JPWO2007110912A1 - Quality monitoring method and receiver - Google Patents

Abstract

A quality monitoring method according to the present invention is a receiver including a quality measuring unit (2) that measures a quality of a received signal that is modulated by a different method and includes a subcarrier group including at least one subcarrier. A quality monitoring method for individually monitoring the quality of a received signal for each subcarrier group, for example, a monitoring target determining step for determining a reception carrier monitoring target subcarrier group for each time slot, and for each time slot A monitoring object notifying step for notifying the determined subcarrier group for reception quality monitoring to the quality measurement unit (2), and the reception quality of the subcarrier group measured by the quality measurement unit (2) according to the notification content And a quality monitoring step for performing quality monitoring for each subcarrier group in a time-sharing manner.

Description

  The present invention relates to a quality monitoring method for monitoring the quality of a received signal and a receiver that implements the quality monitoring method, and in particular, reception configured by subcarriers or subcarrier groups modulated by different methods. The present invention relates to a quality monitoring method for monitoring signal quality.

  In order to provide a high-efficiency broadband digital communication method for transmission signals in a frequency selective fading environment associated with multipath, a large number of information is transmitted by increasing the modulation multi-level number in subcarriers with good transmission path conditions. On the other hand, a method of transmitting a small amount of information by lowering the modulation multi-level number has been proposed for subcarriers with poor transmission path conditions (for example, Patent Document 1 below).

  In order to realize such a scheme, first, the reception side estimates reception quality for each subcarrier or subcarrier group from known symbols transmitted by the transmission side, and feeds back the result to the transmission side. Then, the transmission side determines the modulation multi-level number based on the received reception quality. In addition, the transmission side periodically monitors whether or not the modulation multi-level number determined once is optimal for the transmission path state (signal reception quality on the reception side) that fluctuates with time. When quality degradation or excessive quality of the received signal is detected on the side, it is necessary to reassign the optimum modulation multilevel number.

  Since frequency selective fading occurs due to multipath, adjacent subcarriers exhibit substantially similar characteristics, but the characteristics differ when they are separated to some extent. Such a bandwidth having a correlation on the frequency axis in characteristics is called a correlation bandwidth (coherent bandwidth). Therefore, it is not always necessary to determine the modulation level in units of subcarriers, and the modulation level may be determined in units of subcarriers corresponding to the correlation bandwidth.

Japanese Patent Laid-Open No. 2003-348047

  However, under the following conditions, the number of subcarrier groups (which may be composed of a single subcarrier) corresponding to the correlation bandwidth increases.

1. When the bandwidth is widened for broadband communication, the number of subcarrier groups corresponding to the correlation bandwidth increases as the number of subcarriers increases.
2. When the cell radius is widened in order to suppress the bit unit price, the delay spread becomes large, the correlation bandwidth becomes narrow, and the number of subcarrier groups corresponding to the correlation bandwidth increases.

  Therefore, there is a problem that the number of subcarrier groups for quality monitoring increases and the circuit scale and memory size of the receiver increase.

  In addition, there is a problem that the power consumption of the receiver is increased by performing quality monitoring on all subcarrier groups each time reception is performed.

  The present invention has been made in view of the above, and an object of the present invention is to obtain a quality monitoring method that realizes quality monitoring with a smaller circuit scale and memory size and realizes low power consumption operation.

  It is another object of the present invention to provide a quality monitoring method that prevents an increase in circuit scale and memory size even when the number of subcarrier groups subject to quality monitoring increases.

  In order to solve the above-described problems and achieve the object, a quality monitoring method according to the present invention measures the quality of a received signal that is modulated by a different method and includes a subcarrier group including at least one subcarrier. A quality monitoring method for individually monitoring the quality of the received signal for each subcarrier group in a receiver including a quality measurement unit, and determining a subcarrier group for reception quality monitoring for each time slot A monitoring target determining step, a monitoring target notifying step of notifying the quality measuring unit of a subcarrier group of a reception quality monitoring target determined for each time slot, and a sub that the quality measuring unit measures according to the notification content A quality monitoring step of performing quality monitoring for each subcarrier group in a time-sharing manner with respect to the reception quality of the carrier group. .

