CN109428639B

CN109428639B - Method and apparatus for determining channel state information

Info

Publication number: CN109428639B
Application number: CN201710736921.8A
Authority: CN
Inventors: 孙欢; 宋暖; 李楠
Original assignee: Nokia Shanghai Bell Co Ltd
Current assignee: Nokia Shanghai Bell Co Ltd
Priority date: 2017-08-24
Filing date: 2017-08-24
Publication date: 2021-04-09
Anticipated expiration: 2037-08-24
Also published as: CN109428639A; WO2019037745A1

Abstract

Embodiments of the present disclosure provide methods, apparatuses, and computer program products for determining Channel State Information (CSI). A method implemented at a communication device operating in a wireless communication system, comprising: obtaining CSI of a channel between a communication device and a network device based on a signal from the network device, wherein the channel comprises a first subchannel and a second subchannel; transmitting a reference signal to the network device to indicate information on CSI of the first subchannel; determining information about CSI of the second sub-channel to be transmitted to the network device based on the CSI of the first sub-channel and the CSI of the second sub-channel; and transmitting the determined information on the CSI of the second subchannel to the network device. By using the embodiment of the disclosure, the accuracy of the CSI obtained by the network equipment side can be improved, and/or the capacity of the uplink reference signal can be improved.

Description

Method and apparatus for determining channel state information

Technical Field

The present disclosure relates generally to the field of wireless communications, and in particular, to methods, apparatuses, and computer program products for determining Channel State Information (CSI) in a Time Division Duplex (TDD) -based wireless communication system.

Background

The statements in this section are intended to facilitate a better understanding of the present disclosure. Accordingly, the contents of this section should be read on this basis and should not be construed as an admission as to which pertains to the prior art or which does not.

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

In a 5 th generation (5G) wireless communication system, also called a New Radio (NR) system, multiple antennas or a multi-panel with a large-scale antenna are used on a Transmission and Reception Point (TRP) side as well as a user side. With multiple antennas/multiple panels, TRP can support multi-stream transmission to multiple users simultaneously. In order to effectively reduce multi-user interference through scheduling and/or precoding, accurate downlink CSI for each user needs to be obtained on the TRP side.

Disclosure of Invention

The TRP may obtain information of a downlink channel in different ways for different wireless communication systems. For example, in a Time Division Duplex (TDD) system, the TRP can obtain information of a downlink channel by measuring a corresponding uplink channel using reciprocity between the downlink channel and the uplink channel. In a Frequency Division Duplex (FDD) system, the TRP can obtain information of a downlink channel through CSI feedback of each user. For the scheme based on CSI feedback in FDD-based systems, TRP cannot obtain CSI with high accuracy since CSI is quantized before feedback to save uplink overhead. If TRP uses quantized CSI for multi-user-multiple input multiple output (MU-MIMO) transmission and/or scheduling, severe multi-user interference may be generated, significantly limiting the performance of the system. Thus, in a 5G NR system, TDD mode has a higher priority because it can achieve higher CSI accuracy and thus better performance. However, for TDD systems, there are 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 practical TDD systems by exploiting 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 the 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 networks, systems, and scenarios in which similar issues exist.

Other features and advantages of embodiments of the present disclosure will be understood from the following description of various embodiments, when read in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of embodiments of the disclosure.

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

In one embodiment, the communication device may obtain CSI for 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, respectively, of antenna ports of the communication device. In a further embodiment, the communication device may transmit a reference signal to the network device through a first subset of antenna ports associated with the first subchannel.

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

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

In yet another embodiment, the method of the communication device may further comprise sending an indication of at least one of the following information to the network device: a CSI feedback capability of the communication device; and an antenna configuration state of the communication device.

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

In a second aspect of the disclosure, a method implemented at a network device operating in a TDD wireless communication system is provided. The method comprises the following steps: transmitting, to a communication device, a signal for determining CSI of a channel between the communication device and a network device, wherein the channel comprises a first subchannel and a second subchannel; receiving a reference signal from a communication device; determining CSI for a first subchannel based on the received reference signals; receiving information on CSI of a second sub-channel from a communication device, wherein the received information on CSI of the second sub-channel is based on CSI of a first sub-channel and CSI of the second sub-channel; and determining CSI of the second subchannel based on the received information on CSI of the second subchannel.

In one embodiment, receiving information from the communication device regarding CSI for the second subchannel may include an index for a codeword for the second subchannel, the codeword from a communication device specific codebook; and the network device may determine the CSI of the second subchannel based on the received information on the CSI of the second subchannel by: obtaining a transmission covariance matrix of the first subchannel based on the CSI of the first subchannel; determining a communication device specific codebook based on a transmit covariance matrix and a common codebook for the second subchannel; and determining a codeword for the second subchannel from the determined codebook based on the received index.

In another embodiment, the information received from the communication device regarding CSI of the second subchannel may comprise an indication of an in-phase matrix between the second subchannel and the first subchannel; and the network device may obtain CSI for the second subchannel by obtaining CSI based on the determined CSI for the first subchannel and the received indication of the in-phase matrix.

In yet another embodiment, the network device may 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 CSI feedback capabilities of the communication device and/or an indication of antenna configuration status 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 on CSI of a first sub-channel in the channel. The feedback information determination unit is configured to determine information about CSI of the second sub-channel to be transmitted to the network device based on CSI of the first sub-channel and CSI of the second sub-channel in the channel, and the feedback unit is configured to transmit the determined information about CSI of the second sub-channel to the network device.

