Terminal device, control method, and program for enhancing channel estimation in wireless communication

Abstract

To suppress deterioration in a frequency resolution of channel estimation while expanding a port number of a demodulation reference signal.SOLUTION: A terminal device acquires, from a base station device being connected, first information identifying an orthogonal cover code (OCC), which is used for generating a demodulation reference signal (DMRS) to be transmitted from the base station device to the terminal device, and a resource element to which the DMRS is transmitted, and second information which enables the terminal device to identify whether or not it is possible to perform channel estimation for the unit of a sub-band which is a part of a band to perform the channel estimation thereon by the DMRS. In a case where it is possible to perform the channel estimation for the unit of the sub-band, the channel estimation for the unit of the sub-band is executed using a partial sequence of the OCC corresponding to the sub-band, and data transmitted from the base station device to the terminal device are received using a channel estimate corresponding to each sub-band.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to advanced techniques for channel estimation in wireless communications. [Background technology]

[0002] In the Third Generation Partnership Project (3GPP (registered trademark)), a technique of expanding the number of ports of a demodulation reference signal (DMRS) used for channel estimation is being discussed as a technique for increasing the number of spatially multiplexed layers in a multi-input multi-output (MIMO) of a single user (SU) or a multi-user (MU). Non-Patent Document 1 describes a technique of expanding the frequency range to which one orthogonal cover code (OCC) used for multiplexing is applied in order to expand the number of ports of the DMRS. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] 3GPP contribution, R1-2204370, May 2022 Summary of the Invention [Problem to be solved by the invention]

[0004] Since one channel estimate is obtained for the frequency range to which one OCC is applied, if the frequency range to which one OCC is applied is expanded, one channel estimate is obtained for the expanded range, which may result in a decrease in the frequency resolution of the channel estimate. [Means for solving the problem]

[0005] The present invention provides a technique for suppressing degradation of frequency resolution in channel estimation while increasing the number of ports for demodulation reference signals.

[0006] A terminal device according to one aspect of the present invention includes an acquisition means for acquiring, from the base station device, first information that identifies an orthogonal cover code (OCC) used when generating a demodulation reference signal (DMRS) to be transmitted from a connected base station device to the terminal device and a resource element in which the DMRS is transmitted, and second information that enables the terminal device to identify whether channel estimation is possible in units of subbands that are part of a band in which channel estimation is performed using the DMRS; a determination means for determining whether channel estimation in units of subbands is possible based on the second information; and, when it is determined that channel estimation in units of subbands is possible, a determination means for determining whether channel estimation is possible in units of subbands. and an execution means for performing channel estimation for each subband using a partial sequence of the OCC corresponding to the subband, and, if it is determined that channel estimation for each subband is not possible, performing channel estimation for the entire band using the OCC; and, if channel estimation for each subband is performed, receiving means for receiving data transmitted in the band from the base station device to the terminal device using a channel estimation value corresponding to each subband, and, if channel estimation for the entire band is performed, receiving data transmitted in the band from the base station device to the terminal device using a channel estimation value common to the band. [Effects of the Invention]

[0007] According to the present invention, it is possible to suppress deterioration of frequency resolution in channel estimation while increasing the number of ports of demodulation reference signals. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a wireless communication system. [Figure 2] FIG. 10 is a diagram illustrating an example of mapping of DMRS to resource elements. [Figure 3] 1A and 1B are diagrams illustrating examples of OCCs and correlations between OCCs. [Figure 4] FIG. 2 illustrates an example of a hardware configuration of the apparatus. [Figure 5] FIG. 2 is a diagram illustrating an example of a functional configuration of a base station device. [Figure 6] FIG. 2 is a diagram illustrating an example of a functional configuration of a terminal device. [Figure 7] FIG. 10 is a diagram illustrating an example of a flow of processing executed by a base station device. [Figure 8] FIG. 10 is a diagram illustrating an example of a flow of processing executed by a terminal device. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention as claimed, and not all combinations of features described in the embodiments are necessarily essential to the invention. Two or more of the features described in the embodiments may be combined in any desired manner. Furthermore, the same reference numerals are used to designate identical or similar components, and redundant descriptions will be omitted.

[0010] (System Configuration) FIG. 1 shows an example of the configuration of a wireless communication system according to this embodiment. This wireless communication system is a cellular communication system formed in accordance with, for example, the fifth generation (5G) communication standard of the Third Generation Partnership Project (3GPP (registered trademark)) or its successor standard, and includes a base station device 101 and terminal devices 111 to 116. Note that, for simplicity of explanation, FIG. 1 shows only one base station device and a small number of terminal devices, but it goes without saying that multiple base station devices and a large number of terminal devices may exist. Note that in the following explanation, it is assumed that the base station device 101 transmits data to each of the terminal devices 111 to 116 in one layer. However, this is merely for simplicity of explanation, and it goes without saying that it goes without saying that data is transmitted to one terminal device in multiple layers. In that case, the term "terminal device" in the following explanation may be read as "layer."

