Information processing device, transmitting device, and method

Abstract

To improve quality of wireless communication.SOLUTION: When signals are simultaneously received from K transmission-side apparatuses by a receiving antenna, and repetition is performed by the K transmission-side apparatuses, an information processing apparatus, in order to obtain a transmitted reference signal x(k,n) transmitted from a transmission-side apparatus k (k=1,...,K) by the n-th reference signal transmission in the repetition, acquires a phase rotation amount φ(g,n) given to a transmitted reference signal x(k) and assigned to a group g to which the transmission-side apparatus k belongs, and transmits the phase rotation amount φ(g,n) to the transmission-side apparatus k. The phase rotation amount φ(g,n) is acquired so that received reference signals from transmission-side apparatuses not belonging to the group g are cancelled when a phase rotation amount opposite to the phase rotation amount φ(g,n) is given to a received reference signal r(n) received in the receiving antenna, and the first to N-th received reference signals in the repetition are added.SELECTED DRAWING: Figure 13

Description

[Technical field]

[0001] TECHNICAL FIELD This disclosure relates to wireless communications. [Background technology]

[0002] For example, an increase in mobile IoT devices, such as connected cars and drones, for which low latency is important, is expected. However, frequency resources to accommodate mobile IoT devices are tight. Therefore, low latency and efficient use of frequencies are required for wireless communication.

[0003] To realize low-latency wireless communication, a configured grant (CG) is used. In a conventional communication procedure, when a terminal transmits data to a base station, the terminal first receives permission (grant) for transmission and a designation of wireless resources that can be used for the data transmission from the base station, and transmits the data using the designated wireless resources. On the other hand, in contrast to this, in a CG, for example, the base station notifies the terminal of a transmission parameter that designates wireless resources that can be used for data transmission in advance, and a communication permission. This allows the terminal to omit negotiation with the base station when transmitting data, and immediately use the designated wireless resources to transmit data to the base station.

[0004] To achieve efficient use of frequencies, Non-Orthogonal Multiple Access (NOMA) is used, which is a method in which multiple terminals share the same frequency band and the same time domain. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Masafumi MORIYAMA, Kenichi TAKIZAWA, Masayuki OODO, Hayato TEZUKA, Fumihide KOJIMA, "Experimental Evaluation of a Novel Up-link NOMA System for IoT communication Equipping Repetition Transmission and Receive Diversity," IEICE TRANSACTIONS on Communications, August 1, 2019, Vol.E102-B, No.8, pp1467-1476

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, when using NOMA, since the signals transmitted from each terminal are superimposed and received at the base station, the signals received at the base station are likely to be affected by interference between terminals due to the superposition. As a result, it may be difficult for the base station to restore the original signals transmitted from each terminal, and the communication quality may deteriorate.

[0007] One aspect of the present disclosure is to provide an information processing apparatus, a transmission-side apparatus, and a method capable of improving the quality of wireless communication when a plurality of terminals share the same frequency band and the same time domain.

Means for Solving the Problems

[0008] One aspect of the present disclosure is when receiving signals simultaneously from K (K: positive integer) transmission-side apparatuses by a receiving antenna, and when the K transmission-side apparatuses perform consecutive transmissions of the same signal N times (N: positive integer) in repetition, dividing the K transmission-side apparatuses into G groups (G: positive integer, 1 < G ≦ K), In order to obtain a transmission reference signal x(k,n) transmitted from a transmitting device k (k=1,...,K) included in the K transmitting devices in the n-th (n=1,...,N) reference signal transmission in the continuous transmission, a phase rotation amount φ(g,n) is given to the transmission reference signal x(k), and the phase rotation amount φ(g,n) is assigned to a group g (g=1,...,G) to which the transmitting device k belongs. In the n-th reference signal transmission in the continuous transmission, a received reference signal r(n) is received at the receiving antenna, the received reference signal r(n) including a transmission reference signal from each of the K transmitting side devices. When the received reference signals r(n) are given a phase rotation amount opposite to the phase rotation amount φ(g,n) and are added up from the 1st to the Nth transmissions in the continuous transmission, the received reference signal from the transmitting side device that does not belong to the group g is canceled. To obtain transmitting a phase sequence Φg={φ(g,1),...,φ(g,N)} including the phase rotation amounts φ(g,n) of the group g from the first time to the N time to the transmitting side device k; A control unit that executes The information processing device includes:

[0009] Another aspect of the present disclosure is at least one transmitting antenna; When a signal is transmitted simultaneously with other K-1 transmitting side devices and a continuous transmission is performed in which each of the other K-1 transmitting side devices transmits the same signal repeatedly N times (N: a positive integer) in succession, receiving from a receiving side device a phase sequence Φg={φ(g,1),...,φ(g,N)} including a phase rotation amount φ(g,n) given to a transmission reference signal x(s) (s indicates the device itself) assigned to a group g (g: an integer from 1 to G) to which the transmitting side device itself belongs out of G groups into which the K transmitting side devices, including the other K-1 transmitting side devices and the device itself, are divided in the nth (n=1,...,N) transmission of a reference signal in the continuous transmission; In the n-th reference signal transmission in the continuous transmission, a phase rotation amount φ(g,n) is applied to the transmission reference signal x(s) to obtain a transmission reference signal x(s,n); Transmitting the transmission reference signal x(s,n) from the at least one transmission antenna; a control unit that executes; A transmission-side device comprising:

[0010] One of the other aspects of the present disclosure is that when a computer receives signals from K (K: positive integer) transmission-side devices simultaneously by a receiving antenna, and a continuous transmission in which the same signal is repeatedly transmitted N times (N: positive integer) continuously is performed by the K transmission-side devices, dividing the K transmission-side devices into G groups (G: positive integer, 1 < G ≤ K), and in order to obtain the transmission reference signal x(k,n) transmitted from the transmission-side device k (k = 1,..., K) included in the K transmission-side devices in the transmission of the n-th (n = 1,..., N) reference signal in the continuous transmission, the phase rotation amount given to the transmission reference signal x(k), which is the phase rotation amount φ(g,n) assigned to the group g (g = 1,..., G) to which the transmission-side device k belongs, in the transmission of the n-th reference signal in the continuous transmission, for the received reference signal r(n) received by the receiving antenna, which is the received reference signal r(n) including the transmission reference signals from each of the K transmission-side devices, giving a phase rotation amount opposite to the phase rotation amount φ(g,n) so that the received reference signals from the transmission-side devices not belonging to the group g are canceled when added together from the first to the N-th times in the continuous transmission, obtaining; transmitting to the transmission-side device k a phase sequence Φg = {φ(g,1),..., φ(g,N)} including the phase rotation amounts φ(g,n) from the first to the N-th times of the group g; A method including:

Advantages of the Invention

[0011] According to one aspect of the present disclosure, it is possible to improve the quality of wireless communication when a plurality of terminals share the same frequency band and the same time domain.

Brief Description of the Drawings

[0012] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a wireless communication system according to the first embodiment. [Diagram 2] FIG. 2 is a diagram illustrating SIC. [Diagram 3] FIG. 3 is a diagram for explaining continuous transmission. [Figure 4] FIG. 4 is a diagram showing a radio frame for signal transmission. [Diagram 5] FIG. 5 is a diagram illustrating an example of a hardware configuration of a base station and a terminal. [Figure 6] FIG. 6 is a diagram illustrating an example of a functional configuration of the terminal. [Figure 7] FIG. 7 is a diagram illustrating an example of a functional configuration of a base station. [Figure 8] FIG. 8 is a flowchart of the continuous transmission control process by the base station. [Figure 9] FIG. 9 is an example of a flowchart of a process of acquiring continuous transmission parameters in the base station. [Figure 10] FIG. 10 is an example of a flowchart of a process of measuring a path loss Lk between a base station and a terminal k and sorting the terminals in ascending order of the path loss Lk. [Figure 11] FIG. 11 is an example of a flowchart of a process of measuring a path loss Lk between a base station and a terminal k and sorting the terminals in ascending order of the path loss Lk. [Figure 12] FIG. 12 is an example of a flowchart of a process for allocating a transmission power value Pk and a transmission reference signal x_RS(k) of a terminal k. [Figure 13] FIG. 13 is an example of a flowchart of a process for allocating the amount of phase rotation φ(k,n) used by each terminal in each transmission in continuous transmission. [Figure 14] FIG. 14 is an example of a flowchart of a communication channel estimation process in the base station. [Figure 15] FIG. 15 is an example of a graph showing correlation characteristics of a received reference signal at a base station when no phase rotation is performed on a transmitted reference signal and a received reference signal in continuous transmission of reference signals. [Figure 16] FIG. 16 is an example of a graph showing correlation characteristics of a received reference signal at a base station when phase rotation is performed on a transmitted reference signal and a received reference signal in continuous transmission of reference signals as in the first embodiment. [Figure 17] FIG. 17 is a diagram showing an example of a result of the simulation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] A data signal transmitted from a terminal is affected by the environment on the way to the base station, and reaches the base station with an interference signal added. Therefore, the base station estimates the influence of the communication path, and uses the communication path estimation result to restore the original data signal from the received data signal. In other words, by estimating the communication path with high accuracy, the data signal can be restored more accurately, and the quality of wireless communication can be improved.

