Patent Description:
In a wireless communications system, a mobility technology is a key technology. For a terminal device in a connected state, the terminal device may move between different base stations through a cell handover process.

Currently, a manner for performing cell handover by a terminal device is provided in a long term evolution (Long Term Evolution, LTE) system. In such a manner, a source cell instructs the terminal device to measure the source cell and a target cell of the terminal device. After the measurement, the terminal device autonomously determines, based on an obtained measurement report, whether to perform cell handover.

As can be learned, in such a handover manner, the terminal device autonomously determines whether to perform cell handover, and a disadvantage of such a handover manner is that a network side loses control over the terminal device. In addition, in a process in which the terminal device hands over between two base stations, the base stations need to cooperate with each other. For example, a target base station usually reserves a resource for the terminal device that is to perform handover. Therefore, if the target base station reserves the resource, but the terminal device never initiates handover, a waste of resources is caused.

<NPL>, discusses the principle of a conditional handover command for NR.

<CIT> discloses a method in a primary network node for handling a handover of a wireless device from a primary cell serviced by the primary network node to a neighbour cell serviced by a neighbour network node. The method comprises sending a configuration message to the wireless device, comprising instructions to evaluate in parallel a first handover event and a second handover event. The first event is based on signal quality measurements from both cells. The second event is based on signal strength measurements from both cells. To evaluate comprises determining if an entering condition for each of the events is satisfied. The method further comprises sending a handover command to the wireless device when one of the entering condition for the first handover event is satisfied over a first time period, and the entering condition for the second handover event is satisfied over a second time period.

Embodiments of the present invention provide a cell handover method, an apparatus, and a computer-readable storage medium to strengthen control of a network device over a terminal device. The invention is defined in the claims. The invention corresponds to the embodiment disclosed in <FIG>. Other embodiments are not encompassed by the wording of the claims, but as examples useful for understanding the invention.

The following further describes embodiments of the present invention in detail with reference to the accompanying drawings.

Technical solutions described in this specification may be applied to an LTE system or a fifth generation (<NUM> Generation, <NUM>) mobile communications technology system, or may be applied to a next-generation mobile communications system.

The following describes some terms in the embodiments of the present invention, to help a person skilled in the art have a better understanding.

To better understand the technical solutions in the embodiments of the present invention, the following first describes an application scenario of the embodiments of the present invention.

<FIG> shows an application scenario according to an embodiment of the present invention. <FIG> includes a terminal device and a base station. The base station is provided with three cells, which are a cell <NUM>, a cell <NUM>, and a cell <NUM>. The cell <NUM> is a current serving cell of the terminal device. If the terminal device performs cell handover, the terminal device may hand over to the cell <NUM> or the cell <NUM>.

In the application scenario shown in <FIG>, intra-base station handover is used as an example, to be specific, a source cell before handover and a target cell after the handover belong to a same base station. In this embodiment of the present invention, the source cell before the handover and the target cell after the handover may alternatively belong to different base stations. <FIG> shows another application scenario according to an embodiment of the present invention. <FIG> includes a terminal device, a base station <NUM>, and a base station <NUM>. The base station <NUM> is provided with three cells, which are a cell <NUM>, a cell <NUM>, and a cell <NUM>. The base station <NUM> is provided with two cells, which are a cell <NUM> and a cell <NUM>. The cell <NUM> is a current serving cell of the terminal device. If the terminal device performs cell handover, the terminal device may hand over to the cell <NUM> or the cell <NUM>, that is, perform intra-base station handover, or may hand over to the cell <NUM> or the cell <NUM>, that is, perform inter-base station handover.

The following first describes a cell handover method by using an example. Such a handover method may be referred to as "conditional handover (conditional handover)". In such a handover method, the terminal device determines whether to perform cell handover. Such a determining manner for the terminal device is referred to as "conditional determining". <FIG> is a flowchart of a conditional handover method. In the following description process, an example in which this example is applied to the scenario shown in <FIG> is used. A cell <NUM>, a cell <NUM>, or a cell <NUM> provided by a base station <NUM> is a serving cell of a terminal device before handover, and a cell <NUM> or a cell <NUM> provided by a base station <NUM> is a cell to which the terminal device can hand over.

The terminal device exchanges some user data (User Data) with the base station <NUM>. That is, the terminal device exchanges user data with the serving cell provided by the base station <NUM>.

The base station <NUM> may perform handover determining based on the user data. The handover determining herein is different from determining whether the terminal device performs cell handover described in the following portion of this specification. Instead, the handover determining may be understood as determining whether to send an early handover command (Early HO command) to the terminal device.

The base station <NUM> and the base station <NUM> perform configuration and prepare for handover (Handover, HO).

For example, the base station <NUM> and the base station <NUM> perform active mode reference signal resource pre-configuration and handover preparation (Active mode Reference Signal resource pre-config and HO preparation). The base station <NUM> may notify the base station <NUM> of configuration information for handover of the terminal device. In addition, the base station <NUM> may further reserve a resource for the terminal device.

The base station <NUM> sends the early handover command to the terminal device through the serving cell, and the terminal device receives the early handover command.

The early handover command is used to instruct the terminal device to determine whether to perform cell handover. In other words, the terminal device knows, based on the early handover command, that the terminal device needs to determine whether to perform conditional handover. The base station <NUM> sends a downlink signal beam in an active mode to the terminal device, and the terminal device receives the reference signal beam. It may be understood that the base station <NUM> sends a downlink signal to the terminal device. The downlink signal sent by the base station <NUM> is, for example, a downlink reference signal.

The base station <NUM> sends a downlink signal beam in an active mode to the terminal device, and the terminal device receives the reference signal beam. It may be understood that the base station <NUM> sends a downlink signal to the terminal device. The downlink signal sent by the base station <NUM> is, for example, a downlink reference signal.

S33 may be performed before S34, or S33 is performed after S34, or S33 and S34 are simultaneously performed.

In addition, the base station <NUM> may send a downlink signal to the terminal device, or may not send a downlink signal to the terminal device. Therefore, the arrow used to represent S34 in <FIG> is a dashed arrow.

