JP4700106B2 - Adaptive modulation method and communication apparatus - Google Patents

Description

  The present invention relates to an adaptive modulation method for adaptively selecting and determining an encoding scheme and a modulation scheme at the time of data transmission by orthogonal frequency division multiplexing (OFDM), and in particular, for each subcarrier. The present invention relates to an adaptive modulation method in the case of selecting and determining a coding method and a modulation method for each subcarrier based on communication quality, and a communication apparatus that realizes the adaptive modulation method.

  The adaptive modulation scheme is a scheme that selectively uses a combination of a coding scheme (coding rate and type of error correction code) and a modulation scheme according to the state of the transmission path. That is, when the state of the transmission path is in a poor state due to a large noise or the like, a coding scheme having as high an error correction capability as possible and a modulation scheme that is difficult to error are used in combination. On the other hand, when the transmission path is in good condition, combine a coding method with a small number of redundant bits (error correction bits) and a modulation method with a large number of multiple values that can transmit many bits at once. use. By adopting such an adaptive modulation method, it is possible to realize data transmission as fast as possible while satisfying desired communication quality (bit error rate and packet error rate) according to the state of the transmission path. For example, Patent Document 1 below discloses a method of selectively using an encoding method, a modulation method, or the like according to the state of a transmission path as an adaptive modulation method when performing communication using OFDM.

  Here, in data transmission by OFDM, a plurality of data are transmitted in parallel using a plurality of subcarriers. Each subcarrier can use a different modulation method. However, in the conventional technique disclosed in Patent Document 1 and a wireless LAN using OFDM, the same modulation method is used for all subcarriers. Yes.

JP 2002-261726 A

  Generally, the frequency characteristics of the transmission path are not flat due to the influence of multipath and the like. And, a signal with a large attenuation is difficult to pass through (transmission error is likely to occur), and only a modulation method with a small multi-value number can be used. On the other hand, a signal with low attenuation is easy to pass through, and a modulation system with a large multi-value number can be used.

  As described above, data transmission by OFDM is performed by transmitting data on a plurality of subcarriers in parallel. It is known that a modulation scheme corresponding to the ease of passing a signal can be set for each subcarrier even when the frequency characteristics of the transmission path are not flat.

  Conventionally, however, data transmission is performed by setting the same modulation scheme for all subcarriers. For this reason, the modulation scheme of all subcarriers is selected in consideration of the subcarrier where the signal hardly passes, and efficient data transmission cannot be realized. In addition, a setting method (combination selection method) between an encoding method and a modulation method for each subcarrier for obtaining optimum quality (communication at a high transmission rate) has not been shown.

  Furthermore, not only communication using OFDM, but also a frequency division (FDM) based communication system that transmits data at multiple frequencies, a time division (TDM) base that transmits data at multiple times Communication systems, code division multiplexing (CDM) communication systems that transmit data using a plurality of codes, and space division multiplexing (SDM) -based communication systems that transmit data in a plurality of spaces. If subcarriers are regarded as frequency, time, code, and space, respectively, the same problem occurs. That is, the easiness of passing a signal for each subcarrier in OFDM is the same as the easiness of passing a signal at each frequency in FDM-based communication, and the same as the easiness of passing a signal in each time slot in TDM-based communication. Yes, it is the same as the signal passing through each code in the CDM-based communication, and the same as the signal passing through each space in the SDM-based communication. Therefore, as with OFDM, a setting method of an encoding method and a modulation method set in frequency, time, code, and space for obtaining optimum quality has not been shown.

  The present invention has been made in view of the above, and obtains an adaptive modulation method capable of realizing high-speed data transmission while satisfying desired communication quality in communication using OFDM, and a communication apparatus for realizing the same. With the goal.

  Still another object of the present invention is to provide an adaptive modulation method capable of realizing high-speed data transmission while satisfying desired communication quality in communication using FDM, TDM, CDM, and SDM, and a communication apparatus that implements the method. To do.

  In order to solve the above-described problems and achieve the object, the adaptive modulation method according to the present invention adaptively selects an encoding method and a modulation method at the time of data transmission by orthogonal frequency division multiplexing according to the state of the transmission path. An adaptive modulation method for determining, for example, selecting a modulation scheme for each subcarrier from a predefined modulation scheme and determining a combination of modulation schemes (modulation scheme pattern) for each subcarrier. A modulation scheme pattern determining step, a coding scheme selection step for selecting a coding scheme to be used when coding transmission data from a predetermined coding scheme, and an SIR for each subcarrier of the received signal Based on the above, the transmission rate and communication quality (transmission quality) at the time of data transmission using the determined modulation method pattern and the selected coding method are calculated. A transmission quality calculation step, and by repeatedly executing the modulation scheme pattern determination step, the encoding scheme selection step, and the transmission quality calculation step, all modulation scheme patterns and encoding schemes The transmission quality calculation step is executed for the combination, and the modulation scheme pattern and the coding scheme when the transmission quality that achieves the maximum transmission speed while satisfying the desired communication quality is obtained in the transmission quality calculation results are shown as data transmission. It is characterized in that it is selected and determined as a formal modulation scheme pattern and encoding scheme used sometimes.

  In the adaptive modulation method according to the present invention, data transmission is performed by selecting a combination of an optimal encoding scheme and an optimal modulation scheme for each subcarrier based on the reception quality of the signal. While satisfying communication quality, it is possible to perform data transmission at a higher speed than when using the above-described conventional technology, and in particular, it is possible to increase the transmission speed at the time of data transmission on a transmission path with non-flat frequency characteristics There is an effect.

FIG. 1 is a diagram illustrating a configuration example of a first embodiment of a communication system that implements an adaptive modulation method according to the present invention and a communication device that configures the communication system. FIG. 2 is a flowchart showing an example of an operation for selecting and determining a coding scheme and a modulation scheme for each subcarrier. FIG. 3 is a diagram for explaining an operation of selecting a modulation scheme for each subcarrier. FIG. 4 is a diagram for explaining an encoding method selection operation. FIG. 5 is a diagram for explaining an operation of selecting and determining a modulation scheme and a coding scheme for each subcarrier. FIG. 6 is a flowchart illustrating an operation of generating adaptive modulation instruction information performed by the communication apparatus according to the second embodiment. FIG. 7A is a diagram for explaining the SIR threshold value setting operation. FIG. 7B is a diagram for explaining the SIR threshold value setting operation. FIG. 8 is a diagram illustrating a configuration example of a communication system that implements the adaptive modulation method according to the present invention and a communication device that configures the communication system according to the third embodiment. FIG. 9 is a flowchart showing an operation of adjusting the modulation scheme and encoding scheme for each subcarrier once determined. FIG. 10 is a flowchart showing the SIR threshold value adjusting operation. FIG. 11 is a flowchart showing the encoding method adjustment operation. FIG. 12 is a flowchart showing an operation of updating adaptive modulation instruction information in the adaptive modulation method of the fourth embodiment. FIG. 13 is a flowchart showing an operation of changing the modulation scheme for each subcarrier in the adaptive modulation method of the fifth embodiment. FIG. 14 is a flowchart showing an operation of changing the modulation scheme for each subcarrier in the adaptive modulation method of the fifth embodiment. FIG. 15 is a flowchart showing an operation for updating adaptive modulation instruction information in the adaptive modulation method of the seventh embodiment. FIG. 16A is a diagram for explaining an adaptive modulation method according to the eighth embodiment. FIG. 16-2 is a diagram for explaining an adaptive modulation method according to the eighth embodiment. FIG. 17A is a diagram for explaining an adaptive modulation method according to the ninth embodiment. FIG. 17-2 is a diagram for explaining an adaptive modulation method according to the ninth embodiment. FIG. 17-3 is a diagram for explaining an adaptive modulation method according to the ninth embodiment. FIG. 17-4 is a diagram for explaining an adaptive modulation method according to the ninth embodiment. FIG. 17-5 is a diagram for explaining an adaptive modulation method according to the ninth embodiment. FIG. 18 is a flowchart showing an operation when the adaptive modulation method of the ninth embodiment is applied to the first embodiment.