[0014] The channel is estimated using a reference signal received from a terminal, and therefore, in order to estimate the channel accurately, it is necessary to obtain a sufficient signal-to-noise ratio (SNR) of the reference signal.

[0015] In addition, when a terminal moves, for example, the distance from the base station increases, and a situation occurs in which the SNR of the received signal from the terminal is insufficient. In such a case, the terminal is made to repeatedly transmit the same signal a predetermined number of times, and the SNR of the signal received from the terminal a predetermined number of times is calculated. By adding up the received signals, a sufficient SNR can be obtained for the received signal from the terminal. Repeated transmission of the same signal a predetermined number of times is called repetition. Repetition is performed for both reference signals and data signals.

[0016] However, when multiple terminals share the same frequency band and the same time domain, even if continuous transmission is performed and the SNR of the received reference signal is sufficient, interference between terminals remains in the received reference signal. If interference between terminals remains in the received reference signal and its influence is large, the accuracy of the estimation of the communication channel may decrease, and the accuracy of the restoration of the data signal may decrease.

[0017] In one aspect of the present disclosure, a base station cancels the received reference signals from some of the terminals by adding up a predetermined number of received reference signals in succession from a plurality of terminals, thereby extracting the received reference signals from the remaining terminals. The obtained received reference signals are free of interference from the received reference signals from the remaining terminals, and the communication paths from the remaining terminals to the base station can be accurately estimated.

[0018] Specifically, one aspect of the present disclosure is an information processing device including a control unit. The information processing device may be a device provided in a receiving device, or may be a device independent of the receiving device. The receiving device is, for example, a base station. However, the receiving device is not limited to this, and may be a terminal when receiving a data signal. The control unit may be, for example, a processor such as a CPU (Central Processing Unit). The transmitting device is, for example, The transmitting device is a user terminal (User Equipment: UE), but is not limited thereto, and may be, for example, a base station when transmitting a data signal.

[0019] In one aspect of the present disclosure, it is assumed that signals are simultaneously received by a receiving antenna provided in a receiving device from K (K: a positive integer) transmitting devices, and that each of the K transmitting devices performs a continuous transmission in which the same signal is repeatedly transmitted N (N: a positive integer) times in succession. In such a case, the control unit divides the K transmitting devices into G (G: a positive integer, 1 < G ≦ K) groups. Transmitting devices belonging to the same group use the same phase rotation amount φ(g,n). The phase rotation amount φ(g,n) is the phase rotation amount used by the transmitting device k belonging to group g (g: an integer from 1 to G) in the transmission of the n-th (n: an integer from 1 to N) reference signal in the continuous transmission.

[0020] The transmitting device k (k: an integer from 1 to K) generates a transmission reference signal x(k). The transmission reference signal x(k) is the same signal in the transmissions from the first to the N-th in the continuous transmission. When transmitting the n-th reference signal in the continuous transmission, the transmitting device k transmits a transmission reference signal x(k,n) obtained by applying the phase rotation amount φ(g,n) (g: the group to which the transmitting device k belongs) to the transmission reference signal x(k).

[0021] In the receiving device, the receiving antenna receives a received reference signal r(n) in the transmission of the n-th reference signal in the continuous transmission. The received reference signal r(n) includes received reference signals corresponding to the transmission reference signals from each of the K transmitting devices. The received reference signal r(k,n) corresponds to a signal obtained by applying the influence of the communication path to the transmission reference signal x(k,n) transmitted from the transmitting device k, and includes the transmission reference signal x(k,n) and noise.

[0022] The control unit obtains the phase rotation amount φ(g,n) used by the transmitting device k in the transmission of the n-th transmission reference signal x(k) in the continuous transmission, and gives the received reference signal r(n) in the n-th transmission in the continuous transmission a phase rotation amount opposite to the phase rotation amount φ(g,n) of group g, so that the received reference signals from the transmitting devices not belonging to group g are canceled when added together from the first to the N-th. More specifically, the control unit sets the phase rotation amount φ(g,n) to G The control unit transmits a phase sequence Φg={φ(g,1),...,φ(g,N)} including the phase rotation amount φ(g,n) of group g for each of the first to Nth times to the transmitting device k.

[0023] When each transmitting device k transmits a reference signal continuously using the phase rotation amount φ(k,n), the receiving device obtains a receiving reference signal r(g) by multiplying the receiving reference signal r(n) in the nth transmission of the continuous transmission for group g by the phase rotation amount φ(g,n) of group g and adding up the first to Nth transmissions. The receiving reference signal r(n) in the nth transmission of the continuous transmission includes a receiving reference signal r(k,n) from the transmitting device k belonging to group g and a receiving reference signal r(p,n) from a transmitting device p not belonging to group g. However, the receiving reference signal r(p,n) is cancelled by multiplying the receiving reference signal r(p,n) in the nth transmission of the continuous transmission by the phase rotation amount φ(g,n) of group g to which the transmitting device p does not belong and adding up the first to Nth transmissions of the continuous transmission. As a result, the received reference signal r(g) includes received reference signals received from one or more transmitting devices belonging to group g, but does not include received reference signals from transmitting devices that do not belong to group g.

[0024] That is, the received reference signal r(k) from the transmitting device k belonging to group g, which is included in the received reference signal r(g), is not affected by the interference of the received reference signal from the transmitting device not belonging to group g. By performing the same for each group to obtain the received reference signals r(g1),...,r(G), the received reference signal r(k) from the transmitting device k can be obtained with less influence of interference between terminals. Therefore, when the communication channel is estimated based on the received reference signals r(g1),...,r(G), a more accurate estimation result can be obtained. By obtaining a more accurate estimation result, the data signal corresponding to the reference signal can be restored more accurately, and as a result, the quality of wireless communication can be improved.

[0025] In one aspect of the present disclosure, the control unit may create G groups based on ascending order of propagation loss from each of the K transmitting side devices, descending order of received signal power, or ascending order of signal-to-noise ratio. This allows transmitting side devices with similar magnitude of received signal power to be group members. By calculating r(g) for group g with smaller received signal power among the G groups, it is possible to cancel the received reference signal r(p) from the transmitting side device p of the group with larger received signal power. Usually, the received reference signal r(s) from the transmitting side device s belonging to group g with smaller received signal power is significantly affected by interference from the received reference signal r(p) from the transmitting side device p of the group with larger received signal power. On the other hand, according to one aspect of the present disclosure, it is possible to reduce the influence of interference caused by a received reference signal r(p) from a transmitting device p in a group with a higher received signal power on a received reference signal r(s) from a transmitting device s belonging to a group g with a lower received signal power, and to accurately acquire the correlation characteristics of the received reference signal r(s) from a transmitting device s belonging to a group g with a lower received signal power.

[0026] In addition, when the receiving device has M receiving antennas (M: positive integer), the reference signals transmitted N times in succession for each receiving antenna may be added in the same manner as described above to obtain received reference signals r(g1),...,r(G) and perform communication channel estimation.

[0027] Another aspect of the present disclosure is a transmitting device. The transmitting device includes at least one transmitting antenna and a control unit. The control unit of the transmitting device is, for example, a processor such as a CPU. The control unit of the transmitting side device receives a phase sequence Φg={φ(g,1),...,φ(g,N)} from the receiving side device when performing continuous transmission in which the transmitting side device transmits a signal simultaneously with the other K-1 transmitting side devices and each transmits the same signal repeatedly N times (N: positive integer) with the other K-1 transmitting side devices. The phase sequence Φg includes a phase rotation amount φ(g,n) given to a transmission reference signal x(s) (s indicates the device itself) assigned to a group g to which the transmitting side device belongs among G groups into which K transmitting side devices including the other K-1 transmitting side devices and the device itself are divided, in the n-th reference signal transmission in the continuous transmission. The control unit of the transmitting side device executes the following in the n-th reference signal transmission in the continuous transmission: giving a phase rotation amount φ(g,n) to the transmission reference signal x(s) to obtain a transmission reference signal x(s,n) and transmitting the transmission reference signal x(s,n) from at least one transmitting antenna. The transmitting device transmits the n-th transmission reference signal x(s,n) in succession as described above, so that the receiving device can estimate the communication path with high accuracy.

