CN114466424A - 5G cell switching method for improving UDN connection stability - Google Patents

Abstract

The invention discloses a 5G cell switching method for improving the connection stability of a UDN, which overcomes the problem of poor connection switching stability in a 5G UDN network in the prior art and comprises the following steps: accounting for signal level offsets; analyzing the disconnection rate; system lag synthesis; a modified a3 handover decision; and optimizing ping-pong handover. The invention firstly analyzes the offset of the signal level relative to the transmitting power according to different cell equipment types under the UDN architecture. And establishing a matching curve of the specific offset parameter according to the adjacent cell drop rate index. And evaluating the average minimum residence time of the cell, inclining the system resources towards the cell with longer residence time, filtering out the cell which is not suitable for the access of the current mobile terminal through a speed threshold, and establishing a target neighbor cell list participating in the handover. And judging the ping-pong switching state influencing the connection stability of the UDN, and selecting the optimal cell from the target neighbor cell list as the final target service cell for switching, thereby optimizing the use perception of the user.

Description

5G cell switching method for improving UDN connection stability

Technical Field

The invention relates to the technical field of 5G communication, in particular to a 5G cell switching method for improving the connection stability of a UDN.

Background

The UDN (Ultra Dense Networks) can greatly increase the 5G system capacity by means of abundant and various devices, and is a power assisting for further development of the Internet of things and the Internet in the future. However, the stability deviation of mobile connection in the UDN network is caused just because the UDN network devices are different and the transmission power is different, the ping-pong effect of the switching of the mobile terminal is obvious, and the user perception is further influenced. Therefore, how to perform UDN optimization in a targeted manner and improve the network connection stability becomes one of the 5G problems that needs to be solved at present. At present, effective methods are not too many, and there are methods focusing on user movement state evaluation, methods focusing on reference signal self-adaptation, methods for establishing virtual cells, and the like, but these researches do not start with key indexes of connection stability, and often consider one another.

Disclosure of Invention

The invention provides a 5G cell switching method for improving the connection stability of a UDN (Universal data network) in order to overcome the problem of poor connection switching stability in a 5G UDN (Universal data network) in the prior art, and the method starts from the disconnection rate and carries out point-to-point compensation based on cell specific offset. Analyzing core indexes such as minimum stay time and the like related to cell switching, and dynamically establishing corresponding system delay; each UDN device is provided with a maximum access speed threshold so as to ensure that a smooth and reliable target switching cell set can be established when the terminal moves at different speeds, a corresponding ping-pong switching state is analyzed, and the optimal cell is selected as a target service cell, so that the user perception is improved, and the target of optimizing switching is achieved. And adaptively adjusting the switching parameters, and fully considering the performance of the cell to select a proper target adjacent cell.

In order to achieve the purpose, the invention adopts the following technical scheme:

A5G Cell switching method for improving UDN connection stability comprises N-N +1 CLLN-Cell_s}∪CLLn＝{Cell_s，Cell₁，…，Cell_nThe method comprises the following steps of (1) forming a macro cell, a micro cell, a home base station, a relay station and the like; wherein, Cell_sFor the primary serving Cell of the current mobile terminal, CLLn ═ Cell₁，…，Cell_nThe adjacent area is defined as the position of the adjacent area; cell signal level { RSRP_s，RSRP₁，…，RSRP_n}, transmit power { Rx_s，Rx₁，…，Rx_n}, dropped-line rate { Drp₁，Drp₂，…，Drp_nMean residence time for cell handover { Mts }₁，Mts₂，…，Mts_nEach base station is suitable for accessMaximum terminal velocity { Vap₁，Vap₂，…，Vap_n}, ping-pong switching rate { Pph₁，Pph₂，…，Pph_n}；

The method comprises the following steps:

step one, checking and calculating signal level offset: replacing the absolute value of the signal level by a level offset mode, and calculating the offset of the signal level of each cell at the current moment and the cell transmitting power;

step two, analyzing the disconnection rate: setting a basic hysteresis parameter and a specific offset coefficient, and calculating a basic offset and a specific offset of an adjacent cell according to the call drop rate;

step three, system delay synthesis: setting minimum stay time, a stay time threshold, a hysteresis threshold and a hysteresis coefficient for switching, and distinguishing different conditions to calculate the cell hysteresis;

step four, the corrected A3 switching judgment: the adjacent cells meeting the requirement of the level offset are brought into a candidate set, so that switching is triggered;

step five, optimizing ping-pong switching: and selecting a set meeting the Case4 condition, calculating a target set according to the set, and selecting a neighboring cell with the minimum ping-pong switching rate from the target set as a target cell of the current switching.