The terminal device obtains a measurement report of the reference signal in the active mode.

After receiving the downlink reference signal sent by the base station <NUM>, the terminal device measures the downlink reference signal sent by the base station <NUM>, to obtain a measurement report. Similarly, after receiving the downlink reference signal sent by the base station <NUM>, the terminal device also measures the downlink reference signal sent by the base station <NUM>, to obtain a measurement report. In this way, the terminal device obtains the measurement report of the reference signal in the active mode.

The terminal device sends a random access preamble to the base station <NUM>, to request to access the base station <NUM>. The base station <NUM> receives the random access preamble.

After obtaining the measurement report, the terminal device determines, based on the measurement report and a handover condition, whether to perform cell handover. If the terminal device determines to perform cell handover, the terminal device performs S36.

If the base station <NUM> agrees with the access of the terminal device, the base station <NUM> sends a random access response to the terminal device, and the terminal device receives the random access response.

The terminal device exchanges some user data with the base station <NUM>. That is, the terminal device exchanges user data with the new serving cell provided by the accessed base station <NUM>. The terminal device sends a handover confirm (Handover confirm) to the base station <NUM>, and the base station <NUM> receives the handover confirm.

In the example shown in <FIG>, the terminal device autonomously determines whether to perform cell handover, and a disadvantage of such a handover manner is that a network side loses control over the terminal device. In the description of this example, an example in which the terminal device determines whether to perform handover is used. However, if the terminal device determines not to perform handover, and the base station <NUM> reserves a resource for the terminal device, a waste of resources may be caused.

In view of this, an example useful for understanding the present invention provides a cell handover method. In the method, the terminal device can also perform measurement based on a downlink signal sent by the network device and/or a downlink signal sent by another network device. In other words, the terminal device can still measure a source cell and a target cell. However, the network device may still send a handover command to the terminal device. If the terminal device receives the handover command sent by the network device, the terminal device performs cell handover by executing the handover command. As can be learned, the network device can control the terminal device, and does not lose control over the terminal device even if the terminal device completely determines whether to perform handover. In addition, if a target base station reserves a resource for the terminal device that is to perform handover, the network device may determine, after comprehensively considering various factors, whether to send the handover command to the terminal device, so that the terminal device can perform cell handover, thereby avoiding a waste of resources.

A technical solution provided in this example useful for understanding the present invention is described below with reference to the accompanying drawings.

An example useful for understanding the present invention provides a cell handover method. <FIG> is a flowchart of the method. In the following description process, an example in which the method is applied to the application scenario shown in <FIG> or the application scenario shown in <FIG> is used, and an example in which a cell <NUM>, a cell <NUM>, or a cell <NUM> provided by a base station <NUM> is a serving cell of a terminal device before handover is used.

For S40 in the example shown in <FIG>, refer to S30 in the example shown in <FIG>. For S41 in the example shown in <FIG>, refer to S31 in the example shown in <FIG>. It should be noted that because S40 and S41 are not mandatory steps, to distinguish S40 and S41 from a mandatory step, the arrows used to represent the two steps in <FIG> are dashed arrows.

The base station <NUM> sends an early handover command to the terminal device through the serving cell, and the terminal device receives the early handover command.

The early handover command is used to instruct the terminal device to determine whether to perform cell handover. In other words, the terminal device knows, based on the early handover command, that the terminal device needs to determine whether to perform conditional handover. The early handover command may further carry a handover condition of the conditional handover, and the terminal device may perform determining based on the handover condition.

In an implementation, after sending the early handover command to the terminal device, the base station <NUM> may further send a handover cancel command to the terminal device, and the terminal device receives the handover cancel command. The step of sending the handover cancel command by the base station <NUM> to the terminal device may be performed at any moment after S42.

The handover cancel command may be used to cancel the conditional handover configured by the early handover command, that is, cancel a function of determining, by the terminal device, whether the terminal device performs cell handover.

If the terminal device receives the handover cancel command, the terminal device executes the handover cancel command, to cancel determining whether the terminal device performs cell handover, that is, cancel the conditional handover. In this case, the terminal device may stop measuring a downlink reference signal. This is equivalent to that the base station <NUM> completely determines whether the terminal device performs cell handover. Therefore, for example, if the base station <NUM> finds that a channel condition of the terminal device is getting better, the base station <NUM> may continue providing a service for the terminal device, and does not need to enable the terminal device to perform cell handover.

For S43 in the example shown in <FIG>, refer to S33 in the example shown in <FIG>. For S44 in the example shown in <FIG>, refer to S34 in the example shown in <FIG>. For S45 in the example shown in <FIG>, refer to S35 in the example shown in <FIG>. It should be noted that because S43 to S45 are not mandatory steps, to distinguish S43 to S45 from a mandatory step, the arrows used to represent the three steps in <FIG> are dashed arrows.

The base station <NUM> performs handover determining. In other words, the base station <NUM> determines whether the terminal device performs cell handover. S46 is not a mandatory step. Therefore, to distinguish S46 from a mandatory step, the arrow used to represent S46 in <FIG> is a dashed arrow.

A sequence of S46 and S43 to S45 are not limited in this specification.

That the base station <NUM> performs handover determining includes, but is not limited to, the following manners:.

To be specific, the base station <NUM> measures an uplink reference signal sent by the terminal device, to obtain a measurement report, and the base station <NUM> determines, based on the obtained measurement report, whether the terminal device performs cell handover.

This involves that the terminal device needs to send the uplink reference signal to the base station <NUM>. In this case, the base station <NUM> may first configure uplink measurement for the terminal device. In other words, the base station <NUM> sends uplink configuration information to the terminal device. The uplink configuration information is used to instruct the terminal device to send the uplink reference signal to the base station <NUM>. Specifically, the uplink configuration information indicates information such as a resource used by the terminal device to send the uplink reference signal and a period for sending the uplink reference signal. In this case, the terminal device sends the uplink reference signal to the base station <NUM> after receiving the uplink configuration information. For example, the base station <NUM> may send the uplink configuration information to the terminal device in S42, to be specific, add the uplink configuration information to the early handover command for sending; or the base station <NUM> may send the uplink configuration information to the terminal device at another time, for example, before S42 or before S40, provided that the base station <NUM> completes sending the uplink configuration information to the terminal device before S46. If the base station <NUM> adds the uplink configuration information to the early handover command and sends the early handover command carrying the uplink configuration information to the terminal device, it is equivalent to that the base station <NUM> may start to perform uplink measurement after sending the early handover command. This reduces more resources occupied to send the uplink reference signal and perform measurement than performing uplink measurement from the beginning does.

