WO2007125580A1

WO2007125580A1 - Adaptive modulation method and communication apparatus

Info

Publication number: WO2007125580A1
Application number: PCT/JP2006/308871
Authority: WO
Inventors: Nobuhisa Kataoka
Original assignee: Mitsubishi Denki Kabushiki Kaisha
Priority date: 2006-04-27
Filing date: 2006-04-27
Publication date: 2007-11-08
Also published as: JP4700106B2; JPWO2007125580A1

Abstract

An adaptive modulation method, in a case of adaptively selecting and deciding an encoding scheme and a modulation scheme in data transmission using the orthogonal frequency division multiplexing, comprises a modulation scheme pattern deciding step of selecting a modulation scheme for each of subcarriers and deciding a modulation scheme combination (modulation scheme pattern) for each of the subcarriers; an encoding scheme selecting step of selecting an encoding scheme; and a transmission quality calculating step of calculating, based on SIR for each subcarrier, a transmission rate and a communication quality (transmission quality). In this method, the modulation scheme pattern deciding step, encoding scheme selecting step and transmission quality calculating step are repetitively executed, thereby executing the transmission quality calculating steps for all of the combinations of modulation scheme patterns and encoding schemes. Then, a modulation scheme pattern and an encoding scheme, for which a desired communication quality is satisfied and a transmission quality exhibiting the maximum transmission rate is obtained in the transmission quality calculation results, are selected and decided as a formal modulation scheme pattern and a formal encoding scheme, respectively.

Description

Specification

Adaptive modulation method and communication apparatus

Technical field

TECHNICAL FIELD [0001] The present invention relates to an adaptive modulation method for adaptively selecting and determining an encoding method and a modulation method at the time of data transmission by orthogonal frequency division multiplexing (OFDM). The present invention relates to an adaptive modulation method in the case of selecting and determining a V-code scheme and a modulation scheme for each subcarrier based on communication quality for each subcarrier, and a communication apparatus for realizing the adaptive modulation method.

Background art

[0002] An 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 a transmission path. In other words, when the transmission path is in a poor state due to a large amount of noise or the like, a coding system having as high an error correction capability as possible and a modulation system that is difficult to error are used in combination. On the other hand, if the transmission path is in good condition, a code-type method with a small number of redundant bits (error correction bits) to be added and a multi-valued multi-value modulation method that can transmit many bits at one time. Use in combination. 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 selecting and 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. ing.

[0004] Patent Document 1: Japanese Patent Application Laid-Open No. 2002-261726

Disclosure of the invention

Problems to be solved by the invention [0005] Generally, the frequency characteristics of a transmission line are not flat due to the influence of multipath and the like. In addition, it is difficult for signals to pass through frequencies with large attenuation (transmission errors are likely to occur), and it is not possible to use force by using a modulation method with a small number of multiple values. On the other hand, a low-attenuation frequency is a multivalued signal that passes easily.

Modulation scheme can be used.

[0006] As described above, data transmission using OFDM is performed by transmitting data on a plurality of subcarriers in parallel. Further, 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.

However, in the past, data transmission was performed by setting the same modulation scheme for all subcarriers. For this reason, the modulation scheme for all subcarriers was selected in consideration of the subcarrier where the signal was most difficult to pass, and it was not possible to realize efficient data transmission. Also, there has been no setting method (combination selection method) between the code key method and the modulation method for each subcarrier to obtain optimum quality (communication at a high transmission rate).

[0008] Furthermore, not only communication using OFDM, but also a frequency division multiplexing (FDM) -based communication system that transmits data at multiple frequencies, time division (TDM: Time Division) that transmits data at multiple times Multiplexing (communication system), Code Division Multiplexing (CDM) communication system that transmits data using multiple codes, Space Division Multiplexing (SDM) communication system that transmits data in multiple spaces However, there are similar problems if subcarriers in OFDM are considered as frequency, time, code, and space, respectively. In other words, the ease of passing the signal for each subcarrier in OFDM is the same as the passing of the signal at each frequency in FDM-based communication, and the same as the passing of the signal in each time slot in TDM-based communication. This is the same as the signal spread in each code in CDM-based communication, and the same as the signal in each space in SDM-based communication. Therefore, as with OFDM, there is no indication of how to set the coding method and the modulation method to be set in frequency, time, code, and space in order to obtain optimal quality.

The present invention has been made in view of the above, and in communication using OFDM, It is an object of the present invention to provide an adaptive modulation method capable of realizing high-speed data transmission while satisfying desired communication quality and a communication apparatus for realizing the adaptive modulation method.

[0010] Furthermore, in communication using FDM, TDM, CDM, and SDM, an adaptive modulation method capable of realizing high-speed data transmission while satisfying desired communication quality and a communication apparatus for realizing the same are obtained. With the goal.

Means for solving the problem

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

The invention's effect

[0012] The adaptive modulation method according to the present invention performs data transmission by selecting a combination of an optimal encoding method and an optimal modulation method for each subcarrier based on the reception quality of the signal. Therefore, while satisfying the desired communication quality, it is possible to perform data transmission at a higher speed than when the above-mentioned conventional technology is used, and in particular, transmission at the time of data transmission on a transmission line whose frequency characteristics are not flat. There is an effect that the speed can be increased. Brief Description of Drawings

[FIG. 1] FIG. 1 is a diagram showing a configuration example of a first embodiment of a communication system and a communication apparatus constituting the communication system for realizing an adaptive modulation method according to the present invention.

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 a selection operation of a sign key method.

FIG. 5 is a diagram for explaining an operation of selecting and determining a modulation method and a code key method for each subcarrier.

FIG. 6 is a flowchart showing an operation of generating adaptive modulation instruction information performed by the communication apparatus of the second embodiment.

[Fig. 7-1] Fig. 7-1 is a diagram for explaining the SIR threshold setting operation.

[Fig. 7-2] Fig. 7-2 is a diagram for explaining the SIR threshold setting operation.

[Fig. 8] Fig. 8 is a diagram showing a configuration example of a third embodiment of a communication system and a communication apparatus constituting the communication system for realizing the adaptive modulation method according to the present invention.

[FIG. 9] FIG. 9 is a flowchart showing an operation for adjusting a modulation scheme and a coding scheme for each subcarrier once determined.

FIG. 10 is a flowchart showing an SIR threshold adjustment operation.

FIG. 11 is a flowchart showing a sign key 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. 16-1 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. 17-1 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] 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

[0014] l, 2, 2a communication device

11 Encoder

12 Modulator

21 Demodulator

22 Decryption unit

23, 23a judgment part

31 Comparison part

32 Threshold setting section

33 Selection section

34 Coding method holding unit

35 Control unit

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of an adaptive modulation method and a communication apparatus according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

[0016] Embodiment 1.

FIG. 1 is a diagram showing 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 constitutes 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 The communication apparatus 2 includes an OFDM demodulator 21, a decoder 22, and a determiner 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.

