CN106604335B - Cell switching method - Google Patents

Cell switching method Download PDF

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Publication number
CN106604335B
CN106604335B CN201611191604.4A CN201611191604A CN106604335B CN 106604335 B CN106604335 B CN 106604335B CN 201611191604 A CN201611191604 A CN 201611191604A CN 106604335 B CN106604335 B CN 106604335B
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base station
user equipment
random access
source base
target base
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CN106604335A (en
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马征
章正权
邓滔
范平志
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Southwest Jiaotong University
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Southwest Jiaotong University
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/0005—Control or signalling for completing the hand-off
    • H04W36/0011—Control or signalling for completing the hand-off for data sessions of end-to-end connection
    • H04W36/0016—Hand-off preparation specially adapted for end-to-end data sessions
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/08—Reselecting an access point
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/04—Wireless resource allocation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W74/00—Wireless channel access
    • H04W74/08—Non-scheduled access, e.g. ALOHA
    • H04W74/0833—Random access procedures, e.g. with 4-step access

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

The invention discloses a method for switching cells, which comprises the following steps: the source base station reserves a special random access resource for the user equipment and configures the reserved special random access resource to the user equipment; after the user equipment is switched to the target base station, the target base station does not request a core network to switch a downlink GTP tunnel within the preset waiting time; when the user equipment needs to be switched back to the source base station, the user equipment initiates random access by using the stored special random access preamble, synchronizes the random access to the source base station and switches back to the source base station; and after the user equipment is switched back to the source base station, the source base station releases the reserved special random access resource, performs admission control and configures the allocated wireless resource information to the user equipment. By using the cell switching method provided by the invention, the switching time delay can be reduced, the risk of UE call drop in the switching process can be reduced, and the signaling processing overhead of a base station and a core network can be reduced.

Description

Cell switching method
Technical Field
The present invention relates to the field of wireless communication technologies, and in particular, to a cell switching method.
Background
In order to ensure the service continuity of User Equipment (UE) in a Radio Resource Control (RRC) CONNECTED state RRC _ CONNECTED, a Long Term Evolution (LTE) system performs cell handover in a network controlled user equipment assisted manner. The whole switching process comprises three stages of switching preparation, switching execution and switching completion. The specific switching process is as follows:
in a handover preparation phase, a source base station (for example, a base station in an LTE system is an evolved node B) makes a handover decision, and preferably selects a handover candidate cell; and the source base station interacts with the target base station to which the switching candidate cell belongs to acquire switching resources prepared for the UE by the target base station.
In the switching execution stage, the source base station sends a switching command to the UE to instruct the UE to switch to a specified target cell (namely a switching candidate cell); the source base station performs data back transmission; UE successfully accesses to the target cell and establishes uplink synchronization, and sends a switching confirmation to the target base station to complete the switching.
In the switching completion stage, the target base station and the core network interactively complete the conversion of a downlink general packet radio service tunneling protocol (GTP) tunnel; and the target base station sends the data which are transmitted in advance and newly received in sequence and releases the UE context of the source base station. A GTP tunnel refers to a communication tunnel between two GTP nodes, and is used to divide traffic into different communication flows. The GTP tunnel is identified by a Tunnel Endpoint Identifier (TEID), an Internet Protocol (IP) address and a User Datagram Protocol (UDP) port number; carrying encapsulated transport protocol data units (T-PDUs) and signaling messages between a given pair of GTP user plane GTP-U tunnel endpoints.
Fig. 1 is a schematic diagram of a macro-micro heterogeneous network scenario in the prior art. In the macro-micro heterogeneous network scenario shown in fig. 1, the UE moves between the macro base station and the micro base station, and the coverage area of the micro base station is much smaller than that of the macro base station. When UE is switched from a macro base station to a micro base station, in the existing switching method, after reporting a measurement report, the UE needs to establish air interface connection with a target cell through two stages of switching preparation and switching execution, the switching time is prolonged, and the risk of UE call drop is increased; in addition, when the UE is switched from the macro base station to the micro base station and then back to the macro base station in a short time, the conventional switching procedure needs to perform two downlink GTP tunnel conversions, thereby increasing signaling processing overhead of the base station and the core network.