According to the IUSHA (Improving UDN link Stability based 5G Handover Algorithm) cell switching method for Improving the UDN connection Stability, firstly, the offset of a signal level relative to transmission power is analyzed according to different cell equipment types under a UDN framework. And establishing a matching curve of the specific offset parameter according to the adjacent cell drop rate index. And evaluating the average minimum stay time of the handover of each cell, inclining the system resources towards the cell with longer stay time, filtering out the cells which are not suitable for the access of the current mobile terminal through a speed threshold, and finally establishing a target neighbor cell list participating in the handover. And judging ping-pong switching states affecting the connection stability of the UDN, and selecting an optimal cell from the target neighbor cell list as a final target service cell for switching, thereby further optimizing the use perception of a user.

Preferably, the step one comprises the following: a level offset mode is adopted to replace the traditional absolute value of signal level, and the signal level difference of different types of equipment in the UDN network is eliminated; for each cell in the CLLN, the offset of the signal level at the current time and the cell transmission power is calculated

dRP_N＝{dtRP_s，dtRP₁，…，dtRP_n}＝{RSRP_s-Rx_s，RSRP₁-Rx₁，…，RSRP_n-Rx_n}。

Preferably, the step two comprises the following steps:

step 2-1: setting a basic hysteresis parameter Hysm and a specific offset coefficient CIO_ft；

Step 2-2: cell of main service Cell_sBy a specific offset O_csClearing; for the neighborhood CLLn ═ Cell₁，…，Cell_nEach Cell in_iCalculating the basic offset COB_i＝exp((-1)*Drp_i) Where exp (·) is a natural exponential function; calculating neighbor specific offset CIO_i＝CIO_ft*COB_i＝CIO_ft*exp((-1)*Drp_i)。

Preferably, the third step includes the following steps:

step 3-1: setting a minimum switch residence time MTS and a residence time threshold theta_MTSHysteresis threshold θ_HysCoefficient of retardation σ_Hys；

Step 3-2: for CLLn ═ Cell₁，…，Cell_nEach Cell in_iIf Case1 condition Mts is satisfied_i≥θ_MTSMTS, calculate cell hysteresis Hys _ IUSHA_iHysm; if Case2 condition is satisfied, MTS ≦ Mts_i≤θ_MTSMTS, first calculate the hysteresis slope X_k＝(1-θ_Hys)*Hysm/(θ_MTS-1) MTS, calculating the hysteresis intercept

Y_b＝Hysm-X_k*θ_MTS*MTS＝Hysm-(1-θ_Hys)*Hysm/(θ_MTS-1)*MTS*θ_MTS*MTS＝Hysm-(1-θ_Hys)*Hysm*θ_MTS/(θ_MTS-1)＝(θ_MTS*θ_Hys-1)*Hysm/(θ_MTS-1) then calculating

Mts if Case3 condition is satisfied_i< MTS, calculation

Preferably, the fourth step includes the following steps:

step 4-1: a3 event M_n+O_fn+O_cn-Hys＞M_s+O_fs+O_cs+ Off indicates that the signal quality of the neighbor cell is better than that of the serving cell, triggering handover; otherwise, a3 satisfies the away state;

wherein M is_nAs a result of measurement of a neighboring cell, O_fnFor frequency-specific offsets, O, on frequencies of adjacent cells_cnA specific offset for a neighboring cell, if there is no such configuration, set to 0;

M_sas a result of measurement of the serving cell, O_fsFor frequency specific offsets on the serving cell frequency, O_csHys is the hysteresis of the event and Off is a cheap parameter for the event for a certain offset of the serving cell;

step 4-2: for Clln ═ Cell₁，…，Cell_nEvery neighboring Cell in the Cell_iSwitch A3 to function Hdf_i＝(M_i+O_fi+O_ci-Hys_i)-(M_s+O_fs+O_cs) Modified to Hdf_i＝dtRP_i+CIO_i-Hys_IUSHA_i-dtRP_s；

Step 4-3: will satisfy Case5 condition Hdf_iIncorporation of neighbor cells > Off into candidate set CLL_cndIn (1).

