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

Abstract

Provided is a wireless communication method that is suitable for use in an environment where transmitted power changes and that ensures exceptional communication quality over a wide range of transmitted power. A wireless transmission device 10 that supports at least two multilevel modulation schemes and a wireless reception device are used. The multilevel modulation schemes include a first modulation scheme (QAM) and a second modulation scheme (APSK) in which the minimum Euclidean distance in a constellation is shorter and the peak to average power ratio (PAPR) is lower than in the first modulation scheme. A power amplifier 26 has a function for changing transmitted power. A transmitted power control unit 22 determines the transmitted power, and the power amplifier 26 changes the transmitted power. A modulation scheme selection unit 16 compares the transmitted power and a threshold value that is set on the basis of a boundary point where the linear and the non-linear regions of the power amplifier 26 are switched, the modulation scheme selection unit 16 selecting the QAM when the transmitted power is not greater than the threshold value and selecting the APSK when the transmitted power is greater than the threshold value.

Description

[Technical field]

[0001] The present disclosure relates to a wireless communication method, a wireless communication system, and a wireless transmission device, and more particularly to a wireless communication method, a wireless communication system, and a wireless transmission device suitable for use in an environment in which transmission power varies. [Background technology]

[0002] Non-Patent Document 1 below describes in detail QAM (Quadrature Amplitude Modulation), which is one of the multi-level modulation methods for wireless communication. Non-Patent Document 2 below describes in detail APSK (Amplitude Phase Shift Keying), which is another example of the multi-level modulation method. As typified by these methods, various multi-level modulation methods are used in the field of wireless communication.

[0003] Regarding the influence of the different multi-level modulation methods on the quality of wireless communication, the following non-patent document 3 discloses the following: 1. The PAPR (Peak to Average Power Ratio) differs for each multi-level modulation method; 2. The larger the PAPR, the more likely the signal is misrecognized at the receiving end when the transmitting power amplifier operates in the nonlinear region; 3. When comparing APSK with QAM, APSK, which has a smaller PAPR, is more robust when transmitted in the nonlinear region of the power amplifier. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] IEEE Std 802.11ac-2013, IEEE, 2013 [Non-Patent Document 2] ETSI EN 302 307-1 V1.4.1, Digital Video Broadcasting, November 2014 [Non-Patent Document 3] “M-APSK Modulation for SC-FDMA Communication Systems”, Juraj GAZDA, Denis DUPAK, Dusan KOCUR, Department of Electronics and Multimedia Communications, Faculty of Electrical Engineering and Informatics, Technical University of Kosice, Letna 9, 04200 Kosice, Slovakia, 2011 Summary of the Invention [Problem to be solved by the invention]

[0005] In the symbol constellation used in QAM, multiple symbols are arranged in a grid pattern. On the other hand, in the symbol constellation used in APSK, multiple 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 symbols arranged in a QAM constellation is longer than the minimum Euclidean distance in an APSK constellation.

[0006] In communication using the multi-level modulation method, the receiving side recognizes the received signal as one of the symbols on a pre-stored constellation. Specifically, the likelihood of the received signal and each of the symbols present around it on the constellation 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 identification accuracy of the received signal. Therefore, in an environment in which the received signal is transmitted without distortion, QAM with a long minimum Euclidean distance is more likely to ensure a superior BER (Bit Error Rate) than APSK.

[0007] In a situation where the power amplifier on the transmitting side can amplify the transmission signal in a linear region, the transmission signal is less likely to be distorted. Therefore, in such a situation, QAM is more likely to ensure good communication quality than APSK. On the other hand, in a situation where the transmission power is large and the power amplifier amplifies the signal in a nonlinear region, for the reasons described in Non-Patent Document 3, APSK is more likely to ensure better communication quality than QAM.

[0008] In this way, when comparing the suitability of each multi-level modulation method, the superiority or inferiority may be reversed depending on whether the power amplifier uses a linear region or a nonlinear region. In the field of wireless communication, for example, a technology called Adaptive Transmission Power Control (ATPC) is known that adaptively controls transmission power in order to minimize the transmission power.

