WO2017168254A1

WO2017168254A1 - Method and apparatus of sharing csi-rs resource

Info

Publication number: WO2017168254A1
Application number: PCT/IB2017/000460
Authority: WO
Inventors: Qingchuan ZHANG; Min Zhang; Xun Li
Original assignee: Alcatel Lucent
Priority date: 2016-03-31
Filing date: 2017-03-31
Publication date: 2017-10-05
Also published as: CN107294584B; CN107294584A

Abstract

Embodiments of the present disclosure provide a method and apparatus of sharing a channel state information reference signal resource. The method comprises: obtaining information about a plurality of beam groups, each of the plurality of beam groups being configured to transmit, to one of a plurality of user equipment (UEs), a beamformed CSI-RS specific to the UE; determining degrees of spatial isolation among the plurality of beam groups based on the obtained information; comparing each of the determined degrees of spatial isolation with a predetermined threshold; and in response to each of the determined degrees of spatial isolation being above the threshold, transmitting, on the CSI-RS resource, beamformed CSI-RSs specific to the plurality of UEs. The embodiments of the present disclosure may improve the efficiency of UE specific beamformed CSI-RS by exploiting the characteristic of beamforming operation.

Description

METHOD AND APPARATUS OF SHARING CSI-RS RESOURCE

FIELD

[0001] Embodiments of the present disclosure generally relate to wireless communications, and more particularly, to a method and apparatus of sharing a channel state information reference signal (CSI-RS) resource, and a method and apparatus for reporting channel state information (CSI).

BACKGROUND

[0002] Beamformed CSI-RS is a very important feature introduced in 3 GPP Release 13, which enables the use of large antenna arrays in LTE systems without a need to define complicated codebooks as required by traditional non-precoded CSI-RS. In beamformed CSI-RS, an eNB can determine the beamforming weight used at CSI-RS resources by using long term channel reciprocity or non-precoded CSI-RS in a hybrid approach. UE specific beamformed CSI-RS is supported by using a group of micro beams towards the UE. And the UE then reports the beam selection information as well as phase information in a polarization direction. Since a beamformer has superior directivity, the UE specific beamformed CSI-RS has excellent CSI feedback precision. However, since the required CSI-RS resources are related to the number of active UEs, the CSI-RS overhead might be very high if there are many active UEs. Therefore, there is a need to reduce the CSI-RS overhead.

[0003] Fig. 1 schematically shows a possible scheme for reducing the CSI-RS overhead. In the scheme shown in Fig. 1, less directive beams are used to improve the coverage and thus reduce the CSI-RS overhead. However, beamforming granularity is decreased and further CSI feedback precision is reduced. Therefore, the CSI-RS overhead is the major problem for UE specific CSI-RS.

SUMMARY

[0004] Therefore, in order to solve or at least partially alleviate the above problems in the prior art, there is a need for a scheme to reduce CSI-RS overhead required by UE specific beamformed CSI-RS and have a small impact on beamforming performed on CSI-RS. [0005] In a first aspect, there is provided a method of sharing a CSI-RS resource. The method comprises: obtaining information about a plurality of beam groups, each of the plurality of beam groups being configured to transmit, to one of a plurality of user equipment (UEs), a beamformed CSI-RS specific to the UE; determining degrees of spatial isolation among the plurality of beam groups based on the obtained information; comparing each of the determined degrees of spatial isolation with a predetermined threshold; and in response to each of the determined degrees of spatial isolation being above the threshold, transmitting, on the CSI-RS resource, beamformed CSI-RSs specific to the plurality of UEs.

[0006] In some embodiments, determining the degrees of spatial isolation comprises: determining a plurality of orthogonal projection matrices, each of the plurality of orthogonal projection matrices being associated with one of the plurality of beam groups; calculating distances among the plurality of orthogonal projection matrices; and determining the calculated distances as the degrees of spatial isolation.

[0007] In some embodiments, obtaining the information about the plurality of beam groups comprises: obtaining information about a first beam group and information about a second beam group, the first beam group being configured to transmit, to a first UE, a first beamformed CSI-RS specific to the first UE, and the second beam group being configured to transmit, to a second UE second, a beamformed CSI-RS specific to the second UE.

[0008] In some embodiments, the method further comprises: in response to each of the determined degrees of spatial isolation being above the threshold, transmitting the first beamformed CSI-RS and the second beamformed CSI-RS on a predefined common subband of the CSI-RS resource.

[0009] In a second aspect, there is provided a method of sharing a CSI-RS resource. The method comprises: obtaining information about a plurality of beam groups, each of the plurality of beam groups being configured to transmit, to one of a plurality of user equipment (UEs), a beamformed CSI-RS specific to the UE; estimating received signal strengths of the plurality of UEs based on the obtained information; comparing the estimated received signal strengths with a first predetermined threshold; and in response to each of the estimated received signal strengths being above the first threshold, transmitting, on the CSI-RS resource, beamformed CSI-RSs specific to the plurality of UEs.

[0010] In a third aspect, there is provided a method of sharing a CSI-RS resource. The method comprises transmitting, on one of a plurality of predefined subbands of the CSI-RS resource, a beamformed CSI-RS specific to one of a plurality of user equipment (UEs).

