JP7626294B2 - Transmitting device and transmitting method - Google Patents

Description

The present invention relates to a technology for spatially multiplexing transmission of wireless signals using the orbital angular momentum (OAM) of electromagnetic waves.

In recent years, in order to improve transmission capacity, spatial multiplexing transmission technology for wireless signals using OAM has been studied (for example, Non-Patent Document 1). Electromagnetic waves with OAM have equiphase surfaces distributed in a spiral shape along the propagation direction centered on the propagation axis. Electromagnetic waves with different OAM modes propagating in the same direction have orthogonal spatial phase distributions in the direction of the rotation axis, so signals can be multiplexed and transmitted by separating the signals of each OAM mode modulated with different signal sequences at the receiving device.

In a wireless communication system using this OAM multiplexing technology, a uniform circular array antenna (hereinafter referred to as UCA (Uniform Circular Array)) is used, in which multiple antenna elements are arranged at equal intervals in a circle, to generate, combine, and transmit multiple OAM modes, thereby achieving spatial multiplexing transmission of different signal sequences (for example, Non-Patent Document 2). For example, a Butler circuit (Butler matrix circuit) is used to generate and separate signals for multiple OAM modes.

In addition, as a form of PtMP (Point-to-Multipoint) transmission in future wireless communications, a technology has been proposed that simultaneously accommodates a main line (backbone line) that performs large-capacity communication, such as FPU (Field Pickup Unit) or IAB (Integrated access and backhaul), and a best-effort type secondary line (terminal line). For example, Non-Patent Documents 3 and 4 disclose a technology that uses processing such as precoding at the transmitting station to remove or reduce interference between users in order to realize PtMP transmission using general MIMO technology.

J.Wang et al., "Terabit free-space data transmission employing orbital angular momentum multiplexing," Nature Photonics, Vol.6, pp.488-496, July 2012. Y.Yan et al., "High-capacity millimeter-wave communications with orbital angular momentum multiplexing," Nature Commun., vol.5, p.4876, Sep. 2014. Quentin H. Spencer et al., "Zero-Forcing Methods for Downlink Spatial Multiplexing in Multiuser MIMO Channels," IEEE TRANSACTIONS ON SIGNAL PROCESSING, VOL. 52, NO. 2, FEBRUARY 2004 Wen-Xuan Long et al., "Joint Spatial Division and Coaxial Multiplexing for Downlink Multi-User OAM Wireless Backhaul," IEEE TRANSACTIONS ON BROADCASTING, pp.1-15

As described above, a transmitter using UCA and a Butler circuit enables large-capacity communication, but in the future, it is desired to support multi-direction or mobility. However, in conventional wireless transmission technology, there is a problem that the computation load of precoder derivation to realize PtMP transmission using MIMO technology is large.

The disclosed technology aims to reduce the computational load required to realize PtMP transmission.

The disclosed technology is a transmitting device that includes a signal processing unit that processes PtMP transmission signals so as to use OAM multiplexing transmission for the trunk line and MIMO multiplexing transmission for the terminal line, and a transmitting unit that transmits signals addressed to the trunk line and signals addressed to the terminal line.

The computational load required to achieve PtMP transmission can be reduced.

FIG. 13 is a diagram showing an example of phase setting of a UCA for generating an OAM mode signal. 1A and 1B are diagrams illustrating an example of a phase distribution and a signal intensity distribution of an OAM multiplexed signal. 1 is a configuration diagram of a communication system according to an embodiment of the present invention. FIG. 2 is a diagram for explaining the positional relationship of each device according to the embodiment of the present invention. FIG. 4 is a sequence diagram showing an example of a flow of a communication process according to an embodiment of the present invention. FIG. 2 is a first diagram showing an example of reception power characteristics for each mode according to an embodiment of the present invention. FIG. 11 is a second diagram showing an example of reception power characteristics for each mode according to the embodiment of the present invention. FIG. 4 is a diagram illustrating an example of power control according to an embodiment of the present invention. FIG. 1 is a sequence diagram showing an example of a flow of a conventional communication process.

