KR101037072B1 - Method for handover and mobile device therof - Google Patents

Abstract

A handover method and a handover control apparatus are disclosed. A handover control apparatus for performing a handover in a code division type mobile communication system, comprising: a condition setting unit for setting a threshold value of a Walsh code usage of a base station, an existing handover condition, and an update handover condition; A determination unit determining whether Walsh code usage of the base station is greater than or equal to a preset threshold; A message generator for generating an overload indication message including the update handover condition when the determination result is greater than or equal to a threshold; And a communication unit for transmitting the overload instruction message to a mobile communication terminal, wherein the mobile communication terminal changes an existing handover condition according to the update handover condition included in the overload instruction message. A device can be provided. According to the present invention, when the Walsh Code resource is insufficient due to local traffic increase, the Walsh Code can be effectively used to accommodate as many calls as possible.

Handover, Walsh Code

Description

Handover method and handover control device {Method for handover and mobile device therof}

The present invention relates to a handover, and more particularly, to a handover method and a handover control apparatus in a code division mobile communication system.

In general, a multiple access communication system includes a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, and a CDMA system.

CDMA is a communication method that can spread the frequency of occupied frequency of one channel widely and can call several subscribers at the same time by giving different codes to each user with the spread channel, which is about 10 ~ 20 times compared to the existing analog method. It can increase the frequency capacity, has the advantage of high frequency utilization efficiency, easy data communication and good security, but it is a communication method that is difficult to implement the technology.

In case of a local traffic surge in CDMA or mobile communication systems, call connection failure due to lack of Walsh code of the base station system occurs. At this time, among the resources (dedicated line, base station power, base station channel element, Walsh code, etc.) necessary for call setup in an access network, the first one is usually used as a Walsh code.

In particular, as well as increasing the call volume in the subcells, path connections to other subcells for providing soft / soft handovers in the subcell boundary (cell overlap) area further exacerbate Walsh code resource shortages.

In more detail, when a base station signal overlaps, a terminal in a traffic state has a path connected to two or more subcells for the purpose of soft / soft handover support, thereby consuming Walsh code resources as much as the connection. Done. Of course, although the path connection between adjacent cells is inevitable for smooth handover, the call setup impossibility caused by the lack of Walsh code of a specific cell has a problem in that it cannot accommodate the surging traffic compared to the available capacity of the system.

In order to prevent such a problem, the resources of the base station system should be designed in consideration of eventual (temporary) traffic increase at the source, but there is a disadvantage in that an excessive facility investment cost is required for the base station system.

In addition, conventional techniques for performing call distribution through antenna swing and base station output control during traffic spikes have been used. Many.

An object of the present invention for solving the problems of the prior art as described above is to provide a handover method and a handover control apparatus using a Walsh code.

Another object of the present invention is to accommodate as many calls as possible by effectively using the Walsh code when Walsh Code resources are insufficient due to local traffic increase.

It is still another object of the present invention to modify the handover algorithm to effectively use Walsh codes when used above a certain threshold (load growth).

According to an aspect of the present invention, in a handover control apparatus for performing a handover in a code division type mobile communication system, setting a condition for setting a threshold value of a Walsh code usage of a base station, an existing handover condition, and an update handover condition part; A determination unit determining whether Walsh code usage of the base station is greater than or equal to a preset threshold; A message generator for generating an overload indication message including the update handover condition when the determination result is greater than or equal to a threshold; And a communication unit for transmitting the overload instruction message to a mobile communication terminal, wherein the mobile communication terminal changes an existing handover condition according to the update handover condition included in the overload instruction message. A device can be provided.

According to another aspect of the present invention, in the method for performing a handover in a handover control apparatus of a code division type mobile communication system, at least one of a threshold value of the Walsh code usage of the base station, an existing handover condition and an update handover condition Setting up; Determining whether Walsh code usage of the base station is greater than or equal to a preset threshold; Generating an overload indication message including the update handover condition if the determination result is greater than or equal to a threshold; And transmitting the overload indication message to a mobile communication terminal, wherein the mobile communication terminal changes an existing handover condition according to the update handover condition included in the overload indication message. Can be provided.

According to another aspect of the present invention, a method for providing a recording medium in which instructions executable in a digital processing apparatus are implemented by the above method and in which a program that can be read by the digital processing apparatus is recorded.