[0011] In some embodiments, every two of the plurality of subbands are interleaved based on a predetermined interleaving factor.

[0012] In some embodiments, each of the plurality of subbands comprises one or more consecutive resource blocks.

[0013] In some embodiments, frequency-domain positions of the plurality of subbands hop in different predefined hopping patterns during a plurality of consecutive measurement sub frames.

[0014] In a fourth aspect, there is provided a method of reporting CSL The method comprises: receiving a beamformed CSI-RS specific to user equipment (UE) on a predefined subband of a CSI-RS resource; measuring the CSI based on the received beamformed CSI-RS; and reporting the measured CSI to a base station.

[0015] In some embodiments, the subband is interleaved with a further subband of the

CSI-RS resource based on a predetermined interleaving factor, the further subband being configured for a further UE.

[0016] In some embodiments, the method further comprises receiving control signaling from the base station, the control signaling carrying the interleaving factor and an offset in resource blocks.

[0017] In some embodiments, the subband includes one or more consecutive resource blocks.

[0018] In some embodiments, frequency-domain positions of the subband hops in a predefined hopping pattern during a plurality of consecutive measurement subframes.

[0019] In some embodiments, the method further comprises receiving control signaling from the base station, the control signaling carrying the frequency-domain positions and the predefined hopping pattern.

[0020] In a fifth aspect, there is provided an apparatus for sharing a CSI-RS resource. The apparatus comprises: an obtaining unit configured to obtain information about a plurality of beam groups, each of the plurality of beam groups being configured to transmit, to one of a plurality of user equipment (UEs), a beamformed CSI-RS specific to the UE; and a determining unit configured to determine degrees of spatial isolation among the plurality of beam groups based on the obtained information; a comparing unit configured to compare each of the determined degrees of spatial isolation with a predetermined threshold; and a transmitting unit configured to transmit, on the CSI-RS resource, beamformed CSI-RSs specific to the plurality of UEs in response to each of the determined degrees of spatial isolation being above the threshold.

[0021] In some embodiments, the determining unit is further configured to: determine a plurality of orthogonal projection matrices, each of the plurality of orthogonal projection matrices being associated with one of the plurality of beam groups; calculate distances among the plurality of orthogonal projection matrices; and determine the calculated distances as the degrees of spatial isolation.

[0022] In some embodiments, the obtaining unit is further configured to: obtain information about a first beam group and of a second beam group, the first and second beam groups being configured to transmit to a first UE a first beamformed CSI-RS specific to the first UE and transmit to a second UE a second beamformed CSI-RS specific to the second UE respectively.

[0023] In some embodiments, the transmitting unit is further configured to: in response to each of the determined degrees of spatial isolation being above the threshold, transmit the first beamformed CSI-RS and the second beamformed CSI-RS on the predefined common subband of the CSI-RS resource.

[0024] In a sixth aspect, there is provided an apparatus for sharing a CSI-RS resource. The apparatus comprises: an obtaining unit configured to obtain information about a plurality of beam groups, each of the plurality of beam groups being configured to transmit to one of a plurality of user equipment (UEs) beamformed CSI-RS specific to the UE; an estimating unit configured to estimate received signal strengths of the plurality of UEs based on the obtained information; a comparing unit configured to compare the estimated received signal strengths with a first predetermined threshold; and a transmitting unit configured to transmit, on the CSI-RS resource, beamformed CSI-RSs specific to the plurality of UEs in response to each of the estimated received signal strengths being above the first threshold.

[0025] In a seventh aspect, there is provided an apparatus for sharing a CSI-RS resource. The apparatus comprises: a transmitting unit configured to transmit, on one of a plurality of predefined subbands of the CSI-RS resource, a beamformed CSI-RS specific to one of a plurality of user equipment (UEs).

[0026] In some embodiments, every two of the plurality of subbands are interleaved based on a predetermined interleaving factor.

[0027] In some embodiments, each of the plurality of subbands comprises one or more consecutive resource blocks.

[0028] In some embodiments, frequency-domain positions of the plurality of subbands hop in different predefined hopping patterns during a plurality of consecutive measurement sub frames.

[0029] In an eighth aspect, there is provided an apparatus for reporting CSI. The apparatus comprises: a receiving unit configured to receive a beamformed CSI-RS specific to user equipment (UE) on a predefined subband of a CSI-RS resource; a measuring unit configured to measure the CSI based on the received beamformed CSI-RS; and a reporting unit configured to report the measured CSI to a base station.

[0030] In some embodiments, the subband is interleaved with a further subband of the CSI-RS resource based on a predetermined interleaving factor, the further subband being configured for a further UE.

[0031] In some embodiments, the receiving unit is further configured to: receive from the base station control signaling carrying the interleaving factor and an offset in resource blocks.

[0032] In some embodiments, the subband comprises one or more consecutive resource blocks.

[0033] In some embodiments, frequency-domain positions of the subband hops in a predefined hopping pattern during a plurality of consecutive measurement subframes.

[0034] In some embodiments, the receiving unit is further configured to: receive from the base station control signaling carrying the frequency-domain positions and the predefined hopping pattern.