Disclosure of Invention
In view of this, the present invention provides a method for cell handover, so as to reduce handover delay, reduce the risk of UE call drop during handover, and reduce signaling processing overhead of a base station and a core network.
The technical scheme of the invention is realized as follows:
a method of cell handover, the method comprising:
the source base station reserves a special random access resource for the user equipment and configures the reserved special random access resource to the user equipment; the dedicated random access resources include: random access preamble and preset life time of the random access preamble;
after the user equipment is switched to the target base station, the target base station does not request a core network to convert a downlink general packet radio service tunneling protocol (GTP) tunnel within the preset waiting time;
when the user equipment needs to be switched back to the source base station, the user equipment initiates random access by using the stored special random access preamble, synchronizes the random access to the source base station and switches back to the source base station;
and after the user equipment is switched back to the source base station, the source base station releases the reserved special random access resource, performs admission control and configures the allocated wireless resource information to the user equipment.
Preferably, the reserving, by the source base station, the dedicated random access resource for the ue includes:
the source base station reserves random access preamble for the user equipment and presets the life time of the reserved random access preamble; and setting and starting a first timer with the duration as the life time.
Preferably, the source base station sends a radio resource control connection reconfiguration message to the user equipment;
the rrc connection reconfiguration message carries a handover command and dedicated random access resources configured to the ue.
Preferably, the method further comprises:
the user equipment saves the reserved special random access resource and starts a second timer with the duration as the life time;
and when the second timer is overtime, the user equipment clears the reserved special random access resource.
Preferably, the target base station does not request the core network to switch the downlink GTP tunnel within the preset waiting time includes:
the target base station starts a third timer with preset time; or, the target base station judges whether to start a third timer of preset time according to the base station type, if the target base station is a micro base station, the target base station starts the third timer of preset time;
if the user equipment is switched from the target base station to the source base station, the target base station stops the third timer;
if the ue is still at the target base station, when the third timer times out, the target base station sends a path switching message to a mobility management entity for X2 handover; for S1 handover, the target base station sends a handover notification message to the mobility management entity.
Preferably, when the user equipment judges that the switching back to the source base station is needed, the user equipment sends a switching indication message to the target base station; the target base station stops the third timer;
or, when the user equipment judges that it needs to switch back to the source base station, if the user equipment does not send the switching indication message, the target base station judges whether the user equipment initiates switching to the source base station by detecting the data transmission condition of the air interface.
Preferably, for the X2 handover, when the ue does not decide to handover back to the source base station within the preset time, the lifetime of the random access resource reserved by the source base station ends, and the source base station releases the reserved random access resource;
the target base station judges whether the third timer is overtime or not;
when the third timer is overtime, the target base station sends a path switching request message to the mobile management entity to request the downlink GTP tunnel to be switched to a new GTP tunnel endpoint;
the mobility management entity, the service gateway and the packet data gateway realize the conversion of the downlink GTP tunnel to a new GTP tunnel endpoint through the bearer modification process;
the service gateway sends an end mark packet to the source base station, and the end mark packet is forwarded to the target base station through the source base station to indicate that the data forwarding is ended;
the mobile management entity sends a path switching request response message to the target base station to confirm the success of path switching;
and the target base station sends the user equipment uplink release message to the source base station to release resources.
Preferably, for the S1 handover, when the ue does not decide to handover back to the source base station within the preset time, the lifetime of the random access resource reserved by the source base station ends, and the source base station releases the reserved random access resource;
the target base station judges whether the third timer is overtime or not;
when the third timer times out, the target base station sends a switching notification message to the mobility management entity, indicating that the user equipment has been switched to the target cell and the switching of S1 is successfully completed;
the mobility management entity, the first service gateway and the second service gateway realize the conversion of the downlink GTP tunnel to a new GTP tunnel endpoint through the bearer modification process;
when one of the conditions listed in the 'trigger tracking area update' is met, the user equipment initiates a tracking area update process;
and the mobility management entity releases the logic connection between the target base station and the user equipment through the context release process of the user equipment.
