Communication terminal, communication system, control method, and program

Abstract

To provide a mechanism that allows efficient transmission of feedback information according to a radio wave propagation environment.SOLUTION: A communication terminal disclosed has receiving means that receives a reference signal, and transmission means that transmits feedback information to a transmission source of the reference signal. The transmission means transmits, to the transmission source, selectively any one of feedback information in a wideband and feedback information in a sub-band, on the basis of the reference signal. Preferably, on the basis of a predetermined index value for every sub-band obtained by measuring the reference signal, the transmission means sends the feedback information in the wideband to the transmission source when the difference between the sub-bands related to the predetermined index value is less than a predetermined threshold.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a communication terminal, a communication system, a control method, and a program. [Background technology]

[0002] In recent years, the 3GPP (3rd Generation Partnership Project) has been formulating specifications for LTE (Long Term Evolution) and next-generation (NR: New Radio) standards. In communications (hereinafter referred to as Uu communications) in which a base station controls a user equipment (UE), the UE returns a CSI report to the base station. That is, the UE receives a reference signal and a Channel State Information (hereinafter referred to as CSI) report transmission instruction issued by the base station, and returns a CSI report to the base station based on the received results. The base station is configured in advance with a wideband covering the entire channel bandwidth or a subband obtained by dividing the channel, and the UE returns a CSI report to the base station according to this configuration. The CSI report includes a Channel Quality Indicator (hereinafter referred to as CQI), a Precoding Matrix Index (hereinafter referred to as PMI), etc.

[0003] On the other hand, a standard specification called Sidelink communication (hereinafter referred to as Sidelink) has been developed, which does not go through a base station. This specification enables direct wireless communication between UEs using an interface called PC5, without going through a mobile communication network (core network). Patent Document 1 invents a method for returning CSI to a UE that has transmitted a reference signal based on the reference signal in Sidelink. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Table 2022-526741 Summary of the Invention [Problem to be solved by the invention]

[0005] For example, in a radio wave propagation environment where CQI fluctuations per subband are small, the difference between the subband and wideband CQI is small. However, even in such an environment, if the CSI report return method of the UE receiving the reference signal is set to subband, the CSI report of the subband is returned to the UE that transmitted the reference signal. This poses a problem in that the amount of data to be returned increases.

[0006] The present invention has been made in consideration of at least one of the above-mentioned problems, and an object of the present invention is to provide a mechanism that enables efficient transmission of feedback information in accordance with a radio wave propagation environment. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a communication terminal comprising: a receiving means for receiving a reference signal; a transmitting means for transmitting feedback information to a source of the reference signal; The transmitting means selectively transmits either wideband feedback information or subband feedback information to the transmission source based on the reference signal. [Effects of the Invention]

[0008] According to one aspect of the present invention, it is possible to provide a mechanism that enables efficient transmission of feedback information according to the radio wave propagation environment. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a diagram illustrating an arrangement of communication devices according to the present embodiment. [Figure 2] FIG. 2 is a diagram illustrating a functional configuration of a reference signal transmission device according to the present embodiment. [Figure 3] 1 is a diagram illustrating a functional configuration of a reference signal receiving device according to an embodiment of the present invention. [Figure 4] FIG. 2 is a diagram illustrating a communication sequence between communication devices according to the first embodiment. [Figure 5] FIG. 2 is a diagram illustrating a communication flow between communication devices according to the first embodiment. [Figure 6] FIG. 1 is a diagram illustrating an example of a radio wave propagation environment with large fluctuations in the first embodiment. [Figure 7] FIG. 1 is a diagram illustrating an example of a radio wave propagation environment with little fluctuation in the first embodiment. [Figure 8] FIG. 10 is a diagram illustrating an example of slots to be included in a CSI report when CQI=12 is set as a threshold in an example of a radio wave propagation environment with small fluctuations in the first embodiment. [Figure 9] FIG. 10 is a diagram showing the functional configuration of a reference signal receiving device according to a third embodiment. [Figure 10] FIG. 10 is a diagram illustrating a communication sequence between communication devices according to a third embodiment. [Figure 11] FIG. 11 is a diagram illustrating a communication flow between communication devices according to a third embodiment. [Figure 12] FIG. 11 is a diagram illustrating an example of a radio wave propagation environment with little fluctuation in the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Each embodiment will be described in detail below with reference to the accompanying drawings. In the following description, the "number ***" in TS*** represents the number of the Technical Specification in the 3GPP standard. In the accompanying drawings, the same reference number may be used for the same or similar configuration, and duplicate explanations may be omitted.