FIG. 1 shows a state in which the communication device 1 transmits data to the communication device 2. Therefore, each of the communication devices 1 and 2 includes only a signal transmission processing unit (corresponding to the encoding unit 11 and the modulation unit 12) and a reception processing unit (corresponding to the OFDM demodulating unit 21 and the decoding unit 22). In actuality, both have a transmission processing unit and a reception processing unit, and the communication device 2 transmits a signal to the communication device 1 as necessary.

[0018] In communication device 1, encoding section 11 encodes transmission data in the encoding scheme indicated by "encoding scheme information" that constitutes the adaptive modulation instruction information notified in advance from the communication partner. The OFDM modulation unit 12 is a modulation scheme indicated by “information indicating the modulation scheme for each subcarrier” that constitutes the adaptive modulation instruction information for which the communication partner power has been notified in advance, and the encoding received 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 communication device 2, OFDM demodulator 21 demodulates the received signal from communication device 1. Decoding section 22 performs error correction processing on the demodulated data obtained by OFDM demodulation section 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, this is not a frequency characteristic S flat of the transmission path, so an optimum modulation method is selected for each frequency (subcarrier), and this is combined with an optimum coding method to perform communication. Is. The generated adaptive modulation instruction information is notified (transmitted) to the communication device 1 via the transmission path.

[0020] Operation in which the determination unit 23 generates the adaptive modulation instruction information (encoding method and sub-carrier) The operation of selecting and determining the modulation method for each rear will be described with reference to FIG. FIG. 2 is a flowchart showing an operation for generating adaptive modulation instruction information. The determination unit 23 receives the SIR (Signal to Interference Ratio) for each subcarrier measured by the OFDM demodulation unit 21 (step Sl 1).

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 methods are BPSK and QPSK, select one of the eight patterns shown in Fig. 3 as the combination of modulation methods for each subcarrier. Will be. Note that the conditions for selecting a combination (combination pattern) of modulation methods for each subcarrier are not particularly specified. Therefore, for example, the combination pattern numbers shown in FIG. 3 may be selected in ascending order, 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 two types of encoding methods with different error correction capabilities as shown in Fig. 4, for example. Figure 4 shows an example using Reed-Solomon (RS) codes. RS (255, 239), which is the first encoding method, indicates an encoding method for generating a code in which 16 redundant bytes are added to 239 bytes of information. Also, RS (120, 104), which is the second encoding method, indicates a code method that generates a code in which 16 bytes of redundant bytes are added to 104 bytes of information. The sign rate is approximately 0.94 (= 239,255) when RS (255, 239) is used, and the force is approximately 0.87 (= 104/120) when RS (120, 104) is used. ). Also, the transmission rate when using the same modulation method is higher when RS (255, 239) is used. The error correction capability is higher when RS (120, 104) is used.

[0023] It should be noted that conditions for selecting an encoding method are not particularly defined. Thus, for example, you can select the code numbers shown in Fig. 4 in order of increasing numbers, or you can select them randomly! / ヽ.

[0024] 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 the next step S12 and subsequent times. When executing S13 and S13, the combination force of each selection result is processed so as not to be the same as the combination of the selection result this time. Next, the determination unit 23 calculates a transmission rate and communication quality when communication is performed using the selection results in steps S 12 and S 13 (step S 14). For example, if No. 1 in the example shown in Fig. 3 is selected as the combination of modulation schemes for each subcarrier and No. 1 in the example shown in Fig. 4 is selected as the encoding scheme, the transmission rate is Since the carrier modulation method is BPSK and the coding rate is 0.94, 2.82 (= 3 * 0.94) bits per symbol. When No. 2 in the example shown in FIG. 3 is selected as the combination of modulation schemes for each subcarrier, and No. 2 in the example shown in FIG. 4 is selected as the coding scheme, the transmission rate is Since the modulation method for carrier # 1 is QPSK, the other is BPSK, and the coding rate is 0.87, it is 3.48 (= 4 * 0.87) bits per simponole. Note that the actual transmission speed expressed in units such as bps (bits per second) needs to be divided by the time length of one symbol, but here it is only necessary to be able to compare the transmission speed. Division processing is not essential.

[0026] The communication quality is calculated using the SIR for each subcarrier obtained in step S11. Communication quality is the bit error rate (coded: BER: coded bit error rate) or packet error rate (PER: packet error rate) after error correction, so it can be calculated based on the SIR for each subcarrier. . Specifically, since the BER before error correction (uncoded-BER) of a subcarrier can be calculated based on the modulation scheme and SIR of that subcarrier, the decision unit 23 performs this uncoded-BER for all subcarriers. Then, the BER of the input signal to the decoding unit 22 is calculated. In addition, the error correction capability is determined by the code method used, and the coded_BER (= communication quality) after error correction with respect to the uncoded-BER before error correction can be calculated. Note that in this example, the power shown in the case of using coded BER as the communication quality may be replaced with PER. In addition, although the method for calculating the communication quality by calculation is shown here, the SIR vs. BER characteristics are calculated by simulation in advance of the calculation, and a table showing the result is created and referred to this table. Even so,

[0027] Next, the determination unit 23 determines whether or not the transmission rate calculation and communication quality calculation have been completed for all combinations of the modulation scheme for each subcarrier and the encoding scheme (step S 15 ). In step S15, it is not yet selected (transmission rate calculation and If there is a combination of the modulation scheme for each subcarrier and the encoding scheme (No in step S15), the process returns to step S12 and is still selected. Similar processing (steps S12 to S14) is performed for the combination of the modulation scheme for each subcarrier and the code key scheme. When transmission rate calculation and communication quality calculation for all combinations are completed (step S15, Yes), proceed to step SI6.

[0028] Finally, the determination unit 23 compares the combination of the transmission speed and communication quality held as the processing result of step S14. From the processing results that are held, a combination that satisfies the desired communication quality (for example, the communication quality required by the communication system) and has the maximum transmission speed is selected. Finally, the combination of the modulation scheme for each subcarrier and the coding scheme corresponding to the selection result (where the selection result was obtained) is adaptive modulation instruction information (a combination used for data transmission). (Step S16).

[0029] FIG. 5 shows subcarrier numbers # 1, # 2, and # 3 during data transmission performed by combining any of the modulation schemes shown in FIG. 3 and any of the encoding schemes shown in FIG. An example of the calculation result in step S14 is shown when the SIR of each subcarrier is 8 dB, 9 dB, and 10 dB, respectively. When the calculation results shown in Fig. 5 are obtained, for example, if the desired communication quality is coded-BER = IE-6 (up to 1 bit error per 1,000,000 bits), this is the case. There are six combinations No. 1, 5, 9, 11, 13, and 15 that satisfy the desired communication quality. No. 15 is the combination that gives the highest transmission rate. Therefore, when the calculation result shown in FIG. 5 is obtained and the desired communication quality is coded-BER = lE-6, the determination unit 23 selects and determines the combination of No. 15 in step S16. If 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.