As can be seen from the above, in the cell handover method provided by the present invention, when the ue is handed over from the source base station (or macro base station) to the target base station (or micro base station), the source base station reserves the dedicated random access resource (including the random access preamble and the lifetime preset for the random access preamble) for the ue, and configures the dedicated random access resource to the ue, so that when the ue moves back from the target base station to the source base station, the reserved random access resource can be used to implement fast handover. By the mode of reserving the random access resources for the UE and controlling the switching of the UE, the time for reporting the measurement report, preparing the switching and issuing the switching command is saved, the switching time delay is reduced, and the risk of the UE call drop in the switching process is reduced; and after the user equipment is switched to the target base station, the target base station does not request the core network to switch the downlink GTP tunnel within the preset waiting time so as to prevent the user equipment from carrying out twice GTP tunnel switching processing when being switched back to the source base station within a short time, thereby greatly reducing the signaling processing overhead of the base station and the core network.
Drawings
Fig. 1 is a schematic diagram of a macro-micro heterogeneous network scenario in the prior art.
Fig. 2 is a general flowchart of a cell handover method according to an embodiment of the present invention.
Fig. 3 is a flowchart illustrating a method for cell handover according to a first embodiment of the present invention.
Fig. 4 is a flowchart illustrating a method for cell handover according to a second embodiment of the present invention.
Fig. 5 is a flowchart illustrating a method for cell handover according to a third embodiment of the present invention.
Fig. 6 is a flowchart illustrating a method for cell handover according to a fourth embodiment of the present invention.
Fig. 7 is a flowchart illustrating a method for cell handover according to a fifth embodiment of the present invention.
Fig. 8 is a diagram illustrating a configuration process of a reserved random access preamble according to an embodiment of the present invention.
Fig. 9 is a schematic diagram of path conversion processing in the embodiment of the present invention.
Fig. 10 is a diagram illustrating a process of handover notification according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings and examples.
The embodiment provides a cell switching method.
Fig. 2 is a flowchart illustrating a method for cell handover according to an embodiment of the present invention. As shown in fig. 2, the method for cell handover in the embodiment of the present invention mainly includes the following steps:
step 101, a source base station reserves a dedicated random access resource for user equipment, and configures the reserved dedicated random access resource to the user equipment.
Before the user equipment is switched, the source base station can reserve the special random access resource for the user equipment and configure the special random access resource for the user equipment.
In addition, preferably, in an embodiment of the present invention, the dedicated random access resource includes: a random access preamble and a preset life time of the random access preamble.
In addition, preferably, in an embodiment of the present invention, the dedicated random access resource may be configured to the ue through a rrc connection reconfiguration message.
For example, as shown in fig. 8, a source base station sends a rrc connection reconfiguration message to a ue, where the rrc connection reconfiguration message carries a handover command and dedicated random access resources (random access preambles and lifetime of the random access preambles) configured to the ue.
Further, in a preferred embodiment of the present invention, after allocating the dedicated random access resource to the ue, the ue may save the reserved dedicated random access resource and start a second timer with a lifetime. And when the second timer is over time, the user equipment clears the reserved special random access resource.
Step 102, after the user equipment is switched to the target base station, the target base station does not request the core network to switch the downlink GTP tunnel (i.e. does not request the core network to switch the user plane path) within the preset waiting time.
In the technical scheme of the invention, when the switching command is configured to the user equipment, the user equipment can switch to the target base station.
And after the user equipment is switched to the target base station, the target base station does not request the core network to switch the downlink GTP tunnel within the preset waiting time.
In the technical scheme of the invention, the duration of the waiting time can be preset according to the requirements of actual application conditions. For example, it may be considered that the duration of the waiting time is preset to be equal to or less than the lifetime of the random access preamble preset in the source base station in step 101; of course, it is also conceivable to set the duration of the waiting time to be longer than the life time in advance.
In addition, in the technical solution of the present invention, the step 102 can be implemented in various ways. The technical solution of the present invention will be described below by taking one implementation manner thereof as an example.
For example, in an embodiment of the present invention, preferably, the target base station does not request the core network to switch the downlink GTP tunnel within the preset waiting time may include:
the target base station starts a third timer with preset time; or, the target base station judges whether to start a third timer of preset time according to the base station type, if the target base station is a micro base station, the target base station starts the third timer of preset time;
if the user equipment is switched from the target base station to the source base station, the target base station stops the third timer;
if the ue is still at the target base station, when the third timer times out, the target base station sends a path switching message to a mobility management entity for X2 handover; for S1 handover, the target base station sends a handover notification message to the mobility management entity.