Explanation of symbols

1, 2, 2a Communication device 11 Encoding unit 12 Modulating unit 21 Demodulating unit 22 Decoding unit 23, 23a Determination unit 31 Comparison unit 32 Threshold setting unit 33 Selection unit 34 Encoding method holding unit 35 Control unit

  Embodiments of an adaptive modulation method and a communication apparatus 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 illustrating a configuration example of a first embodiment of a communication system that implements an adaptive modulation method according to the present invention and a communication device that configures the communication system. This communication system includes a communication device 1 and a communication device 2. In addition, the communication device 1 includes an encoding unit 11 and an OFDM modulation unit 12, and the communication device 2 includes an OFDM demodulation unit 21, a decoding unit 22, and a determination unit 23. The determination unit 23 operates as a transmission condition selection unit, a transmission quality calculation unit, an iterative process control unit, and a transmission condition determination unit.

  Further, FIG. 1 illustrates a state in which the communication device 1 transmits data to the communication device 2. Therefore, each of communication apparatuses 1 and 2 includes only a signal transmission processing unit (corresponding to encoding unit 11 and modulation unit 12) and a reception processing unit (corresponding to OFDM demodulating unit 21 and decoding unit 22). However, both are actually provided with a transmission processing unit and a reception processing unit, and the communication device 2 transmits a signal to the communication device 1 as necessary.

  In the communication device 1, the encoding unit 11 encodes transmission data by the encoding method indicated by the “encoding method information” that constitutes the adaptive modulation instruction information notified in advance from the communication partner. The OFDM modulation unit 12 uses the modulation scheme indicated by “information indicating the modulation scheme for each subcarrier” included in the adaptive modulation instruction information notified in advance from the communication partner, and is encoded from the encoding unit 11. The transmission data is modulated to generate a transmission signal. The generated transmission signal is transmitted from the antenna to the communication apparatus 2 that is the communication partner via the transmission path.

  In the communication device 2, the OFDM demodulator 21 demodulates the received signal from the communication device 1. The decoding unit 22 performs error correction processing on the demodulated data obtained by the OFDM demodulating unit 21 demodulating the received signal, and outputs the processing result as received data. Based on the received signal (demodulated data) demodulated by the OFDM demodulator 21, the determination unit 23 determines the encoding method used by the data transmission source device (communication device 1) and the modulation method for each subcarrier. Then, adaptive modulation instruction information indicating the determination result is generated. Specifically, the determination unit 23 selects an encoding method that can maximize the transmission rate and a modulation method for each subcarrier according to the transmission path state estimated based on the received signal. As described above, since the frequency characteristic of the transmission path is not flat as described above, the optimum modulation method is selected for each frequency (subcarrier), and this is combined with the optimum encoding method to perform communication. is there. The generated adaptive modulation instruction information is notified (transmitted) to the communication device 1 via the transmission path.

  The operation of determining section 23 for generating the adaptive modulation instruction information (the operation of selecting and determining the encoding scheme and the modulation scheme for each subcarrier) will be described with reference to FIG. FIG. 2 is a flowchart showing an operation of generating adaptive modulation instruction information. The determination unit 23 receives SIR (Signal to Interference Ratio) for each subcarrier measured by the OFDM demodulation unit 21 (step S11).

  Next, the determination unit 23 selects a modulation scheme for each subcarrier (step S12). For example, if the number of subcarriers is 3 and the selectable modulation schemes are BPSK and QPSK, one of the eight patterns shown in FIG. 3 is selected as a combination of modulation schemes for each subcarrier. It will be. Note that conditions for selecting a combination (combination pattern) of modulation schemes for each subcarrier are not particularly defined. Therefore, for example, the selection may be performed in the order of the combination pattern numbers shown in FIG. 3, or selectable combination patterns may be selected at random.

  Next, the determination unit 23 selects an encoding method (step S13). The encoding method is selected from, for example, two types of encoding methods having different error correction capabilities as shown in FIG. FIG. 4 shows an example of using a Reed-Solomon (RS) code. RS (255, 239), which is the first encoding method, indicates an encoding method for generating a code in which 16 bytes of redundant bytes are added to 239 bytes of information. Also, RS (120, 104) as the second encoding method indicates an encoding method for generating a code in which 16 bytes of redundant bytes are added to 104 bytes of information. The coding rate is about 0.94 (= 239/255) when RS (255, 239) is used, and about 0.87 (= 104 /) when RS (120, 104) is used. 120). Further, the transmission rate when the same modulation method is used is higher when RS (255, 239) is used. Further, the error correction capability is higher when RS (120, 104) is used.

  Note that conditions for selecting an encoding method are not particularly specified. Therefore, for example, the selection may be made in the order of the lowest number of the encoding method shown in FIG. 4, or may be selected at random.

  In addition, the determination unit 23 holds the selection result in step S12 and the selection result in step S13 together (holds a combination of the selection results), and at the time of executing steps S12 and S13 after the next time, Processing is performed so that the combination of the selection results is not the same as the combination of the selection results of this time.

  Next, the determination unit 23 calculates a transmission rate and communication quality when communication is performed using the selection results in steps S12 and S13 (step S14). For example, in the example shown in FIG. No. 1 is selected and No. 1 in the example shown in FIG. When 1 is selected, the transmission rate is 2.82 (= 3 * 0.94) bits per symbol since the modulation scheme of all subcarriers is BPSK and the coding rate is 0.94. Further, as a combination of modulation schemes for each subcarrier, No. in the example shown in FIG. No. 2 is selected, and No. of the example shown in FIG. When 2 is selected, the transmission rate is 3.48 (= 4 * 0.87) bits per symbol because the modulation scheme of subcarrier # 1 is QPSK, the other is BPSK, and the coding rate is 0.87. . The actual transmission rate expressed in units such as bps (bits per second) needs to divide this value by the time length of one symbol, but here it is sufficient if the transmission rates can be compared. Division processing is not essential.

  The communication quality is calculated using the SIR for each subcarrier acquired in step S11. Since the communication quality is a bit error rate (coded-BER: coded bit error rate) or a packet error rate (PER) after error correction, the communication quality can be calculated based on the SIR for each subcarrier. Specifically, since BER (uncoded-BER) before error correction of a certain subcarrier can be calculated based on the modulation scheme and SIR of the subcarrier, the determination unit 23 performs this uncoded-BER for all subcarriers. BER of the input signal to the decoding unit 22 is calculated. In addition, error correction has a correction capability that is determined by the encoding method used, and it is possible to calculate coded-BER (= communication quality) after error correction with respect to uncoded-BER before error correction. In this example, coded-BER is used as communication quality, but PER may be used instead. Although the method for obtaining the communication quality by calculation is shown here, it is not calculated, but the SIR vs. BER characteristic is obtained in advance by simulation, and a table showing the result is created, and this table is referred to. You may do it.

  Next, the determination unit 23 determines whether transmission rate calculation and communication quality calculation have been completed for all combinations of modulation schemes and encoding schemes for each subcarrier (step S15). In step S15, when there is a combination of a modulation scheme for each subcarrier that has not yet been selected (transmission rate calculation and communication quality calculation has not been calculated) and a coding scheme (No in step S15), the process proceeds to step S12. Returning, the same processing (steps S12 to S14) is performed for the combination of the modulation method and the coding method for each subcarrier that has not yet been selected. When the transmission rate calculation and the communication quality calculation for all combinations are completed (step S15, Yes), the process proceeds to step S16.

