CN107294584B

CN107294584B - Method and apparatus for sharing channel state information reference signal resources

Info

Publication number: CN107294584B
Application number: CN201610200932.XA
Authority: CN
Inventors: 张晴川; 张闽; 李迅
Original assignee: Nokia Shanghai Bell Co Ltd; Alcatel Lucent SAS
Current assignee: Nokia Shanghai Bell Co Ltd; Alcatel Lucent SAS
Priority date: 2016-03-31
Filing date: 2016-03-31
Publication date: 2021-05-11
Anticipated expiration: 2036-03-31
Also published as: WO2017168254A1; CN107294584A

Abstract

Embodiments of the present disclosure provide methods and apparatus for sharing channel state information reference signal resources. The method comprises the following steps: obtaining information of a plurality of beam groups, each of the plurality of beam groups configured to transmit a beamformed CSI-RS specific to one of a plurality of User Equipments (UEs) to the one UE; estimating a received signal strength of each of the plurality of UEs based on the obtained information; comparing the estimated received signal strength to a predetermined first threshold; and in response to each of the estimated received signal strengths being greater than the first threshold, transmitting beamformed CSI-RS specific to the each UE on the same CSI-RS resource. Embodiments of the present disclosure improve the efficiency of UE-specific beamformed CSI-RS by taking advantage of the characteristics of the beamforming operation.

Description

Method and apparatus for sharing channel state information reference signal resources

Technical Field

Embodiments of the present disclosure relate generally to wireless communication technology and, more particularly, to a method and apparatus for sharing channel state information reference signal resources and a method and apparatus for reporting channel state information.

Background

Beamformed CSI-RS is a very important feature introduced in 3GPP Release13, which makes it possible to use large-scale antenna arrays in LTE systems without the need to define complex codebooks like traditional non-precoded CSI-RS. In beamformed CSI-RS, the eNB may determine beamforming weights at the CSI-RS resources by using long-term channel reciprocity or a hybrid approach of non-precoded CSI-RS. UE-specific beamformed CSI-RS is supported by using a group of microwave beams directed towards the UE. The UE then reports beam selection information and phase information in the polarization direction. The UE-specific beamformed CSI-RS has a good CSI feedback accuracy due to the strong directivity of the beamformer. However, since the required CSI-RS resources are related to the number of active UEs, the CSI-RS overhead may be very high if there are a large number of active UEs. Thus, there is a need to reduce CSI-RS overhead.

Fig. 1 schematically shows one possible scheme for reducing CSI-RS overhead. In the scheme shown in fig. 1, beams with a directivity that is not too strong are used to improve coverage and thus reduce CSI-RS overhead. However, this leads to a reduction in the granularity of beamforming and thus reduces CSI feedback accuracy. Therefore, CSI-RS overhead is a major issue for UE-specific CSI-RS.

Disclosure of Invention

Therefore, in order to solve or at least partially alleviate the above-mentioned problems in the prior art, a scheme is needed that reduces the CSI-RS overhead required for UE-specific beamformed CSI-RS and has less impact on the beamforming performed on the CSI-RS.

According to a first aspect of embodiments of the present disclosure, there is provided a method for sharing channel state information reference signal, CSI-RS, resources. The method comprises the following steps: obtaining information of a plurality of beam groups, each of the plurality of beam groups configured to transmit a beamformed CSI-RS specific to one of a plurality of User Equipments (UEs) to the one UE; determining a spatial isolation between each two of the plurality of beam groups based on the obtained information; comparing each of the determined spatial isolations to a predetermined threshold; and in response to each of the determined spatial isolations being greater than the threshold, transmitting a beamformed CSI-RS specific to each of the plurality of UEs on the same CSI-RS resource.

In some embodiments, determining the spatial isolation comprises: determining a plurality of orthogonal projection matrices, each of the plurality of orthogonal projection matrices associated with one of the plurality of beam groups; calculating a distance between each two of the plurality of orthogonal projection matrices; and determining the calculated distance as the spatial separation.

In some embodiments, obtaining information for a plurality of beam groups includes obtaining information for a first beam group and information for a second beam group, the first beam group and the second beam group configured to transmit a first beamformed CSI-RS specific to the first UE to a first UE and a second beamformed CSI-RS specific to a second UE to the second UE, respectively.

In some embodiments, the method further comprises: in response to each of the determined spatial isolations being greater than the threshold, transmitting the first beamformed CSI-RS and the second beamformed CSI-RS on predefined same subbands of the CSI-RS resource.

