WO2019037745A1

WO2019037745A1 - Method and apparatus for determining channel state information

Info

Publication number: WO2019037745A1
Application number: PCT/CN2018/101789
Authority: WO
Inventors: 孙欢; 宋暖; 李楠
Original assignee: 上海诺基亚贝尔股份有限公司
Priority date: 2017-08-24
Filing date: 2018-08-22
Publication date: 2019-02-28
Also published as: CN109428639B; CN109428639A

Abstract

Embodiments of the present invention provide a method and apparatus for determining channel state information (CSI), and a computer program product. A method implemented by a communication device running in a wireless communication system comprises: obtaining CSI of a channel between the communication device and a network device on the basis of a signal from the network device, wherein the channel comprises a first sub-channel and a second sub-channel; sending a reference signal to the network device to indicate information about CSI of the first sub-channel; determining, on the basis of the CSI of the first sub-channel and CSI of the second sub-channel, information about the CSI of the second sub-channel to be sent to the network device; and sending the determined information about the CSI of the second sub-channel to the network device. By means of the embodiments of the present invention, CSI precision obtained by a network device can be improved, and/or capacity of an uplink reference signal can be improved.

Description

Method and apparatus for determining channel state information

Cross-reference to related applications

The present application claims priority to Japanese Patent Application No. No. No. No. No. No. No. No. No.

Technical field

The present disclosure relates generally to the technical field of wireless communications, and in particular to a method, apparatus, and computer program product for determining channel state information (CSI) in a time division duplex (TDD) based wireless communication system.

Background technique

This section is intended to facilitate a better understanding of the present disclosure. Therefore, the content of this section should be read on this basis and should not be construed as an admission as to which of the prior art or which are not prior art.

In the wireless communication system, in order to support efficient transmission and reception, reduce interference, and the like, it is desirable to obtain information on the CSI of the communication channel on both the transmitting side and the receiving side.

In a 5th generation (5G) wireless communication system, also known as a new radio (NR) system, a multi-antenna or a multi-panel having a large-scale antenna is used at the transmission and reception point (TRP) side and the user side. With multiple antennas/multi-panels, TRP can simultaneously support multi-stream transmissions to multiple users. In order to effectively reduce multi-user interference by scheduling and/or precoding, it is necessary to obtain accurate downlink CSI for each user on the TRP side.

Summary of the invention

For different wireless communication systems, the TRP can obtain information of the downlink channel in different ways. For example, in a time division duplex (TDD) system, the TRP can utilize the reciprocity between the downlink channel and the uplink channel to obtain information of the downlink channel by measuring the corresponding uplink channel. In a frequency division duplex (FDD) system, the TRP can obtain information of the downlink channel through CSI feedback of each user. For a scheme based on CSI feedback based on FDD systems, since CSI is quantized before feedback to save uplink overhead, TRP cannot obtain high-accuracy CSI. If TRP uses quantized CSI for multi-user-multiple input multiple output (MU-MIMO) transmission and/or scheduling, severe multi-user interference can result, significantly limiting the performance of the system. Therefore, in the 5G NR system, the TDD mode has a higher priority because it can obtain higher CSI accuracy and thus obtain better performance. However, for TDD systems, there are some practical factors that will affect the accuracy of the available CSI, which in turn affects the performance of, for example, downlink MU-MIMO.

In the present disclosure, a new solution for determining CSI in a TDD system is proposed. Some embodiments may be used, for example, to improve CSI acquisition on the TRP side, and/or to enhance SRS capacity for an actual TDD system by utilizing partial reciprocity and limited feedback. Additional signaling for further enhancing the proposed solution is also provided in other embodiments.

It should be understood that although some embodiments of the present disclosure are described with reference to a 5G NR communication scenario, embodiments of the present disclosure are not limited to use in this scenario, but may be more broadly applied to any communication network, system in which similar problems exist. And the scene.

Other features and advantages of the embodiments of the present disclosure will be understood from the description of the accompanying drawings.

In a first aspect of the present disclosure, a method implemented at a communication device operating in a TDD wireless communication system is provided. The method includes obtaining CSI of a channel between a communication device and a network device based on a signal from a network device, wherein the channel includes a first subchannel and a second subchannel; transmitting a reference signal to the network device to indicate Information of the CSI of the subchannel; determining, based on the CSI of the first subchannel and the CSI of the second subchannel, information about the CSI of the second subchannel to be transmitted to the network device; and transmitting the determined second to the network device Information on the CSI of the subchannel.

In one embodiment, the communication device may obtain the CSI of the channel based on a CSI reference signal (CSI-RS) from the network device.

In another embodiment, the first subchannel and the second subchannel may be associated with a first subset and a second subset of antenna ports of the communication device, respectively. In a further embodiment, the communication device can transmit the reference signal to the network device through the first subset of antenna ports associated with the first subchannel.

In some embodiments, the communication device may determine information about CSI of the second subchannel to be transmitted to the network device by: obtaining a transmit covariance matrix of the first subchannel based on CSI of the first subchannel; a variance matrix and a common codebook for the second subchannel, determining a codebook specific to the communication device; selecting a codeword matching the CSI of the second subchannel from the determined codebook specific to the communication device; and the code The indication of the word is determined as information about the CSI of the second subchannel to be transmitted to the network device.

In another embodiment, the communication device may determine information about the CSI of the second subchannel to be transmitted to the network device by: obtaining the second subchannel based on the CSI of the first subchannel and the CSI of the second subchannel. And an in-phase matrix between the first subchannel; and determining the indication of the in-phase matrix as information about CSI of the second subchannel to be transmitted to the network device. In a further embodiment, the indication of the in-phase matrix may comprise an index of a codeword matched to an in-phase matrix selected from a codebook for an in-phase matrix, or a value of an element in the in-phase matrix.

In still another embodiment, a method of a communication device can also include transmitting, to the network device, an indication of at least one of: a CSI feedback capability of the communication device; and an antenna configuration state of the communication device.

In another embodiment, the method of communicating a device may further comprise receiving an indication from the network device of a type of CSI feedback to be used by the communication device.

In a second aspect of the present disclosure, a method implemented at a network device operating in a TDD wireless communication system is provided. The method includes transmitting, to a communication device, a signal for determining CSI of a channel between a communication device and a network device, wherein the channel includes a first subchannel and a second subchannel; receiving a reference signal from the communication device; based on the received Determining CSI of the first subchannel; receiving information about CSI of the second subchannel from the communication device, wherein the received information about CSI of the second subchannel is based on CSI and second of the first subchannel CSI of the subchannel; and determining CSI of the second subchannel based on the received information about the CSI of the second subchannel.

In an embodiment, the information about the CSI of the second subchannel received from the communication device may comprise an index of a codeword for the second subchannel, the codeword being from a communication device specific codebook; and the network device may pass the following Operation determining CSI of the second subchannel based on the received information about the CSI of the second subchannel: obtaining a transmit covariance matrix of the first subchannel based on CSI of the first subchannel; based on the transmit covariance matrix and the Determining a common codebook of the second subchannel, determining a codebook specific to the communication device; and determining a codeword for the second subchannel from the determined codebook based on the received index.

In another embodiment, the information about the CSI of the second subchannel received from the communication device may include an indication of an in-phase matrix between the second subchannel and the first subchannel; and the network device may pass the determined The CSI of a subchannel and the indication of the received in-phase matrix are used to obtain the CSI of the second subchannel.

In yet another embodiment, the network device can also send an indication of the type of CSI feedback to be used by the communication device to the communication device.

In another embodiment, the network device may also receive an indication of the CSI feedback capability of the communication device and/or an indication of an antenna configuration state of the communication device from the communication device.

