JP2019068434A - Automatic connection switching in radio communication network - Google Patents

Abstract

To provide a method for enabling effective management of connection to a radio communication network by UE.SOLUTION: An access point (100-1) of a radio communication network provides connection to a user terminal (50). The access point (100-1) determines a plurality of target access points (100-2 and 100-3). Furthermore, the access point (100-1) transmits a message (204) to the user terminal (50). The message (204) indicates the plurality of target access points (100-2 and 100-3) and permits the user terminal (50) to automatically switch connection to one or more target access points (100-2 and 100-3).SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method of managing a connection between a user terminal and a wireless communication network and to corresponding equipment.

  For example, for cellular networks as specified by the 3GPP (3rd Generation Partnership Project), handovers (HOs) that allow ongoing user terminal (UE) connections to be maintained between different serving cells in transit ) The procedure is defined.

  For example, in the case of LTE (Long Term Evolution) technology, such an HO procedure is defined in 3GG TS36.331 V12.0.0 (January 2014). In these HO procedures, UEs in a state called "RRC_connected", ie having an active connection to the cellular network, usually monitor the set of neighboring cells. These measurements may trigger the transmission of a measurement report from the UE to the serving base station, which in LTE technology is called eNB (Evolved Node B) in the UE. A typical example of such a triggering event, called “event A3” is the measurement result corresponding to the measurement result of the neighboring cell better than the current serving cell plus the offset, eg the reference signal received power ( It may be expressed in terms of RSRP) or reference signal received quality (RSRQ). The triggering event further requires that such a condition be met for a predetermined minimum period of time specified by a parameter called "timeToTrigger". Based on the measurement report, the serving eNB determines whether to perform HO of the UE. If it is decided to perform the HO of the UE, the serving eNB prepares the HO by sending a HO request to the eNB controlling the target cell for the HO. Also, the serving eNB provides context information of the UE, eg, regarding current access layer (AS) configuration and UE specific radio resource management (RRM) information, as part of this HO request. In response, the eNB controlling the target cell generates an HO command. The serving eNB then forwards the HO command to the UE. This is done in a transparent manner, ie the information provided to the UE is determined at the eNB controlling the target cell and is not changed by the serving eNB. The HO command sent to the UE may be, for example, the identity of the target cell and optionally the frequency and random access, individual radio resource configuration, security configuration, or cell-specific radio network temporary identity (C-RNTI) to be used in the target cell. And so on, which is common to all UEs in the target cell. With such information, the UE may then proceed by performing random access to the target cell. If random access is successful, the UE then confirms the successful completion of the HO to the eNB controlling the target cell which will be the new serving cell for the UE.

  In some scenarios, network initiated HO may be performed without prior event A3 and measurement reports from the UE. In such a case, the UE does not know the target cell before receiving the HO command from the serving eNB.

  As will be appreciated, the above-mentioned known HO procedure requires an unnecessarily complex interaction between the serving eNB, the eNB controlling the target cell, and the UE, which makes such HO time consuming sell.

  In order to meet the future demand on wireless communication networks, a network arrangement called ultra-high density network (UDN) is being discussed (e.g. Ericsson white paper "5G wireless access" published in June 2013 on the Internet) See). For such UDNs, using multiple access points (APs) arranged at high density and higher bandwidth and higher frequency band than eg in LTE technology, eg several hundred MHz or GHz range It has been suggested to use bandwidths up to a bandwidth of up to 10-100 GHz.

  A typical application scenario for a UDN deployment is within a densely populated area, such as a hotspot, office building, or downtown, which may have a high data rate service demand.

  However, for UDN deployments in such high frequency bands, weak scattering and diffraction can result in large attenuation differences between NLOS (non-view) radio links and LOS (view) radio links. As a result, there may be multiple areas with weak signal levels or sudden signal outages, i.e. radio coverage holes. Thus, existing mobility concepts may not be appropriate for such a deployment. For example, higher density APs may result in excessive amounts of HO procedures and unacceptable signaling overhead or service degradation. Furthermore, the sudden signal outage also has the effect that the conventional network initiated HO procedure as described above can not be performed, for example, as the signal outage prevents the UE from sending the measurement report or receiving the HO command. It can have.

  Therefore, there is a need for a technology that allows to manage the connection of the UE to the wireless communication network effectively.

  According to an embodiment of the present invention, there is provided a method of managing a connection between a UE and a wireless communication network. According to the method, an access point of a communication network provides a connection to a UE. The access point determines a plurality of target access points. Furthermore, the access point sends a message to the UE. The message indicates multiple target access points and allows the UE to automatically switch connections to one or more of the target access points.

  According to a further embodiment of the invention, there is provided a method of managing the connection between a UE and a wireless communication network. According to the method, a UE receives a message from an access point of a communication network, which is providing a connection of the UE to a wireless communication network. The message indicates multiple target access points and allows the UE to automatically switch to one or more of the indicated target access points. According to the method, the UE further detects a triggering event. In response to detecting the trigger event, the UE switches connection to one or more of the target access points.

  According to a further embodiment of the present invention, an access point for a wireless communication network is provided. The access point has a wireless interface to provide a connection to the UE. Furthermore, the access point comprises at least one processor. At least one processor is configured to determine a plurality of target access points. Additionally, at least one processor is configured to send a message to the UE. The message indicates multiple target access points and allows the UE to automatically switch connections to one or more of the target access points.

  According to a further embodiment of the present invention, a UE is provided. The UE has a wireless interface to establish a connection to a wireless communication network. Furthermore, the UE has at least one processor. At least one processor is configured to receive the message from an access point of the communication network currently providing the connection of the UE to the wireless communication network. The message indicates multiple target access points and allows the UE to automatically switch to one or more of the indicated target access points. Further, the at least one processor is configured to detect a trigger event and to switch connection to one or more of the target access points in response to detecting the trigger event.

  According to a further embodiment of the invention there is provided a computer program or computer program product comprising program code to be executed by at least one processor of an access point for a wireless communication network, for example in the form of a non-transitory storage medium. Provided. Execution of the program code causes at least one processor to determine a plurality of target access points. Further, execution of the program code causes the at least one processor to send a message to the UE. The message indicates multiple target access points and allows the UE to automatically switch connections to one or more of the target access points.