[0035] The embodiments of the present disclosure may improve the efficiency of UE specific beamformed CSI-RS by exploiting the characteristic of beamforming operation, and also strike a balance between beamforming granularity and CSI-RS overhead for a large number of UEs. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Through the detailed description in the accompanying drawings, features, advantages and other aspects of the embodiments of the present disclosure will become more apparent. Several embodiments of the present disclosure are illustrated schematically, rather than limiting the present disclosure. In the drawings:

[0037] Fig. 1 schematically shows a possible scheme for reducing CSI-RS overhead;

[0038] Fig. 2 shows a flowchart of a method of sharing a CSI-RS resource according to a first aspect of the embodiments of the present disclosure;

[0039] Fig. 3 shows a flowchart of a method of sharing a CSI-RS resource according to a second aspect of the embodiments of the present disclosure;

[0040] Fig. 4 shows a flowchart of a method of sharing a CSI-RS resource according to a third aspect of the embodiments of the present disclosure;

[0041] Fig. 5 shows one example of a scheme for CSI-RS resource multiplexing in the frequency domain;

[0042] Fig. 6 shows another example of a scheme for CSI-RS resource multiplexing in the frequency domain;

[0043] Fig. 7 shows a flowchart of a method of reporting CSI according to a fourth aspect of the embodiments of the present disclosure;

[0044] Fig. 8 shows a block diagram of an apparatus for sharing a CSI-RS resource according to a fifth aspect of the embodiments of the present disclosure;

[0045] Fig. 9 shows a block diagram of an apparatus for sharing a CSI-RS resource according to a sixth aspect of the embodiments of the present disclosure;

[0046] Fig. 10 shows a block diagram of an apparatus for sharing a CSI-RS resource according to a seventh aspect of the embodiments of the present disclosure; and

[0047] Fig. 11 shows a block diagram of an apparatus for reporting CSI according to an eighth aspect of the embodiments of the present disclosure.

DETAILED DESCRIPTION

[0048] Principles of the subject matter described herein are now described with reference to several embodiments. It should be understood that the embodiments are described only for causing those skilled in the art to better understand and further implement the subject matter, rather than limiting the scope of the subject matter in any way.

[0049] The term "base station" (BS) used herein may represent 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 repeater, or a low power node such as a Picocell, a Femto cell and the like.

[0050] The term "user equipment" (UE) used herein refers to any device that can communicate with the BS. As an example, the UE may comprise a terminal, a mobile terminal (MT), a subscriber station (SS), a portable subscriber station (PSS), a mobile station (MS) or an access terminal (AT).

[0051] According to the embodiments of the present disclosure, there is provided a scheme for CSI-RS resource multiplexing in a spatial domain so as to improve the CSI-RS efficiency. Hereinafter, description will be presented to the scheme for CSI-RS resource multiplexing in the spatial domain with reference to Figs. 2 and 3.

[0052] In a first aspect, there is provided a method of sharing a channel state information reference signal CSI-RS resource. Fig. 2 shows a flowchart of a method 200 for sharing a CSI-RS resource according to a first aspect of the embodiments of the present disclosure. The method 200 may be executed by an eNB in a wireless communication network, and in particular, the method 200 may be executed by an apparatus 800 to be described with reference to Fig. 8 later.

[0053] The method 200 starts with block S210. At block S210, the eNB obtains information about a plurality of beam groups, each of which is configured to transmit to one of a plurality of UEs beamformed CSI-RS specific to the UE.

[0054] At block S220, the eNB determines degrees of spatial isolation between every two of the plurality of beam groups based on the obtained information.

[0055] At block S230, the eNB compares each of determined degrees of spatial isolation with a predetermined threshold.

[0056] At block S240, in response to each of the determined degrees of spatial isolation being above the threshold, the eNB transmits beamformed CSI-RSs specific to the plurality of UEs on a single CSI-RS resource.

[0057] In some embodiments, determining the degrees of spatial isolation comprises: determining a plurality of orthogonal projection matrices, each of which is associated with one of the plurality of beam groups; calculating distances between every two of the plurality of orthogonal projection matrices; and determining the calculated distances as the degrees of spatial isolation.

[0058] Hereinafter, description will be presented to the method 200 of sharing a CSI-RS resource by means of an example.

[0059] Assume there are κ active UEs in the considering cell, an antenna array at the eNB is dual-polarized with M antenna elements and each UE has N antennas. The channel matrix between UE i and eNB can be expressed as

K° ^H ] (1) wherein ^Ho^} and ^Hi^!) is the N M/2 matrix corresponding to the two polarizations respectively.

[0060] In a UE specific beamformed CSI-RS scheme, eNB can obtain information about the beam group performed on the CSI-RS ports by using either the long-term channel reciprocity or UE's feedback via measuring the long term non-precoded CSI-RS in a hybrid approach. The obtained information about beam group for UE ί is denoted as

where j represents the M/2 X l beamforming vector. No matter which way is used to obtain the information about beam group, a reasonable beamformed CSI-RS scheme should always approxi

Here, spanj. . . } denotes the subspace spanned by the listed vectors or the column vectors of the matrix. For tw

i.e., UEs i and ; have the very similar subspace spanned by their beam groups, then these two UEs can share the same beamformed CSI-RS resource with the same beam group. However, in practice, for UE specific beamformed CSI-RS, most of UEs have their own unique beam group subspaces. Therefore, the required CSI-RS overhead is related to the number of active UEs, i.e., different beam groups should be used on separated CSI-RS resources. If the number of active UEs is large, the overhead of beamformed CSI-RS resources will become unaffordable.

