A handover method using low power wake-up reference signal

Abstract

Invention is a handover method for a system comprising multiple base stations (100) and at least a user equipment (200) comprising a main radio (210) which is configured to operate in a sleep mode and in an operating mode where the main radio (210) performs communication with the base station (100); and a wake up radio (220) which is configured to transmit a trigger signal to main radio (210) for triggering the operating mode; the base stations (100) are configured to transmit and receive communication signals for serving the user equipment (200), wake up signals (WuS) for commanding wake up radio (220) to trigger main radio (210).

Description

[0001] DESCRIPTION

[0002] A HANDOVER METHOD USING LOW POWER WAKE-UP REFERENCE SIGNAL

[0003] TECHNICAL FIELD

[0004] Invention relates to a handover method for a system comprising multiple base stations and at least a user equipment comprising a main radio which is configured to operate in a sleep mode and in an operating mode where the main radio performs communication with the base station; and a wake up radio which is configured to transmit a trigger signal to main radio for triggering the operating mode; the base stations are configured to transmit and receive communication signals for serving the user equipment, wake up signals (WuS) for commanding wake up radio to trigger main radio.

[0005] PRIOR ART

[0006] Handover is a critical function that ensures uninterrupted communication in cellular networks when the User Equipment (UE) is in mobility mode. While the Third Generation Partnership Project (3GPP) standards have introduced several enhancements to guarantee reliable and low-latency handovers, the introduction of low-power wake-up signals (LP-WuS) presents new challenges. User Equipment (UE) equipped with LP-WuS technology spends the majority of its time in sleep mode, also referred to as IDLE mode, where it remains disconnected from the network. This behavior is particularly prevalent in Internet of Things (loT) devices. Due to this disconnection, the UE may face difficulties during mobility, as it becomes unaware of which cell to connect to. Additionally, it cannot reliably distinguish between being out of coverage or simply missing the LP-WuS transmission from the base station, potentially resulting in communication failures.

[0007] Existing solutions suggest periodic reporting mechanisms, where the UE periodically wakes up to measure the low-power synchronization signal (LP-SS) and reports the results using the main radio (MR). However, this approach requires frequent activation of the MR, leading to significant battery consumption. Furthermore, it proves unreliable, as LP-SS signals may not consistently reach neighboring cells or provide comprehensive coverage within a single cell. Another proposed method involves using a dedicated reference signal for Radio Resource Management (RRM) reporting. However, this approach results in high power consumption andreduced spectral efficiency, making it unsuitable for power-constrained devices like loT equipment.

[0008] W02024011572A1 discloses a wireless communication method at a user equipment (UE) involves conducting one or more Radio Resource Management (RRM) measurements on a Low-Power Reference Signal (LP-RS) from at least one cell. The method also includes selecting a cell to camp on based on the RRM measurements taken from the LP-RS. This invention proposes that all the neighbouring BSs transmit a reference signal LP-RS like the 5G NR reference signals that are used for handover. However, this method also considers that the LP-WuR conduct the same RRM metrics on LP-WuS the same as it was done by the main radio on reference signals.

[0009] US2024284328A1A discloses a method and a system. A UE transmits a capability message to a network entity, indicating its ability to process low-power reference signals using a low-power radio. This low-power radio consumes less energy than the UE’s main radio, which is typically used for processing regular reference signals. The network entity then provides a configuration for these low-power reference signals, allowing the UE to efficiently process them. This approach minimizes the power consumption by delegating the reception and processing of first reference signals (low-power signals) to the low-power radio, as opposed to the more power-intensive second reference signals processed by the main radio. In this, disclosure the UE decides whether to take measurements from low power reference signal or the standard reference signals for main radio, and the UE report every measurement using main radio which is applicable only if the main radio is already ON. In addition, the method doesn’t provide a clear solution for the case of Handover when the UE is in sleep (IDLE) mode.

