Wireless communication method, wireless communication system, and wireless transmission device

Abstract

A wireless transmission device 10 and a wireless reception device that are adapted for QAM and APSK are used. The wireless transmission device 10 is provided with a power amplifier 26 with variable transmission power. An SNR degradation amount calculation unit 22 calculates an SNR degradation amount \{QAM\} caused in QAM and an SNR degradation amount \{APSK\} caused in APSK, on the basis of the input / output characteristics of the power amplifier 26 acquired from an input / output characteristics storage unit 30, a QAM modulation signal acquired from a QAM modulation unit 16, an APSK modulation signal acquired from an APSK modulation unit 18, and the transmission power of the power amplifier 26. A modulation scheme selection unit 20 acquires a required SNR\{QAM\} for QAM and a required SNR\{APSK\} for APSK from a required SNR storage unit 24, compares "required SNR\{QAM\} + SNR degradation amount \{QAM\}" with "required SNR\{APSK\} + SNR degradation amount \{APSK\}", and selects one of the modulation schemes with the smaller of the values.

Description

Technical Field

[0001] This disclosure relates to a wireless communication method, a wireless communication system, and a wireless transmission device, and particularly relates to a wireless communication method, a wireless communication system, and a wireless transmission device suitable for use in an environment where the transmission power changes.

Background Art

[0002] The following Non-Patent Document 1 describes details about QAM (Quadrature Amplitude Modulation), which is one of the multi-value modulation methods of wireless communication. Also, the following Non-Patent Document 2 describes details about APSK (Amplitude Phase Shift Keying), which is another example of the multi-value modulation method. As represented by these methods, various multi-value modulation methods are used in the field of wireless communication.

[0003] Regarding the influence of differences in multi-value modulation methods on the quality of wireless communication, the following Non-Patent Document 3 discloses the following matters: 1. That the PAPR (Peak to Average Power Ratio) is different for each multi-value modulation method; 2. That the larger the PAPR, the easier it is for the signal to be misrecognized on the receiving side when the power amplifier on the transmitting side uses the non-linear region; 3. That when comparing APSK and QAM, APSK with a smaller PAPR is more robust when transmitted in the non-linear region of the power amplifier.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in the symbol constellation used in QAM, a plurality of symbols are arranged in a lattice. On the other hand, in the symbol constellation used in APSK, a plurality of symbols are arranged in one or more concentric circles. Comparing the two, if the number of symbols is the same, the minimum Euclidean distance between the symbols arranged on the QAM constellation is longer than the minimum Euclidean distance on the APSK constellation.

[0006] In communication using a multilevel modulation method, on the receiving side, the received signal is recognized as one of the symbols on a pre-stored constellation. Specifically, on the constellation, the likelihood between the received signal and each of the surrounding symbols is calculated, and the symbol with the highest likelihood is recognized as the received signal. In this case, the longer the Euclidean distance between the symbols arranged on the constellation, the higher the discrimination accuracy of the received signal. Therefore, in an environment where the received signal is transmitted without distortion, QAM with a long minimum Euclidean distance is more likely to ensure an excellent BER (Bit Error Rate) compared to APSK.

[0007] When the power amplifier on the transmission side can amplify the transmission signal in the linear region, distortion is less likely to occur in the transmission signal. Therefore, in such a situation, it is easier to ensure better communication quality with QAM than with APSK. On the other hand, when the transmission power is large and the power amplifier amplifies the signal in the non-linear region, for the reasons described in Non-Patent Document 3, it is easier to ensure better communication quality with APSK than when using QAM.

[0008] As described above, when comparing the suitability of each multi-level modulation method, the superiority and inferiority may be reversed depending on whether the power amplifier uses the linear region or the non-linear region. However, conventionally, the control of appropriately switching the multi-level modulation method used for communication according to the transmission power has not been studied. In this regard, the conventional wireless communication technology has room for further improvement by switching and using a plurality of multi-level modulation methods.

[0009] The present disclosure has been made in view of the above problems, and a first object thereof is to provide a wireless communication method that ensures excellent communication quality over a wide transmission power range by appropriately switching and using a plurality of multi-level modulation methods according to the transmission power.

