Base station, control method for base station, and user terminal device

Abstract

A base station according to the present invention comprises at least a processor and a memory and performs wireless communication with a user terminal device. The base station determines whether to retransmit a reference signal for data demodulation in the physical layer to the user terminal device on the basis of past wireless communication with the user terminal device. When a reference signal is not retransmitted to the user terminal device, the most recently transmitted reference signal is used, and when a reference signal is newly transmitted to the user terminal device, the newly transmitted reference signal is used.

Description

Base Station, Base Station Control Method, and User Terminal Device

[0001] The present invention relates to a base station, a base station control method, and a user terminal device. The present application claims priority from Japanese Patent Application No. 2025-053715 filed in Japan on March 27, 2025, the content of which is incorporated herein by reference.

[0002] In 5th generation mobile communication systems, DMRS (DeModulation Reference Signal) is to be transmitted as a demodulation reference signal for decoding downlink radio signals. As a conventional technique, for example, the following Patent Document 1 discloses a method for transmitting and receiving a reference signal in a radio communication system.

[0003] Japanese National Publication of International Patent Application No. 2020-512784

[0004] Here, the maximum number of MIMO (Multi Input Multi Output) layers depends on the number of DMRS ports. In order to increase the maximum number of MIMO layers, the number of DMRS ports has been extended from 12 to 24 in 3GPP (registered trademark) Rel-18. Considering further increases in the number of MIMO multiplexing and distributed MIMO in the future, it is conceivable that the number of DMRS ports will be further extended.

[0005] When attempting to extend allocated DMRS ports, it is conceivable, for example, to utilize the code, time, and frequency domains. An increase in code length leads to an increase in demodulation overhead, and extension of the time and frequency domains increases the usage rate of resource elements (RE). In order to reduce resource congestion, there is a demand for omitting or reusing DMRS transmission.

[0006] The present invention has been made in consideration of such circumstances, and an object of the present invention is to provide a base station, a base station control method, and a user terminal device capable of omitting or reusing DMRS depending on situations.

[0007] (A1) One aspect of the present invention is a base station comprising at least a processor and memory, which performs wireless communication with a user terminal device, which determines whether or not to transmit a reference signal for demodulating data at the physical layer to the user terminal device again based on past wireless communication with the user terminal device, and if it does not transmit the reference signal to the user terminal device again, it reuses the previously transmitted reference signal, and if it transmits the reference signal to the user terminal device anew, it uses the newly transmitted reference signal.

[0008] (A2) In addition, in the base station described in (A1) above, if the change in propagation characteristics is within a predetermined range based on past wireless communication with the user terminal device, it is determined not to transmit the reference signal to the user terminal device again, and the previously transmitted reference signal is reused.

[0009] (A3) In addition, in one aspect of the present invention, if the base station described in (A1) or (A2) above does not transmit the reference signal to the user terminal device again, the position of the symbol of the reference signal to be used is notified to the user terminal device.

[0010] (A4) In addition, in one aspect of the present invention, if the base station described in (A1) or (A2) above does not transmit the reference signal to the user terminal device again, it indirectly instructs the user terminal device to reuse the reference signal that was transmitted previously by not transmitting the reference signal to the user terminal device.

[0011] (A5) In another aspect of the present invention, at any of the base stations described in (A1) to (A4) above, a determination is made as to whether or not to perform semi-fixed resource allocation based on past wireless communication with the user terminal device, and the settings for SPS (Semi-Persistent Scheduling) are shared in advance via an RRC (Radio Resource Control) message. If it is determined that semi-fixed resource allocation should be performed, the transmission or reuse pattern of the reference signal is notified when enabling the use of SPS.

[0012] (A6) In another aspect of the present invention, in the base station described in (A5) above, the reuse of the reference signal is continued until the SPS is terminated.

[0013] (A7) In addition, one aspect of the present invention is to determine whether or not to reuse the reference signal between adjacent subcarriers used by the same user terminal device at any of the base stations described in (A1) to (A6) above, and if it is possible to reuse the reference signal, to reuse the reference signal between adjacent subcarriers.

[0014] (A8) In addition, in one aspect of the present invention, in any of the base stations described in (A1) to (A7) above, the maximum number of times the reference signal can be reused is predetermined, and when the number of times the reference signal has been reused reaches the maximum number, a new reference signal is sent to the user terminal device, even if the reference signal can be reused.

[0015] (A9) In another aspect of the present invention, in the base station described in (A8) above, the maximum number of times is set according to the attributes of the base station.

[0016] (A10) Another aspect of the present invention is a control method for a base station that includes at least a processor and a memory and performs wireless communication with a user terminal device, the control method for a base station that includes a determination step of determining whether or not to transmit a reference signal for demodulating data at the physical layer to the user terminal device again based on past wireless communication with the user terminal device, and a reference signal reuse step of reusing the previously transmitted reference signal if the reference signal is not to be transmitted to the user terminal device again.

[0017] (A11) Another aspect of the present invention is a user terminal device comprising at least a processor and memory, which performs wireless communication with a base station, which receives a reference signal for demodulating data at the physical layer at least once from the base station, and if it is determined to reuse the reference signal based on a notification from the base station, it reuses the already received reference signal to demodulate data at the physical layer.

[0018] (B1) Another aspect of the present invention is a base station comprising at least a processor and a memory, and a plurality of user terminal devices, which perform independent wireless communication, wherein the base station determines whether the plurality of user terminal devices are adjacent to each other, and if it is determined that they are adjacent, it determines that a reference signal for demodulating data at the physical layer will be used in common by the plurality of adjacent user terminal devices, and if the reference signal is common to the plurality of adjacent user terminal devices, it transmits the reference signal to a specific user terminal device among the plurality of user terminal devices, and transmits to the other user terminal devices the user terminal device that transmitted the reference signal and the position of the symbol containing the reference signal.

[0019] (B2) In addition, in one aspect of the present invention, in the base station described in (B1) above, if the propagation characteristics are similar, it is determined that the multiple user terminal devices are adjacent to each other.

[0020] (B3) In addition, in one aspect of the present invention, if it is determined that a plurality of user terminal devices are adjacent to each other in the base station described in (B1) or (B2) above, it is determined that even if there are three or more user terminal devices, they will use the reference signal that is common to them.

[0021] (B4) In addition, in one aspect of the present invention, if, as a result of beam sweeping, it is determined that a plurality of user terminal devices are adjacent to each other at the base station described in (B2) above, the plurality of user terminal devices continue to use the common reference signal with each other until the difference in propagation characteristics falls outside a predetermined range.

[0022] (B5) Another aspect of the present invention is a control method for a base station that includes at least a processor and a memory and performs wireless communication with a user terminal device, comprising: a first determination step of determining whether a plurality of user terminal devices are adjacent to each other; a second determination step of determining, if determined to be adjacent, that a reference signal for demodulating data at the physical layer will be used in common by the plurality of adjacent user terminal devices; and a reference signal transmission step of, if the reference signal is common to the plurality of adjacent user terminal devices, transmitting the reference signal to a specific user terminal device among the plurality of user terminal devices, and transmitting to the other user terminal devices the user terminal device that transmitted the reference signal and the position of the symbol containing the reference signal.

