WO2010130135A1 - 一种长期演进系统中跨基站切换方法及系统 - Google Patents
一种长期演进系统中跨基站切换方法及系统 Download PDFInfo
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- WO2010130135A1 WO2010130135A1 PCT/CN2009/075671 CN2009075671W WO2010130135A1 WO 2010130135 A1 WO2010130135 A1 WO 2010130135A1 CN 2009075671 W CN2009075671 W CN 2009075671W WO 2010130135 A1 WO2010130135 A1 WO 2010130135A1
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- base station
- handover
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- user equipment
- target base
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W36/00—Hand-off or reselection arrangements
- H04W36/02—Buffering or recovering information during reselection ; Modification of the traffic flow during hand-off
Definitions
- the present invention relates to user handover techniques in a long term evolution system, and more particularly to a hard handover method and system across base stations in a long term evolution system. Background technique
- LTE Long Term Evolution
- 3GPP 3rd Generation Partnership Project
- MIMO Multiple Input Multiple Output
- the main performance objectives include: providing 100Mbps downstream and 50Mbps uplink peak rate in 20MHz spectrum bandwidth; Cell edge user performance; Increase cell capacity; Reduce system delay; Support cell coverage of 100km radius; Can provide access services greater than 100kbps for 350km/h high-speed mobile users; Support paired or unpaired spectrum, and flexible configuration bandwidth.
- the 3GPP determines that the architecture of LTE is a flat evolved UTRAN (UMTS Terrestrial Radio Access Network) structure.
- the user plane is mainly composed of an evolved Node B (eNB) and a Serving-Gateway (s-GW).
- the eNB is connected to the s-GW through the base station-gateway interface S1, and the eNBs are connected through the inter-base station interface X2, and the user equipment (User Equitmemt, UE) is connected to the eNB through the wireless air interface Uu.
- eNB evolved Node B
- s-GW Serving-Gateway
- Switching is an ordinary event in a cellular mobile network. It is determined by the user's mobile characteristics. Switching success rate is a very important network indicator. Poor handling can cause serious dropped calls and inconvenience to mobile users.
- the handover of LTE is divided into handover within the base station, handover between the base stations, and handover between the technologies.
- the handover between the base stations refers to that the serving cells before and after the handover belong to different base stations.
- LTE adopts hard handover technology, that is, the user equipment first disconnects from the source base station and then establishes communication with the target base station. Therefore, some mechanisms must be relied to avoid data loss, and the handover process minimizes delay. And facilitate switching failure processing. Summary of the invention
- one of the main purposes of the present invention is to provide a cross-base station handover method in a long term evolution system, which is used to solve the technical problem that the handover speed is slow, the data loss is easy, and the handover failure processing is difficult.
- the technical solution of the present invention is achieved as follows:
- a method for handover across a base station in a long term evolution system includes:
- the user equipment After receiving the handover command, the user equipment feeds back the handover command acknowledgement message to the source base station and buffers the uplink data.
- the source base station buffers the downlink data after sending the handover command, and sends the communication context and the uplink and downlink buffer data between the source base station and the user equipment to the target base station after receiving the handover command acknowledgement message;
- the target base station After the user equipment successfully accesses the target base station, sending, by using the allocated uplink, a handover confirmation message to the target base station; the target base station forwarding the handover confirmation message to the source base station;
- the target base station performs uplink data and downlink data connection with the user equipment according to the communication context and the uplink and downlink buffer data forwarded by the source base station.
- the method further includes: in step B, after the source base station sends the handover command, the context sending timer is started; when the source base station receives the handover command acknowledgement message sent by the user equipment, or the context sending timer When it expires, the communication context and the uplink and downlink buffer data between the source base station and the user equipment are sent to the target base station.
- step A after receiving the handover command sent by the source base station, the user equipment performs the handover decision, and if the handover is supported, the handover is performed immediately, and the handover command confirmation is not immediately sent to the source base station; Communicating with the source base station, backing up the communication context with the source base station, buffering the uplink data, and synchronizing to the target base station, before successfully synchronizing to the target base station, The media access layer entity, the radio access layer entity, and the packet data convergence entity are not reset.
- the method further includes: when the user equipment decides to perform the handover, starting a handover timer, if the timer expires, performing a handover failure processing step; if the timer is advanced, the user terminal successfully accesses the target base station , then terminate the timer.
- step A if the source base station does not receive the handover command acknowledgement message sent by the user equipment, the handover command is retransmitted; when the source base station receives the handover command acknowledgement message fed back by the user terminal, or receives the handover confirmation of the target base station.
- the message stops resending the switching command.
- the uplink data is buffered, and the uplink data includes an uplink data packet sent to the source base station and an uplink data packet sent to the target base station;
- the user equipment sends the buffered uplink data to the target base station; after receiving the data packet reception status report sent by the target base station, the user equipment sends the data that needs to be retransmitted to the target base station, and Data that does not need to be retransmitted is discarded.
- step D when the downlink data connection is performed between the target base station and the user equipment, the target base station determines the data packet to be retransmitted according to the downlink communication context forwarded by the source base station, or determines the data packet that needs to be retransmitted by the following steps: :
- the target base station sends a request for polling the data packet receiving status to the user equipment
- the user equipment After receiving the request for polling the data packet receiving status, the user equipment generates a data packet receiving status report and sends the status report to the target base station.
- the target base station determines the data packet to be retransmitted according to the acceptance status report reported by the user equipment.
- the above method, the present invention further provides a cross-base station handover system in a long-term evolution system, including a user terminal, a source base station, and a target base station, specifically,
- the source base station further includes: a handover notification module and a data cache forwarding module;
- a handover notification module configured to send a handover command to the user terminal if the source base station and the target base station allow handover
- a data buffer forwarding module configured to buffer downlink data after sending a handover command, and send a communication context and uplink and downlink buffer data between the source base station and the user equipment to the target base station after receiving the handover command acknowledgement message
- the user terminal further includes: a handover decision module, a handover response module, a handover execution module, and a handover verification initiation module;
- a handover decision module configured to perform a handover decision after receiving a handover command sent by the source base station; and a handover response module, configured to send a handover command acknowledgement message to the source base station when the user terminal supports the handover;
- a handover execution module configured to perform a handover operation, to enable the user equipment to synchronously access the target base station
- a handover confirmation initiation module configured to send, after the user equipment successfully accesses the target base station, a handover confirmation message to the target base station by using the allocated uplink ;
- the target base station further includes: a handover confirmation forwarding module and a data connection module;
- a handover confirmation forwarding module configured to forward a handover confirmation message to the source base station after receiving the handover confirmation message sent by the user equipment;
- the data connection module is configured to perform uplink data and downlink data connection with the user equipment according to the communication context forwarded by the source base station and the uplink and downlink cache data.
- the handover notification module starts a context sending timer; the data cache forwarding module receives the handover command acknowledgement message sent by the user equipment or the context sending timer expires The communication context and uplink and downlink buffer data between the base station and the user equipment are sent to the target base station.