  According to a further embodiment of the present invention there is provided a computer program or computer program product comprising program code to be executed by at least one processor of a UE, for example in the form of a non-transitory storage medium. Execution of the program code causes the at least one processor to receive messages from an access point of the communication network that is currently providing a connection to the wireless communication network of the UE. The message indicates multiple target access points and allows the UE to automatically switch to one or more of the indicated target access points. Further, execution of the program code causes the at least one processor to detect a trigger event and, in response to detecting the trigger event, causes the connection to one or more of the target access points to switch.

FIG. 1 schematically illustrates a network arrangement for performing automatic connection switching according to an embodiment of the present invention. FIG. 7 is a signaling diagram illustrating an exemplary connection switching procedure according to an embodiment of the present invention. FIG. 7 is a signaling diagram illustrating a further exemplary connection switching procedure according to an embodiment of the present invention. FIG. 7 is a flow chart illustrating a method according to an embodiment of the present invention that may be used to perform the function of connection switching according to an embodiment of the present invention at an access point. FIG. 7 is a flow chart illustrating a method according to an embodiment of the present invention that may be used to perform a connection switching function according to an embodiment of the present invention in a UE. FIG. 4 schematically illustrates an exemplary structure of an access point according to an embodiment of the present invention. FIG. 7 schematically illustrates an exemplary structure of a UE, according to an embodiment of the present invention.

  In the following, the concept according to the embodiments of the present invention will be described in detail by referring to the attached drawings. The described concept relates to managing connection switching in a wireless communication network. In the described embodiment, it is assumed that the wireless communication network is based on a UDN deployment. In particular, the wireless communication network may use closely spaced access points, for example, with a distance between adjacent access points in the range of 1 m to 1000 m, typically in the range of 2 m to 500 m. Furthermore, the access point can operate in a radio frequency band between 10 GHz and 100 GHz, which means that there can be a sufficient difference in link quality between LOS link and NLOS link. However, the concepts described can be applied in a corresponding way to other radio technologies such as LTE, UMTS (Universal Terrestrial Mobile Telecommunications System) or CDMA (Code Division Multiple Access), or CDMA2000. It should be understood that waxing.

  FIG. 1 schematically illustrates the structure of a wireless communication network and an exemplary UE 50. Specifically, FIG. 1 illustrates a plurality of access points 100-1, 100-2, 100-3, 100-4 of a wireless communication network that may be used by the UE 50 to connect to a wireless communication network. . Here, the connection between the UE 50 and the wireless communication network selects an appropriate access point 100-1, 100-2, 100-3, 100-4, and the UE 50 and this access point 100-1, 100-2. , 100-3, 100-4 may be formed by setting up a wireless link. In the exemplary scenario shown in FIG. 1, the connection is formed by a wireless link to access point 100-1. The access point 100-1 maintaining the active connection between the UE 50 and the wireless communication network may also be referred to as the serving access point of the UE 50. In some cases, the connection may utilize multiple wireless links to different access points 100-1, 100-2, 100-3, 100-4 and then cooperate to provide service to UE 50 sell.

  As mentioned above, wireless communication networks may utilize high frequency bands in the range of 10 GHz to 100 GHz, specifically above 30 GHz, such as in the range of about 60 GHz. This frequency range above 30 GHz is also referred to as the MMW (millimeter wave) band.

  In such high frequency bands, relatively large radio attenuation and relatively low radio diffraction have the effect that the LOS radio link will usually have a sufficiently better quality than the NLOS radio link. However, since the LOS radio link is sensitive to propagation obstacles, fast switching between different access points 100-1, 100-2, 100-3, 100-4 is required to maintain connectivity. It is possible. For example, movement of UE 50 causes an obstacle to affect the LOS radio link to access point 100-1, which requires switching of the connection to another access point 100-2, 100-3, 100-4. Means that A similar effect may occur when a person moves to a mobile propagation obstacle, eg, LOS between the UE 50 and the current serving access point 100-1. Because the transition from LOS condition to NLOS condition can occur suddenly, there is a risk of sudden failure of the wireless link to the current serving access point 100-1. This may then have the effect that the UE 50 can not report measurements to the serving access point 100-1 and the serving access point 100-1 can not send control commands to the UE 50. Thus, conventional HO procedures as described, for example, in 3GPP TS 36.331 may not be applicable in these environments.

  According to the concept as described further below, between the access points 100-1, 100-2, 100-3, 100-4, in a way that the UE 50 can perform automatically for the situation described above. It can respond by managing the switching of the For this purpose, the current serving access point 100-1 actively sends a message to UE 50 to allow UE 50 to automatically switch the connection to one or more target access points indicated in the message. It can be sent. Thus, although the overall management of the connection is still network based, the actual switching process may be performed automatically by the UE 50. Hereinafter, the above-mentioned message is also referred to as a switching permission message. The switching grant message may be sent early before it is necessary to switch the connection to another access point and while the connection to the current serving access point 100-1 is still intact. Also, the switching grant message may include information on different indicated target access points to be used by the UE 50 in switching the connection to their target access points. For example, such information may include settings of the target access point, switching conditions, available radio resources, settings that the UE 50 should use to access the target access point, and so on. The UE 50 may then decide to perform the switch and when to perform it, and may select the most appropriate target access point from the indicated target access points. This is accomplished in an automatic manner, ie without requiring further interaction between the UE 50 and the current serving access point 100-1. Thus, fast switching of the connection is also possible in situations where the wireless link to the current serving access point 100-1 fails. In this way, the described concept may allow to avoid interruption of service due to complete failure of the ongoing connection.

  Various conditions may be evaluated by the current serving access point to trigger the transmission of the switching grant message. For example, the current serving access point may perform measurements and trigger the transmission of a switch grant message in response to these measurements. Such measurements may relate, for example, to the quality of the radio link between the UE 50 and the current serving access point 100-1 or the speed at which the UE 50 moves.

  FIG. 2 further illustrates the above concept by reference to an exemplary procedure for switching the connection from the current serving access point 100-1 of the UE 50 to another access point 100-2.

  In the procedure of FIG. 2, in step 201, a connection between the UE 50 and the wireless communication network is established. As explained, the connection is established by setting up a radio link between the UE 50 and the access point 100-1. Thus, the access point 100-1 is a serving access point for the UE 50.