In addition, preferably, in the embodiment of the present invention, when the ue determines that a handover back to the source base station is required, the ue sends a handover indication message to the target base station. At this time, the target base station will stop the third timer.
Or, when the user equipment determines that it needs to switch back to the source base station, if the user equipment does not send the handover indication message, the target base station may determine whether the user equipment initiates handover to the source base station by detecting a data transmission condition of an air interface. For example, if the target base station no longer receives uplink data from the user equipment and downlink data cannot reach the user equipment, it may be determined that the user equipment initiates handover to the source base station.
In addition, preferably, in the embodiment of the present invention, the handover indication message may be a dedicated indication message, or may be a measurement report message carrying indication information.
103, when the user equipment needs to be switched back to the source base station, the user equipment initiates random access by using the stored special random access preamble, synchronizes with the source base station, and switches back to the source base station.
And step 104, after the user equipment is switched back to the source base station, the source base station releases the reserved special random access resource, performs admission control, and configures the allocated wireless resource information to the user equipment.
For example, in an embodiment of the present invention, the source base station may configure information such as the allocated radio resource to the ue through a radio resource control connection reconfiguration process.
In addition, in the technical solution of the present invention, the radio resource connection reconfiguration (RRCConnectionReconfiguration) message in the rrc connection reconfiguration process may carry a lot of information, for example, information such as measurement configuration, mobility control, and radio resource configuration information. The base station may configure some or all of the prescribed information to the user equipment according to the actual situation. Therefore, in this step 104, the base station may configure only the allocated radio resource information for the ue through the radio resource connection reconfiguration message, or may configure the radio resource configuration, the measurement configuration, and the mobility control related information to the ue together.
Through the steps 101-104, the cell switching of the user equipment can be realized, and the user equipment which is switched to the target base station can be quickly switched back to the source base station by using the reserved random access resource within the preset time, so that the time for reporting the measurement report, preparing for switching and issuing the switching command is saved, the switching time delay is reduced, the risk of UE call drop in the switching process is reduced, the user equipment can be prevented from carrying out twice GTP tunnel switching processing when switching back to the source base station in a short time, and the signaling processing overhead of the base station and the core network is reduced.
The technical solution of the present invention will be described in detail below by taking several specific embodiments as examples.
Embodiment one, based on the implementation of switching back to the source base station within a preset time when switching X2.
Fig. 3 is a flowchart illustrating a method for cell handover according to a first embodiment of the present invention, where a source base station is a macro base station and a target base station is a micro base station. As shown in fig. 3, the method for cell handover in the first embodiment may include the following steps:
step 201, the source base station and the target base station interactively acquire resources required by the handover.
In this step 201, the source base station will prepare for handover with the target base station. Therefore, the source base station and the target base station interactively acquire resources required by the switching. For example, the source base station interacts with the target base station to which the handover candidate cell belongs, and obtains handover resources prepared by the target base station for the UE.
Step 202, the source base station reserves random access resources for the user equipment, including random access preambles and the life time of the reserved random access preambles; and setting and starting a first timer with the duration as the life time.
In addition, in the subsequent step, when the first timer times out, the source base station will release the random access resource reserved for the user equipment.
Step 203, the source base station allocates the switching command and the reserved random access resource to the user equipment through the radio resource control connection reconfiguration message; the user equipment saves the reserved random access preamble and the life time thereof, and starts a second timer with the life time as the duration.
In step 202, the source base station starts a timer (i.e. a first timer), and in step 203, the ue starts a timer (i.e. a second timer). The duration of both timers is a preset life time. The source base station and the user equipment jointly maintain the reserved random access resources by respectively starting a timer. For example: when the life of the random access resource (namely, the random access preamble) reserved by the source base station is over (namely, the first timer is overtime), the source base station can allocate the random access resource to other user equipment for use; and when the second timer of the user equipment is timed out, the user equipment discards the reserved random access resource (namely the random access preamble) which is saved.
