CN100551157C - A kind of base station switch method - Google Patents

Abstract

The invention discloses a base station handover method, comprising: setting the first-level buffer of the automatic retransmission request at the medium access control layer of the base station, setting the second-level buffer of the automatic retransmission request at the packet data convergence protocol layer of the access gateway, and setting the second-level buffer of the automatic retransmission request at the base station The measurement module sets the handover preparation threshold and the handover decision threshold; when the source base station judges that the measurement report of the user equipment reaches the handover preparation threshold, it keeps the two-level cache synchronization; when the measurement report reaches the handover decision threshold, the packet data in the second level cache The aggregation protocol layer protocol data unit is sent to the target base station, and the last data packet carries the transmission completion flag; the target base station receives the packet data aggregation protocol layer protocol data unit to the first-level cache, and processes it into a media access control layer protocol data unit; After receiving and corresponding processing, the target base station requests the access gateway to perform a base station handover operation. The invention can reduce the processing load of the source base station and realize the lossless switching of the base station.

Description

A kind of base station switching method

technical field

The present invention relates to a base station switching method, in particular to a base station switching method completed by processing ARQ (automatic repeat request, automatic repeat request) in a third-generation mobile communication long-term evolution system.

Background technique

In the long-term evolution system of the third-generation mobile communication, the mechanism of combining the upper-layer ARQ entity and the lower-layer HARQ (Hybrid Automatic Repeat Request, Hybrid Automatic Repeat Request) entity is used on the user plane to achieve reliable transmission. When the ARQ entity is located at the base station, in the case of base station handover, currently known mobility management solutions include base station forwarding and multicasting.

The working principle of the base station forwarding mode is: when the source base station judges that the UE (User Equipment, user equipment) measurement report reaches the handover decision threshold, all PDUs (Protocol Data Unit, protocol data unit) in the user equipment context and ARQ cache are used respectively The corresponding message is forwarded to the target base station; after the target base station completes receiving and corresponding processing, it requests the access gateway to perform the base station handover operation. The working principle of the multicast mode is: the access gateway always multicasts user data to all cells in the UE fast handover set, or only multicasts user data to all candidate cells during the handover based on the request of the UE, so there is no need to source data from the source before handover The base station forwards all PDUs in the ARQ buffer to the target base station.

However, the disadvantage of the base station forwarding solution is that a long time delay will be generated in the process of forwarding all the PDUs in the ARQ buffer, and the processing load of the source base station will be increased. The disadvantage of the multicast method is that the mechanism for judging which data has been sent to the UE after handover is complicated, and additional target cell resources are occupied during the multicast process, which greatly reduces the system capacity.

Contents of the invention

The technical problem solved by the present invention is to provide a base station handover method, so as to realize the lossless handover of the base station by only forwarding the user equipment context from the source base station to the target base station before the base station handover, reducing the processing load of the source base station.

In order to solve the above technical problems, the present invention provides a base station handover method. When the user equipment measurement report reaches the handover threshold of the source base station, the protocol data unit in the user equipment context and automatic repeat request buffer is forwarded to the target base station. When the target base station After the base station completes the processing, the access gateway performs base station switching. The method includes the following steps:

Step 1, setting the first-level cache of the automatic repeat request in the media access control layer of the source base station, and setting the second-level cache of the automatic repeat request at the data aggregation protocol layer of the access gateway;

Step 2, setting a handover preparation threshold and a handover decision threshold in the source base station;

Step 3: When the source base station determines that the handover preparation threshold has been reached according to the measurement report of the user equipment, it sends a handover preparation notification message to the access gateway, so that the automatic retransmission request level-1 buffer in the source base station is consistent with the The automatic retransmission request in the access gateway is synchronized with the secondary cache. After the synchronization is successful, the source base station sends a synchronization success notification message to the access gateway, and the source base station sends a periodic status report to the access gateway. The two-level automatic retransmission request cache maintains a synchronized state;

Step 4. When the source base station determines that the handover decision threshold is reached according to the user equipment measurement report, send a handover decision notification message to the access gateway; send a user equipment context message to the target base station;

Step 5: After receiving the handover decision notification message, the access gateway establishes a user plane connection with the target base station;

Step 6: After receiving the user equipment context message, the target base station performs resource allocation and resource reservation processing, and returns the user equipment context confirmation message to the source base station after successful execution, and sends the message to the access gateway Data preparation notification message;

