KR100745899B1 - Handover Method and Base Station Control Device - Google Patents

Abstract

In handover control in a wireless communication system in which wireless communication is performed between a plurality of base stations and a plurality of mobile stations, the handover destination wireless base station secures necessary radio resources in advance before handover, and then executes handover. do. In order to secure radio resources, one or more mobile stations which are already communicating in the radio base station of the handover destination are handed over to another radio base station, thereby securing radio resources of the handover destination base station, and then performing handover.

Base station, mobile station, wireless communication system, handover control

Description

HANDOVER METHOD AND BASE STATION CONTROL DEVICE}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a handover method and a base station control apparatus, and more particularly, to a base station control apparatus for controlling a plurality of base stations and the plurality of base stations, wherein the base station and the mobile station communicate wirelessly. A handover method and a base station control apparatus.

In recent years, the practical use of the Code Division Multiple Access (CDMA) communication system is rapidly progressing. Commercial services of wideband CDMA systems (W-CDMA: Wideband-CDMA) for exchanging large data such as moving images, as well as audio and still images, which are the current main services, have already been disclosed. These specifications are the third to be enacted three moves in the standardization organization 3Gpp (3 ^rd Generation Partnership Project) communication system, a variety of specifications aiming system that can achieve a high quality of service than that currently continue to review, and added have.

13 is a schematic configuration diagram of a W-CDMA system of the current 3GPP specification. The system includes a higher core network (CN) 100, a radio network controller (RNC: radio network controller) 101, a radio base station (NodeB) 102_0 to 102_n, and a mobile station (UE: user equipment) ( It consists of four types of nodes (103). In addition, the radio network controller RNC will hereinafter be referred to as a radio base station controller (base station controller).

Each node 100, 101, 102_0 to 102_n is physically connected in an ATM (Asynchronous Transfer Mode) transmission path or the like (wired section). The radio base stations 102_0 to 102_n and the mobile station 103 are connected by radio signals (radio sections).

The user data sent from the terminal (not shown) to the mobile station 103 is transmitted to the radio base station control station 101 that accommodates the mobile station 103 via the core network 100. If the mobile station 103 belongs to the cell 104_1, the radio base station control station 101 transmits user data to the radio base station 102_1 containing the cell, and the radio base station 102_1 transmits the user data to the mobile station. To 103. Thereafter, if the mobile station 103 continues to belong to the cell 104_1, the radio base station control station 101 controls the mobile station 103 to communicate with the counterpart terminal in the path.

However, when the mobile station 103 moves and moves to the adjacent cell 104-2, the radio base station control station 101 receives the radio base station of the relay from the radio base station 102-1 by the handover control. 102-2) without instantaneous interruption. 14 is a procedure explanatory diagram of such handover control.

When the mobile station 103 is in communication with the base station 102-1, the radio base station control station 101 requests the mobile station 103 to measure and report the radio state periodically (step S1). When the mobile station 103 receives the radio state measurement report request, the mobile station 103 measures the reception level from the neighboring base station 102-2 or the like and reports it to the radio base station control station 101 through the base station 102-1 in communication (step). S2). The radio base station control station 101 determines whether handover is necessary based on the radio status report. For example, when the received electric field strength from the neighboring base station 102-2 becomes equal to or greater than the set value, it is determined that handover is necessary, and the traffic channel TCH is instructed to the neighboring base station 102-2 (add radio link). Request, step S3). The neighbor base station 102-2 returns the radio link addition request response to the radio base station control station 101 in response to the radio link addition request (step S4).

Subsequently, the radio base station control station 101 sends a request (active set update request) to the mobile station 103 to prepare for handover through the base station 102-1 (step S5). When the mobile station 103 receives the active set update request, it returns an active set update response to the radio base station control station 101 (step S6), and communicates with the base station 102-2 on the traffic channel TCH to establish a radio link. (Step S7).

In this state, the mobile station 103 notifies the radio base station control station 101 of the reception level when the reception electric field strength from the base station 102-1 is lower than or equal to the setting level continuously for more than a set time (step S8). By this notification, the radio base station control station 101 determines the end of communication between the mobile station 103 and the base station 102-1, and instructs the mobile station 103 to execute handover (step S9). When the mobile station 103 is instructed to execute handover, the mobile station 103 executes handover and continues communication via the base station 102-2 (step S10). Subsequently, the mobile station 103 transmits the handover completion to the radio base station control station 101, and disconnects the radio line between the base stations 102-1 (step S11). Upon reception of the handover completion, the radio base station control station 101 instructs the base station 102-1 to prohibit the use of the traffic channel (step S12), and the handover control is completed. Thereafter, the mobile station 103 may continue to communicate via the wireless base station 102-2.

Various forms have been proposed for such handover control.

