Method for performing i-rat handover in a communication environment

Abstract

The disclosure relates to a 5G or 6G communication system for supporting higher data rates. The embodiments of the disclosure provide a method performed by a target base station in a communication system. The method includes receiving, from a source base station, a first PDU for a terminal in an inter-RAT handover, wherein the inter-RAT handover is performed between an LPS base station which supports a chaining of SDUs in one PDU and a non-LPS base station which does not support the chaining; identifying the number of SDUs in the first PDU, based on a flag indicating whether the chaining is applied for the first PDU, the flag being included in a header of the first PDU; determining a SN based on the number of the SDUs in the first PDU; and transmitting, to the terminal, a second PDU corresponding to the first PDU with the determined SN.

Description

METHOD FOR PERFORMING I-RAT HANDOVER IN A COMMUNICATION ENVIRONMENT

[0001] The disclosure relates to operations of a base station (BS) and a user equipment (UE) in a wireless communication system. More particularly, the disclosure relates to a method and an apparatus for performing in inter / intra-radio access technology (i-RAT) handover in a communication environment.

[0002] In order to meet the increasing demand for wireless data communication services since the deployment of fourth generation (4G) communication systems, efforts have been made to develop improved fifth generation (5G) or pre-5G communication systems. Therefore, 5G or pre-5G communication systems are also called "Beyond 4G networks" or "Post-LTE systems".

[0003] Considering the development of wireless communication from generation to generation, the technologies have been developed mainly for services targeting humans, such as voice calls, multimedia services, and data services. Following the commercialization of 5th-generation (5G) communication systems, it is expected that the number of connected devices will exponentially grow. Increasingly, these will be connected to communication networks. Examples of connected things may include vehicles, robots, drones, home appliances, displays, smart sensors connected to various infrastructures, construction machines, and factory equipment. Mobile devices are expected to evolve in various form-factors, such as augmented reality glasses, virtual reality headsets, and hologram devices. In order to provide various services by connecting hundreds of billions of devices and things in the 6th-generation (6G) era, there have been ongoing efforts to develop improved 6G communication systems.

[0004] 6G communication systems, which are expected to be commercialized around 2030, have various significantly improved metrics compared to the current 5G communication systems. The peak data rate will reach at least 50 Gbit / s, and the user experienced data rate will reach at least 300 Mbit / s, the air-interface latency will be less than 1 ms, and the air-interface reliability will reach . In addition to the above basic communication metrics, the 6G communication systems will also have sensing capabilities, AI-related capabilities, better security, better interoperability and better sustainability.

[0005] In order for the 6G communication systems to fulfill the above metrics, more advanced air-interface technologies and network technologies need to be developed. The evolution of extreme Multiple Input Multiple Output (extreme MIMO) has been already under consideration, including the use of ultra-large scale antenna arrays, the development and evolution of distributed antenna systems, and the design of MIMO air-interface algorithms assisted by Artificial Intelligence (AI). This technology enables higher spectral efficiency, greater coverage, and precise localization and sensing capabilities. Additionally, for technologies that contribute to improve high-frequency band coverage, including metamaterial-based lenses and antennas, new antenna architectures, and reconfigurable intelligent surface (RIS), etc., they also need to be better evolved and developed.

[0006] In order to meet some of newly added functions of the 6G communication systems, new technologies need to be developed in the terms of network energy saving, air-interface security, and network security, meanwhile the feasibility of fusion technologies such as Integrated Sensing and Communication, needs to be studied.

[0007] Moreover, in order to improve the spectral efficiency and the overall network performances, the following technologies have been developed for 6G communication systems: a full-duplex technology for enabling an uplink transmission and a downlink transmission to simultaneously use the same frequency resource at the same time; a network technology for utilizing satellites, high-altitude platform stations (HAPS), and the like in an integrated manner; an improved network structure for supporting mobile base stations and the like and enabling network operation optimization and automation and the like; a dynamic spectrum sharing technology via collision avoidance based on a prediction of spectrum usage; an use of artificial intelligence (AI) in wireless communication for improvement of overall network operation by utilizing AI from a designing phase for developing 6G and internalizing end-to-end AI support functions; and a next-generation distributed computing technology for overcoming the limit of user equipment (UE) computing ability through reachable super-high-performance communication and computing resources (such as mobile edge computing (MEC), clouds, and the like) over the network. In addition, through designing new protocols to be used in 6G communication systems, developing mechanisms for implementing a hardware-based security environment and safe use of data, and developing technologies for maintaining privacy, attempts to strengthen the connectivity between devices, optimize the network, promote softwarization of network entities, and increase the openness of wireless communications are continuing.

[0008] It is expected that research and development of 6G communication systems in hyper-connectivity, including person to machine (P2M) as well as machine to machine (M2M), will allow the next hyper-connected experience. Particularly, it is expected that services such as truly immersive extended reality (XR), high-fidelity mobile hologram, and digital replica could be provided through 6G communication systems. In addition, services such as remote surgery for security and reliability enhancement, industrial automation, and emergency response will be provided through the 6G communication system such that the technologies could be applied in various fields such as industry, medical care, automobiles, and home appliances.

[0009] In NR, each received SDU is associated with multiple protocol headers, such as PDCP, RLC, and MAC headers. In 6G, to reduce protocol-related overhead, the LPS PDCP layer introduces concatenation (or chaining) of packets from upper layers. However, since these changes are not fully compatible with the NR protocol, discussions on how to ensure protocol coexistence are ongoing.

[0010] The above information is presented as background information only to assist with an understanding of the disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the disclosure.

[0011] The disclosure relates to operations of an LPS base station or a non-LPS base station in a communication system. More particularly, the disclosure relates to a method and an apparatus for performing i-RAT handover in a communication environment

[0012] Accordingly, an aspect of the disclosure is to provide a method and apparatus for modifying downlink user data (DUD) packet transmitted from a source base station to a target base station, for co-existence between the LPS base station and the non-LPS base station in the i-RAT handover.

[0013] In addition, an aspect of the disclosure is to provide a method and an apparatus for preventing packet loss based on a negotiation between the LPS base stations and modification on a DRB configuration between the NR PDCP layer and the LPS RLC layer.

[0014] Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments.

[0015] Aspects of the disclosure are to address at least the above-mentioned problems and / or disadvantages and to provide at least the advantages described below.

[0016] The Technical Solution is provided to introduce a selection of concepts, in a simplified format, that are further described in the detailed description of the disclosure. This solution is neither intended to identify key or essential inventive concepts of the disclosure nor is it intended for determining the scope of the disclosure.

[0017] According to an embodiment of the disclosure, a method performed by a target base station in a communication system is provided. The method includes receiving, from a source base station, a first packet data unit (PDU) for a terminal in an inter-radio access technology (RAT) handover, wherein the inter-RAT handover is performed between a lean protocol stack (LPS) base station which supports a chaining of service data units (SDUs) in one PDU and a non-LPS base station which does not support the chaining; identifying the number of SDUs in the first PDU, based on a flag indicating whether the chaining is applied for the first PDU, the flag being included in a header of the first PDU; determining a sequence number (SN) based on the number of the SDUs in the first PDU; and transmitting, to the terminal, a second PDU corresponding to the first PDU with the determined SN.

[0018] According to an embodiment of the disclosure, a target base station in a communication system is provided. The target base station includes a transceiver; memory storing one or more programs; and one or more processors communicatively coupled to the transceiver and the memory, wherein the one or more processors include computer-executable instructions that, when executed by the one or more processors individually or collectively, cause the target base station to: receive, from a source base station, a first packet data unit (PDU) for a terminal in an inter-radio access technology (RAT) handover, wherein the inter-RAT handover is performed between a lean protocol stack (LPS) base station which supports a chaining of service data units (SDUs) in one PDU and a non-LPS base station which does not support the chaining, identify the number of SDUs in the first PDU, based on a flag indicating whether the chaining is applied for the first PDU, the flag being included in a header of the first PDU, determine a sequence number (SN) based on the number of the SDUs in the first PDU, and transmit, to the terminal, a second PDU corresponding to the first PDU with the determined SN.

[0019] Disclosed herein is a method of performing inter-radio access technology (i-RAT) handover in a lean protocol stack (LPS) base station. The method includes receiving, by the LPS base station, a plurality of downlink user data (DUD) packets. Each of the plurality of DUD packets includes a service data unit (SDU) packet and a corresponding sequence number (SN), from a non-LPS base station. Each SDU packet includes at least one flag. The method includes processing, by the LPS base station, each SDU packet based on the at least one flag. The method includes performing, by the LPS base station, the i-RAT handover based on the processed SDU packets.

[0020] Disclosed herein is a method for performing inter-radio access technology (i-RAT) handover by a non-LPS base station. The method includes generating, by the non-LPS base station, a plurality of downlink user data (DUD) packets. Each of the plurality of DUD packets includes a SDU packet. Each SDU packet includes at least one flag. The method includes transmitting, by the non-LPS base station, each SDU packet each SDU packet and corresponding sequence numbers (SN) to a LPS base station for performing the i-RAT handover by the non-LPS base station.

[0021] Disclosed herein is a method for performing inter-radio access technology (i-RAT) handover in a user equipment. The method includes receiving at least one of a plurality of SDU packets from a non-LPS base station. The at least one of the plurality of SDU packets includes at least one flag and is marked as a special at least one of the plurality of SDU packets, when a status of E-Bit, in a header of a packet data convergence protocol (PDCP) of the non- lean protocol stack (LPS) base station, is true. The method includes unchaining the marked at least one of the plurality of SDU packets, for performing inter-radio access technology (i-RAT) handover in the user equipment, when the status of the E-Bit is true.

[0022] Disclosed herein is a method of performing inter-radio access technology (i-RAT) handover by a non- lean protocol stack (LPS) base station. The method includes generating, by the non-LPS base station, a header of a packet data convergence protocol (PDCP) of the non-LPS base station. The header includes an E-Bit indicating a presence of a length indicator (LI) field flag in at least one of a plurality of SDU packets of a downlink user data (DUD) packet received from a LPS base station. The method includes marking, by the non-LPS base station, the at least one of the plurality of SDU packets received from the LPS base station, as a special SDU packet based at least one flag provided in a header of the DUD packet. The method includes transmitting, the marked at least one of the plurality of SDU packets, to a user equipment for performing the inter-radio access technology (i-RAT) handover by the non- LPS base station.

[0023] Disclosed herein is a method of performing inter-radio access technology (i-RAT) handover by a lean protocol stack (LPS) base station. The method includes generating, by the LPS base station, a downlink user data (DUD) packet including a plurality of SDU packets and corresponding sequence numbers (SN). At least one of the plurality of SDU packets includes at least one flag provided in a header of the DUD and a length indicator (LI) field flag indicating a length of the at least one of the plurality of SDU packets packaged inside a packet data unit of the LPS base station. The method includes transmitting, by the LPS base station, the plurality of SDU packets and the corresponding sequence numbers (SN) to a non-LPS base station for performing the i-RAT handover by the LPS base station.

[0024] Disclosed herein is a method of performing intra-radio access technology (i-RAT) handover by a source lean protocol stack (LPS) base station. The method includes transmitting a handover request message to a target LPS base station. The handover request message comprises an information element (IE) indicating a predetermined concatenated count of a plurality of service data unit (SDU) packets of the source LPS base station. The method includes receiving a handover request acknowledge message from the target LPS base station, where the handover request acknowledge message includes an IE indicating a final concatenated count of a plurality of SDU packets for performing the intra-radio access technology (i-RAT) handover by the source LPS base station.

[0025] Disclosed herein is a method of performing intra-radio access technology (i-RAT) handover in a user equipment. The method includes receiving at least one of a plurality of SDU packets from a target-LPS base station. The at least one of the plurality of SDU packets includes at least one flag and is marked as a special at least one of the plurality of SDU packets, when a status of E-Bit, in a header of a packet data convergence protocol (PDCP) of the the target-LPS base station, is true. The method includes unchaining the marked at least one of the plurality of SDU packets, for performing inter-radio access technology (i-RAT) handover in the user equipment, when the status of the E-Bit is true.

[0026] Disclosed herein is a method of performing intra-radio access technology (i-RAT) handover by a target lean protocol stack (LPS) base station. The method includes generating, by the target-LPS base station, a header of a packet data convergence protocol (PDCP) of the target-LPS base station. The header includes an E-Bit indicating a presence of a length indicator (LI) field flag in at least one of a plurality of SDU packets of a downlink user data (DUD) packet received from a LPS base station. The method includes marking, by the target-LPS base station, the at least one of the plurality of SDU packets received from the source-LPS base station, as a special SDU packet based on at least one flag, provided in a header of the DUD packet. The method includes transmitting the marked at least one of the plurality of SDU packets, to a user equipment for performing the intra-radio access technology (i-RAT) handover by the target-LPS base station.

[0027] Disclosed herein is a method of performing intra-radio access technology (i-RAT) handover by a source lean protocol stack (LPS) base station. The method includes generating, by the source LPS base station, a downlink user data (DUD) packet including a plurality of SDU packets and corresponding sequence numbers (SN). At least one of the plurality of SDU packets includes at least one flag provided in a header of the DUD packet and a length indicator (LI) field flag indicating a length of the at least one of the plurality of SDU packets packaged inside a packet data unit of the source LPS base station. The method includes transmitting, by the source LPS base station, the plurality of SDU packets and the corresponding sequence numbers (SN) to a target LPS base station for performing the i-RAT based handover by the source LPS base station.