To be specific, the terminal device sends a measurement report to the base station <NUM>, and the base station <NUM> receives the measurement report sent by the terminal device, and determines, based on the received measurement report, whether the terminal device performs cell handover. Specifically, the terminal device measures the received downlink reference signal. For measurement performed by the terminal device on the downlink reference signal, refer to S43 and S44 in the example shown in <FIG>. After obtaining the measurement report, the terminal device may send the obtained measurement report to the base station <NUM>. The base station <NUM> may first send measurement reporting information to the terminal device, and the measurement reporting information is used to instruct the terminal device to send the measurement report to the base station <NUM>. After receiving the measurement reporting information, the terminal device sends the measurement report obtained by the terminal device to the base station <NUM>.

For example, the base station <NUM> may send the measurement reporting information to the terminal device in S42, to be specific, add the measurement reporting information to the early handover command for sending; or the base station <NUM> may send the measurement reporting information to the terminal device at another time, for example, before S42 or before S40, provided that the base station <NUM> completes sending the measurement reporting information to the terminal device before S46. If the base station <NUM> sends the measurement reporting information to the terminal device before S42, the terminal device performs conditional determining after receiving the early handover command in S42. In this case, the terminal device may continue performing downlink measurement, that is, continue measuring a downlink reference signal sent by the base station <NUM> or another base station (for example, a base station <NUM>), and may continue sending a newly obtained measurement report to the base station <NUM> based on a reporting condition of the measurement report. In this way, the base station <NUM> can conveniently obtain the latest measurement report in time, to more accurately determine whether the terminal device performs cell handover. In addition, the terminal device continuously measures the downlink reference signal. If the terminal device fails to perform handover when the base station instructs the terminal device to perform cell handover, the terminal device may further determine, based on the measurement report obtained by the terminal device, whether to perform cell handover, to ensure that the terminal device can complete handover when handover is required. Alternatively, in this case, the terminal device may stop performing downlink measurement, that is, cancel the process of measuring the downlink reference signal sent by the base station. In this way, consumption of the terminal device may be reduced.

Such a manner may be understood as a determining manner based on implementation of the base station <NUM>. For example, the base station <NUM> sets a timer, and when the timer expires, the base station <NUM> triggers the terminal device to perform cell handover.

In this manner, the base station <NUM> may alternatively perform handover determining according the manner A or manner B described above. If before the timer expires, the base station <NUM> has already triggered, based on the determining in the manner A or the manner B, the terminal device to perform cell handover, the base station <NUM> may turn off the timer. If before the timer expires, the base station <NUM> has not triggered, based on the determining in the manner A or the manner B, the terminal device to perform cell handover, the base station <NUM> triggers, when the timer expires, the terminal device to perform cell handover.

Alternatively, in this manner, the base station <NUM> may not perform handover determining. To be specific, the base station <NUM> does not determine whether the terminal device performs cell handover, and the base station <NUM> triggers, when the timer expires, the terminal device to perform cell handover.

As can be learned, in the manner A or manner B described above, the base station performs handover determining. A determining result may be triggering the terminal device to perform cell handover, or may be determining that the terminal device does not perform cell handover. However, in the manner C, the terminal device basically performs cell handover for sure.

The foregoing three handover determining manners may be selected based on situations.

The base station <NUM> sends a handover command to the terminal device, and the terminal device receives the handover command. The handover command is used to instruct the terminal device to perform cell handover. That is, if the base station <NUM> determines, in the determining manner described in S46, that the terminal device performs cell handover, the base station <NUM> sends the handover command to the terminal device. If the terminal device that is performing conditional determining receives the handover command sent by the base station <NUM>, the terminal device immediately executes the handover command, and starts to perform cell handover instead of performing conditional determining.

After receiving the handover command sent by the base station, the terminal device may stop measuring the downlink reference signal, that is, cancel measurement on the downlink reference signal, to reduce operations and computation of the terminal device by terminating the measurement process. Alternatively, the terminal device continues measuring the downlink reference signal even if the terminal device receives the handover command sent by the base station <NUM>. In this way, if the terminal device fails to access the target cell according to the handover command, the terminal device may reselect, based on a downlink measurement report of the terminal device, a best cell for access.

In another example, the terminal device waits for the handover command. In this example, the base station <NUM> has sent the handover cancel command to the terminal device according to the description in S42, and the terminal device has received the handover cancel command and canceled conditional handover configured by the early handover command. In this case, the terminal device can wait only for the handover command, because the terminal device cannot perform conditional determining by itself.

In an example, the terminal device chooses to execute either of the conditional handover and the handover command that is triggered first. A delay may be reduced in this manner. In this example, the base station <NUM> does not send the handover cancel command to the terminal device according to the description in S42. For example, if the terminal device does not trigger cell handover in the conditional handover process, but the terminal device receives the handover command sent by the base station <NUM>, the terminal device executes the handover command. In other words, the handover command arrives before the handover condition of the conditional handover is met. In this case, before S46, the handover condition of the conditional handover of the terminal device is not met yet. Alternatively, if the terminal device triggers cell handover through a conditional handover process before receiving the handover command sent by the base station <NUM>, the terminal device performs cell handover based on triggering of the conditional handover process. In other words, the handover condition of the conditional handover is already met before the handover command arrives. In this case, the base station <NUM> and the terminal device no longer perform S47. Considering that the terminal device starts conditional determining after S42, if the handover condition of the conditional handover is already met before the handover command arrives, where any one of moments at which steps S43 to S47 are performed may be a moment at which the handover condition is met, a step after the moment at which the handover condition is met is no longer performed. Instead, S48 to be described below is directly performed.

