WO2013038609A1

WO2013038609A1 - Channel state information feedback method and user equipment

Info

Publication number: WO2013038609A1
Application number: PCT/JP2012/005506
Authority: WO
Inventors: Zeng YANG; Ming Ding; Lei Huang
Original assignee: Sharp Kabushiki Kaisha
Priority date: 2011-09-13
Filing date: 2012-08-30
Publication date: 2013-03-21
Also published as: CN103001743A

Abstract

A Channel State Information (CSI) feedback method is provided, which includes steps of: determining a transmission mode set including transmission mode hypotheses between a Base Station (BS) and a User Equipment (UE); calculating CSI corresponding to each transmission mode hypothesis in the transmission mode set; and feeding back the calculated CSI to the BS and notifying the BS of the transmission mode hypothesis corresponding to the calculated CSI. A corresponding UE is also provided.

Description

CHANNEL STATE INFORMATION FEEDBACK METHOD AND USER EQUIPMENT

The present invention relates to the field of communication technology, and more particularly, to a Channel State Information (CSI) feedback method and a User Equipment (UE).

The 3^rd Generation Partnership Project (3GPP) organization is an international organization in mobile communication field and plays an important role in standardization of 3G cellular communication technologies. Since the second half of the year 2004, the 3GPP organization has initiated a so-called Long Term Evolution (LTE, also referred to as LTE Rel-8) project for designing Evolved Universal Terrestrial Radio Access (EUTRA) and Evolved Universal Terrestrial Radio Access Network (EUTRAN). The standardization of LTE Rel-10 RAN 1 has been accomplished in March 2011. In the 3GPP RAN meeting #50, a research program related to Coordinated Multi-Point (CoMP) transmission in LTE Rel-11 RAN 1 is proposed. In the RAN 1 meeting #63bis, four application scenarios of CoMP are initially determined, which include: a intra-station CoMP scenario in homogeneous network, a high-power Remote Radio Head (RRH) scenario in homogeneous network, a low-power RRH scenario in macro cell coverage in heterogeneous network in which the cell ID of the RRH is the same as the cell ID of the macro cell and a low-power RRH scenario in macro cell coverage in heterogeneous network in which the cell ID of the RRH is different from the cell ID of the macro cell. In the 3GPP RAN meeting #51, another research program related to downlink Multiple Input Multiple Output (MIMO) enhancement is proposed, which involves a system scenario with geographically separated antennas (i.e., in this scenario, the antenna system of the BS is composed of a number of geographically separated Transmission Points (TPs) each having one or more antennas). It can be seen that this system scenario with geographically separated antennas is very similar to the above low-power RRH scenario in macro cell coverage in heterogeneous network in which the cell ID of the RRH is the same as the cell ID of the macro cell in that each RRH in the latter scenario can be considered as a TP in the former scenario. According to document R1-110649 (Aspects on Distributed RRUs with Shared Cell-ID for Heterogeneous Deployments, Ericsson, ST-Ericsson), which provides a method for allocating separate Channel State Information - Reference Signal (CSI-RS) resources for each TP, these two scenarios can be handled in a unified manner. As an example, the CSI feedback for these two scenarios can be achieved in a unified manner. That is, the UE measures the CSI-RS and performs CSI feedback for each TP separately according to the LTE Rel-10 scheme, in order to support some basic transmission modes such as Dynamic Point Selection (DPS) or Coordinated Scheduling/Coordinated Beamforming (CS/CB). Then, the UE can feed back Inter-TP (ITP) CSI to support some advanced transmission modes such as Joint Transmission (JT) and network MIMO transmission (in which the antennas of more than one TP constitute a larger transmission antenna array).

Most of the currently existing schemes, such as R1-112156 (On standardization impact of DL CoMP, Texas Instruments), considers that the CSI feedback content per TP, such as Rank Indicator (RI), Precoder Matrix Indicator (PMI) and Channel Quality Indicator (CQI), can be directly combined with the ITP feedback CSI to obtain the CSI required for JT. However, this is not true as can be seen from the following counterexamples:

For single point transmission and joint transmission, the UE receives different transmission energy from the BS. Thus, the RI corresponding to a single point transmission channel may be different from the RI corresponding to a joint transmission channel.

The rank of a single point MIMO transmission channel is significantly different from the rank of a network MIMO transmission channel.