[0061] In practice, the UE specific beam group is determined largely by the elevation and horizontal directions of the UE. Different UEs with different positions may have different subspaces of beam groups. For two UEs ; and i, which are well isolated in either elevation or horizontal direction, there is approximately

span {b , . . . , b^) ± span {b , . . . , b«)

This means if the beam groups of UEs and i are transmitted on the same CSI-RS resource, the received signal at UE i can be given by

y< - ^Hi {^bj_i ^s' ^{+ t)}j_l ^sj) ^{+ n}t ~ ^Ht Bj. Si + nt ^ f e {0, l), ji e {l, . . . e {l, . . where ^s>> ^SJ are the transmitted reference symbols for UEi and UEi respectively. The equality after "~" in expression (6) is derived by using expressions (3) and (5). This means several UE specific beam groups, among which expression (5) is mutually satisfied, can be transmitted on the same CSI-RS resource without loss of the CSI measurement precision. This is somewhat similar with the spatial multiplexing transmission used in the data domain. The recommended strategy for assigning the UE specific CSI-RS resources can be summarized as follows.

[0062] To improve the efficiency of UE specific beamformed CSI-RS resources, while the CSI-RS resources can be shared by UEs with similar beam group subspace, let the UE specific beamformed CSI-RSs of several UEs, whose beam groups have well isolated subspaces, be multiplexed on the same CSI-RS resource.

[0063] In practice, by defining

as the orthogonal projection matrix of beam group ^B' ⁼ [ i^{) ,} - - - ' ^bj,⁾], then the degree of isolation between beam groups i and i can be determined by calculating

Dist = !IP; - VI\\F (8)

[0064] For a plurality of UEs 'Ί - · · · '?, if they satisfy

min Dist_{T 3}, > fi

*,ye _χ + J_y (Q^ where β represents a predefined value less than but approaching 1 ; J_x denotes the number of beams in the beam group of UE x, and J_y denotes the number of beams in the beam group of UE y. Then these UEs can be considered to have approximately orthogonal beam group subspaces, and their beamformed CSI-RSs can be transmitted on the same CSI-RS resource.

[0065] It may be appreciated that the method 200 of sharing a CSI-RS resource can be used for both frequency division duplexing (FDD) systems and time division duplexing (TDD) systems. The scope of the present disclosure is not limited in this regard.

[0066] On the other hand, for TDD systems, actually the beamformed CSI-RS multiplexing can be performed more easily with relaxed limitation on the beam group subspace. In this regard, according to a second aspect of the embodiments of the present disclosure, there is provided a method of sharing a CSI-RS resource. Fig. 3 shows a flowchart of a method 300 of sharing a CSI-RS resource according to a second aspect of the embodiments of the present disclosure. The method 300 may be executed by an eNB in a wireless communication network, and in particular, the method 300 may be executed by an apparatus 900 to be described with reference to Fig. 9 later.

[0067] The method 300 starts with block S310. At block S310, the eNB obtains information about a plurality of beam groups, each of which is configured to transmit to one of a plurality of UEs beamformed CSI-RS specific to the UE.

[0068] At block S320, the eNB estimates received signal strengths of the plurality of UEs based on the obtained information.

[0069] At block S330, the eNB compares the estimated received signal strengths with a predefined first threshold.

[0070] At block S340, in response to each of the estimated received signal strengths being above the first threshold, the eNB transmits beamformed CSI-RSs specific to the UEs on the CSI-RS resource.

[0071] Hereinafter, description will be presented to the method 300 of sharing a CSI-RS resource by means of an example.

[0072] In LTE Release 13, beamformed CSI-RS has been supported by non-precoded matrix indicator (PMI) based feedback, which is mainly used for TDD systems. Thus, for TDD systems, UE can report the channel quality indicator (CQI) and rank indicator (RI) based on the beamformed CSI-RS. Take expression (6) as example, where two

UE specific beams and towards different UEs are not orthogonal with each other and have non-ignorable mutual interference. Therefore there is only

[0073] Then the reported CQI by UE can be obtained by calculating

(11)

.2

where "^"IMR represents the noise-plus-interference level measured via interference measurement resource (IMR). In contrast to SINR' in expression (11), the real CQI is derived from

!|H®b¾!|²

SINR = ^

°\m (12) [0074] Since a channel matrix ^Hi^!> has been already known by the eNB via channel reciprocity, then

can be also known by the eNB.