  According to the present invention, when monitoring the quality of a received signal composed of a plurality of subcarrier groups, the quality monitoring of each subcarrier group is performed by time division processing (in order divided into a plurality of times). As a result, the circuit scale and the memory size can be reduced, and the power consumption can be reduced.

FIG. 1 is a diagram illustrating a configuration example of a receiver that realizes a quality monitoring method according to the present invention. FIG. 2 is a sequence diagram illustrating an example of the quality monitoring operation (method). FIG. 3 is a diagram illustrating an example of a scheduling result performed using the “Round Robin method”. FIG. 4 is a diagram illustrating an example of how subcarriers are grouped. FIG. 5 is a diagram showing a modification of the scheduling result shown in FIG. FIG. 6 is a diagram showing a modification of the scheduling result shown in FIG. FIG. 7 is a diagram illustrating an example of a quality monitoring operation performed by rescheduling a monitoring schedule. FIG. 8 is a diagram illustrating an example of reception quality notified from the quality measurement unit to the control unit. FIG. 9 is a diagram illustrating an example of the quality monitoring operation performed by rescheduling the monitoring schedule. FIG. 10 is a diagram illustrating an example of signal quality calculated based on the decoding result.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Control part 2 Quality measurement part 3 Error correction part 4 Demodulation part

  Embodiments of a quality monitoring method according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. Further, in the following description, the “subcarrier group” includes those composed of a single subcarrier. That is, when “subcarrier group” is described, the meaning thereof indicates “subcarrier or subcarrier group”.

  FIG. 1 is a diagram illustrating a configuration example of a receiver that realizes a quality monitoring method according to the present invention. The receiver includes a control unit 1 that operates as a monitoring target determining unit, and a reception quality measuring unit. A quality measuring unit 2 that performs the operation, an error correcting unit 3, and a demodulating unit 4 are provided.

  The demodulator 4 performs a demodulation process on the received signal and outputs the demodulation result (demodulated signal) to the error corrector 3. Further, the demodulator 4 performs transmission path estimation processing based on the received signal, and outputs the estimation result (transmission path estimation result) to the quality measurement section 2. The error correction unit 3 executes error correction decoding processing of the demodulated signal output from the demodulation unit 4 and outputs the decoding result to the control unit 1. The quality measurement unit 2 measures the reception quality of the subcarrier group instructed from the control unit 1 based on the transmission path estimation result output from the demodulation unit 4, and outputs the measurement result to the control unit 1. . The control unit 1 determines which subcarrier group the reception quality is monitored, and instructs the quality measurement unit 2 to measure the reception quality of the determined subcarrier group. The control unit 1 holds information on the number of modulation multilevels assigned to each subcarrier group.

  Next, a quality monitoring method according to the present invention will be described with reference to the drawings. FIG. 2 is a sequence diagram illustrating an example of a quality monitoring operation (method) executed by the control unit 1 by controlling the quality measurement unit 2 and the error correction unit 3. First, at the start of the quality monitoring operation, the control unit 1 monitors the reception quality of which subcarrier group at which reception timing (time slot) based on the information of the modulation multilevel number assigned to each subcarrier group. (Subcarrier group to be monitored for reception quality at each reception timing) is determined (step S1). That is, the order of monitoring the reception quality of each subcarrier group, which is performed in time division for each time slot, is scheduled. At this time, the control unit 1 schedules which subcarrier group is monitored for reception quality at each reception timing based on conditions determined according to the system. For example, if the condition “simultaneously measure two subcarrier groups in one time slot” is determined, the control unit 1 assigns two subcarrier groups as reception quality monitoring targets in each time slot. Perform scheduling. Details of the scheduling operation will be described later.

  Then, based on the scheduling result, the control unit 1 outputs a quality monitoring request (message) for instructing reception quality measurement of the monitoring target (subcarrier group) at the first reception timing to the quality measuring unit 2 ( Step S2).