[0009] However, in the past, there had been no consideration of controlling the appropriate switching of the multi-level modulation scheme used in communication according to the transmission power. In this respect, there was room for further improvement in ATPC technology by combining it with a technology that switches between multiple multi-level modulation schemes.

[0010] The present disclosure has been made in consideration of the above problems, and has as a first object to provide a wireless communication method that ensures excellent communication quality over a wide range of transmission power by appropriately switching between multiple multi-level modulation schemes depending on the transmission power.

[0011] A second object of the present disclosure is to provide a wireless communication system that ensures excellent communication quality over a wide range of transmission power by appropriately switching between a plurality of multi-level modulation schemes depending on the transmission power.

[0012] A third object of the present disclosure is to provide a wireless transmission device that ensures excellent communication quality over a wide range of transmission power by appropriately switching between a plurality of multi-level modulation schemes depending on the transmission power. [Means for solving the problem]

[0013] In order to achieve the above object, a first aspect is a wireless communication method using a wireless transmitting device and a wireless receiving device that support at least two multi-level modulation schemes, comprising: the at least two multi-level modulation schemes include a first modulation scheme and a second modulation scheme having a shorter minimum Euclidean distance on a constellation and a smaller PAPR than the first modulation scheme; the wireless transmission device has a function of controlling a power amplifier to change transmission power; The wireless transmitting device, determining said transmission power; comparing the transmission power with a threshold value set based on a boundary point where a linear region and a nonlinear region of the power amplifier switch; selecting the first modulation scheme as a multi-level modulation scheme to be used for communication when the transmission power is not greater than the threshold; selecting the second modulation scheme as a multi-level modulation scheme to be used for communication when the transmission power is greater than the threshold; instructing the wireless receiving device to communicate in the selected modulation scheme; a step of the wireless receiving device communicating with the wireless transmitting device in the instructed modulation method; It is preferable that the present invention includes the following:

[0014] A second aspect is a wireless communication system including a wireless transmitting device and a wireless receiving device that support at least two multi-level modulation schemes, the at least two multi-level modulation schemes include a first modulation scheme and a second modulation scheme having a shorter minimum Euclidean distance on a constellation and a smaller PAPR than the first modulation scheme; The wireless transmission device includes: A function of controlling a power amplifier to change transmission power, A process of determining the transmission power; A process of comparing the transmission power with a threshold value set based on a boundary point where a linear region and a nonlinear region of the power amplifier switch; selecting the first modulation scheme as a multi-level modulation scheme to be used for communication when the transmission power is not greater than the threshold; selecting the second modulation scheme as a multi-level modulation scheme to be used for communication when the transmission power is greater than the threshold; and instructing the wireless receiving device to communicate in the selected modulation scheme; It is preferable that the wireless receiving device is configured to communicate with the wireless transmitting device in the instructed modulation method.

[0015] A third aspect is a wireless transmission device that supports at least two multi-level modulation schemes and has a function of communicating with a wireless reception device that supports the at least two multi-level modulation schemes, the at least two multi-level modulation schemes include a first modulation scheme and a second modulation scheme having a shorter minimum Euclidean distance on a constellation and a smaller PAPR than the first modulation scheme; A function of controlling a power amplifier to change transmission power, A process of determining the transmission power; A process of comparing the transmission power with a threshold value set based on a boundary point where a linear region and a nonlinear region of the power amplifier switch; selecting the first modulation scheme as a multi-level modulation scheme to be used for communication when the transmission power is not greater than the threshold; selecting the second modulation scheme as a multi-level modulation scheme to be used for communication when the transmission power is greater than the threshold; A process of instructing the wireless receiving device to communicate using the selected modulation method; Preferably, the system is configured to execute: Effect of the Invention

[0016] According to the first to third aspects, excellent communication quality can be ensured over a wide range of transmission power in an environment in which transmission power is adaptively controlled. [Brief description of the drawings]

