Network-controlled repeater assisted handover process for improved cellular communication

Abstract

This patent document presents a novel NCR (20) assisted handover process aimed at enhancing handover procedures within cellular communication systems, particularly in the context of 5G NR networks. The invention focuses on minimizing interruption times during handovers by enabling continuous uplink and downlink transmissions through NCRs (20). It introduces secure transmission of measurement report messages (108) and handover command messages (109) via the NCR (20), while optimizing handover processes through priori information utilization. By addressing challenges associated with traditional handover mechanisms, Dual Active Protocol Stacks, and Conditional Handover, this innovation contributes to seamless cellular communication transitions, improved data transmission, and enhanced overall network efficiency.

Description

[0001] NETWORK-CONTROLLED REPEATER ASSISTED HANDOVER PROCESS FOR IMPROVED CELLULAR COMMUNICATION

[0002] TECHNICAL FIELD

[0003] The present invention relates to the field of telecommunications and wireless network technologies. More specifically, the invention introduces a novel network-controlled Repeater (NCR)-assisted handover process that enhances Conditional Handover (CHO) procedures and addresses challenges associated with Dual Active Protocol Stacks (DAPs). The invention focuses on optimizing the handover process by enabling seamless downlink (DL) and uplink (UL) transmissions to user equipment (UE) through the NCR during handover events, thereby minimizing the number of measurements taken from multiple base stations for measurement report in the handover process. The invention also encompasses the secure transmission of measurement reports and handover commands via the NCR between the source and target base stations while ensuring that the user equipment remains within the coverage region. Additionally, the invention offers an efficient data forwarding mechanism utilizing the NCR, enabling both source and target base stations to maintain continuous connectivity to the NCR. This connectivity empowers the source BS to selectively choose between early or late data forwarding through the NCR, further optimizing the handover process, and enhancing overall cellular communication efficiency.

[0004] PRIOR ART

[0005] Mobile telecommunications systems are designed to accommodate users' movement between different cellular coverage areas, known as cells. As users move, the signal quality from their current cell may deteriorate, or a neighboring cell may offer stronger signal quality. In response, handover procedures are initiated to facilitate a seamless transition for users as they move between cells. The existing state of the art in handover mechanisms, particularly in the context of 5G NR (New Radio) networks, involves various strategies to minimize interruption times, optimize data transmission, and prevent handover failures.

[0006] Traditional Handover Mechanisms:

[0007] In traditional transition scenarios, when the user's signal quality drops below a certain threshold, the source base station requests the measurement report from the user, the user equipment prepares the measurement report on this request, and then this report is transmitted to the source base station. This report is based on measurements taken from neighboring cells. The source base station then determines the need for handover and selects a target base station. Common handover mechanisms in 5G NR include the Dual Active Protocol Stack (DAPS) and Conditional Handover (CHO).

[0008] DAPS allows users to continue receiving data during handovers, minimizing handover interruption time (HIT). The user maintains connections with both source and target cells momentarily. CHO, on the other hand, is based on predetermined conditions set by the network. When these conditions are met, user equipment initiates the handover and detach from the source without the instruction of source base station.

[0009] Technical Problem:

[0010] One challenge in handover processes is potential handover failure (HOF) due to inadequate transmission of measurement reports or handover commands. If these critical signals are lost, the service quality deteriorates, potentially leading to connection drops and user reconfiguration. To mitigate such risks, Conditional Handover (CHO) mechanisms have been introduced to provide proactive handover initiation based on predefined conditions. This approach reduces the reliance on the user's ability to transmit accurate measurement reports.

[0011] Technical Solution:

[0012] In addressing the coverage enhancement challenge, Network-Controlled Repeaters (NCRs) emerge as a promising solution. Unlike traditional RF repeaters that operate independently and cause interference, NCRs offer intelligent amplification and relay functions. They can receive control signals from base stations and perform sideband processing for enhanced performance.