In a third aspect of the present disclosure, a communication device operating in a wireless communication system is provided. The communication device includes a CSI obtaining unit, a reference signal transmitting unit, a feedback information determining unit, and a feedback unit. Wherein the CSI obtaining unit is configured to obtain CSI of a channel between the communication device and the network device based on a signal from the network device. The reference signal transmitting unit is configured to transmit a reference signal to the network device to indicate information about CSI of the first subchannel in the channel. The feedback information determining unit is configured to determine information about CSI to be transmitted to the network device regarding the second subchannel based on CSI of the first subchannel and CSI of the second subchannel in the channel, and the feedback unit is configured to be to the network The device transmits the determined information about the CSI of the second subchannel.

In one embodiment, the communication device may also optionally include an indication transmitting unit and/or a CSI type indication receiving unit. The indication transmitting unit is configured to transmit an indication of the CSI feedback capability of the communication device and/or an indication of an antenna configuration state of the communication device to the network device, and the CSI type indication receiving unit is configured to receive the CSI to be used by the communication device from the network device An indication of the type of feedback.

In a fourth aspect of the present disclosure, a network device operating in a wireless communication system is provided. The network device includes a signal transmitting unit, a reference signal receiving unit, a first CSI determining unit, a CSI information receiving unit, and a second CSI determining unit. Wherein the signal transmitting unit is configured to transmit a signal for determining a CSI of a channel between the communication device and the network device to the communication device. The channel includes a first subchannel and a second subchannel. The reference signal receiving unit is configured to receive the reference signal from the communication device, and the first CSI determining unit is configured to determine a CSI of the first subchannel based on the received reference signal. The CSI information receiving unit is configured to receive information about CSI of the second subchannel from the communication device, wherein the received information about the CSI of the second subchannel is based on a CSI of the first subchannel and a CSI of the second subchannel. The second CSI determining unit is configured to determine CSI of the second subchannel based on the received information about the CSI of the second subchannel.

In a fifth aspect of the present disclosure, an apparatus is provided. The apparatus includes a processor and a memory, the memory including instructions executable by the processor, whereby the apparatus is operative to perform any of the methods described in the first aspect, the second aspect of the present disclosure.

In a sixth aspect of the present disclosure, a computer program product is provided, comprising instructions that, when executed on one or more processors, cause the one or more processors to perform a first aspect in accordance with the present disclosure And any of the methods of the second aspect.

In a seventh aspect of the present disclosure, a computer readable storage medium having an existing computer program product thereon is provided. The computer program product includes instructions that, when executed on at least one processor, cause the at least one processor to perform any of the first and second aspects of the present disclosure.

DRAWINGS

The above and other aspects, features and advantages of various embodiments of the present disclosure will become more apparent from the detailed description of the appended claims. The same reference numerals in the drawings denote the same or equivalent elements. The drawings are only used to facilitate a better understanding of the embodiments of the present disclosure and are not necessarily drawn to scale.

FIG. 1 illustrates an example communication network in which embodiments of the present disclosure may be implemented;

FIG. 2 schematically shows an example of acquiring CSI of a channel between a network device and a communication device based on measurement of a reference signal;

FIG. 3 illustrates a simplified system model in accordance with some embodiments of the present disclosure;

4A-4C illustrate example flow diagrams of methods implemented at a communication device operating in a wireless communication system, in accordance with an embodiment of the present disclosure;

Figure 5 is a schematic illustration of a comparison of a common codebook and a communication device specific codebook;

6A-6B illustrate an example process for acquiring CSI for a channel between a communication device and a network device in accordance with an embodiment of the present disclosure;

7A-7C illustrate example flow diagrams of methods implemented at a network device operating in a wireless communication system, in accordance with an embodiment of the present disclosure;

Figure 8 shows a simplified block diagram of an apparatus in accordance with an embodiment of the present disclosure;

9-10 illustrate performance comparisons of example and prior art solutions in accordance with an embodiment of the present disclosure.

Detailed ways

In the following, the principles and spirit of the present disclosure will be described with reference to the exemplary embodiments. It is to be understood that the invention is not limited by the scope of the present disclosure. For example, features illustrated or described as part of one embodiment can be used together with another embodiment to yield a further embodiment. For the sake of clarity, some of the features of the actual implementation described in this specification may be omitted.

References to "one embodiment", "an embodiment", "an example embodiment", and the like in the specification are inferred that the described embodiments may include specific features, structures or characteristics, but not necessarily each embodiment includes the specific features and structures Or characteristics. Moreover, such phrases are not necessarily referring to the same embodiments. In addition, it is considered to be within the knowledge of those skilled in the art, whether or not the invention is specifically described, when the specific features, structures, or characteristics are described in conjunction with the embodiments.

It will be understood that, although the terms "first" and "second" and the like may be used herein to describe various elements, these elements are not limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of the example embodiments. The term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.

The terminology used herein is for the purpose of describing particular embodiments only, and The singular forms "a", "the", and "the" It will also be understood that the terms "including", "comprising", "having", "the", "the"," / The presence or addition of a combination thereof. The term "optional" means that the described embodiment or implementation is not mandatory and may be omitted in some cases.

In general, the terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs, unless otherwise explicitly defined.

As used herein, the term "communication network" refers to following any suitable communication standard (such as NR, Long Term Evolution (LTE), LTE Advanced (LTE-A), Wideband Code Division Multiple Access (WCDMA)), High Speed Packet Access (HSPA). ), CDMA2000, Time Division Synchronous Code Division Multiple Access (TD-CDMA), etc. Moreover, communication between devices in a communication network can be performed in accordance with any suitable communication protocol including, but not limited to, Global System for Mobile Communications (GSM), Universal Mobile Telecommunications System (UMTS), Long Term Evolution (LTE), and / or other suitable communication protocols, such as first generation (1G), second generation (2G), 2.5G, 2.75G, 3G, 4G, 4.5G, 5G communication protocols, wireless local area network (WLAN) standards (such as IEEE 802.11 Standard); and/or any other suitable wireless communication standard, and/or any other protocol currently known or to be developed in the future.

As used herein, the term "network device" refers to a device in a communication network through which a terminal device accesses and receives services from a network. Depending on the terminology and technology used, a network device may refer to a base station (BS), an access point (AP), and the like. In some embodiments, "network device" may also refer to a repeater, or a terminal device having a (partial) function of a base station or a repeater.

The term "communication device" refers to any device that has communication capabilities. By way of example and not limitation, a communication device may also be referred to as a terminal device, a user equipment (UE), a subscriber station (SS), a portable subscriber station, a mobile station (MS), or an access terminal (AT). Communication devices may include, but are not limited to, mobile phones, cellular phones, smart phones, voice over IP (VoIP) phones, tablet computers, wearable terminal devices, personal digital assistants (PDAs), portable computers, desktop computers, image capture such as digital cameras. Terminal devices, gaming terminal devices, music storage and playback devices, in-vehicle wireless terminal devices, wireless endpoints, mobile stations, laptop embedded devices (LEEs), laptop-mounted devices (LMEs), USB dongle, smart devices, Wireless Customer Premises Equipment (CPE), D2D equipment, Machine to Machine (M2M) equipment, V2X equipment, etc. In the following description, the terms "communication device", "terminal device", "terminal", "user device" and "UE" may be used interchangeably.

A schematic diagram of an example wireless communication system 100 in which embodiments of the present disclosure can be implemented is shown in FIG. Wireless communication system 100 can include one or more network devices 101. For example, in this example, network device 101 can be embodied as a base station, such as a gNB. It should be understood that the network device 101 may also be embodied in other forms, such as NB, eNB, BTS, BS, or BSS, repeater, and the like. The network device 101 provides a wireless connection for a plurality of communication devices 111-1, 111-2 (hereinafter collectively referred to as communication devices 111) within its coverage. The communication device 111 can communicate with the network device 101 via the

wireless transmission channel

131 or 132. Here, the downlink refers to a communication link from the network device 101 to the communication device 111, and the uplink refers to a communication link from the communication device 111 to the network device 101 in the opposite direction. It will be understood that the arrangement in the figures is merely an example and that the wireless communication system 100 may also include more or fewer communication devices or network devices.