Step 204, the source base station sends a sequence number state transition message to the target base station, wherein the sequence number state transition message comprises an uplink Packet Data Convergence Protocol (PDCP) sequence number and a Hyper Frame Number (HFN) during migration and switching; forwarding the received downlink data from a serving gateway (S-GW) to a target base station;
step 205, the user equipment performs handover to the target base station.
The specific implementation manner of the switching is as follows: the user equipment synchronizes to the target base station, then carries out non-contention based random access to the target base station by the random access preamble carried in the switching command, and sends a radio resource control connection reconfiguration completion (switching confirmation) message to the target base station.
In step 206, the target base station starts a third timer with a preset duration.
In this step, the target base station may start a third timer, and the duration of the third timer may be preset according to the requirement of the actual application. For example, in an embodiment of the present invention, the duration of the third timer may be set as the preset lifetime. Of course, other values may be set.
Step 207, optionally, when the user equipment determines that a handover back to the source base station is required within a preset time (for example, before the first timer is not timed out), the user equipment sends a handover indication message to the target base station (for example, the handover indication message may also be a measurement report carrying indication information); or, if the user equipment does not send the handover indication message, the target base station may determine whether the user equipment initiates handover to the source base station by detecting a data transmission condition of an air interface.
Preferably, the specific implementation manner is as follows: if the target base station does not receive the uplink data from the user equipment any more and the downlink data cannot reach the user equipment, it can be determined that the user equipment initiates switching to the source base station.
And step 208, the target base station stops the third timer, and sends a serial number state transition message to the source base station to indicate to stop forwarding data to the target base station.
Step 209, the ue performs random access using the reserved random access preamble, switches back to the source base station, and sends a rrc connection reconfiguration complete (handover confirm) message to the source base station.
Step 210, the source base station stops the first timer and releases the dedicated random access resource reserved for the user equipment.
In steps 211 to 213, the source base station performs admission control and air interface reconfiguration.
For example, the specific implementation is as follows: the source base station performs admission control and allocates wireless resources; and then configuring the allocated radio resource information to the user equipment through a radio resource control connection reconfiguration process.
In step 214, the source base station sends a user equipment context release message to the target base station, and releases the resource allocated by the target base station for the user equipment.
Through the steps 201 to 214, the processing mode when switching back to the source base station within the preset time can be realized when switching based on the X2.
Second embodiment, based on the implementation mode that when switching is performed by X2, the switching is not performed back to the source base station within the preset time.
Fig. 4 is a flowchart illustrating a method for cell handover in a second embodiment of the present invention, where a source base station is a macro base station and a target base station is a micro base station. As shown in fig. 4, the method for cell handover in the second embodiment may include the following steps:
steps 301 to 306 are the same as steps 201 to 206 of the first embodiment, and are not described herein again.
In step 307, when the ue does not determine that it needs to switch back to the source base station within a preset time (e.g. before the first timer times out), the lifetime of the random access resource reserved by the source base station ends, and the source base station releases the reserved random access resource.
Step 308, the target base station determines whether the third timer is overtime.
When the third timer times out, step 309 may be performed.
Step 309, after the third timer is overtime, the target base station sends a path switching request message to the mobility management entity, requesting the downlink GTP tunnel to be switched to a new GTP tunnel endpoint.
And 310-313, the mobility management entity, the service gateway and the packet data gateway realize the conversion of the downlink GTP tunnel to a new GTP tunnel endpoint by modifying the bearing process.
Step 314, the serving gateway sends an end marker packet to the source base station, and forwards the end marker packet to the target base station through the source base station, indicating that the data forwarding is ended.
Step 315, the mobility management entity sends a path switching request response message to the target base station to confirm the path switching success.
Step 316, the target base station sends the user equipment uplink release message to the source base station to release resources.
Through the steps 301 to 316, the processing mode when the handover is based on the X2 and the handover is not performed back to the source base station within the preset time can be realized.
Third embodiment, when switching based on S1, switching back to the implementation of the source base station within the preset time.
Fig. 5 is a flowchart illustrating a method for cell handover in a third embodiment of the present invention, where a source base station is a macro base station and a target base station is a micro base station. As shown in fig. 5, the method for cell handover in the third embodiment may include the following steps:
step 401, the source base station and the target base station interactively obtain the resources required for the handover
In this step 401, the source base station will prepare for handover with the target base station. For example, the source base station will interact with the target base station through the mobility management entity to acquire resources required for handover.
