WO2024079898A1

WO2024079898A1 - Transmission device and transmission method

Info

Publication number: WO2024079898A1
Application number: PCT/JP2022/038444
Authority: WO
Inventors: 知哉景山; 淳増野; 斗煥李; 健平賀; 裕文笹木; 康徳八木
Original assignee: 日本電信電話株式会社
Priority date: 2022-10-14
Filing date: 2022-10-14
Publication date: 2024-04-18

Abstract

In order to perform PtMP transmission using OAM multiplexing transmission on a backbone line and using power multiplexing transmission on a terminal line, this transmission device comprises: a processing unit that selects two or more terminals to be subjected to power multiplexing; and a transmission unit that transmits an OAM multiplexing signal through the backbone line and that transmits a power multiplexing signal through the terminal line.

Description

Transmitting device and transmitting method

The present invention relates to a technology for spatially multiplexing 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 (hereafter referred to as UCA (Uniform Circular Array)) is used, in which multiple antenna elements are arranged at equal intervals in a circle, to generate, synthesize and transmit multiple OAM modes, thereby achieving spatial multiplexing transmission of different signal sequences (for example, Non-Patent Document 2). A Butler circuit (Butler matrix circuit), for example, is used to generate and separate signals for multiple OAM modes.

Furthermore, 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 communications, such as an 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 technology that uses processing such as precoding at the transmitting station to eliminate or reduce interference between users in order to realize PtMP transmission using general MIMO technology.

As described above, a transmitter using UCA and Butler circuits enables high-capacity communication, but in the future, support for multi-direction or mobility is desired. However, conventional wireless transmission technology has problems with the computational load of precoder derivation to realize PtMP transmission using MIMO technology, and the large overhead due to feedback information from the receiver required for precoder derivation.

The disclosed technology aims to reduce the amount of feedback and the computational load required to achieve PtMP transmission.

According to the disclosed technology, in order to perform PtMP transmission using OAM multiplexing transmission for a backbone line and power multiplexing transmission for a terminal line, a processing unit that selects two or more terminals to be subjected to power multiplexing;
A transmitting device is provided, comprising: a transmitting unit that transmits an OAM multiplexed signal through the trunk line and transmits a power multiplexed signal through the terminal line.

The amount of feedback and 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. FIG. 1 is a configuration diagram of a communication system. FIG. 2 is a diagram for explaining the positional relationship of each device. FIG. 4 is a sequence diagram illustrating an example of a flow of a communication process according to the first embodiment. FIG. 11 is a first diagram showing an example of reception power characteristics for each mode. FIG. 11 is a second diagram showing an example of reception power characteristics for each mode. FIG. 1 illustrates an example of power control. FIG. 1 is a sequence diagram showing an example of a flow of a conventional communication process. FIG. 11 is a diagram for explaining an overview of a second embodiment. FIG. 1 is a diagram showing the relationship between distance and received power in conventional NoMA. FIG. 1 is a diagram showing the relationship between distance and received power in NoMA using OAM. FIG. 11 is a sequence diagram for explaining an operation example 1 of the second embodiment. FIG. 11 is a sequence diagram for explaining an operation example 2 of the second embodiment. FIG. 13 is a diagram for explaining an angle. FIG. 11 is a diagram for explaining a specific example of the second embodiment. FIG. 11 is a diagram for explaining a specific example of the second embodiment.

Below, an embodiment of the present invention (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 embodiment described below.

(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)
First, a basic setting and operation example relating to the UCA used in each device in this embodiment will be described.

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

In Figure 1, 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, signals of OAM mode n are 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 Figure 1, when a signal of OAM mode n = 2 is generated, a phase difference of 360n/m = 90 degrees counterclockwise is set for each antenna element so that the phase rotates two times, as shown in Figure 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 can be generated and synthesized in advance, and the synthesized signal for each OAM mode can be transmitted using a single UCA, or multiple UCAs can be used to transmit signals for 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 receiving UCA 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 OAM mode signals mixed due to interference using digital signal processing such as channel equalization and successive interference cancellation. Note that 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 while its phase rotates 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.

