TWI603637B - Mobile communication system and handover method thereof - Google Patents

Description

Mobile communication system and its handover method

The present invention relates to a mobile communication system and a handover method thereof, and more particularly to a mobile communication system capable of changing a user's equipment in advance or delayed, and a handover method thereof.

In the mobile communication system, the user equipment (such as a mobile communication device) is connected to the communication network through a connection with the base station, wherein the user equipment determines the current connection according to the signal strength between each base station and the user equipment. In the base station of the line, in general, the mobile communication system will preferentially connect the user equipment to the base station with the strongest signal strength to maintain good transmission rate and communication quality. Therefore, when the user equipment is at more than two bases In the overlapping area of the signal range, the mobile communication system will switch the user equipment to the base station with strong signal. However, since only the signal strength is considered regardless of the load status of each base station, the same overlap is often caused. The user equipment in the area is preferentially connected to the same base station, and even the user equipment is changed from the base station with low load status to the base station with high load status, resulting in increased load and data processing of the base station. Congestion, and the user equipment connected to the base station with strong signal can not get better service quality.

The main purpose of the present invention is to determine whether the user equipment changes hands according to the load state of the base station and the receiving strength of the signal, so as to avoid the overload of the specific base station and affect the communication quality.

A mobile communication system of the present invention includes a plurality of base stations (BSs), a user equipment (User Equipment, UE), a classification module, and a hand change module, each of which has a signal Coverage area and a load rate, one of the base stations is the original base station, and one of the base stations is the target base station, and the signal coverage of the original base station partially overlaps with the coverage of the signal of the target base station. Forming a signal overlap area, the user equipment is located in the signal overlap area and is connected to the original base station, and the user equipment and the original base station have an original signal receiving strength, the user equipment and the target base Having a target signal reception strength between the stations, the classification module receives the load rate of the original base station and the load rate of the target base station, and the classification module according to the load rate of the original base station and the target base The load rate of the station is classified to obtain a load state of one of the original base stations and a load state of the target base station, and the handoff module receives the original The load state of the base station, the load state of the target base station, the original signal receiving strength, and the target signal receiving strength. When the user equipment is in a moving state, the handoff module is configured according to the original base station. The load status, the load status of the target base station, the original signal reception strength, and the target signal reception strength determine whether the user equipment hands over to the target base station.

The handoff module of the present invention determines whether the user equipment in the mobile state is changed according to the load state of the original base station, the load state of the target base station, the original signal receiving strength, and the target signal receiving strength. Handling the target device to the target base station, causing the user equipment to be hand-shifted by the high-loaded original base station to the low-load target base station to reduce the load of the original base station in advance, or to make the user equipment low The original base station of the load delays the handover to the target station of the high load to delay the load of the target base station, thereby avoiding the overload of the specific base station of the mobile communication system.

Please refer to FIG. 1 , which is a mobile device system 100 including a user equipment 110 (User Equipment, UE), a plurality of base stations 120 (Base Station, BS), and an action management entity 130. (Mobility Management Entity, MME) and a network 140. The user device 110 is an electronic mobile device with a wireless network connection function, such as a smart phone, a tablet or a notebook computer. The user device 110 is wireless. The network is connected to the network 140 via the base station 120 and the mobile management entity 130 to use the service of the network. In this embodiment, the action management is implemented. The body 130 has a Self-Organizing Network (SON), which is an Internet or a communication network, but the present invention is not limited thereto.

Referring to FIG. 1 , each of the base stations 120 has a signal coverage range and a load rate. The signal covers an area covered by the signals sent by the base stations 120. The user equipment 110 needs to be located at the base station. The signal range of 120 can be connected to the base station 120. The load ratio of each base station 120 is a ratio between the current load of each base station 120 and its rated load, which is used to indicate each. In the current load situation of the base station 120, in the embodiment, the load rate is calculated according to a physical resource block (PRB) of each base station 120, and the calculation formula of the load rate is: Where ρ _i is the load rate of each base station 120, PRB _used is the physical resource block _used by each base station 120, and PRB _total is all available physical resource blocks of each base station 120.