The first conventional technique aims at distributing traffic at each base station, and characterized in that a base station whose number of channels used exceeds a certain threshold value makes the mobile station in communication hand over to another base station (Patent Document 1). .

The second prior art is characterized by a handover destination determination algorithm when resources are scarce (Patent Document 2).

The third conventional technique is related to a method for selecting a base station of a mobile station at the time of handover, wherein the mobile station performs handover to a base station having a large amount of free resources (Patent Document 3).

The fourth conventional technique is characterized in that the mobile station selects a base station corresponding to the call type and makes a connection request at the time of call setup and handover in the multilayer cell (Patent Document 4-7).

The fifth conventional technique is characterized by classifying the mobile stations according to the speed of the mobile station, and assigning channels to the mobile stations in descending order of class when the free portion occurs when there is no free resource in the mobile station base station. 8).

A sixth prior art relates to a hierarchical cell configuration, wherein the size of the base station area is changed in accordance with the moving speed of the mobile station (Patent Document 9).

In the conventional mobile communication system, the handover triggered by the movement of the mobile station is an observation of the electric field strength or the amount of radio wave interference, and the handover considering the use of the radio resources of the radio base station of the handover destination and the empty situation. Over control was not performed. For this reason, in the prior art, a problem arises in that the radio resources of the radio base station of the handover destination are insufficient and the available communication band cannot be secured.

That is, at the time of handover, the radio base station control station allocates a radio resource amount equivalent to the radio resource allocated to the radio base station of the handover source to communicate with the mobile station to the radio base station of the handover destination, thereby establishing a new radio channel. There is a need. However, when an equivalent amount of radio resources cannot be secured or when the electric field strength of the newly set radio channel is insufficient to be suitable for communication, the radio resources are reselected or the handover is stopped. Reselection of radio resources requires a long time to complete handover, which is undesirable, and suspension of handover results in call loss. In addition, even if the communication itself can be continued, there is a fear that the throughput will be greatly reduced, causing inconvenience to the user.

In addition, the mobile station is divided into a general mobile station and a preferred mobile station, and when there is a call from the preferred mobile station, if there is no free resource, the mobile station is handed over from the congested radio base station to the neighboring radio base station forcibly to create an empty portion, and the mobile station is first congested. There is a conventional technique for accommodating a wireless base station (Patent Document 10). However, this prior art does not relate to handover control caused by movement, nor does it handover mobile stations irrelevant to priority.

In view of the above, it is an object of the present invention to ensure handover and to prevent a situation such as reselection of a radio resource or handover suspension due to a handover failure.

Another object of the present invention is to ensure handover by performing handover control in consideration of the use status of the radio resources of the handover destination wireless base station and the free situation.

Another object of the present invention is to make the handover decision processing timing variable according to the communication service, the communication speed, and the moving speed, so that the handover can be performed efficiently and reliably without delay.

Another object of the present invention is to control the handover target range according to the moving speed, thereby making the radio resource allocation of the base station uniform even in an environment where the speed changes.

[Patent Document 1] Japanese Patent Laid-Open No. 2001-175243

[Patent Document 2] Japanese Patent Laid-Open No. 2001-251658

[Patent Document 3] Japanese Patent No. 3204088

[Patent Document 4] Japanese Patent Laid-Open No. 9-200858

[Patent Document 5] Japanese Patent Laid-Open No. 9-205679

[Patent Document 6] Japanese Patent Laid-Open No. 9-200826

[Patent Document 7] Japanese Patent Laid-Open No. 9-205673

[Patent Document 8] Japanese Patent No. 3072289

[Patent Document 9] Japanese Patent 2789987

[Patent Document 10] Japanese Patent Laid-Open No. 3-107218

<Start of invention>

In a first aspect of the invention, a plurality of base stations and a radio base station control station for controlling the plurality of base stations are provided, and prior to handover at the time of handover control in a wireless communication system in which the base station and the mobile station communicate by radio. Handover Destination The wireless base station secures necessary radio resources in advance, and performs handover after securing the radio resources. That is, one or more mobile stations already communicating in the wireless base station of the handover destination are forcibly handed over to another wireless base station, thereby securing the radio resources of the handover destination base station, and then performing the handover. In this way, it is possible to reliably handover, and it is possible to prevent a situation such as reselection of a radio resource or suspension of handover due to handover incapability.

According to a second aspect of the present invention, a handover execution decision is made in a handover control in a wireless communication system including a plurality of base stations and a radio base station control station for controlling the plurality of base stations, and the base station and the mobile station communicate wirelessly. The timing is variably controlled based on one or more combinations of a communication service, a communication speed, and a moving speed. By variably controlling the handover execution determination timing in this manner, the handover execution determination timing of the real-time service can be made faster, and the handover can be performed without any momentary interruption.