[0011] First Embodiment

[0012] [System Configuration] Fig. 1 is a diagram showing an example of the arrangement of communication devices according to this embodiment. In Fig. 1, communication device UE-A (101) and communication device UE-B (102) can communicate directly with each other without going through a base station. UE-A (101) is a device that sends a reference signal, and UE-B (102) is a device that receives the reference signal.

[0013] [Device Functional Configuration] Next, the functional configuration of the communication device according to this embodiment will be described. Note that the functional block configuration described below is merely an example. Some (in some cases, all) of the functional blocks described may be replaced with other functional blocks performing similar functions, some functional blocks may be omitted, or additional functional blocks may be added. Furthermore, one functional block described in the following description may be divided into multiple functional blocks, or multiple functional blocks may be integrated into one functional block.

[0014] Fig. 2 is a block diagram showing an example of the functional configuration of a communication device UE-A (101) that transmits a reference signal in this embodiment. In Fig. 2, 201 is a control unit that controls operation. 202 is a storage unit that stores information used by the control unit 201 for control and information related to communication. 203 is a sidelink processing unit between UEs. 204 is a communication unit that transmits and receives information via wireless communication with other devices.

[0015] FIG. 3 is a block diagram showing an example of the functional configuration of a communication device UE-B (102) that transmits a reference signal in this embodiment. 301 to 304 in FIG. 3 have the same functions as 201 to 204 in FIG. 2, and therefore a description thereof will be omitted. 305 denotes an index measurement / calculation unit, which is a functional unit that measures the reference signal transmitted by UE-A (101) and measures / calculates an index. The index is, for example, a signal-to-interference-noise ratio (SINR) or a channel quality indicator (CQI). The signal-to-interference-noise ratio (SINR) is an index that represents the ratio of the signal levels of a desired signal to an interference signal or noise. The channel quality indicator (CQI) is an index that measures the reception quality in a channel. 306 denotes a threshold determination unit, which is a functional unit that determines whether the difference between subbands for the index output by the index measurement / calculation unit 305 is equal to or greater than a first threshold. That is, this functional unit determines whether the maximum value of the differences between subbands for each subband is equal to or greater than a first threshold. The difference between subbands is also an index value representing channel fluctuation. Furthermore, since there are multiple subbands, the maximum value of the differences between subbands means the difference between the minimum and maximum values ​​of the indexes for each subband. Hereinafter, "the maximum value of the differences between subbands for each index is equal to or greater than a first threshold" is also expressed as "the channel fluctuation of the reference signal index is equal to or greater than a first threshold." This determination may or may not include the first threshold.

[0016] [Processing example] The operation of this embodiment will be described with reference to the operation sequence diagram shown in FIG. 4 and the flowchart shown in FIG.

[0017] FIG. 4 shows an example of CSI report transmission in this embodiment. FIG. 5 shows flowcharts of the sequence of FIG. 4 in this embodiment, for UE-A (101) and UE-B (102). The processing shown in each flowchart is implemented in UE-A (101) by the control unit 201 executing a control program stored in the storage unit 202. The processing shown in each flowchart is implemented in UE-B (102) by the control unit 301 executing a control program stored in the storage unit 302. In this case, the processing can be implemented by each of UE-A (101) and UE-B (102) performing calculations and processing of information and controlling each piece of hardware.