[0023] (B6) Another aspect of the present invention is a user terminal device comprising at least a processor and memory, which performs wireless communication with a base station, which receives from the base station information relating to a reference signal for demodulating data at the physical layer, and if the information relating to the reference signal includes the reference signal itself, it uses the reference signal itself to demodulate data at the physical layer, and if the information relating to the reference signal does not include the reference signal itself, but includes information identifying the user terminal device that the base station transmitted the reference signal itself to, and the position of a symbol that includes the reference signal itself, it queries the user terminal device for the reference signal itself, and uses the reference signal itself obtained as a result of the query to demodulate data at the physical layer.

[0024] According to the present invention, it is possible to provide a base station, a base station control method, and a user terminal device that can omit or reuse DMRS depending on the situation.

[0025] This is a diagram illustrating the general outline of the wireless communication system according to this embodiment. This is a diagram illustrating the positional relationship between the base station and the user terminal device according to the first embodiment. This is a sequence diagram showing an example of the control method according to the first embodiment. This is a schematic diagram showing an example of resources when the control method according to the first embodiment is used. This is a sequence diagram showing a first modified example of the control method according to the first embodiment. This is a sequence diagram showing a second modified example of the control method according to the first embodiment. This is a schematic diagram showing an example of resources when the second modified example of the control method according to the first embodiment is used. This is a diagram illustrating the positional relationship between the base station and the user terminal device according to the second embodiment. This is a sequence diagram showing an example of the control method according to the second embodiment. This is a schematic diagram showing an example of resources when the control method according to the second embodiment is used. This is a flowchart showing the flow at the start of operation led by the user terminal device according to the control method according to the third embodiment. This is a flowchart showing the flow at the end of operation led by the user terminal device according to the control method according to the third embodiment. This is a sequence diagram showing an example of the control method according to the fourth embodiment. This is a block diagram showing an example of the internal configuration of the base station and user terminal device according to this embodiment.

[0026] [Embodiments] Preferred embodiments of a wireless communication system, communication control method, and program according to aspects of the present invention will be described in detail below with reference to the attached drawings. It should be noted that the embodiments of the present invention are not limited to these embodiments, and include various modifications and improvements. In other words, the components described below include those that are easily conceivable by those skilled in the art, and those that are substantially the same, and the components described below can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of components can be made without departing from the spirit of the present invention. Also, in the following drawings, the scale and number of components in each structure may differ from the scale and number of components in the actual structure in order to make each structure easier to understand.

[0027] [Wireless Communication System] Figure 1 is a diagram illustrating the general outline of the wireless communication system according to this embodiment. First, the wireless communication system 1 that forms the basis of this embodiment will be described with reference to the figure. The wireless communication system 1 is composed of a plurality of base stations 20 and a plurality of user terminal devices 10. As an example, the figure shows one base station 20 and a plurality of user terminal devices 10 corresponding to the base station 20. As an example of the plurality of user terminal devices 10, user terminal device 10-1, user terminal device 10-2, and user terminal device 10-n (where n is a natural number of 1 or more) are shown. In the following description, when the plurality of user terminal devices 10 are not distinguished, they may simply be referred to as user terminal device 10.

[0028] The user terminal device 10 includes at least a processor and memory, and communicates wirelessly with the base station 20. The user terminal device 10 is a device used by a user. Specific examples of the user terminal device 10 include smartphones, tablet devices, wearable devices, etc. The user terminal device 10 may also be called UE (User Equipment), user equipment, mobile station, etc.

[0029] The base station 20 is equipped with at least a processor and memory, and communicates wirelessly with the user terminal device 10. Specifically, the base station 20 may also be called a gNodeB (gNB), en-gNB, Next Generation-Radio Access Network (NG-RAN) node, eNB, low-power node, CU, DU, RU, gNB-DU, Remote Radio Head (RRH), Integrated Access and Backhaul / Backhauling (IAB) node, etc.

[0030] Multiple user terminal devices 10 are connected to the base station 20. The base station 20 to which the user terminal devices 10 are connected may be changed as the user terminal devices 10 move.

[0031] [First Embodiment] Next, the first embodiment will be described with reference to Figures 2 to 7. The first embodiment is an example of omitting or reusing DRMS ​​transmission on a per-user basis (per 10-unit user terminal device).

[0032] Figure 2 is a diagram illustrating the positional relationship between the base station and the user terminal device according to the first embodiment. As shown in the figure, the base station 20 performs beam sweeping. Specific implementation methods for beam sweeping may include SSB (Synchronization Signal Block) or CSI-RS (Channel State Information-Refrence Signal). Furthermore, techniques such as beamforming and beam steering may be used to perform beam sweeping.

[0033] Specifically, in the illustrated example, the base station 20 searches for a user terminal device 10 to communicate with by transmitting directional beams in spatially different directions. More specifically, it uses beam BMa to communicate with user terminal device 10a and beam BMb to communicate with user terminal device 10b. Here, the user is located at the position of user terminal device 10a at a first time point, and moves to the position of user terminal device 10b at a second time point after the first time point. This movement is not a large movement, and the propagation characteristics do not substantially change before and after the movement. In such a case, it becomes possible to reuse the DMRS.

[0034] Thus, in the first embodiment, it is assumed that the relative positional relationship between the user terminal device 10 and the base station 20 does not substantially change over time. The statement that the relative positional relationship does not substantially change over time can also be said to mean that the propagation characteristics do not substantially change over time.

[0035] Figure 3 is a sequence diagram showing an example of a control method according to the first embodiment. Referring to this figure, the procedure for omitting the DMRS, assuming the situation described in Figure 2, will be explained. Note that the illustrated example assumes a dynamic scheduling case.

[0036] (Step S11) First, the base station 20 determines whether to omit DMRS. This determination is made based on the results of estimating past channel state information (CSI), etc. For example, the base station 20 may determine, based on the results of CSI estimation, to omit DMRS for user terminal equipment 10 where channel changes are infrequent. In other words, the base station 20 may also determine, based on past wireless communication with user terminal equipment 10, that if the change in propagation characteristics is within a predetermined range, it will reuse DMRS (will not transmit to user terminal equipment 10 again).

[0037] (Step S12) Next, the base station 20 instructs the user terminal device 10 on which resources to use to transmit and receive data. Specifically, this instruction is given via the PDCCH (Physical Downlink Control Channel). In this embodiment, the base station 20 specifies to the user terminal device 10 a resource block (RB) in which the DMRS is stored. In other words, the base station 20 can determine whether or not to transmit a reference signal (specifically, the DMRS) for demodulating data at the physical layer to the user terminal device 10 again, based on past wireless communication with the user terminal device 10. Furthermore, as a preliminary step to the data channel, the control channel can specify which DMRS should be omitted.