The wireless communication system 100 can be a TDD based communication system, i.e., the uplink and downlink can operate in the same frequency band, distinguished by different times. For example, one radio frame for communication may include 10 subframes, and some of the subframes are for the uplink and others are for the downlink.

As previously mentioned, in a TDD system, network device 101 is capable of obtaining information about a downlink channel by measuring a corresponding uplink channel, utilizing reciprocity between the downlink channel and the uplink channel. Similarly, the communication device 111 can also obtain information of the uplink channel by measuring the downlink channel. An example of acquiring a CSI of a channel between the network device 101 and the communication device 111 based on a reference signal (RS) based measurement is schematically illustrated in FIG.

As shown in FIG. 2, a plurality of

antennas

201 and 202 are provided on both sides of the network device 101 and the communication device 111, respectively. The communication device 111 can measure the CSI (from the value of the channel matrix) of the downlink channel by measuring the CSI-RS from the network device. In theory, based on TDD-based channel reciprocity, in an ideal case, the communication device 111 can use the obtained CSI of the downlink channel as the CSI of the uplink channel. Similarly, the network device 101 can measure the sounding reference signal (SRS) from the communication device 111 to determine the CSI of the uplink channel, and use the CSI of the uplink channel for the downlink scheduling and according to the channel reciprocity. transmission.

However, in an actual TDD system, it is difficult to obtain all the CSIs required based on channel reciprocity due to some practical factors. These practical factors will affect the performance of downlink MU-MIMO. Two main factors are listed below as examples.

One is the SRS capacity limit. In a wireless communication system such as NR, the user side can transmit to and receive from the TRP using multiple antennas. If the TRP wants to obtain complete CSI between each UE and the TRP, then more SRS resources need to be configured for uplink channel measurements. In theory, in the case where the SRS resources are not limited, the TRP can perfectly obtain the channel information of all users. In practice, however, the SRS resources for each cell are limited and this will limit the allocation of SRS resources among candidate users. In addition, multi-user scheduling gain is also limited. If the TRP wants to obtain the full CSI of each user's channel, it will take a long time for SRS measurements, which results in partial channel information measured in earlier time slots (or subframes) being outdated. For multi-TRP delivery, the solution will face more challenges.

The second is the UE capability limit. In systems such as NR, the user side can transmit to and receive from the TRP using multiple antennas. However, the antenna port configuration on the user side may be asymmetric for the uplink and downlink. For example, a UE typically has more receive antenna ports than the number of uplink transmit antenna ports for receiving downlink signals to obtain diversity gain and combined gain. In this case, only a subset of the antennas on the user side are used for uplink transmission in order to enhance the transmission power per active antenna. However, this will destroy the reciprocity characteristics between the uplink and the downlink in the TDD system because the receiving side cannot know/determine the complete CSI of the downlink channel based on the measurement of the uplink signal. This situation is also referred to herein as partial reciprocity of the TDD channel.

These practical factors (and some other factors) will result in partial reciprocity between the downlink channel and the uplink channel, which in turn deteriorates the performance of NR TDD MU-MIMO. In response to the above problems, the solutions proposed in the Third Generation Partnership (3GPP) Radio Access Network 1 (RAN1) working group include: 1) partial SRS transmission and partial CSI quantization by common codebook; 2) partial SRS Transmit and antenna group switching; and 3) codebook quantization. For solution 1), the error of partial CSI quantization is large due to the use of a common codebook. Therefore, the quantitative feedback does not reflect the actual channel information very well. For solution 2), the TRP side needs more time to get the complete channel matrix. Therefore, when the transmission scene changes rapidly, there is a risk that the previous CSI measurement portion is out of date. Solution 3) is used for single-user transmission. For multi-user transmissions, this scheme 3) will result in more multi-user interference and degrade the performance of multi-user transmissions.

In order to, for example, improve the CSI accuracy acquired at the TRP side, and/or increase the SRS capacity within the cell, a new solution for acquiring/determining CSI is proposed in the present disclosure taking into account the practical limitations of the TDD system. Some embodiments may be used, for example, but not limited to, in the first phase of the 3GPP NR system, while some embodiments may be used, for example, but not limited to, the second phase of the NR system with low complexity. Additional signaling for further enhancing the proposed solution is also provided in some embodiments.

The basic idea of an embodiment of the present disclosure is to improve the accuracy of CSI acquisition and/or increase the capacity of the SRS by utilizing partial reciprocity of the channel and an improved codebook. For the overall uplink and downlink, there is only a partial reciprocity feature. However, for some subchannels (such as the channel between the TRP and the transmit antenna subgroup on the UE side), there is still complete reciprocity. The UE can obtain the information of the partial channel through CSI-RS measurement, and the TRP can obtain the information of the partial channel through the uplink SRS measurement. That is to say, the information of the partial channel can be known to both the UE and the TRP, which transparently establishes a bridge between the UE and the TRP. The transmit covariance matrix of the partial channel can be derived by the UE and the TRP, respectively. In one embodiment, the covariance matrix can be used to refine the common codebook to a user-specific codebook, for example, the covariance matrix can map an existing common codebook to a subspace on a particular user channel's airspace. space. The updated user-specific codebook has high resolution and can be used to quantize the remaining downlink channels on the user side. The codeword selected from the user-specific new codebook is fed back to the TRP. The TRP side can take the same process to update the common codebook to obtain the same user-specific codebook. The TRP then selects the codeword from the updated codebook based on user feedback and uses it as the remaining downlink channel that cannot be measured by the uplink SRS. Thus, by combining the first partial CSI obtained by the SRS measurement and the second partial CSI fed back by the UE, the TRP can recover the complete downlink channel information for each user.

The basic idea of another embodiment of the present disclosure is to improve the accuracy of CSI acquisition and/or increase the capacity of the SRS by utilizing partial reciprocity of the channel and channel correlation. As mentioned above, although there are only partial reciprocity characteristics for the overall uplink and downlink, for some subchannels, there is still full reciprocity. Therefore, the channel between the transmitting side and the receiving side can be divided into two parts. The first portion of the downlink channel has a corresponding uplink channel, and thus the partial channel is known (e.g., by measurement) for the UE and TRP side due to full reciprocity. The second part of the downlink may not have a corresponding uplink. In this embodiment, the user can calculate an in-phase matrix between the first partial channel and the second partial channel based on, for example, downlink CSI-RS measurements, and feed back the in-phase matrix to the TRP. The TRP may use the first partial CSI and the feedback in-phase matrix obtained (eg, by SRS measurements) to obtain/determine the CSI of the second portion of the downlink channel. By combining the first partial CSI and the obtained second partial CSI, the TRP can recover the complete user downlink channel information. This embodiment can significantly reduce the computational complexity of the user side and avoid the search process of the optimal codeword.

In addition, the above embodiments do not need to obtain complete CSI through SRS, and therefore, the SRS resources configured for each user can be reduced, thereby increasing the capacity of the SRS in the cell. That is, more remaining SRS resources can be used for other candidate users, or other special transmission purposes, for example, to support multi-user transmission based on nonlinear precoding. This helps to improve the overall performance of the system.

A simplified system model in accordance with some embodiments of the present disclosure is shown in FIG. In this example system, TRP 310 and UE 320 are equipped with

multiple antennas

301 and 302, respectively. The UE 320 can obtain complete downlink channel state information H by measuring the CSI-RS of the downlink. In theory, the TRP 310 can obtain the downlink channel H by measuring the uplink channel and utilizing channel reciprocity. However, some practical limitations make it difficult for the TRP 310 to obtain a complete channel by measurement. For example, a user uses multiple antennas 302 for downlink reception, and only one subset 312 of multiple antennas 302 is used for uplink transmission. In this case, the TRP 310 can only obtain the channel corresponding to the antenna subset 312 by measurement. Thus, in some embodiments of the present disclosure, the complete downlink channel matrix H may be represented as [H1; H2], where the first partial channel H1 may pass the reference signal 330 (eg, uplink SRS) on the TRP 310 side. The measurement is obtained, and the second partial channel H2 can be recovered by the TRP 310 by other means.