[0010] A second object of the present disclosure is to provide a wireless communication system that ensures excellent communication quality over a wide transmission power range by appropriately switching and using a plurality of multi-level modulation methods according to the transmission power.

[0011] A third object of the present disclosure is to provide a wireless transmission device that ensures excellent communication quality over a wide transmission power range by appropriately switching and using a plurality of multi-level modulation methods according to the transmission power.

Means for Solving the Problems

[0012] A first aspect is a wireless communication method using a wireless transmission device and a wireless reception device corresponding to at least two multi-level modulation methods, in order to achieve the above object, The at least two multi-level modulation methods include a first modulation method and a second modulation method. The wireless transmission device includes a power amplifier whose transmission power is variable, and when the wireless transmission device, acquires a first required SNR to be ensured when using the first modulation method and a second required SNR to be ensured when using the second modulation method; modulates a transmission signal by the first modulation method to generate a first modulation signal; modulates the transmission signal by the second modulation method to generate a second modulation signal; calculates a first SNR degradation amount expected to occur when the first modulation signal is amplified by the power amplifier at a desired transmission power based on the input / output characteristics of the power amplifier; calculates a second SNR degradation amount expected to occur when the second modulation signal is amplified by the power amplifier at the desired transmission power based on the input / output characteristics; calculates a first index representing the suitability of using the first modulation method for communication based on the first required SNR and the first SNR degradation amount; the second required SNR and the Two calculates a second index representing the suitability of using the second modulation method for communication based on the second SNR degradation amount; selects one of the first modulation method and the second modulation method as a method to be used for communication based on a comparison result between the first index and the second index; commands the wireless reception device to perform communication using the selected modulation method; the wireless reception device performs communication with the wireless transmission device using the commanded modulation method; It is desirable to include.

[0013] Further, a second aspect is a wireless communication system using a wireless transmission device and a wireless reception device corresponding to at least two multilevel modulation methods, wherein the at least two multilevel modulation methods include a first modulation method and a second modulation method, The wireless transmission device includes a power amplifier whose transmission power is variable, a process of obtaining a first required SNR to be ensured when using the first modulation method and a second required SNR to be ensured when using the second modulation method, a process of modulating a transmission signal by the first modulation method to generate a first modulation signal, a process of modulating a transmission signal by the second modulation method to generate a second modulation signal, a process of calculating a first SNR degradation amount expected to occur when the first modulation signal is amplified by the power amplifier at a desired transmission power based on the input-output characteristics of the power amplifier, a process of calculating a second SNR degradation amount expected to occur when the second modulation signal is amplified by the power amplifier at the desired transmission power based on the input-output characteristics, a process of calculating a first index representing the propriety of using the first modulation method for communication based on the first required SNR and the first SNR degradation amount, the second required SNR and the first Two a process of calculating a second index representing the propriety of using the second modulation method for communication based on the SNR degradation amount, a process of selecting, based on the comparison result between the first index and the second index, one of the first modulation method and the second modulation method as a method for use in communication, a process of instructing the wireless reception device to perform communication using the selected modulation method, and is configured to execute, It is desirable that the wireless reception device is configured to communicate with the wireless transmission device using the instructed modulation method.

[0014] Further, a third aspect is a wireless transmission device that corresponds to at least two multilevel modulation methods and has a function of communicating with a wireless reception device corresponding to the at least two multilevel modulation methods, the at least two multilevel modulation methods include a first modulation method and a second modulation method, includes a power amplifier whose transmission power is variable, A process of obtaining a first required SNR to be ensured when using the first modulation method and a second required SNR to be ensured when using the second modulation method, A process of modulating a transmission signal by the first modulation method to generate a first modulated signal, A process of modulating a transmission signal by the second modulation method to generate a second modulated signal, A process of calculating a first SNR degradation amount expected to occur when the first modulated signal is amplified by the power amplifier at a desired transmission power based on the input-output characteristics of the power amplifier, A process of calculating a second SNR degradation amount expected to occur when the second modulated signal is amplified by the power amplifier at the desired transmission power based on the input-output characteristics, A process of calculating a first index representing the propriety of using the first modulation method for communication based on the first required SNR and the first SNR degradation amount, the second required SNR and the first Two A process of calculating a second index representing the propriety of using the second modulation method for communication based on the second SNR degradation amount, A process of selecting one of the first modulation method and the second modulation method as a method to be used for communication based on a comparison result between the first index and the second index, A process of instructing the wireless receiving device to perform communication using the selected modulation method, It is desirable to be configured to execute.

