Wireless communication system, transmitter, receiver, and wireless communication method

Abstract

This wireless communication system comprises a receiver and a transmitter for performing orbital angular momentum (OAM) multiplex transmission. The transmitter comprises: a modulation unit that generates modulation signals of different modes; a multiplexing unit that multiplexes the modulation signals of the different modes generated by the modulation unit to generate a multiplexed signal; and a transmission unit that transmits the multiplexed signal generated by the multiplexing unit. The receiver comprises: a reception unit that receives the multiplexed signal transmitted from the transmitter; a separation unit that separates the multiplexed signal received by the reception unit into the modulation signals of the respective modes; and a demodulation unit that demodulates the modulation signals of the respective modes separated by the separation unit. The transmitter and / or the receiver further comprises a data switching unit that switches, between positive and negative states, the state of a signal of a mode other than the mode 0.　

Description

Wireless communication systems, transmitters, receivers, and wireless communication methods

[0001] The present invention relates to a wireless communication system, transmitter, receiver, and wireless communication method.

[0002] Conventionally, OAM (Orbital Angular Momentum) multiplex transmission has been known as a high-speed, high-capacity communication method between two fixed radio stations (see, for example, Non-Patent Document 1). OAM multiplex transmission is a technology that can increase the number of data signals that can be transmitted simultaneously (multiplexing) by superimposing data onto multiple signals having different OAM modes. When using OAM multiplex transmission, communication using a line-of-sight path by installing two fixed radio stations facing each other is generally required.

[0003] When transmitting radio waves with an OAM mode (OAM waves) by reflecting them off reflective objects such as walls or reflectors, the phase rotation direction of the OAM waves reflected by the reflective object is reversed from that of the transmitted OAM waves. As a result, it is known that the positive and negative signs of the OAM mode are swapped between the transmitting and receiving sides (see, for example, Non-Patent Document 2).

[0004] AE WILLNER, “Communication with a twist”, The orbital angular momentum property of light could dramatically boost data rates, SPECTRUM.IEEE.ORG, vol. 53, no. 8, pp. 34-39, Aug. 2016. A. ALI, M. KHALILY, D. SERGHIOU and R. TAFAZOLLI, “Reflective Metasurface With Steered OAM Beams for THz Communications”, IEEE access vol.11, pp. 12394-12401, 2023.Y Li, et. Al., “Achievable Rate Maximization for Intelligent Reflecting Surface-Assisted Orbital Angular Momentum-Based Communication Systems”, IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 70, NO. 7, JULY 2021.

[0005] As mentioned above, when using OAM waves reflected by a reflector for communication, the positive and negative signs of the OAM mode are reversed, which presents a problem as the receiving end cannot correctly receive the OAM waves. Non-patent document 2 only shows experimental results from within a research laboratory, and non-patent document 3 reports simulation results, but does not propose field experiments or actual implementation methods.

[0006] In view of the above circumstances, the present invention aims to provide a technology that enables the correct reception of data even when communicating using OAM waves reflected by reflective objects such as walls and reflectors.

[0007] One aspect of the present invention is a wireless communication system comprising a transmitter and a receiver that perform OAM (Orbital Angular Momentum) multiplex transmission, wherein the transmitter comprises a modulation unit that generates modulation signals of different modes, a multiplexing unit that multiplexes the modulation signals of different modes generated by the modulation unit to generate a multiplexed signal, and a transmission unit that transmits the multiplexed signal generated by the multiplexing unit; the receiver comprises a receiving unit that receives the multiplexed signal transmitted from the transmitter, a separation unit that separates the multiplexed signal received by the receiving unit into modulation signals of each mode, and a demodulation unit that demodulates the modulation signals of each mode separated by the separation unit; and at least one of the transmitter or the receiver further comprises a data swapping unit that swaps the positive and negative signs of signals of modes other than mode 0.

[0008] One aspect of the present invention is a transmitter comprising: a modulation unit that generates modulated signals of different modes; a data swapping unit that swaps the positive and negative signs of signals of modes other than mode 0 in the modulated signals of different modes generated by the modulation unit; a multiplexing unit that generates a multiplexed signal by multiplexing the modulated signals of different modes that have been processed by the data swapping unit; and a transmission unit that transmits the multiplexed signal generated by the multiplexing unit.

[0009] One aspect of the present invention is a receiver comprising: a receiving unit that receives a multiplexed signal obtained by multiplexing modulated signals of different modes transmitted from a transmitter; a separation unit that separates the multiplexed signal received by the receiving unit into modulated signals of each mode; a data swapping unit that swaps the positive and negative signs of the signals of modes other than mode 0 in the modulated signals of each mode separated by the separation unit; and a demodulation unit that demodulates the modulated signals of different modes that have been processed by the data swapping unit.

[0010] One aspect of the present invention is a wireless communication method performed by a wireless communication system comprising a transmitter and a receiver that perform OAM (Orbital Angular Momentum) multiplex transmission, wherein the transmitter generates modulated signals of different modes, multiplexes the generated modulated signals of different modes to generate a multiplexed signal, transmits the generated multiplexed signal, the receiver receives the multiplexed signal transmitted from the transmitter, separates the received multiplexed signal into modulated signals of each mode, demodulates the separated modulated signals of each mode, and at least one of the transmitter or the receiver reverses the positive and negative signs of the signals of modes other than mode 0.

[0011] This invention makes it possible to correctly receive data even when communicating using OAM waves reflected by reflective objects such as walls or reflectors.

[0012] This is a diagram showing an example configuration of a wireless communication system according to the present invention. This is a diagram showing an example configuration of a transmitter in the first embodiment. This is a diagram for explaining the processing by the data exchange unit in the first embodiment. This is a diagram showing an example configuration of a receiver in the first embodiment. This is a sequence diagram showing the processing flow of the wireless communication system in the first embodiment. This is a diagram showing an example configuration of a transmitter in the second embodiment. This is a diagram showing an example configuration of a receiver in the second embodiment. This is a sequence diagram showing the processing flow of the wireless communication system in the second embodiment. This is a diagram showing an example configuration of a transmitter in the third embodiment. This is a diagram showing an example configuration of a receiver in the third embodiment. This is a sequence diagram showing the processing flow of the wireless communication system in the third embodiment. This is a diagram showing an example configuration of a transmitter in the fourth embodiment. This is a diagram showing an example configuration of a receiver in the fourth embodiment. This is a sequence diagram showing the processing flow of the wireless communication system in the fourth embodiment. This is a diagram showing an example configuration of a transmitter in the fifth embodiment. This is a diagram showing an example configuration of a receiver in the fifth embodiment. This is a sequence diagram showing the processing flow of the wireless communication system in the fifth embodiment. This is a diagram showing an example configuration of a transmitter in the sixth embodiment. This is a diagram showing an example configuration of a receiver in the sixth embodiment. This is a sequence diagram showing the processing flow of the wireless communication system in the sixth embodiment. This is a diagram showing an example configuration of a transmitter in the seventh embodiment. This is a diagram showing an example configuration of a receiver in the seventh embodiment. This is a sequence diagram showing the processing flow of the wireless communication system in the seventh embodiment. This figure shows an example of the transmitter configuration in the eighth embodiment. This is a sequence diagram showing the processing flow of the wireless communication system in the eighth embodiment. This figure shows another example of a method for modifying the interleaver that rearranges the data for each OAM mode. This figure shows another example of a method for modifying the interleaver that rearranges the data for each OAM mode.

[0013] One embodiment of the present invention will be described below with reference to the drawings.

[0014] (System Configuration) Figure 1 shows an example of the configuration of the wireless communication system 100 according to the present invention. The wireless communication system 100 comprises a transmitter 10 and a receiver 20. OAM multiplex transmission is performed between the transmitter 10 and the receiver 20. The transmitter 10 emits an OAM multiplexed signal as a radio wave, which is obtained by multiplexing radio waves (OAM waves) having OAM modes L (L = 0, ±1, ±2, ±3, ...). In the following description, the OAM mode may also be simply referred to as "mode". The receiver 20 receives the OAM multiplexed signal transmitted from the transmitter 10.

[0015] In each embodiment described below, at least one of the transmitter 10 or receiver 20 is provided with a data swapping unit that swaps the positive and negative signs of the transmission data for modes ± n, where n is a natural number. Swapping the positive and negative signs of the transmission data for modes ± n means, for example, swapping the transmission data for mode + 1 with the transmission data for mode - 1. In other words, the transmitting side swaps the positive and negative data of the mode of the signals for each OAM mode, and the receiving side separates the received signal into signals for each OAM mode and then swaps the positive and negative data of the mode. Hereinafter, the swapping of the positive and negative signs of the transmission data by modes ± n performed by the data swapping unit will be simply referred to as swapping positive and negative signs. The embodiments will be described in detail below using each embodiment as an example.

[0016] (First Embodiment) In the first embodiment, the installer of the transmitter 10 and receiver 20 determines whether or not it is necessary to reverse the positive and negative polarity in the transmitter 10, based on installation conditions such as the installation location of the transmitter 10 and receiver 20 and the surrounding environment of the installation location. If there are reflective objects such as walls or reflectors in the communication path between the transmitter 10 and the receiver 20, it is assumed that the OAM multiplexed signal transmitted from the transmitter 10 will be reflected by the reflective object and reach the receiver 20. In such a case, the rotation direction of the phase of the OAM waves of each mode included in the OAM multiplexed signal may be reversed, and the receiver 20 may not be able to receive the data correctly.

