CN1949918A - Double playing switching method and apparatus under two-layer node network architecture - Google Patents

Abstract

The invention discloses a double-cast switching method and equipment under a two-layer node network architecture. The two-layer nodes include an edge wireless base station (ERS) and an IP access gateway (IAGW). When the first handover condition judging means on the SERS determines that the UE needs to handover to the target edge radio base station (TERS) according to the first handover condition based on the measured value received from the user equipment (UE), the handover preparation control means initiates a handover preparation process. During the handover preparation process, after the IAGW starts to send data to the SERS and TERS respectively in a dual-cast manner, when the second handover condition judging device on the SERS uses the measurement value received from the UE to determine that handover execution needs to be initiated according to the second handover condition During the process, the handover execution control device terminates the handover preparation process and initiates the handover execution process. Therefore, the defect that data is easily lost in the existing soft handover process is effectively overcome.

Description

Bicast switching method and device under a two-layer node network architecture

technical field

The present invention relates to a mobile communication system, in particular to a soft handover method and equipment in the mobile communication system.

Background technique

UMTS is a third-generation mobile communication system that adopts WCDMA air interface technology. It is called a universal mobile communication system, and the UMTS system is usually also called a WCDMA communication system. The UMTS system adopts a structure similar to that of the second-generation mobile communication system, including a radio access network (Radio AccessNetwork, RAN) and a core network (Core Network, CN). Among them, the wireless access network is used to handle all wireless-related functions, while the CN handles all voice calls and data connections in the UMTS system, and implements switching and routing functions with external networks. CN is logically divided into Circuit Switched Domain (CS) and Packet Switched Domain (PS). UTRAN, CN and user equipment (User Equipment, UE) together constitute the entire UMTS system. Its system structure is shown in Fig. 1.

UTRAN is the terrestrial radio access network, which includes one or several radio network subsystems (RNS). An RNS consists of a radio network controller (RNC) and one or more base stations (NodeB). The interface between the RNC and the CN is the Iu interface, and the NodeB and the RNC are connected through the Iub interface. Within the UTRAN, radio network controllers (RNCs) are interconnected through Iur, and Iur can be a direct physical connection between RNCs or a connection through a transmission network. The RNC is used to allocate and control the wireless resources of the NodeB connected or related to it. The NodeB completes the conversion of the data flow between the Iub interface and the Uu interface, and also participates in a part of radio resource management. The structure of UTRAN is shown in Figure 2:

NodeB is the base station (that is, the wireless transceiver) of the WCDMA system, including the wireless transceiver and baseband processing components. Through the standard Iub interface and RNC interconnection, it mainly completes the processing of the Uu interface physical layer protocol. Its main functions are spread spectrum, modulation, channel coding and despreading, demodulation, channel decoding, and also include functions such as mutual conversion of baseband signals and radio frequency signals.

The RNC is a radio network controller, which is used to control the radio resources of the UTRAN, and mainly completes functions such as connection establishment and disconnection, handover, macro-diversity combination, and radio resource management and control. details as follows:

(1) Perform system information broadcast and system access control functions;

(2) Mobility management functions such as handover and RNC relocation (Relocation, also called relocation);

(3) Radio resource management and control functions such as macro-diversity combining, power control, and radio bearer allocation.

In the WCDMA system, a key technology introduced is soft handover. The UE measures the Ec/I ₀ of the CPICH channel of the adjacent cell, establishes and maintains a downlink channel (DCH) active set according to the measurement, maintains a soft handover connection with the cell in the DCH active set, and maintains data transmission. The cells in the active set may belong to the same base station or to different base stations. Compared with the GSM system belonging to the second generation mobile communication system, which can only perform hard handover between different base station cells, soft handover improves the smooth transmission of user data between different base station cells, making the service quality of the business better, and it is not easy to cause data lost.

Referring to FIG. 3 , an existing two-layer node evolution architecture is described below.

Considering the competitiveness of the future network, 3GPP is currently considering how the network will evolve in the future. There are many evolution schemes discussed in 3GPP. The purpose of network evolution is to provide a low-latency, high data rate, high system capacity and coverage, low-cost, completely IP-based network.

