terminal 100, and that handover can already be performed in this configured bandwidth portion. Therefore, the mobile communication system is not limited to performing handover with a common configuration of bandwidth portions that are broadcast to all mobile terminals, for example, via a system information message. By the method of the present disclosure, congestion in the common configured bandwidth portion can be avoided.

[0075] In the first embodiment, the mobile terminal 100 processes the information of the handover command so that the processor 130 activates at least one preselected one of the at least first and second configured 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 a limitation in any way. Rather, the mobile terminal 100 may activate two or more preselected bandwidth portions in the uplink and downlink. In the future, it may be beneficial for the mobile terminal to simultaneously activate two bandwidth portions of different numerologies in the uplink and downlink carrier bandwidths to support simultaneous multiple numerology processing. 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 the present disclosure, the term "preselected" is to be understood as emphasizing that the selection is not made by the mobile terminal itself. The selection can be defined by the specification as a bandwidth portion of 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 the mobile terminal is instructed.

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

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

[0079] In the first embodiment, information regarding at least two configured bandwidth portions is provided to the mobile terminal 100. This information is signaled to the mobile terminal 100 even though only one of the at least two bandwidth portions has already been preselected. Despite the addition of a payload to the handover command, this information advantageously enhances the flexibility during handover, i.e., enables switching between at least two configured bandwidth portions already during handover.

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

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

[0082] When at least one of at least two configured bandwidth portions for the uplink and the downlink is selected and activated, 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 in the selected and activated bandwidth portion.

[0083] Here, the target base station 200 - b does not (exactly) know which of the at least two configured bandwidth portions is selected and activated by the mobile terminal 100. Nevertheless, since both of the at least two bandwidth portions are configured to be selected and activated (especially) for the mobile terminal, the target base station 200 - b proceeds with the activation of all of the at least two configured bandwidth portions and can resolve this uncertainty at the earliest stage of communicating with the mobile terminal.

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

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

[0086] Here too, in the second embodiment, it is important to recognize that the mobile terminal 100 is provided with information regarding at least two configured bandwidth portions. This information is signaled to the mobile terminal 100 (along with other information to be described in detail later) to enable the mobile terminal to make a selection and then instruct the target base station of the selection.

[0087] Despite the addition of a payload to the handover command, this information advantageously enhances the flexibility during handover, i.e., enables switching between at least two configured bandwidth portions already at the time of handover.

[0088] FIG. 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, the user equipment UE when performing a handover from a source gNode B, gNB to a target gNB is shown.

[0089] In preparation for handover, the source gNB sends a handover request message (refer to Message 1 in Figure 4) to the target gNB. The handover request message is typically sent via the Xn interface that establishes communication between gNBs in the next-generation NG radio access network RAN. This handover request message provides sufficient details for the target gNB to prepare for the handover of the UE, for example, to perform admission control.

[0090] Via this handover request message, the target gNB receives information regarding the UE's ability to communicate in at least two bandwidth parts in the uplink and downlink. Thereby, the target gNB can configure an appropriate number of bandwidth parts for the UE, for example, in accordance with the UE's capabilities. For example, if the UE can communicate in two narrow bandwidth parts and one wide bandwidth part, the target gNB can successfully configure two bandwidth parts for the UE as well.

[0091] After configuring an appropriate number of bandwidth parts in the uplink and downlink, the target gNB includes that information in a handover (request) response confirmation message (refer to Message 2 in Figure 4). This message is sent from the target gNB to the source gNB. The handover (request) response confirmation message is also typically sent via the Xn interface if the Xn interface between gNBs is available.

[0092] Subsequently, the source gNB relays this information to the UE in a handover command message (refer to Message 3 in Figure 4). As a result, the information regarding the appropriately configured number of bandwidth parts is received by the UE. As discussed for 3GPP NR, the handover command message contains a number of details for the UE to perform the handover to the target gNB.

[0093] With information about the configured bandwidth parts (appropriate number), it is important that the UE is placed in a situation where it can perform a handover to the target gNB using the bandwidth parts configured in a UE-specific manner for the UE. In other words, the UE is not limited to performing handovers in the (common) initial bandwidth parts shared among a large number of UEs at once.

[0094] Therefore, with information about the configured bandwidth parts, the impact of congestion during handover is reduced, and at the same time, this information eliminates the need to configure bandwidth parts at a later time. These advantages are achieved regardless of the fixed handover sequence in which a limited number of messages are exchanged.

[0095] It is advantageous for the UE to be able to already perform random access message transmission with the target gNB in the bandwidth parts configured specifically for the UE without relying solely on the (common) initial bandwidth parts in a random access channel RACH-based handover.

[0096] In particular, with the bandwidth parts configured specifically for the UE, the congestion of RACH message 1 is reduced, and RACH message 2 can be scheduled more flexibly.

