Communication apparatus and method therefor

Abstract

A communication apparatus selects one of a plurality of channel estimates for use in downlink beamforming for downlink transmission to another communication apparatus, or uplink beamforming for uplink reception from the another communication apparatus, at a given frequency and time resource. The plurality of channel estimates includes at least two of: a first channel estimate based on a first type of uplink reference signal transmitted by the other communication apparatus; a second channel estimate based on a second type of uplink reference signal transmitted by the other communication apparatus; and a third channel estimate calculated from both the first channel estimate and the second channel estimate.

Description

COMMUNICATION APPARATUS AND METHOD THEREFOR

[0001] The present disclosure relates to radio communication systems, and in particular to beamforming.

[0002] Patent Literature 1 discloses reception beamforming (or UL beamforming) for uplink (UL) reception (e.g., physical uplink shared channel (PUSCH) reception) performed by an Open Radio Access Network (O-RAN) base station. Patent Literature 1 also discloses transmission beamforming (or DL beamforming) for downlink (DL) transmission (e.g., physical downlink shared channel (PDSCH) transmission) performed by the O-RAN base station. The O-RAN base station in Patent Literature 1 is a fifth generation (5G) new radio (NR) base station, specifically a gNB, or an O-RAN Radio Unit (O-RU) and an O-RAN Distributed Unit (O-DU).

[0003] For example, Fig. 11 and the related paragraphs of Patent Literature 1 disclose a method of applying demodulation reference signal (DMRS)-based noise pre-whitening to UL beamforming based on sounding reference signal (SRS)-based channel estimation. Specifically, the O-DU calculates beamforming weights using SRS-based channel estimate and UL-DMRS (e.g., PUSCH DMRS)-based noise covariance estimate. The beamforming circuitry in the O-RU applies the beamforming weights calculated in the O-DU to perform beamforming on an UL data signal to generate an UL data stream (e.g., PUSCH stream).

[0004] Fig. 12 and the related paragraphs in Patent Literature 1 state that the O-DU may calculate beamforming weights for DL massive multiple-input multiple-output (mMIMO) using the channel estimated from SRS.

[0005] In 5G NR, SRS is an uplink reference signal configured on a user equipment (UE)-specific basis. SRS can be configured using Radio Resource Control (RRC) signaling. For example, a 5G NR base station can send SRS configuration parameters to a UE using RRC signaling. Periodic SRS can be transmitted by the UE to the 5G NR base station in a periodic manner, based on the SRS configuration parameters. Aperiodic SRS can be dynamically triggered by the 5G NR base station using downlink control information (DCI) or other signaling methods. Semi-persistent SRS is transmitted in a periodic manner similar to periodic SRS, but it can be dynamically activated or deactivated by using a medium access control (MAC) control element (CE) or other signaling methods. The configurable parameters of SRS that the 5G NR base station may determine for the UE can include at least one of the number of SRS ports, time-domain position, frequency-domain position, bandwidth, cyclic shift, transmission comb and offset etc.

[0006] In 5G NR, UL-DMRS is transmitted by frequency multiplexing on the same time-domain resource as a UL data channel (i.e., PUSCH) or a UL control channel (i.e., Physical Uplink Control Channel (PUCCH)). UL-DMRS is also referred to as PUSCH DMRS or PUCCH DMRS. The 5G NR base station performs channel estimation based on UL-DMRS that is frequency-multiplexed with PUSCH or PUCCH symbols, and uses this channel estimate for PUSCH or PUCCH demodulation, such as MIMO equalization.

[0007] Patent Literature 1: US 2024 / 0154658 A1

[0008] As described in Patent Literature 1, SRS-based channel estimation, i.e., a channel matrix estimated from SRS transmitted by a UE, can be used to calculate beamforming weights for uplink or reception beamforming at a 5G NR base station (i.e., gNB). In addition, in the case of 5G NR time-division duplex (TDD) systems, SRS-based channel estimation can also be used to calculate beamforming weights for downlink or transmission beamforming at a 5G NR base station.

[0009] The time gap between SRS-based channel estimation and DL beamforming transmission or UL beamforming reception makes the channel estimates outdated. Such outdated channel estimates lead to inaccurate beamforming weight calculations. This phenomenon is called "channel aging". Channel aging is caused, for example, by the mobility of a UE. Channel aging can degrade the performance of DL and UL beamforming based on SRS-based channel estimation.

[0010] The method of using DMRS-based noise covariance estimates, as disclosed in Patent Literature 1, together with SRS-based channel estimates for UL beamforming weight calculations may be useful in mitigating the effects of inter-cell interference by whitening the spatial noise. However, this method may not directly contribute to mitigating the effects of aging on SRS-based channel estimation in UL and DL beamforming.

[0011] Patent Literature 1 discloses that SRS-based channel prediction is effective in mitigating the effects of channel aging. SRS-based channel prediction predicts a current or future channel estimate based on past SRS channel estimates. However, it may be preferable to provide other methods that can mitigate the effects of channel aging and help improve beamforming performance when SRS-based channel prediction cannot be used or when it is used in combination with SRS-based channel prediction.

[0012] One of the objects to be achieved by the example embodiments disclosed herein is to provide an apparatus, method, and / or program that contributes to solving at least one of a plurality of problems related to beamforming, including the above-mentioned problems. It should be noted that this object is only one of the objects to be achieved by the example embodiments disclosed herein. Other objects or problems and novel features will become apparent from the following description and the accompanying drawings.

[0013] In a first aspect, a communication apparatus is configured to select one of a plurality of channel estimates for use in downlink beamforming for downlink transmission to another communication apparatus, or uplink beamforming for uplink reception from the another communication apparatus, at a given frequency and time resource. The plurality of channel estimates includes at least two of: a first channel estimate based on a first type of uplink reference signal transmitted by the another communication apparatus; a second channel estimate based on a second type of uplink reference signal transmitted by the another communication apparatus; and a third channel estimate calculated from both the first channel estimate and the second channel estimate.

[0014] In a second aspect, a method performed by a communication apparatus includes selecting one of a plurality of channel estimates for use in downlink beamforming for downlink transmission to another communication apparatus, or uplink beamforming for uplink reception from the another communication apparatus, at a given frequency and time resource. The plurality of channel estimates includes at least two of: a first channel estimate based on a first type of uplink reference signal transmitted by the another communication apparatus; a second channel estimate based on a second type of uplink reference signal transmitted by the another communication apparatus; and a third channel estimate calculated from both the first channel estimate and the second channel estimate.

[0015] In a third aspect, a program includes instructions (or software codes) that, when loaded into a computer, cause the computer to perform the method according to the above-described second aspect.

[0016] According to the aspects described above, it is possible to provide an apparatus, method, and / or program that contributes to solving at least one of a plurality of problems related to beamforming, including the above-mentioned problems.

[0017] Fig. 1 shows an example configuration of a radio communication system in relation to one or more example embodiments;Fig. 2 shows an example configuration of a radio communication system in relation to one or more example embodiments;Fig. 3 shows an example of a slot format in a 5G NR TDD system;Fig. 4 shows an example of an operation of a base station in relation to one or more example embodiments;Fig. 5 shows an example of an operation of a base station for DL beamforming, in relation to one or more example embodiments;Fig. 6 shows an example of an operation of a base station for DL beamforming, in relation to one or more example embodiments;Fig. 7 shows an example of an operation of a base station for UL beamforming, in relation to one or more example embodiments;Fig. 8 shows an example of an operation of a base station for DL scheduling, in relation to one or more example embodiments;Fig. 9 shows an example of DL resource allocation in relation to one or more example embodiments;Fig. 10 shows an example of an operation of a base station for UL scheduling, in relation to one or more example embodiments;Fig. 11 shows an example of UL resource allocation in relation to one or more example embodiments;Fig. 12 shows an example of an operation of a base station for UL scheduling, in relation to one or more example embodiments;Fig. 13 shows an example of UL resource allocation in relation to one or more example embodiments;Fig. 14 shows an example of an operation of a base station for UL scheduling, in relation to one or more example embodiments;Fig. 15 shows an example of UL resource allocation in relation to one or more example embodiments;Fig. 16 shows an example configuration of a base station in relation to one or more example embodiments;Fig. 17 shows an example configuration of a base station in relation to one or more example embodiments;Fig. 18 shows an example of a block diagram in relation to one or more example embodiments;Fig. 19 shows an example of a block diagram in relation to one or more example embodiments;Fig. 20 shows an example of a block diagram in relation to one or more example embodiments; andFig. 21 shows an example of a modified DL scheduler in relation to one or more example embodiments.

[0018] Specific example embodiments will be described hereinafter in detail with reference to the drawings. The same or corresponding elements are denoted by the same symbols throughout the drawings, and duplicated explanations are omitted as necessary for the sake of clarity.

[0019] The plurality of example embodiments described below may be implemented independently or in combination, as appropriate. These example embodiments include novel features that are different from one another. Accordingly, these example embodiments contribute to the achievement of objectives or the solution of problems that are different from one another and contribute to the achievement of advantages that are different from one another.

[0020] Each of the drawings or figures is merely an example to illustrate one or more example embodiments. Each figure may not be associated with only one particular example embodiment, but may be associated with one or more other example embodiments. As will be appreciated by those of ordinary skill in the art, various features or steps described with respect to any one of the figures may be combined with features or steps illustrated in one or more other figures to produce, for example, example embodiments that are not explicitly illustrated or described. Not all of the features or steps illustrated in any one of the figures to describe an example embodiment are necessarily essential, and some features or steps may be omitted. The order of the steps described in any of the figures may be changed as appropriate.

[0021] The multiple example embodiments shown below are primarily described for 5G NR systems. However, these example embodiments can be applied to other radio communication systems that use beamforming.