- the handover decision module receives the handover command, the handover decision is performed, and if the user terminal supports the handover, the handover execution module is immediately notified to perform the handover, and the handover response module is not sent to send the handover command acknowledgement message; Disconnecting communication with the source base station, backing up the communication context with the source base station, buffering the uplink data, and synchronizing to the target base station, and not resetting the medium access layer entity, the radio access layer entity, and the packet data before successfully synchronizing to the target base station Convergence entity.
- the handover decision module starts a handover timer when the decision result is switchable, and if the timer expires, performs a handover failure processing step; if the user terminal successfully accesses the target base station before the timer expires, the termination is terminated. Timer.
- the handover notification module resends the handover command; when the handover notification module receives the handover command acknowledgement message fed back by the handover response module, or receives the handover confirmation
- the switching confirmation message sent by the forwarding module stops resending the switching command.
- the handover execution module buffers uplink data before establishing a communication connection with the target base station, where the uplink data includes an uplink data packet sent to the source base station and an uplink data packet sent to the target base station; establishing communication with the target base station. After the connection, the handover execution module sends the buffered uplink data to the target base station;
- the handover execution module After the handover execution module receives the data packet reception status report sent by the data connection module, the uplink data that needs to be retransmitted is sent to the data connection module, and the data that does not need to be retransmitted is discarded.
- the data connection module determines, according to the downlink communication context forwarded by the source base station, the data packet to be retransmitted; or the data connection module to the user
- the device sends a request for polling the data packet receiving status; after receiving the request for polling the data packet receiving status, the user equipment sends a data packet receiving status report to the data connection module, and the data connection module receives the data according to the user equipment.
- the status report determines which packets need to be retransmitted.
- the feature of the invention is that the user equipment backs up the communication context with the source base station before the handover succeeds, disconnects the communication with the source base station, and establishes communication with the target base station; the source base station maintains the communication context with the user equipment before the handover succeeds, and the source base station can Obtain uplink signaling and data of the user equipment.
- the invention has the advantages that the switching speed of the user is faster, the data loss is avoided, and the cutting is convenient. Change the failure process. DRAWINGS
- FIG. 1 is a flowchart of a hardware switching method according to the present invention.
- FIG. 2 is a schematic diagram of a handover scenario according to the present invention.
- FIG. 3 is a flowchart of implementing uplink data switching of a user equipment of the solution according to the present invention
- FIG. 5 is a structural diagram of a cross-base station hard handover system according to the present invention.
- BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be further described in detail below with reference to the accompanying drawings.
- FIG. 2 is a handover scenario diagram of the present invention. It is assumed that the system includes a user equipment 207, a source base station 202, a target base station 203, a mobility management entity and a serving gateway 201, and a base station-to-service gateway interface 204, 205 and an inter-base station interface 206.
- the present invention is directed to the problem of handover of a long-term evolution system across base stations, and can be applied to intra-base station handover and inter-technology handover after necessary modification.
- FIG. 1 is a flowchart of execution of a method for cross-base station hard handover in LTE according to the present invention.
- the entire handover process is divided into three main processing processes, namely, a handover preparation phase, a handover execution phase, and a handover failure processing phase. The stage is described.
- Phase 1 The handover preparation phase, including steps 100 - 108;
- Step 100 The source base station initially determines the user equipment to be switched according to the channel quality and the load condition, and sends a measurement request to the user equipment in order to reduce unnecessary handover.
- Step 101 After receiving the measurement request, the user equipment performs measurement in the measurement gap, and forms a measurement report and sends the measurement result to the source base station.
- Step 102 The source base station decides whether to perform handover according to the measurement report.
- Step 103 If the source base station decides to perform handover, send a handover request to the target base station.
- Step 104 The target base station performs an admission detection and a handover decision on the user equipment to be handed over.
- Step 105 When the target base station allows the user equipment to switch, the handover request feedback is sent to the source base station, and the handover request feedback carries related information of the access target base station.
- Step 106 After receiving the handover request feedback of the target base station, the source base station sends a handover command to the user equipment, where the handover command carries related information of the access target base station.
- Step 107 After receiving the handover command, the user equipment performs handover decision according to the handover command and the related information of the access target base station and the capability information of the user equipment, to avoid invalid handover. If the user equipment supports the handover, go to step 108; otherwise, if the user equipment does not support the handover, go to steps 123 ⁇ 124.
- Step 108 If the user equipment supports the handover, send a handover command acknowledgement message to the source base station. After receiving the handover command sent by the source base station, the user equipment performs the handover decision if the handover is supported, and does not need to immediately send the handover command confirmation to the source base station, thereby reducing the delay in the handover process as much as possible.
- the step of performing handover by the user equipment is: disconnecting communication with the source base station, backing up communication information with the source base station, logical channel identifier of the logical channel of the backup communication packet, logical channel encryption parameter, time-frequency resource of the physical channel, and modulation Coding strategy, etc.
- the uplink data is buffered, and then synchronized to the target base station by the non-contention random access method, and the media access layer entity, the radio access layer entity, and the packet data convergence entity are not reset until the target base station is successfully synchronized.
- Phase 2 Switching the execution phase, including steps 109-121;
- Step 109 Determine the frequency and bandwidth of the target cell when the user equipment performs handover, perform MAC (Media Access Control) restart and RLC (Radio Link Control) re-establishment, disconnect communication with the source base station, and back up with the source base station.
- the necessary information for communication, the backup communication information includes logical channel identifiers, logical channel encryption parameters, time-frequency resources of physical channels, and modulation and coding strategies.
- Step 110 After sending the handover command, the source base station buffers downlink data from the serving gateway, and starts a context sending timer.
- the time period of the context sending timer is set to the user equipment processing delay time of the round trip delay time (RTT, Round-Trip delay Time) + 4 ms between the source base station and the target base station.
- RTT Round-Trip delay Time
- the purpose of setting the context sending timer is to maximize the uplink data reception and maximize the downlink data reception, so that after the handover to the destination base station, the data that needs to be retransmitted is minimized, and the air interface load is reduced: before the user equipment receives the handover command.
- the uplink data and the downlink data feedback can still be sent to the source base station. Therefore, the source base station can still receive useful uplink data and downlink data feedback after issuing the handover command, and the receiving time is controlled by the context sending timer, or It is controlled at the time when the switching command of the user equipment is received.
- Step 111 The user equipment performs handover, including initiating random access. If the target base station cannot be successfully accessed, go to steps 122-124.
- Step 112 When the forwarding time point expires, that is, when the context sending timer on the source base station expires, or when receiving the handover command acknowledgement message sent by the user equipment, the communication context and the uplink and downlink cache data between the source base station and the user equipment are received. Transmitted to the target base station, the communication context includes an uplink data state and a downlink data state.
- Step 113 After the user equipment successfully accesses the target base station, send a handover confirmation message to the target base station by using the allocated uplink.
- Steps 114 to 115 After receiving the handover confirmation message, the target base station sends a path change request to the mobility management entity/service gateway, and simultaneously sends a handover confirmation message to the source base station.
