Wireless communication method, wireless communication system, transmitting device, and receiving device

Abstract

This transmission device comprises a determination unit, a filter application unit, a transmission unit, and a changing unit. The determination unit determines a roll-off rate on the basis of at least some of parameters representative of the modulation method changes of an OAM multiplexed signal. The filter application unit uses the determined roll-off rate to apply a roll-off filtering to a transmission signal. The transmission unit transmits an OAM multiplexed signal generated, according to a modulation method, from the transmission signal as roll-off filtered. The changing unit changes roll-off rates on the basis of whether a nonlinear distortion notified of by a reception device is present or not. This reception device comprises a reception unit, an estimation unit, and a notification unit. The estimation unit estimates the nonlinear distortion of the OAM multiplexed signal as reception-processed by the reception unit. The notification unit notifies the transmission device of the estimation result.

Description

[Technical field]

[0001] The present invention relates to a wireless communication method, a wireless communication system, a transmitting device, and a receiving device. [Background technology]

[0002] In recent years, in order to improve communication capacity, spatial multiplexing transmission technology of wireless signals using orbital angular momentum (OAM) has been studied (see, for example, Non-Patent Document 1). Electromagnetic waves with OAM have equiphase surfaces distributed in a spiral shape along the propagation direction centered on the propagation axis. Electromagnetic waves with different OAM modes and propagating in the same direction have spatial phase distributions that are orthogonal in the direction of the rotation axis. Therefore, it is possible to spatially multiplex the signals by separating the signals of each OAM mode modulated with different signal sequences at the receiving device.

[0003] This OAM multiplexed transmission can be realized by generating, multiplexing, and transmitting multiple OAM modes using a uniform circular array (UCA) in which multiple antenna elements are arranged in a circle at equal intervals (for example, Non-Patent Document 2). For example, a discrete Fourier transform (DFT) matrix and an inverse discrete Fourier transform (IDFT) matrix are used to generate and separate the signals of the multiple OAM modes. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] J. Wang et. al., "Terabit free-space data transmission employing orbital angular momentum multiplexing," Nature Photonics, vol.6, pp.488-496, July 2012. [Non-Patent Document 2] Y. Yan, et. al., "High-capacity millimetre-wave communications with orbital angular momentum multiplexing," Nature Communications, vol.5, DOI: 10.1038 / ncomms5876, Sept. 2014. Summary of the Invention [Problem to be solved by the invention]

[0005] In OAM multiplexing transmission, a transmitting device OAM-multiplexes multiple signals and transmits them. Therefore, when the signal point phases of the modulated signals of each mode are combined in phase, the peak-to-average power ratio (PAPR) of the transmitted signal increases. When a signal with a high PAPR is amplified by a power amplifier, a large back-off of the input power is required, which causes a problem of reduced output power. As a result, the received SNR decreases and the signal quality deteriorates.

[0006] In view of the above circumstances, an object of the present invention is to provide a wireless communication method, a wireless communication system, a transmitting device, and a receiving device that can improve the data rate while reducing the PAPR. [Means for solving the problem]

[0007] A wireless communication method according to one embodiment of the present invention includes a determination step in which a transmitting device determines a roll-off factor based on at least a portion of parameters representing a modulation scheme of an OAM multiplexed signal in which signals using each OAM (Orbital Angular Momentum) mode are multiplexed; a filter application step in which the transmitting device applies roll-off filter processing to a transmission signal using the roll-off factor determined in the determination step; a transmission step in which the transmitting device generates an OAM multiplexed signal from the transmission signal that has been subjected to the roll-off filter processing in the filter application step according to the modulation scheme and transmits the generated OAM multiplexed signal; a reception processing step in which a receiving device performs reception processing of the OAM multiplexed signal received from the transmitting device; an estimation step in which the receiving device estimates nonlinear distortion of the OAM multiplexed signal that has been reception-processed in the reception processing step; a notification step in which the receiving device notifies the transmitting device of the estimation result in the estimation step; and a modification step in which the transmitting device changes the roll-off factor based on the estimation result notified from the receiving device.

[0008] One aspect of the present invention is a wireless communication system having a transmitting device and a receiving device, wherein the transmitting device comprises a determination unit that determines a roll-off rate based on at least a portion of parameters that represent a modulation method of an OAM multiplexed signal in which signals using each OAM (Orbital Angular Momentum) mode are multiplexed, a filter application unit that applies roll-off filter processing to a transmission signal using the roll-off rate determined by the determination unit, a transmitting unit that generates an OAM multiplexed signal from the transmission signal that has been subjected to the roll-off filter processing by the filter application unit according to the modulation method and transmits the generated OAM multiplexed signal, and a modification unit that changes the roll-off rate based on an estimation result of nonlinear distortion of the OAM multiplexed signal in the receiving device, and the receiving device comprises a receiving unit that performs reception processing of the OAM multiplexed signal received from the transmitting device, an estimation unit that estimates nonlinear distortion of the OAM multiplexed signal received and processed by the receiving unit, and a notification unit that notifies the transmitting device of the estimation result by the estimation unit.

[0009] A transmitting device of one embodiment of the present invention comprises a determination unit that determines a roll-off factor and a symbol rate based on at least a portion of parameters that represent a modulation method of an OAM multiplexed signal obtained by multiplexing signals using each OAM (Orbital Angular Momentum) mode, a filter application unit that applies roll-off filter processing to a transmission signal using the roll-off factor determined by the determination unit, a transmitting unit that generates an OAM multiplexed signal from the transmission signal that has been subjected to the roll-off filter processing by the filter application unit and transmits the generated OAM multiplexed signal, and a modification unit that changes the roll-off factor based on an estimated result of nonlinear distortion of the OAM multiplexed signal in a receiving device.

