Transmitting device and transmitting method

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

[Technical Field]

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

[0002] 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 planes 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.

[0003] In a wireless communication system using this OAM multiplexing technology, a uniform circular array antenna (hereinafter referred to as a UCA (Uniform Circular Array)) in which multiple antenna elements are arranged at equal intervals in a circle is used to generate, combine, and transmit multiple OAM modes, thereby achieving spatially multiplexed transmission of different signal sequences (see, 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.

[0004] 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 an IAB (Integrated access and backhaul), and a best-effort secondary line (terminal line). For example, Non-Patent Documents 3 and 4 disclose a technology that uses processing such as precoding at a transmitting station to remove or reduce interference between users in order to realize PtMP transmission using a general MIMO technology. [Prior art documents] [Non-patent literature]

[0005] [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. [Non-patent document 3] 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 [Non-patent document 4] 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 Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, a transmitter using UCA and Butler circuits enables high-capacity communications, but in the future, it is desirable to support multi-directional and mobility.However, conventional wireless transmission technologies have problems such as 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.

[0007] The disclosed technology aims to reduce the amount of feedback and the computational load required to achieve PtMP transmission. [Means for solving the problem]

[0008] According to the disclosed technology, in order to perform PtMP transmission using OAM multiplexing transmission for a trunk 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 over the trunk line and transmits a power multiplexed signal over the terminal line. [Effects of the Invention]

[0009] The amount of feedback and the computational load required to achieve PtMP transmission can be reduced. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 10 is a diagram illustrating an example of phase setting of a UCA for generating an OAM mode signal. [Figure 2] 1A and 1B are diagrams illustrating examples of phase distribution and signal intensity distribution of an OAM multiplexed signal. [Figure 3] FIG. 1 is a configuration diagram of a communication system. [Figure 4] FIG. 2 is a diagram for explaining the positional relationship of each device. [Figure 5] FIG. 4 is a sequence diagram showing an example of the flow of communication processing in the first embodiment. [Figure 6] FIG. 10 is a first diagram showing an example of reception power characteristics for each mode. [Figure 7] FIG. 10 is a second diagram showing an example of reception power characteristics for each mode. [Figure 8] FIG. 10 illustrates an example of power control. [Figure 9] FIG. 1 is a sequence diagram showing an example of a flow of conventional communication processing. [Figure 10] FIG. 10 is a diagram for explaining an outline of a second embodiment. [Figure 11] FIG. 1 is a diagram illustrating the relationship between distance and received power in conventional NoMA. [Figure 12] FIG. 1 is a diagram illustrating the relationship between distance and received power in NoMA using OAM. [Figure 13] FIG. 10 is a sequence diagram for explaining an operation example 1 of the second embodiment. [Figure 14] FIG. 10 is a sequence diagram for explaining an operation example 2 of the second embodiment. [Figure 15] FIG. 10 is a diagram for explaining an angle. [Figure 16] FIG. 10 is a diagram for explaining a specific example of the second embodiment. [Figure 17] FIG. 10 is a diagram for explaining a specific example of the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] 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 applied is not limited to the following embodiment.

[0012] (Outline of this embodiment) In this embodiment, OAM multiplex transmission is used for some lines (for example, trunk lines) of PtMP transmission.

[0013] (Basic operation example) First, an example of basic settings and operations related to the UCA used in each device in this embodiment will be described.

[0014] Fig. 1 is a diagram showing an example of phase settings of a UCA for generating an OAM mode signal. The UCA shown in Fig. 1 is a UCA consisting of eight antenna elements.

[0015] In Figure 1, signals for 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. That is, signals for 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 configured with m = 8 antenna elements as shown in Figure 1 and a signal for OAM mode n = 2 is generated, a phase difference of 360n / m = 90 degrees counterclockwise is set for each antenna element (0 degrees, 90 degrees, 180 degrees, 270 degrees, 0 degrees, 90 degrees, 180 degrees, 270 degrees) so that the phase rotates twice, as shown in Figure 1 (3).

[0016] 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.

[0017] Spatial multiplexing wireless communication can be performed by generating different signal sequences as signals in different OAM modes and transmitting the generated signals simultaneously. On the transmitting side, signals to be transmitted in each OAM mode can be generated and combined in advance and the combined 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.