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

In a fourth aspect of the 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 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 a reference signal from the communication device, and the first CSI determination unit is configured to determine CSI of the first subchannel based on the received reference signal. The CSI information receiving unit is configured to receive, from the communication device, information on CSI of the second sub-channel, wherein the received information on CSI of the second sub-channel is based on CSI of the first sub-channel and CSI of the second sub-channel. The second CSI determination unit is configured to determine CSI of the second subchannel based on the received information on CSI of the second subchannel.

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

In a sixth aspect of the present disclosure, there is provided a computer program product comprising instructions which, when executed on one or more processors, cause the one or more processors to perform any of the methods according to the first and second aspects of the present disclosure.

In a seventh aspect of the disclosure, a computer-readable storage medium having a computer program product embodied thereon is provided. The computer program product comprises instructions which, when executed on at least one processor, cause the at least one processor to perform the method according to any one of the first and second aspects of the present disclosure.

Drawings

The above and other aspects, features and benefits of various embodiments of the present disclosure will become more apparent from the following detailed description with reference to the accompanying drawings. The same reference numbers in the drawings identify the same or equivalent elements. The accompanying drawings are only for the purpose of promoting a better understanding of embodiments of the disclosure, and are not necessarily drawn to scale, wherein:

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

fig. 2 schematically shows an example of obtaining CSI of a channel between a network device and a communication device based on measurements of reference signals;

FIG. 3 illustrates a simplified system model according to 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 embodiments of the present disclosure;

FIG. 5 schematically illustrates a comparison of a common codebook and a communication device specific codebook;

6A-6B illustrate an example process performed between a communication device and a network device for obtaining CSI for a channel 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 embodiments of the present disclosure;

FIG. 8 shows a simplified block diagram of an apparatus according to an embodiment of the present disclosure; and

fig. 9-10 show performance comparisons of an example scheme according to embodiments of the present disclosure with a prior art scheme.

Detailed Description

Hereinafter, the principle and spirit of the present disclosure will be described with reference to exemplary embodiments. It is understood that all of these examples are given solely to enable those skilled in the art to better understand and further practice the present disclosure, and are not intended to limit the scope of the present disclosure. For instance, features illustrated or described as part of one embodiment, can be used with another embodiment to yield a still further embodiment. For clarity, some features of the actual implementation described in this specification may be omitted.

References in the specification to "one embodiment," "an example embodiment," etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be 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 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 is not intended to be limiting of example embodiments. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises," comprising, "" has, "" having, "" includes, "" including, "" has, "" having, "" contains, "" containing, "" contains, "" contain a mixture of one or more other features, elements, components, and/or. The term "optional" means that the embodiment or implementation being described is not mandatory, and may be omitted in some cases.

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

As used herein, the term "communication network" refers to a network that conforms to 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), and the like. Further, communication between devices in the communication network may be performed according to 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 standards); and/or any other suitable wireless communication standard, and/or any other protocol now known or later developed in the future.

As used herein, the term "network device" refers to a device in a communication network via which a terminal device accesses the network and receives services therefrom. Depending on the terminology and technology used, a network device may refer to a Base Station (BS), an Access Point (AP), etc. In some embodiments, "network device" may also refer to a relay, or a terminal device having (part of) the functionality of a base station or a relay.

The term "communication device" refers to any device having communication capabilities. By way of example, and not limitation, a communication device may also be referred to as a terminal device, User Equipment (UE), Subscriber Station (SS), portable subscriber station, Mobile Station (MS), or Access Terminal (AT). The communication devices may include, but are not limited to, mobile phones, cellular phones, smart phones, voice over IP (VoIP) phones, tablet computers, wearable terminals, Personal Digital Assistants (PDAs), portable computers, desktop computers, image capture terminals such as digital cameras, gaming terminals, music storage and playback appliances, in-vehicle wireless terminals, wireless endpoints, mobile stations, Laptop Embedded Equipment (LEE), laptop installation equipment (LME), USB dongles, smart devices, wireless Customer Premises Equipment (CPE), D2D devices, machine-to-machine (M2M) devices, V2X devices, and the like. In the following description, the terms "communication device," "terminal," "user equipment," 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. 1. The wireless communication system 100 may include one or more network devices 101. For example, in this example, network device 101 may be embodied as a base station, e.g., 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, relay, etc. Network device 101 provides wireless connectivity to a plurality of communication devices 111-1, 111-2 (hereinafter collectively referred to as communication devices 111) within its coverage area. The communication device 111 may communicate with the network device 101 via the

wireless transmission channel

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

The wireless communication system 100 may be a TDD-based communication system, i.e., the uplink and downlink may 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 uplink and others are for downlink.

As described previously, in the TDD system, the network apparatus 101 can obtain information on 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 an uplink channel by measuring a downlink channel. An example of obtaining CSI of a channel between network device 101 and communication device 111 based on measurements of Reference Signals (RSs) is schematically shown in fig. 2.

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 may measure the CSI-RS from the network device to learn/determine the CSI (e.g., the value of the channel matrix) of the downlink channel. Theoretically, based on the channel reciprocity of TDD, in an ideal case, the communication device 111 may use the obtained CSI of the downlink channel as the CSI of the uplink channel. Similarly, network device 101 may measure Sounding Reference Signals (SRS) from communication device 111 to determine CSI for an uplink channel and use the CSI for downlink scheduling and transmission based on channel reciprocity.

