A handover method for passive target

Abstract

A handover method for passıve target comprise the following main steps; hybrid mono and bistatic sensing based handover for moving passive sensing targets, handover initiation based on measurement reports collected from monostatic sensing form S-BS, measurement reports collection from monostatic sensing form S-BS and bistatic sensing from T-BS, Measurement Report Transfer, sensing information combining for enhancing sensing range, target base-station selection method.

Description

[0001] DESCRIPTION

[0002] A HANDOVER METHOD FOR PASSIVE TARGET TECHNICAL FIELD OF THE INVENTION

[0003] The invention relates to a handover method for passive target.

[0004] PRIOR ART

[0005] In the state of the art, in 5G and beyond, integrating network resources for both communication and sensing is essential to creating a smarter, interconnected world. Passive targets, which do not have communication receivers, present a distinct challenge as they transition between base stations. Unlike active users, they require an innovative handover mechanism to ensure efficient sensing within the existing infrastructure.

[0006] Joint sensing and communication (JSC) has emerged as a transformative paradigm that empowers wireless networks to simultaneously transmit information and sense the environment in the era of 5G and beyond. This duality in functionality now combines the traditional communication services with advanced sensing capabilities, thus enabling applications like autonomous vehicles, smart cities, and industrial automation. JSC reuses the existing network infrastructure, optimizing resource utilization and enabling new functionalities that could not be achieved earlier.

[0007] Depending on the purpose of the JSC systems, they can be broadly differentiated into the following two kinds: active target and passive target.

[0008] An Active Target: A target holding receivers for the transmission or communication component, which will be completely involved in the network contributing to sending out and obtaining signals. As a target is involved with interactions, monitoring its mobility internally inside the system is comparatively manageable and easy as well.

[0009] A Passive target: The target that itself is not able to interact on an active note towards the participation of the network and use any means to communicate anything. For targets such as pedestrians, vehicular systems without communication modules or general objects in an industrial site, tracking is done absolutely by sensing from the network; this usually includes employing radar or other detection machinery.

[0010] One serious challenge is introduced by passive targets' mobility, especially when targets move across areas covered by multiple BSs. While active targets can assist the network in managing the process of handovers with some signaling, passive targets have to depend on independent prediction and management of their transitions by the network. Seamless and reliable tracking requires a robust mechanism for handovers that should facilitate the transfer of tracking responsibilities between BSs with minimal tracking errors and interruptions. Such an approach is critical for maintaining the accuracy and efficiency of JSC systems, especially in dynamic environments characterized by high target mobility or dense BS deployments.

[0011] Due to the effects of double-path fading, the coverage area for passive sensing is inherently smaller than that of active sensing or communication. This discrepancy results in two distinct coverage zones, potentially creating a sensing dead zone (DZ) where certain regions fall outside the sensing range despite uniform transmit power. In such a dead zone, a passive target may be lost, making continuous tracking challenging. To address this issue, sensing must be maintained by starting handover for the sensed target before entering the dead zone to ensure the target remains detectable. Figure 1, illustrates these coverage areas and the concept of the sensing dead zone, providing a visual explanation of the challenge.

[0012] This issue becomes even more pronounced in network-based sensing environments where multiple base stations (BSs) are involved. The increased complexity of coordinating sensing coverage across multiple BSs exacerbates the problem, as overlapping coverage zones may still leave gaps where dead zones occur. Additionally, the handover process in such multi-BS systems must be highly synchronized to avoid latency or mismatched sensing data, which could lead to gaps in tracking or errors in determining the target's location. In scenarios with dense deployments or high mobility, the probability of targets entering and exiting these dead zones increases, further complicating the sensing process. The Figure 2 also illustrates how network-based sensing involving multiple BSs intensifies the challenge, emphasizing the need for efficient handover mechanisms and coordinated sensing strategies to mitigate the impact of dead zones.

[0013] In [1] addresses the challenge of maintaining seamless target tracking in 6G Distributed Integrated Sensing and Communication (DISAC) systems as targets move across base stations (BSs) with limited fields of view (FoV). The authors propose a trajectory sharing algorithm that enables BSs to exchange essential target trajectory data with their neighbors, ensuring smooth handovers during transitions. This approach integrates with the Trajectory Poisson Multi-Bernoulli Mixture (TPMBM) filter for efficient multi-target tracking and is validated through simulations, demonstrating improved sensing performance. However, the study assumes full inter-BS connectivity, which may not be practical in real-world deployments, and raises concerns about communication overhead, scalability in large networks, and environmental variability that could affect tracking accuracy. These limitations highlight the need for further refinement for practical deployment in dynamic and large-scale 6G networks.

