System, method, user equipment and base station for performing handover in wireless network

Abstract

The present disclosure relates to a method for performing a handover of a user equipment from a first base station to a second base station in a wireless network, the user equipment performs random access (413) to the second base station using a random access channel opportunity in a subset selected (406) from a set of random access channel opportunities according to a QoS profile assigned (400) to the user equipment. The disclosure also relates to a user equipment, a base station and a system for implementing the corresponding method.

Description

Technical Field

[0001] The following relates generally to wireless communications, and more particularly to a method of improving handover in non-terrestrial networks and combined terrestrial and non-terrestrial networks. Background Art

[0002] Wireless communication systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on.

[0003] A wireless multiple access communication system may include multiple base stations, each of which supports communication for multiple mobile devices simultaneously. A base station may communicate with user equipment (UE) on downlink and uplink. Each base station has a coverage area, sometimes referred to as a cell coverage area.

[0004] Non-terrestrial networks (NTN) have become a general term for any network involving non-terrestrial flying objects, such as satellite communications networks or high altitude platform systems (HAPS), which include aircraft, balloons and airships.

[0005] Satellite communication networks rely on spaceborne platforms consisting of low earth orbit (LEO) satellites, medium earth orbit (MEO) satellites and geosynchronous earth orbit (GEO) satellites.

[0006] Today, there is growing interest in broadband services supported by LEO NTN with large satellite constellations due to the advantages of lower propagation delay and higher link quality compared to MEO or GEO satellites. The satellite industry is currently working on integrating satellite networks into the 5G ecosystem in the 3GPP process.

[0007] The integration of non-terrestrial networks (NTN) within the 5G framework is in the process of standardization and can bring many advantages, such as wide service coverage capabilities, reduced vulnerability of space / air vehicles to physical attacks and natural disasters, or enhanced service reliability.

[0008] However, NTN integration also brings challenges related to the application and adaptation of technologies originally designed for terrestrial networks to space networks.

[0009] In particular, handovers in LEO satellite networks differ significantly from traditional terrestrial cellular networks in that handovers are triggered by the mobility of the satellite. In terrestrial networks, there are relatively small fixed cells and mobile UEs, while in non-terrestrial networks, cells move as the satellite moves. In contrast, UE movement is slow and sometimes negligible. Once a LEO satellite moves to a new cell, most (if not all) UEs will be handed over to another cell.

[0010] Given the larger cell sizes of non-terrestrial networks, multiple devices can be served within a single cell. Depending on the constellation assumptions (e.g., propagation delay and satellite speed) and UE density, there may be a large number of UEs that need to be handed over in a given time, which may result in large signaling overhead and high power consumption, and pose service continuity challenges. In addition, if many UEs need to be handed over from one base station to another, random access conflicts between UEs will increase.

[0011] Therefore, a handover method is needed to reduce random access conflicts and UE energy consumption. Summary of the invention

[0012] According to a first aspect of the present disclosure, there is provided a method for wireless communication by a user equipment, for supporting handover of the user equipment from a first base station to a second base station in a wireless network, wherein the user equipment performs random access to the second base station using a random access channel opportunity from a subset selected from a set of random access channel (RACH) opportunities according to a quality of service (QoS) profile assigned to the user equipment.

[0013] Thus, the RACH time slots and / or RACH opportunities available for a particular user equipment depend on the quality of service (QoS) profile of the user equipment. Thus, since UEs with different QoS profiles will use different RACH time slots, the risk of contention when performing a random access procedure during handover of a group of UEs from a first base station to a second base station is reduced.

[0014] According to an embodiment, the random access channel opportunity for performing random access is selected by the user equipment according to a mapping between random access channel opportunities and QoS profiles.

[0015] The user equipment is provided with a mapping table in which RACH time slots and / or RACH opportunities are associated with QoS profiles. Thus, the UE can use this mapping to select a RACH opportunity that can be used to establish an uplink channel to the second base station based on its QoS profile.

[0016] According to an embodiment, said mapping between random access channel opportunities and quality of service profiles is pre-configured in said user equipment.

[0017] Therefore, it is envisaged that the association between QoS values ​​and RACH slots / opportunities is statically configured in a memory of the user equipment, rather than being transmitted in a signalling message. This provision makes it possible to save signalling resources by avoiding the transmission of mapping tables.

[0018] According to an embodiment, the subset of random access channel opportunities selected from a set of random access channel opportunities according to a quality of service parameter associated with the UE is received in a handover command message sent by the first base station.

[0019] The base station selects a RACH opportunity and / or RACH time slot for the user equipment to perform RACH on the second base station based on the QoS profile of the specific user equipment. Therefore, the UE only receives the RACH opportunity and / or RACH time slot corresponding to the QoS profile of the UE. This provision allows the mapping between QoS and RACH opportunity to be dynamically configured while saving bandwidth.