  In step 202, the access point 100-1 detects a trigger event. The triggering event may, for example, correspond to the establishment of the connection at step 201. Furthermore, the triggering event may be based on predetermined measurements and / or evaluations performed by the access point 100-1. For example, the access point 100-1 measures and evaluates the quality of the wireless link between the UE 50 and the access point 100-1 in terms of, for example, channel quality indicators, beacon power levels, or achievable bit rates. It can be done. The triggering event may then correspond to the quality of the radio link falling below a given threshold value. Furthermore, the access point 100-1 may determine the probability of failure of the wireless link between the UE 50 and the access point 100-1. For example, this may be accomplished based on statistical information of a wireless coverage hole in the wireless coverage area of the access point 100-1 and information on the position or movement of the UE 50. Furthermore, the access point 100-1 may be able to measure the speed of the UE 50, for example by evaluating the radio signal transmitted by the UE 50, and the triggering event is a speed of the UE 50 exceeding a given threshold value Can correspond to In this case, it may be considered that the fast moving UE is more likely to request switching to another access point than the slow moving or stationary UE. Furthermore, the access point 100-1 evaluates whether or not the switch permission message transmitted to the UE 50 is valid or expired, and the switch permission message is transmitted when the switch permission message transmitted previously is not valid. Can trigger the transmission of This may be accomplished, for example, by providing a timer that is reset when the access point 100-1 transmits a new switching grant message to the UE 50, and using the expiration of that timer as a triggering event.

  In step 203, the access point 100-1 determines a plurality of target access points that constitute candidates for switching the connection between the UE 50 and the wireless communication network. In the example procedure described, these target access points are assumed to be access points 100-2 and 100-3. The access point 100-1 may apply various criteria to determine the target access point 100-2, 100-3. For example, the access point 100-1 may select an access point located in the moving direction of the UE 50, or an access point that provides wireless coverage in a known coverage hole of a wireless within the coverage area of the access point 100-1.

  The access point 100-1 then transmits a switch permission message 204 to the UE 50. This may be accomplished via a control channel supported by the wireless link between the UE 50 and the access point 100-1. The switching permission message indicates the target access points 100-2 and 100-3 determined in step 203. Furthermore, the switching permission message 204 indicates the target access point 100-2 indicated by the switching permission message 204 without requiring the UE 50 to continue the ongoing connection between the UE 50 and the access point 100-1. Allows automatic switching to one or more of 100-3.

  The switch grant message 204 may carry various types of information that may be used by the UE 50 to perform automatic switching of connections. For example, the switch grant message 204 may indicate one or more conditions for triggering a switch at the UE 50. Such conditions indicate, for example, that the expected radio link quality of one of the target access points 100-2, 100-3 exceeds the radio link quality of the current serving access point 100-1 by a given amount. , Corresponding to the measurements performed by the UE 50. Furthermore, such conditions may be such that the radio link quality of the current serving access point 100-1 is below the first threshold and the expected radio link quality of one of the target access points 100-2, 100-3 is second. May correspond to the measurement performed by the UE 50, which indicates that the threshold value of. As a further example, such a condition may correspond to a failure or connection interruption of the wireless link to the current serving access point 100-1.

  Additionally, the switch grant message 204 may indicate information regarding each of the indicated target access points 100-2, 100-3. For example, such information may include the identity of the target access point 100-2, 100-3, eg, in terms of an index. Furthermore, such information may include sequences, timing, and / or radio resources used for beacon or pilot signals transmitted by the target access points 100-2, 100-3. Additionally, information regarding the communication protocol used by the target access point may be included. Such protocol information may be particularly useful if the access points 100-1, 100-2, 100-3, 100-4 differ with respect to the radio access technology utilized. Further, such information may include radio resource mapping of control channels of target access points 100-2, 100-3. Further, such information may indicate a radio access technology used by the target access point 100-2, 100-3. Furthermore, such information may for example be provided to the target access point 100-2, 100-3 in the form of a random access preamble, or in terms of cell-specific temporary identifiers (eg C-RNTI), to be used by the UE 50. It may include system information for connection.

  Furthermore, the switching grant message 204 is applied by the UE 50 for selection between the different target access points 100-2, 100-3 indicated in the switching grant message 204, for example in the form of priority or selection policy It may contain information that should be.

  The switch grant message 204 may be valid for a given period of time. Such a period may be preset in the UE 50 and the access points 100-1, 100-2, 100-3, 100-4 of the wireless communication network. Furthermore, such a period may be dynamically set for each switch grant message. In the described exemplary procedure, the access point 100-1 may set its time period before sending the switching permission message 204 and indicate the time period in the switching permission message 204. Thereafter, the UE 50 is permitted to perform switching automatically while the period has not yet expired. The expiration of the period may be monitored by providing a corresponding timer at UE 50. The access point 100-1 may set the period according to, for example, the current speed of the UE 50. For example, if the UE 50 is moving at high speed, a shorter period may be appropriate. Also, in certain cases, the switching grant message 204 may be valid until a particular event, for example the reception of a new switching grant message or the release of the connection between the UE 50 and the wireless communication network. In certain scenarios, the switch grant message 204 may prioritize a previously sent switch grant message or may be prioritized by a subsequently sent switch grant message.

  In addition to sending the switch grant message 204, as shown by the messages 205 and 206, the access point 100-1 also determines the information about the UE 50 as the target access point 100-2, 100- determined in step 203. Provided to 3. Such information may include, for example, the context of UE 50 as provided to maintain a connection between UE 50 and a wireless communication network. Furthermore, the access point 100-1 may initiate transfer of user plane data addressed to the UE 50 to the target access points 100-2, 100-3. In this manner, the target access points 100-2, 100-3 may be ready to continue providing service to the UE 50 immediately after switching connections. The information provided to the target access points 100-2, 100-3 may also indicate the lifetime of the switching grant message 204. Here, a target access time is indicated for the target cell that is greater than that applied by the UE 50, whereby the target access is attempted when the UE 50 attempts to switch connection at the end of the end of the active period indicated to the UE 50. It may be useful to ensure that points 100-2, 100-3 are ready. When the access point 100-1 determines the priorities of the target access points 100-2 and 100-3, the access point 100-1 sends the different target access points 100-2 and 100-3 in the descending order of priority. The information may be sent.

  In response to receiving the switching grant message 204, the UE 50 may initiate a monitoring procedure for the target access points 100-2, 100-3 indicated in the switching grant message 204. For example, UE 50 may perform measurements to determine which of the indicated target access points 100-2, 100-3 provides the highest expected radio link quality. After such a determination, UE 50 may continue to monitor only target access points 100-2, 100-3 having the highest expected radio link quality. In other scenarios, UE 50 may continue monitoring all indicated target access points 100-2, 100-3. The monitoring uses information provided in the switching grant message 204, eg, a sequence used for beacons or pilot signals transmitted by the target access points 100-2, 100-3 and / or timing and / or radio resources. sell.

