JP2012060539A - Communication apparatus and communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method where a base station changes a transmission power to a terminal flexibly.SOLUTION: A communication apparatus comprises a modulation scheme determination part, a reception quality deciding part, a transmission power determination part, and a transmission part. The modulation scheme determination part determines a modulation scheme of data transmitted to a first terminal and a modulation scheme of data transmitted to a second terminal from either of the first modulation scheme or the second modulation scheme. In the first modulation scheme, data is expressed by a phase variation, and in the second modulation scheme, an amplitude of a reference signal common to the first and second terminal is used as a reference value. The reception quality deciding part decides whether a reception quality reported from the terminal with the first modulation scheme determined is not less than a threshold value. The transmission power determination part adjusts the transmission power of the signal demodulated in the first terminal so that it becomes small if the reception quality of the first terminal is not less than a threshold value in the case of modulating the data transmitted to the first terminal by the first modulation scheme. The transmission part transmits to the first terminal the signal whose transmission power is adjusted.

Description

  The present invention relates to a communication device used for wireless communication.

  In recent years, a transition from a 3G system communication system to a 3.9G system communication system is underway. Here, the communication system of the 3G system includes, for example, Wideband Code Division Multiplex Access (W-CDMA) and CDMA2000. On the other hand, in the 3.9G system, standards such as Long Term Evolution (LTE) and Worldwide interoperability for Microwave Access (WiMAX) are defined, for example. In LTE, a shared channel in which a plurality of terminals share a channel is used for communication between the base station apparatus and the terminal. In LTE, a reference signal for the terminal to detect a downlink signal synchronously is also used. This reference signal is used as a common signal for each cell.

  In LTE, the value of the signal strength of the reference signal is determined for each cell, but a method in which the base station controls the transmission power of the signal for each terminal has been devised. For example, the base station can control the transmission power of the signal for each terminal by changing the ratio of the power intensity of the Physical Downlink Shared Channel (PDSCH) to the power intensity of the reference signal for each terminal. Here, the parameter (PA) representing the ratio is a value representing the ratio between the power intensity of the signal transmitted via the PDSCH and the power intensity of the reference signal in dB. The base station notifies each terminal individually of the value of the parameter PA used for that terminal. Each terminal calculates the PDSCH power intensity using the reference signal and the PA, and decodes the received signal based on the obtained power intensity.

  As a related technique, the maximum transmission block size satisfying a predetermined reception quality can be determined according to the estimated communication signal quality, and a combination of the number of spreading codes and the modulation scheme corresponding to the transmission block size can be assigned. Base station devices are known.

Patent No. 3796212

3GPP TS 36.213 V8.8.0

  When the reception quality of a terminal is good, communication between the base station and the terminal is possible even if the transmission power to the terminal is small. Therefore, the base station can reduce the transmission power to the terminal having good reception quality, and the power consumption of the base station can be reduced by reducing the transmission power. However, the terminal uses the parameter PA notified from the base station when demodulating the received signal. Therefore, when the base station changes the transmission power to a certain terminal, prior to changing the transmission power, the base station sets a parameter PA indicating the ratio of the transmission power intensity to the reference signal of the transmission power intensity after the change to the terminal. Notice. In other words, the base station cannot change the transmission power to the terminal until it transmits a parameter indicating the ratio of the transmission power after the change to the transmission power of the reference signal. For this reason, it is difficult for the base station to flexibly change the transmission power according to the reception quality of the terminal. In the background art, the case of LTE has been described, but the same problem occurs when a plurality of terminals use the same reference signal for demodulation other than LTE.

  An object of the present invention is to provide a method in which a base station flexibly changes transmission power to a terminal.

  A communication apparatus according to an embodiment includes a modulation scheme determination unit, a reception quality determination unit, a transmission power determination unit, and a transmission unit. The modulation scheme determining unit determines each of a modulation scheme of data to be transmitted to the first terminal and a modulation scheme of data to be transmitted to the second terminal from either the first modulation scheme or the second modulation scheme. . Here, the first modulation scheme is a modulation scheme that represents data by a change in phase, and the second modulation scheme uses a reference signal amplitude that is common to the first and second terminals as a reference value. It is. The reception quality determination unit determines whether the reception quality reported from the terminal determined as the first modulation scheme is equal to or higher than a threshold value. When the data to be transmitted to the first terminal is modulated by the first modulation scheme, the transmission power determining unit demodulates the data by the first terminal if the reception quality of the first terminal is equal to or higher than the threshold. The transmission power of the received signal is adjusted to be small. The transmission unit transmits the signal whose transmission power is adjusted to the first terminal.

  The base station can flexibly change the transmission power to the terminal.

It is a figure explaining the example of the control method of the transmission power in a base station. It is a figure which shows the structural example of a base station. It is a figure which shows the example of the hardware constitutions of a baseband signal processing part. It is a flowchart explaining the example of operation | movement of the base station in 1st Embodiment. It is a table which shows the example of the data which a transmission power determination part hold | maintains. It is a figure which shows the example of the result as which transmission power was changed by 1st Embodiment. It is a figure which shows the example of a transmission power table. It is a flowchart explaining the example of operation | movement of the base station in 2nd Embodiment. It is a table which shows the example of the data which a transmission power determination part hold | maintains. It is a figure which shows the example of the result as which transmission power was changed by 2nd Embodiment. It is a figure which shows the structural example of the base station concerning 3rd Embodiment. It is a figure which shows the example of an MCS index table. It is a figure which shows the example of a transport block size table. It is a figure explaining the example in case the data scheduled to be modulated by quadrature amplitude modulation can be transmitted by QPSK. It is a flowchart explaining the example of operation | movement of a change part. It is a flowchart explaining the example of operation | movement of a scheduler. It is a table which shows the example of the data which a change part and a transmission power determination part hold | maintain. It is a figure which shows the example of the result as which transmission power was changed by 3rd Embodiment. It is a flowchart explaining the modification of operation | movement of a scheduler.

  FIG. 1 is a diagram for explaining an example of a transmission power control method in the base station 10. As shown in FIG. 1A, it is assumed that the terminal UE1 and the terminal UE2 are located in a cell 1 configured by the base station 10. The base station 10 transmits the signal 3 (3a, 3b), the reference signal 4, and the like toward the terminals UE1 and UE2 located in the cell 1. Here, the signal 3a is a signal demodulated by the terminal UE1, the signal 3b is a signal demodulated by the terminal UE2, and both the signals 3a and 3b are transmitted to the terminals UE1 and UE2 via the PDSCH. Further, the thickness of the arrows indicating each of the signals 3a and 3b and the reference signal 4 represents the magnitude of the transmission power of each signal. In order to help understanding in the following description, in FIG. 1A, it is assumed that signals 3a and 3b are transmitted to terminals UE1 and UE2 with the same transmission power.