According to a second aspect of embodiments of the present disclosure, there is provided a method of sharing channel state information reference signal, CSI-RS, resources. The method comprises the following steps: obtaining information of a plurality of beam groups, each of the plurality of beam groups configured to transmit a beamformed CSI-RS specific to one of a plurality of User Equipments (UEs) to the one UE; estimating a received signal strength of each of the plurality of UEs based on the obtained information; comparing the estimated received signal strength to a predetermined first threshold; and in response to each of the estimated received signal strengths being greater than the first threshold, transmitting beamformed CSI-RS specific to the each UE on the same CSI-RS resource.

According to a third aspect of embodiments of the present disclosure, there is provided a method for sharing channel state information reference signal, CSI-RS, resources. The method comprises the following steps: transmitting a beamformed CSI-RS specific to one of a plurality of User Equipments (UEs) on each of a predefined plurality of subbands of the CSI-RS resource.

In some embodiments, each two subbands in the plurality of subbands are interleaved with each other based on a predetermined interleaving factor.

In some embodiments, each of the plurality of sub-bands comprises one or more contiguous resource blocks.

In some embodiments, the frequency domain location of each of the plurality of sub-bands hops in a plurality of consecutive measurement sub-frames in a different predetermined hopping pattern.

According to a fourth aspect of embodiments of the present disclosure, there is provided a method for reporting channel state information, CSI. The method comprises the following steps: receiving beamformed CSI-RS specific to a User Equipment (UE) on a predefined subband of CSI-RS resources; measuring the CSI based on the received beamformed CSI-RS; and reporting the measured CSI to the base station.

In some embodiments, the subband and another subband of the CSI-RS resource, the another subband configured for another UE, are interleaved with each other based on a predetermined interleaving factor.

In some embodiments, the method further comprises: control signaling is received from the base station carrying the interleaving factor and the offset number of resource blocks.

In some embodiments, the sub-band comprises one or more contiguous resource blocks.

In some embodiments, the frequency domain locations of the sub-bands are hopped in different predetermined hopping patterns in a plurality of consecutive measurement sub-frames.

In some embodiments, the method further comprises: control signaling carrying the frequency domain location and the predetermined hopping pattern is received from the base station.

According to a fifth aspect of embodiments of the present disclosure, there is provided an apparatus for sharing channel state information reference signal, CSI-RS, resources. The device includes: an obtaining unit configured to obtain information of a plurality of beam groups, each of the plurality of beam groups being configured to transmit a beamformed CSI-RS specific to one of a plurality of user equipments, UEs, to the one UE; a determination unit configured to determine a spatial isolation between each two beam groups of the plurality of beam groups based on the acquired information; a comparison unit configured to compare each of the determined spatial isolation degrees with a predetermined threshold; and a transmitting unit configured to transmit the beamformed CSI-RS specific to each of the plurality of UEs on the same CSI-RS resource in response to each of the determined spatial isolations being greater than the threshold.

In some embodiments, the determining unit is further configured to: determining a plurality of orthogonal projection matrices, each of the plurality of orthogonal projection matrices associated with one of the plurality of beam groups; calculating a distance between each two of the plurality of orthogonal projection matrices; and determining the calculated distance as the spatial separation.

In some embodiments, the obtaining unit is further configured to: obtaining information for a plurality of beam groups includes obtaining information for a first beam group and information for a second beam group, the first beam group and the second beam group configured to transmit a first beamformed CSI-RS specific to a first UE and a second beamformed CSI-RS specific to a second UE, respectively, to the first UE and to the second UE.

In some embodiments, the transmitting unit is further configured to: in response to each of the determined spatial isolations being greater than the threshold, transmitting the first beamformed CSI-RS and the second beamformed CSI-RS on predefined same subbands of the CSI-RS resource.

According to a sixth aspect of embodiments of the present disclosure, there is provided an apparatus for sharing channel state information reference signal, CSI-RS, resources. The device includes: an obtaining unit configured to obtain information of a plurality of beam groups, each of the plurality of beam groups being configured to transmit a beamformed CSI-RS specific to one of a plurality of user equipments, UEs, to the one UE; an estimating unit configured to estimate a received signal strength of each of the plurality of UEs based on the acquired information; a comparison unit configured to compare the estimated received signal strength with a predetermined first threshold; and a transmitting unit configured to transmit the beamformed CSI-RS specific to each UE on the same CSI-RS resource in response to each of the estimated received signal strengths being greater than the first threshold.

According to a seventh aspect of embodiments of the present disclosure, there is provided an apparatus for sharing channel state information reference signal, CSI-RS, resources. The device includes: a transmitting unit configured to transmit a beamformed CSI-RS specific to one of a plurality of user equipments, UEs, on each of a predefined plurality of subbands of the CSI-RS resource.

