KR20080035832A - Apparatus and method for power control in broadband wireless communication terminal - Google Patents

Abstract

An apparatus and a method for controlling power in a broadband wireless communication terminal are provided to prevent the disagreement of the power control mode from generating between a base station and a terminal. An MAC(Media Access Control)(301) produces the power control mode change instruction message to a terminal. After transmitting the instruction message, a power controller(309) sets a re-transmission frame number. When the confirmation message in response to the instruction message is not received, the power controller controls the MAC in order to retransmit the instruction message until the present frame number is reached to the re-transmission frame number. The re-transmission frame number is determined by using the mode change start frame information within the instruction message. A frame number counter(311) counts the present frame number. A transmission modem(303) changes and transmits the message from the MAC according to the transmission protocol. A reception modem(305) recovers the message from the received wireless signal. A duplexer(307) transfers a reception signal from an antenna to the reception modem based on TDD(Time Division Duplex) and transfers a transmission signal from the transmission modem to the antenna.

Description

Power control apparatus and method in broadband wireless communication system {APPARATUS AND METHOD FOR POWER CONTROL IN BROADBAND WIRELESS COMMUNICATION TERMINAL}

1 is a diagram illustrating a signaling procedure for changing a power control mode in a broadband wireless access system.

2 is a diagram illustrating a configuration of a base station in a broadband wireless access system according to an embodiment of the present invention.

3 is a diagram illustrating a configuration of a terminal in a broadband wireless access system according to an embodiment of the present invention.

4 is a diagram illustrating an operation procedure of a base station in a broadband wireless access system according to an embodiment of the present invention.

5 is a diagram illustrating an operation procedure of a terminal in a broadband wireless access system according to an embodiment of the present invention.

FIG. 6 shows an example of practical application for better understanding of the present invention. FIG.

The present invention relates to a power control apparatus and method in a broadband wireless communication system, and more particularly, to an apparatus and method for stably switching the uplink power control mode in the broadband wireless communication system.

In general, communication systems have been developed mainly for voice services, and are gradually developing into communication systems capable of not only voice but also data services and various multimedia services. However, the voice-oriented communication system has not satisfied the rapidly increasing user's service needs due to the relatively small transmission bandwidth and high usage fee. In addition, due to the development of the communication industry and increasing user demand for Internet services, there is an increasing need for a communication system that can efficiently provide Internet services. As a result, a broadband wireless access system has been introduced to efficiently provide Internet services with broadband enough to meet the increasing demand of users.

The broadband wireless access system is a system for integrating and supporting not only voice but also various low speed and high speed data services and multimedia application services such as high definition video. The broadband wireless access system is based on a wireless medium using broadband such as 2GHz, 5GHz, 26GHz and 60GHz, in a mobile or fixed environment, public switched telephone network (PSTN), public switched data network (PSDN), internet network, IMT2000 network, It can connect ATM (Asynchronous Transfer Mode) network and can support channel transfer rate over 2Mbps. The broadband wireless access system may be classified into a broadband wireless subscriber network, a broadband mobile access network, and a high-speed wireless local area network (LAN) according to terminal mobility (fixed or mobile), communication environment (indoor or outdoor), and channel transmission rate. .

The wireless access method of the broadband wireless access system is being standardized by the IEEE 802.16 standardization group of the Institute of Electrical and Electronics Engineers, one of the international standardization organizations.

Compared to the wireless technology for the conventional voice service, the IEEE 802.16 standard has a wider bandwidth of data, which allows a large amount of data to be transmitted in a short time, and enables all users to efficiently use the channel by sharing a channel (or resource). . In addition, quality of service (QoS) is guaranteed so that users can receive different quality services according to the characteristics of the service.

The IEEE 802.16 communication system uses the Orthogonal Frequency Division Multiplexing (OFDM) or Orthogonal Frequency Division Multiple Access (OFDMA) scheme for a physical channel. That is, since the broadband wireless access system uses an OFDM / OFDMA scheme, high-speed data transmission is possible by transmitting a physical channel signal using a plurality of subcarriers.

In the broadband wireless access system, an uplink signal may cause excessive interference to another terminal or an adjacent cell according to transmission power, or may cause a problem that base station reception power is reduced. Therefore, proper power control according to the required signal to interference and noise ratio (hereinafter referred to as CINR) is necessary.

In general, the power control mode can be classified into closed loop power control and open loop power control.

