JP5683724B2 - Transmission power control method and base station in base station of LTE radio communication system - Google Patents

Description

  The present invention relates to a transmission power control method and a base station in a base station of an LTE wireless communication system, and more particularly to a transmission power control method and a base station in performing adaptive modulation and coding rate control (AMC: Adaptive Modulation and Coding). .

  With the spread of mobile phones, especially smartphones, the amount of traffic in mobile radio communications has increased rapidly, and problems such as tight network lines have arisen. To this end, mobile phone operators are working on various attempts to increase wireless capacity, such as speeding up wireless communication and improving frequency utilization efficiency.

  As one of speeding up of data communication in a cellular phone, a service of LTE (Long Term Evolution) wireless communication, which is a long-term development system of a third generation mobile communication system, has been started. In LTE wireless communication, for example, in the downlink, communication with a 20 MHz bandwidth and a peak rate of about 300 Mbps is assumed. In this LTE wireless communication system, various technologies are employed in order to realize high-speed data communication.

  In the LTE wireless communication system, an OFDM (Orthogonal Frequency Division Multiplexing) transmission method is used particularly in downlink communication. This OFDM transmission scheme has advantages such as being strong against intersymbol interference and fading accompanying multipath transmission and having high frequency utilization efficiency.

  The base station of the LTE radio communication system allocates radio resources to each user by scheduling in downlink communication. For resource allocation, a resource block including a time domain slot and a frequency domain subcarrier is used. Scheduling is executed according to a predetermined rule, but such a rule is determined by the mobile phone operator. Examples of rules include guaranteeing the amount of data requested by the user, providing fair service among users, ensuring the maximum amount of transmission as a system, guaranteeing real-time transmission, etc. These combinations are used.

  Further, in LTE wireless communication, an adaptive modulation / coding rate control (AMC) technique that adaptively changes a transmission rate of a transmission signal according to a link state between a base station and a mobile station is applied. The transmission rate in AMC is determined by a combination of a modulation scheme and a coding rate (MCS: Modulation and Coding rate Set). On the signal transmission side, MCS corresponding to the link state is selected, error correction coding of the signal is performed at a coding rate corresponding to this MCS, and the signal is modulated by a modulation scheme corresponding to MCS. Generate a signal.

  However, assuming a FDD (Frequency Division Duplex) wireless communication system, the frequency bands used in the uplink and downlink are different, and the transmitting side measures and detects the link state of the link that transmits the signal. It is not possible. For this reason, the link state is grasped by receiving information about the link state measured on the receiving side from the receiving side.

  In AMC, the transmission rate is adaptively changed according to the link state. For this reason, when AMC is applied, transmission power control when transmitting a signal is not performed, and the transmission power is constant. In the LTE wireless communication system, AMC is used for data transmission in the downlink with a base station as a transmission device and a mobile station as a reception device. For this reason, the transmission power of the signal for the mobile station in the downlink is a constant value.

JP 2010-68501 A

  When AMC is applied to the downlink, the base station modulates and encodes a signal for the mobile station according to CQI (Channel Quality Indicator) information reported from the mobile station. Here, the CQI information is an index representing MCS suitable for downlink received signal quality measured by the mobile station. When the mobile station exists in the vicinity of the base station, the received signal quality in this mobile station is good, and signal transmission using the highest MCS is performed by notifying the base station of CQI information corresponding to the highest MCS. It will be requested to the base station.

  However, if the mobile station is located closer to the base station, the received signal quality at this mobile station may be excessive. In other words, a situation is assumed in which the highest MCS signal transmitted from the base station is received with a received signal quality higher than the received signal quality that can be received at a predetermined error rate or lower.

  In the base station of the LTE wireless communication system, the transmission power in the downlink is set to be constant, and the transmission power is unchanged even in a situation where the mobile station receives a signal with excessive communication quality. The maximum throughput of data that can be received by the mobile station is determined (that is, the amount of transmission data generated using the highest MCS), and the throughput does not increase even if the communication quality at the time of reception becomes excessive. Therefore, transmitting a signal with excessive communication quality to the mobile station is simply a waste of transmission power in the base station. Also, considering the influence on adjacent cells, such excessive communication quality signals cause extra interference to mobile stations in the adjacent cells, resulting in the efficiency of the entire wireless communication system. It degrades.