Hereinafter, an embodiment of the present invention (the present embodiment) will be described with reference to the drawings. The embodiment described below is merely an example, and the embodiment to which the present invention is applicable is not limited to the following embodiment.

(Outline of the present embodiment)
In this embodiment, OAM multiplex transmission is used for some of the lines (for example, the backbone lines) for PtMP transmission.

(Basic operation example)
An example of basic settings and operations related to the UCA used in each device in this embodiment will be described.

Figure 1 shows an example of phase setting of a UCA for generating an OAM mode signal. The UCA shown in Figure 1 is a UCA consisting of eight antenna elements.

In Fig. 1, the signals of OAM modes 0, 1, 2, 3, ... on the transmitting side are generated by the phase difference of the signals supplied to each antenna element (indicated by ●) of the UCA. In other words, the signal of OAM mode n is generated by setting the phase of the signal supplied to each antenna element so that the phase rotates n times (n x 360 degrees). For example, when the UCA is composed of m = 8 antenna elements as shown in Fig. 1 and a signal of OAM mode n = 2 is generated, a phase difference of 360n/m = 90 degrees counterclockwise is set to each antenna element so that the phase rotates two times as shown in Fig. 1 (3).

Note that a signal with the phase rotation direction reversed to that of an OAM mode n signal is called OAM mode -n. For example, the phase rotation direction of a positive OAM mode signal is counterclockwise, and the phase rotation direction of a negative OAM mode signal is clockwise.

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

To separate the OAM multiplexed signal on the receiving side, the phase of each antenna element of the UCA on the receiving side is set to be opposite to the phase of the antenna elements on the transmitting side.

However, if interference occurs between OAM modes due to an axial misalignment between the transmitting and receiving antennas, it becomes necessary to separate the mixed OAM mode signals by digital signal processing such as channel equalization and successive interference cancellation. Interference between OAM modes means, for example, a signal transmitted from a transmitting device in OAM mode 1 being output as an OAM mode 2 signal on the receiving side.

Figure 2 shows an example of the phase distribution and signal intensity distribution of an OAM multiplexed signal. In Figures 2 (1) and (2), the arrows represent the phase distribution of OAM mode 1 and OAM mode 2 signals as viewed from the transmitting side at an end face (propagation orthogonal plane) perpendicular to the propagation direction. The arrows start at 0 degrees, the phase changes linearly, and the arrows end at 360 degrees. In other words, an OAM mode n signal propagates with its phase rotating n times (n x 360 degrees) on the propagation orthogonal plane. Note that the arrows of the phase distribution of OAM mode -1 and -2 signals point in opposite directions.

The signal intensity distribution and the position where the signal intensity is maximum differ for each OAM mode. However, the intensity distribution of the same OAM mode with a different sign is the same. Specifically, the higher the OAM mode, the farther the position where the signal intensity is maximum is from the propagation axis (Non-Patent Document 2). Here, the OAM mode with a larger value is called a higher-order mode. For example, a signal in OAM mode 3 is a higher-order mode than signals in OAM mode 0, OAM mode 1, and OAM mode 2.

Figure 2 (3) shows the position where the signal strength is maximum for each OAM mode as a circle. The higher the OAM mode, the farther the position where the signal strength is maximum is from the central axis. Also, the beam diameter of the OAM mode multiplexed signal widens depending on the propagation distance, and the circle showing the position where the signal strength is maximum for each OAM mode becomes larger.

The system configuration and operation example of this embodiment are described in detail below.

(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 transmitting station 100, a receiving station 200, and a receiving terminal 300. Note that the configuration diagram shown in Fig. 3 is an example, and other configurations may be used. For example, the number of receiving terminals 300 may be one or more.

The transmitting station 100 is an example of a transmitting device that transmits OAM multiplexed radio waves in PtMP transmission. For example, the transmitting station 100 may use OAM multiplex transmission for the backbone line that transmits to the receiving station 200, and may use MIMO multiplex transmission for the terminal line that transmits to the receiving terminal 300.

The transmitting station 100 includes an antenna 110, a transmitting unit 120, and a signal processing unit 130. The antenna 110 is, for example, a UCA. The transmitting unit 120 transmits the OAM multiplexed signal via the antenna 110.