- Steps 116 to 118 The mobility management entity/service gateway changes the path after receiving the request, and simultaneously sends a data end flag to the source base station, and after the path is changed, sends a path change request acknowledgement to the target base station.
- Step 119 After receiving the data end flag of the mobility management entity/service gateway, the source base station refreshes the buffer, and sends the buffered downlink data together with the end flag to the target base station.
- Step 120 After receiving the path change request acknowledgement of the mobility management entity/serving gateway, the target base station sends a resource release command to the source base station.
- Step 121 After receiving the command, the source base station disconnects from the user equipment and releases related resources.
- Stage 3 handover failure processing stage, including steps 122-124;
- Step 122 The user equipment quickly resumes communication with the source base station according to the backed up information.
- Step 123 The user equipment sends a handover failure message to the source base station.
- Step 124 After receiving the handover failure message, the source base station sends a handover cancellation message to the target base station and the mobility management entity/service gateway to cancel the handover.
- the user equipment After receiving the handover command of the source base station, the user equipment starts a handover timer when the user equipment decides to perform handover in step 107, and if the timer expires, the handover failure processing is performed, and the process proceeds to 122 ⁇ If the user terminal successfully accesses the target base station before the timer expires, the timer is terminated; the timing duration of the handover timer is set according to the limitation of the handover delay, and can be set to 50 ms under the LTE system.
- the source base station After the source base station sends a handover command message to the user equipment, it will wait for the handover confirmation of the receiving user equipment. If the handover command acknowledgement message is lost, the source base station does not receive the confirmation message of the handover command; if the handover command message is sent by the source base station If the user equipment does not receive the handover command, the handover command confirmation message will not be sent to the source base station, and the source base station will not receive the handover command acknowledgement message.
- the source base station If it is not confirmed that the handover command message is lost or the handover command acknowledgement message is lost, if the source base station does not receive the handover failure message, the source base station considers that the handover has not failed, and resends the handover command to the user equipment according to a certain time interval to ensure The user equipment can receive the handover command in time.
- the source base station continues to retransmit the handover command to the user equipment because it does not receive the handover command acknowledgement message fed back by the user terminal, and the condition for ending the retransmission may be: the source base station receives the handover confirmation message of the target base station; or the source base station receives A handover command acknowledgement message fed back to the user terminal; or the handover timer expires.
- the user equipment After the source base station sends a handover command to the user equipment, the user equipment sends a handover command acknowledgement message to the source base station. If the source base station does not receive the feedback, the source base station considers that the user equipment does not The handover command is received, so the handover command is retransmitted to the user equipment. Since the user equipment may disconnect the communication at this time, the handover command of the retransmission may not be received, and the source base station continuously resends the handover command. In order to deal with the situation, the present invention sends a handover confirmation message to the source base station after the target base station is successfully accessed by the user equipment, and the source base station stops the retransmission handover command after receiving the message.
- the next switching process repeats the first to third phases.
- FIG. 3 is the downlink data used in the avoidance of handover according to the present invention.
- the missing method flow chart, the steps are as follows:
- Step 301 For the downlink data, before the source base station sends the handover command to the user equipment, the downlink data of the source base station is directly sent to the user equipment through the wireless channel.
- Step 302 After transmitting the handover command, the source base station buffers the downlink data from the serving gateway, and sends the downlink communication context, that is, the transmission window and the sequence number of the unacknowledged data packet to the target base station.
- the target base station After the target base station establishes a wireless channel with the user equipment, the downlink data will be connected. There are two ways to connect.
- Step 303 A The first option:
- the target base station sends a request for polling the data packet reception status to the user equipment.
- the target base station must first establish a physical channel with the user equipment before starting polling.
- the user equipment After receiving the request for polling the data packet reception status, the user equipment generates a data packet reception status report and sends the report to the target base station.
- the target base station determines which data packets need to be retransmitted according to the acceptance status report reported by the user equipment.
- Step 303B The second option:
- the target base station obtains a communication context of the downlink data from the source base station; B2. Different from the first solution, in this solution, the target base station does not perform active rotation training, but initiates transmission at the breakpoint according to the communication context of the downlink data forwarded by the source base station.
- Step 304 The target base station receives data that needs to be retransmitted according to the reception.
- the user equipment reorders the downlink data before and after the handover and submits the data to the upper layer.
- the upper layer forms a reception status report and sends the report to the target base station.
- the target base station determines which data packets need to be retransmitted according to the reception status report, and the data that does not need to be retransmitted is needed. The packet is discarded, and the send window moves forward to send new data.
- the source base station sends the downlink data packet with the sequence number 0 to 10 to the user equipment before transmitting the handover command, and then sends the data packet of 11 to 20 after the handover, and then sends the downlink data packet after the 31th and the user equipment does not receive the data packet after the handover.
- the source base station does not receive feedback from the user equipment's 3, 4, and 6 data packets. After the handover is performed, the source base station will not receive the 3, 4, and 6 data packets from the user equipment.
- the last transmitted data packet sequence number 10 is sent to the target base station, and the destination base station sends a status report polling message to the user equipment after establishing the link with the user equipment, and sends the data packet status report after the user equipment receives the status report polling message.
- the report indicates that the user equipment received a data packet other than packets No. 3 and No. 4, according to which the target base station sends the data packets No. 3 and No. 4 to the user equipment, and discards the No. 6 packet, and sends 11 No.
- the target base station will probably receive the source base station and Serving gateway downlink data, then the priority processing of data from the source base station, in the embodiment, the priority number 0 ⁇ 30 packets.
- FIG. 4 is a flowchart of a method for avoiding uplink data loss during handover according to the present invention, and the steps are as follows:
- Step 401 When the user equipment maintains a communication connection with the source base station, the data is sent to the source base station.
- Step 404 After receiving the data packet reception status report sent by the target base station, the user equipment sends the data that needs to be retransmitted to the target base station, and discards the data that does not need to be retransmitted.
- the user equipment sends the data packet with the sequence number 1 to 10 to the source base station, and the source base station receives all the data packets except the 2nd and the 3rd, and sends the acknowledgement information to the user equipment, because the user equipment performs the handover, therefore, the user The device did not receive confirmation of packets number 6 and 8.
- the user equipment will discard the 1st, 4th, 5th, 7th, and 9th data packets, leaving the 2, 3, 6, and 8 data packets, and the target base station receives the communication context of the source base station, including the last successful reception.
- the serial number of the data packet and the serial number of the unsuccessfully received data packet it is considered that the data packets of No. 2 and No.
- the receiving status report is sent to the user equipment, and the user equipment transmits the data of No. 2 and No. 3 to the target base station. All data with a sequence number less than 10 has been confirmed, so the user equipment will discard packets 2, 3, 6, 8. The transmission window is moved forward to continue the transmission of the uplink data.
- FIG. 5 is a schematic structural diagram of a cross-base station handover system in a long term evolution system according to the present invention.
- the system is mainly composed of a user terminal, a source base station, and a target base station.