[0011] The terminal devices 111 to 116 are connected to the base station device 101, receive a demodulation reference signal (DMRS) transmitted from the base station device 101, perform channel estimation based on the DMRS, and perform demodulation processing on data such as user data using the channel estimation results. The DMRS is transmitted, for example, using different frequency and time resources for each of a predetermined number of layers. Furthermore, the DMRS is spread using an orthogonal cover code (OCC) so that the predetermined number of layers using the same frequency and time resources are separable from each other. For this reason, the terminal devices 111 to 116 first identify the frequency resource corresponding to the layer that they receive and the OCC sequence assigned to that layer. Note that information on the DMRS symbols to be transmitted is naturally shared between the base station device 101 and the terminal devices 111 to 116. A symbol sequence obtained by encoding the DMRS using the OCC is mapped to frequency and time resources so that each symbol in the symbol sequence is transmitted in one resource element. For example, if the code length of OCC is 4, one DMRS symbol is spread into four symbols, and the four symbols are mapped to different resource elements. Terminal devices 111 to 116 can calculate a channel estimation value by despreading symbols received in resource elements where DMRS is transmitted using OCC and dividing the value resulting from the despreading by the transmitted DMRS symbol.

[0012] Conventionally, there are multiple patterns for DMRS allocation to resource elements. For example, configuration type 1 provides a pattern in which every other one of 12 subcarriers in a resource block is used. In this pattern, for example, subcarriers are divided into two groups: a group with subcarrier numbers 2n (0≦n≦5) and a group with subcarrier numbers 2n+1 (0≦n≦5), and each terminal device uses one of these groups. In configuration type 2, the 12 subcarriers in a resource block are divided into two subbands: a subband consisting of six subcarriers at a higher frequency and a subband consisting of six subcarriers at a lower frequency. Each subband is divided into three groups, each consisting of two consecutive frequency resources. Each terminal device uses one of the three groups. In addition, DMRS may use one resource element in the time domain or two consecutive resource elements.

[0013] Among these configurations, mapping of DMRSs of configuration type 1 and configuration type 2 to resource elements when two consecutive resource elements are used is shown in Figures 2(A) and 2(B).

[0014] As shown in FIG. 2(A), in configuration type 1, channel estimation is performed in units of two alternate groups in the frequency domain and two consecutive groups in the time domain. That is, channel estimation is performed for each range of four resource elements in the frequency domain. Note that, to each terminal device, a DMRS is transmitted in either a group of subcarriers with subcarrier numbers 2n (0≦n≦5) or a group of subcarriers with subcarrier numbers 2n+1 (0≦n≦5). According to this configuration, a DMRS is transmitted to each terminal device using four resource elements for the frequency range in which channel estimation is performed. In this case, by using an OCC with a code length of 4, the base station device can multiplex and transmit DMRSs corresponding to four layers using the same resource element. Therefore, in configuration type 1 shown in FIG. 2(A), code division multiplexing is performed using an OCC with a code length of 4 for two groups obtained by grouping in the frequency domain, two each in the time domain and the frequency domain, for a total of four resource elements, and therefore DMRSs can be transmitted in parallel for a total of eight layers. Note that a unit capable of transmitting DMRS in a separable format using resource element grouping and OCC coding is called a port. In the format shown in Figure 2(A), the maximum number of DMRS ports is eight.

[0015] On the other hand, in configuration type 2 shown in FIG. 2(B), channel estimation is performed in units of six resource elements in the frequency domain. Note that a DMRS is transmitted to each terminal device in any of the following subcarrier groups: a group with subcarrier numbers 6m and 6m+1 (m=0, 1), a group with subcarrier numbers 6m+2 and 6m+3 (m=0, 1), and a group with subcarrier numbers 6m+4 and 6m+5 (m=0, 1). With this configuration, even in configuration type 2, a DMRS is transmitted to each terminal device using four resource elements for the frequency range in which channel estimation is performed. Therefore, by using an OCC with a code length of 4, the base station device can multiplex and transmit DMRSs corresponding to four layers using the same resource element. Therefore, in configuration type 2 shown in FIG. 2(B), code division multiplexing is performed using an OCC with a code length of 4 on three groups obtained by grouping in the frequency domain, two each in the time and frequency domains, for a total of four resource elements, resulting in a maximum of 12 DMRS ports. In the Release 15 standard of 3GPP (registered trademark), a maximum of 12 ports can be secured as DMRS ports by using the configuration shown in FIG. 2(B).

[0016] In recent years, with the increasing demand for higher communication speeds and for providing parallel communication opportunities to a large number of terminal devices, there has been a demand for an increase in the number of multiplexing layers in multi-user (MU) / single-user (SU) MIMO (Multi-input Multi-output). In this case, the conventional maximum of 12 ports is no longer sufficient, and there is discussion of allocating up to 24 ports in preparation for the 3GPP (registered trademark) Release 18 standard. To achieve this, for example, it is possible to expand the frequency range unit for channel estimation, thereby enabling the transmission of DMRS spread using a larger number of resource elements and an OCC with a longer code length. For example, as shown in FIG. 2(C), the frequency range unit for channel estimation is doubled compared to FIG. 2(B), and three groups are formed, each using eight resource elements. These groups can be configured in the same way as FIG. 2(B). That is, a group with subcarrier numbers 6m and 6m+1 (m = 0, 1), a group with subcarrier numbers 6m+2 and 6m+3 (m = 0, 1), and a group with subcarrier numbers 6m+4 and 6m+5 (m = 0, 1) can be configured. However, in FIG. 2(B), eight resource elements are divided into two and each is used to transmit a DMRS spread by an OCC with a code length of 4, whereas in FIG. 2(C), eight resource elements are used to transmit a DMRS spread by an OCC with a code length of 8. In this way, for the three groups obtained by grouping in the frequency domain, code division multiplexing is performed by an OCC with a code length of 8 on a total of eight resource elements, two in the time domain and four in the frequency domain, so the maximum number of DMRS ports is 24.