[0010] W02024011572A1 discloses a method of wireless communication ata UE includes performing one or more RRM measurements on a low-power reference signal of at least one cell. The method further includes selecting a cell on which to camp based on the one or more RRM measurements performed on the low-power reference signal. This method requires a simultaneous monitoring for both 5G SSB signal and the low-power reference signal, where the monitoring of the latter is done to make the UE decides to which cell it can connect to when it goes into sleep mode. This method requires an extra energy consumption for the dual monitoring of the 5G SSB signals and the low-power reference signal. In addition, it doesn’t provide a solution for the case of handover when the UE is in the sleep (mode).WO2024092433A1 involves the integration of a main radio and a low-power wake-up radio (LP-WuR) within the UE. The UE receives mobility criteria, which include conditions that trigger a reselection from a first cell to a second cell. The system operates by determining the transmission (TX) power of a low-power wake-up signal (LP-WuS) for both the first and second cells. Based on these parameters — the mobility criteria and the LP-WuS transmission powers — the UE decides when to trigger the reselection from the first cell to the second cell.

[0011] All the problems mentioned above have made it necessary to make an innovation in the relevant technical field as a result.

[0012] BRIEF DESCRIPTION OF THE INVENTION

[0013] The present invention relates to a method to eliminate the above-mentioned disadvantages and bring new advantages to the relevant technical field.

[0014] An object of the invention is allowing user equipment to trigger handover while its main radio is in sleep mode.

[0015] Another object of the invention is to increase efficiency of utilization of the radio resources.

[0016] Another object of the invention is to reduce reporting overhead.

[0017] To achieve all the objects mentioned above and that will emerge from the following detailed description, the present invention relates to a handover method for a system comprising multiple base stations and at least a user equipment comprising a main radio which is configured to operate in a sleep mode and in an operating mode where the main radio performs communication with the base station; and a wake up radio which is configured to transmit a trigger signal to main radio for triggering the operating mode; the base stations are configured to transmit and receive communication signals for serving the user equipment, wake up signals (WuS) for commanding wake up radio to trigger main radio Accordingly, it comprises the steps of:

[0018] - broadcasting, by the base stations, wake up reference signal (WuRS) periodically where each base station broadcasts a sequence ID unique to the transmitting base station, where sequence IDs belonging to neighboring base stations are orthogonal to each other and base stations use same resources for broadcasting WuRS;

[0019] - receiving, by the user equipment, WuRSs;- performing, by the user equipment, correlation to received WuRSs using neighboring cell’s sequence IDs and determining each WuRS broadcasted by each neighboring base station; - performing, by the user equipment, radio resource management (RRM) measurement on each WuRS and storing measurements;

[0020] - if it is determined that the RRM measurements of serving base station are meeting predetermined handover conditions continuing monitoring WuRSs;

[0021] - if it is determined that no WuR is detected belonging to neighboring base station sequence IDs triggering main radio to operate in operating mode in order to re-connect to the network; -if it is determined that the RRM measurements of serving base station is lower than the RRM measurements of other neighboring cells triggering main radio to operate in operating mode to handover to a neighboring base station. Thus, this method allows a user equipment to reconnect to a service or handover if its MR of is in sleep mode and the user equipment moves out of the coverage area of a serving cell. Further, reporting overhead is significantly reduced.

[0022] A possible embodiment of the invention is characterized in that if it is determined that the RRM measurements are a fluctuating trend, connecting a main radio (MR) antenna of the main radio to the wake up radio (WUR) antenna of the wake up radio in order to increase measurement accuracy. Thus, measurement accuracy is increased when seemingly inconsistent measurements are detected.

[0023] A possible embodiment of the invention is characterized in that the base stations uses the same resources as the wake up signal.

[0024] A possible embodiment of the invention is characterized in that the each base station uses the same resources for broadcasting WuRS. Thus, no additional resource is needed in order to realize the method.