Each OAM mode signal has a different signal intensity distribution and a different position where the signal intensity is maximum. However, the intensity distribution is the same for the same OAM mode with a different sign. 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.

In Figure 2 (3), the position where the signal strength is maximum for each OAM mode is shown as a circle; however, the higher the OAM mode, the farther the position where the signal strength is maximum is from the central axis, and the beam diameter of the OAM mode multiplexed signal expands depending on the propagation distance, so that 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 will be described in detail below. The first and second embodiments will be described below. In the first embodiment, the basic system configuration and operation example of PtMP transmission using OAM multiplexing will be described. In the second embodiment, a technology that enables multiple users to be accommodated per OAM mode in PtMP transmission using OAM multiplexing based on the technology of the first embodiment will be described.

[First embodiment]

(System configuration of communication system)
Fig. 3 is a configuration diagram of a communication system according to the present embodiment. This communication system includes a transmitting station 100, a receiving station 200, and a terminal 300. Note that the configuration diagram shown in Fig. 3 is an example, and other configurations are also possible. For example, the number of 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 for transmitting to the receiving station 200, and use MIMO multiplex transmission for the terminal line for transmitting to the terminal 300.

The transmitting station 100 includes an antenna 110, a transmitting unit 120, a processing unit 130, and a location information acquiring unit 140. Note that in the first embodiment, the location information acquiring unit 140 may not be included.

The antenna 110 is, for example, a UCA. The transmitting unit 120 generates an OAM multiplexed signal from the transmission data and transmits the signal via the antenna 110. The transmitting unit 120 may generate the OAM signal using a Butler circuit, or may generate the OAM signal using digital processing.

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

The processing unit 130 may be called a signal processing unit, a control unit, etc. Furthermore, the processing unit 130 may be realized by one or more computers (computers having a CPU and memory) and software, by a dedicated circuit, or by a computer, software, and a dedicated circuit.

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 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 processing unit 230 separates the received OAM multiplexed signal into each OAM mode.

Terminal 300 is an example of a terminal that receives a signal on a terminal line. Terminal 300 includes antenna 310, receiving unit 320, and processing unit 330. Antenna 310 is, for example, a general antenna for wireless communication. Receiving unit 320 receives one (or multiple) OAM mode signals assigned to terminal 300.

The processing unit 330 separates one (or more) OAM mode signals assigned to the terminal 300 by MIMO equalization processing. As described later, in the second embodiment, the processing unit 330 can perform interference removal processing such as SIC.

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

FIG. 4 is a diagram for explaining the positional relationship of each device according to this embodiment. The radio waves transmitted from the transmitting station 100 are signals generated so that the OAM modes are orthogonal toward the receiving station 200 at the opposing position, but due to the characteristics of OAM waves, they become non-orthogonal outside the opposing position within the transmission range.

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

FIG. 5 is a sequence diagram showing an example of the flow of communication processing according to the first embodiment. 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 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 terminal 300 receives the preamble and estimates the received SINR for each OAM mode (step S105). The 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 processing unit 130 of the transmitting station 100 calculates the OAM mode allocation and the allocated power based on the received feedback information (step S107). Details of the OAM mode allocation and the calculation of the allocated power will be described later.

Then, the processing unit 130 controls the transmission power to each device (step S108). The transmitting unit 120 then transmits data addressed to the receiving station 200 to the receiving station 200 using the OAM mode signal assigned to the receiving station 200 (step S109), and transmits data addressed to the terminal 300 to the terminal 300 using the OAM mode signal assigned to the 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 processing unit 230 demodulates the received signal by OAM separation processing (step S111).