Preferably, the step five comprises the following steps:

step 5-1: setting a current terminal moving speed Vct for CLLn { Cell₁，…，Cell_nEach Cell in_iSelecting the condition that Vct is greater than Vap and satisfies Case4_iSet of (CSO) { Cell ═ Cell_j，Cell_j+1…，Cell_j+k-1}, calculating target set TAO ═ CLL_cnd-CSO；

Step 5-2: and selecting the adjacent cell with the minimum ping-pong handover rate from the TAO as the target cell of the handover.

Therefore, the invention has the following beneficial effects: cell specific offset compensation can be performed according to the cell disconnection rate; according to the minimum residence time of the cell during switching, dynamically matching out corresponding system delay; screening out a base station list suitable for participating in switching according to the terminal moving rate, and finally obtaining a target cell set; on the basis, through the analysis of the historical ping-pong switching rate, the target adjacent cell with the optimal ping-pong effect is selected for switching, so that the stability of the UDN switching connection is improved, and the user perception is further optimized.

Drawings

FIG. 1 is a flow chart of the present invention.

Figure 2 is a comparison diagram of the handover target serving cell in the off and on states of the module of the present invention.

Fig. 3 is a comparison graph of the mean values of candidate neighbor levels in the off and on states of the module of the present invention.

Fig. 4 is a comparison graph of the mean load values of the candidate neighbors of the module of the invention in the off and on states.

FIG. 5 is a comparison graph of switching hysteresis for the closed and open states of the module of the present invention.

Fig. 6 is a graph comparing the ping-pong effect of the module of the present invention in the closed and open states.

Detailed Description

The invention is further described with reference to the following detailed description and accompanying drawings.

Example 1:

as shown in fig. 1, the present embodiment provides a 5G Cell handover method for improving UDN connection stability, which includes N +1 Cell CLLN { Cell_s}∪CLLn＝{Cell_s，Cell₁，…，Cell_n}，The system is composed of macro cells, micro cells, home base stations, relay stations and the like; wherein, Cell_sFor the primary serving Cell of the current mobile terminal, CLLn ═ Cell₁，…，Cell_nThe adjacent area is defined as the position of the adjacent area; cell signal level { RSRP_s，RSRP₁，…，RSRP_n}, transmit power { Rx_s，Rx₁，…，Rx_n}, dropped-line rate { Drp₁，Drp₂，…，Drp_nMean residence time for cell handover { Mts }₁，Mts₂，…，Mts_nAnd the maximum terminal speed { Vap suitable for accessing of each base station₁，Vap₂，…，Vap_n}, ping-pong switching rate { Pph₁，Pph₂，…，Pph_n}；

Step 1: accounting for signal level offset;

because the signal level difference of different types of equipment in the UDN is large, the invention adopts a level offset mode to replace the traditional absolute value of the signal level; for each cell in the CLLN, an offset dRP of the signal level at the current time to the cell transmit power is calculated_N＝{dtRP_s，dtRP₁，…，dtRP_n}＝{RSRP_s-Rx_s，RSRP₁-Rx₁，…，RSRP_n-Rx_n}；

Step 2: analyzing the disconnection rate;

step 2-1: setting a basic hysteresis parameter Hysm and a specific offset coefficient CIO_ft；

Step 2-2: cell of main service Cell_sBy a specific offset O_csClearing; for the neighborhood CLLn ═ Cell₁，…，Cell_nEach Cell in_iCalculating the basic offset COB_i＝exp((-1)*Drp_i) Where exp (·) is a natural exponential function; calculating neighbor specific offset CIO_i＝CIO_ft*COB_i＝CIO_ft*exp((-1)*Drp_i)；

And step 3: system lag synthesis

Step 3-1: setting minimum MTS and theta threshold of stay time_MTSHysteresis thresholdθ_HysCoefficient of retardation σ_Hys；

Step 3-2: for CLLn ═ Cell₁，…，Cell_nEach Cell in_iIf Case1 condition Mts is satisfied_i≥θ_MTSMTS, calculate cell hysteresis Hys _ IUSHA_iHysm; if Case2 condition is satisfied, MTS ≦ Mts_i≤θ_MTSMTS, first calculate the hysteresis slope X_k＝(1-θ_Hys)*Hysm/(θ_MTS-1) MTS, calculating the hysteresis intercept