However, in practical TDD systems, it is difficult for the transmitting device to obtain all the CSI needed 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 SRS capacity limitation. In a wireless communication system such as NR, a user side can transmit to and receive from a TRP using multiple antennas. If the TRP wants to obtain the full CSI between each UE and the TRP, more SRS resources need to be configured for uplink channel measurement. Theoretically, the TRP can perfectly obtain channel information of all users without limitation of SRS resources. However, in practice, the SRS resources per cell are limited, and this will limit the allocation of SRS resources among candidate users. In addition, the multi-user scheduling gain is also limited. If a TRP wants to obtain the full CSI of each user's channel, it will take a long time for SRS measurement, which results in the partial channel information measured in an earlier slot (or subframe) being outdated. For multiple TRP transmissions, this scheme will face more challenges.

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

These practical factors above (and some others) will lead to partial reciprocity between the downlink and uplink channels, which in turn deteriorates the performance of NR TDD MU-MIMO. In view of the above problems, the proposed solution in the third generation partnership project (3GPP) radio access network 1(RAN1) working group includes: 1) partial SRS transmission and partial CSI quantization by a common codebook; 2) partial SRS transmission and antenna group switching; and 3) codebook quantization. For solution 1), the error of the partial CSI quantization is large due to the use of the common codebook. The quantized feedback does not reflect the actual channel information well. For solution 2), the TRP side needs more time to obtain the complete channel matrix. Therefore, when the transmission scenario changes fast, there is a risk that the previous CSI measurement part is outdated. Whereas solution 3) is used for single user transmission. For multi-user transmission, this scheme 3) will result in more multi-user interference and degrade the performance of multi-user transmission.

In order to e.g. improve CSI accuracy for TRP side acquisition and/or improve SRS capacity within a cell, new solutions for acquiring/determining CSI are proposed in the present disclosure taking into account the practical limitations of TDD systems. Some embodiments may be used, for example (but not limited to) in a first phase of NR systems of 3GPP, while some embodiments may be used, for example (but not limited to), in a second phase of NR systems 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 to improve the capacity of SRS with partial reciprocity of the channel and an improved codebook. Only partial reciprocity properties exist for the uplink and downlink as a whole. However, for some sub-channels (e.g. channels between TRP and transmit antenna subgroups on the UE side) there is still a complete reciprocity. The UE can obtain information of the partial channel through CSI-RS measurement, and the TRP can obtain information of the partial channel through uplink SRS measurement. That is, the information of the partial channel can be known to both the UE and the TRP, which transparently bridges between the UE and the TRP. The transmit covariance matrices for the partial channels may 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, e.g., the covariance matrix can map an existing common codebook to a subspace over the spatial domain of a particular user channel. The updated user-specific codebook has a high resolution and can be used to quantize the remaining downlink channels on the user side. Codewords selected from the user-specific new codebook are fed back to the TRP. The TRP side can take the same procedure to update the common codebook to obtain the same user specific codebook. The TRP then selects a codeword from the updated codebook according to the 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 through 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 improve the capacity of SRS using the partial reciprocity of the channel and the correlation of the channel. As mentioned above, although only partial reciprocity properties exist for the overall uplink and downlink, full reciprocity still exists for some sub-channels. Therefore, the channel between the transmitting side and the receiving side can be divided into two parts. The first part of the downlink channel has a corresponding uplink channel, and therefore this part of the channel is known (e.g. by measurement) to the UE and TRP side due to its full reciprocity. While the second part of the downlink may not have a corresponding uplink. In this embodiment, the user may calculate an in-phase matrix between the first and second partial channels based on, for example, downlink CSI-RS measurements, and feed back the in-phase matrix to the TRP. The TRP may obtain/determine CSI of the second partial downlink channel using the obtained first partial CSI (e.g., via SRS measurement) and the fed-back in-phase matrix. 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 on the user side and avoid the search process for the optimal codeword.

In addition, none of the above embodiments need to obtain complete CSI through SRS, and thus, SRS resources configured for each user may be reduced, thereby improving SRS capacity in a cell. That is, more remaining SRS resources may be used for other candidate users or for other special transmission purposes, e.g., for supporting multi-user transmission based on non-linear precoding. This helps to improve the overall performance of the system.

A simplified system model according to some embodiments of the present disclosure is shown in fig. 3. In this example system, TRP 310 and UE 320 are equipped with

multiple antennas

301 and 302, respectively. The UE 320 can obtain the full downlink channel state information H by measuring the CSI-RS of the downlink. Theoretically, the TRP 310 can obtain the downlink channel H by measuring the uplink channel, utilizing channel reciprocity. However, some realistic limiting factors make it difficult for TRP 310 to obtain a complete channel by measurement. For example, a user uses multiple antennas 302 for downlink reception, while using only a subset 312 of the multiple antennas 302 for uplink transmission. In this case, TRP 310 can only obtain the channel corresponding to antenna subgroup 312 through 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 be obtained by measurement of the reference signal 330 (e.g., uplink SRS) on the TRP 310 side, while the second partial channel H2 may be recovered by the TRP 310 by other means.

In fig. 3, information about H2 is provided to the TRP through low complexity feedback 340. Recovering the subchannel matrix H2 with high accuracy becomes the key to obtaining an accurate full downlink channel matrix. In some embodiments, to enhance the resolution of user channel quantization, a user-specific codebook is determined for quantization of channel H2 based on a common codebook and with partial reciprocity. And the TRP side can take the same operation as the user side, and high-precision CSI recovery is realized. In other embodiments, the amount of feedback of H2 may be reduced and/or the accuracy of the CSI may be improved based on the correlation of the channel matrix.