In another example, the terminal device always waits for the handover command. In this example, the base station <NUM> does not send the handover cancel command to the terminal device according to the description in S42. In this example, the terminal device does not perform handover even if the handover condition of the conditional handover of the terminal device is already met. Instead, the terminal device waits for the handover command sent by the base station <NUM>. In this case, before S46, the handover condition of the conditional handover of the terminal device may be met already, or may not be met yet. That is, the terminal device always waits for a notification of the base station. Once receiving the handover command sent by the base station <NUM>, the terminal device immediately performs handover. In this way, a network side can better control the terminal device, and factors such as uplink coverage, load, interference, and access policies of a serving base station and a neighboring base station may be comprehensively considered to control handover of the terminal device.

In this example, the handover command sent by the base station <NUM> may carry a cell identifier. The cell identifier is determined by the base station <NUM> by measuring the uplink reference signal sent by the terminal device, and is a cell identifier of a cell to which the terminal device can hand over; or the cell identifier may be determined by another base station (for example, the base station <NUM>) by measuring the uplink reference signal sent by the terminal device, and is a cell identifier of a cell to which the terminal device can hand over. If the cell identifier is obtained by the base station <NUM> through measurement, the base station <NUM> sends the obtained cell identifier to the base station <NUM>, and the base station <NUM> may add, to the handover command, the received cell identifier sent by the base station <NUM>. In this case, if the terminal device receives the handover command sent by the base station <NUM>, the terminal device executes the handover command, and hands over to the target cell indicated by the handover command. In other words, the terminal device may select one cell identifier from cell identifiers carried in the handover command as the cell identifier of the target cell, to hand over to the target cell. In this case, if the terminal device also determines, based on the conditional handover process, some cell identifiers of cells to which the terminal device can hand over, the terminal device may ignore the cell identifiers determined based on the conditional handover process. In other words, the terminal device preferentially performs handover based on an instruction of the base station <NUM>.

Alternatively, the handover command sent by the base station <NUM> may not carry a cell identifier. In other words, the base station <NUM> only instructs the terminal device to perform handover, but does not notify the terminal device of cells to which the terminal device can hand over. Therefore, after receiving the handover command, the terminal device may select the target cell based on the measurement report obtained by the terminal device, where the measurement report may be obtained by the terminal device by measuring the downlink reference signal sent by the base station <NUM> and/or another base station (for example, the base station <NUM>). Obviously, such a manner is more applicable to the case in which the base station <NUM> does not send the handover cancel command to the terminal device.

Either of the cell indicated by the handover command or the cell determined by the terminal device based on the measurement report obtained by the terminal device may be a cell provided by the base station <NUM> or may be a cell provided by another base station (for example, the base station <NUM>).

The terminal device performs an access process. In <FIG>, an example in which the target cell of the terminal device is a cell provided by the base station <NUM> is used.

For a random access process of the terminal device, refer to the prior art.

By implementing the cell handover method provided in this example, the network side can control the terminal device even in the conditional handover process of the terminal device. For example, based on an actual network status, the base station may deliver the handover command before the terminal device obtains a conditional determining result, to trigger in advance the terminal device to perform handover, thereby shortening a handover delay.

In the example shown in <FIG>, how to strengthen control of the network side over the terminal device in the conditional handover process of the terminal device is mainly described. The following describes a cell handover method by using another example. In this example, how a terminal device selects a target cell is mainly described. <FIG> is a flowchart of the method. In the following description process, an example in which the method is applied to the application scenario shown in <FIG> or the application scenario shown in <FIG> is used, and an example in which a cell <NUM>, a cell <NUM>, or a cell <NUM> provided by a base station <NUM> is a serving cell of a terminal device before handover is used.

The base station <NUM> sends uplink configuration information to the terminal device, and the terminal device receives the uplink configuration information. The uplink configuration information is used to instruct the terminal device to send an uplink reference signal to the base station <NUM>. Specifically, the uplink configuration information indicates information such as a resource used by the terminal device to send the uplink reference signal and a period for sending the uplink reference signal.

The terminal device sends the uplink reference signal to the base station <NUM>, and the base station <NUM> receives the uplink reference signal sent by the terminal device. In this case, the base station <NUM> may measure the uplink reference signal sent by the terminal device, to obtain a measurement report.

After obtaining the measurement report, the base station <NUM> may determine cell identifiers based on the obtained measurement report. The cell identifiers are cell identifiers of target cells to which the terminal device can hand over.

The terminal device sends the uplink reference signal to a base station <NUM>, and the base station <NUM> receives the uplink reference signal sent by the terminal device. Specifically, the uplink reference signal that is received by the base station <NUM> and that is sent by the terminal device may be an uplink reference signal directly sent by the terminal device or an uplink reference signal that is received by the base station <NUM> from the base station <NUM> and that is sent by the terminal device. In this case, the base station <NUM> may measure the uplink reference signal sent by the terminal device, to obtain a measurement report.

In addition to being received by the base station <NUM>, the uplink reference signal sent by the terminal device may also be received by another base station. In S52, an example in which the base station <NUM> also receives the uplink reference signal sent by the terminal device is used. If the base station <NUM> measures the uplink reference signal sent by the terminal device and obtains the measurement report, the base station <NUM> may send the obtained measurement report to the base station <NUM>, or the base station <NUM> may send cell identifiers determined based on the measurement report obtained by the base station <NUM> to the base station <NUM>. The cell identifiers are the cell identifiers of the target cells to which the terminal device can hand over.

Because the base station <NUM> may receive the uplink reference signal sent by the terminal device or may not receive the uplink reference signal sent by the terminal device, the arrow used to represent S52 in <FIG> is a dashed arrow.

The terminal device exchanges some user data with the base station <NUM>. That is, the terminal device exchanges user data with the serving cell provided by the base station <NUM>.

The base station <NUM> may perform handover determining based on the user data. The handover determining herein is different from determining whether the terminal device performs cell handover described in the following portion of this specification. Instead, the handover determining may be understood as determining whether to send an early handover command to the terminal device.