[0028] The present disclosure can also specify one of other aspects as a method executed by a computer. The computer is, for example, a computer corresponding to the above information processing apparatus. The method includes: when a computer receives signals from K (K: a positive integer) transmission-side apparatuses simultaneously by a reception antenna, and continuous transmission in which the same signal is repeatedly transmitted N (N: a positive integer) times in succession is performed by the K transmission-side apparatuses, dividing the K transmission-side apparatuses into G (G: a positive integer, 1 < G ≤ K) groups; in order to obtain a transmission reference signal x(k, n) transmitted from a transmission-side apparatus k (k = 1,..., K) included in the K transmission-side apparatuses in the n-th (n = 1,..., N) transmission of a reference signal in the continuous transmission, obtaining a phase rotation amount given to the transmission reference signal x(k), which is a phase rotation amount φ(g, n) assigned to a group g (g = 1,..., G) to which the transmission-side apparatus k belongs, in the n-th transmission of the reference signal in the continuous transmission, and giving a phase rotation amount opposite to the phase rotation amount φ(g, n) to a reception reference signal r(n) received at the reception antenna in the n-th transmission of the reference signal in the continuous transmission, the reception reference signal r(n) including reception reference signals corresponding to the transmission reference signals from each of the K transmission-side apparatuses, so that reception reference signals from transmission-side apparatuses not belonging to the group g are canceled when added together from the 1st to the N-th times in the continuous transmission; and transmitting a phase sequence Φg = {φ(g, 1),..., φ(g, N)} including the phase rotation amounts φ(g, n) from the 1st to the N-th times of the group g to the transmission-side apparatus k.

[0029] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The configurations of the following embodiments are examples, and the present disclosure is not limited to the configurations of the embodiments.

[0030] <First Embodiment> 1 is a diagram illustrating a configuration of a wireless communication system 100 according to the first embodiment. The wireless communication system 100 includes a base station 1 and a plurality of terminals 2-1, 2-2, ..., 2-K that communicate wirelessly between the base station 1 and the base station 1. The terminals 2-1, etc. are also collectively referred to as terminals 2. The terminals 2 can also be referred to as wireless communication terminals, user terminals (UE), transmitting stations, terminal stations, or transmitting side devices. The base station 1 includes M receiving antennas, a wireless processing device 105, and a control device 10.

[0031] In the wireless communication system 100, NOMA is used, and each receiving antenna receives signals from K terminals 2 in the same time domain in the same frequency band. Therefore, the base station 1 receives the signals from the K terminals 2 in a superimposed manner, and therefore eliminates interference between terminals. In the first embodiment, the base station 1 uses, for example, successive interference cancellation (SIC) as a technique for eliminating interference between terminals. In addition, in the wireless communication system 100, when a sufficient SNR cannot be obtained at the base station by transmitting a signal once, each terminal 2 performs continuous transmission by repeatedly transmitting the same signal a predetermined number of times.

[0032] In the first embodiment, the base station 1 divides K terminals 2 into G groups. The base station 1 acquires a phase rotation amount φ for each group and notifies the terminals 2 belonging to each group so that reference signals received from terminals 2 other than the terminals 2 belonging to one group are cancelled out by adding up the received signals for each time in the continuous transmission at the base station 1. In the first embodiment, when the terminal 2 transmits a reference signal continuously, the terminal 2 transmits the reference signal by giving the phase rotation amount φ given to the group g to the transmission reference signal (transmission RS). When adding up the N received reference signals (reception RSs) transmitted in the continuous transmission, the base station 1 gives the received RS for each time an amount of phase rotation -φ that is opposite to the phase rotation amount φ given to the transmission RS of group g. In this way, the base station 1 can cancel the received RSs of terminals 2 other than the terminals 2 belonging to group g from the N received RSs and acquire the received RSs from the terminals 2 belonging to group g. The received RSs from the terminals 2 belonging to group g obtained in this way can be acquired in a state where they are not interfered with by the received RSs from the terminals 2 belonging to other groups.

[0033] The base station 1 uses the estimation result of the communication channel between each terminal 2 and the base station 1 when restoring the data signal transmitted from each terminal 2 from the data signal received from K terminals 2 and when performing SIC. The communication channel is estimated based on the received RS. Therefore, by acquiring the received RS from each terminal 2 in a state with little interference between terminals, the accuracy of the estimation of the communication channel can be improved, and as a result, the quality of wireless communication can be improved.

[0034] FIG. 2 is a diagram explaining SIC. When NOMA is used in the uplink from terminal 2 to base station 1, signals from other terminals become interference signals for terminal 1. SIC removes interference by creating a replica signal that reproduces the received signal from terminal 2 with high received signal power and subtracting the replica signal from the received superimposed signal. By repeating this process, the received data signal from each terminal 2 can be separated and restored from the superimposed signal. An estimated value of the communication channel is used when separating the received data signal from terminal 2 and when creating the replica signal.

[0035] In FIG. 2, the superimposed signal includes the received signals from terminal A, terminal B, and terminal C. The received signal power is assumed to be greater in the order of terminal A>terminal B>terminal C. In SIC, the received signal from terminal A, which has the greatest received signal power, is first separated and restored, and the replica signal of terminal A is subtracted from the superimposed signal. The remaining superimposed signal includes the received signals from terminal B and terminal C. For the received signals from terminal B and terminal C, the received signal from terminal A is an interference signal, and since its signal power is large, the influence of interference is also large. By subtracting the replica signal of terminal A from the superimposed signal, the interference signal that has a large influence on the received signals from terminal B and terminal C is eliminated, so that when the received signal of terminal B is separated and restored from the remaining superimposed signal, a signal with less interference and higher accuracy can be obtained. Here, higher accuracy means that the error between the original signal transmitted from terminal B and the signal restored by SIC is small. In the example shown in FIG. 2, when the replica signal of terminal B is subtracted from the remaining superimposed signal, the received signal from terminal C is obtained.

[0036] However, when performing SIC, if there is not a sufficient difference in received signal power between terminals 2, there is a high possibility that a sufficient SNR cannot be obtained at terminal 2, and it may not be possible to separate and restore the received signals from each terminal 2. The difference in received signal power is, for example, the power difference AB between the received signal from terminal A and the received signal from terminal B, and the power difference BC between the received signal from terminal B and the received signal from terminal C in Fig. 2.

[0037] FIG. 3 is a diagram explaining continuous transmission. FIG. 3 shows signals received by continuous transmission when five terminals 2 share the same frequency band and time domain. In NOMA, signals from each terminal 2, each with a different power value, are stored in a time domain called one slot. In the figure, one block indicates a signal of one terminal 2, and the number in the block indicates the terminal. The transmission power value of the signal of each terminal 2 in the continuous transmission is determined, for example, by the control device 10 of the base station 1 prior to the continuous transmission, and notified to each terminal 2.

[0038] In continuous transmission, each terminal 2 repeatedly transmits the same signal N times. Note that the signal transmitted from terminal 2 from the first to Nth times is the same signal, but the signals are different between terminals 2. In continuous transmission, the number of times N that the same signal is transmitted is set, for example, so that the continuous transmission ends after a time length during which the environment of the communication path is assumed not to fluctuate. The environment of the communication path fluctuates due to, for example, the movement of terminal 2, the movement of obstacles, and the effects of weather, etc.

[0039] 3 also shows the amount of phase rotation φ(k,n) given to the transmission reference signal in the nth transmission from terminal #k. k is a variable indicating the terminal and takes a value from 1 to K. n is a variable indicating the number of transmissions in the continuous transmission and takes a value from 1 to N.

[0040] In the first embodiment, the phase rotation amount φ(k,n) is obtained so as to be different between groups and different between each transmission. Specifically, in FIG. 3, the phase rotation amount {φ(g1,1),φ(g1,2),...,φ(g1,6)} for N times given to terminals #1 to #3 belonging to group 1 is different from the phase rotation amount {φ(g2,1),φ(g2,2),...,φ(g2,6)} for N times given to terminals #4 and #5 belonging to group 2. For example, the phase rotation amount {φ(1,1),φ(2,1),...,φ(5,1)} of each terminal #k used in the first transmission is different from the phase rotation amount {φ(1,2),φ(2,2),...,φ(5,2)} of each terminal #k used in the second transmission.

[0041] Note that the N phase rotation amounts φ(k,n) being different between groups means that not all groups have the same value for the N phase rotation amounts φ(k,n), and some groups may have the same value. For example, when there are three groups, the N phase rotation amounts φ(g,n) given to the three groups need not be the same, and the N phase rotation amounts φ(g,n) of two of the three groups may be the same.

[0042] The phase rotation amount φ(k,n) used in each terminal k is different between each transmission, which means that the phase rotation amount φ(k,n) used in each terminal k does not take the same value in all transmissions, and the phase rotation amount φ(k,n) used in each terminal k may take the same value in some transmissions. For example, in the example shown in FIG. 3, the combination of the values ​​of the phase rotation amount φ of terminals #1 to #5 may not be the same for all transmissions from the first to the sixth. For example, the combination of the phase rotation amount φ(k,1) of terminals #1 to #5 in the first transmission may be the same as the combination of the phase rotation amount φ(k,3) of terminals #1 to #5 in the third transmission. Details of the method of determining the phase rotation amount φ(k,n) will be described later.

