KR100541879B1 - Mobile communication system, control method of random access channel for the same and medium thereof - Google Patents

Abstract

The present invention relates to a method for controlling a random access channel through load control of radio resources in a mobile communication system. The present invention controls the allocation of the access slot and the persistence factor of a plurality of access request channels in the random access channel (RACH) allocation method using a load control method and a method of controlling the allocation of the random access channel (RACH). It is possible to alleviate the load on the system and to distinguish and control the random access channel attempt of the mobile terminal according to the priority of the required radio access service class.

Radio access protocol, radio resource management entity, load control unit, system information block unit

Description

Control method of mobile communication system and random access channel and recording medium storing the same {MOBILE COMMUNICATION SYSTEM, CONTROL METHOD OF RANDOM ACCESS CHANNEL FOR THE SAME AND MEDIUM THEREOF}

1 is a schematic structural diagram showing a part of a wireless access network of a next generation mobile communication system according to the prior art.

2 is a diagram illustrating an internal configuration of a base station of a mobile communication system according to an embodiment of the present invention.

3 is a flowchart illustrating a process of requesting change of system information by a load control unit according to an embodiment of the present invention.

4 is a diagram illustrating terms used for random access channel control according to an embodiment of the present invention.

5 is a flowchart illustrating a process of changing random access control information of a system information block unit according to an exemplary embodiment of the present invention.

The present invention relates to a method for controlling a random access channel (hereinafter referred to as RACH) in a mobile communication system.

Random access transmission is generally composed of a preamble portion and a message portion, based on the Aloha (ALOHA) scheme with a preamble acquisition indication. That is, in the random access procedure, the preamble and the message are transmitted together to reduce the delay time for packet transmission on the radio link, and the preamble is repeatedly transmitted to increase the detection probability of the preamble.

In a conventional multiple access scheme, a mobile station requests a base station to allocate a traffic channel for communication through a random access channel (RACH), and the base station uses a method of allocating a traffic channel by examining a request for channel assignment. However, when a plurality of mobile terminals request channel allocation at the same time, there is a problem in that a collision occurs with each other and communication efficiency is lowered.

In addition, in a multiple access scheme of a mobile communication system, a contention mode RACH scheme is used for a mobile station to be allocated a traffic channel. Therefore, according to the priority of the radio access service class of the mobile terminal, a control method for access slots and collision retries for accessing the RACH should be provided.

Conventionally, in order to solve this disadvantage, a method of controlling a channel allocation request according to a priority of a terminal to a predetermined channel allocation frequency is used. However, when a plurality of terminals request channel allocation, a collision occurs, and since the request channel itself acts as interference with respect to other channels of the same frequency band, frequent RACH connection attempts and collisions lead to problems of low communication efficiency. I still have

In addition, when the occupied load of the system exceeds a predetermined threshold for the system capacity, the mobile terminal not only rejects the channel request, but also the frequent channel request of the mobile terminal acts as interference in the same frequency band, resulting in increased call load of the system. Act as a cause.

The technical problem to be achieved by the present invention is to move the mobile communication system to be assigned a traffic channel according to the priority (Priority) of the radio access service class through a load control method using the traffic load allocated to the radio channel and the total power of the system It is to provide a method for controlling the access method of the random access channel (RACH) of the terminal.

A mobile communication system according to a feature of the present invention for achieving the above object is a mobile communication system for controlling the connection of a random access channel of a user mobile terminal through a wireless access network,

A radio access protocol providing an access protocol according to a radio access standard for allowing access through a fixed radio access network to the mobile terminal, wherein the radio access protocol performs call control, call mobility management, and session management functions. An L3 layer including a system information block portion for managing system information of the mobile communication system; And a radio resource management entity (hereinafter referred to as RRM-E) to which various algorithms according to a radio resource management scheme are applied. Here, the RRM-E controls the load of the mobile communication system and according to the result, the system information. A base station including a load control unit for requesting a system information change to a block unit;

The system information block unit changes system information according to a request of the load controller and broadcasts the changed system information to the mobile terminal through a wireless channel to control access to a random access channel.

The base station,

The apparatus may further include an interface for exchanging information between the load control unit and the system information block unit.