[0013] NCRs are equipped with additional functions such as time division duplex (TDD) information access, beamforming capabilities, and on / off control. These features are enabled by a control unit within the NCR that processes control signals from base stations. NCRs can exploit TDD information for efficient amplification and relaying, adjust beamforming toward users and base stations, and power down to save energy and avoid amplifying noise. Current Patent Literature on NCRs and Handover Procedures:

[0014] While there are existing patents and technical documents related to NCRs and handover procedures, the identified patents do not directly encompass the detailed enhancements and protocols proposed by the invention. The mentioned patents primarily cover aspects such as NCR connectivity, beam management, power saving modes, and device sharing. The invention distinguishes itself by addressing specific challenges in handover procedures, optimizing data forwarding, and introducing new signaling schemes between NCRs and transmission points. Below are summaries of patents that appear in the literature.

[0015] In US20220053433A1 entitled "Information for Wireless communication repeater device" discloses a network access node may configure a repeater device to transmit multiple synchronization signal blocks using different beams. The network controller may determine, or the repeater can indicate how many beams the repeater can use for its operations. The available beam pairs can be used for simultaneous transmission.

[0016] Patent application no US20210067237A1 discloses determining the first set of beams for receiving and synchronization signal blocks (SSB) from base station. Then determining second set of beams for transmitting (SSB) via first set of beams. Then relaying the SSBs from BS to at least one second wireless device using first and second set of beams.

[0017] US20210037459A1 discloses a power saving of smart repeaters based on a triggering signal. This patent is about a wireless repeater may operate in a power saving mode and monitor for control information from a base station according to a low power state or a slow state. Upon detection of triggering signal from a base station, the wireless repeater may transition to monitoring for control information from the base station according to a fast state.

[0018] US20210037574A1 discloses power saving of smart repeaters". In this patent, the repeater just listens to the control signals periodically in low power mode and when a user equipment is attached to it, it transitions into fast state.

[0019] US1 1356943B2 discloses smart directional repeater initialization. This patent is about Initializing other devices in the network as repeaters if they are suitable and capable of repeater operation.

[0020] Programmable Smart Repeater with In - Band Control is described in US20220103247A1 . This patent is about establishing a control link with a control node and receiving, via control link, a configuration or one or more parameters to forward communication between a first a wireless device and a second wireless device. The repeater scheme operates in wake-up mode and turns off the Mobile termination when not needed.

[0021] US patent application no US20220240305A1 discloses Smart Repeater Systems. It is disclosed that a wireless repeater receiving time schedule for communication between base station and plurality of user equipment’s, determining the locations of the plurality of user equipment devices and adjusting one or more beamforming antennas to point a corresponding plurality of beams at the plurality of locations according to time schedule.

[0022] US patent application no US20210036764A1 discloses "Control method for smart repeaters. This patent is about a method for wireless communications by a first wireless device receiving, from a second wireless device, a first radio frequency (RF) signal of a first bandwidth; extracting control information from the first RF signal of the first bandwidth. Selecting, based on the control information, at least one or more receive beams or one or more transmit beams; and using the one or more selected beams to at least one of receive a second RF signal from the second wireless device or forward the second RF signal to a third wireless device.

[0023] US20210194569A1 discloses coverage expansion and interference operating modes for a repeater. According to this patent application, the repeater has three modes: first mode, coverage expansion mode and interference management mode. It decides which mode to select according to whether the amplification of the first signal satisfies the amplification threshold or not. If not, it goes into coverage expansion mode and transmitter sends the message in a narrower bandwidth in a second band and the repeater amplifies it. If repeater senses that the high-power input signal is caused by the interference. Then switches into interference management mode and BS sends a beamformed signal to repeater to mitigate the interference.

[0024] In another patent document no W02020205282A1 repeater communication system with power measurement capability is disclosed. In this patent, a repeater capable of measuring a power metric associated with the input signal; and adjust the communication parameters based on the power metric such as changing the gain of the amplifier within the repeater; or selecting a beamforming configuration of the repeater based on the power metric.

[0025] In RWS-210019NR smart rpeaters for Rel-18 is disclosed. This document shows and presents Qualcomm’s smart repeater definition. A document with the reference “TR 38.867” discloses “Study on NR Network Controlled Repeaters. The document “TR 38.867” presents the technical report on smart repeaters published by 3GPP.