[0075] Therefore, even if the UE measures the polluted SINR and thus the biased CQI as in (11), the eNB can still recover the correct SINR with (13). To summarize, since the channel is already known by the eNB for the TDD system, the subspace isolation condition above described with reference to the method 200 may not be essential. The only limitation is that the aggregation of different UE specific beams like ^bJr ' ^{+ b} ; ^SJ in expression (11) should be non-counteractive. This can keep an acceptable SINR in expression (10) for UE to get a reliable estimation of ll^Hf (^b ; ^{Sl +} ; ^sj)\\ from l!y!l². In other words, the estimated may be used to characterize the US's received signal strength. The estimated received signal strength is compared with the noise ^Ώ¾ variance (i.e. a predetermined threshold) in expression (10) or the product of the noise ¾ variance and an appropriate constant. If the estimated received signal strength is above the noise ¾ variance in expression (10) or the product of the noise ⁿJ ^" variance and an appropriate constant, then beamformed CSI-RSs specific to a plurality of UEs may be sent on the same CSI-RS resource.

[0076] In addition, it should be understood in some embodiments, the method 300 may also be used in conjunction with the method 200. In this regard, in these embodiments, the method 300 may further comprise: in response to each of the estimated received signal strength being less than or equal to the first threshold, determining degrees of spatial isolation between every two of the plurality of beam groups based on the obtained information; comparing each of the determined degrees of spatial isolation with a predetermined second threshold; and in response to the each of the determined degrees of spatial isolation being above the second threshold, transmitting beamformed CSI-RSs specific to the plurality of UEs on the same CSI-RS resource. It may be understood in these embodiments, the method of determining the degrees of spatial isolation as above described with reference to the method 200 may still be used. In particular, a maximum CSI-RS overhead reduction effect may be obtained by utilizing both time and frequency domain multiplexing schemes.

[0077] In addition, according to the embodiments of the present disclosure, there is further provided a scheme for improving the CSI-RS efficiency by CSI-RS resource multiplexing in the frequency domain. Specifically, the measured channel for beamformed CSI-RS is the equivalent channel after beamforming. Usually, the beamforming operation makes the transmission power more focus on a certain main path of the channel. Therefore, this main path should be enhanced by beamforming and other paths should be relatively crippled. As a result, the multipath effect should be weakened for the equivalent channel measured via beamformed CSI-RS. Based on this fact, CSI-RS resources may be multiplexed in the frequency domain so as to reduce the overhead of UE specific beamformed CSI-RS.

[0078] Hereinafter, description will be presented to the scheme for CSI-RS resource multiplexing in the frequency domain with reference to Figs. 4 to 6.

[0079] According to a third aspect of the embodiments of the present disclosure, there is provided a method of sharing channel state information reference signal CSI-RS resources. Fig. 4 shows a flowchart of a method 400 of sharing a CSI-RS resource according to a third aspect of the embodiments of the present disclosure. The method 400 may be executed by an eNB in a wireless communication network, and in particular, the method 400 may be executed by an apparatus 1000 to be described with reference to Fig. 10 later.

[0080] As shown in Fig. 4, at block S410, the eNB transmits beamformed CSI-RS specific to one UE of a plurality of UEs on one of a plurality of predefined subbands of the CSI-RS resources.

[0081] In some embodiments, the eNB may achieve CSI-RS resource sharing by using any of the following three options.

Option 1

[0082] In option 1, one beamformed CSI-RS resource configuration can be shared by different UEs via frequency division multiplexing. In other words, the eNB transmits a first beamformed CSI-RS specific to a first UE (UE1) on a first predefined subband of a CSI-RS resource, and transmits a second beamformed CSI-RS specific to a second UE (UE2) on a second predefined subband of the CSI-RS resource. In some embodiments, the first subband and the second subband are interleaved based on a predetermined interleaving factor.

[0083] More specifically, the UE can just perform one CSI-RS measurement every N resource blocks (RBs) instead of each RB. Herein, N is the CSI-RS frequency domain interleaving factor. For every N RBs, this CSI-RS resource can be used by different UEs in turn with their own beamform groups.

[0084] Fig. 5 shows one example of the scheme for CSI-RS resource multiplexing in the frequency domain according to option 1. In the example shown in Fig. 5, the frequency domain interleaving factor N is 2, and UE1 and UE2 each perform one CSI-RS measurement every 2 RBs (i.e. every other RB).

[0085] In option 1 , new parameters including an interleaving factor and an offset in the sense of RBs may be introduced in a control signaling for configuring the CSI-RS resource (e.g. RRC signaling). Alternatively, the interleaving factor can also be fixed in specification and thus only the offset in RBs is included in the control signaling for configuring the CSI-RS resource. For specification, one possible variant for the frequency domain interleaving method is to use a RB group composed of several consecutive RBs instead of a single RB. Thus, in option 1 , the RB groups are in turn allocated to different UEs and each UE should perform one CSI-RS measurement every N RB groups.

[0086] In contrast to the frequency domain interleaving method where the CSI-RS resource of each UE actually still occupies the whole bandwidth, for UE specific beamformed CSI-RS, the CSI-RS resource of each UE can be just defined on a subband.

[0087] In addition, a first control signaling and a second control signaling, each of which carries the above interleaving factor and the offset in resource blocks, may further be sent to UE 1 and UE2.

Option 2 [0088] In option 2, one beamformed CSI-RS resource can be defined on a subband composed of some consecutive RBs. The subband may comprise one or more consecutive RBs. Each UE can just perform the CSI-RS measurement based on this subband. Different UEs can have their own beamformed CSI-RS resources on different subbands.