Y_b＝Hysm-X_k*θ_MTS*MTS＝Hysm-(1-θ_Hys)*Hysm/(θ_MTS-1)*MTS*θ_MTS*MTS＝Hysm-(1-θ_Hys)*Hysm*θ_MTS/(θ_MTS-1)＝(θ_MTS*θ_Hys-1)*Hysm/(θ_MTS-1) then calculating

Mts if Case3 condition is satisfied_i< MTS, calculation

And 4, step 4: a modified a3 handover decision;

step 4-1: a3 event M_n+O_fn+O_cn-Hys＞M_s+O_fs+O_cs+ Off indicates that the signal quality of the neighbor cell is better than the signal quality of the serving cell, triggering a handover. Otherwise, a3 satisfies the away state. Wherein M is_nAs a result of measurement of a neighboring cell, O_fnFor frequency-specific offsets, O, on frequencies of adjacent cells_cnA particular offset for a neighboring cell, if there is no such configuration, is set to 0. M_sAs a result of measurement of the serving cell, O_fsFor frequency specific offsets on the serving cell frequency, O_csHys is the hysteresis of the event and Off is a cheap parameter for the event for a certain offset of the serving cell;

step 4-2: for Clln ═ Cell₁，…，Cell_nEach neighbor Cell in the Cell_iSwitch A3 to function Hdf_i＝(M_i+O_fi+O_ci-Hys_i)-(M_s+O_fs+O_cB) Modified to Hdf_i＝dtRP_i+CIO_i-Hys_IUSHA_i-dtRP_s；

Step 4-3: will satisfy Case5 condition Hdf_iIncorporation of neighbor cells > Off into candidate set CLL_cndPerforming the following steps;

and 5: optimizing ping-pong handover;

step 5-1: setting a current terminal moving speed Vct for CLLn { Cell₁，…，Cell_nEach Cell in_iSelecting the condition that Vct is greater than Vap and satisfies Case4_iSet of (CSO) { Cell ═ Cell_j，Cell_j+1…，Cell_j+k-1}, calculating target set TAO ═ CLL_cnd-CSO；

Step 5-2: and selecting the adjacent cell with the minimum ping-pong handover rate from the TAO as the target cell of the handover.

Example 2:

in this embodiment, the present invention is specifically described by taking an example where N is 6, N is 7, and terminal speed Vct is 30km/h, and the case of 5G cell-related parameters is shown in table 1:

table 1

The basic data is shown in table 2:

table 2

Serial number	Item	Data of
			1	Basal hysteresis Hysm (dBm)	3
2	Specific offset coefficient CIO ft	3
			3	Switching minimum dwell time MTS (ms)	320
4	Dwell time threshold θMTS	1.2
			5	Hysteresis threshold thetaHys	1.2
6	Retardation coefficient sigmaHys	1.1
			7	A3 event cheap parameter Off	0

The example describes a 5G cell handover method for improving UDN connection stability, including: checking signal level offset, analyzing the disconnection rate, synthesizing system delay, judging corrected A3 switching, optimizing ping-pong switching and the like;

step 1: accounting for signal level offset;

calculating dRP an offset between the signal level at the current time and the cell transmit power_N＝{dtRP_s，dtRP₁，…，dtRP_n}＝{RSRP_s-Rx_s，RSRP₁-Rx₁，…，RSRP_n-Rx_n}＝{-161，-152，-158，-146，-158，-164，-154}dB；

Step 2: analyzing the disconnection rate;

cell of main service Cell_sBy a specific offset O_csClearing; calculating neighbor specific offset CIO_i＝CIO_ft*COB_j＝CIO_ft*exp((-1)*Drp_i)＝{2.41，2.14，2.51，2.31，2.05，1.97}dBm；

And step 3: systematic hysteretic synthesis

{Cell₅Satisfy Case1 condition Mts_i≥θ_MTSMTS, calculate cell hysteresis Hys _ IUSHA₅＝Hysm＝3dBm；

{Cell₃，Cell₆Satisfy Case2 condition MTS ≦ Mts_i≤θ_MTSMTS, first calculate the hysteresis slope X_k＝(1-θ_Hys)*Hysm/(θ_MTS-1) MTS-0.00938, calculating the hysteresis intercept Y_b＝Hysm-X_k*θ_MTS*MTS＝Hysm-(1-θ_Hys)*Hysm/(θ_MTS-1)*MTS*θ_MTS*MTS＝Hysm-(1-θ_Hys)*Hysm*θ_MTS/(θ_MTS-1)＝(θ_MTS*θ_Hys-1)*Hysm/(θ_MTS-1) 6.6, then calculating