[0026] The existing patent literature about NCR related Handover Procedures:

[0027] WO2022253993A2 discloses remote beam management for network-controlled repeaters. This patent covers multi connectivity to NCR and utilize this for Handoff with the following clause; Fig. 21 shows a schematic block diagram illustrating a scenario according to an embodiment according to which the repeater is configured for simultaneously or sequentially connect to more than one base station and, e.g., a number of at least two, at least three or more, and to forward or relaying communication of the plurality of base stations to the user equipment, e.g., to implement handovers or multi-connectivity. Possibly but not necessary this may incorporate to form beams towards the respective base stations. For forwarding, a static or dynamic beam may be used. Such a behavior may be implemented for more than one user equipment at a time for same, partly different, or completely new sets of base stations. According to Fig. 21 , the repeater may be connected to multiple gNBs.

[0028] The connectivity of NCR to multiple base stations is mentioned in this patent, and it is stated that this could be used for handover. However, the aspects of how NCR can assist in handover and how the handover mechanism can be improved are covered, with a focus on pointing out the benefits and proposing a new protocol that considers the signaling schemes between NCR and transmission points. Additionally, the current handover mechanism is developed, and the problems are addressed with detailed explanations about the procedure.

[0029] Another international patent application publication no W02022093380A1 relates an adaptive phase-changing device Sharing and Handover. This patent concerns the clauses related to ARD (Adaptive Phase-Changing), which is typically the phase-changing device of a surface, commonly known as RIS. The utilization of an APD by two base stations and the allocation of the surface are detailed within. The discussion covers the details and procedures concerning how the APD can be accessed by both base stations. The handover procedure remains untouched by the APD; it is solely described. The codebook configuration of the APD is shared by the source base station with the target BS. For instance, an example of a method used to execute aspects of APD sharing and handover, specifically a handover of a UE from a source base station to a target base station involving the provision of APD information, is illustrated. The relevant clauses are situated between paragraphs 99 and 105 in the patent document, as well as between paragraphs 1 17 and 128. In another US patent application no US2021037574A1 relates power saving of smart repeaters. In this patent document, smart repeater has two states: slow state and fast state. The aim of the invention is that when smart repeater monitors the control channel so often when there is no connection or UE around. The smart repeater transitions into slow state where it monitors the control channel less. Upon the reception of a RACH, or if SR detects that a UE trying to connect itself, it transitions to tentative fast state and monitors the control channel more often. If BS send command to transition to fast state, then SR transitions to fast state. Otherwise, it gets back to slow state. Here, the invention relates to handover for the following reasons; the base stations can transition smart repeater to fast state during handover process, the source base station can transition smart repeater to slow state since user equipment is moving to another base station, or the target base station can transition smart repeater to fast state in case of handover for upcoming user equipment. However, these do not conflict with proposed idea.

[0030] In summary, the state of the art in handover mechanisms involves traditional approaches like DAPS and CHO, aiming to minimize interruption times and prevent handover failures. The challenge of coverage enhancement is being tackled through Network-Controlled Repeaters (NCRs), which offer intelligent amplification, beamforming, and energy-efficient operation. Despite existing patents and technical documents, the proposed invention offers novel contributions in optimizing handover processes and NCR-assisted enhancements.

[0031] BRIEF DESCRIPTION OF THE INVENTION

[0032] The invention aims to enhance handover procedures in cellular communication systems, particularly in the context of 5G NR networks. By introducing a network-controlled Repeater (NCR)-assisted handover process, the invention seeks to optimize the transition of User Equipment (user equipment (30)) between different cellular coverage areas or cells. The focus is on minimizing interruption times, improving data transmission, and preventing handover failures.

[0033] The invention addresses the challenges associated with traditional handover mechanisms, specifically Dual Active Protocol Stacks (DAPS) and Conditional Handover (CHO). Rather than solely focusing on improving CHO, it introduces a new method of handover designed to enhance the overall handover process. This innovative approach aims to provide a more robust and efficient way of initiating handovers based on predefined conditions, reducing the dependency on precise measurement reports from the user. The invention addresses the issue of involving multiple target Base Stations (base stations (10)) during the handover process. By utilizing the NCR, the invention intends to streamline the handover process and minimize the number of target base stations (10) involved, thereby improving efficiency, and reducing potential disruptions during handover events.

