WO2016119201A1

WO2016119201A1 - Method and apparatus for facilitating channel state information obtaining

Info

Publication number: WO2016119201A1
Application number: PCT/CN2015/071921
Authority: WO
Inventors: Chuangxin JIANG; Yukai GAO; Hongmei Liu; Gang Wang; Zhennian SUN; Lei Jiang
Original assignee: Nec Corporation
Priority date: 2015-01-30
Filing date: 2015-01-30
Publication date: 2016-08-04

Abstract

Embodiments of the present disclosure provide a method for facilitating channel status information (CSI) obtaining in a wireless system, the method comprises transmitting, to a first device, a first signaling for configuring a first number of CSI processes for the first device, each of the first number of CSI processes being associated with one of the first number of CSI reference signals (CSI-RS) beamformed in a vertical domain towards a different elevation direction respectively; transmitting, to the first device, a second signaling to indicate that a CSI measurement and report for a first CSI process is to be generated at least partly based on measurement of a CSI-RS associated with a second CSI process; transmitting the first number of CSI-RSs to the first device; and receiving the CSI report for the first CSI process from the first device. Corresponding apparatus are also provided.

Description

METHOD AND APPARATUS FOR FACILITATING CHANNEL STATE INFORMATION OBTAINING

TECHNICAL FIELD

The non-limiting and exemplary embodiments of the present disclosure generally relate to the technical field of radio communications， and specifically to a method and apparatus for facilitating channel state information (CSI) obtaining in a wireless system with 3-dimensional (3D) multiple-input-multiple-output (MIMO) technique.

BACKGROUND

This section introduces aspects that may facilitate a better understanding of the disclosure. Accordingly， the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.

In wireless communication， the demand for high data rate keeps increasing. However， the available time-frequency resources are limited， which means it is necessary to increase the data rate without increasing time-frequency resource consumption. That is，spectrum efficiency (SE) has to be improved. MIMO techniques can provide new degrees of freedom from spatial dimension and has been considered as an effective way for improving system throughput. For example， MIMO has been adopted as a key feature of Long Term Evolution (LTE) /LTE-Advanced (LTE-A) system developed by the third generation project partnership (3GPP) . Conventional one-dimensional (horizontal domain) antenna array can provide flexible beam adaption in the azimuth domain only through the horizontal domain precoding process， wherein a fixed down-tilt is applied in the vertical direction. It has been found recently that full MIMO capability can be exploited through leveraging a two dimensional antenna planar such that a user-specific elevation beamforming and spatial multiplexing in the vertical domain are also possible.

A Study Item of 3GPP Release 12 proposed to study user specific beamforming and full dimensional MIMO (i.e.， 3D MIMO) with 2D antenna arrays (also called Active Antenna System (AAS) ) . It can potentially improve transmit and/or receive gain， and reduce intra/inter-cell interference. Studies on improvement schemes for the user specific beamforming and the full dimensional MIMO are ongoing in a Study Item of 3GPP Release 13， the main topics of which include CSI reference signals (CSI-RS) design and CSI feedback schemes. The main targets of the studies are high system performance， low complexity and low standardization effort.

SUMMARY

Various embodiments of the disclosure not only reduce the report overhead， but also reduce the UE measurement complexity. Other features and advantages of embodiments of the disclosure will also be understood from the following description of specific embodiments when read in conjunction with the accompanying drawings， which illustrate， by way of example， the principles of embodiments of the disclosure.

Various aspects of embodiments of the disclosure are set forth in the appended claims and summarized in this section.

In a first aspect of the disclosure， there is provided a method for facilitating channel status information (CSI) obtaining in a wireless system， the method may comprise transmitting， to a first device， a first signaling for configuring a first number of CSI processes for the first device， each of the first number of CSI processes being associated with one of the first number of CSI reference signals (CSI-RS) beamformed in a vertical domain towards a different elevation direction respectively； transmitting， to the first device， a second signaling to indicate that a CSI measurement and report for a first CSI process of the first number of CSI processes is to be generated at least partly based on measurement of a CSI-RS associated with a second CSI process of the first number of CSI processes； transmitting the first number of CSI-RSs to the first device； and receiving the CSI report for the first CSI process from the first device.

In one embodiment， the second signaling may indicate that the CSI measurement and report for the first CSI process is to be generated at least partly based on precoding information derived from the CSI-RS associated with a second CSI process. In another embodiment， the precoding information derived from the CSI-RS associated with a second CSI process comprises a rank indicator and a precoding matrix indicator， and wherein the precoding matrix indicator is one of an overall precoding matrix indicator and a long-term precoding natrix indicator of a dual-codebook scheme.

In another embodiment， the second signaling comprises a radio resource control (RRC) configuration signaling carrying an index of the second CSI process， part of CSI for which is to be reused by the first CSI process. In still another embodiment， the RRC configuration signaling further indicates which part of the CSI for the second CSI process is to be reused by the first CSI process.

In one embodiment， receiving the CSI report for the first CSI process from the first device comprises receiving at least one of the following for the first CSI process： a channel quality indicator (CQI) ， ashort term horizontal domain precoding matrix indicator； a long term precoding matrix indicator； a rank indicator； and an overall horizontal domain precoding indicator.

In one further embodiment， the method may further comprise maintaining two sets of vertical beams， wherein adjacent beams in the second set of vertical beams are more spatially separated compared with that of the first set of vertical beams； configuring one-antenna port CSI-RS for each beam in the first set of vertical beams， and configuring multiple-antenna ports CSI-RS for each beam in the second set of vertical beams； and wherein each of the first number of CSI-RS is associated with a beam included the second set of vertical beams.

In another embodiment， the method may further comprise selecting the second set of vertical beams from the first set of vertical beams by： configuring， for each of a plurality of devices， a second number of one-antenna port CSI-RSs for RSRP measurements， each of the second number one-antenna port CSI-RSs being beamformed to form a beam included in the first set of the vertical beams； wherein the second number being no smaller than the first number； transmitting the second number one-antenna port CSI-RSs to the plurality devices； receiving from each of the plurality of devices a RSRP report for each of the configured second number one-antenna port CSI-RSs； and selecting a third number of beams from the beams corresponding to the second number of one-antenna port CSI-RS based on the received RSRP reports， to form the second set of the vertical beams， wherein the second number being no smaller than or being larger than the third number and the third number being no smaller than or being larger than the first number.

In still another embodiment， the method may further comprise determining 3-dimensional (3D) precoding parameters for data transmission to the first device based on only the CSI report for the first CSI process， or， based on both the CSI report for the first CSI process and a CSI report for the second CSI process from the first device.

In a second aspect of the disclosure， there is provided a method for facilitating channel status information (CSI) obtaining in a wireless system， the method may comprise receiving a first signaling for configuring a first number of CSI processes for the device， each of the plurality of CSI processes being associated with one of the first number of CSI reference signals (CSI-RS) beamformed in a vertical domain towards a different elevation direction respectively； receiving a second signaling indicating that a CSI measurement and report for a first CSI process of the first number of CSI processes is to be generated at least partly based on measurements of a CSI reference signal associated with a second CSI process of the first number of CSI processes； receiving the first number of CSI-RSs； generating the CSI measurement and report for the first CSI process according to the second signaling； and transmitting the CSI report for the first CSI process.

In one embodiment， generating the CSI measurement and report for the first CSI process according to the second signaling may comprise generating the CSI measurement and report at least partly based on precoding information derived from the CSI reference signal associated with the second CSI process. In another embodiment， the precoding information derived from the CSI reference signal associated with the second CSI process comprises a rank indicator and a precoding matrix indicator and wherein the precoding matrix indicator is one of an overall precoding matrix indicator and a long-term precoding matrix indicator of a dual-codebook scheme.

In one embodiment， the transmitting the CSI report for the first CSI process may comprises one of： transmitting the CSI report without an overall precoding information derived from the CSI-RS associated with the first CSI process， transmitting the CSI report without a long term precoding information derived from the CSI-RS associated with the first CSI process， or transmitting the CSI report with the precoding information derived from the CSI reference signal associated with the second CSI process as precoding information for the first CSI process.

In a third aspect of the disclosure， there is provided an apparatus adapted for facilitating channel status information (CSI) obtaining in a wireless system. The apparatus may comprise a first transmitting module， configured to transmit to a first device， a first signaling for configuring a first number of CSI processes for the first device， each of the first number of CSI processes being associated with one of the first number of CSI reference signals (CSI-RS) beamformed in a vertical domain towards a different elevation direction respectively； a second transmitting module， configured to transmit， to the first device， a second signaling to indicate that a CSI measurement and report for a first CSI process of the first number of CSI processes is to be generated at least partly based on measurement of a CSI-RS associated with a second CSI process of the first number of CSI processes； a third transmitting module， configured to transmit the first number of CSI-RSs to the first device； and a first receiving module， configured to receive the CSI report for the first CSI process from the first device.