[0022] As used in this specification, "if" can be interpreted to mean "when", "at or around the time", "after", "upon", "in response to determining", "in accordance with a determination", or "in response to detecting", depending on the context. These expressions can be interpreted to mean the same thing, depending on the context. As used in this specification, "in response to" may be paraphrased as "based on," depending on the context.

[0023] First, the configuration and operation of a plurality of network elements common to a plurality of example embodiments are described. Fig. 1 shows an example configuration of a radio communication system related to a plurality of example embodiments. In the example of Fig. 1, the radio communication system includes a gNB 1 and a plurality of UEs 2. Each element (or network function) shown in Fig. 1 may be implemented, for example, as a network element on dedicated hardware, as a software instance running on dedicated hardware, or as a virtualized function instantiated on an application platform.

[0024] The gNB 1 is configured to perform wireless communication with UEs 2 in its radio coverage area 3 using cellular communication technology (i.e., NR Radio Access Technology (RAT)). The gNB 1 may be referred to by other terms such as base station, RAN node, radio station, or access point. The radio coverage area 3 may include one or more cells. Each UE 2 has at least one radio transceiver and is configured to perform wireless communication with the gNB 1. Each UE 2 is connected to the gNB 1 via an air interface. Each UE 2 may be referred to by other terms such as radio terminal, mobile terminal, mobile station, or wireless transmit receive unit (WTRU).

[0025] The gNB 1 may be a combination of a gNB Central Unit (CU) and one or more gNB Distributed Units (DUs) in a centralized or cloud RAN (C-RAN) deployment. The gNB-CU may be a logical node that hosts the gNB's Radio Resource Control (RRC), Service Data Adaptation Protocol (SDAP), and Packet Data Convergence Protocol (PDCP) protocols. The gNB-DU may be a logical node that hosts the gNB's Radio Link Control (RLC), Medium Access Control (MAC), and Physical (PHY) layers.

[0026] Specifically, as shown in Fig. 2, the gNB 1 may include a gNB-CU 10, one or more gNB-DUs 21 and 22, and one or more Transmission / Reception Points (TRPs) 31 to 35. The gNB-CU 10 is a logical node that controls the operation of the gNB-DUs 21 and 22. Each of the gNB-DUs 21 and 22 is a logical node that hosts the RLC and MAC layers of the gNB 1 and hosts part of the PHY layer of the gNB 1, namely the High PHY layer. The rest of the PHY layer signal processing, i.e. the Low PHY layer, is placed in TRPs 31 to 35. In the example of Fig. 2, the gNB-DU 21 is connected to the TRPs 31 to 33, while the gNB-DU 22 is connected to the TRPs 34 and 35. The TRPs 31 to 33 provide a single cell 51, while the TRPs 34 and 35 provide separate cells 52 and 53, respectively. In other words, the gNB-DU 21 provides a cell 51, and the TRPs 31 to 33 correspond to the cell 51. The gNB-DU 22 provides multiple cells 52 and 53, and the TRPs 34 and 35 correspond to the cells 52 and 53, respectively.

[0027] Each of the TRPs 31 to 35 is capable of communicating with UEs 2 using beams. The TRPs 31 to 35 may be referred to as Radio Units (RUs), Remote Radio Heads (RRHs), access points (APs), or distributed antennas. Each TRP supports one or both of the Transmission Point (TP) function and the Reception Point (RP) function.

[0028] Each of the TRPs 31 to 35 provides analog radio frequency (RF) signal processing. Each TRP may provide low PHY layer signal processing. Each TRP includes or is connected to one or more antenna elements (typically an array antenna). Each TRP includes an RF component coupled to one or more antenna elements. For analog or hybrid beamforming, analog beamforming circuitry may be placed between one or more antenna elements or one or more array antennas and the multiple RF chains of each TRP.

[0029] Each TRP also includes a digital front end (DFE). The DFE provides low PHY layer signal processing and digital radio signal processing. The low PHY layer signal processing for 5G NR downlink, in particular for PDSCH, includes, for example, digital DL beamforming, inverse fast Fourier transform (IFFT) and cyclic prefix addition. The DFE may perform digital baseband precoding for DL beamforming. The low PHY layer signal processing for 5G NR uplink, in particular for PUSCH, includes, for example, FFT, cyclic prefix removal and digital UL beamforming. The digital radio signal processing includes, for example, digital predistortion (DPD), crest factor reduction (CFR), digital up-conversion (DUC) and digital down-conversion (DDC).

[0030] The gNB-CU 10 may be a gNB-CU conforming to the O-RAN technical specifications, namely an O-CU Control Plane (CP), an O-CU User Plane (UP), or a combination of both. The gNB-DUs 21 and 22 may be gNB-DUs conforming to the O-RAN technical specifications, i.e., O-DUs. The TRPs 31 to 35 may be RUs conforming to the O-RAN technical specifications, i.e., O-RUs. Each of the gNB-DUs 21 and 22 may be connected to a TRP via an existing or enhanced O-RAN fronthaul interface.

[0031] Fig. 3 shows an example of the time domain slot format in 5G NR TDD systems. Regardless of the numerology, i.e., subcarrier spacing (SCS) and cyclic prefix (CP), the radio frame length is 10 milliseconds (ms) and the subframe length is 1 ms. In NR, the number of OFDM symbols per slot is fixed and is typically 14 symbols for normal CP and 12 symbols for extended CP. The OFDM symbol duration decreases as the SCS increases. Since the number of OFDM symbols per slot is fixed, the slot duration decreases as the SCS increases. Although the slot duration decreases, the subframe duration is fixed, so the number of slots in a subframe increases as the SCS increases.

[0032] Fig. 3 shows an example of a slot format when the SCS is 30 kHz, the number of slots per subframe is 2, and the number of slots per radio frame is 20. NR supports static, semi-static, or fully dynamic configuration of the slot format. Static and semi-static slot configuration is performed using RRC, while dynamic slot configuration is performed using DCI transmitted in a Physical Downlink Control Channel (PDCCH).

[0033] The NR TDD slot format is much more flexible than that of LTE. Each OFDM symbol in a slot is classified as a DL symbol, UL symbol, or flexible symbol. One of the purposes of introducing flexible symbols is to ensure guard time for switching from DL to UL.

[0034] In the example in Fig. 3, the first pattern (i.e., Pattern 1) and the second pattern (i.e., Pattern 2) are used. The slot configuration period for Pattern 1 is 3 ms, and there are 3 DL slots and 2 UL slots. A DL slot means a slot that consists only of DL symbols. The first 0 or more slots in the slot configuration period can be DL slots. A UL slot means a slot that consists only of UL symbols. The last 0 or more slots in the slot configuration period can be UL slots.

[0035] One or more slots that are neither DL slots nor UL slots (for example, slots #3 and #13 in Fig. 3) are referred to as special slots or flexible slots. A special slot or flexible slot contains one or more flexible symbols. A special slot or flexible slot can contain one or more DL symbols at the beginning of the slot, i.e., immediately after the preceding DL slot. A special slot or flexible slot can contain one or more UL symbols at the end of the slot, i.e., immediately before the following UL slot.

[0036] In the example in Fig. 3, the configuration period for Pattern 2 is 2 ms, and all four slots are downlink slots.

[0037] In the following example embodiments, the terms "PDxCH" and "PUxCH" are used. PDxCH refers to PDSCH or PDCCH. PUxCH refers to PUSCH or PUCCH.

[0038] First Example Embodiment 　　An example configuration of a radio communication system in this example embodiment is the same as the example configuration explained with reference to Figs. 1 and 2. This example embodiment provides details related to beamforming (or precoding) weight calculations for UL and DL beamforming.

[0039] Fig. 4 shows an example of the operation of the gNB 1. The operation shown in Fig. 4 can be performed in a gNB-DU (e.g., the gNB-DU 21 or 22 in Fig. 2). Alternatively, the operation shown in Fig. 4 can be performed in a TRP or O-RU (e.g., any of the TRPs 31 to 35 in Fig. 2).

[0040] In step 401, the gNB 1 selects one of a plurality of channel estimates for use in DL beamforming or UL beamforming for DL transmission to or UL reception from the UE 2 in a given frequency and time resource. The plurality of channel estimates includes at least two of first, second, and third channel estimates. The first channel estimate is a channel estimate based on a first type of UL reference signal (e.g., SRS) transmitted by the UE 2. The second channel estimate is a channel estimate based on a second type of UL reference signal (e.g., UL-DMRS) transmitted by the UE 2. The third channel estimate is a channel estimate calculated from both the first and second channel estimates. The third channel estimate may be a weighted combination (for example, a linear combination) of the first and second channel estimates.

[0041] In step 402, the gNB 1 applies the selected channel estimate to DL beamforming or UL beamforming. Specifically, the gNB 1 calculates beamforming weights (or precoding weights) for DL beamforming using a channel estimation matrix based on the selected channel estimate. Additionally or alternatively, the gNB 1 calculates beamforming weights for UL beamforming using a channel estimation matrix based on the selected channel estimate.

[0042] DL beamforming can also be referred to as transmission beamforming. UL beamforming can also be referred to as reception beamforming. UL beamforming or reception beamforming is an adaptation of the UL reception directivity pattern to produce a peak gain to the direction of the UL transmitting UE.

[0043] In the case of 5G NR, the given frequency and time resource includes one or more subcarriers in the frequency domain and one or more OFDM symbols in the time domain. In other words, the given frequency and time resource includes one or more resource elements. A resource element is defined as the smallest unit of a resource grid and consists of one subcarrier in the frequency domain and one OFDM symbol in the time domain. The given frequency and time resource may contain one or more resource blocks in the frequency domain. A resource block is defined as 12 consecutive subcarriers in the frequency domain.