  Finally, the determination unit 23 compares the combination of the transmission rate and the communication quality held as the processing result of step S14. Then, a combination that maximizes the transmission speed while satisfying desired communication quality (for example, communication quality required by the communication system) is selected from the retained processing results. Finally, the combination of the modulation scheme for each subcarrier and the coding scheme corresponding to the selection result (the selection result is obtained) is set as adaptive modulation instruction information (a combination used at the time of data transmission) ( Step S16).

  FIG. 5 shows subcarriers of subcarrier numbers # 1, # 2, and # 3 at the time of data transmission performed by combining any of the modulation schemes shown in FIG. 3 and any of the encoding schemes shown in FIG. This shows an example of the calculation result in step S14 when the SIR is 8 dB, 9 dB, and 10 dB, respectively. In the case where the calculation result as shown in FIG. 5 is obtained, for example, if the desired communication quality is coded-BER = 1E-6 (up to 1 bit error per 1,000,000 bits), this Combinations satisfying the desired communication quality are No. There are six types: 1, 5, 9, 11, 13, and 15. The combination that can obtain the largest transmission rate is No. 15. Therefore, when the calculation result illustrated in FIG. 5 is obtained and the desired communication quality is coded-BER = 1E-6, the determination unit 23 determines that No. 15 combinations are selected and determined. When there are a plurality of candidates having the same transmission rate among the combinations satisfying the communication quality, the combination having the best communication quality is selected and determined from among the candidates.

  As described above, in the present embodiment, based on the reception quality of a signal, a combination of an optimal encoding scheme and an optimal modulation scheme for each subcarrier is selected, and data transmission is performed using the selected combination. It was decided to do. This makes it possible to perform data transmission at the maximum transmission speed while satisfying the desired communication quality. In particular, the transmission speed at the time of data transmission on a transmission line with a non-flat frequency characteristic can be increased compared to the conventional one. .

Embodiment 2. FIG.
Next, the adaptive modulation method and communication apparatus according to the second embodiment will be described. In the present embodiment, an adaptive modulation method for reducing the amount of calculation and reducing the circuit scale by simplifying the processing described in the first embodiment will be described. The configuration of the communication system that implements the adaptive modulation method of the present embodiment and the configuration of the communication device that configures the communication system are the same as those of the first embodiment described above, and the generation operation of adaptive modulation instruction information performed by the determination unit 23 Only the difference. Therefore, in the present embodiment, the description will focus on the adaptive modulation instruction information generation operation performed by the determination unit 23.

  FIG. 6 is a flowchart illustrating an operation of generating adaptive modulation instruction information performed by the communication device 2 (determination unit 23) according to the second embodiment. In addition, about the process similar to Embodiment 1, the same step number is attached | subjected and the description is abbreviate | omitted.

  The determination unit 23 sets the SIR threshold corresponding to the coding method selected in step S13 after executing the processing in the order of step SS11 and step S13 (step S21). The SIR threshold value is determined in advance for each selectable encoding method based on the communication quality (desired communication quality) that should be satisfied in the communication. The one corresponding to the selected encoding method is selected and set.

  A specific example of the SIR threshold setting operation will be described with reference to FIGS. 7-1 and 7-2. FIGS. 7A and 7B are diagrams illustrating an example of a correspondence relationship between received signal quality before error correction execution (in this example, uncoded-BER which is a BER before error correction execution) and SIR. More specifically, FIG. 7-1 is a diagram illustrating an example of a correspondence relationship between communication quality (coded-BER which is a BER after error correction) and uncoded-BER for each encoding method. This correspondence can be calculated based on the coding rate for each coding method. FIG. 7-2 is a diagram illustrating a relationship example between the uncoded-BER and the SIR for each modulation scheme.

For example, when the desired communication quality is coded-BER = 1E-6, in order to satisfy this, according to FIG. 7A, when using encoding method # 1, uncoded-BER ≦ 1E-4 is established. If the encoding method # 2 is used, uncoded-BER ≦ 1E-3 needs to be satisfied. The example shown in FIG. 7A is for the case where the error correction capability of the encoding scheme # 2 is higher than the error correction capability of the encoding scheme # 1. Also, according to FIG. 7-2, if the desired communication quality is coded-BER = 1E-6 and encoding method # 1 is used, uncoded-BER ≦ 1E-4 needs to be established, and the SIR is γ ₁₁ It must be more than that. Similarly, if the modulation method # 2 is used, the SIR must be γ ₁₂ or more. The example shown in FIG. 7-2 is for the modulation scheme in which the modulation scheme # 2 requires a larger SIR and the number of transmission bits is large.

Here, considering the case where the SIR of a certain subcarrier is between γ ₁₁ and γ ₁₂ and the desired communication quality is coded-BER = 1E-6, modulation method # 1 can be used with that subcarrier. However, modulation method # 2 cannot be used. In contrast, if SIR is greater than gamma _12, the modulation method # 2 is available for that subcarrier. That is, γ ₁₂ and γ ₁₂ are SIR threshold values for the encoding scheme # 1. Similarly, γ ₂₁ and γ ₂₂ are SIR threshold values for the encoding scheme # 2.

Thus, if you select the coding scheme # 1 in step S13, the determination unit 23, SIR threshold for selecting an SIR threshold gamma ₁₂ and the modulation scheme # 2 for selecting a modulation scheme # 1 to set the γ _12. When the encoding method # 2 is selected in step S13, the determination unit 23 selects the SIR threshold value γ ₂₁ for selecting the modulation method # 1 and the SIR threshold value γ for selecting the modulation method # 2. Set ₂₂

Next, the determination unit 23 compares the SIR threshold set in step S21 with the SIR for each subcarrier acquired in step S11, and determines the modulation scheme for each subcarrier (step S22). More specifically, the determination unit 23, with reference to FIGS. 7-1 and 7-2, for example, if between the subcarrier SIR is gamma ₁₁ and gamma ₁₂ of the determination target modulation scheme, the subcarriers Is determined to be modulation method # 1. Note that the determination unit 23 performs such processing (decision of modulation scheme) for all subcarriers.

  Next, the determination unit 23 calculates a transmission rate (step S23). The transmission rate calculation process is the same as the transmission rate calculation process performed in step S14 of the first embodiment described above, and the coding rate of the coding method selected in step S13 and the modulation determined in step S22. Calculate the transmission rate when using the method (modulation method for each subcarrier). The determination unit 23 holds the calculated transmission rate.

  Next, the determination unit 23 determines whether or not the above-described series of processing (steps S13, S21, S22, and S23) has been executed for all selectable encoding methods (step S24). When there is an encoding method that has not yet been selected (the above-described series of processing has not been executed) (No in step S24), the process returns to step S13, and the same processing (steps S13, S21, S22, S23, S24) are performed. When the above-described series of processing is completed for all the encoding methods (Yes in step S24), the process proceeds to step S16.

  Finally, the determination unit 23 selects and determines the combination of the modulation scheme for each subcarrier and the encoding scheme for which the maximum transmission rate is obtained in step S23 as the combination used during data transmission (step S16). .

  As described above, in the present embodiment, based on the reception quality of a signal and the threshold value of the reception quality (for example, the threshold value of SIR), the optimum encoding method and the optimum modulation method for each subcarrier The combination was selected, and data transmission was performed using the selected combination. As a result, not all combinations (combination of encoding schemes and optimum modulation schemes for each subcarrier) are investigated, so that the selection accuracy of the combination is inferior to that of the first embodiment. While reducing the scale, the transmission speed at the time of data transmission can be made higher than before.

Embodiment 3 FIG.
Next, the adaptive modulation method and communication apparatus according to Embodiment 3 will be described. FIG. 8 is a diagram illustrating a configuration example of a communication system that implements the adaptive modulation method according to the present invention and a communication device that configures the communication system according to the third embodiment. The communication system according to the third embodiment includes a communication device 1 and a communication device 2a. The communication device 1 is the same as the communication device 1 of the first embodiment described above.