According to the present invention, when the Walsh code resource is insufficient due to local traffic increase, the Walsh code can be effectively used to accommodate as many calls as possible.

In addition, according to the present invention, the handover algorithm may be changed to effectively use the Walsh code when using more than a certain threshold (load increase state).

As the invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all transformations, equivalents, and substitutes included in the spirit and scope of the present invention. In the following description of the present invention, if it is determined that the detailed description of the related known technology may obscure the gist of the present invention, the detailed description thereof will be omitted.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram of a code division mobile communication system according to an embodiment of the present invention, and FIG. 2 is a layout view of a CDMA Walsh code channel according to an embodiment of the present invention.

The code division mobile communication system according to the present embodiment is a UMTS (Universal Mobile Telecommunication System) based on a synchronous IS-95 network based on CDMA technology and a wideband code division multiple access (WCDMA) scheme. This includes all networks that use Walsh codes, including networks. However, hereinafter, a CDMA system will be described as an example for convenience of description.

Referring to FIG. 1, a general mobile communication system includes a base station 102 and 112, a base station controller 104 and 114, an exchange 108 and 116, a visitor location register (VLR) 106 and 118, and a home. A location register 110, and the base station controllers 104 and 114 further include a handover control device.

The home location register 110 stores a master database of all subscribers subscribed to the network, and may provide subscriber information of the network to components of the network. Here, the subscriber information may include location information of the terminal, terminal status information, service subscription information, additional service information, and route information.

In addition, the home location register 110 receives information stored in the visited location registers 106 and 118 in real time or periodically and stores it in an internal database, and may provide route information on the network for the called terminal at the request of the exchange. have. Here, the route information may include address information of the exchange and the visited location register in which the called terminal is located.

In general, the first exchanger 108 and the second exchanger 116 may perform call processing, billing data generation, and exchange functions for the mobile communication terminal 120. In addition, the exchanges 108 and 116 may acquire location registration information of the mobile communication terminal 120 and store the obtained location registration information in the visited location registers 206 and 218. That is, the exchanges 106 and 116 may obtain location information of the mobile communication terminal 120 that is changed in real time through a location registration message.

In general, the home location register 110 may be subjected to a large load because it needs to process location registration information received from a plurality of exchanges distributed in a wide area. In order to solve this problem, the home location register 110 may perform a location registration procedure for the corresponding mobile communication terminal 120 when the location of the mobile communication terminal is changed and the state of the mobile communication terminal 120 is changed. .

On the other hand, the visiting location registers 106 and 118 may perform functions such as updating detailed location information, registering location information, calling and security of the mobile communication terminal 120 connected to the corresponding exchange, and accessing the corresponding exchange area. Maintain a copy of the subscriber information. For example, the visited location registers 106 and 118 may store location information of relatively detailed mobile communication terminals in units of cell / base station / base station controllers.

The base station controllers 104 and 114 (including the base stations 102 and 112) replace the call path with the moved cell in order to continue the call when the mobile terminal 120 moves out of the area of the cell in service. The master performs HAND-OFF or hand over. The base station and base station controller of the present embodiment are respectively a radio base station (Node B) and a radio control station (RNC) in a WCDMA network.

Soft handover is a handover method of initiating communication with a new base station 112 without breaking communication with an existing base station 102, and softer handover is a kind of soft handover. Is a handover performed when moving between sectors within a cell, rather than between cells.

The mobile terminal 120 compares the threshold for the pilot channel strength received from the first base station 102 with the pilot channel strength of another neighboring second base station 112 that it continues to measure. If at some point in time the comparison of these measurements indicates a value that requires handover, the mobile communication terminal 120 reports this to the CDMA mobile communication system and performs handover under the control of the responsible system according to the type of handover. do.

CDMA spreads the occupied frequency width of one channel widely and assigns different codes to each user by spreading channels. In the CDMA system, Walsh code resources use a fixed number per base station subcell (1FA / 1Sector). It is assigned to fixed overhead (pilot, synchronous, paging) channels and floating traffic channels.

Referring to FIG. 2, Walsh codes of CDMA are divided into 64 channels from 0 to 63 for one reference frequency. A channel having a Walsh code of 0 is a pilot channel, a channel having a Walsh code of 1 to 7 is a paging channel, and a channel having a Walsh code of 32 is used as a synchronization channel. Since other channels are used as communication channels, 55 channels are used for communication.

