CN101668320A - Method for reducing handover delay in long term evolution systems - Google Patents
Method for reducing handover delay in long term evolution systems Download PDFInfo
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Abstract
本发明实施例公开了一种在LTE系统中缩短切换时延的方法，包括：源eNB向所有管理满足切换判决条件的备选目标小区的备选目标eNB发送切换请求，同意所述切换请求的备选目标小区所属的备选目标eNB预留进行当前切换的资源，并存储进行所述当前切换的用户设备UE的上下文，所述备选目标eNB将同意所述切换请求的备选目标小区信息通知给所述源eNB。本发明实施例的方法能够触发所有备选目标eNB均为所述当前切换预留资源，减小由于当前选定的目标eNB不同意进行切换引起的切换时延。另外，在切换执行过程中，源eNB同时向所有返回切换请求应答的备选目标eNB前转数据，这样可以避免由于切换失败而导致数据的丢失。
The embodiment of the present invention discloses a method for shortening the handover delay in an LTE system, including: the source eNB sends a handover request to all candidate target eNBs that manage the candidate target cells that meet the handover decision conditions, and those who agree to the handover request The alternative target eNB to which the alternative target cell belongs reserves resources for the current handover, and stores the context of the user equipment UE performing the current handover, and the alternative target eNB will agree to the information of the alternative target cell of the handover request Notify the source eNB. The method in the embodiment of the present invention can trigger all candidate target eNBs to reserve resources for the current handover, reducing the handover delay caused by the currently selected target eNB not agreeing to handover. In addition, during the handover execution process, the source eNB simultaneously forwards data to all candidate target eNBs that return handover request acknowledgments, so that data loss due to handover failure can be avoided.
Description
Technical field
The present invention relates to the handoff technique of the communications field, relate in particular to a kind of in Long Term Evolution (Long TermEvolution, LTE) method of shortening handover delay in the system.
Background technology
The process of switching in the LTE system comprises that switch decision stage, handoff preparation phase, handover execution stage and switching finish the stage.Idiographic flow below in conjunction with switching in the LTE system at present is introduced the method for switching in the LTE system.
Fig. 1 is the method flow diagram that switches in the LTE system at present, and as shown in Figure 1, this method comprises:
Step 101, (User Equipment UE) measures communication quality between this UE and each neighbor cell to source base station (eNB) control subscriber equipment, and the formation measurement report.
Step 102～step 103 is the switch decision stage.
At switch decision in the stage, the measurement report that source eNB sends according to UE and present load situation of each eNB etc. are selected the alternative target cells that satisfies the switch decision condition, and the described number that satisfies the alternative target cells of switch decision condition may be for (comprising two) more than two.Particularly:
Step 102, UE sends measurement report to source eNB.
Step 103, source eNB carries out switch decision, selects the alternative target cells that satisfies the switch decision condition.
Step 104～step 106 is a handoff preparation phase.
In handoff preparation phase, source eNB selects the target eNB switched from alternative target eNB, trigger target eNB and carry out acceptance judging, target eNB in admission judgment result when accepting this UE, for this UE reservation switchable resource and store the context of this UE.Wherein, alternative target eNB is meant the eNB of management alternative target cells, and target eNB is accepted to have in the sub-district that this UE is meant that this target eNB manages and agreed to accept this UE's.In addition, an alternative target eNB can only manage a sub-district, also can manage a plurality of sub-districts, and the communication means between eNB and its sub-district of managing is a prior art, not in the discussion scope of this paper.
Below step 104～step 106 is specifically described:
Step 104, source eNB selects the optimal objective sub-district from the alternative target cells that satisfies the switch decision condition, send handoff request (HandoverRequest) message to the alternative target eNB of this optimal objective sub-district of management.
Step 105, whether described alternative target eNB admits this UE to make acceptance judging according to described optimal objective sub-district.