[0010] A receiving device of one embodiment of the present invention includes a receiving unit that receives an OAM multiplexed signal obtained by multiplexing signals using each OAM (Orbital Angular Momentum) mode from a transmitting device and performs reception processing of the received OAM multiplexed signal, an estimation unit that estimates nonlinear distortion based on the difference between the mean squared error of a high voltage signal point and the mean squared error of a low voltage signal point in a constellation of the OAM multiplexed signal received and processed by the receiving unit, and a notification unit that notifies the transmitting device of the estimation result by the estimation unit, and the receiving unit receives an OAM multiplexed signal from the transmitting device, generated from a transmission signal to which roll-off filter processing has been applied using a roll-off rate changed based on the estimation result. Effect of the Invention

[0011] According to the present invention, it is possible to improve the data rate while reducing the PAPR in OAM spatial multiplexing transmission. [Brief description of the drawings]

[0012] [Figure 1] FIG. 13 is a diagram illustrating an example of phase setting of a UCA for generating an OAM mode signal. [Diagram 2] 1 is a configuration diagram of a wireless communication system according to an embodiment of the present invention. [Diagram 3]FIG. 2 is a diagram illustrating an example of the configuration of a transmitting device in the embodiment. [Figure 4] 1 is a diagram illustrating an example of a connection configuration of an OAM mode generating device, an RF chain, and a UCA of a transmitting device in the same embodiment. [Diagram 5] 2 is a diagram illustrating an example of a functional configuration of a transmission control device in the embodiment. FIG. [Figure 6] 2 is a diagram illustrating an example of a functional configuration of a transmission parameter determination device in the embodiment. FIG. [Figure 7] 11 is a diagram showing an example of the relationship between the roll-off rate, the number of modes multiplexed, the OAM mode, and the PAPR in the embodiment. FIG. [Figure 8] FIG. 13 is a diagram showing an example of a lookup table in the embodiment. [Figure 9] FIG. 2 is a diagram illustrating an example of the configuration of a receiving device in the embodiment. [Figure 10] 2 is a diagram illustrating an example of a functional configuration of a nonlinear distortion estimation device according to the embodiment. FIG. [Figure 11] FIG. 4 is a sequence diagram showing the processing of the wireless communication system in the embodiment. [Figure 12] FIG. 13 is a diagram showing an example of a received constellation that has been subjected to nonlinear distortion in the embodiment. [Figure 13] FIG. 11 is a flow diagram showing an algorithm for estimating the presence or absence of nonlinear distortion from a received constellation in the embodiment. [Figure 14] FIG. 4 is a flow diagram showing an algorithm for determining a roll-off factor and a symbol rate in the embodiment. [Figure 15] FIG. 2 is a diagram illustrating the hardware configurations of a transmitting device and a receiving device in the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The embodiment described below is merely an example, and the embodiment to which the present invention is applied is not limited to the following embodiment. This embodiment relates to a technology for spatially multiplexing transmission of wireless signals using Orbital Angular Momentum (OAM) of electromagnetic waves.

[0014] The transmission device of this embodiment has an adaptive control unit, a filter application unit, a notification unit, and a transmission unit. The adaptive control unit has a determination unit and a change unit. The determination unit determines the roll-off factor of a band-limiting filter (roll-off filter) to be applied to a transmission signal of each OAM mode based on the number of modes multiplexed. The filter application unit performs a filter process to apply a band-limiting filter with the determined roll-off factor to a transmission signal of each OAM mode. The notification unit notifies the receiving device of the roll-off factor used in the filter process. The transmitting unit OAM-multiplexes the filtered transmission signal of each OAM mode and transmits it. The receiving device of this embodiment has an estimation device for nonlinear distortion of a received signal. The receiving device notifies the transmitting device of information on the estimated nonlinear distortion. The change unit of the transmitting device changes the roll-off factor based on the information on nonlinear distortion notified from the receiving device, and accordingly maximizes the symbol rate within a range in which the bandwidth satisfies a regulation. As described above, in this embodiment, the roll-off rate and symbol rate of the roll-off filter applied to a transmission signal in wireless communication using OAM are controlled based on the nonlinear distortion in the receiving device, thereby reducing the PAPR and improving the data rate while reducing the nonlinear distortion.

[0015] FIG. 1 is a diagram showing an example of phase settings of a UCA for generating signals in OAM modes. FIG. 1(a) to FIG. 1(e) respectively show phase settings of signals transmitted from each UCA for a transmitting device to generate signals in OAM modes 0 to 4. OAM modes are also simply referred to as modes. Circles arranged on the circumference of a dotted line indicate each antenna element of a UCA. In the figure, an example is shown for a case where there are eight antenna elements.

[0016] The transmitting device generates an OAM mode signal by giving a phase difference according to a DFT transformation matrix to the signal supplied to each antenna element of the UCA. The phase difference given to the signal transmitted from the antenna element is shown near each circle representing an antenna element. Specifically, the phase difference given to each antenna element of the OAM mode n signal is set so that the phase rotates n times. For example, as shown in FIG. 1(c), when an OAM mode 2 signal is generated using an 8-element UCA, the phase differences given to each antenna element are 0 degrees, 90 degrees, 180 degrees, 270 degrees, 0 degrees, 90 degrees, 180 degrees, and 270 degrees clockwise. Also, an OAM mode-2 signal is generated by giving a phase difference to each antenna element in the opposite direction to OAM mode 2. The number of multiplex modes can be up to the same number as the number of antenna elements, but may be less than the number of antenna elements.

[0017] To separate the OAM multiplexed signal received by the receiving device, the phase of each antenna element of the UCA of the receiving device is set to rotate in the opposite direction to the phase of the transmitting device.

[0018] Fig. 2 is a configuration diagram of a wireless communication system 1 in an embodiment of the present invention. As shown in Fig. 2, the wireless communication system 1 includes a wireless transmission device 11 and a wireless transmission device 12. The wireless transmission device 11 and the wireless transmission device 12 are installed opposite each other. In this embodiment, it is assumed that the wireless transmission devices 11 and 12 are stationary base stations. However, this assumption is merely an example. In other words, one or both of the wireless transmission devices 11 and 12 may be mobile.