[0018] UE-A (101) and UE-B (102) are performing data communication in sidelink communication not via a base station (F401). UE-A (101) transmits a reference signal to UE-B (102) (F402, S501). The reference signal may be a CSI-RS (Channel State Information Reference Signal). UE-B (102) receives the reference signal (S502), measures and calculates the reference signal using the indicator measurement and calculation unit 305, and outputs an indicator (S503). Next, it determines whether the channel fluctuation of the output reference signal indicator at UE-B (102) is equal to or greater than a first threshold (F403, S504). If it is determined that the fluctuation of the reference signal indicator is equal to or greater than the first threshold, it determines that the radio wave propagation environment is one with large fluctuations. Furthermore, in S505, it determines whether to transmit in wideband. For example, this determination may be made based on whether the device itself is capable of transmitting in wideband. If it is determined that the radio wave propagation environment is highly variable and that wideband transmission is not required, the process proceeds to S506. The precoding indicator (PMI) and CQI for the subbands into which the channel is divided are included in the CSI and transmitted to UE-A (101) (F404, S506).

[0019] On the other hand, if it is determined in S504 that the fluctuation of the reference signal index is less than the first threshold, it is determined that the radio wave propagation environment is one with little fluctuation, and wideband CSI for the entire channel band is sent to UE-A (101) (F404, S507).

[0020] Furthermore, if it is determined in S504 that the fluctuation of the reference signal index is equal to or greater than the first threshold, even if it is determined that the radio wave propagation environment is highly fluctuating, it may be determined in S505 that wideband transmission is to be performed. In this case, similarly, in S507, wideband CSI for the entire channel band is transmitted to UE-A (101) (F404, S507).

[0021] The UE-A (101) determines whether it has received the CSI transmitted by the UE-B (102) (F405, S508). If it has received the CSI, it sends data to the UE-B (102) (F405) based on the received CSI (S509). If it has not received the CSI, it sends data to the UE-B (102) (F405) based on the previous CSI (S510).

[0022] The UE-A (101) may transmit the CSI report transmission instruction to the UE-B (102) simultaneously with the reference signal or at a different timing.

[0023] Furthermore, the UE-A (101) may determine whether or not CSI has been received (S508), and if CSI has not been received, may again transmit a CSI report transmission instruction to the UE-B (102).

[0024] Based on the received CSI, UE-A (101) performs data communication with UE-B (102) (F406, S509).

[0025] In the above F404, S506, and S507, examples of the format of the CSI report sent to UE-A (101) are shown in Tables 1 to 3, and are listed in the 3GPP technical specification TS38.212V17.5.0. Table 1 is the wideband CSI report format, and Tables 2 and 3 are the subband CSI report formats.

[0026] For example, in S506, the CSI report is formatted as in Table 2 or Table 3 for the subband, and in S507, as in Table 1 for the wideband, and sent to UE-A (101).

[0027] [Table 1]

[0028] [Table 2]

[0029] [Table 3] Next, an example of the processing of S504 to 507 will be explained using the radio wave propagation environment simulation diagrams in Figures 6 and 7. Figure 6 shows an example of a radio wave propagation environment with large fluctuations, and Figure 7 shows an example of a radio wave propagation environment simulation with small fluctuations. The simulations in each figure use the propagation models TDL (Tapped Delay Line)-C and TDL-D listed in 3GPP technical report TR38-901. TDL-C is a non-line-of-sight (NLOS) environment, and TDL-D is a line-of-sight (LOS) environment. The simulation parameters are as shown in Table 4.

[0030] [Table 4] FIG. 6(A) shows the results of wideband SINR and CQI for all frames. Since CSI reports are acquired at four-slot intervals, which is the CSI report period, the SINR and CQI data are obtained every four slots. The SINR is displayed in decibels (dB). FIGS. 6(B) and 6(C) show the SINR and CQI for each subband in slot 0 and slot 4, respectively. In this embodiment, there are 56 resource blocks and the subband size is 4, so the number of subbands is 14. FIG. 6(B) shows the SINR and CQI for each subband in slot 0 in FIG. 6(A). The SINR varies from approximately 10 to 15 dB, and the CQI varies from 9 to 12 between subbands. The wideband value represents the average value for all subbands in slot 0. The SINR for slot 0 in FIG. 6(A) is 13.3 dB, and the CQI is 11.