Advantages of the Invention

[0015] According to the first to third aspects, in an environment where a plurality of multi-value modulation methods can be used, by appropriately switching them according to the transmission power, it becomes possible to ensure excellent communication quality in a wide transmission power range.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

[0017] Embodiment 1. [Overall Configuration of Embodiment 1] FIG. 1 shows a configuration example of the wireless communication system according to Embodiment 1 of the present disclosure. As shown in FIG. 1, the system of the present embodiment includes a wireless transmission device 10 and a wireless reception device 12. The wireless transmission device 10 can be, for example, a base station for wireless communication managed by a communication carrier or an access point of a wireless LAN (Local Area Network). On the other hand, the wireless reception device 12 can be a terminal device capable of communicating in both or one of the licensed band and the unlicensed band.

[0018] [Features of Embodiment 1] In the present embodiment, the wireless transmission device 10 and the wireless reception device 12 have functions corresponding to a plurality of multi-valued modulation methods. Here, specifically, the case where the wireless transmission device 10 and the wireless reception device 12 respectively correspond to QAM (Quadrature Amplitude Modulation) and APSK (Amplitude Phase Shift Keying) will be described.

[0019] FIG. 2 is a diagram showing a comparison between the constellation of APSK and the constellation of QAM. More specifically, the left side of FIG. 2 shows the constellation of 16APSK that handles 16 symbols. Also, the right side of FIG. 2 shows the constellation of 16QAM that also handles 16 symbols. The position of each symbol represents the amplitude and the phase.

[0020] In the constellation of 16APSK, 16 symbols are equally spaced at 8 each on two concentric circles. On the other hand, in the constellation of 16QAM, 16 symbols are equally spaced in a lattice pattern. In the figure, the minimum Euclidean distance between symbols in each constellation is represented by a bidirectional arrow. Comparing the two, it can be seen that the minimum Euclidean distance is larger in the case of QAM where the symbols are arranged in a lattice pattern than in the case of APSK.

[0021] Next, the PAPR (Peak to Average Power Ratio) is considered. Transmitting each symbol on the constellation requires more power for those with larger amplitudes. Therefore, in APSK, peak power occurs when transmitting the 8 symbols arranged on the outer concentric circle. On the other hand, in the case of QAM, peak power occurs when transmitting the 4 symbols located at the four corners. For this reason, the ratio of the peak transmission power to the value obtained by averaging the transmission power for all symbols is smaller for APSK. Therefore, the PAPR is likely to be a smaller value when APSK is used than when QAM is used.

[0022] FIG. 3 shows a comparison of the above-mentioned minimum Euclidean distance and the characteristics of PAPR for QAM and APSK. The circles and crosses shown in the figure represent the superiority and inferiority in ensuring a good BER (Bit Error Rate) in wireless communication. The reason for such superiority and inferiority will be explained below.

[0023] The wireless receiver 12 shown in FIG. 1 receives a command regarding the modulation method used for communication from the wireless transmitter 10 and selects a modulation method according to the command. In any modulation method, the wireless receiver 12 arranges the received signal on the constellation based on its amplitude and phase, and calculates the likelihood with respect to each of a plurality of symbols located around it. Then, the received signal is recognized as the symbol with the highest likelihood.

[0024] The longer the minimum Euclidean distance on the constellation, the more likely a large difference will occur in the likelihood calculated for each symbol. Therefore, if the received signal is correctly arranged on the constellation, using QAM with a large minimum Euclidean distance is more likely to ensure a better BER than using APSK with a small distance. The rightmost column in FIG. 3 shows this relationship, representing QAM as "〇 (large)" and APSK as "× (small)".