[0018] To separate the OAM multiplexed signal on the receiving side, the phase of each antenna element of the UCA on the receiving side can be set to be opposite to the phase of the antenna element on the transmitting side.

[0019] However, if interference occurs between OAM modes due to factors such as misalignment between the transmitting and receiving antennas, it becomes necessary to separate the mixed OAM mode signals through digital signal processing such as channel equalization and successive interference cancellation. Interference between OAM modes means, for example, that a signal transmitted from a transmitting device in OAM mode 1 is output as an OAM mode 2 signal on the receiving side.

[0020] Figure 2 shows examples 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 seen from the transmitter at an end face perpendicular to the propagation direction (orthogonal propagation plane). The arrows start at 0 degrees, and the phase changes linearly until they 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 orthogonal propagation plane. Note that the arrows for the phase distribution of OAM mode -1 and -2 signals point in opposite directions.

[0021] The signal intensity distribution and the position where the signal intensity is maximized differ for each OAM mode. However, the intensity distribution is the same for the same OAM mode but with a different sign. Specifically, the higher the order of the OAM mode, the farther the position where the signal intensity is maximized is from the propagation axis (Non-Patent Document 2). Here, an OAM mode with a larger value is referred to as a higher-order mode. For example, an OAM mode 3 signal is a higher-order mode than OAM mode 0, OAM mode 1, and OAM mode 2 signals.

[0022] 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 expands depending on the propagation distance, and the circle showing the position where the signal strength is maximum for each OAM mode becomes larger.

[0023] The system configuration and operation example of this embodiment will be described in detail below. A first embodiment and a second embodiment will be described below. In the first embodiment, a 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.

[0024] [First embodiment]

[0025] (System configuration of communication system) Fig. 3 is a configuration diagram of a communication system according to this 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, there may be one or more terminals 300.

[0026] 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 multiplexing transmission for a trunk line for transmission to the receiving station 200, and may use MIMO multiplexing transmission for a terminal line for transmission to the terminal 300.

[0027] 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 the first embodiment does not necessarily require the location information acquiring unit 140.

[0028] The antenna 110 is, for example, a UCA. The transmitter 120 generates an OAM-multiplexed signal from transmission data and transmits the signal via the antenna 110. The transmitter 120 may generate the OAM signal using a Butler circuit, or may generate the OAM signal through digital processing.

[0029] Processing unit 130 selects an OAM mode, allocates power, controls power, etc. For example, processing unit 130 may allocate a signal addressed to terminal 300 to one (or more) OAM modes with a high received SINR, and allocate a signal addressed to receiving station 200 to another OAM mode, depending on the location of terminal 300. Note that when there are multiple terminals 300, processing unit 130 may allocate OAM modes to all terminals 300 and then allocate another OAM mode to receiving station 200.

[0030] Processing unit 130 may also be called a signal processing unit, a control unit, etc. Processing unit 130 may be realized by one or more computers (computers having a CPU and memory) and software, or may be realized by a dedicated circuit, or may be realized by a computer, software, and a dedicated circuit.

[0031] The receiving station 200 is an example of a receiving device that receives a signal from a trunk line. The receiving station 200 is installed at a position opposite the transmitting station 100.

[0032] 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 signals for each OAM mode.

[0033] Terminal 300 is an example of a terminal that receives a signal on a terminal line. Terminal 300 includes an antenna 310, a receiving unit 320, and a 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.

[0034] The processing unit 330 separates, by MIMO equalization processing, one (or multiple) OAM mode signals assigned to the terminal 300. As will be described later, in the second embodiment, the processing unit 330 can perform interference removal processing such as SIC.

[0035] (Positional relationship of each device) Next, the positional relationship of each device included in the communication system will be described.

[0036] 4 is a diagram illustrating the positional relationship of each device according to this embodiment. The transmission radio wave transmitted from transmitting station 100 is a signal generated so that each OAM mode is orthogonal toward 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.

[0037] (Communication System Operation) Next, the operation of the communication system in the first embodiment will be described.