- the following describes the functions and connection relationships of each module:
- the user terminal side further includes a handover decision module, a handover response module, a handover execution module, and a handover confirmation initiation module;
- the handover decision module is configured to perform a handover decision after receiving the handover command sent by the source base station, and notify the handover response module and the handover execution module to perform a corresponding function if the user terminal supports the handover; optionally, the handover decision module is determined to be A handover timer is started when the handover is performed. If the timer expires, the handover failure processing step is performed; if the user terminal successfully accesses the target base station before the timer expires, the timer is terminated. a handover response module, configured to send a handover command acknowledgement message to the source base station when the user terminal supports the handover;
- a switching execution module configured to perform a handover operation, to enable the user equipment to synchronously access the target base station; optionally, after the handover decision module receives the handover command, the handover decision module, if the user terminal supports the handover, immediately notify the handover execution module The handover is performed without waiting for the handover response module to send a handover command acknowledgement message.
- the performing the handover specifically includes: disconnecting the communication with the source base station, backing up the communication context with the source base station, buffering the uplink data, and synchronizing to the target base station, and not resetting the medium access layer entity and the wireless before successfully synchronizing to the target base station. Access layer entity and packet data convergence entity.
- a handover confirmation initiation module configured to send a handover confirmation message to the target base station by using the allocated uplink after the handover execution module successfully accesses the target base station;
- the source base station side mainly includes a handover notification module and a data cache forwarding module
- a handover notification module configured to send a handover command to the user terminal if the source base station and the target base station decide to allow handover;
- the handover notification module starts a context sending timer after sending the handover command; when the data cache forwarding module receives the handover command acknowledgement message sent by the user equipment or the context sending timer expires Transmitting a communication context and uplink and downlink buffer data between the source base station and the user equipment to the target base station.
- the handover notification module resends the handover command in a certain period; when the handover notification module receives the handover response module feedback
- the handover command acknowledgement message, or the handover confirmation message sent by the handover confirmation forwarding module of the target base station stops resending the handover command.
- the target base station mainly includes a handover confirmation forwarding module and a data connection module.
- a handover confirmation forwarding module configured to forward the handover confirmation message to the handover notification module of the source base station after receiving the handover confirmation message sent by the handover confirmation initiation module of the user equipment;