First, the closed loop power control is performed to correct the uplink transmission power of the terminal according to the control of the base station. However, the closed loop power control may reduce the accuracy of power control in a packet communication system. That is, the base station determines the power control amount using the CINR value for the packet received in the uplink. If a packet is intermittently received by the base station, even if the base station performs power control every time the packet is received, a time difference occurs between the time point at which the terminal transmits an uplink packet and the time point of the power control instruction of the base station. The accuracy of the control may be degraded.

Next, in the open loop power control, the terminal estimates the path loss of the downlink under the assumption that the path loss between the uplink and the downlink is the same and adjusts the transmission power of the uplink signal by itself. That is, the terminal adjusts uplink power by using the required CINR value provided from the base station, uplink interference and noise level information, and downlink path loss. In addition, the base station additionally performs Reverse Link Outer Loop Power Control (ROLPC) to maintain a packet error rate of uplink data at a constant level.

As described above, in the open loop power control, the accuracy of power control can be significantly improved compared to the closed loop power control due to the self-transmission power control of the terminal and the additional power control instruction of the base station. Therefore, in the broadband wireless access system, the terminal performs closed loop power control in an initial network entry step, and then changes power control mode to perform open loop power control.

On the other hand, power control mode conversion is performed by exchanging PMC-REQ (Power control mode change request) / PMC-RSP (Power control mode change response) messages.

1 illustrates a signaling procedure for changing a power control mode in a broadband wireless access system.

Referring to FIG. 1, when the terminal requests power control mode conversion, the terminal prepares a PMC-REQ message including power control mode information requested in step 101 and transmits the same to the base station. In step 103, the base station composes and transmits a PMC-RSP message to the terminal in response to the PMC-REQ message. In this case, the PMC-RSP message includes a start frame number in which the power control mode is changed.

Upon receipt of the PMC-RSP message, the terminal generates a PMC-REQ message informing the reception of the PMC-RSP message and transmits it to the base station. In step 107, the base station and the terminal that terminate the procedure change the power control mode from the frame corresponding to the start frame number included in the PMC-RSP message. Meanwhile, step 101 may be omitted in the above-described power control mode change procedure.

However, FIG. 1 described above shows a case where messages are normally exchanged. In general, message loss may occur in a wireless environment in which the channel is rapidly changing. For example, when the base station does not properly receive the PMC-REQ message from the terminal in step 105, the terminal may control the power control mode in a frame corresponding to the start frame number included in the PMC-RSP message. Although the conversion is performed, the base station maintains the current power control mode as it has not received the PMC-REQ message.

For example, when the base station maintains the closed loop power control mode and the terminal changes to the open loop power control mode, the base station transmits power control information according to the closed loop power control mode to the terminal, but the terminal receives the received power control. There is a problem in that incorrect power control is performed by recognizing the information as power control information in the open loop power control mode.

That is, when a message loss occurs while performing a signaling procedure for changing the power control mode, a power control mode mismatch may occur between the base station and the terminal, and a method for preventing this is needed.

Accordingly, an object of the present invention is to provide an apparatus and method for stably changing a power control mode in a broadband wireless access system.

Another object of the present invention is to provide an apparatus and method for preventing a power control mode mismatch between a base station and a terminal in a broadband wireless access system.

It is still another object of the present invention to provide an apparatus and method for controlling retransmission of a message instructing to change a power control mode in a broadband wireless access system.

It is still another object of the present invention to provide an apparatus and method for ensuring the reliability of message exchange for changing a power control mode in a broadband wireless access system.

According to an aspect of the present invention for achieving the above object, in the base station apparatus in a wireless communication system supporting at least two power control modes, the MAC layer unit for generating a power control mode change instruction message transmitted to the terminal; Set the retransmission frame number after the indication message is transmitted, and if the acknowledgment message is not received in response to the indication message until the current frame number reaches the retransmission frame number, the MAC layer unit to transmit the indication message again. It characterized in that it comprises a power controller for controlling.

According to another aspect of the present invention, in a wireless communication system supporting at least two power control modes, a terminal device for analyzing a power control mode change indication message received from a base station and information in the indication message; And a power controller for setting a mode change start frame number and checking re-receipt of the indication message until a current frame number reaches the start frame number.

According to still another aspect of the present invention, in a communication method of a base station in a wireless communication system supporting at least two power control modes, the step of transmitting a power control mode change indication message to the terminal, and after the indication message is transmitted Setting a retransmission frame number; and if an acknowledgment message is not received in response to the indication message until a current frame number reaches the retransmission frame number, retransmitting the indication message. do.