{Cell₁，Cell₂，Cell₄Satisfy Case3 condition Mts_i< MTS, calculation

Synthesis of Total hysteresis Hys _ IUSHA_i＝{3.98，4.32，3.51，4.29，3，3.55}dBm；

And 4, step 4: a modified a3 handover decision;

satisfy the requirement of

Conditional neighbor candidate set CLL_cnd＝{Cell₁，Cell₂，Cell₃，Cell₄，Cell₆}；

And 5: optimizing ping-pong handover;

selecting a condition that Vct is 30 > Vap and satisfies Case4_iThe set CSO is NULL, the target set TAO is CLL_cnd-CSO＝CLL_cnd；

The ping-pong switching rate in the TAO set is {0.35, 0.64, 0.77, 0.43, 0.15}, and the neighbor Cell having the smallest ping-pong switching rate of 0.15 is selected₆As the target cell of the handover.

Simulation experiment: MATLAB platform simulation is carried out on the IUSHA method under the two states of opening and closing, the target sampling is carried out for 7 times, and the obtained UDN simulation results under the moving speed of 30km/h are shown in attached figures 2-6 respectively.

The target Cell shown in fig. 2 fails handover at the 4 th sampling when the IUSHA algorithm is turned off, and after the algorithm switch is turned on, the Cell with smaller ping-pong handover effect is selected₄Then smoothly switch to Cell₁；

As for the average value of the neighboring cell level shown in fig. 3, when the IUSHA algorithm is turned off, the a3 event is not measured in a level offset manner, and for a non-macro cell base station, the transmission power is low, which results in that the average value of the neighboring cell level will not become a handover target, thereby raising the level value of the candidate neighboring cell;

as shown in fig. 4, when the IUSHA algorithm is turned on, the average load of the neighboring cells tends to be more suitable for selecting the cells with relatively high load but not difficult to access for handover, so that the utilization rate of the whole system is effectively improved;

as shown in fig. 5, the handover hysteresis is unchanged when the IUSHA algorithm is turned off, and cannot be adaptively adjusted according to the load, level, and service conditions of the neighboring cell;

as shown in the ping-pong effect of fig. 6, after the IUSHA algorithm is turned on, the overall ping-pong rate is much lower than the state value when the algorithm is turned off.

The above embodiments are described in detail for the purpose of further illustrating the present invention and should not be construed as limiting the scope of the present invention, and the skilled engineer can make insubstantial modifications and variations of the present invention based on the above disclosure.

Claims (7)

1. A5G cell switching method for improving the connection stability of UDN is characterized by comprising the following steps:

step one, checking and calculating signal level offset: replacing the absolute value of the signal level by a level offset mode, and calculating the offset of the signal level of each cell at the current moment and the cell transmitting power;

step two, analyzing the disconnection rate: setting a basic hysteresis parameter and a specific offset coefficient, and calculating a basic offset and a specific offset of an adjacent cell according to the call drop rate;

step three, system delay synthesis: setting minimum stay time, a stay time threshold, a hysteresis threshold and a hysteresis coefficient for switching, and distinguishing different conditions to calculate the cell hysteresis;

step four, the corrected A3 switching judgment: the adjacent cells meeting the requirement of the level offset are brought into a candidate set, so that switching is triggered;

step five, optimizing ping-pong switching: and selecting a set meeting the Case4 condition, calculating a target set according to the set, and selecting a neighboring cell with the minimum ping-pong switching rate from the target set as a target cell of the current switching.