[0038] (Step S13) Next, the base station 20 transmits data to the user terminal device 10. This transmission is performed via the PDSCH (Physical Data Shared Channel). At this time, the base station 20 notifies the user terminal device 10 of the DCI (PDCCH) and specifies the resource block for which the DMRS will be reused. The user terminal device 10 checks the DCI for each communication on the PDSCH and understands the symbol position of the DMRS to be reused and updated. If the base station 20 does not transmit the DMRS to the user terminal device 10 again, the base station 20 reuses the DMRS that it previously transmitted and performs demodulation.

[0039] Here, various methods can be considered for specifying the symbol position, but one possible method is for the base station 20 to directly specify the symbol position. In this case, if the base station 20 determines that it will reuse the DMRS (i.e., will not transmit it to the user terminal device 10 again), it can directly notify the user terminal device 10 of the position of the DMRS symbol to be used.

[0040] Alternatively, the base station 20 could indirectly instruct the user terminal device 10 to reuse a DMRS by not instructing it to update the DMRS. In this case, if the base station 20 determines that it will reuse the DMRS (i.e., not transmit it to the user terminal device 10 again), it can indirectly instruct the user terminal device 10 to reuse the previously transmitted DMRS by not transmitting the DMRS to the user terminal device 10.

[0041] (Step S14) The base station 20 determines the channel change each time it performs PDSCH communication. This determination may be made based on the estimated CSI result, as described in Step S11.

[0042] (Step S15) Here, when channel variation is equal to or greater than a predetermined value, the base station 20 notifies the user terminal device 10 that it will schedule a DMRS again. In other words, when the base station 20 newly transmits a DMRS to the user terminal device 10, it can be said that the newly transmitted DMRS is used.

[0043] In the present embodiment, the user terminal device 10 needs to receive a reference signal (specifically, a DMRS) for demodulating data in the physical layer from the base station 20 at least once. Further, when the user terminal device 10 determines to reuse the reference signal based on the notification from the base station 20, it reuses the already received reference signal to demodulate data in the physical layer.

[0044] FIG. 4 is a schematic diagram showing an example of resources when the control method according to the first embodiment is used. DMRS and data when the control method according to the present embodiment is used will be described with reference to this figure.

[0045] FIGS. 4(A1) to 4(A4) show conceptual diagrams of DMRS and data transmitted from the base station 20 to the user terminal device 10. The upper part of FIGS. 4(A1) to 4(A4) shows an example of symbols when the conventional technology is used, and the lower part shows an example of symbols when the present embodiment is used. The horizontal axis represents the time axis. For the first information communication in FIG. 4(A1), both the conventional technology (upper part) and the present embodiment (lower part) transmit DMRS and DATA in the same manner. However, looking at subsequent communications, as shown in FIGS. 4(A2) to 4(A4), data is transmitted on symbols that conventionally transmitted DMRS. Note that, since FIGS. 4(A1) to 4(A4) are conceptual diagrams, in practice some or all of the DMRS can be omitted, although the figures make it appear that all DMRS are replaced with DATA.

[0046] 4(B1) to 4(B4) are more detailed conceptual diagrams illustrating resource allocation according to the present embodiment. In each of FIGS. 4(B1) to 4(B4), the horizontal axis represents symbols, and the vertical axis represents subcarriers. The transmission timing of FIG. 4(B1) is the same as the transmission timing of FIG. 4(A1), the transmission timing of FIG. 4(B2) is the same as the transmission timing of FIG. 4(A2), the transmission timing of FIG. 4(B3) is the same as the transmission timing of FIG. 4(A3), and the transmission timing of FIG. 4(B4) is the same as the transmission timing of FIG. 4(A4).

[0047] In FIG. 4(B1), DMRS is transmitted as in the conventional art. In the illustrated example, seven symbols include information related to DMRS. Referring now to FIG. 4(B2), there are four symbols including information related to DMRS, and transmission is omitted for three symbols. For these three symbols, a previously transmitted DMRS will be reused. Further, referring to FIG. 4(B3), no symbols including information related to DMRS are contained at all. That is, no DMRS is transmitted at all, and a previously transmitted DMRS is reused. Similarly, referring to FIG. 4(B4), there are three symbols including information related to DMRS, and these are symbols for which retransmission (update) of DMRS becomes necessary due to a change in propagation characteristics.

[0048] [First Modification] FIG. 5 is a sequence diagram showing a first modification of the control method according to the first embodiment. The first modification of the control method described with reference to FIGS. 3 and 4 will be described with reference to FIG. 5. The first embodiment assumes a case where the relative positional relationship between the user terminal device 10 and the base station 20 does not substantially change over time, whereas the first modification assumes a case where the relative positional relationship does not change for a longer period of time.

[0049] Here, the location of the base station 20 is almost always fixed on land, such as on the roof of a building. If the user terminal device 10 is not expected to move for a long period of time, the relative positional relationship between the user terminal device 10 and the base station 20 is expected to not change substantially over time. In such cases, the base station 20 may instruct a semi-fixed resource allocation. Specifically, a semi-fixed resource allocation is known as communication using SPS (Semi-Persistent Scheduling). When using SPS communication, there should be fewer channel changes. Therefore, in such cases, the base station 20 does not need to meticulously determine the DMRS. The first modification assumes a situation in which such a semi-fixed resource allocation is performed.

[0050] (Step S21) First, the base station 20 shares the SPS settings with the user terminal device 10 in advance using an RRC (Radio Resource Control) message. At this time, the base station 20 instructs the user terminal device 10 on the PDSCH transmission cycle, etc.

[0051] (Step S22) Next, the base station 20 instructs the user terminal device 10 on which resources to use to transmit and receive data. This instruction may be given via the PDCCH, as in step S12 described above, so the explanation is omitted.

[0052] (Step S23) Next, the base station 20 performs a DMRS omission determination. This determination is the same as in step S11 described above, so the explanation is omitted. In the first modified example, the base station 20 also performs a determination to start SPS. If it is determined in this determination to start SPS, the process proceeds to the following step S24. If SPS is not performed, the process described in Figure 3 described above is performed.

[0053] (Step S24) Next, the base station 20 transmits data to the user terminal device 10. This transmission is performed via the PDSCH, similar to step S13 described above. At this time, the base station 20 notifies the user terminal device 10 of the DCI (PDCCH) and specifies the resource block for which the DMRS will be reused. The user terminal device 10 checks the DCI for each communication via the PDSCH and understands the symbol position of the DMRS to be reused and updated. If the base station 20 does not transmit the DMRS to the user terminal device 10 again, the base station 20 reuses the DMRS that it previously transmitted and performs demodulation.

[0054] Here, if it is determined in step S23 described above that SPS should be performed, the base station 20 notifies the user terminal device 10 of the DMRS transmission or reuse pattern when enabling the use of SPS. Notification of DMRS transmission or reuse pattern can also be rephrased as the DMRS RB position, transmission pattern, etc.