[0043] FIG. 4 is a diagram showing radio frames for signal transmission. A radio frame is one unit of signal transmission in the time domain. A radio frame is defined in units of 10 ms. A radio frame further includes multiple subframes. A subframe is defined in units of 1 ms. A subframe further includes multiple slots. A slot is a scheduling unit of data. A slot is, for example, 500 μS.

[0044] When performing wireless communication, either an uplink (UpLink: UL) or a downlink (DownLink: DL) is assigned on a subframe basis. The direction from terminal 2 to base station 1 is the uplink. The direction from base station 1 to terminal 2 is the downlink. When terminal 2 transmits data, the subframe assigned to the uplink is used.

[0045] When the terminal 2 transmits data, a pair of an RS and a DS is transmitted. The RS and the DS are each placed in one slot. However, the slots storing the RS and the DS do not have to be adjacent to each other. In the example shown in FIG. 4, the RS and the DS are alternately placed, but the placement of the RS and the DS is not limited to that shown in FIG. 4. The RS and the DS have different roles and contain different data, so the terminal 2 and the base station 1 process the RS and the DS differently.

[0046] <Device configuration> Fig. 5 is a diagram showing an example of the hardware configuration of the base station 1 and the terminal 2. In Fig. 5, it is assumed that the base station 1 is a receiving device and the terminal 2 is a transmitting device. The base station 1 includes a control device 10, a radio processing device 105, and M antennas 106.

[0047] The control device 10 performs control related to wireless communication of the base station 1. The control device 10 includes a processor 101, a memory 102, an internal interface 103, and a network interface 104 for communicating with other base stations and the like.

[0048] The processor 101 is also called, for example, a Central Processing Unit (CPU) or a Microprocessor Unit (MPU). The processor 101 is not limited to a single processor, and may have a multiprocessor configuration. Also, a single physical CPU connected by a single socket may have a multicore configuration. Furthermore, the processor 101 may include arithmetic devices of various circuit configurations, such as a Digital Signal Processor (DSP) and a Graphics Processing Unit (GPU). Also, the processor 101 may cooperate with an integrated circuit (IC), other digital circuits, or an analog circuit. The integrated circuit may include an LSI, an Application Specific Integrated Circuit (ASIC), or a Programmable Logic Device (PLD). The PLD may include, for example, a Field-Programmable Gate Array (FPGA). Thus, the processor 101 may be, for example, a microcomputer. It may also be what is called a microcontroller (MCU), SoC (System-on-a-chip), system LSI, chipset, etc.

[0049] The memory 102 stores a sequence of instructions (computer program) executed by the processor 101, or data processed by the processor 101. The processor 101 and the memory 102 are sometimes called a baseband unit (BBU). The internal interface 103 is a circuit that connects various peripheral devices to the processor.

[0050] The network interface 104 is a communication device that allows the base station 1 to access a network to which other base stations are connected. The network to which other base stations are connected is also called a backhaul. The backhaul is, for example, a wired network using optical communication.

[0051] The wireless processing device 105 includes a transmitter for transmitting wireless signals, a receiver for receiving wireless signals, and the like, and is connected to M antennas 106. The wireless processing device 105 may have M systems of transmitters and receivers, the same number as the antennas.

[0052] The control device 10 is a device independent of the base station 1, which has a radio processing device 105 and M antennas 106, and the control device 10 and the base station 1 can be configured to be connected, for example, by a wired network using optical communication and installed remotely. Alternatively, a single independent control device 10 may be configured to be connected to a plurality of base stations 1 each having a radio processing device 105 and M antennas 106. In this configuration, the base station 1 having the radio processing device 105 and M antennas 106 is also called a remote radio head, and the network connecting the remote radio head and the control device 10 is also called a fronthaul. .

[0053] Next, the terminal 2 has a processor 201, a memory 202, an external storage device 203, a wireless communication unit 204, and an antenna 205. The terminal 2 is, for example, a smartphone, a tablet terminal, a wearable terminal, a data communication device mounted on a connected car, a drone, or other IoT terminal. However, in FIG. 5, hardware components that perform processing related to wireless communication are extracted and shown, and the hardware components included in the terminal 2 are not limited to those shown in FIG. 5.

[0054] The processor 201 and the memory 202 are similar to the processor 101 and the memory 102. The external storage device 203 stores various programs and data used by the processor 201 when executing each program. The external storage device 203 is, for example, an erasable programmable ROM (EPROM) or a hard disk drive. The programs held in the external storage device 203 include, for example, an operating system (OS), a wireless signal processing program, and various other application programs.

[0055] The wireless communication unit 204 is, for example, a wireless communication circuit conforming to 5G (5th Generation), 6G, and subsequent mobile communication standards. The wireless communication unit 204 includes a transmitter for transmitting a wireless signal and a receiver for receiving a wireless signal, and is connected to the antenna 205. The terminal 2 may include multiple antennas, and the wireless communication unit 204 may be connected to multiple antennas 205. The hardware configurations of the base station 1 and the terminal 2 are not limited to those shown in FIG. 5.

[0056] Fig. 6 is a diagram showing an example of the functional configuration of the terminal 2. The terminal 2 includes, as its functional configuration, an RS transmission processing unit 21 and a data signal transmission processing unit 22. Processing by these functional components is achieved by the processor 201 of the terminal 2 executing a wireless signal processing program. Note that the functional configuration of the terminal 2 shown in Fig. 6 is processing on the side of transmitting signals.

[0057] The RS transmission processing unit 21 performs processing from generating a reference signal to transmitting it. The RS transmission processing unit 21 includes a sequence generation unit 211, a cyclic shift unit 212, a modulation unit 213, and a phase rotation unit 214. The sequence generation unit 211 generates a sequence X_RS in the frequency domain using an orthogonal sequence such as a Zadoff-Chu sequence. The characters following "_" are expressed as subscripts in FIG. 6. Furthermore, uppercase X_RS represents a signal in the frequency domain, and lowercase x_RS represents a signal in the time domain.

[0058] Cyclic shift unit 212 cyclically shifts the starting point of sequence X_RS generated by sequence generation unit 211 by a predetermined number of samples to obtain a sequence to be used as a reference signal. Cyclic shift refers to shifting the starting point of sequence X_RS and moving the sequence up to the shifted starting point to the end to create a sequence of the same size. Cyclic shift unit 212 performs the above-mentioned cyclic shift in the frequency domain.

[0059] The sequence X_RS generated by sequence generation section 211 is a common sequence among K terminals 2 transmitting simultaneously. Therefore, if sequence X_RS is used as is, RS will interfere with each other between terminals 2, so the sequence used by each terminal 2 is made different. Cyclic shift section 212 shifts the starting point of sequence X_RS by a predetermined number of samples depending on terminal 2. Since the starting point of sequence X_RS differs for each terminal 2, the sequence used for RS in each terminal 2 will be different. In FIG. 6, the reference signal obtained by cyclic shift section 212 is displayed as a complex number in the frequency domain. k is a value corresponding to terminal 2 among the K terminals transmitting simultaneously. When the number of samples when cyclically shifting sequence X_RS is displayed as a complex number in the frequency domain, 6 is displayed as a phase difference, and "Δθ" in Fig. 6 is the phase difference between two adjacent terminals 2. Adjacent terminals 2 refer to two terminals with consecutive values ​​of k, which indicate terminals 2 out of K. For example, terminal 2 indicated by k=1 and terminal 2 indicated by k=2 are adjacent terminals 2.

[0060] The modulation unit 213 performs, for example, an inverse discrete Fourier transform (IDFT) on the reference signal obtained by the cyclic shift unit 212, thereby converting the signal from the frequency domain to a signal in the time domain, thereby performing modulation. The reference signal obtained by the modulation unit 213 is represented as x_RS(k). In Fig. 6, the reference signal x_RS(k) is represented by a complex number. "IDFT" in Fig. 6 indicates an inverse discrete Fourier transform.

[0061] Phase rotation section 214 provides an amount of phase rotation φ(k,n) to reference signal x_RS(k) obtained by modulation section 213. n indicates the number of transmissions in the continuous transmission, and takes a value from 1 to N. In Fig. 6, reference signal x_RS(k,n) phase-rotated by phase rotation section 214 is expressed as a complex number. Reference signal x_RS(k,n) phase-rotated by phase rotation section 214 becomes a transmission reference signal transmitted from terminal 2.

[0062] When terminal 2 performs continuous transmission, the reference signal x_RS(k) obtained by sequence generation section 211, cyclic shift section 212, and modulation section 213 has the same value in each transmission of the continuous transmission. Since the amount of phase rotation φ(k,n) given to the reference signal in phase rotation section 214 is set for each transmission of the continuous transmission, the n-th reference signal in the continuous transmission is x(k,n).