[0014] Accurate handover of passive targets is critical in enabling seamless tracking and sensing across various real-world applications where targets lack active communication capabilities. For instance, in autonomous transportation systems, passive objects like pedestrians or non-communicative vehicles must be tracked as they move between coverage zones of roadside sensors to ensure safety and smooth traffic flow. Similarly, in surveillance of critical infrastructure, accurate handover allows continuous monitoring of intruders or drones crossing restricted zones. In industrial automation, handover ensures smooth tracking of packages or obstacles in warehouses, enabling efficient operations and collision avoidance for robots and automated systems.

[0015] In disaster management, passive survivors or debris are tracked by drones or sensors across different regions to coordinate timely rescue operations. Additionally, in wildlife monitoring, migrating animals are seamlessly tracked across large reserves to study movement patterns or prevent poaching [2], These applications demonstrate the technical importance of accurate handover for ensuring uninterrupted tracking, efficient resource usage, and system scalability in integrated sensing and communication networks, supporting the vision of smart cities, autonomous systems, and advanced industrial processes.

[0016] The invention brings technical solves to the technical problems in the state of the art stated above.

[0017] References:

[0018] [1] Ge, Y., Kaltiokallio, O., Chen, H., Talvitie, J., Xia, Y., Madhusudan, G., Valkama, M., & Wymeersch, H. (2024). Target Handover in Distributed Integrated Sensing and Communication. arXiv preprint arXiv:2411.01871.

[0019] [2] 3GPP TR 22.837 V0.3.0 (2023-03), Study on Integrated Sensing and Communication (Release 19).

[0020] BRIEF DESCRIPTION OF THE INVENTION

[0021] The aim of the invention is to develop a handover method that ensures seamless and precise handover of tracked passive targets as they move through areas served by multiple base stations (BSs). By maintaining accurate handover, the invention aims to minimize tracking errors that can arise during the transition of targets between the coverage zones of different BSs. This approach ensures continuous and reliable tracking of passive targets, even in dynamic environments, thereby enhancing the overall performance of sensing communication system.

[0022] The advantage of the invention is as follows:

[0023] 1. It guarantees precise handover of tracked passive targets, ensuring seamless and accurate tracking.

[0024] 2. It minimizes interference caused by the sensing signals of target base stations (T- BSs) by implementing a scheduling mechanism based on the required refresh rate (RR) for the specific tracking scenario. Description of the Figures

[0025] Figure 1. A system model of the coverage areas and the concept of the sensing dead Zone (prior art).

[0026] Figure 2. A system model of the network-based sensing involving multiple BSs intensifies the challenge (prior art).

[0027] Figure 3. Proposed handover method.

[0028] Figure 4. Diagram of proposed handover method’s power recieved threshold.

[0029] DETAILED DESCRIPTION OF THE INVENTION

[0030] The invention proposes a method to achieve seamless handover with reduced failure rates for moving passive targets in a joint communication and sensing (JCS) system:

[0031] 1. A handover method leveraging hybrid mono-static sensing and bi-static sensing capabilities to ensure seamless handover for tracked target.

[0032] 2. A method for combining sensing parameters collected from multiple basestations based mainly on predefined power receive thresholds.

[0033] 3. A method for measurement report collection in passive sensing using multiple base stations, enhancing performance in areas with poor sensing coverage.

[0034] 4. A strategy for interference mitigation between serving and target base stations during measurement report collection, based on target refreshing rates.

[0035] The invention presents a new handover approach for passive target tracking by dynamically switching between monostatic and bistatic sensing strategies. During the handover process, the Sensing Base Station (S-BS) operates in monostatic mode, while neighboring Target Base Stations (T-BSs) engage in bistatic sensing. This dual-mode approach ensures seamless tracking and avoids the risk of targets being lost in sensing dead zones. Figure 3 illustrates a detailed step-by-step illustration of this approach.

[0036] The handover process is triggered when the received power at the S-BS from the target falls below a specified threshold, referred to as threshold A in the Figure 4. This reduction prompts the S-BS to share Measurement Reports (MRs), which may include localization data (Range, Anglr, velocity, Radar Cross Section (RCS), Received Power), with neighboring T-BSs. The T-BSs then commence bistatic sensing, actively monitoring the target and exchanging MRs simultaneously.

[0037] The MRs exchanged among the T-BSs are updated at intervals defined by the Refreshing Rate (RR) required for the sensing application. This means that the T-BSs do not continuously share their MRs; instead, only a subset of T-BSs exchanges their MRs during each RR, thereby reducing the sensing overhead. According to 3GPP standards, this interval typically ranges from 0.05 seconds to 1 second to ensure the sensing data remains current.

