Transmitting device

Abstract

A transmission device comprising: a first frequency converter configured so as to convert the frequency of a broadband signal to an intermediate frequency corresponding to a desired OAM mode; a delay line configured so as to delay the intermediate frequency signal; and a second frequency converter configured so as to convert the delayed intermediate frequency signal to a constant radio frequency.

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, for improving 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 propagating in the same direction have a spatially orthogonal phase distribution in the direction of the rotation axis. Therefore, signals of each OAM mode modulated with different signal sequences can be separated at a receiving device, enabling multiplex transmission of signals.

[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 signal generation and signal separation of a plurality of OAM modes, for example, a Butler circuit (Butler matrix circuit) is used.

[0004] Also, techniques for switching OAM modes have been developed. For example, Patent Document 1 discloses a technique for switching a plurality of OAM modes using discrete Fourier transform. Further, Patent Document 2 discloses a technique for switching an OAM mode by radiation from a pseudo-progressive wave resonator using a metamaterial structure by changing an applied magnetic field.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] [Non-Patent Document 1] J. Wang et al., "Terabit free-space data transmission employing orbital angular momentum multiplexing," Nature Photonics, Vol.6, pp.488-496, July 2012. [Non-Patent Document 2] Y. Yan et al., "High-capacity millimeter-wave communications with orbital angular momentum multiplexing," Nature Commun., vol.5, p.4876, Sep. 2014. [Summary of the Invention] [Problems to be Solved by the Invention]

[0007] As described above, a transmission device using a UCA and a Butler circuit enables high-capacity communication. However, in the future, it is desired to respond to miniaturization, power saving, etc. However, conventional wireless transmission technologies have a problem that it is difficult to realize various OAM modes such as switching of OAM modes and use of fractional OAM modes.

[0008] The disclosed technology aims to realize various OAM modes. [Means for Solving the Problems]

[0009] The disclosed technology is a transmission device including a first frequency converter configured to convert the frequency of a baseband signal into an intermediate frequency corresponding to a desired OAM mode, a delay line configured to generate a delay in the signal of the intermediate frequency, and a second frequency converter configured to convert the signal of the intermediate frequency with the generated delay into a fixed radio frequency.

Effect of the Invention

[0010] A variety of OAM modes can be realized.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments (the present embodiments) of the present invention 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.

[0013] (Problems of the Related Art) Conventionally, in a wireless communication device that performs wireless transmission utilizing an OAM mode with a circular array antenna, a configuration using an OAM mode variable array antenna is known for the purpose of OAM mode modulation or switching and using the OAM mode. However, when using an OAM mode variable array antenna, it is necessary to control the phase shifters provided in each antenna element. Furthermore, when using a large number of phase shifters, there is a possibility that variations in the phase shift amount will occur.

[0014] In addition, there is a method of switching signal input terminals by a matrix circuit, but it is not possible to continuously change the OAM mode including the fractional mode.

[0015] (Overview of this Embodiment) The transmission device according to this embodiment has a delay line in each branch while keeping the RF (Radio Frequency) frequency constant and making the intermediate frequency (IF; Intermediate Frequency) variable. Also, the local oscillation frequency of the first frequency converter from the baseband to the IF and the local oscillation frequency of the second frequency converter from the IF to the RF are made variable to make the IF frequency changeable while keeping the RF frequency constant. By doing this, according to the OAM mode to be used, the phase shift amount in the circuit that generates a fixed time delay is changed by changing the IF frequency.

[0016] (Basic Operation Example) A basic setting and operation example related to the UCA used in each device in this embodiment will be described.

[0017] FIG. 1 is a diagram showing a phase setting example of a UCA for generating signals in the OAM mode. The UCA shown in FIG. 1 is a UCA composed of eight antenna elements.

[0018] 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, a 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 a signal in the OAM mode n = 2 is to be generated, 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.

[0019] For the signal of OAM mode n, a signal with the opposite phase rotation direction is defined as 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.

[0020] By generating different signal sequences as signals of different OAM modes and transmitting the generated signals simultaneously, wireless communication by spatial multiplexing can be performed. On the transmitting side, the signals to be transmitted in each OAM mode may be generated and synthesized in advance, and the synthesized signals of each OAM mode may be transmitted using a single UCA, or using a plurality of UCAs, signals of each OAM mode may be transmitted using different UCAs for each OAM mode.

[0021] In order to separate the OAM multiplexed signal on the receiving side, the phase of each antenna element of the receiving side UCA may be set to be in the opposite direction to the phase of the antenna element on the transmitting side.

[0022] However, when interference occurs between OAM modes due to axis 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 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 the transmitting device is output as a signal in OAM mode 2 on the receiving side.

[0023] Figure 2 is a diagram showing an example of the phase distribution and signal intensity distribution of the OAM multiplexed signal. In Figures 2(1) and (2), the phase distributions of the signals of OAM mode 1 and OAM mode 2 as seen from the end face (propagation orthogonal plane) orthogonal to the propagation direction from the transmitting side are represented by arrows. The beginning of the arrow is 0 degrees, the phase changes linearly, and the end of the arrow is 360 degrees. That is, the signal of 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 of OAM modes -1 and -2 are in the opposite direction.

[0024] 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, the higher the OAM mode, the farther the position where the signal intensity is maximized is from the propagation axis (Non-Patent Document 2). Here, the OAM mode with a larger value is referred to as the higher-order mode. For example, the signal of OAM mode 3 is a higher-order mode than the signals of OAM mode 0, OAM mode 1, and OAM mode 2.

[0025] Figure 2(3) shows the positions where the signal intensity is maximized for each OAM mode as rings. The higher the OAM mode, the farther the position where the signal intensity is maximized is from the central axis, and the beam diameter of the OAM mode multiplexed signal spreads according to the propagation distance, and the ring indicating the position where the signal intensity is maximized for each OAM mode becomes larger.