  The present invention provides a method of controlling transmission power of a base station without affecting existing mobile stations in order to suppress excessive communication quality signal transmission to mobile stations in an LTE wireless communication system. For the purpose.

  Another object of the present invention is to provide a base station that performs transmission power control in an LTE wireless communication system.

The present invention is a method for controlling transmission power for a mobile station in a base station of an LTE radio communication system, wherein channel quality indicator (CQI) information representing received signal quality in a mobile station of a signal transmitted from the base station is The step of receiving from the mobile station, the step of calculating a retransmission rate in hybrid automatic repeat request control for each MCS, the step of comparing the CQI information with a predetermined threshold, and the result of the comparison, the CQI information is If the threshold value is larger than the threshold value, the step of determining the transmission power value to decrease the transmission power value of the signal to be transmitted to the mobile station by a prescribed value; And the retransmission rate of the MCS according to the CQI information is smaller than a predetermined retransmission rate, it is transmitted to the mobile station Determining the transmission power value to decrease the transmission power value of the signal by a specified value, and generating a signal to be transmitted to the mobile station based on the modulation scheme and coding rate (MCS) according to the CQI information And transmitting the generated signal to the mobile station at the determined transmission power value.

In addition, the present invention is a base station in an LTE radio communication system, and a signal receiving unit that receives channel quality indicator (CQI) information representing a received signal quality at a mobile station of a signal transmitted from the base station from the mobile station And a HARQ control unit that calculates a retransmission rate in hybrid automatic repeat request (HARQ) control for each MCS, the CQI information is compared with a predetermined threshold, and if the CQI information is greater than the threshold, The transmission power value is determined so as to decrease a transmission power value of a signal transmitted to the mobile station by a specified value, and the retransmission of the MCS according to the CQI information when the CQI information is equal to the threshold value When the rate is smaller than a predetermined retransmission rate, a schedule for determining the transmission power value so as to decrease the transmission power value of the signal transmitted to the mobile station by a specified value. According to the transmission power value notified from the scheduler, the power control unit for controlling the transmission power for the mobile station, and the modulation scheme and the coding rate according to the CQI information, the mobile station A signal generation unit that generates a signal to be transmitted, and a signal transmission unit that transmits the encoded signal to the mobile station at the transmission power value.

  When the CQI information reported from the mobile station is equal to or greater than the threshold, the transmission power consumption at the base station can be suppressed by reducing the transmission power for the mobile station, and for the mobile station in the adjacent cell Since the interference power can be reduced, the efficiency of the wireless communication system can be improved.

It is a figure which shows the structure of the base station of a LTE radio | wireless communications system. It is a figure which shows the relationship between SINR with respect to each MCS, and a block error rate (BLER). It is a figure which shows the relationship between SINR and throughput with respect to each MCS. It is a figure which shows the example of CQI allocation in AMC. It is a figure explaining reception of a signal and interference in a LTE radio | wireless communications system. It is a figure explaining the subject of this invention. It is a figure which shows the structure of the base station by this invention. It is a figure which shows the effect of the transmission power reduction by this invention. It is a figure explaining the algorithm of this invention. It is a figure for demonstrating the effect by this invention. It is a figure which shows the structure of the base station in the other Example of this invention. It is a figure explaining the algorithm in the other Example of this invention.

  Hereinafter, a transmission power control method in a base station of an LTE radio communication system will be described with reference to the drawings. However, it should be understood that the invention is not limited to the drawings or the embodiments described below.

  First, a base station and adaptive modulation / coding rate control (AMC) in the LTE wireless communication system as the basis of the present invention will be described.

  FIG. 1 is a diagram illustrating a configuration of a base station in an LTE wireless communication system. In FIG. 1, reference numeral 11 is a base station, 12 is CQI information transmitted from a mobile station, 13 is a signal receiver, 14 is a scheduler, 15 is an RLC (Radio Link Control) buffer, and 16 is MAC (Medium Access Control). Multiplexer, 17 is a signal generator, and 18 is a signal transmitter.

  The signal receiving unit 13 of the base station 11 receives signals from a plurality of mobile stations currently managed by the base station (that is, existing in the cell of the base station). This signal includes a data signal and a control signal, and also includes CQI information 12 used for AMC. The CQI information 12 represents a combination (MCS) of a modulation scheme for modulating a signal transmitted from the base station to the mobile station and a coding rate in error correction coding. The received CQI information 12 is sent to the scheduler 14.