In this case, the pilot channel is a channel used by the mobile communication terminal 120 to acquire a CDMA system in the terminal initialization state, and the synchronization channel is a channel having information necessary for the mobile communication terminal 120 to synchronize with the base station. In addition, the paging channel is a channel used to transmit information of the system to the mobile communication terminal 120, the communication channel is a channel for transmitting voice information between the mobile communication terminal and the network. The CDMA mobile communication system manages channels according to Walsh codes in order to increase communication efficiency.

In this embodiment, the base station controllers 104 and 114 periodically manage Walsh code resources in the corresponding subcells, and handover of the mobile communication terminal 120 when the Walsh code usage exceeds a specific threshold (load increase state). A handover control device 140 for changing the algorithm is included.

That is, the handover control device 140 transmits an overflow indicator message and the changed handover algorithm to the mobile communication terminal 120 when the traffic suddenly increases, and handovers the mobile communication terminal 120 to a neighboring cell having a low load. Let's do it. According to the present embodiment, the handovered mobile communication terminal 120 can suppress the handover to the overloaded cell again because a new handover algorithm is applied for a predetermined time.

3 is a flowchart illustrating a procedure for handing over to a neighboring second base station when the first base station is overloaded according to an embodiment of the present invention.

In the present embodiment, the first base station 102 receives a handover request as an active set together with the base station with which the mobile communication terminal 120 is communicating, and the second base station 112 moves. The communication terminal 120 corresponds to a neighbor set of a base station with which communication is being performed.

Since the first base station 102 lacks the Walsh code due to channel overload in steps 310 and 320, the first base station 102 transmits an overflow indicator message (OFIM) indicating the overload state of the cell to the mobile communication terminal 120.

The overload indication message OFIM is transmitted when the Walsh code usage of the base station is greater than or equal to a preset threshold. For example, when more than 90% of the 64 Walsh codes are available, the base station transmits an overload indication message (OFIM) to the mobile communication terminal 120.

In addition, according to the present embodiment, the overload indication message (OFIM) includes a handover condition change command, in addition to the notification of the overload state of the cell. Herein, the handover condition change refers to a handover condition (eg, pilot signal strength) of the base station (eg, the first base station of FIG. 3) that has transmitted the overload indication message (OFIM). Unlike the second base station of the third).

After receiving the overload instruction message (OFIM) in step 330, the mobile communication terminal 120 sets an update handover condition different from the existing handover condition (first handover condition) according to the handover condition change command. , To run the timer.

According to an embodiment of the present invention, the change in the handover condition may be performed by mitigating a condition (eg, pilot signal strength) for the adjacent base station (second base station in FIG. 3) to become an active set. It may be in a direction that allows the base station to accept the call.

According to another embodiment of the present invention, the change of the handover condition may be performed in a direction in which the condition for becoming an active set is enhanced by subtracting the pilot signal strength of the overload base station from the actual value. A more detailed description of the handover condition change will be described later with reference to FIG. 4.

In operation 340, the mobile communication terminal 120 measures power strength of the first base station 102 when the pilot signal strength Ec / Io of the second base station 112 exceeds a reference value set in the update handover condition. transmit a measurement (PSM) message. Thereafter, the mobile communication terminal 120 changes the pilot signal of the second base station 112 from a neighbor set to a candidate set.

In operation 350, the first base station controller 104 receives a request for handover to the second base station 112 via the first base station 102 and the second base station 112. The first base station controller 104 then sends a message to the first base station 102 and the second base station 112 to approve the handover.

In step 360, the first base station 102 transmits a handover direction message (HDM) to the mobile communication terminal 120. The Handover Direction Message (HDM) is a message for requesting handover to the second base station 112.

In operation 370, the first base station 102 transmits the handover information to the handover control device 140 and receives the approval.

In step 380, the mobile communication terminal 120 changes the state of the second base station 112 from a candidate set to an active set, and indicates a handover completion (Handover Completion Message); HCM) is transmitted to the handover control device 140.