  Here, it is assumed that the base station 10 has previously notified the parameter UE_1 to the terminal UE1 and the parameter PA_2 to the terminal UE2. When receiving a signal modulated by quadrature amplitude modulation, such as 16 quadrature amplitude modulation (16QAM), for example, the terminals UE1 and UE2 demodulate the signal using the parameter notified from the base station 10 and the reference signal 4. At this time, a value obtained by multiplying the transmission power ratio obtained from the notified parameter and the amplitude of the reference signal 4 is used as an amplitude reference value for specifying the transmitted symbol. On the other hand, when receiving a signal modulated by phase shift keying such as quadrature phase shift keying (QPSK) or binary phase shift keying (BPSK), the terminals UE1 and UE2 do not use the signal amplitude for signal demodulation. That is, the terminals UE1 and UE2 do not use the parameter notified from the base station 10 when demodulating a signal modulated by phase shift keying.

  A case where the base station 10 transmits signals to the terminals UE1 and UE2 again after the base station 10 transmits signals as illustrated in FIG. 1A will be described with reference to FIG. Assume that the base station 10 does not change the parameters PA_1 and PA_2 after the signal transmission in FIG. 1A until the transmission in FIG. 1B. Further, the terminals UE1 and UE2 are located closer to the base station 10 in FIG. 1B than in the case of FIG. 1A, and the terminals UE1 and UE2 are compared to the case of FIG. In both cases, it is assumed that the reception quality is improved.

  The base station 10 confirms the modulation scheme of the signal to be transmitted for each of the terminals UE1 and UE2. Here, it is assumed that the signal 3a is modulated by QPSK and the signal 3b is modulated by 16QAM. In this case, the terminal UE1 does not demodulate data using the reference value of the amplitude of the signal 3a. That is, the base station 10 determines that the terminal UE1 demodulates the signal without using the parameter PA_1. Next, the base station 10 determines whether the reception quality of the terminal UE1 exceeds a threshold value. Here, since the terminal UE1 is located near the base station 10, it is assumed that the reception quality of the terminal UE1 is equal to or higher than the threshold value. When the reception quality is equal to or higher than the threshold, as shown in FIG. 1 (b), the base station 10 makes the transmission power of the signal 3a demodulated by the terminal UE1 smaller than when the signal is transmitted in FIG. 1 (a). .

  On the other hand, since the signal 3b is modulated by 16QAM, the base station 10 determines that the terminal UE2 demodulates the signal using the reference value obtained by using the parameter PA_2 and the reference signal 4. Therefore, if the transmission power of the signal 3b is changed without changing the value of the parameter PA_2, it is determined that the terminal UE2 cannot correctly calculate the amplitude reference value for demodulating the signal 3b and cannot be demodulated correctly. Therefore, the transmission power of the signal 3b is not changed.

  Thus, when the signal 3 is modulated by phase shift keying, even if the base station 10 reduces the transmission power of the signal 3, if the reception quality is not impaired, the terminal correctly demodulates the signal 3. By utilizing what can be done, the transmission power from the base station 10 can be reduced. By reducing the transmission power, the power consumption of the base station 10 can be reduced.

<Device configuration>
FIG. 2 is a diagram illustrating a configuration example of the base station 10. The base station 10 includes a line termination unit 11, a call processing control unit 12, a transmission / reception amplification unit 13, an antenna 14, and a baseband signal processing unit 20.

  The line termination unit 11 terminates a signal transmitted / received to / from a host device. Note that the host device can be, for example, a security gateway or a mobile management entity (MME) in a network to which LTE is applied. The call processing control unit 12 performs call processing of the base station 10, monitoring of the state of the line termination unit 11, the transmission / reception amplification unit 13, the antenna 14, the baseband signal processing unit 20, and the like. The transmission / reception amplification unit 13 amplifies the baseband signal output from the baseband signal processing unit 20 and converts it into a radio signal using a carrier wave. Further, the transmission / reception amplification unit 13 removes the carrier wave from the signal received from the terminal via the antenna 14, extracts the baseband signal, and outputs it to the baseband signal processing unit 20.

  The baseband signal processing unit 20 processes the data input from the line termination unit 11 and the baseband signal input from the transmission / reception amplification unit 13. The baseband signal processing unit 20 includes a modulation unit 21, an encoding unit 22, a demodulation unit 23, a decoding unit 24, a Media Access Control (MAC) control unit 25, a Radio Link Control (RLC) control unit 26, and a Packet Data Convergence Protocol. (PDCP) The control part 27, the memory | storage part 28, and the scheduler 30 are provided. The scheduler 30 includes a scheduling unit 31, a modulation scheme determination unit 32, a reception quality determination unit 33, a transmission power determination unit 34, and a calculation unit 35.

  The modulation unit 21 modulates the signal input from the encoding unit 22 by the modulation method specified by the scheduler 30. In the following description, a case where modulation is performed by any one of QPSK, 16QAM, and 64QAM will be described. However, the modulation unit 21 modulates a signal using an arbitrary phase shift keying method or quadrature amplitude modulation method. Can do. Furthermore, when the transmission power value is designated by the transmission power determination unit 34, the modulation unit 21 adjusts the signal transmitted from the base station 10 to the designated transmission power. The encoding unit 22 encodes the baseband signal at the coding rate specified by the scheduler 30. Further, the encoding unit 22 outputs the encoded data to the modulation unit 21.

  The demodulator 23 demodulates the signal input from the transmission / reception amplifier 13 according to the modulation method of the signal. The demodulator 23 outputs the demodulated signal to the decoder 24. The decoding unit 24 decodes the signal input from the demodulation unit 23 and outputs the obtained result to the scheduler 30 and the MAC control unit 25. For example, the decoding unit 24 outputs the CQI value sent from the communicating terminal to the scheduler 30 after decoding the CQI value.

  The MAC control unit 25 performs processing such as mapping by the MAC protocol. The RLC control unit 26 controls data retransmission and the like using the RLC protocol. The PDCP control unit 27 performs packet processing according to the PDCP protocol. The storage unit 28 stores data used in processing performed by the baseband signal processing unit 20. For example, threshold values used by the reception quality determination unit 33, the transmission power determination unit 34, and the like are stored. The information stored in the storage unit 28 will be described in detail later.

  Next, processing performed by the scheduler 30 will be described. In the following description, the unit of frequency band allocation to the terminal may be described as “resource block”. Here, one resource block represents a continuous constant time for a fixed number of continuous subcarriers. For example, one resource block can be a continuous 0.5 milliseconds for 12 consecutive subcarriers.

  The scheduling unit 31 uses the amount of data to be transmitted to the terminal, the state of the propagation path, the past selection state of each terminal in communication with the base station 10, and the like so that the throughput of the cell 1 is optimized. Assign to a terminal. For example, the scheduling unit 31 determines the number of terminals that communicate with one radio frame in order to optimize the throughput of the cell 1. For example, the scheduling unit 31 can perform resource block allocation using a scheduling coefficient. The calculation method of the scheduling coefficient may be an arbitrary calculation method such as a proportional fairness method, a round robin method, or a maximum carrier-to-interference-and-noise ratio method (Maximum CINR method). The scheduling unit 31 allocates resource blocks to terminals communicating with the base station 10 using the calculated scheduling coefficient. Further, the scheduling unit 31 outputs the result of allocating resource blocks to the modulation scheme determining unit 32.