[0089] For option 2, the subband size may be fixed or configured in a control signaling (e.g. RRC signaling) based CSI-RS configuration, and the position of subband should be included in the control signaling based CSI-RS configuration.

[0090] In option 2, if a small subband is used, a maximum CSI-RS overhead reduction effect will be achieved. However, it gives rise to the reduced CSI feedback quality brought by the subband measurement. To address this issue, the frequency domain hopping technique is introduced to improve option 2, thereby obtaining option 3 as below. Option 3

[0091] In option 3, one beamformed CSI-RS resource can be defined on a subband composed of a plurality of consecutive RBs, whose frequency-domain positions hop in a predefined hopping pattern during several consecutive measurement subframes, just as shown in Fig. 6. Each UE can perform the CSI-RS measurement based on a single subband or a series of frequency-hopped subband. Different UEs can have their own CSI-RS resources on different subbands with different predefined hopping patterns.

[0092] For option 3, the subband size is fixed or configured by a control signaling (e.g. RRC signaling); the starting position or hopping pattern indicator in the frequency domain may be configured by RRC based CSI-RS configuration. In one example, the hopping pattern can reuse the mechanism used in uplink PUSCH. By using option 3, the potential gain from frequency diversity via subband CSI reporting can be retained.

[0093] In addition, in option 3, a first control signaling and a second control signaling may be sent to UEl and UE2 respectively, the first control signaling carrying the frequency-domain position and hopping pattern of the subband for UEl , the second control signaling carrying the frequency-domain position and hopping pattern of the subband for UE2. In some embodiments, the frequency-domain position and hopping pattern of the subband for UEl differs from the frequency-domain position and hopping pattern of the subband for UE2.

[0094] Possible schemes in the frequency domain to reduce the beamformed CSI-RS resource overhead have been presented above. Furthermore, the overhead may also be reduced by using the time domain. Actually, option 3 can be viewed as the mixture of ways using the frequency and time domains. Moreover, the CSI-RS overhead may further be reduced by enlarging the period of CSI-RS measurement subframes and jointly using option 1, 2 or 3. By utilizing both time and frequency domain approaches, a maximum CSI-RS overhead reduction effect will be produced.

[0095] Once one of the above frequency-domain solutions is adopted, there must be some impacts on the CSI reporting. For the interleaving method as in option 1, the wideband CSI report including PMI/CQI/RI can be performed at UE and used by eNB similarly as before. The subband CSI report including PMI/CQI might be less flexible than before, since now the subband selected by UE or configured by eNB can only be chosen from interleaved RB groups which are scatteredly placed. For the subband method as in option 2 and 3, the wideband PMI/CQI report should be performed by UE actually just based on the measurement on the subband CSI-RS resource, which should be understood by eNB. For the subband PMI/CQI report which is either selected by UE or configured by eNB, the subbands, based on which PMI(s)/CQI(s) are reported, should be defined within the subband of CSI-RS resources itself, which are different from the current resources defined on the whole cell bandwidth. Otherwise, the CSI report is meaningless obviously. To summarize, although the CSI reporting mechanism and behavior should be modified and thus the flexibility in the frequency domain is reduced, this will not affect the overall system performance substantially due to the fact that the equivalent channel in the beamformed CSI-RS scheme becomes less selective in the frequency domain as aforementioned.

[0096] In a fourth aspect of, there is provided a method of reporting CSI. Fig. 7 shows a flowchart of a method 700 of reporting CSI according to a fourth aspect of the embodiments of the present disclosure. The method 700 may be executed by a UE in a wireless communication network, and in particular, the method 700 may be executed by an apparatus 1100 to be described with reference to Fig. 11 later.

[0097] As shown in Fig. 7, at block S710, a UE receives a beamformed CSI-RS specific to the UE on a predefined subband of a CSI-RS resource. At block S720, the UE measures the CSI based on the received beamformed CSI-RS. At block S730, the UE reports the measured CSI to an eNB.

[0098] In some embodiments, the subband is interleaved with another subband of the CSI-RS resource based on a predetermined interleaving factor, the other subband being configured for another UE.

[0099] In some embodiments, the method 700 further comprises receiving from the eNB a control signaling carrying an interleaving factor and an offset in resource blocks.

[00100] In some embodiments, the subband comprises one or more consecutive resource blocks.

[00101] In some embodiments, the frequency-domain positions of the subband hop in different predefined hopping patterns during a plurality of consecutive measurement subframes.

[00102] In some embodiments, the method 700 further comprises receiving from the eNB control a signaling carrying the frequency-domain positions and the predefined hopping p atterns .

[00103] In a fifth aspect, there is provided an apparatus for sharing a CSI-RS resource. Fig. 8 shows a block diagram of an apparatus 800 for sharing a CSI-RS resource according to a fifth aspect of the embodiments of the present disclosure. The apparatus 800 may be implemented in an eNB, for example.