[0017] [Figure 1] 1 is a diagram illustrating a configuration example of a wireless communication system according to a first embodiment of the present disclosure. [Diagram 2] This is a diagram showing a comparison between APSK constellations and QAM constellations. [Diagram 3] This is a diagram comparing the characteristics of QAM and APSK. [Figure 4] 2 is a diagram for explaining input / output characteristics of a power amplifier included in the wireless transmission device shown in FIG. [Diagram 5] This figure shows the suitability of QAM and APSK in contrast when the power amplifier uses a linear region and when it uses a nonlinear region. [Figure 6] 1 is a block diagram illustrating a configuration of a wireless transmission device according to a first embodiment of the present disclosure. [Figure 7] 7 is a diagram for explaining an example of a method for setting a threshold value used by the wireless transmission device shown in FIG. 6 to switch modulation schemes. FIG. [Figure 8] 7 is a flowchart illustrating the flow of main processes performed by the wireless transmission device shown in FIG. 6. [Figure 9] FIG. 11 is a block diagram illustrating a configuration of a wireless transmission device according to a second embodiment of the present disclosure. [Figure 10] 10 is a flowchart illustrating the flow of main processes performed by the wireless transmission device shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Embodiment 1 [Overall configuration of the first embodiment] Fig. 1 illustrates a configuration example of a wireless communication system according to a first embodiment of the present disclosure. As illustrated in Fig. 1, the system according to the present embodiment includes a wireless transmission device 10 and a wireless reception device 12. The wireless transmission device 10 may be, for example, a wireless communication base station managed by a telecommunications carrier, or an access point of a wireless LAN (Local Area Network). Meanwhile, the wireless reception device 12 may be a terminal device capable of communication in both or either of a licensed band and an unlicensed band.

[0019] [Features of the first embodiment] In this embodiment, the wireless transmitting device 10 and the wireless receiving device 12 have a function of supporting a plurality of multi-level modulation methods. Specifically, a case will be described in which the wireless transmitting device 10 and the wireless receiving device 12 support QAM (Quadrature Amplitude Modulation) and APSK (Amplitude Phase Shift Keying), respectively.

[0020] Figure 2 shows a comparison between APSK constellations and QAM constellations. More specifically, the left side of Figure 2 shows a 16APSK constellation that handles 16 symbols. The right side of Figure 2 shows a 16QAM constellation that also handles 16 symbols. The position of each symbol represents the amplitude and phase.

[0021] In a 16APSK constellation, 16 symbols are arranged on two concentric circles, with eight symbols at equal intervals. In a 16QAM constellation, on the other hand, 16 symbols are arranged at equal intervals in a grid pattern. In the figure, the minimum Euclidean distance between symbols in each constellation is indicated by a double-headed arrow. Comparing the two, it can be seen that the minimum Euclidean distance is greater in the case of QAM, where the symbols are arranged in a grid pattern, than in the case of APSK.

[0022] Next, we consider the PAPR (Peak to Average Power Ratio). The larger the amplitude of each symbol on the constellation, the more power is required to transmit it. Therefore, with APSK, a peak power occurs when transmitting the eight symbols arranged on the outer concentric circle. On the other hand, with QAM, a peak power occurs when transmitting the four symbols located at the four corners. For this reason, the ratio of the peak transmission power to the average transmission power for all symbols is smaller with APSK. Therefore, when APSK is used, the PAPR tends to be smaller than when QAM is used.

[0023] Figure 3 shows the minimum Euclidean distance and PAPR characteristics for QAM and APSK. The circles and crosses in the figure indicate the relative merits of each in terms of ensuring a good BER (Bit Error Rate) in wireless communication. The reasons for this difference in merit are explained below.

[0024] The wireless receiving device 12 shown in Fig. 1 receives an instruction from the wireless transmitting device 10 regarding the modulation method to be used for communication, and selects a modulation method according to the instruction. Regardless of the modulation method, the wireless receiving device 12 arranges the received signal on a constellation based on its amplitude and phase, and calculates the likelihood of the received signal for each of the multiple symbols located around it. Then, the wireless receiving device 12 recognizes the received signal as the symbol with the highest likelihood.

[0025] The longer the minimum Euclidean distance on the constellation, the greater the difference in the likelihood calculated for each symbol. For this reason, if the received signal is correctly placed on the constellation, it is easier to ensure a better BER by using QAM, which has a large minimum Euclidean distance, than by using APSK, which has a small minimum Euclidean distance. The rightmost column in Figure 3 shows this relationship as "〇 (large)" for QAM and "× (small)" for APSK.