[0019] The wireless transmission device 11 and the wireless transmission device 12 each have a transmitting device 100 and a receiving device 200. The transmitting device 100 and the receiving device 200 are wireless communication devices that perform wireless communication. The transmitting device 100 has a function of transmitting an OAM multiplexed signal. The transmitting device 100 includes an OAM mode generating device and a UCA. The transmitting device 100 transmits an OAM multiplexed signal in which one or more different OAM mode signals are multiplexed from the UCA. The receiving device 200 has a function of receiving the OAM multiplexed signal. The receiving device 200 includes an OAM mode separating device and a UCA. The receiving device 200 receives an OAM multiplexed signal in which one or more OAM mode signals are multiplexed and transmitted from the opposing transmitting device 100, and separates each OAM mode signal from the received OAM multiplexed signal.

[0020] First, the transmitting device 100 will be described. Fig. 3 is a diagram showing an example of the configuration of the transmitting device 100. As shown in Fig. 3, the transmitting device 100 has a nonlinear distortion acquisition device 110, a transmission control device 120, a signal processing device 130, a transmission parameter determination device 140, a transmission parameter notification device 150, a roll-off filter application device 160, an OAM mode generation device 170, an RF (Radio Frequency) chain 180, and a UCA 190.

[0021] The nonlinear distortion acquisition device 110 acquires nonlinear distortion information notified by the receiving device 200. The nonlinear distortion information indicates the presence or absence of nonlinear distortion in the received signal. The nonlinear distortion acquisition device 110 transmits the acquired nonlinear distortion information to the transmission parameter determination device 140 via the transmission control device 120.

[0022] The transmission control device 120 specifies parameter values ​​such as the number of mode multiplexing, transmission OAM mode, modulation multi-level number, and symbol rate. The modulation method of the OAM multiplexed signal is determined by the values ​​of these parameters. The transmission control device 120 notifies the signal processing device 130, the transmission parameter determination device 140, and the OAM mode generation device 170 of the specified parameter values.

[0023] The signal processing device 130 generates a digital signal to be transmitted on a carrier wave based on the input data and the parameter values ​​notified by the transmission control device 120. The signal processing device 130 converts the generated digital signal into an analog signal. The signal processing device 130 inputs the transmission signal converted into an analog signal to the roll-off filter application device 160. The roll-off filter application device 160 can process both digital and analog signals. When the roll-off filter application device 160 performs processing by digital processing, the transmission signal is converted into an analog signal after application of the roll-off filter.

[0024] The transmission parameter determination device 140 determines the roll-off factor of the roll-off filter based on the transmission OAM mode and the number of mode multiplexing notified from the transmission control device 120. The roll-off filter is used for filtering the transmission signal of each OAM mode. Furthermore, the transmission parameter determination device 140 maximizes the symbol rate within a range that satisfies the specification of the signal bandwidth according to the determined roll-off factor. The transmission parameter determination device 140 inputs information on the determined roll-off factor and symbol rate to the transmission parameter notification device 150 and the roll-off filter application device 160.

[0025] The transmission parameter notification device 150 converts the information on the roll-off factor and the symbol rate input from the transmission parameter determination device 140 into an appropriate form for notification to the receiving device 200, and then notifies the receiving device 200. The receiving device 200 may perform band limiting processing using a roll-off filter using the roll-off factor notified from the transmission parameter notification device 150, or may use a roll-off filter with a predetermined specified roll-off factor. Furthermore, the receiving device 200 may sample the received signal using the symbol rate notified from the transmission parameter notification device 150, or may use a predetermined specified symbol rate. When the receiving device 200 uses the specified roll-off factor and the specified symbol rate, the transmitting device 100 may or may not have the transmission parameter notification device 150.

[0026] The roll-off filter application device 160 converts the transmission signal input from the signal processing device 130 into a signal having a symbol rate notified by the transmission parameter determination device 140. The roll-off filter application device 160 applies roll-off filtering to the converted signal using the roll-off factor notified by the transmission parameter determination device 140. The roll-off filter application device 160 inputs the filtered signal to the OAM mode generation device 170.

[0027] The OAM mode generating device 170 is an analog circuit or a digital signal processing device that applies a DFT transformation matrix. The OAM mode generating device 170 generates a transmission signal of a mode specified by the transmission control device 120 by applying a DFT transformation matrix to the signal input from the roll-off filter application device 160. The OAM mode generating device 170 may generate a transmission signal of each OAM mode by digital processing and then perform frequency conversion. Alternatively, the OAM mode generating device 170 may generate a transmission signal of each OAM mode by an analog circuit after performing frequency conversion. Alternatively, the OAM mode generating device 170 may generate a transmission signal of an OAM mode by an analog circuit and then perform frequency conversion. The OAM mode generating device 170 multiplexes the generated transmission signals of each OAM mode and inputs them to the RF chain 180.

[0028] The RF chain 180 frequency-converts and amplifies the transmission signal input from the OAM mode generating device 170, and then inputs the signal to the UCA 190. The UCA 190 is an antenna in which M antenna elements are arranged in a circle. The UCA 190 transmits and receives an OAM multiplexed signal in which the transmission signals of each OAM mode are multiplexed.

[0029] 4 is a diagram showing an example of a connection configuration of OAM mode generating device 170, RF chain 180, and UCA 190 in transmitting device 100. UCA 190 is an antenna in which M antenna elements 191 are arranged in a circle. The M antenna elements 191 are respectively referred to as antenna elements 191-1 to 191-M.

[0030] OAM mode generation device 170 has output ports #1 to #M. OAM mode generation device 170 applies a DFT transformation matrix corresponding to each mode to each signal of modes 0 to N, and generates a transmission signal to be transmitted from each of antenna elements 191-1 to 191-M. For each antenna element 191-m (m is an integer between 1 and M), OAM mode generation device 170 multiplexes the signals of each mode to be transmitted from antenna element 191-m, and outputs multiplexed signal #m from output port #m.