  The communication device 2a includes a determination unit 23a instead of the determination unit 23 included in the communication device 2. The determination unit 23a performs operations as a transmission condition selection unit, a transmission quality calculation unit, an iterative process control unit, and a transmission condition determination unit. The determination unit 23 a includes a comparison unit 31, a threshold setting unit 32, a selection unit 33, an encoding scheme holding unit 34, and a control unit 35. In addition, since it is the same structure as Embodiment 1 about parts other than the determination part 23a, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  In the present embodiment, an operation for adjusting a modulation scheme and a coding scheme for each subcarrier once determined (in use) will be described. In this embodiment, even if the communication quality changes due to fluctuations in the transmission path condition, the modulation scheme and the coding scheme can be adaptively adjusted (reselected) to increase the transmission speed. Realized. Note that this embodiment is different from the above-described second embodiment only in the adaptive modulation instruction information generation operation (adaptive modulation instruction information update operation) performed by the determination unit 23a. Here, the operation of the determination unit 23a will be mainly described.

  Since the transmission path state varies with the passage of time, there may occur a case where the modulation scheme and the encoding scheme for each subcarrier once determined do not satisfy the desired communication quality with the passage of time. On the other hand, there may be cases where communication quality becomes excessively better than desired communication quality over time. Therefore, in the former case, it is necessary to satisfy the desired communication quality by reducing the transmission rate. In the latter case, in order to transmit data efficiently, it is necessary to increase the transmission rate within a range that satisfies the desired communication quality. In order to realize this, the determination unit 23a included in the communication device 2a of the present embodiment adjusts the modulation scheme and encoding scheme for each subcarrier once determined by the procedure shown in FIG. FIG. 9 is a flowchart showing an operation (operation for updating adaptive modulation instruction information) of adjusting the modulation scheme and encoding scheme for each subcarrier once determined by the determination unit 23a. In addition, about the process similar to Embodiment 2, the same step number is attached | subjected and the description is abbreviate | omitted.

  The comparison unit 31 constitutes a modulation scheme pattern determination unit, and the threshold setting unit 32 and the control unit 35 constitute an SIR threshold adjustment unit. Further, the control unit 35 constitutes a reference communication quality acquisition unit, and the selection unit 33, the encoding scheme holding unit 34, and the control unit 35 constitute an encoding scheme adjustment unit.

  First, the determination unit 23a generates adaptive modulation instruction information by executing any of the adaptive modulation instruction information generation operations described in the first or second embodiment at the start of communication (a modulation scheme for each subcarrier, Determine the encoding method). Thereafter, the control unit 35 of the determination unit 23a acquires communication quality information indicating the communication quality measured by the decoding unit 22 (step S31). Note that the communication quality measured by the decoding unit 22 is measured by a method of detecting a CRC error and obtaining PER, which is generally performed. Further, the communication quality acquired here is held as the reference communication quality until the next step S31 is executed.

  Next, the determination unit 23a adjusts the SIR threshold (see step S21 in FIG. 6) set in the adaptive modulation instruction information generation operation at the start of communication (step S32). Note that this is not the case after the adjustment of the SIR threshold has already been performed, and the latest SIR threshold obtained by the previous adjustment is adjusted (readjusted).

  Here, the operation of step S32 will be described in detail with reference to FIG. FIG. 10 is a flowchart showing details of the SIR threshold value adjusting operation. In step S32, the control unit 35 of the determination unit 23a determines whether or not the communication quality (reference communication quality) indicated by the communication quality information acquired in step S31 is good (a desired communication quality is satisfied) ( Step S41). The communication quality is determined based on a communication quality determination threshold value for determining whether the communication quality is good. Specifically, the control unit 35 determines that the communication quality is good when the communication quality is equal to or higher than the communication determination threshold, and otherwise the communication quality is not good. When the communication quality is not good (No in step S41), the control unit 35 instructs the threshold setting unit 32 to adjust the SIR threshold, and the threshold setting unit 32 is in use. The SIR threshold value (updated SIR threshold value) after the SIR threshold value of (set) is increased by a specified value is reset (step S42). Note that the threshold setting unit 32 adjusts all the SIR thresholds for each of the plurality of modulation schemes. Based on the updated SIR threshold and the SIR for each subcarrier received from OFDM demodulator 21, comparator 31 performs the same processing as step S22 (see FIG. 6) of the second embodiment, and A modulation scheme for each carrier is determined (step S43). Note that the determined modulation scheme for each subcarrier is notified to the communication apparatus 1.

  Thereafter, the control unit 35 acquires communication quality information in a state reflecting the determined modulation scheme for each subcarrier from the decoding unit 22, and confirms whether the communication quality is good (step S44).

  When the communication quality is good (step S44, Yes), the process proceeds to step S33. On the other hand, when the communication quality is not good (step S44, No), the process proceeds to step S42 to adjust the SIR threshold value (increase by a specified value), and execute step S43. Thereafter, the same processing (steps S42 to S44) is repeatedly executed until it is determined in step S44 that the communication quality is good (step S44, Yes).

  When the SIR threshold value is increased in the processes in steps S42 to S44 described above, it is difficult to select a modulation method having a large multi-value number such as 16QAM or 64QAM (a modulation method that is weak against noise). This is based on the characteristic that a modulation method having a small multi-value number (a modulation method resistant to noise) is easily selected. That is, by adjusting the SIR threshold value, it is possible to increase noise tolerance and improve communication quality. Note that the amount of increase in the SIR threshold value in step S42 can be finely adjusted as it is reduced, and the number of executions of the adjustment process decreases as the value increases. That's fine.

  On the other hand, when it is determined in step S41 that the communication quality is good (step S41, Yes), the control unit 35 instructs the threshold setting unit 32 to adjust the SIR threshold. The threshold value setting unit 32 resets the SIR threshold value (updated SIR threshold value) after the SIR threshold value in use is decreased by a specified value (step S45). Note that the threshold setting unit 32 adjusts all the SIR thresholds for each of the plurality of modulation schemes. However, even if the communication quality is good, if the control unit 35 is less than the excess quality determination threshold value obtained by adding a certain margin to the communication quality determination threshold value, the control unit 35 An instruction to adjust the SIR threshold value is not issued to the setting unit 32. That is, the process of step S32 is terminated without adjusting the SIR threshold value.

  Based on the SIR threshold value reset (adjusted) by the threshold value setting unit 32 and the SIR for each subcarrier received from the OFDM demodulation unit 21, the comparison unit 31 performs step S22 in the second embodiment. Similar processing is executed to determine the modulation scheme for each subcarrier (step S46). Note that the determined modulation scheme for each subcarrier is notified to the communication apparatus 1.

  Thereafter, the control unit 35 acquires communication quality information in a state in which the determined modulation scheme for each subcarrier is reflected from the decoding unit 22, and further reduces the SIR threshold based on the acquired communication quality. It is confirmed whether or not communication quality is excessively good enough to increase the transmission rate (step S47). That is, in this step S47, it is determined whether or not the communication quality is in a range not less than the quality determination threshold and less than the excess quality determination threshold.

  When the SIR threshold value cannot be further decreased (No at Step S47), the process proceeds to Step S33. On the other hand, when the SIR threshold value can be further decreased (step S47, Yes), the process proceeds to step S45 to adjust the SIR threshold value (decrease by a specified value) and execute the above step S46. To do. Thereafter, in step S47, the same processing (steps S45 to S47) is repeatedly executed until it is determined that the SIR threshold value cannot be further decreased (No in step S47).

  The processing of the above steps S45 to S47 is based on the characteristic that, when the SIR threshold value is decreased, it is easy to select a modulation method that can transmit a large number of bits at once, such as 16QAM and 64QAM. Is what you do. That is, the transmission rate can be increased by adjusting the SIR threshold.