[0097] The UE completes the handover by sending a handover completion message (refer to message 4 in Figure 4) to the target gNB.

[0098] Although the various configurations of bandwidth parts for the UE have been described in detail, no discussion has been made so far about which of the multiple bandwidth parts will be activated. Since activating more bandwidth will increase both power consumption and processing complexity, it is an important point to mention that neither the UE nor the target gNB (presumably) will activate all the configured bandwidth parts in the uplink and one bandwidth part in the downlink. For this reason, in Release-15, it has been agreed that the NR mobile terminal will always activate one downlink bandwidth part and one uplink bandwidth part.

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

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

[0101] For example, assuming that there is a specific sequence in the information about the configured bandwidth parts, both the UE and the target gNB can (always) activate the first or last bandwidth part of the specific sequence. If there are three or more configured bandwidth parts in the sequence, both the UE and the target gNB can also (always) activate another bandwidth part of the specific sequence, such as the second bandwidth part, the third bandwidth part, etc.

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

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

[0104] However, for this purpose, it is necessary that the sequence in the information about the configured bandwidth part is the same in both the handover (request) response confirmation message and the handover command. In other words, the source gNB relaying this information saves the sequence of information when generating the handover command from the handover (request) response confirmation message.

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

[0106] It is important that the included random access transmission parameters need to be associated with at least one of the preselected ones among the configured bandwidth parts. Thus, the UE uses the random access transmission parameters associated (in particular) with the preselected bandwidth part to be activated to perform random access message transmission (e.g., RACH message 1).

[0107] By freely defining in association with only one pre-selected out of the bandwidth parts configured with random access transmission parameters, the utilization of RACH resources can be improved. In such a case, the target gNB does not need to reserve RACH resources corresponding to configured bandwidth parts other than the pre-selected bandwidth part for the UE performing handover. As a result, more available 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 state of the activated bandwidth part of the source gNB. Alternatively or in addition, the handover request message includes data traffic information predicted by the source gNB, for example, information regarding the data traffic expected after handover.

[0109] For example, the state of the activated bandwidth part may include, for example, a narrowband or wideband descriptor, or a reference to the (band) width of the bandwidth part (e.g., physical resource block) activated at the source gNB before 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 state or information from the buffer state report from the uplink UE before handover.

[0110] In any case, when the source gNB transfers this information to the target gNB in the handover request message, the target gNB can (actively) select which of the configured bandwidth parts is most optimal to be the pre-selected one of the configured bandwidth parts.

[0111] For example, when the traffic demand of the UE is low or non-existent, it may be better to activate a narrower bandwidth portion during and after handover so that the power of the UE is not wasted. On the other hand, when the traffic demand of the UE is high, it may be a wise decision to activate a wider bandwidth portion among the configured bandwidth portions even during handover.

[0112] After that, after handover, without the need to switch additional bandwidth portions (thus avoiding the delay introduced by the bandwidth portion switching), the UE's data can be immediately served in a wider bandwidth portion (at full capacity).

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

[0114] - The BWP switching transition time is still under discussion, but at least one slot (with an SCS of 15 kHz) is likely to be required. Therefore, when the BWP switching DCI is transmitted in slot n and then the UE performs BWP switching in slot n + 1 (since BWP switching DCI by null data scheduling is not supported and the UE has to receive PDSCH in the still narrower BWP in slot n), the first opportunity to schedule UE data in the wide BWP is slot n + 2. When the UE traffic demand is high, the latency of data delivery is impaired.

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

[0116] - There is a risk that the UE may miss the DCI for BWP switching. This is related to the general DCI error cases, but it is more reasonable to avoid unnecessary BWP switching by consistently configuring the BWP during and after handover.

[0117] To convey the selection of this pre-selected bandwidth part to the UE, the target gNB then (re)arranges the information regarding the configured bandwidth parts in a specific sequence. For example, the target gNB can (re)arrange the optimal one of the configured bandwidth parts to be the first or the last bandwidth part among the configured bandwidth parts in a specific sequence included in the handover (request) response confirmation message. And when it is expected that the UE activates the first or the last bandwidth part among the specific sequence of bandwidth parts as the pre-selected bandwidth part, the target gNB (automatically) activates the optimal bandwidth part.

[0118] FIG. 5 shows a sequence diagram of the handover procedure according to different exemplary implementations of the first embodiment in the 3GPP NR configuration scenario. Since this different exemplary implementation is closely related to the aforementioned exemplary implementation shown in FIG. 4, the following discussion focuses only on the differences.

[0119] Similar to before, here too, based on information about the configured bandwidth parts (in an appropriate number), the UE is placed in a situation where it can perform a handover to the target gNB using the bandwidth parts configured for the UE. Therefore, the same or similar advantages are realized.