[0020] Another aspect of the present disclosure relates to a wireless communication device for supporting handover of a user equipment from a first base station to a second base station in a wireless network, the wireless communication device comprising a processor coupled to a memory storing computer program instructions, the instructions being arranged to implement a wireless communication method for supporting handover of the user equipment, wherein the user equipment performs random access to the second base station using a random access channel opportunity selected from a set of random access channel (RACH) opportunities according to a quality of service (QoS) profile assigned to the user equipment.

[0021] The present disclosure also relates to a user equipment, which includes a wireless communication device, which is used to support handover of the user equipment from a first base station to a second base station in a wireless network as described above.

[0022] According to another aspect, the present disclosure relates to a wireless communication method by a second base station, for performing a handover of a user equipment from a first base station to a second base station in a wireless network, the method comprising the following actions:

[0023] - obtaining a set of random access channel opportunities that can be used to perform random access to the second base station,

[0024] - obtaining a quality of service profile assigned to said user equipment,

[0025] - selecting a specific subset of random access channel opportunities from the obtained set of random access channel opportunities, the subset being selected based at least on the quality of service (QoS) assigned to the user equipment,

[0026] - transmitting a message including the selected random access channel opportunity subset to the first base station,

[0027] - receiving a random access request from a user equipment associated with a specific QoS value, the random access request being received at a RACH opportunity associated with the user equipment QoS value in a determined mapping table.

[0028] Instead of simply sending a set of available RACH slots / opportunities in response to a handover request, the target base station sends a subset of RACH opportunities selected according to the QoS profile associated with the UE to be handed over. This provision allows the target base station to spread out the RACH process in the time and frequency domains, thereby limiting the risk of RACH contention.

[0029] In an embodiment, the quality of service assigned to the user equipment is obtained in the handover request message.

[0030] When requesting a handover to a target base station, the source base station includes a quality of service profile assigned to the UE to be handed over. Thus, the target base station knows the QoS associated with the UE and can select a specific RACH opportunity among a specific number of RACH opportunities according to the QoS profile.

[0031] A wireless communication device and a base station apparatus comprising such a wireless communication device are also envisaged, wherein the wireless communication device is used to perform a handover of a user equipment from a first base station to a second base station in a wireless network, the device comprising a processor coupled to a memory storing computer program instructions, the instructions being arranged to implement the wireless communication method described above.

[0032] Another aspect of the present disclosure relates to a wireless communication system for performing handover of a user equipment from a first base station to a second base station in a wireless network, wherein the user equipment performs random access to the second base station using a random access channel opportunity from a subset selected from a set of random access channel opportunities according to a quality of service (QoS) profile assigned to the user equipment, and wherein the second base station receives a random access request at the selected random access channel opportunity.

[0033] According to an embodiment, the selected random access channel opportunity is selected by the second base station, and wherein the quality of service profile assigned to the user equipment is received from the first base station in a handover request message.

[0034] According to an embodiment, the selected random access channel opportunity is selected by the first base station from a group of random access channel opportunities, which are received from the second base station in a switching confirmation message, and wherein the selected random access channel opportunity is sent to the user equipment in an RRC reconfiguration message.

[0035] In a specific embodiment, the steps of the wireless communication method for supporting a user equipment to perform handover and the wireless communication method for performing handover by a base station are determined by instructions of a computer program.

[0036] Therefore, the present disclosure further contemplates computer programs on an information medium, which are suitable for implementation in a user equipment device and a base station, respectively, or more generally in a computer, which programs respectively include instructions adapted to implement the steps of the wireless communication method supported by the user equipment and performed by the base station, respectively, which have just been described.

[0037] These programs may use any programming language and may be in the form of source code, object code, or an intermediate code between source code and object code, such as partially compiled form or any other desired form.

[0038] On the other hand, an information medium readable by a computer is envisaged, which information medium comprises instructions of a computer program such as mentioned above.

[0039] The information medium may be any entity or device capable of storing a program. For example, the medium may include a storage device such as a ROM (e.g., a CD ROM or a microelectronic circuit ROM), an EEPROM, a FLASH memory, or any magnetic recording device (e.g., a hard disk drive).

[0040] Furthermore, the information medium may be a transmissible medium such as an electric signal or an optical signal that can be transmitted via an electric or optical cable by radio or by other means.In particular, the program according to the embodiment of the present invention may be downloaded from a network.

[0041] Alternatively, the information medium may be an integrated circuit in which the program is embodied, the circuit being arranged to execute or to be used for executing the method in question.