[00104] As shown in Fig. 8, the apparatus 800 comprises: an obtaining unit 810 configured to obtain information about a plurality of beam groups, each of which is configured to transmit to one of a plurality of UEs beamformed CSI-RS specific to the UE; a determining unit 820 configured to determine degrees of spatial isolation between every two beam groups of the plurality of beam groups based on the obtained information; a comparing unit 830 configured to compare the determined degrees of spatial isolation with a predetermined threshold; and a transmitting unit 840 configured to, in response to each of the determined degrees of spatial isolation being above the threshold, transmit beamformed CSI-RSs specific to the plurality of UEs on the CSI-RS resource.

[00105] In some embodiments, the determining unit is further configured to: determine a plurality of orthogonal projection matrices, each of which is associated with one of the plurality of beam groups; calculate distances between every two of the plurality of orthogonal projection matrices; and determine the calculated distances as the degrees of spatial isolation.

[00106] In some embodiments, the obtaining unit 810 is further configured to obtain information about a first beam group and of a second beam group, the first and second beam groups being configured to transmit to a first UE a first beamformed CSI-RS specific to the first UE and transmit to a second UE a second beamformed CSI-RS specific to the second UE respectively.

[00107] In some embodiments, the transmitting unit 840 is further configured to: in response to each of the determined degrees of spatial isolation being above the threshold, transmit the first beamformed CSI-RS and the second beamformed CSI-RS on the predefined subband of the CSI-RS resource.

[00108] According to a sixth aspect of the embodiments of the present disclosure, there is provided an apparatus for sharing a CSI-RS resource. Fig. 9 shows a block diagram of an apparatus 900 for sharing a CSI-RS resource. The apparatus 900 may be implemented in an eNB, for example.

[00109] As shown in Fig. 9, the apparatus 900 comprises: an obtaining unit 910 configured to obtain information about a plurality of beam groups, each of which is configured to transmit to one of a plurality of UEs beamformed CSI-RS specific to the UE; an estimating unit 920 configured to estimate received signal strengths of the plurality of UEs based on the obtained information; a comparing unit 930 configured to compare the estimated received signal strengths with a first predetermined threshold; and a transmitting unit 940 configured to, in response to each of the estimated received signal strengths being above the first threshold, transmit beamformed CSI-RSs specific to the UEs on the CSI-RS resource.

[00110] According to a seventh aspect of the embodiments of the present disclosure, there is provided an apparatus for sharing a CSI-RS resource. Fig. 10 shows a block diagram of an apparatus 1000 for sharing a CSI-RS resource. The apparatus 1000 may be implemented in an eNB, for example.

[00111] As shown in Fig. 10, the apparatus 1000 comprises: a transmitting unit 1010 configured to transmit beamformed CSI-RS specific to one of a plurality of UEs on one of a plurality of predefined subbands of the CSI-RS resource.

[00112] In some embodiments, every two of the plurality of subbands are interleaved based on a predetermined interleaving factor.

[00113] In some embodiments, each of the plurality of subbands comprises one or more consecutive resource blocks.

[00114] In some embodiments, the frequency-domain positions of each of the plurality of subbands hop in different predefined hopping patterns during a plurality of consecutive measurement subframes.

[00115] According to an eighth aspect of the 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 the embodiments of the present disclosure. The apparatus 1100 may be implemented in UE, for example.

[00116] As shown in Fig. 11, the apparatus 1100 comprises: a receiving unit 1110 configured to receive a beamformed CSI-RS specific to a UE on a predefined subband of a CSI-RS resource; a measuring 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 a base station.

[00117] In some embodiments, the subband is interleaved with another subband of the CSI-RS resource based on a predetermined interleaving factor, the other subband being configured for another UE.

[00118] In some embodiments, the receiving unit 1110 is further configured to receive from the base station a control signaling carrying the interleaving factor and an offset in resource blocks.

[00119] In some embodiments, the subband comprises one or more consecutive resource blocks.

[00120] In some embodiments, the frequency-domain positions of the subband hop in different predefined hopping patterns during a plurality of consecutive measurement subframes.

[00121] In some embodiments, the receiving unit 1110 is further configured to receive from the base station a control signaling carrying the frequency-domain positions and the predefined hopping patterns.

[00122] Generally, various embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some 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 various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representation, it will be appreciated 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.

[00123] Various blocks in the flowcharts may be regarded as method steps and/or operations generated by operations of computer program code, and/or construed as a plurality of coupled logic circuit elements performing relevant functions. For example, the embodiments of the present disclosure comprise a computer program product, which includes a computer program tangibly embodied on a machine readable medium, the computer program including program code configured to implement the methods described above.

[00124] In the context of this disclosure, a machine readable medium may be any tangible medium that may 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 of the foregoing. More specific examples of the machine readable storage medium would 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 fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[00125] Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program codes, when executed by the processor or controller, cause the functions/operations specified in the flowcharts and/or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

[00126] 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 certain circumstances, multitasking and parallel processing may be advantageous. Likewise, while several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented in a plurality of embodiments separately or in any suitable sub-combination.

[00127] Various modifications and alterations to the exemplary embodiments of the present disclosure will become apparent to those skilled in the art from the foregoing description when taken in conjunction with the accompanying drawings. Any and all modifications are still to fall under the non-limiting scope of the exemplary embodiments of the present disclosure. In addition, the foregoing specification and accompanying drawings offer such an advantage as motivating those skilled in the art related to these embodiments of the present disclosure to devise other embodiments of the present disclosure depicted herein.