  The RLC buffer 15 of the base station 11 is provided for each radio bearer and temporarily stores data for transmission to the mobile station. The RLC buffer 15 notifies the scheduler 14 when data to be transmitted is accumulated in the buffer. The scheduler 14 determines the position (time and frequency) of resource blocks and the number of resource blocks used for signal transmission based on information on data to be transmitted and scheduling rules. As information of data to be transmitted, a required transmission rate, an allowable delay time, an allowable error rate, and the like are assumed.

  The MAC multiplexing unit 16 allocates each mobile station signal to a radio resource based on the scheduling information determined by the scheduler 14. Based on the CQI information 12 notified from the scheduler 14, the signal generator 17 performs error correction encoding and modulation on data to be transmitted to the mobile station, and generates a transmission signal. Other signal processing such as interleaving and framing is omitted here. The generated signal is added with a user-specific reference signal and transmitted from the signal transmission unit 18 to the mobile station.

Next, AMC will be briefly described. FIG. 2 is a diagram showing a relationship between a signal-to-interference plus noise power ratio (SINR) and a block error rate (BLER) for each MCS. MCS is a combination of a signal modulation scheme and a coding rate, and the higher the MCS number, the higher the coding efficiency. BLER indicates an error rate in a block unit of a received signal in the receiver. SINR represents the reception quality of a signal received by a receiver. In each MCS, the higher the SINR, the higher the received signal quality, so the BLER decreases. Also, the higher the MCS number, the higher the transmission amount, and the higher the SINR required to achieve the same BLER (eg, 10 ⁻¹ ).

  FIG. 3 is a diagram showing the relationship between SINR and throughput for each MCS. The throughput is obtained by multiplying the maximum throughput of each MCS by (1-BLER). In the example of FIG. 3, the throughput tp (MCS 1) of MCS1 is obtained by multiplying the maximum throughput Max_tp (MCS 1) of MCS1 by (1.0−BLER (SINR)). Since the MCS is selected in advance so that the throughput characteristics of each MCS intersect, efficient signal transmission is performed by appropriately selecting the MCS that always obtains the highest throughput as shown by the dotted line A in FIG. Can do. For example, when SINR rises and exceeds SINR (t1), switching from MCS1 to MCS2 provides higher throughput than maintaining MCS1.

  FIG. 4 is a diagram illustrating assignment of CQI to SINR. CQI is an index representing MCS. For example, CQI = 1 represents MCS1. Using the throughput characteristics of each MCS shown in FIG. 3, the SINR threshold value at which MCS switching is performed is acquired. This SINR threshold and CQI assignment are shown in FIG. SINR (MCS 2) and SINR (MCS 3) in FIG. 4 correspond to SINR (t1) and SINR (t2) in FIG. 3, and when the SINR is in this section, MCS2 is assigned. In FIG. 4, the SINR threshold interval is shown as being constant, but in reality, it is not constant. However, it is desirable to select the MCS so that the SINR threshold intervals are equal.

  The receiver measures the SINR of the received signal, compares it with the SINR threshold shown in FIG. 4, and obtains the optimum MCS for the current propagation path between the transmitter and the receiver. The receiver feeds back the CQI information representing the acquired MCS to the transmitter. In the transmitter, the MCS corresponding to the CQI information from the receiver is used to encode and modulate the signal for the receiver.

Specific examples of MCS are shown in Table 1 below. In LTE, MCS 1 to 15 are generally used. CQI = 0 is a state in which stable communication cannot be performed because the BLER becomes high even when the MCS1 having the lowest SINR and the lowest transmission amount is used. On the other hand, MCS higher than MCS15 is not supported by both base stations and mobile stations. For this reason, even if the SINR in the mobile station is considerably higher than the SINR required for the MCS 15, the MCS 15 is still used.

  Next, the relationship between the base station and the mobile station in the LTE wireless communication system and the problem of the present invention will be described with reference to FIG. In FIG. 5, reference numeral 21 is an LTE radio communication system, 22 is a base station 1 (eNodeB 1), 23 is a base station 2 (eNodeB 2), 24 is a radio range of the base station 1, and cells 1 and 25 are base stations. 2 and 2 are mobile stations 1 (UE 1) in the cell 1 and wirelessly connected to the base station 1, 27 is a mobile station 2 (UE 1) in the cell 2 and wirelessly connected to the base station 2. 2).