The load control unit,

Set the overload threshold level corresponding to the reference value for determining the overload condition according to the overall load level value corresponding to the overall load capacity of the system and the performance of the system, and periodically determine the overload by measuring the system load. According to the result, the system information block unit requests system information change.

The system information block unit,

The system receives the system information change request from the load controller, changes the access slot information of the random access channel, and then broadcasts the changed system information to the mobile terminal.

A method for controlling access of a random access channel according to an aspect of the present invention is directed to a radio access protocol and a radio resource management scheme for providing an access protocol according to a radio access standard for allowing access through a fixed radio access network to a mobile terminal. A method of controlling access of a random access channel of a user mobile terminal in a mobile communication system including a base station including an RRM-E to which various algorithms are applied,

a) determining, by the RRM-E, whether the occupancy load changes by measuring the load of the system at regular intervals; b) determining whether an overload occurs when the occupancy load changes, and setting an overload index according to the determination result; c) requesting a change in system information with the radio access protocol; d) checking, by the radio access protocol that has received the system information change request, overload index through the overload index and correcting system information; And e) modifying connection information of a random access channel in consideration of a current load state, and broadcasting the modified information to the mobile terminal.

Step a) is

With a current load occupancy level value (L _c) of the previous load occupancy level value (L _state) and to the current load occupancy level value (L _c) that the previous load occupancy level value (L _state) and different compared occupancy load variations The current load occupancy level value L _c is calculated by the following equation.

Where P _total is the _total allowable load of the system, P _now is the current load of the system, and L _total is the load occupancy level of the system.

In addition, the step a),

The method may further include setting the overload threshold level L _overload at an initial stage of the operation of the load controller, and initializing the previous load occupancy level value L _state and the overload index J _overload .

B),

And determined as the current load occupancy level value (L _c) the overload threshold level value (L _overload) and the current load occupancy level value (L _c) compared is larger than the overload threshold level value (L _overload) the overload,

If it is determined that the overload index (J _overload ) is set to 1, and if it is determined that it is not overloaded, the overload index (J _overload ) is set to 0.

In addition, the step b),

Calculating a load factor (L _factor ),

The load factor L _factor is calculated through the following equation.

Where k is a load level proportionality constant.

C),

After requesting a change of system information through the radio access protocol, the current load occupancy level value L _c is input to a previous load occupancy level value L _state to update the load level value, and then the process returns to step a).

In step d),

If it is determined to be overloaded, the system information is corrected by calculating the persistence factor (Pi) according to the wireless access service class.

The persistence factor Pi is calculated by the following equation.

Here, S _total is the _total number of access slots for random access and w _pi is the persistence weight value according to the priority of each wireless access service class.

Further, in step d),

If it is determined that the current load of the system is not an overload, go to step e) without changing the persistence factor Pi.

Step e),

The number of access slots (S _Ci ) of the random access channel is calculated according to the number of occupied access slots (S _C ) for the random access of the uplink frame and the radio access service class.

Occupied access slots (S _C) for random access in the uplink frame, it is calculated by the following be learned.

According to the radio access service class, the number of accessible slots S _Ci of a random access channel is calculated by the following equation.

Here, w _si is an access slot weight value according to the priority of each radio access service class.

According to an aspect of the present invention, a recording medium includes a radio access protocol for providing an access protocol according to a radio access standard for allowing access through a fixed access network to which a mobile terminal is fixed, and radio resources to which various algorithms according to radio resource management schemes are applied. A method of controlling access of a random access channel of a user mobile terminal in a mobile communication system including a base station including a management entity (RRM-E),

a) a function in which the RRM-E measures the load of the system at regular intervals to determine whether the occupancy load changes; b) determining whether an overload occurs when the occupant load changes, and setting an overload index according to the determination result; c) requesting to change system information with the radio access protocol; d) the radio access protocol receiving the request for changing the system information checks whether the overload index is overloaded and corrects system information; And e) modifying access information of a random access channel in consideration of a current load state, and broadcasting the modified information to the mobile terminal.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention. Like parts are designated by like reference numerals throughout the specification.

First, a next generation mobile communication system according to an embodiment of the present invention will be described in detail with reference to FIG. 1.

1 is a block diagram of a wireless access network of a next generation mobile communication system according to an embodiment of the present invention.