[0044] In the case of DL beamforming, the given frequency and time resource may be the resources allocated or scheduled for a DL data channel (e.g., PDSCH) or DL control channel (e.g., PDCCH) transmission to the UE 2. In the case of UL beamforming, the given frequency and time resource may be the resources allocated or scheduled for a UL data channel (e.g., PUSCH) or UL control channel (e.g., PUCCH) transmission by the UE 2.

[0045] In the case of 5G NR, the first type of UL reference signal is SRS, and the second type of UL reference signal may be UL-DMRS (e.g., PUSCH DMRS or PUCCH DMRS).

[0046] As mentioned above, in 5G NR, SRS is a UL reference signal that is configured on a UE-specific basis. SRS can be configured using RRC signaling. For example, the gNB 1 can send SRS configuration parameters to the UE 2 using RRC signaling. Periodic SRS can be transmitted by the UE 2 to the gNB 1 in a periodic manner, based on the SRS configuration parameters. Aperiodic SRS can be dynamically triggered by the gNB 1 using (DCI or other signaling methods. Semi-persistent SRS is transmitted in a periodic manner similar to periodic SRS, but it can be dynamically activated or deactivated by using a MAC CE or other signaling methods. The configurable parameters of SRS that the gNB 1 may determine for the UE 2 can include at least one of the number of SRS ports, time-domain position, frequency-domain position, bandwidth, cyclic shift, transmission comb and offset etc.

[0047] In 5G NR, UL-DMRS is transmitted by frequency multiplexing on the same time-domain resource as a UL data channel (i.e., PUSCH) or a UL control channel (i.e., PUCCH). UL-DMRS is also referred to as PUSCH DMRS or PUCCH DMRS. The gNB 1 performs channel estimation based on UL-DMRS that is frequency-multiplexed with PUSCH or PUCCH symbols, and can use this channel estimate for PUSCH or PUCCH demodulation, such as MIMO equalization.

[0048] For example, the channel estimate selection in step 401 may be performed as follows. The gNB 1 may determine which of the plurality of channel estimates to use based on a first frequency and time resource on which the first type of UL reference signal was previously (e.g., most recently) transmitted, a second frequency and time resource on which the second type of UL reference signal was previously (e.g., most recently) transmitted, and the given frequency and time resource on which DL or UL beamforming is to be performed.

[0049] In the case of 5G NR, each of the first frequency and time resource and the second frequency and time resource, as well as the given frequency and time resource, includes one or more subcarriers in the frequency domain and one or more OFDM symbols in the time domain. In other words, each of the first frequency and time resource and the second frequency and time resource includes one or more resource elements. Each of the first frequency and time resource and the second frequency and time resource may include one or more resource blocks in the frequency domain.

[0050] More specifically, the gNB 1 may consider whether there is an overlap in the frequency domain between the given frequency and time resource and the first frequency and time resource, and whether there is an overlap in the frequency domain between the given frequency and time resource and the second frequency and time resource.

[0051] If the given frequency and time resource where DL or UL beamforming is to be performed overlaps in the frequency domain with the first frequency and time resource where the first type of UL reference signal was last transmitted, the gNB 1 may select the first channel estimate based on the first type of UL reference signal.

[0052] If the given frequency and time resource where DL or UL beamforming is to be performed overlaps in the frequency domain with the second frequency and time resource where the second type of UL reference signal was last transmitted, the gNB 1 may select the second channel estimate based on the second type of UL reference signal.

[0053] If the given frequency and time resource overlaps with both the nearest first frequency and time resource and the nearest second frequency and time resource in the frequency domain, the gNB 1 may operate as follows. For example, the gNB 1 may select one of the first and second channel estimates based on which of the first type UL reference signal and the second type UL reference signal was transmitted more recently. In other words, the gNB 1 may select the more recent one of the first and second channel estimates for use in DL or UL beamforming. Alternatively, the gNB 1 may select one of the first and second channel estimates based on which one of the first and second channel estimates is more reliable. In other words, the gNB 1 may select the more reliable one of the first and second channel estimates for use in DL or UL beamforming. Alternatively, the gNB 1 may select the third channel estimate. The third channel estimate may be a weighted combination (for example, a linear combination) of the first and second channel estimates. The gNB 1 may give a larger weight to the more recent or more reliable of the first and second channel estimates and a smaller weight to the other estimate.

[0054] Fig. 5 shows an example of operation of the gNB 1, according to the example embodiment. In Fig. 5, nine time slots are shown, indexed from slot #1 through slot #9. Uplink slots are indicated by 'UL slot', downlink slots are indicated by 'DL slot', and special slots are indicated by 'S slot'. Slot #1, slot #4, and slot #7 are indicated as either an S slot or an UL slot. Slot #2, slot #5, and slot #8 are indicated as an UL slot. Furthermore, slot #3, slot #6, and slot #9 are indicated as DL slots. The available frequency resource in each time slot is divided into 4 parts: sub-band #1, sub-band #2, sub-band #3, and sub-band #4. Each sub-band may consist of one or more resource blocks (RB). In the example of Fig. 5, SRS transmission is scheduled in the sub-band #1 of slot #1, sub-band #2 of slot #4, and sub-band #4 of slot #7. Furthermore, PUxCH (UL-DMRS) transmission is scheduled on sub-band #2 and #3 of slot #2, sub-band #3 and #4 of slot #5, and sub-band #3 and #4 of slot #8. Also, PDxCH transmission is scheduled on sub-band #1 and #2 of slot #3, sub-band #1 and #2 of slot #6, and sub-band #3 and #4 of slot #9.

[0055] Fig. 5 shows examples of selecting a channel estimate to be used for DL beamforming. In the examples in Fig. 5, the gNB 1 selects at least the most recent channel estimate from the SRS-based channel estimate and the UL-DMRS-based channel estimate to be used for the calculation of DL beamforming weights for the scheduled or upcoming PDxCH transmission.

[0056] Specifically, the gNB 1 selects the channel estimation result based on the SRS transmitted by the UE 2 in sub-band #1 of UL or special slot #1 for use in DL beamforming for PDxCH transmission to that UE 2 in sub-band #1 of DL slot #3.

[0057] The gNB 1 selects the channel estimation result based on the UL-DMRS transmitted by the UE 2 in sub-band #2 of UL slot #2 for use in DL beamforming for PDxCH transmission to that UE 2 in sub-band #2 of DL slot #3.

[0058] The gNB 1 selects the channel estimation result based on the SRS transmitted by the UE 2 in sub-band #1 of UL or special slot #1 for use in DL beamforming for PDxCH transmission to that UE 2 in sub-band #1 of DL slot #6. Some examples may use a predicted value of the SRS-based channel estimate at sub-band #1 of DL slot #6, based on at least the SRS-based channel estimate at sub-band #1 of UL / S slot #1.

[0059] The gNB 1 selects the channel estimation result based on the SRS transmitted by the UE 2 in sub-band #2 of UL or special slot #4 for use in DL beamforming for PDxCH transmission to that UE 2 in sub-band #2 of DL slot #6. Some examples may use a predicted value of the SRS-based channel estimate at sub-band #2 of DL slot #6, based on at least the SRS-based channel estimate at sub-band #2 of UL / S slot #4.

[0060] The gNB 1 selects the channel estimation result based on the UL-DMRS transmitted by the UE 2 in sub-band #3 of UL slot #8 for use in DL beamforming for PDxCH transmission to that UE 2 in sub-band #3 of DL slot #9. Some examples may use a predicted value of the UL-DMRS-based channel estimate at sub-band #3 of DL slot #9, based on at least the UL-DMRS-based channel estimate at sub-band #3 of UL slot #8.

[0061] The gNB 1 selects the channel estimation result based on the UL-DMRS transmitted by the UE 2 in sub-band #4 of UL slot #8 for use in DL beamforming for PDxCH transmission to that UE 2 in sub-band #4 of DL slot #9. Alternatively, the gNB 1 may select a weighted combination (for example, a linear combination) between the channel estimation result based on the SRS transmitted by the UE 2 in sub-band #4 of UL or special slot #7 and the channel estimation result based on the UL-DMRS transmitted by the UE 2 in sub-band #4 of UL slot #8. Some examples may use a predicted value of the channel estimate at sub-band #4 of DL slot #9, based on at least one of the SRS-based channel estimate at sub-band #4 of UL / S slot #7 and the UL-DMRS-based channel estimate at sub-band #4 of UL slot #8. In one example, an AI model can be trained using the channel estimation result based on the SRS and the channel estimation result based on the UL-DMRS to generate the unified or combined channel estimate.

[0062] Fig. 6 shows an example of beamforming weight (or precoding weight) calculation for DL beamforming. A controller 601, a unified channel estimator 602, and a DL beamforming weight calculator 603 shown in Fig. 6 are placed in the gNB 1. For example, the controller 601 may be placed in a gNB-DU, the unified channel estimator 602 may be placed in the gNB-DU or a TRP, and the DL beamforming weight calculator 603 may be placed in the gNB-DU or the TRP. Following the O-RAN terminology, the controller 601 may be placed in an O-DU, the unified channel estimator 602 may be placed in the O-DU or an O-RU, and the DL beamforming weight calculator 603 may be placed in the O-DU or the O-RU.

[0063] The controller 601 receives resource allocations for one or more past SRS transmissions, resource allocations for one or more past PUxCH (or UL-DMRS) transmissions, and a resource allocation for a scheduled or upcoming PDxCH transmission. These resource allocations may be provided to the controller 601 by an SRS scheduler, a UL scheduler, and a DL scheduler. The SRS scheduler, UL scheduler, and DL scheduler may be placed in the gNB-DU or the O-DU.

