Transmitting device and transmitting method

Abstract

A transmission device comprising: a signal processing unit that adds a second-OAM-mode interference signal to a first-OAM-mode transmission signal by means of OAM multiplexing; and a transmission unit that transmits the first-OAM-mode transmission signal and the second-OAM-mode interference signal.

Description

Technical Field

[0001] The present invention relates to a technique for spatially multiplexing wireless signals using the orbital angular momentum (OAM) of electromagnetic waves.

Background Art

[0002] In recent years, in order to improve the transmission capacity, studies on spatial multiplexing techniques for wireless signals using OAM have been underway. (For example, Non-Patent Document 1). Electromagnetic waves with OAM have an equiphase surface that is helically distributed along the propagation direction around the propagation axis. Electromagnetic waves with different OAM modes and propagating in the same direction have a spatially orthogonal phase distribution in the direction of the rotation axis. Therefore, signals can be multiplexed by separating signals of each OAM mode modulated with different signal sequences at a receiving device.

[0003] In a wireless communication system using this OAM multiplexing technique, a uniform circular array antenna (hereinafter referred to as UCA) in which a plurality of antenna elements are circularly arranged at equal intervals is used, and a plurality of OAM modes are generated and synthesized for transmission, thereby enabling spatial multiplexing transmission of different signal sequences. (For example, Non-Patent Document 2). For example, a Butler circuit (Butler matrix circuit) is used for signal generation and signal separation of a plurality of OAM modes.

[0004] In addition, short-range communication technologies have been developed, such as non-contact IC (Integrated Circuit) cards, which form a narrow communication area and start communication by bringing a slave device close to the communication area. Techniques for limiting the communication area have been disclosed in order to avoid the occurrence of communication that the user does not intend.

[0005] For example, Patent Document 1 and Patent Document 2 disclose technologies for limiting a communication area by using other short-distance transmission methods in combination. Patent Document 3 discloses a technology for limiting a communication area by using a static magnetic field. Patent Document 4 discloses a technology for limiting a communication area by using a highly directional antenna. Patent Document 5 discloses a technology for limiting a communication area by reducing transmission power to make cells smaller. Non-Patent Document 3 discloses a technology for limiting a communication area by utilizing the phenomenon that the beam does not spread near the antenna and the received power decreases according to the distance outside the antenna.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Non-Patent Documents

[0007]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] As described above, a transmission device using a UCA and a Butler circuit enables high-capacity communication. In the future, miniaturization, power saving, or coping with the formation of a closed space, etc. are desired. However, in the conventional short-distance communication technology in wireless transmission, in order to form a narrow communication area by reducing the transmission power from the master unit and the decrease in SNR due to distance attenuation, there is a problem that the size of the communication area varies due to differences in the reception sensitivity of the slave units.

[0009] The disclosed technology aims to reduce the variation in the size of the communication area due to differences in reception sensitivity.

Means for Solving the Problems

[0010] The disclosed technology includes a signal processing unit that adds an interference signal of a second OAM mode to a transmission signal of a first OAM mode by OAM multiplex transmission, and a transmission unit that transmits the transmission signal of the first OAM mode and the interference signal of the second OAM mode. The transmission processing unit determines the first OAM mode and the second OAM mode such that the sensitivity of the transmission signal is higher than that of the interference signal, and the reception level of the transmission signal rapidly decreases with respect to the wireless transmission distance as compared with the interference signal. It is a transmission device.

Advantages of the Invention

[0011] Variations in the communication area size due to differences in reception sensitivity can be reduced.

Brief Description of the Drawings

[0012]

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Modes for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present invention (the present embodiments) will be described with reference to the drawings. The embodiments described below are merely examples, and the embodiments to which the present invention is applied are not limited to the following embodiments.

[0014] (Overview of the Present Embodiment) In the present embodiment, OAM multiplex transmission is used for a line of PtP transmission (for example, a wireless line used in a file download kiosk device or the like).

[0015] (Example of Basic Operation) The basic settings and operation examples related to the UCA used in each device in this embodiment will be described.

[0016] FIG. 1 is a diagram showing an example of phase setting of a UCA for generating signals in the OAM mode. The UCA shown in FIG. 1 is a UCA composed of eight antenna elements.

[0017] In FIG. 1, signals in the OAM modes 0, 1, 2, 3,... on the transmission side are generated by the phase difference of the signals supplied to each antenna element (indicated by ●) of the UCA. That is, the signal in the OAM mode n is generated by setting the phase of the signal supplied to each antenna element so that the phase becomes n rotations (n×360 degrees). For example, when the UCA shown in FIG. 1 is composed of m = 8 antenna elements and generating a signal in the OAM mode n = 2, as shown in FIG. 1(3), a phase difference of 360n / m = 90 degrees (0 degrees, 90 degrees, 180 degrees, 270 degrees, 0 degrees, 90 degrees, 180 degrees, 270 degrees) is set counterclockwise for each antenna element so that the phase rotates twice.