[0034] The invention proposes a mechanism for secure transmission of measurement reports and handover commands between the source and target base stations (10) through the NCR. This ensures that critical signals are reliably transmitted, reducing the risk of handover failure and maintaining the quality of service during handover events.

[0035] The invention introduces an efficient data forwarding mechanism utilizing the NCR. This mechanism allows both the source and target base stations (10) to maintain continuous connectivity to the NCR, enabling optimized data forwarding during handover events. The connectivity offered by the NCR empowers the source BS to make informed decisions regarding data forwarding timing, enhancing the overall handover process.

[0036] While there are existing patents and technical documents related to NCRs and handover procedures, the invention distinguishes itself by introducing novel enhancements and protocols that address specific challenges in handover mechanisms. The invention aims to optimize data forwarding, improve signaling schemes between NCRs and transmission points, and provide solutions not covered by existing patents.

[0037] In summary, the invention aims to optimize handover processes in cellular communication systems through the introduction of a network-controlled Repeater (NCR)-assisted handover process. This process represents an innovation centered around Conditional Handover (CHO) procedures. It occupies a unique position between the Dual Active Protocol Stack (DAPS) and CHO. For instance, while CHO typically has user equipment initiating handovers, our proposed method shifts this responsibility to the source base station, akin to the DAPS approach. Additionally, in CHO, user equipment is informed about all possible target base stations based on measurement reports. In contrast, our invention streamlines this process by informing the user equipment of just one target base station. The key innovation in our system lies in optimizing the measurement report phase, reducing the number of base stations the user equipment needs to measure, which enhances system efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and together with the description serve to explain the principle of the invention.

[0039] Figure-1 , Continuous UL transmission through NCR

[0040] Figure-2, NCR with links to multiple gNBs

[0041] Figure-3, NCR Lookup Table and Handover Mechanism

[0042] Figure-4, NCR prevents HOF due to link failure in the UL

[0043] Figure-5, NCR assists the Handover command message transmission and prevent HOF

[0044] Figure-6, Flowchart of the NCR Assisted Handover Mechanism

[0045] Figure-7, NCR Assisted Handover Procedure

[0046] Figure-8, Continuous UL / DL Transmission during Handover

[0047] REFERENCE NUMBERS GIVEN IN THE FIGURES

[0048] 10. Base Stations 101 . Uplink Data

[0049] 1 1. gNB 1 102. Active Transmission Link

[0050] 12. gNB 2 103. Passive Transmission Link

[0051] 13. gNB 3 104. Active Link Source

[0052] 14. gNB 4 105. Inactive Link

[0053] 20. Network Controlled Repeater 106. Active Link Target

[0054] 30. User Equipment 107. Measurement Request Message

[0055] 40. Lookup Table 108. Measurement Report Message

[0056] 50. Source Base Station 109. Handover Command Message

[0057] 60. Target Base Station 1 10. Downlink Data

[0058] DETAILED DESCRIPTION OF THE INVENTION

[0059] Network-controlled repeater (20) might be used by multiple base stations (10) like gNB 1 (1 1 ), gNB 2 (12), gNB 3 (13), gNB 4 (14), simultaneously or at different times depending on its capabilities. Base stations (10) might be multiplexed over time, frequency, or spatial domain to use the network-controlled repeater (20) as follows. After this paragraph, Network- controlled repeater (20) shall be abbreviated as NCR (20). If the NCR (20) has no additional hardware, i.e., only with one amplification and beamforming circuit, there could be only one base station (For example 1 1 ) using the NCR (20) at a time. In this case, base stations (10) are multiplexed in time to use the NCR (20) with different time shares. At a given share dedicated to one base station (10), the NCR (20) aligns its receiving beamforming circuit to receive signals from that base station (10). All such beamforming and time-sharing information are delivered to the NCR (20) by the network. Multiplexing base stations (10) over frequency domain with no additional hardware is also possible but with common channel paths at both sides of the NCR (20). Since analogue beamforming at the NCR (20) is more limited than digital beamforming, usually, the NCR (20) will be limited to beamform a focused beam toward a given direction at any of its sides. Therefore, the channel should be rich enough so that there is at least one arrival angle with non-vanishing gains from all base stations accessing the NCR (20). Moreover, there should be one angle at the transmitting side of the NCR (20) where all users have good coupling, so they get service.

