WO2024070791A1 - Terminal device for enhancing channel estimation in wireless communication, control method, and program - Google Patents

Abstract

This terminal device: acquires, from a base station in connection therewith, first information for identifying an orthogonal cover code (OCC) for use in generating a demodulation reference signal (DMRS) to be transmitted to the terminal device from the base station, and for identifying a resource element to which the DMRS is transmitted, and second information allowing the terminal device to identify whether or not channel estimation is possible for each sub-band which is a part of a band subjected to channel estimation by means of the DMRS; executes, when the channel estimation for each sub-band is possible, the channel estimation for each sub-band by using a partial sequence, of the OCC, corresponding to the sub-band; and receives, by using a channel estimation value corresponding to each sub-band, data transmitted from the base station to the terminal device.

Description

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

The present invention relates to advanced technology for channel estimation in wireless communications.

In the Third Generation Partnership Project (3GPP (registered trademark)), a method 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 single-user (SU) or multi-user (MU) multi-input multi-output (MIMO). Non-Patent Document 1 describes a method of expanding the frequency range to which one orthogonal cover code (OCC) used for multiplexing is applied in order to expand the number of DMRS ports.

3GPP Contribution, R1-2204370, May 2022

One channel estimate is obtained for the frequency range to which one OCC is applied. Therefore, 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.

The present invention provides a technology that suppresses degradation of frequency resolution in channel estimation while increasing the number of ports for demodulation reference signals.

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 in 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 on a subband basis that is a part of a band in which channel estimation is performed using the DMRS, a determination means for determining whether channel estimation is possible on a subband basis based on the second information, and, when it is determined that channel estimation is possible on a subband basis, a determination means for determining the channel estimation on a subband basis. The apparatus has an execution means for performing channel estimation for each subband using a corresponding partial sequence of the OCC, and performing channel estimation for the entire band using the OCC if it is determined that channel estimation for each subband is not possible, and a reception 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 for the entire band is performed, and 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 for the entire band is performed.

According to the present invention, it is possible to suppress degradation of frequency resolution of channel estimation while increasing the number of ports of the demodulation reference signal.

Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which the same or similar components are designated by the same reference numerals.

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
FIG. 1 is a diagram illustrating an example of the configuration of a wireless communication system. FIG. 2A is a diagram illustrating an example of mapping of DMRS to resource elements. FIG. 2B is a diagram illustrating an example of mapping of DMRS to resource elements. FIG. 2C is a diagram illustrating an example of mapping of DMRS to resource elements. FIG. 3A is a diagram illustrating an example of an OCC. FIG. 3B is a diagram illustrating the correlation between OCCs. FIG. 3C is a diagram illustrating the correlation between OCCs. FIG. 2 illustrates an example of a hardware configuration of the apparatus. FIG. 2 is a diagram illustrating an example of a functional configuration of a base station device. FIG. 2 is a diagram illustrating an example of a functional configuration of a terminal device. FIG. 11 is a diagram illustrating an example of a flow of processing performed by a base station device. FIG. 11 is a diagram illustrating an example of a flow of processing executed by a terminal device.

The embodiments are described in detail below with reference to the attached drawings. Note that the following embodiments do not limit 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. In addition, the same reference numbers are used for identical or similar configurations, and duplicate descriptions will be omitted.

(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 the sake of simplicity, FIG. 1 shows only one base station device and a small number of terminal devices, but it is natural that there may be multiple base station devices and a large number of terminal devices. Note that in the following description, it is assumed that the base station device 101 transmits data to each of the terminal devices 111 to 116 at one layer each. However, this is merely for the sake of simplicity, and it is naturally assumed that data is transmitted to one terminal device at multiple layers. In that case, the "terminal device" in the following description may be read as "layer".

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 of data such as user data using the result of the channel estimation. The DMRS is transmitted, for example, using different frequency and time resources for each of a predetermined number of layers. In addition, the DMRS is spread using an orthogonal cover code (OCC) so that a predetermined number of layers using the same frequency and time resources can be separated from each other. For this reason, the terminal devices 111 to 116 first identify the frequency resource corresponding to the layer that the device receives 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. The 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, when the code length of the OCC is 4, one DMRS symbol is spread into four symbols, and each of the four symbols is mapped to a different resource element. The terminal devices 111 to 116 can calculate a channel estimation value by despreading the symbol received in the resource element in which the DMRS is transmitted using the OCC and dividing the value resulting from the despreading by the transmitted DMRS symbol.