[0063] Next, the data signal transmission processing unit 22 outputs a CRC (Cyclic Redundancy Check) encoding unit 2 The base station 1 includes a CRC encoding unit 21, an encoding unit 222, and a modulation unit 223. The CRC encoding unit 221 divides a data block of user data to be transmitted by a generator polynomial, and adds the remainder obtained by dividing the data block by the generator polynomial to the data block as a check bit string. The data block is a bit string. The CRC is used to detect errors in the restored data. When the base station 1 demodulates and decodes a transmission data signal from the terminal 2 to obtain a data block, the base station 1 divides the obtained data block by the same generator polynomial as used for CRC encoding, and if a remainder is generated, an error is detected.

[0064] The encoding unit 222 performs error correction coding on the data block to which the check bit sequence has been added by the CRC encoding unit 221. The error correction code may be a block code or a convolutional code, and there is no limit to the type of coding. The modulation unit 223 digitally modulates the error correction coded data. Examples of the digital modulation method include Quadrature Amplitude Modulation (QAM) and Phase Shift Keying (PSK). The data signal is then transmitted to the wireless communication unit 20. 4 and transmitted from antenna 205.

[0065] When the terminal 2 has a plurality of antennas 205, a transmission diversity process is performed on the signal digitally modulated by the modulation unit 223. In the transmission diversity process, the digitally modulated signal is separated into a plurality of signals, and the separated signals are given coefficients given by complex numbers, and then radiated from the plurality of antennas 205 via the wireless communication unit 204.

[0066] 6 shows the functional configuration related to the signal transmission side processing of the terminal 2, but the terminal 2 also has a functional configuration for processing the signal reception side. For example, the terminal 2 receives from the base station 1 the phase rotation amount φ(k, n) (n=1,...,N) that the terminal 2 uses in each transmission of the continuous transmission.

[0067] 7 is a diagram illustrating an example of the functional configuration of the base station 1. The base station 1 includes, as its functional configuration, RS reception processing units 11-1, 11-2, ..., 11-M, a data signal reception processing unit 12-1, 12-2, ..., 12-M, a synthesis unit 13, a decoding unit 14, a control unit 15, and a transmission unit 16. The processing of these functional components is performed by the processor 101 executing a predetermined program. When the RS reception processing units 11-1, 11-2, ..., 11-M are collectively referred to as the RS reception processing unit 11. When the data signal reception processing units 12-1, 12-2, ..., 12-M are collectively referred to as the data signal reception processing unit 12. When the antennas 106-1, 106-2, ..., 106-M are collectively referred to as the antenna 106. In addition, unless otherwise specified, the RS reception processing unit 11 and the data signal reception processing unit 12 correspond to the same antenna 106. In the following, the antenna 106, the RS reception processing unit 11, and the data signal reception processing unit 12 will be described without being limited to a specific one. In addition, the signal processing when the terminal 2 performs continuous transmission will be described.

[0068] When the terminal 2 starts transmitting data, the control unit 15 transmits transmission parameters specifying radio resources and the like that can be used for data transmission, and a communication permission. The control unit 15 also instructs the terminal 2 to start and end continuous transmission. The control unit 15 determines the start of continuous transmission, for example, when the SNR of the signal received from the terminal 2 becomes lower than a predetermined value. The control unit 15 determines the end of continuous transmission by receiving a data signal from the terminal 2. The transmission parameters, communication permission, instruction to start continuous transmission, and instruction to end continuous transmission from the control unit 15 are transmitted to the terminal 2 via a control channel.

[0069] The control unit 15 notifies the terminal 2 of the continuous transmission start instruction and the continuous transmission parameters including the phase rotation amount φ(k, n) used by the terminal k in the n-th transmission of the reference signal. Details of the continuous transmission parameter acquisition process will be described later.

[0070] The transmitting unit 16 transmits the signal input from the control unit 15 to the terminal 2. In the control unit 15, for example, the same processing as that of the RS transmission processing unit 21 and the data signal transmission processing unit 22 of the terminal 2 is performed, and the signal is sent from the antenna 106 via the wireless processing device 105.

[0071] The RS reception processing unit 11 performs reception processing on the reception reference signal received by the antenna 106. The RS reception processing unit 11 includes an integrating unit 111 and a communication channel estimating unit 112. The integrating unit 111 adds together the reception reference signals for N times in the continuous transmission from K terminals 2. In this way, a reception reference signal having a sufficient SNR is obtained.

[0072] The communication channel estimation unit 112 estimates communication channels from K terminals 2 to the antenna 106 from the received reference signal. In estimating the communication channels, estimated values ​​of the amplitude and phase fluctuations in the communication channel between the terminal 2 and the antenna 106 are obtained as the estimation results. A matrix having the estimated results of the communication channel between the terminal k (k=1,...,K) and the antenna 106-m (m=1,...,M) as elements is called a KxM channel matrix H. That is, the communication channel estimation unit 112 acquires a Kx1 channel vector Hm including, as elements, estimated values ​​of the amplitude and phase fluctuations in the communication channel between one antenna 106 and the terminal 2. The acquired channel vector Hm is notified to the data signal reception processing unit 12. Details of the processing by the integration unit 111 and the communication channel estimation unit 112 will be described later.

[0073] The data signal receiving processor 12 performs receiving processing on the received data signal received by the antenna 106. The data signal receiving processor 12 includes an integrator 121, a replica remover 122, an equalizer / demodulator 123, and a replica creator .

[0074] The integrator 121 sums up N received data signals (superimposed signals) in succession from K terminals 2. The replica remover 122 subtracts the replica signal of the received data signal from terminal 2, which is created by replica creator 124, from the received data signal (superimposed signal). The equalizer / demodulator 123 subtracts the received data signal (superimposed signal) from which the replica signal of terminal k has been subtracted. The received data signal from terminal 2 having the next highest received signal power is separated and demodulated using a channel vector Hm corresponding to antenna 106 acquired by channel estimation unit 112 from the received signal (superimposed signal). By multiplying the received data signal (superimposed signal) by, for example, an MMSE (minimum mean square error) weight, interference from other terminals 2 is suppressed and the received data signal from terminal 2 is acquired. The MMSE weight is acquired from the channel vector Hm. The equalization and demodulation unit 123 acquires a log-likelihood ratio corresponding to the error correction codeword bit string from terminal 2, and outputs the bit string to the combination unit 13.

[0075] When it is determined that there is no error as a result of error detection by CRC in the decoded received data from terminal 2 output from decoding unit 14, replica creation unit 124 generates a replica signal of the received data signal transmitted from terminal 2 and received by receiving antenna 106. Specifically, replica creation unit 124 performs error correction coding again on the data output from decoding unit 14, digitally modulates the bit string obtained by the error correction coding, and multiplies it by channel vector Hm to generate a replica signal. The generated replica signal is output to replica removal unit 122, which removes the replica signal from the received data signal. The replica removal unit 122, equalization / demodulation unit 123, and replica creation unit 124 repeatedly execute the above process K-1 times to obtain a received data signal from each terminal 2.

[0076] The combiner 13 combines log-likelihood ratios corresponding to the error-correcting codeword bit strings from the terminal 2, which are output from the data signal receiving processors 12-1, 12-2, ..., 12-M and received by the receiving antennas 106-1, 106-2, ..., 106-M, respectively. The decoder 14 decodes the error-correcting code from the log-likelihood ratios input from the combiner 13, and acquires the data. Note that the functional configuration of the base station 1 is not limited to that shown in FIG. 7.

[0077] <Processing flow> Fig. 8 is a flowchart of the continuous transmission control process by the base station 1. The process shown in Fig. 8 is repeatedly executed at a predetermined cycle. The process shown in Fig. 8 is executed by the processor 101, but for convenience, the process will be described mainly with respect to the functional components. The same applies to the subsequent flowcharts.

[0078] In OP1, the control unit 15 judges whether or not to start continuous transmission. For example, the control unit 15 judges the start of continuous transmission when the SNR of the received signal from the terminal 2 is less than a predetermined value. This judgment may be made, for example, based on the average value of the SNRs from K terminals 2 that are transmitting simultaneously, or based on the largest or smallest SNR among the K terminals 2. Alternatively, the start of continuous transmission may be judged when the SNR of the received signal from y terminals (y≦K) among the K terminals 2 is less than a predetermined value. If the start of continuous transmission is judged (OP1: YES), the process proceeds to OP2. If the start of continuous transmission is not judged (OP1: NO), the process shown in FIG. 8 ends.

[0079] In OP2, the control unit 15 executes a continuous transmission parameter acquisition process. The continuous transmission parameter acquisition process is a process for acquiring parameters used by the terminal 2 in continuous transmission. Details of the continuous transmission parameter process will be described later. In the continuous transmission parameter acquisition process, for example, the number of continuous transmissions N, the transmission power of each terminal 2, the reference signal x_RS(k) transmitted by each terminal 2, and the phase rotation amount φ(k, n) (n=1,...,N) used for transmitting the reference signal each time in the continuous transmission of each terminal 2 are acquired as continuous transmission parameters.