  The modulation scheme determining unit 32 determines, for each terminal to which a resource block is allocated, a modulation scheme, a coding rate, a transport block size, and the like used for communication between the terminal and the base station 10. In the following description, a case where the baseband signal is modulated by any one of QPSK, 16QAM, and 64QAM will be described. The modulation scheme determination unit 32 is configured to transmit information that is desired to reduce the probability of occurrence of a transmission error as much as possible by QPSK. For example, the modulation scheme determination unit 32 may set the modulation scheme used for transmission of high priority and importance data such as disaster information and emergency information to QPSK, and further set the transport block size to a small value. it can. In addition, data that requires real-time performance at a low rate, such as audio data, is also modulated by QPSK, and the transport block size is set small. It is assumed that the modulation scheme determination unit 32 can identify high priority information or information that requires real-time performance using an identifier such as a QoS Class Identifier (QCI), for example.

  Here, it has been described that the modulation scheme determination unit 32 determines the transport block size, but the transport block size is a value that varies depending on the coding rate of error correction. That is, since the modulation scheme determining unit 32 determines the error correction coding rate and the modulation scheme, the modulation scheme determining unit 32 can also determine the Modulation Coding Scheme (MCS) index value. The modulation scheme determining unit 32 notifies the terminal of the determined MCS index through the Physical Downlink Control Channel (PDCCH). The terminal recognizes the modulation scheme, the transport block size, the coding rate, and the like using the notified MCS index value, and demodulates the signal received via the PDSCH.

  The reception quality determination unit 33 determines whether the reception quality of the terminal located in the cell 1 of the base station 10 is equal to or higher than the reception quality indicated by the threshold. For example, Channel Quality Indicator (CQI) can be used for evaluation of reception quality. The base station 10 acquires the CQI value measured by the terminal via a Physical Uplink Control Channel (PUCCH) or a Physical Uplink Shared Channel (PUSCH). The reception quality judgment unit 33 holds, for each terminal, a pair of terminal identifier and reception quality of the terminal. The reception quality determination unit 33 can also store information in which the identifier of the terminal is associated with the reception quality of the terminal in the storage unit 28.

  The transmission power determination unit 34 checks the modulation scheme of the transmitted signal 3 for each terminal. When the modulation method of data demodulated by a certain terminal is QPSK, the reception quality judgment unit 33 is inquired whether the reception quality of the terminal is equal to or higher than a threshold value. When the reception quality is equal to or higher than the reception quality represented by the threshold, the transmission power determination unit 34 determines that the transmission power of the signal 3 can be reduced. Here, it is assumed that the transmission power determination unit 34 stores in advance transmission power values that can be set when the transmission power is reduced. The transmission power value that can be set is determined in advance by an operator or the like based on an error rate of data transmitted to a terminal having reception quality represented by a threshold value. For example, the transmission power value may be set so that the error rate at the terminal having the reception quality represented by the threshold is less than 10%. The transmission power determination unit 34 notifies the modulation unit 21 of the transmission power. The transmission power determination unit 34 can also notify the transmission power value as a ratio of the reference signal to the transmission power.

  When changing the power intensity of the signal modulated by the quadrature amplitude modulation method to a certain terminal, the calculation unit 35 calculates the ratio of the power intensity after the change and the transmission power intensity of the reference signal 4, and sets the parameter PA Ask for. The base station 10 appropriately notifies the terminal of the calculation result of the calculation unit 35 through the control channel.

  FIG. 3 is a diagram illustrating an example of a hardware configuration of the baseband signal processing unit 20. The baseband signal processing unit 20 includes, for example, a field programmable gate array (FPGA) 41, a switch 42, a central processing unit (CPU) 43, a digital signal processor (DSP) 44 (44a, 44b), and a memory 45 (45a to 45c). ). The FPGA 41 may be replaced with an application specific integrated circuit (ASIC), and the CPU 43 may be replaced with a micro-processing unit (MPU).

  The memory 45 operates as the storage unit 28. The FPGA 41 operates as a modulation unit 21, an encoding unit 22, a demodulation unit 23, and a decoding unit 24 by executing a program stored in the memory 45. The DSP 44 operates as the scheduler 30, the MAC control unit 25, the RLC control unit 26, and the PDCP control unit 27 by executing a program stored in the memory 45. The CPU 43 can also operate as the scheduler 30, the MAC control unit 25, the RLC control unit 26, and the PDCP control unit 27. The switch 42 connects the CPU 43 and the DSP 44 to the FPGA 41 as appropriate. FIG. 3 shows an example of the hardware configuration, and the numbers of the FPGA 41, the CPU 43, the DSP 44, and the memory 45 can be arbitrarily changed. The switch 42 may be included in the FPGA 41.

<First Embodiment>
FIG. 4 is a flowchart for explaining an example of the operation of the base station 10 in the first embodiment. Hereinafter, a method for determining transmission power when the base station 10 transmits a signal to the terminal will be described in detail. Note that FIG. 4 is an example of the operation of the base station 10. For example, the operation of the base station 10 may be changed depending on the implementation, such as step S2 and step S3 being interchanged.

  First, the scheduling unit 31 allocates resource blocks to terminals based on the scheduling coefficient calculated for each terminal located in the cell 1 (step S1). Here, it is assumed that resource blocks are allocated to terminals UE1 to UE4 located in cell 1.

Furthermore, the scheduling unit 31 temporarily sets the transmission power ratio of the signal to each terminal based on the parameter PA notified in advance to each terminal (step S2). In the following description, for the sake of simplicity, the transmission power of each terminal is described as a value expressed in dB with respect to the reference signal 4. The ratio with respect to the reference signal 4 is expressed by the following equation. Therefore, a terminal having a larger transmission power ratio (dB) has a higher transmission power to that terminal.
Transmission power ratio = PDSCH transmission power / reference signal transmission power Here, in order to facilitate understanding, it is assumed that the value of the parameter PA notified to each terminal is PA0 (dB) in any of the terminals UE1 to UE4. To do. Therefore, here, the transmission power ratio is set to PA0 (dB) for each of the terminals UE1 to UE4.

  Next, the modulation scheme determining unit 32 determines the modulation scheme of the signal transmitted to the communication destination terminal (step S3). For example, it is assumed that the reception quality of the terminal UE1 is not good and the reception quality of the terminals UE2 and UE3 is good. Further, it is assumed that the reception quality of the terminal UE4 is better than that of the terminal UE3. Further, it is assumed that the base station 10 receives emergency information addressed to the terminal UE3 from the higher-level device. Then, the modulation scheme determination unit 32 sets the modulation method of the terminals UE1, UE2, and UE4 according to the reception quality of each terminal. Here, it is assumed that the modulation scheme determination unit 32 determines to use QPSK for communication between the terminal UE1 and the base station 10. Similarly, it is assumed that the modulation scheme determination unit 32 determines to use 16QAM for communication with the terminal UE2 and 64QAM for communication with the terminal UE4. On the other hand, since the base station 10 transmits emergency information to the terminal UE3, the modulation scheme determining unit 32 sets the modulation scheme used for communication with the terminal UE3 to QPSK regardless of the reception quality. The modulation scheme determination unit 32 notifies the transmission power determination unit 34 of the determined modulation method.