The receiving unit 320 of the terminal 300 receives a signal including data addressed to the terminal 300. The 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 processing unit 130 in step S107 of Fig. 5 will be described. The 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.

FIG. 6 is a first diagram showing an example of reception power characteristics for each mode according to this embodiment. 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 processing unit 130 selects the OAM mode that maximizes the received SINR according to the position of the terminal 300. For example, graph 904 shows the theoretical value of the received power characteristics when the OAM mode is selected to maintain the maximum received SINR according to the horizontal distance from the orthogonal axis of OAM multiplexed 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 processing unit 130 selects the OAM mode in which to superimpose the signal for the terminal 300 according to the acquired received SINR.

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

Then, the processing unit 130 may select an OAM mode with a high reception SINR for the terminal 300 (for example, [+1, -1] in the situation of FIG. 7). The processing unit 130 also assigns a signal addressed to the receiving station 200 to an OAM mode that has not been assigned to the terminal 300 (for example, [0, +2, -2, +3, -3] in the situation of FIG. 7).

When transmitting the same data to the terminal 300 and the receiving station 200, the processing unit 130 may assign the same OAM mode to the receiving station 200 and the terminal 300.

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

The processing unit 130 allocates power to maximize the communication capacity of the terminal line within the range where the communication capacity of the trunk line is guaranteed. For example, the 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, and reduces the power of the trunk line signals that interfere with the terminal line, thereby increasing the SINR of the desired signal of the terminal 300.

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

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

FIG. 9 is a sequence diagram showing an example of the flow of conventional communication processing. FIG. 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 the 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). The transmitter 1000 then 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 using 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 MU-MIMO communication processing, precoding processing is required, and channel feedback information is also required to derive the precoder.

In contrast, the communication system according to this embodiment does not require precoding processing, so the computational load required to achieve PtMP transmission can be reduced. Also, instead of feedback information on the channel for deriving the precoder, feedback information is only on the received SINR (or received power), so overhead can be reduced.

[Second embodiment]
Next, a second embodiment will be described. The technology of the first embodiment described above can realize PtMP transmission with reduced computation load. However, in the technology of the first embodiment, the number of users (number of terminals) is limited to the number of OAM modes or less. In addition, when the number of users to be accommodated is increased, it is necessary to reduce the power allocated to the OAM mode for the receiving station 200, which reduces the capacity of the trunk line.

In the second embodiment, therefore, in a terminal line, multiple terminals 300 are assigned to the same OAM mode, and signals are transmitted to the multiple terminals 300 in the same OAM mode using NoMA (Non-Orthogonal Multiple Access) multiplexing. NoMA multiplexing may also be called power multiplexing.

In other words, in the second embodiment, two or more terminals 300 having a difference in reception power are selected as targets for power multiplexing, and multi-user transmission by NoMA is performed for the two or more selected terminals 300 using the same OAM mode.

In the following description, the number of terminals 300 accommodated in one OAM mode using NoMA is set to two as an example, but the number of terminals 300 accommodated in one OAM mode using NoMA may be three or more. In other words, the number of terminals targeted for power multiplexing may be three or more.

Figure 10 shows an image of communication in the second embodiment. As shown in Figure 10, transmission is performed by OAM multiplexing on the backbone line between the transmitting station 100 and the receiving station 200. On the other hand, transmission is performed by NoMA multiplexing on the terminal lines. In the example of Figure 10, the pair of terminal 1 and terminal 2, and the pair of terminal 3 and terminal 4 are each NoMA pairs, and one OAM mode is assigned to each pair. For example, OAM mode 1 is assigned to the pair of terminal 1 and terminal 2, and OAM mode 2 is assigned to the pair of terminal 3 and terminal 4.

The technology in the second embodiment makes it possible to increase the number of users multiplexed on terminal lines while ensuring the capacity of the trunk line.

In addition, because OAM transmission is used, restrictions on the combination of terminals that perform power multiplexing can be relaxed compared to conventional NoMA. This point will be explained with reference to Figures 11 and 12.