  However, the UE 50 does not perform an immediate switching of the connection. Rather, UE 50 performs switching of the connection operation only in response to detecting a trigger event, as described by step 207. Such trigger event may be preset in the UE 50 or may be indicated in the switching permission message 204. For example, the triggering event may correspond to a failure of the wireless link between the UE 50 and the current serving access point 100-1. Furthermore, such triggering events may cause the expected radio link quality of one of the target access points 100-2, 100-3 to exceed the radio link quality of the current serving access point 100-1 by a given amount. It may correspond to the measurements performed by the UE 50 shown. Further, such trigger event may cause the radio link quality of the current serving access point 100-1 to fall below a first threshold and the expected radio link quality of one of the target access points 100-2, 100-3 to It may correspond to a measurement performed by the UE 50 indicating that the second threshold is exceeded.

  In response to detecting the trigger event in step 207, the UE 50 initiates switching of the connection to one of the target access points 100-2, 100-3 indicated in the switching grant message 204. For this purpose, UE 50 may make a selection between the indicated target access points 100-2, 100-3 as indicated by step 208. For example, UE 50 may select the target access point 100-2, 100-3 that provides the highest expected radio link quality. In the example procedure described, it is assumed that the UE 50 selects the target access point 100-2. Thereafter, as described by step 209, the UE 50 establishes a new radio link for the target access point 100-2 selected in step 208 to become a new serving access point for the UE 50. Perform a switch.

  FIG. 3 shows an exemplary procedure for switching the connection of the UE 50 from the current serving access point 100-1 to another access point 100-2. The procedure of FIG. 3 is similar to that of FIG. 2 in many aspects. However, in the procedure of FIG. 3, different processes are used to provide the target access point 100-2 with information about the UE 50.

  In the procedure of FIG. 3, in step 301, a connection between the UE 50 and a wireless communication network is established. As explained, the connection is established by setting up a radio link between the UE 50 and the access point 100-1. Thus, the access point 100-1 is a serving access point for the UE 50.

  In step 302, the access point 100-1 detects a trigger event. The triggering event may, for example, correspond to the establishment of a connection at step 301. Furthermore, the triggering event may be based on predetermined measurements and / or evaluations performed by the access point 100-1. For example, the access point 100-1 measures and evaluates the quality of the wireless link between the UE 50 and the access point 100-1 in terms of, for example, channel quality indicators, beacon power levels, or achievable bit rates. It can be done. The triggering event may then correspond to the quality of the radio link falling below a given threshold value. Furthermore, the access point 100-1 may determine the probability of failure of the wireless link between the UE 50 and the access point 100-1. For example, this may be accomplished based on statistical information of a wireless coverage hole in the wireless coverage area of the access point 100-1 and information on the position or movement of the UE 50. Furthermore, the access point 100-1 may be able to measure the speed of the UE 50, for example by evaluating the radio signal transmitted by the UE 50, and the triggering event is a speed of the UE 50 exceeding a given threshold value Can correspond to In this case, it may be considered that the fast moving UE is more likely to request switching to another access point than the slow moving or stationary UE. Furthermore, the access point 100-1 evaluates whether or not the switch permission message transmitted to the UE 50 is valid or expired, and the switch permission message is transmitted when the switch permission message transmitted previously is not valid. Can trigger the transmission of This may be accomplished, for example, by providing a timer that is reset when the access point 100-1 transmits a new switching grant message to the UE 50, and using the expiration of that timer as a triggering event.

  In step 303, the access point 100-1 determines a plurality of target access points that constitute a candidate before switching the connection between the UE 50 and the wireless communication network. In the example procedure described, these target access points are assumed to be access points 100-2 and 100-3. The access point 100-1 may apply various criteria to determine the target access point 100-2, 100-3. For example, the access point 100-1 may select an access point located in the moving direction of the UE 50, or an access point that provides wireless coverage in a known coverage hole of a wireless within the coverage area of the access point 100-1.

  The access point 100-1 then transmits a switch permission message 304 to the UE 50. This may be accomplished via a control channel supported by the wireless link between the UE 50 and the access point 100-1. The switching permission message 304 indicates the target access points 100-2 and 100-3 determined in step 303. Furthermore, the switching permission message 304 indicates the target access point 100-2 indicated in the switching permission message 304, without requesting the ongoing connection of the UE 50 between the UE 50 and the access point 100-1. Allows automatic switching to one or more of 100-3.

  The switch grant message 304 may carry various types of information that may be used by the UE 50 to perform automatic switching of connections. For example, the switch grant message 304 may indicate one or more conditions for triggering a switch at the UE 50. Such conditions indicate, for example, that the expected radio link quality of one of the target access points 100-2, 100-3 exceeds the radio link quality of the current serving access point 100-1 by a given amount. , Corresponding to the measurements performed by the UE 50. Furthermore, such conditions may be such that the radio link quality of the current serving access point 100-1 is below the first threshold and the expected radio link quality of one of the target access points 100-2, 100-3 is second. May correspond to the measurement performed by the UE 50, which indicates that the threshold value of. As a further example, such a condition may correspond to a failure or connection interruption of the wireless link to the current serving access point 100-1.

  Additionally, the switch grant message 304 may indicate information regarding each of the indicated target access points 100-2, 100-3. For example, such information may include the identity of the target access point 100-2, 100-3, eg, in terms of an index. Furthermore, such information may include sequences, timing, and / or radio resources used for beacon or pilot signals transmitted by the target access points 100-2, 100-3. Furthermore, information on the communication protocol used by the target access points 100-2, 100-3 may be included. Such protocol information may be particularly useful if the access points 100-1, 100-2, 100-3, 100-4 differ with respect to the radio access technology utilized. Further, such information may include radio resource mapping of control channels of target access points 100-2, 100-3. Further, such information may indicate a radio access technology used by the target access point 100-2, 100-3. Furthermore, such information may for example be provided to the target access point 100-2, 100-3 in the form of a random access preamble, or in terms of cell-specific temporary identifiers (eg C-RNTI), to be used by the UE 50. It may include system information for connection.