  The quality measurement unit 2 measures the reception quality of the subcarrier group designated by the received quality monitoring request (step S3), and sends a measurement result (message) including information on the measured reception quality to the control unit 1. (Step S5). The quality measuring unit 2 measures, for example, SINR (Signal to Interference Noise Ratio) as reception quality.

  Further, as described above, the error correction unit 3 performs error correction decoding processing of the output signal from the demodulation unit 4 (step S4), and information obtained as a result (for example, the number of received bits and error correction bits) The decoding result (message) including the number is output to the control unit 1 (step S6).

  The control unit 1 determines whether or not to continue the reception quality monitoring measurement of the subcarrier group according to the order determined in the step S1, based on the measurement result and the decoding result received in the steps S5 and S6. If necessary, the monitoring order is rescheduled (step S7). When rescheduling is performed, depending on the content of the measurement result, a timing at which reception quality is not monitored may be inserted in the monitoring order. For example, when the reception quality is sufficiently good, the reception quality is not monitored at all reception timings, but scheduling is performed in which a timing at which the reception quality is not monitored is inserted periodically. Depending on the contents of the decoding result, the reception quality monitoring operation may be stopped (suspended) instead of rescheduling the monitoring order. In this case, the control unit 1 continues to monitor the decoding result, and determines whether to restart the reception quality monitoring operation based on the content of the decoding result.

  Then, the control unit 1 outputs to the quality measurement unit 2 a quality monitoring request that instructs reception quality measurement of the monitoring target (subcarrier group) at the next reception quality monitoring based on the processing result of step S7. The feedback control (step S8) is performed. In step S8, if rescheduling of the monitoring order is performed in step S7, a quality monitoring request for giving an instruction based on the rescheduling result is output. If rescheduling is not performed, the above step is performed. A quality monitoring request for giving an instruction based on the scheduling result in S1 is output.

  Then, the quality measuring unit 2 performs the reception quality measurement process of the subcarrier group instructed by the quality monitoring request and the output process of the measurement result to the control unit 1 in the same manner as steps S3 and S5 (steps). S9, S11). Further, the error correction unit 3 executes an error correction decoding process and an output process for the decoding result control unit 1 (steps S10 and S12).

  Hereinafter, the control unit 1, the quality measurement unit 2, and the error correction unit 3 continue the same processing (processing of steps S13, S14, S15, S16,...) As the processing described above (corresponding to the processing of steps S7 to S12). By doing so, the quality of the received signal is monitored.

  As described above, the quality monitoring method according to the present invention enables the circuit size and the memory size to be reduced by performing the quality monitoring of the received signal for each subcarrier in a time division manner. In addition, because scheduling is performed based on the conditions for each system to be adapted (for example, the condition that “two subcarrier groups are measured simultaneously in one time slot”), the number of subcarrier groups to be measured temporarily increases. Even in this case, it is possible to respond flexibly without requiring a physical change (for example, a change in circuit scale).

  In the above-described processing, the control unit 1 outputs a quality monitoring request to the quality measuring unit 2 at each reception timing. However, the control unit 1 makes a quality monitoring request only when scheduling (rescheduling) is performed. Thus, the scheduling result may be notified to the quality measuring unit 2. In this case, the quality measurement unit 2 holds the notified scheduling result, periodically performs quality measurement according to the contents, and outputs (notifies) the measurement result to the control unit 1. .

  Next, the scheduling operation performed by the control unit 1 will be described. FIG. 3 is a diagram illustrating an example of a scheduling result performed using the “Round Robin method” which is the most basic time division method. In this example, there are subcarrier groups from # 0 to # 5, and the control unit 1 monitors the subcarrier group monitoring frequency based on the condition that “two subcarrier groups are monitored simultaneously in one time slot”. Scheduling is performed so that is uniform. It is assumed that the modulation scheme of each subcarrier group does not change. Also, the condition for scheduling (the number of subcarrier groups monitored simultaneously in one time slot) may be other than two. Further, the number of subcarrier groups monitored simultaneously may be variable for each time slot.