[0026] Hereinafter, the system configuration and operation example in the present embodiment will be described in detail.

[0027] (System Configuration of Communication System) Figure 3 is a configuration diagram of a communication system according to an embodiment of the present invention. As shown in Figure 3, the wireless communication system in the present embodiment includes a transmission device 100 and a reception device 200.

[0028] The transmission device 100 and the reception device 200 each include a UCA. In the transmission and reception of desired data, the transmission device 100 multiplexes and transmits signals of one or more OAM modes, and the reception device 200 receives the signal multiplexed with one or more OAM modes transmitted from the transmission device 100 and separates the signals of each OAM mode.

[0029] The transmission device 100 and the reception device 200 are wireless communication devices that perform wireless communication. In this embodiment, it is assumed that the transmission device 100 is a base station that does not move, and the reception device 200 is a mobile terminal. However, such an assumption is an example. For example, both the transmission device 100 and the reception device 200 may be base stations that do not move, or both the transmission device 100 and the reception device 200 may be mobile terminals. Note that since a plurality of wireless communication devices communicate bidirectionally, each wireless communication device may have the functions of the transmission device 100 and the reception device 200 described later.

[0030] (Hardware Configuration of Transmission Device) Next, the hardware configuration of the transmission device will be described.

[0031] FIG. 4 is a diagram showing an example of the hardware configuration of a transmission device according to an embodiment of the present invention. The transmission device 100 includes a first frequency converter 110-1, a second frequency converter 110-2, one or more delay lines 120, a plurality of filters 130, and a plurality of antennas 140.

[0032] The first frequency converter 110-1 converts the frequency of the baseband signal to an intermediate frequency (IF). The delay line 120 generates a fixed-time delay for the intermediate-frequency signal. The plurality of delay lines 120 may be configured to continuously generate a fixed-time delay for the intermediate-frequency signal, for example, each having a length of l. The second frequency converter 110-2 converts the intermediate frequency to a transmission radio frequency (RF).

[0033] The plurality of filters 130 and the plurality of antennas 140 each constitute a branch without delay and a branch delayed by a fixed time. The plurality of antennas 140 may form, for example, a circular array antenna. Thereby, the transmission device 100 can assign a specific OAM mode to each filter 130 and antenna 140.

[0034] In addition, the transmission device 100 controls the first frequency converter 110-1 to change the intermediate frequency (IF), and controls the second frequency converter 110-2 so that the radio frequency (RF) remains constant regardless of the change in the intermediate frequency (IF). For example, let the transmission frequency of the first frequency converter 110-1 be f1 and the transmission frequency of the second frequency converter 110-2 be f2. The transmission device 100 can transmit a signal in the OAM mode 1.0 by controlling the first frequency converter 110-1 so that f1 = 2 GHz.

[0035] Here, the transmission device 100 controls the second frequency converter 110-2 to set the oscillation frequency f2 as shown in Equation 1, thereby making the radio frequency (RF) constant.

[0036] f2 = RF - f1 ··· (Equation 1)

[0037] Similarly, the transmission device 100 can transmit a signal in the OAM mode 1.5 by controlling the first frequency converter 110-1 so that f1 = 3 GHz. Further, the transmission device 100 can transmit a signal in the OAM mode 2.0 by controlling the first frequency converter 110-1 so that f1 = 4 GHz.

[0038] In this way, the transmission device 100 can continuously switch the OAM mode of the transmitted signal. In addition, the transmission device 100 can realize various OAM modes such as an integer mode and a fractional mode.

[0039] According to the transmission device 100 according to the present embodiment, the OAM mode can be switched with a simple configuration. For example, a plurality of SPPs (Serial Port Profiles), a phase shifter circuit, etc. are unnecessary, and a beam forming circuit, etc. is also unnecessary.

[0040] (Summary of the embodiment) This specification describes at least the transmission devices described in the following respective items. (Item 1) A first frequency converter configured to convert the frequency of a baseband signal into an intermediate frequency corresponding to a desired OAM mode, A delay line configured to generate a delay in the signal of the intermediate frequency, A second frequency converter configured to convert the signal of the intermediate frequency with the generated delay into a fixed radio frequency, and A transmission device. (Item 2) The transmission device according to Item 1, comprising a plurality of the delay lines configured to continuously generate a delay of a fixed time in the signal of the intermediate frequency. The transmission device according to Item 1. (Item 3) The first frequency converter is configured to convert the frequency of the baseband signal into an intermediate frequency corresponding to an OAM mode of a fractional mode. The transmission device according to Item 1 or Item 2.

[0041] According to any of the above configurations, a technique is provided that enables various OAM modes to be realized. According to Item 2, a delay of a fixed time can be continuously generated. According to Item 3, a signal of an OAM mode of a fractional mode can be transmitted.

[0042] Although the present embodiment has been described above, 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 Signs

[0043] 100 Transmission device 110-1 First frequency converter 110-2 Second frequency converter 120 Delay line 130 Filter 140 Antenna 200 Receiver

Claims

1. A first frequency converter configured to convert the frequency of a baseband signal into an intermediate frequency corresponding to a desired OAM mode; A delay line configured to generate a delay in the signal of the intermediate frequency; A second frequency converter configured to convert the signal of the intermediate frequency with the generated delay into a fixed radio frequency, and comprising: A transmission device.

2. The transmission device according to claim 1, further comprising a plurality of the delay lines configured to continuously generate a delay of a fixed time in the signal of the intermediate frequency. The transmission device according to claim 1.

3. The first frequency converter is configured to convert the frequency of the baseband signal into an intermediate frequency corresponding to an OAM mode of a fractional mode. The transmission device according to claim 1 or 2.

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