[0031] Similarly, in Figure 6(C), which shows the SINR and CQI for each subband in slot 4 of Figure 6(A), the SINR varies from about 9 to 17 dB between subbands, and the CQI varies from 8 to 13. Also, in Figure 6(A), which shows the average values ​​for all subbands in slot 4, the SINR for slot 4 is 13.4 dB and the CQI is 11. The wideband SINR and CQI for the other slots are similar.

[0032] For example, if the judgment condition in S504 is that the SINR varies by 4 dB or more across all subbands, then in the radio wave propagation environment of FIG. 6, CSI including the CQI and PMI for each subband is sent to UE-A (101) (F404, S506). The case where the SINR varies by 4 dB or more across all subbands corresponds to the case where the difference between the minimum and maximum SINR values ​​for each subband is 4 dB or more. The judgment condition in S504 may be a CQI variation of 3 or more, rather than SINR. Alternatively, a combination of an SINR variation of 3 dB or more and a CQI variation of 2 or more may be used with SINR and CQI.

[0033] Next, an example of a radio wave propagation environment with little fluctuation is explained using Fig. 7. As in Fig. 6, Fig. 7(A) shows the wideband SINR and CQI results for all frames, and Fig. 7(B) and (C) show the SINR and CQI for each subband in slot 0 and slot 4, respectively.

[0034] In Figure 7(B), the SINR is 14.8 to 16.7 dB, and the CQI is 11 to 12, while in Figure 7(C), the SINR is 12.8 to 15.4 dB, and the CQI is 10 to 12. The wideband SINR for slots 0 and 4 in Figure 7(A) is 16 and 14 dB, respectively, and the wideband CQI is 12 and 11, respectively. The SINR and CQI in Figures 7(B) and 7(C) vary little between subbands, and the difference between the wideband SINR and wideband CQI in Figure 7(A) and those in Figures 7(B) and 7(C) is small.

[0035] As in Fig. 6, if the judgment condition in S504 is that the SINR varies by 4 dB or more across all subbands, then in the radio wave propagation environment of Fig. 7, CSI including wideband PMI and CQI is sent to UE-A (101) (F404, S507). As a result, in this example, by sending 14 subband data as one wideband data, the amount of CQI and PMI data in the CSI report to be sent can be reduced to 1 / 14th.

[0036] In this way, according to this embodiment, in a radio wave propagation environment where CQI fluctuations for each subband are small, a UE receiving a reference signal can select a wideband CSI report in accordance with the reception result of the reference signal, thereby reducing the amount of data to be returned.

[0037] Although this embodiment has been described using sidelink communication between devices as an example, the present invention is not limited to sidelink communication. The present invention can also be applied to cases where UE-A (101) is a base station device, i.e., Uu communication. The UE-B (102) measures a reference signal transmitted by the base station and compares the measured value with a first threshold. Based on the comparison result, fluctuations in the radio wave propagation environment are determined. If the fluctuations are determined to be small, a CSI report including wideband PMI and CQI can be sent.

[0038] Second Embodiment In the second embodiment, an example will be described in which a portion of the subband is sent in the CSI report. The functional configuration of the communication device in the second embodiment (FIGS. 2 and 3) is the same as that in the first embodiment, and the sequence and flow are the same as those in FIGS. 4 and 5. The method of sending the subband in S506 differs from that in the first embodiment, and will be described using the simulation example in FIG. 8.

[0039] 8(B) and (C) are the same as FIG. 6(B) and (C). For example, if CQI=12 is set as the second threshold, subbands equal to or greater than 12 are included in the CSI report. The subbands in the dashed line in FIG. 8 correspond to this, and in slot 0 in FIG. 8(B), subbands 5 to 7, and in slot 4 in FIG. 8(C), subbands 5 to 7 and subbands 11 to 13 are equal to or greater than the second threshold. The PMI and CQI of these subbands are included in the CSI report and sent to UE-A (101). The second threshold may be determined by SINR, or by both CQI and SINR.

[0040] Alternatively, a predetermined number of subbands with the highest subband CQI may be transmitted. As an example, if the predetermined number is 3, then in FIG. 8(B) these correspond to subbands 5 to 7, and in FIG. 8(C) these correspond to subband 6 and any two of subbands 5 to 7 and 11 to 13. As in the example described above in relation to the second threshold, these subband PMIs and CQIs are included in the CSI report and transmitted to UE-A (101). Of course, SINR may be used instead of CQI, and weighted CQI and SINR may also be used as criteria for determination.