[0038] The handover approach processes only the MRs from neighboring T-BSs whose received power exceeds a predefined threshold, minimizing unnecessary computations. As the target moves, the S-BS monitors variations in the received power. When the sensing signal’ s received power goes below a threshold, the S-BS initiates the handover process and requests the potential T-BSs to perform bistatic sensing to collect the measurement reports. T-BSs send and acknowledgement to the S-BS and start collecting the measurements reports, which are sent to the S-BS for combining and / or selecting the T-BSs if necessary for handover. If handover is required, the S-BS selects one of the T-BS as the new S-BS whose sensing received signal power and measurement reports are better than other B Ss’. Until the handover process is completed the current S-BS keep sending the sensing signal and the new S-BS performs bistatic sensing.

[0039] After the target crosses the dead zone (DZ) and / or the monostatic sensing signal’s received power becomes better than the bistatic signal power, the new S-BS transitions from bistatic to monostatic sensing, taking over the primary sensing role to maintain seamless tracking. This approach addresses the challenges posed by sensing dead zones by enabling smooth transitions of sensing responsibilities between base stations. The integration of monostatic and bistatic sensing modes provides a robust and handover solution for target tracking, even in complex network environments. The invention relates to a a handover method for passive target that comprise the following steps;

[0040] Step 201. Handover Initiation: The handover method begins when the received power from the target at the S-BS falls below a specified threshold (Threshold A). This triggers the need for additional sensing support from neighboring T-BSs.

[0041] Step 202. Measurement Report Collection for Multiple BSs: Measurement Reports (MRs) are gathered by the Sensing Base Station (S-BS) and neighboring Target Base Stations (T-BSs). These MRs include parameters such as range, angle, velocity, radar cross-section (RCS), and received power.

[0042] Step 203. Measurement Report Transfer: Upon initiation, the S-BS shares its collected MRs with neighboring T-BSs. This enables the T-BSs to actively monitor the target using bistatic sensing, ensuring continuous tracking.

[0043] Step 204. Sensing Information Transfer for Combining: The T-BSs send their sensing information, sharing updated MRs at intervals defined by the Refreshing Rate (RR). Only a subset of T-BSs exchanges reports during each RR to minimize sensing overhead, and interferance focusing on T-BSs where the received power exceeds a predefined threshold. These measurement reports are combined at the S-BS to enhance the sensing performance in the dead zone (DZ).

[0044] Step 205. Target Base-Station Selection Method: As the target moves, T-BSs monitor changes in received power and reports to the S-BS. When a S-BS's sensing received power surpasses a secondary threshold (Threshold B), it is designates a T-BS as the new S-BS based on the measurement reports sent by the potential T-BSs, ready to take over sensing responsibilities.

[0045] The technical terms (Measurement report, Radar cross section, Mono static sensing, Bi static sensing, Refreshing rate) that used in the invention are as follows: Measurement report: the information periodically transmitted between serving base station or target base station through an interface. This report provides critical data such as the signal quality of the serving cell and neighboring cells, localization data and radar cross section value. The serving base station uses this information to make handover decisions, ensuring that the passive target remains connected to the optimal cell as it moves.

[0046] Radar cross section: is a measure of how detectable an object is by radar. It quantifies the amount of radar signal that an object reflects back to the radar receiver, relative to the signal strength that would be reflected by an idealized point target (a sphere) with a cross-sectional area of 1 square meter. RCS is typically expressed in square meters (m²) and is influenced by the size, shape, material, and orientation of the target relative to the radar.

[0047] Mono static sensing: refers to a radar or sensing configuration in which the transmitter and receiver are co-located, typically sharing the same antenna or being positioned so closely together that they can be considered as a single entity. In this setup, the transmitted signal reflects off a target, and the same system receives the reflected signal for processing and analysis.

[0048] Bi static sensing: refers to a radar or sensing configuration where the transmitter and receiver are located at separate, distinct positions. Unlike monostatic sensing, where transmission and reception occur at the same site, bistatic sensing involves a spatially separated transmitter and receiver, with the target typically positioned in the region between them.

[0049] Refreshing rate: the interval at which measurement reports are updated - is determined by the specific requirements of the application and the network's configuration. For sensing applications, this interval is typically configured to ensure that the data remains current and accurate. A handover method for passive target comprise the following main steps;

[0050] - Hybrid mono and bistatic sensing based handover for moving passive sensing targets,

[0051] - Handover initiation based on measurement reports collected from monostatic sensing form S-BS,

[0052] - Measurement reports collection from monostatic sensing form S-BS and bistatic sensing from T-BS

[0053] - Measurement Report Transfer,

[0054] Sensing information combining for enhancing sensing range,

[0055] Target base-station selection method.