[0042] The advantages of the user equipment, the base station, the system and the corresponding computer program and information medium are the same as those presented with respect to the corresponding method according to any of the above-described embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Other advantages and characteristics of the invention will become more apparent on reading the following description, given by way of simple illustrative and non-limiting examples, and the accompanying drawings, in which:

[0044] - Figure 1 An environment adapted for implementing the methods disclosed herein is presented,

[0045] - Figure 2 is a combined flow chart and block diagram showing a prior art switching process,

[0046] - Figure 3 shows a specific random access resource configuration,

[0047] - Figure 4is a flow chart depicting the main steps of a wireless communication method for supporting and performing handover according to an embodiment,

[0048] - Figure 5 is a flow chart depicting the main steps of a wireless communication method for supporting and performing handover according to an embodiment,

[0049] - Figure 6 is a flow chart depicting the main steps of a wireless communication method for supporting and performing handover according to an embodiment,

[0050] - Figure 7 is a block diagram of a device arranged to implement a wireless communication method for supporting handover of a user equipment, and

[0051] - Figure 8 is a block diagram of an apparatus arranged to implement a wireless communication method for performing a handover by a target base station. DETAILED DESCRIPTION

[0052] The specific embodiments described below with reference to the accompanying drawings are intended as descriptions of various configurations and are not intended to represent the only configurations in which the concepts described herein may be practiced. The specific embodiments include specific details to provide a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In particular, although terminology from 3GPP 5G NR may be used in this disclosure to illustrate the embodiments of the present invention, this should not be viewed as limiting the scope of the invention. Moreover, it should be understood that although the present disclosure is illustrated with respect to non-terrestrial base stations, this should not be viewed as limiting the scope of the invention, as the teachings of the present disclosure may be applied to terrestrial base stations without modifying the present invention.

[0053] Figure 1 An exemplary 5G New Radio (NR) wireless communication system 100 is shown according to an embodiment of the present disclosure, the system being configured to support handover procedures in a non-terrestrial network (NTN).

[0054] The wireless system 100 comprises at least a first NTN base station 101 and a second NTN base station 102. Figure 1 In the examples, NTN base stations 101 and 102 are LEO satellites orbiting the earth with known / or predictable orbital parameters. However, it should be noted that base stations 101 and 102 can be any high altitude platform system (HAPS) (including aircraft, balloons or airships) or even ground base stations. In some examples, NTN base stations 101 and 102 are 5G NR base stations (gNodeB or gNB).

[0055] Figure 1Also shown are a first user equipment (UE) device 105 and a second user equipment device 106, which are initially served by the base station 101 in a source cell. The UE 105 and the UE 106 may be of any type. For example, the UE 105 may be a mobile phone, a connected vehicle, or an IoT (Internet of Things) device. The UE 106 may also be a mobile phone, a connected vehicle, or an IoT device.

[0056] LEO satellites 101 and 102 travel along predictable orbits at a constant speed (e.g., 7.56 km / s) relative to the Earth's surface, causing their respective radio beams 103 and 104 to move over time. Therefore, UE 105 and other UEs served in the same cell (e.g., UE 106) frequently switch to new target cells. Considering the large cell size of NTN, a large number of UEs may need to perform handovers at the same time.

[0057] Figure 2 is a call flow illustrating a conventional inter-cell prior art handover procedure. The UE periodically transmits measurement reports on signal quality in message 200. When the signal strength from the target gNB becomes greater than the signal strength from the source gNB, the source gNB makes a decision 201 to handover the UE and sends a handover request 202 to the target gNB over the inter-gNB Xn interface. The target gNB acknowledges the handover request in a message 204 transmitted to the source gNB after a grant check 203. The source gNB then sends a handover command 205 (i.e., an RRC reconfiguration message) to the UE to instruct the UE to handover to the target gNB.

[0058] Upon receiving the handover command 205, the UE synchronizes with the target gNB and performs a random access procedure 206 to establish a communication channel, and then sends a handover complete message 207 (i.e., an RRC reconfiguration complete message).

[0059] The UE initiates this random access procedure by randomly selecting a signature from a given set of signatures and by transmitting a so-called preamble containing the selected signature to the target gNB. This preamble is also called a "random access preamble".