In FIG. 3, information about H2 is provided to the TRP by low complexity feedback 340. Restoring the subchannel matrix H2 with high precision is the key to obtaining an accurate complete downlink channel matrix. In some embodiments, to enhance the resolution of user channel quantization, based on a common codebook and utilizing partial reciprocity, a user-specific codebook is determined for quantization of channel H2. The TRP side can perform the same operations as the user side to achieve high-accuracy CSI recovery. In other embodiments, the amount of feedback of H2 may be reduced based on the correlation of the channel matrix and/or the accuracy of the CSI may be increased.

A method 400 implemented at a communication device operating in a TDD wireless communication system in accordance with one embodiment of the present disclosure is described below in conjunction with FIG. 4A. The wireless communication system is, for example, the communication system 100 of FIG. 1, and the communication device can be, for example but not limited to, the communication device 111 shown in FIG. 1 or the communication device 320 shown in FIG. For ease of discussion, method 400 will be described below with reference to communication device 111 and network environment 100 depicted in FIG.

As shown in FIG. 4A, at block 410, the communication device 111 obtains the CSI of its channel with the network device 101 based on the signal from the network device 101. The channel includes a first subchannel and a second subchannel. For example, the channel can be represented as H = [H1; H2]. Thus, at block 410, the communication device obtains the first subchannel H1 and the second subchannel H2.

In one embodiment, at block 410, the communication device 111 can obtain the channel H based on the CSI-RS from the network device 101. Embodiments of the present disclosure are not limited to dividing the first subchannel H1 and the second subchannel H2 in any particular manner. For example only, the first sub-channel H1 and the second sub-channel H2 may be associated with a first subset A1 and a second subset A2 of antenna ports of the communication device 111, respectively. In one embodiment, A1 and A2 are configurable. For example, A1 can be configured to include antenna ports 1 and 2 of the four antenna ports of the communication device, and A2 can be configured to include antenna ports 3 and 4 of the four antenna ports of the communication device. In another embodiment, one antenna port may be included in A1, and three antenna ports may be included in A2, or vice versa. In another embodiment, the first sub-channel H1 and the second sub-channel H2 may be associated with different polarization directions of the antenna of the communication device 111, respectively.

At block 420, the communication device 111 transmits a reference signal to the network device 101 to indicate information regarding the CSI of the first subchannel. This enables the network device 101 to obtain the subchannel matrix H1 by measuring the uplink reference signal and utilizing the reciprocity between the uplink channel and the downlink channel. This means that the subchannel matrix H1 is thus known for both the UE and the TRP.

In one embodiment, the reference signal may be an SRS, although embodiments of the present disclosure are not limited thereto. For example, in another embodiment, the reference signal can be a demodulation reference signal (DMRS). In one embodiment, the communication device 111 can transmit the reference signal to the network device 101 via the first subset A1 of the antenna port associated with the first subchannel H1.

As shown in FIG. 4A, at block 430, the communication device 111 determines, based on the CSI H1 of the first subchannel and the CSI H2 of the second subchannel obtained at block 410, about the second subchannel to be transmitted to the network device 101. CSI information. The communication device 111 can determine the information about the CSI of H2 to be transmitted in various ways. Several embodiments of block 430 are shown in Figures 4B and 4C for purposes of example only and not limitation.

In the example of FIG. 4B, at block 431, the communication device 111 can obtain a transmit covariance matrix for the first subchannel based on the CSI of the first subchannel. For example, the communication device 111 can determine the transmit covariance matrix R of the first subchannel by Equation (1):

Where () ^H represents the operation of taking the conjugate, f represents the subcarrier index, and it is assumed that the covariance matrix R is obtained on all N _f subcarrier channels.

In another embodiment, the communication device 111 may be bandwidth of the signal from the network device (i.e., N _f sub-carriers) into a plurality of sub-bands and the plurality of subbands for each subband of each first subchannel is obtained The covariance matrix is sent to obtain a more accurate transmit covariance matrix for each subband.

At block 432, the communication device 111 can determine the codebook specific to the communication device 111 based on the transmit covariance matrix R and the common codebook for the second subchannel H2.

In existing NR systems, the channel matrix can be quantized by a predefined codebook, whereas the TRP and all users use a predefined common codebook. That is, each user uses the same codebook to quantize its channel and feeds the index of the codeword back to the TRP. Using the feedback index and the codebook, the TRP can recover the user channel matrix. In the NR system, both the TRP and the UE have multiple antennas, which makes the channel matrix dimension large; at the same time, the codebook size is limited in order to reduce the uplink feedback overhead. In addition, the current codebook is a common codebook for all users and TRPs. In this case, the common codebook is extended to all spaces on the airspace, which results in the common codebook having a low resolution on the given subspace on the airspace.

Unlike the existing codebook quantization method, the operation of block 432 can obtain a specific codebook of the communication device 111 by utilizing the partial reciprocity of the common codebook and the channel, and limit the common codebook to a smaller subspace. Thereby enhancing the resolution of the user channel quantization. By taking the same operation as the user side, the TRP can also obtain a codebook specific to the communication device 111 for recovery of the CSI.

By way of example and not limitation, at block 432, the communication device 111 may obtain a codebook specific to the communication device 111 by the following equation (2):

Where w _i represents the ith codeword in the common codebook, L represents the total number of codewords in the common codebook, R represents the transmission covariance matrix, || || _F represents the operation of taking the F norm, and c _i denotes the i-th codeword in the determined codebook specific to the communication device 111.

A comparison of the common codebook and the codebook specific to the communication device 111 is schematically illustrated in FIG. The left side of Fig. 5 shows the spatial distribution of the codeword w _i in the common codebook, and as can be seen from the figure, the codebook is extended to the entire space, so that the resolution is low. The codeword of the common codebook can be mapped to a subspace on the airspace of the user channel shown on the right side of FIG. 5 to obtain a user-specific codebook. As can be seen from the right side of FIG. 5, the codebook specific to the communication device 111 obtained by the operation of block 432 is concentrated in a subspace specific to the communication device 111. Since the same size of the refined codebook is used to quantize the spatial subspace, this means that the codeword c _i can represent the channel information in the particular subspace with a higher resolution. Although the transformation of a codebook of size 8 is shown by way of example only in FIG. 5, it should be understood that similar expansion operations in block 432 are applicable to larger codebook sizes.

Returning now to FIG. 4B, at block 433, the communication device 111 can select a codeword that matches the CSI H2 of the second subchannel from the determined communication device specific codebook; and at block 434, determine the indication of the codeword as Information about the CSI of the second subchannel to be transmitted to the network device 101.

Another example embodiment 430' of block 430 is shown in FIG. 4C. In this example, at block 435, the communication device 111 obtains an in-phase matrix between the second subchannel and the first subchannel based on the first subchannel H1 and the second subchannel H2 obtained in block 410; At block 436, the communication device 111 can determine the indication of the in-phase matrix as information about the CSI of the second sub-channel to be transmitted to the network device 101. In this embodiment, the communication device 111 determines the feedback information for the subchannel H2 using the subchannel H1 and the correlation between the subchannel H1 and the subchannel H2, so that the amount of feedback can be reduced and/or the feedback accuracy can be improved.

As an example, the in-phase matrix G can be expressed as follows:

Operation

Indicates the operation of the pseudo-inverse. In another embodiment, the in-phase matrix between H1 and H2 can also be obtained by other suitable algorithms and operations.

The indication of the in-phase matrix to be transmitted determined in block 436 may include, but is not limited to, an index of a codeword selected from the codebook for the in-phase matrix that matches the in-phase matrix G, or, in the in-phase matrix G The value of the element. It can be seen from the formula (3) that the size of the matrix G will be smaller than the number of antennas on the user side. This means that the amount of feedback on the information of the CSI of the second subchannel is relatively small.