[0017] Therefore, the installer determines that, based on the installation conditions, it is expected that the OAM multiplexed signal will be reflected by a reflective object and reach the receiver 20 (for example, when transmitting the OAM multiplexed signal to the receiver 20 using reflection), and that a reversal of positive and negative values ​​is necessary in the transmitter 10. On the other hand, the installer determines that, based on the installation conditions, it is not expected that the OAM multiplexed signal will be reflected by a reflective object and reach the receiver 20 (for example, when transmitting the OAM multiplexed signal to the receiver 20 without using reflection), and that a reversal of positive and negative values ​​is not necessary in the transmitter 10. If the installer determines that a reversal of positive and negative values ​​is necessary, they input an instruction to the transmitter 10 indicating that a reversal of positive and negative values ​​of the OAM mode is necessary (hereinafter referred to as the "reversal instruction").

[0018] Furthermore, if the installer determines that reversing the positive and negative terminals of the OAM mode is unnecessary, they input an instruction to the transmitter 10 indicating that reversing the positive and negative terminals of the OAM mode is unnecessary (hereinafter referred to as the "no reversal instruction"). Although this configuration shows that the instruction is input to the transmitter 10 in both cases, whether reversing the positive and negative terminals of the OAM mode is necessary or not, the installer may input the instruction to the transmitter 10 only if they determine that reversing the positive and negative terminals of the OAM mode is necessary.

[0019] The transmitter 10 determines whether or not it is necessary to reverse the positive and negative signs of the OAM mode according to the input instruction. If the input instruction is a reversal instruction, the transmitter 10 determines that it is necessary to reverse the positive and negative signs of the OAM mode. On the other hand, if the input instruction is a no-reversal instruction, or if no instruction is input when transmitting data, the transmitter 10 determines that it is not necessary to reverse the positive and negative signs of the OAM mode.

[0020] If the transmitter 10 needs to reverse the positive and negative signs of the OAM mode, it reverses the positive and negative signs of the signals of modes other than mode 0. Transmitter 10, for example, reverses the signal of mode 1 with the signal of mode -1. Transmitter 10, for example, reverses the signal of mode -1 with the signal of mode 1.

[0021] (Configuration of Transmitter 10) Fig. 2 is a diagram showing a configuration example of the transmitter 10 in the first embodiment. The transmitter 10 includes a modulation unit 11, a mode switching control unit 12, a data switching unit 13, a multiplexing unit 14, a frequency conversion unit 15, and a UCA 16.

[0022] The modulation unit 11 modulates the input data to be transmitted and generates modulation signals of different modes. It is assumed that which mode of modulation signal the modulation unit 11 generates is preset.

[0023] The mode switching control unit 12 controls the swapping of the positive and negative of the modulation signals of different modes input to the data switching unit 13 according to the input instruction. Specifically, when it is necessary to swap the positive and negative of the OAM mode, the mode switching control unit 12 controls the data switching unit 13 to swap the positive and negative of the modulation signals of different modes input to the data switching unit 13.

[0024] The data switching unit 13 swaps the positive and negative of the input modulation signals of different modes according to the control of the mode switching control unit 12. Specifically, the data switching unit 13 swaps the positive and negative of the modulation signals of the ±n-th mode where n is a natural number. That is, the data switching unit 13 does not perform any special processing on the modulation signal of mode 0. Also, when it is not necessary to swap the positive and negative of the OAM mode, the data switching unit 13 outputs the input modulation signals of different modes to the multiplexing unit 14 as they are.

[0025] The multiplexing unit 14 multiplexes the modulation signals of different modes output from the data switching unit 13. Thereby, the multiplexing unit 14 generates an OAM multiplex signal.

[0026] The frequency conversion unit 15 converts the frequency of the OAM multiplex signal generated by the multiplexing unit 14. For example, the frequency conversion unit 15 converts the frequency of the OAM multiplex signal to a frequency in the RF (Radio Frequency) band.

[0027] UCA16 is an antenna in which a plurality of antenna elements are arranged in an annular shape. For example, UCA16 includes L antenna elements. Thereby, UCA16 can handle up to L modes. UCA16 radiates the OAM multiplex signal frequency-converted by the frequency conversion unit 15 into space.

[0028] FIG. 3 is a diagram for explaining the processing by the data replacement unit 13 in the first embodiment. As shown in FIG. 3, when it is necessary to swap the positive and negative of the OAM mode, the data replacement unit 13 outputs to the multiplexing unit 14 after swapping the positive and negative of the modulation signals other than mode 0 output from the modulation unit 11.

[0029] (Configuration of Receiver 20) FIG. 4 is a diagram showing a configuration example of the receiver 20 in the first embodiment. The receiver 20 includes a UCA21, a frequency conversion unit 22, a separation unit 23, and a data demodulation unit 24.

[0030] UCA21 is an antenna in which a plurality of antenna elements are arranged in an annular shape. For example, UCA21 includes L antenna elements. Thereby, UCA21 can handle up to L modes. UCA21 receives the OAM multiplex signal radiated from the transmitter 10.

[0031] The frequency conversion unit 22 converts the frequency of the OAM multiplex signal received by the UCA21. For example, the frequency conversion unit 22 converts the frequency of the OAM multiplex signal to the frequency of the baseband band.

[0032] The separation unit 23 separates the modulation signals of each mode from the OAM multiplex signal frequency-converted by the frequency conversion unit 22.

[0033] The data demodulation unit 24 demodulates the modulation signals of each mode separated by the separation unit 23. Thereby, the data demodulation unit 24 restores the plurality of transmission data included in the OAM multiplex signal.

[0034] Figure 5 is a sequence diagram showing the processing flow of the wireless communication system 100 in the first embodiment. Note that at the start of processing in Figure 5, the installer is assumed to have input one of the instructions to the transmitter 10. The modulation unit 11 of the transmitter 10 modulates the input data to be transmitted and generates modulated signals of different modes (step S101). Here, for example, suppose the modulation unit 11 generates modulated signals from mode 0 to mode +3 (L = +3) (modulated signals of modes 0, +1, +2, and +3). The modulation unit 11 outputs the generated modulated signals from mode 0 to mode +3 to the data swapping unit 13.

[0035] The mode swapping control unit 12 determines whether or not it is necessary to swap the positive and negative signs of the OAM mode in response to instructions input by the installer (step S102). If the mode swapping control unit 12 determines that it is necessary to swap the positive and negative signs of the OAM mode (step S102-YES), the mode swapping control unit 12 controls the data swapping unit 13 to swap the positive and negative signs of the modulated signals of different modes input to the data swapping unit 13.

[0036] The data swapping unit 13 swaps the positive and negative signs of the input modulated signals of different modes according to the control of the mode swapping control unit 12 (step S103). The data swapping unit 13 receives modulated signals from mode 0 to mode +3. The data swapping unit 13 then swaps the positive and negative signs of the modulated signals of mode +1, mode +2, and mode +3 from the input modulated signals of mode 0 to mode +3. As a result, the data swapping unit 13 generates modulated signals of mode -1, mode -2, and mode -3. The data swapping unit 13 outputs the modulated signal of mode 0 and the modulated signals of modes -1 to mode -3 to the multiplexing unit 14.

[0037] In step S102, if the mode swapping control unit 12 determines that it is not necessary to swap the positive and negative values ​​of the OAM mode (step S102-NO), the mode swapping control unit 12 does not perform any control on the data swapping unit 13. In other words, the modulated signals of different modes input to the data swapping unit 13 are output directly to the multiplexing unit 14.

[0038] The multiplexing unit 14 multiplexes the mode 0 modulated signal output from the data swapping unit 13 with the mode-1 to mode-3 modulated signals. This generates an OAM multiplexed signal (step S104). The multiplexing unit 14 outputs the generated OAM multiplexed signal to the frequency conversion unit 15. The frequency conversion unit 15 converts the frequency of the OAM multiplexed signal generated by the multiplexing unit 14 and outputs it to the UCA 16. The UCA 16 radiates the frequency-converted OAM multiplexed signal into space (step S105).

[0039] The receiver 20's UCA 21 receives the OAM multiplexed signal radiated from the transmitter 10. The receiver 20 performs reception processing on the OAM multiplexed signal received by the UCA 21 (step S106). Here, reception processing includes frequency conversion, mode separation, and demodulation processing performed by at least the frequency conversion unit 22, the separation unit 23, and the data demodulation unit 24.

[0040] According to the wireless communication system 100 configured as described above, the transmitter 10 includes a modulation unit 11 that generates modulated signals of different modes, a data swapping unit 13 that swaps the positive and negative signs of signals of modes other than mode 0 when it is necessary to swap the positive and negative signs of signals of modes other than mode 0 depending on the installation conditions, a multiplexing unit 14 that generates a multiplexed signal by multiplexing the modulated signals of different modes processed by the data swapping unit 13, and a UCA 16 that transmits the multiplexed signal. The receiver 20 includes a UCA 21 that receives the multiplexed signal transmitted from the transmitter 10, a separation unit 23 that separates the received multiplexed signal into modulated signals of each mode, and a data demodulation unit 24 that demodulates the separated modulated signals of each mode.

[0041] In this way, the installer can determine in advance whether or not it is expected that the OAM multiplexed signal will be transmitted by reflection from a reflective object, depending on the installation conditions of the transmitter 10 and receiver 20. If it is expected that the OAM multiplexed signal will be transmitted by reflection from a reflective object, the transmitter 10 is operated to reverse the positive and negative signs of the signals for modes other than mode 0. As a result, even when communicating using OAM waves reflected from reflective objects such as walls or reflectors, it becomes possible to receive data correctly.