[0026] Fig. 4 shows the input / output characteristics of the power amplifier included in the wireless transmission device 10 shown in Fig. 1. As shown in Fig. 4, the power amplifier has an input power of P B The input / output characteristics are linear in the following range, but when the input power is P B In the region exceeding this range, the characteristics become nonlinear. Then, distortion is superimposed on the signal amplified by the power amplifier using the nonlinear region. If distortion occurs in the received signal, the received signal is placed at a position on the constellation in the radio receiving device 12 that is shifted from its original position. As a result, the signal amplified in the nonlinear region is easily misrecognized as an incorrect symbol in the radio receiving device 12.

[0027] 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 nonlinear region of the power amplifier. Such a phenomenon is more likely to occur as the PAPR of the multi-level modulation method used in communication increases. For this reason, from the viewpoint of preventing misidentification of signals caused by distortion without distorting the transmission signal, APSK, which has a small PAPR, is superior to QAM, which has a large PAPR. The center column of FIG. 3 indicates this relationship as "x (large)" for QAM and "o (small)" for APSK.

[0028] Figure 5 shows the suitability of QAM and APSK in comparison when the power amplifier uses the linear region and when it uses the nonlinear region. If the input power to the power amplifier falls within the linear region, no distortion problem will occur regardless of which modulation method is used. In this case, due to the minimum Euclidean distance relationship, a better BER can be obtained by using QAM than by using APSK. The center column of Figure 5 shows this relationship as QAM "Excellent" and APSK "Good".

[0029] In the nonlinear region of the power amplifier, the larger the input power, the larger the distortion superimposed on the transmission signal. Therefore, when the input power enters the nonlinear region, the larger the PAPR of the multi-level modulation method, the larger the distortion superimposed on the signal corresponding to the peak. And the larger the distortion superimposed on the transmission signal, the more likely the signal is to be misrecognized by the wireless receiving device 12. For this reason, in a situation where the power transmitting device uses the nonlinear region, QAM with a large PAPR is more likely to cause a large deterioration in communication quality than 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)".

[0030] As described above, the relative merits of QAM and APSK are reversed depending on whether the power amplifier is operating in a linear region or a nonlinear region. Therefore, in this embodiment, the multi-level modulation method used for communication is appropriately switched between QAM and APSK depending on whether the power amplifier is operating in a linear region or a nonlinear region.

[0031] [Wireless transmitter configuration] Fig. 6 is a block diagram for explaining the configuration of the wireless transmission device 10 used in this embodiment to realize the above functions. Each element shown in Fig. 6 can be configured with dedicated hardware. Moreover, 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.

[0032] 6, the wireless transmission device 10 includes an information bit generation unit 14. The information bit generation unit 14 generates bit data corresponding to 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 modulation scheme selection unit 16.

[0033] The modulation scheme selection unit 16 has a function of selecting a scheme to be used for communication from among a plurality of multi-level modulation schemes. In this embodiment, QAM and APSK are assumed to be the modulation schemes to be used for communication. The modulation scheme selection unit 16 selects either QAM or APSK as the scheme to be used for communication.

[0034] When the modulation scheme selection unit 16 selects QAM, the bit data generated by the information bit generation unit 14 is supplied to a QAM modulation unit 18. On the other hand, when the modulation scheme selection unit 16 selects APSK, the bit data generated by the information bit generation unit 14 is supplied to an APSK modulation unit 20.

[0035] The QAM modulation unit 18 modulates the received bit data using the QAM method. Meanwhile, the APSK modulation unit 20 modulates the bit data using the APSK method. In either case, a signal generated by the modulation is provided to a transmission power control unit 22.

[0036] A command value related to transmission power is provided to the transmission power control unit 22 from the automatic transmission power control unit 24. The automatic transmission power control unit 24 automatically sets the command value appropriately based on the communication environment, etc., so as to obtain a desired communication quality. The command value of transmission power set by the automatic transmission power control unit 24 is provided to the transmission power control unit 22 and, at the same time, is also provided to the modulation method selection unit 16.