According to an eighth aspect of embodiments of the present disclosure, there is provided an apparatus for reporting channel state information, CSI. The device includes: a receiving unit configured to receive a beamformed CSI-RS specific to a User Equipment (UE) on a predefined subband of CSI-RS resources; a measurement unit configured to measure the CSI based on the received beamformed CSI-RS; and a reporting unit configured to report the measured CSI to the base station.

In some embodiments, the receiving unit is further configured to: means for receiving control signaling from the base station carrying the interleaving factor and the offset number of resource blocks.

In some embodiments, the receiving unit is further configured to: control signaling carrying the frequency domain location and the predetermined hopping pattern is received from the base station.

Embodiments of the present disclosure improve the efficiency of UE-specific beamformed CSI-RS by taking advantage of the characteristics of the beamforming operation and provide a balance between beamforming granularity and CSI-RS overhead for a large number of UEs.

Drawings

The features, advantages and other aspects of various embodiments of the present disclosure will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which several embodiments of the present disclosure are shown by way of illustration and not limitation. In the drawings:

fig. 1 schematically illustrates one possible scheme for reducing CSI-RS overhead;

fig. 2 shows a flow diagram of a method for sharing CSI-RS resources according to a first aspect of an embodiment of the present disclosure;

fig. 3 shows a flow diagram of a method for sharing CSI-RS resources according to a second aspect of an embodiment of the present disclosure;

fig. 4 shows a flow diagram of a method for sharing CSI-RS resources according to a third aspect of an embodiment of the present disclosure;

fig. 5 shows an example of a scheme for multiplexing CSI-RS resources in the frequency domain;

fig. 6 shows another example of a scheme for multiplexing CSI-RS resources in the frequency domain;

fig. 7 shows a flow diagram of a method for reporting CSI according to a fourth aspect of an embodiment of the present disclosure;

fig. 8 shows a block diagram of an apparatus for sharing CSI-RS resources according to a fifth aspect of an embodiment of the disclosure;

fig. 9 shows a block diagram of an apparatus for sharing CSI-RS resources according to a sixth aspect of an embodiment of the disclosure;

fig. 10 shows a block diagram of an apparatus for sharing CSI-RS resources according to a seventh aspect of an embodiment of the present disclosure; and

fig. 11 shows a block diagram of an apparatus for reporting CSI according to an eighth aspect of an embodiment of the present disclosure.

Detailed Description

The principles of the subject matter described herein will now be described with reference to a number of exemplary embodiments. It should be understood that these embodiments are described merely to enable those skilled in the art to better understand and thereby implement the subject matter described herein, and are not intended to limit the scope of the subject matter described herein in any way.

The term "base station" (BS) as used herein may refer to a node B (NodeB or NB), an evolved node B (eNodeB or eNB), a Remote Radio Unit (RRU), a Radio Head (RH), a Remote Radio Head (RRH), a relay, a low power node, such as a pico base station, a femto base station, and the like.

The term "user equipment" (UE) as used herein refers to any device capable of communicating with a BS. As an example, the UE may include a terminal, a Mobile Terminal (MT), a Subscriber Station (SS), a Portable Subscriber Station (PSS), a Mobile Station (MS), or an Access Terminal (AT).

According to an embodiment of the present disclosure, a scheme for improving CSI-RS efficiency by multiplexing CSI-RS resources in the spatial domain is provided. Hereinafter, a scheme of multiplexing CSI-RS resources in the spatial domain will be described with reference to fig. 2 and 3.

According to a first aspect of embodiments of the present disclosure, there is provided a method of sharing channel state information reference signal, CSI-RS, resources. Fig. 2 shows a flow diagram of a method 200 for sharing CSI-RS resources according to a first aspect of an embodiment of the present disclosure. The method 200 may be performed by an eNB in a wireless communication network, and in particular, the method 200 may be performed by an apparatus 800 described later herein with reference to fig. 8.

The method 200 begins at step S210. In step S210, the eNB acquires information of a plurality of beam groups, each of the plurality of beam groups being configured to transmit a beamformed CSI-RS specific to one UE of a plurality of UEs to the one UE.

In step S220, the eNB determines a spatial isolation between each two beam groups of the plurality of beam groups based on the acquired information.

In step S230, the eNB compares each of the determined spatial isolations with a predetermined threshold.

In step S240, the eNB transmits the beamformed CSI-RS specific to each of the plurality of UEs on the same CSI-RS resource in response to each of the determined spatial isolations being greater than the threshold.

Hereinafter, the method 200 for sharing CSI-RS resources will be described with reference to a specific example.

Assuming that there are K active UEs in the cell under consideration, the antenna array at the eNB is dual polarized and has M antenna elements, and each UE has N antennas. The channel matrix between UE i and eNB can be described as:

wherein

And

are a matrix of nxm/2 corresponding to the two polarization directions, respectively.