[0018] Note that a signal with the reverse phase rotation direction with respect to the signal in the OAM mode n is defined as the OAM mode -n. For example, the phase rotation direction of the signal in the positive OAM mode is counterclockwise, and the phase rotation direction of the signal in the negative OAM mode is clockwise.

[0019] By generating different signal sequences as signals in different OAM modes and transmitting the generated signals simultaneously, wireless communication by spatial multiplexing can be performed. On the transmission side, the signals to be transmitted in each OAM mode may be generated and synthesized in advance, and the synthesized signals in each OAM mode may be transmitted using a single UCA, or using a plurality of UCAs, signals in each OAM mode may be transmitted using different UCAs for each OAM mode.

[0020] In order to separate the OAM multiplexed signal on the receiving side, the phase of each antenna element of the UCA on the receiving side may be set to be in the opposite direction to the phase of the antenna element on the transmitting side.

[0021] However, when interference occurs between OAM modes due to axial misalignment or the like between the transmitting antenna and the receiving antenna, it is necessary to separate the signals between the OAM modes mixed by the interference by digital signal processing such as channel equalization processing or successive interference cancellation processing. Note that the interference between OAM modes means, for example, that a signal transmitted in OAM mode 1 from a transmitting device is output as a signal in OAM mode 2 on the receiving side.

[0022] FIG. 2 is a diagram showing an example of the phase distribution and signal intensity distribution of an OAM multiplex signal. In FIGS. 2(1) and (2), the phase distributions of the signals in OAM mode 1 and OAM mode 2 as viewed from the end face (propagation orthogonal plane) orthogonal to the propagation direction from the transmitting side are represented by arrows. The starting point of the arrow is 0 degrees, the phase changes linearly, and the end of the arrow is 360 degrees. That is, the signal in OAM mode n propagates while the phase rotates n times (n×360 degrees) in the propagation orthogonal plane. Note that the arrows of the phase distributions of the signals in OAM modes -1 and -2 are in the opposite directions.

[0023] The signals of each OAM mode have different signal intensity distributions and positions where the signal intensity is maximized for each OAM mode. However, the intensity distributions of the same OAM mode with different signs are the same. Specifically, as the OAM mode becomes higher order, the position where the signal intensity is maximized becomes farther from the propagation axis (Non-Patent Document 2). Here, the OAM mode with a larger value is referred to as a higher order mode. For example, the signal in OAM mode 3 is a higher order mode than the signals in OAM mode 0, OAM mode 1, and OAM mode 2.

[0024] FIG. 2(3) shows the positions where the signal intensity is maximized for each OAM mode by rings. As the OAM mode becomes higher order, the position where the signal intensity is maximized becomes farther from the central axis, and the beam diameter of the OAM mode multiplex signal spreads according to the propagation distance, and the rings indicating the positions where the signal intensity is maximized for each OAM mode become larger.

[0025] Hereinafter, the system configuration and operation example in the present embodiment will be described in detail.

[0026] (System Configuration of Communication System) FIG. 3 is a configuration diagram of a communication system according to an embodiment of the present invention. The communication system includes a master unit 100 and a slave unit 200.

[0027] The master unit 100 is an example of a transmission device that transmits radio waves by OAM multiplex transmission.

[0028] The master unit 100 includes an antenna 110, a transmission unit 120, and a signal processing unit 130. The antenna 110 is, for example, a UCA. The transmission unit 120 transmits the OAM multiplexed signal via the antenna 110.

[0029] The signal processing unit 130 acquires information indicating the size of the communication area. For example, the signal processing unit 130 may receive an input of information indicating the size of the communication area by an operation of a user or the like. The signal processing unit 130 generates a transmission signal such as a beacon, and causes the transmission unit 120 to transmit the generated transmission signal. Here, the signal processing unit 130 adds an interference signal to the transmission signal according to the size of the communication area.

[0030] The slave unit 200 is, for example, a mobile terminal or the like, and is an example of a receiving device that receives signals. The slave unit 200 performs proximity communication with the master unit 100.

[0031] The slave unit 200 includes an antenna 210, a receiving unit 220, and a signal processing unit 230. The antenna 210 is a general antenna for wireless communication. The receiving unit 220 receives a signal in the OAM mode assigned to the slave unit 200.