[0055] From step S25 onward, PDSCH transmission continues until the end of SPS. In other words, DMRS reuse continues until the end of SPS.

[0056] [Second variation]

[0057] Figure 6 is a sequence diagram showing a second modification of the control method according to the first embodiment. The second modification of the control method described with reference to Figures 3 and 4 will be explained with reference to Figure 6. The second modification differs from the above-described embodiment in that the DMRS is reused even on adjacent subcarriers. Here, if the user terminal device 10 moves and uses subcarriers with similar propagation characteristics, there is no need to retransmit and update the DMRS, and it can be reused. The second modification assumes this situation.

[0058] Furthermore, as a premise for the second modification, the base station 20 is assumed to have a table capable of identifying subcarriers with high channel correlation. The table capable of identifying subcarriers with high channel correlation may be a table that directly shows the combination of such subcarriers, or it may be a table from which the degree of correlation can be indirectly derived from some value.

[0059] (Step S31) First, the base station 20 determines which user terminal device 10 will reuse the DMRS. This determination may be the same as in step S11 and step S23 described above. A detailed explanation is omitted here.

[0060] (Step S32) Next, the base station 20 instructs the user terminal device 10 on which resources to use to transmit and receive data. This instruction may be given via the PDCCH, similar to steps S12 and S22 described above. A detailed explanation is omitted here.

[0061] (Step S33) Next, the base station 20 transmits data to the user terminal device 10. This transmission is performed via the PDSCH, and may be specifically the same as in steps S13 and S24 described above. At this time, the base station 20 notifies the user terminal device 10 of the DCI (PDCCH) and specifies the resource block for which the DMRS will be reused. The user terminal device 10 checks the DCI for each communication via the PDSCH and understands the symbol position of the DMRS to be reused and updated. If the base station 20 does not transmit the DMRS to the user terminal device 10 again, the base station 20 reuses the DMRS that it previously transmitted and performs demodulation.

[0062] (Step S34) In this second modification, the base station 20 schedules subcarriers with high channel correlation.

[0063] (Step S35) Subcarriers with high channel correlation omit transmitting DMRS by reusing DMRS that they share with each other.

[0064] Thus, in this second modification, the base station 20 determines whether or not to reuse the DMRS between adjacent subcarriers used by the same user terminal device 10. Furthermore, if it is determined that reuse is possible, the base station 20 reuses the DMRS between adjacent subcarriers. In the illustrated example, SC #1 and SC #2 use a common DMRS.

[0065] Figure 7 is a schematic diagram showing an example of resources when a second modification of the control method according to the first embodiment is used. Referring to this figure, the DMRS and data when using the control method according to the second modification will be explained. This figure shows a conceptual diagram of the DMRS and data transmitted from the base station 20 to the user terminal device 10. The first row in this figure shows the operation according to the prior art. That is, in the prior art, the DMRS and data are transmitted with each communication. The second and third rows in this figure show the control according to the second modification, i.e., the reuse of resource blocks with similar propagation characteristics. The horizontal axis in this figure, as in Figure 4, represents the time axis.

[0066] In Figure 7(A), since it is the first information communication, both the conventional technology (first line) and this embodiment (second and third lines) similarly transmit DMRS and DATA. However, in Figure 7(B), since it is the second information communication, UE3 (second line) reuses the DMRS. However, looking at UE4 (third line), even though it is the second information communication, the DMRS is retransmitted. This means that there was a change in propagation characteristics between the first information communication (Figure 7(A)) and the second information communication (Figure 7(B)), making it necessary to retransmit the DMRS.

[0067] Here, Figure 7(C) shows the third information transmission, where UE3 is changed to UE5 (second line), which is a different subcarrier from UE3, and the DMRS is retransmitted. Meanwhile, UE3 is changed to the aforementioned UE3 (third line), and the DMRS is reused. Thus, according to the second modification, the DMRS can be reused across subcarriers.

[0068] In the first embodiment, a method for omitting or reusing DMRS transmission on a per-user basis (per user terminal device 10) was described. Here, the maximum number of times DMRS transmission can be omitted or reused may be predetermined for fail-safe purposes. In this case, if the number of times the DMRS has been reused reaches the predetermined maximum number, the base station 20 will transmit a new DMRS to the user terminal device 10, even if the DMRS can be reused. Note that this maximum number may be set according to various attributes such as the location and characteristics of the base station.

[0069] [Summary of the First Embodiment] According to the embodiment described above, the base station 20 includes at least a processor and memory, and performs wireless communication with the user terminal device 10. Based on past wireless communication with the user terminal device 10, the base station 20 determines whether or not to transmit a reference signal for demodulating data at the physical layer to the user terminal device 10 again. If the base station 20 does not transmit the reference signal to the user terminal device 10 again, it reuses the previously transmitted reference signal. If it transmits the reference signal to the user terminal device 10 anew, it uses the newly transmitted reference signal. By adopting such a configuration, according to this embodiment, it is possible to omit or reuse DMRS depending on the situation. Because it is possible to omit or reuse DMRS depending on the situation, according to this embodiment, even if the allocated ports for DMRS are expanded, resources will not be strained. Therefore, even if the allocated ports for DMRS are expanded to consider an increase in MIMO multiplexing or distributed MIMO, resources will not be strained.

[0070] Furthermore, according to the above-described embodiment, the base station 20 determines, based on past wireless communication with the user terminal device 10, that if the change in propagation characteristics is within a predetermined range, it will not transmit the reference signal to the user terminal device 10 again, and will reuse the previously transmitted reference signal. By adopting such a configuration, the base stations 20 can reuse the same reference signal to each other, thereby suppressing the strain on resource blocks.

[0071] Furthermore, according to the embodiment described above, if the base station 20 does not transmit the reference signal to the user terminal device 10 again, it directly notifies the user terminal device 10 of the position of the symbol of the reference signal to be used. By directly notifying the position of the symbol of the reference signal to be used in this way, the base station 20 can instruct the user terminal device 10 on the reference signal to be used for demodulation.

[0072] Furthermore, according to the embodiment described above, if the base station 20 does not transmit the reference signal to the user terminal device 10 again, it indirectly instructs the user terminal device 10 to reuse the previously transmitted reference signal by not transmitting the reference signal to the user terminal device 10. In this way, by not transmitting the reference signal, the base station 20 can indirectly notify the user terminal device 10 of the position of the symbol of the reference signal to be used, and can instruct the user terminal device 10 on the reference signal to be used for demodulation.

[0073] Furthermore, according to the embodiment described above, the base station 20 determines whether or not to perform semi-fixed resource allocation based on past wireless communication with the user terminal device 10, shares the SPS settings in advance via RRC message, and if it is determined that semi-fixed resource allocation should be performed, it notifies the base station of the transmission or reuse pattern of the reference signal when enabling the use of SPS. By adopting such a configuration, the reference signal can be reused while SPS is enabled.