[0120] In contrast to the above, there is an index (or bandwidth part index) that is additionally included in the handover (request) response confirmation message from the target gNB to the source gNB (refer to message 2 in Figure 5) and is additionally included in the handover command message from the source gNB to the UE (refer to message 3 in Figure 5). This index indicates which of the bandwidth parts configured for uplink and downlink should be activated.

[0121] For example, any of the messages may include an index for uplink and downlink, such as BWP#1, to clearly indicate which of the configured bandwidth parts should be activated. Therefore, the index can also cause the corresponding bandwidth part to be activated to be preselected by the target gNB.

[0122] Considering that both messages include information about the configured first and second bandwidth parts. Next, with the index indicating the first or second configured bandwidth part to which the information is transmitted, the UE can activate the corresponding one of the two preselected bandwidth parts.

[0123] This eliminates the need to provide information about the configured bandwidth parts in a specific sequence, and the information can be arranged in ascending order. For example, as a result, the narrowest bandwidth part is arranged first (the most), and then the wider bandwidth part is arranged (more).

[0124] It is also the same in a further exemplary extension that the request message further includes information regarding the state of the bandwidth part activated at the source gNB or information regarding the data traffic predicted by the source gNB, for example, information on the data traffic expected after handover.

[0125] In any case, when the source gNB transfers this information to the target gNB in the handover request message, the target gNB can (actively) select which of the configured bandwidth parts is most suitable to be the preselected one of the configured bandwidth parts. To convey the selection of this preselected bandwidth part to the UE, the target gNB then incorporates an index corresponding to the information on the bandwidth part configured in the message, as described above.

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

[0127] In preparation for handover, the source gNB sends a handover request message (refer to message 1 in FIG. 6) to the target gNB. The handover request message is also usually sent on the Xn interface (if such a link is available) that establishes communication between gNBs in the next-generation NG radio access network RAN, and 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, for example, to perform admission control.

[0128] Via this handover request message, the target gNB receives information regarding the capabilities of the UE to communicate in at least two bandwidth parts in the uplink and downlink. This enables the target gNB to configure an appropriate number of bandwidth parts for the UE, for example, according to the UE's capabilities. For example, if the UE can communicate in two narrow bandwidth parts and one wide bandwidth part, the target gNB can successfully configure two bandwidth parts for the UE as well.

[0129] After configuring an appropriate number of bandwidth parts in the uplink and downlink, the target gNB includes that information in the handover (request) response confirmation message (refer to message 2 in Figure 6). This message is sent from the target gNB to the source gNB. The handover (request) response confirmation message is also usually sent via the Xn interface if possible.

[0130] In contrast to 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 parts with different 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 parts are configured in the uplink and downlink, and are respectively identified as UL BWP#0 and UL BWP#1 or DL BWP#0 and DL BWP#1. The extra column containing three dots suggests the possibility of including additional configured bandwidth parts.

[0132] From this table, it can be seen that each of the configured bandwidth parts in the uplink and downlink is associated with different transmission parameters.

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

[0134] Each of the configured bandwidth parts for the uplink and downlink is individually (as described above) associated with various random access parameters, but it goes without saying that they are also associated with various random access parameters in combination.

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

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

[0137] Subsequently, the source gNB relays this information to the UE in a handover command message (see message 3 in Figure 6). As a result, information regarding the appropriate number of configured bandwidth parts is received by the UE. Similar to the case explained in Figure 4, the information about the configured bandwidth parts reduces the impact of congestion on the (common) initial bandwidth part during handover and at the same time eliminates the need to configure the bandwidth part at a later point in time.

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

[0139] In a RACH-based handover, the UE can perform random access message transmission with the target gNB in a configured bandwidth part without relying only on the (common) initial bandwidth part.

[0140] In particular, with the configured bandwidth part, the congestion of the uplink RACH message 1 is reduced, and the RACH message 2 in the downlink can be scheduled more flexibly.

[0141] The UE terminates the handover by sending a handover completion message (refer to message 6 in Figure 6) to the target gNB.

[0142] Although various configurations of the bandwidth part for the UE have been described in detail, it is also necessary to establish a common understanding between the target gNB and the UE regarding which of the two configured bandwidth parts should be activated for both the uplink and the downlink.

[0143] In this exemplary implementation, it is assumed that the UE (actively) selects the configured bandwidth part to be activated. In other words, here the UE is placed in a situation where it is not subject to any pre-selection constraints performed by the target gNB and can (freely) select any of the configured bandwidth parts for which information is relayed from the target gNB.

