CN104093176B - A kind of method for avoiding producing pingpang handoff in LTE load balancing is migrated - Google Patents

Abstract

A method for avoiding ping-pong handover during LTE load balancing migration, comprising periodically detecting the load level of a serving cell s in a cell in an LTE network, and judging whether the cell s is overloaded; if the cell s is overloaded, selecting some UEs to issue measurement configurations, Configure UE to continuously report RSRP and RSRQ; cell s obtains and reports the load information of each neighboring cell, compares the load of each neighboring cell with the admission threshold, and obtains the neighboring cell whose load is lower than the admission threshold as a candidate target cell; query and report the measurement Based on the reported historical information of the UE, it is judged whether the cell s has had a ping-pong handover with one of the candidate cells, and by comparing the signal strength of the adjacent cell during this and the historical ping-pong handover, it is judged whether it is suitable to initiate a handover request to the target cell, thereby Avoid ping-pong switching. The invention guarantees that during the load balancing process of the LTE system, the ping-pong switching caused by the migration of the user to the adjacent base station is avoided.

Description

A method to avoid ping-pong switching in LTE load balancing migration

technical field

The invention belongs to the field of mobile communication, and in particular relates to a method for avoiding ping-pong switching when load balancing migrates a UE in an LTE network.

Background technique

In the protocol stack of the 3GPP LTE access network system, Mobility Load Balancing (MLB) distributes measurement configurations to some UEs, obtains measurement reports reported by UEs, and switches some users in overloaded cells to low-loaded neighboring cells in advance. , which is used to solve the unbalanced traffic among multiple cells and improve the utilization rate of wireless resources.

Ping-pong handover means that a user equipment (UE) performs multiple handovers between cells in the system, and after each handover, the UE stays in the target system for a relatively short time. equipment are adversely affected. On the one hand, the user equipment performs unnecessary switching, resulting in a decrease in user service quality. On the other hand, base stations need to frequently send and receive signaling messages, which brings traffic burden to the network and seriously wastes the resources of the wireless access system.

The base station generally uses the A3 event to determine whether the coverage-based handover judgment condition is satisfied, that is, if the UE detects that the signal of the neighboring cell is better than the signal of the serving cell by a difference, the system will handover the UE to the neighboring cell with better signal. The formula of A3 event entry condition: Mn+Ofn+Ocn-Hys>Ms+Ofs+Ocs+Off, the relevant symbols are described in detail in chapter 5.5.4measurement report triggering of the standard protocol "3GPP TS 36.331", please refer to the corresponding literature .

The base station generally uses the A4 or A5 event to judge whether the handover judgment condition based on load balancing is satisfied. When the A4 event is used: when the signal of the neighboring cell is better than the threshold Thresh, the system will handover the UE to the neighboring cell to balance the load. The formula of A4 event entry condition: Mn+Ofn+Ocn-Hys>Thresh; when adopting A5 event: when the signal in the service area is worse than the threshold Thresh1 and the signal in the neighboring cell is better than the threshold Thresh2, the system will switch the UE to the neighboring cell zone for load balancing. The formula of A5 event entry condition: Ms+Hys<Thresh1 and Mn+Ofn+Ocn-Hys>Thresh2.

There may be two reasons for the occurrence of ping-pong handover caused by MLB. One is that the handover judgment conditions based on load balancing and coverage-based handover judgment conditions will conflict. , handover from cell s to cell d, and at this time, the UE triggers the A3 event immediately, and handovers from cell d to cell s. The other is caused by the special movement characteristics of the user, for example, the user moves back and forth between two cells, causing the user equipment to constantly switch between the two cells.

In the existing LTE system standard specification, during the handover preparation process, the source base station transmits the UE history information (UE history information) to the target base station through a handover request (HANDOVER REQUEST) message, so that each base station can The information of the cell that the UE has visited before can be obtained, and it can be judged whether the ping-pong handover has occurred for the UE based on the information.

The UE history information (UE history information) is a linked list, and the linked list is composed of the UE's "Last Visited Cell Information" in descending order of time, that is, the most recent resident information is stored in the first Linked list nodes, each cell information visited in the past includes the following content:

Cell category (category includes E-UTRAN/UTRAN/GERAN);

Cell global identifier (Cell Global Identifier, CGI);

Cell type, which can be "very small", "small", "medium" or "large";

The time that the UE resides in the cell.