[0074] Furthermore, according to the embodiment described above, the reuse of the reference signal continues until the SPS terminates. By adopting such a configuration, the reference signal can be reused while the SPS is enabled, and a new reference signal can be used when the SPS is disabled.

[0075] Furthermore, according to the embodiment described above, the base station 20 determines whether or not to reuse the reference signal between adjacent subcarriers used by the same user terminal device 10, and if it is reusable, it reuses the reference signal between adjacent subcarriers. By adopting such a configuration, according to this embodiment, it is possible to omit or reuse DMRS across subcarriers. Because it is possible to omit or reuse DMRS across subcarriers, according to this embodiment, even if the allocated ports for DMRS are further expanded, it will not strain resources. Therefore, even if the allocated ports for DMRS are further expanded to account for an increase in MIMO multiplexing or distributed MIMO, it will not strain resources.

[0076] Furthermore, according to the above-described embodiment, the maximum number of times the reference signal can be reused is predetermined, and when the number of times the reference signal has been reused reaches the maximum number, a new reference signal is sent to the user terminal device even if the reference signal can be reused. The maximum number of reuses is set according to the attributes of the base station 20. By adopting such a configuration, even if the base station 20 cannot detect that the propagation characteristics have changed, it can suitably communicate information with the user terminal device 10 using the new reference signal.

[0077] [Second Embodiment] Next, a second embodiment will be described with reference to Figures 8 to 10. The second embodiment is an example of omitting or reusing DRMS ​​transmission in multiple user terminal devices 10A. In other words, in the second embodiment, DRMS ​​transmission can also be omitted or reused in the spatial direction. Note that the user terminal device 10A is a modified version of the user terminal device 10 described above.

[0078] Figure 8 is a diagram illustrating the positional relationship between the base station and the user terminal device according to the second embodiment. As shown in the figure, the wireless communication system 1A is composed of a base station 20A and a plurality of user terminal devices 10A. In the figure, user terminal device 10c, user terminal device 10d, and user terminal device 10e are shown as an example of the plurality of user terminal devices 10A. In the second embodiment as in the first embodiment, the base station 20A performs beam sweeping. Note that the base station 20A is a modified version of the base station 20 described above.

[0079] More specifically, base station 20A communicates with user terminal device 10c using beam BMc, with user terminal device 10d using beam BMd, and with user terminal device 10e using beam BMe. In this illustrated example, user terminal devices 10c to 10e are different terminals and are simultaneously located in different locations.

[0080] User terminal devices 10c and 10d are located close to each other. On the other hand, user terminal device 10e is located far away from each other. In such a case, the propagation characteristics when information communication is performed with the base station 20A at the location where user terminal device 10c is located are likely to be similar, or substantially identical, to the propagation characteristics when information communication is performed with the base station 20A at the location where user terminal device 10d is located. In such a case, user terminal devices 10c and 10d can share a common DMRS. In other words, when multiple user terminal devices 10A are close together (the channel propagation structure is similar), it is possible that reusing the DMRS among multiple user terminal devices 10A will not result in significant performance degradation.

[0081] Furthermore, reusing the DMRS of a user terminal device 10A located in a spatially close position means that the DMRS is obtained from a nearby user terminal device 10A (not from the base station 20A) and that DMRS is utilized in the resource block itself. Various interfaces can be used to query the nearby user terminal device 10A for its DMRS.

[0082] On the other hand, user terminal device 10e is located at a distance from user terminal devices 10c and 10d. In such a case, the propagation characteristics when communicating with the base station 20A at the location where user terminal device 10d is located are likely to be different from, or substantially not identical to, the propagation characteristics when communicating with the base station 20A at the locations where user terminal devices 10c and 10d are located. Therefore, user terminal device 10e cannot use the DMRS that user terminal devices 10c and 10d use in common.

[0083] Thus, in the second embodiment, it is assumed that multiple (at least two) user terminal devices 10A are adjacent to each other in terms of their relative position to the base station 20A. Multiple user terminal devices 10A being adjacent to each other can also be said to mean that the propagation characteristics do not change substantially spatially.

[0084] Figure 9 is a sequence diagram showing an example of a control method according to the second embodiment. Referring to this figure, the procedure for omitting the DMRS, assuming the situation described in Figure 8, will be explained.

[0085] (Step S41) First, the base station 20A identifies user terminal devices 10A with similar propagation characteristics based on the results of beam sweeps such as SSB and CSI-RS. In the illustrated example, it is assumed that user terminal devices 10c, 10d, and 10e all have similar propagation characteristics. In reality, there may be user terminal devices 10A with different propagation characteristics, but since the user terminal devices 10A with similar propagation characteristics are the target of control according to this embodiment, the description and explanation of user terminal devices 10A with different propagation characteristics will be omitted in the following explanation.

[0086] (Step S42) Next, the base station 20A determines which user terminal devices 10A share the DMRS. This determination is made based on the understanding of propagation characteristics performed in step S41. Specifically, the base station 20A first determines, based on the propagation characteristics, whether the multiple user terminal devices 10A are adjacent to each other. Next, if it is determined that they are adjacent, it determines that the DMRS will be used in common by the multiple adjacent user terminal devices 10A. If it is determined that the DMRS will be shared, it may also determine which user terminal devices 10A transmit the DMRS (primary user terminal device 10A) and which do not transmit the DMRS (secondary user terminal device 10A).

[0087] The base station 20A can also determine that multiple user terminal devices 10A are adjacent to each other based on the results of a beam sweep (e.g., SSB or CSI-RS) not shown, if their propagation characteristics are similar.

[0088] (Step S43) Next, the base station 20A instructs the user terminal device 10A which resources to use to transmit and receive data. Specifically, this instruction is given via the PDCCH. In this embodiment, the base station 20A specifies to each of the multiple user terminal devices 10A a subcarrier (SC) and a resource block (RB) to store the DMRS. In other words, if the DMRS is common to multiple adjacent user terminal devices 10A, the base station 20A can transmit the DMRS to a specific user terminal device 10A among the multiple user terminal devices 10A, and transmit to the other user terminal devices 10A the user terminal device 10A that transmitted the DMRS and the location of the symbol containing the DMRS.

[0089] (Step S44) Next, the base station 20 transmits data to the user terminal device 10A. This transmission is performed via the PDSCH. At this time, the base station 20A notifies the user terminal device 10A of the DCI (PDCCH) and specifies the resource block for which the DMRS will be reused. The user terminal device 10A checks the DCI for each communication on the PDSCH and understands the symbol location of the DMRS to be reused and updated. In this embodiment, as shown in the figure, the DMRS is notified to the main user terminal device 10A (user terminal device 10e in the illustrated example), but the DMRS is not notified to the secondary user terminal devices 10A (user terminal devices 10c and 10d in the illustrated example).