In this step, if this UE is admitted in this optimal objective sub-district, then the alternative target eNB of this optimal objective sub-district of expression management agrees described handoff request, execution in step 106, otherwise the target eNB of this optimal objective sub-district of expression management is disagreed with described handoff request, and then this alternative target eNB returns to switch to source eNB and prepares failure (Handover Preparation Failure) message, source eNB carries out the corresponding operating after the handoff request failure, specifically asks for an interview hereinafter related description.
Step 106, alternative target eNB returns handoff request to source eNB and replys (Handover RequestACK) message.
Step 107～step 111 is a handover execution stage.
In handover execution stage, after source eNB receives the Handover Request ACK message of alternative target eNB, with this alternative target eNB as target eNB, the sign of optimal objective sub-district is carried in the switching command, send described switching command to UE, source eNB begins to carry out data forwarding to the target eNB of the described optimal objective of management sub-district, wherein, the data of preceding commentaries on classics comprise that high level is issued the new data of this UE, source eNB issues this UE and still do not receive the data of this UE affirmation and the up discontinuous data that UE sends.After described UE receives described switching command, according to the sign of the optimal objective sub-district of carrying in this switching command, set up uplink synchronous from the disengaging of old sub-district and with described target eNB, described target eNB is that this UE authorizes ascending resource and determines Timing Advance.
Below step 107～step 111 is specifically described:
Step 107, source eNB is carried at the sign of optimal objective sub-district and is handed down to UE in the switching command.
Step 108, source eNB is to target eNB state transitions (the SN Status Transfer) message that transmits Sequence Number, and beginning is carried out data forwarding to target eNB.
Step 109, UE sets up uplink synchronous according to the sign of the optimal objective sub-district of carrying in the switching command with the target eNB of this optimal objective sub-district of management.
Step 110, target eNB send uplink synchronous to this UE to be confirmed and Timing Advance, and UE receives described uplink synchronous affirmation and Timing Advance, and the uplink synchronous of then described UE and target eNB is set up and finished.
Step 111, UE sends up switching to target eNB and finishes (Handover Complete) message.
Carry out step 109～process of step 111 in, if the Radio Link connection failure between the Serving cell of UE and this UE or to the Target cell access failure, then this UE need reselect Target cell and carries out wireless link recovery or switching, described needs are reselected the concrete grammar that Target cell recovers or switches, and see hereinafter explanation for details.
Step 112～step 118 is finished the stage for switching.
Finish in the stage in switching, gateway (Serving GW) is finished the conversion of downlink path, and target eNB guarantees to send according to the order of sequence to the data that belong to described UE that receive that preceding transfer and new.Source eNB the data of the order of the release resource of receiving target eNB and described UE change before finish after, discharge the resource that described UE takies.
Below step 112～step 118 is specifically described:
Step 112, target eNB is to MME transmit path transfer request (Path Swith Request) message.
Step 113, MME sends user's face update request (User Plane updaterequest) message to Serving GW.
Step 114, Serving GW carries out data path to be shifted, and after finishing, the data path transfer sends the bag that carries end mark (END MARK) to source eNB, expression Serving GW finishes to the downlink data at described UE that source eNB sends, and Serving GW is to the downlink data of target eNB transmission at described UE afterwards.
Step 115, Serving GW sends user's face to MME and upgrades response (User Plane updaterequest response) message.
Step 116, MME replys (Path Switch RequestACK) message to target eNB transmit path transfer request.
Step 117, target eNB send to source eNB and discharge UE context (UE Context Release) message.
Step 118, source eNB discharges the resource that the UE carry out this handoff procedure takies, and deletes the context of this UE.
Fig. 1 is the switching flow figure that agree to admit in the optimal objective sub-district under the situation of the UE that carries out current switching.In actual handover process, also the situation that the UE that carries out current switching is not admitted in the optimal objective sub-district may appear.