  In downlink communication, the mobile station 1 (26) receives the desired signal S1 from the base station 1 (22), and the mobile station 2 (27) receives the desired signal S2 from the base station 2 (23). In LTE wireless communication, downlink signals are transmitted with a constant power. For this reason, generally, the received signal power at the mobile station 1 (26) in the vicinity of the base station 1 (22) is high, and the mobile station is away from the position of the base station 2 (23) and in the vicinity of the cell boundary. The received signal power at 2 (27) is low. Further, the interference I2 from the base station 2 (23) to the mobile station 1 (26) is weak, and the interference I1 from the base station 1 (22) to the mobile station 2 (27) is relatively strong. As a result, the SINR of the received signal at the mobile station 1 (26) increases, and the SINR of the received signal at the mobile station 2 (27) decreases. As a result, in base station 1 (22), the transmission signal for mobile station 1 (26) is generated using a high MCS, and in base station 2 (23), the transmission signal for mobile station 2 (27) has a low MCS. Generated using.

  It is assumed that the distance between the mobile station 1 (26) and the base station 1 (22) is very close, for example, the mobile station 1 (26) is directly under the antenna of the base station 1 (22). The SINR at mobile station 1 (26) becomes high, and in the example of Table 1, MCS 15 is assigned. However, when the distance to the base station is very close, it is assumed that an excessive SINR signal is received with respect to the SINR required for the MCS 15.

  FIG. 6 is a diagram showing an excessive SINR state in the mobile station. In the current LTE wireless communication system, the maximum usable MCS is MCS15. When the SINR in the mobile station is equal to or greater than the threshold SINR (MCS 15), the MCS 15 is selected, and the MCS 15 is selected even if the SINR is sufficiently larger than the SINR (MCS 15). In FIG. 6, assuming that the current SINR of the mobile station 1 (26) is SINR (UE), SINR (UE) is higher than the threshold SINR (MCS 15) of MCS 15 by SINR_ex. SINR_ex shown here is a value sufficiently larger than the SINR threshold interval between MCSs.

  Even if the mobile station 1 (26) receives an excessive SINR signal, reception characteristics such as throughput are not improved. On the other hand, transmitting an excessive SINR signal is a waste of electric power in the base station, and an extra interference with the mobile station 2 (27) in the adjacent cell. For this reason, in the base station 1 (22), reducing the transmission power of the signal to the mobile station 1 (26) reduces the interference power to the mobile station 2 (27), and the mobile station 2 (27) SINR will be improved.

  In the present invention, when the CQI information notified from the mobile station to the base station is equal to or greater than a predetermined threshold, the base station lowers the transmission power of the transmission signal for the mobile station by a specified value. This suppresses excessive SINR generated in the mobile station and reduces interference with the mobile station in the adjacent cell.

  FIG. 7 is a diagram showing the configuration of the base station in the present invention. A power control unit 19 is added to the base station configuration shown in FIG. Other configurations are the same. Based on the CQI information 12 received from the mobile station, the scheduler 14 controls the transmission power for the mobile station using the following algorithm. The power control unit 19 receives power control information from the scheduler 14 and controls the transmission power of the mobile station.

  FIG. 8 is a diagram for explaining the effect of reducing the transmission power of the base station according to the present invention. By reducing the transmission power so as to reduce the excessive SINR (SINR_ex) shown in FIG. 6 (PD: Power Down in the figure), the transmission power of the base station can be reduced while maintaining the MCS 15. .

  FIG. 9 shows an algorithm for base station transmission power control in the present invention. In S101, the base station receives CQI information from the mobile station. In S102, the received CQI information is compared with a predetermined threshold value. Generally, the threshold is an index representing the highest MCS, and in the example of Table 1, it is 15 representing MCS15. In this case, the comparison of S102 is performed by (CQI information = threshold value). However, the threshold is not limited to the index representing the highest MCS. For example, it is conceivable to limit the MCS depending on the data application. If the data is a relatively low rate communication such as voice or text mail, it is assumed that the MCS used is limited. Also, the base station can determine the communication status and limit the MCS. In such a case, the use of a high MCS can be suppressed by setting the threshold value to a low value and intentionally lowering the transmission power of the base station. When the threshold is not the index representing the highest MCS, the comparison of S102 is performed by (CQI information ≧ threshold).