Step 7. After receiving the user equipment context confirmation message, the source base station sends a handover command to the user equipment;

Step 8: After receiving the handover command, the user equipment establishes a connection process with the target base station, and after the connection process is successfully established, sends a handover confirmation message to the target base station;

Step 9. The access gateway receives the data preparation notification message, sends the packet data convergence protocol layer protocol data unit in the automatic retransmission request secondary cache to the target base station, and notifies the target base station of the completion message;

Step 10, the target base station receives the packet data convergence protocol layer protocol data unit to the automatic repeat request first-level cache, and performs processing to generate the media access control layer protocol data unit;

Step 11. The target base station receives the handover confirmation message of the user equipment, and after receiving the automatic retransmission request from the access gateway to complete the second-level cached packet data convergence protocol layer protocol data unit, sends a message to the access gateway Send a path switching request message;

Step 12: The access gateway performs a path switching operation after receiving the path switching request message.

In Step 3 of the method, the step of synchronizing the first-level cache of the automatic repeat request in the source base station with the second-level cache of the automatic repeat request in the access gateway may include the following steps:

After the access gateway receives the handover preparation notification message, it stores the packet data convergence protocol layer protocol data unit in the automatic retransmission request secondary cache, and sends the stored packet data convergence protocol layer protocol data unit content, number and information to the source The content and number of the packet data convergence protocol layer protocol data unit of the base station are consistent;

The automatic retransmission request level-1 buffer in the source base station starts from receiving the first marked packet data convergence protocol layer protocol data unit of the access gateway to the completion of sending all media access control layer protocols in the original buffer When the data unit is used, a packet data convergence protocol layer service data unit of each media access control layer protocol data unit is generated, and there is corresponding packet data convergence protocol layer protocol data in the second-level cache of the automatic retransmission request of the access gateway unit.

With the present invention, it is only necessary to forward the context of the user equipment from the source base station to the target base station before the base station is handed over, which reduces the processing load of the source base station and realizes lossless handover.

Description of drawings

FIG. 1 is a schematic block diagram of an ARQ structure according to an embodiment of the present invention;

Fig. 2 is a schematic flow diagram of the base station switching in the embodiment of the present invention.

Detailed ways

In the embodiment of the present invention, firstly, the MAC (Medium Access Control) in the base station places the ARQ entity and the ARQ primary cache, and the PDCP (Packet Data Convergence Protocol, packet data convergence protocol) in the access gateway layer) to set the ARQ secondary cache. The content of the ARQ secondary cache is the IP packet after header compression, i.e. the PDCP PDU. The content in the ARQ primary cache is the MAC PDU, and the MAC PDU has two data composition methods: 1), The original PDCP service data unit SDU appends or does not append MAC header information. In this case, the MAC PDU and PDCP PDU have a 1-to-1 relationship; 2), the PDCP SDU is concatenated/segmented according to a fixed length, and then the MAC header is appended or not appended In this case, the relationship between MAC PDU and PDCP PDU is 1-to-many, many-to-1 or many-to-many. The capacity of the ARQ L2 cache is equal to or slightly larger than the ARQ L1 cache, so as to ensure that it can contain all original user data information in the ARQ L1 cache.

Fig. 1 is the schematic block diagram of ARQ structure in the embodiment, as shown in the figure, its structure mainly is the structure of two-stage upper-layer ARQ cache plus bottom layer HARQ cache, wherein:

The access gateway 101 includes a PDCP layer 1011 and an ARQ level 2 cache therein.

The source base station 102 includes a MAC layer 1021 and an ARQ level 1 cache, a HARQ cache, an ARQ entity, and a HARQ entity therein. Part of the statically allocated or dynamically allocated storage space in the ARQ L1 cache and the HARQ cache is their own retransmission buffer 10211, which stores PDUs or PDU pointers that need to be retransmitted, and their contents may be empty.

The target base station 103 also includes the MAC layer 1031 and the ARQ level 1 cache, HARQ cache, ARQ entity, and HARQ entity therein. The ARQ L1 cache and the HARQ cache also have part of the statically allocated or dynamically allocated storage space as their respective retransmission buffers 10311, which store PDUs or PDU pointers that need to be retransmitted, and their contents may be empty.

The ARQ level 1 cache is used for retransmission processing under normal conditions, that is, non-handover. In this case, the participation of the ARQ level 2 cache is not required. The ARQ level 2 cache is only used to cache the PDCP PDU sent from the access gateway to the source base station before the base station handover.