[0037] The transmission power control unit 22 controls the transmission power used for communication based on the command value received from the automatic transmission power control unit 24, and provides the result to the power amplifier 26. The power amplifier 26 amplifies the modulated signal generated by the QAM modulation unit 18 or the APSK modulation unit 20 to a desired transmission power and supplies it to the antenna 28. As a result, a signal having the transmission power controlled by the transmission power control unit is transmitted from the antenna 28 in accordance with the modulation scheme selected by the modulation scheme selection unit 16.

[0038] The wireless transmission device 10 includes a threshold calculation unit 30. The threshold calculation unit 30 is configured to be able to access a PAPR characteristics storage unit 32 and an input / output characteristics storage unit .

[0039] The PAPR characteristic storage unit 32 stores the PAPR characteristics of the multi-level modulation schemes handled by the wireless transmission device 10. More specifically, at least the PAPR characteristics of a scheme that should be used preferentially in the linear region of the power amplifier 26 over other multi-level modulation schemes among available multi-level modulation schemes are stored. In the example of this embodiment, QAM and APSK can be used, and QAM should be prioritized in the linear region, so the PAPR characteristic storage unit 32 stores at least the PAPR characteristic of QAM.

[0040] When there are three available systems, system A, system B, and system C, and the order of superiority of the linear region is system A > system B > system C, at least the PAPR characteristics of system A and system B are stored in the PAPR characteristics storage unit 32. The same applies when there are four or more available systems.

[0041] As the number of signal samples used in the calculation increases, the PAPR converges to a value specific to each multi-level modulation scheme. In this embodiment, the converged value is used as the PAPR of each individual multi-level modulation scheme.

[0042] The input / output characteristic storage unit 34 stores the input / output characteristics of the power amplifier 26. For example, a curve of the input / output characteristics as shown in FIG. 4 is stored. Alternatively, a point where the linear region and the nonlinear region of the power amplifier 26 switch, such as a P1 dB output point, may be stored as the input / output characteristics. The P1 dB output point is a point where the actual output of the power amplifier drops by 1 dB from the ideal output that would be obtained if the linear characteristics were maintained. Hereinafter, such a point is referred to as a "boundary point."

[0043] The threshold calculation unit 30 accesses the PAPR characteristic storage unit 32 to read out the PAPR characteristic of the multi-level modulation method to be prioritized in the linear domain, and also accesses the input / output characteristic storage unit 34 to read out the boundary point of the power amplifier 26. Then, the threshold calculation unit 30 calculates a point backed off by the read PAPR from the read boundary point as the modulation method switching threshold.

[0044] FIG. 7 is a diagram for specifically explaining the above-mentioned method of setting the modulation method switching threshold. In the example shown in FIG. 7, the PAPR of QAM is set to "10 dB". On the other hand, the PAPR of APSK is "6 dB". The PAPR characteristic storage unit 32 stores at least the PAPR of QAM "10 dB" that should be prioritized in the linear domain, and the value is read by the threshold calculation unit 30. The threshold calculation unit 30 also reads information on the boundary point stored in the input / output characteristic storage unit 34, that is, "0 dB" which is the P1 dB output point. Then, the threshold calculation unit 30 sets "-10 dB", which is obtained by subtracting "10 dB" from "0 dB", as the modulation method switching threshold.

[0045] The modulation scheme selection unit shown in FIG. 6 compares the threshold calculated by the threshold calculation unit 30 with the transmission power provided by the automatic transmission power control unit 24. If the transmission power is smaller than the threshold, QAM is selected as the modulation scheme. On the other hand, if the transmission power exceeds the threshold, APSK is selected.

[0046] In the example shown in FIG. 7, the PAPR of QAM is "10 dB" and the threshold is "-10 dB". Therefore, if QAM is used when the transmission power is "-10 dB", the power of a symbol with peak power will not exceed the "boundary point" even if the symbol is transmitted. In other words, it is guaranteed that the symbol modulated by QAM is always amplified in the linear region of the power amplifier 26. On the other hand, when the transmission power exceeds the threshold, APSK is used instead of QAM. With APSK, the probability that the signal is amplified in the nonlinear region can be made smaller than with QAM. Therefore, with this embodiment, stable communication quality can be ensured over a wide transmission power range.