In NoMA, it is necessary to pair two terminals with different reception power. In other words, it is necessary to pair a terminal with high reception power with a terminal with low reception power. When using general transmission radio waves without OAM mode, the reception power of a signal transmitted from a transmitting station gradually decreases as the distance increases, as shown in Figure 11. Also, the degree of decrease decreases as the distance increases. In other words, NoMA terminal pairs (two stars in Figure 11) are limited to a nearby terminal close to the transmitting station and a distant terminal far from the transmitting station.

NoMA using OAM will be described with reference to Figure 12. Figure 12 is a graph showing the relationship between distance from a transmitting station and received power when the OAM mode is 1 or -1. When using OAM, due to the characteristics of OAM waves, the distance at which the power drops and the distance at which it reaches a maximum appear repeatedly multiple times, making it possible to pair two terminals with a difference in received power at various positions of the two terminals, regardless of the distance from the transmitting station.

(System configuration of communication system)
The configuration of the communication system in the second embodiment is basically the same as that of the communication system in the first embodiment, as described with reference to Fig. 3. However, in the second embodiment, it is assumed that the number of terminals 300 is more than one. Each unit of each device in the communication system has a function required to realize NoMA multiplex transmission for each OAM mode in addition to the function in the first embodiment.

(Operation of the communication system)
Next, the operation of the communication system in the second embodiment will be described. Two examples will be described here as operation example 1 and operation example 2. In the first embodiment, mode assignment and the like are performed using the received SINR, but in the second embodiment, mode assignment and the like are performed using the received power. Note that in the first embodiment, mode assignment and the like may be performed using the received power instead of the received SINR.

With reference to FIG. 13, an operation example 1 of the communication system in the second embodiment will be described. In the operation example 1, there is a transmitting station 100, a receiving station 200, a terminal 300-1, and a terminal 300-2.

The transmitting station 100 transmits a preamble that is orthogonal between all OAM modes to the receiving station 200 (step S301), and also transmits it to the terminals 300-1 and 300-2 (steps S302 and S303).

The receiving station 200 receives the preamble and estimates the reception power of each OAM mode based on the preamble of each OAM mode (step S304). The receiving station 200 transmits feedback information of the estimated reception power to the transmitting station 100 (step S305).

The terminal 300-1 receives the preambles and estimates the reception power for each OAM mode based on each preamble (step S306). The terminal 300-1 transmits feedback information of the estimated reception power to the transmitting station 100 (step S307). Similarly, the terminal 300-2 also transmits feedback information of the reception power to the transmitting station 100 (steps S308, S309).

The transmitting station 100 receives feedback information from each device. The processing unit 130 of the transmitting station 100 calculates the OAM mode allocation and the allocated power based on the received feedback information (step S310).

The method of allocating OAM modes to each terminal is basically the same as the "mode selection" method described in the first embodiment. However, in the second embodiment, "received power" is used instead of the "received SINR" in the first embodiment. Note that in the second embodiment, "received SINR" may be used instead of "received power".

In the second embodiment, the processing unit 130 assigns, for each terminal 300, the OAM mode with the highest reception power among multiple OAM modes. For example, if all OAM modes are 1, 2, 3, and the reception power of terminal 300-1 is "OAM mode 1 = -50 dbm, OAM mode 2 = -60 dbm, OAM mode 3 = -70 dbm," and the reception power of terminal 300-2 is "OAM mode 1 = -60 dbm, OAM mode 2 = -70 dbm, OAM mode 3 = -70 dbm," OAM mode 1 is assigned to terminal 300-1, and OAM mode 1 is also assigned to terminal 300-2.

Note that using the maximum received power in this manner is merely an example, and any OAM mode that has the highest received power within the top N of all OAM modes may be assigned.

The calculation of the power allocation is also basically the same as the "power allocation" method described in the first embodiment.