In a fourth aspect of the disclosure， there is provided an apparatus adapted for facilitating channel status information (CSI) obtaining in a wireless system. The apparatus may comprise a first receiving module， configured to receive a first signaling for configuring a first number of CSI processes for the device， each of the plurality of CSI processes being associated with one of the first number of CSI reference siguals (CSI-RS) beamformed in a vertical domain towards a different elevation direction respectively； asecond receiving module， configured to receive a second signaling indicating that a CSI measurement and report for a first CSI process of the first number of CSI processes is to be generated at least partly based on measurements of a CSI reference sigual associated with a second CSI process of the first number of CSI processes； a third receiving module， configured to receive the first number of CSI-RSs； a CSI report generation module， configured to generate the CSI measurement and report for the first CSI process according to the second signaling； and a transmitting module， configured to transmit the CSI report for the first CSI process.

In a fifth aspect of the disclosure， there is provided an apparatus adapted for facilitating channel status information (CSI) obtaining in a wireless system， the apparatus comprising a processor and a memory， said memory containing instruetions executable by said processor whereby said apparatus is operative to perform any method in accordance with the first aspect of the disclosure.

In a sixth aspect of the disclosure， there is provided an apparatus adapted for facilitating channel status information (CSI) obtaining in a wireless system， the apparatus comprising a processor and a memory， said memory containing instructions executable by said processor whereby said apparatus is operative to perform any method in accordance with the second aspect of the disclosure.

In a seventh aspect of the disclosure， there is provided an apparatus adapted for facilitating channel status information (CSI) obtaining in a wireless system， the apparatus comprises process means adapted to perform any method in accordance with the first aspect of the disclosure.

In an eighth aspect of the disclosure， there is provided an apparatus adapted for facilitating channel status information (C SI) obtaining in a wireless system， the apparatus comprises process means adapted to perform any method in accordance with the second aspect of the disclosure.

In a ninth aspect of the disclosure， there is provided a computer program， comprising instructions which， when executed on at least one processor， cause the at least one processor to carry out the method according to the first aspect of the disclosure.

In a tenth aspect of the disclosure， there is provided a computer program， comprising instructions which， when executed on at least one processor， cause the at least one processor to carry out the method according to the second aspect of the disclosure.

Aceording to the various aspects and embodiments as mentioned above， by sharing horizontal channel information between adjacent vertical beams which have high correlation， calculation， or both calculation and feedback for a part of the CSI can be avoided for certain CSI processes， and thus complexity and overhead for CSI feedback can be reduced at the UE side. In accordance with some aspects and embodiments above， CSI-RS overhead can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects， features， and benefits of various embodiments of the disclosure will become more fully apparent， by way of example， from the following detailed description with reference to the accompanying drawings， in which like reference numerals or letters are used to designate like or equivalent elements. The drawings are illustrated for facilitating better understanding of the embodiments of the disclosure and not necessarily drawn to scale， in which：

Fig. 1 schematically illustrate a diagram of vertically beamformed CSI-RS；

Fig. 2 schematically illustrates the relationship between vertical beam and horizontal channels；

Fig. 3 illustrates exemplary results on correlation between horizontal channels associated with adjacent beams；

Fig. 4 schematically illustrates an wireless environment where embodiments according to the present disclosure can be implemented；

Fig. 5 illustrates a flowchart of a method 500 for facilitating CSI obtaining according to an embodiment of the present disclosure；

Fig. 6 schematically illustrates applying a method according to an embodiment of the disclosure in a cell；

Fig. 7 illustrates a flowchart of a method 700 for reducing CSI-RS overhead according to an embodiment of the present disclosure；

Fig. 8 schematically illustrates applying a method according to an embodiment of the disclosure in a cell；

Fig. 9 illustrates a flowchart of a method 900 for facilitating CSI obtaining according to another embodiment of the present disclosure；

Fig. 10 illustrates a schematic block diagram of an apparatus 1000 adapted for facilitating CSI obtaining according to an embodiment of the present disclosure；

Fig. 11 illustrates an apparatus 1100 for facilitating CSI obtaining according to another embodiment of the present disclosure；

Fig. 12 illustrates a simplified block diagram of an apparatus 1210 and an apparatus 1220 that are suitable for use in practicing the embodiments of the present disclosure.

DETAILED DESCRIPTION

Hereinafter， the principle and spirit of the present disclosure will be deseribed with reference to the illustrative embodiments. It should be understood， all these embodiments are given merely for the skilled in the art to better understand and further practice the present disclosure， but not for limiting the scope of the present disclosure. For example， features illustrated or described as part of one embodiment may be used with another embodiment to yield still a further embodiment. In the interest of clarity， not all features of an actual implementation are described in this specification.

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

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

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be liming of example embodiments. As used herein， the singular forms “a” ， “an” and “the” are intended to include the plural forms as well， unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” ， “comprising” ， “has” ， “having” ， “includes” and/or “including” ， when used herein， specify the presence of stated features， elements， and/or components etc.， but do not preclude the presence or addition of one or more other features， elements， components and/or combinations thereof.

In the following description and claims， unless defined otherwise， all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. For example， the term terminal device used herein may refer to any terminal having wireless communication capabilities or user equipment (UE) ， including but not limited to， mobile phone， cellular phones， smart phone， or personal digital assistants (PDAs) ， portable computers， image capture device such as digital cameras， gaming devices， music storage and playback appliances and any portable units or terminals that have wireless communication capabilities， or Internet appliances permitting wireless Internet access and browsing and the like. Likewise， the term base station used herein may be referred to as e.g. eNB， eNodeB， NodeB， Base Transceiver Station BTS or Access Point (AP) ， depending on the technology and terminology used.

The following description of various embodiments aims to illustrate the principle and concept of the present disclosure. For illustrative purposes， several embodiments of the present disclosure will be described in the context of a 3GPP LTE system. Those skilled in the art will appreciate， however， that several embodiments of the present disclosure may be more generally applicable to other wireless systems exploiting 3D MIMO technique.

In order to clearly describe embodiments of the present disclosure， the 3D MIMO technique discussed currently in 3GPP LTE-A is firstly introduced briefly， and details can be found in some 3GPP LTE documents disclosed in 3GPP TSG RAN WG1 Meeting #79， e.g.， R1-144948， R1-145015， R1-144706. Currently in 3GPP， beamformed CSI-RS is regarded as a potential and simple scheme to implement elevated beamforming (EBF) /full dimension-MIMO (FD-MIMO) scheme with existing transmission mode 9 (TM9) /transmission mode 10 (TM10) feature specified in the 3GPP standard， e.g.， TS 36.213 v.c.0.0. In accordance with the beamformed CSI-RS scheme， a CSI-RS configured for UE can be precoded in vertical domain with an elevation (used exchangeable with “vertical” in this disclosure) beamforming vector， and thus each CSI-RS reflects channel characteristic of a beam.

The UE configured with TM9 can be configured with one CSI-RS resource according to its position in a cell. Alternatively， the CSI-RS for the UE could be selected based on long-term uplink measurement in a time division duplex (TDD) system or based on reference signal received power (RSRP) report in a frequency division duplex (FDD) system. For example， an eNB can collect the RSRP reports from UE for a number of CSI-RS beams， and select the CSI-RS beam with the highest RSRP for the UE.

For UEs supporting the TM10 feature， the FD-MIMO could be implemented in a similar manner but with more freedom. A UE could be configured with more than one CSI-RSs beamformed in the elevation domain， and could be configured with more than one CSI processes for reporting CSI for the associated CSI-RSs. An example of the CSI-RS beams is illustrated schematically in Fig. 1 (a) ， and the elevated beamforming (or， precoding) for a CSI-RS (the nth CSI-RS， in this example) is schematically illustrated in Fig. 1 (b) . In this example， vertical domain beamfoming is applied to a 4x4 antenna array to generate a beamformed CSI-RS with 4-antenna-ports， i.e.， {Sn (0) ， Sn (1) ， Sn (2) ， Sn (3) } . By configuring different beamforming weight， different vertical domain beamforming vectors can be obtained， resulting in different beams， i.e.， beams toward different down tilts. By configuring multiple CSI processes for a UE， with each of the multiple CSI processes corresponding to a different CSI-RS beam， it enables the UE to report CSI for multiple CSI-RS beams. Based on the reported CSI for these CSI-RS beams， the eNodeB could select a CSI-RS beam with the best CSI and derive proper transmission parameters for the UE accordingly.