[0060] The preamble transmission can occur in a configurable subset of the periodic RACH slots within the cell. The amount of resources for the Physical Random Access Channel (PRACH) can be configured according to the cell characteristics: if the cell is large (such as in NTN systems), many upload requests may be issued due to the large number of users, while for smaller cells the amount of resources may be limited. Figure 3As shown, the resources of PRACH can be set in both time (t) and frequency (f). The time part indicates how often the upload occurs, while the frequency part indicates the width of the resource. The RACH period can be set between 10 and 160ms, and this value indicates how often this pattern with resources is repeated (RACH slots). Within each RACH slot, there can be multiple RACH opportunities that specify different available times per slot. Figure 3 An exemplary RACH configuration is shown, which includes a first set of RACH opportunities 300 in slot #1, a second set of RACH opportunities 301 in slot #3 within a RACH cycle 302 (including N slots). Thus, the sequence of RACH slots #1 to #N is repeated in each consecutive RACH cycle. Figure 3 In the example of FIG. 4 , each RACH time slot includes four RACH opportunities R1 - R4 .

[0061] Since different UEs can initiate a random access procedure on a common RACH channel at the same time, and since there are only a limited number of different signatures to choose from, different UEs may randomly select the same signature. If this happens, the unique identification of the respective UEs and the messages from or to them are hampered during the synchronization process by so-called collisions. As a result, the random access procedure may fail, resulting in the termination of the random access procedure and the UE having to repeat the random access procedure at a later time.

[0062] It is easy to understand that the risk of such a conflict occurring is particularly high when a large number of UEs are transferred from the source gNB to the target gNB at the same time.

[0063] It is therefore an object of the present disclosure to propose a method for limiting the risk of collisions.

[0064] To achieve this goal, an inventive method is proposed, wherein at least one specific RACH slot or RACH opportunity is assigned to a user equipment according to its quality of service profile. This provision allows UEs with different profiles to use different RACH slots / opportunities, thereby avoiding contention during random access. These specific RACH slots / opportunities can be selected from a whole set of RACH opportunities available for synchronization with the target UE.

[0065] According to an embodiment, the selection may be performed by the target base station 101 .

[0066] According to an embodiment, the selection may be performed by the serving base station 102 .

[0067] In some embodiments, the user equipment 105 may perform selection of US-specific RACH time slots / opportunities.

[0068] For the sake of clarity, like reference numerals refer to like entities in the following description.

[0069] Now refer to Figure 4 A first embodiment of the present disclosure is described.

[0070] Figure 4 is a combined flow chart and block diagram illustrating the main steps of the disclosed method for handing over a user equipment 105 from a first base station 101 to a second base station 102 within a wireless network according to an embodiment.

[0071] During a first step 400, the first base station 101 assigns a specific QoS profile to the user equipment 105. In some embodiments, the QoS profile may be received in an RRC message 401, which is sent by the base station 101 serving the cell in which the UE 105 is located. The received QoS profile may include one or more 5QI values, CQI values, priority values, or specific flags. Thus, both the UE 105 and the base station 101 are aware of the QoS profile associated with the UE 105.

[0072] UE 105 may send periodic or aperiodic measurement reports 402 including quality values ​​of signals received by the UE from base stations 101 and 102. Based on these measurement reports, first base station 101 may make a handover decision in step 403. For example, when the measurement report sent by UE 105 indicates that second base station 102 provides better radio signal quality than serving base station 101, base station 101 may make a handover decision.

[0073] This decision triggers sending a handover request 404 to the second base station 102, the handover request comprising at least the QoS profile assigned to the UE 105 in step 400. The handover request 404 may be sent to the base station 102 over an Xn interface.

[0074] The second base station 102 receives the handover request 404 during step 405 and performs admission control and determines a set of RACH time slots and / or RACH opportunities available for the user equipment to achieve uplink channel synchronization to the base station 102 .

[0075] During step 406, the base station 102 selects a user equipment specific RACH time slot or RACH opportunity subset from the set of RACH time slots or RACH opportunities determined in step 405, the subset being determined at least according to the characteristics of the UE 105 received in the handover request 404. More specifically, the base station 102 may determine the UE specific RACH time slot / opportunity subset according to the QoS profile assigned to the UE 105.

[0076] In some embodiments, the base station 102 selects the RACH time slot / opportunity according to the QoS profile of the UE 105 using a pre-configured mapping table, which contains associations between some RACH time slots or opportunities and specific QoS profiles.

[0077] According to an embodiment, the base station 102 may dynamically assign RACH opportunities to specific UEs according to circumstances. For example, the target base station 102 may assign RACH time slots to the UE 105 taking into account its current load (i.e., the current usage of available radio resources). For example, the target base station 102 may choose to assign a "later" RACH time slot / opportunity to a new UE until another UE has left or the resource configuration is adapted to "support" / adapt to the new UE, i.e., the previously occupied radio resources can be used to serve the new UE.

[0078] In some examples, the number of RACH opportunities selected for high QoS UEs may be greater than the number of RACH opportunities selected for low QoS UEs, thereby reducing collisions occurring for high QoS UEs.