[0028] Disclosed is a method of establishing a multi radio dual connectivity (MRDC) a Lean Protocol Stack (LPS) base station and a non-LPS base station. The method includes receiving, by a packet data convergence protocol (PDCP) of the LPS base station, a plurality of service data unit (SDU) packets, and a corresponding sequence number (SN), from a PDCP of the non-LPS base station. The method includes concatenating, by the LPS base station, the received plurality of SDU packets. The method includes assigning, by the LPS base station, SN, independently, to each of the concatenated received plurality of SDU packets. The method includes transmitting, from the LPS base station, each of the concatenated received plurality of SDU packets with the assigned SN to a user equipment (UE) such that the UE unchains the concatenated received plurality of SDU packets and forward the unchained concatenated received plurality of SDU packets to the PDCP of the non-LPS base station.

[0029] Disclosed herein an apparatus for performing inter-radio access technology (i-RAT) handover at a lean protocol stack (LPS) base station. The apparatus includes at least one processor. The at least one processor is configured to receive a plurality of downlink user data (DUD) packets. Each of the plurality of DUD packet including a service data unit (SDU) packet and a corresponding sequence number (SN), from a non-LPS base station. Each SDU packet includes at least one flag. The at least one processor is configured to process each SDU packet based on the at least one flag. The at least one processor is configured to perform the i-RAT handover based on the processed SDU packets.

[0030] Disclosed herein an apparatus for performing inter-radio access technology (i-RAT) handover at a non-lean protocol stack (LPS) base station. The apparatus includes at least one processor. The at least one processor is configured to generate a plurality of downlink user data (DUD) packets. Each of the plurality of DUD packet includes a SDU packet. Each SDU packet includes at least one flag. The at least one processor is configured to transmit each SDU packet and corresponding sequence numbers (SN) to a LPS base station for performing the i-RAT handover at the non-LPS base station.

[0031] Disclosed herein an apparatus for performing inter-radio access technology (i-RAT) handover at a user equipment. The user equipment includes at least one processor. The at least one processor is configured to receive at least one of a plurality of SDU packets from a non-LPS base station. The at least one of the plurality of SDU packets includes at least one flag and is marked as a special at least one of the plurality of SDU packets, when a status of E-Bit, in a header of a packet data convergence protocol (PDCP) of the non- lean protocol stack (LPS) base station, is true. The at least one processor is configured to unchain the marked at least one of the plurality of SDU packets, for performing inter-radio access technology (i-RAT) handover in the user equipment, when the status of the E-Bit is true.

[0032] Disclosed herein an apparatus for performing inter-radio access technology (i-RAT) handover at a non-lean protocol stack (LPS) base station. The apparatus includes at least one processor. The at least one processor is configured to generate a header of a packet data convergence protocol (PDCP) of the non-LPS base station. The header includes an E-Bit indicating a presence of a length indicator (LI) field flag in at least one of a plurality of SDU packets of a downlink user data (DUD) packet received from a LPS base station. The at least one processor is configured to mark the at least one of the plurality of SDU packets received from the LPS base station, as a special SDU packet based at least one flag provided in a header of the DUD packet. The at least one processor is configured to transmit the marked at least one of the plurality of SDU packets, to a user equipment for performing the inter-radio access technology (i-RAT) handover at the non- LPS base station.

[0033] Disclosed herein an apparatus for performing inter-radio access technology (i-RAT) handover at a lean protocol stack (LPS) base station. The apparatus includes at least one processor. The at least one processor is configured to generate a downlink user data (DUD) packet including a plurality of SDU packets and corresponding sequence numbers (SN). At least one of the plurality of SDU packets includes at least one flag provided in a header of the DUD and a length indicator (LI) field flag indicating a length of the at least one of the plurality of SDU packets packaged inside a packet data unit of the LPS base station. The at least one processor is configured to transmit the plurality of SDU packets and the corresponding sequence numbers (SN) to a non-LPS base station for performing the i-RAT handover at the LPS base station.

[0034] Disclosed herein an apparatus for performing intra-radio access technology (i-RAT) handover at a source lean protocol stack (LPS) base station. The apparatus includes at least one processor. The at least one processor is configured to transmit a handover request message to a target LPS base station. The handover request message includes an information element (IE) indicating a predetermined concatenated count of a plurality of service data unit (SDU) packets of the source LPS base station. The at least one processor is configured to receive a handover request acknowledge message from the target LPS base station, where the handover request acknowledge message includes an IE indicating a final concatenated count of a plurality of SDU packets for performing the intra-radio access technology (i-RAT) handover at the source LPS base station.

[0035] Disclosed herein an apparatus for performing intra-radio access technology (i-RAT) handover at a user equipment. The apparatus includes at least one processor. The at least one processor is configured to receive at least one of a plurality of SDU packets from a target-LPS base station. The at least one of the plurality of SDU packets includes at least one flag and is marked as a special at least one of the plurality of SDU packets, when a status of E-Bit, in a header of a packet data convergence protocol (PDCP) of the the target-LPS base station, is true. The at least one processor is configured to unchain the marked at least one of the plurality of SDU packets, for performing inter-radio access technology (i-RAT) handover in the user equipment, when the status of the E-Bit is true.

[0036] Disclosed herein an apparatus for performing intra-radio access technology (i-RAT) handover at a target lean protocol stack (LPS) base station. The apparatus includes at least one processor. The at least one processor is configured to generate a header of a packet data convergence protocol (PDCP) of the target-LPS base station. The header includes an E-Bit indicating a presence of a length indicator (LI) field flag in at least one of a plurality of SDU packets of a downlink user data (DUD) packet received from a LPS base station. The at least one processor is configured to mark the at least one of the plurality of SDU packets received from the source-LPS base station, as a special SDU packet based on at least one flag, provided in a header of the DUD packet. The at least one processor is configured to transmit the marked at least one of the plurality of SDU packets, to a user equipment for performing the intra-radio access technology (i-RAT) handover at the target-LPS base station.

[0037] Disclosed herein an apparatus for performing intra-radio access technology (i-RAT) handover at a source lean protocol stack (LPS) base station. The apparatus includes at least one processor. The at least one processor is configured to generate a downlink user data (DUD) packet including a plurality of SDU packets and corresponding sequence numbers (SN). At least one of the plurality of SDU packets includes at least one flag provided in a header of the DUD packet and a length indicator (LI) field flag indicating a length of the at least one of the plurality of SDU packets packaged inside a packet data unit of the source LPS base station. The at least one processor is configured to transmit the plurality of SDU packets and the corresponding sequence numbers (SN) to a target LPS base station for performing the i-RAT based handover at the source LPS base station.

[0038] Disclosed herein an apparatus for establishing a multi radio dual connectivity (MRDC) a Lean Protocol Stack (LPS) base station and a non-LPS base station. The apparatus includes at least one processor. The at least one processor is configured to receive, by a packet data convergence protocol (PDCP) of the LPS base station, a plurality of service data unit (SDU) packets and a corresponding sequence number (SN), from a PDCP of the non-LPS base station. The at least one processor is configured to concatenate the received plurality of SDU packets. The at least one processor is configured to assign SN, independently, to each of the concatenated received plurality of SDU packets. The at least one processor is configured to transmit each of the concatenated received plurality of SDU packets with the assigned SN to a user equipment (UE) such that the UE unchains the concatenated received plurality of SDU packets and forward the unchained concatenated received plurality of SDU packets to the PDCP of the non-LPS base station.

[0039] To further clarify the advantages and features of the disclosure, a more particular description of the disclosure will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawing. It is appreciated that these drawings depict only typical embodiments of the disclosure and are therefore not to be considered limiting its scope. The disclosure will be described and explained with additional specificity and detail with the accompanying drawings.

[0040]

[0041] According to an embodiment of the disclosure, a non-LPS or LPS base station can recognize the data units included in the packet, by modifying the structure of data packets transmitted during the i-RAT handover procedure.

[0042] In addition, according to an embodiment of the disclosure, the non-LPS or LPS base station can determine a sequence number (SN) corresponding to each data unit, thereby preventing packet loss and preserving SN synchronization during the i-RAT handover for co-existence.

[0043] Furthermore, according to an embodiment of the disclosure, data packets can be processed without conflicts with the existing RAT, by redefining the packet concatenation scheme between LPS base stations and reconfiguring bearer structure between non-LPS and LPS base stations

[0044] To further clarify the advantages and features of the disclosure, a more particular description of the disclosure will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawing. It is appreciated that these drawings depict only typical embodiments of the disclosure and are therefore not to be considered limiting its scope. The disclosure will be described and explained with additional specificity and detail with the accompanying drawings.

[0045]

[0046] In the drawings, like reference numerals refer to like elements. The foregoing and other features ofembodiments will become more apparent from the following detailed description of embodiments when read in conjunction with the accompanying drawings, in which:

[0047] Figure 1is a schematic diagram illustrating a handover preparation;

[0048] Figure 2ais schematic diagrams illustrating a normal handover;

[0049] Figure 2bis schematic diagrams illustrating a normal handover;

[0050] Figure 3ais schematic diagrams illustrating a DAPS handover;

[0051] Figure 3billustrates a DAPS handover, as per existing art;

[0052] Figure 4illustrates a handover completion, as per existing art;

[0053] Figure 5aillustrates occurring of a problem when the DAPS handover has occurred between the NR to LPS gNB, as per existing art;

[0054] Figure 5billustrates a difference in SDU handling, as per existing art;

[0055] Figure 5cillustrates a scenario of loss of SN synchronization during DAPS handover from NR to LPS, as per existing art;

[0056] Figure 5dillustrates a normal handover scenario in which a UE switches from the NR gNB to the LPS gNB, as per existing art;

[0057] Figures 6a-6eillustrate problems in the LPS to NR handover in a downlink, as per existing art;

[0058] Figure 7illustrates LPS to LPS handover, as per existing art;

[0059] Figure 8illustrates difference in protocol operation at NR and LPS, as per existing art;

[0060] Figure 9illustrates an example block diagram of a communication environment depicting a configuration of a lean protocol stack base station, a non-lean protocol stack (LPS) base station, and a user equipment, in accordance with an embodiment of the disclosure;

[0061] Figure 10aillustratesa plurality of DUD packets in the non-LPS base station, in accordance with an embodiment of the disclosure;

[0062] Figure 10billustratesa header of each of the plurality of DUD packet in the non-LPS base station, in accordance with an embodiment of the disclosure;

[0063] Figure 11aillustrates a plurality of SDU packets in the DUD packet, in accordance with another embodiment of the disclosure;

[0064] Figure 11billustrates a header of the DUD packet, in accordance with another embodiment of the disclosure;

[0065] Figure 11cillustrates a header of a Packet Data Convergence Protocol (PDCP) of the non-LPS base station, in accordance with another embodiment of the disclosure;

[0066] Figure 12illustrates an example block diagram of a communication environment depicting a configuration of a source lean protocol stack (LPS) base station, a target lean protocol stack (LPS) base station, and a user equipment, in accordance with another embodiment of the disclosure;

[0067] Figures 13a-13billustratean operation performed by processors to perform inter-radio technology (i-RAT) handover between the source LPS base station and the target LPS base station in the DAPS handover, in accordance with yet another embodiment of the disclosure;

[0068] Figures 14a-14cillustrate operations performed by the processors for performing the i-RAT handover from the source LPS base station to the target LPS base station and the UE, in accordance with another embodiment of the disclosure;

[0069] Figure 15illustrates an operation performed for establishing a multi radio dual connectivity between the LPS base station and non-LPS base station, in accordance with yet another embodiment of the disclosure;

[0070] Figure 16illustrates a method for performing the i-RAT handover in the LPS base station, in accordance with an embodiment of the disclosure;

[0071] Figure 17illustrates a method for performing the i-RAT handover by the non-LPS base station, in accordance with an embodiment of the disclosure;

[0072] Figure 18illustrates a method for performing the i-RAT handover by the UE, in accordance with another embodiment of the disclosure;

[0073] Figure 19illustrates a method for performing the i-RAT handover by the non-LPS base station , in accordance with another embodiment of the disclosure;

[0074] Figure 20illustrates a method for performing the i-RAT handover by the LPS base station, in accordance with another embodiment of the disclosure;

[0075] Figure 21illustrates a method for performing the i-RAT handover by the source LPS base station, in accordance with yet another embodiment of the disclosure;

[0076] Figure 22illustrates a method for performing the i-RAT handover by the UE, in accordance with yet another embodiment of the disclosure;

[0077] Figure 23illustrates a method for performing the i-RAT handover by the target LPS base station, in accordance with yet another embodiment of the disclosure;

[0078] Figure 24illustrates a method for performing the i-RAT handover by the source LPS base station, in accordance with yet another embodiment of the disclosure;

[0079] Figure 25illustrates a method for establishing the MRDC between the LPS base station and the non-LPS base station, in accordance with yet another embodiment of the disclosure.

[0080]

[0081] For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to the various embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the disclosure as illustrated therein being contemplated as would normally occur to one skilled in the art to which the disclosure relates.

[0082] It will be understood by those skilled in the art that the foregoing general description and the following detailed description are explanatory of the disclosure and are not intended to be restrictive thereof.

[0083] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the disclosure as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Those of ordinary skill in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scope and spirit of the disclosure. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness.