[0064] The controller 601 selects the channel estimate to be used to calculate DL beamforming weights for the upcoming PDxCH transmission, taking into account the resource allocations obtained. As described above, the controller 601 selects one of a plurality of channel estimates, including at least two of SRS-based channel estimate, UL-DMRS-based channel estimate, and channel estimate calculated from both. The controller 601 sends an instruction indicating the selection result to the unified channel estimator 602.

[0065] The unified channel estimator 602 and the DL beamforming weight calculator 603 apply the channel estimation selected by the controller 601 to DL beamforming. Specifically, the unified channel estimator 602 sends the channel estimation matrix to the DL beamforming weight calculator 603 according to the instruction from the controller 601. If the controller 601 instructs to integrate or combine the SRS-based channel estimate and the UL-DMRS-based channel estimate, the unified channel estimator 602 may calculate the unified or combined channel estimation matrix from these two channel estimates. The SRS-based channel estimate may be calculated in the gNB-DU (or O-DU) or in the TRP (or O-RU). The UL-DMRS-based channel estimate may be calculated in the gNB-DU (or O-DU) or in the TRP (or O-RU).

[0066] The DL beamforming weight calculator 603 calculates DL beamforming weights (or precoding weights) using the channel estimation matrix provided by the unified channel estimator 602. The DL beamforming weight calculator 603 provides the calculated DL beamforming weights to the digital DL beamforming processing block. The digital DL beamforming processing block performs DL beamforming using the provided beamforming weights. Additionally or alternatively, the DL beamforming weight calculator 603 provides the calculated precoding weights to the precoding processing block. The precoding processing block performs precoding using the provided precoding weights.

[0067] Fig. 7 shows an example of beamforming weight calculation for UL beamforming. A controller 701, a unified channel estimator 702, and a UL beamforming weight calculator 703 shown in Fig. 7 are placed in the gNB 1. For example, the controller 701 may be placed in a gNB-DU, the unified channel estimator 702 may be placed in the gNB-DU or a TRP, and the UL beamforming weight calculator 703 may be placed in the gNB-DU or the TRP. Following the O-RAN terminology, the controller 701 may be placed in an O-DU, the unified channel estimator 702 may be placed in the O-DU or an O-RU, and the UL beamforming weight calculator 703 may be placed in the O-DU or the O-RU.

[0068] The controller 701 receives resource allocations for one or more past SRS transmissions, resource allocations for one or more past PUxCH (or UL-DMRS) transmissions, and a resource allocation for a current PUxCH transmission. These resource allocations may be provided to the controller 701 by the SRS scheduler and the UL scheduler. The SRS scheduler and the UL scheduler may be placed in the gNB-DU or the O-DU.

[0069] The controller 701 selects the channel estimate to be used to calculate UL beamforming weights for the current PUxCH transmission, taking into account the resource allocations obtained. As described above, the controller 701 selects one of a plurality of channel estimates, including at least two of SRS-based channel estimate, UL-DMRS-based channel estimate, and channel estimate calculated from both. The controller 701 sends an instruction indicating the selection result to the unified channel estimator 702.

[0070] The unified channel estimator 702 and the UL beamforming weight calculator 703 apply the channel estimation selected by the controller 701 to UL beamforming. Specifically, the unified channel estimator 702 sends the channel estimation matrix to the UL beamforming weight calculator 703 according to the instruction from the controller 701. If the controller 701 instructs to integrate or combine the SRS-based channel estimate and the UL-DMRS-based channel estimate, the unified channel estimator 702 may calculate the unified or combined channel estimation matrix from these two channel estimates. The SRS-based channel estimate may be calculated in the gNB-DU (or O-DU) or in the TRP (or O-RU). The UL-DMRS-based channel estimate may be calculated in the gNB-DU (or O-DU) or in the TRP (or O-RU).

[0071] The UL beamforming weight calculator 703 calculates UL beamforming weight using the channel estimation matrix provided by the unified channel estimator 702. The UL beamforming weight calculator 703 provides the calculated UL beamforming weights to the digital UL beamforming processing block. The digital UL beamforming processing block performs UL beamforming using the provided beamforming weights.

[0072] The controller 701 shown in Fig. 7 may be integrated or common with the controller 601 shown in Fig. 6. The unified channel estimator 702 shown in Fig. 7 may be integrated or common with the unified channel estimator 602 shown in Fig. 6.

[0073] For DL and / or UL beamforming weight calculation, in this example embodiment, the gNB 1 selectively uses the first channel estimate (e.g., SRS-based channel estimate) and the second channel estimate (e.g., UL-DMRS-based channel estimate), or uses the second channel estimate in combination with the first channel estimate. In the case where the first channel estimate is an SRS-based channel estimate and the second channel estimate is a UL-DMRS-based channel estimate, the proposed scheme can increase the interval between SRS transmissions by the UE 2 to achieve the same throughput or beamforming performance as the scheme using only SRS-based channel estimates. In other words, the proposed scheme can reduce the number of SRS transmissions by the UE 2 and compensate the deficiency by using UL-DMRS-based channel estimation. The reduced number of SRS transmissions can reduce reference signal overhead, thus opening up more opportunities for data transmission (for example, PUSCH data). In another approach, the freed-up SRS resources can be used to accommodate higher number of UEs that can be served by the gNB. Alternatively, in cases where the same SRS transmission interval is used as in the scheme using only SRS-based channel estimates, the proposed scheme can improve the throughput or beamforming performance by selectively using or jointly using UL-DMRS-based channel estimates. In addition, the option of using a third channel estimate, such as a channel estimate calculated from both the SRS-based channel estimate and the UL-DMRS-based channel estimate, can improve the quality of channel estimation. This can help mitigate the problem of channel aging.

[0074] Second Example Embodiment 　　An example configuration of a radio communication system in this example embodiment is the same as the example configuration explained with reference to Figs. 1 and 2. This example embodiment provides improvements to UL and DL scheduling. These improvements may help to further enhance the improvement in the throughput or beamforming performance achieved by the beamforming (or precoding) weight calculation described in the first example embodiment.

[0075] Fig. 8 shows an example of the operation of the gNB 1 for DL scheduling. In step 801, a DL scheduler of the gNB 1 determines the allocation of frequency and time resources for PDxCH transmission to the UE 2, taking into account the previous allocation of PUxCH (or UL-DMRS) transmission resources to that UE 2, along with other parameters and scheduling criteria. As mentioned above, UL-DMRS is transmitted concurrently with PUxCH using frequency multiplexing. Therefore, the frequency and time resources for PUxCH transmission contain the frequency and time resources for UL-DMRS transmission.

[0076] In step 802, the DL scheduler of the gNB 1 provides the determined PDxCH transmission resource allocation to a controller of the gNB 1. The controller selects one of a plurality of channel estimates for use in calculating DL beamforming weights, as described in the first example embodiment. This controller may be the controller 601 in Fig. 6.

[0077] The DL scheduler of the gNB 1 may determine the PDxCH transmission resource allocation in step 801 as follows. The DL scheduler preferentially selects, as the PDxCH transmission resources, resources that overlap with the past UL-DMRS transmission resources in the frequency domain. More specifically, if there are multiple PDxCH resource allocation candidates that meet the PDxCH scheduling criteria, conditions, or metrics, the DL scheduler may select a PDxCH resource allocation candidate that maximizes the frequency overlap between the past UL-DMRS resources and the upcoming PDxCH resources. For example, if there are three PDxCH resource allocation candidates #1 to #3 as shown in Fig. 9, the DL scheduler may select PDxCH resource allocation candidate #1, which has the largest frequency overlap with the past PUxCH (or UL-DMRS) resources among the three candidates. In some examples, the selection of candidate #1 (in Fig. 9) may necessitate change of scheduling criteria, conditions, or metrics.

[0078] The DL scheduling described with reference to Fig. 8 helps to maximize the overlap in the frequency domain between the resources to be allocated for the PDxCH transmission to the UE 2 and the resources of the past PUxCH (or UL-DMRS) transmission by that UE 2. Accordingly, this can increase the chances of selecting UL-DMRS-based channel estimates for use in DL beamforming weight calculations in the channel estimate selection explained in the first example embodiment.

[0079] Fig. 10 shows an example of the operation of the gNB 1 for UL scheduling. In step 1001, a UL scheduler of the gNB 1 determines the allocation of frequency and time resources for the upcoming (or current) PUxCH (or UL-DMRS) transmission to the UE 2, taking into account a future allocation of PDxCH transmission resources to that UE 2, along with other parameters and scheduling criteria. As mentioned above, UL-DMRS is transmitted concurrently with PUxCH using frequency multiplexing. Therefore, the frequency and time resources for PUxCH transmission contain the frequency and time resources for UL-DMRS transmission.

[0080] In step 1002, the UL scheduler of the gNB 1 provides the determined PUxCH (or UL-DMRS) transmission resource allocation to a controller of the gNB 1. The controller selects one of a plurality of channel estimates for use in calculating DL beamforming weights, as described in the first example embodiment. This controller may be the controller 601 in Fig. 6.

[0081] The operation shown in Fig. 10 can be particularly effective in cases where PDxCH resources are allocated to the UE 2 in a semi-persistent manner. The UL scheduler of the gNB 1 may determine the PUxCH transmission resource allocation in step 1001 as follows. The UL scheduler preferentially selects, as the PUxCH (or UL-DMRS) transmission resources, resources that overlap with the future PDxCH transmission resources in the frequency domain. More specifically, if there are multiple PUxCH resource allocation candidates that meet the PUxCH scheduling criteria, conditions, or metrics, the UL scheduler may select a PUxCH resource allocation candidate that maximizes the frequency overlap between the future PDxCH resources and the upcoming PUxCH resources. For example, if there are three PUxCH resource allocation candidates #1 to #3 as shown in Fig. 11, the UL scheduler may select PUxCH resource allocation candidate #1, which has the largest frequency overlap with the future PDxCH resources among the three candidates. In some examples, the selection of candidate #1 (in Fig. 11) may necessitate change of scheduling criteria, conditions, or metrics.