- the data connection module is configured to perform uplink data and downlink data connection with the user equipment according to the communication context forwarded by the source base station and the uplink and downlink cache data.
- the handover execution module buffers uplink data before establishing a communication connection with the target base station, where the uplink data includes an uplink data packet sent to the source base station and an uplink data packet sent to the target base station; and the handover execution module is established with the target base station.
- the buffered uplink data is sent to the target base station; after the handover execution module receives the data packet reception status report sent by the data connection module, the uplink data that needs to be retransmitted is sent to the data connection module. , discard data that does not need to be retransmitted.
- the data connection module determines, according to the downlink communication context forwarded by the source base station, the data packet to be retransmitted; or the data connection module to the user
- the device sends a request for polling the data packet receiving status; after receiving the request for polling the data packet receiving status, the user equipment sends a data packet receiving status report to the data connection module, and the data connection module receives the data according to the user equipment.
- the status report determines which packets need to be retransmitted.
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Description
一种长期演进系统中跨基站切换方法及系统 技术领域
本发明涉及长期演进系统中的用户切换技术， 尤其涉及一种长期演进 系统中跨基站的硬切换方法和系统。 背景技术
长期演进计划 (LTE, Long Term Evolution)是 3GPP启动的新技术研发项 目， 可以被看成是 "准 4G"技术， 该项目改进并增强 3G的空中接入技术， 采用 OFDM(Orthogonal Frequency Division Multiplexing, 正交频分复用)和 MIMO(Multiple Input Multiple Output , 多输入多输出）作为其无线网络演进 的基础性技术，主要性能目标包括：在 20MHz频谱带宽提供下行 100Mbps、 上行 50Mbps的峰值速率； 改善小区边缘用户的性能； 提高小区容量； 降低 系统延迟； 支持 100km半径的小区覆盖； 能够为 350km/h高速移动用户提 供大于 100kbps的接入服务； 支持成对或非成对频谱， 并可灵活配置带宽。
3GPP 确定 LTE 的架构为扁平化的演进 UTRAN ( UMTS Terrestrial Radio Access Network, 陆地无线接入网）结构。 其用户面主要由演进节点 B ( evolved Node B , eNB )和服务网关 (Serving-Gateway, s-GW)两部分构 成。 eNB与 s-GW通过基站-网关接口 S1连接， eNB之间通过基站间接口 X2连接， 用户设备 ( User Equitmemt, UE )与 eNB通过无线空中接口 Uu 连接。
切换是蜂窝移动网络中的寻常事件， 它是由用户的移动特性决定的， 切换成功率是一个非常重要的网络指标， 处理不好会造成严重的掉话现象， 给移动用户带来不便。 LTE 的切换分为基站内的切换、 跨基站的切换和跨 技术的切换等， 跨基站切换是指切换前后的服务小区属于不同的基站。 一
般的， LTE 采用硬切换技术， 即用户设备首先断开与源基站的通信， 然后 再建立与目标基站的通信， 因此必须依靠某些机制来避免数据的丟失， 同 时使得切换流程尽量减少时延， 并方便切换失败处理。 发明内容
有鉴于此， 本发明的主要目的之一在于提供一种长期演进系统中跨基 站切换方法， 用于解决切换速度慢、 容易造成数据丟失、 切换失败处理困 难的技术问题。 为达到上述目的， 本发明的技术方案是这样实现的：
一种长期演进系统中跨基站的切换方法， 所述方法包括：
A、 用户设备接收到切换命令后， 向源基站反馈切换命令确认消息并緩 存上行数据；
B、 源基站在发送切换命令后緩存下行数据， 并在收到切换命令确认消 息后将源基站与用户设备之间的通信上下文和上下行緩存数据发送给目标 基站；
C、 用户设备成功接入目标基站后， 通过分配的上行链路向目标基站发 送切换证实消息； 目标基站向源基站转发所述切换证实消息；
D、 目标基站根据所述源基站转发的通信上下文和上下行緩存数据 与用户设备进行上行数据和下行数据的接续。
进一步地， 所述方法还包括： 步骤 B中， 源基站在发送切换命令后， 启动上下文发送定时器； 所述源基站在收到用户设备发送的切换命令确认 消息时或所述上下文发送定时器到期时将源基站与用户设备之间的通信上 下文和上下行緩存数据发送给目标基站。
进一步地， 步骤 A中， 用户设备在收到源基站发送的切换命令后， 经 切换判决， 若支持切换则立即执行切换， 不必立刻向源基站发送切换命令 确认； 所述执行切换具体包括： 断开与源基站的通信、 备份与源基站的通 信上下文、 緩存上行数据、 同步到目标基站， 在成功同步到目标基站之前，
不重置媒体接入层实体、 无线接入层实体和分组数据会聚实体。 进一步地， 所述方法进一步包括， 用户设备在判决执行切换时， 启动 一个切换计时器， 若该计时器超时， 则执行切换失败处理步骤； 若在该计 时器超前用户终端成功接入到目标基站， 则终止该定时器。
进一步地， 步骤 A中， 若源基站没有接收到用户设备发送的切换命令 确认消息， 则重发切换命令； 当源基站收到用户终端反馈的切换命令确认 消息， 或收到目标基站的切换证实消息， 则停止重发所述切换命令。
进一步地， 在用户设备接收到切换命令后， 与目标基站建立通信连接 前， 上行数据被緩存， 所述上行数据包括发往源基站的上行数据包和发往 目标基站的上行数据包； 在用户设备与目标基站建立通信连接后， 用户设 备将緩存的上行数据发往到目标基站； 在用户设备接收到目标基站发送的 数据包接收状态报告后， 将需要重传的数据发送给目标基站， 将不需要重 传的数据丟弃。
进一步地， 步骤 D中， 目标基站与用户设备之间进行下行数据接续时， 目标基站根据源基站转发的下行通信上下文决定需重传的数据包， 或通过 如下步骤来确定需要重传的数据包：
D1 : 目标基站向用户设备发送轮询数据包接收状态的请求；