[0079] The base station 102 may reserve specific RACH slots and / or RACH opportunities for a specific UE QoS profile (e.g., 5QI value). For example, the base station 102 may assign a first set of RACH opportunities to UEs associated with a first QoS profile and a second set of RACH opportunities to UEs associated with a second QoS profile.

[0080] At step 407 , the base station 102 sends a handover confirmation message 408 to the base station 101 , the message 408 including the RACH time slot / opportunity subset selected for the UE 105 at step 406 .

[0081] At step 409 , the first base station 101 receives the message 408 , which includes the RACH time slot / opportunity subset selected by the base station 102 for the UE 105 .

[0082] At step 410, base station 101 may forward the specific RACH slot / opportunity subset received in message 408 to UE 105. Base station 101 may forward the RACH opportunity subset using a handover command message 411 (eg, in an RRC reconfiguration message).

[0083] During step 412, the user equipment 105 may receive a message 411 from the first base station 101. The received message includes at least a UE 105 specific subset of RACH slots / opportunities selected from the RACH slots / opportunities available for the UE to perform a RACH to the second base station 102. During step 406, the subset is selected from a set of available RACH opportunities according to the QoS profile assigned to the UE 105.

[0084] At step 413 , the UE 105 may initiate a random access procedure using a RACH opportunity in the received UE-specific RACH time slot / opportunity subset to achieve uplink synchronization to the second base station 102 .

[0085] At step 414 , the base station 102 may receive a random access request from the UE 105 at a RACH opportunity that is associated with the UE 105 QoS value during step 406 .

[0086] Now refer to Figure 5 A second embodiment of the present disclosure is described.

[0087] Figure 5 is a combined flow chart and block diagram illustrating the main steps of the disclosed method for handing over a user equipment 105 from a first base station 101 to a second base station 102 within a wireless network according to an embodiment.

[0088] During a first step 500, the first base station 101 assigns a specific QoS profile to the user equipment 105. In some embodiments, the QoS profile may be received in an RRC message 501, which is sent by the base station 101 serving the cell in which the UE 105 is located. The received QoS profile may include one or more 5QI values, CQI values, priority values, or specific flags. Thus, both the UE 105 and the base station 101 are aware of the QoS profile associated with the UE 105.

[0089] The base station 102 may determine a mapping between RACH opportunities or RACH time slots and a specific QoS profile during preliminary step 502. More specifically, the base station 102 may determine a set of RACH time slots and / or RACH opportunities available for synchronization by the UE and then assign each of these RACH time slots / opportunities to a specific QoS profile. This mapping may be a table in which RACH opportunities are associated with QoS profiles. This mapping may be updated periodically or when a specific event occurs and is transmitted to the base station 102 when updated in a message 503 sent over the Xn interface.

[0090] As an example, the target base station 102 may assign RACH slots / opportunities to a particular QoS profile taking into account its current load (i.e., current usage of available radio resources). For example, the target base station 102 may choose to assign "later" RACH slots / opportunities to a low QoS profile. In some other examples, the base station 102 may assign a first set of RACH opportunities to a first QoS profile and a second set of RACH opportunities to a second QoS profile, the first set of RACH opportunities including more RACH slots or opportunities than the second set.

[0091] In step 504, base station 101 receives the RACH opportunity / Qos mapping table determined by base station 102, and stores it in a memory.

[0092] UE 105 may send periodic or aperiodic measurement reports 505 including quality values ​​of signals received by the UE from base stations 101 and 102. Based on these measurement reports, first base station 101 may make a handover decision in step 506. For example, when the measurement report sent by UE 105 indicates that second base station 102 provides better radio signal quality than serving base station 101, base station 101 may make a handover decision.

[0093] This decision triggers sending a handover request 507 to the second base station 102 .

[0094] The second base station 102 receives the handover request 404 during step 508 and performs admission control. In some embodiments, the base station 102 may update the mapping determined in step 502 if necessary (e.g., based on its current load and / or radio resource usage) and send the updated mapping to the base station 101 in a dedicated message or, for example, in a handover confirmation message 509.

[0095] Once the permission of UE 105 is granted by base station 102, a handover confirmation message 509 may be sent to base station 101, which includes a set of available RACH opportunities that may be used to perform random access.

[0096] Receipt of message 509 may trigger step 510, during which base station 101 may select a subset of RACH slots / opportunities corresponding to the QoS assigned to UE 105 within the set of RACH opportunities received in message 509. More specifically, base station 101 uses the mapping between RACH opportunities and QoS profiles received in step 504 to determine the RACH opportunities corresponding to the QoS profile assigned to UE 105 from the RACH opportunities received in message 509.