A method 400 implemented at a communication device operating in a TDD wireless communication system according to 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 in fig. 1, and the communication device may be, for example and without limitation, the communication device 111 shown in fig. 1 or the communication device 320 shown in fig. 3. For ease of discussion, the method 400 will be described below with reference to the communication device 111 and the network environment 100 described in fig. 1.

As shown in fig. 4A, at block 410, communication device 111 obtains CSI for a channel between it and network device 101 based on a signal from network device 101. The channel includes a first subchannel and a second subchannel. For example, the channel may be denoted as H ═ H1; h2 ]. Thus, at block 410, the communication device obtains a first subchannel H1 and a second subchannel H2.

In one embodiment, communication device 111 may obtain channel H based on the CSI-RS from network device 101 at block 410. 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 subchannel H1 and the second subchannel H2 may be associated with the first subset a1 and the second subset a2, respectively, of antenna ports of the communication device 111. In one embodiment, a1 and a2 are configurable. For example, a1 may be configured to include antenna ports 1 and 2 of the four antenna ports of the communication device, while a2 may be configured to include antenna ports 3 and 4 of the four antenna ports of the communication device. In another embodiment, 1 antenna port may be included in a1 and 3 antenna ports may be included in a2, or vice versa. In another embodiment, the first subchannel H1 and the second subchannel H2 may each be associated with a different polarization direction of the antenna of the communication device 111.

At block 420, communication device 111 transmits a reference signal to network device 101 to indicate information about the CSI for the first subchannel. This enables the network device 101 to obtain the subchannel matrix H1 by measuring the uplink reference signal and utilizing reciprocity between the uplink channel and the downlink channel. This means that the subchannel matrix H1 is thus known to 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 may be a demodulation reference signal (DMRS). In one embodiment, the communication device 111 may transmit the reference signal to the network device 101 through a first subset a1 of antenna ports associated with the first subchannel H1.

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

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

wherein (C)^HDenotes an operation of taking a conjugate, f denotes a subcarrier index, and in which the covariance matrix R is assumed to be in all N_fObtained on a subcarrier channel.

In another embodiment, the communication device 111 may convert the bandwidth (i.e., N) of the signal from the network device_fSub-carriers) into a plurality of sub-bands, and a transmit covariance matrix of a first sub-channel is obtained for each of the plurality of sub-bands, respectively, to obtain a more accurate transmit covariance matrix for each sub-band.

At block 432, the communication device 111 may determine a codebook that is 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 may be quantized by a predefined codebook, whereas the TRP and all users use a predefined common codebook. That is, each user quantizes its channel using the same codebook and feeds back the index of the codeword to the TRP. Using the feedback index and the codebook, the TRP is able to 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; meanwhile, in order to reduce uplink feedback overhead, the codebook size is limited. Furthermore, the current codebook is a common codebook for all users and TRPs. In this case, the common codebook is extended to all spaces in the spatial domain, which results in the common codebook having a low resolution in a given subspace in the spatial domain.

Unlike prior codebook quantization methods, the operation of block 432 can enhance the resolution of user channel quantization by taking advantage of the partial reciprocity of the common codebook and channel to obtain a codebook specific to the communication device 111, limiting the common codebook to a smaller subspace. 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 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 equation (2) below:

wherein w_iRepresents the ith codeword in the common codebook, L represents the total number of codewords in the common codebook, R represents the transmit covariance matrix, | | | | purple_FDenotes an operation of taking the F norm, and c_iRepresenting the ith codeword in the determined codebook specific to the communication device 111.

A comparison of the common codebook and the communication device 111 specific codebook is schematically illustrated in fig. 5. The left side of fig. 5 shows the codeword w in the common codebook_iDistributed in space, and as can be seen from the figure, the codebook is extended to the whole space, so that the resolution is low. The codewords of the common codebook may be mapped to subspaces in the spatial domain 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 communication device 111 specific codebook obtained by the operation of block 432 is centered on the communication device 111 specific subspace. Since a refined codebook of the same size is used to quantize the spatial subspace, this means that codeword c_iThe channel information in this particular subspace can be represented with a higher resolution. Although the transformation of a codebook of size 8 is shown in fig. 5 by way of example only, it should be understood that a similar expansion operation in block 432 applies to larger codebook sizes.

Returning now to fig. 4B, at block 433, the communication device 111 may select a codeword from the determined communication device-specific codebook that matches the CSI H2 of the second subchannel; and an indication of the codeword is determined at block 434 as information regarding CSI of the second subchannel to be transmitted to network device 101.

Fig. 4C shows another example implementation 430' of block 430. 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 at block 410; at block 436, the communication device 111 may determine the indication of the in-phase matrix as information about CSI of the second subchannel to be transmitted to the network device 101. In this embodiment, the communication device 111 determines 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 may be represented as follows:

in which the operation is

Representing the pseudo-inverse operation. In another embodiment, the in-phase matrix between H1 and H2 may 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 a codebook for the in-phase matrix matching the in-phase matrix G, or a value of an element in the in-phase matrix G. It can be known from equation (3) that the size of matrix G will be smaller than the number of antennas on the user side. This means that the amount of feedback of information on the CSI of the second subchannel is relatively small.

After determining information about the CSI for the second subchannel to send to network device 101, for example (but not limited to) in the manner of fig. 4B or 4C, communication device 111 sends this information about the determined CSI for the second subchannel to network device 101 at block 440, as shown in fig. 4A. This information enables the network device to obtain the CSI of the complete channel H in conjunction with the subchannel H1 measured by the reference signal.

An example process 610 for acquiring CSI for channel H between communication device 111 and network device 101 according to an embodiment of the disclosure is shown in fig. 6A.