[0090] (Step S45) Therefore, based on instructions from the base station 20A, the subordinate user terminal device 10A queries the main user terminal device 10A for the DMRS symbol (this can also be called listening).

[0091] Here, the user terminal device 10A continues to reuse the DMRS until a new instruction is given. A new instruction is determined by the base station 20A when, as a result of the beam sweep performed by the base station 20A, the difference in propagation characteristics of the multiple user terminal devices 10A falls outside a predetermined range and the propagation characteristics are no longer considered substantially identical.

[0092] (Step S46) If the base station 20A determines that it will issue new instructions regarding DMRS, the base station 20A will notify each user terminal device 10A of the DMRS separately and independently. The user terminal device 10A may also ask the base station 20A if it is okay to continue reusing the device if it has not received any update instructions from the base station 20A.

[0093] As explained with reference to the figure, according to this embodiment, the main user terminal device 10A (user terminal device 10e in the illustrated example) performs communication based on DMRS notified from the base station 20A as usual. On the other hand, the secondary user terminal devices 10A (user terminal devices 10c and 10d in the illustrated example) perform communication based on DMRS notified from the base station 20A to the user terminal device 10e, unlike usual (in other words, the base station 20A does not notify the secondary user terminal devices 10A of DMRS).

[0094] The figure shows a case where three user terminal devices 10A share one DMRS. However, in this embodiment, the number of user terminal devices 10A that share the DMRS is not limited. For example, two user terminal devices 10A may share the DMRS, or three or more user terminal devices 10A may share the DMRS.

[0095] Figure 10 is a schematic diagram showing an example of resources when using the control method according to the second embodiment. The DMRS and data when using the control method according to the second embodiment will be explained with reference to this figure. This figure shows a conceptual diagram of DMRS and data transmitted from the base station 20 to the user terminal device 10. The first row in this figure shows the operation according to the prior art. That is, in the prior art, DMRS and data are transmitted with each communication. Furthermore, the second to fourth rows in this figure show the control according to the second embodiment. In particular, the second row shows sharing within the same resource block, and the third row shows use within resource blocks having similar propagation characteristics. The horizontal axis in this figure, as in Figures 4 and 7, represents the time axis.

[0096] In Figure 8(A), since this is the first information communication, both the conventional technology (first line) and this embodiment (second and third lines) similarly transmit DMRS and DATA. However, in Figure 8(B), since this is the second information communication, UE3 (second line), which is the same resource block, reuses the DMRS. Furthermore, UE5 (third line) and UE6 (fourth line), which have similar propagation characteristics, also use the same DMRS as UE3. UE5 and UE6 query UE3 for the DMRS and perform demodulation using the queried DMRS.

[0097] Figure 8(C) shows the third information communication, but UE4, which is the same resource block, reuses the resource block from the previous communication. For UE5, it is assumed that it has moved to a location where the propagation characteristics are different, and a new DMRS has been assigned. For UE6, it can be seen that the amount of movement was small, and the same DMRS as the previous communication was reused.

[0098] [Summary of the Second Embodiment] According to the embodiment described above, the base station 20A includes at least a processor and memory, and performs independent wireless communication with a plurality of user terminal devices 10A. The base station 20A determines whether the plurality of user terminal devices 10A are adjacent to each other, and if it is determined that they are adjacent, it determines that a reference signal for demodulating data at the physical layer will be used in common by the plurality of adjacent user terminal devices 10A. Furthermore, if the reference signal is to be used in common by the plurality of adjacent user terminal devices 10A, the base station 20A transmits the reference signal to a specific user terminal device 10A among the plurality of user terminal devices 10A. In addition, the base station 20A transmits to the other user terminal devices 10A the user terminal device 10A that transmitted the reference signal and the position of the symbol containing the reference signal. By adopting such a configuration, according to this embodiment, it is possible to omit or reuse DMRS between a plurality of adjacent user terminal devices 10A. Since DMRS can be omitted or reused between multiple adjacent user terminal devices 10A, according to this embodiment, even if the allocated ports for DMRS are expanded, resources will not be strained. Therefore, even if the allocated ports for DMRS are expanded to accommodate an increase in MIMO multiplexing or distributed MIMO, resources will not be strained.

[0099] Furthermore, adjacent user terminal devices 10A are not limited to those owned by the same person, but may be owned by different people. While security concerns may arise from sharing demodulated signals with other people's devices, DMRS is used for demodulation at the physical layer, and these can be easily resolved by other security measures.

[0100] Furthermore, according to the above-described embodiment, the base station 20A determines that multiple user terminal devices 10A are adjacent to each other based on the results of a beam sweep, if their propagation characteristics are similar. In other words, according to this embodiment, the base station 20A shares a reference signal based on the propagation characteristics, if the propagation characteristics are similar. By adopting such a configuration, according to this embodiment, it becomes possible to easily omit or reuse the DMRS between multiple adjacent user terminal devices 10A.

[0101] Furthermore, according to the above-described embodiment, if the base station 20A determines that multiple user terminal devices 10A are adjacent to each other, it determines that even if there are three or more user terminal devices 10A, they will use a common reference signal. By adopting this configuration, according to this embodiment, even if there are three or more user terminal devices 10A, as long as they are adjacent to each other, it is possible to easily omit or reuse DMRS among multiple user terminal devices 10A. Therefore, according to this embodiment, a large amount of resource blocks that would have been allocated to DMRS can be used for data transmission. Therefore, according to this embodiment, even if the allocated ports for DMRS are expanded, resources will not be strained. Consequently, even if the allocated ports for DMRS are expanded to account for an increase in MIMO multiplexing or distributed MIMO, resources will not be strained.

[0102] Furthermore, according to the above-described embodiment, if the base station 20A determines, as a result of beam sweeping, that multiple user terminal devices 10A are adjacent to each other, the multiple user terminal devices 10A will continue to use a common reference signal until the difference in propagation characteristics falls outside a predetermined range. By adopting such a configuration, according to this embodiment, it becomes possible to easily omit or reuse many DMRSs.

[0103] [Third Embodiment] Next, a third embodiment will be described with reference to Figures 11 and 12. In the third embodiment, the user terminal device 10 takes the lead in starting and ending the DMRS sharing operation as described above.

[0104] Figure 11 is a flowchart illustrating the flow of operation initiation initiated by the user terminal device, according to the control method of the third embodiment. First, with reference to the figure, an example of a case in which the user terminal device 10 initiates the shared operation of the DMRS as described above will be explained. Although the illustrated example is based on the first embodiment, the user terminal device 10-led operation can also be applied to the second embodiment in a similar manner.

[0105] First, with reference to Figure 11(A), we will explain an example in which the user terminal device 10 records the DMRS and autonomously determines whether or not the DMRS can be omitted.