[0025] Invention is also a system comprising multiple base stations and at least a user equipment comprising a main radio which is configured to operate in a sleep mode and in an operating mode where the main radio performs communication with the base station; and a wake up radio which is configured to transmit a trigger signal to main radio for triggering the operating mode; the base stations are configured to transmit and receive communication signals for serving the user equipment, wake up signals (WuS) for commanding wake up radio to trigger main radio characterized in that the system is configured to perform the one of the above methods.Another possible embodiment of the invention is characterized in that the user equipment comprising a switching means for connecting a main radio (MR) antenna of the main radio and awake up radio (WUR) antenna of the wake up radio, the wake up radio is configured to control the switching means and the wake up radio is configured to connecting the MR antenna to the WUR antenna if it is determined that the RRM measurements are a fluctuating trend, in order to increase measurement accuracy.

[0026] BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a drawing illustrating schematic view of the system.

[0028] Figure 2 is a drawing illustrating top schematic view of the system depicting a user equipment moving from a first coverage area to a second coverage area.

[0029] Figure 3 is a drawing illustrating user equipment in more details.

[0030] Figure 4 is a drawing illustrating wake up signal (WUS), low power-synchronization signal (LP-SS) and the wake up reference signal (WuRS).

[0031] Figure 5 comprises graphs showing total successful handover count and total energy consumption of a currently common prior art technology (on the right hand side) and the proposed method (on the left hand side).

[0032] REFERENCE NUMBERS GIVEN IN THE FIGURE

[0033] 100 Base station

[0034] 101 First base station

[0035] 102 Second base station

[0036] 200 User equipment

[0037] 210 Main radio

[0038] 211 MR antenna

[0039] 220 Wake up radio

[0040] 221 WUR antenna

[0041] 230 Switching means

[0042] 300 Wake up reference signal

[0043] 400 Coverage area401 First coverage area

[0044] 402 Second coverage area

[0045] DETAILED DESCRIPTION OF THE INVENTION

[0046] In this detailed description, the subject matter is explained with references to examples without forming any restrictive effect only in order to make the subject more understandable.

[0047] Referring to figure 1 , invention is a handover method realized by a system comprising multiple base stations (100) and user equipment (200). The base stations (100) broadcast wake up signals (WuS) and synchronization signals for the user equipment (200) to synchronize and trigger its main radio (210). The base stations (100) further broadcast wake up reference signals (300) (WuRS) which user equipment (200) monitor radio resource management (RRM) measurements of and trigger its main radio (210) to handover or reconnect to a cell in predetermined conditions. Thus allowing user equipment (200) to asses handover conditions while its main radio (210) is in sleep mode.

[0048] Figure 2 depicts a first base station (101) and a second base station (102). The first base stations (101) provides a first coverage area (401) and the second base station (102) provides a second coverage area (402). The user equipment (200) travels from first coverage area (401) to second coverage area (402) while main radio (210) is in sleep mode.

[0049] The base station (100) may comprise a low-power transmitter configured to broadcast low-power synchronization signals for enabling timing alignment of User Equipment (200) (UE); a wake-up signal generator configured to transmit wake-up signals for activating UEs (200) from an sleep mode; a control unit configured to manage the scheduling and coordination of the low-power synchronization signals and wake-up signal transmissions; and a power amplifier configured to optimize energy efficiency during signal broadcasting (not shown). Referring to figure 4, the base stations (100) are further configured to broadcast wake up reference signals. Wake up reference signals (300) are low power signals. Wake up reference signals (300) share the same radio resources as the wake up signals and synchronization signals, so WuRS (300) does not require extra resources. WuRS (300) comprise sequence IDs unique to each base station (100). Thus, when received, user equipment (200) can identify which WuRS (300) belong to which base station (100). Sequence IDs are orthogonal to each other among neighboring base stations (100). Since sequence IDs in WuRS (300) use the same resources and orthogonal to each other, they may be filtered out in order to acquire each sequence IDusing predetermined sequence ID filters. Thus, user equipment (200) can receive them at the same time and identify each base station (100).

