JP2008312052A - Adaptive modulation control method and communications device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an adaptive modulation control method capable of reducing the overhead of a control signal transmitted and received at both of reception and transmission sides. <P>SOLUTION: In the adaptive modulation control method, modulation multilevel numbers, which are applied to each subcarrier or each group of subcarriers between transmission and reception stations 1, 2, are known mutually. The transmission station 1 transmits a transmission control signal including the maximum modulation multilevel number and main signals that are transmission data. The reception station 2 demodulates and decodes the main signals based on the received transmission control signal, and sends back a reception control signal for delivery confirmation indicating the presence or absence of an error in received data. The transmission station 1 controls the suppression of the maximum modulation multilevel number, when it is determined that reception quality has deteriorated, based on the received reception control signal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an adaptive modulation control method for performing adaptive modulation for each subcarrier or subcarrier group in a system in which a plurality of subcarriers or a plurality of subcarrier groups exist.

  Conventionally, in order to provide high-efficiency broadband digital communication of transmission signals in a frequency-selective fading environment associated with multipath, for example, in subcarriers with good transmission path conditions, the number of modulation multilevels is increased and increased. On the other hand, a scheme has been proposed in which less information is transmitted by lowering the modulation multi-level number for subcarriers with poor transmission path conditions (see Patent Document 1 below).

  In order to implement the above method, the receiving apparatus estimates the reception quality for each subcarrier or subcarrier group based on the known symbols transmitted by the transmitting apparatus, and feeds back the result to the transmitting apparatus. Therefore, it is necessary to determine the modulation level corresponding to the reception quality. Further, it is necessary for the transmission-side apparatus to monitor whether or not the modulation multi-level number once determined is satisfied, and when quality deterioration or excessive quality is detected, it is necessary to reassign the optimum modulation multi-level number.

  Further, 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. A bandwidth having a characteristic correlation on the frequency axis is called a correlation bandwidth (coherent bandwidth). Therefore, in order to realize the above method, 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 according to the correlation bandwidth.

Japanese Patent Laid-Open No. 2003-169036

However, the number of subcarrier groups increases under the following conditions.
(1) Widen the bandwidth for broadband communication.
(2) The cell radius is increased in order to suppress the bit unit price (the correlation bandwidth becomes narrower because the delay spread becomes larger).

  When the number of subcarrier groups increases, the receiving device re-assigns the optimum modulation multilevel number to the transmitting device, so that the receiving device monitors the quality of all subcarrier groups each time reception is performed, and the result is transmitted to the transmitting device. It is necessary to feed back to the device. Therefore, there is a problem that the overhead of the control signal transmitted from the receiving device increases. In addition, when the band that can be allocated to the control signal is narrow, there is a problem that it takes time for feedback, and in particular, when quality degradation occurs, it takes time until error generation is settled.

  On the other hand, it is necessary for the transmitting apparatus to notify the receiving apparatus which modulation multi-level number is assigned to all subcarriers (groups), and the overhead of the control signal transmitted from the transmitting apparatus increases. There is a problem that. In addition, when the bandwidth that can be allocated to the control signal is narrow, it takes time to specify a new modulation multi-value number, and in particular, when quality degradation occurs, it takes time until error generation is settled. There is.

  The present invention has been made in view of the above, and an object of the present invention is to obtain an adaptive modulation control method capable of reducing the overhead of control signals transmitted and received on both the reception side and the transmission side.

  In order to solve the above-described problems and achieve the object, an adaptive modulation control method according to the present invention is a communication system in which a modulation scheme is variable for each subcarrier or subcarrier group. An adaptive modulation control method in a case where modulation multi-value numbers applied for each subcarrier or subcarrier group are known to each other between a transmitting station and a receiving station, for example, wherein the transmitting station A transmission control signal including a maximum modulation multi-level number that can be assigned to a subcarrier group and a data transmission step of transmitting a main signal that is transmission data, and the receiving station demodulates the main signal based on the received transmission control signal And a delivery confirmation transmission step for decoding and sending back a reception control signal for delivery confirmation indicating whether there is an error in the received data, and the transmitting station received If it is determined that the reception quality based on signal control signal is deteriorated, characterized in that it comprises a and a modulation level adjustment step of performing control to suppress the maximum modulation level.