[0144] The UE is typically advantageously optimal for knowing and predicting its own uplink traffic. Despite the buffer status report being signaled from the UE to the source gNB, this may not necessarily be explained at the target gNB during handover. Further, the buffer status report may become stale due to the time gap from when the buffer status is reported until the UE receives the handover command. Therefore, by (actively) selecting the configured bandwidth part that the UE should be activated on, at least in the uplink, it can be guaranteed that the activation is most suitable for the UE's demand during and after handover.

[0145] When selecting one of the configured bandwidth parts, the UE first activates the selected one bandwidth part, and then performs a RACH-based handover by transmitting a random access message using the parameters associated with the selected and activated one bandwidth part.

[0146] The random access message transmission not only uses the associated parameters but is also executed on the selected and activated bandwidth part. Therefore, there is a clear association between the transmission parameters and the bandwidth part on which the transmission is executed. This provides the following advantages.

[0147] For example, assuming the UE selects and activates UL BWP#1, according to the association table in Figure 7, the UE is required to use parameter RACH#1 or RACH#3. In any case, when the UE transmits a random access message with parameter 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. Random access transmission does not occupy the entire uplink bandwidth portion, and thus, it becomes difficult for the target gNB to distinguish different uplink bandwidth portions, especially when, for example, two configured uplink bandwidth portions are centered with respect to each other or are configured to largely overlap.

[0149] Therefore, the association table prevents a situation where the target gNB receives a random access message transmission but cannot determine which uplink bandwidth portion was used by the UE and thus was selected and activated.

[0150] In addition, the parameters of the association table in FIG. 7 also convey information regarding the selected and activated downlink portion. For example, when the UE performs a random access message transmission with parameter RACH#1, the target gNB can also learn that not only UL BWP#1 but also DL BWP#0 has been selected.

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

[0152] Here, the RACH-based handover is referred to in more detail. Based on the information in the handover command, the UE selects and activates one of the bandwidth portions configured for the uplink and downlink. These bandwidth portions are used in subsequent handover procedures.

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

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

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

[0156] However, there are situations where this level of autonomy at the UE is not desirable or even disadvantageous.

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

[0158] This index is particularly advantageous when it indexes the specific downlink bandwidth part to be used while allowing the UE the freedom to (actively) select its uplink bandwidth part for handover. In this case, the index indexes the uplink bandwidth part for a specific downlink bandwidth part corresponding to a subset of combinations of bandwidth parts, i.e., the bandwidth part index.

[0159] With such a definition of the bandwidth part index, the UE is restricted to selecting and activating a bandwidth part from a subset of all configured bandwidth parts in which the handover command contains information. This subset includes all configured uplink bandwidth parts but does not include configured downlink bandwidth parts since the downlink bandwidth parts are preselected by the index.

[0160] An advantageous effect results from the observation that while the UE typically knows and is best placed to predict its own uplink traffic, the source gNB or target gNB may be best placed to predict downlink traffic. In other words, this index stands between two poles: one pole where the target gNB preselects all bandwidth parts and the other pole where the UE selects all bandwidth parts.

[0161] This exemplary extension with an index provides further advantages when combined with the following modifications.

[0162] In a further exemplary extension of this implementation, the handover request message further includes information about the state of the activated bandwidth parts of the source gNB. Alternatively or in addition, the handover request message includes information about the data traffic predicted by the source gNB, e.g., information about the data traffic expected after the handover.

[0163] In either case, when the source gNB transfers this information to the target gNB in the handover request message, it can (actively) select which of the configured bandwidth parts is most suitable to be the preselected downlink bandwidth part without restricting the UE's freedom to (actively) select the uplink bandwidth part from the configured bandwidth parts.

[0164] To convey the selection of this preselected downlink bandwidth part to the UE, the target gNB includes the corresponding index (bandwidth part index) in the handover (request) response confirmation message relayed to the UE in the form of a handover command by the source gNB.

[0165] And when the UE is expected to select and activate the configured bandwidth parts, the UE is restricted to doing so from a subset of all the configured bandwidth parts in which the handover command contains information. As a result, not only can the UE not (actively) select the best uplink bandwidth part, but it also cannot receive guidance when selecting the best downlink bandwidth part.

[0166] Needless to say, through the association table, the target gNB can obtain a reconfirmation of the level regarding which of the configured uplink bandwidth parts are selected and activated by the UE.

[0167] In another exemplary extension of this implementation, the bandwidth part index included in the handover (request) response confirmation message and the handover command indexes one bandwidth part not only for the downlink but also for the uplink. Thereby, the UE is deprived of the freedom to select any one of the configured bandwidth parts for both the downlink and the uplink.

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

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

[0170] Therefore, the target gNB activates not only one but all of the configured bandwidth parts, for example, all uplink bandwidth parts in which information is included in the handover (request) response confirmation and handover command messages. In other words, unlike previous implementations, the target gNB must monitor not one but all of the configured uplink bandwidth parts.