Further, in the handover of high speed data communication, in the first invention, it is necessary to forcibly hand over a large number of radio resources (many mobile stations) at the base station of the handover destination, so that sufficient preparation time is required. According to the second invention, it is possible to secure sufficient preparation time by accelerating the handover execution determination timing, thereby making it possible to efficiently and reliably handover.

Further, in high-speed movement, since handover due to movement occurs frequently, there is a high possibility that it is impossible to secure necessary radio resources. However, according to the second invention, this problem is solved in order to make the handover execution determination timing faster as the moving speed becomes larger.

According to a third aspect of the present invention, a handover determination threshold is provided in a handover control in a wireless communication system including a plurality of base stations and a radio base station control station for controlling the plurality of base stations, and the base station and the mobile station communicate wirelessly. The value is obtained from a function depending on the combination of the communication service type, the communication speed, and the moving speed, and the function value is set as the threshold of the start of the handover execution determination timing. The higher the real-time service, the faster the communication speed, and the faster the moving speed. The smaller the threshold value is, the faster the handover execution determination timing is. According to the third invention, it is possible to control the handover decision timing simply by calculating the threshold value from the function, and also have an effect similar to that of the second invention.

In a fourth aspect of the present invention, a plurality of base stations and a radio base station control station for controlling the plurality of base stations are provided, and when the handover control is performed in a radio communication system in which the base station and the mobile station communicate by radio, The base station range to be investigated is varied for each moving speed of the handover mobile station. In the first invention, it is necessary to check an empty radio resource of the base station in determining the forced handover destination base station. According to the fourth invention, the range of the irradiation target base station can be narrowly controlled in accordance with the moving speed, thereby processing. The load can be reduced and the radio resource allocation of the base station can be made uniform.

1 is a block diagram of a wireless communication system of the present invention.

2 is an explanatory diagram of management contents of a radio resource management unit of an information collection unit;

3 is an explanatory diagram of management contents of a measurement information management unit;

4 is a configuration diagram of a wireless base station.

5 is a configuration diagram of a mobile station.

6 is an explanatory diagram of a handover control sequence of the present invention.

7 is a handover control processing flow of a control unit of a wireless base station control station.

8 is an explanatory diagram of a relationship between a handover process timing and a decision threshold value;

9 is a processing flow of decision threshold determination of a handover decision processing unit that controls the handover decision threshold value for each mobile station in accordance with a combination of communication service, communication speed, and movement speed.

10 is a processing flow of a third embodiment for determining a decision threshold by a function.

11 is a schematic explanatory diagram of a fourth embodiment;

Fig. 12 is a forced handover destination base station range determination processing flow of the fourth embodiment.

Fig. 13 is a schematic configuration diagram of a W-CDMA system with 3GPP specifications.

14 is a procedure explanatory diagram of a conventional handover control.

<Best Mode for Carrying Out the Invention>

(A) First embodiment

1 is a configuration diagram of a wireless communication system of the present invention, in which a core network 11, a wireless base station control station 21, wireless base stations 31, 32, 33, ..., and mobile stations 41, 42, 43, ... are shown. It consists of four types of nodes.

(1) wireless base station control station

The radio base station control station 21 has a core network interface unit 22, a control processing unit 23, and a base station interface unit 24. The core network interface unit 22 receives the user data or the like from the core network 11 and sends it to the signal processing unit 25 of the control processing unit 23.

The signal processing unit 25 transmits user data input from the core network interface unit 22 and control signals (terminal control signals and inter-base station control signals) input from the control unit 26 through the base station interface unit 24. do. Here, the inter-terminal control signal is a control signal transmitted and received between the mobile station and the radio base station control station, and the inter-base station control signal is a control signal transmitted and received between the radio base station and the radio base station control station.

In addition, the signal processing unit 25 extracts a control signal (terminal control signal and inter-base station control signal) input from the base station interface unit 24 and sends it to the control unit 26 and the information collection unit 27. The base station interface unit 24 transmits user data and control signals sent from the signal processing unit 25 to the base stations 31, 32, 33, and sends the user data and control signals sent from the base station to the signal processing unit 25. send.

The radio resource management unit 27a of the information collecting unit 27 manages the maximum capacity (number of users, bands), radio resource usage situation, and radio resource empty situation for each wireless base station under table TB1 in FIG. 2A. In addition, the radio resource management unit 27a manages the IDs of the mobile stations accommodated in the radio base stations 31, 32, 33, etc. under the table TB2 in FIG. 2B, and uses each mobile station in the table TB3 in FIG. 2C. Manage the number of channels and bands used. In response to the free resource report request, each of the wireless base stations 31, 32, ... returns an empty resource report response, so that the radio resource management unit 27a extracts the above information from this free resource report response and manages each of the management tables TB1 to TB3. Preserve it and manage it.