2. The method of claim 1, wherein the 5G Cell comprises N-N +1 CLLN-Cell_s}∪CLLn＝{Cell_s，Cell₁，…，Cell_nThe method comprises the following steps of (1) forming a macro cell, a micro cell, a home base station, a relay station and the like;

wherein, Cell_sFor the primary serving Cell of the current mobile terminal, CLLn ═ Cell₁，…，Cell_nThe adjacent area is defined as the position of the adjacent area; cell signal level { RSRP_s，RSRP₁，…，RSRP_n}, transmit power { Rx_s，Rx₁，…，Rx_n}, dropped-line rate { Drp₁，Drp₂，…，Drp_nMean residence time for cell handover { Mts }₁，Mts₂，…，Mts_nAnd the maximum terminal speed { Vap suitable for accessing of each base station₁，Vap₂，…，Vap_n}, ping-pong switching rate { Pph₁，Pph₂，…，Pph_n}。

3. The method of claim 1, wherein the step one comprises the following steps: a level offset mode is adopted to replace the traditional absolute value of signal level, and the signal level difference of different types of equipment in the UDN network is eliminated; for each cell in the CLLN, the offset of the signal level at the current time and the cell transmission power is calculated

dRP_N＝{dtRP_s，dtRP₁，…，dtRP_n}＝{RSRP_s-Rx_s，RSRP₁-Rx₁，…，RSRP_n-Rx_n}。

4. The method according to claim 1, wherein the second step comprises the following steps:

step 2-1: setting a basic hysteresis parameter Hysm and a specific offset coefficient CIO_ft；

Step 2-2: cell of main service Cell_sBy a specific offset O_csClearing; for the neighborhood CLLn ═ Cell₁，…，Cell_nEach Cell in_iCalculating the basic offset COB_i＝exp((-1)*Drp_i) Where exp (·) is a natural exponential function; calculating neighbor specific offset CIO_i＝CIO_ft*COB_i＝CIO_ft*exp((-1)*Drp_i)。

5. The method of claim 1, wherein the step three comprises the following steps:

step 3-1: setting a minimum switch residence time MTS and a residence time threshold theta_MTSHysteresis threshold θ_HysCoefficient of retardation σ_Hys；

Step 3-2: for CLLn ═ Cell₁，…，Cell_nEach Cell in_iIf the Case1 condition Mts is satisfied_i≥θ_MTSMTS, calculate cell hysteresis Hys _ IUSHA_iHysm; if Case2 condition is satisfied, MTS ≦ Mts_i≤θ_MTSMTS, first calculate the hysteresis slope X_k＝(1-θ_Hys)*Hysm/(θ_MTS-1) MTS, calculating the hysteresis intercept

Y_b＝Hysm-X_k*θ_MTS*MTS＝H_ysm-(1-θ_Hys)*Hysm/(θ_MTS-1)*MTS*θ_MTS*MTS＝Hysm-(1-θ_Hys)*Hysm*θ_MTS/(θ_MTS-1)＝(θ_MTS*θ_Hys-1)*Hysm/(θ_MTS-1) then calculating

If the Case3 condition Mts is satisfied_i< MTS, calculation

6. The method of claim 1, wherein the step four comprises the following steps:

step 4-1: a3 event M_n+O_fn+O_cn-Hys＞M_s+O_fs+O_cs+ Off indicates that the signal quality of the neighbor cell is better than that of the serving cell, andtriggering the switching; otherwise, a3 satisfies the away state;

wherein M is_nAs a result of measurement of a neighboring cell, O_fnFor frequency-specific offsets, O, on frequencies of adjacent cells_cnA specific offset for a neighboring cell, if there is no such configuration, set to 0;

M_sas a result of measurement of the serving cell, O_fsFor frequency specific offsets on the serving cell frequency, O_csHys is the hysteresis of the event and Off is a cheap parameter for the event for a certain offset of the serving cell;

step 4-2: for Clln ═ Cell₁，…，Cell_nEvery neighboring Cell in the Cell_iSwitch A3 to function Hdf_i＝(M_i+O_fi+O_ci-Hys_i)-(M_s+O_fs+O_cs) Modified to Hdf_i＝dtRP_i+CIO_i-Hys_IUSHA_i-dtRP_s；

Step 4-3: will satisfy Case5 condition Hdf_iIncorporation of neighbor cells > Off into candidate set CLL_cndIn (1).

7. The method of claim 1, wherein the step five comprises the following steps:

step 5-1: setting a current terminal moving speed Vct for CLLn { Cell₁，…，Cell_nEach Cell in_iSelecting the condition that Vct is greater than Vap and satisfies Case4_iSet of (CSO) { Cell ═ Cell_j，Cell_j+1…，Cell_j+k-1}, calculating target set TAO ═ CLL_cnd-CSO；

Step 5-2: and selecting the adjacent cell with the minimum ping-pong handover rate from the TAO as the target cell of the handover.

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