In Fig. 1 (b) ， CSI-RS of one antenna port is mapped to one column of the antenna array， and is weighted by the beamforming weight， e.g.， the weight of Wn＝ {Wn (0) ， Wn (1) ， Wn (2) ， Wn (3) } for the nth CSI-RS， where n can be 0， 1， 2， 3 in this example. In accordance with the example of Fig. 1 (b) ， the nth CSI-RS has four antenna ports arranged in the horizontal domain. The UE can estimate horizontal channel (s) associated with a vertical beam based on measurements of the configured beamfomed CSI-RS， and calculate corresponding CSI which may include but not limited to CQI/PMI/RI. The calculated CSI feedback for each CSI-RS resource is indicative of the CSI in the horizontal domain of one vertical beam. The calculated and reported CQI can reflect the channel quality of the transmission from the whole array correctly， as the CSI-RS from which the CQI is derived is already beamformed in the vertical domain. Assuming the calculated horizontal domain precoding matrix can be denoted as V， the precoding matrix for the overall antenna array can be calculated as Vx Wn， where Wn is the vertical domain beamforming weight for the configured CSI-RS， and the horizontal domain precoding matrix V can be expressed as V＝W1xW2 if dual codebooks are applied. The feedback for W1 can be denoted as PMI1 and the feedback for W2 can be denoted as PMI2. PMI1 can reflect a long-term and/or wideband channel characteristic， while PMI2 usually reflects short-term and/or narrow bandwidth channel characteristic. It is also possible to arrange the CSI-RS beamforming pattern such that virtualized CSI-RS antenna ports are arranged in both horizontal and elevation domains.

Configuring a CSI-RS resource for each beam and ordering UEs to measure and report CSI for each beam can enable beam selection， however， it should be noted， such a scheme requifes large measurement complexity at the UE side and high CSI-RS overhead of the system.

It has been observed that horizontal channels virtualized from adjacent vertical beams have high correlation. That is， horizontal channels associated with beam 0 and beam 1 shown in Fig. 2 as an example can be highly correlated. Some supporting results are presented in Fig. 3 for illustrative purpose. Fig. 3 illustrates difference between RI/PMI1/PMI2 of adjacent beams. As shown in Fig. 3， the probability for the rank indicators (RIs) derived from adjacent beams to be the same is 0.9， while the probability for the PMI1 derived from adjacent beams to be the same is 0.7. Regarding PMI2， the correlation is lower than that for RI and PMI1.

Based on the above observations， methods and apparatus have been proposed herein to make use of the high correlation between horizontal channels associated with adjacent beams， and thereby reduce CSI-RS feedback and measurement complexity at the UE side， and/or， reduce CSI-RS overhead.

Reference is now made to Figure 4 which is a diagram of an example wireless network scenario where a method according to an embodiment of the present disclosure can be applied. The wireless network 400 comprises one or more network nodes 401， here in the form of evolved Node B， also known as eNode Bs or eNBs. It will be appreciated that the network nodes 401 could also be in the form of Node Bs， BTSs (Base Transceiver Stations) ， BS (Base Station) and/or BSSs (Base Station Subsystems) ， etc. The network nodes 401 may provide a macro cell or small cell and provide radio connectivity to a plurality of user equipments (UEs) 402. The term user equipment is also known as mobile communication terminal， wireless terminal， mobile terminal， user terminal， user agent， machine-to-machine devices etc.， and can be， for example， what today is commonly known as a mobile phone or a tablet/laptop with wireless connectivity or fixed mounted terminal. Moreover， the UEs 402 may， but not necessarily， be associated with a particular end user. Though for illustrative purpose， the wireless network 400 is described to be a 3GPP LTE network， the embodiments of the present disclosure are not limited to such network scenarios and the proposed methods and devices can also be applied to other wireless networks， e.g.， a non-cellular network， where 3D-MIMO technique is applied， overhead to support 3D-MIMO need to be reduced and the principles described hereinafter are applicable.

In the network 400 depicted in Fig. 4， the network nodes， e.g.， eNB 401 will require CSI to perform efficient scheduling. The eNB may configure multiple CSI processes for a UE， with each CSI process assoeiated with a beam as shown in Figs 1 and 2， such that CSI for multiple beams can be collected from the UE. However， as analyzed above， such a scheme requires large measurement complexity and high feedback overhead.

In one embodiment， the problem can be alleviated by a method which enables CSI sharing between adjacent beams， i.e.， CSI feedback and/or caleulation corresponding to one CSI-RS beam can be avoided or partly avoided if the CSI feedback is similar with that of another CSI-RS beam.

Reference is now made to Fig. 5 which illustrates an example of method 500 for facilitating CSI obtaining in a wireless system. The method 500 can be performed by a base station， e.g.， the eNB 401 shown in Fig. 4， but the present disclosure is not limited thereto. The method 500 may be performed by any other suitable network element.

As shown in Fig. 5， the method 500 comprises a step 501 for transmitting， to a first device， a first signaling for configuring a first number of CSI processes for the first device， each of the first number of CSI processes being associated with one of the first number of CSI reference signals (CSI-RS) beamformed in a vertical domain towards a different elevation direction respectively； a step 502 for transmitting， to the first device， a second signaling to indicate that a CSI measurement and report for a first CSI process of the first number of CSI processes is to be generated at least partly based on measurements of a CSI-RS associated with a second CSI process of the first number of CSI processes； a step 503 for transmitting the first number of CSI-RSs to the first device； and a step 504 for receiving the CSI report for the first CSI process from the first device.

In an embodiment of the disclosure， the first device is UE， e.g.， UE 402 shown in Fig. 4， and in step 501， the eNB can configure N CSI processes for the UE， wherein N is an integer no less than 1， and each of the N CSI processes configured in step 501 may be associated with a beamformed CSI-RS as shown in Fig. 1. In accordance with current 3GPP LTE specification， N can be up to 3， however， embodiments of the disclosure are not limited to this， and N can be any suitable number depends on needs. In an example shown in Fig. 6， the eNB can transmit in four CSI-RS resources， with each CSI-RS being precoded by one vertical precoding vector representing one vertical direction. The eNB can， for example， configure for the UE 3 CSI processes which correspond to the

vertical beams

0， 1， and 2 respectively. In one embodiment， the first signaling transmitted in step 501 can be， but not limited to a radio resource control (RRC) signaling.

In another embodiment of the present disclosure， in step 502， the eNB can configure one or more of the configured CSI processes to share at least part of CSI of another CSI process via the second signaling. Usually， the other CSI process may be associates with a CSI-RS beam adjacent to the CSI-RS beams associated with the one or more configured CSI processes， since some horizontal channel information of adjacent beams can be highly correlated， as shown by the results in Fig. 3. However， embodiments of the present disclosure are not limited thereto， that is， the another CSI-RS beam may also be any other non-adjacent suitable beam.

In one embodiment， in step 502， the eNB may configure via the second signaling that the CSI measurement and report for the first CSI process is to be generated at least partly based on precoding information derived from the CSI-RS associated with the second CSI process. In one embodiment， assuming the UE 1 has been configured， via the first signaling transmitted in

step

501， 3 CSI processes which correspond to the

vertical beams

0， 1， 2 shown in Fig. 6， respectively， wherein the horizontal channels of the vertical beam 0 and the vertical beam 1 are highly correlated， then in step 502， the second signal may be transmitted to configure that a measurement and CSI report for the vertical beam 0 (i.e.， the beam associated with the first CSI process in this example) should reuse part of the CSI for the vertical beam 1， e.g.， (part of) the precoding information measurement and report for the vertical beam 1. In one embodiment， the part of the CSI for the vertical beam 1 to be reused can be rank indicator (RI) and precoding matrix indicator. For example， it can be RI and a long-term pecoding indicator (PMI1) in a dual-codebook precoding scheme， since as shown in Fig. 3， the RI and PMI1 derived from adjacent beams can be similar and thus highly correlated. In another example， the part of the CSI to be shared can be RI and the overall precoding matrix indicator (e.g.， PMI) for a single-codebook scheme. It will be appreciated that the RI/PMI/PMI1 to be reused are just presented here for illustrative purpose， and in other embodiments， the precoding information to be reused can be any suitable information related to precoding.

A CSI report from the UE to the eNB may comprise CQI， RI/PMI， RI/PMI1， or PMI2， wherein the CQI may be estimated based on measurement results of RI， PMI1 and PMI2， or based on RI and the overall precoding matrix indicator PMI. Similarly， the PMI2 can be derived depending on RI and PMI1. Conventionally， a UE configured with 3 CSI processes will report CSI for each CSI process separately， for example， the UE may report CQI， RI and PMI for each CSI process. That is， the UE has to measure the CSI-RS corresponding to each CSI process， calculate respective RI， PMI (or， PMI1 and PMI2 for dual code-book scenario) and CQI for each CSI process， and then report CQI or both CQI and RI/PMI (or， RI/PMI1/PMI2) for each CSI process to the eNB depending on the CSI report configuration， e.g.， whether precoding information is configured to be fedback.