  According to the present invention, there is an effect that it is possible to reduce the overhead of a control signal transmitted and received on both the reception side and the transmission side.

  Embodiments of an adaptive modulation control 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.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration example of a transmitting station and a receiving station that realize an adaptive modulation control method according to the present invention. The illustrated transmission station 1 includes a control unit 11, a transmission unit 12, and a reception unit 13, and the reception station 2 includes a control unit 21, a reception unit 22, and a transmission unit 23.

  The transmitting station 1 and the receiving station 2 exchange known symbols for determining what modulation multilevel number can be assigned to a subcarrier or a subcarrier group at the start of communication. As a result, FIG. 2. Exchange detailed information (control signal) as shown in FIG. FIG. 2 shows an example of a control signal transmitted by the receiving station 2 when quality monitoring is performed in units of subcarriers (groups) at the start of communication and the results (reception quality: 8 dB, 9 dB, 15 dB,..., 20 dB) are fed back. FIG. FIG. 3 shows an example of a control signal transmitted by the transmitting station 1 when a modulation multi-level number (modulation method: BPSK, BPSK, QPSK,..., 16QAM) is designated for each subcarrier (group) at the start of communication. FIG. By this processing, it is known between the transmitting station 1 and the receiving station 2 what modulation multi-value number is assigned to the subcarrier or the subcarrier group. Conventionally, since the detailed information as shown in FIGS. 2 and 3 is exchanged every time it is received, there is a problem that the overhead of the control signal increases. Hereinafter, the “subcarrier or subcarrier group” is referred to as “subcarrier (group)”.

  Hereinafter, the operations of the transmitting station 1 and the receiving station 2 after it has been determined as described above what kind of modulation multilevel number is assigned to the subcarrier (group) will be described.

  The transmitting station 1 transmits a main signal and a transmission control signal to the receiving station 2, and receives a receiving control signal for confirming delivery of the main signal from the receiving station 2. On the other hand, the receiving station 2 receives the main signal and the transmission control signal from the transmitting station 1 and returns a reception control signal for confirming the delivery of the main signal to the transmitting station 1. The transmission control signal includes information necessary for receiving the main signal.

  First, the operation of the transmitting station 1 will be described. In the transmission station 1, the control unit 11 controls the transmission unit 12 and the reception unit 13. The control unit 11 holds information on what kind of modulation multilevel number is used for the subcarrier (group). Based on the reception control signal transmitted from the receiving station 2, the control unit 11 determines the presence / absence of adjustment of the held modulation multilevel number and notifies the transmission unit 12 of the result as modulation multilevel number adjustment information. To do.

  Before transmitting the main signal, the transmission unit 12 includes the modulation multilevel adjustment information notified from the control unit 11 in the transmission control signal and transmits the transmission control signal to the reception station 2. Thereafter, the transmission unit 12 modulates the main signal based on the modulation multilevel number adjustment information notified from the control unit 11 and transmits the modulated main signal to the reception station 2. Further, when receiving the reception control signal for delivery confirmation, the receiving unit 13 transfers it to the control unit 11.

  Here, a specific example of the reception control signal transmitted from the receiving station 2 to the transmitting station 1 is shown in FIG. A specific example of the transmission control signal transmitted from the transmitting station 1 to the receiving station 2 is shown in FIG.