[0047] [Processing flow in the first embodiment] Fig. 8 is a flowchart for explaining the flow of main processes performed by the wireless transmission device 10 shown in Fig. 6. More specifically, it is a flowchart for explaining the flow of processes executed in the modulation scheme selection unit 16, the automatic transmission power control unit 24, and the threshold calculation unit 30.

[0048] 8, the process of step 100 is executed by the automatic transmission power control unit 24. Here, the optimum transmission power for the wireless transmission device 10 to establish good communication with all of the wireless reception devices 12 belonging thereto is determined (step 100).

[0049] The processes of steps 102, 104, and 106 are executed in the threshold calculation unit 30. Specifically, the PAPR characteristic for the QAM to be prioritized in the linear domain is acquired from the PAPR characteristic storage unit 32 (step 102). In addition, the input / output characteristic of the power amplifier 26 is acquired from the input / output characteristic storage unit 34 (step 104). Then, a back-off according to the PAPR of the QAM is applied to the boundary point of the power amplifier 26, thereby calculating the modulation scheme switching threshold (step 106). Note that these processes, that is, the processes enclosed in the dashed line frame in FIG. 8, may be executed only once as an initialization process when the operation of the wireless transmission device 10 starts.

[0050] The processes of steps 108, 110 and 112 are executed in the modulation scheme selection unit 16. Here, first, it is determined whether or not the transmission power determined in the current routine is greater than the threshold calculated in step 106 (step 108). If it is determined that the transmission power used in this routine is greater than the threshold, APSK, which has excellent robustness in the nonlinear domain, is selected (step 110). On the other hand, if it is determined that the transmission power is not greater than the threshold, QAM, which has excellent accuracy in the linear domain, is selected (step 112).

[0051] According to the above process, by adaptively changing the transmission power and appropriately switching between QAM and APSK depending on the determined transmission power, it is possible to stably ensure excellent communication quality over a wide range of transmission power.

[0052] [Modification of the first embodiment] Incidentally, in the above-mentioned first embodiment, two multi-level modulation methods, 16QAM and 16APSK, are used, but the present disclosure is not limited to this. The number of symbols is not limited to 16, and the number of symbols of the two modulation methods may be different. In addition, various transmission methods 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, methods such as FTN (Faster-than-Nyquist) transmission and Nyquist transmission can also be applied. In addition, three or more modulation methods may be used, two or more thresholds may be set, and the modulation methods may be appropriately switched according to the transmission power.

[0053] In the above-mentioned first embodiment, the PAPR is calculated as a fixed value for each multi-level modulation method, but the present disclosure is not limited to this. For example, the PAPR may be calculated according to the probability of occurrence of a peak using a complementary cumulative distribution function (CCDF). For example, in a case where it is acceptable for the peak power to enter a nonlinear region with a certain degree of probability according to the required quality of communication, the PAPR of QAM may be lowered to "8 dB" or the like in the example shown in FIG. 7. According to such a setting, the frequency of switching the modulation method can be reduced by expanding the QAM use region.

[0054] Embodiment 2 [Configuration of the second embodiment] Next, a second embodiment of the present disclosure will be described with reference to Fig. 9 and Fig. 10. The wireless communication system of the present embodiment can be realized by replacing the wireless transmission device 10 with a wireless transmission device 40 in the configuration shown in Fig. 1. In the present embodiment as well, the wireless reception device 12 receives a command from the wireless transmission device 40 and appropriately switches the modulation method used for communication.

[0055] Fig. 9 is a block diagram for explaining the configuration of a wireless transmission device 40 used in this embodiment. In Fig. 9, elements that are the same as or correspond to those shown in Fig. 6 above are given the same reference numerals, and their explanations are omitted or simplified.

[0056] In the above-mentioned first embodiment, the threshold calculation unit 30 calculates the modulation scheme switching threshold based on the PAPR calculated as a convergence value specific to QAM, and the modulation scheme selection unit 16 always selects the modulation scheme to be used for communication based on the threshold. The wireless transmission device 40 in this embodiment is characterized in that the threshold calculation unit 44 calculates the PAPR of QAM for each frame, and calculates the modulation scheme switching threshold for each frame based on the PAPR.