Referring to FIG. 1 again, one of the base stations 120 of the base stations 120 is the base station 120 currently connected to the user equipment 110, and is referred to as the original base station 120A. One of the base stations 120 is the same. The base station 120, which the user equipment 110 can change hands, is referred to as the target base station 120B. The signal coverage area SA of the original base station 120A partially overlaps with the signal coverage area SB of the target base station 120B to form a signal. In the overlapping area, the user equipment 110 is located in the signal overlap area and is connected to the original base station 120A. As described above, the user equipment 110 needs to be located in the signal coverage range of the base station 120 to be associated with the base station. 120 is connected, so the user equipment 110 is selectively connected to the original base station 120A or the target base station 120B.

The user equipment 110 has a signal receiving strength between the base station 120 and the base station 120. Therefore, the user equipment 110 and the original base station 120A have an original signal receiving strength. The user equipment 110 Having a target signal receiving strength with the target base station 120B, in the embodiment, the signal receiving strength between the user equipment 110 and each of the base stations 120 is the user equipment 110 for each of the base stations. Reference signal receiving power (RSRP) of 120, the original signal receiving strength is the reference signal receiving power of the user equipment 110 for the original base station 120A, and the target signal receiving strength is the user equipment 110 The reference signal receiving power of the target base station 120B is used to indicate the connection strength between the user equipment 110 and the original base station 120A and the target base station 120B.

Referring to FIG. 2, the mobile communication system 100 includes a classification module 150. The classification module 150 is disposed in a self-organizing network (SON) of the action management entity 130, and the classification module 150 receives each of the base stations. The load rate of 120, wherein the classification module 150 performs state classification according to the load rate of each base station 120 to obtain a load status of each of the base stations 120, and broadcasts the load status of each base station 120. (Broadcast) to each of the base stations 120, so that each of the base stations 120 can know the load status of the other base stations 120, and then determine whether to switch the user equipment 110 connected to itself to another base. Taiwan 120.

The classification module 150 receives the load rate of the original base station 120A and the load rate of the target base station 120B, and performs the load rate of the original base station 120A and the load rate of the target base station 120A. The classification module is configured to obtain the load state of the original base station 120A and the load state of the target base station 120B. In this embodiment, the classification module 150 determines each of the first threshold value and a second threshold value. The load status of the base station 120 includes the load status of the original base station 120A and the target base station 120B, wherein when the load rate of the original base station 120A or the target base station 120B is greater than the first threshold The classification module 150 classifies the original base station 120A or the target base station 120B into a high load state. When the load rate of the original base station 120A or the target base station 120B is less than the second threshold, the classification is performed. The module 150 classifies the original base station 120A or the target base station 120B into a low load state, when the load ratio of the original base station 120A or the target base station 120B is between the first threshold value and the second When the value is between the thresholds, the classification module 150 classifies the original base station 120A or the target base station 120B into a medium load state, wherein the first threshold is greater than the second threshold, in this embodiment, The first critical value is 70% and the second critical value is 30%.

Referring to FIG. 2, in the embodiment, the mobile communication system 100 further includes a measurement module 160. The measurement module 160 is composed of a plurality of measurement units 161, and each of the measurement units 161 is separately set. Each of the measurement units 161 of the measurement module 160 is configured to calculate the load rate of each of the base stations 120 and transmit the load rate to the action management entity 130. In the module 150, the classification module 150 causes the base stations 120 to classify the base stations 120.

Referring to FIG. 2, the mobile communication system 100 includes a hand change module 170. In this embodiment, the hand change module 170 is composed of a plurality of hand change units 171, and each of the hand change units 171 is disposed in each In the base station 120, each of the handoff units 171 of the handoff module 170 is configured to receive the load status and signal receiving strength of each of the base stations 120, including the load status of the original base station 120A and the original signal. Receive strength, the load status of the target base station 120B, and the target signal reception strength.