[0042] (Variation) The installer may determine whether or not it is necessary to reverse the positive and negative signs of the OAM mode in the transmitter 10 depending on the number of reflectors. Since the direction of phase rotation of the OAM wave reflected by a reflector is reversed, if the number of reflectors between the transmitter 10 and the receiver 20 is even, it is possible that the direction of phase rotation of the OAM wave of each mode transmitted from the transmitter 10 and the direction of phase rotation of the OAM wave of each mode received by the receiver 20 will be the same. Therefore, the installer may determine that it is not necessary to reverse the positive and negative signs of the OAM mode in the transmitter 10 if the number of reflectors is even. On the other hand, the installer may determine that it is necessary to reverse the positive and negative signs of the OAM mode in the transmitter 10 if the number of reflectors is odd.

[0043] (Second Embodiment) In the first embodiment, the installer determined whether or not it was necessary to reverse the positive and negative OAM modes in the transmitter based on installation conditions such as the installation location of the device and the surrounding environment of the installation location. In the second embodiment, the installer determined whether or not it was necessary to reverse the positive and negative OAM modes based on the same criteria as in the first embodiment, notified the receiver of the need to reverse the modes using a mode 0 signal, and described a configuration in which the receiver reverses the positive and negative modes as necessary.

[0044] The wireless communication system 100 in the second embodiment includes a transmitter 10a and a receiver 20a. In the second embodiment, the receiver 20a includes a data exchange unit.

[0045] (Configuration of Transmitter 10a) Figure 6 shows an example of the configuration of transmitter 10a in the second embodiment. Transmitter 10a includes a modulation unit 11, a mode switching control unit 12a, a data switching unit 13, a multiplexing unit 14, a frequency conversion unit 15, and a UCA 16. Transmitter 10a differs from transmitter 10 in that it includes a mode switching control unit 12a instead of a mode switching control unit 12, and does not include a data switching unit 13.

[0046] The mode swapping control unit 12a controls the mode swapping of modulated signals of different modes according to the input instruction. Specifically, if it is necessary to swap the positive and negative signs of the OAM modes, the mode swapping control unit 12a controls the modulation unit 11 to insert swapping information into the mode 0 signal. This controls the receiving side of the OAM multiplexed signal to swap the positive and negative signs of modulated signals of different modes. On the other hand, if it is not necessary to swap the positive and negative signs of the OAM modes, the mode swapping control unit 12a does not perform any special processing.

[0047] The modulation unit 11 modulates the input data to be transmitted to generate modulated signals of different modes. The modulation unit 11 generates a modulated signal of mode 0 that includes swapping information in response to control from the mode swapping control unit 12a.

[0048] (Configuration of receiver 20a) Figure 7 shows an example of the configuration of receiver 20a in the second embodiment. Receiver 20a includes a UCA 21, a frequency conversion unit 22, a separation unit 23a, a data demodulation unit 24a, a mode switching control unit 25, and a data switching unit 26. Receiver 20a differs from receiver 20 in that it replaces the separation unit 23 and data demodulation unit 24 with a separation unit 23a and a data demodulation unit 24a, and newly includes a mode switching control unit 25 and a data switching unit 26.

[0049] The separation unit 23a separates the modulated signals of each mode from the OAM multiplexed signal whose frequency has been converted by the frequency conversion unit 22. Of the separated modulated signals of each mode, the separation unit 23a outputs the modulated signal of mode 0 to the data demodulation unit 24a.

[0050] The data demodulation unit 24a demodulates the modulated signals of each mode separated by the separation unit 23a. Specifically, the data demodulation unit 24a first demodulates the modulated signal of mode 0 output from the separation unit 23a. As a result, if the modulated signal of mode 0 contains swapping information, the data demodulation unit 24a restores the swapping information contained in the modulated signal. The data demodulation unit 24a then outputs the restored swapping information to the mode swapping control unit 25. The data demodulation unit 24a also demodulates the modulated signals of each mode output from the data swapping unit 26. As a result, the data demodulation unit 24a restores the multiple transmission data that was contained in the OAM multiplexed signal.

[0051] The mode swapping control unit 25 controls the mode swapping of modulated signals of different modes input to the data swapping unit 26. Specifically, if swapping information is obtained from the data demodulation unit 24a, the mode swapping control unit 25 determines that it is necessary to swap the positive and negative signs of the OAM mode. In this case, the mode swapping control unit 25 controls the data swapping unit 26 to swap the positive and negative signs of modulated signals of different modes input to the data swapping unit 26. However, if nothing is obtained from the data demodulation unit 24a, the mode swapping control unit 25 does not control the data swapping unit 26. That is, it does not cause the data swapping unit 26 to swap the positive and negative signs of modulated signals of different modes.

[0052] The data swapping unit 26 swaps the positive and negative signs of the input modulated signals of different modes in accordance with the control of the mode swapping control unit 25. Specifically, the data swapping unit 26 swaps the positive and negative signs of the ±nth order modulated signals. Furthermore, if swapping the positive and negative signs of the OAM mode is not necessary (for example, if there is no instruction from the mode swapping control unit 25), the data swapping unit 26 outputs the input modulated signals of different modes as they are to the data demodulation unit 24a.

[0053] Figure 8 is a sequence diagram showing the processing flow of the wireless communication system 100 in the second embodiment. Note that at the start of processing in Figure 8, the installer is assumed to have input one of the instructions to the transmitter 10a. The mode swapping control unit 12a of the transmitter 10a determines whether or not it is necessary to swap the positive and negative values ​​of the OAM mode in response to the instruction input from the installer (step S201). If the mode swapping control unit 12a determines that it is necessary to swap the positive and negative values ​​of the OAM mode (step S201-YES), the mode swapping control unit 12a controls the modulation unit 11 to insert the swapping information into the mode 0 signal (step S202).

[0054] As a result, the modulation unit 11 modulates the input data to be transmitted and generates modulated signals of different modes. At this time, the modulation unit 11 generates a modulated signal of mode 0 that includes swapping information in response to control from the mode swapping control unit 12a. Here, for example, suppose the modulation unit 11 generates a modulated signal from mode 0 to mode +3 (L = +3) (modulated signals of modes 0, +1, +2, and +3). The modulation unit 11 outputs the generated modulated signals from mode 0 to mode +3 to the multiplexing unit 14.

[0055] Furthermore, in the process of step S201, if the mode swapping control unit 12a determines that it is not necessary to swap the positive and negative values ​​of the OAM mode (step S201-NO), the modulation unit 11 modulates the input data to be transmitted and outputs a modulated signal of a different mode to the multiplexing unit 14. In this case, the modulated signal of mode 0 does not include swapping information.

[0056] The multiplexing unit 14 multiplexes the modulated signals from mode 0 to mode +3 output from the modulation unit 11. This generates an OAM multiplexed signal (step S203). The multiplexing unit 14 outputs the generated OAM multiplexed signal to the frequency conversion unit 15. The frequency conversion unit 15 converts the frequency of the OAM multiplexed signal generated by the multiplexing unit 14 and outputs it to the UCA 16. The UCA 16 radiates the frequency-converted OAM multiplexed signal into space (step S204).

[0057] The UCA 21 of the receiver 20a receives the OAM multiplexed signal radiated from the transmitter 10a. The frequency conversion unit 22 converts the frequency of the OAM multiplexed signal received by the UCA 21 and outputs it to the separation unit 23a. The separation unit 23a separates the modulated signals of each mode from the OAM multiplexed signal whose frequency has been converted by the frequency conversion unit 22. Of the separated modulated signals of each mode, the separation unit 23a outputs the modulated signals of all modes except mode 0 to the data swapping unit 26 and outputs the modulated signal of mode 0 to the data demodulation unit 24a.

[0058] If the OAM multiplexed signal transmitted from transmitter 10a is reflected by a reflector, the phase rotation of the modulation signals other than mode 0 included in the OAM multiplexed signal (for example, modulation signals from mode +1 to mode +3) may be reversed.

[0059] The data demodulation unit 24a demodulates the mode 0 modulated signal output from the separation unit 23a (step S205). If swapping information is obtained from the mode 0 modulated signal through demodulation, the data demodulation unit 24a outputs the obtained swapping information to the mode swapping control unit 25. The mode swapping control unit 25 determines whether or not it is necessary to swap the positive and negative signs of the OAM modes (step S206). If the mode swapping control unit 25 determines that it is necessary to swap the positive and negative signs of the OAM modes (step S206-YES), the mode swapping control unit 25 controls the data swapping unit 26 to swap the positive and negative signs of the modulated signals of different modes input to the data swapping unit 26.

[0060] The need to reverse the positive and negative signs of the OAM modes means that the phase rotation of modulated signals other than mode 0 (for example, modulated signals from mode +1 to mode +3) included in the received OAM multiplexed signal may be inverted. In other words, modulated signals other than mode 0 may be modulated signals from mode -1 to mode -3. In this case, the receiver 20a may not be able to correctly reconstruct the data.

[0061] The data swapping unit 26 swaps the positive and negative signs of the input modulated signals of different modes according to the control of the mode swapping control unit 25 (step S207). As a result, the data swapping unit 26 generates modulated signals of different modes with the positive and negative signs swapped. The data swapping unit 26 outputs the generated modulated signals of different modes with the positive and negative signs swapped to the data demodulation unit 24a.

[0062] In step S206, if the mode swapping control unit 25 determines that it is not necessary to swap the positive and negative values ​​of the OAM mode (step S206-NO), the mode swapping control unit 25 does not control the data swapping unit 26. That is, the modulated signals of different modes input to the data swapping unit 26 are output directly to the data demodulation unit 24a. The data demodulation unit 24a demodulates the modulated signals of different modes output from the data swapping unit 26 (step S208).

[0063] According to the wireless communication system 100 in the second embodiment configured as described above, the installer can determine in advance whether or not it is expected that the OAM multiplexed signal will be transmitted by reflection from a reflective object, depending on the installation conditions of the transmitter 10a and the receiver 20a. If it is expected that the OAM multiplexed signal will be transmitted by reflection from a reflective object, the transmitter 10a transmits a mode 0 signal that includes information instructing mode reversal. This allows the receiver 20a to determine whether or not it is necessary to reverse the positive and negative signs of signals in modes other than mode 0. The receiver 20a then reverses the positive and negative signs of signals in modes other than mode 0 if necessary, and then demodulates the data. Therefore, even when communicating using OAM waves reflected from reflective objects such as walls or reflectors, it becomes possible to receive data correctly.