  In FIG. 3, the control unit 1 selects a monitoring target in ascending order of subcarrier group numbers, and performs scheduling by setting two adjacent subcarrier groups such as # 0 and # 1. However, it is not always necessary to select the adjacent ones in ascending order.

  In FIG. 3, the subcarrier group has a fixed width, but may have a variable width. Here, the subcarrier group calculates a correlation value for the reception quality of each subcarrier measured when determining the modulation multilevel number, and determines based on the calculation result. For example, as shown in FIG. 4, subcarriers having a correlation value for reception quality equal to or higher than a threshold value are grouped as the same subcarrier group.

  FIG. 5 is one of the modified examples of the scheduling result shown in FIG. 3, in which importance is given to the subcarrier group, and quality monitoring is executed in order from the subcarrier group having the highest importance. The control unit 1 performs scheduling. In this example, a subcarrier group having a high modulation multi-level number is assumed to be highly important, and the order of the modulation multi-level number is 16QAM> QPSK> BPSK. Is scheduled so that 16QAM → QPSK → BPSK.

  6 is a modification of the scheduling result shown in FIG. 3 under conditions different from those in FIG. 5. The importance level is given to the subcarrier group, and the quality monitoring frequency of the subcarrier group having high importance is high. Thus, the control unit 1 performs scheduling. In this example, it is assumed that the importance level of the assigned subcarrier group having a high modulation multi-level number is high, and the control unit 1 performs scheduling so that the high monitoring frequency satisfies 16QAM> QPSK> BPSK. .

  Note that the control unit 1 calculates the monitoring frequency for each subcarrier group based on the correspondence between the modulation multi-value number determined and set (held) in advance and the importance, and performs scheduling. In the example illustrated in FIG. 6, the control unit 1 performs scheduling on the assumption that the correspondence between the modulation level and the importance is 16QAM: QPSK: BPSK = 3: 2: 1. Therefore, the subcarrier group to which 16QAM is assigned is assigned to once every 2 time slots, the subcarrier group to which QPSK is assigned is assigned to once every 3 time slots, and the subcarrier group to which BPSK is assigned is assigned to 6 time slots. The scheduling result is such that quality monitoring is executed at a frequency of once.

  In addition, the control unit 1 performs scheduling so that quality monitoring of a certain subcarrier group is not performed in continuous time slots. Therefore, the control unit 1 performs the quality monitoring of the subcarrier group to which 16QAM is assigned in the time slot where the remainder obtained by dividing the time slot number by 6 is 0, 2, and 4, and the remainder obtained by dividing the time slot number by 6 Quality monitoring of the subcarrier group to which QPSK is assigned in the time slot whose number is 1, 3 and the quality of the subcarrier group to which BPSK is assigned in the time slot whose remainder is 5 when the time slot number is divided by 6 Scheduling is performed to perform monitoring.

  Next, the rescheduling operation performed by the control unit 1 will be described. FIG. 7 is a diagram illustrating an example of a quality monitoring operation performed by rescheduling the monitoring schedule once determined by the control unit 1 based on the measurement result (reception quality) reported from the quality measuring unit 2. Specifically, FIG. 7 shows that when quality degradation or excessive quality of a subcarrier group with a low modulation multi-level number is detected, the quality measurement unit 2 does not follow the scheduling result determined in advance by the control unit 1. , Monitor the quality of the subcarrier group with a high modulation multilevel number at the next reception timing (the control unit 1 instructs the quality measurement unit 2 to perform the quality measurement of the subcarrier group with a high modulation multilevel number) Is shown).

  In the example shown in FIG. 7, quality degradation of subcarrier group # 2 to which BPSK is assigned in time slot # 1 is detected. Therefore, in the next time slot # 2, the quality measurement unit 2 replaces the quality measurement of the subcarrier group # 2 to which BPSK is assigned with the subcarrier group # 0 to which 16QAM having a high modulation multi-level number is assigned. Measure quality. Instead, in the next time slot # 3, the quality measurement of the subcarrier group # 4 that was not previously measured (skip) is performed. When such quality deterioration is detected, the operation of reviewing the schedule once determined and executing the quality monitoring can be applied to the operation of performing the scheduling shown in FIGS.