[0017] In this embodiment, the grouping of resource elements in the frequency domain is the same as that in FIG. 2(B), but is not limited to this. For example, a group with subcarrier numbers 0 to 3, a group with subcarrier numbers 4 to 7, and a group with subcarrier numbers 8 to 11 may be configured. Also, a group with subcarrier numbers {0, 1, 8, 9}, a group with subcarrier numbers {2, 3, 6, 7}, and a group with subcarrier numbers {4, 5, 10, 11} may be configured. That is, the grouping in the frequency domain may be performed arbitrarily. Furthermore, in the above example, an example is described in which four groups for four subcarriers are formed in the frequency domain, but arbitrary grouping may be performed so that a total of eight resource elements are secured in the frequency domain and the time domain.

[0018] As shown in Figure 2(C), if the sequence length of the OCC used is increased, the frequency domain unit for channel estimation becomes larger. In other words, only one channel estimate is obtained for a large number of subcarriers. This reduces the frequency resolution of the channel estimate, which can lead to degradation of communication quality, especially in environments where the channel fluctuates significantly in the frequency domain.

[0019] On the other hand, by its very nature, OCC sequences are constructed so that orthogonality is naturally guaranteed for the entire sequence, but there are also combinations of sequences that guarantee orthogonality even when only a portion of the sequence is viewed. Figure 3(A) shows an example of an OCC sequence with a code length of 8. Figure 3(B) shows the correlation value between the top 4 bits of two sequences in this OCC sequence, and Figure 3(C) shows the correlation value between the bottom 4 bits. The correlation value is Σ i a i b i (However, a i is the i-th bit of the first sequence, b iindicates the ith bit of the second sequence. Note that the upper four bits are 0≦i≦3, and the lower four bits are 4≦i≦7. Each sequence shown in FIG. 3(A) is naturally orthogonal to other sequences as a whole (i.e., the correlation value is 0). However, as shown in FIGS. 3(B) and 3(C), for example, when focusing on only the upper four bits and the lower four bits of sequence A, orthogonality is not ensured with sequence E. On the other hand, sequence A maintains orthogonality with other sequences even when only the upper four bits and the lower four bits are used (i.e., the correlation value is 0). For this reason, in a situation where sequence A is used but sequence E is not used, a terminal device to which sequence A is assigned can perform channel estimation using only the upper four bits or the lower four bits of the OCC, which are the units of the frequency range in which channel estimation is performed. Here, the upper four bits of the OCC are transmitted in four resource elements at higher frequencies within the frequency range in which the DMRS is transmitted (for example, the upper portion of FIG. 2(C)), and the lower four bits are transmitted in four resource elements at lower frequencies within the frequency range in which the DMRS is transmitted (for example, the lower portion of FIG. 2(C)). By doing so, the terminal device can calculate channel estimation values ​​for a first subband at higher frequencies and a second subband at lower frequencies within the frequency range in which the DMRS is transmitted, using the upper four bits and the lower four bits separately, thereby suppressing a decrease in frequency resolution.

[0020] Note that, although an example has been described above in which a band in which a DMRS is transmitted (here, a band with 12 subcarriers corresponding to one resource block) is divided into two subbands, the band in which a DMRS is transmitted may be divided into three or more subbands. That is, to enable channel estimation in the subbands described above, when a partial sequence that is part of an OCC sequence used for a predetermined layer when a DMRS is transmitted is transmitted in a resource element corresponding to the predetermined subband, it is required to be orthogonal to all of the OCC partial sequences transmitted in the resource element for layers different from the predetermined layer. That is, as long as a partial sequence transmitted in a resource element within a certain subband is orthogonal to all of the other partial sequences, channel estimation in that subband is possible separately from the entire band. However, there are no particular limitations on the length of the partial sequence or the size of the corresponding subband, i.e., the number of subbands obtained by division. For example, if an OCC sequence with a code length of 8 is transmitted every three subcarriers in two time-contiguous resource elements, and if a 2-bit partial sequence transmitted in the two resource elements of one subcarrier is orthogonal to other partial sequences transmitted in the same frequency and time resource, the terminal device can use that partial sequence to perform channel estimation for the corresponding subband of three subcarriers.