  Furthermore, the switching grant message 304 is applied by the UE 50 for selection between the different target access points 100-2, 100-3 indicated in the switching grant message 304, for example in the form of priority or selection policy It may contain information that should be.

  The switch grant message 304 may be valid for a given period of time. Such a period may be preset in the UE 50 and the access points 100-1, 100-2, 100-3, 100-4, and 100-5 of the wireless communication network. Furthermore, such a period may be dynamically set for each switch grant message. In the illustrated exemplary procedure, the access point 100-1 may set its period before transmitting the switch permission message 304 and indicate the period in the switch permission message 304. Thereafter, the UE 50 is permitted to perform switching automatically while the period has not yet expired. The expiration of the period may be monitored by providing a corresponding timer at UE 50. The access point 100-1 may set the period according to, for example, the current speed of the UE 50. For example, if the UE 50 is moving at high speed, a shorter period may be appropriate. Also, in certain cases, the switching grant message 304 may be valid until a particular event, for example the reception of a new switching grant message or the release of the connection between the UE 50 and the wireless communication network. In certain scenarios, the switch grant message 304 may prioritize a previously sent switch grant message or may be prioritized by a subsequently sent switch grant message.

  In response to receiving the switching grant message 304, the UE 50 may initiate a monitoring procedure for the target access points 100-2, 100-3 indicated in the switching grant message 304. For example, UE 50 may perform measurements to determine which of the indicated target access points 100-2, 100-3 provides the highest expected radio link quality. After such a determination, UE 50 may continue to monitor only target access points 100-2, 100-3 having the highest expected radio link quality. In other scenarios, UE 50 may continue monitoring all indicated target access points 100-2, 100-3. The monitoring uses information provided in the switching grant message 304, eg, a sequence used for beacons or pilot signals transmitted by the target access points 100-2, 100-3 and / or timing and / or radio resources. sell.

  However, the UE 50 does not perform an immediate switching of the connection. Rather, UE 50 performs switching of the connection operation only in response to detecting a trigger event, as described by step 305. Such trigger event may be preset in the UE 50 or may be indicated in the switching permission message 304. For example, the triggering event may correspond to a failure of the wireless link between the UE 50 and the current serving access point 100-1. Furthermore, such triggering events may cause the expected radio link quality of one of the target access points 100-2, 100-3 to exceed the radio link quality of the current serving access point 100-1 by a given amount. It may correspond to the measurements performed by the UE 50 shown. Further, such trigger event may cause the radio link quality of the current serving access point 100-1 to fall below a first threshold and the expected radio link quality of one of the target access points 100-2, 100-3 to It may correspond to a measurement performed by the UE 50 indicating that the second threshold is exceeded.

  In response to detecting the trigger event in step 305, the UE 50 initiates switching of the connection to one of the target access points 100-2, 100-3 indicated in the switching grant message 304. For this purpose, the UE 50 may make a selection between the indicated target access points 100-2, 100-3 as indicated by step 306. For example, UE 50 may select the target access point 100-2, 100-3 that provides the highest expected radio link quality. In the example procedure described, it is assumed that the UE 50 selects the target access point 100-2. Thereafter, as described by step 307, the UE 50 establishes a new radio link for the target access point 100-2 selected in step 306 to become a new serving access point for the UE 50. Perform a switch.

  When switching connectivity in step 307, the UE 50 also indicates the previous serving access point identity to the new serving access point 100-2, for example in terms of an index. The new serving access point 100-2 may use this identity to transmit a request 308 for information regarding the UE 50 to the previous serving access point 100-1.

  In response to the request 308, as indicated by the message 309, the access point 100-1 provides information about the UE 50 to the new serving access point 100-2. Such information may include, for example, the context of UE 50 as provided to maintain a connection between UE 50 and a wireless communication network.

  The connection switching procedure described above may be used in conjunction with other types of connection switching procedures, for example, the UE 50 is instructed by the current serving access point to immediately switch to a predetermined target access point. In such a case, the automatic switching procedure may be used as a backup for the case where an instruction for immediate switching is not available, eg due to a failure of the radio link between the UE 50 and the current serving access point. Therefore, when the UE 50 first receives the switch permission message and then receives a command for immediate switching of the connection, the UE 50 first attempts to perform the immediate switching, and the automatic switching procedure is performed if this immediate switching fails. To continue.

  FIG. 5 illustrates a method that may be used to implement the above-described concept at an access point of a wireless communication network, eg at one of the access points 100-1, 100-2, 100-3, 100-4. The flowchart for demonstrating is shown. If a processor based implementation of the access point is used, the method steps may be performed by one or more processors of the access point. For this purpose, the processor may execute correspondingly configured program code. Furthermore, at least some of the corresponding functionality may be implemented in hardware in the processor.

  At step 410, the access point provides a connection between a UE, eg, UE 50, and a wireless communication network. The connection is based on the radio link between the UE and the access point. In some scenarios, the connection may be further based on an additional wireless link between the UE and another access point.

  At step 420, the access point detects a trigger event. Various types of trigger events may be used. For example, the access point may send a message in response to the connection between the UE and the communication network being established. In addition, the access point may determine a failure probability of the wireless link between the UE and the access point and may send a message in response to the failure probability exceeding a threshold. In addition, the access point may measure the quality of the wireless link between the user terminal and the access point and may send a message in response to the quality of the wireless link falling below a threshold. In addition, the access point may measure the velocity of the UE and may send a message in response to the velocity exceeding a threshold. Further, the access point may send a message in response to determining that additional target access points previously indicated to the user terminal are no longer valid. In the example procedure of FIGS. 2 and 3, this is accomplished by considering the lifetime of the switch grant message.

  In step 430, the access point determines a plurality of target access points. This determination may be based, for example, on the measurements performed by the access point.

  At step 440, the access point sends a message to the UE. The message indicates the target access point determined in step 430 and allows the UE to automatically switch connections to one or more of the target access points. As mentioned above, this automatic switching does not require any further communication between the UE and the access point. The switching allowance messages 204 and 304 described above are examples of such messages.

  The message may further indicate conditions to be evaluated by the UE to trigger a switch to one or more of the target access points. For example, such conditions may be based on measurements performed by the UE, eg, to determine radio link quality. For example, switching may be triggered if the radio link quality expected for one of the target access points exceeds the radio link quality of the access point by a given amount. Further, switching may be triggered if the radio link quality expected for one of the target access points is above a first threshold and the radio link quality of the access point is below a second threshold. Furthermore, switching may be triggered if the radio link between the UE and the access point fails.