After the first-level cache and the second-level cache are set, the handover preparation threshold and the handover decision threshold are set in the measurement module of the source base station.

FIG. 2 is a schematic diagram of the flow of base station handover in the embodiment. As shown in the figure, after setting the first-level and second-level caches, as well as the handover preparation threshold and the handover decision threshold, the implementation process of the base station handover is as follows:

Step 201, the UE sends a measurement report to the source base station.

Step 202, the source base station judges that the handover preparation threshold is reached according to the measurement report.

Step 203, the source base station sends a handover preparation notification message to the access gateway.

Step 204, the access gateway starts to buffer the PDCP PDU in the ARQ secondary buffer.

Step 205, the source base station sends an ARQ two-level cache synchronization success message to the access gateway.

In step 206, the source base station sends a periodic status report to the access gateway, and the two-stage ARQ maintains a synchronization state.

Among them, the synchronization process of the two-level buffer is: when the source base station judges that the handover preparation threshold in the measurement report of the UE has reached, it sends a handover preparation notification message to the access gateway; Cache the PDCP PDU, the content and number of the cached PDCP PDU are consistent with the content and number of the PDCP PDU sent to the source base station; the ARQ level-1 cache starts from receiving the first marked PDCP PDU to sending all the original cache When MAC PDU is generated, the generated PDCP SDU (Service Data Unit) of each MAC PDU will have a corresponding PDCP PDU in the ARQ L2 cache. This state is also called ARQ L2 cache synchronization. Synchronization Afterwards, the source base station sends a synchronization success notification message to the access gateway; when the MAC PDU in the ARQ first-level cache is successfully deleted from the cache, it sends a periodic status report message to the access gateway, so that the ARQ first-level cache deletes the relevant PDCP PDU ;

Step 207, the UE sends a measurement report to the source base station.

Step 208, the source base station judges that the handover decision threshold is reached, and executes the handover decision.

Step 209, the source base station sends a handover decision notification message to the access gateway.

Step 210, the source base station sends the user equipment context to the target base station.

Wherein, the user equipment context includes: UE identity, UE address, UE capability, cell information, source base station information, target base station information, QoS information, radio bearer information, etc.;

Step 211, the access gateway establishes a user plane connection with the target base station.

Step 212, the target base station performs resource allocation and resource reservation processing.

Step 213, the target base station sends a user equipment context confirmation message to the source base station.

Step 214, the target base station sends a data preparation notification to the access gateway.

Step 215, the source base station sends a handover command to the UE.

Step 216, the access gateway sends the PDCP PDU in the ARQ secondary cache to the target base station.

Step 217, the UE is synchronized with the cell of the target base station, and the RB (Radio Bearer, radio bearer) is reconfigured.

Step 218, the UE sends a handover confirmation message to the target base station.

At this time, after the connection is established successfully, after the UE sends a handover confirmation message to the target base station, the access gateway receives the data preparation notification message, sends the PDCP PDU in the ARQ secondary buffer to the target base station, and carries the PDCP PDU in the last data packet. The sending completion flag, or notify the target base station with a separate message after the sending is completed; the target base station receives the PDCP PDU to the ARQ level 1 cache and performs corresponding processing, and then generates a MAC PDU; the target base station receives the UE handover confirmation message, and receives After the access gateway ARQ secondary cache PDCP PDU is completed, the next step is to send a path switching request message to the access gateway.

Step 219, the target base station sends a path switching request message to the access gateway.

Step 220, the access gateway performs a path switching operation, and modifies the target address to the original target base station.

Step 221, the access gateway performs a user plane resource release process with the source base station.

The present invention provides a new mobility management solution during base station handover, so that only the user equipment context needs to be forwarded from the source base station to the target base station before the handover, thereby reducing the processing load of the source base station and realizing the lossless switching.