There are many candidates for network evolution, among which the two-layer node network architecture is more popular. Under this architecture, Edge Radio Station (ERS, Edge Radio Station) is an evolved Node B, which has most of the functions of the previous RNC, and adopts new physical layer technologies, such as OFDM; IP Access Gateway (IAGW, IP Access Gateway) has some functions of the SGSN and the functions of the previous GGSN.

In order to ensure the smooth evolution of the existing UTRAN architecture, the two-layer node architecture reuses the existing protocols to the greatest extent. On the radio interface side, ERS merges most of the functions of the previous RNC, so in addition to retaining the original physical layer (L1), it also adds MAC layer, RLC layer, and PDCP layer. Between the ERS and the IAGW, a tunnel-related protocol of the GPRS tunnel protocol user plane (GTP-U) is used. The evolved two-layer node network architecture reduces the number of transmission nodes due to the downshifting of the radio interface protocol stack or user plane protocol stack, which shortens call setup delay and transmission delay, and improves data transmission performance.

In the evolution architecture, the ERS is directly connected to the IAGW. To implement soft handover between the ERS using macro-diversity, only a dual-cast method is used at the IAGW, and the source edge wireless base station (SERS) and the target edge wireless base station ( TERS) to send data. Because in the two-layer node architecture, ERS will cache data frames that have been sent to UE but have not received confirmation, so the buffer of SERS will store data frames before TERS joins the active set. After the handover process is completed, as the UE continues to move to the TERS, the quality of the link between it and the SERS will continue to deteriorate until it is deleted from the active set. At this time, if the data frames before the TERS in the internal cache are added to the active set are not delivered, the data will be lost.

Contents of the invention

In order to overcome the defect that data is easily lost in the existing soft handover technology, the present invention provides a bicast handover method and equipment under a two-layer node network architecture.

On the one hand, a method for bicast handover under a two-layer node network architecture is proposed, the two-layer nodes include an Edge Radio Station (ERS) and an IP Access Gateway (IAGW). Wherein, the edge radio base station (ERS) is divided into a source edge radio base station (SERS) and a target edge radio base station (TERS) during the handover process. The method includes steps: A. When the source edge radio base station (SERS) determines that the user equipment (UE) needs to handover to the target edge radio base station (TERS) according to the first handover condition, initiate a handover preparation process; B. during the handover preparation process After the IP access gateway (IAGW) starts to send data to the source edge wireless base station (SERS) and the target edge wireless base station (TERS) in a dual-cast manner, when the source edge wireless During the handover execution process, the handover preparation process is terminated and the handover execution process is initiated.

The first handover condition in the above step A is that within the first time period, the measurement value periodically reported by the user equipment (UE) to the source edge radio base station (SERS) always conforms to the handover judgment algorithm.

The second handover condition in the above step B is that within the second time period, the measurement value periodically reported by the user equipment (UE) to the source edge radio base station (SERS) always conforms to the handover judgment algorithm.

The above handover judging algorithm is that the difference between the source cell signal strength measurement value and the target cell signal strength measurement value is less than or equal to the difference between the handover threshold value and the handover threshold hysteresis value.

The two durations of the first time period and the second time period are determined according to the RRM algorithm of radio resource management and field environment measurement.

The handover preparation process in the above step A further includes: after receiving the message triggering the handover preparation process from the source edge wireless base station (SERS), the IP access gateway (IAGW) initiates a transmission link to the target edge wireless base station (TERS) Establishment process: After the IP access gateway (IAGW) receives the message that the transmission link is successfully established fed back by the target edge wireless base station (TERS), it adopts a dual-cast method to the source edge wireless base station (SERS) and the target edge wireless base station (TERS) The downlink data is sent, and at the same time, a message triggering the handover execution process is sent to the source edge radio base station (SERS).

The above step B further includes: After receiving the message from the IP access gateway (IAGW) that triggers the handover execution process, the source edge wireless base station (SERS) judges whether the second handover condition is satisfied by using the measurement value reported by the user equipment (UE) , if satisfied, the source edge radio base station (SERS) terminates the handover preparation process, and notifies the user equipment (UE) to add the above-mentioned transmission link established by the target edge radio base station (TERS) to its active set.

The above step B also includes: if the second handover condition is not satisfied, the source edge wireless base station (SERS) initiates a transmission link release process to the target edge wireless base station (TERS) through the IP access gateway (IAGW).

The first handover condition in the above step A is that the reported air interface signal strength measurement value between the target edge radio base station (TERS) and the user equipment (UE) reaches the handover preparation threshold.