[0041] Additionally, the CSI report may include the subband number to be sent. <Third embodiment> In the third embodiment, an example will be described in which the number of resource blocks constituting a subband (subband size) is changed based on the error rate.

[0042] The case where UE-B (102) determines the error rate will be described. In this case, the functional configuration of UE-A (101) may be as shown in FIG. 2, and the functional configuration of UE-B (102) is as shown in FIG. 9. Descriptions of the same numbers will be omitted. UE-B (102) additionally includes an error rate measurement unit 905 and an error rate determination unit 906. The error rate measurement unit 905 is a functional unit that measures errors during communication, and the errors are any one of bit errors, frame errors, block errors, packet errors, or any combination of two or more of these. The error rate determination unit 906 is a functional unit that compares the error value of the error rate measurement unit 905 with a predetermined third threshold value to determine whether it is larger or smaller.

[0043] The process performed by UE-B (102) to determine the error rate will be described using the process sequence diagram of FIG. 10 and the flowchart of FIG. 11. The data communication in F201 and the reference signal transmission and reception in F202, S501, and S502 are the same as those in the first embodiment. As a result of the data communication, UE-B (102) measures the error rate using the error rate measurement unit 905 (S1103). In F1003 and S1104, it is determined whether the subband size can be changed or is necessary. If it is determined that the subband size cannot be changed or is not necessary, the process proceeds to S1109 and S1110, and the same operation as in the first embodiment is performed without changing the subband size. If it is determined that the subband size can be changed and is necessary, a subband size change request is made to UE-A (101) (S1105). Upon receiving the subband size change request, UE-A (101) changes the subband size (S1107). The subsequent operation is the same as in the first embodiment and will not be described.

[0044] The two decisions F1003 and S1104 will be explained.

[0045] The determination is based on the subband configuration and the third error rate threshold in Table 5 below, which is published in the 3GPP technical specification TS38.214-h20.

[0046] For example, if the number of resource blocks is 80, the current subband size is 16, and the error rate is equal to or greater than the third threshold, it is determined that it is useful to reduce the subband size, i.e., that changing the subband size is useful. In Table 5, when the number of resource blocks is 80, the subband size can be selected from 8 and 16, so in this case it is determined that changing the subband size is necessary and possible. If the error rate is equal to or less than the third threshold, it is determined that it is useful to increase the subband size, i.e., that changing the subband size is useful. However, in this example, the subband size cannot be increased beyond 16, so it is determined that changing the size is not possible.

[0047] [Table 5] An example of a simulation of this embodiment is shown in Figure 12. The propagation model is TDL-D, as in Figure 7, and the parameters in Table 4 are the same except that the subband size is 8 resource blocks (number of resource blocks = 8). As in Figure 7, Figure 12(A) shows the results of wideband SINR and CQI for all frames, and Figures 12(B) and (C) show the SINR and CQI for each subband in slot 0 and slot 4. The SINR and CQI in Figures 12(A) to (C) are close to the SINR and CQI in Figures 7(A) to (C).

[0048] For example, if communication is initially performed with a subband size of 4 resource blocks, and the error rate is equal to or lower than the third threshold, the subband size can be changed to 8 resource blocks. In such a radio wave propagation environment with little fluctuation, changing the subband size to a larger value makes it possible to reduce the data size of the CSI returned to UE-A (101).

[0049] The error rate threshold can be determined when it exceeds (falls below) a certain number of times or by a certain percentage for a certain period of time. The error rate increase or decrease rate can also be used as the threshold. For example, let's assume that an error rate increase rate of 2% is set as the third threshold for determination, and the error rate is 5% for the first five slots, and then 7.5% for the next five slots. In this case, the error rate has increased by 2.5%, and it can be determined that this exceeds the third threshold, and that a change in the subband size is necessary.

[0050] The subband size may be other than that shown in Table 5, and may conform to a standard wireless specification or a unique configuration. The UE-A (101) may measure the error rate and change the subband.