[0031] RF chain 180 has RF chains #1 to #M. RF chains #1 to #M respectively receive signals #1 to #M from OAM mode generating device 170. RF chain #m converts the frequency of signal #m, amplifies the signal, and outputs the signal to antenna element 191-m. UCA 190 transmits signals #1 to #M received from RF chain 180 as radio waves from antenna elements 191-1 to 191-M, respectively.

[0032] 5 is a diagram showing an example of a functional configuration of the transmission control device 120. The transmission control device 120 includes a communication performance acquisition unit 121, a transmission OAM mode determination unit 122, a multiplex number determination unit 123, and a transmission signal parameter determination unit .

[0033] The communication performance acquisition unit 121 is a device that acquires communication characteristic information. The communication characteristic information indicates characteristics of communication between the transmitting device 100 and the receiving device 200. The characteristics indicated by the communication characteristic information include, for example, a transmission / reception distance, a received signal power to interference noise power ratio (SINR), inter-mode interference, etc. The transmission / reception distance is the distance between the transmitting device 100 and the receiving device 200.

[0034] The transmission OAM mode determination unit 122 determines a transmission OAM mode based on the communication characteristic information, and inputs information on the determined OAM mode to the transmission parameter determination device 140. The multiplex number determination unit 123 determines, for example, a mode multiplex number and a modulation multi-level number that maximize the transmission capacity based on the communication characteristic information, and inputs information on the determined mode multiplex number and modulation multi-level number to the transmission parameter determination device 140. The transmission signal parameter determination unit 124 determines values ​​of transmission signal parameters such as a coding rate based on the communication characteristic information, and inputs information on the determined values ​​of the transmission signal parameters to the transmission parameter determination device 140. The transmission OAM mode determination unit 122, the multiplex number determination unit 123, and the transmission signal parameter determination unit 124 use, for example, a transmission / reception distance and a reception SINR as the communication characteristic information.

[0035] In FIG. 5, as an example, the processing is performed in the order of communication performance acquisition section 121, transmission OAM mode determination section 122, and multiplex number determination section 123, but the order may be reversed.

[0036] 6 is a diagram showing an example of a functional configuration of transmission parameter determination device 140. Transmission parameter determination device 140 determines a roll-off rate of a roll-off filter so as to reduce the PAPR, based on at least a part of the parameter values ​​input from transmission control device 120. Transmission parameter determination device 140 includes communication parameter acquisition section 141, PAPR information holding section 142, roll-off rate determination section 143, and symbol rate determination section 144.

[0037] The communication parameter acquisition unit 141 acquires information on parameters such as the modulation multi-level number, the mode multiplexing number, and the transmission OAM mode notified from the transmission control device 120, and notifies the roll-off factor determination unit 143 of the information on these parameters.

[0038] The PAPR information storage unit 142 is a storage medium that stores PAPR information indicating the relationship between the roll-off factor, the number of mode multiplexing, the OAM mode, and the PAPR. The PAPR information storage unit 142 may store PAPR information for each modulation method. For example, PAPR information generated by calculating the relationship between the roll-off factor, the number of mode multiplexing, the OAM mode, and the PAPR may be stored in advance in the PAPR information storage unit 142. Alternatively, the PAPR information storage unit 142 may sequentially calculate the above relationship and store it as PAPR information.

[0039] The roll-off factor determination unit 143 determines a roll-off factor based on information on the number of mode multiplexing and transmission OAM mode notified by the communication parameter acquisition unit 141 and information stored in the PAPR information holding unit 142. Specifically, the roll-off factor determination unit 143 determines the roll-off factor by executing an algorithm described in Fig. 14, which will be described later. The symbol rate determination unit 144 determines a symbol rate based on the roll-off factor determined by the roll-off factor determination unit 143.

[0040] 7 is a diagram showing the relationship between the roll-off factor, the number of mode multiplexings, the OAM mode, and the PAPR in the case of a 16QAM (Quadrature Amplitude Modulation) signal. Each value in [ ] in the legend indicates the type of OAM mode. The number of numerical values ​​in [ ] indicates the number of mode multiplexings. For example, [0 1 -1] indicates OAM modes 0, 1, -1, and the number of mode multiplexings 3. The PAPR information storage unit 142 stores the PAPR information showing the relationship shown in FIG. 7 in association with, for example, information on the modulation method.

[0041] FIG. 8 is a diagram showing an example of a lookup table (LUT). Instead of storing the relationship shown in FIG. 7, the PAPR information storage unit 142 may store the lookup table shown in FIG. 8 as PAPR information in association with modulation method information. The lookup table is data in which the number of mode multiplexings is associated with the roll-off rate that minimizes the PAPR. The symbol L in the graph shown in FIG. 7 is a point connecting the points at which the PAPR is minimized for each number of multiplexings. Based on the points on the symbol L, the relationship between the number of mode multiplexings and the roll-off rate that minimizes the PAPR can be obtained. The lookup table may be created using a result of a prior simulation evaluation, or may be created based on actual measurement values.

[0042] Next, a description will be given of the receiving device 200. Fig. 9 is a diagram showing an example of a functional configuration of the receiving device 200. The receiving device 200 includes a UCA 210, an RF chain 220, an OAM mode separation device 230, a received signal processing device 240, a roll-off factor acquisition device 250, a nonlinear distortion estimation device 260, a demodulator 270, and a nonlinear distortion notification device 280.

[0043] The UCA 210 receives radio waves transmitted from the transmitting device 100 and inputs the signals to the RF chain 220. The RF chain 220 performs frequency conversion and amplification of the signals input from the UCA 210, and inputs the signals to the OAM mode separation device 230. The OAM mode separation device 230 is an analog circuit or a digital signal processing device that applies an IDFT transformation matrix. The OAM mode separation device 230 separates the signals input from the RF chain 220 into signals of each mode, and inputs the separated signals to the receiving signal processing device 240.