The signal processing unit 130 selects an OAM mode, performs power control, etc. For example, the signal processing unit 130 may assign a signal addressed to the receiving terminal 300 to one (or more) OAM modes with a high reception SINR depending on the position of the receiving terminal 300, and assign a signal addressed to the receiving station 200 to other OAM modes. Note that, when there are multiple receiving terminals 300, the signal processing unit 130 may assign OAM modes to all receiving terminals 300 and then assign other OAM modes to the receiving station 200.

The receiving station 200 is an example of a receiving device that receives signals from a backbone line. The receiving station 200 is installed opposite the transmitting station 100.

The receiving station 200 includes an antenna 210, a receiving unit 220, and a signal processing unit 230. The antenna 210 is, for example, a UCA. The receiving unit 220 receives the OAM multiplexed signal via the antenna 210. The signal processing unit 230 separates the received OAM multiplexed signal into each OAM mode.

The receiving terminal 300 is an example of a terminal that receives a signal from a terminal line. The receiving terminal 300 includes an antenna 310, a receiving unit 320, and a signal processing unit 330. The antenna 310 is, for example, a general antenna for wireless communication. The receiving unit 320 receives one (or more) OAM mode signals assigned to the receiving terminal 300.

The signal processing unit 330 separates one (or more) OAM mode signals assigned to the receiving terminal 300 using MIMO equalization processing.

(Positional relationship of each device)
Next, the positional relationship of each device included in the communication system will be described.

Figure 4 is a diagram for explaining the positional relationship of each device according to an embodiment of the present invention. The transmission radio wave transmitted from the transmitting station 100 is a signal generated so that each OAM mode is orthogonal toward the receiving station 200 at the opposite position, but due to the characteristics of OAM waves, it becomes non-orthogonal outside the opposite position within the transmission range.

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

Figure 5 is a sequence diagram showing an example of the flow of communication processing according to an embodiment of the present invention. The transmitting station 100 transmits a preamble that is orthogonal between all OAM modes to the receiving station 200 (step S101), and also transmits it to the receiving terminal 300 (step S102).

The receiving station 200 receives the preamble and estimates the received SINR for each OAM mode (step S103). The receiving station 200 transmits feedback information of the estimated SINR to the transmitting station 100 (step S104).

The receiving terminal 300 receives the preamble and estimates the received SINR for each OAM mode (step S105). The receiving terminal 300 transmits feedback information of the estimated SINR to the transmitting station 100 (step S106).

The transmitting station 100 receives feedback information from each device. The signal processing unit 130 of the transmitting station 100 calculates the allocation of OAM modes and the allocated power based on the received feedback information (step S107). Details of the allocation of OAM modes and the calculation of the allocated power will be described later.

Next, the signal processing unit 130 controls the transmission power to each device (step S108). Then, the transmission unit 120 transmits data addressed to the receiving station 200 to the receiving station 200 by the OAM mode signal assigned to the receiving terminal 300 (step S109), and transmits data addressed to the receiving terminal 300 to the receiving terminal 300 by the OAM mode signal assigned to the receiving terminal 300 (step S110).

The receiving unit 220 of the receiving station 200 receives a signal including data addressed to the receiving station 200. The signal processing unit 230 demodulates the received signal by OAM multiplexing processing (step S111).

The receiving unit 320 of the receiving terminal 300 receives a signal including data addressed to the receiving terminal 300. The signal processing unit 330 demodulates the received signal by MIMO equalization processing (step S112).

(Mode Selection)
Next, a method for selecting an OAM mode by the signal processing unit 130 in step S107 of Fig. 5 will be described. The signal processing unit 130 may select an OAM mode for a terminal line so as to maximize the communication capacity of the terminal line within a range in which the communication capacity of the backbone line is guaranteed.

Figure 6 is a first diagram showing an example of reception power characteristics for each mode according to an embodiment of the present invention. Graph 901 shows the reception power characteristics for OAM mode 0. Graph 902 shows the reception power characteristics for OAM modes ±1. Graph 902 shows the reception power characteristics for OAM modes ±2.