[00128] It is to be appreciated the embodiments of the present disclosure are not limited to these specific embodiments disclosed herein, and modifications and other embodiments should be included in the scope of the appended claims. Although specific terms are employed here, they are merely used in a broad and descriptive sense, rather than for the limitation purpose.

Claims

I/We Claim:

1. A method of sharing a channel state information reference signal (CSI-RS) resource, comprising:

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

determining degrees of spatial isolation among the plurality of beam groups based on the obtained information;

comparing each of the determined degrees of spatial isolation with a predetermined threshold; and

in response to each of the determined degrees of spatial isolation being above the threshold, transmitting, on the CSI-RS resource, beamformed CSI-RSs specific to the plurality of UEs.

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

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

calculating distances among the plurality of orthogonal projection matrices; and determining the calculated distances as the degrees of spatial isolation.

3. The method according to claim 1 or 2, wherein obtaining the information about the plurality of beam groups comprises:

obtaining information about a first beam group and information about a second beam group, the first beam group being configured to transmit, to a first UE, a first beamformed CSI-RS specific to the first UE, and the second beam group being configured to transmit, to a second UE second, a beamformed CSI-RS specific to the second UE.

4. The method according to claim 3, further comprising: in response to each of the determined degrees of spatial isolation being above the threshold, transmitting the first beamformed CSI-RS and the second beamformed CSI-RS on a predefined common subband of the CSI-RS resource.

5. A method of sharing a channel state information reference signal (CSI-RS) resource, comprising:

estimating received signal strengths of the plurality of UEs based on the obtained information;

comparing the estimated received signal strengths with a first predetermined threshold; and

in response to each of the estimated received signal strengths being above the first threshold, transmitting, on the CSI-RS resource, beamformed CSI-RSs specific to the plurality of UEs.

6. A method of sharing a channel state information reference signal (CSI-RS) resource, comprising:

transmitting, on one of a plurality of predefined subbands of the CSI-RS resource, a beamformed CSI-RS specific to one of a plurality of user equipment (UEs).

7. The method according to claim 6, wherein every two of the plurality of subbands are interleaved based on a predetermined interleaving factor.

8. The method according to claim 6, wherein each of the plurality of subbands includes one or more consecutive resource blocks.

9. The method according to claim 6, wherein frequency-domain positions of the plurality of subbands hop in different predefined hopping patterns during a plurality of consecutive measurement subframes.

10. A method of reporting channel state information (CSI), comprising:

receiving a beamformed CSI-RS specific to user equipment (UE) on a predefined subband of a CSI-RS resource;

measuring the CSI based on the received beamformed CSI-RS; and

reporting the measured CSI to a base station.

11. The method according to claim 10, wherein the subband is interleaved with a further subband of the CSI-RS resource based on a predetermined interleaving factor, the further subband being configured for a further UE.

12. The method according to claim 10, further comprising:

receiving control signaling from the base station, the control signaling carrying the interleaving factor and an offset in resource blocks.

13. The method according to claim 10, wherein the subband includes one or more consecutive resource blocks.

14. The method according to claim 10, wherein frequency-domain positions of the subband hops in a predefined hopping pattern during a plurality of consecutive measurement sub frames.

15. The method according to claim 10, further comprising:

receiving control signaling from the base station, the control signaling carrying the frequency-domain positions and the predefined hopping pattern.

16. An apparatus for sharing a channel state information reference signal (CSI-RS) resource, comprising:

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

a determining unit configured to determine degrees of spatial isolation among the plurality of beam groups based on the obtained information; a comparing unit configured to compare each of the determined degrees of spatial isolation with a predetermined threshold; and

a transmitting unit configured to transmit, on the CSI-RS resource, beamformed CSI-RSs specific to the plurality of UEs in response to each of the determined degrees of spatial isolation being above the threshold.

17. The apparatus according to claim 16, wherein the determining unit is further configured to:

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

calculate distances among the plurality of orthogonal projection matrices; and determine the calculated distances as the degrees of spatial isolation.

18. An apparatus for sharing a channel state information reference signal

(CSI-RS) resource, comprising:

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

an estimating unit configured to estimate received signal strengths of the plurality of UEs based on the obtained information;

a comparing unit configured to compare the estimated received signal strengths with a first predetermined threshold; and

a transmitting unit configured to transmit, on the CSI-RS resource, beamformed CSI-RSs specific to the plurality of UEs in response to each of the estimated received signal strengths being above the first threshold.

19. An apparatus for sharing a channel state information reference signal (CSI-RS) resource, comprising:

a transmitting unit configured to transmit, on one of a plurality of predefined subbands of the CSI-RS resource, a beamformed CSI-RS specific to one of a plurality of user equipment (UEs).

20. An apparatus for reporting channel state information CSI, the apparatus comprising:

a receiving unit configured to receive a beamformed CSI-RS specific to user equipment (UE) on a predefined subband of a CSI-RS resource;

a measuring unit configured to measure the CSI based on the received beamformed CSI-RS; and

a reporting unit configured to report the measured CSI to a base station.