WO2018027804A1

WO2018027804A1 - Apparatus and method for unified csi feedback framework for control and data channel

Info

Publication number: WO2018027804A1
Application number: PCT/CN2016/094648
Authority: WO
Inventors: Xiaoyi Wang; Frederick Vook; Eugene Visotsky; Deshan Miao
Original assignee: Nokia Technologies Oy; Nokia Technologies (Beijing) Co., Ltd.
Priority date: 2016-08-11
Filing date: 2016-08-11
Publication date: 2018-02-15

Abstract

A method comprises determining a set of candidate multiple input multiple output (MIMO) transmission schemes, wherein each MIMO transmission scheme is associated with a channel state information (CSI) calculation mechanism and a feedback format for channel state information; indicating the determined set of candidate MIMO transmission schemes to a user equipment; and receiving a channel state information with a feedback format associated with a MIMO transmission scheme selected from the set of candidate MIMO transmission schemes.

Description

APPARATUS AND METHOD FOR UNIFIED CSI FEEDBACK FRAMEWORK FOR CONTROL AND DATA CHANNEL

TECHNICAL FIELD

The present application relates generally to an apparatus and a method for unified channel state information feedback framework for control and data channel.

BACKGROUND

This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued， but are not necessarily ones that have been previously conceived， implemented or described. Therefore， unless otherwise indicated herein， what is described in this section is not prior art to the description and claims in this application.

Third generation partnership project (3GPP) 5^th generation (5G) technology is a new generation of radio systems and network architecture that can deliver extreme broadband and ultra-robust， low latency connectivity. 5G can improve the telecommunication services offered to the end users， and help support massive machine-to-machine (M2M) communications. 5G is also expected to increase network expandability up to hundreds of thousands of connections. The signal technology of 5G is anticipated to be improved for greater coverage as well as spectral and signaling efficiency.

5G networks are expected to use multiple input and multiple output (MIMO) technology for multiplying the capacity of a radio link by using multiple transmit and receive antennas. Channel state information (CSI) feedback is the key to harvest MIMO performance gain. In traditional long term evolution (LTE) MIMO framework， CSI feedback format is tied to MIMO transmission mode (TM) . Once configured to a certain TM， UE should report corresponding CSI feedback accordingly.

SUMMARY

According to a first embodiment， a method can include determining a set of candidate multiple input multiple output (MIMO) transmission schemes， wherein each MIMO transmission scheme is associated with a channel state information (CSI) calculation mechanism and a feedback format for channel state information； indicating the determined set of candidate MIMO transmission schemes to a user equipment； and receiving a channel state information with a feedback format associated with a MIMO transmission scheme selected from the set of candidate MIMO transmission schemes.

According to a second embodiment， an apparatus can include at least one processor and at least one memory including computer program code， wherein the at least one memory and the computer program code are configured to， with the at least one processor， cause the apparatus at least to determine a set of candidate multiple input multiple output (MIMO) transmission schemes， wherein each MIMO transmission scheme is associated with a channel state information (CSI) calculation mechanism and a feedback format for channel state information； indicate the determined set of candidate MIMO transmission schemes to a user equipment； and receive a channel state information with a feedback format associated with a MIMO transmission scheme selected from the set of candidate MIMO transmission schemes.

According to a third embodiment， a computer program product can include a computer-readable medium bearing computer program code embodied therein for use with a computer， the computer program code comprising code for determining a set of candidate multiple input multiple output (MIMO) transmission schemes， wherein each MIMO transmission scheme is associated with a channel state information (CSI) calculation mechanism and a feedback format for channel state information； indicating the determined set of candidate MIMO transmission schemes to a user equipment； and receiving a channel state information with a feedback format associated with a MIMO transmission scheme selected from the set of candidate MIMO transmission schemes.

According to a fourth embodiment， an apparatus can include means for determining a set of candidate multiple input multiple output (MIMO) transmission schemes， wherein each MIMO transmission scheme is associated with a channel state information (CSI) calculation mechanism and a feedback format for channel state information； means for indicating the determined set of candidate MIMO transmission schemes to a user equipment； and means for receiving a channel state information with a feedback format associated with a MIMO transmission scheme selected from the set of candidate MIMO transmission schemes.

According to a fifth embodiment， a method can include receiving from a network element a set of candidate multiple input multiple output (MIMO) transmission schemes， wherein each MIMO transmission scheme is associated with a channel state information calculation mechanism and a feedback format for channel state information； selecting a MIMO transmission scheme from the received set of candidate MIMO transmission schemes； calculating a channel state information and determining a feedback format based on the selected MIMO transmission scheme； and sending to the network element the channel state information with the determined feedback format.