Claims (10)

1. A base station handover method. When the user equipment measurement report reaches the handover threshold of the source base station, the protocol data unit in the user equipment context and the automatic repeat request buffer is forwarded to the target base station. After the target base station completes the processing, the access gateway Execute base station handover, it is characterized in that, comprises the following steps: Step 1, setting the first-level cache of the automatic repeat request in the media access control layer of the source base station and the target base station, and setting the second-level cache of the automatic repeat request at the data aggregation protocol layer of the access gateway; Step 2, setting a handover preparation threshold and a handover decision threshold in the source base station; Step 3: When the source base station determines that the handover preparation threshold has been reached according to the measurement report of the user equipment, it sends a handover preparation notification message to the access gateway, so that the automatic retransmission request level-1 buffer in the source base station is consistent with the The automatic retransmission request in the access gateway is synchronized with the secondary cache. After the synchronization is successful, the source base station sends a synchronization success notification message to the access gateway, and the source base station sends a periodic status report to the access gateway. The two-level automatic retransmission request cache maintains a synchronized state; Step 4. When the source base station determines that the handover decision threshold is reached according to the user equipment measurement report, send a handover decision notification message to the access gateway; send a user equipment context message to the target base station; Step 5: After receiving the handover decision notification message, the access gateway establishes a user plane connection with the target base station; Step 6: After receiving the user equipment context message, the target base station performs resource allocation and resource reservation processing, and returns the user equipment context confirmation message to the source base station after successful execution, and sends the message to the access gateway Data preparation notification message; Step 7. After receiving the user equipment context confirmation message, the source base station sends a handover command to the user equipment; Step 8: After receiving the handover command, the user equipment establishes a connection process with the target base station, and after the connection process is successfully established, sends a handover confirmation message to the target base station; Step 9. The access gateway receives the data preparation notification message, sends the packet data convergence protocol layer protocol data unit in the automatic retransmission request secondary cache to the target base station, and notifies the target base station of the completion message; Step 10, the target base station receives the first-level cache of the automatic retransmission request from the packet data convergence protocol layer protocol data unit to the target base station, and processes it to generate the media access control layer protocol data unit; Step 11. The target base station receives the handover confirmation message of the user equipment, and after receiving the automatic retransmission request from the access gateway to complete the second-level cached packet data convergence protocol layer protocol data unit, sends a message to the access gateway Send a path switching request message; Step 12: The access gateway performs a path switching operation after receiving the path switching request message. 2. The method according to claim 1, wherein in step 2, the setting of the handover preparation threshold and the handover decision threshold is set in the measurement module of the source base station. 3. The method according to claim 1, wherein in step 3, the first-level cache of the automatic repeat request in the source base station and the second-level cache of the automatic repeat request in the access gateway Synchronization steps include the following steps: After the access gateway receives the handover preparation notification message, it stores the packet data convergence protocol layer protocol data unit in the automatic retransmission request secondary cache, and sends the stored packet data convergence protocol layer protocol data unit content, number and information to the source The content and number of the packet data convergence protocol layer protocol data unit of the base station are consistent; The automatic retransmission request level-1 buffer in the source base station starts from receiving the first marked packet data convergence protocol layer protocol data unit of the access gateway to the completion of sending all media access control layer protocols in the original buffer When the data unit is used, a packet data convergence protocol layer service data unit of each media access control layer protocol data unit is generated, and there is corresponding packet data convergence protocol layer protocol data in the second-level cache of the automatic retransmission request of the access gateway unit. 4. The method according to claim 1, characterized in that said step 3 further comprises the following steps: After the synchronization, the source base station sends a synchronization success notification message to the access gateway; when the automatic retransmission request of the source base station sends the media access control layer protocol data unit in the first-level cache successfully, and deletes it from the cache Afterwards, a periodic status report message is sent to the access gateway, so that the source base station automatically retransmits the request level-1 cache deletion related packet data convergence protocol layer protocol data unit. 5. The method according to claim 1, wherein in step 4, the sending of the user equipment context message is sending user equipment identification, user equipment address, user equipment capability, cell information, source base station information, target base station information, quality of service information, radio bearer information. 6. The method according to claim 1, wherein in step 8, the process of establishing a connection between the user equipment and the target base station is a process of establishing cell synchronization and radio bearer circuit reconfiguration with the target base station. 7. The method according to claim 1, wherein in step 9, the notification of the completion message to the target base station is to notify the target base station of the completion message by carrying a transmission completion flag in the last data packet base station. 8. The method according to claim 1, wherein in step 9, the notifying the target base station of the completion message is to notify the target base station of the completion message with a separate message after the transmission is completed. Notify the target base station. 9. The method according to claim 1, wherein in step 12, the path switching operation is completed by modifying the target address to the target base station address. 10. The method according to claim 1, characterized in that said step 12 further includes the following steps: After the handover is completed, the access gateway releases user plane resources with the source base station.

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