  The reception control signal shown in FIG. 4 includes two information elements, that is, a CRC determination result and an error correction rate. The CRC determination result is information indicating whether or not the CRC calculated by the receiving station 2 from the received bit string matches the CRC given by the transmitting station 1. This takes binary values of coincidence and non-coincidence and can be expressed by 1 bit. The error correction rate is a value indicating the ratio of the number of bits corrected by error correction to the number of transmitted bits, and takes a continuous value between 0% and 100%. Here, the common logarithm is taken and expressed as a discrete value such as 10% or more, less than 10%, less than 1%, less than 0.1%, etc., for example, expressed in about 6 bits (64 ranks). Therefore, the reception control signal of this embodiment is about 7 bits in total.

  On the other hand, the conventional control signal shown in FIG. 2 has 4096 subcarriers (groups) (which can be expressed in 12 bits), and it is considered that the reception quality is fed back from 0 dB to 40 dB in 1 dB steps (which can be expressed in 6 bits). When the reception quality is returned sequentially, 24576 bits (= 4096 × 6 bits) are required. Further, when a subcarrier number is assigned so that the reception quality can be returned randomly, 73728 bits (= 4096 × (6 + 12) bits) are required. When this is transmitted through a 64 kbit / sec line, it takes 0.384 sec and 1.152 sec, respectively.

  Thus, the reception control signal of the present embodiment has a significantly smaller number of bits compared to the conventional control signal in units of subcarriers (groups) shown in FIG.

  By the way, in the wireless LAN, only the CRC determination result is fed back as a reception control signal, but in comparison with this, in this embodiment, the overhead increases as much as the error correction rate is added. However, in the present embodiment, even if the CRC determination results are the same, if the error correction rate exceeds a certain threshold, it is considered that quality degradation has occurred and the modulation multi-level number can be adjusted. This can prevent a CRC mismatch from occurring.

  Also, the transmission control signal shown in FIG. 5 is composed of one information element called the maximum modulation multilevel number. The maximum modulation multi-level number is a value that limits the maximum value of the modulation multi-level number that can be assigned to the subcarrier, and the value of BPSK (modulation multi-level number = 1) to 1024QAM (modulation multi-level number = 10) Therefore, it can be expressed by 4 bits.

  On the other hand, the conventional transmission control signal shown in FIG. 3 has 4096 subcarriers (groups) (which can be expressed in 12 bits), and the modulation multilevel number is BPSK (modulation multilevel number = 1) to 1024QAM (modulation multilevel number). = 16) Considering feedback in one step (representable in 4 bits), 16,384 bits (= 4096 × 4 bits) are required. When this is transmitted through a 64 kbit / sec line, it takes 0.256 sec.

  Thus, the transmission control signal of the present embodiment has a significantly smaller number of bits compared to the control signal in units of subcarriers shown in FIG.

  By the way, in the wireless LAN, since the same modulation multilevel number is assigned to all subcarriers, the overhead is the same. However, in the present embodiment, it is possible to assign the modulation multilevel number in units of subcarriers as long as the range is less than the specified modulation multilevel number, so a more appropriate modulation multilevel number can be selected. Thus, CRC mismatch is less likely to occur. Note that the transmission control signal shown in FIG. 5 designates only the modulation multi-level number, but it may be expressed in combination with the coding rate as in the wireless LAN.

  Next, the operation of the receiving station 2 will be described. In the receiving station 2, when receiving the transmission control signal from the transmitting station 1, the receiving unit 22 extracts the modulation multilevel number adjustment information from the transmission control signal and transfers it to the control unit 21. The control unit 21 holds what modulation multi-value number is used for the subcarrier (group), and what modulation multi-value is used for the subcarrier (group) from the information transferred from the reception unit 22. The receiver 22 is instructed by interpreting whether the number is used.

  When receiving the main signal according to the modulation multi-value number instructed from the control unit 21, the receiving unit 22 performs error correction and transfers to the control unit 21 how much error has been corrected. Then, the transmission unit 23 transfers a reception control signal for delivery confirmation to the transmission station 1 in accordance with an instruction from the control unit 21.