[0064] (Third Embodiment) In the third embodiment, the transmitter uses a Mode 0 signal to notify the receiver of information indicating the transmitted OAM mode (information indicating either a positive OAM mode or a negative OAM mode), the receiver measures the power of all OAM mode signals, and uses the power values ​​of the positive and negative received OAM modes and the transmitted OAM mode notified by Mode 0 to determine whether or not to swap the data of the positive and negative received OAM modes.

[0065] The wireless communication system 100 in the third embodiment includes a transmitter 10b and a receiver 20b. In the third embodiment, the receiver 20b includes a data exchange unit.

[0066] (Configuration of Transmitter 10b) Figure 9 shows an example of the configuration of transmitter 10b in the third embodiment. Transmitter 10b comprises a modulation unit 11b, a multiplexing unit 14, a frequency conversion unit 15, and a UCA 16. Transmitter 10b differs from transmitter 10 in that it has a modulation unit 11b instead of a modulation unit 11, and does not have a mode switching control unit 12 and a data switching unit 13.

[0067] The modulation unit 11b modulates the input data to be transmitted to generate modulated signals of different modes. In this process, the modulation unit 11b generates modulated signals of either a preset positive mode or a preset negative mode. That is, the modulation unit 11b generates modulated signals of either a positive mode (+1, +2, +3, ...) or a negative mode (-1, -2, -3, ...). Furthermore, the modulation unit 11 inserts mode information (ON mode information) indicating whether the transmission was made in a positive or negative mode into the signal to be transmitted in mode 0, thereby generating a modulated signal of mode 0.

[0068] (Configuration of receiver 20b) Figure 10 shows an example of the configuration of receiver 20b in the third embodiment. Receiver 20b includes a UCA 21, a frequency conversion unit 22, a separation unit 23b, a data demodulation unit 24b, a mode switching control unit 25b, and a data switching unit 26. Receiver 20b differs from receiver 20 in that it includes a separation unit 23b and a data demodulation unit 24b instead of the separation unit 23 and data demodulation unit 24, and newly includes a mode switching control unit 25b and a data switching unit 26.

[0069] The separation unit 23b separates the modulated signals of each mode from the OAM multiplexed signal whose frequency has been converted by the frequency conversion unit 22. The separation unit 23b outputs the separated modulated signal of mode 0 to the data demodulation unit 24b, outputs the modulated signals of each mode to the mode swapping control unit 25b, and outputs the modulated signals of modes other than mode 0 to the data swapping unit 26.

[0070] The data demodulation unit 24b demodulates the mode 0 modulated signal output from the separation unit 23b. This allows the data demodulation unit 24b to acquire the mode information contained in the mode 0 modulated signal. Furthermore, the data demodulation unit 24b demodulates the modulated signals of each mode output from the data swapping unit 26.

[0071] The mode swapping control unit 25b controls the operation of the data swapping unit 26 based on the modulated signals of each mode output from the separation unit 23b and the mode information output from the data demodulation unit 24b. Specifically, first the mode swapping control unit 25b calculates the received power of the modulated signals of each mode output from the separation unit 23b. Next, the mode swapping control unit 25b calculates the sum of the received powers of the positive modes and the sum of the received powers of the negative modes. Then, the mode swapping control unit 25b determines that it is not necessary to swap the positive and negative signs of the modulated signals of different modes input to the data swapping unit 26 if the mode with the highest sum of received power matches the mode indicated by the mode information.

[0072] On the other hand, the mode swapping control unit 25b determines that if the mode with the highest total received power does not match the mode indicated by the mode information, it is necessary to swap the positive and negative signs of the modulation signals of different modes input to the data swapping unit 26.

[0073] The data swapping unit 26 swaps the positive and negative polarity of the input modulation signals of different modes in accordance with the control of the mode swapping control unit 25b.

[0074] Figure 11 is a sequence diagram showing the processing flow of the wireless communication system 100 in the third embodiment. At the start of processing in Figure 11, the transmission mode of the transmitter 10b (either a positive mode or a negative mode) is set.

[0075] The modulation unit 11b generates a modulation signal in either the positive or negative mode installed in its device, and also includes mode information I in the signal to be transmitted in mode 0. Ｍ The modulator 11b inserts a signal to generate a modulated signal for mode 0 (step S301). The modulator 11b outputs the generated modulated signals for each mode to the multiplexer 14. The multiplexer 14 multiplexes the modulated signals for each mode output from the modulator 11b to generate an OAM multiplexed signal (step S302). The transmitter 10b then performs frequency conversion on the OAM multiplexed signal and radiates it into space via the UCA 16 (step S303).

[0076] The UCA 21 of the receiver 20b receives the OAM multiplexed signal radiated from the transmitter 10b. The frequency conversion unit 22 converts the frequency of the OAM multiplexed signal received by the UCA 21 and outputs it to the separation unit 23b. The separation unit 23b outputs the separated mode 0 modulated signal to the data demodulation unit 24b, outputs the modulated signals of each mode to the mode swapping control unit 25b, and outputs the modulated signals of modes other than mode 0 to the data swapping unit 26.

[0077] The data demodulation unit 24b demodulates the mode 0 modulated signal output from the separation unit 23b (step S304). The data demodulation unit 24b obtains mode information I by demodulating the mode 0 modulated signal. Ｍ The signal is output to the mode switching control unit 25b. The mode switching control unit 25b calculates the received power of the modulated signals for each mode output from the separation unit 23b (step S305). Next, the mode switching control unit 25b calculates the sum P of the received powers of the positive modes. ｒ ＋ And the sum of the received powers in the negative mode P ｒ － Calculate the result.

[0078] The mode switching control unit 25b calculates the total received power P of the positive modes ｒ ＋ and determines whether it is greater than the total received power P of the negative modes ｒ － (P ｒ ＋ > P ｒ － ) (step S306). If the mode switching control unit 25b determines that P ｒ ＋ > P ｒ － (step S306 - YES), the mode switching control unit 25b determines whether the mode information I obtained from the data demodulation unit 24b indicates a negative mode (in FIG. 11, it is shown as "-1") (step S307).

[0079] If the mode switching control unit 25b determines that the mode information I obtained from the data demodulation unit 24b indicates a negative mode (step S307 - YES), the mode switching control unit 25b determines that it is necessary to swap the positive and negative of the modulation signals of different modes input to the data swapping unit 26.

[0080] The reason is as follows. That the mode information I Ｍ indicates a negative mode means that the transmitter 10b transmitted a signal in the negative mode. In this case, the positive mode does not contain data, and the negative mode contains data. Therefore, originally, the total received power P of the negative modes ｒ － should be higher than the total received power P of the positive modes ｒ ＋ . Thus, when there is a contradiction between the mode indicated by the mode information I Ｍ and the total received power, it is highly likely that the signal was reflected by a reflector in the space between the transmitter 10b and the receiver 20b. Therefore, in order to correctly demodulate the data in the receiver 20b, it is necessary to swap the positive and negative of the modulation signals of different modes input to the data swapping unit 26.​​​​

[0081] Therefore, the mode swapping control unit 25b controls the data swapping unit 26 to swap the positive and negative signs of the different mode modulated signals input to the data swapping unit 26. The data swapping unit 26 swaps the positive and negative signs of the different mode modulated signals that have been input to the data swapping unit 26 according to the control of the mode swapping control unit 25b (step S308). As a result, the data swapping unit 26 generates a different mode modulated signal with the positive and negative signs swapped. The data swapping unit 26 outputs the generated different mode modulated signal with the positive and negative signs swapped to the data demodulation unit 24b.

[0082] The data demodulation unit 24b demodulates the modulated signals of different modes output from the data swapping unit 26 (step S309). In the process of step S307, the mode swapping control unit 25b receives the mode information I obtained from the data demodulation unit 24b. Ｍ If it is determined that the signal does not indicate a negative mode (step S307-NO), the mode swapping control unit 25b determines that it is not necessary to swap the positive and negative signs of the modulated signals of different modes input to the data swapping unit 26. In this case, the mode swapping control unit 25b does not perform any control on the data swapping unit 26. That is, the modulated signals of different modes input to the data swapping unit 26 are output directly to the data demodulation unit 24b. The data demodulation unit 24b demodulates the modulated signals of different modes output from the data swapping unit 26 (step S309).

[0083] Furthermore, in the process of step S306, the mode switching control unit 25b, ｒ ＋ >P ｒ － If it is determined that this is not the case (step S306-NO), the mode switching control unit 25b receives the mode information I obtained from the data demodulation unit 24b. Ｍ It is determined whether or not this indicates a positive mode (shown as "1" in Figure 11) (step S310).

[0084] The mode switching control unit 25b receives mode information I from the data demodulation unit 24b. ＭIf it is determined that the signal is in a positive mode (step S310-YES), the mode swapping control unit 25b determines that it is necessary to swap the positive and negative signs of the modulated signals of different modes input to the data swapping unit 26. The mode swapping control unit 25b controls the data swapping unit 26 to swap the positive and negative signs of the modulated signals of different modes input to the data swapping unit 26. The data swapping unit 26 swaps the positive and negative signs of the input modulated signals of different modes according to the control of the mode swapping control unit 25b (step S308). As a result, the data swapping unit 26 generates a modulated signal of a different mode with the positive and negative signs swapped. The data swapping unit 26 outputs the generated modulated signal of a different mode with the positive and negative signs swapped to the data demodulation unit 24b.