In other words, the processing unit 130 allocates power to maximize the communication capacity of the terminal lines within a range that ensures the communication capacity of the trunk line. For example, the processing unit 130 allocates power to the trunk line so as to ensure the communication capacity of the trunk line, and distributes surplus power to the terminal lines.

In the second embodiment, NoMA multiplexing is performed for two or more terminals 300 that use the same OAM mode, so the processing unit 130 further determines the power allocation between two or more terminals that use the same OAM mode.

Here, it is assumed that the same OAM mode is assigned to two terminals 300. The processing unit 130 assigns high transmission power to the terminal 300 with low reception power, and assigns low transmission power to the terminal 300 with high reception power. Note that if there is no reception power difference between two terminals 300 assigned the same OAM mode (for example, if there is no reception power difference equal to or greater than a threshold value), the two terminals 300 may not be subject to power multiplexing.

In the above example of terminals 300-1 and 300-2, the received power of terminal 300-2 is lower, so a higher transmission power is assigned to terminal 300-2 than the transmission power assigned to terminal 300-1.

Next, the processing unit 130 controls the transmission power to each device (step S311). Here, controlling the transmission power means, for example, notifying the transmitting unit 120 of the transmission power for each destination. Then, the transmitting unit 120 transmits the OAM mode signal assigned to the receiving station 200 to the receiving station 200 at the assigned transmission power (step S312). The transmission signal contains data.

Suppose that terminals 300-1 and 300-2 are a NoMA pair. In S313, the transmitter 120 transmits signals of the same OAM mode assigned to terminals 300-1 and 300-2 (a multiplexed signal in which a signal addressed to terminal 300-1 and a signal addressed to terminal 300-2 are multiplexed) to terminals 300-1 and 300-2. The signal addressed to terminal 300-1 contains data addressed to terminal 300-1, and the signal addressed to terminal 300-2 contains data addressed to terminal 300-2.

A higher transmission power is assigned to the signal addressed to terminal 300-2, which has low received power, than the transmission power assigned to the signal addressed to terminal 300-1, which has high received power.

The receiving unit 220 of the receiving station 200 receives a signal including data addressed to the receiving station 200. The processing unit 230 demodulates the received signal by OAM separation processing (step S314).

The receiver 320-1 of the terminal 300-1, which has high reception power, receives the multiplexed signal. The processor 330-1, which is the processing unit of the terminal 300-1, demodulates the signal addressed to the terminal 300-2 from the received signal (multiplexed signal), and subtracts the demodulated signal from the received signal to separate the signal addressed to itself (terminal 300-1) (S315), and demodulates the separated signal (S316). This type of interference subtraction process is called successive interference cancellation (SIC). The signal subtracted from the received signal may be called a replica.

In S317, the receiver 320-2 of the terminal 300-2 with the low reception power receives the multiplexed signal. The processor 330-2 regards the signal addressed to the terminal 300-1 as interference, and directly demodulates the received signal. Because low transmission power is assigned to the signal addressed to the interfering terminal 300-1, the processor 330-2 is able to demodulate the signal addressed to the processor 330-2 without applying the above-mentioned SIC, etc.

<Operation example 2>
An operation example 2 of the communication system in the second embodiment will be described with reference to Fig. 14. In the operation example 2, there are also a transmitting station 100, a receiving station 200, a terminal 300-1, and a terminal 300-2.

In S401, the location information acquisition unit 140 of the transmitting station 100 acquires the location information of each terminal 300. Note that the location information of the receiving station 200 is assumed to be known. Any method may be used to acquire the location information of the terminal 300.

In S402, the processing unit 130 estimates the reception power for each OAM mode for each terminal 300 based on the position information of each terminal 300. For example, the processing unit 130 calculates the spatial reception power distribution for each OAM mode (or reads the calculated reception power distribution from a storage unit such as a memory) and estimates the reception power for each OAM mode for each terminal 300 from the reception power distribution and the position information. Similarly, the processing unit 130 estimates the reception power for each OAM mode at the receiving station 200. The processing after estimating the reception power is the same as the processing from S310 onwards in operation example 1.