  FIG. 6 is a diagram illustrating an example of interpretation of the modulation multilevel number when the control unit 21 instructs the reception unit 22 what modulation multilevel number is used. This is because when the modulation multilevel number shown in FIG. 3 is allocated to each subcarrier, the modulation multilevel number assigned to each subcarrier is read based on the maximum modulation multilevel number shown in FIG. An example is shown. Here, since QPSK is designated as the maximum modulation multilevel number, 16QAM having a high modulation multilevel number is read as QPSK. Such replacement is applied to all corresponding subcarriers (groups) as shown in FIG. 7, for example. In FIG. 7, since the maximum modulation multilevel number is “2”, all subcarriers (groups) having the multilevel number “3” are read as “2”.

  Subsequently, a control sequence by the transmitting station 1 and the receiving station 2 of the present embodiment will be described. FIG. 8 is a diagram showing a control sequence by the transmitting station 1 and the receiving station 2.

  The control unit 11 of the transmission station 1 determines the modulation multi-level number to be assigned to each subcarrier (group) (step S1), and sends the result to the transmission unit 12 as a transmission control signal transmission instruction (step S2). The transmission unit 12 that has received the transmission control signal transmission instruction performs CRC addition, error correction coding, modulation, and the like (step S3), and transmits a transmission control signal to the receiving station 2 (step S4).

  Further, the control unit 11 determines how many bits of data are to be transmitted based on the modulation multi-level number assigned to each subcarrier (group), and sends a main signal transmission instruction designating transmission data to the transmission unit 12 ( Step S5). The transmission unit 12 that has received the main signal transmission instruction performs CRC assignment, error correction coding, and the like (step S6), and transmits the main signal to the receiving station 2 (step S7).

  On the other hand, when receiving the transmission control signal, the receiving unit 22 of the receiving station 2 performs demodulation and error correction of the received data, recalculates the CRC (step S8), and then transmits a transmission control signal reception notification to the control unit 21. Send (step S9). Receiving the transmission control signal reception notification, the control unit 21 interprets the modulation multilevel number assigned to each subcarrier (group) from the transmission control signal (step S109), and sends the transmission control signal interpretation notification to the reception unit 22 ( Step S11). At this time, if the transmission control signal is different from the previously received transmission control signal, it means that the maximum modulation multi-level number has been changed, so that a new modulation allocated to each subcarrier (group). The multi-value number is stored.

  When receiving the main signal, the receiving unit 22 demodulates the received data and corrects the error based on the transmission control signal interpretation notification notified from the control unit 21 and recalculates the CRC (step S12). A reception notification is sent to the control unit 21 (step S13). The control unit 21 compares the CRC given to the received signal with the recalculated CRC, determines whether there is an error in the received data (step S14), and generates a control signal for delivery confirmation. Then, a reception control signal transmission instruction designating a control signal is sent to the transmission unit 23 (ACK when the retransmission is unnecessary, NACK when the retransmission is necessary) (step S15). Receiving the reception control signal transmission instruction, the transmission unit 23 performs CRC addition, error correction coding, and modulation (step S16), and transmits the reception control signal obtained as a result to the transmission station 1 (step S17).

  When receiving the reception control signal, the reception unit 13 of the transmission station 1 performs demodulation and error correction, recalculates the CRC (step S18), and then sends a reception control signal reception notification to the control unit 11 (step S19). . The control unit 11 determines the next transmission control signal based on the reception control signal reception notification (step S20).

  Next, a method for determining the next transmission control signal will be described. When the CRC judgment result of the reception control signal returned from the receiving station 2 is identical, the control unit 11 of the transmitting station 1 compares the error correction rate with the reference value held by itself. For example, if the error correction rate exceeds the reference value by Δ%, it is determined that quality degradation has occurred and the modulation multi-level number is lowered. At this time, how much the modulation multi-level number is reduced is determined based on the control amount held by itself. The control amount may be defined as a fixed value regardless of the difference between the error correction rate and the reference value, or may be defined individually depending on the magnitude of the difference.