Next, an example of a method in which the control unit 1 detects quality degradation based on the reception quality notified from the quality measurement unit 2 will be described with reference to FIG. FIG. 8 is a diagram illustrating an example of reception quality notified from the quality measurement unit 2 to the control unit 1. When the reception quality notified from the quality measurement unit 2 is N ₁ times lower than the predetermined reception quality standard (threshold value) by Δ ₁ dB, the control unit 1 It is judged that there is deterioration. Further, if the state where the difference from the threshold value is less than Δ ₁ dB continues N ₂ times, it is determined that there is no quality deterioration. These parameters (“threshold value”, “Δ ₁ ”, “N ₁ ”, “N ₂ ”) are set for each modulation multilevel number.

Note that the method in which the control unit 1 detects excessive quality based on the reception quality notified from the quality measurement unit 2 can also be realized by performing the same operation as the quality degradation detection method. That is, when a state in which the reception quality is higher than a threshold value by a certain value (for example, Δ _H dB) or more continues N _H times, it is determined as “excessive quality”.

  In addition, the control unit 1 may perform a filtering process on the reception quality notified from the quality measurement unit 2 and smooth the reception quality, and then determine quality deterioration and excessive quality. At this time, for example, a FIR (Finite Impulse Response) filter, an IIR (Infinite Impulse Response) filter, a maximum value filter, a minimum value filter, and a median filter are used for the filter processing.

  Next, the rescheduling operation performed by the control unit 1 under conditions different from those shown in FIG. 7 will be described. FIG. 9 is a diagram illustrating an example of a quality monitoring operation performed by rescheduling the monitoring schedule once determined by the control unit 1 based on the decoding result reported from the error correction unit 3. For example, the control unit 1 calculates an error correction bit rate (= number of error correction bits / number of received bits) from the number of received bits and the number of error correction bits reported as a decoding result, and the signal quality is calculated from the error correction bit rate. If it is determined that there is no deterioration, the monitoring schedule is reviewed so that reception quality monitoring is not executed in the next time slot. On the other hand, when it is determined from the error correction bit rate that the signal quality has deteriorated, the control unit 1 reviews the monitoring schedule so as to perform reception quality monitoring in the next time slot.

  In the example shown in FIG. 9, since it is determined from the decoding result of time slot # 1 that the signal quality has deteriorated, the control unit 1 controls the quality measurement unit 2 to measure the reception quality of the subcarrier group. I do. Thereafter, since it is determined from the decoding result of time slot # 6 that the signal quality has not deteriorated, the control unit 1 controls the quality measurement unit 2 so as not to measure the reception quality of the subcarrier group.

  The control unit 1 performs the quality measurement unit 2 so that the reception quality is measured only when such signal quality degradation occurs, while the reception quality measurement is not performed when the signal quality degradation does not occur. The operation for controlling is applicable to the operation for performing the scheduling shown in FIGS. Further, it can be applied to the rescheduling operation shown in FIG. In addition, once reception quality monitoring is interrupted, monitoring may be resumed based on a schedule result before the interruption, or may be resumed as an initial state so that monitoring is performed from the beginning.

  In the above description, the error correction bit rate calculated from the number of received bits and the number of error correction bits is used as the decoding result used for determination of signal quality degradation, but the present invention is not limited to this. For example, when a convolutional code is used, signal quality degradation may be determined using a re-encoding error rate obtained by comparing a bit string obtained by re-encoding a decoded bit string and a bit string before decoding. . When turbo codes are used, signal quality degradation may be determined by taking out a decoding result in the middle of decoding processing repeatedly performed by the turbo decoder and performing CRC check. Furthermore, when using an LDPC code, parity check may be performed using a parity check matrix, and signal quality degradation may be determined using a ratio of zero parity.