If the UE that carries out current switching is not admitted in the optimal objective sub-district, the target eNB of then managing this optimal objective sub-district sends Handover Preparation Failure message to source eNB, after source eNB receives this Handover Preparation Failure message, restart handoff preparation phase, i.e. select target sub-district in satisfying the alternative target cells of judgment condition again, send Handover Request message to the alternative target eNB of this Target cell of management then, and carry out associative operation according to HandoverRequest ACK message or Handover Preparation Failure message that this eNB returns.When not admitting the UE of request switching in the optimal objective sub-district, source eNB re-executes handoff preparation phase and has increased time delay for switching.
In addition, after Target cell agree to be admitted this UE, also may occur between this UE and Serving cell Radio Link Failure or to the situation of Target cell access failure.
For the situation of the Radio Link Failure between UE and Serving cell, according to present 3GPPTS 36.332 agreements (" Evolved Universal Terrestrial Radio Access (E-UTRA); " Radio Resource Control (RRC) protocol specification " .) regulation, if occur Radio Link Failure in the handoff procedure, then UE carries out wireless link recovery and can only finish in those have stored the sub-district that eNB managed of context data of this UE.
Introduce the detailed process of carrying out wireless link recovery below:
According to present 3GPP TS 36.300 agreements (" Evolved Universal Terrestrial RadioAccess (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); Overall description; The regulation that Stage 2 "): if UE detects the Radio Link Failure of this UE and current service cell; then this UE reselects Target cell and carries out wireless link recovery; the management UE of target eNB by random access procedure of selected Target cell again identifies this UE of authentication; particularly; this target eNB is searched the context that whether stores this UE in this target eNB according to this UE sign; if, then indicate UE to carry out wireless link recovery with the described Target cell of reselecting, if not, then refusing described UE recovers in this sub-district, this moment, UE may need to enter wireless connections free time (RRC_IDLE) state, initiated initial connection procedure again.UE enters the RRC_IDLE state and resends initial connection procedure and can increase and carry out time delay for switching.
Usually, after target eNB received the Handover Request message of source eNB, if agree to admit the UE that carries out current switching, then this target eNB was stored the context of this UE.In handoff procedure, because will satisfying the cell notification of switch decision condition, source eNB do not give this UE, therefore, the target eNB that UE reselects may not satisfy the switch decision condition, then can not store the context of this UE in this target eNB of reselecting.According to the flow process of Fig. 1, store the context of this UE among the optimal objective eNB that only active eNB and agreement are switched, therefore, this UE can only carry out wireless link recovery in source eNB and described target eNB.
For the situation of UE to the Target cell access failure, UE need reselect Target cell and insert, if this Target cell of reselecting is not described UE reserved resource or the context of not storing this UE, then described UE can't successfully insert the Target cell that this is reselected.
By such scheme as seen, switch in the set-up procedure, source eNB selects the optimal objective sub-district from the alternative target cells that satisfies the switch decision condition, only send Handover Request message to the alternative target eNB of this optimal objective sub-district of management, triggering this alternative target eNB is current handoff reservation resource, in case disagreeing with, this optimal objective sub-district switches, because management other except that this optimal objective sub-district satisfies the unpromising described handoff reservation respective resources of alternative target eNB of the sub-district of switching condition, do not store the context of this UE yet, therefore, source eNB needs to initiate again to switch set-up procedure, promptly need to reselect another one and satisfy the sub-district of judgment condition as new Target cell, send Handover Request message to the alternative target eNB of this new Target cell of management, and carrying out associative operation according to Handover Request ACK message or Handover Preparation Failure message that this eNB returns, this must increase and carry out time delay for switching.
And when between UE and this Serving cell Serving cell, Radio Link Failure occurring, because source eNB only sends Handover Request message to the target eNB of management optimal objective sub-district, trigger this target eNB and carry out switching preparation, therefore, only in source eNB and described optimal objective eNB, store the context of this UE, if this UE has selected the sub-district of other eNB management except that source eNB and described optimal objective eNB when carrying out wireless link recovery, then wireless link recovery can't normally carry out, UE may need to be introduced into the RRC_IDLE state, and this can increase and carry out time delay for switching.