The single point PMI and the joint transmission PMI are different from each other with respect to some PMI generation algorithms for JT.

The CQI is necessarily different from one transmission mode hypothesis to another.

It is therefore a need for a technique for the UE to notify, when feeding back CSI to the BS, a transmission mode hypothesis corresponding to the fed back CSI to the BS. This problem constitutes the major content of the present invention.

It is an object of the present invention to solve the problem of how to feed back the CSI from the UE to the BS along with the corresponding transmission mode hypothesis by providing a novel method for CSI feedback and a UE, which supplements the current standard.

According to an aspect of the present invention, a Channel State Information (CSI) feedback method is provided, which includes steps of: determining a transmission mode set including transmission mode hypotheses between a Base Station (BS) and a User Equipment (UE); calculating CSI corresponding to each transmission mode hypothesis in the transmission mode set; and feeding back the calculated CSI to the BS and notifying the BS of the transmission mode hypothesis corresponding to the calculated CSI.

Preferably, the method further includes: receiving from the BS an indication of the transmission mode set. The transmission mode set is determined in response to the received indication.

Preferably, the transmission mode hypotheses included in the transmission mode set are determined based on communication scenarios.

Preferably, an indicator is transmitted to indicate the transmission mode hypothesis corresponding to the calculated CSI.

Preferably, the CSI corresponding to each of the transmission mode hypotheses in the transmission mode set is fed back to the BS in a predetermined order, such that the feedback order of the CSI indicates the corresponding transmission mode hypothesis.

Preferably, the transmission mode hypotheses comprise at least one of Dynamic Point Selection (DPS), Coordinated Scheduling/Coordinated Beamforming (CS/CB), Joint Transmission (JT) and network MIMO transmission.

Preferably, the CSI comprises at least one of Rank Indicator (RI), Precoder Matrix Indicator (PMI) and Channel Quality Indicator (CQI).

According to another aspect of the present invention, a User Equipment (UE) is provided, which includes: a determination unit configured to determine a transmission mode set including transmission mode hypotheses between a Base Station (BS) and the UE; a calculation unit configured to calculate CSI corresponding to each transmission mode hypothesis in the transmission mode set; and a feedback unit configured to feed back the calculated CSI to the BS and notify the BS of the transmission mode hypothesis corresponding to the calculated CSI.

The above and other objects, features and advantages of the present invention will be more apparent from the following preferred embodiments illustrated with reference to the figures, in which:
Fig. 1 shows a block diagram of the UE according to the present invention; Fig. 2 shows a sequence diagram of the CSI feedback according to the present invention; Fig. 3 shows a CoMP scenario in which TPs 1-3 constitute the CSI-RS measurement set of UE 1; Fig. 4 shows a MIMO scenario in which TPs 1-3 constitute the CSI-RS measurement set of UE 1; and Fig. 5 shows a flowchart illustrating the CSI feedback method according to the present invention.

Preferred embodiments of the present invention will be detailed with reference to the drawings. In the following description, details and functions unnecessary to the present invention are omitted so as not to obscure the concept of the invention.

For clear and detailed explanation of the implementation steps of the present invention, some specific examples applicable to the LTE-A (Rel-10, Rel-11 and subsequent releases) cellular communication system are given below. Herein, it is to be noted that the present invention is not limited to the application exemplified in the embodiments. Rather, it is applicable to other communication systems, such as the future 5G system.

In the case where the present invention is applied to the above CoMP scenario or downlink MIMO scenario, before a UE feeds back CSI, a BS can configure a CSI-RS measurement set and a zero-power CSI-RS set for the UE. The CSI-RS measurement set includes a set of CSI-RS resources used by the UE for CSI measurement. Configuration parameters of the CSI-RS measurement set include CSI-RS sequence, number of CSI-RS antenna ports, CSI-RS format, period, subframe offset and Energy Per Resource Element (EPRE) between data and CSI-RS, etc. The zero-power CSI-RS set includes a set of CSI-RS on which the BS's transmission power is zero and is mainly used for improving the accuracy of neighbor cell channel information or interference channel information measured by the UE. Configuration parameters for the zero-power CSI-RS set include zero-power CSI-RS format, period and subframe offset, etc.