  If the CQI information is greater than or equal to the threshold value in S102, the transmission power of the base station is decreased by a specified value in S103. In S104, the transmission signal is modulated and encoded using MCS based on the CQI information. Here, the fluctuation amount (specified value) of the transmission power is set smaller than the interval of the SIRS threshold value of MCS, for example. In FIG. 4, when an average of threshold intervals (for example, SINR (MCS3) −SINR (MCS2)) is X dB, a value smaller than X is set. Thereby, it is possible to prevent a rapid decrease in transmission power. However, it is not limited to such a setting.

  When the SINR at the mobile station is very good, the state where the CQI information is equal to or greater than the threshold value continues. As a result, the transmission power for the mobile station continues to decrease. Under such circumstances, when the propagation path state deteriorates rapidly, the transmission power is controlled to be low, so that the communication quality of the transmission signal for the mobile station may be greatly lowered. In consideration of such a situation, a guaranteed value of transmission power can be set so that the transmission power does not fall below a certain level.

  If the CQI information is smaller than the threshold value in S102, it is checked in S105 whether the current transmission power for the mobile station matches the maximum value of the transmission power. If the transmission power is the maximum value, the transmission power is maintained as it is, and in S106, the transmission signal is modulated and encoded by MCS based on the CQI information. If the transmission power is smaller than the maximum value, the transmission power of the base station is increased by a specified value in S107. In S108, the transmission signal is modulated and encoded by MCS based on the CQI information. The fluctuation amount for increasing the transmission power can be the same as the fluctuation amount at the time of decrease, or can be set to be different. For example, when the CQI information is smaller than the threshold value and the transmission power is not the maximum value, the mobile station is not receiving sufficient service. The situation can be improved.

  The CQI information includes the influence of fluctuations in the propagation path state in the mobile station and the influence of measurement errors. For this reason, in the comparison between the CQI information and the threshold value in S102, the influence of the variation in the CQI information can be eliminated by considering the time window. For example, if the time window is five times when CQI information is received, the transmission power can be reduced in S103 only when the CQI information becomes equal to or greater than the threshold value five times in succession. Alternatively, the average value of the five CQI information can be compared with a threshold value.

  Furthermore, if the signal when the transmission power is reduced is retransmitted using information related to the retransmission status of Hybrid Automatic Repeat reQuest (HARQ) control, the signal is retransmitted to reduce the number of retransmissions. Can be increased from the current transmission power value. Furthermore, the increase in transmission power can be increased as the number of retransmissions increases.

  Further, in the downlink of the LTE wireless communication system, a user-specific reference signal is added to the transmission signal for mobile stations and transmitted. The user individual reference signal is used for propagation path estimation in the mobile station. In the present invention, when controlling the transmission power of the data signal, the transmission power of the user individual reference signal is also controlled to the same value. This is because if the transmission power value of the user individual reference signal is different from the transmission power value of the data signal, the result of propagation path estimation is not properly reflected in the demodulation of the data signal in the mobile station.

  Although the present invention has been described using the LTE wireless communication system, the present invention is not limited to the LTE wireless communication system and can be applied to other systems.

The effect of transmission power reduction according to the present invention will be described using the model shown in FIG. In FIG. 10, suppose UE1 wirelessly connected to eNodeB1 and UE2 wirelessly connected to eNodeB2. UE2 is assumed to exist on the cell boundary between eNodeBs. The distance between two eNodeB ISD (Inter-Site Distance) , the eNodeB l and the distance between UE1 R _11, eNodeB 2 and the distance between the UE1 the distance between R _21, eNodeB l and UE2 R _12, eNodeB 2 and UE2 Let R ₂₂ be the distance. In the calculation, the values in Table 2 were used.

  In a state where the base station does not perform transmission power control, the transmission power of each eNodeB is designed so that the reference signal received power (RSRP) at the cell boundary is −90 dBm. The distance attenuation of the propagation signal is assumed to follow the cube of distance.

Table 3 shows calculation results of desired signal power, interference signal power, and SINR in each UE when transmission power control is not performed. In Table 3, RSRP ₁₁ is signal power transmitted from eNodeB1 to UE1, and is the desired signal power of UE1. RSRP ₁₂ represents interference signal power from eNodeB1 to UE2, RSRP ₂₂ represents desired signal power from eNodeB2 to UE2, and RSRP ₂₁ represents interference signal power from eNodeB2 to UE1. I + N is the sum of interference signal power and noise power at each UE.