[0021] In view of these circumstances, this embodiment enables channel estimation using a partial sequence of an OCC assigned to a terminal device, the partial sequence corresponding to a partial band (subband) of a frequency band (band) in which channel estimation is performed using the entire sequence. In the above example, when sequence A is assigned to a terminal device, the terminal device cannot recognize whether sequence E is to be used. Therefore, in this embodiment, a base station device can notify each terminal device whether channel estimation is possible using the partial sequence of an OCC assigned to the terminal device. In one example, a base station device notifies each terminal device of information indicating whether channel estimation for each subband is possible. That is, a terminal device is notified of whether an OCC partial sequence transmitted in a subband that is part of the band in which the DMRS is transmitted, among the DMRS transmitted for the terminal device, is orthogonal to all of the OCC partial sequences transmitted in the same resource elements of the subband for other terminal devices. When multiple layers are assigned to a terminal device, information about each of the multiple layers can be notified to the terminal device. In one example, a band is a frequency band of one resource block consisting of 12 subcarriers, and a subband is a frequency band of half that, i.e., 6 subcarriers. In addition, the base station device transmits the above-mentioned notification, for example, via a physical downlink control channel (PDCCH).

[0022] For example, the base station device may report to the terminal device, for each subband, "0" if channel estimation is possible (the OCC partial sequence transmitted in that subband is orthogonal to the partial sequences of other assigned OCCs), or "1" if channel estimation is not possible (there is another assigned OCC partial sequence that is not orthogonal to the OCC partial sequence transmitted in that subband). For example, if the band in which the DMRS is transmitted is divided into two subbands, information "00" may indicate that channel estimation is possible in both of the two subbands. Furthermore, information "01" may indicate that channel estimation is possible in the first subband (e.g., the subband with a higher frequency) but not in the second subband (e.g., the subband with a lower frequency). Similarly, information "10" may indicate that channel estimation is not possible in the first subband (e.g., the subband with a higher frequency) but is possible in the second subband (e.g., the subband with a lower frequency), and information "11" may indicate that channel estimation is not possible in both of the two subbands. Note that the meanings of 0 and 1 may be reversed, i.e., a terminal device may be notified of "1" when channel estimation is possible and "0" when channel estimation is not possible.

[0023] The base station device may further notify information indicating that the band is divided into two subbands. As an example, the base station device may notify the terminal device using information "2, 1, 1" that the subband can be divided into two and that channel estimation is possible in both of the two subbands. Alternatively, the base station device may notify the terminal device using information "4, 1, 1, 0, 0" that the subband can be divided into four and that channel estimation is possible in the first and second subbands, but not in the third and fourth subbands. By notifying the number of subbands, the terminal device can identify the length of the information indicating whether channel estimation is possible for each subband. If the number of subbands is determined in advance, this information does not need to be notified.

[0024] Even if there is another allocated OCC partial sequence that is not orthogonal to the OCC partial sequence transmitted in the subband, if the correlation value is expected to be lower than a predetermined value, or if channel estimation can be performed with a certain degree of accuracy, information indicating that channel estimation is possible may be transmitted to the terminal device. For example, when a base station device forms multiple beams using multiple antennas and spatially multiplexes signals, the orthogonality of the above-mentioned OCC partial sequences may be evaluated taking into account the spatial separation performance. In other words, even if the OCC partial sequences allocated to multiple terminal devices receiving DMRS transmitted in the same resource element are not orthogonal, the spatial separation performance of the base station device can reduce the impact on channel estimation in each subband. For this reason, the base station device may evaluate the impact of such spatial separation using the following equation (1).

[0025] Formula (1) TIFF0007779818000001.tif13150 where n indicates the subband index, and takes the value of 0 or 1 when, for example, the band in which channel estimation is performed by DMRS is divided into two subbands. k'is a precoding vector for forming a beam directed to terminal device k', and h ^ k is the channel estimation value from the base station device to the terminal device k, and b k' is a vector indicating the partial sequence corresponding to subband n among the OCCs set for terminal device k'. k' h ^ k b k' T can represent a vector indicating the received signal in terminal device k of a partial sequence corresponding to subband n of the OCC set for terminal device k'. Note that the superscript T indicates the transposition of a vector. In terminal device k, for the received signal, a vector a indicating a partial sequence corresponding to subband n of the OCC set for terminal device k is k Here, the correlation value is calculated by multiplying the vectors b k' and vector a k If and are orthogonal, b k' T a k is zero, so w k' h ^ k b k' T a k is also zero. On the other hand, the vector b k' and vector a k Even if and are not orthogonal, k' h ^ k The weight vector w is small enough k' is used, it is assumed that the value of equation (1) is sufficiently small and the influence on channel estimation in terminal device k is sufficiently small.

[0026] The base station device uses the channel estimation value h ^ kThe base station apparatus may obtain the channel estimation value calculated by the terminal apparatus k when it last transmitted the DMRS, based on an uplink signal (for example, a sounding reference signal (SRS)) received from the terminal apparatus k. The base station apparatus may also receive a report of the channel estimation value calculated by the terminal apparatus k when it last transmitted the DMRS, and may obtain the channel estimation value as h ^ k It is possible to use it as: Note that the channel estimation value obtained by SRS may not necessarily accurately represent the state of the transmission path in the subband, and the channel estimation value based on the previous DMRS may not accurately reflect the current channel state. For this reason, the base station device may evaluate the influence of spatial separation by the following equation (2), taking into account the inaccuracy of the channel estimation value. Formula (2) TIFF0007779818000002.tif13150 Note: e k can be a random variable corresponding to the error of the transmission channel estimation value. k The magnitude of the power of can be determined empirically based on, for example, the accuracy of past channel estimates.