[0032] The signal processing unit 230 converts the signal in the OAM mode assigned to the slave unit 200 into digital data by A / D conversion.

[0033] (Operation of the communication system) Next, the operation of the communication system will be described.

[0034] FIG. 4 is a flowchart showing an example of the flow of transmission processing according to an embodiment of the present invention. The master unit 100 starts the transmission processing periodically or in response to a user operation or the like.

[0035] The signal processing unit 130 acquires information indicating the communication area size (step S11). Then, the signal processing unit 130 generates a transmission signal (step S12). Subsequently, the signal processing unit 130 adds an interference signal to the transmission signal (step S13). Then, the transmission unit 120 transmits the signal (the transmission signal to which the interference signal is added) (step S14).

[0036] In the process of step S13, the signal processing unit 130 performs OAM multiplexing with the transmission signal as the OAM mode L (L = ±1, ±2, ±3, ···) and the interference signal as the OAM mode 0. Here, the interference signal is pseudo noise and may be a signal obtained by band-limiting a PN sequence, an M sequence, or the like. Also, the OAM mode of the interference signal does not have to be the OAM mode 0. For example, the signal processing unit 130 may determine the OAM mode (first OAM mode) of the transmission signal and the OAM mode (second OAM mode) of the interference signal so that the transmission signal has higher sensitivity than the interference signal and the reception level of the transmission signal rapidly decreases with respect to the wireless transmission distance compared to the interference signal.

[0037] Also, the signal processing unit 130 may determine the OAM mode of the transmission signal based on the communication area size. For example, the signal processing unit 130 may estimate the reception SNR based on the distance to the communication area edge and determine the OAM mode of the transmission signal.

[0038] Also, the signal processing unit 130 may determine the OAM mode of the interference signal based on the communication area size. For example, the signal processing unit 130 may estimate the reception SNR based on the distance to the communication area edge and determine the OAM mode of the interference signal.

[0039] Further, the signal processing unit 130 may determine the noise level of the interference signal based on the communication area size. For example, the signal processing unit 130 may estimate the received SNR based on the distance to the edge of the communication area and determine the noise level of the interference signal.

[0040] Furthermore, the signal processing unit 130 may make the bandwidth of the interference signal smaller than the bandwidth of the transmission signal. Thereby, the leakage of noise outside the band can be reduced, and the interference to other wireless links using adjacent channels can be minimized.

[0041] Also, when the signal processing unit 130 satisfies a specified condition, for example, when transmitting a beacon signal, it may add an interference signal to the transmission signal and not add an interference signal in other cases. Thereby, when it is not desired to limit the communication area, the communication area can be expanded according to the sensitivity of the slave unit 200.

[0042] (Characteristics of Conventional Short-Range Communication) Next, for comparison with the present embodiment, the characteristics of conventional short-range communication will be described.

[0043] FIG. 5 is a diagram for explaining the characteristics of conventional short-range communication. In conventional short-range communication, the size of the communication area is determined according to the decrease in SNR (Signal-to-Noise power Ratio) attenuated according to the distance from the master unit. For example, assuming that connection is possible when the SINR (Signal-to-Interference and Noise power Ratio) exceeds a threshold value, the size of the connectable communication area varies greatly depending on the sensitivity of the slave unit.

[0044] (Characteristics of Short-Range Communication According to the Present Embodiment) FIG. 6 is a diagram for explaining the characteristics of short-range communication according to an embodiment of the present invention. In this embodiment, when the distance from the master unit 100 increases, the distance attenuation of the interference signal (e.g., OAM mode 0) is slower than that of the transmission signal (e.g., OAM mode 2) with respect to the distance attenuation. Therefore, the Signal-to-Interference Ratio (SIR) is determined by the distance from the master unit 100.

[0045] This is because the signal transmitted into space in OAM mode L, for example, when L is an even number (L = 2, 4,...), the received power of the signals in OAM mode L and OAM mode L + 1 rapidly attenuates to the 2*(L + 2) power with respect to the distance from the master unit. Also, the SNR depends on the sensitivity of the slave unit, but the SIR does not.

[0046] For example, the master unit 100 may transmit an interference signal at a level such that the SIR is dominant in the SINR (e.g., about 5 dB or more higher than the noise (N) at the edge of the communication area) based on the size of the communication area. Thereby, the size of the communication area can be determined with little dependence on the sensitivity of the slave unit.

[0047] (Effect of the Embodiment of the Present Invention) Next, the effects of the embodiment of the present invention will be described.