[0030] As described above, in this embodiment, a combination of an optimal encoding scheme and an optimal modulation scheme for each subcarrier is selected based on the reception quality of the signal, and the selected combination is used. Data transmission. This makes it possible to perform data transmission at the highest transmission speed while satisfying the desired communication quality.In particular, the transmission speed at the time of data transmission on the transmission line, which is not the frequency characteristic force S flat, is higher than before. Speed up The

[0031] Embodiment 2.

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 Embodiment 1 will be described. Note that the configuration of the communication system that implements the adaptive modulation method of the present embodiment and the configuration of the communication device that constitutes the communication system are the same as those of the above-described first embodiment, and the adaptive modulation instruction information that is determined by the determination unit 23 Only the generation operation is different. 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 showing an operation for generating adaptive modulation instruction information performed by communication apparatus 2 (determination unit 23) according to the second embodiment. Note that the same steps as those in the first embodiment are denoted by the same step numbers, and the description thereof is omitted.

[0033] After executing the processing in the order of step SS11 and step SI3, the determination unit 23 sets the SIR threshold corresponding to the coding scheme selected in step S13 (step S21). Further, this SIR threshold is determined in advance for each selectable encoding method based on the communication quality (desired communication quality) that should be satisfied in the communication. To select and set the one corresponding to the selected encoding method.

A specific example of the SIR threshold setting operation will be described with reference to FIGS. 7-1 and 7-2. FIGS. 7-1 and 7-2 are diagrams showing 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 showing an example of a correspondence relationship between communication quality (coded-BER which is a BER after error correction) and uncoded-BER for each coding method. This correspondence can be calculated based on the coding rate for each coding method. Fig. 7-2 shows an example of the relationship between uncoded-BER and SIR for each modulation method.

[0035] For example, if the desired communication quality is coded-BER = IE-6, to satisfy this, according to Fig. 7-1, uncoded_BER≤lE-4 is If coded method # 2 is used, uncoded-BER≤ IE-3 must be established. The example shown in Fig. 7-1 shows that the error correction capability of code method # 2 is This is for a case where the error correction capability is higher than the above. Also, according to Figure 7-2, if the desired communication quality is coded-BER = IE-6 and encoding method # 1 is used, uncoded-BER ≤ IE-4 must be satisfied, and the SIR is γ or more. Must. Similarly, modulation

11

If method # 2 is used, SIR must be greater than or equal to γ. Example shown in Fig. 7-2

12

The modulation scheme # 2 requires a larger SIR, and this is the case for modulation schemes with a large number of transmission bits.

[0036] Here, the SIR of a certain subcarrier is between γ and γ, and the desired communication quality is coded-

11 12

Considering the case of BER = IE—6, modulation scheme # 1 can be used on that subcarrier. Force modulation scheme # 2 cannot be used. On the other hand, if SIR is greater than γ

12

Then, modulation scheme # 2 can be used on the subcarrier. That is, γ and γ are signs

This is the SIR threshold value for 12 12 conversion method # 1. Similarly, γ and y correspond to encoding method # 2.

21 22

SIR threshold to be used.

[0037] As described above, when sign key scheme # 1 is selected in step S13, determination unit 23 selects SIR threshold value γ for selecting modulation scheme # 1 and modulation scheme # 2. of

12

SIR threshold γ

Set 12. In addition, when encoding method # 2 is selected in step S13, determination unit 23 determines SIR threshold value γ and modulation method for selecting modulation method # 1.

twenty one

Set the SIR threshold for selecting Equation # 2 and the value γ.

twenty two

[0038] 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 S 22). Specifically, based on FIGS. 7-1 and 7-2, for example, if the SIR of the subcarrier for which the modulation scheme is determined is between γ and γ, the determination unit 23 determines the subcarrier

11 12

The modulation method is determined to be modulation method # 1. Note that the determination unit 23 performs such processing (determination of the modulation scheme) for all subcarriers.

Next, the determination unit 23 calculates a transmission rate (step S23). Note that 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 and step of the coding method selected in step S13 above. In step S22, the transmission rate is calculated when the modulation method (modulation method for each subcarrier) determined in step S22 is used. 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, S23) for all selectable encoding methods has been executed (step S24). If there is an encoding method (step S24, No) (if the above processing is executed) (step S24, No), the process returns to step S13 and the same processing is performed for the remaining encoding methods. (Steps S13, S21, S22, S23, S24) are performed. When the above-described series of processing is completed for all the code keys (step S24, Yes), the process proceeds to step S16.

[0041] 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 a combination to be used during data transmission ( Step S 16).

[0042] Thus, in the present embodiment, based on the signal reception quality and the threshold of reception quality (for example, the SIR threshold), the optimum coding scheme and the optimum for each subcarrier are described. A combination with a suitable modulation method was selected, and data transmission was performed using the selected combination. As a result, not all combinations (combination of encoding scheme and optimal modulation scheme for each subcarrier) are investigated, so the selection accuracy of the combination is inferior to that of the first embodiment, but the amount of calculation is reduced. While reducing the circuit scale, the transmission speed during data transmission can be increased faster than before.

[0043] Embodiment 3.

Next, the adaptive modulation method and communication apparatus of Embodiment 3 will be described. FIG. 8 is a diagram showing a configuration example of a third embodiment of a communication system for realizing an adaptive modulation method according to the present invention and a communication apparatus constituting the communication system. The communication system according to the third embodiment includes a communication device 1 and a communication device 2a. Communication device 1 is the same as communication device 1 of the first embodiment described above.

[0044] 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. Further, the determination unit 23a 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. Note that parts other than the determination unit 23a have the same configurations as those of the first embodiment, and thus the same reference numerals are given and description thereof is omitted. In the present embodiment, an operation for adjusting the modulation scheme and the coding scheme for each subcarrier that is determined (in use) will be described. In this embodiment, even when the communication quality changes due to fluctuations in the transmission path condition, etc., the modulation scheme and code scheme can be adjusted (reselected) adaptively to increase the transmission speed. Is realized. Note that the present embodiment differs from the second embodiment described above 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.

[0046] Since the transmission path state changes with time, the case where the modulation method for each subcarrier and the coding method determined do not satisfy the desired communication quality with time. Can occur. 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 reduce the transmission rate to satisfy the desired communication quality. In the latter case, in order to transmit data efficiently, it is necessary to increase the transmission speed 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) in which the determination unit 23a adjusts the modulation scheme for each subcarrier once determined and the encoding scheme. Note that the same steps as those in the second embodiment are denoted by the same step numbers, and the description thereof is omitted.

Note that 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 code key scheme holding unit 34, and the control unit 35 constitute a coding scheme adjustment unit.

[0048] First, determination section 23a generates adaptive modulation instruction information by executing any of the adaptive modulation instruction information generation operations shown in Embodiment 1 or 2 at the start of communication (modulation for each subcarrier). System and coding system). 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 a CRC error as is generally done. This is measured by the method of detecting the perception and obtaining PER. The communication quality acquired here is retained as the standard communication quality until the next step S31 is executed.

Next, determination unit 23a adjusts the SIR threshold value (see step S21 in FIG. 6) set in the adaptive modulation instruction information generation operation at the start of communication (step S32). It should be noted that after the adjustment of the SIR threshold has already been performed, the latest SIR threshold value obtained by the previous adjustment is adjusted (readjustment).