[0097] In some embodiments, the base station 101 may select a RACH time slot / opportunity according to the QoS profile of the UE 105 using a pre-configured mapping table containing associations between some RACH time slots or opportunities and specific QoS profiles.

[0098] At step 511, base station 101 may send the selected subset of RACH time slots / opportunities determined at step 510 to UE 105 in a handover command message 512 (eg, in an RRC reconfiguration message).

[0099] During step 513, the user equipment 105 may receive a message 512 from the first base station 101. The received message includes at least a UE 105 specific subset of RACH slots / opportunities selected from the RACH slots / opportunities available for the UE to perform a RACH to the second base station 102. During step 510, the subset is selected from a set of available RACH opportunities according to the QoS profile assigned to the UE 105.

[0100] At step 514 , the UE 105 may initiate a random access procedure using a RACH opportunity in the received UE-specific RACH time slot / opportunity subset to achieve uplink synchronization to the second base station 102 .

[0101] At step 515 , base station 102 may receive a random access request from UE 105 at a RACH opportunity that is associated with the UE 105 QoS value during step 406 .

[0102] Now refer to Figure 6 A third embodiment of the present disclosure is described.

[0103] Figure 6 is a combined flow chart and block diagram illustrating the main steps of the disclosed method for handing over a user equipment 105 from a first base station 101 to a second base station 102 within a wireless network according to an embodiment.

[0104] During the first step 400, the first base station 101 assigns a specific QoS profile to the user equipment 105. In some embodiments, the QoS profile may be received in an RRC message 601, which is sent by the base station 101 serving the cell where the UE 105 is located. The received QoS profile may include one or more 5QI values, CQI values, priority values, or specific flags. Therefore, both the UE 105 and the base station 101 are aware of the QoS profile assigned to the UE 105.

[0105] UE 105 may send periodic or aperiodic measurement reports 602 including quality values ​​of signals received by the UE from base stations 101 and 102. Based on these measurement reports, first base station 101 may make a handover decision in step 603. For example, when the measurement report sent by UE 105 indicates that second base station 102 provides better radio signal quality than serving base station 101, base station 101 may make a handover decision.

[0106] This decision triggers sending a handover request 604 to the second base station 102. The handover request 604 may be sent to the base station 102 over an Xn interface.

[0107] The second base station 102 receives the handover request 604 during step 605 and performs admission control and determines a set of RACH time slots and / or RACH opportunities available for the user equipment to achieve uplink channel synchronization to the base station 102 .

[0108] During step 606 , base station 102 sends a handover confirmation to base station 101 including the RACH time slot and / or RACH occasion determined in step 405 .

[0109] At step 609, base station 101 may forward the set of RACH slots / opportunities received in message 607 to UE 105. Base station 101 may forward the subset of RACH opportunities using handover command message 610 (eg, in an RRC reconfiguration message).

[0110] The UE 105 receives the set of RACH time slots / opportunities during step 611. The UE 105 thus receives a message from the first base station 101, the message comprising a set of RACH opportunities available for the UE 105 to perform a random access to the base station 102. It is envisaged that the message may be a handover command message, such as an RRC reconfiguration request message sent by the first base station 101 in which at least one RACH opportunity is provided.

[0111] During step 612, the base station 102 selects a user equipment specific subset of RACH time slots or RACH opportunities from the set of RACH time slots or RACH opportunities received in step 611, the subset being determined at least according to the characteristics of the UE 105. In some examples, the RACH time slot / opportunity subset is selected according to a QoS profile assigned to the UE 105.

[0112] In some embodiments, the UE 105 may use a pre-configured mapping table to select a RACH slot / opportunity according to the QoS profile of the UE 105, the mapping table containing associations between some RACH slots or opportunities and specific QoS profiles. The mapping table may be configured by the network or pre-configured in the firmware of the UE 105. According to an embodiment, the mapping table may assign multiple RACH slots / opportunities within a RACH cycle according to the QoS profile. In some examples, the number of RACH opportunities associated with a high QoS UE may be greater than the number of RACH opportunities associated with a low QoS UE.

[0113] The UE 105 may select a specific RACH time slot and / or opportunity within the received RACH time slot / opportunity by looking up its assigned QoS profile in a mapping table and selecting the RACH time slot / opportunity corresponding to the QoS profile. Thus, during step 600, a subset is selected from a set of available RACH opportunities according to the QoS profile assigned to the UE 105. In this way, the UE 105 may obtain a UE-specific RACH time slot / opportunity subset from the available RACH time slots / opportunities to perform a RACH to the second base station 102.

[0114] At step 613 , the UE 105 may initiate a random access procedure using a RACH opportunity in the received UE-specific RACH time slot / opportunity subset to achieve uplink synchronization to the second base station 102 .