Referring to FIG. 2, in the embodiment, the mobile communication system 100 further includes an unloading module 180. The unloading module 180 is disposed in a self-organizing network (SON) of the action management entity 130. The group 180 calculates an unloading parameter of the base stations 120 and an unloading amount of each of the base stations 120 according to the load rate of the base station 120 and the load status, and the unloading parameters of the base stations 120 are used to determine each Whether the base station 120 needs to be unloaded, the amount of unloading of each base station 120 is used to indicate the amount of load that each base station 120 needs to be unloaded at least.

In this embodiment, the calculation formula of the unloading parameter is: among them, For this uninstallation parameter, For the load rate of each base station 120, For the number of base stations 120, For the i- th base station 120, the calculation formula of the unloading amount is: among them, For the amount of unloading of each of the base stations 120, For the load rate of each base station 120, For the first critical value, Is the second critical value.

Please refer to FIG. 3 , which is a mobile phone system replacement method 200 for the mobile communication system 100 . Referring to FIG. 2 and FIG. 3 , in step 210 , the measurement module 160 The measuring unit 161 calculates the load rate according to the above: The load rate of each of the base stations 120 is obtained. After the load rate calculation of each of the base stations 120 is completed, each of the measurement units 161 of the measurement module 160 transmits the load rate of each of the base stations 120 to The classification module 150 of the action management entity 130.

Referring to FIGS. 2 and 3, in step 220, the classification module 150 of the action management entity 130 receives the load rate transmitted by each of the base stations 120, and then, in step 230, the action management entity 130 The classification module 150 determines whether each of the base stations 120 performs unloading, wherein the classification module 150 calculates a formula according to the unloading parameters: Calculating the unloading parameter, and determining whether each of the base stations 120 performs unloading according to the unloading parameter. When the unloading parameter is equal to 1, the classification module 150 determines that each of the base stations 120 does not need to be unloaded. When the unloading parameter is less than 1, The classification module 150 determines that each of the base stations 120 is to be unloaded.

Referring to FIGS. 2 and 3, when the classification module 150 determines that each of the base stations 120 is to be unloaded, step 240 is performed, and the classification module 150 classifies the base stations 120 according to the load rate to obtain the respective The load state of the base station 120, wherein the classification module 150 determines the load state of each base station 120 by using the first threshold value and the second threshold value, and classifies each base station 120 into a high load. State, medium load state, or low load state.

Referring to FIG. 3, in step 250, the unloading module 180 calculates the unloading amount of each of the base stations 120. In this embodiment, the unloading module 180 according to the loading rate of each of the base stations 120 and the The load state calculates the unloading amount of each of the base stations 120, and the unloading amount of each of the base stations 120 is unicasted to each of the base stations 120. The unloading amount is calculated as: .

Referring to Figures 1, 2 and 3, in step 260, the handoff module 170 determines whether the user equipment 110 is located in the signal overlap area, that is, whether the user equipment 110 has received more than two. The base station 120 signals to determine whether the user equipment 110 is located in the signal overlap area. When the user equipment 110 is located in the signal overlap area, proceed to step 270, the hand change module 170 selects the original base station 120A. The base station 120 is the target base station 120B. In the embodiment, when the signal overlap area includes two or more base stations 120, the handoff module 170 selects the base station with the strongest signal receiving strength as the base station. Target base station 120B.

Referring to FIG. 2 and FIG. 3, in step 280, the handoff module 170 determines whether the user equipment 110 moves according to the target signal receiving strength between the user equipment 110 and the target base station 120B. When the target signal receiving strength changes, the handoff module 170 determines that the user equipment 110 is in a moving state, and when the target signal receiving strength remains unchanged, the handoff module 170 determines that the user equipment 110 is in a stationary state. .