[0084] In order to make the objectives, technical schemes and advantages of the embodiments of the disclosure, a clear and complete description will be made with respect to the technical schemes of the embodiments of the disclosure, in conjunction with the accompanying drawings of the embodiments of the disclosure. Apparently, the described embodiments are a part of the embodiments of the disclosure, not all of the embodiments. Based on the described embodiments of the disclosure, all other embodiments obtained by common skilled in the art without creative labor belong to the protection scope of the disclosure.

[0085] The terms and words used in the following description and claims are not limited to the bibliographical meanings, but are merely used by the inventor to enable a clear and consistent understanding of the disclosure. Accordingly, it should be apparent to those skilled in the art that the following description of various embodiments of the disclosure is provided for illustration purpose only and not for the purpose of limiting the disclosure as defined by the appended claims and their equivalents.

[0086] It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a component surface" includes reference to one or more of such surfaces.

[0087] Before undertaking the DETAILED DESCRIPTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The term "couple" and its derivatives refer to any direct or indirect communication between two or more elements, whether those elements are in physical contact with one another. The terms "transmit," "receive," and "communicate," as well as derivatives thereof, encompass both direct and indirect communication. The terms "include" and "comprise," as well as derivatives thereof, mean inclusion without limitation. The term "or" is inclusive, meaning and / or. The phrase "associated with," as well as derivatives thereof, means to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, have a relationship to or with, or the like. The term "controller" means any device, system or part thereof that controls at least one operation. Such a controller may be implemented in hardware or a combination of hardware and software and / or firmware. The functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. The phrase "at least one of," when used with a list of items, means that different combinations of one or more of the listed items may be used, and only one item in the list may be needed. For example, "at least one of: A, B, and C" includes any of the following combinations: A, B, C, A and B, A and C, B and C, and A and B and C. Likewise, the term "set" means one or more. Accordingly, a set of items can be a single item or a collection of two or more items.

[0088] Furthermore, the expressions "if" and "in case that" as used in the present specification or claims may, depending on the context, be interpreted to mean "when," "in response to," "based on," or "according to," and such expressions may be used interchangeably. In addition, other expressions having substantially the same meaning may also be used in place of these expressions, as long as the technical features of the present disclosure are not impaired. Furthermore, the term "configured" to indicate that predetermined information is set by a base station or a network may imply that the predetermined information is received via a predetermined message (for example, an RRC message).

[0089] Moreover, various functions described below can be implemented or supported by one or more computer programs, each of which is formed from computer readable program code and embodied in a computer readable medium. The terms "application" and "program" refer to one or more computer programs, software components, sets of instructions, procedures, functions, objects, classes, instances, related data, or a portion thereof adapted for implementation in a suitable computer readable program code. The phrase "computer readable program code" includes any type of computer code, including source code, object code, and executable code. The phrase "computer readable medium" includes any type of medium capable of being accessed by a computer, such as read only memory (ROM), random access memory (RAM), a hard disk drive, a compact disc (CD), a digital video disc (DVD), or any other type of memory. A "non-transitory" computer readable medium excludes wired, wireless, optical, or other communication links that transport transitory electrical or other signals. A non-transitory computer readable medium includes media where data can be permanently stored and media where data can be stored and later overwritten, such as a rewritable optical disc or an erasable memory device.

[0090] As described above, it should be noted that each block of the flowcharts and combinations of the flowcharts described in the disclosure may be performed by one or more computer programs including instructions. The entirety of the one or more computer programs may be stored in a single memory device, or the one or more computer programs may be stored in a plurality of memory devices in a distributed manner.

[0091] In addition, the functions or operations described in the disclosure may be processed by a single processor or a combination of processors. The single processor or the combination of processors may be a circuit that performs processing and may include an application processor (AP, e.g., a central processing unit (CPU)), a communication processor (CP, e.g., a modem), a graphics processing unit (GPU), a neural processing unit (NPU) (e.g., an artificial intelligence (AI) chip), a Wi-Fi chip, a Bluetooth® chip, a global positioning system (GPS) chip, a near-field communication (NFC) chip, a connectivity chip, a sensor controller, a touch controller, a fingerprint sensor controller, a display driver integrated circuit (IC), an audio codec (CODEC) chip, a universal serial bus (USB) controller, a camera controller, an image processing IC, a microprocessor unit (MPU), a system on chip (SoC), an IC, or a similar circuit.

[0092] Furthermore, it should be noted that various embodiments in the claims and descriptions of the disclosure may be implemented in the form of hardware, software, or a combination of hardware and software. Such software may be stored in a non-transitory computer-readable storage medium. The non-transitory computer-readable storage medium stores one or more computer programs (software modules), and the one or more computer programs include computer-executable instructions which, when executed individually or collectively by one or more processors of an electronic device, operate the electronic device to perform the method according to the disclosure.

[0093] The software may be stored in a transient or non-transitory storage device, for example, in the form of read-only memory (ROM) (regardless of whether it is erasable or rewritable), or random access memory (RAM), memory chips, devices, or integrated circuits (ICs). Also, the software may be stored in optically or magnetically readable media such as compact discs (CDs), digital versatile discs (DVDs), magnetic disks, or magnetic tapes. It should be understood that the storage devices and storage media are examples of non-transitory machine-readable storage media suitable for storing a program for implementing various embodiments of the disclosure.

[0094] Accordingly, various embodiments provide a program including code for implementing a device or method according to any one of the claims of the disclosure, and a non-transitory machine-readable storage medium storing such a program.

[0095] Definitions for other certain words and phrases are provided throughout the disclosure. Those of ordinary skill in the art should understand that in many if not most instances, such definitions apply to prior as well as future uses of such defined words and phrases.

[0096] The figures included herein, and the various embodiments used to describe the principles of the disclosure are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Further, those skilled in the art will understand that the principles of the disclosure may be implemented in any suitably arranged wireless communication system.

[0097] Whether or not a certain feature or element was limited to being used only once, it may still be referred to as "one or more features" or "one or more elements" or "at least one feature" or "at least one element." Furthermore, the use of the terms "one or more" or "at least one" feature or element do not preclude there being none of that feature or element, unless otherwise specified by limiting language including, but not limited to, "there needs to be one or more쪋" or "one or more elements is required."

[0098] Reference is made herein to some "embodiments." It should be understood that an embodiment is an example of a possible implementation of any features and / or elements of the disclosure. Some embodiments have been described for the purpose of explaining one or more of the potential ways in which the specific features and / or elements of the proposed disclosure fulfil the requirements of uniqueness, utility, and non-obviousness.

[0099] Use of the phrases and / or terms including, but not limited to, "a first embodiment," "a further embodiment," "an alternate embodiment," "one embodiment," "an embodiment," "multiple embodiments," "some embodiments," "other embodiments," "further embodiment", "furthermore embodiment", "additional embodiment" or other variants thereof do not necessarily refer to the same embodiments. Unless otherwise specified, one or more particular features and / or elements described in connection with one or more embodiments may be found in one embodiment, or may be found in more than one embodiment, or may be found in all embodiments, or may be found in no embodiments. Although one or more features and / or elements may be described herein in the context of only a single embodiment, or in the context of more than one embodiment, or in the context of all embodiments, the features and / or elements may instead be provided separately or in any appropriate combination or not at all. Conversely, any features and / or elements described in the context of separate embodiments may alternatively be realized as existing together in the context of a single embodiment.

[0100] Any particular and all details set forth herein are used in the context of some embodiments and therefore should not necessarily be taken as limiting factors to the proposed disclosure.

[0101] The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by "comprises... a" does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.

[0102] The solution as disclosed in the disclosure introduces a new field having a flag for a Downlink User Data (DUD) packet which indicates a Lean Protocol Stack (LPS) base station about the presence of a plurality of service data unit (SDU) packets. The new field indicates the LPS base station such that when the flag is set, the LPS base station interprets the incoming data as a special SDU and applies it for concatenation factor as 1. The solution also introduces an LI Exist flag as a special DUD field to ensure that the received packet gets a special treatment along with the presence of the Length Indicator fields. The solution also introduces a new field in the PDCP Header for the non-LPS base station, such that the PDCP Header understands that the received SDU may be required to be handled newly as it contains the LI fields which can be later separated for delivery of individual packets. The solution also discloses a handshake mechanism between the source gNB and target gNB to decide on the target concatenation factor so that, during handover, the already prepared packets may be handled appropriately.

[0103] Embodiments of the disclosure will be described below in detail with reference to the accompanying drawings.

[0104] For the sake of clarity, the first digit of a reference numeral of each component of the disclosure is indicative of the Figure number, in which the corresponding component is shown. For example, reference numerals starting with digit "1" are shown at least in Figure 1. Similarly, reference numerals starting with digit "2" are shown at least in Figure 2.

[0105] A telecommunication network enables users to stay connected and enjoy internet services while maintaining mobility. Mobility management is a fundamental function that telecom operators are expected to support and is defined in TS 38.300 by 3GPP. Over time, multiple generations of mobile technology have emerged, and the coexistence of different Radio Access Technologies (RATs) is supported to provide broader coverage and meet the needs of various user types. Further, users are likely to move across different coverage areas that involve multiple generations or RATs. As telecommunications networks evolve and deployed in stages, the coexistence of multiple RATs remains a constant feature. This coexistence primarily supports functions such as handover and dual connectivity. Handover ensures uninterrupted service for mobile users, while dual connectivity enhances reliability and increases data rates through split bearer technology.

[0106] Further, referring to the handover at New Radio (NR) 5G communication, the handover is performed mainly in three steps: a handover reparation, a handover execution, and a handover completion.The handover preparation covers aspects, for example, measurements and decision making related to requirement of the handover and a target cell, i.e., target gNB to which the handover is done.Referring to Figure 1, in the handover preparation, a handover decision is made by a source g-NodeB (gNB) on the basis of measurement control and reports shared by a user equipment. The source gNB decides the target gNB and sends a handover request message. The target gNB performs admission control and replies with a handover request acknowledge message to the source gNB. A handover request acknowledge message contains the Radio Resource Control (RRC) reconfiguration message containing the information required for a user equipment (UE) to access the target cell.

[0107] Further, the handover execution performs the handover by reconnecting the UE to the target gNB and thereafter, sends the buffered service data units (SDUs) from the source gNB to the target gNB along with a transfer of the status of sequence number (SN). The handover execution includes a normal handover, a dual active protocol stack (DAPS), and a conditional handover. In the normal handover,referring to Figure 2a, the handover is performed. Particularly, the UE detaches from the source gNB, i.e., cell and attaches to the target gNB, i.e., a cell. The UE receives RRCReconfiguration message containing details of the target gNB from the source gNB. The UE applies the configuration and attaches to the target gNB / cell. The source gNB forwards the buffered data to the target gNB over Xn interface and performs the transfer of the status of SN. The source gNB keeps forwarding the data received from a user plane function (UPF) to the target gNB over Xn interface which gets buffered at the target gNB, thus performing the handover.

[0108] Referring to Figure 2b, in the normal handover execution, data transfer from the source gNB to the target gNB is performed for lossless handover. After sending the buffered data at source gNB, the transfer of the status of the SN is performed to target gNB. The SN status conveys a uplink packet data convergence protocol (UL PDCP) about a SN receiver status and a downlink PDCP about a SN transmitter status of data radio bearer (DRBs) for which PDCP status preservation applies. The source gNB keeps forwarding the DL User Data received from the UPF to the target gNB over Xn interface. Upon establishing a connection with UE, the target gNB performs retransmission of unacknowledged SDUs, transfers buffered SN, and assigned SDU sent by source gNB, and transfers fresh SDU after assigning SN based on received SN status.

[0109] In the DAPS Handover, referring to Figure 3a, the handover is performed, i.e., the UE attaches to the target gNB (cell) and remains connected to the source gNB. This ensures zero handover interruption time and provides a fallback mechanism to the source gNB in case of the failure of the handover. The UE receives RRCReconfiguration message containing details of the target gNB from the source gNB. The UE applies the configuration and attaches to the target gNB, i.e., cell . The source gNB forwards the buffered data to the target gNB over Xn interface and performs early SN status transfer. The source gNB keeps forwarding the data received from the UPF to the target gNB over Xn interface which gets buffered at the target gNB. The source gNB keeps sending the data to the UE after assigning the SN to enable zero handover interruption time. Based on early SN status, the target gNB also starts forwarding the data received from source gNB to the UE.

[0110] Referring to Figure 3B, data transfer from the source gNB to target gNB is performed for lossless DAPS handover. Both source gNB and target gNB forward downlink data to the UE. In order to maintain synchronization between the source gNB and the target gNB, an early status transfer is made to the target gNB. The DL COUNT value conveyed in the early status transfer message indicates PDCP SN and HFN of the first PDCP SDU that the source gNB forwards to the target gNB. The source gNB continues forwarding the data to the target gNB over Xn interface. On the basis of early status, the target gNB keeps assigning SN independently to the SDUs and forwards SDUs to the UE. The source gNB also forwards the data to the UE after assigning SN.

[0111] Referring to Figure 4, the handover completion finalizes the handover by updating the path of traffic to target gNB and releasing context of the UE from the source gNB. In NR, there are multiple methods to perform handover. In this stage, handover is completed, and path switch is also performed to receive data at the target gNB directly. Firstly, the target gNB sends handover success message to the source gNB marking the completion of the handover. Source gNB sends SN status transfer again in case of DAPS handover. Meanwhile, the target gNB keeps on receiving DL data via source gNB only. Both DL and UL data are forwarded to the UE by the target gNB itself. A Path switch request is sent to Access and Mobility Function (AMF) by the target gNB. The UPF performs a path switch and sends an end marker over the DRB and thereafter the target gNB directly receives PDUs from the UPF. Further, Path switch acknowledge is sent by the AMF to the target gNB. The target gNB sends the UE context release message to source gNB where the UE context is removed from the source gNB.