Step 402, the source base station reserves random access preamble for the user equipment, and presets the life time of the reserved random access preamble; and setting and starting a first timer with the duration as the life time.
Step 403, the source base station sends the handover command, the reserved random access preamble and the life time of the random access preamble to the user equipment through a radio resource control connection reconfiguration message; the user equipment saves the reserved random access preamble and the life time thereof, and starts a second timer with the life time as the duration.
And 404-405, performing data back transmission.
For example, in a preferred embodiment of the present invention, the data back-transmission is implemented in the following manner:
the source base station sends a base station state transfer message to the mobility management entity, and transfers the receiving and sending states of the PDCP sequence number;
the mobile management entity sends a mobile management entity state transfer message to a target base station, and transfers the receiving and sending states of the PDCP sequence number;
and the source base station reversely transmits the downlink data from the S-GW to the target base station.
In step 406, the ue performs handover to the target base station and sends a rrc connection reconfiguration complete (handover confirm) message to the target base station after the handover is successful.
In step 407, the target base station starts a third timer for a preset time.
Step 408 is the same as step 207 in the first embodiment, and is not described herein again.
Step 409-410, the target base station stops the third timer and sends a base station state transfer message to the mobility management entity; and the mobile management entity sends a mobile management entity state transfer message to the source base station and indicates to stop forwarding data to the target base station.
Step 411, the ue performs random access using the reserved random access preamble, switches back to the source base station, and sends a rrc connection reconfiguration complete (handover confirm) message to the source base station.
In step 412, the source base station stops the first timer and releases the dedicated random access resource reserved for the ue.
In step 413, the source base station performs admission control and air interface reconfiguration.
Step 413 is the same as steps 211 to 213 in the first embodiment, and is not described herein again.
Step 414, the logical connection between the target base station and the ue is released through the ue context release process.
Through the steps 401 to 414, the processing mode when switching back to the source base station within the preset time can be realized when switching based on the S1.
Fourth, based on the implementation manner that when switching is performed in S1, the source base station is not switched back within the preset time.
Fig. 6 is a flowchart illustrating a method for cell handover in a fourth embodiment of the present invention, and as shown in fig. 6, the method for cell handover in the fourth embodiment may include the following steps:
steps 501 to 507 are the same as steps 401 to 407 of the first embodiment, and are not described herein again.
In step 508, when the ue does not decide that it needs to switch back to the source base station within the preset time (e.g. before the timeout of the first timer), the lifetime of the random access preamble reserved by the source base station ends, and the source base station releases the reserved random access resource.
In step 509, the target base station determines whether the third timer is expired.
Step 510, after the third timer is over, the target base station sends a handover notification message to the mobility management entity, indicating that the user equipment has been handed over to the target cell and the handover S1 is successfully completed.
And 511-514, the mobility management entity, the first service gateway and the second service gateway realize the conversion of the downlink GTP tunnel to a new GTP tunnel endpoint through a bearer modification process.
When one of the conditions listed as "trigger tracking area update" is met, the user equipment initiates a tracking area update procedure, step 515.
516-517, the mobility management entity releases the logical connection between the target base station and the user equipment through the user equipment context release process.
For example, in a preferred embodiment of the present invention, the specific implementation manner is:
the mobility management entity sends a user equipment uplink release command message to a target base station;
the target base station releases the logic connection associated with the user equipment and replies a user equipment context release completion message to the mobility management entity.
Through the steps 501 to 517, the processing mode when the handover is based on S1 and the handover is not performed back to the source base station within the preset time can be realized.
Fifth, based on the implementation manner that when the X2 handover is performed, the ue is handed over from the source base station to the target base station, and the target base station receives the measurement report of the ue when the third timer expires and hands over back to the source base station.
Fig. 7 is a flowchart illustrating a method for cell handover according to a fifth embodiment of the present invention, where a source base station is a macro base station and a target base station is a micro base station. As shown in fig. 7, the method for cell handover in the fifth embodiment may include the following steps:
steps 601 to 606 (not shown in fig. 7) are the same as steps 201 to 206 in the first embodiment, and are not described again here.