  Returning to the description of FIG. 9, following the process of step S <b> 23, the control unit 35 confirms whether or not the number of encoding scheme selections has reached a specified number (step S <b> 33). When the number of encoding scheme selections has reached the specified number (step S33, Yes), the process proceeds to step S16. On the other hand, when the number of encoding scheme selections has not reached the prescribed number (step S33, No), the determination unit 23a adjusts the encoding scheme in use (step S34).

  Here, the operation of step S34 will be described in detail with reference to FIG. FIG. 11 is a flowchart showing the encoding method adjustment operation. In step S34, the control unit 35 of the determination unit 23a checks whether or not the reference communication quality indicated by the communication quality information acquired in step S31 is good (desired to satisfy desired communication quality) (step S51). .

  When the communication quality is not good (step S51, No), the control unit 35 instructs the selection unit 33 to adjust the encoding method, and the selection unit 33 selects the encoding method used. A coding method having a higher error correction capability is selected from the coding methods held in the coding method holding unit 34, and thereafter changed to use this coding method (step S52). As a result, the number of redundant bits included in the encoded data is increased and noise resistance is increased.

  On the other hand, when it is determined in step S51 that the communication quality is good (step S51, Yes), the control unit 35 instructs the selection unit 33 to adjust the encoding scheme, and the selection unit 33. Selects a coding method having a lower error correction capability from among the coding methods held in the coding method holding unit 34, and uses this coding method thereafter. (Step S53). As a result, the number of redundant bits included in the encoded data is reduced and the transmission rate is increased. However, even if the communication quality is good, the control unit 35 selects the selection unit 33 if it is less than the excess quality determination threshold value obtained by adding a certain margin to the communication quality determination threshold value. Is not instructed to adjust the encoding method. That is, the process of step S34 is terminated without adjusting the encoding method.

  And after performing step S34, it changes to step S31 and performs a series of said processes (step S31, S32, S23, S33) again. Thereafter, the same processing (steps S31, S32, S23, S33, S34) is continued until it is determined in step S33 that the number of encoding scheme selections has reached the specified number (step S33, Yes). Here, the reason why the change of the coding method is limited to the specified number of times is to reduce the number of processing executions and shorten the time until the combination of the coding method and the modulation method for each subcarrier can be reset. It is to do. However, all coding methods may be selected if time and circuit scale are sufficient. In this case, it is possible to select a more appropriate encoding scheme and modulation scheme for each subcarrier.

  Finally, the control unit 35 selects and determines the combination of the modulation method and the coding method for each subcarrier that has obtained the maximum transmission rate among the values calculated and retained in step S23 ( Step S16). When the combination selected and determined in step S16 is different from the combination of the modulation scheme for each subcarrier being used and the encoding scheme, the selected combination is notified to the communication apparatus 1.

  As described above, in this embodiment, the time variation of the transmission path is monitored, and when the encoding scheme in use and the modulation scheme for each subcarrier are not optimal for the transmission path state, The encoding method to be used and the modulation method for each subcarrier are appropriately changed. As a result, for example, when the communication quality cannot be satisfied or the communication quality becomes excessively good, the high speed is always achieved while following the change and satisfying the desired communication quality. High transmission speed can be realized.

Embodiment 4 FIG.
Next, the adaptive modulation method and communication apparatus according to Embodiment 4 will be described. In the present embodiment, by simplifying the processing shown in the third embodiment, the amount of calculation is reduced and the circuit scale is reduced. The configuration of the communication system that implements the adaptive modulation method of the present embodiment and the configuration of the communication device that configures the communication system are the same as those of the third embodiment described above, and the update operation of the adaptive modulation instruction information performed by the determination unit 23a Only the difference.

  FIG. 12 is a flowchart illustrating an operation in which the determination unit 23a according to the fourth embodiment updates the adaptive modulation instruction information. The adaptive modulation instruction information update operation of the present embodiment is different from the adaptive modulation instruction information update operation of Embodiment 3 (see FIG. 9) in that the encoding method is not adjusted. Specifically, the processes in steps S23, S33, and S34 shown in the third embodiment are deleted and not executed. Accordingly, step S61 is executed instead of step S16. In addition, although the process of step S61 is a process which determines the modulation system for every subcarrier, as mentioned above, the modulation system for every subcarrier using the adjusted SIR threshold value has already been determined in step S32. Therefore, it is adopted as it is as a modulation scheme for each subcarrier after adjustment. Other processes are the same as those in the adaptive modulation instruction information update operation (see FIG. 9) of the third embodiment to which the same step numbers are assigned.

  The reason why the communication quality deteriorates or becomes too good is that the time variation of the transmission path as described above, the SIR measurement accuracy is insufficient, the accuracy of the receiver (reception processing unit) that performs OFDM demodulation in the communication device, etc. Various causes are involved. Therefore, it is generally difficult to always select a modulation method for each subcarrier with high accuracy. For this reason, in this embodiment, adjustment of the encoding method is not performed to simplify processing, and the processing time is shortened to frequently adjust the modulation method for each subcarrier.

  As described above, in the present embodiment, among the coding schemes and modulation schemes for each subcarrier once determined, only the modulation scheme for each subcarrier is focused and the modulation scheme is adjusted with high frequency. . Thereby, the followability of the modulation scheme adjustment operation for each subcarrier with respect to the time variation of the transmission path is improved, and the modulation scheme for each subcarrier can be selected with higher accuracy.

Embodiment 5 FIG.
Next, the adaptive modulation method and communication apparatus according to Embodiment 5 will be described. In the present embodiment, an adaptive modulation method in which the process described in the third embodiment is partially changed will be described. The configuration of the communication system that implements the adaptive modulation method of the present embodiment and the configuration of the communication device that configures the communication system are the same as those of the third embodiment described above, and the update operation of the adaptive modulation instruction information performed by the determination unit 23a Only the difference. Therefore, in the present embodiment, the update operation of adaptive modulation instruction information performed by the determination unit 23a will be mainly described.

  FIG. 13 is a flowchart showing the operation of changing the modulation scheme for each subcarrier by the determination unit 23a of the fifth embodiment. The operation is executed in place of step S32 of FIG. 9 described in the third embodiment (step S32b). Other processes in the adaptive modulation instruction information update operation (processes other than step S32 in FIG. 9) are the same as those in the third embodiment.

  In the operation shown in FIG. 13, step S71 is added between steps S42 and S43 with respect to the operation shown in FIG. 10 (SIR threshold adjustment operation in the third embodiment), and steps S45 and S46 are performed. Step S72 is added between the two. The other parts are the same as those shown in FIG.

  In step S71 and step S72, the same processing is executed. Specifically, in steps S42 and S45, each SIR threshold value that is uniformly adjusted with the same adjustment amount is added to each of the modulation schemes, and a different offset value is added for each modulation scheme. adjust. The reason for adding this offset value will be described below.

A modulation method having a small multi-value number, such as BPSK and QPSK, generally has a tendency to be resistant to disturbances such as noise and signal fluctuation (phase fluctuation) due to imperfection of the apparatus, and to have little deterioration. On the other hand, a modulation method having a large multi-value number, such as 16QAM and 64QAM, is generally weak against disturbance. That is, when there is a signal fluctuation of the same degree, the required SIR greatly increases in 16 QAM and 64 QAM compared to BPSK and QPSK. For example, in FIG. 7-2 used in the description of the second embodiment, in a state where γ ₁₁ is required to be 1 dB larger, γ ₁₂ is required to be 2 dB (the numerical value is merely an example). . For this reason, in the present embodiment, a different offset is added for each modulation scheme to avoid the phenomenon that the amount of degradation in communication quality differs depending on the number of modulation levels. That is, the influence of disturbance is avoided by adding a larger offset value to a modulation scheme having a larger multi-value number.

  As described above, in the present embodiment, an offset corresponding to the modulation scheme corresponding to each of the SIR threshold values used in the modulation scheme adjustment operation for each subcarrier is given. As a result, the SIR threshold can be adjusted with a different adjustment amount for each modulation method, and even when there is a disturbance such as signal fluctuation due to incompleteness of the device, the modulation method can be selected with high accuracy for each subcarrier. Is possible.