[0038] 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 to all OAM modes to the receiving station 200 (step S101), and also to the terminal 300 (step S102).

[0039] The receiving station 200 receives the preamble and estimates the received SINR for each OAM mode (step S103), and transmits feedback information of the estimated SINR to the transmitting station 100 (step S104).

[0040] 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).

[0041] The transmitting station 100 receives feedback information from each device. The processing unit 130 of the transmitting station 100 calculates the allocation of OAM modes and the allocation power based on the received feedback information (step S107). The details of the allocation of OAM modes and the calculation of the allocation power will be described later.

[0042] Next, the processing unit 130 controls the transmission power to each device (step S108). Then, the transmitting unit 120 transmits data addressed to the receiving station 200 to the receiving station 200 by using the signal in the OAM mode assigned to the receiving station 200 (step S109), and transmits data addressed to the terminal 300 to the terminal 300 by using the signal in the OAM mode assigned to the terminal 300 (step S110).

[0043] 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 demultiplexing (step S111).

[0044] 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).

[0045] (Mode selection) Next, we will explain how the processing unit 130 selects the OAM mode in step S107 of Fig. 5. The processing unit 130 may select the OAM mode for the terminal line so as to maximize the communication capacity of the terminal line within the range in which the communication capacity of the backbone line is guaranteed.

[0046] 6 is a first diagram showing an example of reception power characteristics for each mode according to the present embodiment. Graph 901 shows the reception power characteristics for OAM mode 0. Graph 902 shows the reception power characteristics for OAM modes ±1. Graph 903 shows the reception power characteristics for OAM modes ±2.

[0047] Processing unit 130 selects the OAM mode that maximizes the received SINR according to the position of 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 transmitting station 100 and the UCA of receiving station 200). In this way, processing unit 130 selects the OAM mode in which to superimpose the signal intended for terminal 300 according to the acquired received SINR.

[0048] 7 is a second diagram showing an example of the received power characteristics for each mode according to the present embodiment. When processing unit 130 determines the position of terminal 300, processing unit 130 may calculate the received power characteristics for each OAM mode as shown in FIG.

[0049] Then, the processing unit 130 may select an OAM mode (e.g., [+1, -1] in the situation of FIG. 7) with a high reception SINR at the terminal 300. Furthermore, the processing unit 130 may assign a signal addressed to the receiving station 200 to an OAM mode that was not assigned to the terminal 300 (e.g., [0, +2, -2, +3, -3] in the situation of FIG. 7).

[0050] 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.

[0051] (Power Allocation) Next, the power allocation method performed by the processing unit 130 in step S107 of FIG. 5 will be described.

[0052] 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 ensured. For example, the processing unit 130 may distribute surplus power to the terminal line while ensuring the communication capacity of the trunk line. This enables effective use of the surplus power of the trunk line, reduces the power of signals on the trunk line that interfere with the terminal line, and increases the SINR of the desired signal of the terminal 300.

[0053] 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. Processing unit 130 may uniformly reduce the power of the OAM mode used by the trunk line by α dB and uniformly increase the power of the OAM mode used by the terminal line by β dB. Here, processing unit 130 determines α and β so that the total transmit power does not change before and after the control. Note that the total transmit power is constant here.

[0054] (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.

[0055] 9 is a sequence diagram showing an example of the flow of conventional communication processing, in which MU-MIMO communication is performed from a transmitter 1000 to a first receiver 2000 and a second receiver 3000.

[0056] The transmitter 1000 transmits a preamble to the first receiver 2000 (step S201), and also to the second receiver 3000 (step S202).

[0057] The first receiver 2000 receives the preamble and estimates the channel (step S203), and transmits feedback information of the estimated channel to the transmitter 1000 (step S204).

[0058] The second receiver 3000 receives the preamble and estimates the channel (step S205), and transmits feedback information of the estimated channel to the transmitter 1000 (step S206).

[0059] The transmitter 1000 receives feedback information from each device and performs precoder calculation based on the received feedback information (step S207).

[0060] Next, the transmitter 1000 pre-codes the signals 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).

[0061] 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).