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 adjustment operation. In step S32, the control unit 35 of the determination unit 23a has a good communication quality (reference communication quality) indicated by the communication quality information acquired in step S31 (the desired communication quality is satisfied). (Step S41). Note that the communication quality is determined based on a communication quality determination threshold value for determining whether the communication quality is good or not. 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. If the communication quality is not good (step S41, No), the control unit 35 instructs the value setting unit 32 to adjust the SIR threshold, and the threshold! /, Value setting unit 32 After the SIR threshold value in use (set) is increased by a specified value, the SIR threshold value (updated SIR threshold value) is reset (step S42). Note that the threshold value setting unit 32 adjusts all the SIR thresholds for each of the plurality of modulation schemes. Based on the updated SIR threshold value and the SIR for each subcarrier received from OFDM demodulator 21, comparator 31 performs the same processing as step S22 in Embodiment 2 (see FIG. 6). The modulation method for each carrier is determined (step S43). Note that the determined modulation scheme for each subcarrier is notified to the communication device 1.

[0051] After that, 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). ).

[0052] If the communication quality is good (step S44, Yes), the process proceeds to step S33. On the other hand, if the communication quality is not good (step S44, No), the process proceeds to step S42 and the SIR Adjust the threshold (increase by the specified value) and execute step S43 above. 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).

[0053] In the processing of steps S42 to S44, when the SIR threshold value is increased, 16QAM and 64QAM, such as a large multi-value number! /, And a modulation method (weak to noise !, modulation method) are selected. On the contrary, it is based on the characteristic that a modulation system with a small multi-level number (modulation system resistant to noise) such as BPSK and QPSK is easily selected. In other words, by adjusting the SIR threshold, it is possible to increase noise resistance and improve communication quality. Note that the amount of increase in the SIR threshold in step S42 can be finely adjusted as the value is reduced, and the number of executions of the adjustment process is reduced as the value is increased. However, depending on the convenience of the system to which the present invention is applied. You only have to set it.

On the other hand, when it is determined in step S41 that the communication quality is good (step S41, Yes), the control unit 35 sets the SIR threshold value to the threshold setting unit 32. The threshold value setting unit 32 resets the SIR threshold value (updated SIR threshold value) after reducing the SIR threshold value in use by a specified value. Step S45). Note that there are a plurality of threshold V and value setting units 32, and the adjustment is performed according to all the SIR thresholds and values for each modulation method. However, even if the communication quality is good, the control unit 35 determines the communication quality, determines the excess quality with a certain margin for the value, and if it is less than the value, Does not issue an instruction to adjust the SIR threshold to the threshold 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 The same processing as in step S22 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.

[0056] After that, 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 based on the acquired communication quality! /, SIR threshold, It is checked whether the value can be further decreased (whether the communication quality is excessively good enough to further increase the transmission rate) (step S47). That is, this In step S47, it is determined whether or not the communication quality is within the above-mentioned quality judgment threshold and is in a range that is greater than the value and less than the above-mentioned excess quality judgment threshold value.

[0057] SIR threshold! / If the value cannot be further decreased (step S47, No), the process proceeds to step S33. On the other hand, if the SIR threshold can be further reduced (step S47, Yes), the process proceeds to step S45 to adjust the SIR threshold (decrease by the specified value) and Execute. Thereafter, in step S47, the same processing (steps S45 to S47) is repeatedly executed until it is determined that the SIR threshold cannot be further decreased (No in step S47).

[0058] The processing of steps S45 to S47 described above makes it easier to select a modulation scheme that can transmit a large number of bits at once, such as 16QAM and 64QAM, by reducing the SIR threshold. This is based on the characteristic. In other words, the transmission rate can be increased by adjusting the SIR threshold.

Returning to the description of FIG. 9, following the processing of step S23, the control unit 35 checks whether or not the coding scheme selection count has reached the specified count (step S33). If the number of encoding method selections has reached the specified number (step S33, Yes), the process proceeds to step S16. On the other hand, if the number of selections of the coding scheme has reached the specified number (step S33, No), the determination unit 23a adjusts the coding 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 code adjustment method. In step S34, the control unit 35 of the determination unit 23a confirms whether or not the reference communication quality indicated by the communication quality information acquired in step S31 is good (satisfying the desired communication quality). (Step S51).

[0061] 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 uses the encoding used. Select a coding method with a higher error correction capability from the coding methods held in the coding method holding unit 34, and change the method to use this coding method thereafter (step S52). This increases the number of redundant bits included in the encoded data and increases noise resistance.

On the other hand, if 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 method, and the selection unit 33 sends the encoding method used to the encoding method holding unit 34. A code scheme with a lower error correction capability is selected from the stored code schemes, and thereafter changed to use this code scheme (step S53). This reduces the number of redundant bits contained in the encoded data and increases the transmission rate. However, even if the communication quality is good, the control unit 35, if it is less than the excess quality determination threshold value obtained by adding a certain margin to the communication quality determination threshold value, the selection unit 33 Does not give instructions for adjusting the encoding method. That is, the process of step S34 is terminated without adjusting the encoding method.

[0063] Then, after executing step S34, the process proceeds to step S31, and the series of processes (steps S31, S32, S23, S33) are executed again. Thereafter, in step S33, the same processing (steps S31, S32, S23, S33, S34) is continued until it is determined that the number of selections of the sign key method has reached the specified number (step S33, Yes). Here, the change in the code method is limited to the specified number of times because the number of processing executions is reduced and the time required to reset the combination of the coding method and the modulation method for each subcarrier. This is to shorten the time. However, if the time and circuit scale are sufficient, all the coding methods can be selected. In this case, it is possible to select a more appropriate code scheme and modulation scheme for each subcarrier.

[0064] Finally, the control unit 35 obtains the combination of the modulation scheme for each subcarrier and the encoding scheme that has obtained the maximum transmission rate among the calculations and stored in step S23. Make a selection (step S16). The combination force selected and determined in step S16 When the combination of the modulation scheme for each subcarrier in use and the encoding scheme is different, the selected combination is notified to the communication apparatus 1.

As described above, in the present embodiment, the time variation of the transmission path is monitored, and the encoding scheme being used and the modulation scheme for each subcarrier are not optimal for the transmission path state. In this case, the code scheme to be used and the modulation scheme for each subcarrier were appropriately changed. With this, for example, even if the communication quality cannot be satisfied, the communication quality becomes excessively good, etc., the change follows, A high transmission speed can always be realized while satisfying desired communication quality.

[0066] Embodiment 4.

Next, the adaptive modulation method and communication apparatus according to Embodiment 4 will be described. In this embodiment, by simplifying the processing shown in Embodiment 3, the amount of calculation is reduced and the circuit scale is reduced. Note that the configuration of the communication system that implements the adaptive modulation method of the present embodiment and the communication device that constitutes the communication system are the same as those of the third embodiment described above, and the update of the adaptive modulation instruction information performed by the determination unit 23a Only the operation is different.