Embodiment 6 FIG.
Next, the adaptive modulation method and communication apparatus according to Embodiment 6 will be described. In the present embodiment, an adaptive modulation method in which the process described in the third embodiment is partially changed will be described. The configuration of the communication system that implements the adaptive modulation method of the present embodiment and the configuration of the communication device that configures the communication system are the same as those of the third embodiment described above, and the update operation of the adaptive modulation instruction information performed by the determination unit 23a Only the difference. Therefore, in the present embodiment, the update operation of adaptive modulation instruction information performed by the determination unit 23a will be mainly described.

  FIG. 14 is a flowchart showing an operation in which the determination unit 23a according to the sixth embodiment changes the modulation scheme for each subcarrier, and is performed in place of step S32 in FIG. 9 described in the third embodiment (step S32c). Other processes in the adaptive modulation instruction information update operation (processes other than step S32 in FIG. 9) are the same as those in the third embodiment.

  The process shown in FIG. 14 adds step S81 between steps S41 and S42 to the operation shown in FIG. 10 (SIR threshold value adjusting operation in the third embodiment), and steps S41 and S45. Step S82 is added between the two. The other parts are the same as those shown in FIG.

  The processing in step S81 and step S82 is the same, and is processing for limiting the threshold adjustment amount (increase / decrease amount). Specifically, in executing the process of increasing / decreasing the SIR threshold (steps S42 / S45), the current adjustment is made with respect to the cumulative adjustment amount of the SIR threshold that has been increased / decreased in step S32c so far. When the amounts are added, it is confirmed whether or not the cumulative adjustment amount falls within a specified range (steps S81 / S82). If the result of adding the current adjustment amount to the cumulative adjustment amount is within the specified range (step S81, Yes / S82, Yes), the SIR threshold value is increased / decreased (step S43 / S45). On the other hand, if the result of adding the current adjustment amount to the cumulative adjustment amount is not within the specified range (step S81, No / S82, No), the process of step S32c ends.

  The reason why the SIR threshold value is adjusted with reference to the cumulative adjustment amount as described above will be described. For example, the more the SIR threshold value is increased, the easier it is to select a modulation method having a small multi-value number. However, when the SIR threshold value is extremely increased, the transmission speed is extremely reduced, and the transmission efficiency is deteriorated. Further, as the SIR threshold value is decreased, a modulation system having a large multi-value number is easily selected, but becomes weak against a time change of the transmission path and communication becomes unstable. In this way, when the adjustment exceeds a certain range, the effect of adjusting the SIR threshold is hardly seen, and there is a possibility that another problem such as an increase in calculation amount may occur. In this embodiment, the adjustment amount is set within a certain range.

  As described above, in this embodiment, the adjustment of the SIR threshold used in the modulation scheme adjustment operation for each subcarrier is performed only within a certain range. As a result, the modulation scheme for each subcarrier is not excessively adjusted with respect to fluctuations in the transmission path state, and stable communication can be realized.

Embodiment 7 FIG.
Next, the adaptive modulation method and communication apparatus according to Embodiment 7 will be described. In the present embodiment, by simplifying the processing shown in the third embodiment, the amount of calculation is reduced and the circuit scale is reduced. The configuration of the communication system that implements the adaptive modulation method of the present embodiment and the configuration of the communication device that configures the communication system are the same as those of the third embodiment described above, and the update operation of the adaptive modulation instruction information performed by the determination unit 23a Only the difference. Therefore, in the present embodiment, the update operation of adaptive modulation instruction information performed by the determination unit 23a will be mainly described.

  FIG. 15 is a flowchart illustrating an operation in which the determination unit 23a according to the seventh embodiment updates the adaptive modulation instruction information. The adaptive modulation instruction information update operation of the present embodiment is different from the adaptive modulation instruction information update operation of Embodiment 3 (see FIG. 9) in that the modulation scheme for each subcarrier is not adjusted. Specifically, the process in step S32 shown in the third embodiment is deleted and not executed. Accordingly, step S91 is executed instead of step S16. Note that the process of step S91 is a process of determining the encoding method, and the encoding method that obtained the maximum transmission rate in step S23 is selected and determined as the adjusted encoding method. Other processes are the same as those in the adaptive modulation instruction information update operation (see FIG. 9) of the third embodiment to which the same step numbers are assigned.

  When the number of subcarriers is large or there are many modulation scheme candidates, the time required to determine the modulation scheme for each subcarrier becomes long. Therefore, in this embodiment, in such a case, the adjustment of the modulation scheme for each subcarrier is not performed, so that the processing is simplified and the processing time is shortened so that the encoding scheme is frequently adjusted. I have to.

  As described above, in the present embodiment, out of the encoding schemes and modulation schemes for each subcarrier that have been determined, only the encoding scheme is focused, and the encoding is performed more frequently with respect to the time variation of the transmission path. It was decided to change the method. As a result, the followability of the encoding method adjustment operation with respect to the time variation of the transmission path is improved, and the encoding method for each subcarrier can be selected with higher accuracy.

Embodiment 8 FIG.
Next, the adaptive modulation method and communication apparatus according to Embodiment 8 will be described. In the present embodiment, the process of selecting (determining) the modulation scheme for each subcarrier in the above-described embodiment is performed for each of a plurality of neighboring subcarriers. Therefore, the configuration of the communication system that implements the adaptive modulation method of the present embodiment and the communication device that configures the communication system is the same as that of either the first or third embodiment described above.

  FIGS. 16A and 16B are diagrams for explaining the adaptive modulation method according to the eighth embodiment. FIG. 16A is an example of the frequency characteristic (amplitude characteristic) of the transmission line, and shows that the signal easily passes in proportion to the magnitude of the value of the amplitude characteristic indicated on the vertical axis. FIG. 16B is an example of the reception level of the OFDM signal received through the transmission path having the amplitude characteristics shown in FIG. The reception level is proportional to the magnitude of the amplitude characteristic of the transmission path, and a subcarrier with a higher reception level can easily pass a signal, and a modulation system having a large multi-value number that can transmit many bits at a time can be used. On the other hand, a subcarrier with a low reception level can use only a modulation method with a small multi-level number, and can transmit only a few bits at a time.

  Here, the frequency characteristics of the transmission path are determined by the influence of the reflected wave (multipath wave), and the delay time of the multipath wave (the time difference between the signal that arrives first and the signal that arrives after being delayed by reflection) If it is not so large, the frequency characteristic undulation (the number of peaks and valleys) is relatively small. In this case, as in the example shown in FIG. 16-2, the ease of passing the signal (reception level) is almost the same in the neighboring subcarriers. Therefore, even if processing such as selecting the modulation scheme for each subcarrier as in the above-described embodiment is executed, there is a possibility that the same modulation scheme will be used in neighboring subcarriers as a result. Is expensive and unnecessarily increases the amount of calculation.

  For this reason, in this embodiment, the modulation scheme is not set for each subcarrier, but a plurality of subcarriers are grouped together and the subcarriers are grouped (subcarrier group). Set the same modulation method. For example, if the number of subcarriers is 100, and if two waves are combined into a subcarrier group, the number of targets for setting modulation schemes (corresponding to the number of subcarriers in the above-described embodiment) is halved. Therefore, the time and labor for setting the modulation scheme for each subcarrier (processing for setting the modulation scheme for each subcarrier in the above-described embodiment) can be halved.

  In addition, the operation | movement which sets the modulation system mentioned above for every adjacent subcarrier (subcarrier group) is applicable with respect to Embodiment 1-6.

  As described above, in the present embodiment, the modulation scheme setting processing, which has been individually executed for each subcarrier in the above-described first to sixth embodiments, is performed for each subcarrier group including a plurality of neighboring subcarriers. I decided to do it. Thereby, the processing time and circuit scale required for setting the modulation method can be reduced.