The present embodiment aims to reduce the traffic of a corresponding cell by changing a handover condition of the mobile communication terminal 120 when an Overflow Indicator Message (OFIM) indicating an overload condition is transmitted in a specific cell. . Therefore, according to the present embodiment, if the communication channel is already connected to the base station to which the mobile communication terminal 120 has transmitted the overload instruction message, the channel is more easily blocked, and if the communication channel is not connected, the user handovers to another base station. It is effective to let.

4 is a flowchart illustrating a procedure of applying an update handover condition in a handover control apparatus according to an embodiment of the present invention, and FIG. 5 illustrates an existing handover condition and an update handover condition according to an embodiment of the present invention. The table is an example. In addition, each step described below is performed by each of the internal components of the handover control device 140, but will be collectively described as a handover control device for the convenience of understanding and explanation.

In step 410, the handover control device 140 determines whether the cell is overloaded, that is, whether the base station has exceeded the Walsh code usage threshold. The Walsh code usage threshold may be set in advance by the handover control device 140.

In step 420, the handover control device 140 sets an update handover condition to be applied to the base station in the overloaded state. This will be described in detail with reference to FIG. 5. In the case of ADD, even if the signal strength of the new pilot (Energey of carrier / Interference of others'; Ec / Io) is smaller than that of the pilot signal received from the existing base station, If the reference value T_ADD set in the update handover condition is exceeded, a condition is set to allocate a new call channel to the corresponding base station. Also, even in the case of base station blocking (DROP), even if the signal strength (Ec / Io) smaller than T_DROP of the first handover condition (the existing handover condition shown in FIG. 4), the reference value (N_T_DROP) of the update handover condition If it is, the condition is set to maintain the call channel of the new base station.

For example, when the first handover condition is T_ADD: -13dB and T_DROP: -15dB, the update handover condition applied to the mobile communication terminal 120 that receives the overload instruction message (OFIM) is -2 dB, respectively. You can set it to -1 dB, T_ADD: -15 dB or T_DROP: -16 dB. Therefore, according to the present embodiment, more adjacent cells may be candidate sets.

According to another embodiment of the present invention, the update handover condition includes changing a pilot signal of an existing base station that has sent an overload indication message (OFIM). For example, the handover control device 140 may manage the existing base station (overload cell) as a value reduced from the actual received pilot signal strength.

In the example of FIG. 5, when the pilot signal strength of the base station lacking the Walsh code is −13 dB, the handover controller 140 calculates −16 dB by applying a subtracted value (−) 3 dB. In this case, since the calculated pilot signal strength is smaller than the new reference value (N_T_ADD: -15dB), the mobile communication terminal 120 does not transmit a power strength measurement message (PSMM) to the base station.

In step 430, a specific base station generates an overload indication message (OFIM) including a message indicating that the base station is overloaded due to the Walsh code shortage and the update handover condition, and transmits it to the mobile communication terminal 140. The overload indication message (OFIM) may further include time information for applying the update handover condition in addition to the pilot signal strength as the update handover condition.

In step 440, the mobile communication terminal 140 changes the first handover condition to an update handover condition by referring to the subcell information in the overload indication message OFIM. When the overload instruction message (OFIM) includes time information for applying the update handover condition, the mobile terminal 140 starts a timer (N_Timer: 60 s) for a predetermined time and updates the handover condition for the timer driving time. Keep it.

6 is a functional block diagram of the handover control device 140 according to an embodiment of the present invention.

Referring to FIG. 6, the handover control device 140 includes a determination unit 610, a condition setting unit 620, a message generating unit 630, and a communication unit 640.

The determination unit 640 determines whether the Walsh code usage of the base station is greater than or equal to a preset threshold. Therefore, the Walsh code usage threshold is a parameter for determining whether the base station is overloaded, and if the base station is determined to be overloaded, the handover condition is changed.

The condition setting unit 642 sets a threshold value of the Walsh code usage of the base station, a first handover condition, and an update handover condition. The condition setting unit 642 sets whether to determine overload when the Walsh code is used, and sets pilot signal strength as a handover condition. The condition setting unit 642 also determines how long to maintain the update handover condition.

The communication unit 640 is an aggregate including a plurality of channel transceivers, and includes a pilot channel, a synchronization channel, a paging channel, a forward communication channel, and a reverse communication channel. In addition, the communication unit 640 may transmit an Overflow Indicator Message, a Power Strength easurement (PSM) message, a Handover Completion Message (HCM), and the base station 102 and 112 and the mobile communication terminal (HCM). 120) to transmit and receive.