As shown in Fig. 3, the measurement information management unit 27b stores the electric field strength and the mobile station position (longitude) of the plurality of base stations measured and reported from each mobile station in response to the measurement report request. In addition, the mobile station position (longitude) is not necessarily reported.

The control unit 26 performs handover control. The handover decision processing section 26a of the control section 26 compares the electric field strength of each base station reported from the mobile station with the set threshold value to the measurement report request and determines whether to handover. Preparation (establishment of a radio link between the handover destination base station and the mobile station) is performed. When the forced handover decision processing unit 26b determines that the handover is performed, the handover destination base station forcibly hands over one or more mobile stations that are communicating with the other wireless base station according to a predetermined criterion. This ensures that the radio resources are secured and can be handed over reliably.

(2) wireless base station

4 is a configuration diagram of a wireless base station, wherein the wired transmission line interface unit 51 sends user data or a control signal between terminals to the modulation / demodulation unit 52, which is sent from the wireless base station control station 21, and the control signal between base stations. To the control unit 53. Further, user data input from the modulation / demodulation section 52, inter-terminal control signals, and inter-base station control signals input from the control section 53 are sent to the wireless base station control station 21. The modulation and demodulation unit 52 performs error correction code processing and modulation processing on the user data sent from the wired transmission line interface unit 51 and the control signals between the terminals according to the instructions from the control unit 53. In addition, the demodulation unit 52 performs demodulation and error correction on the inter-terminal control signal and user data sent from the mobile station in accordance with an instruction from the control unit 53, inputs it to the wired transmission line interface unit 51, and then inputs the base station from the mobile station. Is input to the control unit 53. The transmission / reception section 54 receives a signal from the mobile station, amplifies it with a low noise amplifier, and performs detection. The modulated signal input from the modulation / demodulation section 52 is an RF signal, amplified by a transmission power amplifier, and transmitted from the antenna toward the mobile station.

The control unit 53 receives an inter-base station control signal (calling / cutting control signal) from the wired transmission line interface unit 51 and instructs the demodulation unit 52 to set or release a radio resource (channel type, radio channel). In addition, the radio resource manager 55 inputs and sets the radio resources. In addition, when the control unit 53 receives an inter-base station control signal (empty resource report request) from the radio base station control station 21, the radio base station receives radio resource management information managed by the radio resource management unit 55 in response to an empty resource report. The control station 21 is notified.

The radio resource management unit 55 manages the use status and the free status of radio resources in the radio base station, manages IDs of mobile stations that are accommodated, and manages usage bands and the number of users used for each mobile station. . A mobile phone that accepts 64 kbps of bandwidth (for 3 users), 12.2 kbps of bandwidth (for 1 user) in a telephony service, and a predetermined band for other services. Based on the communication service, the radio resource management unit 55 manages the radio resource use situation and the free situation of the radio base station, and manages the use band of each mobile station and the number of use users.

(3) mobile station

5 is a configuration diagram of a mobile station. The receiving unit 61 receives a signal from the base station, performs a frequency conversion of the high frequency signal into a baseband signal, and performs detection. The demodulator 62 performs demodulation and error correction on the received signal in accordance with the settings from the controller 63 to obtain user data, and sends them to the data processor 64. Further, the demodulator 62 similarly acquires the inter-control station control signal (control signal between the wireless base station control station 21) and the inter-base station control signal (control signal between the wireless base station) sent from the receiving unit. To the control unit 63. The reception electric field strength detection unit 65 detects the reception signal strength (receive electric field strength) in the in-zone and peripheral zones and sends the measurement result to the control unit 63. The GPS 66 detects the position of the mobile station and inputs it to the control unit 63.

The modulator 67 performs encoding and modulation processing for error correction on the data sent from the data processor 64 in accordance with the setting from the controller 63, and sends the processing result to the transmitter 68. FIG. In addition, the modulation section 67 performs the encoding and modulation processing for error correction according to the settings from the control section, and sends them to the transmission section 68 in accordance with the settings from the control section. In addition, the control signal between the control stations suitably includes the position data and the measurement result of the reception electric field strength detection unit 65.

The transmitter 68 uses the modulated signal input from the modulator 67 as an RF signal, amplifies it by a transmission power amplifier, and transmits the signal from the antenna to the base station.

The data processing unit 64 performs processing according to the type of data sent from the demodulation unit 62, sends it to the display unit 69 and the speaker unit 70, and outputs the drawing output and the audio. The data processor 64 also transmits the transmission data to the modulator 67. The operation unit 71 inputs various data.

The control unit 63 performs the following processing.

Receive control signals from the wireless base station control station and the base station from the demodulator 62.

The control signal to the base station control station and base station is transmitted to the modulator 67.

• Instructs the modulator 67 and the demodulator 62 to set radio resources (for example, channel type, radio channel) according to a control procedure predetermined based on a control signal from the radio base station control station.