  For each of the target access points, the message may further indicate the information to be used by the UE to connect to this target access point. For example, this may include radio settings, access parameters, radio resources, cell-specific temporary identifiers to be used by the UE, etc. Additionally, the message may indicate the priority of the target access point.

  Further, the access point may transmit information regarding the UE to each of the plurality of target access points. This information may be used by the target access point to prepare for potential switching of connections. As mentioned above, this information may in particular include the context of the UE, as it is used to maintain the ongoing connection between the UE and the wireless communication network. As an option, the access point may transmit such information after switching of the connection to one or more of the plurality of target access points. In such a case, the access point may receive a request from the target access point to which the connection has been switched, and may transmit information on the UE to the target access point in response to the request.

  FIG. 5 shows a flow chart to illustrate a method that may be used to implement the above described concept at the UE, eg at UE 50. If a processor based implementation of a UE is used, the method steps may be performed by one or more processors of the UE. For this purpose, the processor may execute correspondingly configured program code. Furthermore, at least some of the corresponding functionality may be implemented in hardware in the processor.

  At step 510, a connection is established to a wireless communication network, eg, the wireless communication network using the arrangement described in connection with FIG. The connection is based on the wireless link between the UE and the access point of the wireless communication network. In some scenarios, the connection may be further based on an additional wireless link between the UE and another access point.

  In step 520, the UE receives a message from the access point currently providing the connection. The message indicates multiple target access points and allows the UE to automatically switch connections to one or more of the target access points. As mentioned above, this automatic switching does not require any further communication between the UE and the access point. The switching allowance messages 204 and 304 described above are examples of such messages. In some scenarios, a UE may receive a message in response to establishing a connection between the UE and a communication network.

  For each of the target access points, the message may further indicate the information to be used by the UE to connect to this target access point. For example, this may include radio settings, access parameters, radio resources, cell-specific temporary identifiers to be used by the UE, etc. Additionally, the message may indicate the priority of the target access point.

  In step 530, the UE determines if a trigger event has occurred. If a triggering event has occurred, the method continues with steps 540 and 550, as indicated by branch "Y". If a triggering event has not occurred, the method continues with step 560, as indicated by branch "N".

  The triggering event may be based on the quality of the radio link between the UE and the target access point indicated in the message, as measured by the UE. The triggering event may be based on the quality of the radio link between the UE and the access point as measured by the UE. For example, the triggering event may correspond to the expected radio link quality for one of the target access points exceeding the access point's radio link quality by a given amount. Furthermore, the triggering event may correspond to the expected radio link quality for one of the target access points being above the first threshold and the radio link quality of the seven access points being below the second threshold. Furthermore, the triggering event may correspond to a failure or a disconnection of the wireless link between the UE and the access point. The message of step 520 indicates the condition to be evaluated by the UE to trigger the switch to the target access point, and the triggering event may be based on the indicated condition.

  At step 540, the UE may select one or more target access points from the plurality of target access points indicated in the message of step 520. This may be accomplished based on the information indicated in the message of step 520. For example, the message may indicate the priority of the target access point, and the UE may select the target access point according to the indicated priority. Alternatively, more complex selection policies may be applied by the UE, eg, selection policies based on measurements performed by the UE, and may be indicated in the message.

  In step 550, the UE switches connection to the target access point selected in step 540. This may be accomplished based on the information indicated in the message of step 520. Specifically, the message may include, for each of the indicated target access points, information to be used by the UE to connect to this target access point, and the UE switches based on the indicated information. Can be performed. In some scenarios, after switching to the target access point, the UE may indicate to the target access point information about the access point, eg the identity of the access point. If this target access point will be a new serving access point for the UE, this target access point may use this information to obtain information about the UE from the previous serving access point.

  In step 560, if no trigger event is detected in step 530, the UE may maintain the current access point to maintain connection.

  It should be understood that the methods of FIGS. 4 and 5 may be used, for example, in combination in a UE operating according to the method of FIG. 5 and an access point serving UEs operating according to the method of FIG. .

  FIG. 6 shows an exemplary structure of an access point for a wireless communication network that can be used to implement the above described concept. For example, the illustrated structure may be used to implement the functions described above of access point 100-1 currently providing a connection between UE 50 and a wireless communication network.

  In the illustrated example, the access point includes a wireless interface 610 that may be used to provide a connection between the wireless communication network and the UE. Additionally, the access point may include a backhaul interface 620 that may be used to communicate with other nodes of the wireless communication network, eg, other access points or gateway nodes.

  Further, the access point includes one or more processors connected to the interfaces 610 and 620 and a memory 660 connected to the processors. Memory 660 may include read only memory (ROM), such as flash ROM, RAM, such as dynamic RAM (DRAM) or static RAM (SRAM), mass storage, such as hard disk or solid state disk, or the like. . The memory includes suitably configured program code modules to be executed by the processor 650 to implement the functions described with respect to the method of FIG. 4, in particular the functions described above for the access node 100-1. More specifically, the program code module in the memory 660 performs the above-mentioned function of performing a measurement to trigger the transmission of the switch grant message or to determine the target access point indicated in the switch grant message. A measurement module 670 may be included to implement. In addition, the program code module in memory 660 provides a connection between the UE and the wireless communication network, selects a target access point or addresses communication with such target access point, and a switch grant message And a connection management module 680 for implementing the functions described above. Still further, the memory 660 may include a control module 690 for implementing general control functions, such as control of the wireless interface, processing of messages, control of transfer of data, or the like.

  It should be understood that the structure shown in FIG. 6 is merely schematic, and the access point may actually include additional components not illustrated for the sake of clarity, such as additional interfaces or additional processors. is there. It should also be understood that memory 660 may include additional types of program code modules not illustrated, such as program code modules for performing the known functions of the access point. Also, in some implementations, a computer program is accessed, for example, in the form of a physical medium storing program code modules to be stored in memory 660, or by making such program code available for download. It can be provided to implement point functionality.

  FIG. 7 shows an exemplary structure of a UE that may be used to implement the above-described concept. For example, the described structure may be used to perform the above-described functions of UE 50.

  In the illustrated example, the UE includes a wireless interface 710 that may be used to establish a connection to a wireless communication network.