[0044] The reception signal processing device 240 samples the signal input from the OAM mode separation device 230 based on the symbol rate notified from the roll-off factor acquisition device 250 or a predetermined one. Furthermore, the reception signal processing device 240 performs band-limiting filter processing on the sampled signal or performs band-limiting filter processing using an analog filter based on the roll-off factor notified from the roll-off factor acquisition device 250 or a predetermined one. The reception signal processing device 240 inputs the filtered signal to the nonlinear distortion estimation device 260. The roll-off factor acquisition device 250 notifies the reception signal processing device 240 of information on the roll-off factor and the symbol rate transmitted from the transmission parameter notification device 150 of the transmission device 100.

[0045] The nonlinear distortion estimation device 260 estimates nonlinear distortion based on the constellation of the signal input from the received signal processing device 240. The nonlinear distortion estimation device 260 inputs the signal input from the received signal processing device 240 directly to the demodulator 270. The demodulator 270 demodulates the signal input from the nonlinear distortion estimation device 260. The nonlinear distortion notification device 280 converts the nonlinear distortion information indicating the presence or absence of nonlinear distortion notified from the nonlinear distortion estimation device 260 into an appropriate form, and outputs it to the transmitting device 100 via wireless or a backbone line.

[0046] 10 shows an example of the configuration of nonlinear distortion estimation device 260. Nonlinear distortion estimation device 260 includes constellation extraction section 261, EVM (Error Vector Magnitude) calculation section 262, and EVM comparison section 263. Constellation extraction section 261 classifies signal points based on the voltage of the signal points of the received signal. EVM calculation section 262 calculates the EVM of each signal point. EVM comparison section 263 compares the EVM of each signal point and determines whether or not nonlinear distortion occurs.

[0047] Next, a description will be given of the processing of the wireless communication system 1. Fig. 11 is a sequence diagram showing the processing of the transmitting device 100 of the wireless transmission device 11 and the receiving device 200 of the wireless transmission device 12. First, the transmission parameter determining device 140 of the transmitting device 100 reads out the roll-off rate that minimizes the PAPR from the lookup table stored in the PAPR information holding unit 142, and sets the roll-off rate as an initial value (step S11).

[0048] Specifically, the transmission control device 120 of the transmitting device 100 determines parameter values ​​such as the mode multiplexing number, the transmission OAM mode, the modulation multi-level number, and the symbol rate. The roll-off factor determination unit 143 reads out the roll-off factor from a lookup table stored in the PAPR information holding unit 142 corresponding to the information of the coding method specified by the parameter value notified from the transmission control device 120, using the mode multiplexing number as a search condition. Note that the lookup table may use information on a combination of the mode multiplexing number and the OAM mode instead of the information on the mode multiplexing number. In this case, the roll-off factor determination unit 143 reads out the roll-off factor from the lookup table, using the mode multiplexing number and the transmission OAM mode as search conditions. Furthermore, the symbol rate determination unit 144 determines the symbol rate corresponding to the read out roll-off factor.

[0049] The transmitting device 100 transmits an OAM multiplexed signal generated using the parameter values ​​determined by the transmission control device 120 and the roll-off factor and symbol rate determined by the transmission parameter determination device 140 (step S12).

[0050] The receiving device 200 receives the OAM multiplexed signal transmitted by the transmitting device 100. The nonlinear distortion estimation device 260 of the receiving device 200 estimates the presence or absence of nonlinear distortion based on the received signal (step S13). The nonlinear distortion notification device 280 of the receiving device 200 notifies the transmitting device 100 of nonlinear distortion information indicating the estimation result in step S13 (step S14). The nonlinear distortion acquisition device 110 of the transmitting device 100 acquires the nonlinear distortion information notified from the receiving device 200.

[0051] Transmission control device 120 of transmitting device 100 inputs the nonlinear distortion information acquired by nonlinear distortion acquisition device 110 to transmission parameter determination device 140. Roll-off factor determination unit 143 changes the roll-off factor depending on the presence or absence of nonlinear distortion indicated by the nonlinear distortion information. Furthermore, symbol rate determination unit 144 changes the symbol rate based on the changed roll-off factor (step S15).

[0052] The transmitting device 100 generates and transmits an OAM multiplexed signal using the changed roll-off factor and symbol rate (step S16). The UCA 210 of the receiving device 200 receives the OAM multiplexed signal transmitted from the transmitting device 100. In parallel with step S16, the transmission parameter notifying device 150 of the transmitting device 100 notifies the receiving device 200 of information on the roll-off factor and the symbol rate (step S17). The roll-off factor acquiring device 250 of the receiving device 200 receives the information on the roll-off factor and the symbol rate transmitted from the transmitting device 100, and outputs it to the receiving signal processing device 240.

[0053] Receiving device 200 performs reception processing on the received OAM multiplexed signal using the notified roll-off factor and symbol rate. Demodulator 270 of receiving device 200 demodulates the received signal (step S18). In parallel with step S18, receiving device 200 may repeat the processing from step S13, estimate the presence or absence of nonlinear distortion in the received OAM multiplexed signal, and notify transmitting device 100 again.

[0054] The wireless communication system 1 performs the processes of steps S12 to S18 periodically or for each transmission of a signal frame, thereby adaptively controlling the roll-off factor and the symbol rate in accordance with the amount of nonlinear distortion.

[0055] Next, the detailed processing of the non-linear distortion estimation device 260 in step S13 of FIG. 11 will be described. FIG. 12 shows an example of the constellation of a 16QAM signal that has undergone non-linear distortion. As shown in FIG. 12, the non-linear distortion received at the transmission RF has a greater impact on the outer signal points P1 to P4 with high voltage. Therefore, the non-linear distortion estimation device 260 estimates the presence or absence of non-linear distortion by comparing the average EVM of the outer signal points P1 to P4 with the average EVM of the inner signal points Q1 to Q4. The average EVM is obtained by normalizing the mean square error by the average power of the signal. The signal points P1 to P4 are collectively referred to as signal point P, and the signal points Q1 to Q4 are collectively referred to as signal point Q.