Next, an example of a method in which the control unit 1 detects signal quality degradation based on the decoding result notified from the error correction unit 3 will be described with reference to FIG. FIG. 10 is a diagram illustrating an example of signal quality calculated based on the decoding result notified from the error correction unit 3. Further, for example, an error correction bit rate is used as the signal quality. The control unit 1 indicates that the signal quality calculated based on the decoding result notified from the error correction unit 3 is higher by Δ ₂ % or more than a predetermined signal quality standard (threshold) N ₃ If there are consecutive times, it is determined that “quality is degraded”. Further, when the state where the difference from the threshold is less than Δ ₂ % continues N ₄ times, it is determined that “no quality deterioration”. Note that the method of detecting excessive quality based on the decoding result notified from the error correction unit 3 by the control unit 1 can also be realized based on the threshold value and the signal quality in the same manner as the quality deterioration detection method.

  In addition, the control unit 1 may perform a filter process on the decoding result reported from the error correction unit 3 and smooth the error correction bit rate, and then determine quality deterioration or excessive quality. . At this time, for example, an FIR filter, an IIR filter, a maximum value filter, a minimum value filter, and a median filter are used for the filter processing.

  In the above-described operation, the “modulation multi-level number” of the subcarrier group is used as a reference for assigning the importance. However, the present invention is not limited to this. The “frequency of quality degradation” and “the magnitude of variation in reception quality” may be used.

  At this time, if the frequency of quality degradation and the magnitude of variation in reception quality have a correlation with daily time fluctuation, statistics of quality degradation frequency and reception quality for each time zone are taken, and Scheduling may be performed based on the result of counting the statistics. For example, if a tendency that the frequency of quality deterioration of the subcarrier group # 0 becomes high in the time zone A is obtained, a rule that the frequency of quality monitoring of the subcarrier group # 0 is increased in the time zone A. Scheduling based on

  Furthermore, a combination of two or more of the “number of modulation levels”, “frequency of quality degradation”, and “size of reception quality variation” may be used as a reference for assigning importance.

  As described above, in the present embodiment, when monitoring the quality of a reception signal composed of a plurality of subcarrier groups, the quality monitoring of all the subcarrier groups is not performed at the same time, but the individual subcarrier groups are monitored. The quality monitoring is executed by time-sharing processing (in order divided into multiple times). As a result, it is possible to reduce the circuit scale and the memory size, and to realize low power consumption.

  In addition, the frequency of quality monitoring is adjusted in consideration of the number of modulation levels, the frequency of quality deterioration, and the magnitude of variation in reception quality. As a result, quality degradation can be detected at an early stage in a state where the quality monitoring of the subcarrier group is executed by the time division processing.

  In addition, when quality deterioration / excessive quality is detected based on the monitoring result of a certain subcarrier group, the subcarrier group to be monitored is switched. As a result, quality degradation can be detected at an early stage in a state where the quality monitoring of the subcarrier group is executed by the time division processing. In addition, it is possible to discover quality deterioration more efficiently and earlier by executing a combination of the operation of switching the subcarrier group to be monitored and the operation of adjusting the frequency of the quality monitoring.

  Further, when quality degradation / excessive quality is detected based on the decoding result, it is determined whether or not quality monitoring is necessary. Thereby, low power consumption operation | movement is realizable.

  As described above, the quality monitoring method according to the present invention is useful for a radio communication system, and is suitable as a quality monitoring method for a receiver that monitors the quality of a received signal modulated by a different method for each subcarrier group. . Furthermore, it can be applied not only to a wireless communication system but also to a power line communication system.