[0060] Additional amplification and beamforming circuits might be added to the NCR (20). These circuits might also have mixers for frequency shifting. With such circuits, base stations (10) might be multiplexed simultaneously to use the NCR (20). For instance, there could be a LoS (line of side) path between the NCR (20) and every base station (10), where each beamforming circuit generates a beam toward that path. At the users’ sides, there could be also multiple beams, where each one (or multiple) carries a signal coming from one base station. If base stations are operating at the same frequency, then they should coordinate for transmission in the area covered by the NCR (20) so that interference at users’ side is minimized. On the other hand, if base stations are using different bands, there will be no interference issue. Between the NCR (20) and base stations (10), it might not be easy to multiplex base stations (10) in space with no interference. For this case, the link between base stations (10) and NCRs (20) might have different frequencies for different base stations (10), even if the base stations (10) are operating at the same frequency. At the NCR (20), mixers are used to bring all signals back to one carrier and send them to users. Such design requires mixers in the amplification and beamforming circuits.

[0061] NCR (20) can be utilized in the network to enable and help the handover mechanism. NCR (20) can assist the handover procedure and can resolve the problems of current 5G handover mechanisms by utilizing connectivity to the multiple base stations (10). In DAPS handover, although we have the continuous downlink transmission from both source and target base stations (10), the continuous uplink data (101 ) transmission is very hard to achieve due to hardware limitations of the user equipment (30). Since user equipment (30) cannot direct data towards two different base stations (11 ,12), the uplink data (101 ) transmission is switched between source base stations (50) and target base stations (60). NCR (20) can enable continuous transmission of uplink data (101 ) to both source base stations (50) and target base stations (60). Fig. 1 illustrates the uplink data (101 ) transmission scheme through NCR (20). The user equipment (30) can send uplink data (101 ) to the NCR (20), and NCR (20) can forward uplink data to both source base stations (50) and target base stations (60) during handover process by using the links maintained with both source base stations (50) and target base stations (60). This way, both continuous uplink / downlink transmission without interruption can be achieved by exploiting the NCR (20) in the environment.