Referring to the first, second, and third embodiments, when the handoff module 170 determines that the user equipment 110 is in a moving state, step 290 is performed, and the handoff module 170 is based on the load state of the original base station 120A, the target. The load state of the base station 120B, the original signal receiving strength, and the target signal receiving strength determine whether the user equipment 110 is handed over by the original base station 120A to the target base station 120B. In this embodiment, the hand is changed. The module 170 determines, according to a judgment formula, whether the user equipment 110 hands over to the target base station 120B. The judgment formula is: among them, Receive strength for the target signal, Receive strength for the original signal, For a standard threshold, Receive a strength threshold for a signal, For a hand change parameter, For the logical AND operator, the standard threshold value and the received threshold value of the signal are constant values. The judgment formula represents that the target signal receiving intensity is greater than the original signal receiving intensity. When the target signal receiving strength is greater than the signal receiving strength threshold, the handoff module 170 will handoff the user equipment 110 from the original base station 120A to the target base station 120B. In this embodiment, the standard threshold is set to 5, the signal receiving strength threshold is set to 55, and the handoff module 170 calculates the handoff according to the load state of the original base station 120A and the target base station 120B. Parameters to dynamically adjust the handoff parameters.

Referring to FIG. 4, it is a flowchart of step 290, which is used to determine the value of the handoff parameter according to the load state of the original base station 120A and the target base station 120B. Wherein, when the original base station 120A is in a high load state and the target base station 120B is in a low load state, the calculation formula of the handoff parameter is: For the load rate of the original base station 120A, The load rate of the target base station 120B. Therefore, when the original base station 120A is in a high load state and the target base station 120B is in a low load state, the handoff parameter is calculated to be less than 1, and then nested. Judgment After that, you can see that because the handoff parameter is less than 1, The value is also smaller than the original Therefore, the handoff module 170 can advance the user equipment 110 to the target base station 120B to mitigate the load rate of the original base station 120A.

Referring to Figures 1 and 4, when the original base station 120A is in a low load state and the target base station 120B is in a high load state, the handoff parameter calculation formula is: When the original base station 120A is in a low load state and the target base station 120B is in a high load state, the handoff parameter is calculated to be greater than 1, and then nested into the judgment formula. After that, you can see that since the handoff parameter is greater than 1, The value is also greater than the original The value of the handoff module 170 can delay the user equipment 110 to the target base station 120B to delay increasing the load rate of the target base station 120B.

Referring to FIGS. 1 and 4, when the load status of the original base station 120A and the target base station 120B does not belong to the above situation, that is, when both the original base station 120A and the target base station 120B are in a high load state, Or when the original base station 120A and the target base station 120B are in a medium load state, or when the original base station 120A and the target base station 120B are in a low load state, or the original base station 120A is in a high load. When the target base station 120B is in the medium load state, or the original base station 120A is in the medium load state and the target base station 120B is in the high load state or the low load state, the handoff parameter is 1 when the state or the low load state is in the medium load state. Make The value is equal to the original The value, therefore, the user equipment 110 will not be handed over to the target base station 120B by the original base station 120A in advance or delayed.

Referring to FIGS. 2 and 3, when the handoff module 170 determines that the user equipment 110 is in a stationary state, step 290' is performed, and the handoff module 170 is based on the load state of the original base station 120A and the target. The load status of the base station 120B determines whether the user equipment 110 has been handed over by the original base station 120A to the target base station 120B.

Referring to FIG. 5, it is a flowchart of step 290', which is used to determine whether to change hands according to the load state of the original base station 120A and the target base station 120B, wherein the original base station 120A is under high load. The handoff module 170 enables the use when the target base station 120B is in the medium load state or the low load state, or when the original base station 120A is in the medium load state and the target base station 120B is in the low load state. The device 110 is handed over by the original base station 120A to the target base station 120B to mitigate the load rate of the original base station 120A. Conversely, when both the original base station 120A and the target base station 120B are in a high load state, or when the original base station 120A is in a medium load state and the target base station 120B is in a high load state or a medium load state, or When the original base station 120A is in a low load state, the handoff module 170 does not perform the step of changing hands, and the user equipment 110 is still connected to the original base station 120A to avoid adding the target base station 120B. The load rate.