According to still another aspect of the present invention, in a communication method of a terminal in a wireless communication system supporting at least two power control modes, receiving a power control mode change indication message from a base station and using the information in the indication message; And setting a mode change start frame number, and checking whether the indication message is received again until a current frame number reaches the start frame number.

Hereinafter, the operating principle of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, detailed descriptions of well-known functions or configurations will be omitted if it is determined that the detailed description of the present invention may unnecessarily obscure the subject matter of the present invention. Terms to be described later are terms defined in consideration of functions in the present invention, and may be changed according to intentions or customs of users or operators. Therefore, the definition should be made based on the contents throughout the specification.

Hereinafter, a method for stably changing a power control mode in a wireless communication system will be described. In the following description, an OFDM-based broadband wireless access system is described as an example, but the present invention can be easily applied to a communication system providing at least two power control modes.

2 illustrates a configuration of a base station in a broadband wireless access system according to an embodiment of the present invention. Hereinafter, a description will be made on the assumption of a time division duplexing (OFD) -OFDM system. However, the present invention can be easily applied to any system that performs power control, such as a frequency division duplexing (FDD) -OFDM system, a hybrid system using TDD and FDD together.

As shown, the base station according to the present invention, the MAC layer 201, the transmission modem 203, the reception modem 205, the duplexer 207, the scheduler 209, power connected to the upper layer The controller 211 and the frame number counter 213 are configured.

Referring to FIG. 2, first, the MAC layer unit 401 receives transmission data from an upper layer (for example, an IP layer unit), processes the transmission data according to a connection method with the transmission modem 203, and transmits the transmission modem. Forward to 203. The MAC layer unit 201 receives the received data from the reception modem 205, processes the received data according to a connection method with the upper layer, and delivers the received data to the upper layer.

The transmission modem 203 includes a channel code block, a modulation block, an RF transmission block, and the like. The transmission modem 203 converts data (burst data) from the MAC layer unit 201 into a form necessary for radio section transmission and thus a duplexer ( 207). Here, the channel code block includes a channel encoder, an interleaver, a modulator, and the like, and the modulation block is an IFFT (Inverse Fast Fourier Transform) for loading transmission data on a plurality of orthogonal subcarriers. The RF transmission block may include a frequency converter and a filter.

Meanwhile, the reception modem 205 includes an RF reception block, a demodulation block, a channel decoding block, and the like, and recovers data from a radio section signal from the duplexer 207 and transfers the data to the MAC layer unit 201. do. Here, the RF reception block includes a frequency converter and a filter, and the demodulation block includes a fast fourier transform (FFT) operator for extracting data carried on each subcarrier, and the channel decoding block includes a demodulator. , A deinterleaver, a channel decoder, and the like.

The duplexer 207 transfers a reception signal (uplink signal) from the antenna to the reception modem 205 and transmits a transmission signal (downlink signal) from the transmission modem 203 to the antenna in a TDD manner. do.

The scheduler 209 plays a role of planning and indicating uplink and downlink data transmission in consideration of a data transmission situation and a channel state of an individual terminal. For example, in case of the IEEE 802.16 communication system, the scheduler 209 generates UL / DL MAP which is uplink and downlink configuration information, and the MAC layer unit 201 is assigned to the UL / DL MAP from the scheduler 209. Accordingly, a downlink frame is transmitted and an uplink frame is received.

The power controller 211 is a block for performing power control in accordance with the currently set power control mode (closed loop power control mode or open loop power control mode). The power controller 211 generates power control information to be transmitted to each terminal and provides it to the MAC layer unit 201. In addition, when the change of the power control mode is determined by a request of the terminal or another event, information necessary for constructing the PMC-RSP message is generated and provided to the MAC layer unit 201. Then, the MAC layer unit 201 constructs a MAC message (power control message, power control mode change instruction message, etc.) with information related to power control from the power controller 211 to the transmission modem 203. To pass.

Meanwhile, according to the present invention, the power controller 211 transmits a message indicating the change of the power control mode (PMC-RSP) to the terminal and checks whether a confirmation message is received from the terminal. At this time, the power controller 211 sets a retransmission frame number which is a retransmission reference of the PMC-RSP message, and checks whether the retransmission frame number is reached by checking the current frame number counted by the frame number counter 213. . If the confirmation message is received before reaching the retransmission frame number, the power controller 211 waits until the start frame specified in the PMC-RSP message and then changes the power control mode in the start frame. . If the confirmation message is not received until the retransmission frame number is reached, the power controller 211 controls the MAC layer unit 201 to retransmit the PMC-RSP message. Here, the retransmission frame number is preferably set so that the retransmission message can reach the terminal before the start frame.