In a UE-specific beamformed CSI-RS scheme, the eNB may derive beamforming information performed on CSI-RS ports by using long-term channel reciprocity or feedback of the UE obtained by measuring long-term non-precoded CSI-RS in a mixed manner. Here, the obtained beam group of UE i is represented as:

wherein

Is a beamforming vector of M/2 x 1. Regardless of the way beam group information is obtained, a reasonable beamformed CSI-RS scheme should always approximately satisfy:

here, span {.. } denotes a subspace spanned by the listed vectors in the matrix or the column vectors of the matrix. For two UEs i and j, if there are:

that is, if UE i and UE j have very similar subspaces spanned by their beam groups, the two UEs may share the same beamformed CSI-RS resource with the same beam group. In practice, however, for UE-specific beamformed CSI-RS, most UEs have their own unique beam group subspace. Therefore, the required CSI-RS overhead is related to the number of active UEs, i.e. different beam groups should be used on separate CSI-RS resources. If the number of active UEs is large, the overhead of beamformed CSI-RS resources may become intolerable.

In practice, the UE-specific beam group is mainly determined by the vertical and horizontal direction of the UE. Different UEs with different locations may have different beam group subspaces. For two UEs i and j that are well separated in the vertical or horizontal direction, there may be approximately:

this means that if the beam groups of UE i and j are transmitted on the same CSI-RS resource, the signal received at UE i can be derived by:

wherein s is_iAnd sj are for U respectivelyE i and UE j. The expressions after "≈" in formula (6) are obtained using formulae (3) and (5). This means that a plurality of UE-specific beam groups that satisfy equation (5) with each other can be transmitted on the same CSI-RS resource without loss of CSI measurement accuracy. This is somewhat similar to the spatial multiplexing transmission used in the data domain. The proposed approach for allocating UE-specific CSI-RS resources can be summarized as follows:

to improve the efficiency of UE-specific beamformed CSI-RS resources, UE-specific beamformed CSI-RSs of multiple UEs having well-isolated subspaces may be made to be multiplexed on the same CSI-RS resource, although the CSI-RS resources may be shared by UEs having similar beam subspaces.

In practice, the following equation (7) may be defined as a beam group

Orthogonal projection matrix of (a):

the spatial separation between beam groups i and j can then be determined by the following equation (8):

Dist_i，l＝||P_i-P_l||_F (8)

for multiple UE i₁，....i_qIf they satisfy:

wherein β is a predefined value and β < 1 but close to 1; j. the design is a square_xDenotes the number of beams in the beam group of UE x, J_yRepresenting the number of beams in the beam group for UE y. These UEs may then be considered to have approximately orthogonal beam-group subspaces, and their beamformed CSI-RS may be transmitted on the same CSI-RS resource.

It is to be appreciated that the method 200 for sharing CSI-RS resources may be utilized in both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) systems, and the scope of the present disclosure is not limited in this respect.

On the other hand, for TDD systems, beamformed CSI-RS multiplexing can also be performed more easily with relaxed constraints on the beam group subspace. In this regard, according to a second aspect of embodiments of the present disclosure, there is provided a method of sharing channel state information reference signal, CSI-RS, resources. Fig. 3 shows a flow diagram of a method 300 for sharing CSI-RS resources according to a second aspect of an embodiment of the present disclosure. The method 300 may be performed by an eNB in a wireless communication network, and in particular, the method 300 may be performed by an apparatus 900 described later herein with reference to fig. 9.

The method 300 begins at step S310. In step S310, the eNB acquires information of a plurality of beam groups, each of the plurality of beam groups being configured to transmit a beamformed CSI-RS specific to one UE of a plurality of UEs to the one UE.

In step S320, the eNB estimates a received signal strength of each UE of the plurality of UEs based on the acquired information.

At step S330, the eNB compares the estimated received signal strength with a predetermined first threshold.

In step S340, the eNB transmits beamformed CSI-RS specific to each UE on the same CSI-RS resource in response to each of the estimated received signal strengths being greater than the first threshold.

Hereinafter, the method 300 for sharing CSI-RS resources will be described with reference to a specific example.