[0171] Nevertheless, once it becomes clear which of the bandwidth parts configured by the association table has been selected, the uncertainty is removed from the target gNB, and the target gNB can proceed with deactivating all unselected bandwidth parts.

[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 can the target gNB ensure that it receives the message regardless of the selection.

[0173] Upon receiving the random access preamble transmission in this RACH#1, the target gNB is provided with knowledge about the result of the UE's selection, for example, knowing that the UE has selected DL BWP#0 and UL BWP#1 as shown in FIG. 7. The target gNB can immediately proceed with the remaining deactivation that is configured but not selected.

[0174] FIG. 8 shows a sequence diagram of a handover procedure according to different exemplary implementations of a second embodiment in a 3GPP NR deployment scenario. Since this different exemplary implementation is closely related to the aforementioned exemplary implementation shown in FIG. 6, the following discussion focuses only on the differences.

[0175] As a starting point, this implementation is based on the understanding that a RACH transmission (referred to as a RACH-based handover) is not necessarily required for a handover, and a handover can also be considered in a RACH-less manner (referred to as a RACH-less handover).

[0176] Such a RACH-less handover is envisioned in a mobile communication system where, for example, there is time synchronization between multiple gNBs or the UE performing the handover already knows the time advance regarding 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 the source cell to the target cell.

[0177] For example, the UE will reuse the same timing advance command when communicating with the source gNB or 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 a random access transmission, e.g., a random access preamble transmission.

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

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

[0180] Other than this basic difference, the handover procedure is included in the handover (request) response confirmation message (see message 2 in FIG. 8) and the handover command message (see message 3 in FIG. 8), which are transmitted from the target gNB to the UE via the source gNB, and only differs in terms of the information included therein.

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

[0182] With the various uplink shared channel transmission parameters, the target gNB also obtains a useful level of reconfirmation here. Since the handover completion transmission does not occupy the entire uplink bandwidth portion, it becomes difficult for the target gNB to distinguish different uplink bandwidth portions, especially when, for example, two configured uplink bandwidth portions are centered with respect to each other or are configured to largely overlap.

[0183] Therefore, here too, the situation where the target gNB receives uplink shared channel transmission but cannot determine which uplink bandwidth part was used by the UE and thus which was selected and activated is advantageously prevented. For the remaining details, please refer to the above description of FIG. 6, which can be understood as explaining the procedure and advantages in a similar form.

[0184] In the case of carrier aggregation where a plurality of component carriers are configured for the UE, it must be mentioned that the configuration and activation method of the bandwidth part of the present disclosure are for each component carrier. In other words, each component carrier has an independent configuration of the bandwidth part. During handover, the PCell of the UE is changed. However, the configuration of the SCell of the UE can still be maintained without being released according to the handover response confirmation received by the UE. Similarly, a configuration of a new bandwidth part can be provided as appropriate.

[0185] Putting it in the most general terms, it can be summarized that the present disclosure provides a mechanism that enables a coordinated configuration of the bandwidth part during handover, thereby minimizing the interruption time and reducing power consumption during handover. Figuratively speaking, if the utilization level of the target base station permits, the bandwidth part can be configured the same in the source cell and the target cell as discussed with respect to FIG. 2B.

[0186] This is particularly relevant when the handover request message (refer to messages 1 in FIGS. 4, 5, 6, and 8) further includes information regarding at least the third and different fourth bandwidth parts configured by the source base station and / or information regarding the activated ones among at least the third and fourth bandwidth parts configured by the source base station.

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

[0188] In this way, a coordinated configuration of the bandwidth portions is achieved during handover, and a number of the advantages discussed above are realized.

[0189] Finally, if information regarding the most recently activated bandwidth portion at the source base station is made immediately available at the target base station, this target base station can not only configure the bandwidth portion for the mobile terminal in a coordinated manner, 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 of the source base station.

[0190] The present disclosure can be implemented by software, by hardware, or by software cooperating with hardware. Each functional block used in the description of each of the above embodiments can be implemented in part or in whole by 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 individually as a chip, or one chip can be formed so as to include part or all of the functional blocks. The LSI can include a data input / output section coupled thereto. Depending on the degree of integration, the LSI is also referred to as an IC, a system LSI, a super LSI, or an ultra LSI.