[0062] The second receiver 3000 receives a signal including data addressed to the second receiver 3000, and demodulates the received signal by MIMO equalization processing (step S212).

[0063] As described above, conventional general MU-MIMO communication processing requires precoding processing, and further requires channel feedback information for deriving the precoder.

[0064] In contrast, the communication system according to the present embodiment does not require precoding processing, and therefore can reduce the computation load for realizing PtMP transmission. Also, instead of feedback information of a channel for deriving a precoder, feedback information of only the received SINR (or received power) is used, and therefore overhead can be reduced.

[0065] [Second embodiment] Next, a second embodiment will be described. The technology of the first embodiment described above makes it possible to realize PtMP transmission with a reduced computational load. However, with the technology of the first embodiment, the number of users (number of terminals) is limited to the number of OAM modes or less. Furthermore, 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.

[0066] Therefore, in the second embodiment, multiple terminals 300 are assigned to the same OAM mode in a terminal line, 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.

[0067] That is, 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 selected two or more terminals 300 using the same OAM mode.

[0068] In the following description, the number of terminals 300 accommodated in one OAM mode using NoMA is assumed to be two, 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 to be subjected to power multiplexing may be three or more.

[0069] Fig. 10 shows an image of communication in the second embodiment. As shown in Fig. 10, transmission using OAM multiplexing is performed on the trunk line between the transmitting station 100 and the receiving station 200. On the other hand, transmission using NoMA multiplexing is performed on the terminal lines. In the example of Fig. 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.

[0070] The technology according to the second embodiment makes it possible to increase the number of users multiplexed on terminal lines while ensuring the capacity of the trunk line.

[0071] In addition, the use of OAM transmission can ease the restrictions on the combination of terminals that perform power multiplexing compared to conventional NoMA. This point will be explained with reference to Figs. 11 and 12.

[0072] NoMA requires pairing two devices with different received power. In other words, a device with high received power must be paired with a device with low received power. When using general transmission radio waves without OAM mode, the received power of a signal transmitted from a transmitting station gradually decreases as the distance increases, as shown in Figure 11. Furthermore, the rate of decrease decreases as the distance increases. In other words, NoMA device 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.

[0073] NoMA using OAM will be described with reference to Fig. 12. Fig. 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 OAM is used, due to the characteristics of the OAM wave, the distance at which power drops and the distance at which power 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.

[0074] (System configuration of communication system) The configuration of the communication system in the second embodiment is basically the same as the configuration of the communication system in the first embodiment, as explained with reference to Fig. 3. However, in the second embodiment, it is assumed that there are a plurality of terminals 300. Each unit of each device in the communication system has a function required to realize NoMA multiplexed transmission for each OAM mode in addition to the function in the first embodiment.

[0075] (Communication System Operation) 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 also be performed using the received power instead of the received SINR.

[0076] <Example 1>

[0077] An operation example 1 of the communication system in the second embodiment will be described with reference to Fig. 13. In the operation example 1, a transmitting station 100, a receiving station 200, a terminal 300-1, and a terminal 300-2 exist.

[0078] The transmitting station 100 transmits a preamble that is orthogonal to all OAM modes to the receiving station 200 (step S301), and also transmits it to the terminal 300-1 and the terminal 300-2 (steps S302, S303).

[0079] The receiving station 200 receives the preamble and estimates the received 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 received power to the transmitting station 100 (step S305).

[0080] Terminal 300-1 receives the preambles and estimates the received power for each OAM mode based on each preamble (step S306). Terminal 300-1 transmits feedback information of the estimated received power to transmitting station 100 (step S307). Similarly, terminal 300-2 transmits feedback information of the received power to transmitting station 100 (steps S308 and S309).

[0081] The transmitting station 100 receives feedback information from each device. The processing unit 130 of the transmitting station 100 allocates OAM modes and calculates allocated power based on the received feedback information (step S310).

[0082] 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 "received SINR" in the first embodiment. Note that in the second embodiment, "received SINR" may be used instead of "received power."