The base station <NUM> and the base station <NUM> perform configuration and prepare for HO.

For example, the base station <NUM> and the base station <NUM> perform active mode reference signal resource pre-configuration and handover preparation. The base station <NUM> may notify the base station <NUM> of configuration information for handover of the terminal device.

The base station <NUM> sends the early handover command to the terminal device through the serving cell, and the terminal device receives the early handover command.

In addition, the early handover command may further carry the cell identifiers determined by the base station <NUM> and/or the cell identifiers determined by the base station <NUM>.

For S56 in the example shown in <FIG>, refer to S33 in the example shown in <FIG>. For S57 in the example shown in <FIG>, refer to S34 in the example shown in <FIG>. For S58 in the example shown in <FIG>, refer to S35 in the example shown in <FIG>. It should be noted that because S56 and S57 are not mandatory steps, to distinguish S56 and S57 from a mandatory step, the arrows used to represent the two steps in <FIG> are dashed arrows.

The terminal device performs an access process. In <FIG>, an example in which the target cell of the terminal device is a cell provided by the base station <NUM> is used.

The terminal device hands over from the current serving cell to the target cell. The target cell is determined by the terminal device based on the measurement report obtained by the terminal device through measurement, and/or is determined by the terminal device based on the received cell identifiers sent by the base station <NUM>.

In an example, the terminal device may determine, based on the conditional handover, whether to perform cell handover. If the terminal device determines to perform cell handover, the terminal device determines the target cell based on the measurement report obtained by the terminal device through measurement and/or based on the received cell identifiers sent by the base station <NUM>.

In another example, the terminal device may determine, based on a handover command sent by the base station <NUM>, to perform cell handover. In this manner, the base station <NUM> determines, based on the measurement report obtained by the base station <NUM> and/or the received measurement report sent by the base station <NUM>, that the terminal device needs to perform cell handover, and the base station <NUM> sends the handover command to the terminal device before S59, referring to S60 in <FIG>. Because the base station <NUM> already sends the cell identifiers to the terminal device by using the early handover command in S55, the base station <NUM> may no longer add the cell identifiers to the handover command. In addition, because sending the handover command by the base station <NUM> to the terminal device is only an optional implementation and is not a mandatory step, the arrow used to represent S60 in <FIG> is a dashed arrow.

If the terminal device receives the handover command sent by the base station <NUM>, the terminal device may stop performing conditional determining, and immediately execute the handover command. Similarly, the target cell is still determined based on the measurement report obtained by the terminal device through measurement and/or based on the received cell identifiers sent by the base station <NUM>.

That is, this example also relates to two processes: the conditional handover and the handover that is notified of by the base station. The terminal device may choose to perform handover that is triggered first. For example, if the terminal device does not trigger cell handover in the conditional handover process, but the terminal device receives the handover command sent by the base station <NUM>, the terminal device executes the handover command. Alternatively, if the terminal device triggers cell handover through a conditional handover process before receiving the handover command sent by the base station <NUM>, the terminal device performs cell handover based on triggering of the conditional handover process.

In this example, the terminal device may select a best cell, as the target cell, from cells whose cell identifiers are sent by the base station <NUM> and/or cells whose cell identifiers are determined by the terminal device, so that a selection range of the target cell is wider, and it is more helpful to select a cell having better performance.

In the example shown in <FIG>, how to strengthen control of the network side over the terminal device in the conditional handover process of the terminal device is mainly described. In the example shown in <FIG>, how the terminal device selects the target cell is mainly described. The following describes a cell handover method by using an embodiment. In this embodiment, when a terminal device sends a measurement report in a conditional handover process is mainly described. <FIG> is a flowchart of the method. In the following description process, an example in which the method is applied to the application scenario shown in <FIG> or the application scenario shown in <FIG> is used, and an example in which a cell <NUM>, a cell <NUM>, or a cell <NUM> provided by a base station <NUM> is a serving cell of a terminal device before handover, and a cell <NUM> or a cell <NUM> provided by a base station <NUM> is a target cell of the terminal device is used.

For S60 in the embodiment shown in <FIG>, refer to S30 in the example shown in <FIG>. For S61 in the embodiment shown in <FIG>, refer to S31 in the example shown in <FIG>. It should be noted that because S60 and S61 are not mandatory steps, to distinguish S60 and S61 from a mandatory step, the arrows used to represent the two steps in <FIG> are dashed arrows.

The base station <NUM> sends an early handover command to the terminal device through the serving cell, and the terminal device receives the early handover command.

The early handover command is used to instruct the terminal device to determine whether to perform cell handover. In other words, the terminal device knows, based on the early handover command, that the terminal device needs to determine whether to perform conditional handover. The early handover command may further carry a handover condition of the conditional handover, and the terminal device may perform determining based on the handover condition. For S63 in the embodiment shown in <FIG>, refer to S33 in the example shown in <FIG>. For S64 in the embodiment shown in <FIG>, refer to S34 in the example shown in <FIG>. For S65 in the embodiment shown in <FIG>, refer to S35 in the example shown in <FIG>. It should be noted that because S63 to S65 are not mandatory steps, to distinguish S63 to S65 from a mandatory step, the arrows used to represent the three steps in <FIG> are dashed arrows.

The base station <NUM> sends measurement reporting information to the terminal device through the serving cell, and the terminal device receives the measurement reporting information. The measurement reporting information is used to instruct the terminal device to send an obtained measurement report to the base station <NUM>.

The measurement reporting message may further carry a reporting condition of the measurement report, or a reporting condition of the measurement report may be determined by the terminal device, or may be determined based on a protocol or a standard. In conclusion, the terminal device sends the measurement report obtained by the terminal device to the base station <NUM> only when the reporting condition of the measurement report is met. For example, a reporting condition of the measurement report is that the measurement report obtained by the terminal device continuously meets a measurement threshold within timer-to-trigger (Timer to trigger, TTT) duration.