As shown in FIG. 9, when the reference value exceeds Δ% continuously a plurality of times, it may be determined that quality degradation has occurred and the modulation multi-level number may be lowered. Also, as shown in FIG. 10, when the reference value exceeds Δ% for N ₂ times in N ₁ times, it may be determined that quality degradation has occurred and the modulation multi-level number may be lowered.

  Even when the CRC judgment results of the reception control signals returned from the receiving station 2 do not match, the control unit 11 determines that quality degradation has occurred and lowers the modulation multi-level number. At this time, how much the modulation multi-level number is reduced is determined based on the control amount held by itself. The control amount may be the same value as the quality deterioration determination using the error correction rate, or another value may be defined.

In addition, when the CRC determination results do not coincide with each other a plurality of times, the modulation multi-level number may be lowered as a determination that quality degradation has occurred. In addition, when the CRC determination results do not match N ₂ times in N ₁ times, it may be determined that quality degradation has occurred and the modulation multi-level number may be lowered.

  Next, a radio frame that realizes the control sequence will be described. FIG. 11 is a diagram illustrating an example of a radio frame for realizing the control sequence illustrated in FIG. This radio frame is composed of three parts: Preamble, Header, and Payload that are continuous in the time direction. Preamble is used when detecting the presence of received data or when performing channel estimation. The Header is used for transmitting a transmission control signal. Payload is used to transmit the main signal. The illustrated Payload portion is modulated with the modulation multi-level number specified by the Header. Note that the header is modulated by the transmission station 1 and the reception station 2 with a known modulation multilevel number. Since the payload cannot be demodulated unless the transmission control signal is extracted from the header, the receiving unit 22 of the receiving station 2 needs to store the payload until the transmission control signal interpretation notification is received from the control unit 21.

  However, since a main signal cannot be received if a reception error occurs in the transmission control signal, a transmission method that is resistant to the reception error is applied to the transmission control signal. FIG. 12 is a diagram illustrating an example of a transmission method that is resistant to reception errors. For example, CRC is given to a new control signal created by copying a plurality of control signals (maximum modulation multi-level number) (steps S21 and S22). Then, for example, an error correction code having a high error correction capability such as a coding rate of 1/3 is applied (step S23). Further, for example, modulation is performed by applying a modulation scheme having a low modulation multi-level number such as BPSK (step S24). Further, for example, the transmission power is increased and the transmission signal is amplified and transmitted (step S25). In the above transmission method, all the processes in steps S21 to S25 are executed to realize a transmission method that is resistant to reception errors. However, the present invention is not limited to this, the processes in steps S21 and S22, the processes in step S23, At least one of the process of step S24 and the process of step S25 may be executed to realize a transmission method that is resistant to reception errors.

  In addition, by applying the transmission method, each bit of the control signal is mapped to a plurality of subcarriers. Therefore, the receiving station 2 combines and demodulates each bit of the control signal mapped to a plurality of subcarriers. By applying such a transmission method, a frequency diversity effect can be obtained, so that a control signal reception error is less likely to occur.

  In addition, if a reception error occurs in the reception control signal, adaptive modulation control cannot be performed. Therefore, a transmission method that is resistant to reception errors is applied to the reception control signal as well.

  Further, if transmission is performed with the modulation multi-level number being suppressed after a CRC error has occurred, the subcarriers to which each bit of transmission data is assigned differ between initial transmission and retransmission, as shown in FIG. For this reason, Hybrid ARQ that can soft-combine the initial transmission data and retransmission data to increase the combined gain is applied. As a result, a frequency diversity effect can be obtained, and reception errors are less likely to occur.