• Receives a control signal of a call from a wireless base station control station or a wireless base station and sends a control signal of the response to the modulator 67.

The measured value from the received electric field strength detection unit 65 and the mobile station position information are sent to the modulator 67 to notify the radio base station control station.

(4) handover control sequence

·outline

Each of the mobile stations 41, 42, 43, ... measures the electric field strength, the code error rate, the packet discard rate, or a combination of these in response to the measurement report request, and reports them to the radio base station control station 21, respectively. (Measurement report). In addition, the radio base stations 31, 32, 33, ... report the radio resource usage status or radio resource empty status of the local station to the radio base station control station 21 in response to the free resource report request (empty resource report). The radio base station control station 21 determines the mobile station and the handover destination base station to hand over to based on the measurement report, and determines the forced handover destination base station based on the free resource report. Subsequently, the radio base station control station 21 forcibly hands over the mobile station communicating in the handover destination base station to the forced handover destination base station and secures radio resources in the handover destination base station. Then, the radio base station control station 21 hands over the base station to the handover destination base station.

As a result, it is possible to prevent the occurrence of a situation in which the communication band desired by the user cannot be secured or cannot be handed over due to the lack of radio resources of the handover destination wireless base station.

·sequence

6 is an explanatory diagram of a handover control sequence of the present invention. The mobile station 41 is also in communication with the radio base station 31 and the mobile station 42 is in communication with the radio base station 32.

When the mobile station 41 is communicating with the base station 31, the handover decision processing unit 26a of the radio base station control station 21 measures and reports the radio state (received electric field strength from the base station). (Step S1). When the mobile station 41 receives the radio state measurement report request, it measures the reception level from the neighboring base stations and reports it to the radio base station control station 21 via the base station 31 in communication (step S2). The measurement information management unit 27b of the radio base station control station 21 stores the measurement report (received electric field strength of the neighboring base station) received from the mobile station.

When the handover decision processing unit 26a determines that the mobile station 41 is to be handed over to the radio base station 32 on the basis of the radio status report, it instructs the mobile station 41 and the radio base station 32, respectively. (Step S3). That is, in step S3, the handover decision processing unit 26a determines whether handover is necessary based on the measurement report. For example, when the received electric field strength from the neighboring base station 32 becomes equal to or larger than the set value, it is determined that handover is necessary, and the traffic channel TCH is determined to the base station by considering the neighboring base station 32 as the handover destination base station. (The request for adding a radio link, see FIG. 12). The handover destination base station 32 returns the radio link addition request response to the radio base station control station 21 in response to the radio link addition request. Subsequently, the radio base station control station 21 sends a request to the mobile station 41 for preparing for handover (active set update request, see Fig. 12). When the mobile station 41 receives the active set update request, it returns the active set update response to the radio base station control station 21 and communicates with the base station 32 on the traffic channel TCH to establish a radio link. … Abnormal step S3

After that, the forced handover decision processing unit 26b transmits an empty resource report request to each radio base station (step S4). As a result, each radio base station returns an empty resource report response, and the radio resource management unit 27a stores and manages the radio resource state shown in FIG. 2 based on the empty resource report response (step S5).

In addition, the mobile handover unit 26b requests the mobile station 42 to communicate with the handover destination base station 32 to measure and report the radio state (step S6). When the mobile station 42 receives the radio state measurement report request, it measures the reception level from the neighboring base stations and reports it to the radio base station control station 21 via the base station 32 in communication (step S7). The measurement information management unit 27b of the radio base station control station 21 stores the measurement report (received electric field strength from the neighboring base station of the mobile station 42) received from the mobile station 42.

The forced handover processing unit 26b determines, based on the measurement report response, the forced handover destination base station of the mobile station 42 as the radio base station 33, and issues a forced handover instruction for forced handover. The radio base station 33 is instructed (step S8).

That is, in step S8, the forced handover processing unit 26b determines the forced handover destination base station of the mobile station 42 based on the measurement report. If the received electric field strength from the base station 33 is equal to or larger than the set value and the free resource is maximum, the base station 33 is determined as the forced handover destination base station. Subsequently, the forced handover processing unit 26b instructs the traffic channel TCH to the base station 33, which is the forced handover destination base station (radio link addition request). The base station 33 returns the radio link addition request response to the radio base station control station 21 in response to the radio link addition request. Subsequently, the radio base station control station 21 sends a request (active set update request) to the mobile station 42 to prepare for forced handover. Upon receipt of the active set update request, the mobile station 42 returns the active set update response to the radio base station control station 21 and communicates with the base station 33 on the traffic channel TCH to establish a radio link. … Abnormal step S8

After that, the radio base station control station 21 instructs the mobile station 42 to execute the forced handover (step S9). When the execution of the forced handover is instructed, the mobile station 42 executes handover and continues communication via the base station 33 (step S10). Subsequently, the mobile station 42 transmits the handover completion to the radio base station control station 21 and disconnects the radio line between the base stations 32 (step S11). Upon reception of the handover completion, the radio base station control station 21 instructs the base station 32 to prohibit the use of the traffic channel TCH (step S12), and the forced handover control is completed. The mobile station 42 then continues to communicate via the wireless base station 33. This forced handover ensures an empty resource sufficient to accommodate the mobile station 41 in the base station 32.