[0080] In OP3, the control unit 15 transmits the acquired continuous transmission parameters, an instruction to start continuous transmission, and a frequency and a slot to be used in continuous transmission to the K terminals 2 through the downlink control channel.

[0081] In OP4, the control unit 15 judges whether or not N transmissions in the continuous transmission by the K terminals 2 have been completed. If N transmissions in the continuous transmission by the K terminals 2 have been completed (OP4: YES), the process proceeds to OP5. The control unit 15 waits until N transmissions in the continuous transmission by the K terminals 2 have been completed (OP4: NO).

[0082] In OP5, the control unit 15 judges whether or not to end the continuous transmission. For example, the control unit 15 judges the end of the continuous transmission when a reception data signal is obtained from the terminal 2. If the end of the continuous transmission is judged (OP5: YES), the process proceeds to OP7. If the end of the continuous transmission is not judged (OP5: NO), the process proceeds to OP2, where a continuous transmission parameter acquisition process is performed for the next continuous transmission, and new continuous transmission parameters are acquired again.

[0083] 9 is an example of a flowchart of the continuous transmission parameter acquisition process of the base station 1. The process shown in FIG. 9 is the process executed in OP2 of FIG.

[0084] In OP10, the control unit 15 measures the path loss Lk between the base station 1 and terminal k (k=1,...,K) and rearranges the K terminals 2 in ascending order of path loss Lk. In OP20, the control unit 15 assigns the transmission power value Pk and transmission reference signal x_RS(k) of each terminal k. In OP30, the control unit 15 assigns the phase rotation amount φ(k,n) used by terminal k in each transmission in the continuous transmission. The processing of OP10, OP20, and OP30 will be described in detail later. When the processing of OP30 is completed, the processing proceeds to OP3 in FIG. 8.

[0085] 10 and 11 are examples of a flowchart showing the process of measuring the path loss Lk between the base station 1 and terminal k and sorting the terminals 2 in ascending order of the path loss Lk in OP10 in Fig. 9. The process in OP10 in Fig. 9 may be performed in either Fig. 10 or Fig. 11.

[0086] FIG. 10 shows the process when the base station 1 measures the received signal strength. In OP101A, the control unit 15 instructs the downlink control channel to transmit a signal to each of the K terminals 2 with the transmission power p_UE(k) (k=1,...,K). In OP102A, the control unit 15 measures the received power r_BS(k) of the transmission signal from the terminal k in the uplink control channel. In OP103A, the control unit 15 subtracts the received power r_BS(k) measured in OP102A from the transmission power p_UE(k) specified in OP101A to obtain the path loss Lk of the terminal k. In OP104A, the control unit 15 sorts the K terminals 2 in ascending order of the path loss. After that, the process proceeds to OP20 in FIG. 9.

[0087] If the base station 1 has a plurality of antennas, the propagation loss of terminal k may be obtained for each antenna, and the average of the propagation losses of terminal k for all antennas may be obtained as the propagation loss Lk.

[0088] FIG. 11 shows the process when the terminal 2 measures the received signal strength. In OP101B, the control unit 15 transmits a signal with transmission power p_BS(k) (k=1,...,K) to each of the K terminals 2 on the downlink control channel, and instructs the terminals 2 to measure and report the received power of the signal. In OP102B, the control unit 15 receives, from the terminal k on the uplink control channel, the measurement result of the received power r_UE(k) of the transmission signal transmitted by the base station 1 in OP101B. In OP103B, the control unit 15 subtracts the received power r_UE(k) measured from the terminal k in OP102B from the transmission power p_BS(k) of the signal transmitted in OP101B, to obtain the propagation loss Lk of the terminal k. In OP104B, the control unit 15 rearranges the K terminals 2 in ascending order of the propagation loss. After that, the process proceeds to OP20 in FIG. 9.

[0089] FIG. 12 is an example of a flowchart of a process of allocating a transmission power value Pk and a transmission reference signal x_RS(k) of a terminal k. The process shown in FIG. 12 is executed in OP20 of FIG. In the process shown in Fig. 12, the variable k indicates the order of the terminal 2 when sorted in ascending order of the propagation loss Lk.

[0090] In OP201, the control unit 15 sets a variable k to 1. In OP202, the control unit 15 determines whether or not the variable k is 1. If the variable k is 1 (OP202: YES), the process proceeds to OP203. If the variable k is not 1 (OP202: NO), the process proceeds to OP204.

[0091] In OP203, the control unit 15 sets the transmission power value Pk of terminal k to the maximum transmission power P_max. In OP204, the control unit 15 determines the transmission power value Pk of terminal k to be the smaller of the maximum transmission power P_max and a value obtained by subtracting the difference between the path loss Lk of terminal k and the path loss Lk-1 of terminal k-1 from the transmission power value Pk-1 of terminal k-1, and the power difference ΔP required between the terminals.

[0092] In OP205, the control unit 15 obtains a transmission reference signal x_RS(k) for terminal k. The method of obtaining the transmission reference signal x_RS(k) is the same as that for terminal 2 (see FIG. 6). In OP206, the control unit 15 judges whether or not the variable k is K. If the variable k is K (OP206: YES), the process shown in FIG. 12 ends, and the process proceeds to OP30 in FIG. 9. If the variable k is not K (OP206: NO), the process proceeds to OP207. In OP207, the control unit 15 updates the variable k by adding 1. After that, the process proceeds to OP202, and a transmission power value Pk and a transmission reference signal r_RS(k) are obtained for the next terminal k.

[0093] 12, the transmission power value of terminal 2 is determined so that the smaller the propagation loss of terminal 2, the larger the received signal power value at base station 1. Furthermore, the transmission power value Pk of terminal k is determined so that the power difference between terminal k-1 and terminal k is at least the required power difference ΔP, so that the received signals of all terminals 2 can be separated in SIC (see FIG. 2).

[0094] 13 is an example of a flowchart of a process of allocating the amount of phase rotation φ(k,n) used by each terminal 2 in each transmission in the continuous transmission. The process shown in FIG. 13 is a process executed in OP 30 in FIG.

[0095] In OP301, the control unit 15 divides K terminals 2 into G groups. In the first embodiment, the terminals 2 are grouped in groups of K / G from the top in ascending order of propagation loss Lk. Specifically, when there are nine terminals 2 that transmit simultaneously and they are divided into three groups, group #1 is made up of the first to third terminals 2 with the smallest propagation loss Lk, group #2 is made up of the fourth to sixth terminals 2 with the smallest propagation loss Lk, and group #3 is made up of the seventh to ninth terminals 2 with the smallest propagation loss Lk. The grouping is not limited to being performed based on the propagation loss, and may be performed based on, for example, the received signal power, the SNR of the received signal, or the like.

[0096] In OP302, the control unit 15 obtains the amount of phase rotation φ(g,n) used by the terminals 2 belonging to each group in each transmission in the continuous transmission. The amount of phase rotation φ(g,n) is calculated so as to satisfy the following formula 1.

number

[0097] g1 and g2 are variables indicating groups, and take integers from 1 to G. Also, assume that g1 ≠ g2. That is, for each combination of two groups out of G, a phase rotation amount φ(g,n) is obtained so that the phase sequence Φg1 of one group g1 and the phase sequence Φg2 of the other group g2 are orthogonal. The phase sequence Φg includes a phase rotation amount φ(g,n) assigned to a terminal 2 belonging to group g. Specifically, the phase sequence Φ1 of group #1 (g=1) is the phase sequence Φ1={φ(1,1),φ(1,2),...,φ(1,N)}.

[0098] For example, when three groups are created, the phase rotation amount φ(k, n) is determined so that the phase sequence Φ1 of group #1 is orthogonal to the phase sequence Φ2 of group #2, the phase sequence Φ1 of group #1 is orthogonal to the phase sequence Φ3 of group #3, and the phase sequence Φ2 of group #2 is orthogonal to the phase sequence Φ3 of group #3.

[0099] The amount of phase rotation φ(k,n) used by terminal k in the n-th transmission in the continuous transmission is acquired as the amount of phase rotation φ(g,n) of group g to which terminal k belongs. After the process of OP302 ends, the process proceeds to OP3 in FIG.

[0100] Fig. 14 is an example of a flowchart of a communication channel estimation process in the base station 1. The process shown in Fig. 14 is started when a reference signal is received by continuous transmission.

[0101] The processing from OP401 to OP402 is performed for each group, and is repeated the number of times equal to the number of groups, G. A group g (g ∈ {1, ..., G}) indicates a group to be processed.