[0048] FIG. 7 is a diagram for explaining the effects of the embodiment of the present invention. According to the communication system according to this embodiment, the variation in the communication area due to the sensitivity of the slave unit can be reduced more than before. For example, conventionally, when the sensitivity increases by about 3 dB, it is considered that the radius of the communication area (both the major axis radius and the minor axis radius in the case of an ellipse) becomes 1.4 times. In contrast, according to this embodiment, if the OAM mode of the interference signal, the noise level, etc. are appropriately set, the communication area can be made hardly change even when the sensitivity increases by about 3 dB.

[0049] Further, the master device 100 may determine the OAM mode to be used for the transmission signal and the interference signal according to the shape or size of the communication area. Thereby, the shape or size of the communication area can be determined.

[0050] (Summary of Embodiment) This specification describes at least the transmission device and the transmission method described in each of the following items. (Item 1) A signal processing unit that adds an interference signal of a second OAM mode to a transmission signal of a first OAM mode by OAM multiplex transmission, A transmission unit that transmits the transmission signal of the first OAM mode and the interference signal of the second OAM mode, Transmission device. (Item 2) The signal processing unit determines the first OAM mode based on information indicating the communication area size. The transmission device according to Item 1. (Item 3) The signal processing unit determines the second OAM mode based on information indicating the communication area size. The transmission device according to Item 1 or Item 2. (Item 4) The signal processing unit determines the noise level of the interference signal based on information indicating the communication area size. The transmission device according to any one of Items 1 to 3. (Item 5) The signal processing unit makes the bandwidth of the interference signal smaller than the bandwidth of the transmission signal. The transmission device according to any one of Items 1 to 4. (Item 6) The signal processing unit adds the interference signal to the transmission signal when a specified condition is satisfied. The transmission device according to any one of Items 1 to 5. (Item 7) A step of adding an interference signal of a second OAM mode to a transmission signal of a first OAM mode by OAM multiplex transmission, transmitting a transmission signal in the first OAM mode and an interference signal in the second OAM mode A transmission method executed by a transmission device.

[0051] According to any of the above configurations, a technique is provided that can reduce variations in communication area size due to differences in reception sensitivity. According to paragraph 2, a transmission signal in an OAM mode corresponding to the communication area size can be transmitted. According to paragraph 3, an interference signal in an OAM mode corresponding to the communication area size can be transmitted. According to paragraph 4, an interference signal with a noise level corresponding to the communication area size can be transmitted. According to paragraph 5, leakage of noise outside the band can be reduced, and interference with other wireless links using adjacent channels can be minimized. According to paragraph 6, when it is not desired to limit the communication area, the communication area can be expanded according to the sensitivity of the slave unit 200.

[0052] As described above, the present embodiment has been explained. However, the present invention is not limited to such a specific embodiment, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

Explanation of Reference Numerals

[0053] 100 Master unit 110 Antenna 120 Transmission unit 130 Signal processing unit 200 Slave unit 210 Antenna 220 Reception unit 230 Signal processing unit

Claims

1. A signal processing unit that adds an interference signal of a second OAM mode to a transmission signal of a first OAM mode by OAM multiplex transmission; A transmission unit that transmits the transmission signal of the first OAM mode and the interference signal of the second OAM mode, and The signal processing unit determines the first OAM mode and the second OAM mode such that the transmission signal has higher sensitivity than the interference signal and the reception level of the transmission signal rapidly decreases with respect to the wireless transmission distance compared to the interference signal. A transmission device.

2. The transmission unit according to claim 1, wherein the transmission unit transmits the interference signal at a level such that the SIR is dominant in the SINR based on the size of the communication area.

3. The signal processing unit determines the first OAM mode and / or the second OAM mode based on information indicating the communication area size. The transmission device according to claim 1 or 2.

4. The signal processing unit determines the noise level of the interference signal based on information indicating the communication area size. The transmission device according to any one of claims 1 to 3.

5. The signal processing unit makes the bandwidth of the interference signal smaller than the bandwidth of the transmission signal. The transmission device according to any one of claims 1 to 4.

6. When transmitting a beacon signal, the signal processing unit adds the interference signal to the transmission signal. The transmission device according to any one of claims 1 to 5.

7. A transmission device includes: A signal processing step of adding an interference signal of a second OAM mode to a transmission signal of a first OAM mode by OAM multiplex transmission; A transmission step of transmitting the transmission signal of the first OAM mode and the interference signal of the second OAM mode, and Executes, In the signal processing step, the first OAM mode and the second OAM mode are determined such that the transmission signal has higher sensitivity than the interference signal and the reception level of the transmission signal rapidly decreases with respect to the wireless transmission distance compared to the interference signal. A transmission method.

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