The signal processing unit 130 selects the OAM mode that maximizes the received SINR according to the position of the receiving terminal 300. For example, graph 904 shows the theoretical value of the received power characteristic when the OAM mode is selected to maintain the maximum received SINR according to the horizontal distance from the orthogonal axis of OAM multiplex transmission (the straight line in the transmission direction connecting the center of the UCA of the transmitting station 100 and the UCA of the receiving station 200). In this way, the signal processing unit 130 selects the OAM mode in which the signal for the receiving terminal 300 is superimposed according to the acquired received SINR.

Figure 7 is a second diagram showing an example of the reception power characteristics for each mode according to an embodiment of the present invention. When the signal processing unit 130 determines the position of the receiving terminal 300, the signal processing unit 130 may calculate the reception power characteristics for each OAM mode as shown in Figure 7.

Then, the signal processing unit 130 may select an OAM mode with a high receiving SINR at the receiving terminal 300 (e.g., [+1, -1] in the situation of FIG. 7). Also, the signal processing unit 130 assigns a signal addressed to the receiving station 200 to an OAM mode that was not assigned to the receiving terminal 300 (e.g., [0, +2, -2, +3, -3] in the situation of FIG. 7).

In addition, when the signal processing unit 130 transmits the same data to the receiving terminal 300 and the receiving station 200, it may assign the same OAM mode to the receiving station 200 and the receiving terminal 300.

(Power Control)
Next, a power control method performed by the signal processing unit 130 in step S107 of FIG. 5 will be described.

The signal processing unit 130 performs power control so as to maximize the communication capacity of the terminal line within a range in which the communication capacity of the trunk line is guaranteed. For example, the signal processing unit 130 may distribute surplus power to the terminal line while guaranteeing the communication capacity of the trunk line. This makes it possible to effectively utilize the surplus power of the trunk line, reduce the power of the signal of the trunk line that interferes with the terminal line, and increase the power of the desired signal of the receiving terminal 300.

Figure 8 is a diagram showing an example of power control according to an embodiment of the present invention. Figure 8 shows an example of power control when, for example, the backbone line is 100 Gbps or more. The signal processing unit 130 may uniformly lower the power of the OAM mode used by the backbone line by α dB, and uniformly raise the power of the OAM mode used by the terminal line by β dB. Here, the signal processing unit 130 determines α and β so that the total transmission power does not change before and after the control.

(Effects of the embodiment)
For comparison with this embodiment, a process of PtMP transmission using conventional general MU (Multi-User)-MIMO communication will be described.

Figure 9 is a sequence diagram showing an example of the flow of conventional communication processing. Figure 9 shows an example of MU-MIMO communication from a transmitter 1000 to a first receiver 2000 and a second receiver 3000.

The transmitter 1000 transmits a preamble to the first receiver 2000 (step S201) and also to the second receiver 3000 (step S202).

The first receiver 2000 receives the preamble and estimates the channel (step S203). The first receiver 2000 transmits feedback information of the estimated channel to the transmitter 1000 (step S204).

The second receiver 3000 receives the preamble and estimates the channel (step S205). The second receiver 3000 transmits feedback information of the estimated channel to the transmitter 1000 (step S206).

The transmitter 1000 receives feedback information from each device. The transmitter 1000 performs precoder calculations based on the received feedback information (step S207).

Next, the transmitter 1000 precodes the signal to each device (step S208). Then, the transmitter 1000 transmits data addressed to the first receiver 2000 to the first receiver 2000 (step S209), and transmits data addressed to the second receiver 3000 to the second receiver 3000 (step S210).

The first receiver 2000 receives a signal including data addressed to the first receiver 2000, and demodulates the received signal by MIMO equalization processing (step S211).

The second receiver 3000 receives a signal including data addressed to the second receiver 3000, and demodulates the received signal using MIMO equalization processing (step S212).

As such, in conventional general MU-MIMO communication processing, a precoding process is required, and channel feedback information is also required to derive the precoder.

In contrast, the communication system according to the present embodiment does not require precoding processing, so the computational load required to realize PtMP transmission can be reduced. In addition, instead of feedback information on the channel for deriving the precoder, feedback information on the received SINR only is used, so overhead can be reduced.