[0085] The data demodulation unit 24b demodulates the modulated signals of different modes output from the data swapping unit 26 (step S309). In the process of step S310, the mode swapping control unit 25b receives the mode information I obtained from the data demodulation unit 24b. Ｍ If it is determined that the signal does not indicate a positive mode (step S310-NO), the mode swapping control unit 25b determines that it is not necessary to swap the positive and negative signs of the modulated signals of different modes input to the data swapping unit 26. In this case, the mode swapping control unit 25b does not perform any control on the data swapping unit 26. That is, the modulated signals of different modes input to the data swapping unit 26 are output directly to the data demodulation unit 24b. The data demodulation unit 24b demodulates the modulated signals of different modes output from the data swapping unit 26 (step S309).

[0086] According to the wireless communication system 100 in the third embodiment configured as described above, the receiver 20b determines whether to swap the positive and negative signs of signals for modes other than mode 0 based on the relationship between the mode information transmitted by the transmitter 10b and the sum of the received powers of the positive and negative modes. For example, the receiver 20b determines that it is not necessary to swap the positive and negative signs of signals for modes other than mode 0 if the mode indicated by the mode information transmitted by the transmitter 10b matches the mode with the highest sum of received powers, and determines that it is not necessary to swap the positive and negative signs of signals for modes other than mode 0 if the mode indicated by the mode information transmitted by the transmitter 10b does not match the mode with the highest sum of received powers. As a result, the receiver 20b can swap the positive and negative signs of signals for modes other than mode 0 when it is necessary. Therefore, even when communicating using OAM waves reflected by reflective objects such as walls and reflectors, it becomes possible to receive data correctly.

[0087] (Fourth Embodiment) In the fourth embodiment, the transmitter inserts index information that can identify the OAM mode (for example, information indicating modes 0, +1, -1, +2, -2, ...) into the preamble signal transmitted in each OAM mode and transmits it. The receiver compares the index information of a specific mode contained in the demodulated preamble signal with the received OAM mode, and if the signs are reversed, it swaps the positive and negative data of the received OAM mode.

[0088] The wireless communication system 100 in the fourth embodiment includes a transmitter 10c and a receiver 20c. In the fourth embodiment, the receiver 20c includes a data exchange unit.

[0089] (Configuration of Transmitter 10c) Figure 12 shows an example of the configuration of transmitter 10c in the fourth embodiment. Transmitter 10c comprises a modulation unit 11c, a multiplexing unit 14, a frequency conversion unit 15, and a UCA 16. Transmitter 10c differs from transmitter 10 in that it has a modulation unit 11c instead of a modulation unit 11, and does not have a mode switching control unit 12 and a data switching unit 13.

[0090] The modulation unit 11c modulates the input data to be transmitted to generate modulated signals of different modes. When generating modulated signals for each mode, the modulation unit 11c inserts index information that identifies the OAM mode (for example, information indicating mode 0, +1, -1, +2, -2, ...) into the preamble signal transmitted in each OAM mode. For example, the modulation unit 11c inserts index information indicating mode 0 into the preamble signal transmitted in mode 0 to generate a modulated signal for mode 0. In this way, the modulation unit 11c generates modulated signals for each mode that include index information.

[0091] (Configuration of receiver 20c) Figure 13 shows an example of the configuration of receiver 20c in the fourth embodiment. Receiver 20c comprises a UCA 21, a frequency conversion unit 22, a separation unit 23c, a data demodulation unit 24c, a mode switching control unit 25c, and a data switching unit 26. Receiver 20c differs from receiver 20 in that it replaces the separation unit 23 and data demodulation unit 24 with a separation unit 23c and a data demodulation unit 24c, and newly includes a mode switching control unit 25c and a data switching unit 26.

[0092] The separation unit 23c separates the modulated signals of each mode (modulated signals of all modes included in the OAM multiplexed signal) from the OAM multiplexed signal whose frequency has been converted by the frequency conversion unit 22. The separation unit 23c outputs the separated modulated signals of each mode (modulated signals of all modes included in the OAM multiplexed signal) to the data demodulation unit 24c and the data swapping unit 26. In other words, the separation unit 23c outputs the same modulated signal to the data demodulation unit 24c and the data swapping unit 26.

[0093] The data demodulation unit 24c demodulates the modulated signals of each mode output from the separation unit 23c. The data demodulation unit 24c obtains index information from the preamble of each mode's transmitted data after demodulation. The data demodulation unit 24c outputs the multiple index pieces of information obtained to the mode switching control unit 25c.

[0094] The mode swapping control unit 25c controls the operation of the data swapping unit 26 based on multiple index information obtained from the data demodulation unit 24c. The mode swapping control unit 25c determines whether each mode indicated by each of the multiple index information matches the OAM mode (receiving mode) received by the device. If each mode indicated by each of the multiple index information matches the OAM mode received by the device, the mode swapping control unit 25c determines that it is not necessary to swap the positive and negative signs of the modulated signals of different modes input to the data swapping unit 26. On the other hand, if each mode indicated by each of the multiple index information does not match the OAM mode received by the device, the mode swapping control unit 25c determines that it is necessary to swap the positive and negative signs of the modulated signals of different modes input to the data swapping unit 26.

[0095] The data swapping unit 26 swaps the positive and negative signs of the input modulated signals of different modes in accordance with the control of the mode swapping control unit 25c. Specifically, the data swapping unit 26d swaps the positive and negative signs of the input modulated signals of different modes when the modes indicated by each of the multiple index information do not match the OAM mode received by the device.

[0096] Figure 14 is a sequence diagram showing the processing flow of the wireless communication system 100 in the fourth embodiment. The modulation unit 11c of the transmitter 10c inserts index information into the preamble signal to be transmitted in each OAM mode to generate a modulated signal for each mode (step S401). The modulation unit 11c outputs the generated modulated signals for each mode to the multiplexing unit 14. The multiplexing unit 14 multiplexes the modulated signals for each mode output from the modulation unit 11c to generate an OAM multiplexed signal (step S402). Subsequently, the transmitter 10c performs frequency conversion on the OAM multiplexed signal and radiates it into space using the UCA 16 (step S403).

[0097] The UCA 21 of the receiver 20c receives the OAM multiplexed signal radiated from the transmitter 10c. The frequency conversion unit 22 converts the frequency of the OAM multiplexed signal received by the UCA 21 and outputs it to the separation unit 23c. The separation unit 23c separates the modulated signals of each mode from the OAM multiplexed signal whose frequency has been converted by the frequency conversion unit 22. The separation unit 23c outputs the separated modulated signals of each mode to the data demodulation unit 24c and the data swapping unit 26.

[0098] The data demodulation unit 24c demodulates the preamble portion of the modulated signal for each mode output from the separation unit 23c (step S404). The data demodulation unit 24c acquires index information from the preamble portion of the demodulated modulated signal for each mode. The data demodulation unit 24c outputs the acquired index information to the mode switching control unit 25c.

[0099] The mode swapping control unit 25c determines, based on the multiple index information output from the data demodulation unit 24c, whether each mode indicated by the multiple index information matches the OAM mode received by the device (step S405). If the mode swapping control unit 25c determines that each mode indicated by the multiple index information does not match the OAM mode received by the device (step S405-NO), the mode swapping control unit 25c controls the data swapping unit 26 to swap the positive and negative signs of the different mode modulation signals input to the data swapping unit 26.

[0100] The data swapping unit 26 swaps the positive and negative signs of the input modulated signals of different modes according to the control of the mode swapping control unit 25c (step S406). As a result, the data swapping unit 26 generates modulated signals of different modes with the positive and negative signs swapped. The data swapping unit 26 outputs the generated modulated signals of different modes with the positive and negative signs swapped to the data demodulation unit 24c.

[0101] In step S405, if the mode swapping control unit 25 determines that each mode indicated by the multiple index information matches the OAM mode received by the device (step S405-YES), the mode swapping control unit 25c does not control the data swapping unit 26. That is, the modulated signals of different modes input to the data swapping unit 26 are output directly to the data demodulation unit 24c. The data demodulation unit 24c demodulates the modulated signals of different modes output from the data swapping unit 26 (step S407).

[0102] According to the wireless communication system 100 in the fourth embodiment configured as described above, the transmitter 10c inserts index information that can identify the OAM mode (for example, information indicating mode 0, +1, -1, +2, -2, ...) into the preamble signal transmitted in each OAM mode and transmits it. The receiver 20c compares the index information of a specific mode included in the demodulated preamble signal with the received OAM mode, and if the signs are reversed, it swaps the positive and negative data of the received OAM mode. As a result, the receiver 20c can swap the positive and negative signs of signals of modes other than mode 0 when necessary. Therefore, even when communicating using OAM waves reflected by reflective objects such as walls or reflectors, it becomes possible to correctly receive the data.

[0103] (Fifth Embodiment) In the fifth embodiment, a configuration is described in which the receiver demodulates two signals, one with the positive and negative OAM mode signals swapped and one without, and uses the correctly demodulated signal as the received signal. For example, the receiver uses a CRC (Cyclic Redundancy Check) test bit or the like to determine whether the demodulation result is correct.

[0104] The wireless communication system 100 in the fifth embodiment includes a transmitter 10d and a receiver 20d. In the fifth embodiment, the receiver 20d includes a data exchange unit.

[0105] (Configuration of Transmitter 10d) Figure 15 shows an example of the configuration of transmitter 10d in the fifth embodiment. Transmitter 10d comprises a modulation unit 11, a multiplexing unit 14, a frequency conversion unit 15, and a UCA 16. Transmitter 10d differs from transmitter 10 in that it does not include a mode switching control unit 12 and a data switching unit 13. The differences will be explained below.