[0112] This Handover operation as discussed above ensures smooth and efficient handover between 5G-5G handover, or 4G-5G handover. However, the Handover operation as explained is not compatible with establishing a handover between 5G-6G or vice versa, or in another communication environment. Further, the handover operation may face different challenges for example, power inefficiency due to duplication of functionalities, for example, reordering, duplication detection at PDCP and Radio Link Control (RLC), and no support for multi-device ecosystem having diverse requirements with different device capabilities.

[0113] Particularly, the NR has high number of protocol header as PDCP, RLC and media access control (MAC) Header assigned to each SDU received. Further, a lean stack protocol (LPS) 6G suggests concatenating the packets at the PDCP layer in a particular manner. Further, SDUs received from the upper layer are concatenated at PDCP based on the concatenation factor. Further, the RLC assigns one byte header for complete packets and assigns 3 byte header consisting of SN for segmented packets. Thereafter, an error reporting via status report and retransmission of lost Packet Data Units (PDUs) is handled at the PDCP.

[0114] However, during the handover between the NR (5G) to LPS (6G), 6G to 5G, 6G to 6G etc., the following problems may occur:

[0115] a. The modifications may directly impact the way PDUs are formed by the PDCP entity.

[0116] b. It can be noted that depending on a number of SDUs packaged in a single PDU, different LPS entities end up assigning different SNs to a set of SDUs.

[0117] c. Till the current generation of the network, PDCP in 4G and 5G utilizes same method to assign SN to SDUs, thereby avoiding such coherency issues which is existing in 5G to 6G communication or in another communication environment.

[0118] d. Further, with the proposed changes in PDCP, SN synchronization between protocols is not automatically maintained.

[0119] e. This specifically impacts the Handover procedure.

[0120] Elaborating the problems further in detail:

[0121] Problem 1:Referring to Figure 5a, when the DAPS handover occurs between the NR to LPS gNB: When the DAPS handover occurs from the NR to LPS gNB, then during handover, NR PDCP SDUs are sent to LPS PDCP. Both NR and LPS PDCP keep assigning SN to SDUs and transmit it to the UE. At NR PDCP, each PDCP SDU has a SN associated to it whereas on the other end, LPS PDCP concatenates multiple SDUs in one SN. During handover, this difference in SN assignment leads to a mismatch in SN operational at source and target gNB. This results in the receiving of different PDUs for the same PDCP SN, thus, resulting in loss of SN synchronization between both stacks at a receiving window of UE PDCP. This differential handling of SDUs at PDCP layers of both the stacks leads to loss of order of SDUs in case of normal handover.

[0122] Problem 1A:Different packet data units for same SN in Rx (5G to 6G Handover, DL): In the DAPS handover, both NR PDCP (Protocol Data Unit) and LPS PDCP sends the data PDU to the UE after assigning SN independently. Thus, leading to the receipt of inconsistent PDUs at the receiving window of UE. Particularly, the difference in SDU handling at NR and LPS PDCP is shown in Figure 5b. The NR assigns a single SN to a single SDU whereas LPS assigns a single SN to multiple SDUs. This leads to differences in formed PDUs at each node, in scenarios like DAPS Handover where both the source gNB and target gNB independently send packets to the UE in downlink. This leads to a mismatch in packets received by the UE for a given SN. Ultimately this results in a loss of data packets at the UE as some of the SNs are filled by the NR PDUs whereas some others are filled by LPS PDUs.

[0123] Problem 1B: Loss of SN synchronization: In the DAPS handover, both NR PDCP and LPS PDCP entities may end up operating on different SN. Thus, leading to synchronization issues between protocol stacks. Particularly, Figure 5c indicates the scenario of loss of SN synchronization during DAPS handover from NR to LPS. The source NR entity sends PDCP SDUs to target LPS entity during the handover execution phase. The target LPS entity, depending on concatenation count value and Early Status received from NR, concatenates 3 NR PDCP SDUs into 1 LPS PDCP PDU and assigns SN=1. This results in different PDCP SN operational at both stacks. For example, NR is operational at SN=4 whereas LPS is operational at SN=2. At this instance, if NR PDCP sends SN Status then it mentions the next SN to be assigned as 4. Further, the LPS PDCP assigns SN to the next packet based on SN Status sent by NR PDCP entity meaning thereby that next SN assigned at LPS entity would be 4. Thus, the LPS PDCP assigns next SN as 4 skipping SN=2,3. Further, if NR PDUs with SN=2,3 are lost, then LPS PDCP window stall occurs while waiting for feedback of SN=2,3. Simultaneously, a receiver side, also, does not receive the PDU with SN=2,3 resulting in an error in protocol.

[0124] Problem 1C:In normal handover, unacknowledged PDUs at NR PDCP has to be sent to the UE by the LPS PDCP after assigning SN as per LPS protocol. Thus, leading to loss of order of SDUs. Particularly, Figure 5D highlights a normal handover scenario in which the UE switches from the NR gNB to the LPS gNB. The NR PDCP is the source gNB and LPS PDCP is the target gNB. There are some unacknowledged SDUs present at the NR PDCP that are transferred to LPS PDCP over Xn interface. It can be observed that at the NR PDCP, the SN assigned to SDUs are 1,3 and 7. As the LPS assigns 1 SN to multiple SDUs, in that case, the LPS entity assigns SN = 1 to the SDUs after chaining them based on the value of the concatenation factor (3 in this case). In the receiving side, when UE receives these packets, these packets are placed together. Thus, SDUs that originally corresponded to SN 1,3 and 7 are placed along with 1. Thus, failing in-sequence delivery.

[0125] Problem 2:Problems in LPS to NR handover in DL: TheLPS PDCP assigns multiple SDUs, one SN depending on the concatenation factor whereas the NR PDCP assigns single SDU a SN. During handover execution, the buffered SDUs at LPS PDCP has to be sent to NR PDCP and these PDUs consist of chained SDUs. Thus, it would lead to errors at NR as it cannot form PDUs that contain multiple SDUs. Referring to Figure 6a, if the DAPS handover occurs from the LPS to the NR gNB, then, during the handover, the LPS PDCP SDUs are sent to the NR PDCP. At the LPS PDCP, multiple PDCP SDUs have a single SN associated with it whereas NR PDCP assigns one SN to a single SDU. Thus, this difference in SN assignment leads to the following problems: the receiving window at a UE PDCP receives different PDUs for the same PDCP leading to SN mismatch in SN operational at source gNB and target gNB . This leads to the loss of SN synchronization between both stacks. In case any unacknowledged SDUs are present at LPS PDCP then it results in loss of order of SDUs at receiving NR PDCP entity for normal handover.

[0126] Problem 2A:Receipt of Different PDUs for a SN: Figure 6b highlights the difference in the SDU handling at the NR and the LPS PDCP. The NR assigns a single SN to a single SDU whereas LPS assigns a single SN to multiple SDUs. This leads to differences in formed PDUs at each node. In scenarios like DAPS Handover where both the source gNB and target gNB independently send packets to UE in downlink. This results in mismatching in packets received by the UE for a given SN. Ultimately, this leads to a loss of data packets at the UE as some of the SNs are filled by NR PDUs whereas some others are filled by LPS PDUs.

[0127] Problem 2B:Loss of synchronization: Referring to Figure 6c, when the last set of SDUs are sent by the LPS PDCP to the NR PDCP. In that case, the SN status sent by the LPS PDCP mentions the next SN to be assigned as 3. But SN=3 has already been assigned by the NR entity and reassignmnet of SN=3 to a new SDU leads to a duplication of SDU at the receiver window. This leads to the dropping of the SDU leading to errors in the operation of protocol.

[0128] Problem 2C:loss of order of SDUs (LPS to NR, DL): Figure 6d indicates a normal handover scenario in which the UE switches from the LPS gNB to the NR gNB. The LPS PDCP is the source gNB and NR PDCP is the target gNB. Further, there are some unacknowledged SDUs present at LPS PDCP which are transferred to the NR PDCP over Xn interface. It is observed that at the LPS PDCP, the SN assigned to SDUs are 1 and 3. Further, as the NR assign only 1 SN to a SDU, so in this case, the NR assigns SN = 1,3,4,5 and 6 to the SDUs. Furthermore, on the receiving side, when UE receives these packets, these packets are placed in the window. Thus, SDU which originally corresponded to SN 1 and 3 are placed along with 1,3,4,5,6 and 7. Thus failing in-sequence delivery. This issue is probable in both normal as well as DAPS handover as well.

[0129] Problem 2D:loss of SDUs (LPS to NR, DL): Figure 6e indicates the scenario in which loss of SDU happens in case of the DAPS handover from LPS gNB to NR gNB. It is observed that the LPS PDCP transfers the data to the NR PDCP over Xn interface. As per the DAPS handover, both LPS and NR independently keep on sending PDUs to the UE. It is observed that while forming PDUs, LPS assigns SN=1,3 and 4 to SDUs, NR assigns SN=1,3,4,5,6,7 and 8 to send these SDUs. In both the case SN=2 is skipped because it has already been received and acknowledged. Due to differences in the assignment of SN, the same SN carries different packets, thereby leading to the discarding of any one of the packets. In the present case, the packet with NR SN=4 gets discarded as LPS packet with SN=4 has already been placed in the window. Thus, appropriate handling is required to overcome this challenge.

[0130] Problem 3:LPS to LPS handover: Referring to Figure 7, in normal handover, buffered SDUs are chained with sourceConcat which is different than targetConcat. If the target gNB doesn't forward the SDUs under same SN and with same concatCount as sourceConcat, this leads to errors as mentioned in the Problem 2B. Particularly, In the DAPS handover, sourceConcat is different than targetConcat, leading to loss of SN synchronization and loss of SDUs as well. Further, there is a possibility that both the source LPS gNB and target gNB operate at different concatenation factors. Thus, during handover execution, the buffered data at the source LPS PDCP has to be forwarded to the target LPS PDCP. However, the difference in active concatenation factor at both LPSs leads to different problems in different scenario. In normal handover, it leads to either loss of SDUs or loss of order of SDUs depending on concatenation factor values at source and target gNBs. In DAPS handover, it leads to a loss of SN synchronization between both LPS gNBs.

[0131] Problem 4:Loss of NR PDUs (multi radio dual connectivity (MRDC)): MRDC enables different RATs to use split bearer and packet duplication for improving throughput and duplication to improve reliability. In the case of the split bearer, a packet stream is split across two bearers and forwarded to lower layers. In case of duplication, the same packet is forwarded to both the entities in lower layers. To enable both of the features, PDCP of master node relies on RLC of both master and secondary node. Particularly, in a scenario, NR is configured with LPS for MRDC and if a split bearer is configured with NR as master node and LPS as secondary node, then NR PDCP PDU splits the packet stream and forwards the PDUs to both NR RLC and LPS RLC, i.e., PDCP of master node forwards PDUs to lower layer of both master as well as secondary node. When the NR is master node and the LPS is secondary node, the NR PDCP forwards NR PDUs to both NR Radio Link Control (RLC) and LPS RLC. However, the LPS RLC does not support recovery of packets leading to loss of PDUs / loss of SDUs. Thus, a new method is required to allow lossless transfer of PDUs in case of NR-LPS MRDC.

[0132] However, as described above, conventional techniques do not provide methods for performing handover, particularly, i (inter / intra)-RAT handover, in different communication environments. Thus, it is desired to address at least the above-mentioned shortcomings.

[0133]

[0134] Figure 9illustrates an example block diagram of a communication environment 900 depicting a configuration of a lean protocol stack base station 910, a non-lean protocol stack (LPS) base station 920, and a user equipment 930, in accordance with an embodiment of the disclosure. The LPS base station 910, the non-LPS base station 920 may be configured to communicate with the UE 930, as depicted in Figure 9. The configurations as disclosed in Figure 9 may be understood as parts of the configuration of the LPS base station 910, the non-LPS base station 920, and the UE 930. Hereinafter, it is understood that terms including "unit" or "module" at the end may refer to the unit for processing at least one function or operation and may be implemented in hardware, software, or a combination of hardware and software.

[0135] In an embodiment, the communication environment may be a 5thGeneration (5G) New Radio (NR)- 6thGeneration (6G) (LPS) communication environment.

[0136] In an embodiment, the UE 930 may be a mobile telephone, a smartphone, a tablet, a personal computer, a Personal Digital Assistant (PDA), a data terminal, etc.

[0137] It is appreciated that although the LPS base station 910, the non-LPS base station 920 are depicted in Figure 9, the communication environment 900 may include additional base station as well, and the details explained in the disclosure for the LPS base station 910, the non-LPS base station 920 are equally applicable for additional base station as well. Further, the communication environment 900 may include additional UEs (not shown) and details in the disclosure explained with reference to the UE 930 are equally applicable for the additional UEs as well.

[0138] Referring to Figure 9, the LPS base station 910 may include an apparatus 911 comprising one or more processor(s) 912 (also, referred to as the processor 912), a storage unit (e.g., memory 914), and a communication unit 916 (e.g., communicator or communication interface). The LPS base station 910 may perform functions for transmitting and receiving a plurality of packets. The memory 914 may include executable instructions that, when executed by the processor, cause the apparatus 911 to perform the steps as described with reference to Figures 10a to 11c.