[0027] When the base station device determines that the value calculated using the above-described formula (1) or (2) is smaller than a predetermined value, the base station device may notify the terminal device that channel estimation is possible in the subband corresponding to the OCC partial sequence even if the OCC partial sequence is not orthogonal to other partial sequences. The base station device may also notify the terminal device of information indicating whether the OCC partial sequence is orthogonal to other partial sequences and the value calculated using the above-described formula (1) or (2). The base station device may also notify the terminal device of only the calculation result of the above-described formula (1) or (2). The base station device may also notify the terminal device of the result of calculating the correlation value without taking into account the effects of spatial multiplexing or the channel.

[0028] When channel estimation is possible on a subband basis based on information received from a base station device, the terminal device may perform channel estimation on a subband basis. Note that, for example, when a channel estimate is calculated on a subband basis, the terminal device may determine whether to average the channel estimate based on the magnitude of fluctuation in the channel estimate for each subband. For example, if the change in the channel estimate between subbands is equal to or less than a predetermined value, the terminal device may determine to average the channel estimate (by adding the channel estimates and dividing by the number of added samples). The magnitude of the change in the channel estimate between subbands may be determined, for example, by calculating a correlation value between the calculated channel estimates, and may be determined to be small when the correlation value is large, and large when the correlation value is small. Alternatively, the magnitude of the change may be determined based on the magnitude of the difference between the channel estimates. This allows the terminal device to suppress the influence of, for example, thermal noise and obtain a more accurate channel estimate. On the other hand, if the change in the channel estimate between subbands exceeds a predetermined value, the terminal device may determine not to average the channel estimate. Here, the terminal device may add channel estimation values ​​in adjacent bands (e.g., adjacent resource blocks) beyond the band (e.g., resource block) corresponding to the DMRS to calculate an average value. When the terminal device has calculated the average value, the terminal device may notify the base station device that the calculation has been performed or that it is assumed that channel estimation for each subband is not necessary. Note that the terminal device may notify the base station device in advance of capability information indicating whether or not it has the capability to perform channel estimation for each subband.

[0029] (Device configuration) An example of the hardware configuration of a base station apparatus and a terminal apparatus will be described using FIG. 4. In one example, the base station apparatus and the terminal apparatus include a processor 401, a ROM 402, a RAM 403, a storage device 404, and a communication circuit 405. The processor 401 is a computer including one or more processing circuits, such as a general-purpose CPU (Central Processing Unit) or an ASIC (Application Specific Integrated Circuit), and performs overall processing of the apparatus and each of the above-mentioned processes by reading and executing programs stored in the ROM 402 or the storage device 404. The ROM 402 is a read-only memory that stores information such as programs and various parameters related to the processes executed by the base station apparatus and the terminal apparatus. The RAM 403 functions as a workspace when the processor 401 executes a program and is a random access memory that stores temporary information. The storage device 404 is, for example, a removable external storage device. The communication circuit 405 is, for example, a circuit for wireless communication of 5G or its successor standards. Although FIG. 4 illustrates one communication circuit 405, the base station device and the terminal device may have two or more communication circuits. The base station device and the terminal device may have a common antenna for wireless communication circuits for 5G and its successor standards. The base station device and the terminal device may have separate antennas for 5G and its successor standards. The terminal device may also have a communication circuit for other wireless communication networks, such as a wireless LAN. The base station device and the terminal device may have separate communication circuits for each of multiple available frequency bands, or may have a common communication circuit for at least some of these frequency bands. In this embodiment, the terminal device is assumed to have multiple communication circuits capable of communication in a common frequency band. The base station device may also have a wired communication circuit used when communicating with other base station devices or nodes in the core network.

[0030] FIG. 5 is a diagram illustrating an example of the functional configuration of a base station device. The base station device includes, for example, an OCC determination unit 501, a DMRS generation unit 502, a DMRS information notification unit 503, and a transmission unit 504. Note that FIG. 5 illustrates only functions particularly related to this embodiment, and does not illustrate various other functions that the base station device may have. For example, the base station device naturally has other functions that base station devices of 5G and its successor standards generally have. The functional blocks in FIG. 5 are illustrated schematically, and each functional block may be integrated or further subdivided. Each function in FIG. 5 may be realized, for example, by the processor 401 executing a program stored in the ROM 402 or the storage device 404, or by a processor within the communication circuit 405 executing predetermined software. Details of the processing performed by each functional unit will not be described here, and only their general functions will be outlined.

[0031] The OCC determination unit 501 determines an orthogonal cover code (OCC) to be used when transmitting a DMRS for each terminal device. The OCC determination unit 501 assigns, to each terminal device to which data is to be transmitted, an OCC with a code length corresponding to the number of resource elements for transmitting the DMRS, which are included in, for example, the band corresponding to the coarsest frequency resolution. For example, as shown in FIG. 2(C), when eight resource elements are used to transmit the DMRS in a band equivalent to one resource block, which is the coarsest frequency resolution, the base station device assigns an OCC with a code length of eight, as shown in FIG. 3(A), to each terminal device. The DMRS generation unit 502 generates a DMRS for channel estimation for each terminal device using the OCC determined by the OCC determination unit 501. The DMRS information notification unit 503 generates information indicating whether channel estimation is possible for each subband corresponding to a frequency resolution finer than the above-mentioned coarsest frequency resolution, using a subsequence of the OCC assigned to each terminal device. This information includes, for example, information indicating whether a partial sequence corresponding to each subband, which is a part of the OCC sequence assigned by the OCC determiner 501 as described above, is orthogonal to all of the partial sequences of other OCCs for other terminal devices transmitted in the same resource element. Furthermore, this information may indicate that channel estimation for each subband is possible even if the partial sequence for the assigned OCC is not orthogonal to the partial sequences of other OCCs, if channel estimation for each subband is possible by suppressing interference through spatial multiplexing. This information may also include information indicating the degree of impact on channel estimation accuracy when a non-orthogonal OCC partial sequence exists through spatial multiplexing, for example, the value of the calculation result of Equation (1) or (2) described above. The transmitter 504 transmits a downlink signal including, for example, the DMRS generated by the DMRS generator 502 and user data.