  FIG. 5 is a table showing an example of data held by the transmission power determination unit 34. As shown in FIG. 5A, the transmission power determination unit 34 stores the modulation scheme notified from the modulation scheme determination unit 32 in association with the identifier of the terminal. Furthermore, the transmission power determination unit 34 acquires the transmission power ratio set for each terminal from the scheduling unit 31. This transmission power ratio is PA0 (dB) in any terminal as shown in FIG.

  The transmission power determination unit 34 confirms whether or not the determined modulation scheme is QPSK for each of the terminals to which resource blocks are allocated (step S4). For example, the transmission power determination unit 34 can check whether there is a terminal that receives a signal modulated by QPSK with reference to the modulation scheme in the table of FIG. In the example illustrated in FIG. 5A, the terminal UE1 and the terminal UE3 receive a signal modulated by QPSK.

When detecting a terminal that receives a signal modulated by QPSK, the transmission power determination unit 34 determines, for each detected terminal, whether or not the reception quality of the terminal is better than the reception quality represented by the threshold value. The reception quality determination unit 33 is requested (step S5). The reception quality determination unit 33 determines the terminal requested from the transmission power determination unit 34. Here, for example, the reception quality determination unit 33 determines the reception quality using the CQI value, and the threshold value and the CQI values of the terminals UE1 and UE3 are as follows.
CQI value as threshold: 5
CQI value obtained by terminal UE1: 3
CQI value obtained at terminal UE3: 9
Since the reception quality improves as the CQI value increases, the reception quality determination unit 33 determines that the reception quality of the terminal UE1 is less than the reception quality represented by the threshold. On the other hand, the reception quality determination unit 33 determines that the reception quality of the terminal UE3 is equal to or higher than the reception quality represented by the threshold value. The reception quality determination unit 33 notifies the transmission power determination unit 34 of the determination result.

  The transmission power determination unit 34 decreases the transmission power ratio for a terminal determined to have received quality equal to or higher than the reception quality represented by the threshold (Yes in step S5, step S6). In addition, the transmission power determination part 34 shall memorize | store the change value when making transmission power ratio small previously. For example, the transmission power determination unit 34 changes the transmission power ratio of the terminal UE3 to X (dB). Note that X is a value smaller than PA0. On the other hand, the transmission power determining unit 34 does not change the transmission power ratio of the signal for a terminal determined that the reception quality equal to or higher than the reception quality represented by the threshold is not obtained, and sets the value to a temporarily set value. Set (No in step S5, step S7). For example, the transmission power determination unit 34 does not change the transmission power ratio of the signal to the terminal UE1, but sets the temporarily set PA0 (dB) as the transmission power ratio. For a terminal whose received signal is not modulated by QPSK, the transmission power determination unit 34 does not change the transmission power ratio of the signal and sets it to a temporarily set value (No in step S4, step S8). For example, the transmission power determination unit 34 does not change the transmission power ratio of signals to the terminals UE2 and UE4, and sets the temporarily set PA0 (dB) as the transmission power ratio.

  FIG. 5B shows an example of the result of setting the transmission power ratio for each terminal. In the table shown in FIG. 5B, the reception quality is indicated by a CQI value, the CQI value of the terminal UE1 is less than the threshold value, and the CQI value of the terminal UE3 is recorded to be equal to or higher than the threshold value. FIG. 5B is an example of recording information held by the transmission power determination unit 34. For example, the type of information to be recorded and the method for recording information indicating reception quality are changed according to the implementation. There is a case.

  FIG. 6 is a diagram illustrating an example of a result of changing the transmission power ratio according to the first embodiment. FIG. 6A is a diagram showing that the transmission power ratio is temporarily set to PA0 (dB) for each of terminals UE1 to UE4. The vertical axis in FIG. 6A is the ratio of the transmission power provisionally set for each terminal to the transmission power of the reference signal 4. As described above, since the scheduling unit 31 temporarily sets the same transmission power ratio in any of the terminals UE1 to UE4, there is no difference in the transmission power ratio between the terminals in FIG. FIG. 6B shows an example of the transmission power ratio when the transmission power ratio is changed. As described with reference to FIGS. 4 and 5, when the CQI value is greater than or equal to the threshold among the terminals that receive the signal modulated by QPSK, the transmission power ratio is set to a value smaller than PA0 (dB). Be changed. Accordingly, as illustrated in FIG. 6B, the transmission power ratio to the terminal UE3 among the terminals UE1 to UE4 is changed to X (dB).

  Thus, when the reception quality of a terminal that receives a signal transmitted by phase shift keying such as QPSK is good, the base station 10 according to the present embodiment can reduce the transmission power of the signal to that terminal. it can. Therefore, the amount of power consumed by the base station 10 can be reduced. Further, before changing the transmission power of the signal modulated by the phase shift keying, the base station 10 transmits the transmission power without changing the ratio of the transmission power after the change and the transmission power of the reference signal 4 to the receiving terminal. The power can be changed. Therefore, the base station 10 can flexibly adjust the transmission power according to the reception quality of the terminal and the signal modulation scheme. The base station 10 is particularly effective when a signal transmitted to a terminal having good reception quality is modulated by phase shift keying. Therefore, as described above, when scheduling is performed to transmit high-priority information such as emergency information and disaster information or data that requires real-time performance at a low rate, such as voice data, by QPSK. The effect of reducing power consumption by the base station 10 is increased.

<Second Embodiment>
In the second embodiment, a description will be given of the base station 10 that can change the transmission power to a smaller value as the reception quality of a terminal that receives a signal modulated by phase shift keying improves. Also in the second embodiment, the modulation unit 21, the encoding unit 22, the demodulation unit 23, the decoding unit 24, the MAC control unit 25, the RLC control unit 26, the PDCP control unit 27, the modulation scheme determination unit 32, and the scheduling unit 31 The operation is the same as in the first embodiment. The operations of the line termination unit 11, the call processing control unit 12, the transmission / reception amplification unit 13, and the antenna 14 are the same as those in the first embodiment.

  In the second embodiment, it is assumed that the base station 10 stores information associating reception quality and transmission power of a terminal such as a transmission power table in the storage unit 28. The transmission power table shown in FIG. 7 records the CQI value of the terminal in association with the ratio of the transmission power of the signal to the transmission power of the reference signal 4. Here, in FIG. 7, A is a value larger than B, and is a smaller value in the order of PA0> Z> Y. FIG. 7 is an example of a transmission power table, and the number of thresholds can be any number greater than or equal to two. For example, eight transmission power ratios corresponding to the reception quality of the terminal are stored in the transmission power table storing seven threshold values. Moreover, the determination method of a threshold value and the determination method of transmission power ratio can be arbitrarily changed according to mounting. For example, when the ratio of the transmission power at which the error rate of data transmitted to a terminal having a CQI value is 10% to the transmission power of the reference signal is Y (dB), it is set according to the error rate. The transmission power value may be recorded in the transmission power table.