D2: 用户设备接收到轮询数据包接收状态的请求后， 产生数据包接收 状态报告发送给目标基站，
D3: 目标基站根据用户设备上报的接受状态报告决定需重传的数据包。 技术上述方法， 本发明还提出一种长期演进系统中跨基站切换系统， 包括用户终端、 源基站、 目标基站， 具体地，
源基站还包括： 切换通知模块、 数据緩存转发模块；
切换通知模块， 用于在源基站和目标基站允许切换的情况下， 向用户 终端发送切换命令；
数据緩存转发模块， 用于在发送切换命令后緩存下行数据， 并在收到 切换命令确认消息后将源基站与用户设备之间的通信上下文和上下行緩存 数据发送给目标基站；
用户终端还包括： 切换判决模块、 切换响应模块、 切换执行模块、 切 换证实发起模块；
切换判决模块， 用于在接收到源基站发送的切换命令后执行切换判决； 切换响应模块， 用于在用户终端支持切换时向源基站发送切换命令确 认消息；
切换执行模块， 用于执行切换操作， 使用户设备同步接入到目标基站； 切换证实发起模块， 用于在用户设备成功接入目标基站后， 通过分配 的上行链路向目标基站发送切换证实消息；
目标基站还包括： 切换证实转发模块、 数据接续模块；
切换证实转发模块， 用于在接收到用户设备发送的切换证实消息后向 源基站转发切换证实消息；
数据接续模块， 用于根据源基站转发的通信上下文和上下行緩存数据 与用户设备进行上行数据和下行数据的接续。
进一步地， 所述切换通知模块在发送切换命令后， 启动上下文发送定 时器； 所述数据緩存转发模块在收到用户设备发送的切换命令确认消息时 或所述上下文发送定时器到期时将源基站与用户设备之间的通信上下文和 上下行緩存数据发送给目标基站。
进一步地， 所述切换判决模块接收到切换命令后， 经切换判决， 若用 户终端支持切换则立即通知切换执行模块执行切换， 不等待切换响应模块 发送切换命令确认消息； 所述执行切换具体包括： 断开与源基站的通信、 备份与源基站的通信上下文、 緩存上行数据、 同步到目标基站， 在成功同 步到目标基站之前， 不重置媒体接入层实体、 无线接入层实体和分组数据
会聚实体。
进一步地， 切换判决模块在判决结果为可切换时启动一个切换计时器， 若该计时器超时， 则执行切换失败处理步骤； 若在该计时器超前用户终端 成功接入到目标基站， 则终止该定时器。
进一步地， 若切换通知模块没有收到切换响应模块发送的切换命令确 认消息， 则切换通知模块重发切换命令； 当切换通知模块收到切换响应模 块反馈的切换命令确认消息， 或收到切换证实转发模块发送的切换证实消 息， 则停止重发所述切换命令。
进一步地， 所述切换执行模块在与目标基站建立通信连接前， 緩存上 行数据， 所述上行数据包括发往源基站的上行数据包和发往目标基站的上 行数据包； 在与目标基站建立通信连接后， 所述切换执行模块将緩存的上 行数据发往目标基站；
在所述切换执行模块接收到所述数据接续模块发送的数据包接收状态 报告后， 将需要重传的上行数据发送给所述数据接续模块， 将不需要重传 的数据丟弃。
进一步地， 所述数据接续模块与用户设备之间进行下行数据接续时， 所述数据接续模块根据源基站转发的下行通信上下文决定需重传的数据 包； 或所述数据接续模块向所述用户设备发送轮询数据包接收状态的请求； 用户设备接收到轮询数据包接收状态的请求后， 产生数据包接收状态报告 发送给所述数据接续模块， 所述数据接续模块根据用户设备上报的接受状 态报告决定需重传的数据包。
发明的特征为用户设备在切换成功前备份与源基站的通信上下文， 断 开与源基站的通信， 建立与目标基站的通信； 源基站在切换成功前保持与 用户设备的通信上下文， 源基站可以获取用户设备的上行信令和数据。 本 发明优点是使得用户的切换速度较快， 避免了数据丟失， 同时也方便了切
换失败的处理。 附图说明
图 1为本发明所述硬件切换方法的流程图；
图 2为本发明切换场景示意图；
图 3为本发明方案用户设备上行数据切换实施流程图；
图 4为本发明方案用户设备下行数据切换实施流程图；
图 5为本发明所述跨基站硬切换系统的组成结构图。 具体实施方式 为使本发明的目的、 技术方案和优点更加清楚明白， 以下举实施例并 参照附图， 对本发明进一步详细说明。
图 2为本发明切换场景图， 假设系统中有用户设备 207, 源基站 202, 目标基站 203 , 移动管理实体和服务网关 201 ,基站与服务网关间接口 204, 205 , 基站间接口 206。 本发明针对长期演进系统跨基站的切换问题， 经过 必要修改， 也可以运用于基站内切换和跨技术间切换。
图 1为本发明 LTE中跨基站硬切换的方法的执行流程图， 整个切换过 程分为 3 个主要处理过程， 分别是切换准备阶段、 切换执行阶段和切换失 败处理阶段， 以下分别对这几个阶段进行描述。
第 1阶段： 切换准备阶段， 包括步骤 100-步骤 108;
步骤 100: 源基站根据信道质量和负载情况， 初步确定需切换的用户设 备， 为了减少不必要的切换， 向用户设备发出测量请求。
步骤 101 : 用户设备收到测量请求后， 在测量间隙内进行测量， 将测量 结果形成测量报告并发送给源基站。
步骤 102: 源基站根据测量报告决策是否进行切换。
步骤 103: 若源基站决策进行切换， 则向目标基站发送切换请求。
步骤 104: 目标基站对待切换的用户设备进行准入检测和切换决策。 步骤 105:目标基站允许用户设备切换时，向源基站发送切换请求反馈， 切换请求反馈中携带接入目标基站的相关信息。
步骤 106: 源基站收到目标基站的切换请求反馈后， 向用户设备发送切 换命令， 切换命令中携带接入目标基站的相关信息。
步骤 107:用户设备在收到切换命令后根据切换命令及接入目标基站的 相关信息结合用户设备的能力信息进行切换判决， 以避免无效切换。 若用 户设备支持切换则执行步骤 108; 否则用户设备不支持该切换， 则转到步骤 123~124„
步骤 108:若用户设备支持该切换，则向源基站发送切换命令确认消息。 用户设备在收到源基站发送的切换命令后， 经切换判决， 若支持切换 则立即执行切换， 不必立刻向源基站发送切换命令确认， 从而尽可能地减 少切换过程中的时延。
用户设备执行切换的步骤为： 断开与源基站的通信， 备份与源基站的 通信信息， 备份的通信信息包逻辑信道的逻辑信道标识符、 逻辑信道加密 参数、 物理信道的时频资源和调制编码策略等。 同时緩存上行数据， 然后 通过非竟争的随机接入方法同步到目标基站， 在成功同步到目标基站之前， 不重置媒体接入层实体、 无线接入层实体和分组数据会聚实体。
第 2阶段： 切换执行阶段， 包括步骤 109-步骤 121 ;
步骤 109:用户设备执行切换时确定目标小区的频点和带宽，进行 MAC (媒体接入控制）重启和 RLC (无线链路控制） 重建立， 断开与源基站的 通信， 并备份与源基站通信的必要信息， 备份的通信信息包括逻辑信道标 志符、 逻辑信道加密参数、 物理信道的时频资源和调制编码策略等。
步骤 110: 源基站在发送切换命令后， 緩存来自服务网关的下行数据， 并启动上下文发送定时器。
上下文发送定时器的时间周期设置为源基站与目标基站之间的回程延 时时间 （RTT, Round-Trip delay Time ) +4ms的用户设备处理延迟时间。 设 置上下文发送定时器的目的在于最大化上行数据接收和最大化下行数据接 收， 使得在切换到目的基站后， 需要重传的数据达到最小化， 降低了空口 负荷： 由于用户设备收到切换命令之前仍然可以向源基站发送上行数据和 下行数据反馈， 因此源基站在发出切换命令之后仍然能够收到有用的上行 数据和下行数据反馈， 这段接收时间正是通过上下文发送定时器来控制， 或者通过收到用户设备的切换命令确认的时间点来控制。
步骤 111 : 用户设备执行切换， 包括发起随机接入， 如果不能成功接入 目标基站， 则转到步骤 122〜124。
步骤 112: 转发时间点到时， 即源基站上的上下文发送定时器到期， 或 收到用户设备发送的切换命令确认消息时， 将源基站与用户设备之间的通 信上下文和上下行緩存数据发送给目标基站， 通信上下文包括上行数据状 态和下行数据状态。
步骤 113: 用户设备成功接入目标基站后， 通过分配的上行链路向目标 基站发送切换证实消息。
步骤 114〜115： 目标基站收到切换证实消息后， 向移动管理实体 /服务 网关发送路径更改请求， 同时向源基站发送切换证实消息。
步骤 116 〜118： 移动管理实体 /服务网关收到请求后更改路径， 同时向 源基站发送数据结束标志， 更改路径后向目标基站发送路径更改请求确认。