In this state, the mobile station 41 notifies the radio base station control station 21 of the reception level when the reception electric field strength from the base station 31 is lower than or equal to the setting level continuously for a set time or more (step S13). By this notification, the radio base station control station 21 determines the end of communication between the mobile station 41 and the base station 31, and instructs the mobile station 41 to execute handover (step S14). When the mobile station 41 is instructed to execute handover, the mobile station 41 executes handover and continues communication via the base station 32 (step S15). Subsequently, the mobile station 41 transmits the handover completion to the radio base station control station 21 and disconnects the radio line between the base stations 31 (step S16). Upon reception of the handover completion, the radio base station control station 21 instructs the base station 31 to prohibit the use of the traffic channel TCH (step S17), and the handover control is completed. Thereafter, the mobile station 41 may continue to communicate via the wireless base station 32.

7 is a handover control processing flow of the control unit 26 of the radio base station control station 21. The handover decision processing unit 26a of the control unit 26 requests each mobile station (as the mobile station 41) to measure and report the radio state by the measurement report request control signal, and receives a measurement report response from the mobile station 41. The reception level from the neighboring base stations is received by the message, and stored in the measurement information management unit 27b (step 201).

Subsequently, the handover decision processing unit 26a examines the electric field strength from each base station (step 202), determines whether to handover the mobile station 41, and when handing over, the mobile station and the handover destination base station to hand over to. (Step 203, further handover the mobile station 41 to the radio base station 32).

Subsequently, the handover decision processing unit 26a instructs the mobile station 41 and the radio base station 32 to give a handover instruction. As a result, a radio link is established between the mobile station 41 and the base station 32 (step 204).

By the above, the process of the handover determination processing part is complete | finished, and it transfers to the process of the forced handover determination processing part 26b after that.

The forced handover decision processing unit 26b transmits an empty resource report request and acquires an empty radio resource state of each radio base station based on the empty resource report response to the request (step 205). Subsequently, the forced handover decision processing unit 26b checks whether there is enough free resource in the handover destination base station 32 to accommodate the mobile station 41 (step 206), and if not, does not perform a forced handover process, The mobile station 41 performs the same handover control as before (step 207).

However, if there are not enough free resources for handing over the mobile station 41 to the handover destination base station 32 in step 206, one or more mobile stations are forced from the handover destination base station 32 so that sufficient free resources occur. Handover. For this reason, the mobile station in communication with the handover destination base station 32 is determined so that sufficient free resources are generated (the mobile station 42. Step 208). If enough free resources do not occur with only one mobile station, a plurality of mobile stations are determined.

Subsequently, the determined mobile station 42 can search for a base station (forced handover destination base station) 33 capable of communicating with the largest free radio resource (step 209), and the mobile station 42 and the forced handover destination base station ( 33) is instructed to force handover (step 210). This establishes a radio link between the mobile station 42 and the forced handover destination base station 33.

Thereafter, the control unit 26 instructs the mobile station 42 to execute the forced handover (step 211). When the mobile station 42 is instructed to execute the forced handover, the mobile station 42 performs handover and continues communication through the base station 33. This forced handover ensures sufficient free resources to accommodate the base station.

After that, the mobile station 41 performs the same handover control as before (step 207). In other words, the mobile station 41 is handed over to the radio base station 32 by recognizing that the received electric field strength from the base station 31 has fallen below the set level continuously for more than a set time.

·summary

In summary, the radio base station control station 21 determines that the communication quality of the mobile station 41 communicating with the base station 31 is deteriorated, and determines handover to the base station 32. The radio base station control station 21 then checks the free radio resources of the base station 32 to confirm whether the mobile station 41 is capable of handover. If there are not enough free radio resources in the base station 32, the base station 32 checks whether there is a mobile station that is capable of moving to another base station. For example, if the mobile station 42 can determine that the mobile station 42 can move to the base station 33, first, the mobile station 42 is forced to hand over to the base station 33, and the mobile station 41 is accommodated in the base station 32. Reserves sufficient free resources, and then hands over the mobile station 41 to the base station 32.

Decision making of forced handover destination base station and forced handover mobile station

The following two methods can be considered as a criterion for selecting a mobile station forcibly handing over from a handover destination base station to another base station (forced handover destination base station).