  As described above, in the present embodiment, when the modulation scheme is variable for each subcarrier (group), control that suppresses the application of the highest modulation multilevel number from the transmitting station to the receiving station when quality deteriorates. It was decided to send a signal. Thereby, the overhead of the control signal can be reduced. In addition, when the main signal is received, it is not necessary to perform quality measurement for each subcarrier (group) at the receiving station, so that it can be operated with low power consumption. In addition, since the receiving station feeds back information on the number of error correction bits, the transmitting station can detect quality deterioration at an early stage. In addition, since the transmitting station and the receiving station transmit control signals using a transmission method that is resistant to reception errors, it is possible to reduce control delays associated with control signal reception errors. Further, the bit error rate can be further improved by combining the adaptive modulation control method of the present embodiment and the retransmission control method that combines the maximum ratio of the initial transmission data and the retransmission data.

  The adaptive modulation control method according to the present invention is applied to a system (ex. Power Line Communication, 802.16e, 3GPP Evolved UTRA) in which a plurality of subcarriers (groups) exist and adaptive modulation is performed for each subcarrier (group). Widely applicable.

Embodiment 2. FIG.
In the first embodiment described above, as shown in FIG. 11, since there is a header immediately before the payload, the demodulation process of the payload cannot be started unless a control signal is extracted from the header. Therefore, the receiving station must store a part of the payload that has already been received in the memory. Therefore, in the present embodiment, for example, as shown in FIG. 14, a case will be described in which the modulation multi-level number is limited in a radio frame configuration that does not include a header part. The configurations of the transmitting station and the receiving station are the same as those in the first embodiment.

  In the present embodiment, as shown in FIG. 15, a transmission control signal is transmitted from the transmitting station 1 to the receiving station 2 (step S31), and a response signal from the receiving station 2 to the transmitting station 1 is correctly received ( In step S32), the transmission station 1 allocates transmission data to each subcarrier (group) in which the number of modulation multilevels is limited based on the transmission control signal transmitted previously, and transmits the main signal.

  Thus, in this embodiment, the transmitting station transmits the main signal after correctly receiving the transmission control signal at the receiving station. As a result, the same effects as those of the first embodiment can be obtained, and a memory for storing a part of the payload can be eliminated.

  As an example, when the HyperLAN / 2 frame format is applied, the same effect as described above can be obtained by a method different from the above. Specifically, as shown in FIG. 16, a radio frame is configured by BCH, FCH, ACH, SCH / LCH (DL), SCH / LCH (UL), and RCH. Since BCH, FCH, ACH, and RCH are common channels, the modulation multi-level number is fixed. On the other hand, since SCH / LCH (DL) and SCH / LCH (UL) are dedicated channels, it is possible to adaptively assign modulation multi-level numbers. In addition, SCH / LCH (DL) destination and SCH / LCH (UL) transmission permission are performed by FCH. At this time, this FCH is used to instruct suppression of the modulation multi-level number of SCH / LCH (DL) and SCH / LCH (UL). In this frame format, since ACH is included between FCH and SCH / LCH (DL), if the time taken to extract information related to suppression of the modulation multi-value number from FCH is within ACH, Embodiment 2 The same effect can be obtained. Note that even if the ACH is greater than or equal to ACH, the amount of memory can be reduced by the amount corresponding to ACH.

  As described above, the adaptive modulation control method according to the present invention is useful for a system in which a plurality of subcarriers or a plurality of subcarrier groups exist, and in particular, in a system that performs adaptive modulation for each subcarrier or subcarrier group. Is suitable.

It is a figure which shows the structural example of the transmitting station and receiving station which implement | achieve the adaptive modulation control method concerning this invention. It is a figure which shows an example of the control signal in the case of quality monitoring in the subcarrier (group) unit at the time of communication start, and feeding back the result. It is a figure which shows an example of the control signal in the case of designating the modulation | alteration multi-value number per subcarrier (group) at the time of communication start. It is a figure which shows the specific example of a reception control signal. It is a figure which shows the specific example of a transmission control signal. It is a figure which shows the example of interpretation of the modulation | alteration multi-value number. It is a figure which shows the case where 16QAM is read as QPSK. It is a figure which shows the control sequence by a transmission station and a receiving station. It is a figure which shows an example of the method of determining a control signal. It is a figure which shows an example of the method of determining a control signal. It is a figure which shows an example of a radio | wireless frame. It is a figure which shows an example of the transmission method strong against a reception error. It is a figure which shows the case where the subcarrier to which transmission data is allocated differs between initial transmission and retransmission. It is a figure which shows an example of a radio | wireless frame. FIG. 10 is a diagram illustrating a characteristic operation of the second embodiment. It is a figure which shows an example of a radio | wireless frame.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transmission station 2 Reception station 11 Control part 12 Transmission part 13 Reception part 21 Control part 22 Reception part 23 Transmission part