In contrast， in accordance with one embodiment of the present disclosure， if the second signaling is transmitted in step 502， the UE can directly reuse the RI and PMI， or RI and PMI1 for the second CSI process as that for the first CSI process， thereby avoiding additional calculation for the RI and PMI， or RI and PMI1 based on the CSI-RS associated with the first CSI process. Regarding the CQI and/or PMI2， the UE may compute based on the channel estimation for the first CSI process and the reused precoding information of the second process. That is， the UE can compute CQI for the first CSI process based on， for example， the channel estimation H1 for the first CSI process and the RI and PMI for the second process. In a dual codebook case， the UE can also compute CQI for the first CSI process based on， for example， channel estimation H1 and short-term precoding matrix indicator PMI2 for the first CSI process， and RI and PMI1 for the second CSI process， wherein the PMI2 may also be derived based on the RI and the PMI1 for the second CSI process.

As described above， in one embodiment， the second signaling enables the UE to reduce measurement complexity， since it can directly reuse the RI and PMI， or RI and PMI1 for the second CSI process as that for the first CSI process， thereby avoiding additional calculation for the RI and PMI， or RI and PMI1 based on the CSI-RS for the first CSI process. In one embodiment， the UE may still report RI and PMI， or RI and PMI1 for the first CSI process by using same value as that for the second CSI process without additional calculation to get these values for the first CSI process. In another embodiment， the UE may be configured not to report the precoding information (for example RI and PMI) ， or part of the precoding information (for example RI and PMI1) for the first CSI process， and at the eNB side， the precoding information reported for the CSI process 2 from the same UE can be reused for determining the precoding parameters for the UE. In such case， the UE may only need to report CQI， or both CQI and part of precoding information (for example PMI2) for the CSI process 1. Thereby the feedback overhead is also reduced. Accordingly， in step 504， receiving the CSI report for the first CSI process from the first device comprises receiving at least one of： a channel quality indicator (CQI) ， a short term horizontal domain precoding matrix indicatof； a long term precoding matrix indicator； a rank indicator； and an overall horizontal domain precoding indicator. It can be appreciated that in step 504， the eNB can also receive the CSI report for other CSI processes of the configured first number of CSI process.

As described above， the precoding information derived for the second CSI process， to be reused for the generation of the CSI for the first CSI process may comprise a rank indicator and a precoding matrix indicator， and the precoding matrix indicator can be an overall precoding matrix indicator (PMI) or a long-term precoding matrix indicator (for example， the PMI1) of a dual-codebook scheme. However， embodiments of the present disclosure are not limited to any specific precoding information. It will be appreciated that with advance of the wireless technique， the precoding information may change， and then the precoding information which can be reused may vary accordingly.

In one embodiment of the present disclosure， the second signaling transmitted in step 502 may comprise a RRC configuration signaling which carries an index of the second CSI process. For example， the RRC signaling may indicate a CSI process associated with the vertical beam 1 as the second CSI process. In one embodiment， the eNB may configure multiple CSI processes to reuse (part of) the CSI of the second CSI process. For example， the eNB can configure the CSI processes associated with the

vertical beam

0 and 2 as shown in Fig. 6 to reuse the CSI for the CSI process associated with the vertical beam 1 for UE 1.

In another embodiment， the RRC configuration signaling may further indicate which part of the CSI report for the second CSI process is to be reused by the first CSI process. That is， which part of the CSI report of the second CSI process may be reused for the generation of the CSI report for the first CSI process. For example， the RRC signaling may configure to reuse the RI/PMI of the second CSI process， or to reuse the RI/PMI1 of the second CSI process. However， it will be appreciated that the RRC signaling is presented just for illustrative purpose rather than limitation. That is， in another embodiment， any other suitable signaling can be used as the second signaling. Similarly， the RI/PMI and RI/PMI1 for the second CSI process are just listed as an example of the part of the CSI to be reused. It will be appreciated that the part of CSI to be reused can be any other suitable information related to horizontal channel in other embodiments.

In one embodiment of the disclosure， the second CSI process can be determined by the eNB based on at least one of： aprevious CSI report associated with the first number of CSI processes from the first device； a reference signal received power (RSRP) report associated with the first number of CSI processes from the first device； and measurements based on at least one of reference signals and/or data signals from the first device. For example， eNB can choose the second CSI process according to previous CSI feedback from UE. As the correlation of horizontal channels derived from high correlation vertical beams， e.g. of horizontal channels derived from vertical beam 0 and vertical beam 1 for UE1， can be very high， CSI information (e.g. RI， PMI) for the corresponding CSI processes may always be same or very similar. If the best vertical beam is the beam 0 for the UE， i.e. the CQI or channel capacity derived from CSI process 0 is larger than that of other beams， the eNB can configure the corresponding CSI process 0 as the second CSI process for CSI process 1 (the first CSI process in step 502) . In one embodiment， if RI/PMI1 feedback from CSI process 0 and process 1 are always same or similar， eNB can configure the CSI process 0 as the second CSI process and may further indicate that RI/PMI1 of the CSI process 0 can be reused for the CSI process 1 (the first CSI process in step 502) . Alternatively， the eNB can choose the second CSI process according to CSI-RS RSRP feedback from the UE， uplink SRS measurement or others. For example， the eNB can select a CSI process as the second CSI process if the offset of the RSRP value for the selected CSI process and RSRP value for the first CSI process is smaller than a threshold. However， embodiments of the disclosure are not limited to this， and in another embodiment， the second CSI process can be selected based on any suitable information available at the eNB or reported by the UE.

In another embodiment， the method 500 may further comprise step 505， for determining 3-dimensional (3D) precoding parameters for data transmission to the first deviee based on only the CSI report for the first CSI process. This may be implemented， for example， when the UE report CQI and precoding information for the first CSI process， though the precoding information may be same as that of the second CSI process. Alternatively， in another embodiment， in step 505， the eNB may determine the 3D precoding parameters for data transmission to the first device based on both the CSI report for the first CSI process and a CSI report for the second CSI process from the first device， e.g， based on the CQI for the first CSI process and precoding information for the second CSI process.

As described above， each of the configured CSI processes may be associated with a CSI-RS beamformed in the vertical domain towards an elevation beam direction， and it means， the CSI-RS overhead will increase linearly with the number of vertical beams. As shown in Fig. 1 (b) ， each CSI-RS may be transmitted from multiple antenna ports and each of the antenna port corresponding to a physical resource allocation. That is，the resources required for CSI-RS transmission may increase linearly with the number of beams and the number of antenna ports. One possible way to reduce the CSI-RS overhead is to reduce the number of antenna ports for each CSI-RS beam， however， it will make the 3D CSI measurement not accurate.

In an embodiment of the disclosure， methods and apparatus are proposed to address the above problem， i.e， to reduce the CSI-RS overhead without degrade the system performance obvioasly. In one embodiment， the objective can be achieved by making use of the correlation between the horizontal channels virtualized from adjacent vertical beam. As described above， CSI information including RI/PMI or/and CQI are always same or similar for adjacent vertical beams. Thus， CSI-RS resources corresponding to one beam of the adj acent vertical beams can be reduced to some degree due to the similarity in corresponding horizontal channels. For example， less CSI-RS ports can be configured to some CSI-RS resources， and thereby to reduce CSI-RS overhead.

In Fig. 7， a flow chart for an exemplary method 700 for reducing CSI-RS overhead is illustrated. The method 700 may be implemented by the same eNB which performs the method 500， or may be implemented by another node.

As shown in Fig. 7， in one embodiment， in step 710， the eNB can maintain， for example， two sets of vertical beams， wherein the first set of vertical beams may be fine granulated， i.e.， adjacent beams in the first set are close in vertical spatial domain to each other， and the second set of vertical beams may be coarsely granulated， i.e.， adjacent beams in the second set are well separate in vertical spatial domain to each other compared with that of the first set and lead to lower correlation horizontal channels. That is， adjacent beams in the second set of vertical beams are more spatially separated compared with that ofthe first set of vertical beams. Regarding the first set of beams， the eNB can configure， in step 720， CSI-RS with small number of antenna ports， e.g.， only configure 1-port CSI-RS， mainly for RSRP measurement； while for the second set of beams， the eNB can configure， in step 720， CSI-RS with larger number of antenna ports， e.g.， the eNB may configure 4-ports， or 8-ports CSI-RS for each beam of the second set of vertical beams， mainly for CSI measurement.

Since the beams in the second set are coarsely granulated， i.e.， spatially separate， the number of beams in the second set can be less than that of the fine granulated beams. That is， there may be only small number of beams (i.e.， beams in the second set) associated with 4-ports CSI-RS， while the other beams (i.e.， beams in the first set but not in the second set) will be associated only with 1-port CSI-RS. By this way， the CSI-RS overhead can be reduced， and at the same time accurate CSI can still be available. The eNB can calculate 3D precoding matrix and scheduling MCS according to UE CSI feedback and RSRP feedback.