3 shows the configuration of a terminal in a broadband wireless access system according to an embodiment of the present invention.

As shown, the terminal according to the present invention, the MAC layer unit (MAC) 301, the transmission modem 303, the reception modem 305, the duplexer 307, the power controller 309 and connected to the upper layer and The frame number counter 311 is configured.

Referring to FIG. 3, the MAC layer unit 301 receives transmission data from an upper layer (for example, an IP layer unit), processes the transmission data according to a connection method with the transmission modem 303, and transmits the transmission modem ( 303). The MAC layer unit 301 receives the received data from the reception modem 305, processes the received data according to a connection method of the upper layer, and transmits the received data to the upper layer. The function of the MAC layer unit 301 is performed according to the instructions of the base station scheduler 209. For example, in the IEEE 802.16 communication system, the base station generates UL and DL MAPs, which are uplink and downlink configuration information, and transmits them to the terminal, and the MAC layer unit 301 of the terminal transmits a downlink frame according to the MAP information. Receive and transmit an uplink frame.

The transmission modem 303 includes a channel code block, a modulation block, an RF transmission block, and the like. The transmission modem 303 converts the data to be transmitted into a form necessary for radio section transmission and transfers the data to the duplexer 307. In particular, the transmission modem 303 adjusts the transmission power of the uplink signal according to the uplink transmission power value received from the power controller 309.

The reception modem 305 includes an RF reception block, a demodulation block, a channel decoding block, and the like, and recovers data from a radio section signal from the duplexer 307 and transfers the data to the MAC layer unit 301. The duplexer 307 transmits a reception signal (downlink signal) from the antenna to the reception modem 305 and transmits a transmission signal (uplink signal) from the transmission modem 303 to the antenna in a TDD manner. To pass.

The power controller 309 is a block for performing power control according to the currently set power control mode (closed loop power control mode or open loop power control mode). In the closed loop power control mode, the uplink transmission power is determined using the power control command received from the base station and transmitted to the transmission modem 303. In the open loop power control mode, uplink transmission power is determined by a predetermined method and transmitted to the transmission modem 303.

Meanwhile, according to the present invention, the power controller 309 changes the power control mode according to the power control mode change instruction message (PMC-RSP message) received from the base station. The power control mode change indication message includes start frame information in which the power control mode is changed. The power controller 309 waits to receive the PMC-RSP message again until the start frame after the instruction message is received. If the PMC-RSP message is not received again until the start frame is reached, the power controller 309 changes the power control mode to the mode specified in the PMC-RSP message in the start frame. If the PMC-RSP message is received again before reaching the start frame, the PMC-RSP message is re-received until the start frame is set again after changing the power control mode.

Meanwhile, the power controller 309 may request the base station to change the power control mode or transmit a confirmation message for the power control change instruction message to the base station. For example, when it is determined that the power control mode needs to be changed, the power controller 309 generates information necessary for constructing the PMC-REQ message and transmits the information to the MAC layer unit 301. Then, the MAC layer unit 301 forms a MAC message (PMC-REQ message) with the information from the power controller 309 and transmits it to the transmission modem 303. As such, the terminal only requests the change of the power control mode, and the final determination of the mode change is performed at the base station.

4 is a flowchart illustrating an operation procedure of a base station in a broadband wireless access system according to an embodiment of the present invention.

Referring to FIG. 4, the base station first checks whether a power control mode change request message (PMC-REQ message) is received from the terminal in step 401. When the power control mode change request message is received, the base station proceeds to step 403 to configure a power control mode change indication message (PMC-RSP message). The power control mode change instruction message may include, for example, power control mode information, start frame information for changing the power control mode, and the like.

In step 405, the base station sets a mode change start frame number using the start frame information included in the power control mode change instruction message, and sets a retransmission frame number as a reference for retransmission of the power control mode change instruction message. do. Here, the retransmission frame number is preferably set so that the retransmission message can reach the terminal before the start frame.

In step 407, the base station transmits the configured power control mode change indication message to the terminal. In step 409, the base station determines whether a confirmation message is received from the terminal in response to the power control mode change instruction message.