The second handover condition in the above step B is that the reported air interface signal strength measurement value between the target edge radio base station (TERS) and the user equipment (UE) reaches the handover execution threshold.

On the other hand, a bicast switching device under a two-layer node network architecture is proposed, and the two-layer nodes include an Edge Radio Station (ERS) and an IP Access Gateway (IAGW). The device is located on the edge radio base station (ERS), and includes: a first handover condition judging device, used to judge whether a handover preparation process needs to be triggered according to the first handover condition; a handover preparation control device, used for judging the device according to the first handover condition The output judgment result is used to control the handover preparation process; the second handover condition judging device is used to judge whether the handover execution process needs to be triggered according to the second handover condition; the handover execution control device is used to judge the output of the second handover condition judgment means results to control the switching execution process.

The above-mentioned first handover condition judging means further includes: a first handover condition setting means, configured to set the first handover condition as the measurement value periodically reported by the user equipment (UE) to the source edge radio base station (SERS) at the first time The segment always conforms to the handover judgment algorithm.

The above-mentioned second handover condition judging means further includes: a second handover condition setting means, configured to set the second handover condition as the measurement value periodically reported by the user equipment (UE) to the source edge radio base station (SERS) at the second time The segment always conforms to the handover judgment algorithm.

The above-mentioned first handover condition judging means further includes: a first handover condition setting means for setting the first handover condition as the air interface signal strength measurement between the reported target edge radio base station (TERS) and the user equipment (UE) The value reaches the handover preparation threshold.

The above-mentioned second handover condition judging means further includes: a second handover condition setting means for setting the second handover condition as the air interface signal strength measurement between the reported target edge radio base station (TERS) and the user equipment (UE) value reaches the switching execution threshold.

The present invention achieves the following advantages and features. The improved soft handover method and equipment proposed by the invention adopts an optimized radio resource management (RRM) algorithm, and effectively overcomes the defect that data is easily lost in the existing soft handover process.

Description of drawings

FIG. 1 is a schematic structural diagram of a UMTS system;

Fig. 2 is a schematic diagram of the network structure of UTRAN;

Fig. 3 shows a kind of existing two-layer node network evolution architecture;

FIG. 4 shows a two-layer node architecture user plane protocol stack;

FIG. 5 is a schematic diagram of a data transmission process after switching;

FIG. 6 is a flowchart of a soft handover method according to an embodiment of the present invention;

Fig. 7 is a schematic structural diagram of a bicast switching device implementing the method of the present invention.

Detailed ways

In the existing migration process, the buffer of the source edge radio base station (SERS) will store data frames before the target edge radio base station (TERS) joins the active set. If the link quality of SERS continues to deteriorate until it is deleted from the active set, and the data frames before the TERS in the internal cache are added to the active set have not been delivered, it may cause a large amount of data loss, which will make the service experience quality of users deteriorate. very bad. The invention proposes a new soft handover process to overcome the defect of data loss in the existing soft handover process and ensure the quality of user handover.

The present invention divides the existing handover evaluation time T into two time periods: handover estimated time period T1 and handover confirmation time period T2. The duration of the two time periods is set according to different RRM algorithms and actual on-site environment measurements. In the handover estimated time period T1, if the measurement value reported by the UE is always within a predetermined value range, the SERS initiates a handover preparation process. After the preparation process is completed, the SERS waits for the handover confirmation period T2 before formally triggering the UE handover. If the measurement value reported by the UE is always within the predetermined value range from the handover estimated time period T1 to the handover confirmation time period T2, the SERS officially triggers the handover process. During the handover confirmation period T2, if the signal quality of the SERS suddenly deteriorates, the handover may be triggered in advance. The entire handover procedure according to the method of the present invention will be described below.

If within the time interval T1, in the measurement report reported by the UE, the difference between the signal strength of the current cell and the signal strength of the target cell is continuously less than or equal to the difference between the handover threshold and the handover threshold hysteresis, then the ERS sends a transmission link to the CN. Transport Link Setup Required message to initiate the handover preparation process. The soft handoff judgment algorithm here is defined by the following formula:

Old_Sign-Meas_Sign≤AS_Th-AS_Th_Hyst

The variables in the formula are defined as follows: Meas_Sign is the signal strength measurement value of the target cell, Old_Sign is the signal strength measurement value of the source cell, AS_Th is the macro-diversity threshold, and AS_Th_Hyst is the hysteresis of the macro-diversity threshold.