<Example of OAM mode allocation without using reception power and transmission power allocation>
In the second operation example, by utilizing location information, it is also possible to perform allocation of OAM modes and allocation of transmission power without using an estimated value of the received power of each terminal 300 .

For example, the processing unit 130 uses the position information of each terminal 300 to select two terminals 300 that are located at the same angle as seen from the transmitting station 100 as two terminals 300 to which the same OAM mode is to be assigned (i.e., targets for power multiplexing).

The above "angle" will be explained using FIG. 15. FIG. 15 is a diagram of the transmitting station 100 and the receiving station 200 as viewed from above. As shown in FIG. 15, the angle θ as seen from the transmitting station 100 with respect to the axis connecting the transmitting station 100 and the receiving station 200 (the axis of the backbone line) corresponds to the above angle.

In the example of FIG. 15, for example, two terminals 300 that are located in a direction of the same angle θ1 as seen from the transmitting station 100 are selected as two terminals 300 to which the same OAM mode is assigned. Also, two terminals 300 that are located in a direction of the same angle θ2 as seen from the transmitting station 100 are selected as two terminals 300 to which the same OAM mode is assigned.

OAM mode radio waves also have the property of attenuating as the distance from the transmitting station 100 increases, so the processing unit 130 can consider that, of two terminals 300 that exist in the same angular direction as seen from the transmitting station 100, the terminal 300 closer to the transmitting station 100 (nearby terminal) has a higher received power than the terminal 300 farther from the transmitting station 100 (far terminal). Therefore, the processing unit 130 assigns low transmission power to the near terminal and high transmission power to the far terminal.

Regarding which OAM mode is assigned to which terminal pair, as explained in FIG. 2, the higher the mode order of the OAM wave, the more energy spreads in the angular direction, so a lower order OAM mode is assigned to the two terminals 300 with a small angle θ, and a higher order OAM mode is assigned to the two terminals 300 with a large angle θ.

For example, in the example of FIG. 15, OAM mode 1 is assigned to two terminals 300 located in a direction of angle θ1, and OAM mode 2 is assigned to two terminals 300 located in a direction of angle θ2.

(Concrete example)
Fig. 16 is a diagram showing the transmitting station 100, the receiving station 200, and the terminals 1 to 3 as viewed from above. It is assumed that the received power of each terminal in each OAM mode is obtained by the above-mentioned operation example 1 or operation example 2 as shown in Fig. 17. Fig. 17 also shows the angles of each terminal in the situation of Fig. 16 (the angles explained in Fig. 15, where the clockwise direction is positive).

The shaded/shaded areas in Figure 16 show an image of the areas where the received power is strong in each OAM mode (received power distribution).

The processing unit 130 assigns OAM mode 2 to terminal 1 and terminal 2, and OAM mode 0 to terminal 3, based on the reception power of each OAM mode of each terminal shown in FIG. 17. In addition, the processing unit 130 assigns OAM modes 1, -1, and -2 to the receiving station 200. Note that this assignment method is one example.

The transmitter 120 allocates a lower transmission power to the signal from terminal 1 than to the signal from terminal 2, power-multiplexes the signals for terminal 1 and terminal 2, and transmits them in OAM mode 2. The transmitter 120 also transmits the signal for terminal 3 in OAM mode 0, and multiplexes the signal for the receiving station 200 in OAM modes 1, -1, and -2.

The receiving station 200 demodulates signals in OAM modes 1, -1, and -2. Terminal 1 demodulates the signal addressed to terminal 2 from the received signal, subtracts the demodulated signal from the received signal, and demodulates the signal addressed to terminal 1 from the received signal after subtraction.

Terminals

2 and 3 each demodulate the received signal as a signal addressed to themselves.