[0056] FIG. 13 is a flowchart showing an algorithm for estimating the amount of non-linear distortion in the non-linear distortion estimation device 260. The constellation extraction unit 261 of the non-linear distortion estimation device 260 normalizes the constellation of the received signal and classifies it into the outer signal point P and the inner signal point Q (step S31). Let the n-th (n is an integer greater than or equal to 1) complex received signal be z[n] = x[n] + jy[n]. j represents a complex number. As shown in FIG. 12, the constellation extraction unit 261 sets the signal point n where |x[n]| > A and |y[n]| > A as the outer signal point P. The signal point P is classified into signal points P1, P2, P3, and P4 according to the combination of the signs of x[n] and y[n]. Also, as shown in FIG. 12, the constellation extraction unit 261 sets the signal point n where |x[n]| < A and |y[n]| < A as the inner signal point Q. The signal point Q is also classified into signal points Q1, Q2, Q3, and Q4 according to the combination of the signs of x[n] and y[n].

[0057] EVM calculation unit 262 of nonlinear distortion estimation device 260 obtains the average EVM of outer signal point P and the average EVM of inner signal point Q (step S32). EVM calculation unit 262 uses, for example, an original signal point shared in advance between transmitting device 100 and receiving device 200 by using the preamble of the OAM multiplexed signal as a reference, and calculates the average error of each signal point from the reference as the average EVM. The reference differs for each classification of signal points P1, P2, P3, P4, Q1, Q2, Q3, and Q4. Alternatively, EVM calculation unit 262 may use the average value of the voltage of the signal points for each classification as a reference, and simply estimate the average error from the reference as the average EVM.

[0058] EVM comparison unit 263 of nonlinear distortion estimation device 260 compares the average EVM of outer signal point P with the average EVM of inner signal point Q to determine whether nonlinear distortion has occurred (step S33). Specifically, when EVM comparison unit 263 determines that the following formula (1) is satisfied, it considers that nonlinear distortion has occurred.

[0059] (Average EVM of outer signal point P) - (Average EVM of inner signal point Q) > α … (1)

[0060] EVM comparator 263 notifies transmitting apparatus 100 via nonlinear distortion notifying apparatus 280 of nonlinear distortion information indicating the occurrence of nonlinear distortion.

[0061] On the other hand, if EVM comparator 263 determines that the following formula (2) is satisfied, it determines that nonlinear distortion is not occurring.

[0062] (Average EVM of outer signal point P)-(Average EVM of inner signal point Q)<α …(2)

[0063] EVM comparator 263 notifies transmitting apparatus 100 of nonlinear distortion information indicating that nonlinear distortion has not occurred via nonlinear distortion notifying device 280. Nonlinear distortion notifying device 280 notifies transmitting apparatus 100 of the nonlinear distortion information input from EVM comparator 263 via radio or a backbone line (step S14 in FIG. 11).

[0064] Here, α is a margin. α is, for example, a value such as 1 dB, but may be designed arbitrarily. Nonlinear distortion notifying device 280 of receiving device 200 may notify transmitting device 100 of nonlinear distortion information in which the average EVM of outer signal point P and the average EVM of inner signal point Q, or the difference between the average EVM of outer signal point P and the average EVM of inner signal point Q, is set. Transmission parameter determining device 140 of transmitting device 100 may obtain information on the difference between the average EVM of outer signal point P and the average EVM of inner signal point Q based on the received nonlinear distortion information, and may determine the presence or absence of nonlinear distortion depending on whether the obtained difference exceeds α.

[0065] Next, the details of the processing executed by transmission parameter determination device 140 of transmitting device 100 in steps S11 and S15 of Fig. 11 will be described. Fig. 14 is a flow diagram showing an algorithm for determining a roll-off factor and a symbol rate executed by transmission parameter determination device 140 of transmitting device 100. The algorithm shown in Fig. 14 determines a roll-off factor β and a symbol rate ρ for the purpose of improving the data rate. In this algorithm, the roll-off factor β and the symbol rate ρ are changed depending on the presence or absence of a nonlinear distortion amount estimated by receiving device 200, thereby improving the data rate.

[0066] First, roll-off factor determination unit 143 of transmission parameter determination device 140 refers to a lookup table stored in PAPR information storage unit 142, selects a roll-off factor corresponding to the number of mode multiplexings or corresponding to the number of mode multiplexings and transmission OAM mode, and sets the roll-off factor as an initial value (step S51). This roll-off factor is a value that minimizes the PAPR. Symbol rate determination unit 144 sets a symbol rate corresponding to the initial roll-off factor (step S52). The symbol rate is determined in advance as a value that maximizes the data rate within the limited range of the occupied bandwidth according to the roll-off factor. Roll-off factor determination unit 143 sets variable i, which indicates the number of repetitions, to 0 (step S53).

[0067] The communication parameter acquisition unit 141 of the transmitting device 100 acquires the nonlinear distortion information received by the nonlinear distortion acquisition device 110 from the receiving device 200 (step S54). The roll-off factor determination unit 143 determines whether the acquired nonlinear distortion information indicates the presence of nonlinear distortion (step S55).

[0068] When the roll-off factor determiner 143 determines that the nonlinear distortion information indicates no nonlinear distortion (step S55: NO), it performs the process of step S56. That is, the roll-off factor determiner 143 updates the roll-off factor to a value reduced by Δβ from the current value β. Furthermore, the symbol rate determiner 144 changes the symbol rate to ρ(β) corresponding to the updated roll-off factor β (step S56). The roll-off factor determiner 143 adds 1 to the value of the variable i (step S57). The transmission parameter determiner 140 notifies the roll-off filter application device 160 of the information on the changed roll-off factor and symbol rate, and repeats the process from step S54.