The prior art document R1-110649 provides a technique in which each TP is assigned with separate CSI-RS resource and the UE can discriminate among different TPs based on the CSI-RS resources. However, in fact the TP information can be transparent to the UE, i.e., the BS only needs to know the CSI-RS resources for the UE while the mapping between the CSI-RS resources and the TP antennas can be transparent to the UE. Thus, according to an embodiment of the present invention, the CSI feedback for each TP and the ITP CSI feedback can be CSI feedback for each CSI-RS resource and inter-CSI-RS-resource CSI feedback, respectively. For example, in the network MIMO transmission mode, the antennas of a number of TPs together constitute a logic MIMO antenna system having its number of antennas being the total numbers of antennas of the respective TPs. In the case where the network MIMO transmission mode is the transmission mode hypothesis, the TP corresponding to the CSI-RS resource is a virtual logic TP composed of a number of TPs constituting the logic MIMO antenna system.

For example, in the case where the present invention is applied to the above CoMP scenario or downlink MIMO scenario, the BS can transmit downlink data to the UE using various transmission modes, such as the above DPS, CS/CB, JT and network MIMO. In conventional LTE systems, the BS configures a single transmission mode for the UE via semi-static Radio Resource Control (RRC) signaling and the UE uses this transmission mode as the transmission mode hypothesis, calculates CSI and feeds it back to the BS. Whereas, in the present invention, the UE calculates and feeds back CSI based on one or more transmission modes as transmission mode hypothesis (hypotheses) and notifies the BS of the transmission mode hypotheses corresponding to the fed back CSI.

Fig. 1 shows a block diagram of the UE 100 according to the present invention. The UE 100 includes: a determination unit 110, a calculation unit 120 and a feedback unit 130. It can be appreciated by those skilled in the art that the UE 100 further includes other functional units necessary for its operation, such as a transceiver, a processor and a memory.

The functions and operations of the UE 100 shown in Fig. 1 will be described in the following.

The determination unit 110 is configured to determine a transmission mode set including transmission mode hypotheses between the BS and the UE.

In an embodiment of the present invention, the UE 100 further includes a receiving unit (not shown) configured to receive from the BS an indication of the transmission mode set. In this case, the determination unit 110 is configured to determine the transmission mode set in response to the received indication.

In an embodiment of the present invention, the BS selects, as a transmission mode set, a set of transmission mode hypotheses from a number of possible transmission modes and notifies it to the UE 100 via semi-static RRC signaling. For example, the BS can select, from the above possible transmission modes, a transmission mode set including CS/CB and JT or another transmission mode set including DPS and network MIMO. The BS notifies the UE 100 of the transmission mode set via semi-static RRC signaling. The UE 100 receives from the BS an indication of transmission mode set and determines the transmission mode set in response to the received indication. By configuring the transmission mode set for the UE, the BS can dynamically switch between various transmission mode hypotheses, thereby flexibly selecting suitable transmission mode hypotheses for the UE.

Alternatively, the determination unit 110 can be configured to determine the transmission mode hypotheses included in the transmission mode set based on communication scenarios.

For example, if the transmission mode hypotheses are predetermined for a particular communication scenario (e.g., a transmission mode set including DPS and JT is predetermined for the CoMP scenario and a transmission mode set including DPS and network MIMO is predetermined for MIMO scenario), it is unnecessary to select the transmission mode hypotheses from the full set, which eliminates the need for the RRC signaling procedure used by the BS to notify the UE 100 of the transmission mode set. At this time, it is possible that one or more transmission mode hypotheses are set and stored in the UE 100 in advance and the determination unit 110 can select from the stored transmission mode hypotheses the transmission mode hypotheses to be included in the transmission mode set.

The calculation unit 120 is configured to calculate CSI corresponding to each transmission mode hypothesis in the transmission mode set.

In particular, the calculation unit 120 calculates the CSI corresponding to each transmission mode hypothesis included in the transmission mode set determined by the determination unit 110 (in response to the notification from the BS or based on communication scenarios). The details for measuring or calculating CSI based on CSI-RS are well known in the art and will not be described here.

The feedback unit 130 is configured to feed back the calculated CSI to the BS and notify the BS of the transmission mode hypothesis corresponding to the calculated CSI.

In particular, the feedback unit 130 feeds back the CSI calculated to the calculation unit 120 to the BS and notifies the BS of the transmission mode (transmission mode hypothesis) corresponding to the calculated CSI.