[0106] (Step S51) First, the base station 20 transmits data to the user terminal device 10. This transmission is performed via PDSCH. At this time, in step S13 according to Embodiment 1 described above, the base station 20 notified the user terminal device 10 of the DCI (PDCCH), but in this embodiment, since the sharing of DMRS has not yet been decided, it is a normal data transmission (not including the transmission of DCI). However, in this embodiment, the user terminal device 10 records the DMRS each time it is received, which is different from step S13 described above.

[0107] (Step S52) Next, the user terminal device 10 notifies the base station 20 that the DMRS can be reused. In this case, the determination of whether the DMRS can be reused is made by the user terminal device 10, and the notification of the DMRS's reusability may be specifically made via PUSCH (Physical Uplink Shared Channel) or PUCCH (Physical Uplink Control Channel).

[0108] The following description is the same as that of Embodiment 1, and will therefore be referred to as Em1, with the explanation omitted. Note that after step S52, Embodiment 2 may be applied instead of Embodiment 1.

[0109] Next, referring to Figure 11(B), an example will be described in which the user terminal device 10 continuously feeds DMRS back to the base station 20, and the base station 20 determines whether or not DMRS can be omitted.

[0110] (Step S56) First, the base station 20 transmits data to the user terminal device 10. This transmission is performed via PDSCH. At this time, the user terminal device 10 differs from step S51 in that it notifies (feeds back) the base station 20 of the DMRS reception result via PUSCH or PUCCH. That is, in the example shown in Figure 11(B), the user terminal device 10 differs from steps S13 and S51 described above in that it provides DMRS feedback each time it receives data.

[0111] (Step S57) Next, the base station 20 makes a decision on whether to omit DMRS based on the feedback obtained in step S56, and then either Embodiment 1 or Embodiment 2 is carried out. In the figure, as an example, the flow when Embodiment 1 is carried out is labeled Em1.

[0112] Figure 12 is a flowchart illustrating the flow of the user terminal device-led operation termination in a control method according to the third embodiment. Next, with reference to the figure, an example of a case in which the user terminal device 10 takes the lead in terminating the DMRS shared operation as described above will be explained. Although the illustrated example is based on the first embodiment, the user terminal device 10-led operation can also be applied to the second embodiment in a similar manner.

[0113] In this embodiment, during normal operation, the base station 20 monitors the deterioration of the block error rate (BLER), changes in the CSI, etc., and detects channel fluctuations. When the base station 20 detects a channel fluctuation, it stops reusing the DMRS. However, if the DMRS continues to be reused for some reason despite the channel changing, in this embodiment, the user terminal device 10 notifies the base station 20 to stop reusing the DMRS.

[0114] First, with reference to Figure 12(A), an example of a case where the user terminal device 10 is forcibly terminated after a certain period of time using a timer will be explained.

[0115] (Step S61) First, the base station 20 determines whether to omit DMRS. This step may be the same as the process described in step S11, etc.

[0116] (Step S62) Next, the base station 20 notifies the user terminal device 10 that the DMRS is reusable. Specifically, the notification of DMRS reusability may be made via the PDCCH. When the user terminal device 10 receives the notification of DMRS reusability, it starts to reuse the DMRS and simultaneously sets a timer and starts counting. Note that, as shown in Figure 11, if the user terminal device 10 is the one that decides whether or not to reuse the DMRS, the user terminal device 10 may start the timer count as a result of making its own decision. Hereafter, since it is the same as Embodiment 1, it will be referred to as Em1 and the explanation will be omitted. Note that after step S52, Embodiment 2 may be applied instead of Embodiment 1.

[0117] (Step S63) If the timer set in step S62 expires while the process of Embodiment 1 is being executed (while the reuse of the DMRS is continuing), the user terminal device 10 determines that the upper limit for DMRS reuse has been reached and stops the timer count.

[0118] (Step S64) In this case, the user terminal device 10 notifies the base station 20 that the DMRS reuse has ended. This notification may be made, for example, via PUSCH. If the base station 20 determines that the DMRS reuse has ended while the processing of Embodiment 1 is being executed, the timer count is stopped without proceeding to step S63.

[0119] Figure 12(A) illustrates an example where the user terminal device 10 performs the timer count, but the base station 20 may also perform the count.

[0120] Next, an example of detecting DMRS degradation will be described with reference to Figure 12(B). In the example shown in the figure, it is assumed that a portion of the DMRS is transmitted even while the DMRS is being reused. When a portion of the DMRS is transmitted from the base station 20 to the user terminal device 10, the user terminal device 10 can compare the decoding result when using the reused DMRS with the decoding result when using the partially updated DMRS and detect a change in decoding performance.

[0121] (Step S66) After the processing of Embodiment 1 or Embodiment 2 has been performed, suppose that a channel fluctuation has occurred for some reason. Such a channel fluctuation may occur, for example, when the relative positional relationship between the user terminal device 10 and the base station 20 changes, or when a barrier that blocks or interferes with radio waves appears between the user terminal device 10 and the base station 20.

[0122] (Step S67) In this case, the user terminal device 10 will detect a deterioration in the decoding performance of the DMRS. This deterioration detection is performed by comparing the DMRS before and after the update, or by detecting a deterioration in the decoding accuracy, as described above.

[0123] (Step S68) When the user terminal device 10 detects a deterioration in the decoding performance of the DMRS, it notifies the base station 20 that the DMRS reuse has ended. This notification may be made, for example, via PUSCH. In the case of no reuse, the user terminal device 10 will make the decision based solely on the decoding performance by the DMRS, but normally the base station 20 may make the decision based on ACK / NACK feedback.

[0124] [Fourth Embodiment] Next, a fourth embodiment will be described with reference to Figure 13. The fourth embodiment is an example of a combination of the first embodiment and the second embodiment described above.

[0125] Figure 13 is a sequence diagram showing an example of a control method according to the fourth embodiment. An example of processing according to this embodiment will be described with reference to the figure. In the illustrated example, user terminal device 10-12 is a UE that reuses the DMRS, as described in Embodiment 1. Also, user terminal devices 10-13 and 10-14 are UEs that share the DMRS, as described in Embodiment 2. When user terminal devices 10-12 to 10-14 are not distinguished, they may simply be referred to as user terminal device 10.

[0126] (Step S71) First, the base station 20 identifies user terminal devices 10 with similar propagation characteristics based on the results of beam sweeps such as SSB and CSI-RS. In the illustrated example, it is assumed that user terminal devices 10-13, 10-14, and 10-15 all have similar propagation characteristics. In reality, there may be user terminal devices 10 with different propagation characteristics, but since the user terminal devices 10 with similar propagation characteristics are the target of control according to this embodiment, the description and explanation of user terminal devices 10 with different propagation characteristics will be omitted in the following explanation. This step corresponds to step S41 described above.

[0127] (Step S72) Next, the base station 20 determines which user terminal devices 10 share the DMRS. This determination is made based on the understanding of propagation characteristics performed in step S71. This step corresponds to step S42 described above.

[0128] (Step S73) Furthermore, the base station 20 determines which user terminal device 10 will reuse the DMRS. This determination is made based on the results of past CSI estimations, etc. This step corresponds to step S11, etc., described above.