To sum up, from the introduction of the above prior art, it can be found that the ping-pong handover cannot be avoided based on the existing historical information of the UE, because this method only judges that the UE switches back and forth between two cells, and that the UE stays in each wireless system. time, does not take into account the specific signal strength or quality of each adjacent base station cell of the UE during each handover, so effective measures cannot be taken to adjust the handover decision conditions based on load balancing to avoid the occurrence of handover decision conditions based on coverage conflict.

Contents of the invention

The problem to be solved by the present invention is how to avoid the ping-pong handover caused by handing over the UE to an adjacent cell in order to balance the traffic during the MLB process, resulting in the degradation of user service quality and serious waste of resources in the wireless access system.

The technical solution of the present invention is a method for avoiding generation of ping-pong handover in LTE load balance migration, comprising the following steps,

Step 1, the base station in the LTE network periodically detects the load level of each cell, sets the current cell detected by the base station S as the cell s, and judges whether the cell s is overloaded, if so, enters step 2, otherwise ends the process;

Step 2, the base station S selects some UEs in the cell s to issue A4 or A5 measurement configurations, and the configured UEs continue to report measurement reports, and the measurement reports include RSRP and RSRQ, the RSRP is the reference signal received power, and the RSRQ is the reference signal reception quality;

Step 3, when the base station S receives the measurement report reported by any UE, the base station S obtains the reported RSRP and RSRQ of each neighboring cell from the measurement report reported by the UE;

Step 4, base station S obtains the load information of all neighboring cells of cell s through the X2 interface, compares the corresponding load with the admission threshold for each neighboring cell reported by the UE in step 3, and takes the neighboring cells whose load is lower than the admission threshold as Alternative destination cells, judging whether the number n of alternate destination cells is 0, if so, end the process, if not, enter step 5;

Step 5. The base station S queries the UE history information reported in the measurement report, and compares whether there is a record of the UE history information. The cell where the UE resides is one of the candidate destination cells in step 4, and the reason for the handover is the handover caused by coverage. , and the residence time is very short; if it is, then set this record as the mth item, set the alternative destination cell as cell d, and enter step six, if no, enter step eight;

Step 6, the base station S continues to look up the UE history information, and compares whether the cell where the UE resides in the m+1th record of the UE history information is a local cell. Eight;

Step 7, the base station S compares whether the RSRP and RSRQ of the cell d obtained in the step 2 are greater than the RSRP and RSRQ of the cell d recorded in the m+1th item of the UE history information, if it is, enter the step 8, if not, end the process;

Step 8, base station S fills in the Last VisitedUTRAN Cell Information in the UE history IE of the X2HANDOVER REQUEST message, including adding information elements destination cell RSRP and destination cellRSRQ to record the RSRP and RSRQ of cell d obtained in step 2, and send it to the corresponding base station of cell d .

Moreover, in step 1, it is judged whether the cell is overloaded by judging whether the cell load value is greater than a threshold value.

Moreover, in step 2, the UE reporting the A2 measurement report is marked as an edge UE, and the edge UE is preferentially selected to deliver the measurement configuration.

The present invention proposes a simple method for judging UE handover in an LTE network, enabling the base station to obtain additional information about UE handover, thereby avoiding ping-pong handover caused by load balancing to a certain extent. Through the above technical solutions conceived by the present invention, compared with the prior art, the present invention has the following beneficial effects:

1. The parameters are simple and easy to obtain. The historical RSRP and RSRQ used in the comparison in step 7 are added in step 8. This parameter is transmitted to each other through the X2 interface in the LTE network, so it is more convenient for the cell to obtain the handover parameters of its neighboring cells .

2. There is no need to adjust the handover parameters according to the handover statistical results, the algorithm has high precision and fast adjustment speed, and pays attention to user perception. By adopting steps 6, 7, and 8, the handover decision algorithm from each UE to the target cell can be accurately controlled to avoid the MLB process Ping-pong switching occurs in the middle, thereby improving user perception.

3. The complexity of the algorithm is low, and there is no need to consider the conflict caused by the different measurement configurations of the serving cell and the neighboring cell. Since step 8 will update the destination cell RSRP and destination cell RSRQ at each handover, the comparison and judgment of step 7 can finally avoid service Ping-pong handover caused by conflicts caused by different measurement configurations between the cell and neighboring cells.

Description of drawings

Fig. 1 is a basic flowchart of an embodiment of the present invention.

detailed description

The implementation of the present invention provides a detection and processing mechanism of ping-pong switching to avoid the ping-pong switching caused by load balancing, thereby improving user experience and network performance. Hereinafter, the present invention will be further described in detail through specific embodiments in conjunction with FIG. 1 .