Embodiment 9 FIG.
Next, the adaptive modulation method and communication apparatus according to Embodiment 9 will be described. In Embodiments 1 to 8 described above, the adaptive modulation method in the communication system using OFDM has been described. However, in the present embodiment, the adaptive modulation method described above is applied to a communication system using a method other than OFDM. The case where it does is demonstrated. Therefore, the configuration of the communication system that realizes the adaptive modulation method of the present embodiment is the same as that of either of the first or third embodiment described above, and only the multiplexing scheme used is different.

  FIGS. 17-1 to 17-5 are diagrams for explaining the adaptive modulation method according to the ninth embodiment. 17A to 17C illustrate an example of the spectrum of the OFDM signal, an example of the spectrum of the FDM signal, and an example of the spectrum of the CDM signal, respectively. FIG. 17-4 schematically shows an example of a time waveform of a TDM signal, and FIG. 17-5 shows a configuration example of a communication system that performs SDM. As described above, Embodiments 1 to 8 are inventions based on OFDM signals as shown in FIG. 17A. In this method, data is transmitted in parallel using a plurality of subcarriers. .

  On the other hand, in the case of a communication system using an FDM signal as shown in FIG. 17-2, data is transmitted in parallel using a plurality of frequencies (carriers having different frequency bands) and modulated for each carrier. If the system is set, the frequency in the FDM signal can be handled in the same manner as the subcarrier in the OFDM signal. That is, the adaptive modulation method shown in Embodiments 1 to 8 can be applied to a communication system using an FDM signal.

  Similarly, in the case of a communication system using a CDM signal as shown in FIG. 17-3, data is transmitted in parallel using a plurality of codes (carriers spread by different codes) and modulated for each code. If the system is set, the code in the CDM signal can be handled in the same manner as the subcarrier in the OFDM signal. That is, the adaptive modulation method shown in Embodiments 1 to 8 can be applied to a communication system using a CDM signal.

  Similarly, in the case of a communication system using a TDM signal as shown in FIG. 17-4, if data is transmitted in parallel using a plurality of time slots and a modulation method is set for each time slot. The time slot in the TDM signal can be handled in the same manner as the subcarrier in the OFDM signal. That is, the adaptive modulation method shown in Embodiments 1 to 8 can be applied to a communication system using a CDM signal.

  Further, in the case of a communication system that performs SDM as shown in FIG. 17-5, data is transmitted in parallel using a plurality of spaces (using a plurality of transmission antennas and reception antennas), and space (transmission) is used. If the modulation scheme is set for each transmission signal from the antenna), the space in the communication system that performs SDM can be handled in the same manner as the subcarrier in the OFDM signal. That is, the adaptive modulation method shown in Embodiments 1 to 8 can be applied to a communication system that performs SDM.

  For example, by changing the operation procedure shown in FIG. 2 in the first embodiment to the procedure shown in FIG. 18, the present invention can be applied to any of the above communication systems. Specifically, in the operation procedure shown in FIG. 2, a transmission channel (transmission channel (communication system based on any one of FDM, CDM, TDM, and SDM) used for processing a subcarrier is used. The channel is multiplexed so that it is targeted using any one of frequency, code, time slot, and space.

  By making such a change, the communication apparatus on the receiving side can perform the following processing to select and determine the modulation scheme and the coding scheme for each transmission channel. The communication device on the receiving side first measures the SIR for each transmission channel (step S111), then selects the modulation method for each transmission channel (step S112), and then selects the encoding method (step S113). Next, whether the transmission rate and communication quality are calculated (step S114), and step S114 has been executed for all combinations of the modulation method for each transmission method selected in step S112 and the coding method selected in step S113. After confirming whether or not (step S115), if step S114 has been executed for all combinations (step S115, Yes), while satisfying the desired communication quality from among the combinations of the selection results of steps S112 and S113, Modulation method for each transmission channel corresponding to the combination with the maximum transmission rate The combination of a coding scheme is selected determines (step S116). If it is determined in step S115 that step S114 has not been executed for all combinations (step S115, No), the processes in steps S112 to S115 are repeated until the above processing is executed for all combinations. Execute.

  In addition, in order to apply the operation procedure shown in Embodiments 2 to 8 to a communication system other than the communication system using the OFDM signal, the operation of FIG. What is necessary is just to make the change similar to the change with respect to a procedure.

  As described above, in the present embodiment, it has been shown that the adaptive modulation method described in the first to seventh embodiments can be applied to a communication system that performs multiplex transmission other than OFDM. That is, the transmission channels (frequency, code, time slot, space) of each communication system that performs multiplex transmission other than OFDM are handled in the same manner as subcarriers in a communication system using OFDM, and are shown in the first to eighth embodiments. By performing the operation, the same effects as those of the above-described embodiments can be obtained in each communication system.

  As described above, the adaptive modulation method according to the present invention is useful for, for example, a communication system using OFDM. In particular, based on the communication quality for each subcarrier, the encoding method and the modulation method for each subcarrier are changed. This is suitable for an adaptive modulation method of a communication apparatus that performs communication by adaptively selecting and determining.

Claims (16)