[0025] FIG. 4 shows the input-output characteristics of the power amplifier included in the wireless transmitter 10 shown in FIG. 1. As shown in FIG. 4, the power amplifier shows linear input-output characteristics in the following region, but the characteristics become non-linear in the region where the input power exceeds P B In the following region, it shows linear input-output characteristics, but in the region where the input power exceeds P B When the power amplifier amplifies using the non-linear region, distortion is superimposed on the signal. If distortion occurs in the received signal, in the wireless receiver 12, the received signal is arranged at a position shifted from its original position on the constellation. As a result, the signal amplified in the non-linear region is likely to be misrecognized as an incorrect symbol in the wireless receiver 12.

[0026] When the wireless transmission device 10 transmits a wireless signal, even if the average power is within the linear region, a signal with a large amplitude may enter the non-linear region of the power amplifier. And such a phenomenon is more likely to occur as the PAPR of the multilevel modulation scheme used for communication is larger. For this reason, from the viewpoint of preventing signal misrecognition due to distortion without imparting distortion to the transmission signal, APSK with a small PAPR is superior to QAM with a large PAPR. The middle column of FIG. 3 shows this relationship as QAM "× (large)" and APSK "〇 (small)".

[0027] FIG. 5 shows a comparison of the suitability of QAM and APSK for each of the cases where the power amplifier uses the linear region and the non-linear region. When the input power to the power amplifier is within the linear region, no distortion problem occurs regardless of the modulation scheme used. In this case, a better BER can be obtained by using QAM rather than APSK in terms of the relationship of the minimum Euclidean distance. The middle column of FIG. 5 shows this relationship as QAM "◎ (excellent)" and APSK "〇 (good)".

[0028] In the non-linear region of the power amplifier, the distortion superimposed on the transmission signal increases as the input power increases. For this reason, when the input power enters the non-linear region, a larger distortion is superimposed on the signal corresponding to the peak for a multilevel modulation scheme with a larger PAPR. And the larger the distortion superimposed on the transmission signal, the more easily the signal is misrecognized in the wireless receiving device 12. For such reasons, in a situation where the power transmission device uses the non-linear region, in the case of QAM with a large PAPR, a greater deterioration in communication quality is likely to occur compared to the case of APSK with a low PAPR. The rightmost column of FIG. 5 shows this relationship as QAM "× (due to large PAPR)" and APSK "△ (due to low PAPR)".

[0029] As described above, the superiority and inferiority of QAM and APSK are reversed depending on whether the operating region of the power amplifier is a linear region or a non-linear region. Therefore, in this embodiment, in response to this reversal, the multi-value modulation method used for communication is appropriately switched between QAM and APSK so that excellent communication quality can be obtained in a real environment.

[0030] [Configuration of Wireless Transmission Device] FIG. 6 is a block diagram for explaining the configuration of a wireless transmission device 10 used in this embodiment to realize the above functions. Each element shown in FIG. 6 can be configured by dedicated hardware. In addition to the dedicated hardware, these elements can also be configured using an arithmetic processing unit and a program for causing the arithmetic processing unit to execute desired processing.

[0031] As shown in FIG. 6, the wireless transmission device 10 includes an information bit generation unit 14. The information bit generation unit 14 generates bit data corresponding to the information to be transmitted to the wireless reception device 12. The bit data generated by the information bit generation unit 14 is provided to a QAM modulation unit 16 and an APSK modulation unit 18.

[0032] The QAM modulation unit 16 modulates the received bit data in the QAM method. On the other hand, the APSK modulation unit 18 modulates the bit data in the APSK method. In either case, the modulation signal generated by the modulation is provided to a modulation method selection unit 20 and an SNR (Signal-Noise Ratio) degradation amount calculation unit 22.