In step 607, the third timer of the target base station times out.
In step 608, the ue sends a measurement report to the target base station.
Step 609, the target base station makes a switching decision, and the decision result is that the user equipment is switched back to the source base station; and the target base station and the source base station interactively acquire switching resources.
Step 610, the target base station sends a radio resource control connection reconfiguration message to the user equipment, and the message carries a handover command.
Step 611, the target base station sends a sequence number state transition message to the source base station, carrying the uplink PDCP sequence number and the downlink HFN state.
Step 612, the user equipment initiates random access to the source base station and establishes uplink synchronization, and then replies a radio resource control connection reconfiguration complete message to the source base station, carrying a handover confirmation.
Step 613, the source base station sends a message for releasing the uplink of the user equipment to the target base station; and the target base station releases the resources.
In addition, in the technical solution of the present invention, when performing handover based on S1, a processing manner in which the ue is handed over from the source base station to the target base station, and the target base station receives a measurement report of the ue when the third timer expires and switches back to the source base station is similar to the processing manner in the handover based on X2 in the above embodiment 5, and the difference is that:
when preparing for handover, the target base station interacts with the source base station through the mobility management entity to acquire handover resources, as shown in step 401 above;
when data is reversely transmitted, the target base station forwards the state transfer message to the source base station through the mobility management entity, as shown in the above steps 409-410;
and when releasing the resource of the user equipment at the target base station, notifying the target base station to release the resource through the mobility management entity, as shown in step 414 above.
In addition, preferably, fig. 8 is a schematic diagram illustrating a configuration process of a reserved random access preamble in an embodiment of the present invention, as shown in step 701 of fig. 8, in an embodiment of the present invention, a source base station sends a rrc connection reconfiguration message to a ue, where the rrc connection reconfiguration message carries a handover command and dedicated random access resources (a random access preamble and a lifetime of the random access preamble) configured to the ue.
In addition, in the technical solution of the present invention, there may be a plurality of implementation manners for steps 306, 308, 309, and 315.
For example, fig. 9 is a schematic diagram of path conversion processing in the embodiment of the present invention, and as shown in fig. 9, each of the steps 306, 308, 309, or 315 may include the following steps:
step 801: the target base station judges the type of the target base station according to the configuration, and if the target base station is a micro base station, the target base station starts a third timer with preset waiting time until the third timer is overtime; otherwise, the third timer is not started, and step 802 is executed.
Step 802: the base station sends a path switching request message to the mobility management entity.
Step 803: and after the mobile management entity finishes the processing, replying a path switching request response message to the base station.
In addition, in the technical solution of the present invention, there may be a plurality of implementation manners for steps 507, 509, and 510.
For example, fig. 10 is a schematic diagram of a handover notification process in the embodiment of the present invention, and as shown in fig. 10, the step 507, 509, or 510 may include the following steps:
step 901: the target base station judges the type of the target base station according to the configuration, and if the target base station is a micro base station, the target base station starts a third timer with preset waiting time until the third timer is overtime; otherwise, the third timer is not started, and step 902 is executed;
step 902: the target base station sends a handover notification message to the mobility management entity indicating that the mobility management entity has handed over the user equipment to the target cell and S1 that the handover has been successfully completed.
In summary, in the cell handover method of the present invention, when the ue is handed over from the source base station (or macro base station) to the target base station (or micro base station), the source base station reserves a dedicated random access resource (including a random access preamble and a preset life cycle) for the ue, and configures the dedicated random access resource to the ue, so that when the ue moves back to the source base station from the target base station, the reserved random access preamble can be used to implement fast handover. By the mode of reserving the random access preamble for the UE and controlling the switching of the UE, the time for reporting the measurement report, preparing the switching and issuing the switching command is saved, the switching time delay is reduced, and the risk of the UE call drop in the switching process is reduced; and after the user equipment is switched to the target base station, the target base station does not request the core network to switch the downlink GTP tunnel within the preset waiting time so as to prevent the user equipment from carrying out twice GTP tunnel switching processing when being switched back to the source base station within a short time, thereby greatly reducing the signaling processing overhead of the base station and the core network.