[0082] The UL scheduling described with reference to Fig. 10 helps to maximize the overlap in the frequency domain between the resources to be allocated for the PUxCH (or UL-DMRS) transmission by the UE 2 and the resources of the future PDxCH transmission to that UE 2. Accordingly, this can increase the chances of selecting UL-DMRS-based channel estimates for use in DL beamforming weight calculations in the channel estimate selection explained in the first example embodiment.

[0083] Fig. 12 shows an example of the operation of the gNB 1 for UL scheduling. In step 1201, a UL scheduler of the gNB 1 determines the allocation of frequency and time resources for the upcoming (or current) PUxCH (or UL-DMRS) transmission by the UE 2, taking into account the previous allocation of PUxCH (or UL-DMRS) transmission resources to that UE 2, along with other parameters and scheduling criteria. As mentioned above, UL-DMRS is transmitted concurrently with PUxCH using frequency multiplexing. Therefore, the frequency and time resources for PUxCH transmission contain the frequency and time resources for UL-DMRS transmission.

[0084] In step 1202, the UL scheduler of the gNB 1 provides the determined PUxCH (or UL-DMRS) transmission resource allocation to a controller of the gNB 1. The controller selects one of a plurality of channel estimates for use in calculating at least one of a UL beamforming weight and a DL beamforming weight, as described in the first example embodiment. This controller may be the controller 701 in Fig. 7. This controller may be the controller 601 in Fig. 6.

[0085] The UL scheduler of the gNB 1 may determine the PUxCH transmission resource allocation in step 1201 as follows. The UL scheduler preferentially selects, as the upcoming PUxCH (or UL-DMRS) transmission resources, resources that overlap with the previous PDxCH transmission resources in the frequency domain. More specifically, if there are multiple PUxCH resource allocation candidates that meet the PUxCH scheduling criteria, conditions, or metrics, the UL scheduler may select a PUxCH resource allocation candidate that maximizes the frequency overlap between the previous PDxCH resources and the upcoming PUxCH resources. For example, if there are two PUxCH resource allocation pattern candidates #1 and #2 as shown in Fig. 13, the UL scheduler may select PUxCH resource allocation pattern candidate #2, which has a greater frequency overlap between successive PUxCH transmission resources.

[0086] The UL scheduling described with reference to Fig. 12 helps to maximize the overlap in the frequency domain between the resources to be allocated for the upcoming PUxCH (or UL-DMRS) transmission by the UE 2 and the resources of the past PDxCH transmission by that UE 2. Accordingly, such overlap between the frequency allocations of consecutive PUxCH (or UL-DMRS) resource will enable obtaining higher reliability in UL-DMRS-based channel estimation. More specifically, since the overlapped frequency resource is estimated repeatedly over consecutive PUxCH (or UL-DMRS) transmissions, thus the probability of error in channel estimation can be reduced, and thus the reliability of channel estimation can be improved. Such improved reliability of channel estimation can result in better beamforming performance and higher throughput in uplink beamforming or downlink beamforming.

[0087] Fig. 13 shows an example where two resource allocation pattern candidates of PUxCH resource allocation is shown. In Candidate #1, the consecutive PUxCH resource allocations have minimal or no overlap in frequency domain. In contrast, the Candidate #2 has a greater overlap between the consecutive PUxCH resource allocations in frequency domain. Thus, as explained earlier, channel estimation on a same resource block (overlapped resource block) may be performed repeatedly over different time-slots. This can help in combining the channel estimates of the overlapped resource blocks to obtain an averaged estimate which can help in reducing channel estimation error in some examples. If there are multiple such PUxCH resource allocation candidates that meet the PUxCH scheduling criteria, conditions, or metrics, the UL scheduler may select a PUxCH resource allocation candidate that maximizes the frequency overlap between the consecutive PUxCH resource allocations in frequency domain. Thus, in the example in Fig. 13, the PUxCH resource allocation pattern candidate #2 may be selected by the UL scheduler. In some examples, the selection of candidate #2 (in Fig. 13) may necessitate change of scheduling criteria, conditions, or metrics. The improved UL-DMRS-based channel estimate may benefit at least one of UL beamforming and DL beamforming, or both.

[0088] Fig. 14 shows an example of the operation of the gNB 1 for UL scheduling. In step 1401, a UL scheduler of the gNB 1 determines the allocation of frequency and time resources for the upcoming (or current) PUxCH transmission by the UE 2, taking into account the previous or future allocation of SRS transmission resources to that UE 2, along with other parameters and scheduling criteria.

[0089] In step 1402, the UL scheduler of the gNB 1 provides the determined PUxCH transmission resource allocation to a controller of the gNB 1. The controller selects one of a plurality of channel estimates for use in calculating at least one of UL beamforming weights and DL beamforming weights, as described in the first example embodiment. This controller may be the controller 701 in Fig. 7. This controller may be the controller 601 in Fig. 6.

[0090] The UL scheduler of the gNB 1 may determine the PUxCH transmission resource allocation in step 1401 as follows. The UL scheduler preferentially selects, as the upcoming PUxCH transmission resources, resources that overlap with the previous or future SRS transmission resources in the frequency domain. More specifically, if there are multiple PUxCH resource allocation candidates that meet the PUxCH scheduling criteria, conditions, or metrics, the UL scheduler may select a PUxCH resource allocation candidate that maximizes the frequency overlap between the SRS resources and the upcoming PUxCH resources. For example, if there are two PUxCH resource allocation pattern candidates #1 and #2 as shown in Fig. 15, the UL scheduler may select PUxCH resource allocation pattern candidate #2, which has a greater frequency overlap with the SRS resources.

[0091] The UL scheduling described with reference to Fig. 14 helps to maximize the overlap in the frequency domain between the resources to be allocated for the upcoming PUxCH transmission by the UE 2 and the resources of the past or future SRS transmission by that UE 2. Accordingly, this can increase the chances of selecting SRS-based channel estimates for use in UL beamforming weight calculations in the channel estimate selection explained in the first example embodiment. Also, the channel estimate used for UL beamforming can be obtained by an appropriate combination (for example, a linear combination) of SRS-based channel estimate and UL-DMRS-based channel estimate since the channel estimation in an overlapped frequency resource has been performed by both SRS and UL-DMRS which can increase the reliability or accuracy of channel estimation. In some examples, the UL-DMRS may be used for noise whitening, while channel estimation may be performed by SRS. The higher accuracy channel estimate obtained by at least one of the above methods can result in improved beamforming performance and higher throughput. Additionally, the increased accuracy of channel estimation can also be exploited in enhancing the downlink beamforming performance and associated throughput. In that case, scheduling the downlink transmission with maximum overlap with the frequency resources that have such accuracy channel estimation will help to improve the throughput and beamforming performance in downlink.

[0092] The above example is further explained using Fig. 15. Two PUxCH resource allocation pattern candidates are shown in Fig. 15: Candidate #1 and Candidate #2. In Candidate #1, there is minimal or no overlap between the SRS resources and PUxCH resources in the frequency domain. In contrast, Candidate #2 shows relatively higher overlap between the SRS resources and PUxCH resources in the frequency domain. If there are multiple such PUxCH resource allocation candidates that meet the PUxCH scheduling criteria, conditions, or metrics, the UL scheduler may select a PUxCH resource allocation candidate that maximizes the frequency overlap between the PUxCH resource and SRS resource in frequency domain. Thus, in the example in Fig. 15, the PUxCH resource allocation pattern candidate #2 may be selected by the UL scheduler. In some examples, the selection of candidate #2 (in Fig. 15) may necessitate change of scheduling criteria, conditions, or metrics. The method described in Fig. 15 may benefit at least one of UL beamforming and DL beamforming, or both.

[0093] Other Example Embodiments 　　The above example embodiments describe cases where one or both of the first channel estimate based on the first type of reference signal and the second channel estimate based on the second type of reference signal are selected for the DL or UL beamforming weight calculation. In addition, the above example embodiments describe a specific case where the first channel estimate is an SRS-based channel estimate and the second channel estimate is a UL-DMRS-based channel estimate. These may be modified as appropriate. In some implementations, other combinations of reference signal types may be used, such as SRS and a phase tracking reference signal (PTRS). The gNB 1 may select one or both of an SRS-based channel estimate and a PTRS-based channel estimate for the DL or UL beamforming weight calculation. Alternatively, the gNB 1 may use a PTRS-based channel estimate in addition to an SRS-based channel estimate and a UL-DMRS-based channel estimate for the DL or UL beamforming weight calculation. The gNB 1 may select one or any combination of an SRS-based channel estimate, a UL-DMRS-based channel estimate, and a PTRS-based channel estimate to use for the DL or UL beamforming weight calculation.

[0094] In the above example embodiments, the gNB 1 may further consider other information for selecting a channel estimate to be used for the DL or UL beamforming weight calculation. For example, the gNB 1 may receive, from the UE 2, beam information based on a Synchronization Signal (SS) / Physical Broadcast Channel (PBCH) block (SSB), and may consider this information in the selection of a channel estimate to be used for the DL or UL beamforming weight calculation. Additionally or alternatively, the gNB 1 may consider a Channel State Information (CSI) feedback received from the UE 2 in the selection of a channel estimate to be used for the DL or UL beamforming weight calculation. Such information may also be used as an input to the DL and / or UL scheduler as described in the second example embodiment.

[0095] In the above example embodiments, machine learning techniques may be used to optimize the selection of a channel estimate to be used for the DL or UL beamforming weight calculation. The gNB 1 may select a channel estimate to be used for the DL or UL beamforming weight calculation by performing inference on a trained artificial intelligence or machine learning model.