The example of fig. 6A is associated with the embodiment of fig. 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 communication device 111 sides. Thus, with partial channel reciprocity, the covariance matrix can be considered as common information between network device 101 and a given communication device 111. If communication device 111 informs network device 101 that it will use the user-specific codebook, or the TRP informs the UE to use the user-specific codebook, or both, that a consensus is obtained by a predetermined configuration, network device 101 may take the same action as communication device 111 to update the common codebook to obtain the same communication device 111-specific codebook. Thus, using the feedback index from the communication device 111, the network device 101 is able to recover a partial channel matrix (due to e.g. SRS capacity limitation or UE uplink transmission capability limitation) that cannot be obtained by uplink SRS measurement.

As shown in fig. 6A, communication device 111 receives/measures (611) the downlink CSI-RS from network device 101, estimates/obtains (612) the complete downlink channel matrix H, and the user divides the channel matrix into two parts according to its uplink transmission configuration [ H1; h2 ]. The communication device 111 then determines 613 information about sub-channel H2 to be sent to the network device 101 by, for example, the embodiment shown in fig. 4B based on H1 and H2. The reference signal (e.g., SRS) for H1 measurements and information about H2 are transmitted (614) by communication device 111 to network device 101 over the uplink. In one embodiment, communication device 111 transmits SRS through the subset of antennas associated with subchannel H1, such that network device 101 obtains subchannel H1 by measuring SRS, and feeds back to network device 101 the index of channel H2 quantized based on user-specific codebook C. It should be noted that the SRS and the information on H2 are not necessarily transmitted simultaneously. For example, the SRS may be transmitted earlier than the information on H2.

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

As can be seen from the above process, the covariance matrix R can be obtained by partial channel reciprocity, and the communication device 111 does not need to feed back the transmit 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 a plurality of communication apparatuses exist in the communication system, each communication apparatus 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 network device 101 side, the operation shown in fig. 6A should be performed independently for different communication devices.

Another example process 620 is shown in fig. 6B, in accordance with an embodiment of the present disclosure. This example is associated with the method of fig. 4C, i.e., the phase relationship between H1 and H2 is utilized to obtain CSI for H2. The phase relationship may appear as an in-phase matrix between H1 and H2, and the in-phase matrix may be fed back (e.g., in an explicit manner) to network device 101. Network device 101 then uses the in-phase matrix and the measured H1 (e.g., via SRS) to obtain H2. This example can significantly reduce the computational complexity on the communication device side and the operational complexity on the network side for channel recovery of a particular communication device. This scheme may be used, for example, in NR phase II in 3 GPP.

As shown in fig. 6B, communication device 111 receives 621 a downlink transmission (e.g., CSI-RS) and obtains a complete downlink channel matrix H through downlink CSI-RS measurements. The channel matrix may be divided into two parts H1; h2 ]. The communication device 111 may determine (622) an in-phase matrix G between H1 and H2, for example, in the manner described by equation (3) above. An indication of the in-phase matrix G (e.g., an index of the corresponding codeword) and a reference signal for measuring subchannel H1 are sent 623 to network device 101. Based on the reference signal from the communication device 111, the network device 101 may determine (624) H1 and obtain (625) H2 based on H1 and the received indication of G. In the case where G is defined as shown in formula (3), the network device may obtain H2 by the following formula (4):

H₂＝GH₁(4) where G is the user-specific in-phase matrix fed back by the communication device 111. The above procedure 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 ═ H2 by combining/concatenating H1 and H2₁；H₂]. The obtained H may be used by the network device for, for example (but not limited to), multi-user scheduling and downlink transmission precoder design to suppress inter-user interference.

As discussed above, in the example of fig. 6B, the in-phase matrix G may be explicitly fed back to the network device 101, such that the network device 101 derives the subchannel matrix H2 directly based on G. This reduces the operational complexity on both the user side and the network side. In addition, since the size of G is small, the uplink overhead is also under control. In some embodiments, the communication device 111 may send the index of the codeword corresponding to the G matrix to the network device, or send the elements 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 approach 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 so that network device 101 can determine the feedback content of communication device 111.

In other embodiments, new signaling may optionally be introduced to coordinate/synchronize the operation of network device 101 with the operation of communication device 111 for efficient multi-user downlink transmission. For example, communication device 111 may receive an indication of a type of CSI feedback to be used by communication device 111 from network device 101, as shown at block 450 in fig. 4A. As an example, the indication signaling may contain two bits XY to indicate CSI acquisition schemes for different users or different groups of users. Examples of values and corresponding meanings of XY are shown in table 1 below. In another embodiment, the CSI acquisition scheme may also be indicated with 1 bit.

TABLE 1 indication of CSI scheme

Alternatively or additionally, in another embodiment, the communication device 111 may, at block 460 in fig. 4A, send an indication of its CSI feedback capability to the network device 101, e.g. indicating whether the communication device 111 supports the feedback scheme shown in fig. 4B or 4C, for example. And alternatively, at block 460, communication device 111 may also send an indication of its antenna configuration status to network device 101 to cause the network device to determine the CSI acquisition scheme that may 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 may be, for example, but is not limited to, system 100 in fig. 1, and the network device may be, for example, network device 101 in fig. 1 or network device 310 in fig. 3. For ease of discussion, method 700 will be described below with reference to network device 101 and network environment 100 of fig. 1.

As shown in fig. 7A, network device 101 sends a signal to communication device 111 at block 710 for determining CSI for a channel between communication device 111 and network device 101. The channel includes a first subchannel and a second subchannel. In one embodiment, the signal transmitted by network device 101 at block 710 may include, but is not limited to, a 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, among others.