Referring to Fig. 1, the flow process of embodiment is as follows:

Step 1. The base station in the LTE network periodically detects the load level of each cell. Generally, the base station will traverse all the corresponding cells for detection. The current cell detected by the base station S is set as the cell s, and it is judged whether the cell s is overloaded. If the cell is overloaded, Go to step 2, otherwise end the process.

During specific implementation, it can be judged whether the cell is overloaded by judging whether the cell load value is greater than the threshold value. It is suggested that the preset value of the threshold value is when all physical resource blocks (Physical Resource Blocks, referred to as PRBs) in the cell are occupied. Between 75% and 85% of the total load, the load detection cycle can be set by those skilled in the art, generally ranging from 1s to 10s.

Step 2, the base station S selects some UEs in the cell s according to the UE context, and delivers the measurement configuration to these UEs, and the UEs that accept the configuration continue to report the measurement report, and the measurement report includes RSRP (Reference Signal Received Power, reference signal received power) and RSRQ (Reference Signal Received Quality, reference signal received quality).

It is recommended that the number of UEs selected to deliver the measurement configuration each time is 5% to 10% of the number of active users (active UEs). During specific implementation, the UE reporting the A2 measurement report can be marked as an edge UE, the edge UE is preferentially selected to deliver the measurement configuration, and the rest can be randomly selected.

Generally, some UEs are selected to issue A4 or A5 measurement configurations, and the UEs are configured to continuously report RSRP (Reference Signal Received Power, Reference Signal Received Power) and RSRQ (Reference Signal Received Quality, Reference Signal Received Quality) through measurement reports. The embodiment configures the UE to adopt A4 measurement configuration, configures the UE to continuously report measurement reports, and the measurement reports include RSRP and RSRQ. Subsequent processing of selecting the A5 measurement configuration is similar, and will not be described in detail in the present invention.

Step 3, when the base station S receives the measurement report reported by any UE, the base station S obtains the RSRP and RSRQ of each neighboring cell reported by the UE from the measurement report reported by the UE.

In the embodiment, the UE reports the A4 measurement report, and obtains the reported RSRP and RSRQ of each neighboring cell.

Step 4, base station S obtains the load information of all neighboring cells of cell s through the X2 interface, compares the corresponding load with the admission threshold for each neighboring cell reported by the UE in step 3, and takes the neighboring cells whose load is lower than the admission threshold as Alternative destination cells, determine whether the number n of alternative destination cells is 0, where n is a positive integer, if n is equal to 0, it means that the overloaded cell s has not found a neighbor cell that can perform load balancing, and the process ends, if n is not 0 to step five.

During specific implementation, the base station of the general cell s can obtain the load information of each neighboring cell from the base station of the consular area through the X2 interface specified in the LTE protocol. It is recommended that the preset value of the admission threshold be used when all PRBs in the cell are occupied. between 50% and 60% of the total load.

Step 5, the base station S queries the UE history information (UE history Information IE) reported in the measurement report, and compares whether the cell where the UE resides in a certain record of the UE history information (set as the mth item) is the candidate destination cell in step 4 One of them (recorded as cell d if yes), and the handover reason is the handover caused by coverage, and the dwell time is very short, less than the set threshold T. If yes go to step 6, if no go to step 8. The UE History Information IE can be extracted from the UE handover signaling, and stored in the base station, the information of the base station where the UE once camped.

That is, if any of the following three conditions are not met, go to step 8, and if all of them are met, go to step 6:

1. There is a record in the UE history information that the cell where the UE resides matches one of the candidate target cells in step 4.

2. The reason for switching is due to coverage.

3 The dwell time is less than the set threshold.

During specific implementation, the time threshold T can be preset by those skilled in the art, generally ranging from 2s to 10s.

Step 5 provides the primary condition for judging whether the UE has ever had ping-pong handover between the current serving cell and the candidate target cell. The current serving cell is cell s, which may also be called a local cell.

Step 6, the base station S continues to look up the UE history information mentioned in step 5, and compares whether the cell where the UE resides in the m+1th record of the UE historyInformation IE is a local cell (that is, the cell s), and if so, it is judged as a ping-pong To switch, go to step seven, if not go to step eight.

Step 6 provides a second condition for judging whether the UE has ever had a ping-pong handover between the serving cell and the candidate target cell.

Step 7, the base station S compares whether the current RSRP and RSRQ of the candidate target cell (cell d) are greater than the RSRP and RSRQ of the neighboring cell (cell d) in the m+1th record of the UE historical information described in step 6, If yes, switch is allowed, go to step 8, otherwise end the process.