[0102] In OP401, the integrator 111 applies a phase rotation amount opposite to the phase rotation amount φ(g,n) of group g to the received reference signal r_RS(n) received at the receiving antenna 106 by transmitting the reference signal each time in the continuous transmission, and adds them up from the first time to the Nth time to obtain r_RS(g). The process by OP401 is shown in the following formula 2.

number

[0103] r_RS(n) is expressed by the following equation 3: h_k is the amount of fluctuation in amplitude and phase of the communication path from terminal k to receiving antenna 106.

number

number

[0104] Here, we focus on terminal s that does not belong to group g. If the received reference signal r_RS(s,n) from terminal s is multiplied by a phase rotation amount opposite to the phase rotation amount φ(g,n) of group g, and then summed up from the 1st to the Nth times, it can be expanded as shown in the following formula 5.

number

[0105] On the other hand, if we focus on terminal k belonging to group g, by giving the received reference signal r_RS(k,n) from terminal k an amount of phase rotation that is opposite to the amount of phase rotation φ(g,n) of group g and adding them up from the 1st to the Nth time, we can expand it into the following equation 6.

number

[0106] In OP402, the channel estimator 112 acquires correlation characteristics Ck(g) between r_RS(g) and the transmission reference signal x_RS(1) of the terminal 2 having the smallest propagation loss. The transmission reference signal x_RS(1) is generated by the controller 15 and is known to the base station 1. Specifically, the correlation characteristics Ck(g) are obtained by a convolution operation of r_RS(g) and the complex conjugate of the transmission reference signal x_RS(1). From the correlation characteristics Ck(g), the correlation characteristics Ck of the terminal k belonging to the group g can be acquired.

[0107] When the processes of OP401 and OP402 are executed for each group, a correlation characteristic Ck is acquired for each of the K terminals 2. In OP403, the communication channel estimation unit 112 acquires a channel vector Hm based on the correlation characteristic Ck of each terminal 2. Since the reference signal is generated from a sequence in which the starting point is shifted by a different number of samples for each terminal k for the same Zadoff-Chu sequence and cyclically shifted, in the correlation characteristic Ck(g), each element of the channel vector Hm for each terminal k appears at a sample position corresponding to the number of samples shifted by the cyclic shift. That is, in the correlation characteristic Ck(g), each element of the channel vector Hm appears at a different sample position for each terminal k belonging to group g. Next, by using a window function to extract a predetermined range of the correlation characteristic Ck from the sample position corresponding to the terminal k, an estimate of the amplitude and phase fluctuation amount h_k of the communication path between the terminal k and the receiving antenna 106 is obtained.

[0108] In OP404, the communication channel estimating unit 112 outputs the acquired channel vector Hm to the data signal receiving and processing unit 12. After that, the process shown in FIG.

[0109] In the example shown in Fig. 14, the received reference signal r_RS(n) by the nth transmission in the continuous transmission is given a phase rotation amount opposite to the phase rotation amount φ(g,n) of group g, and then added up N times, and the correlation characteristic is obtained, but the process for obtaining the correlation characteristic is not limited to this. The correlation characteristic Ck(g) is expressed by, for example, the following formulas 7 and 8.

number

[0110] Fig. 15 is an example of a graph showing the correlation characteristics of the received reference signal at base station 1 when no phase rotation is performed on the transmitted reference signal and the received reference signal during continuous transmission of the reference signals. In the graph of Fig. 15, the horizontal axis represents the sample number and the vertical axis represents the received signal power. Fig. 15 shows correlation characteristics both when there is jitter and when there is no jitter. Jitter refers to a time axis shift in the timing of signal transmission, and is generated by the movement of terminal 2, the characteristics of the device, the surrounding environment, etc. When there is no jitter, it is a theoretical value.

[0111] In the absence of jitter, the received signal power appears at the sample positions corresponding to each terminal 2 as indicated by the arrows in FIG. 15. In the absence of jitter, the peaks of the received signal power of each terminal 2 are spread out. Since the distance between the terminals is small, there is no interference from the received signal power of other terminals 2 appearing at nearby sample positions, and therefore the communication path can be estimated with high accuracy.

[0112] On the other hand, when jitter is present, the influence of the jitter tends to increase the spread of the peak of the received signal power of each terminal 2. For example, in Fig. 15, terminal B, which is close to the sampling position of terminal A with large received signal power, has a smaller received signal power than terminal A, and is therefore affected by the spread of the peak of the received signal power of terminal A, causing the peak of the received signal power to be buried. This may make it impossible to obtain the received signal power (correlation characteristics) of terminal B, and may result in a decrease in the accuracy of the communication channel estimation.

[0113] Fig. 16 is an example of a graph showing correlation characteristics of a received reference signal in a base station 1 when phase rotation is performed on a transmitted reference signal and a received reference signal as in the first embodiment in continuous transmission of reference signals. The graph shown in Fig. 16 is a graph under the same conditions as the graph shown in Fig. 15. Fig. 16 shows a graph showing correlation characteristics of group 1 and group 2 when terminals 2 are grouped into two groups, group 1 for terminals 2 with low received signal power and group 2 for terminals 2 with high received signal power. In Fig. 16, the graphs when there is no jitter are the same as those when phase rotation is not performed, and are displayed overlapping each graph.

[0114] 16, the graph for group 1 shows peaks of received signal power for each terminal 2 that is a member of group 1 and has low received signal power, but does not show peaks of received signal power for terminals 2 that are members of group 2 and have high received signal power. Similarly, the graph for group 2 shows peaks of received signal power for each terminal 2 that is a member of group 2 and has high received signal power, but does not show peaks of received signal power for terminals 2 that are members of group 1 and have low received signal power. This shows that for terminals 2 that do not belong to group g, the received reference signal is canceled by adding up the received reference signals received in each round of continuous transmission at base station 1.

[0115] Furthermore, in the graphs for Group 1 and Group 2, the influence of the spread of the peaks of the received signal power between the terminals 2 that are members of the group is small, and the peaks of the received signal power can be read for any of the terminals 2. Therefore, according to the wireless communication system 100 according to the first embodiment, the communication channel can be estimated with higher accuracy.

[0116] FIG. 17 is a diagram showing an example of a simulation result. In FIG. 17, graph GF1, which is a simulation result when there is no phase rotation for the transmission reference signal and the reception reference signal, and graph GF2, which is a simulation result when there is a phase rotation, are shown. The simulation result in FIG. 17 is for a simulation in which the number of terminals K=8 and the number of times N=8 transmissions are performed in the continuous transmission are transmitted from each terminal by continuous transmission and the received data signal from each terminal is separated and restored from the data signal received by the receiving antenna under the simulation conditions. In the simulation in which there is a phase rotation for the transmission reference signal and the reception reference signal, the terminals are divided into two groups based on the magnitude of the received signal power. In addition, other parameters such as the transmission power value and jitter are also set to the same values ​​in both cases.

[0117] In the graphs GF1 and GF2, the horizontal axis indicates terminal 2, and the vertical axis indicates the estimation error. The estimation error is the error between the data transmitted by each terminal and the data restored from the received data signal, and is calculated by the root-mean-squared error (RMSE). In other words, in the graphs GF1 and GF2, terminal #1 has the highest received signal power, and terminal #8 has the lowest received signal power. In addition, graphs GF1 and GF2 show the average estimation error (◯) and the worst estimation error (●) for multiple simulations of continuous transmission of data signals.

[0118] For example, when focusing on terminal #8 with the smallest received signal power, the worst estimation error is smaller in graph GF2 than in graph GF1, and it can be seen that the error is improved by applying phase rotation to the transmitted reference signal and the received reference signal as described in the first embodiment. In addition, the average estimation error is lower in graph GF2 than in graph GF1 for all terminals, and it can be seen that the error is improved by applying phase rotation to the transmitted reference signal and the received reference signal as described in the first embodiment. The smaller the error, the better the communication quality.

[0119] <Effects of the First Embodiment> According to the first embodiment, when multiple terminals 2 sharing the same frequency band and the same time region perform continuous transmission, the base station 1 can suppress the influence of interference between the terminals on the received reference signal. This allows the base station 1 to accurately estimate the communication path between each terminal 2, improving the wireless communication quality.

[0120] <Other embodiments> The above-described embodiment is merely an example, and the present disclosure can be modified and implemented as appropriate without departing from the spirit and scope of the present disclosure.

[0121] The processes and means described in this disclosure can be freely combined and implemented as long as no technical contradiction occurs.

[0122] Furthermore, a process described as being performed by one device may be shared and executed by multiple devices. Alternatively, a process described as being performed by different devices may be executed by one device. In a computer system, the hardware configuration (server configuration) by which each function is realized can be flexibly changed.