[0032] FIG. 6 is a diagram illustrating an example of the functional configuration of a terminal device. The terminal device includes, for example, a DMRS information receiving unit 601, a receiving unit 602, a channel estimating unit 603, and an averaging processing unit 604. Note that FIG. 6 illustrates only functions particularly related to this embodiment, and does not illustrate various other functions that the terminal device may have. For example, the terminal device naturally has other functions that terminal devices of 5G and its successor standards generally have. The functional blocks in FIG. 6 are illustrated schematically, and the respective functional blocks may be integrated or further subdivided. Each function in FIG. 6 may be realized, for example, by the processor 401 executing a program stored in the ROM 402 or the storage device 404, or may be realized by a processor within the communication circuit 405 executing predetermined software. Details of the processes performed by each functional unit will not be described here, and only their general functions will be outlined.

[0033] The DMRS information receiving unit 601 receives, for example, information that enables identification of resource elements in which DMRSs are transmitted and information on OCC sequences. The DMRS information receiving unit 601 also receives information that enables determination of whether channel estimation on a subband basis is possible, which is notified by the above-mentioned DMRS information notifying unit 503. The receiving unit 602 receives, for example, a downlink signal including a DMRS and user data transmitted from a base station apparatus. The channel estimating unit 603 performs channel estimation using the DMRS based on the information received by the DMRS information receiving unit 601. If the information received by the DMRS information receiving unit 601 indicates that channel estimation on a subband basis is possible, the channel estimating unit 603 performs channel estimation on a subband basis. Note that, when channel estimation on a subband-by-subband basis is possible only for some subbands but not for other subbands (i.e., interference is so great that channel estimation cannot be performed with sufficient accuracy), the channel estimation unit 603 may perform subband-by-subband channel estimation only for those subbands and perform only channel estimation for the entire band (e.g., resource block) in which the DMRS is transmitted for the other subbands. Furthermore, when the information received by the DMRS information receiving unit 601 indicates that channel estimation on a subband-by-subband basis is not possible, the channel estimation unit 603 performs channel estimation for the entire band and does not perform channel estimation on a subband-by-subband basis. For example, when the channel estimation unit 603 performs subband-by-subband channel estimation for multiple subbands, the averaging processing unit 604 determines whether to average the channel estimation values ​​obtained for each of the multiple subbands. For example, the averaging unit 604 may identify the magnitude of change in the channel estimation value for each subband by calculating a difference value or a correlation value between the channel estimation values, and may average the channel estimation value if the change is small (e.g., if the difference value is equal to or smaller than a predetermined value, or if the correlation value is equal to or larger than a predetermined value). The channel estimation value or its average value obtained by the channel estimation unit 603 or the averaging unit 604 may be input to the receiving unit 602 and used when demodulating user data.When a channel estimate for each subband is used, the channel estimate corresponding to that subband is used to demodulate signals within that subband, whereas when a channel estimate for the entire band (e.g., resource block) is used, the channel estimate for the entire band is used to demodulate signals within that band.

[0034] (Processing flow) Next, an example of the flow of processing executed by the base station device will be described with reference to Fig. 7. Note that, since the details of the processing steps shown in Fig. 7 are as described above, only an overview of the processing flow will be given here, and the details will not be repeated. Also, the order of the processing steps shown in Fig. 7 is one example, and the order may be reversed.

[0035] First, the base station device determines an OCC to be allocated to each terminal device (S701). Here, the OCC allocation is, for example, as shown in FIG. 2C, an extended frequency range for channel estimation with one DMRS, and an OCC with an extended code length of, for example, 8 is allocated. The base station device then evaluates the orthogonality of the OCC allocated to the first terminal device with the OCC allocated to the second terminal device on a subband-by-subband basis (S702). For example, the base station device divides resource elements on which DMRSs are transmitted into subbands, and calculates a correlation value between a partial sequence of the OCC for the first terminal device, which is mapped to a resource element for DMRS in that subband, and a partial sequence of the OCC for the second terminal device, which is mapped to the same resource element. If the correlation value is zero, the base station device evaluates that the partial sequence of the OCC for the first terminal device and the partial sequence of the OCC for the second terminal device are orthogonal; if the correlation value is not zero, the base station device evaluates that the partial sequence of the OCC for the first terminal device and the partial sequence of the OCC for the second terminal device are not orthogonal. As described above, the base station apparatus may calculate the correlation value using the weight vector used for spatial multiplexing.