Claims (14)

In a receiver including a quality measurement unit that measures the quality of a received signal that is modulated by a different method and includes at least one subcarrier group, the quality of the received signal is individually determined for each subcarrier group. A quality monitoring method for monitoring
A monitoring target determination step for determining (scheduling) a subcarrier group for reception quality monitoring for each time slot;
A monitoring target notification step of notifying the quality measurement unit of a subcarrier group to be monitored for reception quality determined for each time slot;
A quality monitoring step of performing quality monitoring in a time-sharing manner for each subcarrier group with respect to the reception quality of the subcarrier group measured according to the notification content by the quality measurement unit;
The quality monitoring method characterized by including.   2. The monitoring target determining step performs scheduling so that reception quality is monitored in order from a subcarrier group having a high importance determined based on a modulation multi-level number of each subcarrier group. The quality monitoring method described in 1.   2. The monitoring target determining step, wherein scheduling is performed so that a reception quality monitoring frequency of a subcarrier group having high importance determined based on a modulation multi-level number of each subcarrier group is increased. The quality monitoring method described in 1.   The processing is performed using importance determined based on the frequency of reception quality deterioration of each subcarrier group instead of the importance determined based on the modulation multi-level number of each subcarrier group. The quality monitoring method according to claim 2.   The processing is performed using importance determined based on the frequency of reception quality deterioration of each subcarrier group instead of the importance determined based on the modulation multi-level number of each subcarrier group. The quality monitoring method according to claim 3.   Instead of the importance determined based on the modulation multi-value number of each subcarrier group, processing is performed using the importance determined based on the magnitude of variation in reception quality of each subcarrier group. The quality monitoring method according to claim 2.   Instead of the importance determined based on the modulation multi-value number of each subcarrier group, processing is performed using the importance determined based on the magnitude of variation in reception quality of each subcarrier group. The quality monitoring method according to claim 3. further,
A quality deterioration excessive detection step for detecting reception quality deterioration or excessive reception quality of a subcarrier group having a low modulation multi-level number based on the reception quality monitoring result;
Including
In the quality deterioration excessive detection step, when reception quality deterioration or excessive reception quality of a subcarrier group with a low modulation multi-value number is detected,
In the monitoring target notifying step, regardless of the determination result in the monitoring target determining step, the next time the reception quality is monitored, the subcarrier group having the highest modulation multi-level number is set as the reception quality monitoring target to the quality measuring unit. The quality monitoring method according to claim 1, wherein notification is performed. further,
A quality state determination step for determining a state of reception quality based on a decoding result of the received signal;
Including
The monitoring target notification step notifies the quality measurement unit of a subcarrier group to be monitored for reception quality only when it is determined in the quality state determination step that reception quality is poor. Item 6. The quality monitoring method according to Item 1. further,
A quality state determination step for determining a state of reception quality based on a decoding result of the received signal;
Including
The monitoring target notification step notifies the quality measurement unit of a subcarrier group to be monitored for reception quality only when it is determined in the quality state determination step that reception quality is poor. Item 9. The quality monitoring method according to Item 8. A receiver that receives a signal modulated in a different manner for each subcarrier group including at least one subcarrier and individually monitors the quality of the received signal for each subcarrier group,
Reception quality measuring means for measuring the quality of the received signal for each subcarrier group;
Monitoring target determining means for determining (scheduling) a subcarrier group for monitoring reception quality for each time slot;
With
The receiver, wherein the monitoring target determining unit instructs the reception quality measuring unit to measure the quality of the reception quality monitoring target subcarrier group determined for each time slot in each time slot.   When the monitoring target determining unit detects reception quality deterioration or excessive reception quality of a subcarrier group with a low modulation multi-level number based on the measurement result of the reception quality measuring unit, the reception quality at the next reception quality monitoring is detected. The receiver according to claim 11, wherein rescheduling is performed so that a target to be monitored is a subcarrier group having the highest modulation multi-level number. The monitoring target determining means further includes:
Based on the decoding result of the received signal, the quality of the received signal is determined, and only when the received signal quality is determined to be poor as a result of the processing, a subcarrier group quality measurement instruction is given to the received quality measuring means. The receiver according to claim 11. The monitoring target determining means further includes:
Based on the decoding result of the received signal, the quality of the received signal is determined, and only when the received signal quality is determined to be poor as a result of the processing, a subcarrier group quality measurement instruction is given to the received quality measuring means. The receiver according to claim 12.

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