[0139] As an example, the one or a plurality of processors 912 may be a general-purpose processor, such as a central processing unit (CPU), an application processor (AP), or the like, a graphics-only processing unit such as a graphics processing unit (GPU), a visual processing unit (VPU), and / or an AI-dedicated processor such as a neural processing unit (NPU). In one embodiment, the processor 912 may include an artificial intelligence (AI) engine (AIE). In one embodiment, the processor 912 may include at least one data processor for executing processes in a virtual storage area network. The processor 912 may include specialized processing units such as, integrated system (bus) controllers, memory management control units, floating point units, graphics processing units, digital signal processing units, etc. In one embodiment, the processor 204 may include the central processing unit (CPU). The processor 912 may be one or more general processors, digital signal processors, application-specific integrated circuits, field-programmable gate arrays, servers, networks, digital circuits, analog circuits, combinations thereof, or other now-known or later developed devices for analyzing and processing data. The processor 912 may execute a software program, such as code generated manually (i.e., programmed) to perform the desired operation.

[0140] In some embodiments, the memory 914 may be in communication with the processor 912. The memory 914 may be configured to store data, and instructions executable by the processor 912. In one embodiment, the memory 912 may be provided within the apparatus 911. In another embodiment, the memory 914 may communicate with the processor 912 via a bus within the apparatus 911. In yet another embodiment, the memory 914 may be located remotely from the processor 912 and may be in communication with the processor 912 via a network. The memory 914 may include, but is not limited to, a non-transitory computer-readable storage media, such as various types of volatile and non-volatile storage media including, but not limited to, random access memory, read-only memory, programmable read-only memory, electrically programmable read-only memory, electrically erasable read-only memory, flash memory, magnetic tape or disk, optical media and the like.

[0141] In some embodiments, the apparatus 911 may be implemented as dedicated hardware units. In some embodiments, the apparatus 911 may be implemented in the form of virtualized software units in hardware or cloud environments.

[0142] The non-LPS base station 920 may also include an apparatus 921 comprising one or more processor(s) 922 (also, referred to as the processor 922), a storage unit (e.g., memory 924), and a communication unit 926 (e.g., communicator or communication interface). The functionalities and features of the processor 922, communication unit 926, and memory 924 may be similar to those of the processor 912, communication unit 916, and memory 914, respectively of the LPS base station 910. Therefore, a detailed explanation of the same is omitted herein for the sake of brevity of the disclosure.

[0143] Further, the UE 930 may also include an apparatus 931 comprising one or more processor(s) 932 (also, referred to as processor 932), a storage unit (e.g., memory 934), and a communication unit 936 (e.g., communicator or communication interface). The functionalities and features of the processor 932, communication unit 936, and memory 934 may be similar to those of the processor 912, communication unit 916, and memory 914, respectively of the LPS base station. Therefore, a detailed explanation of the same is omitted herein for the sake of brevity of the disclosure.

[0144] Further, the processors 912, 922, and 932 may be configured to perform specific operations in the subsequent paragraphs. The subsequent paragraphs explain the operations of the processors 912, 922, and 932 for solving problems 1 to 2D as explained in the background section of the disclosure.

[0145] Figure 10aillustrates a plurality of downlink user data (DUD) packets1001a쪋1001n,in accordance with an embodiment of the disclosure.Figure 10billustrates a header 1002 of each of the plurality of DUD packets1001a쪋1001n, in accordance with an embodiment of the disclosure.

[0146] In an embodiment, the processor 922 of the non-LPS base station 920 may be configured to generate the plurality of downlink user data (DUD) packets 1001a쪋1001n. In an embodiment, the non-LPS base station 920 may be a source base station, without departing from the scope of the disclosure. Each of the plurality of DUD packets 1001a쪋1001n may include a service data unit (SDU) packet 1008. In an embodiment, the SDU packet 1008 may be part of a payload 1006 of the corresponding DUD packet. Further, each SDU packet may include at least one flag 1004. In an embodiment, the at least one flag 1004 may be also termed as a special SDU flag as shown in Figure 10b. The at least one flag 1004 may be provided in a header 1002 of the plurality of DUD packets 1001a쪋1001n.

[0147] In an embodiment, each SDU packet may include the at least one flag 1004 based on at least one of a dual active protocol stack (DAPS) handover scenario or at least one of an unacknowledged SDU packet from among each SDU packet.

[0148] In an embodiment, the processor 922 may be configured to transmit each SDU packet and corresponding sequence number (SN) to the LPS base station 910 for performing the i-RAT handover at the non-LPS base station 920. In an embodiment, the non-LPS base station 920 may be the NR base station.

[0149] In an embodiment, at the LPS base station 910, the processor 912 may be configured to receive the plurality of DUD packets 1001a쪋1001n. In an embodiment, the LPS base station 910 may be a target base station, without departing from the scope of the disclosure. In an embodiment, the processor 912 may be configured to receive the plurality of DUD packets 1001a쪋1001n while performing dual active protocol stands (DAPS) handover between the LPS base station 910 and the non-LPS base station 920 or in a normal handover scenario. At least one unacknowledged packet data unit (PDU) may be present at the non-LPS base station 920.

[0150] Each of the plurality of DUD packets 1001a쪋1001n may include the service data unit (SDU) packet 1008 and a corresponding sequence number (SN), from the non-LPS base station 920. Particularly, the processor 912 may receive one SDU packet per SN, without departing from the scope of the disclosure. In an embodiment, the SDU packet 1008 may be a part of the payload 1006 of the corresponding DUD packet. In an embodiment, the non-LPS base station 920 may be the new radio (NR) base station. Each SDU packet may include at least one flag 1004.

[0151] In an embodiment, the at least one flag 1004 may be provided in the header 1002 of the plurality of DUD packets 1001a쪋1001n. The processor 912 may be configured to process each SDU packet based on the at least one flag 1004. In an embodiment, the at least one flag 1004 may indicate that the corresponding SDU packet is to be transmitted with the corresponding SN. Further, to process each SDU packet 1008, the processor 912 may be configured to chain each SDU packet as per a concatenation factor 1.

[0152] In an embodiment, the processor 912 may be configured to identify a value of the at least one flag 1004 corresponding to each SDU packet. Further, the processor 912 may be configured to determine that the corresponding SDU packet corresponds to a handover packet, in response to identifying the value of the at least one flag 1004 as true.

[0153] The processor 912 may be configured to perform the i-RAT handover based on the processed SDU packets. Here, a receiving window of the UE 930 may receive the same SDU packet corresponding to the SN from both the LPS base station 910 and the non-LPS base station 920 in the DAPS handover.

[0154] The operation as disclosed above resolves the problem 1 to 1C as mentioned in the background section of the disclosure during the handover from the non-LPS base station 920 to the LPS base station 910. Particularly, the disclosed operation resolves the loss of SN synchronization as both LPS base station 910 and the non-LPS base station 920 assign SNs to each SDU at the same rate. Further, this operation also resolves the problem associated with the same SN carrying different SDU and loss of SN synchronization in the case of the DAPS handover and in the normal handover. Further, this operation resolves the problem associated with a mismatch in packets received by the UE as the receiving window of the UE 930 may receive the same SDU packet corresponding to the SN from both the LPS base station 910 and the non-LPS base station 920 in the DAPS handover, thus, eliminating the loss of data packet and maintains in-sequence delivery. This operation also eliminates the problem of loss of order of the SDU packet 1008.

[0155] Figures 11a-11cillustrate figures associated with an operation performed by the processors 912, 922, and932 for performing the i-RAT handover from the LPS base station 910 to the non-LPS base station 920 and the UE 930, without departing from the scope of the disclosure.Figure 11aillustrates a plurality of SDU packets 1008a, 1008b in the DUD packet 1001, in accordance with another embodiment of the disclosure.Figure 11billustrates a header 1002 of the DUD packet 1001, in accordance with another embodiment of the disclosure.Figure 11cillustrates a header 1108 of a Packet Data Convergence Protocol (PDCP) of the non-LPS base station 920, in accordance with another embodiment of the disclosure.

[0156] In another embodiment, Figures 11a to 11cmay be explained in conjunction withFigure 9.

[0157] In another embodiment, the processor 912 of the LPS base station 910 may be configured to generate a downlink user data (DUD) packet 1001. In another embodiment, the LPS base station 910 may be the source base station, without departing from the scope of the disclosure. Further, the DUD packet 1001 may include the plurality of SDU packets 1008a, 1008b, and corresponding sequence number. Further, at least one of the plurality of SDU packets 1008a, 1008b may include at least one flag and a length indicator flag 1104. In another embodiment, the at least one flag may be provided in the header 1002 of the DUD packet 1001. In the illustrated embodiment, a first SDU packet 1008a, from the plurality of SDU packets 1008a, 1008b, may include a flag 1004a, and a second SDU packet 1008b, from the plurality of SDU packets 1008a, 1008b, may include a flag 1004b, without departing from the scope of the disclosure.

[0158] In another embodiment, the length indicator (LI) field flag may indicate a length of the at least one of the plurality of SDU packets 1008a, 1008b packages inside a packet data unit of the LPS base station 910. In the illustrated embodiment, the LI filed flag 1104 may be indicated by LI exist flag, without departing from the scope of the disclosure. The LI filed flag 1104 may be configured to inform the PDCP of the non-LPS base station 920 about the individual length of the plurality of SDU packets 1008a, 1008b, packaged inside the PDU of the LPS base station 910.

[0159] The processor 912 may be configured to store the plurality of SDU packets 1008a, 1008b with the corresponding LI field flags in the header 1002 of the DUD packet 1001. Further, the processor 912 may be configured to chain the at least one of the plurality of SDU packets 1008a, 1008b as per the configured concatenation factor at the LPS base station 910. Further, in case of the DAPS handover, the processor 912 may be configured to update the concatenation factor as 1 to avoid error in SN synchronization between the LPS base station 910 and the non-LPS base station 920, without departing from the scope of the disclosure.

[0160] In another embodiment, the processor 912 may be configured to transmit the plurality of SDU packets 1008a, 1008b, and the corresponding sequence numbers (SN) to the non-LPS base station 920 for performing the i-RAT handover at the LPS base station 910.

[0161] Further, at the non-LPS base station 920, the processor 922 at the non-LPS base station 920 may be configured to generate the header 1108 of the Packet Data Convergence Protocol (PDCP), as shown in Figure 11c, of the non-LPS base station 920. In another embodiment, the non-LPS base station 920 may be the target base station, without departing from the scope of the disclosure. In another embodiment, the header 1108 may include an E-Bit 1106. The E-bit 1106 indicates a presence of the length indicator (LI) field flag 1104 in at least one of the plurality of SDU packets 1008a,1008b of the DUD packet 1001 received from the LPS base station 910.

[0162] In another embodiment, the processor 922 may be configured to mark the at least one of the plurality of SDU packets 1008a, 1008b received from the LPS base station 910 as a special SDU packet. The processor 922 may be configured to mark the at least one of the plurality of SDU packets 1008a, 1008b based on at least one flag provided in the header 1002 of the DUD packet 1001.

[0163] In another embodiment, the processor 922 may be configured to transmit the marked at least one of the plurality of SDU packets 1008a, 1008b, to the UE 930 for performing the i-RAT handover at the non-LPS base station 920. In such an embodiment, the processor 922 may be configured to identify a value of the at least one flag corresponding to the marked at least one of the plurality of SDU packets 1008a, 1008b. In another embodiment, the processor 922 may receive the marked at least one of the plurality of SDU packets 1008a, 1008b over Xn interface. Further, the processor 922 may be configured to assign a sequence number (SN) to the marked at least one of the plurality of SDU packets 1008a, 1008b, when the value of the at least one flag is true.

[0164] The processor 922 may be configured to identify the value of the E-Bit 1106, after assigning the SN. The processor is configured to transmit the marked at least one of the plurality of SDU packets 1008a, 1008b, to the UE 930, when the identified value of the E-Bit 1106 may be true. The marked at least one of the plurality of SDU packets 1008a, 1008b may be a distinct at least one of the plurality of SDU packets 1008a, 1008b which may require a special processing before delivering the plurality of SDU packets to an upper layer. Further, the required special processing may be shared to the UE 930 via RRC signalling, without departing from the scope of the disclosure. Additionally, the presence of the E-Bit 1106 may assists the PDCP of the non-LPS base station 920 to create a packet data unit having the plurality of SDUs 1008a, 1008b, etc.

[0165] In another embodiment, the processor 922 may be configured to receive the at least one of the plurality of SDU packets 1008a, 1008b, while performing the Dual Active Protocol Stands (DAPS) handover between the LPS base station and the non-LPS base station, or in the normal handover. Further, at least one unacknowledged packet data unit (PDU) may be present at the LPS base station 910.

[0166] In another embodiment, at the UE 930, the processor 932 may be configured to receive at least one of the plurality of SDU packets 1008a, 1008b from the non-LPS base station 920. The at least one of the plurality of SDU packets 1008a, 1008b may include the at least one flag. Further, the at least one of the plurality of SDU packets 1008a, 1008b may be marked as a special at least one of the plurality of SDU packets, when a status of the E-Bit 1106 in the header 1108 of the PDCP of the non-LPS base station 920, may be true. The processor 932 may be configured to unchain the marked at least one of the plurality of SDU packets 1008a, 1008b, for performing the i-RAT handover at the UE 930, when the status of E-Bit 1106 may be true. Additionally, if another SDU packet from the plurality of SDU packets 1008a, 1008b may not be marked as special, then in that case, the processor 932 may not be able to unchain the another SDU packet.