[0106] The modulation unit 11 modulates the input data to be transmitted to generate modulated signals of different modes. The multiplexing unit 14 multiplexes the modulated signals of different modes generated by the modulation unit 11. As a result, the multiplexing unit 14 generates an OAM multiplexed signal.

[0107] (Configuration of receiver 20d) Figure 16 shows an example of the configuration of receiver 20d in the fifth embodiment. Receiver 20d includes a UCA 21, a frequency conversion unit 22, a separation unit 23d, a data demodulation unit 24d, a mode switching control unit 25d, and a data switching unit 26d. Receiver 20d differs from receiver 20 in that it includes a separation unit 23d and a data demodulation unit 24d instead of the separation unit 23 and data demodulation unit 24, and newly includes a mode switching control unit 25d and a data switching unit 26d. The differences will be explained below.

[0108] The separation unit 23d separates the modulated signals of each mode (modulated signals of all modes included in the OAM multiplexed signal) from the OAM multiplexed signal whose frequency has been converted by the frequency conversion unit 22. The separation unit 23d outputs the separated modulated signals of each mode (modulated signals of all modes included in the OAM multiplexed signal) to the data demodulation unit 24d and the data swapping unit 26d. In other words, the separation unit 23d outputs the same modulated signal to the data demodulation unit 24d and the data swapping unit 26d.

[0109] The mode swapping control unit 25d controls the data swapping unit 26d to swap the positive and negative signs of the modulated signals of different modes input to the data swapping unit 26.

[0110] The data swapping unit 26d swaps the positive and negative signs of the input modulated signals of different modes in accordance with the control of the mode swapping control unit 25d. Specifically, the data swapping unit 26d swaps the positive and negative signs of the modulated signals of ±nth modes.

[0111] The data demodulation unit 24d demodulates the modulated signals of each mode output from the separation unit 23d and the modulated signals of each mode output from the data swapping unit 26d. Subsequently, the data demodulation unit 24d checks each demodulated result using an existing method such as a CRC check bit. For example, the data demodulation unit 24d checks the demodulation result of the modulated signals of each mode output from the separation unit 23d and the demodulation result of the modulated signals of each mode output from the data swapping unit 26d. Based on the check results, the data demodulation unit 24d acquires the demodulated result with fewer errors as the received signal.

[0112] The modulated signals for each mode output from the data swapping unit 26d are modulated signals in which the positive and negative signs of modulated signals for different modes have been swapped. Therefore, the modulated signals for each mode output from the separation unit 23d and the modulated signals for each mode output from the data swapping unit 26d have different positive and negative signs for modes other than mode 0. Consequently, when the demodulation results of the modulated signals for each mode output from either the separation unit 23d or the data swapping unit 26d are inspected, many errors occur in signals that have not been demodulated correctly. Therefore, the data demodulation unit 24d acquires the correctly demodulated signal (the demodulation result with fewer errors) as the received signal.

[0113] Figure 17 is a sequence diagram showing the processing flow of the wireless communication system 100 in the fifth embodiment. The transmitter 10d generates an OAM multiplexed signal and radiates it into space via the UCA 16 (step S501). The UCA 21 of the receiver 20d receives the OAM multiplexed signal radiated from the transmitter 10d. The frequency conversion unit 22 converts the frequency of the OAM multiplexed signal received by the UCA 21 and outputs it to the separation unit 23d. The separation unit 23d separates the modulated signals of each mode from the OAM multiplexed signal whose frequency has been converted by the frequency conversion unit 22. The separation unit 23d outputs the modulated signals of each separated mode to the data demodulation unit 24d and the data swapping unit 26.

[0114] After processing in step S503, the data demodulation unit 24d demodulates the modulated signals of each mode output from the separation unit 23d (step S504). Subsequently, the data demodulation unit 24d inspects the demodulation result (step S505). Here, if the phase of the modulated signals of each mode included in the OAM multiplexed signal received by the receiver 20d is inverted by a reflector, the data demodulation unit 24d cannot correctly demodulate the modulated signals of each mode output from the separation unit 23d. Therefore, when the demodulation result is inspected, many errors are detected. On the other hand, if the phase of the modulated signals of each mode included in the OAM multiplexed signal received by the receiver 20d is not inverted, the data demodulation unit 24d can correctly demodulate the modulated signals of each mode output from the separation unit 23d. Therefore, when the demodulation result is inspected, there are few errors (and sometimes no errors).

[0115] Furthermore, after processing in step S503, the data swapping unit 26d swaps the positive and negative signs of the input modulated signals of different modes according to the control of the mode swapping control unit 25d (step S506). As a result, the data swapping unit 26d generates modulated signals of different modes with the positive and negative signs swapped. The data swapping unit 26d outputs the generated modulated signals of different modes with the positive and negative signs swapped to the data demodulation unit 24d.

[0116] The data demodulation unit 24d demodulates the modulated signals of different modes with their positive and negative values ​​swapped, which are output from the data swapping unit 26d (step S507). After that, the data demodulation unit 24d checks the demodulation result (step S508). Here, if the phase of the modulated signals of each mode included in the OAM multiplexed signal received by the receiver 20d is inverted by a reflector, the data demodulation unit 24d can correctly demodulate the modulated signals of each mode output from the data swapping unit 26d. Therefore, when the demodulation result is checked, there are few errors (and sometimes no errors). On the other hand, if the phase of the modulated signals of each mode included in the OAM multiplexed signal received by the receiver 20d is not inverted, the data demodulation unit 24d cannot correctly demodulate the modulated signals of each mode output from the data swapping unit 26d. Therefore, when the demodulation result is checked, many errors are detected.

[0117] The data demodulation unit 24d acquires as a received signal the signal that has been correctly demodulated from among the modulated signals of different modes output from the data demodulation unit 24d and the data swapping unit 26d (step S509).

[0118] In the wireless communication system 100 of the fifth embodiment configured as described above, the receiver 20d demodulates two signals: one with the positive and negative OAM mode signals swapped and one without, and uses the correctly demodulated signal as the received signal. As a result, either signal can be demodulated. Therefore, even when communicating using OAM waves reflected by reflective objects such as walls or reflectors, it becomes possible to correctly receive data.

[0119] (Sixth Embodiment) In the sixth embodiment, a configuration is described in which a feedback function is added to the configuration shown in the third embodiment, which notifies the transmitter from the receiver that a mode change is necessary. Specifically, in the sixth embodiment, mode information I Ｍ If the mode indicated by the signal does not match the mode with the highest total received power, the receiver provides feedback to the transmitter indicating that a mode swap is necessary.

[0120] The wireless communication system 100 in the sixth embodiment includes a transmitter 10e and a receiver 20e. In the sixth embodiment, the transmitter 10e includes a data exchange unit.

[0121] (Configuration of Transmitter 10e) Figure 18 shows an example of the configuration of transmitter 10e in the sixth embodiment. Transmitter 10e comprises a modulation unit 11b, a mode switching control unit 12e, a data switching unit 13e, a multiplexing unit 14, a frequency conversion unit 15, and a UCA 16. Transmitter 10e differs from transmitter 10c in that it newly includes a mode switching control unit 12e and a data switching unit 13e. The differences will be explained below.

[0122] The mode swapping control unit 12e controls the swapping of modulated signals of different modes input to the data swapping unit 13e. For example, the mode swapping control unit 12e determines that it is necessary to swap the positive and negative signs of the OAM mode when it receives request information fed back from the receiver 20e. On the other hand, the mode swapping control unit 12e determines that it is not necessary to swap the positive and negative signs of the OAM mode when it does not receive request information fed back from the receiver 20e. When it is necessary to swap the positive and negative signs of the OAM mode, the mode swapping control unit 12e controls the data swapping unit 13e to swap the positive and negative signs of modulated signals of different modes input to the data swapping unit 13e.

[0123] The data swapping unit 13e swaps the positive and negative signs of the input modulated signals of different modes in accordance with the control of the mode swapping control unit 12e. Specifically, the data swapping unit 13e swaps the positive and negative signs of the modulated signals of the ±nth mode, where n is a natural number. In other words, the data swapping unit 13e does not perform any special processing on the modulated signal of mode 0. Furthermore, if swapping the positive and negative signs of the OAM mode is not necessary, the data swapping unit 13e outputs the input modulated signals of different modes directly to the multiplexing unit 14.

[0124] (Configuration of receiver 20e) Figure 19 shows an example of the configuration of receiver 20e in the sixth embodiment. Receiver 20e includes a UCA 21, a frequency conversion unit 22, a separation unit 23b, a data demodulation unit 24b, and a mode switching control unit 25e. Receiver 20e differs from receiver 20b in that it includes a mode switching control unit 25e instead of a mode switching control unit 25b, and does not include a data switching unit 26.

[0125] The mode swapping control unit 25e controls the swapping of the positive and negative signs of the OAM modes in the transmitter 10e based on the modulation signals of each mode output from the separation unit 23b and the mode information output from the data demodulation unit 24b. Specifically, the mode swapping control unit 25e does not perform any special processing when the mode with the highest total received power matches the mode indicated by the mode information.

[0126] The mode swapping control unit 25e determines that if the mode with the highest total received power does not match the mode indicated by the mode information, it is necessary to swap the positive and negative signs of the modulation signals of different modes. In this case, the mode swapping control unit 25e generates request information to request the transmitter 10e to swap the positive and negative signs of the modes. The mode swapping control unit 25e may also feed back the generated request information to the transmitter 10e via the UCA 21. If the UCA 21 is used, the request information can be inserted into the mode 0 signal and fed back to the transmitter 10e.

[0127] Figure 20 is a sequence diagram showing the processing flow of the wireless communication system 100 in the sixth embodiment. In Figure 20, processes similar to those shown in Figure 11 are denoted by the same reference numerals as in Figure 11 and their descriptions are omitted.