Please refer to FIGS. 6 and 7 , which are the measured data of the mobile communication system and the mobile communication system of the present invention in the moving state of the user equipment. In the actual test, the mobile communication system has a first base station and a second base station, and the user equipment is located in the signal overlap area of the first base station and the second base station and connected to the first base station, in this actual test The user equipment is carried by a self-propelled vehicle and moves between the first base station and the second base station at a speed of 3 km/hour to observe the load state of the first base station, The load status of the second base station and the change of the handover time of the user equipment, and the time of the early handover and the delay of the handover are compared by the residence time of the user equipment, wherein the residence time The time is the time difference between the point in time at which the user equipment is connected to the first base station and the point in time when the user equipment is connected to the second base station.

Please refer to FIG. 6 for the change of the load state of the first base station and the second base station within 20 minutes. Please refer to FIG. 7 , which is a change of the residence time of the user equipment, as shown in FIGS. 6 and 7 At the 2.5th, 5th, 8.5th, 13th, 18.5th and 20th minutes, the first base station is in a high load state and the second base station is in a low load state, and the residence time of the user equipment is the shortest, that is, the present The hand-switching module of the invention can ensure that the user equipment can be handed over to the second base station in advance when the first base station is in a high load state and the second base station is in a low load state. At 10.5, 12, 14.5, and 19.5 minutes, the first base station is in a low load state and the second base station is in a high load state, and the user equipment has the longest residence time, that is, the hand change mode of the present invention When the first base station is in a low load state and the second base station is in a high load state, the user equipment can be delayed to be handed over to the second base station, and the remaining time is earlier than the second base station. Change of residence time and delay Handoff between residence time, indicating that the user equipment normally change hands, there is no advance or delay handover.

Please refer to Figure 8, which is the average residence time of the user equipment. As can be seen from the figure, the average residence time of the early handover is about 47% less than the average residence time of the normal handover, and the average residence time of the delayed handover. The average residence time of the normal hand change is about 49%. Therefore, the hand change module 170 of the present invention can make the user equipment achieve the purpose of changing hands or delaying the hand change.

Please refer to FIG. 9 and FIG. 10 , which are the measured data of the mobile communication system and the mobile communication system of the present invention in the static state of the user equipment. In the actual test, the user equipment is still. The signal is overlapped with the signal overlap area of the first base station and the second base station to observe that the user equipment changes hands between the first base station and the second base station.

Please refer to FIG. 9 , which is a change of the load status of the first base station and the second base station. Referring to FIG. 10 , the service base station of the user equipment is used, and the service base station is the user. The base station currently connected to the device, as shown in Figures 9 and 10, initially, the user equipment is connected to the first base station, and at the second minute, the user equipment is in the middle of the medium load state. The base station hands over to the second base station in a low load state. At the 2.5th minute, the user equipment is handed over by the second base station in the medium load state to the first base station in the low load state. At 7.5 minutes, the user equipment is handed over from the first base station in the medium load state to the second base station in the low load state. At 9.5 minutes, the user equipment is in the second base station in a high load state. The first base station changing hands to the medium load state, at 10.5 minutes, the user equipment is changed from the first base station in the high load state to the second base station in the medium load state, at 12.5 minutes, The user equipment is second by the high load state The first base station is changed to the first base station in the medium load state, and the user equipment is changed from the first base station in the high load state to the second base station in the medium load state at 14.5 minutes, at 15 In the minute, the user equipment is switched from the second base station in the high load state to the first base station in the low load state. At 16 minutes, the user equipment is changed by the first base station in the medium load state. The second base station in the hand-to-low load state, the user equipment is handed over by the second base station in the medium load state to the first base station in the low load state at 17.5 minutes, at 18 minutes, The user equipment is changed from the first base station in the high load state to the second base station in the low load state, and it can be seen that the handoff module of the present invention can be used when the user equipment is in a stationary state. The heavily loaded service base station hands over to the lightly loaded base station to reduce the load on the service base station and improve the overall service quality.

The scope of the present invention is defined by the scope of the appended claims, and any changes and modifications made by those skilled in the art without departing from the spirit and scope of the invention are within the scope of the present invention. .