As shown in FIG. 1, a next generation mobile communication system according to an exemplary embodiment of the present invention includes a mobile terminal (MT) 100, a wireless channel 200, a base station (BS) 300. And a radio resource management entity (RRM-E) 400.

The MT 100 is a subject that a user wants to receive a wireless service by connecting to a fixed local access network in a wireless access network of a next generation mobile communication system, and the BS 300 supports access of a wireless channel 200 to a fixed access network. That is, it includes a transceiver and a controller of a base station to perform RF signal processing of wireless data.

The RRM-E 400 is configured in the form of a tool box to which various algorithms of the radio resource management method are applied. The RRM-E 400 of the BS 300 includes a plurality of algorithms (for example, according to the radio resource management policy). For example, load control algorithm, call admission control algorithm, etc.). In the next generation mobile communication system according to an embodiment of the present invention, the RRM-E 400 has a load control unit accommodating a load control algorithm.

In addition, in the next-generation mobile communication system according to an embodiment of the present invention, a local system control server that manages local resources of the mobile communication system and performs a connection function with an external network may be further configured, which ensures mobility between base stations. As a system provided with a connection protocol function, the system may be accommodated separately in the access network or accommodated in the BS 300.

2 is a diagram illustrating an internal structure of a BS of a next generation mobile communication system according to an embodiment of the present invention, wherein a load control (LC) 410 of a radio resource management entity 400 of the BS 300 is wirelessly connected to the BS. The relationship of the system information block part (SIB) 511 of the connection protocol 500 L3 layer 510 is shown.

In FIG. 2, the RRM-E 400 is a radio resource management entity described above, and the radio access protocol 500 is an L3 layer 510 as an access protocol according to a radio access standard for the MT 100 to access through a fixed access network. ), L2 layer 520 and L1 layer 530.

The L3 layer 510 is a protocol that performs functions such as call control, call mobility management, and session management for connection and disconnection of a call, and the L2 layer 520 is provided through access to a wireless physical medium and control of a radio link. A protocol for performing a function of radio access control and link control that provides a call channel and an access channel, etc., and the L1 layer 530 corresponds to a physical layer (PHY) that is closely related to the radio transmission technology of the radio access protocol.

In addition, the RRM-E 400 according to an embodiment of the present invention includes a load control unit (LC) 410, and requests the SIB 511 to change the system information through the primitive 512 determined according to the control result, As a result, the SIB 511 changes the broadcast information and broadcasts it to the terminals on the wireless channel 200 corresponding to the downlink control channel.

In the next-generation mobile communication system according to an embodiment of the present invention will be described in detail the operation of each part as follows.

The MT 100 attempts to be allocated a radio traffic channel in order to receive a radio access service. At this time, the BS 100 requests channel allocation through a random access channel (RACH). When an outgoing and incoming call request from the MT 100 is increased through the required control channel, a load is generated for processing not only the outgoing and incoming calls, but also the traffic volume of the traffic channel. Provides a way to control overload.

In particular, when there is an overload, there may be a number of methods for handling the call volume of the outgoing and incoming calls in the next generation mobile communication system. Except in the above description, a method of controlling a load in a BS 300 in which a function of a radio resource management method is accommodated for an outgoing call, particularly a random access channel (RACH), will be described.

Hereinafter, a method of controlling a random access channel through load control according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

3 is a flowchart illustrating a method for requesting a change of system information according to load control information of a mobile communication system according to an embodiment of the present invention, and FIG. 4 is a system information block unit (SIB) of a mobile communication system according to an embodiment of the present invention. 511 shows a random access control flowchart.

As shown in FIG. 3, first, the load control unit (LC) 410 of the RRM-E 400 sets an initial value of the overload threshold level L _overload at the same time the algorithm is started, and the previous load occupancy level value. (L _state ), the load constant (k) and the value such as the overload index (J _overload ) indicating whether the state of the _overload is initialized (S301).

Here, the overload threshold level (L _overload ) is determined according to the performance and capacity of the system, and the overload threshold level (L _overload ) and the previous load occupancy level value (L _state ) are not absolute values of the load. It is the level value that adjusted the _total allowable load value (P _total ) to a certain level. In addition, the total load level value L _total of the system expresses the _total acceptable load value P _total of the system, which is an absolute value, at a constant level. These level values can be expressed as values that match the load value. The load constant k is described below.