In LTE Release13, beamformed CSI-RS has been supported by non-Precoding Matrix Indicator (PMI) based feedback, which is mainly used in TDD systems. Thus, for a TDD system, a UE may report a Channel Quality Indication (CQI) and a Rank Indication (RI) based on beamformed CSI-RS. Take equation (6) above as an example, where two UE-specific beams are directed to different UEs

And

are not orthogonal to each other and have non-negligible mutual interference. And therefore only has the following formula:

the CQI reported by the UE may then be calculated by:

wherein

Is the noise plus interference level measured via an Interference Measurement Resource (IMR). In contrast to SINR' in equation (11), the actual CQI is given by:

since the eNB is already aware of the channel matrix through channel reciprocity

The eNB may therefore also know:

therefore, even if the UE measures a contaminated SINR and thus derives a deviated CQI as shown in equation (11), the eNB can still derive a correct SINR by equation (13). In general, for TDD systems, since the channel is already known by the eNB, the subspace isolation condition as described above with reference to method 200 may not be necessary. The only limitation being as in formula (11)

The aggregation of the indicated, different UE-specific beams should not cancel each other out. This may maintain an acceptable SINR in equation (10) for the UE to ceiling from | | | y |)²To obtain

A reliable estimate of. In other words, estimated

Can be used to characterize the received signal strength of the UE, and the estimated received signal strength is compared to the noise in equation (10)

Variance (i.e. predetermined threshold) or noise

The product of the variance and a suitable constant is compared if the estimated received signal strength is greater than the noise

Variance or noise

The product of the variance and an appropriate constant, then beamformed CSI-RS specific to multiple UEs may be sent on the same CSI-RS resource.

Further, it should be understood that the method 300 described above may also be used in conjunction with the method 200 in some embodiments. In this regard, in these embodiments, the method 300 may further comprise: in response to each of the estimated received signal strengths being less than or equal to the first threshold, determining a spatial isolation between each two beam groups of the plurality of beam groups based on the obtained information; comparing each of the determined spatial isolation degrees with a predetermined second threshold; and in response to each of the determined spatial isolations being greater than the second threshold, transmitting a beamformed CSI-RS specific to each of the plurality of UEs on the same CSI-RS resource. It will be appreciated that in these embodiments, the method of determining spatial isolation described above with reference to method 200 may still be employed. In particular, the combined use of the spatial domain multiplexing scheme and the frequency domain multiplexing scheme may result in a maximized CSI-RS overhead reduction effect.

In addition, according to the embodiment of the present disclosure, a scheme for improving CSI-RS efficiency by multiplexing CSI-RS resources in the frequency domain is also provided. Specifically, the channel measured for the beamformed CSI-RS is the beamformed equivalent channel. In general, beamforming operation makes the transmit power more concentrated on a certain main path of the channel. Thus, the main path should be emphasized by beamforming and the other paths should be correspondingly attenuated. As a result, multipath effects should be reduced for the equivalent channel measured by the beamformed CSI-RS. Based on this fact, CSI-RS resources may be multiplexed in the frequency domain to reduce the overhead of UE-specific beamformed CSI-RS.

Hereinafter, a scheme of multiplexing CSI-RS resources in the frequency domain will be described with reference to fig. 4 to 6.

According to a third aspect of embodiments of the present disclosure, there is provided a method of sharing channel state information reference signal, CSI-RS, resources. Fig. 4 shows a flow diagram of a method 400 for sharing CSI-RS resources according to a third aspect of an embodiment of the present disclosure. The method 400 may be performed by an eNB in a wireless communication network, and in particular, the method 400 may be performed by the apparatus 1000 described later herein with reference to fig. 10.

As shown in fig. 4, the eNB transmits a beamformed CSI-RS specific to one of a plurality of UEs on each of a predefined plurality of subbands of the CSI-RS resource at step S410.

In some embodiments, the eNB may implement sharing of CSI-RS resources, for example, with any of the following three options.

Option 1

In option 1, one beamformed CSI-RS resource configuration may be shared by different UEs through frequency division multiplexing. In other words, the eNB sends a first beamformed CSI-RS specific to a first UE (UE 1) on a predefined first subband of a CSI-RS resource and a second beamformed CSI-RS specific to a second UE (UE 2) on a predefined second subband of the CSI-RS resource. In some embodiments, the first and second sub-bands are interleaved with each other based on a predetermined interleaving factor.

More specifically, the UE may perform CSI-RS measurements every N Resource Blocks (RBs) instead of performing CSI-RS measurements on every RB. Where N is the CSI-RS frequency domain interleaving factor. For every N RBs, the CSI-RS resources may be used by different UEs in turn with their respective beam sets.

Fig. 5 shows one example of a scheme for multiplexing CSI-RS resources in the frequency domain according to option 1. In the example of fig. 5, the frequency domain interleaving factor N is 2, and UE 1 and UE 2 perform CSI-RS measurements every 2 RBs (i.e., every 1 RB), respectively.

In option 1, new parameters may be introduced in the control signaling (e.g., RRC signaling) for configuring the CSI-RS resource, including the interleaving factor and the number of offsets in the RB sense. Alternatively, in the specification, the interleaving factor may also be fixed, thus only the offset number of resource blocks is included in the control signaling for configuring the CSI-RS resource. For the specification, one possible variant of the frequency domain interleaving method is to use a RB group comprising a plurality of consecutive RBs, instead of a single RB. Thus, in option 1, RB groups are allocated to different UEs in turn and each UE performs CSI-RS measurements every N RB groups.