100 Mobile Communication System 110 User Equipment 120 Base Station 120A Original Base Station 120B Target Base Station 130 Mobile Management Entity 140 Network 150 Classification Module 160 Measurement Module 161 Measurement Unit 170 Handoff Module 171 Handoff Unit 180 Unloading Module SA signal coverage SB signal coverage 200 mobile communication system handover method 210 measurement module calculation base Load rate 220 Classification module receiving base station load rate 230 Classification module determines whether the base station performs unloading 240 Classification module performs base station status classification 250 Unloading module calculates base station unloading amount 260 Classification module determines user equipment Whether it is located in the signal overlap area 270 Change the module to select the target base station 280 Change the module to determine whether the user equipment moves 290. The hand change module determines whether the user equipment changes hands 290' according to the load status of the base station and the received strength of the signal. The hand module determines whether the user equipment changes hands according to the load status of the base station.

Figure 1 is a schematic illustration of a mobile communication system in accordance with an embodiment of the present invention.

2 is a schematic diagram of a sorting module, a measuring module, a hand changing module and an unloading module according to an embodiment of the invention.

Figure 3 is a flow chart showing a method of handing over a mobile communication system in accordance with an embodiment of the present invention.

Figure 4 is a flow chart showing the determination of a hand change parameter in accordance with an embodiment of the present invention.

Figure 5 is a flow chart showing the handover of a user equipment according to an embodiment of the present invention.

Figure 6: Load state change diagram of the base station.

Figure 7: Diagram of the change in residence time of user equipment.

Figure 8: Analysis of the average residence time of user equipment.

Figure 9: Load state change diagram of the base station.

Figure 10: Schematic diagram of the service base station of the user equipment.

200 mobile communication system handover method 210 measurement module calculation base station load rate 220 classification module receiving base station load rate 230 classification module to determine whether the base station is uninstalled 240 classification module for base station status classification 250 uninstall The module calculates the unloading amount of the base station. The classification module determines whether the user equipment is located in the signal overlap area. 270 The hand change module selects the target base station. 280 The hand change module determines whether the user equipment moves 290. The hand change module is based on the base station. The load status and the signal receiving strength determine whether the user equipment changes hands 290'. The hand change module determines whether the user equipment changes hands according to the load status of the base station.

Claims (19)