Summary of the invention
In view of this, the purpose of the embodiment of the invention is to provide a kind of method that shortens handover delay in the LTE system, disagrees with the Target cell that reduces current selected and switches the handover delay that causes.
For achieving the above object, the technical scheme of the embodiment of the invention specifically is achieved in that
A kind of method of in Long Term Evolution LTE system, switching, this method comprises:
Source base station eNB satisfies alternative target eNB from the alternative target cells of switch decision condition to all management sends handoff request;
The affiliated alternative target eNB of alternative target cells that agrees described handoff request reserves the resource of carrying out current switching, and storage carries out the context of user equipment (UE) of described current switching, and described alternative target eNB will agree that the alternative target cells information of described handoff request is notified to described source eNB.
As seen, in the embodiment of the invention, source eNB satisfies alternative target eNB from the alternative target cells of switch decision condition to all management sends handoff request, agree described handoff request if having in the described alternative target cells of described alternative target eNB management, then described alternative target eNB reserves the resource of switching, and storage carries out the context of user equipment (UE) of described current switching, and the alternative target cells of agreeing described handoff request is notified to described source eNB.Therefore, the method for the embodiment of the invention can trigger all alternative target eNB and be described handoff reservation resource, carries out switching preparation.Like this, the Target cell of current selected is disagreed with when switching, if reselecting Target cell from the alternative target cells that other agreements are switched, UE switches, then source eNB does not need to initiate handoff preparation phase again, and the Target cell that has reduced current selected is disagreed with and switched the handover delay that causes.
Description of drawings
Fig. 1 is the switching flow figure that agree to admit in the optimal objective sub-district under the situation of the UE that carries out current switching;
Fig. 2 is the method flow diagram that switches in the LTE system that the embodiment of the invention provides;
Fig. 3 is the switching flow figure of UE under selected Target cell access failure situation in the process of switching in the LTE system.
Embodiment
Core concept of the present invention is that source base station eNB satisfies alternative target eNB from the alternative target cells of switch decision condition to all management sends handoff request; Agree described handoff request if having in the described alternative target cells of described alternative target eNB management, then described alternative target eNB reserves the resource of carrying out current switching, and storage carries out the context of user equipment (UE) of described current switching, and the alternative target cells of agreeing described handoff request is notified to described source eNB.
For making purpose of the present invention, technical scheme and advantage clearer, below with reference to the accompanying drawing embodiment that develops simultaneously, the present invention is described in more detail.
Fig. 2 is the method flow diagram that switches in the LTE system that the embodiment of the invention provides, and as described in Figure 2, this method comprises:
Step 201 is with step 101.
Step 202～step 203 is for the switch decision stage, with step 102～step 103.
In the switch decision stage, source eNB judges the alternative target cells that satisfies the switch decision condition, judge alternative target eNB according to the eNB under the alternative target cells that satisfies judgment condition, promptly judge the alternative target eNB that the alternative target cells of switch decision condition is satisfied in management.
Step 204～step 206 is handoff preparation phase.
In handoff preparation phase, source eNB satisfies alternative target eNB from the alternative target cells of switch decision condition to all management all sends handoff request message, after each alternative target eNB receives described handoff request message, all carry out acceptance judging, when court verdict is to admit the UE that carries out current switching, when promptly agreeing this handoff request, alternative target eNB sends Handover Request ACK message to source eNB, and reserve the resource carry out current switching, the context of the user equipment (UE) of described current switching is carried out in storage, otherwise target eNB sends Handover Preparation Failure message to source eNB.Wherein, alternative target eNB admits the UE that current request is switched to be meant, the alternative target cells of the UE that agrees that the admittance current request is switched is arranged in the sub-district of this alternative target eNB management.
In Fig. 2, the alternative target eNB that the alternative target cells of switch decision condition is satisfied in management has two, i.e. target eNB 1 and target eNB 2.Below step 204 and step 206 are described.