In contrast to frequency-domain interleaving methods, where the CSI-RS resources of each UE still actually occupy the entire bandwidth, for UE-specific beamformed CSI-RS, the CSI-RS resources of each UE may be defined only on subbands.

In addition, in option 1, a first control signaling and a second control signaling may also be sent to UE 1 and UE 2, respectively, where each of the first control signaling and the second control signaling carries the above interleaving factor and the offset number of resource blocks.

Option 2

In option 2, one beamformed CSI-RS resource may be defined over a subband including some consecutive RBs. Each subband may include one or more contiguous RBs. Each UE may make CSI-RS measurements based on this subband only. Different UEs may have their respective beamformed CSI-RS resources on different subbands.

For option 2, the size of the subband may be fixed or configured in a control signaling (e.g., RRC signaling) based CSI-RS configuration, and the location of the subband should be included in the control signaling based CSI-RS configuration.

In option 2, there will be a maximum CSI-RS overhead reduction effect if a smaller subband size is used. However, this has to withstand the reduced CSI feedback quality brought about by the subband measurements. To solve this problem, option 2 is improved by introducing a frequency hopping technique, resulting in option 3 as described below.

Option 3

In option 3, one beamformed CSI-RS resource may be defined over a subband comprising a plurality of consecutive RBs, the frequency domain location of the subband hopping in a predetermined hopping pattern in a plurality of consecutive measurement subframes, as shown in fig. 6. Each UE may perform CSI-RS measurements based on a single subband or a series of frequency hopped subbands. Different UEs may have their respective CSI-RS resources on different subbands with different predefined hopping patterns.

For option 3, the size of the sub-band is fixed or configured by control signaling (e.g., RRC signaling). The starting position or hopping pattern indication in the frequency domain may be configured by RRC-based CSI-RS configuration. In one example, hopping patterns may reuse the mechanisms used in uplink PUSCH. By using option 3, the potential gain from frequency diversity through sub-band CSI reporting can be preserved.

Furthermore, in option 3, it is also possible to send to UE 1 and UE 2 first control signaling and second control signaling, respectively, the first control signaling carrying the frequency domain position and hopping pattern for the sub-band of UE 1, and the second control signaling carrying the frequency domain position and hopping pattern for the sub-band of UE 2. In some embodiments, the frequency domain position and hopping pattern for the sub-band for UE 1 is different from the frequency domain position and hopping pattern for the sub-band for UE 2.

In the above, a possible scheme of frequency domain to reduce the beamformed CSI-RS resource overhead is given. In addition, overhead can also be reduced by using the time domain. In practice, option 3 may be viewed as using a combination of frequency and time domains. In addition, the periodicity of the CSI-RS measurement subframe may also be increased in combination with using options 1, 2, or 3 to further reduce CSI-RS overhead. By using the time domain and frequency domain methods, the maximum CSI-RS overhead reduction effect can be obtained.

Once the frequency domain scheme described above is used, there is necessarily some impact on CSI reporting. For the method of interleaving in option 1, similar to today, wideband CSI reporting including PMI/CQI/RI may be performed at the UE and used by the eNB. Subband CSI reports including PMI/CQI may not be as flexible as before, as the subbands now selected by the UE or configured by the eNB can only be selected from a scattered arrangement of interleaved RB groups. For the subband approach in options 2 and 3, wideband PMI/CQI reporting should be performed by the UE actually based on measurements on the subband CSI-RS resources, which should be understood by the eNB. For sub-band PMI/CQI reporting, selected by the UE or configured by the eNB, the sub-band on which PMI/CQI is reported should be defined in the sub-band of the CSI-RS resource itself, which is different from the resource currently defined over the entire cell bandwidth. Otherwise, the CSI reporting is clearly meaningless. In summary, although the CSI reporting mechanism and behavior should be modified and thus the flexibility in the frequency domain is reduced, this does not affect the overall system performance, since the selectivity of the equivalent channel in the beamformed CSI-RS scheme in the frequency domain becomes weaker as described earlier.

According to a fourth aspect of embodiments of the present disclosure, there is provided a method for reporting CSI. Fig. 7 shows a flow diagram of a method 700 for reporting CSI according to a fourth aspect of an embodiment of the present disclosure. The method 700 may be performed by a UE in a wireless communication network, and in particular, the method 700 may be performed by an apparatus 1100 described later herein with reference to fig. 11.