In an embodiment, the feedback unit 130 can be configured to transmit an indicator to indicate the transmission mode hypothesis corresponding to the calculated CSI. In other words, it is possible to notify the transmission mode hypothesis by explicitly adding an indicator, or several bits, in the CSI feedback. For example, if the BS configures for the UE 100 a transmission mode set including n transmission mode hypotheses, the UE 100 can add an indicator consisting of

bits (where

is the ceiling function) in the CSI feedback to indicate the transmission mode hypothesis corresponding to the currently fed back CSI.

In another embodiment, the feedback unit 130 can be configured to feed back the CSI corresponding to each of the transmission mode hypotheses in the transmission mode set to the BS in a predetermined order, such that the feedback order of the CSI indicates the corresponding transmission mode hypothesis. In other words, the transmission mode hypothesis can be implicitly indicated using the order of the corresponding CSI in the CSI feedback. For example, the CSI feedback can be carried out in a period of several reports and each report in each period corresponds to a transmission mode hypothesis.

In the above explicit notification approach, the UE can select a transmission mode hypothesis which is most suitable currently (e.g., the optimal transmission mode hypothesis in the sense of throughput maximization) based on the channel state obtained by measuring CSI-RS, calculate the corresponding CSI and feed back the calculated CSI along with the selected transmission mode hypothesis to the BS. The explicit approach is more flexible and more efficient in feedback resource utilization than the explicit approach.

Fig. 2 shows a sequence diagram of the CSI feedback according to the present invention. In Fig. 2, the UE receives from the BS an indication of the transmission mode set (including transmission mode hypotheses 1-n). As explained above, this step is optional. Alternatively, the UE can determine the transmission mode hypotheses included in the transmission mode set based on communication scenarios. Then, the UE feeds back the CSI to the BS and notify the BS of the corresponding transmission mode hypotheses 1-n. While the explicit notification is assumed in Fig. 2, the transmission mode hypotheses can also be notified in the implicit manner, as described above.

In the following, some examples in the LTE system will be described for better understanding of the above contents. However, it is to be noted that the present invention is not limited to the following examples. The following examples should not be considered as essential to the present invention.

Example 1
As shown in Fig. 3, the CSI-RS measurement set of UE 1 is composed of TPs 1-3. Assuming that the transmission mode set includes DPS and JT, according to the above explicit notification approach, a 1-bit Transmission Mode Indicator (TMI) can be added in the CSI feedback to discriminate between these two transmission mode hypotheses.

Here, a new feedback mode can be defined for which a feedback period includes the following three reports:
Report 1 for transmission of RI and TMI:
When TMI=0, the RI is based on the DPS transmission mode hypothesis and calculated from a channel of a selected TP.

When TMI=1, the RI is based on the JT transmission mode hypothesis and calculated from a joint transmission channel of the three TPs.

Report 2:
When TMI=0 in Report 1, a broadband CQI, a broadband PMI of the channel corresponding to the selected TP in the DPS transmission mode hypothesis as calculated based on the DPS transmission mode hypothesis as well as a Transmission Point Index (TPI) of the TP are transmitted. In this example, the TPIs of the TPs 1-3 can be represented in 2 bits as e.g., 00, 01 and 10, respectively.

When TMI=1 in Report 1, a broadband PMI corresponding to TP 1 as calculated based on the JT transmission mode hypothesis, a broadband PMI and a broadband ITP (i.e., information on the channel between TP 1 and TP 2, e.g., phase/amplitude offset) corresponding to TP 2, a broadband PMI and a broadband ITP corresponding to TP 3 as well as a broadband CQI are transmitted. It is to be noted here that, when TMI=1, feedback resources of more than one Physical Uplink Control Channel (PUCCH) may be required for transmitting Report 2.

Report 3:
When TMI=0 in Report 1, a sub-band CQI, a sub-band PMI of the channel corresponding to the selected TP in the DPS transmission mode hypothesis as calculated based on the DPS transmission mode hypothesis as well as a corresponding sub-band index are transmitted.

When TMI=1 in Report 1, a sub-band PMI corresponding to TP 1 as calculated based on the JT transmission mode hypothesis, a sub-band PMI and a sub-band ITP corresponding to TP 2, a sub-band PMI and a sub-band ITP corresponding to TP 3, a sub-band CQI as well as a common sub-band index corresponding to these calculation results are transmitted. It is to be noted here that, when TMI=1, feedback resources of more than one PUCCH may be required for transmitting Report 3.