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

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

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

At block 740, network device 101 receives information from communication device 111 regarding the CSI for the second subchannel. 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 regarding CSI for the second subchannel received by network device 101 at block 740 was determined at block 430 and transmitted at block 440 by communication device 111 based on method 400. Therefore, the description of the information on the CSI of the second subchannel described in connection with method 400 is equally applicable here.

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

For example, the information on the CSI of the second subchannel may be a codeword index of the second subchannel H2 quantized via a codebook specific to the communication device 111. In this example, network device 101 may determine H2 by performing operations 751-.

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

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

At block 753, 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 regarding CSI of the second subchannel received by network device 101 at block 740 may be an indication of an 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 the in-phase matrix matching the in-phase matrix, or a value of an element in the in-phase matrix G. In this example, network device 101 may determine H2 by performing operation 754 shown in fig. 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 received indication of the in-phase matrix G. For example, network device 101 may determine H2 by equation (4) as described previously.

In some embodiments, method 700 may optionally include the operations of block 760, where network device 101 sends an indication of a 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 transmitted by Radio Resource Control (RRC) signaling or Medium Access Control (MAC) Control Element (CE). If the system or network is stable. The system overhead can be reduced by RRC or MAC transmission.

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

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

An aspect of the present disclosure also provides a communication device in a wireless communication network (e.g., the communication network 100 shown in fig. 1). The communication device may be, for example, the communication device 111 shown in fig. 1.

In one embodiment, a 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 on CSI of a first sub-channel in the channel. The feedback information determination unit is configured to determine information about CSI of the second sub-channel to be transmitted to the network device based on CSI of the first sub-channel and CSI of the second sub-channel in the channel, and the feedback unit is configured to transmit the determined information about CSI of the second sub-channel to the network device.

In one embodiment, the communication device may perform the method 400 described in conjunction with fig. 4A-4C, and thus the description of the method 400 is equally applicable here and will not be repeated.

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

Another aspect of the 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 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 a reference signal from the communication device, and the first CSI determination unit is configured to determine CSI of the first subchannel based on the received reference signal. The CSI information receiving unit is configured to receive, from the communication device, information on CSI of the second sub-channel, wherein the received information on CSI of the second sub-channel is based on CSI of the first sub-channel and CSI of the second sub-channel. The second CSI determination unit is configured to determine CSI of the second subchannel based on the received information on CSI of the second subchannel.

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

In one embodiment, the communication device may perform the method 700 described in conjunction with fig. 7A-7C, and thus the operations described in conjunction with the method 700 are equally applicable here and will not be described in detail.

Fig. 8 illustrates a simplified block diagram of an apparatus 800 that may be implemented in or as a communication device or network device (e.g., network device 101 or communication device 111 shown in fig. 1).

The apparatus 800 may include one or more processors 810 (such as a data processor) and one or more memories 820 coupled to the processors 810. Apparatus 800 may also include one or more transmitter/receivers 840 coupled to processor 810. The memory 820 may be a non-transitory machine-readable storage medium and it may store a program or computer program product 830. The computer program (product) 830 may include instructions that, when executed on the associated processor 810, enable the apparatus 800 to operate according to embodiments of the disclosure (e.g., perform the methods 400 or 700). The combination of one or more processors 810 and one or more memories 820 may form a processing component 850 suitable for implementing various embodiments of the present disclosure.

Various embodiments of the 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 may be of any type suitable to the local technical environment, and may be implemented using any suitable data storage technology, such as semiconductor-based memory terminal devices, magnetic memory terminal devices and systems, optical memory terminal devices and systems, fixed memory and removable memory, as non-limiting examples.

The processor 810 may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, Digital Signal Processors (DSPs) and processors based on a multi-core processor architecture, as non-limiting examples.

Although 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 present 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 containing a computer program or computer program product as described above, including a machine-readable medium and a machine-readable transmission medium. The machine-readable medium may also be referred to as a computer-readable medium and may 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 disk, etc. A machine-readable transmission medium may also be referred to as a carrier and may include, for example, electrical, optical, radio, acoustic, or other form of propagated signals, such as carrier waves, infrared signals, etc.

The techniques described herein may be implemented by various means, so that an apparatus implementing one or more functions of a corresponding apparatus described with an embodiment includes not only prior art means but also means for implementing one or more functions of a corresponding apparatus described with an embodiment, and it may include separate means for each separate function or means configured to perform two or more functions. For example, these techniques may 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, implementation can be through modules (e.g., procedures, functions, and so on) that perform the functions described herein.

Example embodiments herein are described above with reference to block diagrams and flowchart illustrations of methods and apparatus. It should be understood that each block of the block diagrams and flowchart illustrations, and combinations of blocks in the block diagrams and flowchart illustrations, respectively, can be implemented by various means including hardware, software, firmware, and combinations thereof. For example, in one embodiment, each block 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 may be loaded onto a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions which execute on the computer or other programmable data processing apparatus create means for implementing the functions specified in the flowchart block or blocks.