[0083] In the second embodiment, processing unit 130 assigns the OAM mode that maximizes the received power from among multiple OAM modes to each terminal 300. For example, assuming that all OAM modes are 1, 2, and 3, and the received power of terminal 300-1 is "OAM mode 1=-50dbm, OAM mode 2=-60dbm, OAM mode 3=-70dbm," and the received power of terminal 300-2 is "OAM mode 1=-60dbm, OAM mode 2=-70dbm, OAM mode 3=-70dbm," OAM mode 1 is assigned to terminal 300-1, and OAM mode 1 is also assigned to terminal 300-2.

[0084] Note that using the maximum received power in this manner is an example, and it is also possible to assign, for example, any OAM mode that is within the top N in terms of the magnitude of received power from among all OAM modes.

[0085] The calculation of the power allocation is also basically the same as the "power allocation" method described in the first embodiment.

[0086] That is, 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.

[0087] In the second embodiment, NoMA multiplexing is performed for two or more terminals 300 that use the same OAM mode, and therefore the processing unit 130 further determines the power allocation between two or more terminals that use the same OAM mode.

[0088] Here, it is assumed that the same OAM mode is assigned to two terminals 300. Processing unit 130 assigns high transmission power to terminal 300 with low received power, and low transmission power to terminal 300 with high received power. Note that if there is no difference in received power between two terminals 300 assigned the same OAM mode (for example, if there is no difference in received power equal to or greater than a threshold), those two terminals 300 may not be targets for power multiplexing.

[0089] In the example of terminal 300-1 and terminal 300-2 described above, the received power of terminal 300-2 is lower, so higher transmission power is allocated to terminal 300-2 than to terminal 300-1.

[0090] 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 includes data.

[0091] Assume that terminal 300-1 and terminal 300-2 are a NoMA pair. In S313, transmitter 120 transmits signals of the same OAM mode assigned to terminal 300-1 and terminal 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 terminal 300-1 and terminal 300-2. The signal addressed to terminal 300-1 includes data addressed to terminal 300-1, and the signal addressed to terminal 300-2 includes data addressed to terminal 300-2.

[0092] A signal addressed to terminal 300-2 with low received power is assigned a higher transmission power than the transmission power assigned to the signal addressed to terminal 300-1 with high received power.

[0093] 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 demultiplexing (step S314).

[0094] The receiver 320-1 of the terminal 300-1 with high reception power receives the multiplexed signal. The processor 330-1, which is a 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 processing is called successive interference cancellation (SIC). The signal subtracted from the received signal may also be called a replica.

[0095] In S317, receiver 320-2 of terminal 300-2 with low received power receives the multiplexed signal. Processing unit 330-2 regards the signal addressed to terminal 300-1 as interference and directly demodulates the received signal. Because low transmission power is assigned to the signal addressed to interfering terminal 300-1, processing unit 330-2 can demodulate the signal addressed to processing unit 330-2 without applying the above-mentioned SIC or the like.

[0096] <Example 2> A second operational example of the communication system in the second embodiment will be described with reference to Fig. 14. In the second operational example, there are also a transmitting station 100, a receiving station 200, a terminal 300-1, and a terminal 300-2.

[0097] In S401, the location information acquisition unit 140 of the transmitting station 100 acquires the location information of each terminal 300. It is assumed that the location information of the receiving station 200 is known. Any method may be used to acquire the location information of the terminal 300.

[0098] In S402, processing unit 130 estimates the received power for each OAM mode for each terminal 300 based on the location information of each terminal 300. For example, processing unit 130 calculates the spatial received power distribution for each OAM mode (or reads out the calculated received power distribution from a storage unit such as a memory), and estimates the received power for each OAM mode for each terminal 300 from the received power distribution and the location information. Similarly, processing unit 130 estimates the received power for each OAM mode at receiving station 200. The processing after estimating the received power is the same as the processing from S310 onwards in operation example 1.

[0099] <Example of OAM mode allocation without using receive power, and transmit power allocation> In the second operational example, by using location information, it is possible to allocate OAM modes and transmit power without using estimated values ​​of received power of each terminal 300.

[0100] For example, the processing unit 130 uses the location 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).

[0101] The above-mentioned "angle" will be explained using Fig. 15. Fig. 15 is a diagram showing 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 trunk line) corresponds to the above-mentioned angle.