[0115] At step 614 , the base station 102 may receive a random access request from the UE 105 at a RACH opportunity that is associated with the UE 105 QoS value during step 600 .

[0116] Therefore, it can be understood that UEs with different QoS profiles will receive different RACH opportunities in the handover command message, thereby limiting the occurrence of contention when a large number of UEs perform handovers.

[0117] Figure 7 is a block diagram showing a schematic architecture of a device 700 suitable for implementing a wireless communication method for supporting handover of a user equipment device from a first base station to a second base station according to an embodiment.

[0118] The device 700 comprises a processor 701 and a memory 702, such as a random access memory (RAM). The processor 701 may be controlled by a computer program 703 stored in the memory 702, the computer program comprising instructions configured to implement a wireless communication method for supporting handover according to a particular embodiment.

[0119] More precisely, the computer program 803 comprises instructions for performing a random access procedure to the second base station using a random access channel opportunity (RACH opportunity or RO) selected from a set of random access channel opportunities according to a QoS profile assigned to the user equipment.

[0120] At initialization, the instructions of the computer program 703 may be loaded into the memory 702 before being executed by the processor 701. The processor 701 implements the steps of the method according to the instructions of the computer program 703.

[0121] The device 700 includes a wireless communication unit 704, such as a 3G, 4G, 5G, 5GNR, WiFi or WiMax transceiver, for exchanging messages with other devices. In particular, the communication unit 704 is configured to synchronize and exchange data with a base station (e.g., NodeB (NB), eNodeB (eNB) or gNodeB (gNB)) of a wireless access network.

[0122] The communication unit 704 may be further configured by computer program instructions to receive at least one QoS profile transmitted by the first base station. For example, the communication unit may be arranged to receive an RRC message transmitted by the first base station and extract at least a QCI or 5QI value defining a QoS profile of the device 700 from the message.

[0123] In an embodiment, the communication unit 704 may be configured to receive a subset of RACH opportunities selected by a base station according to a QoS profile assigned to the device 700 .

[0124] According to an embodiment, the device may include a mapping unit 705, the mapping unit including a preconfigured mapping table including associations between some RACH time slots / opportunities and specific QoS profiles. The preconfigured mapping may be configured by a network node when the device is initialized, or embedded in firmware. The device 700 may further include a selection unit 706. The selection unit 706 may be implemented by computer program instructions, which are arranged to perform the selection of at least one RACH opportunity and / or RACH time slot by using the mapping unit 705 to find a specific RACH opportunity according to the QoS value received by the communication unit 704.

[0125] In some embodiments, the device 700 may further include a RACH module 707. The RACH module 707 may be implemented by computer program instructions arranged to perform a random access procedure to establish an uplink communication channel to the second base station using the RACH opportunity selected by the selection unit 706.

[0126] In some embodiments, apparatus 700 is integrated into a user equipment device, such as a mobile phone, a telecommunication unit of a connected vehicle, or any IoT (Internet of Things) device.

[0127] Figure 8 is a block diagram illustrating a schematic architecture of an apparatus 800 suitable for implementing a wireless communication method for performing handover of a user equipment device from a first base station to a second base station according to an embodiment.

[0128] The device 800 comprises a processor 801 and a memory 802, such as a random access memory (RAM). The processor 801 may be controlled by a computer program 803 stored in the memory 802, the computer program comprising instructions configured to implement a wireless communication method for performing a handover according to a particular embodiment.

[0129] More specifically, the computer program 803 includes instructions for implementing the following actions:

[0130] - obtaining a set of random access channel opportunities that can be used to perform random access to the second base station,

[0131] - obtaining a quality of service profile assigned to said user equipment,

[0132] - selecting a specific subset of random access channel opportunities from the obtained set of random access channel opportunities, the subset being selected based at least on the quality of service (QoS) assigned to the user equipment,

[0133] - transmitting a message including the selected random access channel opportunity subset to the first base station,

[0134] - receiving a random access request from a user equipment associated with a specific QoS value, the random access request being received at a RACH opportunity associated with the user equipment QoS value in a determined mapping table.

[0135] At initialization, the instructions of the computer program 803 may be loaded into the memory 802 before being executed by the processor 801. The processor 801 implements the steps of the method according to the instructions of the computer program 803.

[0136] The device 800 includes a wireless communication unit 804 for exchanging messages with other devices, such as a 3G, 4G, 5G, 5GNR, WiFi or WiMax transceiver. In particular, the communication unit 804 is configured to exchange data with the first base station via an Xn interface. In particular, the communication unit 804 is configured to receive a handover request message from the base station via the Xn interface.