  Further, the UE includes one or more processors connected to the interfaces 710 and 720 and a memory 760 connected to the processor 750. Memory 760 may include ROM, eg, flash ROM, RAM, eg, DRAM or SRAM, mass storage, eg, hard disk or solid state disk, or the like. Memory 760 includes suitably configured program code modules to be executed by processor 750 for performing the functions described with respect to the method of FIG. 5, in particular the functions described above of UE 50. More specifically, a program code module in memory 760 is a measurement module for implementing the above-described function of triggering a switch or performing a measurement to select a target access point among a plurality of candidates. 770 may be included. Furthermore, the program code module in the memory 760 maintains the connection between the UE and the wireless communication network, selects the target access point, and performs the switching of the connection as permitted by the switching grant message. A connection management module 780 may be included to perform the Still further, memory 760 may include control module 790 for performing general control functions, such as control of the wireless interface, processing of control messages, or the like.

  It is understood that the structure as illustrated in FIG. 7 is merely schematic and that the UE may in fact include further components not illustrated for the purpose of clarity, eg further interfaces or further processors. It should. Also, it should be understood that memory 760 may include additional types of program code modules not illustrated, eg, program code modules for performing known functions of the UE. Also, in some implementations, the computer program is a UE, for example, in the form of a physical medium storing program code modules to be stored in memory 760, or by making such program code available for download. Can be provided to implement the functionality of

  As will be appreciated, the above described concept can be used to effectively manage the connection of the UE to the wireless communication network. Specifically, by allowing the UE to automatically switch connections from one or more target access points to one or more, the radio link between the UE and the UE's current serving access point fails Even in this case, connection switching can be performed.

  It should be understood that the examples and embodiments described above are for illustration only and are easily affected by various modifications. For example, the concepts described may be used in connection with various types of wireless communication networks, without being limited to the UDN techniques used in the example implementations described above. Furthermore, it is understood that the above described concept can be implemented by using correspondingly designed software to be executed by one or more processors of existing equipment or by using dedicated device hardware It should be.

Claims (46)