In one embodiment， eNB can configure UE with a small number of CSI-RSs associated with at least one of the vertical beams from the second set of vertical beams， wherein each CSI-RS has full CSI-RS ports (e.g.， 4， or 8 antenna ports) and corresponds to one CSI process. These vertical beams in the second set may have relative large vertical space gap， and lead to lower correlation horizontal channels compared with that of the first set. Meanwhile， eNB may eonfigure the UE a larger number of CSI-RS associated with vertical beams from the first set which are finer granulated， for RSRP measurement. In one embodiment， the first number of CSI-RS which are associated with the first number of CSI processes configured for the UE via the first signaling in step 501 of the method 500 can be CSI-RS associated with vertical beams in the second set of vertical beams. That is to say， the method 700 can work in combination with the method 500.

In another embodiment of the disclosure， the method 700 may comprise a step 730， where the eNB can select beams of the second set from the beams in the first set， based on RSRP reports for the beams in the first set. In an embodiment of the disclosure， in step 730， the eNB may select the second set of vertical beams by： configuring， for each of a plurality of devices， a second number of one-antenna port CSI-RSs for RSRP measurements， each of the second number one-antenna port CSI-RSs being beamformed in the vertical domain to form a beam included in the first set of vertical beams； transmitting the second number one-antenna port CSI-RSs to the plurality devices； receiving from each of the plurality of devices a RSRP report for each of the configured second number one-antenna port CSI-RSs； selecting a third number of beams from the beams corresponding to the second number of one-antenna port CSI-RS based on the received RSRP reports， wherein the third number being no larger than or being smaller than the second number. The third number of beams can form the second set of vertical beams or a part of it， and the second number of beams for which 1-antenna port CS-RS are configured can form the first set of vertical beams or a part of it， in one embodiment.

In another embodiment， the method 700 may configure a third number of the multiple-antenna ports CSI-RSs for the selected third number of vertical beams (i.e， the second set of vertical beams， or part of it) in step 720； and the method 700 may further comprise step 740 for further selecting a first number of CSI-RSs from the third number of multiple-antenna ports CSI-RSs based on a reference signal received power (RSRP) report associated with the one-antenna port CSI-RSs from a first device and/or measurements based on at least one of reference signals and data signals from the first device， wherein the first number being no larger or being smaller than than the third number.

In one embodiment， the method 700 can be implemented by the same eNB which performs the method 500， and the first number of CSI-RSs selected in step 740 of the method 700 can be the first number of CSI-RS associated with the first number of CSI processes configured in the step 501 of the method 500. This may be advantageous when the number of beams in the second set is still large， and the horizontal channels derived from the first number of CSI-RS are still highly correlated.

It will be appreciated that the method 700 can also be implemented independently from the method 500. That is， a base station may implement the method 700 without implementing the method 500. In such case， normal CSI process configured and performed， with each CSI process associated with one of the first number of CSI-RS selected in step 740. In another embodiment， the eNB can also implement the method 500 without implementing the method 700. That is， the first number of CSI process may each be associated with a normal beam with normal vertical spatial separation， rather than being associated with the beams of the second set， i.e.， the beams selected in step 730 of the method 700.

In Fig. 8， a schematic diagram is show for illustrate the beam selection at the eNB side in accordance with an embodiment of the disclosure. An eNB may configure each UE multiple 1 port CSI-RS for RSRP measurement， where each CSI-RS is associated with one vertical beams. According to current LTE-A standard， one DRS CSI-RS port can be configured for RSRP measurement. For example， as shown in the Fig. 8， all UEs are configured 6 1-port CSI-RSs for RSRP measurement and feedback which correspond to

vertical beam

0， 1， 2， 3， 4， 5 shown as dashed lines in Fig. 8， respectively. These 6 vertical beams can be the first set of beams， in one embodiment. Then， as shown in the Fig. 8， the eNB can select， based on RSRP values from all users， the

vertical beam

1 and 3 to form the second set of beams， with these beams well spatially separated， and than the eNB can transmit multiple full port (the number of ports equals to the number of horizontal antenna ports， which are used for conventional CSI measurement， and the number may be configured via a radio resource control (RRC) signaling) CSI-RSs only corresponding to the selected

vertical beams

1 and 3， which is illustrated as solid lines in Fig. 8.

As described in Fig. 8， the eNB can determine to transmit full port CSI-RS only for some coarse granularity vertical beams (the

vertical beams

1 and 3 in this example) ， because eNB can obtain horizontal channel information for some vertical beams from other adjacent vertical beams. For example， for UE0， eNB can compute horizontal channel information for vertical beam 0 based on the CSI feedback for vertical beam 1. Similarly， the eNB needn’t transmit full port CSI-RS for some vertical beams e.g.

vertical beam

4 and 5， in which all feedback RSRP values are very low. In the Fig. 8， an 8x8 antenna array is used， and the number of full antenna ports is 8 after virtualized based on the vertical vectors. It will be appreciated that embodiments are not limited to such an antenna array， and in other embodiment， any suitable antenna array can be used.

In an embodiment， the eNB can configure each UE at least one CSI process with each CSI process corresponding to one of the full antenna port CSI-RS. The eNB can determine CSI process corresponding to which full antenna port CSI-RS should be configured for the UE based on RSRP feedback from the UE. For example， if UE 3 feeds back RSRP values R0， R1， R2， R3， R4， R5 for vertical beam 0， 1， 2， 3 4， 5 respectively， where R2＞R3＞R1＞R0＞R4＞R5， and then the eNB can configure， for example， CSI process 0 and CSI process 1 corresponding to vertical beam 3 and vertical beam 1 respectively for the UE. In another example， the eNB may only configure one CSI process 0 corresponding to vertical beam 3 for the UE. The eNB can compute 3D precoder according to the RSRP feedback and CSI report for transmitting transmit data to the UE. For example， assuming that UE 3 is configured with one CSI process corresponding to vertical beam 3 and the best RSRP value reported by UE3 is R2， since the horizontal channels derived from vertical beam 3 and beam 2 have very high correlation， the eNB can compute 3D precoder based on vertical beam 2 and horizontal CSI derived for vertical beam 3， i.e.，

In this case， the eNB can determine CQI based on the CSI feedback for the vertical beam 3， or can compute the CQI based on the CSI feedback for the vertical beam 3 and a RSRP offset between R2 and R3.

In another embodiment， assuming more CSI process are configured for the UE for avoiding interference or multiple user scheduling， for example， assuming UE 3 is configured with two CSI processes， the eNB can determine the 3D precoder for UE3 based on vertical beam 1 or vertical beam 3. The 3D precoder can be obtained by CSI feedback corresponding

vertical beam

1 or 3. In this case， CQI can be obtained accurately from the CSI feedback.

In still another embodiment， the eNB can configure the UE to reuse at least part CSI of a CSI process for determining CSI for another CSI process to further reduce measurement complexity， as described with reference to method 500.

Reference is now made to Fig. 9， which illustrate a flow chart of a method 900 in a device for facilitating channel status information (CSI) obtaining in a wireless system. The method can be implemented by a UE， e.g.， UE 402 shown in Fig. 4， or any suitable devices which need to report CSI.

As shown in Fig. 9， the method 900 comprises step 901 for receiving a first signaling for configuring a first number of CSI processes for the device， each of the first number of CSI processes being associated with one of the first number of CSI-RS beamformed in a vertical domain towards a different elevation direction respectively； step 902 for receiving a second signaling indicating that a CSI report corresponding to a first CSI process of the first number of CSI processes is to be generated at least partly based on measurements of a CSI reference signal associated with a CSI process of the first number of CSI processes； step 903 for receiving the first number of CSI-RSs； step 904 for generating the CSI report for the first CSI process according to the second signaling； and step 905 for transmitting the CSI report for the first CSI process.

In one embodiment， the first signaling and the second signaling are same as that transmitted in step 501 and step 502 of the method 500， respectively， and thus descriptions for these signaling with reference to step 50 1 and step 502 also apply here， and thus will not be repeated.

In another embodiment， the second signaling received in the step 902 indicates that the CSI report corresponding to the first CSI process of the first number of CSI processes is to be generated at least partly based on precoding information derived from the CSI-RS associated with the second CSI process. As described with reference to the method 500 and Fi.g 5， the precoding information may include， but not limited to， RI and PMI， or RI and PMI1. Accordingly， in one embodiment， in step 904， the UE may generate the CSI report for the first CSI process at least partly based on precoding information derived from the CSI RS for the second CSI process. For example， in step 904， the UE can directly reuse the RI and PMI， or RI and PMI1 for the second CSI process as that for the first CSI process， thereby avoiding additional calculation for the RI and PMI， or RI and PMI1 based on the CSI-RS for the first CSI process. Regarding the CQI and/or PMI2， in step 904， the UE may compute based on the channel estimation for the first CSI process and the reused precoding information of the second CSI process. That is，the UE can compute CQI for the first CSI process based on， for example， the channel estimation H1 for the first CSI process and the RI and PMI for the second process. In a dual codebook case， the UE can also compute CQI for the first CSI process based on， for example， channel estimation H1 and short-term precoding matrix indicator PMI2 for the first CSI process， and RI and PMI1 for the second CSI process， wherein the PMI2 may also be derived based on the RI and the PMI1 for the second CSI process.