4 is a table showing symbols used in a mobile communication system according to an embodiment of the present invention.

Load control algorithm of a radio resource management entity is to reduce catastrophic failure due to overload of the communication system to result that can not be incoming or outgoing call processing in the system, the total load level value (L _total) and the overload threshold level value (L _overload ), And measure and check the system load periodically. The total load level value L _total corresponds to the total load capacity of the system, and the overload threshold level value L _overload corresponds to a reference value for determining an overload condition according to the performance of the system.

That is, for this purpose, after a predetermined time delay (S302), the load of the system is periodically measured (S303), and the load occupancy level value L _{c of the} system is calculated through Equation 1 (S304).

Where P _now is the current load of the system.

The calculated L _c indicates the occupancy level of the current system load.

Thereafter, when L _c (current load occupancy level value) and L _state (previous load occupancy level value) are compared (S305), if the two values are equal to each other, that is, the load of the system has not changed, the process returns to step S302. After a certain time delay, the load of the system is measured, and L _c is calculated and compared to L _state (S302 to S305).

As a result of the comparison in step S305, if the L _c and L _state level values are different, that is, if the occupied load of the current system is changed with respect to the previous value, the next step algorithm is performed.

First, it is checked whether the current load is overloaded by comparing the overload threshold level L _overload set at the start of the load control algorithm with the current load occupancy level value L _c (S306). That is, L _c If the level value is smaller than L _overload , it is determined that it is not an overload condition, and the overload index J _overload (J _overload is a value to be transmitted to the SIB 511. Is set to the null value (0) and L _c is The overload index J _overload is set to a non-null value (1) by determining that the overload state is a level value greater than L _overload (S307 to S308).

Thereafter, in order to request a change of system information, a load control factor L _factor is calculated through Equation 2 below (S309).

The load control factor L _factor is a ratio of the load constant to the current load occupancy level, and is an important parameter value transmitted to the SIB 511 as a parameter indicating a change value of the load level later. Also, in the above equation, the load level proportional constant k is initially set from the relationship between the total load level value (L _total ) of the system and the total number of access slots S _total for random access of the uplink frame, which is obtained at the start of the load control algorithm. It is a constant and is calculated by the following equation.

That is, the load level proportional constant k is a proportional constant with respect to the total number of access slots for random access of the uplink frame to the level value of the total load of the system. In addition, as shown in Equation 3 above, the total load level value L _total of the system has a constant multiple with the _total number of access slots S _total for random access of the uplink frame.

Therefore, a system information change request having the parameter L _factor and the overload index J _overload value obtained from Equation 2 as fields is transmitted to the SIB 511 (S310). Also, in order to update the changed load level value, the previous load occupancy level value L _stat The current load occupancy level value L _c is input to use the changed current level as a reference value in the next load control determination (S311).

Through this process, one cycle of the algorithm of the system information change request according to the load control policy of the load control algorithm is completed, and the process returns to step S302 again to repeat the load control algorithm.

Next, the random access control process of the SIB 511 of the mobile communication system according to an embodiment of the present invention will be described in detail.

As shown in FIG. 5, first, the SIB 511, which is a system information block part of the L3 layer 510 of the radio access protocol 500, starts with a total access slot for random access of an uplink frame, which is an initial setting value. The priority weight w _i for each radio access service class is initialized according to the number S _total and the radio resource management and service policy, and the primitive reception of a system information change request is waited.

In particular, as shown in FIG. 2, in the embodiment of the present invention, the SIB 511 may generate a primitive regarding a request for changing system broadcast information for a random access channel from the load control unit (LC) 410 through an interface 512. Receive.

When the SIB 511 receives a primitive requesting a system information change from the LC 410 through the interface 512 (S501), first, it is checked whether the information of the load control is _{overloaded by using} the value of the overload index J _overload . (S502).

If the result of the check is that the load state of the system is overloaded (J _overload == 1), the priority of the radio access service class is to induce different retransmission delays for the delay time of retries due to collisions in connection attempts of random access channels. To set P _i (Persistence factor) differentially. As such, the L _factor value of the received primitive and the total number of access slots S of the uplink frame, which is the setting value of the initial SIB 511, to differentially set P _i according to the priority of the radio access service class of the MT 100. P _i is obtained according to the following Equation 4 through the persistence weight w _pi according to the _total and priority for each wireless access service class (S503).