A mobile communication system includes: a plurality of base stations (BSs) each having a signal coverage range and a load rate, wherein one of the base stations is a original base station, and one of the base stations is a target base station. The signal coverage of the original base station partially overlaps with the coverage of the signal of the target base station to form a signal overlap area; a user equipment (User Equipment, UE) located in the signal overlap area and the original base a connection between the user equipment and the original base station, the target device receiving strength between the user equipment and the target base station, and a classification module receiving the original base station And the load rate and the load rate of the target base station, the classification module performs state classification according to the load rate of the original base station and the load rate of the target base station to obtain a load state of the original base station and a load state of the target base station, the classification module determining the original base station and the target base by using a first threshold value and a second threshold value The load state of the station, when the load rate of the original base station or the target base station is greater than the first threshold, the classification module classifies the original base station or the target base station into a high load state, when When the load rate of the original base station or the target base station is less than the second threshold, the classification module classifies the original base station or the target base station into a low load state, when the original base station or the target base station When the load ratio is between the first threshold and the second threshold, the classification module classifies the original base station or the target base station into a medium load state, wherein the first threshold is greater than the a second threshold; and a handoff module, receiving the load state of the original base station, the load state of the target base station, the original signal receiving strength, and the target signal receiving strength, when the user equipment is moving In the state, the handoff module determines, according to the load state of the original base station, the load state of the target base station, the original signal receiving strength, and the target signal receiving strength. Whether the user equipment changes hands to the target base station, and the hand change module determines whether the user equipment changes hands to the target base station according to a judgment formula: ( RSRP _tgt - RSRP _src > [ Offset × HF ])&&( RSRP _tgt > Threshold ) where RSRP _{tgt is} the received strength of the target signal, RSRP _{src is} the received strength of the original signal, Offset is a standard threshold, Threshold is the threshold of the received strength of the signal, and HF is a change The hand parameter, && is a logical AND operator, the standard threshold value and the signal receiving strength threshold value are fixed values, and the handoff module calculates the handoff parameter according to the load state of the original base station and the target base station, When the original base station is in a high load state and the target base station is in a low load state, the calculation formula of the handoff parameter is: When the original base station is in a low load state and the target base station is in a high load state, the calculation formula of the handoff parameter is: When the load state of the original base station and the target base station does not belong to the foregoing situation, the handoff parameter is 1, wherein ρ _src is the load rate of the original base station, and ρ _{tgt is} the target base station Load rate. The mobile communication system of claim 1, wherein the original signal receiving strength is a reference signal receiving power (RSRP) of the user equipment for the original base station, and the target signal receiving strength is The user equipment receives power for a reference signal of the target base station. The mobile communication system according to claim 1, wherein the hand change module is based on The target signal receiving strength determines whether the user equipment moves. When the target signal receiving strength changes, the handoff module determines that the user equipment is in a moving state, and when the target signal receiving strength remains unchanged, the switching The hand module determines that the user device is at a standstill. The mobile communication system of claim 3, wherein when the user equipment is in a stationary state, the handoff module determines the load state according to the load state of the original base station and the load state of the target base station. Whether the user equipment changes hands to the target base station. The mobile communication system of claim 4, wherein when the user equipment is in a stationary state and the original base station is in a high load state and the target base station is in a medium load state or a low load state, the exchange The hand module causes the user device to switch hands to the target base station. The mobile communication system of claim 4, wherein when the user equipment is in a stationary state and the original base station is in a medium load state and the target base station is in a low load state, the handoff module enables The user equipment hands over to the target base station. The mobile communication system of claim 1, further comprising an unloading module, wherein the unloading module calculates an unloading amount of each of the base stations according to the load ratio of the base stations and the load state, The calculation formula of the unloading amount is: Where Δ _i is the unloading amount of each base station, ρ _i is the loading rate of each base station, TH _{max is} the first critical value, and TH _{min is} the second critical value. The mobile communication system of claim 7, wherein the classification module calculates an unloading parameter according to the load ratio of each of the base stations, and the calculation formula of the unloading parameter is: Wherein, F _{t is} the unloading parameter, ρ _i is the load rate of each base station, N is the number of the base stations, i is the i- th base station, and the classification module determines each base according to the unloading parameter Whether the station performs unloading, when the unloading parameter is less than 1, the classification module determines that each of the base stations must be unloaded. For example, in the mobile communication system described in claim 1, 7, or 8, wherein the load rate calculation formula is: Where ρ _i is the load rate of each base station, PRB _used is a physical resource block (PRB) _used by each base station, and PRB _total is all available physical resource blocks of each base station. A mobile communication system, the mobile communication system includes a plurality of base stations (BS), a user equipment (User Equipment, UE), a classification module and a hand change module, each of the bases The station has a signal coverage range and a load rate, and one of the base stations is the original base station, and one of the base stations is the target base station, and the signal coverage range of the original base station and the signal coverage