[0056] A handover method for passive target comprise the following working steps;

[0057] The Sensing Base Station (S-BS) operates in monostatic mode, while neighboring Target Base Stations (T-BSs) engage in bistatic sensing wherein this dual-mode approach ensures seamless tracking and avoids the risk of targets being lost in sensing dead zones.

[0058] The invention is triggered when the received power at the S-BS from the target falls below a specified threshold, referred to as threshold A, wherein this reduction prompts the S-BS to share Measurement Reports (MRs), which may include localization data like range, anglr, velocity, radar cross section (RCS), received power, with neighboring T-BSs and the T-BSs then commence bistatic sensing, actively monitoring the target and exchanging MRs simultaneously, The MRs exchanged among the T-BSs are updated at intervals defined by the Refreshing Rate (RR) required for the sensing application which means the T- BSs do not continuously share their MRs; instead, only a subset of T-BSs exchanges their MRs during each RR, thereby reducing the sensing overhead wherein this interval typically ranges from 0.05 seconds to 1 second to ensure the sensing data remains current, according to 3GPP standards,

[0059] The invention processes only the MRs from neighboring T-BSs whose received power exceeds a predefined threshold, minimizing unnecessary computations wherein as the target moves, the S-BS monitors variations in the received power. - When the sensing signal’s received power goes below a threshold, the S-BS initiates the handover process and requests the potential T-BSs to perform bistatic sensing to collect the measurement reports.

[0060] T-BSs send and acknowledgement to the S-BS and start collecting the measurements reports, which are sent to the S-BS for combining and / or selecting the T-BSs if necessary for handover.

[0061] If handover is required, the S-BS selects one of the T-BS as the new S-BS whose sensing received signal power and measurement reports are better than other BSs’ wherein until the handover process is completed the current S-BS keep sending the sensing signal and the new S-BS performs bistatic sensing.

[0062] After the target crosses the dead zone (DZ) and / or the monostatic sensing signal’s received power becomes better than the bistatic signal power, the new S-BS transitions from bistatic to monostatic sensing, taking over the primary sensing role to maintain seamless tracking wherein this approach addresses the challenges posed by sensing dead zones by enabling smooth transitions of sensing responsibilities between base stations and the integration of monostatic and bistatic sensing modes provides a robust and handover solution for target tracking, even in complex network environments.

[0063] The invention is not limited to the above exemplary embodiments, and a person skilled in the art can readily put forward embodiments of the invention. These are considered within the scope of the invention as claimed by the accompanying claims.

Claims

CLAIMS1. A handover method for passive target comprise the following working steps;The Sensing Base Station (S-BS) operates in monostatic mode, while neighboring Target Base Stations (T-BSs) engage in bistatic sensing wherein this dual-mode approach ensures seamless tracking and avoids the risk of targets being lost in sensing dead zones.The invention is triggered when the received power at the S-BS from the target falls below a specified threshold, referred to as threshold A, wherein this reduction prompts the S-BS to share Measurement Reports (MRs), which may include localization data like range, anglr, velocity, radar cross section (RCS), received power, with neighboring T-BSs and the T-BSs then commence bistatic sensing, actively monitoring the target and exchanging MRs simultaneously, The MRs exchanged among the T-BSs are updated at intervals defined by the Refreshing Rate (RR) required for the sensing application which means the T- BSs do not continuously share their MRs; instead, only a subset of T-BSs exchanges their MRs during each RR, thereby reducing the sensing overhead wherein this interval typically ranges from 0.05 seconds to 1 second to ensure the sensing data remains current, according to 3GPP standards,The invention processes only the MRs from neighboring T-BSs whose received power exceeds a predefined threshold, minimizing unnecessary computations wherein as the target moves, the S-BS monitors variations in the received power.- When the sensing signal’s received power goes below a threshold, the S-BS initiates the handover process and requests the potential T-BSs to perform bistatic sensing to collect the measurement reports.T-BSs send and acknowledgement to the S-BS and start collecting the measurements reports, which are sent to the S-BS for combining and / or selecting the T-BSs if necessary for handover.If handover is required, the S-BS selects one of the T-BS as the new S-BS whose sensing received signal power and measurement reports are better than other BSs’ wherein until the handover process is completed the current S-BSkeep sending the sensing signal and the new S-BS performs bistatic sensing. After the target crosses the dead zone (DZ) and / or the monostatic sensing signal’s received power becomes better than the bistatic signal power, the new S-BS transitions from bistatic to monostatic sensing, taking over the primary sensing role to maintain seamless tracking wherein this approach addresses the challenges posed by sensing dead zones by enabling smooth transitions of sensing responsibilities between base stations and the integration of monostatic and bistatic sensing modes provides a robust and handover solution for target tracking, even in complex network environments.

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