[0069] On the other hand, when the roll-off factor determination unit 143 determines that the nonlinear distortion information indicates the presence of nonlinear distortion (step S55: YES), it determines whether or not the variable i is 0 (step S58). When the variable i is 0, the current roll-off factor is the initial roll-off factor that minimizes the PAPR. Therefore, when the roll-off factor determination unit 143 determines that the variable i is 0 (step S58: YES), it instructs the signal processing device 130 to reduce the transmission power (step S59). When the signal processing device 130 receives this instruction, it reduces the amplitude of the signal to be output to the roll-off filter application device 160.

[0070] On the other hand, if the variable i is not 0, the current roll-off factor does not minimize the PAPR. If the roll-off factor determiner 143 determines that the variable i is not 0 (step S58: NO), it performs the process of step S60. That is, the roll-off factor determiner 143 updates the roll-off factor to a value increased by Δβ from the current value β. Furthermore, the symbol rate determiner 144 sets the symbol rate to ρ(β) corresponding to the updated roll-off factor β (step S60). The transmission parameter determiner 140 notifies the roll-off filter application device 160 of information on the changed roll-off factor and symbol rate.

[0071] Here, Δβ is the step size of the roll-off rate. For Δβ, a value such as 0.05 is used. ρ(β) is the symbol rate that maximizes the data rate under the constraint of the occupied bandwidth for the roll-off rate β. The relationship between the roll-off rate and the symbol rate is, for example, calculated in advance and stored in the transmitting device 100, or is calculated each time by the transmission parameter determining device 140. The algorithm shown in FIG. 14 may be executed only at the start of communication, or may be executed multiple times at appropriate intervals.

[0072] 15 is a device configuration diagram showing an example of the hardware configuration of the transmitting device 100 and the receiving device 200. The transmitting device 100 and the receiving device 200 each include a processor 71, a storage unit 72, a communication interface 73, and a user interface 74.

[0073] The processor 71 is a central processing unit that performs calculations and control. The processor 71 is, for example, a CPU. The processor 71 reads out and executes a program from the storage unit 72. Some of the functions of the transmitting device 100 and the receiving device 200 may be realized using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array). The storage unit 72 further has a work area and the like for the processor 71 to execute various programs. The communication interface 73 is connected to other devices so as to be able to communicate with them. The user interface 74 is an input device such as a keyboard, a pointing device (mouse, tablet, etc.), a button, or a touch panel, or a display device such as a display. Human operations are input through the user interface 74.

[0074] According to the above-described embodiment, the wireless communication system includes a transmitting device and a receiving device. The transmitting device includes a determining unit, a filter applying unit, a transmitting unit, and a changing unit. The determining unit corresponds to, for example, the transmission parameter determining device 140 of the embodiment. The determining unit determines the roll-off rate based on at least a part of parameters representing a modulation scheme of an OAM multiplexed signal in which signals using each OAM mode are multiplexed. The filter applying unit corresponds to, for example, the roll-off filter applying device 160 of the embodiment. The filter applying unit applies roll-off filter processing to the transmission signal using the roll-off rate determined by the determining unit. The transmitting unit corresponds to, for example, the OAM mode generating device 170, the RF chain 180, and the UCA 190 of the embodiment. The transmitting unit generates an OAM multiplexed signal according to the modulation scheme from the transmission signal subjected to the roll-off filter processing by the filter applying unit, and transmits the generated OAM multiplexed signal. The changing unit corresponds to, for example, the transmission parameter determining device 140 of the embodiment. The changing unit changes the roll-off rate based on an estimation result of nonlinear distortion of the OAM multiplexed signal in the receiving device.

[0075] The determination unit may include an information storage unit, a roll-off factor determination unit, and a symbol rate determination unit. The information storage unit corresponds to, for example, PAPR information storage unit 142 of the embodiment. The information storage unit stores information indicating the correspondence between the roll-off factor and the parameter. The roll-off factor determination unit reads out the roll-off factor from the information storage unit based on at least a part of the parameter representing the modulation scheme. The symbol rate determination unit determines the symbol rate based on the roll-off factor read out by the roll-off factor determination unit. The filter application unit applies roll-off filter processing using the roll-off factor read out by the roll-off factor determination unit to the transmission signal using the symbol rate determined by the symbol rate determination unit.

[0076] The parameters are one or more of the number of mode multiplexing, the transmission mode, the modulation multi-level number, and the symbol rate.

[0077] The receiving device includes a receiving unit, an estimating unit, and a notifying unit. The receiving unit corresponds to, for example, the UCA 210, the RF chain 220, the OAM mode separating device 230, and the receiving signal processing device 240 of the embodiment. The receiving unit performs reception processing of the OAM multiplexed signal received from the transmitting device. The estimating unit corresponds to, for example, the nonlinear distortion estimating device 260 of the embodiment. The estimating unit estimates nonlinear distortion of the OAM multiplexed signal received and processed by the receiving unit. The estimating unit may estimate the nonlinear distortion based on a difference between a mean square error of a high voltage signal point and a mean square error of a low voltage signal point in the constellation of the OAM multiplexed signal received and processed by the receiving unit. The notifying unit corresponds to, for example, the nonlinear distortion notifying device 280 of the embodiment. The notifying unit notifies the transmitting device of the estimation result by the estimating unit. The receiving unit receives from the transmitting device an OAM multiplexed signal generated from a transmission signal to which roll-off filter processing using a roll-off rate changed based on the estimation result has been applied.

[0078] The estimation unit may include a classification unit, a calculation unit, and a comparison unit. The classification unit corresponds to, for example, the constellation extraction unit 261 in the embodiment. The classification unit classifies the signal points based on the voltages of the signal points of the OAM multiplexed signal received and processed by the reception unit. The calculation unit corresponds to, for example, the EVM calculation unit 262 in the embodiment. The calculation unit calculates the error vector amplitude of the first signal point, which is a signal point classified as a high voltage, and the error vector amplitude of the second signal point, which is a signal point classified as a low voltage. The comparison unit corresponds to, for example, the EVM comparison unit 263 in the embodiment. The comparison unit determines that nonlinear distortion occurs when the difference between the mean square error of the error vector amplitude of the first signal point and the mean square error of the error vector amplitude of the second signal point is equal to or greater than a predetermined value.