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

Compared to the adaptive modulation instruction information update operation in Fig. 3 (see Fig. 9), the encoding system is not adjusted. Specifically, the processing of step S23, step S33, and S34 shown in the third embodiment is deleted and not executed. Accordingly, step S61 is executed instead of step S16. Note that the process of step S61 is a process for determining the modulation scheme for each subcarrier. As described above, in step S32, the adjusted SIR threshold! /, And the modulation scheme for each subcarrier using the value are set. Since it has been determined, it is adopted as the modulation method for each subcarrier after adjustment. Other processing is the same as that in the adaptive modulation instruction information update operation of Embodiment 3 (see Fig. 9) with the same step number.

[0068] The reason why the communication quality deteriorates or becomes too good is because of the time variation of the transmission path as described above, insufficient accuracy of SIR measurement, and a receiver that performs OFDM demodulation in the communication device (reception processing unit) Various causes, such as accuracy, are involved. Therefore, it is generally difficult to always select the modulation method for each subcarrier with high accuracy. Therefore, in this embodiment, the adjustment of the code method is not performed to simplify processing, and the processing time is shortened so that the modulation method for each subcarrier is frequently adjusted. The

[0069] Thus, in the present embodiment, out of the determined coding scheme and modulation scheme for each subcarrier, only the modulation scheme for each subcarrier is focused, and the modulation scheme is frequently used. It was decided to adjust. This improves the follow-up performance of the modulation scheme adjustment operation for each subcarrier with respect to the time variation of the transmission path, and allows the modulation scheme for each subcarrier to be adjusted with higher accuracy. You can choose.

[0070] Embodiment 5.

Next, the adaptive modulation method and communication apparatus according to the fifth embodiment will be described. In this embodiment, an adaptive modulation method in which the processing described in Embodiment 3 is partially changed will be described. Note that 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 are the same as those of the above-described third embodiment, and update of the adaptive modulation instruction information performed by the determination unit 23a Only the operation is different. Therefore, in the present embodiment, the update operation of adaptive modulation instruction information performed by determination unit 23a will be mainly described.

FIG. 13 is a flowchart showing an operation in which the determination unit 23a of the fifth embodiment changes the modulation scheme for each subcarrier, and is executed instead of step S32 of FIG. 9 described in the third embodiment. Operation (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.

[0072] The operation shown in FIG. 13 is the same as the operation shown in FIG. 10 described above (the SIR threshold adjustment operation in the third embodiment), and step S71 is added between steps S42 and S43. Step S45 and S46 are interspersed with step S72. The other parts are the same as those shown in FIG.

[0073] In step S71 and step S72, the same processing is executed. Specifically, in steps S42 and S45, each SIR threshold value, which is uniformly adjusted with the same adjustment amount, is added to each modulation method, and different offset values are added for each modulation method. adjust. The reason for adding this offset value will be described below.

[0074] Like BPSK and QPSK, modulation methods with a small number of multi-values generally tend to be less susceptible to disturbances such as noise and signal fluctuations (phase fluctuations) due to device imperfections. is there. On the other hand, modulation methods with large multi-levels, such as 16QAM and 64QAM, are generally vulnerable to disturbances. In other words, when the same level of signal fluctuation occurs, the required SIR increases greatly in 16QAM and 64QAM compared to BPSK and QPSK. For example, in FIG. 7-2 used in the description of Embodiment 2, it is necessary to increase the γ force ldB. In a state where γ is 2 dB, etc. (The numerical values are just examples.

12

is there). For this reason, in the present embodiment, different offsets are added for each modulation scheme, so that the phenomenon of deterioration is avoided when the amount of communication quality degradation differs depending on the number of modulation levels. In other words, the influence of disturbance is avoided by adding a larger offset value to modulation schemes with a large multi-level number.

As described above, in this embodiment, the SIR threshold used in the modulation scheme adjustment operation for each subcarrier is given an offset corresponding to the modulation scheme corresponding to each value. 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, a highly accurate modulation method for each subcarrier. Selection becomes possible.

[0076] Embodiment 6.

Next, the adaptive modulation method and communication apparatus according to Embodiment 6 will be described. In this embodiment, an adaptive modulation method in which the processing described in Embodiment 3 is partially changed will be described. Note that 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 are the same as those of the above-described third embodiment, and update of the adaptive modulation instruction information performed by the determination unit 23a Only the operation is different. Therefore, in the present embodiment, the update operation of adaptive modulation instruction information performed by determination unit 23a will be mainly described.

FIG. 14 is a flowchart showing an operation in which the determination unit 23a of the sixth embodiment changes the modulation scheme for each subcarrier, and is executed instead of step S32 of FIG. 9 described in the third embodiment. Operation (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 with respect to the operation shown in FIG. 10 (SIR threshold adjustment operation in the third embodiment). Step S41 and S45 are interpolated from Step S82. The other parts are the same as those shown in FIG.

[0079] The processes in step S81 and step S82 are the same, and the threshold value is adjusted. This is a process to limit the amount (increase / decrease amount). Specifically, when executing the process to increase and decrease the SIR threshold (step S42ZS45), the current adjustment amount is compared to the cumulative adjustment amount of the SIR threshold that has been increased and decreased in step S32c. When is added, it is confirmed whether or not the cumulative adjustment amount falls within the specified range (step S81ZS82). If the result of adding the current adjustment amount to the cumulative adjustment amount is within the specified range (steps S81, YesZS82, Yes), the SIR threshold value is increased and decreased (step S43ZS45). 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, NoZS82, No), the process of step S32c is terminated.

[0080] The reason for adjusting the value by referring to the cumulative adjustment amount as described above will be explained as follows. For example, the higher the SIR threshold, the easier it is to select a modulation scheme with a small multi-level number. However, if it increases excessively, the transmission rate will be extremely reduced and transmission efficiency will deteriorate. Also, the smaller the SIR threshold, the easier it is to select a modulation scheme with a large number of values, but it becomes weaker with respect to the time variation 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 may occur due to an increase in the amount of calculation. In the present embodiment, the adjustment amount is set within a certain range.

As described above, in the present 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.

[0082] Embodiment 7.

Next, the adaptive modulation method and communication apparatus according to Embodiment 7 will be described. In this embodiment, by simplifying the processing shown in Embodiment 3, the amount of calculation is reduced and the circuit scale is reduced. Note that the configuration of the communication system that implements the adaptive modulation method of the present embodiment and the communication device that constitutes the communication system are the same as those of the third embodiment described above, and the update of the adaptive modulation instruction information performed by the determination unit 23a Only the operation is different. Therefore, in the present embodiment, the update operation of adaptive modulation instruction information performed by determination unit 23a will be mainly described. FIG. 15 is a flowchart illustrating an operation in which the determination unit 23a of the seventh embodiment updates the adaptive modulation instruction information. The adaptive modulation instruction information update operation of the present embodiment

Compared to the adaptive modulation instruction information update operation in Fig. 3 (see Fig. 9), the difference is 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 S 91 is executed instead of step S 16. 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 processing is the same as that in the adaptive modulation instruction information update operation (see FIG. 9) of Embodiment 3 to which the same step number is assigned.