  The reception quality judgment unit 33 indicates the reception quality of a terminal that receives a signal modulated by phase shift keying among terminals to which resource blocks are allocated, and is represented by a threshold recorded in the transmission power table. Compare with For example, the reception quality determination unit 33 compares the CQI value of the terminal UE1 with A and B recorded in the transmission power table shown in FIG. The reception quality determination unit 33 notifies the transmission power determination unit 34 of the comparison result. The transmission power determination unit 34 adjusts the transmission power ratio of the signal transmitted to the terminal according to the result received from the reception quality determination unit 33. A specific example of the adjustment method will be described later.

  FIG. 8 is a flowchart for explaining an example of the operation of the base station 10 in the second embodiment. Hereinafter, an example of the base station 10 in the second embodiment will be described with reference to FIG. FIG. 8 shows an example of the operation of the base station 10. For example, the operation of the base station 10 may be changed depending on the implementation, such as step S12 and step S13 being interchanged.

  The operations performed in steps S11 to S13 are the same as the operations in steps S1 to S3 described with reference to FIG. Here, it is assumed that resource blocks are allocated to the terminals UE1 to UE4 in step S11. In step S12, it is assumed that PA0 (dB) is temporarily set as the ratio between the transmission power of the signal and the transmission power of the reference signal 4 in each of the terminals UE1 to UE4. Furthermore, in step S13, it is assumed that the modulation scheme determination unit 32 determines to modulate the signal to the terminals UE1 to UE3 with QPSK and the signal to the terminal UE4 with 64QAM. In this case, the transmission power determination unit 34 can acquire information shown in the table of FIG.

  When the modulation scheme is determined, the transmission power determination unit 34 checks whether the modulation scheme is QPSK for each terminal (step S14). For example, the transmission power determination unit 34 recognizes that the terminals UE1 to UE3 receive a signal modulated by QPSK based on the table shown in FIG.

  Next, the transmission power determination unit 34 notifies the reception quality determination unit 33 of an identifier for identifying a terminal that receives a signal modulated by QPSK. The reception quality determination unit 33 compares the value indicating the reception quality for the notified terminal with a threshold value (step S15). The reception quality determination unit 33 notifies the transmission power determination unit 34 of the comparison result. For example, when the transmission power table of FIG. 7 is used, the reception quality determination unit 33 compares the CQI value of the terminal with a threshold value. Here, it is assumed that the CQI value of terminal UE1 is B or more and less than A. Further, it is assumed that the CQI value of the terminal UE2 is less than B and the CQI value of the terminal UE3 is A or more. When the reception quality determination unit 33 notifies the transmission power determination unit 34 of the comparison result, the data held in the transmission power determination unit 34 is changed as shown in FIG.

  The transmission power determination unit 34 sets a transmission power ratio corresponding to the reception quality for a terminal that receives a signal modulated by QPSK (step S16). The transmission power determination unit 34 acquires, for each terminal, a transmission power ratio corresponding to the comparison result between the reception quality and the threshold from the transmission power table. For example, as illustrated in FIG. 9B, the CQI value of the terminal UE1 is greater than or equal to B and less than A. Therefore, the transmission power determination unit 34 refers to the transmission power table illustrated in FIG. 7 and sets the transmission power ratio of the terminal UE1 to Z (dB). Similarly, since the CQI value of the terminal UE3 is greater than or equal to A, the transmission power determination unit 34 sets the transmission power ratio to the terminal UE1 to Y (dB). On the other hand, since the CQI value of the terminal UE2 is less than B, the transmission power determination unit 34 sets the transmission power ratio of the signal to the terminal UE2 to PA0 (dB).

  On the other hand, for a signal demodulated by a terminal whose modulation method is not QPSK, the transmission power determination unit 34 sets PA0 (dB), which is temporarily set, as the transmission power ratio without changing the transmission power ratio (step S1). No in S14, step S17). Therefore, the transmission power of the signal demodulated by the terminal UE4 is not changed. FIG. 9C shows the set transmission power ratio value.

  FIG. 10 is a diagram illustrating an example of a result of changing the transmission power according to the second embodiment. As illustrated in FIG. 10A, before the process by the transmission power determination unit 34 is performed, the transmission power ratio is temporarily set to PA0 (dB) for each of the terminals UE1 to UE4. FIG. 10B shows an example of the transmission power ratio when the transmission power ratio is changed by the transmission power determination unit 34. As described with reference to FIGS. 7 to 9, for a terminal that receives a signal modulated by QPSK, the transmission power determination unit 34 adjusts so that the transmission power ratio decreases as the CQI value increases. That is, for the terminals UE1 to UE3, the CQI value increases in the order of UE2 <UE1 <UE3. Therefore, the transmission power determination unit 34 decreases the transmission power ratio of the signals demodulated by the terminals UE1 to UE3 in the order of UE2> UE1> UE3. On the other hand, the transmission power determination unit 34 does not change the transmission power ratio of signals that are not modulated by QPSK. For example, as shown in FIG. 10B, since the terminal UE4 demodulates a signal modulated by 64QAM, the base station 10 is temporarily set without changing the transmission power ratio of the signal demodulated by the terminal UE4. PA0 (dB) is used as the transmission power ratio.

  Thus, in the second embodiment, the transmission power ratio can be finely adjusted compared to the first embodiment. In addition, since the number of thresholds and the number of transmission power ratios stored in the transmission power table used as described above can be arbitrarily changed, for example, by increasing the number of thresholds, the transmission power according to the reception quality of the terminal The ratio can also be fine tuned. Therefore, in the present embodiment, the signal transmission power intensity can be adjusted more appropriately than in the first embodiment according to the reception quality of the terminal.

<Third Embodiment>
FIG. 11 is a diagram illustrating a configuration example of the base station 50 according to the third embodiment. The base station 50 includes a line termination unit 11, a call processing control unit 12, a transmission / reception amplification unit 13, an antenna 14, and a baseband signal processing unit 60. The baseband signal processing unit 60 includes a modulation unit 21, an encoding unit 22, a demodulation unit 23, a decoding unit 24, a MAC control unit 25, an RLC control unit 26, a PDCP control unit 27, a storage unit 80, and a scheduler 70. I have. The scheduler 70 includes a scheduling unit 31, a reception quality determination unit 33, and a calculation unit 35 in addition to the modulation scheme determination unit 71, the change unit 72, and the transmission power determination unit 73. Here, the line termination unit 11, the call processing control unit 12, the transmission / reception amplification unit 13, the antenna 14, the modulation unit 21, the encoding unit 22, the demodulation unit 23, the decoding unit 24, the MAC control unit 25, the RLC control unit 26, The operation of the PDCP control unit 27 is the same as in the first and second embodiments. The operations of the scheduling unit 31, the reception quality determination unit 33, and the calculation unit 35 are the same as those in the first and second embodiments.

The storage unit 80 includes an MCS index table 81 and a transport block size table 82. FIG. 12 is a diagram illustrating an example of the MCS index table 81. The MCS index table 81 records a modulation scheme and a transport block size (TBS) index in association with the value of the MCS index. The MCS index is a number that can uniquely identify the TBS index and the modulation scheme. Modulation Order (Qm) in the second column of the MCS index table 81 represents a modulation method as follows.
Qm = 2: QPSK
Qm = 4: 16QAM
Qm = 6: 64QAM

On the other hand, the TBS index identifies the number of data bits that can be included in one resource block. FIG. 13 is a diagram illustrating an example of the transport block size table 82. The transport block size table 82 corresponds to the number of resource blocks (N _PRB ) and TBS index (I _TBS ) used for communication, and the number of bits of data that can be transmitted from the base station 50 to the terminal in one frame. Is recorded. Processing using the MCS index table 81 and the transport block size table 82 will be described later.