步骤 119: 源基站收到移动管理实体 /服务网关的数据结束标志后将刷 新緩存， 并将緩存的下行数据和结束标志一起发送给目标基站。
步骤 120: 目标基站收到移动管理实体 /服务网关的路径更改请求确认 后， 向源基站发送资源释放命令。
步骤 121 : 源基站收到命令后断开与用户设备的通信并释放相关资源。
第 3阶段： 切换失败处理阶段， 包括步骤 122-步骤 124;
步骤 122: 用户设备根据备份的信息迅速恢复与源基站的通信。
步骤 123: 用户设备向源基站发送切换失败消息。
步骤 124: 源基站受到切换失败消息后， 向目标基站和移动管理实体 \ 服务网关发送切换取消消息， 取消切换。
基于上述切换流程， 本发明优选实施例中还做了如下改进，
( 1 )用户设备在收到源基站的切换命令后， 即在步骤 107中， 用户设 备决策执行切换时， 启动一个切换计时器， 若该计时器超时， 则按切换失 败处理， 转到 122〜124； 若在该计时器超前用户终端成功接入到目标基站， 则该定时器终止； 所述切换定时器的定时时长按照切换时延的规定设置， 在 LTE系统下可设为 50ms。
( 2 )源基站向用户设备发出切换命令消息后， 将等待接收用户设备的 切换确认， 如果切换命令确认消息丟失， 则源基站收不到切换命令的确认 消息； 如果源基站发出的切换命令消息丟失， 则由于用户设备没有收到切 换命令， 所以也不会向源基站发送切换命令确认消息， 源基站也会收不到 切换命令确认消息。 由于无法确认是切换命令消息丟失还是切换命令确认 消息丟失， 因此如果源基站没有收到切换失败消息， 则源基站认为切换没 有失败， 并且按照一定的时间间隔向用户设备重发切换命令， 以保证用户 设备能够及时接收到切换命令。
( 3 )源基站由于没有收到用户终端反馈的切换命令确认消息而持续重 发切换命令给用户设备， 结束重发的条件可以是： 源基站收到目标基站的 切换证实消息； 或源基站收到用户终端反馈的切换命令确认消息； 或切换 定时器超时。
当源基站向用户设备发送切换命令后， 用户设备将向源基站发送切换 命令确认消息， 如果源基站没有收到该反馈， 则源基站认为用户设备没有
收到切换命令， 因此向用户设备重传切换命令， 由于用户设备此时可能断 开通信， 因此可能无法接收到重传的切换命令， 源基站于是不停的重发切 换命令。 本发明为了处理这种情况， 在目标基站被用户设备成功接入后， 向源基站发送切换证实消息， 源基站收到该消息后停止重发切换命令。
下一个切换过程重复第 1阶段到第 3阶段。
本发明为避免切换时数据的丟失， 分别对下行数据和上行数据的处理 流程进行了改进， 以下分别对上行数据和下行数据的处理方式进行描述： 图 3 为本发明采用的避免切换时下行数据丟失的方法流程图， 步骤如 下：
步骤 301 : 对于下行数据， 在源基站发送切换命令给用户设备前， 源基 站的下行数据直接通过无线信道发送给用户设备。
步骤 302:在发送切换命令后，源基站将緩存来自服务网关的下行数据， 并将下行通信上下文， 即发送窗口以及未得到确认的数据包的序号发往目 标基站。
目标基站在建立起与用户设备的无线信道后， 将进行下行数据的接续。 接续方法有两种。
步骤 303 A: 第一种方案：
Al、 目标基站向用户设备发送轮询数据包接收状态的请求。 目标基站 开始轮询前首先必须确立与用户设备间的物理信道。
A2、 用户设备接收到轮询数据包接收状态的请求后， 产生数据包接收 状态报告发送给目标基站，
A3、 目标基站根据用户设备上报的接受状态报告决定哪些数据包需要 重传。
步骤 303B: 第二种方案：
Bl、 目标基站从源基站获得下行数据的通信上下文；
B2、 与第一种方案不同的是， 该方案中， 目标基站不进行主动的轮训， 而是根据源基站转发的下行数据的通信上下文启动断点处的传输。
步骤 304: 目标基站根据接收需要重传的数据。
用户设备将切换前后的下行数据进行重排序后提交给上层， 由上层形 成接收状态报告发送给目标基站， 目标基站再根据接收状态报告决定哪些 数据包需要重传， 并将不需要重传的数据包丟弃， 同时发送窗口向前移动， 以进行新数据的发送。
例如， 源基站在发送切换命令前发送序号为 0到 10的下行数据包给用户 设备， 切换后发送 11到 20的数据包， 路径变更后又发送 31号以后的下行数 据包， 用户设备没有收到 3 , 4号数据包， 源基站没有收到用户设备的 3 , 4, 6号数据包的反馈， 执行切换后， 源基站将用户设备没有收到 3 , 4、 6号数 据包的情况和最后发送的数据包序号 10发送给目标基站， 目的基站在建立 起与用户设备的链接后向用户设备发状态报告轮询消息， 在用户设备收到 状态报告轮询消息后将数据包状态报告发送给目标基站， 该报告说明用户 设备收到了除 3 , 4号数据包之外的数据包， 据此， 目标基站发送 3 , 4号数 据包给用户设备， 并丟弃 6号包， 并发送 11号及以后的数据包给用户设备， 移动管理实体 \服务网关执行路径更改后， 目标基站将可能同时收到来自源 基站和来自服务网关的下行数据， 此时优先处理来自源基站的数据， 在上 例中， 优先处理 0〜30号数据包。
图 4为本发明采用的避免切换时上行数据丟失的方法流程图， 步骤如 下：
步骤 401 :在用户设备与源基站还保持通信连接时，数据被发往源基站。 步骤 402: 源基站在发出切换命令后继续能够接收用户设备的上行数 据，收到的上行数据直接经过基站 -网关接口递交给移动性管理实体 /服务网 关。
步骤 403 :在用户设备接收到切换命令后，与目标基站建立通信连接前， 上行数据被緩存， 同样， 没有得到确认的上行数据也被緩存， 所述上行数 据包括发往源基站的数据包和发往目标基站的数据包； 在用户设备与目标 基站建立通信连接后， 上行数据被发往目标基站。
步骤 404: 在用户设备接收到目标基站发送的数据包接收状态报告后， 将需要重传的数据发送给目标基站， 将不需要重传的数据丟弃。
比如： 用户设备发送了序号为 1到 10的数据包给源基站， 源基站收到 了除 2和 3号外的所有数据包， 并向用户设备发送确认信息， 由于用户设 备进行了切换， 因此， 用户设备没有收到 6号和 8号数据包的确认。 这时， 用户设备将丟弃 1 , 4, 5 , 7 , 9, 10数据包， 留下 2、 3、 6、 8号数据包， 目标基站收到源基站的通信上下文， 包括最后一个成功接收的数据包的序 号和未成功接收的数据包的序号， 认为 2号和 3号数据包需要重传， 于是 发送接收状态报告给用户设备， 用户设备将 2号和 3号数据传给目标基站， 序号小于 10的所有数据都已经得到确认， 因此用户设备将丟弃 2, 3 , 6, 8 号数据包。 并将发送窗口向前移动， 继续上行数据的发送。
图 5 为本发明提出的长期演进系统中跨基站切换系统的实现结构图， 该系统主要由用户终端、 源基站、 目标基站组成。 以下对各模块的功能及 连接关系进行描述：
用户终端侧进一步包括切换判决模块、 切换响应模块、 切换执行模块 和切换证实发起模块；
切换判决模块， 用于在接收到源基站发送的切换命令后执行切换判决， 若用户终端支持切换则通知切换响应模块和切换执行模块执行相应功能； 可选地， 切换判决模块在判决结果为可切换时启动一个切换计时器， 若该计时器超时， 则执行切换失败处理步骤； 若在该计时器超前用户终端 成功接入到目标基站， 则终止该定时器。
切换响应模块， 用于在用户终端支持切换时向源基站发送切换命令确 认消息；
切换执行模块， 用于执行切换操作， 使用户设备同步接入到目标基站； 可选地， 所述切换判决模块接收到切换命令后， 经切换判决， 若用户 终端支持切换则立即通知切换执行模块执行切换， 不必等待切换响应模块 发送切换命令确认消息。 所述执行切换具体包括： 断开与源基站的通信、 备份与源基站的通信上下文、 緩存上行数据、 同步到目标基站， 在成功同 步到目标基站之前， 不重置媒体接入层实体、 无线接入层实体和分组数据 会聚实体。
切换证实发起模块， 用于在切换执行模块成功接入目标基站后， 通过 分配的上行链路向目标基站发送切换证实消息；
源基站侧主要包括切换通知模块和数据緩存转发模块；
切换通知模块， 用于在源基站和目标基站决策允许切换的情况下， 向 用户终端发送切换命令；
可选地， 所述切换通知模块在发送切换命令后， 启动一个上下文发送 定时器； 所述数据緩存转发模块在收到用户设备发送的切换命令确认消息 时或所述上下文发送定时器到期时将源基站与用户设备之间的通信上下文 和上下行緩存数据发送给目标基站。