[0051] In the third embodiment described above, a modification is possible in which the subband and the wideband are switched depending on the error rate, because, for example, when the error rate is small, it is highly likely that the radio wave propagation environment is one with little fluctuation. <Other embodiments> The present invention can also be realized by supplying a program that realizes one or more functions of each of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC or FPGA) that realizes one or more functions. ASIC is an abbreviation for Application Specific Integrated Circuit. FPGA is an abbreviation for Field Programmable Gate Array. Furthermore, some or all of the various processes described in the above flowcharts can be realized by using a hardware circuit in cooperation with a processor such as a CPU or MPU.

[0052] Although each embodiment has been described in detail above, it is not limited to the specific embodiment, and various modifications and changes are possible within the scope of the claims. It is also possible to combine all or a plurality of components of the above-described embodiments.

[0053] The following additional notes are provided regarding the above-described embodiments.

[0054] [Appendix 1] receiving means for receiving a reference signal; a transmitting means for selectively transmitting either wideband feedback information or subband feedback information to a source of the reference signal based on the reference signal. [Appendix 2] The communication terminal described in Appendix 1, characterized in that the transmitting means sends wideband feedback information to the source when a difference between subbands regarding the predetermined index value is less than a predetermined threshold based on a predetermined index value for each subband obtained by measuring the reference signal. [Appendix 3] The communication terminal according to claim 2, wherein the transmitting means transmits feedback information of the subband to the source when the difference is equal to or greater than the predetermined threshold. [Appendix 4] The communication terminal according to claim 2 or 3, wherein, if the difference is equal to or greater than the predetermined threshold, feedback information of some subbands is sent to the source. [Appendix 5] The communication terminal described in Appendix 4, characterized in that the feedback information of the some subbands includes feedback information of a predetermined number of subbands whose predetermined indicator is higher than a predetermined value, or feedback information of subbands whose predetermined indicator is equal to or higher than a predetermined value. [Appendix 6] The communication terminal according to Supplementary Note 4, wherein the feedback information of the part of the subbands includes a corresponding subband number. [Appendix 7] 7. The communication terminal according to any one of Supplementary Notes 2 to 6, wherein the predetermined indicator is a signal-to-interference-and-noise ratio, an error rate, or a signal quality indicator. [Appendix 8] 8. The communication terminal according to any one of Supplementary Notes 1 to 7, wherein the feedback information comprises a precoding matrix index or a signal quality index. [Appendix 9] receiving means for receiving a reference signal; a transmitting means for transmitting feedback information to a source of the reference signal; The communication terminal is characterized in that the transmitting means changes a subband size related to feedback information of the subband to be sent to the source of transmission based on the reference signal. [Appendix 10] The communication terminal described in Supplementary Note 9, characterized in that the transmitting means increases the subband size when the difference between subbands regarding the predetermined index value is less than a predetermined threshold, based on a predetermined index value for each subband obtained by measuring the reference signal. [Appendix 11] The communication terminal according to claim 10, wherein the transmitting means reduces the subband size when the difference is equal to or greater than the predetermined threshold. [Appendix 12] 12. The communication terminal according to any one of Supplementary Notes 9 to 11, wherein the predetermined indicator is a signal-to-interference-plus-noise ratio, an error rate, or a signal quality indicator. [Appendix 13] 13. The communication terminal according to any one of Supplementary Notes 9 to 12, wherein the feedback information comprises a precoding matrix index or a signal quality index. [Appendix 14] a first communication device and a second communication device; the first communication device, a transmitting means for transmitting a reference signal or a data signal; and a change means for changing the subband size, the second communication device, receiving means for receiving a reference signal or a data signal; an error rate measuring means for measuring an error rate based on the reference signal or the data signal; a change request means for requesting a change in subband size from a source of the reference signal or data signal, A communication system, wherein the change means of the first communication device changes the subband size based on the change request. [Appendix 15] the second communication device further comprises a determination means for determining whether a subband size needs to be changed; the determining means determines whether or not a change in subband size is necessary based on the error rate measured by the error rate measuring means; The communication system described in Appendix 14, characterized in that the change request means requests the sender of the reference signal or data signal to change the subband size when the determination means determines that a change in the subband size is necessary. [Appendix 16] The communication system described in Appendix 14 or 15, characterized in that the change request means requests that the subband size be reduced when the error rate measured by the error rate measurement means is greater than or equal to a predetermined value, and requests that the subband size be increased when the error rate is less than the predetermined value. [Appendix 17] 17. A communication system according to any one of appendices 12 to 16, wherein the errors relating to the error rate include at least one of bit errors, block errors, frame errors, and packet errors. [Explanation of symbols]