  For each terminal to which a resource block is allocated, modulation scheme determining section 71 determines candidate values such as a modulation scheme, coding rate, and TBS used for communication between the terminal and base station 50. For example, similar to the modulation method determination unit 32, the modulation method determination unit 71 may set candidate values so that the modulation method of some data such as an emergency signal and audio data is QPSK. Also, the modulation scheme determination unit 71 can determine candidate values according to the reception quality of the terminal. That is, the candidate value determination method of the modulation scheme determination unit 71 can be arbitrarily changed according to the implementation of the base station 50.

  The changing unit 72 determines whether the modulation method can be changed to QPSK when the modulation method candidate determined by the modulation method determining unit 71 is quadrature amplitude modulation such as 64QAM or 16QAM. When the modulation method can be changed to QPSK, the changing unit 72 changes the modulation method candidate determined by the modulation method determining unit 71 to QPSK. The changing unit 72 outputs the changed result to the transmission power determining unit 73. The operation of the changing unit 72 will be described later in detail.

  The transmission power determination unit 73 adjusts the transmission power of a signal for a terminal that demodulates a signal modulated by QPSK according to the reception quality of the terminal. The transmission power determination method is the same as that of the transmission power determination unit 34. The transmission power determination unit 73 adjusts the transmission power for the terminal whose modulation scheme determination unit 71 determines that QPSK is a modulation scheme candidate value. Further, the changing unit 72 also adjusts the transmission power for the terminal whose modulation scheme is changed to QPSK. The adjustment method in this case is also the same as that of the transmission power determination unit 34.

  FIG. 14 is a diagram illustrating an example in which data scheduled to be modulated by quadrature amplitude modulation can be transmitted by QPSK. Hereinafter, the operation of the changing unit 72 will be described by taking as an example a case where the candidate of the modulation scheme for data addressed to the terminal UE5 is determined to be 16QAM. Note that it is assumed that five resource blocks are allocated to the terminal UE5.

  As shown in FIG. 14A, the MAC Protocol Data Unit (MAC PDU) includes a MAC header, a MAC Control Element (MAC CE), a MAC Service Data Unit (MAC SDU), and padding. Further, as shown in FIGS. 14B and 14C, the transport block size is the total number of bits of the MAC PDU and the cyclic redundancy check (CRC). Here, data transmitted from the base station 50 to the terminal is data and CRC included in the MAC header, MAC CE, and MAC SDU. On the other hand, padding is data included in a MAC PDU in order to match the transport block size. That is, the padding content need not be transmitted to the terminal. Therefore, the base station 50 can discard the padding information in order to reduce the transport block size used for communication with the terminal. Therefore, as shown in FIG. 14 (d), the base station 50 communicates using a transport block that can transmit a larger number of bits than the sum of the MAC header, MAC CE, MAC SDU, and CRC. Can do. For example, it is assumed that the transport block size temporarily set for data to be transmitted to the terminal UE5 is 1000 bits and the padding is 400 bits. In this case, since the difference between the transport block size and the number of padding bits is 600 bits, the base station 50 may transmit data to the terminal UE5 using a transport block that can transmit data of 600 bits or more. it can.

Therefore, when the change unit 72 obtains the difference between the transport block size and the number of bits of padding, the change unit 72 refers to the transport block size table 82 (FIG. 13). The changing unit 72 acquires a TBS index corresponding to the transport block size including the number of bits larger than the obtained difference. At this time, the changing unit 72 refers to the transport block size corresponding to the number of resource blocks allocated to the terminal. For example, when five resource blocks are allocated to the terminal UE5, the changing unit 72 refers to the column N _PRB = 5 in the transport block size table 82. In the example of FIG. 13, when the _TPR index is 7 in the N _PRB = 5 column, the transport block size is 584 bits, and when the TBS index is 8, the transport block size is 680 bits. As the number of TBS indexes increases, the transport block size also increases. Therefore, if N _PRB = 5 and the TBS index is 8 or more, the changing unit 72 determines that information excluding padding can be used to send to the terminal UE5.

  Further, the changing unit 72 refers to the MCS index table 81 (FIG. 12) and confirms whether the acquired TBS index is associated with QPSK. When the acquired TBS index is associated with QPSK, the changing unit 72 changes the data modulation scheme to QPSK without changing the number of resource blocks allocated to the terminal UE5, and communication with the terminal UE5 is performed. Determine that it is possible. For example, when the TBS index is 8, the value of Qm is 2 as shown in FIG. Therefore, in this case, the TBS index acquired by the changing unit 72 is associated with QPSK. Therefore, the changing unit 72 changes the modulation method to QPSK.

When determining that the data modulation scheme can be changed to QPSK without increasing the number of resource blocks, the changing unit 72 sets the transport block size corresponding to the acquired TBS index to the transport block size used for communication. For example, the changing unit 72 determines that the transport block size associated with N _PRB = 5 and TBS index = 8 is used for data to be transmitted to the terminal UE5, and modulates data addressed to the terminal UE5. Change the method to QPSK. Here, the processing when 16QAM is a modulation scheme candidate has been described, but the changing unit 72 performs the same processing when 64QAM is a modulation scheme candidate.

  On the other hand, if the TBS index acquired by the changing unit 72 is not associated with QPSK, the number of resource blocks assigned to the terminal increases when the data modulation scheme is changed to QPSK. Therefore, the changing unit 72 determines that the data modulation method cannot be changed to QPSK without increasing the number of resource blocks for the terminal.

  FIG. 15 is a flowchart illustrating an example of determination performed by the changing unit 72. The changing unit 72 first obtains a difference between the transport block size candidate value and the number of padding bits (step S21). Next, the changing unit 72 refers to the transport block size table 82 and acquires the minimum value of the TBS indexes having a transport block size larger than the obtained difference value (step S22). At this time, the changing unit 72 refers to the transport block size associated with the number of resource blocks allocated to the processing target terminal. Furthermore, the changing unit 72 refers to the MCS index table 81 and confirms whether the acquired TBS index is associated with QPSK (step S23). When the acquired TBS index is associated with QPSK, the changing unit 72 determines that the number of resource blocks does not increase even when the modulation scheme is changed to QPSK (step S24).

  For example, it is assumed that two resource blocks are allocated to the terminal UE6 for which the modulation scheme candidate is determined to be 64QAM, and the transport block size candidate value is determined to be 840 bits. Here, if the padding size is 600 bits, in the terminal UE6, the difference between the transport block size and the padding is 240 bits. Then, the changing unit 72 refers to the transport block size table 82 in FIG. 13 and acquires TBS index = 8 for the terminal UE6. When the TBS index is 8, the modulation scheme is QPSK. Therefore, the changing unit 72 determines that the number of resource blocks does not increase for the terminal UE6 even if the modulation scheme is changed to QPSK.