As shown in fig. 7, the UE receives beamformed CSI-RS specific to the user equipment UE on predefined subbands of the CSI-RS resource at step S710. In step S720, the UE measures the CSI based on the received beamformed CSI-RS. At step S730, the UE reports the measured CSI to the eNB.

In some embodiments, the method 700 further comprises: control signaling is received from the eNB carrying the interleaving factor and the offset number of resource blocks.

In some embodiments, the method 700 further comprises: control signaling carrying a frequency domain location and a predetermined hopping pattern is received from the eNB.

According to a fifth aspect of embodiments of the present disclosure, there is provided an apparatus for sharing channel state information reference signal, CSI-RS, resources. Fig. 8 shows a block diagram of an apparatus 800 for sharing channel state information reference signal, CSI-RS, resources according to a fifth aspect of an embodiment of the disclosure. Apparatus 800 may be implemented in an eNB, for example.

As shown in fig. 8, the apparatus 800 includes: an obtaining unit 810 configured to obtain information of a plurality of beam groups, each of the plurality of beam groups being configured to transmit a beamformed CSI-RS specific to one of a plurality of user equipments, UEs; a determining unit 820 configured to determine a spatial isolation between each two beam groups of the plurality of beam groups based on the acquired information; a comparing unit 830 configured to compare each of the determined spatial isolation degrees with a predetermined threshold; and a transmitting unit 840 configured to transmit the beamformed CSI-RS specific to each UE of the plurality of UEs on the same CSI-RS resource in response to each of the determined spatial isolations being greater than the threshold.

In some embodiments, the obtaining unit 810 is further configured to obtain information of a first beam group and information of a second beam group, the first beam group and the second beam group being configured to transmit a first beamformed CSI-RS specific to the first UE and a second beamformed CSI-RS specific to the second UE, respectively.

In some embodiments, the transmitting unit 840 is further configured to: means for transmitting the first beamformed CSI-RS and the second beamformed CSI-RS on predefined same subbands of the CSI-RS resource in response to each of the determined spatial isolations being greater than the threshold.

According to a sixth aspect of embodiments of the present disclosure, there is provided an apparatus for sharing channel state information reference signal, CSI-RS, resources. Fig. 9 shows a block diagram of an apparatus 900 for sharing channel state information reference signal, CSI-RS, resources according to a sixth aspect of an embodiment of the disclosure. Apparatus 900 may be implemented in an eNB, for example.

As shown in fig. 9, the apparatus 900 includes: an obtaining unit 910 configured to obtain information of a plurality of beam groups, each of the plurality of beam groups being configured to transmit a beamformed CSI-RS specific to one of a plurality of user equipments, UEs; an estimating unit 920 configured to estimate a received signal strength of each UE of the plurality of UEs based on the acquired information; a comparing unit 930 configured to compare the estimated received signal strength with a predetermined first threshold; and a transmitting unit 940 configured to transmit the beamformed CSI-RS specific to each UE on the same CSI-RS resource in response to each of the estimated received signal strengths being greater than the first threshold.

According to a seventh aspect of embodiments of the present disclosure, there is provided an apparatus for sharing channel state information reference signal, CSI-RS, resources. Fig. 10 shows a block diagram of an apparatus 1000 for sharing channel state information reference signal, CSI-RS, resources according to a seventh aspect of an embodiment of the disclosure. Apparatus 1000 may be implemented in an eNB, for example.

As shown in fig. 10, the apparatus 1000 includes: a transmitting unit 1010 configured to transmit a beamformed CSI-RS specific to one of a plurality of user equipments, UEs, on each of a predefined plurality of subbands of the CSI-RS resource.

According to an eighth aspect of embodiments of the present disclosure, there is provided an apparatus for reporting CSI. Fig. 11 shows a block diagram of an apparatus 1100 for reporting CSI according to an eighth aspect of an embodiment of the disclosure. The apparatus 1100 may be implemented in a UE, for example.

As shown in fig. 11, the apparatus 1100 includes: a receiving unit 1110 configured to receive beamformed CSI-RS specific to a user equipment UE on predefined subbands of CSI-RS resources; a measurement unit 1120 configured to measure the CSI based on the received beamformed CSI-RS; and a reporting unit 1130 configured to report the measured CSI to the base station.

In some embodiments, the receiving unit 1110 is further configured to: means for receiving control signaling from the base station carrying the interleaving factor and the offset number of resource blocks.

In some embodiments, the receiving unit 1110 is further configured to: control signaling carrying the frequency domain location and the predetermined hopping pattern is received from the base station.

In general, the various example embodiments of this disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Certain aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. While aspects of embodiments of the disclosure have been illustrated or described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that the blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

Also, blocks in the flow diagrams may be viewed as method steps, and/or as operations that result from operation of computer program code, and/or as a plurality of coupled logic circuit elements understood to perform the associated functions. For example, embodiments of the present disclosure include a computer program product comprising a computer program tangibly embodied on a machine-readable medium, the computer program containing program code configured to implement the above-described methods.