[0096] Examples of configurations of the gNB-CU 10, the gNB-DUs 21 and 22, and the TRPs 31 to 35 according to the plurality of example embodiments described above are provided below. Fig. 16 is a block diagram of an example configuration of the gNB-DU 21. The configurations of the gNB-CU 10 and the gNB-DU 22 may also be similar to those shown in Fig. 16. Referring to Fig. 16, the gNB-DU 21 includes a network interface 1601, a processor 1602, and a memory 1603. The network interface 1601 is used to communicate with network nodes (e.g., the gNB-DU and one or more TRPs). The network interface 1601 may include a plurality of interfaces. The network interface 1601 may include a fiber optic interface for CU-DU communication and a network interface compliant with the IEEE 802.3 series. The network interface 1601 may include a fronthaul interface for DU-to-TRP communication.

[0097] The processor 1602 may include a plurality of processors. The processor 1602 performs digital baseband signal processing (or data plane processing) and control plane processing for wireless communications. For example, the processor 1602 may include a modem processor (e.g., Digital Signal Processor (DSP)) for digital baseband signal processing and a protocol stack processor (e.g., Central Processing Unit (CPU) or Micro Processing Unit (MPU)) for control plane processing. The digital baseband signal processing may include RLC, MAC, and PHY layer signal processing. The control plane processing may include processing of MAC CEs and DCIs. The processor 1602 may include a digital beamformer module for beamforming. The digital beamformer module may include a MIMO encoder and precoder.

[0098] The memory 1603 is composed of a combination of volatile and non-volatile memory. The volatile memory can be, for example, a Static Random Access Memory (SRAM), a Dynamic RAM (DRAM), or a combination thereof. The non-volatile memory can be, for example, a Mask Read Only Memory (MROM), an Electrically Erasable Programmable ROM (EEPROM), a flash memory, a hard disk drive, or any combination thereof. The memory 1603 may include storage that is remote from the processor 1602. In this case, the processor 1602 may access the memory 1603 through the network interface 1601 or another I / O interface.

[0099] The memory 1603 may store one or more software modules (or computer programs) 1604 containing a set of instructions and data for processing by the gNB-DU 21 described in the plurality of example embodiments described above. In some implementations, the processor 1602 may be configured to load and execute the one or more software modules 1604 from the memory 1603, thereby performing the processing of the gNB-DU 21 described in the example embodiments described above.

[0100] Fig. 17 shows a block diagram of the TRPs 31 to 35. Referring to Fig. 17, each of the TRPs 31 to 35 includes an RF transceiver 1701, a network interface 1703, a processor 1704, and memory 1705. The RF transceiver 1701 performs analog RF signal processing to communicate with the UEs 2. The RF transceiver 1701 may include a plurality of transceivers. The RF transceiver 1701 is coupled to an antenna array 1702 and the processor 1704. The RF transceiver 1701 receives modulated symbol data from the processor 1704, generates a transmit RF signal, and provides the transmit RF signal to the antenna array 1702. The RF transceiver 1701 also generates a baseband receive signal based on a receive RF signal received by the antenna array 1702, and provides the receive baseband signal to the processor 1704. The RF transceiver 1701 may include analog beamformer circuitry for beamforming. For example, the analog beamformer circuitry may include a plurality of phase shifters and a plurality of power amplifiers.

[0101] The network interface 1703 is used to communicate with network nodes (e.g., DUs, other TRPs). The network interface 1703 may include a plurality of interfaces. For example, the network interface 1703 may include a fiber optic interface for DU-to-TRP communication (and inter-TRP communication) and an IEEE 802.3 series compliant network interface.

[0102] The processor 1704 may include one or more processors. The processor 1704 may include a DFE and a controller. The DFE performs lower PHY layer signal processing and digital radio signal processing.

[0103] Memory 1705 is composed of a combination of volatile and non-volatile memory. The volatile memory can be, for example, an SRAM, a DRAM, or a combination thereof. The non-volatile memory can be, for example, MROM, EEPROM, flash memory, a hard disk drive, or any combination thereof. The memory 1705 may include storage that is remote from the processor 1704. In this case, the processor 1704 may access the memory 1705 through the network interface 1703 or another I / O interface.

[0104] The memory 1705 may store one or more software modules (or computer programs) 1706 containing a set of instructions and data for performing at least some of the processing by the TRPs 31 to 35 described in the plurality of embodiments described above. In some implementations, the processor 1704 may be configured to load and execute the software module 1706 from the memory 1705, thereby performing at least some of the processing by the TRPs 31 to 35 described in the example embodiments described above.

[0105] As explained using Figures 16 and 17, each of the processors of the gNB-CU 10, the gNB-DUs 21 and 22, and the TRPs 31 to 35 according to the example embodiments described above is capable of executing one or more programs containing a set of instructions for causing a computer to perform the algorithm described with reference to the drawings. The program(s) contains a set of instructions (or software codes) that, when loaded into a computer, causes the computer to perform one or more of the functions described in the example embodiments. The program(s) may be stored in a non-transitory computer readable medium or a tangible storage medium. By way of example, and not limitation, non-transitory computer readable media or tangible storage media can include a random-access memory (RAM), a read-only memory (ROM), a flash memory, a solid-state drive (SSD) or other memory technologies, CD-ROM, digital versatile disk (DVD), Blu-ray (registered mark) disc or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices. The program(s) may be transmitted on a transitory computer readable medium or a communication medium. By way of example, and not limitation, transitory computer readable media or communication media can include electrical, optical, acoustical, or other form of propagated signals.

[0106] Fig. 18 shows an example of a block diagram of one example embodiment. Please note that Fig. 18 shows only some essential components or features, and does not include all components in an exhaustive manner. This block diagram omits the UL beamforming. The SRS-based channel estimate 1801 obtained from the SRS received at all antennas of the base station (BS) (e.g., gNB 1) is fed to a unified channel estimator 1803. Furthermore, the UL-DMRS-based channel estimate 1802 is also sent to the unified channel estimator 1803, as well as to the UL MIMO receiver 1804. The controller 1805, makes a decision on how the unified channel estimate 1809 should be constructed from the SRS-based channel estimate 1801 and UL-DMRS-based channel estimate 1802. As explained earlier, the decision is made by the controller 1805 by seeking input from an SRS scheduler 1806, PUxCH scheduler 1807, and PDxCH scheduler 1808. The unified channel estimate 1809 obtained based on the instruction of the controller 1805 is then sent to the DL beamforming (BF) block 1810 where it is used for beamforming in DL transmission. There can be other examples where the UL MIMO receiver 1804 also makes use of the unified channel estimate 1809 instead of the UL-DMRS-based channel estimate 1802 only. Furthermore, although it is shown that the DL BF block 1810 has input from both SRS-based channel estimator 1811 and unified channel estimator 1803, it may be able to choose between them appropriately.

[0107] Fig. 19 shows an example of a block diagram of another example embodiment. Please note that Fig. 19 shows only some essential components or features, and does not include all components in an exhaustive manner. This block diagram includes both the UL beamforming block 1911 and the DL beamforming block 1910. The SRS-based channel estimate 1901 obtained from the SRS received at all antennas of the BS (e.g., gNB 1) is fed to a unified channel estimator 1904. Furthermore, the UL-DMRS-based channel estimation 1902 is performed before the UL BF operation 1911. Performing UL DMRS-based channel estimation 1902 before UL BF 1911 does not reduce the dimension, and thus the dimension of the channel estimate is preserved to the number of antennas. Such a technique may have very good accuracy in channel estimation and may be relatively robust to channel aging. However, it may cause high complexity to the RU. Anyway, the UL-DMRS-based channel estimate 1903 thus obtained before UL BF 1911 is sent to the unified channel estimator block 1904. The controller 1905, makes a decision on how the unified channel estimate 1909 should be constructed from the SRS-based channel estimate 1901 and UL-DMRS-based channel estimate 1903. As explained earlier, the decision is made by the controller by seeking input from an SRS scheduler 1906, PUxCH scheduler 1907, and PDxCH scheduler 1908. The unified channel estimate 1909 obtained based on the instruction of the controller 1905 is then sent to the DL BF block 1910 as well as to the UL BF block 1911. There can be other examples where the UL MIMO receiver 1912 also makes use of the unified channel estimate 1909 instead of the UL-DMRS-based channel estimate only. Furthermore, although it is shown that the DL BF block 1910 has input from both SRS-based channel estimator 1913 and unified channel estimator 1904, it may be able to choose between them appropriately. Similarly, although it is shown that the UL BF block 1911 has input from both UL-DMRS-based channel estimator 1902 and unified channel estimator 1904, it may be able to choose between them appropriately.

[0108] Fig. 20 shows an example of a block diagram of another example embodiment. Please note that Fig. 20 shows only some essential components or features, and does not include all components in an exhaustive manner. This block diagram includes both the UL beamforming block 2011 and the DL beamforming block 2010. The SRS-based channel estimate 2001 obtained from the SRS received at all antennas of the BS (e.g., gNB 1) is fed to a unified channel estimator 2004. Furthermore, the UL-DMRS-based channel estimation 2002 is performed after the UL BF operation 2011. Performing UL DMRS-based channel estimation 2002 after UL BF 2011 reduces the dimension of the channel estimate from the number of antennas to the number of multiplexed beams. Such a technique may compromise on the accuracy in channel estimation as compared to the example discussed in Fig. 19, but it may reduce the complexity in the RU. Thus, a trade-off between performance and complexity may be observed in different implementations depending on whether the UL-DMRS-based channel estimation 2002 is performed before or after the UL BF operation 2011. Anyway, the UL-DMRS-based channel estimate 2003 thus obtained after UL BF 2011 is sent to the unified channel estimator block 2004. The controller 2005 makes a decision on how the unified channel estimate 2009 should be constructed from the SRS-based channel estimate 2001 and UL-DMRS-based channel estimate 2003. As explained earlier, the decision is made by the controller 2005 by seeking input from an SRS scheduler 2006, PUxCH scheduler 2007, and PDxCH scheduler 2008. The unified channel estimate 2009 obtained based on the instruction of the controller 2005 is then sent to the DL BF block 2010 as well as to the UL BF block 2011. There can be other examples where the UL MIMO receiver 2012 also makes use of the unified channel estimate 2009 instead of the UL-DMRS-based channel estimate 2003 only. Furthermore, although it is shown that the DL BF block 2010 has input from both SRS-based channel estimator 2013 and unified channel estimator 2004, it may be able to choose between them appropriately.