[0036] The base station device then generates DMRS information including the result of the orthogonality evaluation performed in S702 and transmits it to the terminal device (S703). For example, if the base station device determines in S702 that the correlation value of the partial sequence of the OCC of a first terminal device for a certain subband is zero with the partial sequence of the OCC of any second terminal device different from the first terminal device, the base station device transmits the DMRS information including information indicating that channel estimation on a subband-by-subband basis is possible for that subband to the first terminal device. Furthermore, the base station device may transmit the DMRS information including information indicating whether the partial sequence of the OCC for each terminal device is orthogonal to the OCCs for other terminal devices and the correlation value calculated including the weight vector for spatial multiplexing in S702. Note that the DMRS information includes, for example, information on the OCC assigned to the terminal device to which the DMRS information is transmitted and information on the resource element to which the OCC is mapped. Furthermore, the DMRS information may include information indicating which frequency range corresponds to the subband. The method of dividing the frequency bands into subbands may be defined in advance by a standard, in which case, information such as which frequency ranges correspond to the subbands does not need to be notified to the terminal device. The base station device generates a DMRS using the OCC assigned to the terminal device, and also generates a radio signal including user data addressed to the terminal device and transmits it to the terminal device (S704).

[0037] Next, an example of the flow of processing executed by the terminal device will be described with reference to Fig. 8. Note that the details of the processing steps shown in Fig. 8 have been described above, so only an overview of the processing flow will be given here, and the details will not be repeated. Also, the order of the processing steps shown in Fig. 8 is an example, and the order may be reversed.

[0038] First, the terminal device receives DMRS information from the base station device (S801). From the DMRS information, the terminal device receives information identifying the OCC sequence used in the DMRS for the terminal device and the resource element on which the DMRS is transmitted. Furthermore, the terminal device determines, based on the received DMRS information, whether channel estimation on a subband basis is possible using the OCC sequence assigned to the terminal device (S802). For example, if the DMRS information includes information indicating whether channel estimation on a subband basis is possible, the terminal device follows that information. On the other hand, if the DMRS information includes the calculation result of the above-described formula (1) or (2), the terminal device may determine that channel estimation on a subband basis is possible if it determines that a predetermined channel estimation accuracy can be obtained on a subband basis, for example, based on the reception strength of the DMRS for the terminal device or the performance of the receiver. In this way, it is sufficient for the base station device to transmit information that can identify whether channel estimation on a subband basis is possible in the terminal device, such as the calculation result of the above-described formula (1) or (2). In one example, when a first terminal device and a second terminal device receive the same DMRS information, the first terminal device may determine that channel estimation on a subband basis is possible, and the second terminal device may determine that channel estimation on a subband basis is not possible.

[0039] When the terminal device determines that channel estimation is possible on a subband basis (YES in S802), it performs channel estimation for each subband using a subsequence of the OCC corresponding to each subband (S803). Then, the terminal device determines whether to average the channel estimation values ​​on a subband basis (S804). For example, if the amount of change in the channel estimation values ​​on a subband basis is equal to or greater than a predetermined value or if the correlation value of the channel estimation values ​​is equal to or less than a predetermined value, the terminal device determines not to average the channel estimation values ​​(NO in S804). In this case, the terminal device performs reception processing of user data, etc., for each subband using the corresponding channel estimation value (S805). On the other hand, if the amount of change in the channel estimation values ​​on a subband basis is less than the predetermined value or if the correlation value of the channel estimation values ​​exceeds the predetermined value, the terminal device determines to average the channel estimation values ​​(YES in S804). In this case, the terminal device averages the channel estimation values ​​(S806) and uses the averaged channel estimation value as a channel estimation value common to the entire band (e.g., resource block) to perform reception processing of user data, etc., for the entire band (S807). As a result, while suppressing a decrease in frequency resolution by channel estimation in subband units, if the amount of change is small and the channel estimation value can be considered constant across the entire band, it is possible to suppress the influence of thermal noise, etc., by performing averaging processing, thereby improving the accuracy of the channel estimation value. Note that, when averaging the channel estimation values, the terminal device may notify the base station device that averaging has been performed or that channel estimation in subband units is not necessary.

[0040] Note that averaging may be performed across bands, for example, using channel estimates between adjacent subbands. That is, channel estimates may be averaged over different ranges for each subband. For example, an average may be calculated of a channel estimate for a specific subband, a channel estimate for a subband adjacent to that subband in the higher frequency direction, and a channel estimate for a subband adjacent to that subband in the lower frequency direction. In this case, a different set of channel estimates is used to calculate the average for each subband, resulting in a different averaged channel estimate for each subband. When an average is calculated for each subband in this way, the terminal device may use the average to perform reception processing for data for each subband, as in S805.

[0041] If the terminal device determines that channel estimation on a subband basis is not possible (NO in S802), the terminal device performs channel estimation for the entire band using the entire OCC sequence (S808).Then, the terminal device performs reception processing of user data, etc. for the entire band using the channel estimation value (S807).