(Summary of the embodiment)
This specification describes at least the transmission apparatus and transmission method described in the following items.
(Section 1)
a signal processing unit for processing a PtMP transmission signal so as to use OAM multiplexing transmission for the trunk line and MIMO multiplexing transmission for the terminal line;
a transmitting unit for transmitting a signal addressed to the trunk line and a signal addressed to the terminal line,
Transmitting device.
(Section 2)
The signal processing unit controls transmission power so as to distribute surplus power to the terminal lines while ensuring the capacity of the trunk line.
2. A transmitting device as described in claim 1.
(Section 3)
The signal processing unit selects an OAM mode to be used for the terminal line based on feedback information of reception SINR acquired from a receiving station which is a transmission destination of the trunk line and a receiving terminal which is a transmission destination of the terminal line.
3. The transmitting device according to claim 1 or 2.
(Section 4)
the signal processing unit selects an OAM mode to be used for the terminal line so as to maximize the communication capacity of the terminal line while ensuring the communication capacity of the trunk line based on the feedback information of the received SINR.
A transmitting device as described in claim 3.
(Section 5)
The signal processing unit controls transmission power based on the feedback information of the received SINR so as to maximize the communication capacity of the terminal line while ensuring the communication capacity of the trunk line.
A transmitting device according to claim 3 or 4.
(Section 6)
A step of processing a PtMP transmission signal so as to use OAM multiplexing transmission for the trunk line and MIMO multiplexing transmission for the terminal line;
transmitting a signal addressed to the trunk line and a signal addressed to the terminal line;
A transmission method executed by a transmitting device.

Any of the above configurations provides a technology that makes it possible to reduce the computational load required to realize PtMP transmission. According to paragraph 2, surplus power can be distributed to terminal lines while ensuring the capacity of the trunk line. According to paragraph 3, PtMP transmission can be realized based on feedback information of the received SINR. According to paragraph 4, an OAM mode to be used for a terminal line can be selected so as to maximize the communication capacity of the terminal line while ensuring the communication capacity of the trunk line. According to paragraph 5, transmission power can be controlled so as to maximize the communication capacity of the terminal line while ensuring the communication capacity of the trunk line.

Although the present embodiment has been described above, the present invention is not limited to such a specific embodiment, and various modifications and variations are possible within the scope of the gist of the present invention as described in the claims.

100 Transmitting station 110 Antenna 120 Transmitting unit 130 Signal processing unit 200 Receiving station 210 Antenna 220 Receiving unit 230 Signal processing unit 300 Receiving terminal 310 Antenna 320 Receiving unit 330 Signal processing unit

Claims (6)

a signal processing unit for processing a PtMP transmission signal so as to use OAM multiplexing transmission for the trunk line and MIMO multiplexing transmission for the terminal line;
a transmitting unit for transmitting a signal addressed to the trunk line and a signal addressed to the terminal line,
Transmitting device. The signal processing unit controls transmission power so as to distribute surplus power to the terminal lines while ensuring the capacity of the trunk line.
The transmitting device according to claim 1 . The signal processing unit selects an OAM mode to be used for the terminal line based on feedback information of reception SINR acquired from a receiving station which is a transmission destination of the trunk line and a receiving terminal which is a transmission destination of the terminal line.
3. A transmitting device according to claim 1 or 2. the signal processing unit selects an OAM mode to be used for the terminal line so as to maximize the communication capacity of the terminal line while ensuring the communication capacity of the trunk line based on the feedback information of the received SINR.
The transmitting device according to claim 3. The signal processing unit controls transmission power based on the feedback information of the received SINR so as to maximize the communication capacity of the terminal line while ensuring the communication capacity of the trunk line.
5. A transmitting device according to claim 3 or 4. A step of processing a PtMP transmission signal so as to use OAM multiplexing transmission for the trunk line and MIMO multiplexing transmission for the terminal line;
transmitting a signal addressed to the trunk line and a signal addressed to the terminal line;
A transmission method executed by a transmitting device.

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