The first method is a method of forcibly handing over a mobile station having the lowest radio resource allocation at the handover destination base station to a wireless base station having the largest free radio resource (excluding base stations currently communicating), and the second method is handover. A method of handing over a mobile station having a maximum radio resource allocation at a target base station to a wireless base station having a maximum free radio resource (excluding base stations currently communicating).

According to the first and second methods, it is possible to determine the forced handover destination base station so that the radio resource allocation is uniform among the respective radio base stations. In addition, according to the first method, although fine uniformity is possible, there is a possibility that the handover mobile station increases. On the other hand, according to the second method, although the degree of uniformity is large, the number of handover mobile stations can be reduced.

(B) Second embodiment

In real-time communication (video and voice service), it is necessary to shorten the interruption time as much as possible. Also, in high-speed data communication, since handover forcibly hands over many radio resources (many mobile stations) in the base station of the handover destination, sufficient preparation time is required. In the case of high-speed movement, since handover occurs frequently due to movement, there is a high possibility that necessary radio resources cannot be secured. Therefore, it is necessary to speed up the handover execution timing of the first embodiment in real time communication, high speed data communication, and communication at high speed.

In order to speed up the handover execution timing, the determination threshold of the handover start may be reduced. As the relationship described in Fig. 8A, Fig. 8B is a handover execution timing and the determination threshold value, the horizontal axis indicates the position of the mobile station, and the vertical axis is a reception electric field intensity from the radio base station, P _A is the base station A position, Ps is the base station B Where E _A is the received field strength from base station A, and E _B is the received field strength from base station B. Currently, when there is a mobile station in a cell of the base station A, if the mobile station moves and exceeds the position P _H 'and the received field strength E _B from the neighboring base station _B becomes equal to or larger than the threshold T _H , the radio base station control station hands over. Start processing. When this threshold value T _H is lowered to T _H 'as shown in Fig. 8B, the radio base station control station starts the handover process from the front P _H ' at the position P _H. In other words, when the determination threshold of the handover start is made small, the handover execution timing can be accelerated.

As described above, in the second embodiment, the handover execution timing is controlled by varying the determination threshold value of the handover execution start by the combination of the communication service, the communication speed, and the moving speed. In other words,

(1) The threshold value is set by distinguishing between real-time communication users such as video and audio and non-real-time communication users such as E-mail and WWW. For example, the timing of handover execution determination of a real-time communication user is increased, and the timing of non-real-time handover execution determination is slowed.

(2) The threshold value is set by distinguishing the high speed data communication user and the low speed data communication user at high speed. The handover execution determination timing of the high speed data communication user is accelerated, and the handover execution determination timing of the low speed data communication user is slowed.

(3) The handover execution determination timing of the high speed mobile user is accelerated, and the handover execution determination timing of the low speed mobile user is slowed.

9 is a processing flow of determination threshold determination in which the handover determination threshold is controlled for each mobile station by a combination of a communication service, a communication speed, and a movement speed. In addition, Th is a non-real-time service, and also a low speed communication, and also a threshold in the low speed travel time.

It is determined whether the service of the mobile station of interest is a real-time service (step 301), and if it is a real-time service, the threshold value Thi is

Thi = Thi-Thr

By this, Thr (real-time threshold margin margin) is reduced (step 302). However, for non-real-time services, the threshold is not changed.

Subsequently, it is determined whether the service is high speed data communication (step 303).

Thi = Thi-Thh

By this, Thh (threshold margin for high speed data communication) is reduced (step 304). However, in the case of low speed data communication, the threshold value is not changed.

Subsequently, it is determined whether the movement speed is a high speed movement (step 305).

Thi = Thi-Thf

By this, Thf (high-speed moving threshold margin) is reduced (step 306), and the threshold value determination process is finished. In addition, in the case of a slow movement, the threshold value is not changed.

As mentioned above, although the determination threshold value of one mobile station can be determined, the determination threshold value can be determined with the same process also about another mobile station.

In the above case, the determination threshold is determined based on a combination of three or more parameters (communication service, communication speed, and moving speed). However, the determination threshold may be determined using one or two parameters.

According to the second embodiment, by shortening the handover execution timing in real-time communication, high-speed data communication, and high-speed mobile communication, the instantaneous interruption time in real-time communication (video and voice service) can be shortened. Even in high-speed data communication and high-speed movement, it is possible to securely secure radio resources required for the handover destination base station to perform handover.

(C) Third embodiment

In the third embodiment, the handover decision threshold value is determined from the function depending on the combination of the communication service, the communication speed, and the moving speed, and the handover decision processing timing is determined based on the obtained decision threshold value.

In a wireless communication system having a base station and a plurality of mobile stations, the handover decision threshold Thi of the mobile station i is obtained as follows.

FuncAi [] is not particularly defined, but can be expressed as the following function, for example.