Conventionally, there are multiple patterns of DMRS allocation for resource elements. For example, as configuration type 1, a pattern is prepared in which every other one of the 12 subcarriers in a resource block is used. In this pattern, for example, the subcarrier numbers are divided into two groups, a group with 2n (0≦n≦5) and a group with 2n+1 (0≦n≦5), and each terminal device uses one of the groups. In configuration type 2, the 12 subcarriers in a resource block are divided into two subbands, a subband consisting of six subcarriers with a higher frequency and a subband consisting of six subcarriers with a lower frequency, and three groups consisting of two consecutive frequency resources are formed in each subband. Then, each terminal device uses one of the three groups. In addition, there are cases in which the DRMS uses one resource element in the time domain and cases in which it uses two consecutive resource elements.

　Figures 2A and 2B show the mapping of DMRS to resource elements for configuration type 1 and configuration type 2 when two consecutive resource elements are used among these configurations.

As shown in FIG. 2A, in configuration type 1, channel estimation is performed in two units, one for each in the frequency domain and two consecutive units in the time domain. That is, channel estimation is performed for each range of four resource elements in the frequency domain. For each terminal device, DMRS is transmitted in either a group of subcarriers with subcarrier numbers of 2n (0≦n≦5) or a group of subcarriers with subcarrier numbers of 2n+1 (0≦n≦5). According to this setting, DMRS is transmitted to each terminal device using four resource elements for the frequency range in which channel estimation is performed. In this case, the base station device can multiplex and transmit DMRS corresponding to four layers using the same resource element by using an OCC with a code length of 4. Therefore, in configuration type 1 shown in FIG. 2A, code division multiplexing is performed by an OCC with a code length of 4 for two groups obtained by grouping in the frequency direction, two each in the time and frequency domains, for a total of four resource elements, so that DMRS can be transmitted in parallel for a total of eight layers. In this way, one unit that can transmit DMRS in a format that can be separated by grouping resource elements or OCC code is called one port. In the format of FIG. 2A, it can be said that the number of DMRS ports is a maximum of 8 ports.

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

In recent years, with the increase in the required communication speed and the growing demand for providing communication opportunities to a large number of terminal devices in parallel, there is a demand for an increase in the number of multiple layers of multi-user (MU)/single user (SU) MIMO (Multi-input Multi-output). At this time, the conventional maximum of 12 ports is not sufficient, and there is discussion of securing up to 24 ports for the Release 18 standard of 3GPP (registered trademark). For this purpose, for example, it is possible to expand the unit of the frequency range for channel estimation, and transmit DMRS spread using a larger number of resource elements and an OCC with a longer code length. For example, as shown in FIG. 2C, the unit of the frequency range for channel estimation is doubled compared to the case of FIG. 2B, and three groups are formed, each using eight resource elements. These groups can be configured in the same way as in FIG. 2B. 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. 2B, 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. 2C, eight resource elements transmit a DMRS spread by an OCC with a code length of 8. According to this, for three groups obtained by grouping in the frequency direction, code division multiplexing is performed by an OCC with a code length of 8 in a total of eight resource elements, two in the time domain and four in the frequency domain, so that the number of DMRS ports is a maximum of 24 ports.

In this embodiment, the grouping of resource elements in the frequency domain is the same as that in FIG. 2B, 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, grouping in the frequency domain may be performed arbitrarily. Also, in the above example, an example is described in which 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.

As shown in Figure 2C, when 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 many 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 greatly in the frequency direction.