A method of managing the connection between a user terminal (50) and a wireless communication network, comprising
The access point (100-1) of the communication network providing a connection to the user terminal (50);
The access point (100-1) determines a plurality of target access points (100-2, 100-3);
The access point (100-1) sending a message (204; 304) to the user terminal (50), the message (204; 304) comprising the plurality of target access points (100-2) , 100-3) and allow the user terminal (50) to automatically switch the connection to one or more of the target access points (100-2, 100-3). And how to. The message (204; 304) is further evaluated by the user terminal (50) to trigger the switching to the one or more of the target access points (100-2, 100-3) Indicate the conditions to be
A method according to claim 1, characterized in that. The message (204; 304) further indicates, for each of the target access points (100-2, 100-3), the user terminal for connection to the target access point (100-2, 100-3). Indicates the information to be used by (50),
The method according to claim 1 or 2, characterized in that: The message (204; 304) further indicates the priority of the target access point (100-2, 100-3),
A method according to any one of the preceding claims, characterized in that. Including transmitting the message (204; 304) in response to the access point (100-1) establishing the connection between the user terminal (50) and the communication network.
5. A method according to any one of the preceding claims, characterized in that. The access point (100-1) determining a failure probability of a wireless link between the user terminal (50) and the access point (100-1);
The access point (100-1) transmitting the message (204; 304) in response to the failure probability exceeding a threshold value;
A method according to any one of the preceding claims, characterized in that. The access point (100-1) measuring the quality of a wireless link between the user terminal (50) and the access point (100-1);
The access point (100-1) sending the message (204; 304) in response to the quality of the wireless link falling below a threshold.
The method according to any one of claims 1 to 6, characterized in that. The access point (100-1) measuring the speed of the user terminal (50);
The access point (100-1) sending the message (204; 304) in response to the speed exceeding a threshold;
A method according to any one of the preceding claims, characterized in that. That the access point (100-1) sends the message (204; 304) in response to the further plurality of target access points previously indicated to the user terminal (50) being no longer valid Including
A method according to any one of the preceding claims, characterized in that. The access point (100-1) is a potential of the connection to the target access point (100-2, 100-3) for each of the plurality of target access points (100-2, 100-3). Transmitting information associated with the user terminal (50) to prepare for the transition.
10. A method according to any one of the preceding claims, characterized in that. After switching the connection to one or more (100-2) of the plurality of target access points, the access point (100-1) requests (308) from the target access point (100-2). To receive
And in response to the request (308), the access point transmits information on the user terminal (50) to the target access point (100-2).
11. A method according to any one of the preceding claims, characterized in that. A method of managing the connection between a user terminal (50) and a wireless communication network, comprising
Comprising the user terminal (50) receiving a message (204; 304) from the access point (100-1) of the communication network, wherein the access point (100-1) is the user terminal (50) The message (204; 304) indicates a plurality of target access points (100-2, 100-3) and the user terminal (50) indicates Permit to automatically switch the connection to one or more of the target access points (100-2, 100-3)
The user terminal (50) detecting a trigger event;
The user terminal (50) switching the connection to one or more of the target access points (100-2, 100-3) in response to detecting the trigger event;
A method characterized by comprising. The trigger event is a radio link between the user terminal (50) and the one or more of the target access points (100-2, 100-3) measured by the user terminal (50). Based on quality,
A method according to claim 12, characterized in that. The triggering event is based on the quality of the radio link between the user terminal (50) and the access point (100-1), measured by the user terminal (50),
Method according to claim 12 or 13, characterized in that. The trigger event includes an interruption of the connection,
The method according to any one of claims 12 to 14, characterized in that. The message (204; 304) is further evaluated by the user terminal (50) to trigger the switching to the one or more of the target access points (100-2, 100-3) Indicate the conditions to be
The trigger event is based on the indicated condition,
The method according to any one of claims 12 to 15, characterized in that. The message (204; 304) is further connected to the target access point (100-2, 100-3) for each of the indicated target access points (100-2, 100-3). Indicates the information to be used by the user terminal (50),
The user terminal (50) performs the switching to the one or more of the target access points (100-2, 100-3) based on the indicated information.
17. A method according to any one of claims 12 to 16, characterized in that. The message further indicates the priority of the target access point (100-2, 100-3),
The user terminal (50) determines the one or more of the target access points (100-2, 100-3) according to the indicated priority.
The method according to any one of claims 12 to 17, characterized in that. Receiving the message (204; 304) in response to the user terminal (50) establishing the connection between the user terminal (50) and the communication network;
19. A method according to any one of the claims 12-18, characterized in that. After switching to the one or more (100-2) of the target access points, the user terminal (50) indicates information regarding the access point to the target access point (100-2). ,
20. A method according to any one of the claims 12-19, characterized in that. An access point (100-1; 100-2; 100-3) for a wireless communication network,
A wireless interface (610) for providing a connection to the user terminal (50);
And at least one processor (650), said at least one processor (650) comprising
Determine multiple target access points (100-2, 100-3),
Configured to transmit a message (204; 304) to the user terminal (50), the message (204; 304) indicating the plurality of target access points (100-2, 100-3) and the user Allow the terminal (50) to automatically switch the connection to one or more of the target access points (100-2, 100-3),
An access point characterized by The message (204; 304) is further evaluated by the user terminal (50) to trigger the switching to the one or more of the target access points (100-2, 100-3) Indicate the conditions to be
The access point according to claim 21, characterized in that. The message (204; 304) further indicates, for each of the target access points (100-2, 100-3), the user terminal for connection to the target access point (100-2, 100-3). Indicates the information to be used by (50),
The access point according to claim 21 or 22, characterized in that: The message (204; 304) further indicates the priority of the target access point (100-2, 100-3),
The access point according to any one of claims 21 to 23, characterized in that: The at least one processor (650) is configured to send the message (204; 304) in response to establishing the connection between the user terminal (50) and the communication network.
The access point according to any one of claims 21 to 24, characterized in that. The at least one processor (650) is
Determining the probability of failure of the radio link between the user terminal (50) and the access point (100-1);
-Sending the message (204; 304) in response to the failure probability rising above a threshold,
The access point according to any one of claims 21 to 25, characterized in that. The at least one processor (650) is
Measuring the quality of the radio link between the user terminal (50) and the access point (100-1);
-Sending the message (203; 304) in response to the quality of the wireless link falling below a threshold,
The access point according to any one of claims 21 to 26, characterized in that. The at least one processor (650) is
-Measuring the speed of the user terminal (50);
-Sending the message (204; 304) in response to the speed rising above a threshold,
The access point according to any one of claims 21 to 27, characterized in that. Said at least one processor (650) in response to having determined that a further plurality of target access points previously indicated to said user terminal (50) have become invalid; Configured to send,
The access point according to any one of claims 21 to 28, characterized in that. The at least one processor (650), for each of the plurality of target access points (100-2, 100-3), prepares the target access point for potential switching of the connection, Configured to transmit information regarding the user terminal (50),
The access point according to any one of claims 21 to 29, characterized in that. The at least one processor (650) is
Receiving a request (308) from the target access point (100-2) after switching of the connection to one or more (100-2) of the plurality of target access points;
-Sending information regarding the user terminal (50) to the target access point (100-2) in response to the request (308),
The access point according to any one of claims 21 to 30, characterized in that: The at least one processor (650) is configured to perform the steps of the method according to any one of the preceding claims.
The access point according to claim 21, characterized in that. A user terminal (50),
A wireless interface (710) for establishing a connection to a wireless communication network;
And at least one processor (750), said at least one processor (750) comprising
-Receiving a message (204; 304) from the access point (100-1) of the communication network, wherein the access point (100-1) is configured to send the user terminal (50) to the wireless communication network A connection is currently provided and the message (204; 304) indicates a plurality of target access points (100-2, 100-3) and the target access point (100-) to which the user terminal (50) is indicated. Automatically switching the connection to one or more of 2, 100-3),
-Detect trigger events,
Switching the connection to one or more of the target access points (100-2, 100-3) in response to detecting the trigger event;
A user terminal characterized in that: The trigger event is a radio link between the user terminal (50) and the one or more of the target access points (100-2, 100-3) measured by the user terminal (50). Based on quality,
The user terminal according to claim 33, characterized in that: The triggering event is based on the quality of the radio link between the user terminal (50) and the access point (100-1), measured by the user terminal (50),
A user terminal according to claim 33 or 34, characterized in that: The trigger event includes an interruption of the connection,
The user terminal according to any one of claims 33 to 35, characterized in that: The message (204; 304) is further evaluated by the user terminal (50) to trigger the switching to the one or more of the target access points (100-2, 100-3) Indicate the conditions to be
The trigger event is based on the indicated condition,
The user terminal according to any one of claims 33 to 36, characterized in that. The message (204; 304) is further connected to the target access point (100-2, 100-3) for each of the indicated target access points (100-2, 100-3). Indicates the information to be used by the user terminal (50),
The at least one processor (750) is configured to perform the switching to the one or more of the target access points (100-2, 100-3) based on the indicated information. The
38. The user terminal according to any one of claims 33 to 37, characterized in that: The message further indicates the priority of the target access point (100-2, 100-3),
The at least one processor (750) is configured to determine the one or more of the target access points (100-2, 100-3) according to the indicated priority.
The user terminal according to any one of claims 33 to 38, characterized in that: The at least one processor (750) is configured to receive the message (204; 304) in response to establishing the connection between the user terminal (50) and the communication network.
The user terminal according to any one of claims 33 to 39, characterized in that: The at least one processor (750) may present information about the access point to the target access point (100-2) after switching to the one or more (100-2) of the target access points Configured to
41. The user terminal according to any one of claims 33 to 40, characterized in that: The at least one processor (750) is configured to perform the steps of the method according to any one of claims 12 to 20.
The user terminal according to claim 33, characterized in that:   A computer program comprising program code to be executed by at least one processor (650) of an access point (100-1, 100-2, 100-3) of a wireless communication network, the execution of said program code comprising A computer program, causing the at least one processor (650) to perform the steps of the method according to any one of the preceding claims.   A computer program product comprising program code to be executed by at least one processor (650) of an access point (100-1, 100-2, 100-3) of a wireless communication network, said program code executing A computer program product, characterized in that it causes the at least one processor (650) to carry out the steps of the method according to any one of the preceding claims.   A computer program comprising program code to be executed by at least one processor (750) of a user terminal (50), the execution of said program code being claimed in said at least one processor (750). A computer program comprising performing the steps of the method according to any one of the preceding claims.   A computer program product comprising program code to be executed by at least one processor (750) of a user terminal (50), the execution of said program code comprising claim 12 from said at least one processor (750). 20. A computer program product for performing the steps of the method according to any one of 20.

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