[0191] However, the technology for implementing integrated circuits is not limited to LSIs, and can be implemented by using application-specific circuits, general-purpose processors, or dedicated processors. Furthermore, it is also possible to use an FPGA (Field Programmable Gate Array) that can be programmed after the manufacture of the LSI, or a reconfigurable processor that can reconfigure the connection and setting of circuit cells arranged inside the LSI. The present disclosure can be implemented as digital processing or analog processing. As a result of the progress of semiconductor technology or other derivative technologies, if LSIs are replaced by future integrated circuit technologies, the functional blocks can be integrated using such future integrated circuit technologies. 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 is composed of at least a first bandwidth portion and a different second bandwidth portion within its cell bandwidth for the mobile terminal. The mobile terminal includes a transceiver that receives a handover command message including information regarding at least a first bandwidth portion and a second bandwidth portion configured from the source base station during operation, and a processor that controls the transceiver to activate at least one preselected one of the configured at least a first bandwidth portion or a second bandwidth portion and communicate with the target base station as part of the handover procedure using at least one of the activated at least a first bandwidth portion or a second bandwidth portion during operation and when receiving the handover command message.

[0193] According to a second aspect that can be combined with the first aspect, the information regarding the configured at least a first bandwidth portion and a second bandwidth portion has a specific sequence, and the processor activates, during operation, the first bandwidth portion or the last bandwidth portion of the specific sequence, or a specific other bandwidth portion when more bandwidth portions than at least the first bandwidth portion and the second bandwidth portion are configured, as one of the preselected ones 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 part index, and the processor activates a preselected one of at least the first configured bandwidth part or the second configured bandwidth part corresponding to the bandwidth part index.

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

[0196] According to a fifth aspect that can be combined with the first to fourth aspects, when the received handover command message further includes a plurality of different random access transmission parameters associated with at least a preselected one of at least the first configured bandwidth part and the second configured bandwidth part, the processor uses the random access transmission parameters associated with the activated preselected one of at least the first configured bandwidth part or the second configured bandwidth part to control the transceiver to transmit at least a random access message to the target base station.

[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 composed of at least a first bandwidth portion and a different second bandwidth portion within its cell bandwidth for the mobile terminal. The mobile terminal includes a transceiver that receives a handover command message including information regarding at least the first bandwidth portion and the second bandwidth portion configured by the source base station during operation, and a processor that controls the transceiver to select and activate at least one of the configured at least the first bandwidth portion or the second bandwidth portion in the transceiver during operation and when receiving the handover command message, and communicate with the target base station as part of the handover procedure using at least one of the selected and activated at least the first bandwidth portion or the second bandwidth portion configured.

[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 selects and activates one of the subsets of the configured at least the first bandwidth portion or the second bandwidth portion corresponding to the bandwidth portion index in the transceiver during operation.

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

[0200] According to a ninth aspect that 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 at least the first bandwidth portion and the second bandwidth portion of the configured respective or subsets, and the processor, during operation, uses the random access transmission parameters associated with one of the selected and activated at least the first bandwidth portion or the second bandwidth portion of the configured to control the transceiver to perform at least random access message transmission.

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

[0202] According to an eleventh aspect, a target base station for performing a handover procedure of a mobile terminal from a source base station in a mobile communication system is proposed. The target base station can communicate with the mobile terminal in at least the first bandwidth portion and the different second bandwidth portion within its cell bandwidth. The target base station includes a transceiver that receives a handover request message including information about the capabilities of the mobile terminal communicating in at least the first bandwidth portion and the second bandwidth portion from the source base station during operation, and a processor that controls the transceiver to configure at least the first bandwidth portion and the second bandwidth portion for the mobile terminal during operation and when receiving the handover request message, and controls the transceiver to transmit a handover request response confirmation message to the source base station, where the handover request response confirmation message includes information about the configured at least the first bandwidth portion and the second bandwidth portion.

[0203] According to a 12th aspect that can be combined with the 11th aspect, after the processor controls the transceiver to send an operation-time and handover request response confirmation message, the transceiver activates, as the same preselected one, at least one of the configured first bandwidth part or second bandwidth part where the mobile terminal is expected to be activated.

[0204] According to a 13th aspect that can be combined with the 12th aspect, information regarding at least the configured first bandwidth part and second bandwidth part has a specific sequence, and the processor, during operation, activates, as a preselected one of the bandwidth parts, the first bandwidth part or the last bandwidth part of the specific sequence, or, when more bandwidth parts than at least the first bandwidth part and the second bandwidth part are configured, a specific other bandwidth part.

[0205] According to a 14th aspect that can be combined with the 12th aspect, the handover request response confirmation message further includes a bandwidth part index, and the processor, during operation, activates, as a preselected one of at least the configured first bandwidth part or second bandwidth part, the one corresponding to the bandwidth part index.

[0206] According to a 15th aspect that can be combined with the 11th to 14th aspects, the handover request message further includes information regarding the state of the activated bandwidth part or predicted traffic information, and the processor, during operation and upon receiving the handover request message, controls the transceiver to select and activate at least one of at least the first bandwidth part and the second bandwidth part where the mobile terminal is expected to be activated as a preselected bandwidth part as part of the handover procedure.