range of the target base station Partially overlapping to form a signal overlap area, the user equipment is located in the signal overlap area and connected to the original base station, and the user equipment and the original base station have an original signal receiving strength, the user equipment Having a target signal reception strength with the target base station, wherein the handover method includes: the classification module receives the load rate of the original base station and the load rate of the target base station; The load rate of the original base station and the load rate of the target base station are classified into states to obtain a load state of the original base station and obtain the target base. a load state of the station, the classification module determines the load state of the original base station and the target base station by using a first threshold value and a second threshold value, when the original base station or the target base station When the load ratio is greater than the first threshold, the classification module classifies the original base station or the target base station into a high load state, when the load rate of the original base station or the target base station is less than the second threshold When the classification module classifies the original base station or the target base station into a low load state, when the load ratio of the original base station or the target base station is between the first threshold value and the second threshold value, In the meantime, the classification module classifies the original base station or the target base station into a medium load state, wherein the first threshold value is greater than the second threshold value; the handoff module receives the load of the original base station a state, a load state of the target base station, the original signal reception strength, and the target signal reception strength; and when the user equipment is in a mobile state, the handoff module is configured according to the original base station The load status, the load status of the target base station, the original signal receiving strength, and the target signal receiving strength determine whether the user equipment changes hands to the target base station, and the hand change module determines the user according to a judgment formula. Whether the device is handed over to the target base station, the judgment formula is: ( RSRP _tgt - RSRP _src > [ Offset × HF ]) && ( RSRP _tgt > Threshold ), where RSRP _{tgt is} the target signal reception strength, and RSRP _{src is} the The original signal receiving strength, Offset is a standard threshold, Threshold is a signal receiving strength threshold, HF is a hand-changing parameter, && is a logical AND operator, the standard threshold value and the signal receiving intensity threshold are a certain value, The handoff module calculates the handoff parameter according to the load state of the original base station and the target base station. When the original base station is in a high load state and the target base station is in a low load state, the handoff parameter calculation formula for: When the original base station is in a low load state and the target base station is in a high load state, the handoff parameter is: When the load state of the original base station and the target base station does not belong to the foregoing situation, the handoff parameter is 1, wherein ρ _src is the load rate of the original base station, and ρ _{tgt is} the target base station Load rate. The method for changing the mobile communication system according to claim 10, wherein the original signal receiving strength is a reference signal receiving power (RSRP) of the user equipment for the original base station, the target The signal receiving strength is the reference signal receiving power of the user equipment for the target base station. The method for changing the mobile communication system according to claim 10, wherein the handoff module determines whether the user equipment moves according to the target signal receiving strength, and when the target signal receiving strength changes, the switching The hand module determines that the user equipment is in a moving state, and when the target signal receiving strength remains unchanged, the handoff module determines that the user equipment is in a stationary state. The method for changing the mobile communication system according to claim 12, wherein when the user equipment is in a stationary state, the handoff module is based on the load state of the original base station and the target base station The load status determines whether the user equipment is handed over to the target base station. The handover method of the mobile communication system according to claim 13, wherein the user equipment is in a stationary state, and the original base station is in a high load state and the target base station is in a medium load state or a low load state. The handoff module causes the user equipment to switch hands to the target base station. The method for changing the mobile communication system according to claim 13, wherein the user equipment is in a stationary state, and the original base station is in a medium load state and the target base station When in a low load state, the handoff module causes the user equipment to switch hands to the target base station. The method for changing the mobile communication system according to claim 10, wherein the mobile communication system further comprises an unloading module, wherein the unloading module calculates each of the loading rates according to the base station and the load state. The unloading amount of one of the base stations, wherein the unloading amount is calculated as: Where Δ _i is the unloading amount of each base station, ρ _i is the loading rate of each base station, TH _{max is} the first critical value, and TH _{min is} the second critical value. The method for changing the mobile communication system according to claim 16 of the patent application, further comprising: the classification module determining whether each base station performs unloading, and the classification module calculates an unloading according to the load ratio of each base station The parameter, the calculation formula of the unloading parameter is: Wherein, F _{t is} the unloading parameter, ρ _i is the load rate of each base station, N is the number of the base stations, i is the i- th base station, and the classification module determines each base according to the unloading parameter Whether the station performs unloading, when the unloading parameter is less than 1, the classification module determines that each of the base stations must be unloaded. The method for changing the mobile communication system according to claim 12, wherein the hand change module further determines whether the user equipment is moved according to the target signal receiving strength, and further includes the hand change module to determine the use. Whether the device is in the overlapping area of the signal. The method for changing the mobile communication system as described in claim 10, 16 or 17, wherein the load rate calculation formula is: Where ρ _i is the load rate of each base station, PRB _used is a physical resource block (PRB) _used by each base station, and PRB _total is all available physical resource blocks of each base station.