可选地， 若切换通知模块在发送完切换命令后， 没有收到切换响应模 块发送的切换命令确认消息， 则切换通知模块以一定周期重发切换命令； 当切换通知模块收到切换响应模块反馈的切换命令确认消息， 或收到目标 基站的切换证实转发模块发送的切换证实消息， 则停止重发所述切换命令。
数据緩存转发模块， 用于在发送切换命令后緩存下行数据， 并在收到 用户终端反馈的切换命令确认消息后将源基站与用户设备之间的通信上下 文和上下行緩存数据发送给目标基站；
目标基站主要包括切换证实转发模块、 数据接续模块。
切换证实转发模块， 用于在接收到用户设备的切换证实发起模块发送 的切换证实消息后向源基站的切换通知模块转发切换证实消息；
数据接续模块， 用于根据源基站转发的通信上下文和上下行緩存数据 与用户设备进行上行数据和下行数据的接续。
进一步地， 切换执行模块在与目标基站建立通信连接前， 緩存上行数 据， 所述上行数据包括发往源基站的上行数据包和发往目标基站的上行数 据包； 切换执行模块在与目标基站建立通信连接后， 将緩存的上行数据发 往目标基站； 在所述切换执行模块接收到所述数据接续模块发送的数据包 接收状态报告后， 将需要重传的上行数据发送给所述数据接续模块， 将不 需要重传的数据丟弃。
进一步地， 所述数据接续模块与用户设备之间进行下行数据接续时， 所述数据接续模块根据源基站转发的下行通信上下文决定需重传的数据 包； 或所述数据接续模块向所述用户设备发送轮询数据包接收状态的请求； 用户设备接收到轮询数据包接收状态的请求后， 产生数据包接收状态报告 发送给所述数据接续模块， 所述数据接续模块根据用户设备上报的接受状 态报告决定需重传的数据包。
以上所述， 仅为本发明的较佳实施例而已， 并非用于限定本发明的保 护范围。
Claims
1、 一种长期演进系统中跨基站切换方法， 其特征在于：
A、 用户设备接收到切换命令后， 向源基站反馈切换命令确认消息并緩 存上行数据；
B、 源基站在发送切换命令后緩存下行数据， 并在收到切换命令确认消 息后将源基站与用户设备之间的通信上下文和上下行緩存数据发送给目标 基站；
C、 用户设备成功接入目标基站后， 通过分配的上行链路向目标基站发 送切换证实消息； 目标基站向源基站转发所述切换证实消息；
D、 目标基站根据所述源基站转发的通信上下文和上下行緩存数据 与用户设备进行上行数据和下行数据的接续。
2、 根据权利要求 1所述的方法， 其特征在于， 该方法还包括： 步骤 B中， 源基站在发送切换命令后， 启动上下文发送定时器； 所述 源基站在收到用户设备发送的切换命令确认消息时或所述上下文发送定时 器到期时将源基站与用户设备之间的通信上下文和上下行緩存数据发送给 标基站。
3、 根据权利要求 1所述的方法， 其特征在于， 步骤 A中， 用户设备在 收到源基站发送的切换命令后， 经切换判决， 若支持切换则立即执行切换， 不必立刻向源基站发送切换命令确认； 所述执行切换具体包括： 断开与源 基站的通信、 备份与源基站的通信上下文、 緩存上行数据、 同步到目标基 站， 在成功同步到目标基站之前， 不重置媒体接入层实体、 无线接入层实 体和分组数据会聚实体。
4、 根据权利要求 3所述的方法， 其特征在于， 用户设备在判决执行切 换时， 启动一个切换计时器， 若该计时器超时， 则执行切换失败处理步骤；
若在该计时器超前用户终端成功接入到目标基站， 则终止该定时器。
5、 根据权利要求 1所述的方法， 其特征在于， 步驟 A中, 若源基站没 有接收到用户设备发送的切换命令确认消息， 则重发切换命令； 当源基站 收到用户终端反馈的切换命令确认消息， 或收到目标基站的切换证实消息， 则停止重发所述切换命令。
6、 根据权利要求 1所述的方法， 其特征在于， 在用户设备接收到切换 命令后， 与目标基站建立通信连接前， 上行数据被緩存， 所述上行数据包 括发往源基站的上行数据包和发往目标基站的上行数据包； 在用户设备与 目标基站建立通信连接后， 用户设备将緩存的上行数据发往到目标基站； 在用户设备接收到目标基站发送的数据包接收状态报告后， 将需要重 传的数据发送给目标基站， 将不需要重传的数据丟弃。
7、 根据权利要求 1所述的方法， 其特征在于， 步骤 D中， 目标基站与 用户设备之间进行下行数据接续时， 目标基站根据源基站转发 下行通信 上下文决定需重传的数据包， 或通过如下步骤来确定需要重传的数据包：
D1: 目标基站向用户设备发送轮询数据包接收状态的请求；
D2: 用户设备接收到轮询数据包接收状态的请求后， 产生数据包接收 状态报告发送给目标基站，
D3: 目标基站根据用户设备上报的接受状态报告决定需重传的数据包。
8、 一种长期演进系统中跨基站切换系统， 包括用户终端、 源基站、 目 标基站， 其特征在于，
源基站还包括：
切换通知模块， 用于在源基站和目标基站允许切换的情况下， 向用户 终端发送切换命令；
数据緩存转发模块， 用于在发送切换命令后緩存下行数据， 并在收到 切换命令确认消息后将源基站与用户设备之间的通信上下文和上下行緩存
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数据发送给目标基站；
用户终端还包括：
切换判决模块， 用于在接收到源基站发送的切换命令后执行切换判决； 切换响应模块， 用于在用户终端支持切换时向源基站发送切换命令确 认消息；
. 切换执行模块， 用于执行切换操作， 使用户设备同步接入到目标基站； 切换证实发起模块， 用于在用户设备成功接入目标基站后， 通过分配 的上行链路向目标基站发送切换证实消息；
目标基站还包括：
切换证实转发模块， 用于在接收到用户设备发送的切换证实消息后向 源基站转发切换证实消息；
数据接续模块， 用于根据源基站转发的通信上下文和上下行緩存数据 与用户设备进行上行数据和下行数据的接续。
9、 根据权利要求 8所述的系统， 其特征在于， 所述切换通知模块在发 送切换命令后， 启动上下文发送定时器； 所述数据緩存转发模块在收到用 户设备发送的切换命令确认消息时或所述上下文发送定时器到期时将源基 站与用户设备之间的通信上下文和上下行緩存数据发送给目标基站。
10、 根据权利要求 8所述的系统， 其特征在于， 所述切换判决模块接 收到切换命令后， 经切换判决， 若用户终端支持切换则立即通知切换执行 模块执行切换， 不等待切换响应模块发送切换命令确认消息； 所述执行切 换具体包括： 断开与源基站的通信、 备份与源基站的通信上下文、 緩存上 4亍数据、 同步到目标基站， 在成功同步到目标基站之前， 不重置媒体接入 层实体、 无线接入层实体和分组数据会聚实体。
11、 根据权利要求 8 所述的系统， 其特征在于， 切换判决模块在判决 结果为可切换时启动一个切换计时器， 若该计时器超时， 则执行切换失败
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更正页 （细则第 91条)
处理步骤； 若在该计时器超前用户终端成功接入到目标基站， 则终止该定 时器。
12、 根据权利要求 8所述的系统， 其特征在于， ^切换通知模块没有 收到切换响应模块发送的切换命令确认消息， 则切换通知模块重发切换命 令； 当切换通知模块收到切换响应模块反馈的切换命令确认消息， 或收到 切换证实转发模块发送的切换证实消息， 则停止重发所述切换命令。
.
13、 根据权利要求 8所述的系统， 其特征在于， 所述切换执行模块在 与目标基站建立通信连接前， 緩存上行数据， 所述上行数据包括发往源基 站的上行数据包和发往目标基站的上行数据包； 在与目标基站建立通信连 接后， 所述切换执行模块将緩存的上行数据发往目标基站；
在所述切换执行模块接收到所述数据接续模块发送的数据包接收状态 报告后， 将需要重传的上行数据发送给所述数据接续模块， 将不需要重传 的数据丢弃。
14、 根据权利要求 8所述的系统， 其特征在于， 所述数据接续模块与 用户设备之间进行下行数据接续时， 所述数据接续模块根据源基站转发的 下行通信上下文决定需重传的数据包； 或所述数据接续模块向所述用户设 备发送轮询数据包接收状态的请求； 用户设备接收到轮询数据包接收状态 的请求后， 产生数据包接收状态报告发送给所述数据接续模块， 所述数据 接续模块根据用户设备上报的接受状态报告决定需重传的数据包。
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更正页 （细则第 91条)
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