On the other hand, the OCC sequence is naturally configured so that the orthogonality is guaranteed as a whole sequence, but there are combinations of sequences that guarantee the orthogonality even when only a part of the sequence is viewed. Here, FIG. 3A shows an example of an OCC sequence with a code length of 8. FIG. 3B shows the correlation value between the upper 4 bits of two sequences of this OCC sequence, and FIG. 3C shows the correlation value between the lower 4 bits. The correlation value is calculated by Σ _i a _i b _i (where a _i indicates the i-th bit of the first sequence, and b _i indicates the i-th bit of the second sequence. The upper 4 bits are 0≦i≦3, and the lower 4 bits are 4≦i≦7). Each sequence shown in FIG. 3A naturally guarantees orthogonality with other sequences as a whole sequence (i.e., the correlation value is 0), but as shown in FIG. 3B and FIG. 3C, for example, when focusing on only the upper 4 bits and the lower 4 bits of sequence A, orthogonality is not guaranteed with sequence E. On the other hand, even if only the upper 4 bits and the lower 4 bits are used, the orthogonality of the sequence A is maintained between the other sequences (i.e., the correlation value is 0). Therefore, in a situation where the sequence A is used and the sequence E is not used, the terminal device to which the sequence A is assigned can perform channel estimation using only the upper 4 bits or the lower 4 bits of the OCC in the unit of the frequency range in which the channel estimation is performed. Here, the upper 4 bits of the OCC are transmitted in four resource elements at the higher frequency (e.g., the upper part of FIG. 2C) in the frequency range in which the DMRS is transmitted, and the lower 4 bits are transmitted in four resource elements at the lower frequency (e.g., the lower part of FIG. 2C) in the frequency range in which the DMRS is transmitted. In this way, the terminal device can calculate channel estimation values for the first subband at the higher frequency and the second subband at the lower frequency in the frequency range in which the DMRS is transmitted, using the upper 4 bits and the lower 4 bits separately, and can suppress a decrease in frequency resolution.

Here, an example has been described in which the band in which the DMRS is transmitted (here, a band of 12 subcarriers corresponding to one resource block) is divided into two subbands, but the band in which the DMRS is transmitted may be divided into three or more subbands. That is, in order to enable channel estimation in the subband as described above, when a partial sequence that is a part of the sequence of the OCC used for a specific layer when the DMRS is transmitted is transmitted in a resource element corresponding to a specific subband, it is required to be orthogonal to all of the partial sequences of the OCC transmitted in that resource element for other layers different from the specific layer. That is, as long as a partial sequence transmitted in a resource element in a certain subband is orthogonal to all of the other partial sequences, channel estimation in that subband is possible separately from the entire band, and there is no particular restriction 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-consecutive resource elements, and a 2-bit partial sequence transmitted in the two resource elements of one subcarrier is orthogonal to another partial sequence 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.

In this embodiment, in consideration of such circumstances, it is possible to perform channel estimation using a partial sequence corresponding to a partial band (subband) of a frequency band (band) in which channel estimation is performed using the entire sequence of the OCC sequence assigned to the terminal device. In the above example, when sequence A is assigned to the terminal device, the terminal device cannot recognize whether sequence E is used or not. For this reason, in this embodiment, the base station device can notify each terminal device whether channel estimation is possible using the partial sequence of the OCC assigned to the terminal device. In one example, the base station device notifies each terminal device of information indicating whether channel estimation for each subband is possible. That is, a certain terminal device is notified of whether a partial sequence of the OCC 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 partial sequences of the OCC transmitted in the same resource element of the subband for other terminal devices. In addition, when multiple layers are assigned to the 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, six subcarriers. The base station device also transmits the above-mentioned notification, for example, via a physical downlink control channel (PDCCH).

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

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 the information "2, 1, 1" that the subband can be divided into two and that channel estimation is possible in both of the two subbands. The base station device may also notify the terminal device using the information "4, 1, 1, 0, 0" that the subband can be divided into four and that channel estimation is possible in the first subband and the second subband, but not in the third subband and the fourth subband. By being notified of the number of subbands, the terminal device can specify 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.

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

　ここで、ｎは、サブバンドのインデクスを示し、例えば、ＤＭＲＳによってチャネル推定が行われるバンドが２つのサブバンドに分割される場合は０又は１の値をとる。また、ｗ_k'は、端末装置ｋ’に向けるビームを形成するためのプリコーディングベクトルであり、ｈ^＾ _ｋは、基地局装置から端末装置ｋまでのチャネル推定値であり、ｂ_k'は、端末装置ｋ’のために設定されたＯＣＣのうち、サブバンドｎに対応する部分系列を示すベクトルである。これらの値により、ｗ_k'ｈ^＾ _ｋｂ_k' ^Tは、端末装置ｋ’のために設定されたＯＣＣのうちのサブバンドｎに対応する部分系列の端末装置ｋにおける受信信号を示すベクトルを表すことができる。なお、上付きのＴは、ベクトルの転置を示す。端末装置ｋでは、受信信号に対して、端末装置ｋのために設定されたＯＣＣのうちのサブバンドｎに対応する部分系列を示すベクトルａ_kを乗じることにより、相関値を算出する。ここで、それぞれ部分系列を示すベクトルｂ_k'とベクトルａ_kとが直交している場合、ｂ_k' ^Tａ_kがゼロであるから、ｗ_k'ｈ^＾ _ｋｂ_k' ^Tａ_kもゼロである。一方で、ベクトルｂ_k'とベクトルａ_kとが直交していない場合であっても、ｗ_k'ｈ^＾ _ｋが十分に小さくなるようなウェイトベクトルｗ_k'が用いられている場合には、式（１）の値が十分に小さく、端末装置ｋにおけるチャネル推定に対する影響が十分に小さいことが想定される。 Formula (1)