In one embodiment， the second signaling received in the step 902 may comprise a RRC configuration signaling carrying an index of the second CSI process， part of a CSI report for which is to be reused by the first CSI process. In another embodiment， the second signaling may further indicate which part of the CSI report for second CSI process is to be reused by the first CSI process. For example， it may indicate whether to reuse RI and PMI or RI and PMI1.

As described above， in one embodiment， the second signaling enables the UE to reduce measurement complexity， since it can directly reuse the RI and PMI， or RI and PMI1 for the second CSI process as that for the first CSI process， thereby avoiding additional calculation for the RI and PMI， or RI and PMI1 based on the CSI-RS for the first CSI process. In one embodiment， in step 905， the UE may still report RI and PMI， or RI and PMI1 for the first CSI process by using same value as that for the CSI process 2 without additional calculation for the first CSI process. In another embodiment， in step 905， the UE may not report the precoding information (for example RI and PMI) ， or part of the precoding information (for example RI and PMI1) for the first CSI process， and at the eNB side， the precoding information reported for the CSI process 2 from the same UE can be reused for determining the precoding parameters for the UE. In such case， in step 905， the UE may only need to report CQI， or both CQI and part of precoding information (for example PMI2) for the CSI process 1. Thereby the feedback overhead is also reduced. It can be appreciated that in step 905， the UE can also report CSI for other configured CSI processes including the second CSI process. Based on the above description， it can be observed that in step 905， the UE may transmit the CSI report without overall precoding information derived from the CSI reference signal for the first CSI process， or the UE may transmit the CSI report without long term precoding information derived from the CSI reference signal for the first CSI process， or the UE may transmit the CSI report with the precoding information derived from the second CSI reference signal as precoding information for the first CSI process.

By virtue of the

methods

500 and 900， CSI measurement complexity at the UE side can be reduced by sharing CSI between CSI processes associated with adjacent beams； further CSI feedback overhead can also be reduced. By further utilizing the method 700， CSI-RS overhead can also be further reduced without significant performance loss.

Reference is now made to Fig. 10， which illustrates a schematic block diagram of an apparatus 1000 adapted for facilitating CSI obtaining in a wireless system according to an embodiment of the present disclosure. In one embodiment， the apparatus 1000 may be implemented as a base station or a part thereof. Alternatively or additionally， the apparatus 1000 may be implemented as any other suitable network element in the wireless communication system. The apparatus 1000 is operable to carry out the example method 500 and/or 700 described with reference to FIGs. 5-8 and possibly any other processes or methods. It is also to be understood that the method 500 and/or 700 are not necessarily carried out by the apparatus 1000. At least some steps of the

method

500 or 700 can be performed by one or more other entities.

As illustrated in Fig. 10， the apparatus 1000 comprises a first transmitting module 1001， configured to transmit to a first device， a first signaling for configuring a first number of CSI processes for the first device， each of the first number of CSI processes being associated with one of the first number of CSI reference signals (CSI-RS) beamformed in a vertical domain towards a different elevation direction respectively； asecond transmitting module 1002， configured to transmit， to the first device， a second signaling to indicate that a CSI measurement and report for a first CSI process of the first number of CSI processes is to be generated at least partly based on measurement of a CSI-RS associated with a second CSI process of the first number of CSI processes； a third transmitting module 1003， configured to transmit the first number of CSI-RSs to the first device； and a receiving module 1004， configured to receive the CSI report for the first CSI process from the first device.

In one embodiment， the first transmitting module 1001， the second transmitting module 1002， the third transmitting module 1003， and the receiving module 1004 may be configured to perform the steps 501 to 504 of the method 500， respectively， and thus， the operations described with reference to these steps and the features related to the first signaling and the second signaling also apply here and will not be repeated. For example， the second signaling transmitted by the second transmitting module 1002 may indicate that the CSI measurement and report for the first CSI process from the first UE is to be generated at least partly based on precoding information derived from the CSI-RS associated with a second CSI process. In one embodiment of the disclosure， the precoding information derived from the CSI-RS associated with a second CSI process may comprise a rank indicator and a precoding matrix indicator， and wherein the precoding matrix indicator can be one of an overall precoding matrix indicator and a long-term precoding matrix indicator of a dual-codebook scheme. In another embodiment， the second signaling may comprise a radio resource control (RRC) configuration sigualing carrying an index of the second CSI process， part of CSI for which is to be reused by the first CSI process. In still another embodiment， the RRC configuration sigualing can further indicate which part of the CSI for the second CSI process is to be reused by the first CSI process.

In another embodiment， the receiving module 1004 can be configured to receive at least one of the following for the first CSI process： a channel quality indicator (CQI) ， ashort term horizontal domain precoding matrix indicator； a long term precoding matrix indicator； a rank indicator； and an overall horizontal domain precoding indicator. In one embodiment， these CSI report received for the first CSI process can be generated by the first device at least partly based on CSI derived for the second CSI process according to the second signaling transmitted by the second transmitting module.

In another embodiment， the apparatus 1000 may further comprise a beam management module 1005， configured to maintain two sets of vertical beams， wherein adjacent beams in the second set of vertical beams are more spatially separated compared with that of the first set of vertical beams； and a configuration module 1006， adapted to configure one-antenna port CSI-RS for each beam in the first set of beams， and multiple-antenna ports CSI-RS for each beam in the second set of beams； and wherein each of the first number of CSI-RS is associated with a beam included the second set of vertical beams.

In still another embodiment， the apparatus 1000 may further comprise a beam selection module 1007， configured to select the second set of vertical beams from the first set of vertical beams by： configuring， for each of a plurality of devices， a second number of one-antenna port CSI-RSs for RSRP measurements， each of the second number one-antenna port CSI-RSs being beamformed to form a beam included in the first set of the vertical beams； wherein the second number being no smaller than the first number； transmitting the second number one-antenna port CSI-RSs to the plurality devices； receiving from each of the plurality of devices a RSRP report for each of the configured second number one-antenna port CSI-RSs； and selecting a third number of beams from the beams corresponding to the second number of one-antenna port CSI-RS based on the received RSRP reports， to form the second set of the vertical beams， wherein the second number being no smaller than the third number.

In one embodiment， the beam management module 1006， the configuration module 1006 and the beam selection module 1007 may be adapted to perform the steps 710-730 of the method 700， and thus operations described with reference to the method 700 also apply here， and will not be repeated.

In one embodiment of the present disclosure， the apparatus may further comprise a precoding determination module 1008， configured to determining 3-dimensional (3D) precoding parameters for data transmission to the first device based on only the CSI report for the first CSI process， or， based on both the CSI report for the first CSI process and a CSI report for the second CSI process from the first device. The precoding module can be adapted to perform the operations described with reference to the step 505 of method 500.

As described with reference to the

method

500 and 700， the beam management module 1005， the configuration module 1006 and the beam selection module 1007 are not necessarily to operation in conjunction with the others modules 100 1 to 1004. In one embodiment， the beam management module 1005， the configuration module 1006 and the beam selection module 1007 may be implemented as another apparatus for reducing CSI-RS overhead， while the apparatus 1000 with the module 1001 to 1004 can be implemented for reducing CSI measurement complexity and CSI feedback overhead. In another embodiment， all the modules can be implemented in a single apparatus to achieve multiple advantages.

Reference is now made to Fig. 11， which illustrate a schematic block diagram of an apparatus 1100 adapted for facilitating CSI obtaining in a wireless system according to an embodiment of the present disclosure. In one embodiment， the apparatus 1100 may be implemented as user terminal or a part thereof. Alternatively or additionally， the apparatus 1000 may be implemented as any other suitable devices in the wireless communication system. The apparatus 1100 is operable to carry out the example method 900 described with reference to FIG. 9 and possibly any other processes or methods. It is also to be understood that the method 900 is not necessarily carried out by the apparatus 1100. At least some steps of the method 900 can be performed by one or more entities.

As shown in Fig. 11， the apparatus 1100 comprises a first receiving module 1101， configured to receive a first signaling for configuring a first number of CSI processes for the device， each of the plurality of CSI processes being associated with one of the first number of CSI reference signals (CSI-RS) beamformed in a vertical domain towards a different elevation direction respectively； a second receiving module 1102， configured to receive a second signaling indicating that a CSI report for a first CSI process of the first number of CSI processes is to be generated at least partly based on measurements of a CSI reference sigual associated with a second CSI process of the first number of CSI processes； a third receiving module 1103， configured to receive the first number of CSI-RSs； a CSI report generation module 1104， configured to generate the CSI report for the first CSI process according to the second signaling； and a transmitting module 1105， configured to transmit the CSI report for the first CSI process.