[0033] The modulation method selection unit 20 is provided with the SNR degradation amount {QAM} and the SNR degradation amount {APSK} from the SNR degradation amount calculation unit 22. Further, the modulation method selection unit 20 is provided with the required SNR {QAM} and the required SNR {APSK} from the required SNR storage unit 24. The modulation method selection unit 20 has a function of selecting a method to be used for communication from among a plurality of multi-value modulation methods based on that information. In the present embodiment, since QAM and APSK are assumed as the modulation methods to be used for communication, the modulation method selection unit 20 selects either QAM or APSK as the method to be used for communication. Note that the process by which the modulation method selection unit 20 selects a modulation method will be described in detail later.

[0034] When the modulation method selection unit 20 selects QAM, the signal modulated by the QAM modulation unit 16 is supplied to the power amplifier 26. On the other hand, when the modulation method selection unit 20 selects APSK, the signal modulated by the APSK modulation unit 18 is supplied to the power amplifier 26.

[0035] The power amplifier 26 amplifies the modulation signal generated by the QAM modulation unit 16 or the APSK modulation unit 18 to a desired transmission power and supplies it to the antenna 28. As a result, from the antenna 28, a signal amplified to the desired power by the power amplifier 26 is transmitted in accordance with the modulation method selected by the modulation method selection unit 20.

[0036] The wireless transmission device 10 in the present embodiment includes an input / output characteristic storage unit 30. In the input / output characteristic storage unit 30, the input / output characteristics of the power amplifier 26 are stored in advance. For example, a curve of the input / output characteristics as shown in FIG. 4 is stored. The input / output characteristic storage unit 30 can provide the SNR degradation amount calculation unit 22 with the information on the input / output characteristics.

[0037] As described above, the required SNR memory unit 24 provides the required SNR{QAM} and the required SNR{APSK} to the modulation method selection unit 20. The required SNR necessary to ensure the desired communication quality is a different value for each modulation method. The required SNR{QAM} is the value of the SNR that should be ensured to obtain the desired communication quality when QAM is used as the modulation method. On the other hand, the required SNR{APSK} is the value of the SNR that should be ensured when APSK is used.

[0038] The minimum Euclidean distance on the constellation is larger in the case of QAM than in the case of APSK. Therefore, assuming a situation where the transmission signal is transmitted without distortion, the required SNR of QAM is a smaller value than the required SNR of APSK. And since the lower the required SNR, the higher the robustness of the communication, under the above premise, QAM with a smaller required SNR is evaluated to have a higher priority of adoption than APSK.

[0039] As described above, the SNR degradation amount calculation unit 22 provides the SNR degradation amount{QAM} and the SNR degradation amount{APSK} to the modulation method selection unit 20. The wireless transmission device 10 transmits the signal amplified by the power amplifier 26. As described above, distortion is superimposed on the signal amplified by the power amplifier 26 in the non-linear region. If distortion is superimposed on the transmission signal, the SNR deteriorates. The SNR degradation amount{QAM} is the assumed SNR degradation amount that occurs when the signal modulated by the QAM modulation unit 16 is amplified by the power amplifier 26. Also, the SNR degradation amount{APSK} is the assumed SNR degradation amount that occurs when the signal modulated by the APSK modulation unit 18 is amplified by the power amplifier 26.

[0040] In this embodiment, the SNR degradation amount is calculated based on the EVM (Error Vector Magnitude). The EVM is the magnitude of the deviation between the symbols included in the signal reaching the wireless receiver 12 and their original positions on the constellation. The EVM can be obtained by calculation if the symbols included in the transmission signal, the transmission power given to them, and the input / output characteristics of the power amplifier 26 are known. The SNR degradation amount calculation unit 22 calculates the SNR degradation amount {QAM} based on the modulation signal generated by the QAM modulation unit 16, the input / output characteristics acquired from the input / output characteristics storage unit 30, and the setting of the transmission power used by the power amplifier 26, and similarly calculates the SNR degradation amount {APSK} based on the modulation signal generated by the APSK modulation unit 18.

[0041] The value of the EVM represents the magnitude of the degradation of the transmission signal. Therefore, the EVM can be used directly as the SNR degradation amount. Alternatively, the average SNR may be calculated for each modulation method, the predicted SNR for the transmission signal may be calculated based on the EVM, and the difference between the two may be used as the SNR degradation amount. Further, the EVM may be a convergence value for each modulation method determined according to the transmission power, or a value for each transmission data determined by the combination of the transmission power and the symbols to be transmitted.