Thus obtained with a P _i replaced by modifying the P _i of the system broadcast information after (S504), calculates the number of S _c connected to a slot for random access in the uplink frame in a radio channel (200) (S505).

On the other hand, if it is determined that the overload index of the received primitive is not an overload state (J _overload == 0), immediately calculating the number of occupied access slots S _c for random access of the uplink frame without modifying the value of P _i ( S505).

Here, S _c is the number of slots for access for transmitting a preamble and transmitting a message to a predetermined access slot through the uplink random access channel of the radio channel 200, and is controlled by the LC 410. It is affected by the value. S _c is calculated through the following equation (5).

The calculated S _c is mapped to the number of accessible slots of the random access channel in the current load state, which corresponds to the number of accessible slots for all radio access service classes.

Furthermore, by applying the previously obtained S _c to Equation 6 below, the number of accessible slots (S _ci ) of the random access channel is differentially calculated according to the radio access service class (S505), and the broadcast channel of the SIB 511 is obtained. The value of the number of access slots is corrected according to the radio access service class of system information to be transmitted (S506).

As described above, S _ci in Equation 6 is obtained for each radio access service class, and its value is determined by the access slot weight w _si according to the priority of each radio access service class according to the radio resource management policy.

Thereafter, the SIB 511 broadcasts the system information on the access slot of the random access channel (RACH) (S507), and waits for receiving the system information change request primitive again in relation to the load of the system from the LC 410 ( Return to S501) and repeat the above process.

Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited thereto, and various other changes and modifications are possible.

As described above, according to the present invention, in the random access channel (RACH) allocation scheme using a load control scheme and a method of controlling the allocation of the random access channel (RACH), a plurality of access request channels are allocated to the access slot allocation and persistence ( By controlling the Persistence factor, the load of the system can be alleviated, and the attempt of the random access channel of the mobile terminal can be distinguished and controlled according to the priority of the required radio access service class.

In addition, the number of collisions is reduced through delay induction and attempt control for a random access channel of a lower service class for a mobile terminal having a very high priority of a wireless access service class, and as a result of faster access, There is an effect that can greatly improve the efficiency.

Claims (19)

In the mobile communication system for controlling the connection of the random access channel of the user mobile terminal through a wireless access network, A radio access protocol providing an access protocol according to a radio access standard for allowing access through a fixed radio access network to the mobile terminal, wherein the radio access protocol performs call control, call mobility management, and session management functions. An L3 layer including a system information block portion for managing system information of the mobile communication system; And Radio Resource Management Entity (hereinafter referred to as RRM-E) to which various algorithms are applied according to a radio resource management method-Here, RRM-E controls the load of the mobile communication system and according to the result, the system information block It includes a load control unit for requesting a change of system information. Includes a base station, The system information block unit changes system information according to a request of the load controller and broadcasts the changed system information to the mobile terminal through a wireless channel to control access to a random access channel. Mobile communication system. The method of claim 1, The base station, The apparatus further includes an interface for exchanging information between the load control unit and the system information block unit. Mobile communication system. The method of claim 1, The load control unit, Set the overload threshold level corresponding to the reference value for determining the overload condition according to the overall load level value corresponding to the overall load capacity of the system and the performance of the system, and periodically determine the overload by measuring the system load. Requesting system information change to the system information block unit according to a result Mobile communication system. The method of claim 1, The system information block unit, Receiving a system information change request from the load control unit and changing access slot information of a random access channel accordingly to broadcast the changed system information to the mobile terminal; Mobile communication system. Radio Resource Management Entity (hereinafter referred to as Radio Resource Management Entity) to which various algorithms according to a radio access protocol and a radio resource management scheme are provided to provide an access protocol according to a radio access standard for allowing access through a fixed radio access network to a mobile terminal. A method of controlling access of a random access channel of a user mobile terminal in a mobile communication system including a base station including RRM-E), a) determining, by the RRM-E, whether the occupancy load changes by measuring the load of the system at regular intervals; b) determining whether an overload occurs when the occupancy load changes, and setting an overload index J _overload according to the determination result; c) requesting a change in system information with the radio access protocol; d) checking, by the radio access protocol that has received the system information change request, overload index through the overload index and correcting system information; And e) modifying access information of a random access channel in consideration of a current load state, and broadcasting the modified information to the mobile terminal; Connection control method of the random access channel of the mobile communication system comprising a. The method of claim 5, Step a) is With a current load occupancy level value (L _c) of the previous load occupancy level value (L _state) and to the current load occupancy level value (L _c) that the previous load occupancy level value (L _state) and different compared occupancy load variations Determined to be A method for controlling access of a random access channel in a mobile communication system. The method of claim 6, In step a), And the current load occupancy level value L _c is calculated by the following equation.