After receiving the Transport Link Setup Required message, the IAGW initiates a transport link setup process to the TERS. After receiving the acknowledgment of the establishment of the transmission link fed back by the TERS, the IAGW sends downlink data to the SERS and the TERS in a dual-cast manner. The data transmission process after the handover is completed is shown in FIG. 5 .

After receiving the transmission link setup confirmation from TERS, IAGW sends a Transport Link Setup Complete message to SERS, notifying SERS to trigger the soft handover execution process. At this time, the SERS does not send an active set update message to the UE immediately so as to add the transmission link newly created in the TERS to the active set of the UE, but waits for a time interval T2. If within the time interval T2, the difference between the signal strength of the current cell and the signal strength of the target cell is continuously less than or equal to the difference between the handover threshold value and the handover threshold hysteresis value, SERS triggers the soft handover execution process and sends an active set update to the UE message, informing the UE to add the newly created transmission link in the TERS to its active set. At this time, since the SERS has received the acknowledgment of the first bicast data frame sent by the UE, the data in the PDCP buffer on the TERS will include all unacknowledged data in the SERS buffer. In this way, even if the wireless link between the SERS and the UE is broken due to a fault, since the PDCP buffers in the TERS and the SERS are already in a synchronized state, data loss will not occur.

Next, the improved soft handover method of the present invention will be described in conjunction with the embodiment shown in FIG. 6 .

In step 1, the UE periodically sends a measurement report of the signal quality of the source cell and the neighboring cell to the SERS.

In step 2, after the measurement data is collected, the SERS determines that the UE needs to switch to the TERS according to predetermined switching conditions. Since there is no Iur interface between SERS and TERS in the evolution architecture, data cannot be exchanged. SERS sends a TL Setup Required message to IAGW to trigger the handover process.

In step 3, after receiving the TL Setup Required message, the IAGW sends a TL Setup Request message to TERS, requesting TERS to pre-allocate required resources for the UE.

In step 4, after receiving the TL Setup Request message, the TERS starts the relevant resource allocation procedure, and establishes a radio resource control (RRC) connection and a radio access bearer (RAB). TERS establishes a Packet Data Convergence Protocol/Radio Link Control/Media Access Control (PDCP/RLC/MAC) entity, establishes a new wireless link, and initiates transmission and reception on the new wireless link. At the same time, the establishment of GTP-U tunnels (GTP-U Tunnels for PS RABs) for packet switching RABs is started to transmit the bearer, and the user plane bearer between TERS and IAGW is established. After all necessary resources are successfully allocated, the target ERS will send a transmission link establishment response (TL Setup Response) message to the IAGW to confirm that the resource allocation is successful.

In step 5, after receiving the TL Setup Response message, IAGW copies the data sent to SERS and sends it to TERS through the newly established GTP-U channel with TERS. At the same time, the IAGW sends a transmission link establishment complete (TL Setup Complete) message to the source ERS to notify the source ERS to trigger the execution process of soft handover.

In step 6, after receiving the TL Setup Complete message, the source ERS does not initiate the soft handover execution process immediately, but waits for the time interval T2. If within the time interval T2, the difference between the signal strength of the current cell and the signal strength of the target cell is continuously smaller than or equal to the difference between the handover threshold and the handover threshold hysteresis, the source ERS terminates the soft handover preparation process. And, SERS sends an active set update (ActiveSet Update) message to the UE, notifying the UE to add the wireless link newly created by TERS to its active set.

In step 7, after receiving the Active Set Update message, the UE will reconfigure the air interface resources according to the information provided by the message, and add the new wireless link to the active set. After the UE successfully accesses the target cell, it will send an Active Set Update Complete (Active Set Update Complete) message to notify that the SERS handover is successful. At this time, the UE simultaneously receives data from the SERS and the TERS. In this solution, the diversity function of the data flow is completed in the IAGW, so the time delay between the two channels of data received by the UE is relatively large. Therefore, for UE local data stream combination, selection ratio combination is usually adopted.