[0129] (Step S74) Next, the base station 20 notifies the user terminal device 10 of the subcarrier and resource block on which to store the DMRS. This notification is made via the PDCCH. This step corresponds to steps S11 and S43 described above.

[0130] (Step S75) Next, the base station 20 transmits data to the user terminal device 10. This transmission is performed via PDSCH. At this time, the base station 20 notifies the user terminal device 10 of the DCI (PDCCH). This step corresponds to steps S13 and S44, etc., described above.

[0131] (Step S76) Next, the user terminal device 10 listens for the DMRS symbols of the designated subcarrier and resource block based on instructions from the base station 20. This step corresponds to step S45 described above.

[0132] (Step S77) Furthermore, the base station 20 notifies via PDSCH whether to continue reusing the DMRS or to renew the DMRS. This step corresponds to step S46 described above.

[0133] [Internal Configuration] This is a block diagram showing an example of the internal configuration of a base station and a user terminal device according to this embodiment. At least some of the functions of the user terminal device 10 and the base station 20 can be realized using a computer. As shown in the figure, the computer is composed of a central processing unit 901, RAM 902, input / output ports 903, input / output devices 904 and 905, etc., and a bus 906. The computer itself can be realized using existing technology. The central processing unit 901 executes instructions contained in a program read from the RAM 902, etc. The central processing unit 901 writes data to the RAM 902, reads data from the RAM 902, and performs arithmetic and logical operations according to each instruction. The RAM 902 stores data and programs. Each element included in the RAM 902 has an address and can be accessed using that address. RAM stands for "Random Access Memory". The input / output port 903 is a port for the central processing unit 901 to exchange data with external input / output devices, etc. Input / output devices 904 and 905 are input / output devices. Input / output devices 904 and 905 exchange data with the central processing unit 901 via input / output ports 903. Bus 906 is a common communication channel used within the computer. For example, the central processing unit 901 reads and writes data to RAM 902 via bus 906. Also, for example, the central processing unit 901 accesses input / output ports via bus 906. Furthermore, all or part of the functional units of the user terminal device 10 and the base station 20 may be implemented using hardware such as ASICs, PLDs, or FPGAs. Furthermore, all or part of the functional units may be implemented by a combination of software and hardware.

[0134] Furthermore, with the above-described embodiment, "it becomes possible to omit or reuse DMRS depending on the situation," so the maximum number of MIMO layers no longer depends on the number of DMRS ports. Therefore, according to this embodiment, it is possible to increase the maximum number of MIMO layers without straining resources. Thus, according to this embodiment, it is possible to contribute to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), "build resilient infrastructure, promote sustainable industrialization and foster innovation."

[0135] Although embodiments of the present invention have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments, and design modifications and the like are also included within the scope of the gist of the present invention.

[0136] Alternatively, computer programs for realizing the functions of each of the above-mentioned devices may be recorded on a computer-readable recording medium, and the programs recorded on this recording medium may be loaded into a computer system and executed. The term "computer system" here may include hardware such as an operating system and peripheral devices. Furthermore, "computer-readable recording medium" refers to writable non-volatile memory such as flexible disks, magneto-optical disks, ROMs, and flash memory, portable media such as DVDs (Digital Versatile Discs), and storage devices such as hard disks built into a computer system.

[0137] Furthermore, "computer-readable recording media" includes volatile memory (e.g., DRAM (Dynamic Random Access Memory)) within a computer system that acts as a server or client when a program is transmitted via a network such as the Internet or a communication line such as a telephone line, which retains the program for a certain period of time. In addition, the above program may be transmitted from the computer system that stores the program in a storage device, etc., to another computer system via a transmission medium or by transmission waves within the transmission medium. Here, the "transmission medium" for transmitting the program refers to a medium that has the function of transmitting information, such as a network such as the Internet or a communication line such as a telephone line. Furthermore, the above program may be for the purpose of realizing a part of the above-mentioned functions. Moreover, it may be a so-called differential file (differential program) that can realize the above-mentioned functions in combination with a program already recorded in the computer system.

[0138] According to the present invention, DMRS can be omitted or reused depending on the situation.

[0139] 1... Wireless communication system, 10... User terminal device, 20... Base station

Claims

1. A base station comprising at least a processor and memory, which performs wireless communication with a user terminal device, wherein, based on past wireless communication with the user terminal device, it determines whether or not to transmit a reference signal for demodulating data at the physical layer to the user terminal device again, and if it does not transmit the reference signal to the user terminal device again, it reuses the previously transmitted reference signal, and if it transmits the reference signal to the user terminal device anew, it uses the newly transmitted reference signal.

2. Based on past wireless communication with the user terminal device, if the change in propagation characteristics is within a predetermined range, the base station determines not to transmit the reference signal to the user terminal device again and reuses the reference signal that was transmitted previously.

3. The base station according to claim 1 or 2, which, if it does not transmit the reference signal to the user terminal device again, notifies the user terminal device of the position of the symbol of the reference signal to be used.

4. The base station according to claim 1 or 2, wherein if the reference signal is not transmitted to the user terminal device again, the base station indirectly instructs the user terminal device to reuse the previously transmitted reference signal by not transmitting the reference signal to the user terminal device.

5. The base station according to claim 1 or 2, which determines whether or not to perform semi-fixed resource allocation based on past wireless communication with the user terminal device, shares the SPS (Semi-Persistent Scheduling) settings in advance using an RRC (Radio Resource Control) message, and, if it is determined that semi-fixed resource allocation should be performed, notifies the transmission or reuse pattern of the reference signal when enabling the use of SPS.

6. The base station according to claim 5, wherein the reuse of the reference signal is continued until the SPS is terminated.

7. The base station according to claim 1 or 2, which determines whether or not to reuse the reference signal between adjacent subcarriers used by the same user terminal device, and reuses the reference signal between adjacent subcarriers if it is reusable.

8. The base station according to claim 1 or 2, wherein the maximum number of times the reference signal can be reused is predetermined, and when the number of times the reference signal has been reused reaches the maximum number, a new reference signal is sent to the user terminal device, even if the reference signal can be reused.

9. The base station according to claim 8, wherein the maximum number of times is set according to the attributes of the base station.

10. A control method for a base station that performs wireless communication with a user terminal device, comprising at least a processor and memory, the method comprising: a determination step of determining whether or not to transmit a reference signal for demodulating data at the physical layer to the user terminal device again based on past wireless communication with the user terminal device; and a reference signal reuse step of reusing the previously transmitted reference signal if the reference signal is not to be transmitted to the user terminal device again.

11. A user terminal device comprising at least a processor and memory, which performs wireless communication with a base station, wherein it receives a reference signal for demodulating data at the physical layer from the base station at least once, and, if it determines to reuse the reference signal based on a notification from the base station, it reuses the already received reference signal to demodulate data at the physical layer.

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