[0207] According to the 16th aspect that can be combined with the 11th aspect, after the processor controls the transceiver to send a handover request response confirmation message during operation, the transceiver activates all of the configured at least first bandwidth portion or second bandwidth portion.

[0208] According to the 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 respectively associated with different ones of the configured at least first bandwidth portion and second bandwidth portion, and the processor controls the transceiver to schedule candidates for sending a handover completion message using all of the plurality of uplink shared channel transmission parameters associated with the configured at least first bandwidth portion or second bandwidth portion during operation.

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

[0210] According to the 19th aspect that can be combined with the 17th or 18th aspect, when the handover request response confirmation message further includes a plurality of uplink shared channel transmission parameters respectively associated with different ones of the configured at least first bandwidth portion and second bandwidth portion, the transceiver further receives a handover completion message transmission using one of the plurality of uplink shared channel transmission parameters associated with the portion selected and activated by the mobile terminal among the configured at least first bandwidth portion and second bandwidth portion from the mobile terminal during operation, and the processor deactivates the remaining portions of the configured at least first bandwidth portion and second bandwidth portion that are not selected and activated by the mobile terminal during operation.

[0211] According to the 20th aspect that can be combined with the 11th aspect, the handover request response confirmation message further includes a plurality of different random access transmission parameters respectively associated with different ones of at least the configured first bandwidth portion and the 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 at least the configured first bandwidth portion or the second bandwidth portion.

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

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

[0214] According to the 23rd aspect that can be combined with the 11th aspect, the handover request message further includes information regarding 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 the 24th aspect that can be combined with the 23rd aspect, the handover request message further includes information regarding at least one activated one of the configured third bandwidth part and the fourth bandwidth part of the source base station.

[0216] According to the 25th aspect that can be combined with the 24th aspect, during operation, the processor configures the first bandwidth part and the second bandwidth part based on the third bandwidth part and the fourth bandwidth part respectively in the transceiver for the mobile terminal.

[0217] According to the 26th aspect that can be combined with the 25th aspect, during operation, the processor controls the transceiver to send a handover request response confirmation message including a bandwidth part index, and the bandwidth part index indicates the same bandwidth part as the previously activated one of at least the configured third bandwidth part and the fourth bandwidth part of the source base station.

[0218] According to the 27th aspect, 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 is proposed. The target base station is composed of at least a first bandwidth part and a different second bandwidth part within its cell bandwidth for the mobile terminal. This method includes receiving, from the source base station, a handover command message including information regarding at least the configured first bandwidth part and the second bandwidth part; at the time of receiving the handover command message, activating at least one preselected one of at least the configured first bandwidth part or the second bandwidth part, and communicating with the target base station as part of the handover procedure using at least one activated one of at least the configured first bandwidth part or the second bandwidth part.

[0219] According to a 28th aspect, 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 is proposed. The target base station is composed of at least a first bandwidth portion and a different second bandwidth portion within its cell bandwidth. This method includes receiving, from the source base station, a handover command message including information regarding the configured at least first bandwidth portion and second bandwidth portion; and at the time of receiving the handover command message, selecting and activating at least one of the configured at least first bandwidth portion or second bandwidth portion, and communicating with the target base station as part of the handover procedure using at least one of the selected and activated at least first bandwidth portion or second bandwidth portion.

[0220] According to a 29th aspect, a method for performing a handover procedure of a mobile terminal from a source base station by a target base station in a mobile communication system is proposed. The target base station can communicate with the mobile terminal in at least a first bandwidth portion and a different second bandwidth portion within its cell bandwidth. This method includes receiving, from the source base station, a handover request message including information regarding the capabilities of the mobile terminal to communicate in at least the first bandwidth portion and the second bandwidth portion; and at the time of 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 first bandwidth portion and second bandwidth portion.

Claims

1. A communications system including a target base station and a user equipment, The target base station, a transceiver for receiving a handover request message from a source base station, the handover request message including information regarding a capability of the user equipment to communicate on at least a configured first bandwidth portion and a configured second bandwidth portion; a processor for controlling the transceiver to configure at least the first and second bandwidth portions for the user equipment upon receipt of the handover request message and to control the transceiver to send a handover request response confirmation message to the source base station, the handover request response confirmation message including information about the configured at least first and second bandwidth portions; Including, The user equipment, a transceiver of a user equipment for receiving a handover command message from the source base station, the handover command message including information regarding the configured first bandwidth portion and the configured second bandwidth portion; a processor of a user equipment for controlling a transceiver of the user equipment to activate at least a pre-selected one of the configured at least first or second bandwidth portions upon receipt of the handover command message and to communicate with the target base station on the activated at least one of the configured at least first or second bandwidth portions as part of a handover procedure; Including, Communication systems.