After determining, for example, but not limited to, the information about the CSI of the second subchannel to be transmitted to the network device 101 in the manner of FIG. 4B or FIG. 4C, at block 440, the communication device 111 transmits the determined to the network device 101. This information about the CSI of the second subchannel is as shown in FIG. 4A. This information enables the network device to obtain the CSI of the complete channel H in combination with the subchannel H1 measured by the reference signal.

An example process 610 for obtaining CSI for channel H between communication device 111 and network device 101 in accordance with an embodiment of the present disclosure is illustrated in FIG. 6A.

The example of Figure 6A is associated with the embodiment of Figure 4B. The key point of this example is that the transmit covariance matrix R of channel H1 is available on both the network device 101 and the communication device 111 side. Thus, utilizing partial channel reciprocity, the covariance matrix can be considered to be common information between the network device 101 and a given communication device 111. If the communication device 111 informs the network device 101 that it will use the user-specific codebook, or the TRP notifies the UE to use the user-specific codebook, or both obtain a consensus through a predetermined configuration, the network device 101 can assume the same as the communication device 111. The action is to update the common codebook to obtain the same codebook for the same communication device 111. Thus, using the feedback index from the communication device 111, the network device 101 can recover (due to, for example, SRS capacity limitations or UE uplink transmission capability limitations) a partial channel matrix that cannot be obtained by uplink SRS measurements.

As shown in FIG. 6A, the communication device 111 receives/measures (611) the downlink CSI-RS from the network device 101, estimates/obtains (612) the complete downlink channel matrix H, and the user transmits according to its uplink. The configuration divides the channel matrix into two parts [H1; H2]. Then, the communication device 111 determines (613) information about the subchannel H2 to be transmitted to the network device 101 based on H1 and H2, for example, by the embodiment shown in FIG. 4B. A reference signal (e.g., SRS) for H1 measurement and information about H2 is transmitted (614) to the network device 101 by the communication device 111 via the uplink. In one embodiment, the communication device 111 transmits the SRS through the subset of antennas associated with the subchannel H1, so that the network device 101 obtains the subchannel H1 by measuring the SRS, and the channel H2 quantized based on the user-specific codebook C The index is fed back to the network device 101. It should be noted that the SRS and the information about H2 are not necessarily sent at the same time. For example, the transmission of the SRS may be earlier than the transmission of information about H2.

The network device 101 obtains (615) H1 by measuring the uplink SRS, and uses the H1 to update the common codebook to obtain (616) the same user-specific codebook C as the communication device 111 side. In addition, based on the feedback index of the codeword corresponding to H2 from the communication device 111, the network device 101 can find the corresponding codeword from the user-specific codebook C, and restore (617) the subchannel H2 using the corresponding codeword. By combining H1 and H2, network device 101 is able to obtain the CSI of the complete channel matrix H. The obtained CSI for this channel H can be used for multi-user scheduling and/or used for downlink transmission and encoder design to pre-suppress multi-user interference.

As can be seen from the above process, the covariance matrix R can be obtained through partial channel reciprocity, and the communication device 111 does not need to feed back the transmission covariance matrix R to the network device 101 to implement the same common codebook update. This keeps the amount of feedback at a low level.

It should be noted that in the case where there are a plurality of communication devices in the communication system, each communication device should independently calculate the transmission covariance matrix R, update the common codebook to obtain its specific codebook C, and quantize the remaining subchannels. On the side of the network device 101, the operation shown in Fig. 6A should be performed independently for different communication devices.

Another example process 620 in accordance with an embodiment of the present disclosure is illustrated in FIG. 6B. This example is associated with the method of FIG. 4C, ie, using the phase relationship between H1 and H2 to obtain the CSI of H2. This phase relationship can be represented as an in-phase matrix between H1 and H2, and the in-phase matrix can be fed back to the network device 101 (eg, in an explicit manner). The network device 101 then uses the in-phase matrix and H1 measured (eg, by SRS) to obtain H2. This example can significantly reduce the computational complexity on the communication device side and the operational complexity of the channel recovery for the particular communication device on the network side. This scheme can be used, for example, in NR Phase II in 3GPP.

As shown in FIG. 6B, the communication device 111 receives (621,) a downlink transmission (e.g., CSI-RS), and obtains a complete downlink channel matrix H by downlink CSI-RS measurement. The channel matrix can be divided into two parts [H1; H2]. The communication device 111 can determine (622) the in-phase matrix G between H1 and H2, for example, by the manner described in the foregoing equation (3). An indication of the in-phase matrix G (e.g., an index of the corresponding codeword) and a reference signal for measuring the subchannel H1 are transmitted (623) to the network device 101. Based on the reference signal from the communication device 111, the network device 101 can determine (624) H1 and obtain (625) H2 based on the indication of H1 and the received G. In the case where G is defined as shown in the formula (3), the network device can obtain H2 by the following formula (4):

H ₂ =GH ₁ (4)

Where G is the user-specific in-phase matrix fed back by the communication device 111. The above process enables the network device to obtain more accurate H1 and H2 and enables the network device 101 to obtain a complete estimated channel matrix H = [H ₁ ; H ₂ ] by combining/cascading H1 and H2. The obtained H can be used by network devices for, for example, but not limited to, multi-user scheduling and downlink transmit precoder designs to suppress inter-user interference.

As discussed above, in the example of FIG. 6B, the in-phase matrix G can be explicitly fed back to the network device 101 so that the network device 101 derives the sub-channel matrix H2 directly based on G. This reduces the operational complexity of both the user side and the network side. In addition, due to the small size of G, the uplink overhead is also under control. In some embodiments, the communication device 111 may transmit an index of a codeword corresponding to the G matrix to the network device, or send an element in the G matrix to the network device.

In addition, as can be seen from the above embodiments, the communication device 111 and the network device 101 have a common understanding of the CSI determination manner used. That is, the network device 101 can determine the feedback content of the communication device 111 and correctly determine H2 using the feedback content. In some embodiments, the content, type, and/or format of the CSI feedback may be predefined such that the network device 101 can determine the feedback content of the communication device 111.

In other embodiments, new signaling may optionally be introduced to cause the operation of network device 101 to be consistent/synchronized with the operation of communication device 111 for efficient multi-user downlink transmission. For example, the communication device 111 can receive an indication of the CSI feedback type to be used by the communication device 111 from the network device 101, as shown by block 450 in Figure 4A. As an example, the indication signaling may include two bits XY to indicate a CSI acquisition scheme for different users or different groups of users. An example of the value of XY and the corresponding meaning is shown in Table 1 below. In another embodiment, 1 bit may also be used to indicate the CSI acquisition scheme.

Table 1. Instructions for the CSI scheme

Alternatively or additionally, in another embodiment, the communication device 111 may, at block 460 in FIG. 4A, transmit an indication of its CSI feedback capability to the network device 101, for example indicating, for example, whether the communication device 111 supports FIG. 4B or The feedback scheme shown in 4C. And or, at block 460, the communication device 111 can also send an indication of its antenna configuration status to the network device 101 to cause the network device to determine a CSI acquisition scheme that can be used.

FIG. 7A illustrates a flow diagram of a method 700 implemented at a network device operating in a TDD wireless communication system, in accordance with an embodiment of the present disclosure. The wireless communication system can be, for example but not limited to, the system 100 of FIG. 1, and the network device can be, for example, the network device 101 of FIG. 1 or the network device 310 of FIG. For ease of discussion, method 700 will be described below with reference to network device 101 and network environment 100 of FIG.

As shown in FIG. 7A, at block 710, the network device 101 transmits a signal to the communication device 111 for determining the CSI of the channel between the communication device 111 and the network device 101. The channel includes a first subchannel and a second subchannel. In one embodiment, the signals transmitted by network device 101 at block 710 may include, but are not limited to, CSI-RS. In another embodiment, the signal may also be, for example, a DMRS, a CRS, a Positioning Reference Signal (PRS), or a data signal or the like.

As an example, the first subchannel and the second subchannel may be associated with a first subset and a second subset of antenna ports of the communication device 111, respectively, or with different polarizations of the antenna of the communication device 111. However, embodiments of the present disclosure are not limited to any particular subchannel division.