  On the other hand, when the acquired TBS index is not associated with QPSK, 64QAM or 16QAM is used to transmit the difference bit number obtained in step S21 with the number of resource blocks allocated to the terminal. . That is, in order to use QPSK, the base station 70 transmits a part of data to be transmitted to the terminal using another resource block. Therefore, the changing unit 72 determines that the number of resource blocks increases when the modulation scheme is changed to QPSK (step S25).

  For example, it is assumed that three resource blocks are allocated to the terminal UE7 for which the modulation scheme candidate is determined to be 64QAM, and the transport block size candidate value is determined to be 1160 bits. Here, if the size of the padding is 480 bits, in the terminal UE7, the difference between the transport block size and the padding is 680 bits. Then, the changing unit 72 refers to the transport block size table 82 and acquires TBS index = 12 for the terminal UE7. As shown in FIG. 12, when the TBS index is 12, the associated modulation scheme is 16QAM. Therefore, the changing unit 72 recognizes that, for the terminal UE7, even if the padding is discarded, the modulation scheme is 16QAM in the case of transmitting with three resource blocks. That is, unless the number of resource blocks is increased, data to be transmitted to the terminal UE7 cannot be transmitted by QPSK. Therefore, the changing unit 72 determines that the terminal UE7 cannot perform modulation using QPSK unless the resource block is increased.

  FIG. 16 is a flowchart for explaining an example of the operation of the scheduler 70. Here, the modulation scheme is selected from any one of QPSK, 16QAM, and 64QAM. Note that FIG. 16 is an example. For example, there is a case where a change is made such that the transmission power ratio to be changed in steps S35 and S41 is determined using the transmission power table as described in the second embodiment. is there. In this case, it is assumed that the storage unit 80 stores a transmission power table.

  FIG. 17 is a table showing an example of data held by the changing unit 72 and the transmission power determining unit 73. Hereinafter, the operation of the scheduler 70 will be described with reference to FIGS. 16 and 17 taking as an example the case where the base station 50 adjusts the transmission power of the terminals UE8 to UE11. Here, PA0 (dB) is assumed to be larger than X (dB).

  When the scheduling unit 31 assigns resource blocks (RBs) to the terminals UE8 to UE11, the modulation scheme determining unit 71 determines candidate values for the modulation scheme and transport block size (TBS, block size). Furthermore, the scheduling unit 31 sets the transmission power ratio notified in advance to each terminal as the transmission power ratio in each terminal (step S31).

  The transmission power determination unit 73 checks whether the modulation scheme candidate value is QPSK (step S32). When QPSK is a modulation scheme candidate, the transmission power determination unit 73 checks with the reception quality determination unit 33 whether the reception quality of the terminal is equal to or higher than the threshold (step S33). The transmission power determination unit 73 sets the modulation scheme to QPSK for terminals whose reception quality is equal to or higher than the threshold (step S34). Further, the transmission power ratio is changed to X (dB), and the transport block size candidate value is set to the transport block size (steps S35 and S36). For example, as illustrated in FIG. 17A, the terminal UE9 has QPSK as a modulation scheme candidate, and the reception quality is equal to or higher than a threshold value. Therefore, the transmission power determination unit 73 sets the transmission power ratio to X (dB).

  On the other hand, for terminals for which QPSK is a modulation scheme candidate and the reception quality is less than the threshold, the transmission power determination unit 73 sets the modulation scheme to QPSK and sets the transmission power ratio to the value set by the scheduling unit 31. (No in step S33, step S37). Further, the transmission power determination unit 73 sets the transport block size candidate value determined by the modulation scheme determination unit 71 as the transport block size (step S38). For example, in the terminal UE8, as shown in FIG. 17A, QPSK is a modulation scheme candidate, but the reception quality is less than the threshold. Therefore, the transmission power determining unit 73 sets the modulation method to QPSK and the transmission power ratio to PA0 (dB).

  If QPSK is not determined as a modulation scheme candidate, the changing unit 72 checks whether the number of resource blocks does not increase even when the modulation scheme is changed to QPSK (step S39). The confirmation method in step S39 is as described with reference to FIG. If the number of allocated resource blocks does not increase even after modulation with QPSK, the changing unit 72 notifies the transmission power determining unit 73 to that effect and changes the modulation method to QPSK (Yes in step S39, step S40). ). Upon receiving the notification from the changing unit 72, the transmission power determining unit 73 changes the transmission power ratio to X (dB) (step S41). The changing unit 72 changes the transport block size (step S42).

For example, in the case of the terminal UE10, it is assumed that five resource blocks are allocated, and the number of bits obtained by subtracting the padding from the transport block size candidate value is 680 bits. As shown in FIG. 13, the TBS index of the transport block size used for transmitting 680 bits with N _PRB = 5 is 8. As shown in FIG. 12, the modulation scheme corresponding to TBS index = 8 is QPSK. Therefore, the changing unit 72 determines that the number of resource blocks does not increase even when the modulation scheme is changed to QPSK. The changing unit 72 changes the modulation scheme to QPSK and notifies the transmission power determining unit 73 of the determination result. Then, the transmission power determination unit 73 changes the transmission power to the terminal UE10 to X (dB).

  If the number of resource blocks increases when the modulation scheme is set to QPSK, the changing unit 72 notifies the transmission power determining unit 73 to that effect (No in step S39). Then, the transmission power determination unit 73 sets the determined candidate values for the modulation scheme, transport block size, and transmission power ratio (steps S43 and S44).

  For example, in the case of the terminal UE11, it is assumed that three resource blocks are allocated and the number of bits obtained by subtracting the padding from the transport block size candidate value is 680 bits. The TBS index corresponding to the transport block size that can be used to transmit 680 bits is then 12. The modulation scheme corresponding to TBS index = 12 is 16QAM. Therefore, the changing unit 72 determines that the number of resource blocks increases when the modulation scheme is changed to QPSK. When the changing unit 72 notifies the determination result, the transmission power determining unit 73 sets the transport block size to a candidate value, sets the modulation scheme to 64QAM, and sets the transmission power ratio to PA0.

  FIG. 18 is a diagram illustrating an example of a result of changing the transmission power according to the third embodiment. As illustrated in FIG. 18A, the transmission power ratio is temporarily set to PA0 (dB) for each of the terminals UE8 to UE11. FIG. 18B shows an example of the transmission power ratio when the transmission power ratio is changed by the transmission power determination unit 73. As described above, for a terminal that receives a signal modulated by QPSK, the transmission power determination unit 73 adjusts a transmission power ratio to be small for a terminal having better reception quality than the threshold. Therefore, the transmission power ratio of the terminal UE9 is adjusted to X (dB). Also, even if a modulation scheme other than QPSK is a modulation scheme candidate, for a terminal that can change the modulation scheme to QPSK without increasing the resource block, the changing unit 72 changes the modulation scheme to QPSK. Furthermore, the transmission power determination unit 73 changes the transmission power ratio to the terminal whose modulation method has been changed to QPSK, to X (dB). Therefore, the transmission power ratio of the terminal UE10 is adjusted to X (dB). On the other hand, when the number of resource blocks increases when the modulation scheme is changed from a modulation scheme other than QPSK to QPSK, respective candidate values are set for the modulation scheme and transmission power. Therefore, the terminal UE11 does not adjust the transmission power. This is because increasing the number of resource blocks allocated to a terminal increases the amount of power used for data transmission to the terminal. That is, if the number of resource blocks used for communication between the terminal and the base station 50 is increased, there is a possibility that the effect of reducing the power consumption cannot be obtained even if the power consumption is reduced by changing to QPSK. Therefore, the base station 50 does not change the modulation scheme or the transport block size when modulation using QPSK is not possible unless the resource block is increased.