[0062] NCR (20) can also comfort the user equipment (30) tasks during handover (HO) process. User equipment (30) needs to measure necessary parameters such as RSSI, SNR, cell identification, RSRP, CSI-RS and report to source base station (50) which is a significant workload for user equipment (30) since it needs to switch between multiple frequencies and capture multiple SSBs (Synchronization Signal Blocks) from different gNBs and take average and report back to source gNB. The number of measurements can be reduced by sending some priori information to the user equipment (30) about the measurement procedure and priorities. Multiple base stations (10) can utilize NCR (20) in the environment if they are capable of reaching and establishing links with the said NCR (20). Based on the availability of NCR (20), base stations (10) in the environment can utilize the NCR (20) simultaneously or individually to accomplish various operations and tasks. The access information of the NCR (20) can be stored in the network center and can be monitored by any base station (10). The access information about NCRs (20) can include, the history of the base stations (10) connected to said NCR (20), the history of the user equipment (30) served through said NCR (20), the active connections through said NCR (20) from a certain BS to a certain user equipment (30), the beam index indication between NCR (20) and active user equipment (30), operating frequencies of connected base stations (10), etc. A source BS can access to this information and prepare a primary list of base stations (10) indicating some metrics (i.e., operating frequencies, relative positions to the user equipment (30), order of the probability of target base stations (10) to take first set of measurements with the user equipment (30). The source BS can send priori information about measurements to the user equipment (30) and user equipment (30) can perform first set of measurements based on the priori information provided by the source BS. This way, measurement process can take less time and can be less power consuming task for the user equipment (30). Fig. 2 illustrates the example of the described network where NCR (20) can maintain active transmission link (102) and passive transmission links (103) to multiple base stations (10) like gNB 1 (11 ), gNB 2 (12), gNB 3 (13), gNB 4 (14). If a user equipment (30) is in the region of the NCR (20) and handover is triggered, it is highly likely that the handover will occur to one of the near and neighboring base stations (10) in the environment. The source BS can monitor and access this information via the NCR (20) lookup table (40) stored in the network center where NCR (20) acts a regional data and information monitoring device. Fig. 3 illustrates a sample lookup table (40) and handover mechanism through NCR (20). The user equipment (30) is connected to gNB 1 (11 ). The user equipment (30) could be on the edge of the cell, or the signal quality of user equipment (30) can be below a certain threshold and user equipment (30) is served through NCR (20) by gNB 1 (11 ). Here, gNB 1 (1 1 ) decides the handover user equipment (30) to another base station (10). gNB 1 (11 ) can monitor the nearby base stations (10) by checking the NCR (20) lookup table (40) accessing various information about the region, nearby base stations (10), nearby user equipment (30), could be any information about the network or devices in the network. Based on this gNB 1 (1 1 ) prepares the priori information for the measurement report may include primary candidate gNBs as gNB 2 (12), gNB 3 (13), and gNB 4 (14) along with their operating frequencies. Following, user equipment (30) performs the first set of measurements based on the priori information. If source base station (50) fails to select a target base station (60) based on the first set of measurements. Then, the user equipment (30) can perform a second set of measurements as in conventional methods. Assuming that, gNB 3 (13) is selected as the target base station (60) by the source base station (50) - gNB 1 (1 1 ) in Fig. 3-the gNB 3 (13) could be either connected to NCR (20) or can establish a new connection or can perform handover without NCR (20) as well. In case, the handover is performed through NCR (20), gNB 3 (13) can monitor that user equipment (30) is served through SSB index 4 between NCR (20) and user equipment (30) channel. Therefore, gNB 3 (13) does not need to send a synchronization signal burst to the NCR (20) to perform beam sweeping. Instead, it can directly send a specific SSB signal and avoid beam search procedure by monitoring the NCR (20) lookup table (40) information. Fig 3. Illustrates active link source (104) and active link target (106) between gNB 1 (1 1 ) and gNB 3 (13) using via NCR (20). The link between the unused base stations (gNB 2, gNB 4) and the NCR is referred to as an inactive link (105).

[0063] One of the most important reasons of handover failure (HOF) is measurement request message (107) cannot reach to the source base station (50) due to link failure. To prevent handover failure, conditional handover (CHO) is preferred even it is not an efficient handover mechanism in terms of signaling and resource utilization. NCR (20) assistance can overcome the link failure issue and decrease the handover failure rate significantly. Fig. 4 illustrates the sample setup where NCR (20) assists the measurement request message (107) transmission and prevent handover failure. Despite receiving the measurement request message (107) from the base station (10) - which is gNB 1 (1 1 ) -, when they respond with the measurement report message (108) at uplink, the uplink message may not reach the base station (10) as user equipment (30) are not powerful and advanced devices that support very sharp beamforming at uplink. In this case, the user equipment (30) can send measurement report message (108) to source base station (50) - which is gNB 1 (11 ) - through NCR (20) in the uplink transmission as shown in Fig. 4 where the direct link failure occurs in uplink which is shown by solid dashed line in Fig.4.

[0064] Another reason of handover failure could be handover command from source base station (50) cannot reach to the user equipment (30) due to link failure. NCR (20) assistance can overcome the link failure issue and decrease the HOF rate significantly. Fig. 5 illustrates the sample setup where NCR (20) assists the handover command message (109) transmission and prevent handover failure. Despite receiving the measurement request message (107) from the user equipment (30), when the source base station (50) responds with the handover command message (107) in downlink, the downlink message may not reach the base stations (10) as the user equipment (30) can be moving as the time passes and link quality degrades rapidly which is shown by solid dashed line in Fig.5. In this case, the source base station (50) - which is gNB 1 (1 1 ) can send handover command message (109) to the user equipment (30) through NCR (20) in the downlink transmission as shown in Fig. 5 where the direct link failure occurs in uplink.