Step 204, target eNB 1 and target eNB 2 that source eNB judged to the switch decision stage send Handover Request message respectively.
In this step, carry the sign of alternative target cells in the Handover Request message.If have a plurality of sub-districts to satisfy the switch decision condition in the sub-district that alternative target eNB is managed, then preferably, source eNB only sends a Handover Request message to this alternative target eNB, and carry in this handoff request message that this target eNB manages each satisfy the sign of the alternative target cells of switch decision condition, described sign can be carried in the described HandoverRequest message with the form of identification list, certainly, the number of the alternative target cells that satisfies the switch decision condition that source eNB also can be managed according to alternative target eNB all sends Handover Request message to alternative target eNB at each described alternative target cells.
Step 205, target eNB 1 and target eNB 2 are made acceptance judging respectively according to the Handover Request message of receiving separately, and agreeing to admit the UE that carries out current switching, when promptly agreeing to carry out described switching, execution in step 206, otherwise, return Handover Preparation Failure message to source eNB.
Step 206, the alternative target eNB that current switching is carried out in agreement is current handoff reservation resource, and stores the context of the UE that carries out current switching, returns Handover Request ACK message to source eNB.
In this step, agree that the alternative target eNB that carries out current switching is meant the affiliated alternative target eNB of alternative target cells that agrees handoff request.
In Fig. 2, target eNB 1 and eNB2 all agree to carry out described switching, and therefore, target eNB 1 and eNB2 are respectively current handoff reservation resource, and return Handover Request ACK message to source eNB.
Step 207～step 213 is handover execution stage.
In handover execution stage, the sign of the alternative target cells that source eNB on the one hand switches all agreements is carried at issues UE in the switching command, on the other hand to all management agree the alternative target eNB of the alternative target cells switched transmit Sequence Number state transitions (SN Status Transfer) message, give all described target eNB with the data forwarding of this UE.Wherein, the data of preceding commentaries on classics comprise that high level is issued the new data of this UE, source eNB issues this UE and still do not receive the data of this UE affirmation and the up discontinuous data that UE sends.
In handover execution stage, switch the corresponding alternative target cells select target sub-district of alternative target cells sign that UE carries from switching command, set up uplink synchronous with selected Target cell, and behind uplink synchronous affirmation of receiving described Target cell and Timing Advance, notify described selected Target cell to switch and finish.
Below step 207～step 213 is described.
Step 207, source eNB sends switching command to UE, and carries the sign of agreeing the alternative target cells switch in this switching command.
When the number of the alternative target cells of agreeing to switch is two when above, the sign of the alternative target cells that all agreements are switched can be carried in the switching command with the form of identification list.
Step 208, source eNB sends SN Status Transfer message respectively to all alternative target cells, and all carries out data forwarding to all alternative target cells.
Step 209, UE switches according to the sign select target sub-district of the alternative target cells of carrying in the switching command, promptly carries out uplink synchronous with this selected target eNB.If UE and this target eNB have been set up uplink synchronous, then execution in step 210.
In Fig. 2, selected target eNB is a target eNB 1.
Step 210, this selected target eNB 1 send uplink synchronous to UE and confirm and Timing Advance.
Step 211, UE sends to switch to target eNB 1 and finishes (Handover Complete) message, notifies this target eNB to switch and finishes.
For step 209～211, if set up in the process of uplink synchronous with selected target eNB at UE, perhaps target eNB sends in the process of uplink synchronous affirmation and Timing Advance to UE, perhaps UE sends in the process of handoff completion message to target eNB, occurred with the situation of Serving cell Radio Link connection failure or to Target cell access failure situation, then UE reselects Target cell and carries out wireless link recovery or initiate access procedure again from the corresponding alternative target cells of the entrained alternative target cells sign of switching command tabulation, and concrete switching flow sees also hereinafter and to the explanation of Fig. 3.
Step 212, the target eNB 1 that this switching is finished send handover success to source eNB and confirm (Handover commite) message.