[0084] When the number of subcarriers is large or the number of modulation scheme candidates is large, the time required to determine the modulation scheme for each subcarrier increases. Therefore, in this embodiment, in such a case, the adjustment of the modulation method for each subcarrier is not performed, so that the processing is simplified, and the encoding method is frequently adjusted by reducing the processing time. I try to do it.

As described above, in the present embodiment, of the determined coding schemes and modulation schemes for each subcarrier, only the coding scheme is focused on, and the time variation of the transmission path is reduced. The coding method was changed frequently. Thereby, the followability of the code key method adjustment operation with respect to the time fluctuation of the transmission path is improved, and the code key method for each subcarrier can be selected with higher accuracy.

[0086] Embodiment 8.

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 collectively 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 constitutes the communication system is the same as that of either the first or third embodiment described above.

FIG. 16-1 and FIG. 16-2 are diagrams for explaining the adaptive modulation method of the eighth embodiment. is there. Figure 16-1 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 amplitude characteristic shown on the vertical axis. Figure 16-2 is an example of the received signal level of the OFDM signal received through the transmission line with the amplitude characteristics shown in Figure 16-1. The reception level is proportional to the amplitude characteristics of the transmission line, and a subcarrier with a higher reception level can easily use a multi-level modulation method that can transmit many bits at a time. On the other hand, a subcarrier with a low reception level has a small multi-level number and cannot be used as a modulation method, and can transmit only a few bits at a time.

[0088] Here, the frequency characteristics of the transmission path are determined by the influence of the reflected wave (multipath wave) and the like. The delay time of the multipath wave (the signal that arrives first and the signal that arrives after being delayed by reflection) If the time difference is not so large, the frequency characteristics undulation (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 neighboring subcarriers. Therefore, even if a process for selecting a modulation scheme for each subcarrier as in the above-described embodiment is executed, the same modulation scheme may be used for neighboring subcarriers as a result. The amount of calculation is unnecessarily high.

For this reason, in the present embodiment, a plurality of subcarriers that are not set for each subcarrier are grouped into a plurality of subcarriers (subcarrier group). On the other hand, the same modulation method is set. For example, if there are 100 subcarriers and 2 waves are combined into a subcarrier group, the number of targets for which the modulation scheme is set (corresponding to the number of subcarriers in the above-described embodiment) is 1Z2. The effort for setting the modulation method for each carrier (processing for setting the modulation method for each subcarrier in the above-described embodiment) can be set to 1Z2.

Note that the operation for setting the above-described modulation scheme for each neighboring subcarrier (subcarrier group) is applicable to Embodiments 1 to 6.

[0091] As described above, in this embodiment, the modulation scheme setting processing that has been individually executed for each subcarrier in Embodiments 1 to 6 described above is performed by subcarriers having a plurality of neighboring subcarriers. It was decided to carry out every group. As a result, the processing time and circuit scale required for setting the modulation method can be reduced. [0092] Embodiment 9.

Next, the adaptive modulation method and communication apparatus according to Embodiment 9 will be described. In Embodiments 1 to 8 described above, the power of explaining an adaptive modulation method in a communication system using OFDM In this 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 to be used is different.

FIGS. 17-1 to 17-5 are diagrams for explaining the adaptive modulation method according to the ninth embodiment. Figures 17-1 to 17-3 show 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 the time waveform of the 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. 17-1, and in this system, data is transmitted in parallel using multiple subcarriers. To do.

[0094] 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 a key is used. If the modulation scheme is set for each carrier, the frequency in the FDM signal can be handled in the same way as the subcarrier in the OFDM signal. That is, the adaptive modulation methods shown in Embodiments 1 to 8 can be applied to a communication system using FDM signals.

[0095] 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 If the modulation scheme is set for each, the code in the CDM signal can be handled in the same way as the subcarrier in the OFDM signal. That is, the adaptive modulation methods 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, data is transmitted in parallel using a plurality of time slots, and a modulation scheme is set for each time slot. If so, the time slot in the TDM signal can be handled in the same way as the subcarrier in the OFDM signal. In other words, it is practical for communication systems using CDM signals. The adaptive modulation methods shown in Embodiments 1 to 8 can be applied.

[0097] 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 If the modulation scheme is set for each space (transmission signal from the transmission antenna), the space in the communication system that performs SDM can be handled in the same way 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 the above-described miscommunication system. Become. Specifically, in the operation procedure shown in FIG. 2, the transmission channel used in each communication system (communication system based on one of FDM, CDM, TDM, and SDM) is a process targeting subcarriers. (Channels multiplexed using one of frequency, code, time slot, and space) are changed.

[0099] By making such a change, the communication apparatus on the receiving side can execute the following processing to select and determine the modulation scheme and code 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 coding method (step S112). S113), then calculate the transmission rate and communication quality (step S114), and determine all combinations of the modulation scheme for each transmission scheme selected in step S112 and the encoding scheme selected in step S113. After confirming whether or not step S114 has been executed (step S115), if all combinations have been executed! / And step S114 has been executed (step S115, Yes), then step S112 and S113 Selects and determines the combination of the modulation method and the encoding method for each transmission channel corresponding to the combination that maximizes the transmission speed while satisfying the desired communication quality in the combination of the selection results. (Step S11 6). If it is determined in step S115 that step S114 has not been executed for all combinations (step S115, No), steps S112 to S112 are performed until the above processing is executed for all combinations. The process of S115 is repeatedly executed.

[0100] The operation procedure shown in Embodiments 2 to 8 is the same as the communication system using OFDM signals. In order to apply to communication systems other than the above, the operation procedure of each embodiment has been described above.

The same change as the change to the operation procedure of FIG.

[0101] Thus, in this embodiment, it is shown that the adaptive modulation method shown in Embodiments 1 to 7 described above can be applied to a communication system that performs multiplex transmission other than OFDM. It was. 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 way as subcarriers in a communication system using OFDM, and are shown in Embodiments 1 to 8. By performing the operation, the same effects as those of the above-described embodiments can be obtained in each communication system. Industrial applicability

[0102] As described above, the adaptive modulation method according to the present invention is useful for, for example, a communication system using OFDM, and particularly based on the communication quality for each subcarrier. It is suitable for the adaptive modulation method of communication equipment that performs communication by adaptively selecting and determining each modulation method.

Claims

The scope of the claims

[1] An adaptive modulation method for adaptively selecting and determining a coding scheme and a modulation scheme in data transmission by orthogonal frequency division multiplexing (OFDM) according to the state of a transmission line,

A modulation scheme pattern determining step for selecting a modulation scheme for each subcarrier from among modulation schemes defined in advance, and determining a modulation scheme combination (modulation scheme pattern) for each subcarrier;

An encoding method selection step for selecting an encoding method to be used when encoding transmission data from pre-defined encoding methods;

Based on the SIR (Signal to Interference Ratio) for each subcarrier of the received signal, the transmission rate and communication quality (transmission quality) at the time of data transmission using the modulation scheme pattern determined above and the selected code scheme A transmission quality calculation step for calculating

Further, by repeatedly executing the modulation scheme pattern determination step, the encoding scheme selection step, and the transmission quality calculation step, the transmission quality calculation step for all combinations of modulation scheme patterns and encoding schemes. The modulation method pattern and code method used when transmitting the data with the maximum transmission speed while satisfying the desired communication quality in the transmission quality calculation results are used for data transmission. An adaptive modulation method characterized in that it is selected and determined as a specific modulation scheme pattern and coding scheme.