In Table 3, the SINR of UE1 is 31.2 dB. Assuming that the SINR required to satisfy MCS15 is 20 dB, UE1 receives a signal with a SINR that is about 11 dB higher. For this reason, it is assumed that the transmission power for UE1 of eNodeB1 is reduced by 11 dB. Table 4 shows the calculation results when the eNodeB1 transmission power is reduced by 11 dB. The transmission power of eNodeB2 is not changed.

  Due to the 11 dB decrease in transmit power for UE1 of eNodeB1, the SINR of UE1 decreases by 11 dB from 31.2 dB to 20.2 dB. On the other hand, since the interference with UE2 also decreases by 11 dB, the SINR of UE2 is improved from 0 dB to 11 dB. It has been shown that reducing the transmission power to a mobile station with excessive SINR reduces interference to mobile stations in adjacent cells and improves the mobile station's SINR. Thereby, the throughput characteristic as the whole system can be improved.

  Other embodiments of the present invention will be described below. In the present invention, when the CQI information is equal to or greater than the threshold value, the transmission power for the mobile station is reduced. As a result, the SINR of the received signal is reduced in the mobile station. If the transmission power continues to decrease, the SINR is assumed to be less than or equal to the current MCS threshold. For example, in FIG. 8, SINR (SINR (UE)) in the mobile station may decrease due to a decrease in transmission power, and may be equal to or less than SINR (MCS 15) that is the threshold value of MCS 15. In this case, the mobile station receives a signal generated using the MCS 14, and can enjoy the service (that is, the maximum transmission rate) by the MCS 15 even though the transmission power is reduced. become unable.

  For this reason, when the SINR of the received signal in the mobile station is in the range of MCS15 which is the maximum MCS, the transmission power for the mobile station is controlled so that the SINR becomes the SINR threshold value + α of MCS15. This prevents SINR from becoming SINR (MCS 15) or less due to a decrease in transmission power when using MCS15. In this embodiment, the HARQ control retransmission rate is used. The HARQ control unit of the base station calculates a retransmission rate (retransmission rate) for each MCS when a signal is generated and transmitted by each MCS. The SINR threshold value and the like are adjusted so that this ratio becomes a predetermined value, for example, 10%. In this embodiment, a function of controlling transmission power is added so that the retransmission rate of the maximum MCS (that is, MCS 15) is equal to a predetermined retransmission rate.

  FIG. 11 is a diagram illustrating the configuration of a base station in another embodiment of the present invention. A HARQ control unit 30 is added to the base station configuration shown in FIG. However, the HARQ control unit is installed in the base station in the downlink and performs control related to HARQ. The HARQ control unit 30 always calculates and stores the retransmission rate for each MCS. The HARQ control unit 30 receives the mobile station information and CQI information of the signal to be transmitted next from the scheduler 14. The HARQ control unit 30 notifies the scheduler 14 of the retransmission rate of the MCS 15 in this mobile station when the CQI information corresponds to the MCS 15. The scheduler 14 determines the transmission power according to the notified retransmission rate according to the algorithm shown below, and transmits the transmission power value to the power control unit 19.

  FIG. 12 is a diagram showing an algorithm according to another embodiment of the present invention. A process in the case of CQI information = threshold value is added to the algorithm of FIG. In S110, it is determined whether the received CQI information is small, equal, or large compared to the threshold value. If the CQI information matches the threshold value in S110, the retransmission rate R of the MCS corresponding to the CQI information is compared with a predetermined retransmission rate P in S111. The predetermined retransmission rate is, for example, 10%. When the retransmission rate and the predetermined retransmission rate are the same (R = P), the transmission power maintains the current value in S113. That is, it is assumed that the current transmission power is at an appropriate level. When the retransmission rate is larger than the predetermined retransmission rate (R> P), the SINR at the mobile station is lower than the expected value, the received signal error at the mobile station increases, and the retransmission rate is high. That is, it is determined that the current transmission power is lower than an appropriate level. For this reason, in S112, the transmission power is increased by a specified value. When the retransmission rate is smaller than the predetermined retransmission rate (R <P), it is determined that the SINR in the mobile station is higher than the expected value, and the current transmission power is higher than an appropriate level. For this reason, in S114, the transmission power is decreased by a specified value. In S115, a transmission signal is generated using MCS corresponding to the CQI information.