In the above formula, Th is a handover decision threshold used in the past. In addition, the functions f, g, and h are, for example, linear functions.

10 is a processing flow of the third embodiment in which each determination threshold value of the N mobile stations is determined by a function. N is the number of mobile stations.

i = 1 (step 501), and then the parameters (communication service, communication speed, moving speed) of the i-th mobile station are obtained (step 502), and these are substituted into the function Func [] of Equation 3 to determine the i-th mobile station. The decision threshold is calculated (step 503). Subsequently, it is checked whether i < N, and if &quot; Yes &quot;, i + 1 &gt;

In the above, the determination threshold is determined based on the combination of the communication service, the communication speed, and the movement speed. However, the determination threshold may be determined using one or two parameters.

According to the third embodiment, the decision threshold can be more flexibly determined using a function.

(D) Fourth Example

When the movement speed becomes high, handover processing by movement frequently occurs. For this reason, forced handover processing frequently occurs such that the radio resource allocation is made uniform among the respective radio base stations. By increasing the range of the base station to be the target radio resource investigation for determining the forced handover destination base station as the moving speed of the handover mobile station becomes higher, the load of the empty radio resource investigation processing can be reduced.

11 is a schematic explanatory diagram of the fourth embodiment, when Z is the handover destination base station area, the forced handover destination base station target area at low speed is Q to X, and the forced handover destination base station target area at high speed is shown in FIG. It expands to A-X.

12 is a forced handover destination base station range determination processing flow of the present invention. The forced handover decision processing unit 26b (FIG. 1) of the radio base station control station receives the electric field strength of each base station from the mobile station 42 of the handover destination base station 32 (step 601) and is notified from the mobile station at the same time. The speed of the mobile station is calculated from the mobile station position data (longitude and latitude) and the mobile station position data received before the predetermined time (step 602).

Subsequently, it is determined whether the moving speed of the mobile station is high speed or low speed (step 603). If the speed is low, the areas Q to X that are closer to each other than the handover destination base station are set as the forced handover destination base station target area (step 604). The base station with which the communication is possible and the maximum free resource is searched is determined as a forced handover destination base station (step 605). On the other hand, when the moving speed of the mobile station is high, A to X including an area farther away from the handover destination base station are set as the forced handover destination base station target area (step 606), and communication is possible among them. The base station whose maximum is is searched for and determined as a forced handover destination base station (step 605).

As described above, according to the fourth embodiment, the range of the forced handover destination base station is varied based on the moving speed of the mobile station to be handed over, thereby selecting a base station remotely at a high speed as the forced handover destination base station. It is possible to reduce the forced handover destination base station search processing load.

Effect of the Invention

According to the present invention, since the necessary wireless resources are secured in advance to the transition base station before handover, handover is executed and the handover execution determination timing is varied according to the communication service and the moving speed. This makes it possible to efficiently and reliably handover.

Claims (16)

delete delete A handover method in a wireless communication system including a plurality of base stations and a radio base station control station for controlling the plurality of base stations, wherein the base station and the mobile station communicate by radio. Determining whether to perform a handover for a mobile station communicating with a predetermined base station, and if so, determining a handover destination base station; Forcing a mobile station already communicating at the handover destination base station to another base station; and Handing over the handover target mobile station to the handover destination base station; Including, And a timing for determining whether to perform a handover based on at least one of a type of communication service, a communication speed, or a moving speed of a mobile station. The method of claim 3, And determining the handover execution timing for each mobile station, and making the handover execution timing faster as real-time service, high speed communication, or high speed movement. The method of claim 3, And a handover execution timing is calculated using a function having at least one of a communication service, a communication speed, or a moving speed of a mobile station as a variable. delete delete delete delete A radio base station control station in a radio communication system including a plurality of base stations and a radio base station control station for controlling the plurality of base stations, the base station and the mobile station communicating by radio, A handover decision processing unit that determines whether or not to perform a handover to a mobile station communicating with a predetermined base station, and determines a handover destination base station when executing; A forced handover decision processing unit for forcibly handing over a mobile station that is already communicating at the handover destination base station to another base station, and Means for handing over the handover target mobile station to the handover destination base station after a forced handover execution; Including, The handover determination processing unit, Means for determining a timing for determining whether to perform a handover based on at least one or a combination of two or more of a type of communication service or a communication speed or a moving speed of a mobile station. Wireless base station control station comprising a. The method of claim 10, The handover execution timing determining means determines the handover execution timing for each mobile station, and speeds up the handover execution timing as the real-time service, the high-speed communication, or the high-speed movement. Base station control station. The method of claim 10, The handover determination processing unit, Means for calculating the handover execution timing by using a function having at least one of a communication service or a communication speed or a moving speed of a mobile station as a variable; Wireless base station control station comprising a. delete delete delete delete

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