[0123] The present disclosure can also be realized by supplying a computer program implementing the functions described in the above embodiments to a computer, and having one or more processors of the computer read and execute the program. Such a computer program may be provided to the computer by a non-transitory computer-readable storage medium connectable to the system bus of the computer, or may be provided to the computer via a network. Non-transitory computer-readable storage media include, for example, any type of disk, such as a magnetic disk (floppy disk, hard disk drive (HDD), etc.), an optical disk (CD-ROM, DVD disk, Blu-ray disk, etc.), a read-only memory (ROM), a random access memory (RAM), an EPROM, an EEPROM, a magnetic card, a flash memory, an optical card, and any type of medium suitable for storing electronic instructions. [Explanation of symbols]

[0124] 1...Base station 2. Terminal 11 RS receiving processing unit 12 Data signal receiving processing unit 15 Control section 21 RS transmission processing unit 22 Data signal transmission processing unit 100 Wireless communication system 101, 201 Processor 102, 202...Memory 103 Internal Interface 104 Network Interface 105 Radio processing device 106 Antenna 111...Integrator part 112 Communication channel estimation unit 203...External storage device 204 Wireless communication unit 214 Phase rotation unit

Claims

1. When signals are simultaneously received from K (K: positive integer) transmitting devices by a receiving antenna, and the K transmitting devices repeatedly transmit the same signal N times (N: positive integer), Dividing the K transmitting devices into G groups (G: a positive integer, 1<G≦K); In the n-th (n=1, . . . , N) reference signal transmission in the continuous transmission, the transmitting device k (k=1 In order to obtain a transmission reference signal x(k,n) transmitted from a group g (g=1, . . . , K), a phase rotation amount φ(g,n) assigned to a group g (g=1, . . . , G) to which the transmitting side device k belongs is defined as In the n-th reference signal transmission in the continuous transmission, a received reference signal r(n) is received at the receiving antenna, the received reference signal r(n) including a transmission reference signal from each of the K transmitting side devices. When the received reference signals r(n) are given a phase rotation amount opposite to the phase rotation amount φ(g,n) and are added up from the 1st to the Nth transmissions in the continuous transmission, the received reference signal from the transmitting side device that does not belong to the group g is canceled. To obtain The transmitting device k receives a phase sequence Φg={φ(g,1) , . . . , φ(g,N)}; An information processing device comprising:

2. The control unit is The phase rotation amount φ(g, n) is calculated for two groups g1 and g2 (g1=1 、. .. .. ,G,g2=1 , . . . , G, g1 ≠ g2), the phase sequence Φg1 and the phase sequence Φg2 are obtained so as to be orthogonal to each other. The information processing device according to claim 1 .

3. The control unit is creating the G groups based on ascending order of path loss from each of the K transmitting side devices, descending order of received signal power, or ascending order of signal-to-noise ratio; 3. The information processing device according to claim 1 or 2.

4. The control unit is The received reference signal r(n) is assigned to group g (g=1 , . . . , G), and add them up from the first to Nth times in the continuous transmission, so that the received reference signal from the transmitting side apparatus that does not belong to the group g is cancelled, and a received reference signal r(g) (g=1, . . . , G) of the group g including the received reference signal from one or more transmitting side apparatuses that belong to the group g is obtained. , . . . , G); The received reference signal r(g) (g=1 , . . . , G) to perform channel estimation; Further execute The information processing device according to claim 1 .

5. The control unit is The data signals are transmitted from the K transmitting devices by the n-th transmission in the continuous transmission, and are received by the receiving antenna. . . . , K) for N times in the continuous transmission to obtain a data signal d; using the result of the channel estimation to separate a data signal d(k) received from the transmitting device k from the data signal d; Further execute The information processing device according to claim 4.

6. The control unit is When signals are simultaneously received from the K transmitting side devices by M receiving antennas (M: a positive integer) and each of the K transmitting side devices performs the continuous transmission, the communication channel estimation is performed for each receiving antenna.

6. The information processing device according to claim 4 or 5.

7. at least one transmit antenna; In the case where a signal is transmitted simultaneously together with other K-1 transmitting side devices and a continuous transmission is performed in which each of the other K-1 transmitting side devices transmits the same signal repeatedly N times (N: a positive integer) in succession, a phase sequence Φg={φ(g,n)} including a phase rotation amount φ(g,n) given to a transmission reference signal x(s) (s indicates the transmitting side device) assigned to group g (g: an integer from 1 to G) to which the transmitting side device belongs out of G groups into which the K transmitting side devices, including the other K-1 transmitting side devices and the transmitting side device itself, are divided in the nth (n=1, . . . , N) transmission of a reference signal in the continuous transmission is , . . . , φ(g,N)) from the receiving device; In the n-th reference signal transmission in the continuous transmission, a phase rotation amount φ(g,n) is applied to the transmission reference signal x(s) to obtain a transmission reference signal x(s,n); Transmitting the transmission reference signal x(s,n) from the at least one transmitting antenna; A control unit that executes the above. A transmitting device comprising:

8. The phase rotation amount φ(g, n) is A received reference signal r(n) is received at a receiving antenna in an n-th reference signal transmission in the continuous transmission, and the received reference signal r(n) includes a transmission reference signal from each of the K transmitting side devices. The received reference signal r(n) is given a phase rotation amount opposite to the phase rotation amount φ(g,n) and is acquired such that, when the received reference signals r(n) are added up from the first transmission to the Nth transmission in the continuous transmission, the received reference signal from the transmitting side device that does not belong to the group g is cancelled. The transmitting device according to claim 7.

9. The phase rotation amount φ(g, n) is calculated for two groups g1 and g2 (g1=1) out of the G groups. 、. .. .. ,G,g2=1 , . . . , G, g1 ≠ g2), the phase sequence Φg1 and the phase sequence Φg2 are obtained so as to be orthogonal to each other. The transmitting device according to claim 8.

10. The G groups are created based on an ascending order of path loss from each of the K transmitting side devices, a descending order of received signal power, or an ascending order of signal-to-noise ratio.

10. The transmitting device according to claim 8 or 9.

11. The receiving device includes: The received reference signal r(n) is assigned to group g (g=1 , . . . , G), and add them up from the first to Nth times in the continuous transmission, so that the received reference signal from the transmitting side apparatus that does not belong to the group g is cancelled, and a received reference signal r(g) (g=1, . . . , G) of the group g including the received reference signal from one or more transmitting side apparatuses that belong to the group g is obtained. , . . . , G), The received reference signal r(g) (g=1 , . . . , G) to perform channel estimation. A transmitting device according to any one of claims 8 to 10.

12. The computer The receiving antenna receives signals simultaneously from K (K: positive integer) transmitting devices. , and the K transmitting devices transmit the same signal N times (N: a positive integer) in succession. The K transmitting devices are divided into G groups (G: a positive integer, 1<G≦K), and a transmitting device k (k=1) included in the K transmitting devices is selected by transmitting the nth (n=1, . . . , N) reference signal in the continuous transmission. In order to obtain a transmission reference signal x(k,n) transmitted from a group g (g=1, . . . , K), a phase rotation amount φ(g,n) assigned to a group g (g=1, . . . , G) to which the transmitting side device k belongs is defined as In the n-th reference signal transmission in the continuous transmission, a received reference signal r(n) is received at the receiving antenna, the received reference signal r(n) including a transmission reference signal from each of the K transmitting side devices. When the received reference signals r(n) are given a phase rotation amount opposite to the phase rotation amount φ(g,n) and are added up from the 1st to the Nth transmissions in the continuous transmission, the received reference signal from the transmitting side device that does not belong to the group g is canceled. To obtain The transmitting device k receives a phase sequence Φg={φ(g,1) , . . . , φ(g,N)}.

13. The computer, The phase rotation amount φ(g, n) is divided into two groups g1 and g2 (g1=1 、. .. .. ,G,g2=1 , . . . , G, g1 ≠ g2) , the phase sequence Φg1 and the phase sequence Φg2 are obtained so as to be orthogonal to each other. The method of claim 12.

14. The computer, creating the G groups based on ascending order of path loss from each of the K transmitting side devices, descending order of received signal power, or ascending order of signal-to-noise ratio; 14. The method according to claim 12 or 13.

15. The computer The received reference signal r(n) is assigned to group g (g=1 , . . . , G), and add them up from the first to Nth times in the continuous transmission, so that the received reference signal from the transmitting side apparatus that does not belong to the group g is cancelled, and a received reference signal r(g) (g=1, . . . , G) of the group g including the received reference signal from one or more transmitting side apparatuses that belong to the group g is obtained. , . . . , G); The received reference signal r(g) (g=1 , . . . , G) to perform channel estimation; Further comprising:

15. The method according to any one of claims 12 to 14.

16. The computer The data signals are transmitted from the K transmitting devices by the n-th transmission in the continuous transmission, and are received by the receiving antenna. . . . , K) for N times in the continuous transmission to obtain a data signal d; using the result of the channel estimation to separate a data signal d(k) received from the transmitting device k from the data signal d; Further comprising: The method of claim 15.

17. The computer When signals are simultaneously received from the K transmitting side devices by M receiving antennas (M: a positive integer) and each of the K transmitting side devices performs the continuous transmission, the communication channel estimation is performed for each receiving antenna.

17. The method according to claim 15 or 16.

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