In this process, if within the SERS monitoring time T2, the difference between the signal strength of the current cell and the signal strength of the target cell does not meet the requirement that the difference between the handover threshold value and the handover threshold hysteresis value is continuously smaller than or equal to the handover threshold value, SERS will not notify The UE updates its active set, and initiates a transmission link release procedure to the TERS through the IAGW.

Now, referring to FIG. 7, the device for performing the bicast switching method of the present invention will be described. The device is located on the ERS, and includes first handover condition judging means, handover preparation control means, second handover condition judging means and handover execution control means.

The first handover condition judging means is used for judging whether a handover preparation process needs to be triggered according to the first handover condition. In the above embodiment, the first handover condition is preset as, within the time interval T1, in the measurement data reported by the UE to the SERS, the difference between the signal strength of the current cell and the signal strength of the target cell is continuously less than or equal to the handover threshold and the difference between the switching threshold hysteresis. The first handover condition judging means reads the measurement data currently collected by the SERS, and judges whether the UE needs to handover to the TERS according to the predetermined first handover condition.

The handover preparation control means is used for controlling the handover preparation process according to the judgment result output by the first handover condition judgment means. If the judgment result received from the first handover condition judging means is that handover is required, the handover preparation control means initiates a handover preparation process and manages the preparation process in the entire soft handover process. If the judging result is that switching is not required, the switching preparation control means cyclically detects the judging result output by the first switching condition judging means.

The second handover condition judging means is used for judging whether the handover execution process needs to be triggered according to the second handover condition. In the above-mentioned embodiment, the second handover condition is preset as, within the SERS monitoring time T2, the difference between the signal strength of the current cell and the signal strength of the target cell does not meet the requirement of continuously being less than or equal to the handover threshold and the handover threshold hysteresis value difference. After the second handover condition judging means obtains the notification that the source ERS has received the TL Setup Complete message, it reads the measurement data currently collected by the SERS, and judges whether the handover execution process needs to be triggered according to the predetermined second handover condition.

Here, the first handover condition judging means further includes a first handover condition setting means, which is used to set the first handover condition to be that the measurement value periodically reported by the UE to the SERS always conforms to the handover judging algorithm within the T1 time period, and the second handover condition The condition judging means further includes a second handover condition setting means, configured to set the second handover condition to be that the measurement value periodically reported by the UE to the SERS always conforms to the handover judging algorithm within the T2 time period.

The switching execution control means is used for controlling the switching execution process according to the judgment result output by the second switching condition judging means. If the judgment result received from the first handover condition judging means is that the handover execution process needs to be triggered, the handover execution control means terminates the soft handover preparation process, starts the soft handover execution process and manages the execution process in the entire soft handover flow. If the judgment result is that the handover execution process does not need to be triggered, the handover preparation control device initiates a transmission link release process to the TERS through the IAGW.

The main principle of the technical solution described in the present invention is to carry out the handover preparation process in advance to avoid the SERS disconnection caused by the sudden change of the air interface quality between the SERS and the UE, thereby avoiding data loss.

The soft handover scheme proposed by the present invention has other implementation manners, for example, setting a handover preparation threshold and a handover trigger threshold. When the air interface signal strength between the TERS and the UE reaches the handover preparation threshold, start the handover preparation process; when the air interface signal strength between the TERS and the UE reaches the handover execution threshold, start the handover execution process. In this way, the purpose of switching in advance can also be achieved.

In the case of adopting this method, the above-mentioned first handover condition judging means further includes a first handover condition setting means for setting the first handover condition as the reported air interface signal strength measurement value between TERS and UE reaches Handover preparation threshold; the second handover condition judging means further includes a second handover condition setting means for setting the second handover condition as the reported air interface signal strength measurement value between TERS and UE reaches the handover execution gate limit.

Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims (15)