Handover commite message in this step is the signaling message that increases newly, the switching that is used for this UE of timely notification source eNB and target eNB 1 is successful, so that source eNB in time notifies other alternative target eNB to be released to this UE reserved resource, described other alternative target eNB leaves described resource for UE that other need switch, improves the resource utilization of system.
Step 213, source eNB sends handover cancelling (Handover Cancel) message to other alternative target eNB.
In this step, source eNB is by sending Handover Cancel message to other alternative target eNB, the resource of in time notifying other alternative target eNB to be released to current handoff reservation is left resource for UE that other need switch or insert, improves the resource utilization of system.
Other alternative target eNB among Fig. 2 is a target eNB 2, and target eNB 2 is released to this UE reserved resource after receiving HandoverCancel message.
Step 214～step 220 is for the stage is finished in switching, identical with step 112～step 118.
As seen, handoff preparation phase in flow process shown in Figure 2, promptly in step 204～step 206, because source eNB all sends Handover Request message to all alternative target eNB, and each alternative target eNB makes acceptance judging according to the Handover Request message of receiving separately respectively, and when agreeing to switch, send Handover Request ACK message to source eNB, therefore, in the switch decision stage, only need experience one to take turns the time of " send Handover Request ACK message-carry out acceptance judging-return Handover Request ACK or Handover Preparation Failure message ", source eNB just can learn the alternative target cells that all agreements are switched, and then judges all alternative target eNB.In handoff preparation phase shown in Figure 1, source eNB only sends handoff request message to a target eNB, when disagreeing with in this target eNB when switching, send handoff request message to the another one target eNB again and compare, can shorten owing to the target eNB of current selection is disagreed with and switched the handover delay that causes.
In step 208, source eNB changes the data of described UE before all alternative target eNB are equal, therefore, source eNB needn't the described UE of buffer memory data, can guarantee if cause needs to change target eNB to a certain target eNB handoff failure, the switching that the target eNB of described UE after changing carried out is the switching that can't harm, the data of described UE are not lost after promptly guaranteeing to switch, this has saved the spatial cache of source eNB on the one hand, also avoided on the other hand owing to the forwarding data that handoff failure causes is lost, the data of UE are complete after having guaranteed to switch.
By step 212～213, can also further improve resource utilization ratio.Wherein, the Handover commite message of step 212 is the signaling messages that increase newly.Target eNB by the current UE that switches of the timely notification source eNB of Handover commite message in the step 212 successful switch on this target eNB, source eNB is by the Handover Cancel message in the step 213, in time notify other alternative target eNB to be released to this UE reserved resource, so that described other alternative target eNB leaves resource for UE that other need switch or newly insert, improve the resource utilization of system.
Also can not increase the Handover commite message in the step 212, in this case, direct execution in step 214～219 after step 210, after the execution of step 219, promptly after source eNB receives the message of the release resource that the target eNB of handover success is sent, source eNB discharges the resource that this UE takies on the one hand in the eNB of this source, agree that to other alternative target eNB that switches sends Handover Cancel message on the other hand, after described other agree that the alternative target eNB that switches receives this HandoverCancel message, be released to the resource that this UE carries out handoff reservation, the context of this UE that deletion is preserved.But it is more late than last method that this method makes that other alternative target eNB that agree to switch are released to the related resource that UE reserves, and can make resource utilization descend.
In addition, between step 207～step 211, (do not comprise step 207 and step 211), if the Radio Link Failure of UE and Serving cell, then UE can be according to the identification list of the Target cell that carries in the switching command, wireless link recovery is carried out in the select target sub-district, if carry out the wireless link recovery success with selected Target cell, then UE has promptly switched on the Target cell of this wireless link recovery success.
What the process of wireless link recovery of carrying out UE and selected Target cell adopted is RRC connection reconstruction flow process, and particularly, this flow process comprises:
Step 1 only is with the difference of step 209, the uplink synchronous code difference that UE sends to described selected Target cell.