At block 720, network device 101 receives the reference signal from communication device 111, and at block 730, determines the CSI for the first subchannel based on the received reference signal.

In an example embodiment, the reference signal received from communication device 111 is from a first subset of antenna ports associated with the first subchannel. Alternatively or additionally, the reference signal may be, but is not limited to, an uplink SRS.

At block 740, the network device 101 receives information about the CSI of the second subchannel from the communication device 111. This information about the CSI of the second subchannel is based on the CSI of the first subchannel and the CSI of the second subchannel.

In one embodiment, the information about the CSI of the second subchannel received by network device 101 at block 740 is determined by communication device 111 at block 430 and transmitted at block 440 based on method 400. Thus, the description of the information about the CSI of the second subchannel described in connection with method 400 applies here as well.

At block 750, the network device 101 determines the CSI for the second subchannel based on the received information about the CSI of the second subchannel. Depending on the different form of information received regarding the CSI of the second subchannel, network device 101 may take different actions to determine the CSI of the second subchannel. Figures 7B and 7C show different embodiments 750-1 and 750-2 of block 750, respectively.

For example, the information about the CSI of the second subchannel may be a codeword index quantized by the codebook specific to the second subchannel H2 via the communication device 111. In this example, network device 101 can determine H2 by performing operations 751-753 shown in Figure 7B.

As shown in FIG. 7B, at block 751, the network device 101 obtains a transmit covariance matrix R for the first subchannel based on the CSI H1 of the first subchannel. For example, R can be obtained by the above formula (1). In one embodiment, network device 101 may divide the bandwidth of the signal transmitted to communication device 111 into a plurality of sub-bands and obtain a transmit covariance matrix for the first sub-channel for each of the plurality of sub-bands, respectively.

At block 752, the network device 101 determines a codebook C specific to the communication device 111 based on the obtained transmit covariance matrix R and the common codebook for the second subchannel. The codebook C can be determined, for example, by the above formula (2).

At block 753, the network device 101 determines the codeword for the second subchannel H2 from the determined codebook C based on the received codeword index of H2, thereby determining H2.

In another example, the information about the CSI of the second subchannel received by network device 101 at block 740 may be an indication of the in-phase matrix G between the second subchannel and the first subchannel. The indication of the in-phase matrix G may be, for example, an index of a codeword selected from a codebook for an in-phase matrix that matches the in-phase matrix, or a value of an element in the in-phase matrix G. In this example, network device 101 can determine H2 by performing operation 754 shown in Figure 7C. As shown in FIG. 7C, at block 754, the network device 101 obtains the second subchannel H2 based on the determined CSI H1 of the first subchannel and the indication of the received in-phase matrix G. For example, the network device 101 can determine H2 by the equation (4) described above.

In some embodiments, method 700 can optionally include the operation of block 760, wherein network device 101 transmits an indication of the type of CSI feedback to be used by communication device 111 to communication device 111. For example, network device 101 may send an indication of 1 bit or 2 bits as shown in Table 1 to communication device 111 to indicate the CSI acquisition scheme to use. The indication may be carried, for example, by new downlink control signaling or by radio resource control (RRC) signaling or a medium access control (MAC) control unit (CE). If the system or network is stable. System overhead can be reduced by RRC or then MAC transfer.

Alternatively or additionally, method 700 can optionally include the operation of block 770, wherein network device 101 receives an indication of the ability of CSI feedback of communication device 111 from communication device 111. In another embodiment, network device 101 may receive an indication of the antenna configuration status of the communication device 111 from communication device 111. These indications can help the network device determine the feedback content of the communication device 111.

Embodiments of the present disclosure have a number of advantages. For example, some embodiments may improve the accuracy of CSI acquisition, reduce feedback overhead, and/or increase the capacity of the SRS.

One aspect of the disclosure also provides a communication device in a wireless communication network (e.g., communication network 100 shown in FIG. 1). The communication device can be, for example, the communication device 111 shown in FIG.

In one embodiment, the communication device includes a CSI obtaining unit, a reference signal transmitting unit, a feedback information determining unit, and a feedback unit. Wherein the CSI obtaining unit is configured to obtain CSI of a channel between the communication device and the network device based on a signal from the network device. The reference signal transmitting unit is configured to transmit a reference signal to the network device to indicate information about CSI of the first subchannel in the channel. The feedback information determining unit is configured to determine information about CSI to be transmitted to the network device regarding the second subchannel based on CSI of the first subchannel and CSI of the second subchannel in the channel, and the feedback unit is configured to be to the network The device transmits the determined information about the CSI of the second subchannel.

In one embodiment, the communication device can perform the method 400 described in connection with Figures 4A-4C, and thus the content described in connection with the method 400 is equally applicable herein and will not be described again.

In another embodiment, the communication device may also optionally include an indication transmitting unit and/or a CSI type indication receiving unit. The indication transmitting unit is configured to transmit an indication of the CSI feedback capability of the communication device and/or an indication of an antenna configuration state of the communication device to the network device, and the CSI type indication receiving unit is configured to receive the CSI to be used by the communication device from the network device An indication of the type of feedback.

Another aspect of the present disclosure also provides a network device in a wireless communication network (e.g., communication network 100 shown in FIG. 1). The network device includes a signal transmitting unit, a reference signal receiving unit, a first CSI determining unit, a CSI information receiving unit, and a second CSI determining unit. Wherein the signal transmitting unit is configured to transmit a signal for determining a CSI of a channel between the communication device and the network device to the communication device. The channel includes a first subchannel and a second subchannel. The reference signal receiving unit is configured to receive the reference signal from the communication device, and the first CSI determining unit is configured to determine a CSI of the first subchannel based on the received reference signal. The CSI information receiving unit is configured to receive information about CSI of the second subchannel from the communication device, wherein the received information about the CSI of the second subchannel is based on a CSI of the first subchannel and a CSI of the second subchannel. The second CSI determining unit is configured to determine CSI of the second subchannel based on the received information about the CSI of the second subchannel.

In a further embodiment, the network device may also optionally include an indication receiving unit and/or a CSI type indication transmitting unit. U indicating that the receiving unit is configured to receive an indication of the capability of the communication device regarding CSI feedback and/or an indication of an antenna configuration state of the communication device from the communication device, and the CSI type indication transmitting unit is configured to transmit to the communication device An indication of the type of CSI feedback used by the communication device.

In one embodiment, the communication device can perform the method 700 described in connection with Figures 7A-7C, and thus the operations described in connection with the method 700 are equally applicable herein and will not be described again.

FIG. 8 shows a simplified block diagram of an apparatus 800 that can be implemented in or implemented as a communication device or network device (eg, network device 101 or communication device 111 shown in FIG. 1).

Apparatus 800 can include one or more processors 810 (such as a data processor) and one or more memories 820 coupled to processor 810. Device 800 may also include one or more transmitters/receivers 840 coupled to processor 810. Memory 820 can be a non-transitory machine readable storage medium and can store a program or computer program product 830. Computer program (product) 830 can include instructions that, when executed on associated processor 810, enable device 800 to operate (e.g., perform method 400 or 700) in accordance with an embodiment of the present disclosure. The combination of one or more processors 810 and one or more memories 820 may form processing component 850 suitable for implementing various embodiments of the present disclosure.

Various embodiments of the present disclosure may be implemented by a computer program or computer program product, software, firmware, hardware, or a combination thereof, executable by processor 810.

The memory 820 can be of any type suitable for the local technical environment and can be implemented using any suitable data storage technology, such as, by way of non-limiting example, a semiconductor-based memory terminal device, a magnetic memory terminal device and system, an optical memory terminal device And systems, fixed memory and removable storage.

Processor 810 can be of any type suitable for the local technical environment and can include, by way of non-limiting example, one or more general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), and multi-core processor-based architectures Processor.

While some of the above description has been made in the context of the communication system shown in FIG. 1, this should not be construed as limiting the spirit and scope of the disclosure. The principles and concepts of the present disclosure may be more generally applicable to other scenarios.