Further, while operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In some cases, multitasking and parallel processing may be advantageous. Likewise, although several specific implementation details are included in the above discussion, these should not be construed as limitations on the scope of the subject matter described herein, but rather as descriptions of features specific to particular embodiments. 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 also be implemented in multiple embodiments separately or in any suitable subcombination. Furthermore, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

It is obvious to a person skilled in the art that with the advancement of technology, the inventive concept may be implemented in various ways. The above-described embodiments are given for the purpose of illustration and not limitation of the present disclosure, and it is to be understood that modifications and variations may be made without departing from the spirit and scope of the present disclosure as readily understood by those skilled in the art. Such modifications and variations are considered to be within the scope of the disclosure and the appended claims. The scope 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, a vector [ M, N, P, Q ] is used to represent a planar antenna configuration, where M denotes the number of rows, N denotes the number of columns, P denotes the polarization mode, and Q denotes the number of transmitting radio units (TXRU). P ═ 1 indicates single polarization, and P ═ 2 indicates cross polarization. The main system configurations used in computer simulations are as follows:

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

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

3. Greedy search on maximum sum rate based on the obtained user channel information is used for multi-user and multi-stream scheduling. Up to 8 streams per TRP and up to 2 streams per user are restricted in the scheduling algorithm.

The following 5 solutions a) -e for CSI acquisition were evaluated:

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

b) SRS + user specific codebook. This is one of the example embodiments presented in this disclosure. Partial channel information is obtained through SRS measurements and the remaining channels are obtained through user-specific adaptive codebook quantization and feedback. The common codebook is a codebook defined in version 13(R13) having 4 times oversampling in the horizontal and vertical domains. In the simulation, SrsPortNum is used to indicate SRS resources actually used per user.

c) SRS + in-phase matrix. This is another example embodiment presented in this disclosure. Also, in the simulation, SrsPortNum is used to indicate SRS resources actually used per user.

d) SRS + R13 common codebook. This is one of the prior art solutions. Wherein, part of the channel information is obtained through SRS measurement, and the rest channels are obtained through quantization and feedback of a common codebook. The common codebook is a codebook defined in R13 having 4 times oversampling in the horizontal and vertical domains. In the simulation, SrsPortNum is used to indicate SRS resources actually used per user.

e) The R13 codebook. This is another prior art solution. In this scheme, the user channel is entirely 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 having 4 times oversampling in the horizontal and vertical domains.

Solution a) always uses 4 SRS resources to help a TRP to obtain a complete downlink channel, so this solution has an upper limit performance. For other solutions, including solutions b) -d), each user uses partial SRS resources (SrsPortNum ═ 2 or 3) and limited feedback. In scheme e), the user does not use any SRS resource in the uplink, and its operation is the same as that of the FDD system.

Fig. 9 shows a performance comparison of the five solutions in a configuration of SrsPortNum ═ 2. Where the abscissa is the signal-to-noise ratio (SNR) and the ordinate is the Spectral Efficiency (SE) obtained for each scheme. Fig. 9 shows that both proposed solutions b) and c) exceed the performance of existing solutions d) and e), and that the gap between the proposed solution and the upper limit remains close to a constant value as the SNR increases. Whereas the performance of the existing solutions d) and e) deteriorates drastically with increasing SNR. For MU-MIMO transmission, it can be assumed that each user has a high quality channel corresponding to a high SNR region. This means that the proposed solutions b) and c) work well for MU-MIMO. As previously described, in the simulation, the number of total transmission streams is limited to up to 8, and the number of streams per user is limited to up to 2. Multi-user and multi-stream scheduling is performed using a greedy search algorithm to maximize the sum rate of the system.

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

A comparison of performance in the SrsPortNum-3 scenario is shown in fig. 10. It can be seen that the gap between the complete reciprocal CSI solution a) (upper bound) and the proposed solution diminishes as more SRS resources are used per user. Fig. 10 also shows that in 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 seen that embodiments of the present disclosure (e.g., evaluated scenarios b) and c)) have advantages in a variety of scenarios, such as those listed below.

i) The proposed solutions b) and c) can help the TRP to obtain a more accurate downlink CSI per user and to obtain a performance close to the upper limit if the user uses different antenna configurations for downlink reception and uplink transmission, e.g. the number of antenna ports for downlink is larger than the number of antenna ports for uplink. Alternatively, the user may feed back the antenna configuration status 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 operation of CSI acquisition.

ii) if the user uses the same antenna configuration for downlink reception and uplink transmission, e.g., the number of antenna ports for downlink is equal to the number of antenna ports for uplink, then theoretically complete channel reciprocity can be obtained and perfect channel state information can be obtained for TRP. While for practical systems, SRS resources are limited. If TRP uses the proposed solution for CSI acquisition, TRP can perform scheduling from a larger user candidate set to obtain higher multi-user scheduling gain. In this case, the TRP may for example inform the user of a specific CSI acquisition scheme, e.g. using scheme b) or c), to synchronize/match the operation of the two.

iii) if the TRP assumes different transmit precoding schemes for different users, e.g. linear precoding for non-related user groups and non-linear precoding for highly related user groups, different SRS configuration strategies may be used for different user groups. For example, for high-correlation user groups, it is preferable to use accurate CSI because non-linear transmission schemes are used for these users, which require more accurate CSI. Accordingly, more SRS resources may be allocated to those users. For non-related user groups, a linear precoding based transmission scheme may be used, and the proposed CSI acquisition scheme may be used. In this case, the TRP may also inform the user of the CSI acquisition scheme. In other embodiments, the user may know the CSI scheme to use through a predetermined configuration or implicit manner. In addition, if a precoding scheme for a user changes due to a decision of the TRP or a movement of the user, the TRP may also notify the user of a new CSI acquisition scheme.