Here, n indicates the index of the subband, and takes a value of 0 or 1 when, for example, the band in which channel estimation is performed by DMRS is divided into two subbands. In addition, w _{k '} is a precoding vector for forming a beam directed to the terminal device k ', h ^{^} _k is a channel estimation value from the base station device to the terminal device k, and b _{k '} is a vector indicating a partial sequence corresponding to subband n among the OCCs set for the terminal device k '. With these values, w _{k '} h ^{^} _k b _{k '} ^T can represent a vector indicating a received signal in the terminal device k of a partial sequence corresponding to subband n among the OCCs set for the terminal device k '. Note that the superscript T indicates the transposition of the vector. In the terminal device k, the correlation value is calculated by multiplying the received signal by a vector a _k indicating a partial sequence corresponding to subband n among the OCCs set for the terminal device k. Here, when vector bk _' and vector _ak , which respectively indicate partial sequences _{, are orthogonal, bk'Ta k is zero, and therefore wk'h^kbk'Ta k} ^is _also ^zero _{. On} the other hand, even when vector bk _' and ^vector _ak are not orthogonal, if a weight vector wk _' is used that makes _wk'h ^{^} _k sufficiently small, _it is assumed that the value of equation (1) is sufficiently small and the effect on channel estimation in terminal device k is sufficiently small.

The base station device may acquire the channel estimation value h ^{^} _k in the above formula (1) based on an uplink signal (e.g., a sounding reference signal (SRS)) received from the terminal device k. The base station device may also receive a report of a channel estimation value calculated by the terminal device k when the DMRS was transmitted last time, and use the channel estimation value as h ^{^} _k . The channel estimation value acquired by the SRS may not necessarily accurately represent the state of the transmission path in the subband, and it is assumed that the channel estimation value based on the last DMRS does not accurately reflect the current channel state. For this reason, the base station device may evaluate the effect of spatial separation by the following formula (2), taking into account the inaccuracy of the channel estimation value.

　なお、ｅ_kは、伝送路推定値の誤差に相当するランダム変数でありうる。なお、ｅ_kの電力の大きさは、例えば、過去のチャネル推定値の正確性などに基づいて、経験的に定められうる。 Equation (2)

Here, e _k may be a random variable corresponding to an error in the channel estimation value. The magnitude of the power of e _k may be empirically determined based on, for example, the accuracy of past channel estimation values.

When the base station device determines that the value calculated by the above-mentioned formula (1) or formula (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 by the above-mentioned formula (1) or formula (2). The base station device may also notify the terminal device of only the calculation result of the above-mentioned formula (1) or formula (2). The base station device may also notify the terminal device of the result of calculating the correlation value without including the effects of spatial multiplexing or the effects of the channel.

　The terminal device may perform channel estimation on a subband basis when channel estimation on a subband basis is possible based on information received from the base station device. In addition, when the terminal device calculates a channel estimation value on a subband basis, for example, the terminal device may determine whether to average the channel estimation value based on the magnitude of the fluctuation of the channel estimation value for each subband. For example, the terminal device may determine to average the channel estimation value (add the channel estimation values together and divide by the number of samples added) when the change in the channel estimation value between subbands is equal to or less than a predetermined value. The magnitude of the change in the channel estimation value between subbands may be determined to be small when the correlation value is large and large when the correlation value is small, for example, by calculating the correlation value between the calculated channel estimation values. The magnitude of the change may also be determined based on the magnitude of the difference between the channel estimation values. In this way, the terminal device can suppress the influence of, for example, thermal noise and obtain a more accurate channel estimation value. On the other hand, the terminal device may determine not to average the channel estimation value between subbands when the change in the channel estimation value between subbands exceeds a predetermined value. 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 the average value. When the terminal device calculates 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. In addition, the terminal device may notify the base station device in advance of capability information indicating whether or not the terminal device has the capability to perform channel estimation on a subband basis.