[0055] 101 Communication device UE-A 102 Communication device UE-B

Claims

1. receiving means for receiving a reference signal; a transmitting means for selectively transmitting either wideband feedback information or subband feedback information to a source of the reference signal based on the reference signal.

2. 2. The communication terminal according to claim 1, wherein the transmitting means sends feedback information of the wideband to the source when a difference between subbands regarding the predetermined index value obtained by measuring the reference signal is less than a predetermined threshold value based on the predetermined index value for each subband.

3. 3. The communication terminal according to claim 2, wherein said transmitting means transmits subband feedback information to said source when said difference is equal to or greater than said predetermined threshold value.

4. 3. The communication terminal according to claim 2, wherein when the difference is equal to or greater than the predetermined threshold, feedback information of a part of the subbands is sent to the source.

5. 5. The communication terminal according to claim 4, wherein the feedback information of the part of the subbands includes feedback information of subbands whose predetermined indicators are in a top predetermined number, or feedback information of subbands whose predetermined indicators are equal to or greater than a predetermined value.

6. The communication terminal according to claim 4, wherein the feedback information of the partial subband includes a corresponding subband number.

7. The communication terminal according to claim 2, wherein the predetermined indicator is a signal-to-interference-and-noise ratio, an error rate, or a signal quality indicator.

8. The communications terminal according to any one of claims 1 to 7, characterized in that the feedback information comprises a precoding matrix index or a signal quality index.

9. receiving means for receiving a reference signal; a transmitting means for transmitting feedback information to a source of the reference signal; The communication terminal is characterized in that the transmitting means changes a subband size related to feedback information of the subband to be sent to the source of transmission based on the reference signal.

10. 10. The communication terminal according to claim 9, wherein the transmitting means increases a subband size when a difference between subbands regarding a predetermined index value obtained by measuring the reference signal is less than a predetermined threshold, based on the predetermined index value for each subband.

11. 11. The communication terminal according to claim 10, wherein said transmitting means reduces the subband size when said difference is equal to or greater than said predetermined threshold value.

12. a first communication device and a second communication device; the first communication device, a transmitting means for transmitting a reference signal or a data signal; and a changing means for changing the subband size, the second communication device, receiving means for receiving a reference signal or a data signal; an error rate measuring means for measuring an error rate based on the reference signal or the data signal; a change request means for requesting a change in subband size from a source of the reference signal or data signal; A communication system, wherein the change means of the first communication device changes the subband size based on the change request.

13. the second communication device further comprises a determination means for determining whether a subband size needs to be changed; the determining means determines whether or not a subband size needs to be changed based on the error rate measured by the error rate measuring means; 13. The communication system according to claim 12, wherein the change request means requests a source of the reference signal or data signal to change the subband size when the determination means determines that a change in the subband size is necessary.

14. The communication system according to claim 12 or 13, characterized in that the change request means requests a reduction in the subband size when the error rate measured by the error rate measurement means is equal to or greater than a predetermined value, and requests an increase in the subband size when the error rate is less than the predetermined value.

15. 13. The communication system according to claim 12, wherein the errors relating to the error rate include at least one of a bit error, a block error, a frame error, and a packet error.

16. A control method for controlling communication, comprising: a receiving step of receiving a reference signal; a transmitting step of selectively sending either wideband feedback information or subband feedback information to a source of the reference signal based on the reference signal.

17. On the computer, a receiving process for receiving a reference signal; a transmission process of selectively transmitting either wideband feedback information or subband feedback information to a transmission source of the reference signal based on the reference signal; A program characterized by executing the following.

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