[0042] As described above, in a situation where not only the entire OCC sequence but also a portion of it is orthogonal to other sequences, the base station device notifies the terminal device that subband-level channel estimation using the partial sequence is possible. This suppresses degradation of the frequency resolution of the channel estimate and prevents the associated degradation of communication performance. Furthermore, by averaging the channel estimate for each subband as needed, the accuracy of the channel estimate can be improved when there is little fluctuation in the frequency direction of the channel estimate. This contributes to Goal 9 of the United Nations' Sustainable Development Goals (SDGs), which states, "Build resilient infrastructure, promote sustainable industrialization, and foster innovation."

[0043] The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the gist of the invention.

Claims

1. A terminal device, An acquisition means for acquiring, from the base station device, first information that identifies an orthogonal cover code (OCC) used when generating a demodulation reference signal (DMRS) to be transmitted from a connected base station device to the terminal device and a resource element in which the DMRS is transmitted, and second information that enables the terminal device to identify whether channel estimation is possible in units of subbands that are part of a band in which channel estimation is performed using the DMRS; a determining means for determining whether or not channel estimation in units of the subband is possible based on the second information; an execution means for executing channel estimation for each subband using a partial sequence of the OCC corresponding to the subband when it is determined that channel estimation for each subband is possible, and for executing channel estimation for the entire band using the OCC when it is determined that channel estimation for each subband is not possible; receiving means for receiving data transmitted in the band from the base station device to the terminal device using a channel estimation value corresponding to each subband when channel estimation is performed in units of the subband, and for receiving data transmitted in the band from the base station device to the terminal device using a channel estimation value common to the band when channel estimation is performed for the entire band; A terminal device comprising:

2. the second information includes information indicating whether channel estimation in units of the subbands is possible; the determining means determines whether channel estimation is possible in units of the subbands according to the second information.

2. The terminal device according to claim 1, wherein:

3. the second information includes information indicating whether a first partial sequence of a first OCC for the terminal device corresponding to the subband is orthogonal to all second partial sequences of second OCCs for other terminal devices that are transmitted in the subband using the same resource elements as the first partial sequence, and the determining means determines that channel estimation in units of the subbands is possible when the first subsequence is orthogonal to all of the second subsequences.

2. The terminal device according to claim 1, wherein:

4. the second information includes information indicating a correlation value between a first partial sequence of a first OCC for the terminal device corresponding to the subband and a second partial sequence of a second OCC for another terminal device that is transmitted in the subband using the same resource element as the first partial sequence, the determining means determines whether channel estimation is possible in units of the subbands based on the correlation value.

2. The terminal device according to claim 1, wherein:

5. 5. The terminal device according to claim 4, wherein the correlation value is a correlation value between the second partial sequence and the first partial sequence when precoding is performed to form a beam by which the second OCC is transmitted.

6. the execution means averages the channel estimation values ​​when the magnitude of a difference between the channel estimation values ​​corresponding to the plurality of subbands is equal to or less than a predetermined value when the channel estimation is executed in units of the subbands.

2. The terminal device according to claim 1, wherein:

7. 2. The terminal device according to claim 1, further comprising: a notifying means for, when said executing means has performed averaging of said channel estimation values, notifying said base station device that averaging has been performed.

8. 2. The terminal device according to claim 1, further comprising a notification means for notifying the base station device of capability information indicating that channel estimation can be performed in units of subbands.

9. 2. The terminal device according to claim 1, wherein the acquisition means acquires the second information from the base station device via a physical downlink control channel (PDCCH).

10. A control method executed by a terminal device, comprising: Acquire from the base station device first information that identifies an orthogonal cover code (OCC) used when generating a demodulation reference signal (DMRS) to be transmitted from a connected base station device to the terminal device and a resource element in which the DMRS is transmitted, and second information that enables the terminal device to identify whether channel estimation is possible in units of subbands that are part of a band in which channel estimation is performed using the DMRS; determining whether channel estimation is possible in units of the subband based on the second information; When it is determined that channel estimation is possible in units of the subbands, performing channel estimation in units of the subbands using a partial sequence of the OCC corresponding to the subbands, and when it is determined that channel estimation in units of the subbands is not possible, performing channel estimation for the entire band using the OCC; When channel estimation is performed in units of the subband, data transmitted in the band from the base station device to the terminal device is received using a channel estimation value corresponding to each subband, and when channel estimation is performed for the entire band, data transmitted in the band from the base station device to the terminal device is received using a channel estimation value common to the band; A control method comprising:

11. The computer provided in the terminal device acquires from the base station device first information that identifies an orthogonal cover code (OCC) used when generating a demodulation reference signal (DMRS) to be transmitted from a connected base station device to the terminal device and a resource element in which the DMRS is transmitted, and second information that enables the terminal device to identify whether channel estimation is possible in units of subbands that are part of a band in which channel estimation is performed using the DMRS; determining whether or not channel estimation is possible in units of the subband based on the second information; When it is determined that channel estimation is possible in units of the subbands, channel estimation is performed in units of the subbands using a partial sequence of the OCC corresponding to the subbands, and when it is determined that channel estimation is not possible in units of the subbands, channel estimation is performed for the entire band using the OCC; When channel estimation is performed in units of the subband, data transmitted in the band from the base station device to the terminal device is received using a channel estimation value corresponding to each subband, and when channel estimation is performed for the entire band, data transmitted in the band from the base station device to the terminal device is received using a channel estimation value common to the band. Program for.

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