Example 2
As shown in Fig. 3, the CSI-RS measurement set of UE 1 is composed of TPs 1-3. As shown in Fig. 4, in the MIMO scenario, the antennas of the TPs 1-3 can be combined into a logic TP 0 having its number of antennas being the total number of antennas of the TPs 1-3. The BS configures CSI-RS resources for the TPs 1-3 and for the TP 0. It can be understood that the CSI-RS resources for the TP 0 can be the aggregation of the respective CSI-RS resources for the TPs 1-3 and thus can be easily configured. Assuming that the transmission mode set includes DPS and network MIMO, according to the above explicit notification approach, a 1-bit TMI can be added in the CSI feedback to discriminate between these two transmission mode hypotheses.

Here, a new feedback mode can be defined for which a feedback period includes three sub-periods. The information fed back in these sub-periods corresponds to the CSI feedback for the TP1, TP 2 and TP 3 each being the TP dynamically selected based on the DPS transmission mode hypothesis, respectively. Each sub-period can be divided into the following three reports:

Report 1 for transmission of RI and TMI:
When TMI=0, the RI is based on the DPS transmission mode hypothesis and calculated from a channel of the TP corresponding to the current sub-period.

When TMI=1, the RI is based on the network MIMO transmission mode hypothesis and calculated from a channel of the TP 0.

Report 2:
When TMI=0 in Report 1, a broadband CQI and a broadband PMI of the channel of the TP corresponding to the current sub-period as calculated based on the DPS transmission mode hypothesis are transmitted.

When TMI=1 in Report 1, a broadband PMI and a broadband CQI corresponding to the TP 0 as calculated based on the network MIMO transmission mode hypothesis are transmitted.

Report 3:
When TMI=0 in Report 1, a sub-band CQI and a sub-band PMI of the channel of the TP corresponding to the current sub-period as calculated based on the DPS transmission mode hypothesis as well as a corresponding sub-band index are transmitted.

When TMI=1 in Report 1, a sub-band CQI and a sub-band PMI corresponding to the TP 0 as calculated based on the network MIMO transmission mode hypothesis as well as a corresponding sub-band index are transmitted.

It is to be noted that the above divisions of the periods, sub-periods and the reports are exemplary only. The present invention is not limited to any specific configuration. In addition, the Report 3 in the example 2 is optional and can be fed back along with the Report 1 and the Report 2 after the UE configures the sub-band related feedback modes.

Next, the CSI feedback method according to the embodiments of the present invention will be described with reference to the figure. In the following description, the method will be described in connection with the above embodiments of the UE for the purpose of clarity. However, it can be appreciated by those skilled in the art that it is illustrative only to describe the method of present invention in connection with the specific functional units of the UE. In the case where the method is implemented in computer program, for example, such definitions of the functional units and components are unnecessary and the UE can act as a whole to implement the method of the present invention. Therefore, all the features described above with respect to the embodiments of the UE 100 are also applicable to the following method embodiments.

Fig. 5 shows a flowchart illustrating the CSI feedback method 200 according to the present invention.

The CSI feedback method 200 as shown in Fig. 5 can be performed by the UE 100 and includes the following steps.

At step S210, the determination unit 120 determines a transmission mode set including transmission mode hypotheses between a BS and the UE.

Preferably, the method 200 further includes receiving from the BS an indication of the transmission mode set. In this case, the step S210 includes determining the transmission mode set in response to the received indication.

Preferably, the step S210 includes determining the transmission mode hypotheses included in the transmission mode set based on communication scenarios.

At step S220, the calculation unit 120 calculates CSI corresponding to each transmission mode hypothesis in the transmission mode set.

At step S230, the feedback unit 130 feeds back the calculated CSI to the BS and notifies the BS of the transmission mode hypothesis corresponding to the calculated CSI.

Preferably, the step S230 includes transmitting an indicator to indicate the transmission mode hypothesis corresponding to the calculated CSI.

Preferably, the step S230 includes feeding back the CSI corresponding to each of the transmission mode hypotheses in the transmission mode set to the BS in a predetermined order, such that the feedback order of the CSI indicates the corresponding transmission mode hypothesis.