[0042] The value of the EVM becomes larger as the distortion of the transmission signal becomes larger. The distortion of the transmission signal is likely to occur when the power amplifier 26 uses the non-linear region. When that region is used, a QAM signal with a large PAPR is more likely to have a larger distortion than an APSK signal with a small PAPR. Therefore, in a situation where the power amplifier 26 uses the non-linear region, it can be evaluated that APSK, for which the transmission signal is less likely to be distorted and the SNR degradation amount is likely to be small, has a higher priority of adoption than QAM.

[0043] The modulation method selection unit 20 selects the modulation method to be used for communication by the following process: (1) Calculate the required SNR{QAM} + SNR degradation amount{QAM} = "QAM index"; (2) Calculate the required SNR{APSK} + the SNR degradation amount{APSK} = the 「APSK index」; (3) Compare the QAM index and the APSK index, and select the modulation method with the smaller value.

[0044] Both the required SNR and the SNR degradation amount are characteristic values that become smaller for the method with a higher priority of adoption. Therefore, if the method with a smaller 「index」, which is their sum, is selected, the method that should be adopted to obtain good communication quality can be correctly selected. However, the processes in (1) and (2) above handle the required SNR and the SNR degradation amount with the same weighting, but the present disclosure is not limited to this. The processes in (1) and (2) above may be changed to give a larger weighting to one of the required SNR and the SNR degradation amount compared to the other.

[0045] [Flow of processing in Embodiment 1] FIG. 7 is a flowchart for explaining the flow of main processing performed in the wireless transmission device 10 shown in FIG. 6. More specifically, it is a flowchart for explaining the flow of processing executed in the modulation method selection unit 20 and the SNR degradation amount calculation unit 22.

[0046] In FIG. 7, the processing in step 100 is executed in the modulation method selection unit 20. Here, the required SNR{QAM} and the required SNR{APSK} are read from the required SNR storage unit 24 (step 100).

[0047] The processing in steps 102 to 110 is executed in the SNR degradation amount calculation unit 22. Specifically, first, the input / output characteristics of the power amplifier 26 are read from the input / output characteristics storage unit 30 (step 102). The processing in steps 100 and 102 above, that is, the processing surrounded by the dashed frame in FIG. 7, may be performed only once as an initialization process at the start of the operation of the wireless transmission device 10.

[0048] Next, in the SNR degradation amount calculation unit 22, a modulation signal by QAM is acquired from the QAM modulation unit 16 (step 104), and a modulation signal by APSK is acquired from the APSK modulation unit 18 (step 106). Subsequently, an SNR degradation amount {QAM} predicted to occur when the modulation bits of QAM are transmitted at the transmission power set in the power amplifier 26 is calculated (step 108). Also, an SNR degradation amount {APSK} predicted to occur when the modulation bits by APSK are transmitted at the same transmission power is calculated (step 110).

[0049] The processes of steps 112 to 116 are executed in the modulation method selection unit 20. That is, when the processes of steps 100 to 110 are completed, the modulation method selection unit 20 first compares a QAM index, which is the sum of the required SNR {QAM} and the SNR degradation amount {QAM}, with an APSK index, which is the sum of the required SNR {APSK} and the SNR degradation amount {APSK} (step 112).

[0050] If it is determined that the QAM index > APSK index, APSK is selected as the modulation method to be used for communication (step 114). On the other hand, if the above relationship is not satisfied, QAM is selected as the modulation method to be used for communication (step 116). Note that the processes of steps 104 to 116 are repeatedly executed for each transmission frame.

[0051] As described above, according to the wireless communication system of this embodiment, a plurality of multi - value modulation methods can be appropriately switched and used based on their required SNR and SNR degradation amounts. And regardless of the transmission power used by the power amplifier 26, it is always possible to select and use a modulation method that is advantageous for obtaining high communication quality. Therefore, according to the wireless communication system of this embodiment, excellent communication quality can be stably ensured over a wide transmission power range.