In addition, further, by optimizing the path switching process, the UE is switched from the macro base station to the micro base station within the preset time and then switched back to the macro base station without downlink GTP tunnel switching, so that the signaling processing overhead of the base station and the core network is reduced, and the method is particularly suitable for macro-micro heterogeneous network scenes.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (8)

1. A method of cell handover, the method comprising:
the source base station reserves a special random access resource for the user equipment and configures the reserved special random access resource to the user equipment; the dedicated random access resources include: random access preamble and preset life time of the random access preamble;
after the user equipment is switched to the target base station, the target base station does not request a core network to convert a downlink general packet radio service tunneling protocol (GTP) tunnel within the preset waiting time;
when the user equipment needs to be switched back to the source base station, the user equipment initiates random access by using the stored special random access preamble, synchronizes the random access to the source base station and switches back to the source base station;
and after the user equipment is switched back to the source base station, the source base station releases the reserved special random access resource, performs admission control and configures the allocated wireless resource information to the user equipment.
2. The method of claim 1, wherein the source base station reserving dedicated random access resources for the user equipment comprises:
the source base station reserves random access preamble for the user equipment and presets the life time of the reserved random access preamble; and setting and starting a first timer with the duration as the life time.
3. The method of claim 2, wherein:
a source base station sends a radio resource control connection reconfiguration message to user equipment;
the rrc connection reconfiguration message carries a handover command and dedicated random access resources configured to the ue.
4. The method of claim 3, further comprising:
the user equipment saves the reserved special random access resource and starts a second timer with the duration as the life time;
and when the second timer is overtime, the user equipment clears the reserved special random access resource.
5. The method of claim 4, wherein the target base station does not request the core network to switch the downlink GTP tunnel within a preset waiting time comprises:
the target base station starts a third timer with preset time; or, the target base station judges whether to start a third timer of preset time according to the base station type, if the target base station is a micro base station, the target base station starts the third timer of preset time;
if the user equipment is switched from the target base station to the source base station, the target base station stops the third timer;
if the ue is still at the target base station, when the third timer times out, the target base station sends a path switching message to a mobility management entity for X2 handover; for S1 handover, the target base station sends a handover notification message to the mobility management entity.
6. The method of claim 5, wherein:
when user equipment judges that switching back to a source base station is needed, the user equipment sends a switching indication message to the target base station; the target base station stops the third timer;
or, when the user equipment determines that it needs to switch back to the source base station, if the user equipment does not send a switching indication message, the target base station determines whether the user equipment initiates switching to the source base station by detecting a data transmission condition of an air interface.
7. The method of claim 6, wherein:
for the X2 handover, when the user equipment does not judge that the handover to the source base station is needed within the preset time, the life time of the random access resource reserved by the source base station is over, and the source base station releases the reserved random access resource;
the target base station judges whether the third timer is overtime or not;
when the third timer is overtime, the target base station sends a path switching request message to the mobile management entity to request the downlink GTP tunnel to be switched to a new GTP tunnel endpoint;
the mobility management entity, the service gateway and the packet data gateway realize the conversion of the downlink GTP tunnel to a new GTP tunnel endpoint through the bearer modification process;
the service gateway sends an end mark packet to the source base station, and the end mark packet is forwarded to the target base station through the source base station to indicate that the data forwarding is ended;
the mobile management entity sends a path switching request response message to the target base station to confirm the success of path switching;
and the target base station sends the user equipment uplink release message to the source base station to release resources.
8. The method of claim 5, wherein:
for the S1 handover, when the user equipment does not decide within the preset time that it needs to be handed over back to the source base station, the life time of the random access resource reserved by the source base station ends, and the source base station releases the reserved random access resource;
the target base station judges whether the third timer is overtime or not;
when the third timer times out, the target base station sends a switching notification message to the mobility management entity, indicating that the user equipment has been switched to the target cell and the switching of S1 is successfully completed;
the mobility management entity, the first service gateway and the second service gateway realize the conversion of the downlink GTP tunnel to a new GTP tunnel endpoint through the bearer modification process;
when one of the conditions listed in the 'trigger tracking area update' is met, the user equipment initiates a tracking area update process;
and the mobility management entity releases the logic connection between the target base station and the user equipment through the context release process of the user equipment.
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