In the mobile communication terminal 120 according to the present invention, the handover method may be implemented in the form of program instructions that can be executed by various computer means and recorded in a computer readable medium. The computer readable medium may include program instructions, data files, data structures, etc. alone or in combination. Program instructions recorded on the media may be those specially designed and constructed for the purposes of the present invention, or they may be of the kind well-known and available to those having skill in the computer software arts. Examples of computer-readable recording media include magnetic media, such as hard disks, floppy disks, and magnetic tape, optical media such as CD-ROMs, DVDs, and magnetic disks, such as floppy disks. Magneto-optical media, and hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. The medium may be a transmission medium such as an optical or metal line, a wave guide, or the like, including a carrier wave for transmitting a signal designating a program command, a data structure, or the like. Examples of program instructions include not only machine code generated by a compiler, but also high-level language code that can be executed by a computer using an interpreter or the like. The hardware device described above may be configured to operate as one or more software modules to perform the operations of the present invention, and vice versa.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention as defined in the appended claims. It will be understood that the invention may be varied and varied without departing from the scope of the invention.

1 is a block diagram of a mobile communication system of the code division method according to an embodiment of the present invention.

2 is a layout diagram of a CDMA Walsh code channel in accordance with an embodiment of the present invention.

3 is a flowchart illustrating a procedure of handing over to a neighboring second base station when the first base station is overloaded according to an embodiment of the present invention.

4 is a flowchart illustrating a procedure of applying an update handover condition in a handover control apparatus according to an embodiment of the present invention.

5 is a table illustrating an existing handover condition and an update handover condition in one embodiment of the present invention.

6 is a functional block diagram of a handover control apparatus according to an embodiment of the present invention.

Description of the Related Art [0002]

102 and 112: base station 104 and 114: base station controller

108 and 116: Exchange 106 and 118: Location register

110: home location register 120: mobile communication terminal

610: channel transceiver 620: message transceiver

630: storage unit 640: control unit

642: condition setting unit 644: timer driving unit

Claims (7)

In the handover control device for performing a handover in a mobile communication system, A first handover condition that sets a threshold of Walsh code usage of a first base station and includes a pilot signal strength condition of the second base station required for the mobile terminal to perform handover from the first base station to a second base station; A condition setting unit for setting an update handover condition that reduces the pilot signal strength condition of the second base station included in the first handover condition; A determination unit determining whether Walsh code usage of the first base station is greater than or equal to the threshold; A message generating unit generating an overload instruction message including the update handover condition when the Walsh code usage of the first base station is greater than or equal to the threshold as a result of the determination; And Including a communication unit for transmitting the overload instruction message to the mobile communication terminal, And the mobile communication terminal changes the first handover condition according to the update handover condition included in the overload instruction message. The method of claim 1, The mobile communication terminal And a timer for maintaining the update handover condition for a predetermined time. A method for performing handover in a handover control apparatus of a mobile communication system, A first handover condition that sets a threshold of Walsh code usage of a first base station and includes a pilot signal strength condition of the second base station required for the mobile terminal to perform handover from the first base station to a second base station; Setting an update handover condition that reduces the pilot signal strength condition of the second base station included in the first handover condition; Determining whether Walsh code usage of the first base station is greater than or equal to a preset threshold; Generating an overload indication message including the update handover condition if the Walsh code usage of the first base station is greater than or equal to a threshold as a result of the determination; And Transmitting the overload instruction message to the mobile communication terminal; And the mobile communication terminal changes the first handover condition according to the update handover condition included in the overload indication message. delete The method of claim 3, The update handover condition is When the signal is applied to a neighbor set of a base station transmitting the overload indication message, the signal strength of the pilot is reduced compared to the channel blocking (T_DROP) and addition (T_ADD) conditions of the first handover condition. Handover method. The method of claim 3, The update handover condition is When applied to the first base station that has transmitted the overload indication message, handover method characterized in that the calculation to the value reduced from the pilot signal strength actually received from the first base station. A recording medium in which instructions executable in a digital processing apparatus are implemented by the method of any one of claims 3, 5 and 6 and in which a program can be read by the digital processing apparatus.

Images