[0137] The device 800 further includes a RACH opportunity determination unit 805. The RACH opportunity determination unit can be implemented using computer program instructions, which are arranged to determine a set of RACH opportunities in the frequency domain and the time domain that can be used by the UE to perform uplink synchronization. The RACH opportunity can be determined based on several factors, such as based on the cell size (more RACH opportunities can be configured for larger cells, and a limited number of RACH opportunities can be configured for smaller cell sizes).

[0138] The device 800 also includes a RACH opportunity selection unit 806. The RACH opportunity selection unit can be implemented using computer program instructions, which are arranged to associate some RACH opportunities determined by the unit 805 with specific QoS profiles (such as 5QI values). The RACH opportunity selection unit can be further configured to select one or more RACH time slots / opportunities based on the QoS profile of the user equipment received by the communication unit 804. In some examples, the number of RACH opportunities selected for high QoS user equipment can be greater than the number of RACH opportunities selected for low QoS user equipment, thereby reducing conflicts occurring to high priority UEs.

[0139] The wireless communication unit 804 may be further arranged to send a handover confirmation message to the first base station, the message comprising at least the selected RACH time slot / opportunity determined by the selection unit 806 .

[0140] The device 800 further comprises a random access unit 807 arranged to receive a RACH request from a user equipment associated with a specific QoS value, the random access request being received at a RACH opportunity associated with the user equipment QoS value in the determined mapping table.

[0141] In some embodiments, the apparatus 800 is included in a base station (eg, a NodeB (NB), an eNodeB (eNB), or a gNodeB (gNB)) of a wireless access network.

Claims

1. A method for wireless communication by a user equipment, for supporting handover of the user equipment from a first base station to a second base station in a wireless network, wherein: The user equipment performs random access (413, 514, 613) to the second base station using a random access channel opportunity from a subset selected (406, 510, 612) from a set of random access channel opportunities according to a quality of service (QoS) profile assigned (400, 500, 600) to the user equipment.

2. The method according to claim 1, wherein: The random access channel opportunity for performing random access is selected by the user equipment according to a mapping between random access channel opportunities and QoS profiles.

3. The method according to claim 2, wherein: The mapping between random access channel opportunities and quality of service profiles is pre-configured in the user equipment.

4. The method according to claim 1, wherein: A subset of random access channel opportunities selected from a set of random access channel opportunities according to a quality of service profile assigned to the UE is received in a handover command message sent by the first base station.

5. A wireless communication device for supporting handover of a user equipment from a first base station to a second base station in a wireless network, the wireless communication device comprising a processor (701) coupled to a memory (702) storing computer program instructions (703), the instructions being arranged to implement a wireless communication method according to any one of claims 1 to 4.

6. A user equipment, comprising the wireless communication device according to claim 5.

7. A method for wireless communication by a second base station, for performing handover of a user equipment from a first base station to the second base station in a wireless network, the method comprising the following actions: obtaining (405) a set of random access channel opportunities that can be used to perform random access to the second base station, obtaining (405) a quality of service profile assigned to the user equipment, selecting (406) a specific subset of random access channel opportunities from the obtained set of random access channel opportunities, the subset being selected based at least on the quality of service (QoS) assigned to the user equipment, transmitting (407) to the first base station a message including the selected subset of random access channel opportunities, A random access request is received (414) from a user equipment associated with a particular QoS value, the random access request being received at a RACH opportunity associated with the QoS value of the user equipment in the determined mapping table.

8. The method according to claim 7, wherein: The quality of service assigned to the user equipment is obtained in a handover request message received from the first base station.

9. A wireless communication device for performing a handover of a user equipment from a first base station to a second base station in a wireless network, the wireless communication device comprising a processor (801) coupled to a memory (802) storing computer program instructions (803), the instructions being arranged to implement the wireless communication method according to claims 7 to 8.

10. A base station device, comprising the wireless communication device according to claim 9.

11. A wireless communication system for performing handover of a user equipment from a first base station to a second base station in a wireless network, wherein: The user equipment (105) performs random access (413, 514, 613) to the second base station (102) using a random access channel opportunity from a subset selected (406, 510, 612) from a set of random access channel opportunities according to a quality of service (QoS) profile assigned (400, 500, 600) to the user equipment, and wherein the second base station (102) receives a random access request at the selected random access channel opportunity.

12. The wireless communication system according to claim 11, wherein: The selected random access channel opportunity is selected by the second base station, and wherein the quality of service profile assigned to the user equipment is received from the first base station in a handover request message.

13. The wireless communication system according to claim 11, wherein: The selected random access channel opportunity is selected by the first base station from a set of random access channel opportunities, the set of random access channel opportunities being received from the second base station in a handover confirmation message, and wherein the selected random access channel opportunity is sent to the user equipment in an RRC reconfiguration message.

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