Claims

1. 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 a network device based on a signal from the network device; the channel comprises a first sub-channel and a second sub-channel;

transmitting a reference signal to the network device to indicate information on CSI of the first subchannel;

determining information about CSI of the second sub-channel to be transmitted to the network device based on the CSI of the first sub-channel and the CSI of the second sub-channel; and

transmitting the determined information on the CSI of the second sub-channel to the network device,

wherein determining information about CSI of the second sub-channel to be transmitted to the network device based on the CSI of the first sub-channel and the CSI of the second sub-channel comprises:

obtaining a transmission covariance matrix of the first subchannel based on the CSI of the first subchannel;

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

selecting a codeword from the determined communication device specific codebook that matches CSI for the second sub-channel; and

determining the indication of the codeword as the information regarding CSI for the second subchannel to be sent to the network device.

2. The method of claim 1, wherein obtaining CSI of a channel between the communication device and a network device based on a signal from the network device comprises:

obtaining CSI for the channel based on a CSI reference signal, CSI-RS, from the network device.

3. The method of claim 1, wherein the first subchannel and the second subchannel are associated with a first subset and a second subset, respectively, of antenna ports of the communication device.

4. The method of claim 3, wherein transmitting a reference signal to the network device comprises:

transmitting the reference signal to the network device through the first subset of antenna ports associated with the first subchannel.

5. The method of claim 1, wherein obtaining a transmit covariance matrix for the first subchannel based on the CSI for the first subchannel comprises:

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

obtaining the transmit covariance matrix for the first subchannel separately for each of the plurality of subbands.

6. The method of claim 1, wherein determining the communication device specific codebook based on the transmit covariance matrix and a common codebook for the second subchannel comprises:

obtaining the communication device specific codebook by:

wherein w_iRepresenting an ith codeword in the common codebook, L representing a total number of codewords in the common codebook, R representing the transmit covariance matrix, | | | | survival_FDenotes an operation of taking F norm, and c_iRepresenting the ith codeword in the determined codebook specific to the communication device.

7. The method of claim 1, wherein determining information about the CSI of the second subchannel to be transmitted to the network device based on the CSI of the first subchannel and the CSI of the second subchannel comprises:

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

determining an indication of the in-phase matrix as the information regarding CSI of the second sub-channel to be sent to the network device,

wherein the in-phase matrix is represented as:

in which the operation is

Representing the pseudo-inverse operation.

8. The method of claim 7, wherein the indication of the in-phase matrix comprises:

an index of a codeword selected from a codebook for the in-phase matrix matching the in-phase matrix, or

The values of the elements in the in-phase matrix.

9. The method of claim 1, further comprising sending an indication of at least one of the following information to the network device:

a CSI feedback capability of the communication device; and

an antenna configuration state of the communication device.

10. The method of claim 1, further comprising:

receiving, from the network device, an indication of a type of CSI feedback to be used by the communication device.

11. A method implemented at a network device operating in a time division duplex, TDD, wireless communication system, comprising:

transmitting a signal for determining channel state information, CSI, of a channel between the communication device and the network device to a communication device, the channel comprising a first subchannel and a second subchannel;

receiving a reference signal from the communication device;

determining CSI for the first subchannel based on the received reference signals;

receiving, from the communication device, information on CSI for the second subchannel, wherein the received information on CSI for the second subchannel is based on CSI for the first subchannel and CSI for the second subchannel; and

determining CSI for the second sub-channel based on the received information on CSI for the second sub-channel,

wherein receiving information on CSI for the second sub-channel from the communication device comprises:

receiving, from the communication device, an index of a codeword for the second subchannel, the codeword from the communication device-specific codebook; and is

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

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

determining the codeword for the second subchannel from the determined codebook based on the received index.

12. The method of claim 11, wherein transmitting a signal to a communication device for estimating CSI of a channel between the communication device and the network device comprises:

transmitting a CSI reference signal (CSI-RS) to the communication device.

13. The method of claim 11, wherein the first subchannel and the second subchannel are associated with a first subset and a second subset, respectively, of antenna ports of the communication device.

14. The method of claim 13, wherein the reference signal received from the communication device is from the first subset of antenna ports associated with the first subchannel.

15. The method of claim 11, wherein obtaining a transmit covariance matrix for the first subchannel based on the CSI for the first subchannel comprises:

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

16. The method of claim 11, wherein determining the communication device-specific codebook for the second subchannel based on the transmit covariance matrix and a common codebook for the second subchannel comprises:

obtaining a codebook specific to the communication device by:

17. The method of claim 11, wherein receiving information from the communication device regarding CSI for the second subchannel comprises:

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

obtaining CSI for the second sub-channel based on the determined CSI for the first sub-channel and the received indication of the in-phase matrix,

wherein the in-phase matrix is represented as:

in which the operation is

Representing the pseudo-inverse operation.

18. The method of claim 17, wherein the indication of the in-phase matrix comprises:

The values of the elements in the in-phase matrix.

19. The method of claim 11, further comprising:

transmitting, to the communication device, an indication of a type of CSI feedback to be used by the communication device.

20. The method of claim 19, further comprising receiving an indication of at least one of the following information from the communication device:

a CSI feedback capability of the communication device; and

an antenna configuration state of the communication device.

21. An apparatus for a time division duplex, TDD, wireless communication system, comprising a processor and a memory, the memory storing instructions executable by the processor whereby the apparatus is operative to perform the method of any of claims 1 to 10.

22. An apparatus for a time division duplex, TDD, wireless communication system, comprising a processor and a memory, the memory storing instructions executable by the processor whereby the apparatus is operative to perform the method of any of claims 11 to 20.

23. A computer-readable storage medium having instructions stored thereon, which when executed on at least one processor causes the at least one processor to perform the method of any one of claims 1 to 20.