[0128] In the process of step S307, the mode switching control unit 25e receives the mode information I obtained from the data demodulation unit 24b. Ｍ If it is determined that the mode is not negative (step S307-NO), the mode switching control unit 25e generates request information. The mode switching control unit 25e feeds back the generated request information to the transmitter 10e via the UCA 21 (step S601).

[0129] Furthermore, in the processing of step S310, the mode switching control unit 25b receives the mode information I obtained from the data demodulation unit 24b. Ｍ If it is determined that the mode is not positive (step S310-NO), the mode switching control unit 25e generates request information. The mode switching control unit 25e feeds back the generated request information to the transmitter 10e via the UCA 21 (step S602).

[0130] When the mode swapping control unit 12e of the transmitter 10e receives request information transmitted from the receiver 20e via the UCA 16, it controls the data swapping unit 13e to swap the positive and negative signs of the different mode modulated signals input to the data swapping unit 13e (step S603). This process enables the transmitter 10e to transmit an OAM multiplexed signal with the positive and negative signs of the different mode modulated signals swapped.

[0131] (Seventh Embodiment) In the seventh embodiment, a configuration is described in which a feedback function is added to the configuration shown in the fourth embodiment, which notifies the transmitter from the receiver that a mode change is necessary. Specifically, in the seventh embodiment, if the modes notified by the transmitter do not match the mode of the receiver, the receiver provides feedback to the transmitter that a mode change is necessary.

[0132] The wireless communication system 100 in the seventh embodiment includes a transmitter 10f and a receiver 20f. In the fth embodiment, the transmitter 10f includes a data exchange unit.

[0133] (Configuration of Transmitter 10f) Figure 21 shows an example of the configuration of transmitter 10f in the seventh embodiment. Transmitter 10f comprises a modulation unit 11c, a mode switching control unit 12f, a data switching unit 13f, a multiplexing unit 14, a frequency conversion unit 15, and a UCA 16. Transmitter 10f differs in configuration from transmitter 10f in that it newly includes a mode switching control unit 12f and a data switching unit 13f. The differences will be explained below.

[0134] The mode swapping control unit 12f controls the swapping of modulated signals of different modes input to the data swapping unit 13f. For example, the mode swapping control unit 12f determines that it is necessary to swap the positive and negative signs of the OAM mode when it receives request information fed back from the receiver 20f. On the other hand, the mode swapping control unit 12f determines that it is not necessary to swap the positive and negative signs of the OAM mode when it does not receive request information fed back from the receiver 20f. If it is necessary to swap the positive and negative signs of the OAM mode, the mode swapping control unit 12f controls the data swapping unit 13f to swap the positive and negative signs of modulated signals of different modes input to the data swapping unit 13f.

[0135] The data swapping unit 13f swaps the positive and negative signs of the input modulated signals of different modes in accordance with the control of the mode swapping control unit 12f. Specifically, the data swapping unit 13f swaps the positive and negative signs of the modulated signals of the ±nth mode, where n is a natural number. In other words, the data swapping unit 13f does not perform any special processing on the modulated signal of mode 0. Furthermore, if swapping the positive and negative signs of the OAM mode is not necessary, the data swapping unit 13f outputs the input modulated signals of different modes directly to the multiplexing unit 14.

[0136] (Configuration of receiver 20f) Figure 22 shows an example of the configuration of receiver 20f in the seventh embodiment. Receiver 20f includes a UCA 21, a frequency conversion unit 22, a separation unit 23c, a data demodulation unit 24c, and a mode switching control unit 25f. Receiver 20f differs from receiver 20c in that it includes a mode switching control unit 25f instead of the mode switching control unit 25c, and does not include a data switching unit 26.

[0137] The mode swapping control unit 25f controls the reversal of the positive and negative OAM modes in the transmitter 10f based on the multiple index information output from the data demodulation unit 24f. Specifically, the mode swapping control unit 25f determines whether each mode indicated by each of the multiple index information obtained from the data demodulation unit 24c matches the OAM mode received by the device. If each mode indicated by each of the multiple index information matches the OAM mode received by the device, the mode swapping control unit 25f does not perform any special processing.

[0138] On the other hand, if the modes indicated by each of the multiple index pieces do not match the OAM mode received by the device, the mode swapping control unit 25f determines that it is necessary to swap the positive and negative signs of the modulation signals of different modes. In this case, the mode swapping control unit 25f generates request information to request the transmitter 10f to swap the positive and negative signs of the modes. The mode swapping control unit 25f may also feed back the generated request information to the transmitter 10f via the UCA 21. When using the UCA 21, the request information can be inserted into the mode 0 signal and fed back to the transmitter 10f.

[0139] Figure 23 is a sequence diagram showing the processing flow of the wireless communication system 100 in the seventh embodiment. In Figure 23, processes similar to those shown in Figure 14 are denoted by the same reference numerals as in Figure 14, and their explanation is omitted.

[0140] If the mode switching control unit 25f determines that each mode indicated by the multiple index information does not match the OAM mode received by the device (step S405-NO), the mode switching control unit 25f generates request information. The mode switching control unit 25f feeds back the generated request information to the transmitter 10f via the UCA 21 (step S701).

[0141] When the mode swapping control unit 12f of the transmitter 10f receives request information transmitted from the receiver 20f via the UCA 16, it controls the data swapping unit 13f to swap the positive and negative signs of the modulated signals of different modes input to the data swapping unit 13f (step S702). This process enables the transmitter 10f to transmit an OAM multiplexed signal with the positive and negative signs of the modulated signals of different modes swapped.

[0142] According to the wireless communication system 100 in the seventh embodiment configured as described above, the receiver 20f provides feedback to the transmitter 10f indicating that a mode change is necessary when one is required. This allows the transmitter 10f to transmit the OAM multiplexed signal based on the feedback result. Therefore, even when communicating using OAM waves reflected by reflective objects such as walls or reflectors, it becomes possible to receive data correctly.

[0143] (Eighth Embodiment) The eighth embodiment describes a configuration in which a feedback function is added to the configuration shown in the fifth embodiment, which notifies the transmitter from the receiver that a mode swap is necessary. Specifically, in the eighth embodiment, if the demodulation is correct when the positive and negative signs of the modes are swapped during the demodulation process, the receiver provides feedback to the transmitter to that effect.

[0144] The wireless communication system 100 in the eighth embodiment includes a transmitter 10g and a receiver 20d. In the eighth embodiment, the transmitter 10g and the receiver 20d include a data exchange unit.

[0145] In the eighth embodiment, a receiver 20d similar to the receiver 20d in the fifth embodiment is provided, but some processing in the receiver 20d differs from that in the fifth embodiment. Specifically, in the eighth embodiment, if the receiver 20d has successfully demodulated the signal with the positive and negative signs of the mode swapped after processing by the data demodulation unit 24d, it feeds this information back to the transmitter 10g. For example, if the data demodulation unit 24d of the receiver 20d has successfully demodulated the modulated signal of a different mode output from the data swapping unit 26d, it notifies the mode swapping control unit 25d of this fact. Based on the result obtained from the data demodulation unit 24d, the mode swapping control unit 25d generates request information to request the transmitter 10g to swap the positive and negative signs of the mode. The mode swapping control unit 25d may also feed the generated request information back to the transmitter 10g via the UCA 21. When using the UCA 21, the request information can be inserted into the mode 0 signal and fed back to the transmitter 10g.

[0146] (Configuration of Transmitter 10g) Figure 24 shows an example of the configuration of transmitter 10g in the eighth embodiment. Transmitter 10g comprises a modulation unit 11, a mode switching control unit 12g, a data switching unit 13g, a multiplexing unit 14, a frequency conversion unit 15, and a UCA 16. Transmitter 10g differs in configuration from transmitter 10d in that it newly includes a mode switching control unit 12g and a data switching unit 13g. The differences will be explained below.

[0147] The mode swapping control unit 12g controls the swapping of modulated signals of different modes input to the data swapping unit 13g. For example, the mode swapping control unit 12g determines that it is necessary to swap the positive and negative signs of the OAM mode when it receives request information fed back from the receiver 20d. On the other hand, the mode swapping control unit 12g determines that it is not necessary to swap the positive and negative signs of the OAM mode when it does not receive request information fed back from the receiver 20d. When it is necessary to swap the positive and negative signs of the OAM mode, the mode swapping control unit 12g controls the data swapping unit 13g to swap the positive and negative signs of modulated signals of different modes input to the data swapping unit 13g.

[0148] The data swapping unit 13g swaps the positive and negative signs of the input modulated signals of different modes in accordance with the control of the mode swapping control unit 12g. Specifically, the data swapping unit 13g swaps the positive and negative signs of the modulated signals of the ±nth mode, where n is a natural number. In other words, the data swapping unit 13g does not perform any special processing on the modulated signal of mode 0. Furthermore, if swapping the positive and negative signs of the OAM mode is not necessary, the data swapping unit 13g outputs the input modulated signals of different modes directly to the multiplexing unit 14.

[0149] Figure 25 is a sequence diagram showing the processing flow of the wireless communication system 100 in the eighth embodiment. In Figure 25, processes similar to those shown in Figure 17 are denoted by the same reference numerals as in Figure 17, and their explanation is omitted.

[0150] After processing in step S509, the data demodulation unit 24d determines whether or not the demodulation was correct when the positive and negative modes were swapped (step S801). For example, if the data demodulation unit 24d was able to correctly demodulate the modulated signals of each mode output from the separation unit 23d, it determines that the demodulation was not correct when the positive and negative modes were swapped. For example, if the data demodulation unit 24d was able to correctly demodulate the modulated signals of different modes with the positive and negatives swapped output from the data swapping unit 26d, it determines that the demodulation was correct when the positive and negative modes were swapped.