If the reporting condition of the measurement report is met before the handover condition carried in the early handover command, the following S67 is performed. If the handover condition carried in the early handover command is met before the reporting condition of the measurement report, or the handover condition carried in the early handover command and the reporting condition of the measurement report are simultaneously met, the following S68 is performed.

S66 may be performed before S62, or may be performed at any time from S62 to S65, or may be performed after S65. This is not limited in this embodiment of the present invention.

If the reporting condition of the measurement report is met before the handover condition carried in the early handover command, the terminal device sends the measurement report to the base station <NUM>.

In this way, after receiving the measurement report, the base station <NUM> may determine, based on the measurement report, whether the terminal device needs to perform cell handover.

If the handover condition carried in the early handover command is met before the reporting condition of the measurement report, or the handover condition carried in the early handover command and the reporting condition of the measurement report are simultaneously met, the terminal device hands over from the current serving cell to a target cell. That is, the terminal device performs an access process of accessing the base station <NUM>. In this case, the terminal device performs cell handover based on a determining result of the conditional handover.

In this manner, the base station <NUM> and/or the terminal device may determine in time whether the terminal device performs cell handover, so that the terminal device may perform cell handover as soon as possible.

The foregoing embodiments all describe the method for performing cell handover by the terminal device. After performing cell handover, the terminal device needs to communicate with a new cell. This relates to a problem of determining an uplink transmit power used by the terminal device for the new cell. The following provides an embodiment, to describe a method for determining an uplink transmit power by a terminal device. This embodiment may be combined with the embodiment shown in <FIG>. <FIG> is a flowchart of the method. In the following description process, an example in which the method is applied to the application scenario shown in <FIG> or the application scenario shown in <FIG> is used, and an example in which a cell <NUM>, a cell <NUM>, or a cell <NUM> provided by a base station <NUM> is a serving cell of a terminal device before handover, and a cell <NUM> or a cell <NUM> provided by a base station <NUM> is a target cell of the terminal device is used.

For S70 in the embodiment shown in <FIG>, refer to S50 in the example shown in <FIG>.

Before handing over to the base station <NUM>, the terminal device sends an uplink reference signal to the base station <NUM>, and the base station <NUM> receives the uplink reference signal sent by the terminal device. In this case, the serving cell of the terminal device is still a cell provided by the base station <NUM>. Specifically, the uplink reference signal that is received by the base station <NUM> and that is sent by the terminal device may be an uplink reference signal directly sent by the terminal device or an uplink reference signal that is received by the base station <NUM> from the base station <NUM> and that is sent by the terminal device.

The base station <NUM> may obtain reference information based on the received uplink reference signal, where the reference information is used to indicate an uplink transmit power of the terminal device.

For example, the reference information obtained by the base station <NUM> may include an offset and/or an uplink path loss. The offset is an offset based on an initial transmit power of the terminal device. To be specific, the base station <NUM> may determine the initial transmit power of the terminal device based on the received uplink reference signal. The base station <NUM> adds the offset to the initial transmit power. A sum of the initial transmit power and the offset may be used as an uplink transmit power of the terminal device after handover. Because the terminal device knows the initial transmit power of the terminal device, the base station <NUM> only needs to send the offset to the terminal device. For example, the uplink transmit power of the terminal device that is determined based on the offset is as follows: <MAT>.

In Formula (<NUM>), PPRACH represents an uplink transmit power of the terminal device, PCMAX represents a maximum transmit power of the terminal device, PREAMBLE_RECEIVED_TARGET_POWER represents a target uplink receive power of the base station <NUM>, PL represents an uplink path loss (Pathloss), and offset represents an offset.

The uplink path loss is obtained by the base station <NUM> based on an initial transmit power for the uplink reference signal that is sent by the terminal device and that is received from the base station <NUM> and a receive power at which the base station <NUM> receives the uplink reference signal. For example, the uplink path loss is calculated in the following manner: <MAT>.

In Formula (<NUM>), P1 represents the initial transmit power at which the terminal device sends the uplink reference signal, and P2 represents a receive power at which the base station <NUM> receives the uplink reference signal. In this way, if the determined uplink path loss is relatively large, the terminal device needs to access the base station <NUM> at a relatively high uplink transmit power; and if the determined uplink path loss is relatively small, the terminal device needs to access the base station <NUM> at a relatively low transmit power. In this manner, the uplink transmit power of the terminal device after handover can be relatively accurately determined, and a delay during initial access of the terminal device caused by increasing a power because the uplink transmit power is relatively low can be reduced, or interference during initial access of the terminal device caused due to an excessively high uplink transmit power can be reduced.

In addition, the terminal device also sends the uplink reference signal to the base station <NUM>, and the base station <NUM> may also obtain the reference information based on the uplink reference signal sent by the terminal device.

The base station <NUM> sends the obtained reference information to the base station <NUM>, and the base station <NUM> receives the reference information sent by the base station <NUM>.

The base station <NUM> sends reference information to the terminal device, and the terminal device receives the reference information sent by the base station <NUM>.

For example, the base station <NUM> sends the reference information to the terminal device by using an early handover command, or if the base station <NUM> sends a handover command to the terminal device, the base station <NUM> may send the reference information to the terminal device by using the handover command.

The reference information sent by the base station <NUM> to the terminal device may include the reference information determined by the base station <NUM> and/or the reference information determined by the base station <NUM>.

The terminal device determines, based on the received reference information, an uplink transmit power at which the terminal device sends a message to the base station <NUM>.

When the terminal device is handing over to the base station <NUM> or after the terminal device has handed over to the base station <NUM>, the base station <NUM> can receive the message sent by the terminal device at the determined uplink transmit power. For example, when accessing the base station <NUM> through a random access process, the terminal device uses the determined uplink transmit power when sending the first message in the random access process, or the terminal device uses the determined uplink transmit power when sending the first scheduling-free message.

In this embodiment of the present invention, a target cell may determine an uplink transmit power of the terminal device after the handover, so that the determined uplink transmit power is more accurate.

An apparatus provided in an example is described below with reference to the accompanying drawings.