[0102] 15, for example, two terminals 300 that are located at the same angle θ1 as seen from transmitting station 100 are selected as two terminals 300 to which the same OAM mode is to be assigned. Also, two terminals 300 that are located at the same angle θ2 as seen from transmitting station 100 are selected as two terminals 300 to which the same OAM mode is to be assigned.

[0103] Radio waves in OAM mode also have the property of attenuating as the distance from the transmitting station 100 increases, so the processing unit 130 can determine that, of two terminals 300 that are present in the same angular direction as viewed from the transmitting station 100, the terminal 300 closer to the transmitting station 100 (nearby terminal) has higher received power than the terminal 300 farther from the transmitting station 100 (far terminal). Therefore, the processing unit 130 allocates low transmission power to the near terminal and high transmission power to the far terminal.

[0104] Regarding which OAM mode is assigned to which terminal pair, as explained in FIG. 2, the higher the mode order of an OAM wave, the more energy spreads in the angular direction. Therefore, 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.

[0105] For example, in the example of FIG. 15, OAM mode 1 is assigned to two terminals 300 present in the direction of angle θ1, and OAM mode 2 is assigned to two terminals 300 present in the direction of angle θ2.

[0106] (Example) Fig. 16 is a diagram showing transmitting station 100, receiving station 200, and terminals 1 to 3 viewed from above. Assume that the received power of each terminal in each OAM mode is obtained by the above-described 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, but with clockwise rotation considered positive).

[0107] The shaded / diagonally shaded areas in FIG. 16 show an image of the area where the received power is strong in each OAM mode (received power distribution).

[0108] 17, processing unit 130 assigns OAM mode 2 to terminal 1 and terminal 2, and OAM mode 0 to terminal 3. Furthermore, OAM modes 1, -1, and -2 are assigned to receiving station 200. Note that this assignment method is one example.

[0109] Transmitter 120 allocates lower transmission power to the signal for terminal 1 than to the signal for terminal 2, power-multiplexes the signal for terminal 1 and the signal for terminal 2, and transmits the multiplexed signal in OAM mode 2. Transmitter 120 also transmits the signal for terminal 3 in OAM mode 0, and multiplexes the signal for receiving station 200 in OAM modes 1, -1, and -2 and transmits the multiplexed signal.

[0110] 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.

[0111] (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 (securing) line capacity. Furthermore, compared to conventional NoMA, it can ease the restrictions on the combination of terminals that perform power multiplexing.

[0112] (Addendum) This specification describes at least the transmitting device and transmitting method described in the following sections. (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 the trunk line and power multiplexing transmission for the terminal line; a transmitter 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 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. Item 1. A transmitting device according to item 1. (Additional note 3) 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. 3. The transmitting device according to claim 1 or 2. (Additional note 4) 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. A transmitting device according to claim 3. (Additional note 5) The processing unit selects the two or more terminals based on location information of each terminal and a received power distribution for each OAM mode. A transmitting device according to claim 3. (Additional note 6) The processing unit assigns an OAM mode that results in maximum received power to each terminal, and selects two or more terminals to which the same OAM mode is assigned as targets for power multiplexing. A transmitting device according to claim 3. (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 line; transmitting an OAM multiplexed signal over the trunk line and a power multiplexed signal over the terminal line; Sending method.

[0113] 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 symbols]

[0114] 100 transmitting stations 110 Antenna 120 Transmitter 130 Processing section 140 Location information acquisition unit 200 receiving stations 210 Antenna 220 Receiving unit 230 Processing section 300 devices 310 Antenna 320 Receiving Unit 330 Processing Section

Claims

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 the trunk line and power multiplexing transmission for the terminal lines; a transmitter that transmits an OAM multiplexed signal via the trunk line and a power multiplexed signal via the terminal line, Transmitting device.

2. 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 .

3. 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.

3. The transmitting device according to claim 1 or 2.

4. 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 .

5. The processing unit selects the two or more terminals based on location information of each terminal and a received power distribution for each OAM mode. The transmitting device according to claim 3 .

6. 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. The transmitting device according to claim 3 .

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 over the trunk line and a power multiplexed signal over the terminal line; Sending method.

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