[0065] Fig. 6 shows flowchart of the method of performing handover with NCR (20) assistance. When there is an NCR (20) in the environment, it can be used to ensure the link quality to avoid link failure between source base station (50), target base station (60), and the user equipment (30) links. NCR (20) can help the measurement process with priori information provided by the NCR (20) Lookup table (40). Even though, it is not shown in the diagram, if source base station (50) cannot decide on the target base station (60) based on the first set of measurements with priori information provided by the source base station (50), the second set of measurement is performed as in conventional measurement methods in 5G handover procedure. The example transaction diagram of NCR (20) assisted handover mechanism is shown in Fig. 7. The simplified signaling scheme is shown and all transaction between nodes can be through NCR (20), even if it is not shown in the transaction diagram. Fig. 8 shows the transaction diagram to explain how continuous uplink and downlink transmission is conducted with both source and target cell during handover process to achieve uninterrupted handover or to reduce handover interruption time. During handover process, NCR (20) acts as a regional bus to monitor regional information and becomes a transition point guarantees link quality and continuous transmission in both uplink and downlink transmission. NCR (20) assisted handover can overcome the problems of dual active protocol stack (DAPS) and improves conditional handover (CHO).

[0066] Fig. 7 shows the NCR Assisted Handover Procedure. The detailed description of the figure in question is as follows; source base station (50) receives a priori information via NCR (20) and then transmits measurement request and a priori information to the user equipment (30), the priori information includes the first base station (10) set that is likely to be the target base station (60) from which the measurements will be taken, user equipment (30) transmits measurement report to the source base station (50) via NCR (20), the source base station (50) decides whether or not to perform a handover and communicates the decision to the target base station (60), transmission of the handover decision by the source base station (50) to the user equipment (30) via NCR (20), user equipment (30) initiates RACH (Random Access Channel) procedure to establish uplink connection with the target base station (60) via NCR (20), the user equipment (30) communicates with the source base station (50) and the target base station (60) using both uplink and downlink over the NCR (20) after the RACH procedure is executed, the user device (30) transmits the handover completed message to the target base station (60) via NCR (20), The target base station (60) informs the source base station (50) that the handover process is over.

[0067] Fig. 8 shows the continuous uplink / downlink transmission during handover. The detailed description of the figure in question is as follows; transmission of the uplink data (101 ) transmitted by the user equipment (30) to the NCR (20), transmission of the transmitted uplink data (101 ) to the source base station (50) and the target base station (60) via the NCR (20), transmission of downlink data (1 10) to the NCR (20) by both the source base station (50) and the target base station (60), the NCR (20) transmits the downlink data (1 10) to the user equipment (30).

[0068] Unlike conventional network with no NCR (20), the channel with a user at the cell edge is in good condition. This feature of NCR (20)-enabled networks might be exploited to reduce data forwarding overhead and relax the base stations (10) synchronization requirement even though it is not shown in the flowchart and transactions diagrams provided. During handover, the source base station (50) might continue transmitting to the user. Once handover is done successfully and the user is assigned to the target base station (60), source base station (50) might continue transmitting any buffered data to the user through NCR (20), instead of forwarding data to the target. After such transmission, the user is instructed to access the target base station (60) to continue communication. In this scheme, there is no need to synchronize base stations (10) as they are not transmitting simultaneously. To achieve all the objects mentioned above and that will emerge from the following detailed description above, the present invention relates to A method for enhancing handover procedures in a cellular communication system. This method is characterized by comprising steps of;

[0069] • receiving a measurement report from a user equipment (30), the measurement report based on measurements taken from neighboring cells,

[0070] • determining a target base station (60) for handover based on the measurement report,

[0071] • sending a handover command message (109) from a source base station (50) to the user equipment (30) through a network-controlled repeater (20) during a handover event; and facilitating continuous uplink (UL) and downlink (DL) transmissions between the user equipment (30) and the source base station (50) and the target base station (60) via the network-controlled NCR (20) during the handover event.

[0072] A possible embodiment of the invention is characterized by; in this method network-controlled repeater (20) maintains a lookup table (40) storing access information about neighboring base stations (10), user equipment (30), and regional data, and the source base station (50) utilizes the access information to prepare priori information for measurement reports sent to the user equipment (30).