<Others>
The embodiment is not limited to the above-described embodiment, and can be variously modified. Some examples are described below.

  For example, the operation of the transmission power determination unit 34 in the first embodiment can be modified as shown in the flowchart of FIG. In FIG. 19, the modulation scheme and the reception quality at the terminal are determined based on the MCS index value. Steps S51 to S53 in FIG. 19 are the same as steps S1 to S3 described with reference to FIG. In step S54, it is determined whether the MCS index is 9 or less. As shown in FIG. 12, MCS indexes 0 to 9 correspond to QPSK. Further, in step S55, it is determined whether the reception quality at the terminal is good depending on whether the value of the MCS index is equal to or greater than a threshold value. The processing in steps S56 to S58 is the same as that in steps S6 to S8 described with reference to FIG. In the second and third embodiments, the reception quality and modulation scheme can also be determined by the MCS index, as in the first embodiment.

  The base station 10 can also include an MCS index table 81 and a transport block size table 82. In this case, the base station 10 can determine the modulation method and the transport block size using the MCS index table 81 and the transport block size table 82.

  The method for determining the modulation method and the like in the modulation method determining unit 32 described in the above description is an example, and can be arbitrarily changed according to the implementation of the base station 10. For example, the modulation scheme determination unit 32 can adjust according to the communication quality of the propagation path by adaptive modulation and coding (AMC). For example, the modulation scheme determining unit 32 can determine the modulation scheme and the like according to the Channel Quality Indicator (CQI) value received from the terminal. In this case, the modulation scheme determination unit 32 can store in advance a table in which modulation schemes used for modulation of baseband signals are associated with each CQI value.

  The hardware configuration described with reference to FIG. 3 can be arbitrarily changed according to the implementation. Further, the operation executed by the DSP 44 and the like can be changed according to the implementation. For example, by changing the program, the DSP 44 can be used as a modulation unit 21, an encoding unit 22, a demodulation unit 23, a decoding unit 24, a MAC control unit 25, an RLC control unit 26, a PDCP control unit 27, and a scheduler 30. It can be operated.

  Further, FIG. 2 is an example of the base station 10 and may not be included in the MAC control unit 25, the RLC control unit 26, and the PDCP control unit 27, for example. In this case, the MAC control unit 25, the RLC control unit 26, and the PDCP control unit 27 are realized by a DSP 44 provided outside the baseband signal processing unit 20.

  Furthermore, the above-described transmission power adjustment method can also be used when the function of the base station is realized by two devices, a base band unit (BBU) and a remote radio head (RRH). In this case, the BBU includes the baseband signal processing unit 20 or the baseband signal processing unit 60.

DESCRIPTION OF SYMBOLS 1 Cell 3 Signal 4 Reference signal 10, 50 Base station 11 Line termination part 12 Call processing control part 13 Transmission / reception amplification part 14 Antenna 20, 60 Baseband signal processing part 21 Modulation part 22 Encoding part 23 Demodulation part 24 Decoding part 25 MAC control unit 26 RLC control unit 27 PDCP control unit 28, 80 Storage unit 30, 70 Scheduler 31 Scheduling unit 32, 71 Modulation method determination unit 33 Reception quality determination unit 34, 73 Transmission power determination unit 35 Calculation unit 41 FPGA
42 switch 43 CPU
44 DSP
45 Memory 72 Change unit 81 MCS index table 82 Transport block size table

Claims (6)

Transmitted to the first terminal from either the first modulation method that represents data by phase change or the second modulation method that uses the amplitude of the reference signal common to the first and second terminals as a reference value A modulation scheme determining unit that determines each of a modulation scheme of data to be transmitted and a modulation scheme of data to be transmitted to the second terminal;
A reception quality determination unit that determines whether the reception quality reported from the terminal determined as the first modulation scheme is equal to or higher than a threshold;
When the data to be transmitted to the first terminal is modulated by the first modulation scheme, if the reception quality of the first terminal is equal to or higher than the threshold, the transmission power of the signal demodulated by the first terminal A transmission power determining unit that adjusts the
A communication apparatus comprising: a transmission unit that transmits the signal with the adjusted transmission power to the first terminal. When the ratio of the transmission power of the reference signal and the transmission power of the signal demodulated by the first terminal is calculated and the transmission power of the signal demodulated by the first terminal is scheduled to be changed, A calculation unit for changing the ratio to the ratio of the transmission power after the change and the transmission power of the reference signal;
The transmitter transmits the ratio to the first terminal;
When data to be transmitted to the first terminal is modulated by the first modulation scheme, the transmission power determination unit transmits a signal demodulated by the first terminal even if the ratio is not changed. The communication apparatus according to claim 1, wherein power is controlled. Transmission of data transmitted to the first terminal when data transmitted to the first terminal is modulated by the first modulation scheme and when modulated by the second modulation scheme A change unit that changes the second modulation scheme to the first modulation scheme when the number of subcarriers used for transmission and the transmission time do not change,
The communication apparatus according to claim 1, wherein the transmission power determination unit controls transmission power of a data signal transmitted by the first modulation method. The transmission power determination unit reduces transmission power of a signal demodulated by the first terminal as reception quality of the first terminal is improved. 4. The communication device described. Transmitted to the first terminal from either the first modulation method that represents data by phase change or the second modulation method that uses the amplitude of the reference signal common to the first and second terminals as a reference value A modulation scheme determining unit that determines each of a modulation scheme of data to be transmitted and a modulation scheme of data to be transmitted to the second terminal;
A reception quality determination unit that determines whether the reception quality reported from the terminal determined as the first modulation scheme is equal to or higher than a threshold;
When the data to be transmitted to the first terminal is modulated by the first modulation scheme, if the reception quality of the first terminal is equal to or higher than the threshold, the transmission power of the signal demodulated by the first terminal A transmission power determining unit that adjusts the
A power adjustment device comprising: Transmitted to the first terminal from either the first modulation method that represents data by phase change or the second modulation method that uses the amplitude of the reference signal common to the first and second terminals as a reference value Determining a data modulation method to be transmitted and a data modulation method to be transmitted to the second terminal,
Determining whether the reception quality reported from the terminal determined as the first modulation scheme is equal to or higher than a threshold;
When the data to be transmitted to the first terminal is modulated by the first modulation scheme, if the reception quality of the first terminal is equal to or higher than the threshold, the transmission power of the signal demodulated by the first terminal Adjust the
The communication method characterized by transmitting the signal whose transmission power is adjusted to the first terminal.

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