Claims (10)

In a communication system in which the modulation method is variable for each subcarrier or subcarrier group, the modulation multi-value applied for each subcarrier or subcarrier group between the transmitting station and the receiving station by transmission / reception processing at the start of communication An adaptive modulation control method when the numbers are known to each other,
A data transmission step in which the transmitting station transmits a transmission control signal including a maximum modulation multi-level number that can be assigned to a subcarrier or a subcarrier group, and a main signal that is transmission data;
A delivery confirmation transmitting step in which the receiving station demodulates and decodes the main signal based on the received transmission control signal and returns a reception control signal for delivery confirmation indicating the presence or absence of an error in the received data;
A modulation multi-level number adjusting step for performing control to suppress the maximum modulation multi-level number when the transmitting station determines that reception quality is deteriorated based on the received reception control signal;
An adaptive modulation control method comprising:   In the delivery confirmation transmission step, a CRC determination result that is information indicating whether or not the CRC calculated from the received bit string by the receiving station matches the CRC assigned by the transmitting station, and information on the number of error correction bits The adaptive modulation control method according to claim 1, wherein a reception control signal including a certain error correction rate is returned. In the modulation multi-level number adjusting step,
When the CRC determination result included in the returned reception control signal indicates that it matches, the error correction rate included in the reception control signal is compared with the reference value held by the transmitting station,
The adaptive modulation control method according to claim 2, further comprising performing control to suppress the maximum modulation multi-level number when it is determined that reception quality is deteriorated based on the comparison result. In the modulation multi-level number adjusting step,
When the CRC determination result included in the returned reception control signal indicates that they do not match, it is determined that reception quality has deteriorated, and control is performed to suppress the maximum modulation multilevel number. The adaptive modulation control method according to claim 2 or 3.   The adaptive modulation control method according to any one of claims 2 to 4, wherein the transmission control signal and the reception control signal are created by copying a plurality of pieces of information as constituent elements.   6. The adaptive modulation control according to claim 2, wherein an error correction code having a higher error correction capability capable of avoiding a reception error is applied to the transmission control signal and the reception control signal. Method.   The adaptive modulation control according to any one of claims 2 to 6, wherein a modulation scheme having a lower modulation multi-level that can avoid a reception error is applied to the transmission control signal and the reception control signal. Method.   The adaptive modulation control method according to claim 2, wherein transmission power of the transmission control signal and the reception control signal is amplified and transmitted.   The adaptive modulation control method according to any one of claims 1 to 8, wherein when a subcarrier to be allocated is different between initial transmission and retransmission, the receiving station combines the initial transmission data and the retransmission data with a maximum ratio. . Used in a communication system in which the modulation method is variable for each subcarrier or subcarrier group, and the transmission / reception processing at the start of communication allows the modulation multilevel number applied to each subcarrier or subcarrier group between the partner station Communication devices known to each other,
A data transmission means for transmitting a transmission control signal including a maximum number of modulation multi-values that can be assigned to a subcarrier or a subcarrier group, and a main signal that is transmission data;
When it is determined that the reception quality has deteriorated based on the reception control signal returned for confirmation of delivery indicating the presence or absence of errors in the received data by the counterpart station, control is performed to suppress the maximum modulation multi-level number Modulation multi-level number adjusting means;
A communication apparatus comprising:

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