(Effects of the Second Embodiment)
In addition to the effects of the first embodiment, the technology according to the second embodiment has the effect of increasing the number of multiplexed terminal lines while ensuring (ensuring) line capacity. Also, compared to conventional NoMA, the constraints on the combination of terminals that perform power multiplexing can be relaxed.

(Additional Note)
This specification describes at least the transmission device and transmission method described in the following items.
(Additional Note 1)
A processing unit that selects two or more terminals that are targets for power multiplexing in order to perform PtMP transmission using OAM multiplexing transmission for a trunk line and power multiplexing transmission for a terminal line;
a transmission unit that transmits an OAM multiplexed signal through the trunk line and a power multiplexed signal through the terminal line,
Transmitting device.
(Additional Note 2)
The processing unit selects a nearby terminal and a distant terminal that are in the same angular direction as seen from the transmitting device as targets for power multiplexing, and assigns the same OAM mode to the nearby terminal and the distant terminal.
(Additional Note 3)
3. The transmitting device according to claim 1, wherein the processing unit selects two or more terminals having a difference in reception power as targets for power multiplexing, and assigns the same OAM mode to the two or more terminals.
(Additional Note 4)
The transmitting device according to supplementary claim 3, wherein the processing unit selects the two or more terminals based on an estimated value of received power for each OAM mode received from each terminal.
(Additional Note 5)
The transmitting device according to claim 3, wherein the processing unit selects the two or more terminals based on location information of each terminal and a reception power distribution for each OAM mode.
(Additional Note 6)
The transmission device according to claim 3, wherein the processing unit assigns an OAM mode that provides maximum reception power to each terminal, and selects two or more terminals to which the same OAM mode is assigned as targets for power multiplexing.
(Additional Note 7)
A step of selecting two or more terminals to be subjected to power multiplexing in order to perform PtMP transmission using OAM multiplexing transmission for the trunk line and power multiplexing transmission for the terminal lines;
transmitting an OAM multiplexed signal through the trunk line and a power multiplexed signal through the terminal line;
Transmission method.

The present embodiment has been described above, but the present invention is not limited to this 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 Processing unit 140 Location information acquiring unit 200 Receiving station 210 Antenna 220 Receiving unit 230 Processing unit 300 Terminal 310 Antenna 320 Receiving unit 330 Processing unit

Claims

A processing unit that selects two or more terminals that are targets for power multiplexing in order to perform PtMP transmission using OAM multiplexing transmission for a trunk line and power multiplexing transmission for a terminal line;
a transmission unit that transmits an OAM multiplexed signal through the trunk line and a power multiplexed signal through the terminal line,
Transmitting device.
The transmitting device according to claim 1 , wherein the processing unit selects a nearby terminal and a distant terminal that are present in the same angular direction as seen from the transmitting device as targets for power multiplexing, and assigns the same OAM mode to the nearby terminal and the distant terminal.
The transmitting device according to claim 1 , wherein the processing unit selects two or more terminals having a difference in reception power as targets for power multiplexing, and assigns the same OAM mode to the two or more terminals.
The transmitting device according to claim 3 , wherein the processing unit selects the two or more terminals based on an estimated value of received power for each OAM mode received from each terminal.
The transmitting device according to claim 3 , wherein the processing unit selects the two or more terminals based on location information of each terminal and a reception power distribution for each OAM mode.
The transmitting device according to claim 3 , wherein the processing unit assigns an OAM mode that provides a maximum reception power to each terminal, and selects two or more terminals to which the same OAM mode is assigned as targets for power multiplexing.
A step of selecting two or more terminals to be subjected to power multiplexing in order to perform PtMP transmission using OAM multiplexing transmission for the trunk line and power multiplexing transmission for the terminal lines;
transmitting an OAM multiplexed signal through the trunk line and a power multiplexed signal through the terminal line;
Transmission method.