If the confirmation message is not received, the base station proceeds to step 413 and compares the current frame number with the set retransmission frame number to check whether they are the same. If the current frame number reaches the retransmission frame number, the base station returns to step 403, reconfigures the power control mode change instruction message, and performs the following steps again. At this time, the start frame information set in the power control mode change indication message is set to a value different from the initial transmission. That is, if the acknowledgment message is not received from the terminal until the previous frame reaches a predetermined value from the start frame for changing the power control mode, the power control mode change instruction message is transmitted again.

If the confirmation message is received in step 409, the base station proceeds to step 411 and compares the current frame number with the set starting frame number to check whether they are the same. If the current frame number does not reach the starting frame number, the base station continuously compares the current frame number with the starting frame number. If the current frame number reaches the start frame number, the base station proceeds to step 415 to change the power control mode of the terminal to the mode specified in the power control mode change instruction message. That is, when the acknowledgment message is received from the terminal before reaching the predetermined frame from the start frame for changing the power control mode, the base station waits until the start frame and changes the power control mode.

5 illustrates an operation procedure of a terminal in a broadband wireless access system according to an embodiment of the present invention.

Referring to FIG. 5, first, a terminal checks whether a power control mode change is necessary in step 501. For example, the necessity of changing the power control mode may be determined considering the moving speed of the terminal. If it is necessary to change the power control mode, the terminal proceeds to step 503 and forms a power control mode change request message (PMC-REQ message). The power control mode change request message may include power control mode information requested by the terminal. After configuring the power control mode change request message, the terminal proceeds to step 505 and transmits the power control mode change request message to the base station.

In step 507, the terminal checks whether a power control mode change instruction message (PMC-RSP message) is received from the base station. When the power control mode change instruction message is received, the terminal proceeds to step 509 to set the mode change start frame number using the start frame information included in the power control mode change instruction message. In step 511, the terminal configures a confirmation message in response to the power control mode change instruction message, and transmits the confirmation message to the base station.

After transmitting the confirmation message, the terminal proceeds to step 513 to check whether the power control mode change instruction message is received again. If the re-receipt of the power control mode change instruction message is detected, the terminal returns to step 509 to set the mode change start frame number again and then perform the following steps again.

If the re-receipt of the power control mode change instruction message is not detected, the terminal proceeds to step 515 and compares the current frame number with the set start frame number to check whether they are the same. In this case, when the current frame number does not reach the start frame number, the terminal returns to step 513 and performs the following steps. On the other hand, when the current frame number reaches the start frame number, the terminal proceeds to step 517 to change the power control mode to the mode set in the power control mode change instruction message.

4 and 5 illustrate the case in which the power control mode is changed at the request of the terminal, the base station can directly change the power control mode without the request of the terminal as described above. .

Figure 6 shows an example of practical application to help better understanding of the present invention.

Referring to FIG. 6, in the nth frame, the terminal transmits a power control mode change request message (PMC-REQ message) to the base station. The base station receiving the power control mode change request message determines a start frame to change the power control mode, and configures a power control mode change instruction message including the start frame information (Nth frame). In the (n + 5) th frame, the base station transmits the power control mode change indication message to the terminal. Here, it is assumed that the UL processing delay of the base station is 3 frames and the DL processing delay is 2 frames. That is, it is assumed that a delay of 5 frames occurs after the terminal transmits the request message and the instruction message is transmitted to the terminal.

Meanwhile, the terminal receiving the power control mode change instruction message from the base station sets a mode change start frame number and configures a confirmation message (PMC-REQ message) in response to the power control mode change instruction message. . In the mth frame, the terminal transmits the confirmation message to the base station. Here, it is assumed that the confirmation message is lost.

Meanwhile, when transmitting the power control mode change instruction message, the base station sets a mode change start frame number and a retransmission frame number as a reference for retransmission of the power control mode change instruction message. Here, the retransmission frame number is preferably set so that the retransmission message can reach the terminal before the start frame.

After transmitting the power control mode change indication message, the base station checks whether the current frame number reaches the retransmission frame number. As shown, if the acknowledgment message is not received until the retransmission frame number is reached, the base station reconfigures the power control mode change indication message. At this time, the start frame information (Mth frame) in the power control mode change indication message is set to a value different from the initial transmission. In the (N-3) th frame, the base station retransmits the power control mode change indication message to the terminal. Here, it is assumed that the retransmission frame number is set to (N-5) in consideration of the processing delay. For example, assuming downlink processing delay of the base station as 2 frames, the base station waits to receive an acknowledgment message until the (N-5) th frame, and if the acknowledgment message is not received, the power control mode for 2 frames. The change instruction message is reconfigured, and the power control mode change instruction message is retransmitted to the terminal in the (N-3) th frame.