[0052] [Modification Example of Embodiment 1] Incidentally, in the above-described Embodiment 1, two types of multi-value modulation schemes, 16QAM and 16APSK, are used. However, the present disclosure is not limited thereto. The number of symbols is not limited to 16, and the number of symbols of these two modulation schemes may be different. In addition, various transmission schemes such as OFDM (Orthogonal Frequency Division Multiplexing) transmission, DFT-s-OFDM (Discrete Fourier Transform-Spread-OFDM) transmission, and SC (Single Carrier) transmission can be applied. Various system configurations such as SISO (Single Input and Single Output) configuration and MIMO (Multiple Input and Multiple Output) configuration can be applied. Furthermore, schemes such as FTN (Faster-than-Nyquist) transmission and Nyquist transmission can also be applied. In addition, it is also possible to use three or more modulation schemes and appropriately select the optimal modulation scheme from among them.

[0053] Also, in the above-described Embodiment 1, the required SNR is treated as a fixed value for each multi-value modulation scheme. However, the present disclosure is not limited thereto. For example, the required SNR may be appropriately set according to the required quality of communication. According to such a setting, the switching frequency of the modulation scheme may be reduced.

[0054] Furthermore, in the above-described Embodiment 1, the QAM index and the APSK index are updated for each frame to select the optimal modulation scheme for each frame. However, the present disclosure is not limited thereto. That is, the SNR degradation amount {QAM} and the SNR degradation amount {APSK} may be updated for each of a plurality of frames or at regular intervals, so that the switching frequency of the modulation scheme may be lower than that for each frame.

[0055] Also, in the above-described Embodiment 1, the wireless transmission device 10 does not include an automatic transmission power control unit (ATPC: Adaptive Transmission Power Control), but the present disclosure is not limited thereto. That is, an ATPC may be incorporated into the wireless transmission device 10 to cause the transmission power used by the power amplifier 26 to be specified by the ATCP.

Explanation of Signs

[0056] 10 Wireless transmission device 12 Wireless reception device 16 QAM modulation unit 18 APSK modulation unit 20 Modulation method selection unit 22 SNR degradation amount calculation unit 24 Required SNR storage unit 26 Power amplifier 30 Input / output characteristic storage unit

Claims

1. A wireless communication method using a wireless transmission device and a wireless reception device corresponding to at least two multi-value modulation methods, The at least two multi-value modulation methods include a first modulation method and a second modulation method, The wireless transmission device includes a power amplifier whose transmission power is variable, When the wireless transmission device, obtaining a first required SNR to be ensured when using the first modulation method and a second required SNR to be ensured when using the second modulation method; modulating a transmission signal by the first modulation method to generate a first modulation signal; modulating the transmission signal by the second modulation method to generate a second modulation signal; calculating a first SNR degradation amount expected to occur when the first modulation signal is amplified by the power amplifier at a desired transmission power based on the input-output characteristics of the power amplifier; calculating a second SNR degradation amount expected to occur when the second modulation signal is amplified by the power amplifier at the desired transmission power based on the input-output characteristics; calculating a first index representing the propriety of using the first modulation method for communication based on the first required SNR and the first SNR degradation amount; calculating a second index representing the propriety of using the second modulation method for communication based on the second required SNR and the second SNR degradation amount; selecting, based on a comparison result between the first index and the second index, one of the first modulation method and the second modulation method as a method for use in communication; instructing the wireless reception device to perform communication using the selected modulation method; the wireless reception device performing communication with the wireless transmission device using the instructed modulation method, A wireless communication method including the above steps.

2. The wireless communication method according to claim 1, wherein the first required SNR is a fixed value set for the first modulation method, and the second required SNR is a fixed value set for the second modulation method.

3. The wireless communication method according to claim 1, wherein the first required SNR and the second required SNR are values set based on the quality of communication to be established.

4. The step of calculating the first SNR degradation amount includes: estimating a first EVM, which is an EVM for the first modulation signal included in the transmission signal of one frame; calculating the first SNR degradation amount based on the first EVM, and the step of calculating the second SNR degradation amount includes: estimating a second EVM, which is an EVM for the second modulation signal included in the transmission signal of one frame; calculating the second SNR degradation amount based on the second EVM, and the wireless communication method according to any one of claims 1 to 3.