Furthermore, the present disclosure may also provide a computer readable storage medium, such as a memory comprising a computer program or computer program product as described above, comprising a machine readable medium and a machine readable transmission medium. A machine-readable medium can also be referred to as a computer-readable medium, and can include a machine-readable storage medium such as a magnetic disk, magnetic tape, optical disk, phase change memory or electronic memory terminal device, such as random access memory (RAM), read only Memory (ROM), flash memory device, CD-ROM, DVD, Blu-ray Disc, etc. A machine-readable transmission medium can also be referred to as a carrier, and can include, for example, electrical, optical, radio, acoustic, or other forms of propagation signals, such as carrier waves, infrared signals, and the like.

The techniques described herein may be implemented by various means, such that the means for implementing one or more of the functions of the corresponding devices described in the embodiments includes not only prior art means but also corresponding means for implementing the embodiments described. One or more functional components, and which may include separate components for each individual function, or components that may be configured to perform two or more functions. For example, these techniques can be implemented in hardware (one or more devices), firmware (one or more devices), software (one or more modules), or a combination thereof. For firmware or software, implementations may be performed by modules (eg, procedures, functions, etc.) that perform the functions described herein.

The example embodiments herein have been described in terms of block diagrams and flowchart illustrations of the method and apparatus. It will be understood that each block of the block diagrams and flowchart illustrations and combinations of blocks in the block diagrams and flowchart illustrations can be implemented by various means including hardware, software, firmware, and combinations thereof, respectively. For example, in one embodiment, various blocks of the block diagrams and flowchart illustrations, and combinations of blocks in the block diagrams and flowchart illustrations can be implemented by a computer program or computer program product comprising computer program instructions. These computer program instructions can be loaded onto a general purpose computer, special purpose computer or other programmable data processing device to produce a machine such that instructions executed on a computer or other programmable data processing device are created for implementation in one or more flowcharts. The part of the function specified in the box.

In addition, although the operations are depicted in a particular order, this should not be construed as requiring such operations to be performed in the particular order shown or in the sequence, or all the illustrated operations are performed to achieve the desired results. In some cases, multitasking and parallel processing may be advantageous. Also, although the invention has been described with a particular embodiment of the invention, it is not to be construed as limiting the scope of the subject matter described herein. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can be implemented in various embodiments separately or in any suitable sub-combination. Moreover, although the above features may be described as working in some combination, and even so initially claimed, one or more features of the claimed combination may be removed from the combination in some cases, and Combinations claimed may involve variations of sub-combinations or sub-combinations.

It will be apparent to those skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The above-described embodiments are given for the purpose of illustration and not limitation of the present invention, and it is understood that modifications and variations may be made without departing from the spirit and scope of the disclosure. Such modifications and variations are considered to be within the scope of the disclosure and the appended claims. The scope of protection of the disclosure is defined by the appended claims.

Additionally, in the present disclosure, performance evaluation results for some of the proposed solutions are also provided. In the following evaluation/analysis, the vector [M, N, P, Q] is used to represent a planar antenna configuration, where M represents the number of rows, N represents the number of columns, P represents the polarization mode, and Q represents the transmitting radio unit. The number of (TXRU). P = 1 indicates single polarization and P = 2 indicates cross polarization. The main system configurations used in computer simulation are as follows:

1. TRP antenna configuration [2, 8, 2, 32] is fixed for all simulations;

2. There are a total of 9 users, each user's antenna configuration is [1, 2, 2, 4], in the uplink transmission, the user can be configured with up to 4 SRS resources. For large-scale multi-user scenarios, SRS should be used to support more user channel measurements, and antenna subgroups are used for SRS transmission. In the simulation, SrsPortNum is used to indicate the SRS resources actually used by each user.

3. Greedy search based on obtained user channel information, maximum and rate is used for multi-user and multi-stream scheduling. The scheduling algorithm limits up to 8 streams per TRP, up to 2 streams per user.

The following five solutions for CSI acquisition a)-e) were evaluated:

a) Complete reciprocal CSI. In this scheme, each user uses 4 SRS resources in the uplink transmission and helps the TRP obtain complete downlink channel state information. This performance is the upper performance limit.

b) SRS + user-specific codebook. This is one of the example embodiments presented by the present disclosure. Part of the channel information is obtained by SRS measurement, and the remaining channels are obtained by user-specific adaptive codebook quantization and feedback. The common codebook is a codebook with a 4x oversampling in the horizontal and vertical domains as defined in Release 13 (R13). In the simulation, SrsPortNum is used to indicate the SRS resources actually used by each user.

c) SRS+ in-phase matrix. This is another example embodiment proposed in the present disclosure. Also, in the simulation, SrsPortNum is used to indicate the SRS resources actually used by each user.

d) SRS+R13 public codebook. This is one of the solutions of the prior art. Among them, part of the channel information is obtained by SRS measurement, and the remaining channels are obtained by common codebook quantization and feedback. The common codebook is a codebook defined in R13 that has 4 times oversampling in the horizontal and vertical domains. In the simulation, SrsPortNum is used to indicate the SRS resources actually used by each user.

e) R13 codebook. This is another prior art solution. In this scheme, the user channel is completely quantized by the common codebook, and the index of the selected codeword is fed back to the TRP. The common codebook is a codebook defined in R13 that has 4 times oversampling in the horizontal and vertical domains.

Solution a) Always use 4 SRS resources to help the TRP get the full downlink channel, so this solution has upper limit performance. For other solutions, including scenarios b)-d), each user uses partial SRS resources (SrsPortNum=2 or 3) and limited feedback. In scenario e), the user does not use any SRS resources on the uplink and operates the same as the FDD system.

Figure 9 shows a performance comparison of five solutions in the configuration of SrsPortNum = 2. The abscissa is the signal-to-noise ratio (SNR), and the vertical index is the spectral efficiency (SE) obtained by each scheme. Figure 9 shows that both proposed solutions b) and c) exceed the performance of existing solutions d) and e), and as the SNR increases, the gap between the proposed solution and the upper limit remains close to one Constant value. The performance of existing solutions d) and e) deteriorates sharply with increasing SNR. For MU-MIMO transmission, it can be assumed that each user has a high quality channel that is appropriate for a high SNR region. This means that the proposed solutions b) and c) work well for MU-MIMO. As mentioned earlier, in the simulation, the total number of streams sent is limited to as many as 8, and the number of streams per user is limited to as many as two. A greedy search algorithm is used to perform multi-user and multi-stream scheduling to maximize system and rate.

Figure 9 also shows that the performance of scheme c) exceeds scheme b), but the gain difference is limited and the performance curves of the two are substantially coincident. The advantage of scheme c) is that the computational complexity on the UE side and the TRP side is low.

A performance comparison in the scenario of SrsPortNum=3 is shown in FIG. It can be seen that the gap between the complete reciprocal CSI solution a) (upper limit) and the proposed solution is reduced when more SRS resources are used per user. Figure 10 also shows that under this transmission configuration (SrsPortNum = 3), the performance of the proposed solutions b) and c) still exceeds the existing solutions d) and e).

Based on the above analysis and simulation results, it can be found that embodiments of the present disclosure (e.g., evaluated schemes b) and c)) have advantages in various scenarios such as those listed below.

i) If the user uses a different antenna configuration for downlink reception and uplink transmission, for example, the number of antenna ports for the downlink is greater than the number of antenna ports for the uplink, the proposed solution b) And c) can help the TRP to obtain a more accurate downlink CSI per user and get close to the upper limit performance. Alternatively, the user may feed back the antenna configuration state to the TRP, and the TRP sends an acknowledgement message to the user to make the TRP and the UE consistent (match) with respect to the CSI acquisition operation.