[0167] The operation as disclosed above solves the problems 2 to 2D as mentioned in the background section of the disclosure while performing the handover from the LPS base station 910 to the non-LPS base station 920. The introduction of LI field flag 1104, the E-Bit 1106 along with the at least one flag ensures the simultaneous packet handling at the LPS base station 910 and the non-LPS base station 920, thus reducing the loss of SN synchronization problem, discarding of packets, and mismatching in the packets. Additionally, the operation as disclosed also reduces the loss of the plurality of SDU packets 1008a, 1008b, avoids duplication of SDU at the receiver window, and maintains the order of each SDU and in-sequence delivery.

[0168] Figure 12illustrates an example block diagram of a communication environment 1200 depicting a configuration of a source lean protocol stack (LPS) base station 1210, a target lean protocol stack (LPS) base station 1220, and a user equipment 930, in accordance with an embodiment of the disclosure. The source LPS base station 1210, the target LPS base station 1220 may be configured to communicate with the UE 930, as depicted in Figure 12. The configurations as disclosed in Figure 12 may be understood as parts of the configuration of the source LPS base station 1210, the target LPS base station 1220, and the UE 930. Hereinafter, it is understood that terms including "unit" or "module" at the end may refer to the unit for processing at least one function or operation and may be implemented in hardware, software, or a combination of hardware and software.

[0169] In an embodiment, the communication environment 1200 may be a 6thGeneration (6G) LPS- 6thGeneration (6G) LPS communication environment.

[0170] In an embodiment, the UE 930 may be a mobile telephone, a smartphone, a tablet, a personal computer, a Personal Digital Assistant (PDA), a data terminal, etc.

[0171] It is appreciated that although the source LPS base station 1210, the target LPS base station 1220 are depicted in Figure 12, the communication environment 1200 may include additional base station as well, and the details explained in the disclosure for the source LPS base station 1210, the target LPS base station 1220 are equally applicable for additional base station as well. Further, the communication environment 1200 may include additional UEs (not shown) and details in the disclosure explained with reference to the UE 930 are equally applicable for the additional UEs as well.

[0172] Referring to Figure 12, the source LPS base station 1210 may include an apparatus 1211 comprising one or more processor(s) 1212 (also, referred to as the processor 1212), a storage unit (e.g., memory 1214), and a communication unit 1216 (e.g., communicator or communication interface). The source LPS base station 1210 may perform functions for transmitting and receiving a plurality of packets. The memory 1214 may include executable instructions that, when executed by the processor, cause the apparatus 1211 to perform the steps as described with reference to Figures 13a to 14c. The functionalities and features of the processor 1212, communication unit 1216, and memory 1214 may be similar to those of the processor 912, communication unit 916, and memory 914, respectively of the LPS base station 910. Therefore, a detailed explanation of the same is omitted herein for the sake of brevity of the disclosure.

[0173] The target LPS base station 1220 may also include an apparatus 1221 comprising one or more processor(s) 1222 (also, referred to as the processor 1222), a storage unit (e.g., memory 1224), and a communication unit 1226 (e.g., communicator or communication interface). The functionalities and features of the processor 1222, communication unit 1226, and memory 1224 may be similar to those of the processor 922, communication unit 926, and memory 924, respectively of the non-base station 910. Therefore, a detailed explanation of the same is omitted herein for the sake of brevity of the disclosure.

[0174] Further, the processors 1212, 1222, and 932, may be configured to perform specific operations in the subsequent paragraphs. The subsequent paragraphs explain the operations of the processors 1212, 1222, and 932 for solving problem 3 as explained in the background section of the disclosure.

[0175] Figures 13a-13billustratesan operation performed by the processors 1212, 1222, and 1232 to perform intra-radio technology (i-RAT) handover between the source LPS base station 1220 and the target LPS base station 1210 in the DAPS handover, in accordance with yet another embodiment of the disclosure.

[0176] Referring to Figures 13a and 13b, the processor 1212 of the source LPS base station (source LPS gNB having a concatenation factor as a Source Concatenation equals to A) 1210 may be configured to transmit a handover request message to the target LPS base station (target LPS gNB having a concatenation factor as a Target Concatenation equals to B) 1220. The handover request message may contain HandoverConcatCount = SourceConcat representing source gNB 1210 concatenation factor. Further, if the SourceConcat may be lesser than the TargetConcat, then the TargetConcat may be equal to SourceConcat i.e. A. Additionally, if the SourceConcat may be greater than the TargetConcat, then the TargetConcat may remain same as B. Further, the handover request message may include an information element (IE). The IE indicates a predetermined concatenated count of the plurality of SDUs packets of the source LPS base station 1210.

[0177] The processor 1212 may be configured to receive a handover request acknowledge message from the target LPS base station 1220. The handover request acknowledge may contain FinalHandoverConcatCount = targetConcat. The handover request acknowledge message may include an IE. The IE indicates a final concatenated count of the plurality of SDU packets for performing the intra-RAT handover at the source LPS base station 1210. Further, after receiving the handover request acknowledge message, the source LPS base station 1210 may change the concatenation factor same as the value of the FinalHandoverConcatCount.

[0178] In another embodiment, the final concatenated count of the plurality of SDU packets may be smaller than at least one of the predetermined concatenated count of a plurality of SDU packets of the source base station 1210 and a predetermined concatenated count of a plurality of SDU packets of the target LPS base station 1220.

[0179] Further, the processor 1212 may be configured to the handover request acknowledge message from the target LPS base station 1220, while performing the dual active protocol stands (DAPS) handover between the source LPS base station 1210 and the target LPS base station 1220 or in the normal handover scenario. Further, at least one unacknowledged packet data unit (PDU) may be present at the target-LPS base station 1220.

[0180] Further, as the same concatenation factor value may be operational at the source LPS base station 1210 and the target LPS base station 1212, thus this reduces the problem associated with the loss of SN synchronization. Additionally, upon successful negotiation between the source LPS base station 1210 and the target LPS base station 1212, both base stations may independently package the same payload for the corresponding SN. Thus, the problem associated with the loss of SN synchronization gets resolved for the DAPS handover as both the base station assigns SN at the same rate to the plurality of SDU packets. Further, this also retain the plurality of SDU packets.

[0181] Figures 14a-14cillustrate operations performed by the processors 1212, 1222, and932 for performing the i(intra)-RAT handover from the source LPS base station 1210 to the target LPS base station 1220 and the UE 930, without departing from the scope of the disclosure.Figure 14aillustrates a plurality of SDU packets 1208a, 1208b in a DUD packet 1201, in accordance with another embodiment of the disclosure.Figure 14billustrates a header 1002 of each of the plurality of DUD packet 1201, in accordance with another embodiment of the disclosure.Figure 14cillustrates a header 1408 of a Packet Data Convergence Protocol (PDCP) of the target LPS base station 1220, in accordance with another embodiment of the disclosure.

[0182] In another embodiment, Figures 14a to 14cmay be explained in conjunction withFigure 12.

[0183] In another embodiment, the processor 1212 of the source LPS base station 1210 may be configured to generate the downlink user data (DUD) packet 1201. In another embodiment, the source LPS base station 1210 may be the source base station, without departing from the scope of the disclosure. Further, the DUD packet 1201 may include the plurality of SDU packets 1208a, 1208b, and corresponding sequence number. Further, at least one of the plurality of SDU packets 1208a, 1208b may include at least one flag and a length indicator field flag 1404. In another embodiment, the at least one flag may be provided in a header 1202 of the DUD packet 1201. In the illustrated embodiment, a first SDU packet 1208a, from the plurality of SDU packets 1208a, 1208b, may include a flag 1204a, and a second SDU packet 1208b, from the plurality of SDU packets 1208a, 1208b, may include a flag 1204b, without departing from the scope of the disclosure.

[0184] In another embodiment, the length indicator (LI) field flag 1404 may indicate a length of the at least one of the plurality of SDU packets 1208a, 1208b packages inside a packet data unit of the source LPS base station 1210. In the illustrated embodiment, the LI field flag 1404 indicates by LI exist flag, without departing from the scope of the disclosure. The LI field flag 1404 may be configured to inform the PDCP of the target LPS base station 1220 about the individual length of the plurality of SDU packets 1208a, 1208b, packaged inside the PDU of the source LPS base station 1210.

[0185] The processor 1212 may be configured to store the plurality of SDU packets 1208a, 1208b with the corresponding LI field flags in the header 1202 of the DUD packet 1201. Further, the processor 1212 may be configured to chain the at least one of the plurality of SDU packets 1208a, 1208b as per the mutually agreed concatenation factor. Further, in case of the DAPS handover, the processor 1212 may be configured to update concatenation factor as 1 to avoid error in SN synchronization between the source LPS base station 1210 and the target LPS base station 1220, without departing from the scope of the disclosure.

[0186] In another embodiment, the processor 1212 may be configured to transmit the plurality of SDU packets 1208a, 1208b and the corresponding sequence numbers (SN) to the target LPS base station 1220 for performing the i-RAT handover at the source LPS base station 1210.

[0187] Further, at the target LPS base station 1220, the processor 1222 at the target LPS base station 1220 may be configured to generate a header 1408 of the Packet Data Convergence Protocol (PDCP), as shown in Figure 14c, of the target LPS base station 1220. In another embodiment, the target LPS base station 1220 may be the target base station, without departing from the scope of the disclosure. In another embodiment, the header 1408 may include an E-Bit 1406. The E-bit 1406 indicates a presence of a length indicator (LI) field flag 1404 in at least one of the plurality of SDU packets 1208a,1208b of the DUD packet 1201 received from the source LPS base station 1210.

[0188] In another embodiment, the processor 1222 may be configured to mark the at least one of the plurality of SDU packets 1208a, 1208b received from the source LPS base station 1210 as a special SDU packet. The processor 922 may be configured to mark the at least one of the plurality of SDU packets 1208a, 1208b based on at least one flag provided in the header 1202 of the DUD packet 1201.

[0189] In another embodiment, the processor 1222 may be configured to transmit the marked at least one of the plurality of SDU packets 1208a, 1208b, to the UE 930 for performing the i-RAT handover at the target LPS base station 1220. In such an embodiment, the processor 1222 may be configured to identify a value of the at least one flag corresponding to the marked at least one of the plurality of SDU packets 1208a, 1208b. Further, the processor 1222 may be configured to assign a sequence number (SN) to the marked at least one of the plurality of SDU packets 1208a, 1208b, when the value of the at least one flag is true.

[0190] In another embodiment, the processor 1222 may receive the marked at least one of the plurality of SDU packets 1208a, 1208b over Xn interface. The processor 1222 may be configured to identify the value of the E-Bit 1406, after assigning the SN. The processor 1222 may be configured to transmit the marked at least one of the plurality of SDU packets 1208a, 1208b, to the UE 930, when the identified value of the E-Bit 1406 may be true. The marked at least one of the plurality of SDU packets 1208a, 1208b may be a distinct at least one of the plurality of SDU packets 1208a, 1208b which may require a special processing before delivering the plurality of SDU packets to a upper layer. Further, the required special processing may be shared to the UE 930 via RRC signalling, without departing from the scope of the disclosure. Additionally, the presence of the E-Bit 1406 may assist the PDCP of the target LPS base station 1220 to create a packet data unit having the plurality of SDUs 1208a, 1208b, etc.

[0191] In another embodiment, the processor 1222 may be configured to receive the at least one of the plurality of SDU packets 1208a, 1208b, while performing the Dual Active Protocol Stands (DAPS) handover between the source LPS base station 1210 and the target LPS base station 1220, or in the normal handover. Further, at least one unacknowledged packet data unit (PDU) may be present at the source LPS base station 1210.

[0192] In another embodiment, at the UE 930, the processor 932 may be configured to receive at least one of the plurality of SDU packets 1208a, 1208b from the target LPS base station 1220. The at least one of the plurality of SDU packets 1208a, 1208b may include the at least one flag. Further, the at least one of the plurality of SDU packets 1208a, 1208b may be marked as a special at least one of the plurality of SDU packets, when a status of the E-Bit 1406 in the header 1408 of the PDCP of the target LPS base station 1220, may be true. The processor 932 may be configured to unchain the marked at least one of the plurality of SDU packets 1208a, 1208b, for performing the i-RAT handover at the UE 930, when the status of the E-Bit 1406 may be true. Additionally, if another SDU packet from the plurality of SDU packets 1008a, 1008b may not be marked as special, then in that case, the processor 932 may not be able to unchain the another SDU packet. The operation as disclosed ensures receipt of the plurality of SDU packets 1208a, 1208b in the same manner as generated at the source LPS base station 1210, thus reducing loss of order of the SDU packet and also, reducing loss of SN synchronization.

[0193] Figure 15illustrates an operation performed for establishing a multi radio dual connectivity between the LPS base station 910 and the non-LPS base station 920, in accordance with yet another embodiment of the disclosure.