[2] An adaptive modulation method in the case of adaptively selecting and determining an encoding method and a modulation method in data transmission by orthogonal frequency division multiplexing (OFDM) according to the state of a transmission line,

In the process of selecting a modulation scheme for each subcarrier from the modulation schemes defined in advance based on the selected encoding scheme and determining a combination of modulation schemes (modulation scheme notch) for each subcarrier. Ratio when determining whether or not can be selected The SIR threshold value used as a comparison target, the SIR threshold value to select and set the intermediate force of the SIR threshold value, the value setting step,

A modulation scheme pattern determining step for determining a modulation scheme pattern based on the SIR for each subcarrier of the received signal and the SIR threshold value selected and set;

A transmission rate calculating step of calculating a transmission rate at the time of data transmission using the selected coding scheme and the determined modulation scheme pattern based on SIR for each subcarrier of the received signal;

Including

Further, the previously defined code method is used by repeatedly executing the code method selection step, the SIR threshold setting step, the modulation method pattern determination step, and the transmission rate calculation step. The transmission rate is calculated for all cases, and the encoding method and modulation method pattern when the transmission rate calculated in the transmission rate calculation step reaches the maximum are used as the official encoding method and modulation used for data transmission. An adaptive modulation method characterized by selection and determination as a method pattern.

[3] In data transmission using Orthogonal Frequency Division Multiplexing (OFDM), adaptive modulation is used when the coding method and modulation method in use are adaptively selected and changed according to the state change of the transmission path. A method,

A reference communication quality acquisition step 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 change in the state of the transmission path;

In the case where the reference communication quality satisfies the desired communication quality, a modulation method is selected in the process of selecting a modulation method for each subcarrier and determining a combination of modulation methods (modulation method pattern) for each subcarrier. The SIR (Signal to Interference Ratio) threshold used as a comparison target when determining whether or not can be selected is increased by a specified adjustment amount, while the reference communication quality satisfies the desired communication quality. The SIR threshold value is decreased by a specified adjustment amount, and the SIR threshold adjustment step,

In the SIR threshold value adjustment step, the SIR threshold value is increased by a specified adjustment amount. A modulation pattern determining step for determining a modulation scheme pattern based on the SIR threshold value after being reduced or the value and the SIR for each subcarrier;

A transmission rate calculation step for calculating the 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 reached the specified number of times, and if the reference communication quality does not satisfy the desired communication quality, it is in use. If the encoding method is adjusted to use a coding method having a higher error correction capability than that of the coding method, while the reference communication quality satisfies the desired communication quality, it is used. A coding method adjustment step for performing adjustment processing for changing the coding method so as to use a code method having a lower error correction capability than the middle code method,

First, the communication quality falls within the range between the communication quality judgment threshold for judging that the communication quality is good and the excessive quality judgment threshold for judging that the communication quality is excessively good. Until the SIR threshold value is adjusted by repeatedly executing the SIR threshold, the value adjustment step and the modulation pattern determination step, and then the SIR threshold adjustment is completed.

The transmission rate calculation step is executed to calculate the transmission rate, and after the transmission rate calculation step is executed, the code key method adjustment step is executed to adjust the code key method. After executing the encoding scheme adjustment step, until the encoding scheme adjustment count reaches a specified count, the reference communication quality acquisition step, the SIR threshold adjustment processing, the transmission rate calculation step, and the encoding scheme adjustment are performed. Steps are repeatedly executed, and when the number of times of adjustment of the encoding method reaches the specified number of times, the code key method and the modulation method pattern when the transmission rate calculated in the transmission rate calculation step becomes maximum are displayed. An adaptive modulation method characterized in that it is selected and determined as a formal code scheme and modulation scheme pattern used during data transmission. 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 for data transmission. Claim characterized by The adaptive modulation method according to Item 3.

[5] In the SIR threshold, in the value adjustment step, the SIR threshold is set to a larger value as the SIR threshold used for determining whether the modulation multi-value number is large and the modulation method can be selected. 4. The adaptive modulation method according to claim 3, wherein the adjustment is performed with an appropriate adjustment amount.

[6] In the SIR threshold, in the value adjustment step, the SIR threshold is set to a larger value as the SIR threshold used for determining whether the modulation multi-value number is larger and the modulation scheme can be selected. 5. The adaptive modulation method according to claim 4, wherein the adjustment is performed with a proper adjustment amount.

[7] In the SIR threshold adjustment step, the accumulated value of the adjustment amount (SIR threshold, the amount of increase or decrease in value) adjusted within the specified range is within the specified range after the processing of that step is started. 4. The adaptive modulation method according to claim 3, wherein the SIR threshold value is adjusted only when it is settled! /.

[8] In the SIR threshold adjustment step, the accumulated value of the adjustment amount (SIR threshold, the amount of increase or decrease of the value) adjusted within the specified range is within the specified range after the processing of that step is started. 5. The adaptive modulation method according to claim 4, wherein the SIR threshold value is adjusted only when it falls within the range.

[9] After executing the reference communication quality acquisition step, the transmission rate calculation step is immediately performed without performing the SIR threshold adjustment step, and thereafter, until the coding method adjustment number reaches a specified number. The reference communication quality acquisition step, the transmission rate calculation step, and the coding method adjustment step are repeatedly executed, and when the number of times of adjusting the encoding method reaches a specified number, the calculation is performed in the transmission rate calculation step. 4. The adaptive modulation method according to claim 3, wherein the encoding method when the transmission rate is maximized is selected and determined as a formal encoding method used during data transmission.

[10] The method according to claim 1, wherein a modulation scheme is individually assigned to each subcarrier group by processing a subcarrier group composed of a plurality of neighboring subcarriers as if it were the subcarrier. The adaptive modulation method described.

[11] The method according to claim 2, wherein a modulation scheme is individually assigned to each subcarrier group by processing a subcarrier group composed of a plurality of neighboring subcarriers as if it were the subcarrier. The adaptive modulation method described. [12] The method according to claim 3, wherein a modulation scheme is individually assigned to each subcarrier group by processing a subcarrier group including a plurality of neighboring subcarriers as if it were the subcarrier. The adaptive modulation method described.

[13] 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, An adaptive modulation method in the case of performing data transmission by assigning different modulation schemes to each transmission channel divided by time slots or spaces,

2. The adaptive modulation method according to claim 1, wherein a selection determination process of a modulation scheme and a coding scheme for each transmission channel is executed on the transmission channel instead of the subcarrier or the subcarrier group. .