Ii) if the user uses the same antenna configuration for downlink reception and uplink transmission, for example, the number of antenna ports for the downlink is equal to the number of antenna ports for the uplink, then theoretically a complete Channel reciprocity, and TRP can obtain perfect channel state information. For actual systems, SRS resources are limited. If the TRP uses the proposed solution for CSI acquisition, the TRP can perform scheduling from a larger set of user candidates to achieve higher multi-user scheduling gain. In this case, the TRP may, for example, notify the user of a particular CSI acquisition scheme, for example, using scheme b) or c), so that the operations of both are synchronized/matched.

Iii) If the TRP adopts different transmit precoding schemes for different users, for example, linear precoding for non-correlated user groups and nonlinear precoding for high correlation user groups, different users can be used differently SRS configuration strategy. For example, for highly correlated user groups, it is preferred to use accurate CSI because non-linear transmission schemes are used for these users, while non-linear transmission schemes require more accurate CSI. Accordingly, more SRS resources can be allocated to those users. For non-related user groups, a linear precoding based transmission scheme can be used and the proposed CSI acquisition scheme can be used. In this case, the TRP can also notify the user of the CSI acquisition scheme. In other embodiments, the user may be informed of the CSI scheme to be used in a predetermined configuration or implicit manner. In addition, if the precoding scheme for the user changes due to the decision of the TRP or the movement of the user, the TRP may also notify the user of the new CSI acquisition scheme.

Claims

A method implemented at a communication device operating in a time division duplex (TDD) wireless communication system, comprising:

Obtaining channel state information (CSI) of a channel between the communication device and the network device based on a signal from a network device; the channel includes a first subchannel and a second subchannel;

Transmitting a reference signal to the network device to indicate information about a CSI of the first subchannel;

Determining information about CSI of the second subchannel to be transmitted to the network device based on CSI of the first subchannel and CSI of the second subchannel;

Sending the determined information about the CSI of the second subchannel to the network device.
The method of claim 1, wherein obtaining CSI of a channel between the communication device and the network device based on a signal from a network device comprises:

The CSI of the channel is obtained based on a CSI reference signal (CSI-RS) from the network device.
The method of claim 1 wherein said first subchannel and said second subchannel are associated with a first subset and a second subset of antenna ports of said communication device, respectively.
The method of claim 3, wherein transmitting the reference signal to the network device comprises:

The reference signal is transmitted to the network device by the first subset of antenna ports associated with the first subchannel.
The method of claim 1, wherein the information about the CSI of the second subchannel to be transmitted to the network device is determined based on a CSI of the first subchannel and a CSI of the second subchannel, including :

Obtaining a transmit covariance matrix of the first subchannel based on CSI of the first subchannel;

Determining a codebook specific to the communication device based on the transmit covariance matrix and a common codebook for the second subchannel;

Selecting, from the determined codebook specific to the communication device, a codeword that matches a CSI of the second subchannel;

The indication of the codeword is determined as the information about the CSI of the second subchannel to be sent to the network device.
The method of claim 5, wherein obtaining a transmit covariance matrix of the first subchannel based on CSI of the first subchannel comprises:

Dividing the bandwidth of the signal from the network device into a plurality of sub-bands;

The transmit covariance matrix of the first subchannel is obtained for each of the plurality of subbands.
The method of claim 5, wherein determining the communication device specific codebook comprises: based on the transmit covariance matrix and a common codebook for the second subchannel:

The communication device specific codebook is obtained by the following formula:

Where w i represents the ith codeword in the common codebook, L represents the total number of codewords in the common codebook, R represents the transmission covariance matrix, and || || F represents the F norm Operation, and c i represents the determined i-th codeword in the specific codebook of the communication device.
The method of claim 1, wherein the information about the CSI of the second subchannel to be transmitted to the network device is determined based on a CSI of the first subchannel and a CSI of the second subchannel, including :

Obtaining an in-phase matrix between the second subchannel and the first subchannel based on a CSI of the first subchannel and a CSI of the second subchannel;

The indication of the in-phase matrix is determined as the information about the CSI of the second subchannel to be sent to the network device.
The method of claim 8 wherein the indication of the in-phase matrix comprises:

An index of a codeword selected from the codebook for the in-phase matrix that matches the in-phase matrix, or

The value of the element in the in-phase matrix.
The method of claim 1 further comprising transmitting an indication of at least one of the following information to the network device:

CSI feedback capability of the communication device;

The antenna configuration state of the communication device.
The method of claim 1 further comprising:

An indication of the type of CSI feedback to be used by the communication device is received from the network device.
A method implemented at a network device operating in a time division duplex (TDD) wireless communication system, comprising:

Transmitting, to the communication device, a signal for determining channel state information (CSI) of a channel between the communication device and the network device, the channel including a first subchannel and a second subchannel;

Receiving a reference signal from the communication device;

Determining a CSI of the first subchannel based on the received reference signal;

Receiving information about CSI of the second subchannel from the communication device, wherein the received information about CSI of the second subchannel is based on CSI and the second sub of the first subchannel CSI of the channel;

The CSI of the second subchannel is determined based on the received information about the CSI of the second subchannel.
The method of claim 12, wherein transmitting, to the communication device, a signal for estimating CSI of a channel between the communication device and the network device comprises:

A CSI reference signal (CSI-RS) is transmitted to the communication device.
The method of claim 12 wherein said first subchannel and said second subchannel are associated with a first subset and a second subset of antenna ports of said communication device, respectively.
The method of claim 14 wherein said reference signal received from said communication device is from said first subset of antenna ports associated with said first subchannel.
The method of claim 12, wherein receiving information about the CSI of the second subchannel from the communication device comprises:

Receiving, from the communication device, an index of a codeword for the second subchannel, the codeword being from a codebook specific to the communication device;

Determining the CSI of the second subchannel based on the received information about the CSI of the second subchannel includes:

Obtaining a transmit covariance matrix of the first subchannel based on CSI of the first subchannel;

Determining a codebook specific to the communication device based on the transmit covariance matrix and a common codebook for the second subchannel;

The codeword for the second subchannel is determined from the determined codebook based on the received index.
The method of claim 16, wherein obtaining the transmit covariance matrix of the first subchannel based on CSI of the first subchannel comprises:

Dividing the bandwidth of the signal transmitted to the communication device into a plurality of sub-bands;

The transmit covariance matrix of the first subchannel is obtained for each of the plurality of subbands.
The method of claim 16, wherein the communication device specific codebook for the second subchannel is determined to be included based on the transmit covariance matrix and a common codebook for the second subchannel :

A codebook specific to the communication device is obtained by the following formula:

Where w i represents the ith codeword in the common codebook, L represents the total number of codewords in the common codebook, R represents the transmission covariance matrix, and || || F represents the F norm Operation, and c i represents the determined i-th codeword in the specific codebook of the communication device.
The method of claim 12, wherein receiving information about the CSI of the second subchannel from the communication device comprises:

Receiving, from the communication device, an indication of an in-phase matrix between the second subchannel and the first subchannel; and

Determining the CSI of the second subchannel based on the received information about the CSI of the second subchannel includes:

And obtaining CSI of the second subchannel based on the determined CSI of the first subchannel and the received indication of the in-phase matrix.
The method of claim 19 wherein the indication of the in-phase matrix comprises:

An index of a codeword selected from the codebook for the in-phase matrix that matches the in-phase matrix, or

The value of the element in the in-phase matrix.
The method of claim 12 further comprising:

An indication of the type of CSI feedback to be used by the communication device is sent to the communication device.
The method of claim 21, further comprising receiving an indication of at least one of the following information from the communication device:

CSI feedback capability of the communication device;

The antenna configuration state of the communication device.
An apparatus comprising a processor and a memory, the memory comprising instructions executable by the processor, whereby the apparatus is operative to perform the method of any one of claims 1 to 11.
An apparatus comprising a processor and a memory, the memory comprising instructions executable by the processor, whereby the apparatus is operative to perform the method of any one of claims 12-22.
A computer readable storage medium having a computer program product embodied thereon, the computer program product comprising instructions that, when executed on at least one processor, cause the at least one processor to perform according to the claims The method of any one of 1 to 22.