[0151] If the data demodulation unit 24d determines that demodulation is not performed correctly when the positive and negative modes are reversed (step S801-NO), the receiver 20d terminates the process shown in Figure 25. This is because demodulation can be performed correctly without reversing the positive and negative modes. On the other hand, if the data demodulation unit 24d determines that demodulation is performed correctly when the positive and negative modes are reversed (step S801-YES), the data demodulation unit 24d notifies the mode reversal control unit 25g of this fact. The mode reversal control unit 25g generates request information in response to the notification from the data demodulation unit 24d. The mode reversal control unit 25g feeds back the generated request information to the transmitter 10g via the UCA 21 (step S802).

[0152] When the mode swapping control unit 12g of the transmitter 10g receives request information transmitted from the receiver 20d via the UCA 16, it controls the data swapping unit 13g to swap the positive and negative signs of the different mode modulation signals input to the data swapping unit 13g (step S703). This process enables the transmitter 10g to transmit an OAM multiplexed signal with the positive and negative signs of the different mode modulation signals swapped.

[0153] According to the wireless communication system 100 in the eighth embodiment configured as described above, the receiver 20g provides feedback to the transmitter 10g indicating that a mode change is necessary when one is required. This allows the transmitter 10g to transmit the OAM multiplexed signal based on the feedback result. Therefore, even when communicating using OAM waves reflected by reflective objects such as walls or reflectors, it becomes possible to receive data correctly.

[0154] (Modification 1 common to the first to eighth embodiments) The method for reversing the positive and negative signs of the OAM modes is not limited to the method described above. For example, as a method for reversing the positive and negative signs of the OAM modes, either a method of modifying the interleaver that rearranges the data of each OAM mode, or a method of swapping the preamble on the transmitting side and determining the mode from the preamble on the receiving side may be used. Each method will be described in detail below.

[0155] First, we will explain how to modify the interleaver that rearranges the data for each OAM mode using Figure 26. As shown in Figure 26, the transmitter notifies the receiver of the reversal of the sign of the data rearrangement information (interleaver) which shows the correspondence between the transmitted bit sequence and the mode to which each bit is transmitted. In the example shown in Figure 26, the transmitter is configured to multiplex signals for three modes: mode 0, mode 1, and mode -1. In the example shown in Figure 26, the modes to which each bit in the transmitted bit sequence M is transmitted are in the order of -1, 1, 0, ..., -1, 1, 0, -1, 1, 0. Therefore, the transmitter notifies the receiver of 1, -1, 0, ..., 1, -1, 0, 1, -1, 0 as data rearrangement information, which is obtained by reversing the sign of -1, 1, 0, ..., -1, 1, 0, -1, 1, 0.

[0156] In the transmitter, each bit in the transmitted bit sequence M is assigned to one of the following modes: -1, 1, 0, ..., -1, 1, 0, -1, 1, 0. Then, the modulation section generates modulated signals for mode 0, mode 1, and mode -1. Subsequently, the multiplexing section multiplexes the modulated signals for mode 0, mode 1, and mode -1 and transmits them to the receiver. The receiver rearranges the bit sequences received in each OAM mode according to the data rearrangement information notified by the transmitter.

[0157] Next, we will explain, using Figure 27, how to swap the preamble on the transmitting side and determine the mode from the preamble on the receiving side. In explaining Figure 27, we will refer to the preamble sequence that indicates mode m as a ｍ Let's assume that the data sequence for mode m is x ｍ The transmitter swaps the positive and negative OAM modes of the preamble sequence and adds them to the data sequence for transmission. The receiver demodulates the received signals of each OAM mode and processes them as the modes specified in the preamble. Figure 27(A) shows the case where the OAM mode is not inverted, and Figure 27(B) shows the case where it is inverted.

[0158] In the embodiments described above, some or all of the transmitters 10, 10a, 10b, 10c, 10d, 10e, 10f, 10g, or receivers 20, 20a, 20b, 20c, 20d, 20e, 20f may be implemented using a computer. In that case, the program for implementing this function may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be loaded into a computer system and executed. The term "computer system" as used herein includes hardware such as an OS (Operating System) and peripheral devices.

[0159] Furthermore, "computer-readable recording media" refers to portable media such as flexible disks, magneto-optical disks, ROMs (Read Only Memory), and CD-ROMs, as well as storage devices such as hard disks built into computer systems. Additionally, "computer-readable recording media" may include those that dynamically hold programs for a short period, such as communication lines used when transmitting programs over networks like the Internet or telephone lines, as well as those that hold programs for a fixed period, such as volatile memory within computer systems acting as servers or clients. The above programs may also be recorded on computer-readable recording media. Examples of computer-readable recording media include portable media such as flexible disks, magneto-optical disks, ROMs, CD-ROMs, and semiconductor storage devices (e.g., SSDs: Solid State Drives), as well as storage devices such as hard disks and semiconductor storage devices built into computer systems. The above programs may also be transmitted via telecommunication lines.

[0160] Although embodiments of this invention have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and includes designs and the like that do not depart from the spirit of this invention.

[0161] This invention can be applied to wireless communication systems that perform OAM multiplex transmission.

[0162] 10, 10a, 10b, 10c, 10d, 10e, 10f, 10g... Transmitter, 20, 20a, 20b, 20c, 20d, 20e, 20f... Receiver, 11, 11b, 11c... Modulation unit, 12, 12a, 12e, 12f, 12g... Mode switching control unit, 13, 13e, 13f, 13g... Data switching unit, 14... Multiplexing unit, 15, 22... Frequency conversion unit, 16, 21... UCA, 23, 23a, 23b, 23c, 23d... Separation unit, 24, 24a, 24b, 24c, 24d... Data demodulation unit, 25, 25b, 25c, 25d, 25e, 25f... Mode switching control unit, 26, 26d... Data switching unit

Claims

1. A wireless communication system comprising a transmitter and a receiver that perform OAM (Orbital Angular Momentum) multiplex transmission, wherein the transmitter comprises: a modulation unit that generates modulated signals of different modes; a multiplexing unit that multiplexes the modulated signals of different modes generated by the modulation unit to generate a multiplexed signal; and a transmission unit that transmits the multiplexed signal generated by the multiplexing unit; the receiver comprises: a receiving unit that receives the multiplexed signal transmitted from the transmitter; a separation unit that separates the multiplexed signal received by the receiving unit into modulated signals of each mode; and a demodulation unit that demodulates the modulated signals of each mode separated by the separation unit; and at least one of the transmitter or the receiver further comprises a data swapping unit that swaps the positive and negative signs of signals of modes other than mode 0.

2. The wireless communication system according to claim 1, wherein the data swapping unit provided in either the transmitter or the receiver swaps the positive and negative signs of signals in modes other than mode 0 when it is necessary to swap the positive and negative signs of signals in modes other than mode 0, depending on the installation conditions of the transmitter and the receiver.

3. The modulation unit generates a modulated signal in either a positive mode or a negative mode, and inserts mode information indicating that it is either the positive mode or the negative mode into the signal transmitted in mode 0 to generate a modulated signal in mode 0; the receiver calculates the sum of the received powers of the positive mode and the sum of the received powers of the negative mode, calculated based on the modulated signals of each mode included in the received multiplexed signal; and the data swapping unit, provided in either the transmitter or the receiver, swaps the positive and negative signs of the signals of modes other than mode 0 when the mode indicated by the mode information included in the modulated signal of mode 0 is different from the mode with a higher sum of received powers; the wireless communication system according to claim 1.

4. The modulation unit generates modulated signals of different modes by inserting index information indicating each mode to be transmitted into the preamble signals transmitted in each mode, and the data swapping unit provided in either the transmitter or the receiver swaps the positive and negative signs of the signals of modes other than mode 0 when the index information included in the preamble signals of the modulated signals of different modes differs from the mode received by the receiver, the wireless communication system according to claim 1.

5. The wireless communication system according to claim 1, wherein the receiver includes the data swapping unit, the data swapping unit swaps the positive and negative signs of the signals of modes other than mode 0 in the modulated signals of each mode separated by the separation unit, and the demodulation unit demodulates the modulated signals of each mode separated by the separation unit and the modulated signals of each mode processed by the data swapping unit, and acquires the correctly demodulated signal as a received signal.

6. A transmitter comprising: a modulation unit that generates modulated signals of different modes; a data swapping unit that swaps the positive and negative signs of signals of modes other than mode 0 in the modulated signals of different modes generated by the modulation unit; a multiplexing unit that multiplexes the modulated signals of different modes processed by the data swapping unit to generate a multiplexed signal; and a transmission unit that transmits the multiplexed signal generated by the multiplexing unit.

7. A receiver comprising: a receiving unit that receives a multiplexed signal obtained by multiplexing modulated signals of different modes transmitted from a transmitter; a separation unit that separates the multiplexed signal received by the receiving unit into modulated signals of each mode; a data swapping unit that swaps the positive and negative signs of the signals of modes other than mode 0 in the modulated signals of each mode separated by the separation unit; and a demodulation unit that demodulates the modulated signals of different modes that have been processed by the data swapping unit.

8. A wireless communication method performed by a wireless communication system comprising a transmitter and a receiver that perform OAM (Orbital Angular Momentum) multiplex transmission, wherein the transmitter generates modulated signals of different modes, multiplexes the generated modulated signals of different modes to generate a multiplexed signal, transmits the generated multiplexed signal, the receiver receives the multiplexed signal transmitted from the transmitter, separates the received multiplexed signal into modulated signals of each mode, demodulates the separated modulated signals of each mode, and at least one of the transmitter or the receiver reverses the positive and negative signs of the signals of modes other than mode 0.

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