[0073] In another embodiment of the invention, in the method network-controlled repeater (20) assists in preventing handover failure by forwarding measurement report messages (108) from the user equipment (30) to the source base station (50) in the uplink transmission,

[0074] In another embodiment of the invention, in the method the network-controlled repeater (20) assists in preventing handover failure by forwarding handover command messages (109) from the source base station (50) to the user equipment (30) in the downlink transmission.

[0075] One aspect of the invention also provides a system for optimizing handover procedures in a cellular communication network, comprising:

[0076] • a user equipment (30) configured to send measurement reports based on neighboring cell measurements,

[0077] • a source base station (50) configured to determine a target base station (60) for handover based on the measurement reports,

[0078] • a network-controlled repeater (20) configured to receive handover command messages (109) from the source base station (50) and forward them to the user equipment (30) during a handover event,

[0079] • a target base station (60) configured to communicate with the user equipment (30) and the source base station (50) via the network-controlled repeater (20) during the handover event, enabling continuous uplink (UL) and downlink (DL) transmissions. In a possible embodiment of the system, the network-controlled repeater (20) maintains a lookup table (40) storing access information about neighboring base stations (10), user equipment (30), and regional data, and the source base station (50) utilizes the access information to prepare priori information for measurement reports sent to the user equipment (30).

[0080] In another embodiment of the system the network-controlled repeater (20) assists in preventing handover failure by forwarding measurement report messages (108) from the user equipment (30) to the source base station (50) in the uplink transmission. In the system, the network- controlled repeater (20) assists in preventing handover failure by forwarding handover command messages (109) from the source base station (50) to the user equipment (30) in the downlink transmission.

Claims

CLAIMS1. A method for enhancing handover procedures in a cellular communication system, comprising the steps of:• receiving a measurement report from a user equipment (30), the measurement report based on measurements taken from neighboring cells,• determining a target base station (60) for handover based on the measurement report,• sending a handover command message (109) from a source base station (50) to the user equipment (30) through a network-controlled repeater (20) during a handover event; and facilitating continuous uplink (UL) and downlink (DL) transmissions between the user equipment (30) and the source base station (50) and the target base station (60) via the network-controlled NCR (20) during the handover event.

2. The method of claim 1 , wherein the network-controlled repeater (20) maintains a lookup table (40) storing access information about neighboring base stations (10), user equipment (30), and regional data, and the source base station (50) utilizes the access information to prepare priori information for measurement reports sent to the user equipment (30).

3. The method of claim 1 , wherein the network-controlled repeater (20) assists in preventing handover failure by forwarding measurement report messages (108) from the user equipment (30) to the source base station (50) in the uplink transmission.

4. The method of claim 1 , wherein the network-controlled repeater (20) assists in preventing handover failure by forwarding handover command messages (109) from the source base station (50) to the user equipment (30) in the downlink transmission.

5. A system for optimizing handover procedures in a cellular communication network, comprising:• a user equipment (30) configured to send measurement reports based on neighboring cell measurements,• a source base station (50) configured to determine a target base station (60) for handover based on the measurement reports,• a network-controlled repeater (20) configured to receive handover command messages (109) from the source base station (50) and forward them to the user equipment (30) during a handover event,• a target base station (60) configured to communicate with the user equipment (30) and the source base station (50) via the network-controlled repeater (20) during the handover event, enabling continuous uplink (UL) and downlink (DL) transmissions.

6. The system of claim 5, wherein the network-controlled repeater (20) maintains a lookup table (40) storing access information about neighboring base stations (10), user equipment (30), and regional data, and the source base station (50) utilizes the access information to prepare priori information for measurement reports sent to the user equipment (30).

7. The system of claim 5, wherein the network-controlled repeater (20) assists in preventing handover failure by forwarding measurement report messages (108) from the user equipment (30) to the source base station (50) in the uplink transmission.

8. The system of claim 5, wherein the network-controlled repeater (20) assists in preventing handover failure by forwarding handover command messages (109) from the source base station (50) to the user equipment (30) in the downlink transmission.

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