<FIG> is a schematic structural diagram of a communications apparatus <NUM>. The communications apparatus <NUM> may implement functions of the terminal device described above. The communications apparatus <NUM> may include a processing unit <NUM> and a receiving unit <NUM>. Optionally, the communications apparatus <NUM> may further include a sending unit <NUM>. The processing unit <NUM> may be configured to perform S35 and S38 in the example shown in <FIG>, and S45 and S48 in the example shown in <FIG>, and/or configured to support another process of the technology described in this specification. The receiving unit <NUM> may be configured to perform S32, S33, and S34 in the example shown in <FIG>, and S42, S43, S44, and S47 in the example shown in <FIG>, and/or configured to support another process of the technology described in this specification. The sending unit <NUM> may be configured to perform S36 and S39 in the example shown in <FIG>, and/or configured to support another process of the technology described in this specification. All related content of the steps in the foregoing method examples may be cited in function descriptions of corresponding functional modules.

<FIG> is a schematic structural diagram of a communications apparatus <NUM>. The communications apparatus <NUM> may implement functions of the network device described above. The communications apparatus <NUM> may include a processing unit <NUM> and a sending unit <NUM>. Optionally, the communications apparatus <NUM> may further include a receiving unit <NUM>. The processing unit <NUM> may be configured to perform S46 in the example shown in <FIG>, and/or configured to support another process of the technology described in this specification. The sending unit <NUM> may be configured to perform S32, S33, and S37 in the example shown in <FIG>, and S42 and S47 in the example shown in <FIG>, and/or configured to support another process of the technology described in this specification. The receiving unit <NUM> may be configured to perform S36 and S39 in the example shown in <FIG>, and/or configured to support another process of the technology described in this specification. All related content of the steps in the foregoing method examples may be cited in function descriptions of corresponding functional modules.

<FIG> is a schematic structural diagram of a communications apparatus <NUM>. The communications apparatus <NUM> may implement functions of the terminal device described above. The communications apparatus <NUM> may include a processing unit <NUM> and a receiving unit <NUM>. The processing unit <NUM> may be configured to perform S59 in the example shown in <FIG>, and/or configured to support another process of the technology described in this specification. The receiving unit <NUM> may be configured to perform S55 and S60 in the example shown in <FIG>, and/or configured to support another process of the technology described in this specification. All related content of the steps in the foregoing method examples may be cited in function descriptions of corresponding functional modules.

<FIG> is a schematic structural diagram of a communications apparatus <NUM>. The communications apparatus <NUM> may implement functions of the network device described above. The communications apparatus <NUM> may include a processing unit <NUM>, a receiving unit <NUM>, and a sending unit <NUM>. The processing unit <NUM> may be configured to perform S51 and S53 in the example shown in <FIG>, and/or configured to support another process of the technology described in this specification. The receiving unit <NUM> may be configured to perform S51 in the example shown in <FIG>, and/or configured to support another process of the technology described in this specification. The sending unit <NUM> may be configured to perform S55 and S60 in the example shown in <FIG>, and/or configured to support another process of the technology described in this specification. All related content of the steps in the foregoing method examples may be cited in function descriptions of corresponding functional modules.

<FIG> is a schematic structural diagram of a communications apparatus <NUM>. The communications apparatus <NUM> may implement functions of the network device described above. The communications apparatus <NUM> may include a processing unit <NUM> and a sending unit <NUM>. Optionally, the communications apparatus <NUM> further includes a receiving unit <NUM>. The processing unit <NUM> may be configured to perform S72 in the embodiment shown in <FIG>, and/or configured to support another process of the technology described in this specification. The sending unit <NUM> may be configured to perform S73 in the embodiment shown in <FIG>, and/or configured to support another process of the technology described in this specification. The receiving unit <NUM> may be configured to perform S71 in the embodiment shown in <FIG>, and/or configured to support another process of the technology described in this specification. All related content of the steps in the foregoing method embodiments may be cited in function descriptions of corresponding functional modules.

<FIG> is a schematic structural diagram of a communications apparatus <NUM>. The communications apparatus <NUM> may implement functions of the terminal device described above. The communications apparatus <NUM> may include a processing unit <NUM> and a receiving unit <NUM>. Optionally, the communications apparatus <NUM> further includes a sending unit <NUM>. The processing unit <NUM> may be configured to perform S75 in the embodiment shown in <FIG>, and/or configured to support another process of the technology described in this specification. The receiving unit <NUM> may be configured to perform S74 in the embodiment shown in <FIG>, and/or configured to support another process of the technology described in this specification. The sending unit <NUM> may be configured to perform S71 in the embodiment shown in <FIG>, and/or configured to support another process of the technology described in this specification. All related content of the steps in the foregoing method embodiments may be cited in function descriptions of corresponding functional modules.

<FIG> is a schematic structural diagram of a communications apparatus <NUM>. The communications apparatus <NUM> may implement functions of the terminal device described above. The communications apparatus <NUM> may include a sending unit <NUM> and a receiving unit <NUM>. Optionally, the communications apparatus <NUM> further includes a processing unit <NUM>. The sending unit <NUM> may be configured to perform S67 in the embodiment shown in <FIG>, and/or configured to support another process of the technology described in this specification. The receiving unit <NUM> may be configured to perform S62 and S66 in the embodiment shown in <FIG>, and/or configured to support another process of the technology described in this specification. The processing unit <NUM> may be configured to perform S68 in the embodiment shown in <FIG>, and/or configured to support another process of the technology described in this specification. All related content of the steps in the foregoing method embodiments may be cited in function descriptions of corresponding functional modules.

In the embodiments of the present invention, the communications apparatus <NUM> to the communications apparatus <NUM> are presented in a form in which each functional module is defined in a correspondence to each function, or may be presented in a form in which each functional module is defined in an integrated manner. The "module" herein may be an application-specific integrated circuit (application-specific integrated circuit, ASIC), a processor and a memory for executing one or more software or firmware programs, an integrated logic circuit, and/or another component that can provide the foregoing function.

In a simple embodiment, a person skilled in the art can figure out that any one of the communications apparatus <NUM> to the communications apparatus <NUM> may be implemented by using a structure shown in <FIG>.