Where P _total is the acceptable load value of the whole system, P _now is the current load value of the system, and L _total is the load occupancy level value of the entire system. The method of claim 6, The RRM-E includes a load control unit for controlling the load of the mobile communication system and requesting system information change to the radio access protocol according to the result. Step a) is Setting an overload threshold level L _overload at an initial stage of the operation of the load control unit and initializing the previous load occupancy level value L _state and the overload index J _overload Connection control method of the random access channel of the mobile communication system further comprising. The method of claim 8, B), As compared to the current occupancy level of the load value (L _c) The overload threshold level value (L _overload) current to the load occupancy level value (L _c) is determined to be greater than the overload overload threshold level value (L _overload) A method for controlling access of a random access channel in a mobile communication system. The method according to claim 5 or 9, B), If it is determined that the overload index (J _overload ) is set to 1, and if it is determined that the overload index (J _overload ) is set to 0 A method for controlling access of a random access channel in a mobile communication system. The method of claim 5, B), Calculating a load factor (L _factor ), The load factor (L _factor ) is a connection control method for a random access channel of the mobile communication system calculated by the following equation.

Where k is a load level proportionality constant. The method of claim 5, C), After requesting the system information change to the radio access protocol, the current load occupancy level value (L _c ) is input to the previous load occupancy level value (L _state ) to update the load level value and returning to the step a). Containing more A method for controlling access of a random access channel in a mobile communication system. The method of claim 5, In step d), If it is determined to be overloaded, the system information is corrected by calculating the persistence factor (Pi) according to the wireless access service class. A method for controlling access of a random access channel in a mobile communication system. The method of claim 13, And the persistence factor Pi is calculated by the following equation.

Here, L _factor is a load factor, S _total is the _total number of access slots for random access, and w _pi is a persistence weight value according to the priority of each wireless access service class. The method of claim 13, In step d), If it is determined that the current load of the system is not overloaded, go to step e) without changing the persistence factor Pi. A method for controlling access of a random access channel in a mobile communication system. The method of claim 5, Step e), The number of occupied access slots (S _C ) for random access of an uplink frame and the number of accessible slots (S _Ci ) of a random access channel are calculated according to a radio access service class. A method for controlling access of a random access channel in a mobile communication system. The method of claim 16, In step e), The number of occupied access slots (S _C ) for the random access of the uplink frame is calculated by the following equation.

Where L _factor is the load factor and S _total is the _total number of access slots for random access The method according to claim 15 or 16, The number S _Ci of accessible slots of the random access channel according to the radio access service class is calculated by the following equation. A method for controlling access of a random access channel in a mobile communication system.

Here, L _factor is a load factor, S _total is the _total number of access slots for random access, and w _si is an access slot weight value according to the priority of each wireless access service class. Radio Resource Management Entity (hereinafter referred to as Radio Resource Management Entity) to which various algorithms according to a radio access protocol and a radio resource management scheme are provided to provide an access protocol according to a radio access standard for allowing access through a fixed radio access network to a mobile terminal. In a recording medium storing a program that implements a method for controlling a connection of a random access channel of a user mobile terminal in a mobile communication system including a base station including an RRM-E), a) a function in which the RRM-E measures the load of the system at regular intervals to determine whether the occupancy load changes; b) determining whether an overload occurs when the occupant load changes, and setting an overload index according to the determination result; c) requesting to change system information with the radio access protocol; d) the radio access protocol receiving the request for changing the system information checks whether the overload index is overloaded and corrects system information; And e) modifying access information of a random access channel in consideration of a current load state, and broadcasting the modified information to the mobile terminal; Record medium that stores the program to implement.

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