[0194] In another embodiment, the processor 912 may be configured to receive a plurality of SDU packets 1502 and a corresponding sequence number, from a PDCP of the non-LPS base station 920. Particularly, the processor 912 receives by a PDCP of the LPS base station 910. Herein, the PDCP of the LPS base station 910 may be configured to interface with PDCP of the non-LPS base station 920 instead of interfacing of the PDCP of the non-LPS base station 920 with RLC of the LPS base station 910. The processor 912 may be configured to concatenate the received plurality of SDU packets 1502. The processor 912 may be configured to assign SN, independently, to each of the concatenated receiving plurality of SDU packets 1502. The processor 912 may be configured to transmit each of the concatenated received plurality of SDU packets 1502 with the assigned SN to the UE 930. Particularly, the processor 912 with the assistance of DRB may be configured to transmit each of the concatenated received plurality of SDU packets 1502. The processor 912 may transmit each of the concatenated received plurality of SDU packets 1502 to the UE 930 such that the UE 930 unchains the concatenated received plurality of SDU packets 1502 and forward the unchained concatenated received plurality of SDU packets 1502 to the PDCP of the non-LPS base station 920.

[0195] Further, t-concat and t-reassembly may be configured lower than t-reordering at the PDCP of the non-LPS base station 920, thus ensuring the efficient transferring of the plurality of SDU packets from the LPS base station 910 to the non-LPS base station 920 before expiry of the timer of each of the PDCP.

[0196] The operation as disclosed above reduces the loss of the plurality of SDU packets 1502 and supports recovery of packets.

[0197] Figure 16illustrates a method 1600 performed by the apparatus 911 for performing the i-RAT handover in the LPS base station 910, in accordance with an embodiment of the disclosure.

[0198] The method 1600 can be performed by programmed computing devices, for example, based on instructions retrieved from non-transitory computer-readable media. The computer-readable media can include machine-executable or computer-executable instructions to perform all or portions of the described method. The computer-readable media may be, for example, digital memories, magnetic storage media, such as magnetic disks and magnetic tapes, hard drives, or optically readable data storage media.

[0199] The method 1600 includes a series of operations shown at step 1602 through step 1606 of Figure 16. The method 1600 may be performed by the apparatus 911 in conjunction with the processor 912, the details of which are explained in conjunction with Figures 10a and 10b, and the same are not repeated here for the sake of brevity in the disclosure. The method 1600 begins at step 1602.

[0200] At step 1602, receiving, by the LPS base station 910, the plurality of downlink user data (DUD) packets 1001a, 1001b, 쪋1001n. The LPS base station 910 may receive the plurality of DUD packets 1001a, 1001b, 쪋1001n while performing dual active protocol stands (DAPS) handover between the LPS base station 910 and the non-LPS base station 920 or in the normal handover scenario. At least one unacknowledged packet data unit (PDU) may be present at the non-LPS base station 920.

[0201] Each of the plurality of DUD packet 1001a, 1001b, 쪋1001n may include the service data unit (SDU) packet 1008 and a corresponding sequence number (SN), from the non-LPS base station 920. Each SDU packet may include the at least one flag 1004. The at least one flag 1004 may be provided in the header 1002 of the plurality of DUD packets 1001a, 1001b, 쪋1001n. The at least one flag 1004 may indicates that the corresponding SDU packet is to be transmitted with the corresponding SN. Further, the non-LPS base station 920 may include the new radio (NR) base station.

[0202] At step 1604, the method 1600 includes processing, by the LPS base station 910, each SDU packet based on the at least one flag 1004. The method 1600 includes chaining, by the LPS base station 910, each SDU packet as per the concatenation factor 1. Further, the SDU packet may be the part of the payload 1006 of the corresponding DUD packet.

[0203] The method 1600 include identifying by the LPS base station 910, the value of the at least one flag corresponding to each SDU packet. The method 1600 includes determining that the corresponding SDU packet corresponds to the handover SDU packet.

[0204] At step 1606, the method 1600 includes performing, by the LPS base station 910, the i-RAT handover based on the processed SDU packets.

[0205] Figure 17illustrates a method 1700 performed by the apparatus 921 for performing the i-RAT handover by the non-LPS base station 920, in accordance with an embodiment of the disclosure.

[0206] The method 1700 can be performed by programmed computing devices, for example, based on instructions retrieved from non-transitory computer-readable media. The computer-readable media can include machine-executable or computer-executable instructions to perform all or portions of the described method. The computer-readable media may be, for example, digital memories, magnetic storage media, such as magnetic disks and magnetic tapes, hard drives, or optically readable data storage media.

[0207] The method 1700 includes a series of operations shown at step 1702 through step 1702 of Figure 17. The method 1700 may be performed by the apparatus 921 in conjunction with the processor 922, the details of which are explained in conjunction with Figures 10a and 10b, and the same are not repeated here for the sake of brevity in the disclosure. The method 1700 begins at step 1702.

[0208] At step 1702, the method 1700 includes generating, by the non-LPS base station 920, the plurality of downlink user data (DUD) packets 1001a, 1001b, 쪋1001n. Each of the plurality of DUD packets 1001a, 1001b, 쪋1001n may include the SDU packet 1008. Each SDU packet may include the at least one flag 1004. The at least one flag 1004 may be provided in the header 1002 of the plurality of DUD packets 1001a, 1001b, 쪋1001n. The non-LPS base station 920 may be the NR base station. Each SDU packet may include the at least one flag 1004 based on at least one of the dual active protocol stack (DAPS) handover scenario or at least one of the unacknowledged SDU packet from among each SDU packet. Further, the SDU packet may be the part of the payload 1006 of corresponding DUD packet.

[0209] At step 1704, the method 1700 includes transmitting, by the non-LPS base station 920, each SDU packet and corresponding sequence numbers (SN) to the LPS base station 910 for performing the i-RAT handover by the non-LPS base station 920.

[0210] Figure 18illustrates a method 1800 performed by the processor 932 for performing the i-RAT handover in the UE 930, in accordance with another embodiment of the disclosure.

[0211] The method 1800 can be performed by programmed computing devices, for example, based on instructions retrieved from non-transitory computer-readable media. The computer-readable media can include machine-executable or computer-executable instructions to perform all or portions of the described method. The computer-readable media may be, for example, digital memories, magnetic storage media, such as magnetic disks and magnetic tapes, hard drives, or optically readable data storage media.

[0212] The method 1800 includes a series of operations shown at step 1802 through step 1804 of Figure 18. The 1800 method may be performed in the UE 930 in conjunction with the processor 932, the details of which are explained in conjunction with Figures 11a to 11c and the same are not repeated here for the sake of brevity in the disclosure. The method 1800 begins at step 1802.

[0213] At step 1802, the method 1800 includes receiving at least one of the plurality of SDU packets 1008a, 1008b from the non-LPS base station 920. The at least one of the plurality of SDU packets 1008a, 1008b may include the at least one flag and is marked as a special at least one of the plurality of SDU packets 1008a, 1008b, when the status of E-Bit 1106, in the header 1108 of the packet data convergence protocol (PDCP) of the non- lean protocol stack (LPS) base station 920, is true.

[0214] At step 1804, the 1800 method includes unchaining the marked at least one of the plurality of SDU packets 1008a, 1008b, for performing inter-radio access technology (i-RAT) handover in the user equipment 930, when the status of the E-Bit 1106 is true.

[0215] Figure 19illustrates a method 1900 performed by the processor 922 for performing the i-RAT handover by the non-LPS base station 920, in accordance with another embodiment of the disclosure.

[0216] The method 1900 can be performed by programmed computing devices, for example, based on instructions retrieved from non-transitory computer-readable media. The computer-readable media can include machine-executable or computer-executable instructions to perform all or portions of the described method. The computer-readable media may be, for example, digital memories, magnetic storage media, such as magnetic disks and magnetic tapes, hard drives, or optically readable data storage media.

[0217] The method 1900 includes a series of operations shown at step 1902 through step 1906 of Figure 19. The 1900 method may be performed by the non-LPS base station 920 in conjunction with the processor 922, the details of which are explained in conjunction with Figures 11a to 11c and the same are not repeated here for the sake of brevity in the disclosure. The method 1900 begins at step 1902.

[0218] At step 1902, the method 1900 includes generating, by the non-LPS base station 920, the header 1108 of the packet data convergence protocol (PDCP) of the non-LPS base station 920. The header 1108 may include the E-Bit 1106 indicating the presence of the length indicator (LI) field flag 1104 in at least one of the plurality of SDU packets 1008a, 1008b of the downlink user data (DUD) packet 1001 received from the LPS base station 910.

[0219] At step 1904, the method 1900 includes marking, by the non-LPS base station 920, the at least one of the plurality of SDU packets 1008a, 1008b received from the LPS base station 910, as the special SDU packet based the at least one flag provided in the header 1002 of the DUD packet 1001.

[0220] At step 1906, the method 1900 includes transmitting, the marked at least one of the plurality of SDU packets 1008a, 1008b, to the user equipment 930 for performing the inter-radio access technology (i-RAT) handover by the non- LPS base station 920.

[0221] The method 1900 includes identifying, by the non-LPS base station 920, the value of the at least one flag corresponding to the marked at least one of the plurality of SDU packets 1008a, 1008b. The method 1900 includes assigning the sequence number (SN) to the marked at least one of the plurality of SDU packets 1008a, 1008b, when the value of the at least one flag is true. The method 1900 identifying, by the non-LPS base station 920, the value of the E-Bit 1106, after assigning the SN. The method 1900 includes transmitting the marked at least one of the plurality of SDU packets 1008a, 1008b, to the user equipment 930, when the identified value of the E-Bit 1106 is true.

[0222] The method 1900 includes the non-LPS base station 920 receives the at least one of the plurality of SDU packets 1008a, 1008b, while performing the dual active protocol stands (DAPS) handover between the LPS base station 910 and the non-LPS base station 920 or in the normal handover scenario. At least one unacknowledged packet data unit (PDU) is present at the LPS base station 910.

[0223] Figure 20illustrates a method 2000 performed by the processor 912 for performing the i-RAT handover by the LPS base station 910, in accordance with another embodiment of the disclosure.

[0224] The method 2000 can be performed by programmed computing devices, for example, based on instructions retrieved from non-transitory computer-readable media. The computer-readable media can include machine-executable or computer-executable instructions to perform all or portions of the described method. The computer-readable media may be, for example, digital memories, magnetic storage media, such as magnetic disks and magnetic tapes, hard drives, or optically readable data storage media.

[0225] The method 2000 includes a series of operations shown at step 2002 through step 2004 of Figure 20. The method 2000 may be performed by the LPS base station 910 in conjunction with the processor 912, the details of which are explained in conjunction with Figures 11a to 11c and the same are not repeated here for the sake of brevity in the disclosure. The method 2000 begins at step 2002.

[0226] At step 2002, the method 2000 includes generating, by the LPS base station 910, the downlink user data (DUD) packet 1001 including the plurality of SDU packets 1008a, 1008b and corresponding sequence numbers (SN). At least one of the plurality of SDU packets 1008a, 1008b includes the at least one flag provided in the header 1002 of the DUD packet and the length indicator (LI) field flag 1104 indicating the length of the at least one of the plurality of SDU packets 1008a, 1008b packaged inside the packet data unit of the LPS base station 910.

[0227] The method 2000 includes storing, by the LPS base station 910, the plurality of SDU packets 1008a, 1008b with the corresponding LI field flags in the header 1002 of the DUD packet 1001.

[0228] The method 2000 includes chaining, by the LPS base station 910, the at least one of the plurality of SDU packets 1008a, 1008b as per configured concatenation factor at the LPS base station 910.

[0229] At step 2004, the method 2002 includes transmitting, by the LPS base station 910, the plurality of SDU packets 1008a, 1008b, and the corresponding sequence numbers (SN) to the non-LPS base station 920 for performing the i-RAT handover by the LPS base station 910.

[0230] Figure 21illustrates a method 2100 performed by the processor 1212 for performing the i-RAT handover by the source LPS base station 1210, in accordance with another embodiment of the disclosure.

[0231] The method 2100 can be performed by programmed computing devices, for example, based on instructions retrieved from non-transitory computer-readable media. The computer-readable media can include machine-executable or computer-executable instructions to perform all or portions of the described method. The computer-readable media may be, for example, digital memories, magnetic storage media, such as magnetic disks and magnetic tapes, hard drives, or optically readable data storage media.

[0232] The method 2100 includes a series of operations shown at step 2102 through step 2104 of Figure 21. The method 2100 may be performed by the source LPS base station 1210 in conjunction with the processor 1212, the details of which are explained in conjunction with Figures 13a to 13b and the same are not repeated here for the sake of brevity in the disclosure. The method 2100 begins at step 2102.

[0233] At step 2102, the method 2100 includes transmitting the handover request message to the target LPS base station 1220. The handover request message may include the information element (IE) indicating the predetermined concatenated count of the plurality of service data unit (SDU) packets of the source LPS base station 1210.

[0234] At step 2104, the method 2100 includes receiving the handover request acknowledge message from the target LPS base station 1220, where the handover request acknowledge message includes the IE indicating the final concatenated count of the plurality of SDU packets for performing the intra-radio access technology (i-RAT) handover by the source LPS base station 1210.

[0235] The method 2100 includes the final concatenated count of the plurality of SDU packets may be smaller than at least one of the predetermined concatenated count of the plurality of SDU packets of the source LPS base station 1210 and the predetermined concatenated count of the plurality of SDU packets of the target LPS base station 1220.

[0236] The method 2100 includes the source LPS base station 1210 receives the handover request acknowledge message from the target LPS base station 1220, while performing the dual active protocol stands (DAPS) handover between the source LPS base station 1210 and the target LPS base station 1220 or in the normal handover scenario. The at least one unacknowledged packet data unit (PDU) is present at the target-LPS base station 1220.

[0237] Figure 22illustrates a method 2200 performed by the processor 1212 for performing the i-RAT handover in the user equipment 930, in accordance with another embodiment of the disclosure.