[0050] Referring to figure 3, user equipment (200) comprises a main radio (210) configured to operate in a sleep (idle) mode and an operating mode where it performs main communication with a base station (100). The user equipment (200) further includes a main radio (210) antenna operably connected to the main radio (210) for transmitting and receiving communication signals, and a wake-up radio configured to process wake-up signals dedicated to activating the main radio (210). The wake-up radio is operably connected to a wake-up radio antenna for receiving low-power signals and is configured to trigger the main radio (210) to transition from the sleep mode to the operating mode upon receiving a dedicated wake-up signal. Additionally, the user equipment (200) comprises switching means (230) configured to selectively connect and disconnect the main radio (210) antenna and the wake-up radio antenna, enabling the wake-up radio to utilize the main radio (210) antenna for performing more precise measurements when necessary. Utilization of MR antenna (211) is known in the art as given in the standard (Study on low-power wake-up signal and receiver for NR (Release 18) (3GPP TR 38.869 V2.0.0). 3rd Generation Partnership Project (3GPP), Technical Specification Group Radio Access Network). Thus it is not explained with more details herein.

[0051] User equipment (200), receives WuRS (300) and measures radio resource management (RRM) measurement on WuRS (300). It decides to trigger WuR (220) based on measurement results and measurement history. User equipment (200) filters sequence IDS using stored sequence ID filters and identifies the base station (100) that the WuRSs (300) received from.

[0052] Sleep mode (also referred to as idle mode) is a low-power operational state in which the main radio (210) is deactivated or minimally active to conserve energy while maintaining basic network connectivity. During this mode, the user equipment (200) does not actively transmit or receive data but remains partially operational, typically relying on a wake-up radio to monitor for specific low-power wake-up signals or other triggers from the base station (100). The sleep mode allows the user equipment (200) to significantly reduce power consumption, particularly for devices with limited energy resources, such as loT devices, while still being able to transition to full communication mode upon receiving a wake-up signal.

[0053] In more detail, the proposed handover method comprises following steps performed by the system:- The base stations (100) broadcast wake up reference signal (300) (WuRS) periodically where each base station (100) broadcasts an sequence ID unique to the transmitting base station (100), where sequence IDs belonging to neighboring base stations (100) are orthogonal to each other and base stations (100) use same resources for broadcasting WuRS (300).

[0054] - User equipment (200) receives WuRSs (300).

[0055] - The user equipment (200), performs correlation to received WuRSs (300) using neighboring cell’s sequence IDs and determining each WuRS (300) broadcasted by each neighboring base station (100).

[0056] - The user equipment (200), performs radio resource management (RRM) measurement on each WuRS (300) and storing measurements.

[0057] - If the user equipment (200) determines that the RRM measurements of serving base station (100) are meeting predetermined handover conditions, it continues monitoring WuRSs (300); - If the user equipment (200) determines that no WuR (220) is detected belonging to neighboring base station (100) sequence IDs, it triggers main radio (210) to operate in operating mode in order to re-connect to the network;

[0058] - If the user equipment (200) determines that the RRM measurements of serving base station (100) is lower than the RRM measurements of other neighboring cells, it triggers main radio (210) to operate in operation mode to handover to a neighboring base station (100).

[0059] Fluctuating trend may comprise increasing and decreasing measurement results in consecutive RRM measurements. Such results may for example be inconsistent results such that it wouldn’t be possible to be caused by a physical phenomenon due to results being taken in short period of times. For example, having varying measurement results in a predetermined time window, where varying measurements having a margin larger than a predetermined threshold would also be considered a fluctuating trend. In the standard, fluctuating trends in RRM measurements can arise due to dynamic factors like small-scale fading, interference variability, or mobility-induced Doppler effects. For instance, Reference Signal Received Power (RSRP) measurements may exhibit sudden changes exceeding a predefined threshold (e.g., ±3 dB) within a short time window, even in the absence of significant physical changes in the environment. Such inconsistencies, caused by rapid channel dynamics or measurement noise, can lead to unreliable measurement reports, complicating handover decisions or triggering unnecessary radio link failure (RLF) procedures.