(Device configuration)
An example of the hardware configuration of the base station device and the terminal device will be described with reference to FIG. 4. In one example, the base station device and the terminal device are configured to 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 configured to include one or more processing circuits such as a general-purpose CPU (Central Processing Unit) or an ASIC (Application Specific Integrated Circuit), and executes the overall processing of the device and each of the above-mentioned processes by reading and executing a program 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 processing executed by the base station device and the terminal device. 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 configured, for example, by a removable external storage device. The communication circuit 405 is configured, for example, by a circuit for wireless communication of 5G or its successor standard. In addition, although one communication circuit 405 is illustrated in FIG. 4, for example, the base station device and the terminal device may have two or more communication circuits. In addition, for example, the base station device and the terminal device may have a common antenna with the wireless communication circuit for 5G and its successor standard. In addition, the base station device and the terminal device may have an antenna for 5G and an antenna for its successor standard separately. In addition, the terminal device may have a communication circuit for other wireless communication networks such as a wireless LAN. In addition, the base station device and the terminal device may have separate communication circuits for each of a plurality of usable frequency bands, or may have a common communication circuit for at least a part of those frequency bands. In this embodiment, it is assumed that the terminal device has a plurality of communication circuits capable of communication in a common frequency band. In addition, the base station device may further have a wired communication circuit used when communicating with other base station devices and nodes of the core network.

5 is a diagram showing 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 shows only functions that are particularly related to this embodiment, and does not show 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. Also, the functional blocks in FIG. 5 are shown in schematic form, and each functional block may be integrated and realized, or may be further subdivided. Also, 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 may be realized, for example, by a processor inside the communication circuit 405 executing a predetermined software. Note that the details of the processing performed by each functional unit will not be described here in detail, and only the general functions will be outlined.

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 an OCC with a code length according to the number of resource elements for transmitting a DMRS, for example, included in a band corresponding to the coarsest frequency resolution, to each terminal device to which data is to be transmitted. For example, as shown in FIG. 2C, in a band of one resource block, which is the coarsest frequency resolution, when eight resource elements are used to transmit a DMRS, the base station device assigns an OCC with a code length of 8, as shown in FIG. 3A, to each terminal device. The DMRS generation unit 502 uses the OCC determined by the OCC determination unit 501 to generate a DMRS for channel estimation of each terminal device. The DMRS information notification unit 503 uses a partial sequence of the OCC assigned for each terminal device to generate information indicating whether channel estimation is possible for each subband corresponding to a frequency resolution finer than the above-mentioned coarsest frequency resolution. This information includes, for example, information indicating whether a partial sequence corresponding to each subband, which is a part of the sequence of the OCC assigned by the OCC determination unit 501 as described above, is orthogonal to all partial sequences of other OCCs for other terminal devices transmitted in the same resource element. In addition, this information may indicate that channel estimation for each subband is possible, for example, 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. In addition, this information may include information indicating the extent to which the channel estimation accuracy is affected by spatial multiplexing when a partial sequence of an OCC that is not orthogonal exists, for example, information indicating the value of the calculation result of the above-mentioned formula (1) or formula (2). The transmission unit 504 transmits a downlink signal including, for example, the DMRS generated by the DMRS generation unit 502 and user data.

6 is a diagram showing 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 estimation unit 603, and an averaging processing unit 604. Note that FIG. 6 shows only functions that are particularly related to this embodiment, and various other functions that the terminal device may have are omitted from the illustration. For example, the terminal device naturally has other functions that terminal devices of 5G and its successor standards generally have. Also, the functional blocks in FIG. 6 are shown in schematic form, and each functional block may be integrated and realized, or may be further subdivided. Also, 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, for example, by a processor inside the communication circuit 405 executing a predetermined software. Note that the details of the processing performed by each functional unit will not be described here in detail, and only the rough functions will be outlined.