[0238] The method 2200 can be performed by programmed computing devices, for example, based on instructions retrieved from non-transitory computer-readable media. The computer-readable media can include machine-executable or computer-executable instructions to perform all or portions of the described method. The computer-readable media may be, for example, digital memories, magnetic storage media, such as magnetic disks and magnetic tapes, hard drives, or optically readable data storage media.

[0239] The method 2200 includes a series of operations shown at step 2202 through step 2204 of Figure 22. The method 2200 may be performed by the UE 930 in conjunction with the processor 1232, the details of which are explained in conjunction with Figures 14a to 14c and the same are not repeated here for the sake of brevity in the disclosure. The method 2200 begins at step 2202.

[0240] At step 2202, the method 2200 includes receiving at least one of the plurality of SDU packets 1208a, 1208b from the target-LPS base station 1220. The at least one of the plurality of SDU packets 1208a, 1208b may include at least one flag and is marked as the special at least one of the plurality of SDU packets 1208a, 1208b, when the status of E-Bit 1406, in the header 1408 of the packet data convergence protocol (PDCP) of the the target-LPS base station 1220, is true.

[0241] At 2204, the method 2200 includes unchaining the marked at least one of the plurality of SDU packets, for performing inter-radio access technology (i-RAT) handover in the user equipment 930, when the status of the E-Bit 1406 is true.

[0242] Figure 23illustrates a method 2300 performed by the processor 1222 for performing the i-RAT handover by the target LPS base station 1220, in accordance with another embodiment of the disclosure.

[0243] The method 2300 can be performed by programmed computing devices, for example, based on instructions retrieved from non-transitory computer-readable media. The computer-readable media can include machine-executable or computer-executable instructions to perform all or portions of the described method. The computer-readable media may be, for example, digital memories, magnetic storage media, such as magnetic disks and magnetic tapes, hard drives, or optically readable data storage media.

[0244] The method 2300 includes a series of operations shown at step 2302 through step 2306 of Figure 23. The method 2300 may be performed by the target LPS base station 1220 in conjunction with the processor 1222, the details of which are explained in conjunction with Figures 14a to 14c and the same are not repeated here for the sake of brevity in the disclosure. The 2300 method begins at step 2302.

[0245] At step 2302, the method 2300 includes generating, by the target-LPS base station 1220, the header 1408 of the packet data convergence protocol (PDCP) of the target-LPS base station 1220. The header 1408 includes the E-Bit 1406 indicating the presence of the length indicator (LI) field flag 1404 in at least one of the plurality of SDU packets 1208a, 1208b of the downlink user data (DUD) packet 1201 received from the source LPS base station 1210.

[0246] At step 2304, the method 2300 includes marking, by the target-LPS base station 1220, the at least one of the plurality of SDU packets 1208a, 1208b received from the source-LPS base station 1210, as the special SDU packet based on at least one flag, provided in the header 1202 of the DUD packet 1201.

[0247] At step 2306, the method 2300 includes transmitting the marked at least one of the plurality of SDU packets, to the user equipment 930 for performing the intra-radio access technology (i-RAT) handover by the target-LPS base station 1220.

[0248] The method 2300 includes identifying, by the target-LPS base station 1220, the value of the at least one flag corresponding to the marked at least one of the plurality of SDU packets 1208a, 1208b. The method 2300 includes assigning the sequence number (SN) to the marked at least one of the plurality of SDU packets 1208a, 1208b, when the value of the at least one flag is true. The method 2300 includes identifying, by the target-LPS base station 1220, the value of the E-Bit 1406, after assigning the SN. The method 2300 includes transmitting, the marked at least one of the plurality of SDU packets 1208a, 1208b, to the user equipment 930, when the identified value of the E-Bit 1406 is true.

[0249] The method 2300 includes the target LPS base station 1220 receives the at least one of the plurality of SDU packets 1208a, 1208b, while performing the dual active protocol stands (DAPS) handover between the source LPS base station 1210 and the target LPS base station 1220 or in the normal handover scenario. The at least one unacknowledged packet data unit (PDU) is present at the source LPS base station 1210.

[0250] Figure 24illustrates a method 2400 performed by the processor 1212 for performing the i-RAT handover by the source LPS base station 1210, in accordance with another embodiment of the disclosure.

[0251] The method 2400 can be performed by programmed computing devices, for example, based on instructions retrieved from non-transitory computer-readable media. The computer-readable media can include machine-executable or computer-executable instructions to perform all or portions of the described method. The computer-readable media may be, for example, digital memories, magnetic storage media, such as magnetic disks and magnetic tapes, hard drives, or optically readable data storage media.

[0252] The method 2400 includes a series of operations shown at step 2402 through step 2404 of Figure 24. The method 2400 may be performed by the source LPS base station 1210 in conjunction with the processor 1212, the details of which are explained in conjunction with Figures 14a to 14c and the same are not repeated here for the sake of brevity in the disclosure. The method 2400 begins at step 2402.

[0253] At step 2402, the method 2400 includes generating, by the source LPS base station 1210, the downlink user data (DUD) packet 1201 including the plurality of SDU packets 1208a, 1208b and corresponding sequence numbers (SN). The at least one of the plurality of SDU packets 1208a, 1208b may include the at least one flag provided in the header 1202 of the DUD packet 1201 and the length indicator (LI) field flag 1404 indicating the length of the at least one of the plurality of SDU packets 1208a, 1208b, packaged inside the packet data unit of the source LPS base station 1210.

[0254] The method 2400 includes storing by the source LPS base station 1210 the plurality of SDU packets 1208a, 1208b, with the corresponding LI field flags in the header 1202 of the DUD packet 1201.

[0255] The method 2400 includes chaining, by the source LPS base station 1210, the at least one of the plurality of SDU packets 1208a, 1208b as per the mutually agreed concatenation factor.

[0256] At step 2404, the method 2400 includes transmitting, by the source LPS base station 1210, the plurality of SDU packets 1208a, 1208b and the corresponding sequence numbers (SN) to the target LPS base station 1220 for performing the i-RAT based handover by the source LPS base station 1210.

[0257] Figure 25illustrates a method 2500 for establishing the MRDC between the LPS base station 910 and the non-LPS base station 920 in accordance with another embodiment of the disclosure.

[0258] The method 2500 can be performed by programmed computing devices, for example, based on instructions retrieved from non-transitory computer-readable media. The computer-readable media can include machine-executable or computer-executable instructions to perform all or portions of the described method. The computer-readable media may be, for example, digital memories, magnetic storage media, such as magnetic disks and magnetic tapes, hard drives, or optically readable data storage media.

[0259] The method 2500 includes a series of operations shown at step 2402 through step 2408 of Figure 25. The method 2500 may be performed between the LPS base station 910 and the non LPS base station 920, the details of which are explained in conjunction with Figure 15 and the same are not repeated here for the sake of brevity in the disclosure. The method 2500 begins at step 2502.

[0260] At step 2502, the method 2500 includes receiving, by the packet data convergence protocol (PDCP) of the LPS base station 910, the plurality of service data unit (SDU) packets and the corresponding sequence number (SN), from the PDCP of the non-LPS base station 920.

[0261] At step 2504, the 2500 method includes concatenating, by the LPS base station 910, the received plurality of SDU packets.

[0262] At step 2506, the method 2500 includes assigning, by the LPS base station 910, SN, independently, to each of the concatenated received plurality of SDU packets.

[0263] At step 2508, the method 2500 includes transmitting, from the LPS base station 910, each of the concatenated received plurality of SDU packets with the assigned SN to the user equipment (UE) 930 such that the UE 930 unchains the concatenated received plurality of SDU packets and forward the unchained concatenated received plurality of SDU packets to the PDCP of the non-LPS base station 920.

[0264] The disclosure provides apparatus and methods for i-RAT handover between the LPS base station 910 and the non-LPS base station 920, the source LPS base station 1210, and the target LPS base station 1220, and also established MRDC between the LPS base station 920 and the non-LPS base station 920. The apparatus and method as disclosed overcome the problems as discussed by incorporating the at least one flag 1004a, 1004b, LI field flag 1104, 1404, the E-Bit 1106, etc. This operation ensures a seamless connectivity of the UE 930 to the user. Further, the present apparatus and method ensures information exchange between the non-LPS base station 920 and the LPS base station 910, thus improving the performance.

[0265] In this application, unless specifically stated otherwise, the use of the singular includes the plural, and the use of "or" means "and / or." Furthermore, the use of the terms "including" or "having" is not limiting. Any range described herein will be understood to include the endpoints and all values between the endpoints. Features of the disclosed embodiments may be combined, rearranged, omitted, etc., within the scope of the invention to produce additional embodiments. Furthermore, certain features may sometimes be used to advantage without a corresponding use of other features.

[0266] While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist.

Claims

1.A method performed by a target base station in a communication system, the method comprising:receiving, from a source base station, a first packet data unit (PDU) for a terminal in an inter-radio access technology (RAT) handover, wherein the inter-RAT handover is performed between a lean protocol stack (LPS) base station which supports a chaining of service data units (SDUs) in one PDU and a non-LPS base station which does not support the chaining;identifying the number of SDUs in the first PDU, based on a flag indicating whether the chaining is applied for the first PDU, the flag being included in a header of the first PDU;determining a sequence number (SN) based on the number of the SDUs in the first PDU; andtransmitting, to the terminal, a second PDU corresponding to the first PDU with the determined SN.2.The method of claim 1,wherein the non-LPS base station assigns a single SN to one SDU in one PDU, andwherein the LPS base station assigns the single SN to a plurality of SDUs in one PDU.3.The method of claim 1,wherein, in case that the number of the SDUs is identified as one, a SDU with a single SN corresponding to the SDU is included in the PDU, andwherein the target base station is the LPS base station and the source base station is the non-LPS base station.4.The method of claim 3,wherein the determining the SN further includes:determining to maintain the single SN;chaining the SDU based on a concatenation factor, wherein the concatenation factor indicates the number of SDUs to be chained in the second PDU; andgenerating the second PDU with the chained SDU,wherein the concatenation factor is configured as one.5.The method of claim 1,wherein, in case that the number of the SDUs is identified as more than one, chained SDUs with a single SN corresponding to the chained SDUs are included in the PDU,wherein the target base station is the non-LPS base station and the source base station is the LPS base station, andwherein the header further includes a length indicator indicating a length of a single SDU in the chained SDUs.6.The method of claim 5,wherein the determining the SN further includes:identifying the single SDU based on the length indicator and the flag;assigning a SN for each SDU in the chained SDUs; andgenerating the second PDU including the first PDU and a packet data convergence protocol (PDCP) header,wherein the PDCP header includes information on the assigned SN and an extension field indicating whether the length indicator exists in the first PDU, andwherein the length indicator instructs the terminal to unchain the chained SDUs.7.The method of claim 5,wherein, in case that the inter-RAT handover corresponds to a DAPS handover, the concatenation factor is one.8.A target base station in a communication system, the target base station comprising:a transceiver;memory storing one or more programs; andone or more processors communicatively coupled to the transceiver and the memory,wherein the one or more processors include computer-executable instructions that, when executed by the one or more processors individually or collectively, cause the target base station to:receive, from a source base station, a first packet data unit (PDU) for a terminal in an inter-radio access technology (RAT) handover, wherein the inter-RAT handover is performed between a lean protocol stack (LPS) base station which supports a chaining of service data units (SDUs) in one PDU and a non-LPS base station which does not support the chaining,identify the number of SDUs in the first PDU, based on a flag indicating whether the chaining is applied for the first PDU, the flag being included in a header of the first PDU,determine a sequence number (SN) based on the number of the SDUs in the first PDU, andtransmit, to the terminal, a second PDU corresponding to the first PDU with the determined SN.9.The target base station of claim 8,wherein the non-LPS base station assigns a single SN to one SDU in one PDU, andwherein the LPS base station assigns the single SN to a plurality of SDUs in one PDU.10.The target base station of claim 8,wherein, in case that the number of the SDUs is identified as one, a SDU with a single SN corresponding to the SDU is included in the PDU, andwherein the target base station is the LPS base station and the source base station is the non-LPS base station.11.The target base station of claim 10,wherein the computer-executable instructions that, when executed by the one or more processors individually or collectively, further cause the target base station to:determine to maintain the single SN, the single SN being the determined SN;chain the SDU based on a concatenation factor, wherein the concatenation factor indicates the number of SDUs to be chained in the second PDU; andgenerate the second PDU with the chained SDU,wherein the concatenation factor is configured as one.12.The target base station of claim 8,wherein, in case that the number of the SDUs is identified as more than one, chained SDUs with a single SN corresponding to the chained SDUs are included in the PDU,wherein the target base station is the non-LPS base station and the source base station is the LPS base station, andwherein the header further includes a length indicator indicating a length of a single SDU in the chained SDUs.13.The target base station of claim 12,wherein the computer-executable instructions that, when executed by the one or more processors individually or collectively, further cause the target base station to:identify the single SDU based on the length indicator and the flag;assign a SN for each SDU in the chained SDUs, the assigned SN being the determined SN; andgenerate the second PDU including the first PDU and a packet data convergence protocol (PDCP) header,wherein the PDCP header includes information on the assigned SN and an extension field indicating whether the length indicator exists in the first PDU, andwherein the length indicator instructs the terminal to unchain the chained SDUs.14.The target base station of claim 12,wherein, in case that the inter-RAT handover corresponds to a DAPS handover, the concatenation factor is one.

Images