Since in some embodiments of the disclosure， the modules 1101 to 1105 can be adapted to perform the steps of 901 to 905 of the method 900， and thus operations described with reference to these steps of the method 900 also apply here and thus will not be detailed here.

In one embodiment， the CSI report generation module 904 is configured to generate the CSI report at least partly based on precoding information derived from the CSI reference signal associated with the second CSI process. In an embodiment， the precoding information derived from the CSI reference signal associated with the second CSI process comprises a rank indicator and a precoding matrix indicator and wherein the precoding matrix indicator is one of an overall precoding matrix indicator and a long-term precoding matrix indicator of a dual-codebook scheme.

As described above with reference to

method

500， and 900， in one embodiment， the second signaling comprises a radio resource control (RRC) configuration signaling carrying an index of the second CSI process， part of a CSI report for which is to be reused by the first CSI process. In another embodiment， the RRC configuration sigualing further indicates which part of the CSI report for second CSI process is to be reused by the first CSI process.

In an embodiment， the transmitting module 1105 can be configured to transmit the CSI report without an overall precoding information derived from the CSI-RS associated with the first CSI process， transmit the CSI report without a long term precoding information derived from the CSI-RS associated with the first CSI process， or transmit the CSI report with the precoding information derived from the CSI reference signal associated with the second CSI process as precoding information for the first CSI process. In thefirst two cases， feedback overhead can be reduced， while for the third case， the feedback signaling may be kept unchanged， but the measurement complexity is reduced.

Fig. 12 illustrates a simplified block diagram of an apparatus 1210， and an apparatus 1220 that are suitable for use in practicing the embodiments of the present disclosure. The apparatus 1210 may be implemented in a base station； the apparatus 1220 may be implemented in UE.

The apparatus 1210 comprises at least one processor 1211， such as a data processor (DP) 1211 and at least one memory (MEM) 1212 coupled to the processor 1211. The apparatus may further comprise a suitable RF transmitter TX and receiver RX 1213 (which may be implemented in a single component or separate components) coupled to the processor 1211. The MEM 1212 stores a program (PROG) 1214. The PROG 1214 may include instructions that， when executed on the associated processor 1211， enable the apparatus 1210 to operate in accordance with the embodiments of the present disclosure， for example to perform the method 500 and/or 700. The TX/RX 1213 may be used for bidirectional radio communication with other apparatuses or devices in the network， e.g. the apparatus 1220. Note that the TX/RX 1213 has at least one antenna to facilitate the communication. A combination of the at least one processor 1211 and the at least one MEM 1212 may form processing means 1215 adapted to implement various embodiments of the present disclosure.

The apparatus 1220 comprises at least one processor 1221， such as a DP， at least one MEM 1222 coupled to the processor 1221. The apparatus 1220 may further comprise a suitable RF TX/RX 1223 (which may be implemented in a single component or separate components) coupled to the processor 1 221. The MEM 1322 stores a PROG 1224. The PROG 1224 may include instructions that， when executed on the associated processor 1221， enable the apparatus 1220 to operate in accordance with the embodiments of the present disclosure， for example to perform the method 900. The TX/RX 1223 is for bidirectional radio communications with other apparatuses or devices in the network， e.g. the apparatus 1210 or the terminal device 1230. Note that the TX/RX 1223 has at least one antenna to facilitate the communication. A combination of the at least one processor 1221 and the at least one MEM 1222 may form processing means 1225 adapted to implement various embodiments of the present disclosure.

Various embodiments of the present disclosure may be implemented by computer program executable by one or more of the

processor

1211， 1221 in software， firmware， hardware or in a combination thereof.

The

MEMs

1212， 1222 may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology， such as semiconductor based memory devices， magnetic memory devices and systems， optical memory devices and systems， fixed memory and removable memory， as non-limiting examples. While only one MEM is shown in the

apparatuses

1210， 1220， there may be several physically distinct memory units in them.

The

processors

1211， 1221 may be of any type suitable to the local technical environment， and may include one or more of general purpose computers， special purpose computers， microprocessors， digital signal processors (DSPs) and processors based on multicore processor architecture， as non-limiting examples. Each of the

apparatuses

1210， 1220 may have multiple processors， such as an application specific integrated circuit (ASIC) chip that is slaved in time to a clock which synchronizes the main processor.

Although the above description is made in the context of LTE 3D-MIMO， it should not be construed as limiting the spirit and scope of the present disclosure. The idea and concept of the present disclosure can be generalized to also cover other wireless networks with the feature of 3D-MIMO including non-cellular network， e.g.， ad-hoc network.

In addition， the present disclosure proyides a carrier containing the computer program as mentioned above， wherein the carrier is one of an electronic signal， optical signal， radio signal， or computer readable storage medium. The computer readable storage medium can be， for example， an optical compact disk or an electronic memory device like a RAM (random access memory) ， a ROM (read only memory) ， Flash memory， magnetic tape， CD-ROM， DVD， Blue-ray disc and the like.

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

Exemplary embodiments herein have been described above with reference to block diagrams and flowchart illustrations of methods， apparatuses， i.e. systems. It will be understood that each block of the block diagrams and flowchart illustrations， and combinations of blocks in the block diagrams and flowchart illustrations， respectively， can be implemented by various means including computer program instructious. These computer program instructions may be loaded onto a general purpose computer， special purpose computer， or other programmable data processing apparatus to produce a machine， such that the instructions which execute on the computer or other programmable data processing apparatus create means for implementing the functious specified in the flowchart block or blocks.

While this specification contains many specific implementation details， these should not be construed as limitations on the scope of any implementation or of what may be claimed， but rather as descriptions of features that may be specific to particular embodiments of particular implementations. 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 sub-combination. Moreover， although features may be described above as acting in certain combinations and even initially claimed as such， one or more features from a claimed combination can in some cases be excised from the combination， and the claimed combination may be directed to a sub-combination or variation of a sub-combination.

It should also be noted that the above described embodiments are given for describing rather than limiting the disclosure， and it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the disclosure as those skilled in the art readily understand. Such modifications and variations are considered to be associated with the scope of the disclosure and the appended claims. The protection scope of the disclosure is defined by the accompanying claims.

Claims

A method for facilitating channel status information (CSI) obtaining in a wireless system， comprising：

transmitting， to a first device， a first signaling for configuring a first number of CSI processes for the first device， each of the first number of CSI processes being associated with one of the first number of CSI reference signals (CSI-RS) beamformed in a vertical domain towards a different elevation direction respectively；

transmitting， to the first device， a second signaling to indicate that a CSI measurement and report for a first CSI process of the first number of CSI processes is to be generated at least partly based on measurement of a CSI-RS associated with a second CSI process of the first number of CSI processes；

transmitting the first number of CSI-RSs to the first device； and

receiving the CSI report for the first CSI process from the first device.
The method of Claim 1， wherein a CSI measurement and report for a first CSI process of the first number of CSI processes is to be generated at least partly based on measurement of a CSI-RS associated with a second CSI process of the first number of CSI processes comprises：

the CSI measurement and report for the first CSI process is to be generated at least partly based on precoding information derived from the CSI-RS associated with a second CSI process.
The method of Claim 2， wherein the precoding information derived from the CSI-RS associated with a second CSI process comprises a rank indicator and a precoding matrix indicator， and

wherein the precoding matrix indicator is one of an overall precoding matrix indicator and a long-term precoding matrix indicator of a dual-codebook scheme.
The method of Claim 1， wherein the second signaling comprises a radio resource control (RRC) configuration signaling carrying an index of the second CSI process， part of CSI for which is to be reused by the first CSI process.
The method of Claim 4， wherein the RRC configuration signaling further indicates which part of the CSI for the second CSI process is to be reused by the first CSI process.
The method of Claim 1， wherein receiving the CSI report for the first CSI process from the first device comprises receiving at least one of the following for the first CSI process：

a channel quality indicator (CQI) ，

a short term horizontal domain precoding matrix indicator；

a long term precoding matrix indicator；

a rank indicator； and

an overall horizontal domain precoding indicator.
The method of Claim 1， further comprises：

maintaining two sets of vertical beams， wherein adjacent beams in the second set of vertical beams are more spatially separated compared with that of the first set of vertical beams；

configuring one-antenna port CSI-RS for each beam in the first set of vertical beams， and configuring multiple-antenna ports CSI-RS for each beam in the second set of vertical beams； and

wherein each of the first number of CSI-RS is associated with a beam included the second set of vertical beams.
The method of Claim 7， further comprises selecting the second set of vertical beams from the first set of vertical beams by：

configuring， for each of a plurality of devices， a second number of one-antenna port CSI-RSs for RSRP measurements， each of the second number one-antenna port CSI-RSs being beamformed to form a beam included in the first set of the vertical beams； wherein the second number being no smaller than or being larger than the first number；

transmitting the second number one-antenna port CSI-RSs to the plurality devices；

receiving from each of the plurality of devices a RSRP report for each of the configured second number one-antenna port CSI-RSs； and