Within the context of this disclosure, a machine-readable medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. The machine-readable medium may be a machine-readable signal medium or a machine-readable storage medium. A machine-readable medium may include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination thereof. More detailed examples of a machine-readable storage medium include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical storage device, a magnetic storage device, or any suitable combination thereof.

Computer program code for implementing the methods of the present disclosure may be written in one or more programming languages. These computer program codes may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program codes, when executed by the computer or other programmable data processing apparatus, cause the functions/acts specified in the flowchart and/or block diagram block or blocks to be performed. The program code may execute entirely on the computer, partly on the computer, as a stand-alone software package, partly on the computer and partly on a remote computer or entirely on the remote computer or server.

Additionally, 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 or parallel processing may be beneficial. Likewise, while the above discussion contains certain specific implementation details, this should not be construed as limiting the scope of any invention or claims, but rather as describing particular embodiments that may be directed to particular inventions. 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.

Various modifications, adaptations, and exemplary embodiments of the foregoing disclosure may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. Any and all modifications will still fall within the scope of the non-limiting and exemplary embodiments of this disclosure. Moreover, the foregoing description and drawings present instructive benefits, and other embodiments of the present disclosure set forth herein will occur to those skilled in the art to which these embodiments of the present disclosure pertain.

It is to be understood that the embodiments of the disclosure are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

1. A method for sharing channel state information reference signal, CSI-RS, resources, comprising:

obtaining information of a plurality of beam groups, each of the plurality of beam groups configured to transmit a beamformed CSI-RS specific to one UE of a plurality of User Equipments (UEs);

determining a spatial isolation between each two of the plurality of beam groups based on the obtained information;

comparing each of the determined spatial isolations to a predetermined threshold; and

transmitting a beamformed CSI-RS specific to each UE of the plurality of UEs on the same CSI-RS resource in response to each of the determined spatial isolations being greater than the threshold.

2. The method of claim 1, wherein determining the spatial isolation comprises:

determining a plurality of orthogonal projection matrices, each of the plurality of orthogonal projection matrices associated with one of the plurality of beam groups;

calculating a distance between each two of the plurality of orthogonal projection matrices; and

determining the calculated distance as the spatial separation.

3. The method of claim 1 or 2, wherein obtaining information for a plurality of beam groups comprises obtaining information for a first beam group and information for a second beam group, the first beam group and the second beam group configured to send a first beamformed CSI-RS specific to a first UE and a second beamformed CSI-RS specific to a second UE, respectively, to the first UE and to the second UE.

4. The method of claim 3, further comprising:

in response to each of the determined spatial isolations being greater than the threshold, transmitting the first beamformed CSI-RS and the second beamformed CSI-RS on predefined same subbands of the CSI-RS resource.

5. A method for sharing channel state information reference signal, CSI-RS, resources, comprising:

estimating a received signal strength for each UE of the plurality of UEs based on the obtained information;

comparing the estimated received signal strength to a predetermined first threshold; and

transmitting beamformed CSI-RS specific to the each UE on the same CSI-RS resource in response to each of the estimated received signal strengths being greater than the first threshold.

6. An apparatus for sharing channel state information reference signal, CSI-RS, resources, comprising:

an obtaining unit configured to obtain information of a plurality of beam groups, each of the plurality of beam groups being configured to transmit a beamformed CSI-RS specific to one UE of a plurality of User Equipments (UEs);

a determination unit configured to determine a spatial isolation between each two of the plurality of beam groups based on the acquired information;

a comparison unit configured to compare each of the determined spatial isolation degrees with a predetermined threshold; and

a transmitting unit configured to transmit the beamformed CSI-RS specific to each of the plurality of UEs on the same CSI-RS resource in response to each of the determined spatial isolations being greater than the threshold.

7. The apparatus of claim 6, wherein the determining unit is further configured to: determining a plurality of orthogonal projection matrices, each of the plurality of orthogonal projection matrices associated with one of the plurality of beam groups; calculating a distance between each two of the plurality of orthogonal projection matrices; and determining the calculated distance as the spatial separation.

8. An apparatus for sharing channel state information reference signal, CSI-RS, resources, comprising:

an estimating unit configured to estimate a received signal strength of each of the plurality of UEs based on the acquired information;

a comparison unit configured to compare the estimated received signal strength with a predetermined first threshold; and

a transmitting unit configured to transmit beamformed CSI-RS specific to the each UE on the same CSI-RS resource in response to each of the estimated received signal strengths being greater than the first threshold.