Upon receiving the power control mode change instruction message, the terminal resets the mode conversion start frame number and configures a confirmation message (PMC-REQ message) in response to the power control mode change instruction message. The acknowledgment message is transmitted to the base station in the k th frame. Here, it is assumed that the acknowledgment message has been delivered to the base station without loss. Therefore, both the base station and the terminal change the power control mode in the Mth frame.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. For example, the above-described messages are just examples to help the understanding of the present invention, and those skilled in the art can easily perform the modifications. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the scope of the following claims, but also by those equivalent to the scope of the claims.

As described above, the present invention has the advantage of increasing the reliability of the message exchange when changing the power control mode. If the base station fails to receive an acknowledgment message after transmitting the power control mode change indication message, the base station transmits the indication message again before the start frame set in the indication message, thereby preventing power control mode mismatch between the base station and the terminal. You can prevent it. That is, the present invention can prevent power control mode mismatches, thereby ensuring reliability of reverse data and increasing cell capacity.

Claims (20)

A base station apparatus in a wireless communication system supporting at least two power control modes, A MAC layer unit for generating a power control mode change instruction message transmitted to the terminal; Set the retransmission frame number after the indication message is transmitted, and if the acknowledgment message is not received in response to the indication message until the current frame number reaches the retransmission frame number, the MAC layer unit to transmit the indication message again. Apparatus comprising a power controller for controlling. The method of claim 1, The retransmission frame number is determined using the mode change start frame information set in the indication message. The method of claim 1, And the retransmission frame number is determined such that the retransmitted indication message can reach the terminal before the mode change start frame set in the previously transmitted indication message. The method of claim 1, wherein the power controller, And when the acknowledgment message is received before the retransmission frame number is reached, changing the power control mode in the mode change start frame set in the indication message. The method of claim 1, And a frame number counter for counting the current frame number. The method of claim 1, A transmission modem for converting and transmitting a message from the MAC layer unit according to a transmission standard; And a receiving modem for restoring a message from the received wireless signal and delivering the message to the MAC layer unit. A terminal device in a wireless communication system supporting at least two power control modes, A MAC layer unit for analyzing the power control mode change instruction message received from the base station; And a power controller configured to set a mode change start frame number by using the information in the indication message, and to check re-receipt of the indication message until a current frame number reaches the start frame number. The method of claim 7, wherein the power controller, And when the indication message is received again before the start frame number is reached, resetting the start frame number and checking the reception of the indication message again using the set start frame. The method of claim 7, wherein the power controller, And if the instruction message is not received again until the start frame number is reached, changing the power control mode in a frame corresponding to the start frame number. The method of claim 7, wherein the vein layer portion, And generate a confirmation message transmitted to the base station in response to the indication message. The method of claim 7, wherein And a frame number counter for counting the current frame number. The method of claim 7, wherein A reception modem for restoring a message from the received wireless signal and delivering the message to the MAC layer unit; And a transmission modem for converting and transmitting a message from the MAC layer unit according to a transmission standard. A communication method of a base station in a wireless communication system supporting at least two power control modes, Transmitting a power control mode change instruction message to the terminal; Setting a retransmission frame number after the instruction message is transmitted; If the acknowledgment message is not received until the current frame number reaches the retransmission frame number, transmitting the indication message again. The method of claim 13, The retransmission frame number is determined using the mode change start frame information set in the indication message. The method of claim 13, And the retransmission frame number is determined such that the retransmitted indication message can reach the terminal before the mode change start frame set in the previously transmitted indication message. The method of claim 13, And if the confirmation message is received before the retransmission frame number is reached, changing the power control mode in the mode change start frame set in the indication message. A communication method of a terminal in a wireless communication system supporting at least two power control modes, Receiving a power control mode change indication message from a base station; Setting a mode change start frame number by using the information in the indication message; And checking whether the indication message is received again until a current frame number reaches the start frame number. The method of claim 17, Resetting the start frame number if the instruction message is received again before reaching the start frame number; And re-receiving the indication message by using the set start frame number. The method of claim 17, If the instruction message is not received again until the start frame number is reached, changing the power control mode in a frame corresponding to the start frame number. The method of claim 17, And transmitting a confirmation message to the base station in response to the indication message.

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