  If the CQI information is larger than the threshold value in S110, the transmission power of the base station is lowered by a specified value in S121. In S122, the transmission signal is modulated and encoded using MCS based on the CQI information. If the CQI information is smaller than the threshold value in S110, it is checked in S105 whether the current transmission power for the mobile station matches the maximum value of the transmission power. If the transmission power is the maximum value, the transmission power is maintained as it is, and in S106, the transmission signal is modulated and encoded by MCS based on the CQI information. If the transmission power is smaller than the maximum value, the transmission power of the base station is increased by a specified value in S107. In S108, the transmission signal is modulated and encoded by MCS based on the CQI information.

  Thus, by considering the retransmission rate in HARQ control, it is possible to prevent the transmission power from being excessively reduced.

DESCRIPTION OF SYMBOLS 11 Base station 12 CQI information 13 Signal receiving part 14 Scheduler 15 RLC buffer 16 MAC multiplexing part 17 Signal generation part 18 Signal transmission part 19 Power control part 30 HAQR control part

Claims (7)

A method for controlling transmission power for a mobile station in a base station of an LTE wireless communication system, comprising:
Receiving from the mobile station channel quality indicator (CQI) information representing received signal quality at the mobile station of the signal transmitted from the base station;
Calculating a retransmission rate in hybrid automatic repeat request control for each MCS;
Comparing the CQI information with a predetermined threshold;
Determining the transmission power value to decrease the transmission power value of the signal transmitted to the mobile station by a specified value when the CQI information is larger than the threshold value as a result of the comparison;
As a result of the comparison, when the CQI information is equal to the threshold value and the retransmission rate of the MCS according to the CQI information is smaller than a predetermined retransmission rate, transmission of a signal to be transmitted to the mobile station Determining the transmit power value to decrease the power value by a specified value;
Generating a signal to be transmitted to the mobile station based on a modulation scheme and a coding rate (MCS) according to the CQI information;
Transmitting the generated signal to the mobile station at the determined transmission power value;
A transmission power control method comprising:   The transmission power according to claim 1, further comprising a step of increasing the transmission power value by a specified value when the CQI information is less than the threshold value and the transmission power value to the mobile station is not a maximum value. Control method.   When the retransmission rate of MCS according to the CQI information is larger than the predetermined retransmission rate, the transmission power value is increased by a prescribed value, and when the retransmission rate is equal to the predetermined retransmission rate, the transmission power value is maintained. The transmission power control method according to claim 1, further comprising a step of determining the transmission power value.   The transmission power control method according to any one of claims 1 to 3, further comprising a step of determining a transmission power value of the user-specific reference signal for the mobile station according to the transmission power value to the mobile station. . A base station in an LTE wireless communication system,
A signal receiving unit that receives from the mobile station channel quality indicator (CQI) information indicating the received signal quality of the signal transmitted from the base station at the mobile station;
A HARQ control unit that calculates a retransmission rate in hybrid automatic repeat request (HARQ) control for each MCS;
The CQI information is compared with a predetermined threshold value, and when the CQI information is larger than the threshold value, the transmission power value is determined so that the transmission power value of a signal transmitted to the mobile station is decreased by a specified value. When the CQI information is equal to the threshold value and the retransmission rate of the MCS according to the CQI information is smaller than a predetermined retransmission rate, a transmission power value of a signal to be transmitted to the mobile station is defined. A scheduler for determining the transmission power value to decrease by a value;
A power control unit that controls transmission power for the mobile station according to the transmission power value notified from the scheduler;
A signal generation unit that generates a signal to be transmitted to the mobile station based on a modulation scheme and a coding rate according to the CQI information;
A signal transmission unit for transmitting the encoded signal to the mobile station at the transmission power value;
A base station comprising:   The scheduler increases the transmission power value by a prescribed value when the retransmission rate of the MCS according to the CQI information is larger than the predetermined retransmission rate, and when equal to the predetermined retransmission rate, the transmission power value The base station according to claim 5, wherein the transmission power value is determined so as to be maintained.   The base station according to claim 5 or 6, wherein the scheduler determines a transmission power value of the user-specific reference signal for the mobile station in accordance with the transmission power value to the mobile station.

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