Preferably, the transmission mode hypotheses include at least one of Dynamic Point Selection (DPS), Coordinated Scheduling/Coordinated Beamforming (CS/CB), Joint Transmission (JT) and network MIMO transmission.

Preferably, the CSI includes at least one of Rank Indicator (RI), Precoder Matrix Indicator (PMI) and Channel Quality Indicator (CQI).

It should be noted that the solution of the present invention has been described above by a way of example only. However, the present invention is not limited to the above steps and element structures. It is possible to adjust, add and remove the steps and elements structures depending on actual requirements. Thus, some of the steps and elements are not essential for achieving the general inventive concept of the present invention. Therefore, the features necessary for the present invention is only limited to a minimum requirement for achieving the general inventive concept of the present invention, rather than the above specific examples.

A number of examples have been illustrated in the above description. While the inventor has tried to list the examples in association with each other, it does not imply that it is required for the listed examples to have such correspondence as described. A number of solutions can be achieved by selecting examples having no correspondence as long as the conditions underlying the selected examples do not conflict with each other. Such solutions are encompassed by the scope of the present invention.

The present invention has been described above with reference to the preferred embodiments thereof. It should be understood that various modifications, alternations and additions can be made by those skilled in the art without departing from the spirits and scope of the present invention. Therefore, the scope of the present invention is not limited to the above particular embodiments but only defined by the claims as attached.

Claims

A Channel State Information (CSI) feedback method, comprising steps of:
determining a transmission mode set including transmission mode hypotheses between a Base Station (BS) and a User Equipment (UE);
calculating CSI corresponding to each transmission mode hypothesis in the transmission mode set; and
feeding back the calculated CSI to the BS and notifying the BS of the transmission mode hypothesis corresponding to the calculated CSI.
The method of claim 1, further comprising:
receiving from the BS an indication of the transmission mode set,
wherein the transmission mode set is determined in response to the received indication.
The method of claim 1, wherein
the transmission mode hypotheses included in the transmission mode set are determined based on communication scenarios.
The method of claim 1, wherein
an indicator is transmitted to indicate the transmission mode hypothesis corresponding to the calculated CSI.
The method of claim 1, wherein
the CSI corresponding to each of the transmission mode hypotheses in the transmission mode set is fed back to the BS in a predetermined order, such that the feedback order of the CSI indicates the corresponding transmission mode hypothesis.
The method of any of claims 1-5, wherein
the transmission mode hypotheses comprise at least one of Dynamic Point Selection (DPS), Coordinated Scheduling/Coordinated Beamforming (CS/CB), Joint Transmission (JT) and network MIMO transmission.
The method of any of claims 1-5, wherein
the CSI comprises at least one of Rank Indicator (RI), Precoder Matrix Indicator (PMI) and Channel Quality Indicator (CQI).
A User Equipment (UE), comprising:
a determination unit configured to determine a transmission mode set including transmission mode hypotheses between a Base Station (BS) and the UE;
a calculation unit configured to calculate CSI corresponding to each transmission mode hypothesis in the transmission mode set; and
a feedback unit configured to feed back the calculated CSI to the BS and notify the BS of the transmission mode hypothesis corresponding to the calculated CSI.
The UE of claim 8, further comprising:
a receiving unit configured to receive from the BS an indication of the transmission mode set,
wherein the determination unit is configured to determine the transmission mode set in response to the received indication.
The UE of claim 8, wherein
the determination unit is configured to determine the transmission mode hypotheses included in the transmission mode set based on communication scenarios.
The UE of claim 8, wherein
the feedback unit is configured to transmit an indicator to indicate the transmission mode hypothesis corresponding to the calculated CSI.
The UE of claim 8, wherein
the feedback unit is configured to feed back the CSI corresponding to each of the transmission mode hypotheses in the transmission mode set to the BS in a predetermined order, such that the feedback order of the CSI indicates the corresponding transmission mode hypothesis.
The UE of any of claims 8-12, wherein
the transmission mode hypotheses comprise at least one of Dynamic Point Selection (DPS), Coordinated Scheduling/Coordinated Beamforming (CS/CB), Joint Transmission (JT) and network MIMO transmission.
The UE of any of claims 8-12, wherein
the CSI comprises at least one of Rank Indicator (RI), Precoder Matrix Indicator (PMI) and Channel Quality Indicator (CQI).