The DMRS information receiving unit 601 receives, for example, information that enables identification of the resource element from which the DMRS is transmitted and information on the OCC series. The DMRS information receiving unit 601 also receives information that enables determination of whether or not 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 the DMRS and user data sent from the base station device. The channel estimation 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 estimation unit 603 performs channel estimation on a subband basis. In addition, when the channel estimation unit 603 can estimate the channel on a subband basis only in some subbands and cannot estimate the channel on a subband basis in other subbands (interference is large and channel estimation cannot be performed with sufficient accuracy), the channel estimation unit 603 may perform channel estimation on a subband basis only in the part of subbands, and perform only channel estimation of the entire band (e.g., resource block) in which the DMRS is transmitted for the other subbands. In addition, when the information received by the DMRS information receiving unit 601 indicates that channel estimation on a subband basis cannot be performed, the channel estimation unit 603 performs channel estimation on the entire band and does not perform channel estimation on a subband basis. For example, when the channel estimation unit 603 performs channel estimation on a subband basis for multiple subbands, the averaging processing unit 604 determines whether or not to average the channel estimation values obtained for each of the multiple subbands. For example, the averaging processing unit 604 specifies the magnitude of change in the channel estimation value on a subband basis by calculating a difference value or a correlation value between the channel estimation values, and may average the channel estimation value when the change is small (when the difference value is equal to or less than a predetermined value, or the correlation value is equal to or more than a predetermined value, etc.). The channel estimation value or its average value obtained by the channel estimation unit 603 or the averaging processing unit 604 can be input to the receiving unit 602 and used when demodulating user data. When a channel estimation value for each subband is used, the channel estimation value corresponding to that subband is used to demodulate the signal in that subband. On the other hand, when a channel estimation value for the entire band (e.g., resource block) is used, the channel estimation value for the entire band is used to demodulate the signal in that band.

(Processing flow)
Next, an example of the flow of the process executed by the base station device will be described with reference to Fig. 7. Since the details of the process steps shown in Fig. 7 are as described above, the process flow will be merely outlined here and the details will not be repeated. Also, the order of the process steps shown in Fig. 7 is one example, and the order may be reversed.

First, the base station device determines the OCC to be assigned to each terminal device (S701). In this case, the OCC is assigned such that the frequency range in which channel estimation is performed with one DMRS is extended, for example, as shown in FIG. 2C, and an OCC with an extended code length of, for example, 8 is assigned. Then, the base station device evaluates the orthogonality of the OCC assigned to the first terminal device with the OCC assigned to the second terminal device in subband units (S702). For example, the base station device divides the resource element in which the DMRS is transmitted into subbands, and calculates the correlation value between the partial sequence of the OCC for the first terminal device that is mapped to the resource element for DMRS in that subband and the partial sequence of the OCC for the second terminal device that 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 of the first terminal device and the partial sequence of the OCC of the second terminal device are orthogonal, and if the correlation value is not zero, the base station device evaluates that the partial sequence of the OCC of the first terminal device and the partial sequence of the OCC of the second terminal device are not orthogonal. Note that the base station device may calculate the correlation value using a weight vector used for spatial multiplexing, as described above.

Then, the base station device generates DMRS information including the result of the orthogonality evaluation performed in S702 and transmits it to the terminal device (S703). For example, in S702, if the correlation value of the partial sequence of the OCC of the 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 to the first terminal device information including information indicating that channel estimation is possible for that subband on a subband basis as DMRS information. In addition, 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 OCC for other terminal devices in S702 and the correlation value calculated including the weight vector for spatial multiplexing. 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. In addition, the DMRS information may include information indicating which frequency range corresponds to the subband. The method of dividing the subbands may be defined in advance, for example, in a standard. In that case, information such as which frequency range corresponds to the subband 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).

Next, an example of the process flow executed by the terminal device will be described with reference to FIG. 8. Note that since the details of the process steps shown in FIG. 8 have been described above, the process flow will be merely outlined here and the details will not be repeated. Also, the order of the process steps shown in FIG. 8 is one example, and the order may be reversed.

First, the terminal device receives DMRS information from the base station device (S801). From the DMRS information, the terminal device receives information that identifies the OCC sequence used in the DMRS for the device itself and which resource element the DMRS is transmitted on. The terminal device also determines whether channel estimation is possible on a subband basis using the OCC sequence assigned to the device itself based on the received DMRS information (S802). For example, if the DMRS information includes information indicating whether channel estimation is possible on a subband basis, the terminal device follows the information. On the other hand, if the DMRS information includes the calculation result of the above-mentioned formula (1) or formula (2), the terminal device may determine that channel estimation is possible on a subband basis when it is determined that a predetermined channel estimation accuracy can be obtained on a subband basis based on, for example, the reception strength of the DMRS for the device itself 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 is possible on a subband basis in the terminal device, such as the calculation result of the above-mentioned formula (1) or formula (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.