[0060] Figure 5 shows energy consumption and number of handovers between a prior art system and the invention. It shows that approximately same handovers are achieved with invention using significantly less power, compared to the prior art.The scope of protection of the invention is specified in the attached claims and cannot be limited to those explained for sampling purposes in this detailed description. It is evident that a person skilled in the art may exhibit similar embodiments in light of the above-mentioned facts without drifting apart from the main theme of the invention.

Claims

CLAIMS1. A handover method for a system comprising multiple base stations (100) and at least a user equipment (200) comprising a main radio (210) which is configured to operate in a sleep mode and in an operating mode where the main radio (210) performs communication with the base station (100); and a wake up radio (220) which is configured to transmit a trigger signal to main radio (210) for triggering the operating mode; the base stations (100) are configured to transmit and receive communication signals for serving the user equipment (200), wake up signals (WuS) for commanding wake up radio (220) to trigger main radio (210) characterized in that comprising the steps of:broadcasting, by the base stations (100), wake up reference signal (300) (WuRS) periodically where each base station (100) broadcasts an sequence ID unique to the transmitting base station (100), where sequence IDs belonging to neighboring base stations (100) are orthogonal to each other and base stations (100) use same resources for broadcasting WuRS (300);receiving, by the user equipment (200), WuRSs (300);performing, by the user equipment (200), correlation to received WuRSs (300) using neighboring cell’s sequence IDs and determining each WuRS (300) broadcasted by each neighboring base station (100);performing, by the user equipment (200), radio resource management (RRM) measurement on each WuRS (300) and storing measurements;if it is determined that the RRM measurements of serving base station (100) are meeting predetermined handover conditions continuing monitoring WuRSs (300); if it is determined that no WuR (220) is detected belonging to neighboring base station (100) sequence IDs triggering main radio (210) to operate in operating mode in order to re-connect to the network;if it is determined that the RRM measurements of serving base station (100) is lower than the RRM measurements of other neighboring cells triggering main radio (210) to operate in operating mode to handover to a neighboring base station (100).

2. The method according to claim 1, wherein base stations (100) uses the same resources as the wake up signal.

3. The method according to claim 1 or 2, wherein each base station (100) uses the same resources for broadcasting WuRS (300).

4. The method according to any one of the preceding claims, characterized in that if it is determined that the RRM measurements are a fluctuating trend, connecting a main radio (210) (MR) antenna of the main radio (210) to the wake up radio (220) (WUR) antenna of the wake up radio (220) in order to increase measurement accuracy.

5. A system comprising multiple base stations (100) and at least a user equipment (200) comprising a main radio (210) which is configured to operate in a sleep mode and in an operating mode where the main radio (210) performs communication with the base station (100); and a wake up radio (220) which is configured to transmit a trigger signal to main radio (210) for triggering the operating mode; the base stations (100) are configured to transmit and receive communication signals for serving the user equipment (200), wake up signals (WuS) for commanding wake up radio (220) to trigger main radio (210) characterized in that t e system is configured to perform the method of claim 1 or 4.

6. The system according to claim 5, characterized in that the user equipment (200) comprising a switching means (230) for connecting a main radio (210) (MR) antenna of the main radio (210) and awake up radio (220) (WUR) antenna of the wake up radio (220), the wake up radio (220) is configured to control the switching means (230) and the wake up radio (220) is configured to connecting the MR antenna (211) to the WUR antenna (221) if it is determined that the RRM measurements are a fluctuating trend, in order to increase measurement accuracy.

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