selecting a third number of beams from the beams corresponding to the second number of one-antenna port CSI-RS based on the received RSRP reports， to form the second set of the vertical beams， wherein the second number being no smaller than or being larger than the third number and the third number being no smaller than or being larger than the first number.
The method of any of Claims 1 to 8， further comprises：

determining 3-dimensional (3D) precoding parameters for data transmission to the first device based on only the CSI report for the first CSI process， or， based on both the CSI report for the first CSI process and a CSI report for the second CSI process from the first device.
A method implemented in a device for facilitating channel status information (CSI) obtaining in a wireless system， comprising：

receiving a first signaling for configuring a first number of CSI processes for the device， each of the plurality of CSI processes being associated with one of the first number of CSI reference signals (CSI-RS) beamformed in a vertical domain towards a different elevation direction respectively；

receiving a second signaling indicating that a CSI measurement and report for a first CSI process of the first number of CSI processes is to be generated at least partly based on measurements of a CSI reference signal associated with a second CSI process of the first number of CSI processes；

receiving the first number of CSI-RSs；

generating the CSI measurement and report for the first CSI process according to the second signaling； and

transmitting the CSI report for the first CSI process.
The method of Claim 10， wherein generating the CSI measurement and report for the first CSI process according to the second signaling comprise：

generating the CSI measurement and report at least partly based on precoding information derived from the CSI reference signal associated with the second CSI process.
The method of Claim 11， wherein the precoding information derived from the CSI reference signal associated with the second CSI process comprises a rank indicator and a precoding matrix indicator and

wherein the precoding matrix indicator is one of an overall precoding matrix indicator and a long-term precoding matrix indicator of a dual-codebook scheme.
The method of Claim 10， wherein the second signaling comprises a radio resource control (RRC) configuration signaling carrying an index of the second CSI process， part of CSI for which is to be reused by the first CSI process.
The method of Claim 13， wherein the RRC configuration signaling further indicates which part of the CSI for the second CSI process is to be reused by the first CSI process.
The method of any of Claims 10 to 14， wherein the transmitting the CSI report for the first CSI process comprises one of：

transmitting the CSI report without an overall precoding information derived from the CSI-RS associated with the first CSI process，

transmitting the CSI report without a long term precoding information derived from the CSI-RS associated with the first CSI process， or

transmitting the CSI report with the precoding information derived from the CSI reference signal associated with the second CSI process as precoding information for the first CSI process.
An apparatus adapted for facilitating channel status information (CSI) obtaining in a wireless system， comprising：

a first transmitting module， configured to transmit to a first device， a first signaling for configuring a first number of CSI processes for the first device， each of the first number of CSI processes being associated with one of the first number of CSI reference signals (CSI-RS) beamformed in a vertical domain towards a different elevation direction respectively；

a second transmitting module， configured to transmit， to the first device， a second signaling to indicate that a CSI measurement and report for a first CSI process of the first number of CSI processes is to be generated at least partly based on measurement of a CSI-RS associated with a second CSI process of the first number of CSI processes；

a third transmitting module， configured to transmit the first number of CSI-RSs to the first device； and

a first receiving module， configured to receive the CSI report for the first CSI process from the first device.
The apparatus of Claim 16， wherein a CSI measurement and report for a first CSI process of the first number of CSI processes is to be generated at least partly based on measurement of a CSI-RS associated with a second CSI process of the first number of CSI processes comprises：

the CSI measurement and report for the first CSI process is to be generated at least partly based on precoding information derived from the CSI-RS associated with a second CSI process.
The apparatus of Claim 17， wherein the precoding information derived from the CSI-RS associated with a second CSI process comprises a rank indicator and a precoding matrix indicator， and

wherein the precoding matrix indicator is one of an overall precoding matrix indicator and a long-term precoding matrix indicator of a dual-codebook scheme.
The apparatus of Claim 16， wherein the second signaling comprises a radio resource control (RRC) configuration signaling carrying an index of the second CSI process， part of CSI for which is to be reused by the first CSI process.
The apparatus of Claim 19， wherein the RRC configuration signaling further indicates which part of the CSI for the second CSI process is to be reused by the first CSI process.
The apparatus of Claim 16， wherein the first receiving module is configured to receive at least one of the following for the first CSI process：

a channel quality indicator (CQI) ，

a short term horizontal domain precoding matrix indicator；

a long term precoding matrix indicator；

a rank indicator； and

an overall horizontal domain precoding indicator.
The apparatus of Claim 16， further comprising：

a beam management module， configured to maintain two sets of vertical beams， wherein adjacent beams in the second set of vertical beams are more spatially separated compared with that of the first set of vertical beams；

a configuration module， adapted to configure one-antenna port CSI-RS for each beam in the first set of vertical beams， and multiple-antenna ports CSI-RS for each beam in the second set of vertical beams； and

wherein each of the first number of CSI-RS is associated with a beam included the second set of vertical beams.
The apparatus of Claim 22， further comprising：

a beam selection module， configured to select the second set of vertical beams from the first set of vertical beams by：

configuring， for each of a plurality of devices， a second number of one-antenna port CSI-RSs for RSRP measurements， each of the second number one-antenna port CSI-RSs being beamformed to form a beam included in the first set of the vertical beams； wherein the second number being no smaller than or being larger than the first number；

transmitting the second number one-anterma port CSI-RSs to the plurality devices；

receiving from each of the plurality of devices a RSRP report for each of the configured second number one-antenna port CSI-RSs； and

selecting a third number of beams from the beams corresponding to the second number of one-antenna port CSI-RS based on the received RSRP reports， to form the second set of the vertical beams， wherein the second number being no smaller than or being larger than the third number and the third number being no smaller than or being larger than the first number.
The apparatus of any of Claims 16 to 23， further comprises：

a precoding determination module configured to determining 3-dimensional (3D) precoding parameters for data transmission to the first device based on only the CSI report for the first CSI process， or， based on both the CSI report for the first CSI process and a CSI report for the second CSI process from the first device.
An apparatus implemented in a device for facilitating channel status information (CSI) obtaining in a wireless system， comprising：

a first receiving module， configured to receive a first signaling for configuring a first number of CSI processes for the device， each of the plurality of CSI processes being associated with one of the first number of CSI reference signals (CSI-RS) beamformed in a vertical domain towards a different elevation direction respectively；

a second receiving module， configured to receive a second signaling indicating that a CSI measurement and report for a first CSI process of the first number of CSI processes is to be generated at least partly based on measurements of a CSI reference signal associated with a second CS I process of the first number of C SI processes；

a third receiving module， configured to receive the first number of CSI-RSs；

a CSI report generation module， configured to generate the CSI measurement and report for the first CSI process according to the second signaling； and

a transmitting module， configured to transmit the CSI report for the first CSI process.
The apparatus of Claim 25， wherein the CSI report generation module is configured to generate the CSI measurement and report at least partly based on precoding information derived from the CSI reference signal associated with the second CSI process.
The apparatus of Claim 26， wherein the precoding information derived from the CSI reference signal associated with the second CSI process comprises a rank indicator and a precoding matrix indicator and

wherein the precoding matrix indicator is one of an overall precoding matrix indicator and a long-term precoding matrix indicator of a dual-codebook scheme.
The apparatus of Claim 25， wherein the second signaling comprises a radio resource control (RRC) configuration signaling carrying an index of the second CSI process， part of CSI for which is to be reused by the first CSI process.
The apparatus of Claim 28， wherein the RRC configuration signaling further indicates which part of the CSI for the second CSI process is to be reused by the first CSI process.
The apparatus of any of Claims 25 to 29， wherein the transmitting module is configured to

transmit the CSI report without an overall precoding information derived from the CSI-RS associated with the first CSI process，

transmit the CSI report without a long term precoding information derived from the CSI-RS associated with the first CSI process， or

transmit the CSI report with the precoding information derived from the CSI reference signal associated with the second CSI process as precoding information for the first CSI process.
An apparatus adapted for facilitating channel status information (CSI) obtaining in a wireless system， comprising a processor and a memory， said memory containing instructions executable by said processor whereby said apparatus is operative to perform the method of any of Claims 1-9.
An apparatus adapted for facilitating channel status information (CSI) obtaining in a wireless system， comprising a processor and a memory， said memory containing instructions executable by said processor whereby said apparatus is operative to perform the method of any of Claims 10-15.
An apparatus adapted for facilitating channel status information (CSI) obtaining in a wireless system， comprising process means adapted to perform the method of any of Claims 1-9.
An apparatus adapted for facilitating channel status information (CSI) obtaining in a wireless system， comprising process means adapted to perform the method of any of Claims 10-15.
A computer program， comprising instructions which， when executed on at least one processor， cause the at least one processor to carry out the method according to any one of claims 1 to 9.
A computer program， comprising instructions which， when executed on at least one processor， cause the at least one processor to carry out the method according to any one of claims 10 to 15.