If 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 partial sequence of the OCC corresponding to each subband (S803). Then, the terminal device determines whether to average the channel estimation value on a subband basis (S804). For example, if the amount of change in the channel estimation value on a subband basis is equal to or greater than a predetermined value or the correlation value of the channel estimation value is equal to or less than a predetermined value, the terminal device determines not to average the channel estimation value (NO in S804). In this case, the terminal device performs reception processing of user data, etc., using the corresponding channel estimation value for each subband (S805). On the other hand, if the amount of change in the channel estimation value on a subband basis is less than a predetermined value or the correlation value of the channel estimation value exceeds a predetermined value, the terminal device determines to average the channel estimation value (YES in S804). In this case, the terminal device averages the channel estimation value (S806) and uses the averaged channel estimation value as a common channel estimation value for 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 deterioration of frequency resolution by channel estimation on a subband basis, if the amount of change is small and the channel estimation value can be considered constant across the entire band, the influence of thermal noise and the like can be suppressed by performing averaging processing, thereby improving the accuracy of the channel estimation value. Note that when averaging of the channel estimation value is performed, the terminal device may notify the base station device that averaging has been performed or that channel estimation on a subband basis is not necessary.

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

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

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 channel estimation is possible on a subband basis using the partial sequence. This makes it possible to suppress deterioration in the frequency resolution of the channel estimate, and to prevent the associated deterioration in communication performance. In addition, by averaging the channel estimate for each subband as necessary, it is possible to improve the accuracy of the channel estimate when there is little fluctuation in the frequency direction of the channel estimate. This makes it possible to contribute to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), which is to "build resilient infrastructure, promote sustainable industrialization and foster innovation."

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

This application claims priority based on Japanese Patent Application No. 2022-156362, filed on September 29, 2022, the entire contents of which are incorporated herein by reference.

Claims (11)

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 to which the DMRS is transmitted, and second information that enables the terminal device to identify whether channel estimation is possible on a subband basis, which is a part of a band in which channel estimation is performed using the DMRS;
a determining means for determining whether or not channel estimation in subband units 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;
a 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 having the above configuration. the second information includes information indicating whether channel estimation in units of the subbands is possible;
the determining means determines whether or not channel estimation is possible in units of the subbands according to the second information.
The terminal device according to claim 1. 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 of second partial sequences of second OCCs for other terminal devices transmitted in the subband using the same resource element as the first partial sequence,
the determining means determines that channel estimation in subband units is possible when the first partial sequence is orthogonal to all of the second partial sequences.
The terminal device according to claim 1. 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 transmitted in the subband using the same resource element as the first partial sequence,
The determining means determines whether or not channel estimation is possible in units of the subbands based on the correlation value.
The terminal device according to claim 1. 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 along which the second OCC is transmitted. the execution means, when the channel estimation is executed in units of the subbands, averages the channel estimation values if a magnitude of a difference value between channel estimation values corresponding to a plurality of subbands is equal to or greater than a predetermined value.
The terminal device according to claim 1. The terminal device according to claim 1, further comprising a notification means for notifying the base station device that averaging has been performed when the execution means has performed averaging of the channel estimation values. 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 the subband. 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). A control method executed by a terminal device, comprising:
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 to which the DMRS is transmitted, and second information that enables the terminal device to identify whether or not channel estimation is possible on a subband basis that is a part of a band in which channel estimation is performed using the DMRS;
determining whether or not channel estimation is possible on a subband basis 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 on a subband basis, 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: A computer installed in the terminal device
acquires from the base station device first information for identifying an orthogonal cover code (OCC) used in generating a demodulation reference signal (DMRS) to be transmitted from a connected base station device to the terminal device and a resource element to which the DMRS is transmitted, and second information for enabling the terminal device to identify whether or not channel estimation is possible on a subband basis, which is a 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, a 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, a channel estimation is performed for the entire band using the OCC;
When channel estimation is performed on a subband basis, 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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