Referring to step 8, when the present invention sets a new record to be added, the RSRP and RSRQ of the neighboring cell are recorded, so when the cell where the UE resides in the mth record is cell d, the m+1th record also contains cell d (historical ) RSRP and RSRQ.

Through steps 5 and 6, it is judged whether the cell s has had ping-pong handover with one of the alternative destination cells. In the step 7, the RSRP and RSRQ of the adjacent cell measured in this step 2 are respectively greater than the result of the ping-pong handover Only when the RSRP and RSRQ recorded at the time can it be allowed to switch to the corresponding neighboring cell again.

In this way, by comparing the signal strength of the adjacent cell during this time and the historical ping-pong handover, it can be judged whether it is suitable to initiate a handover request to the target cell, thereby avoiding ping-pong handover.

Step 8, the base station S adds the information elements destination cell RSRP and destination cell RSRQ to the Last Visited UTRAN Cell Information in the UE history Information IE of the X2 HANDOVER REQUEST message (see Chapter 9.2.1.43 of the TS 36.413 protocol) to record the UE in step 2 Measured neighboring cell signal strength (reference signal received power of cell d, reference signal received quality). Step 8 is entered each time to form a new record in the UE historyInformation IE.

The HANDOVER REQUEST message is a handover request message. The X2 HANDOVER REQUEST message is the handover request message sent through the X2 interface. Specifically, you can fill in the Last Visited UTRAN Cell Information in the UE history InformationIE of the X2 HANDOVER REQUEST message, and fill in the Global Cell ID, Cell Type, Time UE stayed in Cell and other information elements respectively. , and destination cell RSRP, destination cell RSRQ are sent by the base station S to the destination base station where the alternative destination cell d is linked, and then the procedure ends. Chapter 9.2.1.42 of the standard protocol "3GPP TS36.413" explains in detail each information element contained in the UE history Information IE, and the present invention does not repeat them.

In particular, for a certain UE that reports a measurement report, there may be multiple candidate target cells that all meet the conditions of steps 5, 6, and 7. In principle, the UE can preferentially select a cell with a good signal for handover. In order to improve efficiency, if there are multiple candidate target cells (that is, n is greater than 1), UE can first make an arrangement according to the quality of the signal, and put the good signal first, and the base station traverses one by one from the cell with good signal. The traversal starts from the condition of step 5 to judge, find the cell that meets the conditions in step 5, 6, and 7 and switch, otherwise check the next cell according to the signal sorting. Those skilled in the art can apply the basic flow provided by the embodiment according to the situation, and the modification and adjustment based on it should be within the protection scope of the present invention.

During specific implementation, the process of the present invention can realize automatic and continuous operation based on software technology.

For ease of implementation and reference, the following provides an example using the method provided by the embodiment of the present invention:

Cell 1 and cell 2 belong to different base stations and are adjacent to each other, and both have enabled the MLB function.

Cell 1 uses the A3 event as the judgment condition for coverage switching. When the RSRP of the neighboring cell is greater than the RSRP of the serving cell by 3dBm, the UE will report the A3 measurement report.

Cell 2 uses the A3 event as the judgment condition for coverage switching. When the RSRP of the neighboring cell is greater than the RSRP of the serving cell by 2dBm, the UE will report the A3 measurement report.

UE1 accesses cell 1, reports the A2 measurement report, and is marked as an edge user in the UE context.

At this time, it is detected that the load of cell 1 exceeds the threshold, while the load of cell 2 is lower than the admission threshold. Select some UEs, including UE1, and deliver the A4 measurement configuration. According to the delivered measurement configuration, if the UE detects that the RSRP of the neighboring cell is greater than or equal to -104dBm, it will report the A4 measurement report.

UE1 reported the measurement report of A4, serving cell RSRP:-101dBm, serving cell RSRQ:-8dB, neighbor cell RSRP:-104dBm, RSRQ:-10dB. At this time, the historical information of UE is empty, and there is no need to make a handover decision based on this, directly Handover UE1 to cell 2, that is, the result of step 5 is no and then enter step 8.

In the UE history information of the X2 handover request, it is recorded that the destination cell RSRP of UE1 in cell 1: -104dBm, the destination cell RSRQ: -10dB, and the dwell time is 50s.

Assume that UE1 does not move and the received signal remains unchanged. At this time, UE1 reports the A3 measurement report immediately after switching to cell 2. The measured result is the same as the signal quality in the A4 measurement report reported in cell 1, that is, the neighbor cell RSRP It is -101dBm, RSRQ of the neighboring cell: -8dB, RSRP of the serving cell: -104dBm, RSRQ of the serving cell: -10dB, and UE1 is handed over to cell 1 at this time.