2. the processor, after controlling the transceiver to transmit the handover request response confirmation message, activates, at the transceiver, the same pre-selected one of the configured at least first or second bandwidth portions that the user equipment is expected to activate; the information about the configured at least first and second bandwidth portions is a specific sequence, and the processor activates a first or a last bandwidth portion of the specific sequence, or a specific other bandwidth portion if more bandwidth portions than the at least first and second bandwidth portions are configured, as the preselected one of the bandwidth portions; or the handover request response confirmation message further includes a bandwidth portion index, and the processor activates the preselected one of the configured at least the first bandwidth portion or the second bandwidth portion corresponding to the bandwidth portion index. The communication system according to claim 1 .

3. the handover request message further includes information about a status of an activated bandwidth portion or predicted traffic information; and wherein the processor controls the transceiver, upon receipt of the handover request message, to select and activate at least one of the at least the first bandwidth portion and the second bandwidth portion that the user equipment is expected to activate as the preselected bandwidth portion as part of a handover procedure. The communication system according to claim 1 .

4. and activating, at the transceiver, all of the configured at least the first bandwidth portion or the second bandwidth portion after controlling the transceiver to transmit the handover request response confirmation message. The communication system according to claim 1 .

5. The handover request response confirmation message is a plurality of different uplink shared channel transmission parameters respectively associated with different ones of the configured at least first and second bandwidth portions; Further comprising: the processor controls the transceiver to schedule candidates for transmission of a handover complete message using all of the plurality of uplink shared channel transmission parameters associated with the configured at least first bandwidth portion or the second bandwidth portion, and optionally: The plurality of uplink shared channel transmission parameters include: - the time and frequency of radio channel resources to be used by the user equipment when transmitting the handover complete message to the target base station; Including, If the handover request response confirmation message further includes a plurality of uplink shared channel transmission parameters respectively associated with different ones of the configured at least first and second bandwidth portions, the transceiver further receives a handover completion message transmission from the user equipment using one of the plurality of uplink shared channel transmission parameters associated with the one of the configured at least first or second bandwidth portions selected and activated by the user equipment; the processor deactivates the remainder of the configured at least first and second bandwidth portions that have not been selected and activated by the user equipment. The communication system according to claim 1 .

6. The handover request response confirmation message is a plurality of different random access transmission parameters respectively associated with different ones of the configured at least first and second bandwidth portions; Further comprising: the processor controls the transceiver to schedule transmission of a random access message using all of the plurality of random access transmission parameters associated with the configured at least the first bandwidth portion or the second bandwidth portion; The random access transmission parameters include: a random access preamble sequence transmitted together with said random access message; - the time and frequency of radio channel resources used by the user equipment when transmitting the random access message to the target base station; and if the handover request response confirmation message further includes a plurality of different random access transmission parameters respectively associated with different ones of the configured at least first and second bandwidth portions, the transceiver further receives from the user equipment a random access message transmission using one of the plurality of random access transmission parameters associated with the one of the configured at least first or second bandwidth portions selected and activated by the user equipment; the processor deactivates the remainder of the configured at least first and second bandwidth portions that have not been selected and activated by the user equipment. The communication system according to claim 1 .

7. The handover request message: information regarding at least a third bandwidth portion and a different fourth bandwidth portion configured for the user equipment at the source base station; Further comprising: The handover request message: - information regarding an activated one of the configured at least a third and a fourth bandwidth portion of the source base station; Further comprising: the processor configures, for the user equipment, the first and second bandwidth portions based on the third and fourth bandwidth portions, respectively, at the transceiver; the processor controls the transceiver to transmit the handover request response confirmation message including a bandwidth portion index; the bandwidth portion index indicates a bandwidth portion of the source base station that is the same as a previously activated bandwidth portion of the configured at least a third bandwidth portion and a fourth bandwidth portion; The communication system according to claim 1 .

8. A method for a communication system including a target base station and a user equipment to perform a handover procedure, comprising: receiving a handover request message from a source base station, the handover request message including information regarding a capability of the user equipment to communicate on at least the first bandwidth portion and the second bandwidth portion; upon receiving the handover request message, configuring at least the first and second bandwidth portions for the user equipment and sending a handover request response confirmation message to the source base station, the handover request response confirmation message including information about the configured at least first and second bandwidth portions; receiving a handover command message from the source base station, the handover command message including information regarding the configured first bandwidth portion and the configured second bandwidth portion; upon receipt of the handover command message, activating at least a pre-selected one of the configured at least first or second bandwidth portions and communicating with the target base station as part of the handover procedure on the activated at least one of the configured at least first or second bandwidth portions; A method comprising:

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