[0109] Fig. 21 shows an example of a modified DL scheduler 2101, according to an example embodiment. In this example, it is shown that the DL scheduler 2101 may take inputs such as channel state information (CSI), quality of service (QoS) requirements, UE capabilities (e.g., supported modulation, MIMO configuration etc.), hybrid automatic repeat request (HARQ) feedback information (for e.g., success / failure of previous transmission), mobility information (for e.g., speed and trajectory of a UE), network load and interference (e.g., overall network congestion, inter-cell interference etc.), traffic patterns and buffer status (e.g., type and volume of traffic, waiting data etc.) etc. In some examples, some other information or parameters may also be considered as input to the DL scheduler 2101, and some of the parameters listed above may not be used. In an example, the past PUxCH schedule 2102 may be fed as input to the DL scheduler 2101. The DL scheduler 2101 may compute scheduling metrics corresponding to different UEs, and may output the UEs to be scheduled, time / frequency resource allocation, modulation and coding scheme (MCS) for each allocation, MIMO configuration (number of layers, precoding matrix etc.), transmission power level (e.g. UL), HARQ process information etc. In another example, one or more of the PUxCH schedule, PDxCH schedule, and the SRS schedule may also be used as input to the DL scheduler 2101. In a similar fashion, the UL scheduler may also be modified in some examples.

[0110] The above-described example embodiments are merely examples of applications of the technical ideas obtained by the inventor. These technical ideas are not limited to the above-described example embodiments and various modifications can be made thereto.

[0111] For example, the whole or part of the example embodiments disclosed above can be described as, but not limited to, the following supplementary notes. Of course, some or all of the elements (e.g., configurations and functionalities) described in the Supplementary Notes directed to an apparatus may also be described as Supplementary Notes directed to methods and programs. For example, some or all of the elements listed in Supplementary Notes 2-17 that depend on Supplementary Note 1 may also be listed as Supplementary Notes that depend on Supplementary Note 35 with the same dependency as Supplementary Notes 2-17. Some or all of the elements described in a Supplementary Note may be applicable to various hardware, software, storage for storing software, systems, and methods.

[0112] (Supplementary Note 1) 　　A communication apparatus comprising: 　　means for selecting one of a plurality of channel estimates for use in downlink beamforming for downlink transmission to another communication apparatus, or uplink beamforming for uplink reception from the another communication apparatus, at a given frequency and time resource, 　　wherein the plurality of channel estimates includes at least two of: a first channel estimate based on a first type of uplink reference signal transmitted by the another communication apparatus; a second channel estimate based on a second type of uplink reference signal transmitted by the another communication apparatus; and a third channel estimate calculated from both the first channel estimate and the second channel estimate. (Supplementary Note 2) 　　The communication apparatus according to Supplementary Note 1, wherein the means for selecting is configured to determine which of the plurality of channel estimates to use based on a first frequency and time resource on which the first type of uplink reference signal was previously transmitted, a second frequency and time resource on which the second type of uplink reference signal was previously transmitted, and the given frequency and time resource on which the downlink beamforming or the uplink beamforming is to be performed. (Supplementary Note 3) 　　The communication apparatus according to Supplementary Note 2, wherein the means for selecting is configured to consider whether there is an overlap in a frequency domain between the given frequency and time resource and the first frequency and time resource, and whether there is an overlap in a frequency domain between the given frequency and time resource and the second frequency and time resource. (Supplementary Note 4) 　　The communication apparatus according to any one of Supplementary Notes 1 to 3, wherein the means for selecting is configured to select a more recent one of the first channel estimate and the second channel estimate to be used for the downlink beamforming or the uplink beamforming. (Supplementary Note 5) 　　The communication apparatus according to any one of Supplementary Notes 1 to 3, wherein the means for selecting is configured to select a more reliable one of the first channel estimate and the second channel estimate to be used for the downlink beamforming or the uplink beamforming. (Supplementary Note 6) 　　The communication apparatus according to any one of Supplementary Notes 1 to 5, wherein 　　the first type of uplink reference signal is transmitted in a periodic, aperiodic, or semi-persistent manner according to a configuration by the communication apparatus, and 　　the second type of uplink reference signal is used to demodulate an uplink data channel or an uplink control channel and is transmitted in a same time domain resource as the uplink data channel or the uplink control channel. (Supplementary Note 7) 　　The communication apparatus according to any one of Supplementary Notes 1 to 6, wherein 　　the first type of uplink reference signal is a sounding reference signal (SRS), and 　　the second type of uplink reference signal is an uplink demodulation reference signal (DMRS). (Supplementary Note 8) 　　The communication apparatus according to Supplementary Note 6 or 7, further comprising means for determining an allocation of downlink frequency and time resources for downlink transmission to the another communication apparatus while considering a previous allocation of transmission resources of the second type of uplink reference signal to the another communication apparatus. (Supplementary Note 9) 　　The communication apparatus according to Supplementary Note 8, wherein the means for determining is configured to preferentially select, as the downlink frequency and time resources, resources that overlap in a frequency domain with the transmission resources of the second type of uplink reference signal. (Supplementary Note 10) 　　The communication apparatus according to Supplementary Note 6 or 7, further comprising means for determining an allocation of uplink frequency and time resources for uplink transmission by the another communication apparatus, including transmission of the second type of uplink reference signal, while considering an allocation of downlink frequency and time resources for future downlink transmission to the other apparatus. (Supplementary Note 11) 　　The communication apparatus according to Supplementary Note 10, wherein the means for determining is configured to preferentially select, as the uplink frequency and time resources, resources that overlap in a frequency domain with the downlink frequency and time resources. (Supplementary Note 12) 　　The communication apparatus according to Supplementary Note 6 or 7, further comprising means for determining an allocation of uplink frequency and time resources for uplink transmission by the another apparatus while considering a previous allocation of transmission resources of the second type of uplink reference signal to the another communication apparatus. (Supplementary Note 13) 　　The communication apparatus according to Supplementary Note 12, wherein the means for determining is configured to preferentially select, as the uplink frequency and time resources, resources that overlap in a frequency domain with the transmission resources of the second type of uplink reference signal. (Supplementary Note 14) 　　The communication apparatus according to Supplementary Note 6 or 7, further comprising means for determining an allocation of uplink frequency and time resources for uplink transmission by the another apparatus while considering a previous or future allocation of transmission resources of the first type of uplink reference signal to the another communication apparatus. (Supplementary Note 15) 　　The communication apparatus according to Supplementary Note 14, wherein the means for determining is configured to preferentially select, as the uplink frequency and time resources, resources that overlap in a frequency domain with the transmission resources of the first type of uplink reference signal. (Supplementary Note 16) 　　The communication apparatus according to any one of Supplementary Notes 1 to 15, further comprising means for applying the selected channel estimate to the downlink beamforming or the uplink beamforming. (Supplementary Note 17) 　　The communication apparatus according to any one of Supplementary Notes 1 to 16, further comprising means for performing the downlink beamforming or the uplink beamforming using beamforming weights calculated based on the selected channel estimate. (Supplementary Note 18) 　　A method performed by a communication apparatus, the method comprising: 　　selecting one of a plurality of channel estimates for use in downlink beamforming for downlink transmission to another communication apparatus, or uplink beamforming for uplink reception from the another communication apparatus, at a given frequency and time resource, 　　wherein the plurality of channel estimates includes at least two of: a first channel estimate based on a first type of uplink reference signal transmitted by the another communication apparatus; a second channel estimate based on a second type of uplink reference signal transmitted by the another communication apparatus; and a third channel estimate calculated from both the first channel estimate and the second channel estimate. (Supplementary Note 19) 　　The method according to Supplementary Note 18, wherein the selecting comprises determining which of the plurality of channel estimates to use based on a first frequency and time resource on which the first type of uplink reference signal was previously transmitted, a second frequency and time resource on which the second type of uplink reference signal was previously transmitted, and the given frequency and time resource on which the downlink beamforming or the uplink beamforming is to be performed. (Supplementary Note 20) 　　The method according to Supplementary Note 19, wherein the selecting comprises considering whether there is an overlap in a frequency domain between the given frequency and time resource and the first frequency and time resource, and whether there is an overlap in a frequency domain between the given frequency and time resource and the second frequency and time resource. (Supplementary Note 21) 　　The method according to any one of Supplementary Notes 18 to 20, wherein the selecting comprises selecting a more recent one of the first channel estimate and the second channel estimate to be used for the downlink beamforming or the uplink beamforming. (Supplementary Note 22) 　　The method according to any one of Supplementary Notes 18 to 20, wherein the selecting comprises selecting a more reliable one of the first channel estimate and the second channel estimate to be used for the downlink beamforming or the uplink beamforming. (Supplementary Note 23) 　　The method according to any one of Supplementary Notes 18 to 22, wherein 　　the first type of uplink reference signal is transmitted in a periodic, aperiodic, or semi-persistent manner according to a configuration by the communication apparatus, and 　　the second type of uplink reference signal is used to demodulate an uplink data channel or an uplink control channel and is transmitted in a same time domain resource as the uplink data channel or the uplink control channel. (Supplementary Note 24) 　　The method according to any one of Supplementary Notes 18 to 23, wherein 　　the first type of uplink reference signal is a sounding reference signal (SRS), and 　　the second type of uplink reference signal is an uplink demodulation reference signal (DMRS). (Supplementary Note 25) 　　The method according to Supplementary Note 23 or 24, further comprising determining an allocation of downlink frequency and time resources for downlink transmission to the another communication apparatus while considering a previous allocation of transmission resources of the second type of uplink reference signal to the another communication apparatus. (Supplementary Note 26) 　　The method according to Supplementary Note 25, wherein the determining the allocation of the downlink frequency and time resources comprises preferentially selecting, as the downlink frequency and time resources, resources that overlap in a frequency domain with the transmission resources of the second type of uplink reference signal. (Supplementary Note 27) 　　The method according to Supplementary Note 23 or 24, further comprising determining an allocation of uplink frequency and time resources for uplink transmission by the another communication apparatus, including transmission of the second type of uplink reference signal, while considering an allocation of downlink frequency and time resources for future downlink transmission to the other apparatus. (Supplementary Note 28) 　　The method according to Supplementary Note 27, wherein the determining the allocation of the uplink frequency and time resources comprises preferentially selecting, as the uplink frequency and time resources, resources that overlap in a frequency domain with the downlink frequency and time resources. (Supplementary Note 29) 　　The method according to Supplementary Note 23 or 24, further comprising determining an allocation of uplink frequency and time resources for uplink transmission by the another apparatus while considering a previous allocation of transmission resources of the second type of uplink reference signal to the another communication apparatus. (Supplementary Note 30) 　　The method according to Supplementary Note 29, wherein the determining the allocation of the uplink frequency and time resources comprises preferentially selecting, as the uplink frequency and time resources, resources that overlap in a frequency domain with the transmission resources of the second type of uplink reference signal. (Supplementary Note 31) 　　The method according to Supplementary Note 23 or 24, further comprising determining an allocation of uplink frequency and time resources for uplink transmission by the another apparatus while considering a previous or future allocation of transmission resources of the first type of uplink reference signal to the another communication apparatus. (Supplementary Note 32) 　　The method according to Supplementary Note 31, wherein the determining the allocation of the uplink frequency and time resources comprises preferentially selecting, as the uplink frequency and time resources, resources that overlap in a frequency domain with the transmission resources of the first type of uplink reference signal. (Supplementary Note 33) 　　The method according to any one of Supplementary Notes 18 to 32, further comprising applying the selected channel estimate to the downlink beamforming or the uplink beamforming. (Supplementary Note 34) 　　The method according to any one of Supplementary Notes 18 to 33, further comprising performing the downlink beamforming or the uplink beamforming using beamforming weights calculated based on the selected channel estimate. (Supplementary Note 35) 　　A program for causing a computer to perform a method for a communication apparatus, the method comprising: 　　selecting one of a plurality of channel estimates for use in downlink beamforming for downlink transmission to another communication apparatus, or uplink beamforming for uplink reception from the another communication apparatus, at a given frequency and time resource, 　　wherein the plurality of channel estimates includes at least two of: a first channel estimate based on a first type of uplink reference signal transmitted by the another communication apparatus; a second channel estimate based on a second type of uplink reference signal transmitted by the another communication apparatus; and a third channel estimate calculated from both the first channel estimate and the second channel estimate.