Step 2 is with step 210.
Step 3, the target eNB of UE under described selected Target cell send rebuilds request message.
Step 4, described target eNB is returned reconstruction message to described UE.
Step 5, UE returns to rebuild to described target eNB and finishes message.
Described target eNB is after receiving that message is finished in described reconstruction, can return one to the source of described UE eNB and rebuild successful affirmation message, the affirmation message that this reconstruction is successful is equivalent to the Handover commite message in the step 212, the Radio Link that is used for described UE of notification source eNB and described Target cell is rebuild successful, source eNB can notify other target eNB to be released to this UE reserved resource then, and deletes the context of this UE.Source eNB receives that the flow process after the successful affirmation message of described reconstruction is identical with step 212 flow process (not comprising step 212) afterwards among Fig. 2.
Described target eNB is after receiving that message is finished in described reconstruction, also can not return and rebuild successful affirmation message to the source of described UE eNB, but direct execution in step 214～219, after the execution of step 219, source eNB agrees that to other alternative target eNB that switches sends Handover Cancel message again.
In the method for carrying out wireless link recovery among the present invention and the prior art can only with source eNB or optimal objective eNB in carry out wireless link recovery method compare, increased the choice of UE selection carrying out wireless link recovery, reduced owing to carrying out the probability that wireless link recovery causes that handover delay increases.
In addition, the sign of the Target cell that source eNB switches all agreements all is carried at and is handed down to UE in the switching command, this UE switches the select target sub-district from the alternative target cells that described agreement is switched, promptly insert selected Target cell, if UE is in the process that inserts selected Target cell, UE is to described selected Target cell access failure, because the alternative target eNB that all agreements are switched has all reserved the context that carries out the resource of current switching and stored this UE for this UE in handoff preparation phase, therefore, this UE can also reselect Target cell and insert according to the sign of the alternative target cells of carrying in the switching command.
Switching flow in the process of UE and target eNB being switched below in conjunction with Fig. 3 under selected Target cell access failure situation is elaborated.
Fig. 3 is the switching flow figure of UE under selected target eNB access failure situation in the process of switching in the LTE system, and as shown in Figure 3, this flow process specifically comprises:
Step 301～step 308 is with step 201～step 208.
Step 309, UE is to target eNB 1 access failure, then UE can be to the another one target eNB, be that target eNB 2 is set up wireless connections, particularly, UE and target eNB 2 are set up uplink synchronous, and target eNB 2 is returned uplink synchronous acknowledge message and Timing Advance to this UE then, and UE returns to target eNB 2 and switches the message of finishing then.
In Fig. 3, UE with target eNB 1 carry out access failure after, be connected with the Radio Link of target eNB 2 and set up successfully.
Step 310～step 318 only is that with the difference of step 212～step 220 target eNB of handover success becomes target eNB 2 by target eNB 1.
Among Fig. 3, because in handoff preparation phase, be in step 304～306, source eNB triggers all management agreements and carries out the context that the alternative target eNB of the alternative target cells of current switching is described handoff reservation resource, stores the UE that carries out current switching, and the sign that the alternative target cells of current switching is carried out in described agreement is handed down to UE, therefore, when the Target cell access failure that UE selects, this UE can reselect target eNB and insert from all alternative target eNB.
As seen from the above technical solution, the method for the embodiment of the invention can trigger all alternative target eNB and be described handoff reservation resource, carries out switching preparation.Like this, disagree with in the target eNB of current selected and to switch, if reselecting target eNB from the alternative target eNB that other agreements are switched, UE switches, then source eNB does not need to initiate handoff preparation phase again, and the target eNB that has reduced current selected is disagreed with and switched the handover delay that causes.
The above is preferred embodiment of the present invention only, is not to be used to limit protection scope of the present invention, all any modifications of being made within the spirit and principles in the present invention, is equal to replacement, improvement etc., all should be included within protection scope of the present invention.
Claims (9)
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