[0057] 9, the wireless transmission device 40 in this embodiment includes a QAM modulation unit 18 and an APSK modulation unit 20 immediately following the information bit generation unit 14. In this embodiment, regardless of which modulation scheme is adopted, the information bits generated by the information bit generation unit 14 are always modulated by both QAM and APSK.

[0058] The information bits modulated by the QAM modulation unit 18 are provided to a PAPR characteristic calculation unit 42 for each frame. The PAPR characteristic calculation unit 42 then calculates the PAPR for each frame based on the received information bits. The PAPR calculated in this manner is provided to a threshold calculation unit 44 for each frame.

[0059] The threshold calculation unit 44 receives the input / output characteristics of the power amplifier 26 from the input / output characteristics storage unit 34. The threshold calculation unit 44 then calculates a modulation method switching threshold for each frame based on the input / output characteristics and the PAPR for each frame. Specifically, the threshold calculation unit 44 calculates a modulation method switching threshold for each frame by applying a back-off corresponding to the PAPR calculated for each frame to a boundary point such as a P1 dB output point.

[0060] The threshold calculated in this manner is provided to the modulation scheme selection unit 46. The modulation scheme selection unit 46 then compares the transmission power received from the automatic transmission power control unit 24 with the threshold and selects the modulation scheme to be used for communication. Specifically, if the transmission power exceeds the threshold, APSK is selected and the information bits modulated by the APSK modulation unit 20 are provided to the transmission power control unit 22. On the other hand, if the transmission power does not exceed the threshold, QAM is selected and the information bits modulated by the QAM modulation unit 18 are provided to the transmission power control unit 22.

[0061] According to the above configuration, the modulation scheme switching threshold reflects the PAPR of the information bits actually transmitted. The PAPR value changes for each frame according to the combination of symbols included in the frame. According to the present embodiment, it is possible to keep setting a threshold suitable for maximally utilizing QAM while following such changes and preventing the symbols modulated by QAM from entering the nonlinear region for each frame.

[0062] [Processing flow in the second embodiment] Fig. 10 is a flowchart for explaining the flow of main processes performed by the wireless transmission device 40 shown in Fig. 9. More specifically, it is a flowchart for explaining the flow of processes executed in the automatic transmission power control unit 24, the PAPR characteristic calculation unit 42, the threshold calculation unit 44, and the modulation scheme selection unit 46. Among the processes shown in Fig. 10, processes that are the same as or correspond to the processes shown in Fig. 8 above are denoted by the same reference numerals, and their descriptions are omitted or simplified.

[0063] In the flowchart shown in Fig. 10, the process of step 120 is executed by the PAPR characteristic calculation unit 42. This process is executed every time the QAM modulation unit 18 modulates information bits on a frame-by-frame basis. Specifically, the PAPR is calculated based on all symbols included in the information bits generated for each frame (step 120).

[0064] The process of step 104 is executed in the same manner as in the first embodiment. Specifically, here, the input / output characteristics of the power amplifier 26 are acquired from the input / output characteristics storage unit 34. The process of step 104, that is, the process enclosed in a dashed box in Fig. 10, may be executed only once as an initialization process, as in the first embodiment.

[0065] The process of step 122 is repeatedly executed by the threshold calculation unit 44 every time a frame of information bits is generated. Specifically, a back-off value corresponding to the PAPR obtained in step 120 is applied to the boundary point indicated by the input / output characteristics obtained in step 104, and the result is calculated as the modulation scheme switching threshold (step 122).

[0066] The processes in steps 100, 108 to 112 are substantially the same as those in the first embodiment. According to the above processes, it is possible to determine, for each frame of data that is actually transmitted, whether QAM or APSK is suitable for transmitting that data. Then, based on the result of the determination for each frame, it is possible to constantly make the optimal selection over a wide range of transmission power. Therefore, according to this embodiment, it is possible to provide even better communication quality than in the first embodiment.

[0067] [Modification of the second embodiment] Incidentally, the above-mentioned first embodiment has been described as a modified example in which the application of the present disclosure is not limited to the two multi-level modulation methods of 16QAM and 16APSK. This point is also the same for the second embodiment. That is, the configuration of the second embodiment can be applied to a larger number of various modulation methods, similar to the first embodiment.