[0079] Although an embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and designs that do not deviate from the gist of the present invention are also included. [Explanation of symbols]

[0080] 1. Wireless communication systems 11 Radio transmission equipment 12 Radio transmission equipment 71 Processor 72 Memory section 73 Communication Interface 74 User Interface 100 Transmitting device 110 Acquisition device 120 Transmission control device 121 Communication performance acquisition section 122 Transmission OAM mode decision unit 123 Multiplex number determination unit 124 Transmission signal parameter determination unit 130 Signal Processing Device 140 Transmission parameter determination device 141 Communication parameter acquisition unit 142 PAPR information holding unit 143 Roll-off rate determination unit 144 Symbol rate determination unit 150 Transmission parameter notification device 160 Roll-off filter application device 170 OAM mode generator 180 RF Chain 190 UCA 191-1~191-M Antenna elements 200 Receiving device 210 UCA 220 RF Chain 230 OAM mode separator 240 Receiving signal processing device 250 Roll-off rate acquisition device 260 Estimation device 261 Constellation Extraction Unit 262 EVM calculation section 263 EVM comparison section 270 Demodulator 280 Notification device

Claims

1. A determination step in which a transmitting device determines a roll-off rate based on at least a part of a parameter representing a modulation method of an OAM multiplexed signal in which signals using each OAM mode are multiplexed; a filter applying step of the transmitting device applying roll-off filtering to a transmission signal using the roll-off factor determined in the determining step; a transmitting step in which the transmitting device generates an OAM multiplexed signal from the transmission signal that has been subjected to the roll-off filter processing in the filter application step in accordance with the modulation method, and transmits the generated OAM multiplexed signal; a receiving processing step in which a receiving device performs a receiving process of the OAM multiplexed signal received from the transmitting device; an estimation step in which the receiving device estimates nonlinear distortion of the OAM multiplexed signal that has been received and processed in the reception processing step; a notification step in which the receiving device notifies the transmitting device of an estimation result in the estimation step; a change step of the transmitting device changing the roll-off rate based on the estimation result notified from the receiving device; A wireless communication method comprising:

2. A wireless communication system having a transmitting device and a receiving device, The transmitting device a determination unit that determines a roll-off rate based on at least a part of a parameter that represents a modulation method of an OAM multiplexed signal in which signals using each OAM mode are multiplexed; a filter application unit that applies roll-off filtering to a transmission signal using the roll-off factor determined by the determination unit; a transmitting unit that generates an OAM multiplexed signal from the transmission signal that has been subjected to the roll-off filter processing by the filter applying unit in accordance with the modulation method, and transmits the generated OAM multiplexed signal; a change unit that changes the roll-off factor based on an estimation result of a nonlinear distortion of the OAM multiplexed signal in the receiving device, The receiving device includes: a receiving unit that performs reception processing of the OAM multiplexed signal received from the transmitting device; an estimation unit that estimates nonlinear distortion of the OAM multiplexed signal that has been received and processed by the receiving unit; a notification unit that notifies the transmission device of an estimation result by the estimation unit, Wireless communication system.

3. a determination unit that determines a roll-off factor and a symbol rate based on at least a part of parameters that indicate a modulation method of an OAM multiplexed signal in which signals using each OAM mode are multiplexed; a filter application unit that applies roll-off filtering to a transmission signal using the roll-off factor determined by the determination unit; a transmitting unit that generates an OAM multiplexed signal from the transmission signal that has been subjected to the roll-off filter processing by the filter applying unit in accordance with the modulation method, and transmits the generated OAM multiplexed signal; a change unit that changes the roll-off factor based on an estimation result of nonlinear distortion of the OAM multiplexed signal in a receiving device; A transmitting device comprising:

4. The determination unit is an information storage unit that stores information indicating a correspondence between a roll-off rate and a parameter; a roll-off factor determination unit that reads out the roll-off factor from the information storage unit based on at least a part of a parameter that represents the modulation scheme; a symbol rate determination unit that determines a symbol rate based on the roll-off rate read by the roll-off rate determination unit, the filter application unit applies the roll-off filter processing using the roll-off rate read by the roll-off rate determination unit to the transmission signal using the symbol rate determined by the symbol rate determination unit. The transmitting device according to claim 3.

5. The parameter is one or more of a mode multiplexing number, a transmission mode, a modulation multi-level number, and a symbol rate. The transmitting device according to claim 3.

6. a receiving unit that receives an OAM multiplexed signal obtained by multiplexing signals using each OAM (Orbital Angular Momentum) mode from a transmitting device and performs reception processing of the received OAM multiplexed signal; an estimation unit that estimates nonlinear distortion based on a difference between a mean square error of a high voltage signal point and a mean square error of a low voltage signal point in a constellation of the OAM multiplexed signal received and processed by the receiving unit; a notification unit that notifies the transmission device of an estimation result by the estimation unit; Equipped with The receiving unit receives, from the transmitting device, an OAM multiplexed signal generated from a transmission signal to which roll-off filtering using a roll-off rate changed based on the estimation result has been applied. Receiving device.

7. The estimation unit is a classification unit that classifies signal points based on voltages of the signal points of the OAM multiplexed signal received and processed by the receiving unit; A calculation unit that calculates an error vector amplitude of a first signal point that is the signal point classified as a high voltage and an error vector amplitude of a second signal point that is the signal point classified as a low voltage; a comparator that determines that nonlinear distortion is occurring when a difference between a mean square error of the error vector magnitude of the first signal point and a mean square error of the error vector magnitude of the second signal point is equal to or greater than a predetermined value.

7. The receiving device according to claim 6.

Images