[14] In a communication system using FDM (Frequency Division Multiplexing), CDM (Code Division Multiplexing), TDM (Time Division Multiplexing), or SDM (Space Division Multiplexing), frequency, spreading code, An adaptive modulation method in the case of performing data transmission by assigning different modulation schemes to each transmission channel divided by time slots or spaces,

3. The adaptive modulation method according to claim 2, wherein a selection determination process of a modulation scheme and a coding scheme for each transmission channel is executed on the transmission channel instead of the subcarrier or the subcarrier group. .

[15] In a communication system using FDM (Frequency Division Multiplexing), CDM (Code Division Multiplexing), TDM (Time Division Multiplexing) or SDM (Space Division Multiplexing), frequency, spreading code, An adaptive modulation method in the case of performing data transmission by assigning different modulation schemes to each transmission channel divided by time slots or spaces,

4. The adaptive modulation method according to claim 3, wherein a selection determination process of a modulation scheme and a coding scheme for each transmission channel is executed on the transmission channel instead of the subcarrier or the subcarrier group. .

[16] For Orthogonal Frequency Division Multiplexing (OFDM) A communication apparatus that adaptively selects and determines an encoding method and a modulation method during data transmission according to a state of a transmission path,

A transmission condition selection means for selecting a combination (transmission condition) of a combination of modulation schemes for each subcarrier (modulation scheme pattern) 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, the transmission condition selection means and the transmission quality calculation means On the other hand, a repetitive process control means for performing control so as to repeatedly calculate the transmission quality while reselecting the transmission condition under the condition that the transmission condition selected before is not selected again.

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. And a transmission condition determining means for selecting and determining a transmission condition when the transmission quality is obtained as a formal transmission condition used at the time of data transmission.

[17] The transmission condition selection means determines the modulation scheme pattern by selecting a modulation scheme for each subcarrier from a predefined modulation scheme, and further defines a predefined codeh scheme. Select the sign-rich method from

17. The communication apparatus according to claim 16, wherein the transmission quality calculation means calculates the communication quality and the transmission rate based on a SIR (Signal to Interference Ratio) for each subcarrier of the received signal.

[18] The transmission condition selection means is defined in advance, based on an encoding scheme selected from among the encoding schemes, and a modulation scheme for each subcarrier is defined in advance. SIR (Signal to Interference Ratio) threshold value used in the process of determining the modulation scheme pattern by selecting from among the schemes to be compared when determining whether the modulation scheme can be selected A plurality of SIR threshold values selected and set from among the values, and further, the modulation scheme pattern is determined based on the SIR for each subcarrier of the received signal and the SIR threshold value selected and set, and The transmission quality calculation means calculates a transmission rate at the time of data transmission using the transmission condition selected by the transmission condition selection means based on the SIR for each subcarrier of the received signal, and the transmission condition determination means 17. The communication apparatus according to claim 16, wherein the transmission condition when the transmission rate calculated by the transmission quality calculating means is maximized is selected and determined as an official transmission condition used during data transmission.

The transmission condition selection means includes

A reference communication quality acquisition means for acquiring a reference communication quality for judging whether or not the power to adaptively select and change a coding scheme and a modulation scheme in use according to a change in the state of the transmission path;

If the reference communication quality satisfies the desired communication quality, if the modulation scheme can be selected by selecting the modulation scheme for each subcarrier and determining the modulation scheme pattern? Increase the SIR (Signal to Interference Ratio) threshold used as a comparison target when making judgments by the specified adjustment amount! On the other hand, if the acquired reference communication quality meets the desired communication quality, the SIR threshold adjustment means adjusts the SIR threshold by decreasing the specified adjustment amount. When,

A modulation scheme pattern determining means for determining a modulation scheme pattern based on the SIR threshold adjusted by the value adjusting means, the value 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 reached the specified number of times, and if the reference communication quality does not satisfy the desired communication quality, it is in use. If the code method is adjusted to use a code method that has higher error correction capability than the other code method, and if the reference communication quality meets the desired communication quality, Encoding method adjusting means for adjusting the encoding method to use a code key method having a lower error correction capability than the code key method being used;

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 for determining that the communication quality is excessively good. Communication quality is within the range between the excess quality judgment threshold. The SIR threshold value adjusting means and the modulation method pattern determining means repeatedly perform the process until it is round,

In addition,

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 modulation method pattern determination means,

The iterative processing control means is configured to repeat the 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 the encoding method adjustment processing by the encoding method adjustment means are repeatedly executed,

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. 17. The communication device according to claim 16, wherein the communication device is selected and determined as an appropriate transmission condition.

[20] The transmission condition selection means performs only the reference communication quality acquisition process and the SIR threshold value repeated adjustment process,

The transmission condition determining means selects and determines the modulation scheme pattern at the time when the SIR threshold and the value repetition adjustment process in the transmission condition selection section is completed as a normal modulation scheme pattern used at the time of data transmission. The communication device according to claim 19.

[21] 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 and value adjustment processing is more SIR. 20. The communication apparatus according to claim 19, wherein adjustment is performed with an adjustment amount such that the threshold value becomes a large value.

[22] The SIR threshold used by the transmission condition selection means for determining whether or not a modulation scheme having a large number of modulation multi-values can be selected in the SIR threshold and value adjustment processing is more SIR. 21. The adjustment according to claim 20, wherein the adjustment is performed with an adjustment amount such that the threshold value becomes a large value. Communication equipment.

[23] After the transmission condition selection means starts the SIR threshold and value adjustment processing, the accumulated value of the adjustment amount (SIR threshold, the amount of increase or decrease of the value) adjusted within the specified range is within the specified range. 20. The communication device according to claim 19, wherein the SIR threshold value is adjusted only when it is within the range.

[24] After the transmission condition selection means starts the SIR threshold and value adjustment processing, the accumulated value of the adjustment amount (SIR threshold, the amount of increase or decrease of the SIR threshold) is within a specified range. 21. The communication device according to claim 20, wherein the SIR threshold value is adjusted only when it falls within the range!

[25] The transmission condition selection means, after executing the reference communication quality acquisition process, immediately executes the transmission rate calculation process without performing the SIR threshold adjustment process, and thereafter performs the encoding method adjustment. The reference communication quality acquisition process, the transmission speed calculation process, and the encoding method adjustment process are repeatedly executed until the number of times reaches the specified number. 20. The communication apparatus according to claim 19, wherein the transmission condition when the transmission speed calculated by the transmission quality calculation means is maximized is selected and determined as an official transmission condition used during data transmission.

[26] The modulation scheme is individually assigned to each subcarrier group by processing a subcarrier group including a plurality of neighboring subcarriers as if it were the subcarrier. 16. The communication device according to 16.

[27] 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, A communication device that performs data transmission by assigning different modulation schemes to transmission channels divided by time slots or spaces,

17. The communication apparatus according to claim 16, wherein a selection determination process for a modulation scheme and a coding scheme for each transmission channel is executed on the transmission channel instead of the subcarrier or the subcarrier group.