[0068] Furthermore, in the above-described second embodiment, the PAPR is calculated for each frame, and the threshold is changed for each frame. However, the present disclosure is not limited to this. That is, the frequency of calculating the PAPR and the threshold is not limited to every frame, and they may be updated every several frames or every specified time according to a preset rule. [Explanation of symbols]

[0069] 10, 40 Radio transmitting device 12 Radio receiving device 16, 46 Modulation method selection section 18 QAM Modulation Section 20 APSK Modulation Section 22 Transmission power control section 24 Automatic transmission power control unit 26 Power Amplifier 30, 44 Threshold calculation unit 32 PAPR characteristic storage section 34 Input / output characteristics storage section 42 PAPR characteristic calculation section

Claims

1. A wireless communication method using a wireless transmitting device and a wireless receiving device that support at least two multi-level modulation methods, the at least two multi-level modulation schemes include a first modulation scheme and a second modulation scheme having a shorter minimum Euclidean distance on a constellation and a smaller PAPR than the first modulation scheme; the wireless transmission device has a function of controlling a power amplifier to change transmission power; The wireless transmitting device, determining said transmission power; comparing the transmission power with a threshold value set based on a boundary point where a linear region and a nonlinear region of the power amplifier switch; selecting the first modulation scheme as a multi-level modulation scheme to be used for communication when the transmission power is not greater than the threshold; selecting the second modulation scheme as a multi-level modulation scheme to be used for communication when the transmission power is greater than the threshold; instructing the wireless receiving device to communicate in the selected modulation scheme; a step of the wireless receiving device communicating with the wireless transmitting device in the instructed modulation method; A wireless communication method comprising:

2. The wireless communication method according to claim 1 , wherein the threshold value is a value obtained by applying a back-off corresponding to a first PAPR, which is a PAPR of the first modulation scheme, to a transmission power corresponding to the boundary point.

3. The wireless communication method according to claim 2 , wherein the first PAPR is a convergence value for the first modulation scheme.

4. The wireless communication method according to claim 3 , wherein the first PAPR is a value set so as to allow occurrence of a symbol with a peak power exceeding that value with a probability corresponding to a required communication quality.

5. The wireless communication method according to claim 2 , wherein the first PAPR is calculated based on a plurality of symbols occurring within a range defined by a predetermined rule, and is updated at a predetermined cycle.

6. 6. The wireless communication method according to claim 1, wherein the first modulation scheme and the second modulation scheme are QAM and APSK, which have the same number of symbols.

7. A wireless communication system including a wireless transmitting device and a wireless receiving device that support at least two multi-level modulation methods, the at least two multi-level modulation schemes include a first modulation scheme and a second modulation scheme having a shorter minimum Euclidean distance on a constellation and a smaller PAPR than the first modulation scheme; The wireless transmission device includes: A function of controlling a power amplifier to change transmission power, A process of determining the transmission power; A process of comparing the transmission power with a threshold value set based on a boundary point where a linear region and a nonlinear region of the power amplifier switch; selecting the first modulation scheme as a multi-level modulation scheme to be used for communication when the transmission power is not greater than the threshold; selecting the second modulation scheme as a multi-level modulation scheme to be used for communication when the transmission power is greater than the threshold; and instructing the wireless receiving device to communicate in the selected modulation scheme; A wireless communication system, wherein the wireless receiving device is configured to communicate with the wireless transmitting device in the instructed modulation method.

8. A wireless transmission device that supports at least two multi-level modulation methods and has a function of communicating with a wireless reception device that supports the at least two multi-level modulation methods, the at least two multi-level modulation schemes include a first modulation scheme and a second modulation scheme having a shorter minimum Euclidean distance on a constellation and a smaller PAPR than the first modulation scheme; A function of controlling a power amplifier to change transmission power, A process of determining the transmission power; A process of comparing the transmission power with a threshold value set based on a boundary point where a linear region and a nonlinear region of the power amplifier switch; selecting the first modulation scheme as a multi-level modulation scheme to be used for communication when the transmission power is not greater than the threshold; selecting the second modulation scheme as a multi-level modulation scheme to be used for communication when the transmission power is greater than the threshold; A process of instructing the wireless receiving device to communicate using the selected modulation method; 23. A wireless transmitting device configured to:

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