In data transmission by Orthogonal Frequency Division Multiplexing (OFDM), an adaptive modulation method in the case of adaptively changing the coding scheme and modulation scheme in use according to the state variation of the transmission path,
A reference communication quality acquisition step of acquiring a reference communication quality for determining whether to adaptively select and change a coding scheme and a modulation scheme in use according to a state change of the transmission path;
If the reference communication quality does not satisfy the desired communication quality, is it possible to select the modulation method in the process of selecting the modulation method for each subcarrier and determining the modulation method combination (modulation method pattern) for each subcarrier? When the SIR (Signal to Interference Ratio) threshold value used as a comparison target in determining whether or not is increased by a predetermined adjustment amount, while the reference communication quality satisfies a desired communication quality, and S IR threshold adjustment step of Ru is decreased by the adjustment amount of defining the SIR threshold,
In the SIR threshold adjustment step, a modulation pattern determination step for determining a modulation scheme pattern based on the SIR threshold after increasing or decreasing the SIR threshold by a predetermined adjustment amount and the SIR for each subcarrier; ,
A transmission rate calculating step for calculating a transmission rate based on the SIR for each subcarrier of the received signal;
If the number of encoding method adjustment processing executions performed so far (the number of encoding method adjustments) has not reached the specified number, and if the reference communication quality does not satisfy the desired communication quality, encoding in use performs adjustment processing of the encoding scheme to use high coding scheme with error correction capability than method, whereas, if the reference communication quality that meets the desired communication quality, coding in use An encoding method adjustment step for performing adjustment processing for changing the encoding method so as to use an encoding method having a lower error correction capability than the method;
Including
First, until the communication quality falls within the range between the communication quality determination threshold for determining that the communication quality is good and the excessive quality determination threshold for determining that the communication quality is excessively good Then, the SIR threshold adjustment step and the modulation pattern determination step are repeatedly executed to adjust the SIR threshold, and after the SIR threshold adjustment is completed, the transmission rate calculation step is executed to perform transmission. After the transmission rate calculation step is performed, the encoding scheme adjustment step is performed to adjust the encoding scheme, and the encoding scheme adjustment step is performed, and then the encoding is performed. The reference communication quality acquisition step, the SIR threshold adjustment process, the transmission rate calculation step, and the encoding method adjustment step until the number of system adjustments reaches the specified number. When the number of adjustments of the encoding method reaches the specified number, the encoding method and modulation method pattern when the transmission rate calculated in the transmission rate calculation step is maximized are An adaptive modulation method characterized by selecting and determining as a formal encoding scheme and modulation scheme pattern used sometimes. Only the reference communication quality acquisition step and the SIR threshold adjustment step are executed, and the modulation scheme pattern determined in the SIR threshold adjustment step is selected and determined as a formal modulation scheme pattern used at the time of data transmission. The adaptive modulation method according to claim 1 , wherein: In the SIR threshold adjustment step, the SIR threshold used for determining whether a modulation scheme with a large number of modulation multi-values can be selected is adjusted with an adjustment amount such that the SIR threshold becomes a larger value. The adaptive modulation method according to claim 1 , wherein: In the SIR threshold adjustment step, the SIR threshold used for determining whether a modulation scheme with a large number of modulation multi-values can be selected is adjusted with an adjustment amount such that the SIR threshold becomes a larger value. The adaptive modulation method according to claim 2 , wherein: In the SIR threshold adjustment step, the cumulative value of the adjustment amount (the increase or decrease amount of the SIR threshold) adjusted within the SIR threshold is within a specified range after the processing of the step is started. The adaptive modulation method according to claim 1 , wherein the SIR threshold is adjusted only in the case. In the SIR threshold adjustment step, the cumulative value of the adjustment amount (the increase or decrease amount of the SIR threshold) adjusted within the SIR threshold is within a specified range after the processing of the step is started. 3. The adaptive modulation method according to claim 2 , wherein the SIR threshold is adjusted only in the case. After the execution of the reference communication quality acquisition step, the transmission rate calculation step is immediately executed without executing the SIR threshold adjustment step, and thereafter, the reference communication is performed until the encoding method adjustment count reaches a specified number. When the quality acquisition step, the transmission rate calculation step, and the encoding scheme adjustment step are repeatedly executed and the encoding scheme adjustment count reaches a specified count, the transmission rate calculated in the transmission rate calculation step is the maximum. 2. The adaptive modulation method according to claim 1 , wherein the encoding method in such a case is selected and determined as a formal encoding method used at the time of data transmission. The adaptation according to claim 1 , wherein a modulation scheme is individually assigned to each subcarrier group by processing a subcarrier group including a plurality of neighboring subcarriers as the subcarrier. Modulation method. In a communication system using FDM (Frequency Division Multiplexing), CDM (Code Division Multiplexing), TDM (Time Division Multiplexing) or SDM (Space Division Multiplexing), the frequency, spreading code, time slot or An adaptive modulation method in the case of performing data transmission by assigning a different modulation method to each transmission channel divided by space,
Wherein instead of the sub-carrier or group of the sub-carrier adaptive modulation method according to claim 1, characterized in that executing the selected process of determining the modulation and coding scheme for each transmission channel to the transmission channel. A communication device that adaptively selects and determines an encoding method and a modulation method in data transmission by orthogonal frequency division multiplexing (OFDM) according to a state of a transmission line,
Transmission condition selection means for selecting a combination (transmission condition) of a combination of modulation schemes (modulation scheme pattern) for each subcarrier and a coding scheme used when encoding transmission data;
Transmission quality calculation means for calculating transmission quality (communication quality and transmission speed, or transmission speed) at the time of data transmission using the transmission condition selected by the transmission condition selection means;
For the transmission condition selection means and the transmission quality calculation means, the transmission quality is repeatedly calculated while reselecting the transmission conditions under the condition that the previously selected transmission condition is not selected again. Repetitive process control means for performing control,
When the transmission quality calculation means calculates the transmission quality for all transmission conditions to be selected by the transmission condition selection means, the transmission speed is maximized while satisfying the desired communication quality among the calculated transmission quality. Transmission condition determining means for selecting and determining the transmission condition when the transmission quality of the transmission quality is obtained as an official transmission condition used at the time of data transmission;
Equipped with a,
The transmission condition selection means includes
A reference communication quality acquisition means for acquiring a reference communication quality for determining whether or not to adaptively select and change a coding scheme and a modulation scheme in use according to a state change of a transmission path;
When the reference communication quality does not satisfy the desired communication quality, used as a comparison target when determining whether a modulation method can be selected in the process of selecting a modulation method for each subcarrier and determining the modulation method pattern The SIR (Signal to Interference Ratio) threshold value is adjusted by increasing it by a prescribed adjustment amount. On the other hand, if the acquired reference communication quality satisfies the desired communication quality, the SIR threshold is set. SIR threshold value adjusting means for reducing the value by a predetermined adjustment amount and adjusting the value;
Modulation scheme pattern determining means for determining a modulation scheme pattern based on the SIR threshold adjusted by the SIR threshold adjusting section and the SIR for each subcarrier;
If the number of encoding method adjustment processing executions performed so far (the number of encoding method adjustments) has not reached the specified number, and if the reference communication quality does not satisfy the desired communication quality, encoding in use Adjust the coding method to use a coding method with higher error correction capability than the coding method. On the other hand, if the reference communication quality meets the desired communication quality, the coding method in use Encoding method adjusting means for adjusting the encoding method to use an encoding method with low error correction capability,
With
A communication quality determination threshold value for determining that the communication quality using the modulation method pattern determined by the modulation method pattern determining means is good, and an excess value for determining that the communication quality is excessively good Until the communication quality falls within the range between the quality judgment threshold value, the SIR threshold value adjusting means and the modulation scheme pattern determining means repeatedly execute the processing,
further,
The transmission quality calculation means, after the repetition processing performed by the SIR threshold adjustment means and the modulation scheme pattern determination means included in the transmission condition selection means is completed, based on the SIR for each subcarrier of the received signal, Calculate the transmission rate during data transmission using the modulation method pattern determined by the method pattern determination means,
The iterative processing control means is configured to perform the iterative processing by the SIR threshold adjusting means and the modulation scheme pattern determining means until the coding scheme adjustment count reaches a specified count after the coding scheme adjustment section has adjusted the coding scheme. And control to repeatedly execute the encoding method adjustment processing by the encoding method adjustment means,
The transmission condition determining means, when the number of times of adjustment of the encoding method reaches a specified number of times, the transmission condition when the transmission rate calculated by the transmission quality calculating means is maximized is used for data transmission. A communication apparatus characterized in that it is selected and determined as an appropriate transmission condition . The transmission condition selection means executes only the reference communication quality acquisition process and the SIR threshold repetition adjustment process,
The transmission condition determining means selects and determines the modulation scheme pattern at the time when the SIR threshold repetitive adjustment processing in the transmission condition selection section is completed as a formal modulation scheme pattern used at the time of data transmission. The communication device according to claim 10 . The SIR threshold used by the transmission condition selection means to determine whether or not a modulation scheme having a large number of modulation multi-values can be selected in the SIR threshold adjustment process has a larger SIR threshold. The communication apparatus according to claim 10 , wherein adjustment is performed with an adjustment amount such that The SIR threshold used by the transmission condition selection means to determine whether or not a modulation scheme having a large number of modulation multi-values can be selected in the SIR threshold adjustment process has a larger SIR threshold. The communication apparatus according to claim 11 , wherein adjustment is performed with such an adjustment amount. After the transmission condition selection means starts the SIR threshold adjustment process, the accumulated value of the adjustment amount (the increase amount or decrease amount of the SIR threshold value) adjusted for the SIR threshold falls within a specified range. The communication apparatus according to claim 10 , wherein the SIR threshold value is adjusted only when there is an error. After the transmission condition selection means starts the SIR threshold adjustment process, the accumulated value of the adjustment amount (the increase amount or decrease amount of the SIR threshold value) adjusted for the SIR threshold falls within a specified range. 12. The communication apparatus according to claim 11 , wherein the SIR threshold value is adjusted only when it is present. The transmission condition selection means, after executing the reference communication quality acquisition process, immediately executes the transmission rate calculation process without executing the SIR threshold value adjustment process. The reference communication quality acquisition process, the transmission rate calculation process, and the encoding method adjustment process are repeatedly executed until the number of times the encoding method adjustment reaches the specified number. The communication apparatus according to claim 10 , wherein the transmission condition when the transmission rate is maximized is selected and determined as a formal transmission condition used during data transmission.

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