As shown in <FIG>, a communications apparatus <NUM> may include: a memory <NUM>, a processor <NUM>, a system bus <NUM>, and a communications interface <NUM>. The processor <NUM>, the memory <NUM>, and the communications interface <NUM> are connected by using the system bus <NUM>. The memory <NUM> is configured to store a computer-executable instruction. When the communications apparatus <NUM> runs, the processor <NUM> executes the computer-executable instruction stored in the memory <NUM>, so that the communications apparatus <NUM> performs the method provided in any one of the embodiment shown in <FIG> to the embodiment shown in <FIG>. For a specific method, refer to the foregoing descriptions and related descriptions in the accompanying drawings. The communications interface <NUM> may be a transceiver, or may be an independent receiver and transmitter.

In an example, the receiving unit <NUM> may correspond to the communications interface <NUM> in <FIG>. The processing unit <NUM> may be built in or independent of the memory <NUM> of the communications apparatus <NUM> in a hardware/software form.

In an example, the sending unit <NUM> may correspond to the communications interface <NUM> in <FIG>. The processing unit <NUM> may be built in or independent of the memory <NUM> of the communications apparatus <NUM> in a hardware/software form.

In an example, the receiving unit <NUM> and the sending unit <NUM> may correspond to the communications interface <NUM> in <FIG>. The processing unit <NUM> may be built in or independent of the memory <NUM> of the communications apparatus <NUM> in a hardware/software form.

Optionally, the communications apparatus <NUM> may be a field-programmable gate array (field-programmable gate array, FPGA), an application-specific integrated circuit (application-specific integrated circuit, ASIC), a system on chip (system on chip, SoC), or a central processing unit (central processing unit, CPU), a network processor (network processor, NP), a digital signal processor (digital signal processor, DSP), or a micro controller unit (micro controller unit, MCU), or a programmable logic device (programmable logic device, PLD) or another integrated chip may be used. Alternatively, the communications apparatus <NUM> may be an independent network element, for example, a network device or a terminal device.

Because the communications apparatus <NUM> to the communications apparatus <NUM> provided in the embodiments of the present invention may be configured to perform the method provided in any one of the example shown in <FIG> to the embodiment shown in <FIG>, for technical effects that can be achieved by the communications apparatus <NUM> to the communications apparatus <NUM>, refer to the foregoing method embodiments.

In the embodiments of the present invention, the terminal device can also perform measurement based on the downlink signal sent by the network device and/or the downlink signal sent by the another network device. In other words, the terminal device can still measure the source cell and the target cell. However, the network device may still send the handover command to the terminal device. If the terminal device receives the handover command sent by the network device, the terminal device performs cell handover by executing the handover command. As can be learned, the network device can control the terminal device, and does not lose control over the terminal device even if the terminal device completely determines whether to perform handover. In addition, if a target base station reserves a resource for the terminal device that is to perform handover, the network device may determine, after comprehensively considering various factors, whether to send the handover command to the terminal device, so that the terminal device can perform cell handover, thereby avoiding a waste of resource.

The embodiments of the present invention are described with reference to the flowcharts and/or block diagrams of the method, the device (system), and the computer program product according to the embodiments of the present invention. It should be understood that computer program instructions may be used to implement each process and/or each block in the flowcharts and/or the block diagrams and a combination of a process and/or a block in the flowcharts and/or the block diagrams. These computer program instructions may be provided for a general-purpose computer, a dedicated computer, an embedded processor, or a processor of any other programmable data processing device to generate a machine, so that the instructions executed by a computer or a processor of any other programmable data processing device generate an apparatus for implementing a specific function in one or more procedures in the flowcharts and/or in one or more blocks in the block diagrams.

All or some of the foregoing embodiments may be implemented by using software, hardware, firmware, or any combination thereof. When software is used to implement the embodiments, the embodiments may be implemented completely or partially in a form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on the computer, the procedure or functions according to the embodiments of the present invention are all or partially generated. The computer may be a general-purpose computer, a dedicated computer, a computer network, or other programmable apparatuses. The computer instructions may be stored in a computer-readable storage medium or may be transmitted from a computer-readable storage medium to another readable storage medium. For example, the computer instructions may be transmitted from a website, computer, server, or data center to another website, computer, server, or data center in a wired (for example, a coaxial cable, an optical fiber, or a digital subscriber line (DSL)) or wireless (for example, infrared, radio, or microwave) manner. The computer-readable storage medium may be any available medium accessible by a computer, or a data storage device, such as a server or a data center, integrating one or more available media. The available medium may be a magnetic medium (for example, a floppy disk, a hard disk, or a magnetic tape), an optical medium (for example, a DVD), a semiconductor medium (for example, a solid-state drive (Solid State Disk, SSD)), or the like.

Claim 1:
A cell handover method, comprising:
receiving (S32, S42, S55, S62), by a terminal device, an early handover command from a network device, wherein the network device includes a base station, wherein the early handover command is used to instruct the terminal device to determine whether to perform cell handover;
measuring, by the terminal device, a downlink signal from the network device and/or a downlink signal from another network device;
determining, by the terminal device based on an obtained measurement report and a handover condition that is carried in the early handover command, whether to perform cell handover; and
if the terminal device determines, based on the obtained measurement report and the handover condition, to perform cell handover, performing, by the terminal device according to the determination, cell handover; and
before the terminal device determines, based on the obtained measurement report and the handover condition, to perform cell handover and after the receiving the early handover command and after the measuring the downlink signal sent by the network device and/or a downlink signal sent by another network device:
receiving (S66) a measurement reporting information from the serving base station instructing the terminal device to send an obtained measurement report to the serving base station,
if the reporting condition of the measurement report is met before the handover condition carried in the early handover command, sending (S67), by the terminal device to the network device, the measurement report obtained by measuring the downlink signal from the network device and/or the downlink signal from the another network device,
if the handover condition carried in the early handover command is met before the reporting condition of the measurement report, or the handover condition carried in the early handover command and the reporting condition of the measurement report are simultaneously met, handing over (S68), by the terminal device, from the current serving cell to a target cell.