5. The step of calculating the first SNR degradation amount includes: estimating a first EVM, which is an EVM for the first modulation signal included in the transmission signal spanning a plurality of frames; calculating the first SNR degradation amount based on the first EVM, and the step of calculating the second SNR degradation amount includes: estimating a second EVM, which is an EVM for the second modulation signal included in the transmission signal spanning a plurality of frames; calculating the second SNR degradation amount based on the second EVM, and the wireless communication method according to any one of claims 1 to 3.

6. The step of calculating the first SNR degradation amount includes: A step of calculating a first average SNR which is the average SNR for the first modulation method; A step of calculating a first predicted SNR which is the SNR predicted to occur when the first modulation signal is transmitted based on the first EVM; The method further includes a step of calculating a difference between the first average SNR and the first predicted SNR as the first SNR degradation amount; The step of calculating the second SNR degradation amount includes: A step of calculating a second average SNR which is the average SNR for the second modulation method; A step of calculating a second predicted SNR which is the SNR predicted to occur when the second modulation signal is transmitted based on the second EVM; The wireless communication method according to claim 4 or 5, further including a step of calculating a difference between the second average SNR and the second predicted SNR as the second SNR degradation amount.

7. A wireless communication system using a wireless transmission device and a wireless reception device corresponding to at least two multi-value modulation methods, The at least two multi-value modulation methods include a first modulation method and a second modulation method, The wireless transmission device includes: A power amplifier with variable transmission power, A process of obtaining a first required SNR to be ensured when using the first modulation method and a second required SNR to be ensured when using the second modulation method; A process of modulating a transmission signal by the first modulation method to generate a first modulation signal; A process of modulating a transmission signal by the second modulation method to generate a second modulation signal; A process of calculating a first SNR degradation amount expected to occur when the first modulation signal is amplified by the power amplifier at a desired transmission power based on the input-output characteristics of the power amplifier; A process of calculating a second SNR degradation amount expected to occur when the second modulation signal is amplified by the power amplifier at the desired transmission power based on the input-output characteristics, A process of calculating a first index representing the propriety of using the first modulation method for communication based on the first required SNR and the first SNR degradation amount, A process of calculating a second index representing the propriety of using the second modulation method for communication based on the second required SNR and the second SNR degradation amount, A process of selecting, based on the comparison result between the first index and the second index, one of the first modulation method and the second modulation method as a method to be used for communication, A process of instructing the wireless receiving device to perform communication using the selected modulation method, and is configured to execute, A wireless communication system in which the wireless receiving device is configured to communicate with the wireless transmitting device using the instructed modulation method.

8. A wireless transmitting device that corresponds to at least two multilevel modulation methods and has a function of communicating with a wireless receiving device corresponding to the at least two multilevel modulation methods, The at least two multilevel modulation methods include a first modulation method and a second modulation method, Equipped with a power amplifier whose transmission power is variable, A process of obtaining a first required SNR to be ensured when using the first modulation method and a second required SNR to be ensured when using the second modulation method, A process of modulating a transmission signal by the first modulation method to generate a first modulation signal, A process of modulating a transmission signal by the second modulation method to generate a second modulation signal, A process of calculating a first SNR degradation amount expected to occur when the first modulation signal is amplified by the power amplifier at the desired transmission power based on the input-output characteristics of the power amplifier, A process of calculating, based on the input / output characteristics, a second SNR degradation amount expected to occur when the second modulation signal is amplified by the power amplifier at the desired transmission power; A process of calculating a first index representing the propriety of using the first modulation method for communication based on the first required SNR and the first SNR degradation amount; A process of calculating a second index representing the propriety of using the second modulation method for communication based on the second required SNR and the second SNR degradation amount; A process of selecting, based on the comparison result between the first index and the second index, one of the first modulation method and the second modulation method as a method to be used for communication; A process of instructing the wireless receiving device to perform communication using the selected modulation method; A wireless transmission device configured to execute the above.

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