1. A dual-cast switching method under a two-layer node network architecture, wherein the two-layer node includes an edge wireless base station (ERS) and an IP access gateway (IAGW), wherein the edge wireless base station (ERS) is in a handover process Divided into source edge radio base station (SERS) and target edge radio base station (TERS), the method comprises the steps of: A. When the source edge radio base station (SERS) determines that the user equipment (UE) needs to be handed over to the target edge radio base station (TERS) according to the first handover condition, initiate a handover preparation process; B. During the handover preparation process, after the IP access gateway (IAGW) starts to send data to the source edge wireless base station (SERS) and the target edge wireless base station (TERS) in a bicast manner, when the source edge wireless base station (SERS) according to When the second handover condition determines that the handover execution process needs to be initiated, the handover preparation process is terminated and the handover execution process is initiated. 2. The method according to claim 1, characterized in that the first handover condition in the step A is that within the first time period, the user equipment (UE) periodically reports to the source edge radio base station (SERS) The measured value always complies with the handover decision algorithm. 3. The method according to claim 1, characterized in that the second handover condition in the step B is that within the second time period, the user equipment (UE) periodically reports to the source edge radio base station (SERS) The measured value always complies with the handover decision algorithm. 4. The method according to claim 2 or 3, characterized in that the handover judgment algorithm is that the difference between the source cell signal strength measurement value and the target cell signal strength measurement value is less than or equal to the handover threshold and Difference between switching threshold hysteresis. 5. The method according to claim 2 or 3, characterized in that the two durations of the first time period and the second time period are determined according to a radio resource management (RRM) algorithm and field environment measurements. 6. The method according to claim 1, characterized in that the handover preparation process in step A further comprises: After the IP access gateway (IAGW) receives the message triggering the handover preparation process sent by the source edge wireless base station (SERS), it initiates the transmission link establishment process to the target edge wireless base station (TERS); After the IP access gateway (IAGW) receives the message that the transmission link is successfully established fed back by the target edge wireless base station (TERS), it sends downlink data to the source edge wireless base station (SERS) and the target edge wireless base station (TERS) in a dual-cast manner , and at the same time send a message triggering the handover execution process to the source edge radio base station (SERS). 7. The method according to claim 6, characterized in that said step B further comprises: After receiving the message from the IP access gateway (IAGW) that triggers the handover execution process, the source edge radio base station (SERS) judges whether the second handover condition is satisfied by using the measurement value reported by the user equipment (UE), If so, the source edge radio base station (SERS) terminates the handover preparation process, and notifies the user equipment (UE) to add the transmission link established by the target edge radio base station (TERS) to its active set. 8. The method according to claim 7, characterized in that said step B further comprises: if the second handover condition is not satisfied, the source edge wireless base station (SERS) sends the target edge wireless base station to the target edge wireless base station through the IP access gateway (IAGW) (TERS) initiates the transmission link release procedure. 9. The method according to claim 1, characterized in that the first handover condition in the step A is the reported air interface signal strength measurement value between the target edge radio base station (TERS) and the user equipment (UE) The handover readiness threshold is reached. 10. The method according to claim 1, characterized in that the second handover condition in the step B is the air interface signal strength measurement value reported between the target edge radio base station (TERS) and the user equipment (UE) The switching execution threshold is reached. 11. A dual-cast switching device under a two-layer node network architecture, the two-layer node includes an edge wireless base station (ERS) and an IP access gateway (IAGW), and the device is located on the edge wireless base station (ERS), It is characterized in that the device comprises: A first handover condition judging device, configured to judge whether a handover preparation process needs to be triggered according to the first handover condition; Handover preparation control means for controlling the handover preparation process according to the judgment result output by the first handover condition judging means; The second handover condition judging device is used to judge whether the handover execution process needs to be triggered according to the second handover condition; The switching execution control means is used for controlling the switching execution process according to the judgment result output by the second switching condition judging means. 12. The device according to claim 11, characterized in that said first handover condition judging means further comprises: first handover condition setting means for setting the first handover condition as user equipment (UE) to source edge The measurement value periodically reported by the wireless base station (SERS) always conforms to the handover judging algorithm in the first time period. 13. The device according to claim 11, characterized in that said second handover condition judging means further comprises: second handover condition setting means for setting the second handover condition as user equipment (UE) to source edge The measurement value periodically reported by the wireless base station (SERS) always conforms to the handover judging algorithm in the second time period. 14. The device according to claim 11, characterized in that said first handover condition judging means further comprises: a first handover condition setting means for setting the first handover condition as the reported target edge wireless base station ( TERS) and the air interface signal strength measurement value between the user equipment (UE) reaches the handover preparation threshold. 15. The device according to claim 11, characterized in that said second handover condition judging means further comprises: a second handover condition setting means for setting the second handover condition as the reported target edge wireless base station ( TERS) and the air interface signal strength measurement value between the user equipment (UE) reaches the handover execution threshold.

Images