In the first entry of the UE history information of the X2 handover request, it records that UE1 is in cell 2. Destination cell RSRP: -101dBm, destination cell RSRQ: -8dB, dwell time is 1s, and the handover reason is caused by coverage.

When cell 1 detects that the load exceeds the threshold again, the load of cell 2 is lower than the admission threshold. Select some UEs, including UE1, and deliver the A4 measurement configuration.

Assuming that UE1 does not move and the received signal remains unchanged, report A4 measurement report at this time, and the measured result is the same as the signal quality in A3 measurement report reported in cell 2, that is, the serving cell RSRP is -101dBm, and the serving cell RSRQ:- 8dB, RSRP of adjacent cell: -104dBm, RSRQ of adjacent cell: -10dB. At this time, the historical information of the UE is traversed, and it is found that the first record matches the first condition of the ping-pong handover, that is, it is found that the UE has camped in the alternate destination cell, the reason for the handover is coverage, and the dwell time is very short, less than the set Set the threshold to 2s. It is found that the second record matches the second condition of the ping-pong handover, that is, in the second record of the UE history message, it is found that the UE has camped in the serving cell. Comparing the RSRP and RSRQ reported by A4 with the RSRP and RSRQ in the second record of the UE history message, it is found that the signal strength and quality have not improved, so UE1 is not handed over to cell 2 again, thereby avoiding frequent ping-pong handovers .

It can be seen that the present invention adds simple parameters to the existing x2 interface signaling, and by analyzing and comparing historical data, frequent ping-pong switching in the MLB process can be avoided.

The above content is a further detailed description of the present invention in conjunction with specific embodiments, and it cannot be assumed that the specific implementation of the present invention is limited to these descriptions. For those of ordinary skill in the technical field of the present invention, without departing from the concept of the present invention, some simple deduction or replacement can be made, which should be regarded as belonging to the protection scope of the present invention.

Claims (2)

1. A method for avoiding generation of ping-pong switching in LTE load balancing migration, is characterized in that: comprise the following steps, Step 1, the base station in the LTE network periodically detects the load level of each cell, sets the current cell detected by the base station S as the cell s, and judges whether the cell s is overloaded, if so, enters step 2, otherwise ends the process; Step 2, the base station S selects some UEs in the cell s to issue A4 or A5 measurement configurations, and the configured UEs continue to report measurement reports, and the measurement reports include RSRP and RSRQ, the RSRP is the reference signal received power, and the RSRQ is the reference signal reception quality; When selecting, the UE reporting the A2 measurement report is marked as an edge UE, and the edge UE is preferentially selected to deliver the measurement configuration; Step 3, when the base station S receives the measurement report reported by any UE, the base station S obtains the reported RSRP and RSRQ of each neighboring cell from the measurement report reported by the UE; Step 4, base station S obtains the load information of all neighboring cells of cell s through the X2 interface, compares the corresponding load with the admission threshold for each neighboring cell reported by the UE in step 3, and takes the neighboring cells whose load is lower than the admission threshold as Alternative destination cells, judging whether the number n of alternate destination cells is 0, if so, end the process, if not, enter step 5; Step 5. The base station S queries the UE history information reported in the measurement report, and compares whether there is a record of the UE history information. The cell where the UE resides is one of the candidate destination cells in step 4, and the reason for the handover is the handover caused by coverage. , and the residence time is very short; if it is, then set this record as the mth item, set the alternative destination cell as cell d, and enter step six, if no, enter step eight; Step 6, the base station S continues to look up the UE history information, and compares whether the cell where the UE resides in the m+1th record of the UE history information is a local cell. Eight; Step 7, the base station S compares whether the RSRP and RSRQ of the cell d obtained in the step 2 are greater than the RSRP and RSRQ of the cell d recorded in the m+1th item of the UE history information, if it is, enter the step 8, if not, end the process; Step 8, base station S fills in the Last VisitedUTRAN Cell Information in the UE history IE of the X2HANDOVER REQUEST message, including adding information elements destination cell RSRP and destination cellRSRQ to record the RSRP and RSRQ of cell d obtained in step 2, and send it to the corresponding base station of cell d . 2. avoid the method for producing ping-pong handover in LTE load balancing migration as claimed in claim 1, it is characterized in that: in step 1, judge whether cell is overloaded by judging whether cell load value is greater than threshold value.