[0113] This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2024-176902, filed on October 9, 2024, the disclosure of which is incorporated herein in its entirety by reference.

[0114] 1　　gNB 2　　UE 3　　Radio Coverage Area 10　　gNB-CU 21、22　　gNB-DU 31、32、33、34、35　　TRP 51、52、53　　Cell 601　　Controller 602　　Unified Channel Estimator 603　　DL Beamforming Weight Calculator 701　　Controller 702　　Unified Channel Estimator 703　　UL Beamforming Weight Calculator 1602　　Processor 1603　　Memory 1604　　Modules 1704　　Processor 1705　　Memory 1706　　Modules

Claims

A communication apparatus comprising:　　means for selecting one of a plurality of channel estimates for use in downlink beamforming for downlink transmission to another communication apparatus, or uplink beamforming for uplink reception from the another communication apparatus, at a given frequency and time resource,　　wherein the plurality of channel estimates includes at least two of: a first channel estimate based on a first type of uplink reference signal transmitted by the another communication apparatus; a second channel estimate based on a second type of uplink reference signal transmitted by the another communication apparatus; and a third channel estimate calculated from both the first channel estimate and the second channel estimate.　　The communication apparatus according to claim 1, wherein the means for selecting is configured to determine which of the plurality of channel estimates to use based on a first frequency and time resource on which the first type of uplink reference signal was previously transmitted, a second frequency and time resource on which the second type of uplink reference signal was previously transmitted, and the given frequency and time resource on which the downlink beamforming or the uplink beamforming is to be performed.　　The communication apparatus according to claim 2, wherein the means for selecting is configured to consider whether there is an overlap in a frequency domain between the given frequency and time resource and the first frequency and time resource, and whether there is an overlap in a frequency domain between the given frequency and time resource and the second frequency and time resource.　　The communication apparatus according to any one of claims 1 to 3, wherein the means for selecting is configured to select a more recent one of the first channel estimate and the second channel estimate to be used for the downlink beamforming or the uplink beamforming.　　The communication apparatus according to any one of claims 1 to 3, wherein the means for selecting is configured to select a more reliable one of the first channel estimate and the second channel estimate to be used for the downlink beamforming or the uplink beamforming.　　The communication apparatus according to any one of claims 1 to 5, wherein　　the first type of uplink reference signal is transmitted in a periodic, aperiodic, or semi-persistent manner according to a configuration by the communication apparatus, and　　the second type of uplink reference signal is used to demodulate an uplink data channel or an uplink control channel and is transmitted in a same time domain resource as the uplink data channel or the uplink control channel.　　The communication apparatus according to any one of claims 1 to 6, wherein　　the first type of uplink reference signal is a sounding reference signal (SRS), and　　the second type of uplink reference signal is an uplink demodulation reference signal (DMRS).　　The communication apparatus according to claim 6 or 7, further comprising means for determining an allocation of downlink frequency and time resources for downlink transmission to the another communication apparatus while considering a previous allocation of transmission resources of the second type of uplink reference signal to the another communication apparatus.　　The communication apparatus according to claim 8, wherein the means for determining is configured to preferentially select, as the downlink frequency and time resources, resources that overlap in a frequency domain with the transmission resources of the second type of uplink reference signal.　　The communication apparatus according to claim 6 or 7, further comprising means for determining an allocation of uplink frequency and time resources for uplink transmission by the another communication apparatus, including transmission of the second type of uplink reference signal, while considering an allocation of downlink frequency and time resources for future downlink transmission to the other apparatus.　　The communication apparatus according to claim 10, wherein the means for determining is configured to preferentially select, as the uplink frequency and time resources, resources that overlap in a frequency domain with the downlink frequency and time resources.　　The communication apparatus according to claim 6 or 7, further comprising means for determining an allocation of uplink frequency and time resources for uplink transmission by the another apparatus while considering a previous allocation of transmission resources of the second type of uplink reference signal to the another communication apparatus.　　The communication apparatus according to claim 12, wherein the means for determining is configured to preferentially select, as the uplink frequency and time resources, resources that overlap in a frequency domain with the transmission resources of the second type of uplink reference signal.　　The communication apparatus according to claim 6 or 7, further comprising means for determining an allocation of uplink frequency and time resources for uplink transmission by the another apparatus while considering a previous or future allocation of transmission resources of the first type of uplink reference signal to the another communication apparatus.　　The communication apparatus according to claim 14, wherein the means for determining is configured to preferentially select, as the uplink frequency and time resources, resources that overlap in a frequency domain with the transmission resources of the first type of uplink reference signal.　　The communication apparatus according to any one of claims 1 to 15, further comprising means for applying the selected channel estimate to the downlink beamforming or the uplink beamforming.　　The communication apparatus according to any one of claims 1 to 16, further comprising means for performing the downlink beamforming or the uplink beamforming using beamforming weights calculated based on the selected channel estimate.　　A method performed by a communication apparatus, the method comprising:　　selecting one of a plurality of channel estimates for use in downlink beamforming for downlink transmission to another communication apparatus, or uplink beamforming for uplink reception from the another communication apparatus, at a given frequency and time resource,　　wherein the plurality of channel estimates includes at least two of: a first channel estimate based on a first type of uplink reference signal transmitted by the another communication apparatus; a second channel estimate based on a second type of uplink reference signal transmitted by the another communication apparatus; and a third channel estimate calculated from both the first channel estimate and the second channel estimate.　　The method according to claim 18, wherein the selecting comprises determining which of the plurality of channel estimates to use based on a first frequency and time resource on which the first type of uplink reference signal was previously transmitted, a second frequency and time resource on which the second type of uplink reference signal was previously transmitted, and the given frequency and time resource on which the downlink beamforming or the uplink beamforming is to be performed.　　A program for causing a computer to perform a method for a communication apparatus, the method comprising:　　selecting one of a plurality of channel estimates for use in downlink beamforming for downlink transmission to another communication apparatus, or uplink beamforming for uplink reception from the another communication apparatus, at a given frequency and time resource,　　wherein the plurality of channel estimates includes at least two of: a first channel estimate based on a first type of uplink reference signal transmitted by the another communication apparatus; a second channel estimate based on a second type of uplink reference signal transmitted by the another communication apparatus; and a third channel estimate calculated from both the first channel estimate and the second channel estimate.

Images