According to a sixth embodiment， an apparatus can include at least one processor and at least one memory including computer program code， wherein the at least one memory and the computer program code are configured to， with the at least one processor， cause the apparatus at least to receive from a network element a set of candidate multiple input multiple output (MIMO) transmission schemes， wherein each MIMO transmission scheme is associated with a channel state information calculation mechanism and a feedback format for channel state information； select a MIMO transmission scheme from the received set of candidate MIMO transmission schemes； calculate a channel state information and determine a feedback format based on the selected MIMO transmission scheme； and send to the network element the channel state information with the determined feedback format.

According to a seventh embodiment， a computer program product can include a computer-readable medium bearing computer program code embodied therein for use with a computer， the computer program code comprising code for receiving from a network element a set of candidate multiple input multiple output (MIMO) transmission schemes， wherein each MIMO transmission scheme is associated with a channel state information calculation mechanism and a feedback format for channel state information； selecting a MIMO transmission scheme from the received set of candidate MIMO transmission schemes； calculating a channel state information and determining a feedback format based on the selected MIMO transmission scheme； and sending to the network element the channel state information with the determined feedback format.

According to an eighth embodiment， an apparatus can include means for receiving from a network element a set of candidate multiple input multiple output (MIMO) transmission schemes， wherein each MIMO transmission scheme is associated with a channel state information calculation mechanism and a feedback format for channel state information； mean for selecting a MIMO transmission scheme from the received set of candidate MIMO transmission schemes； means for calculating a channel state information and determining a feedback format based on the selected MIMO transmission scheme； and means for sending to the network element the channel state information with the determined feedback format.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of example embodiments of the present invention， reference is now made to the following descriptions taken in connection with the accompanying drawings in which：

Figure 1 illustrates a flowchart in accordance with an example embodiment of the application.

Figure 2 illustrates a flowchart in accordance with another example embodiment of the application.

Figure 3 illustrates a simplified block diagram of example apparatuses that are suitable for use in practicing various example embodiments of this application.

DETAILED DESCRIPTON

Associating the channel state information (CSI) feedback with multiple input and multiple output (MIMO) transmission mode may simplify the operation procedure. Once configured into one transmission mode， a user equipment (UE) has a fixed procedure to measure and feedback related CSI content. However， it may be hard for evolved NodeB (eNB) to decide what CSI feedback mostly fits the user. With CSI feedback associated with transmission mode， it may also be difficult to accommodate scheduling and link adaption for control channel. As a result， some long term evolution (LTE) control channels， e.g. physical downlink control channel (PDCCH) ， or enhanced physical downlink control channel (ePDCCH) ， can only depend on less efficient outer loop controlling schemes for scheduling and link adaptation.

Single MIMO transmission mode (or no transmission mode) has been discussed within third generation partnership project (3GPP) 5^th generation (5G) MIMO work force. The design target is to use one MIMO transmission mode to cover all MIMO transmission schemes. The eNB could dynamically switch transmission scheme (TS) from transmission time interval (TTI) to TTI using downlink control information (DCI) . A unified CSI feedback framework to fit all the transmission schemes may be needed.

In an example embodiment， a unified CSI feedback framework for both data and control channels and different transmission schemes is proposed.

In an example embodiment， an eNB may configure a set of candidate MIMO transmission schemes and optionally an uplink (UL) resource for UE selected transmission scheme reporting：

- A MIMO transmission scheme is a general term which may apply to data or control channel.

- A MIMO transmission scheme for data channel may include for example：

- Transmit diversity (TxD) such as for example space frequency block coding (SFBC)

- Open loop spatial multiplexing such as for example large delay cyclic delay diversity (CDD) (with multiple ranks)

- Close loop spatial multiplexing (e.g. with precoding matrix indicator (PMI) feedback)

- A MIMO transmission scheme for control channel may include for example：

- Distributed PDCCH like (with interleaved control channel element (CCE) configuration)

- Localized ePDCCH like (with localized enhanced CCE (eCCE) configuration)

Each MIMO transmission scheme is associated with a CSI calculation mechanism and a CSI feedback format. Note that the eNB can preclude some transmissions schemes for UE to select. For example， if eNB decides to pair a particular UE with others for multi-user MIMO (MU-MIMO) . It may not want this UE to select TxD as hypothetical transmission scheme. In that case， eNB can preclude the TxD scheme from the candidate transmission scheme set.

In an example embodiment， when triggered by eNB， a UE can select a MIMO transmission scheme from the candidate set as hypothetical transmission scheme for the CSI feedback. The selected hypothetic transmission scheme will determine the CSI calculation mechanism and corresponding feedback format.

In an example embodiment， the selection may be based on observed channel changing rate， credibility of the CSI accuracy and link adaptation (LA) efficiency between control and data channels. For example， if the UE observes inefficient control scheduling (e.g. block error rate (BLER) is too high) ， it may select a transmission scheme for control channel as for CSI feedback to allow eNB better adjust the control channel scheduling and link adaption. In another example， if UE observes the channel is changing too fast， it may select TxD as hypothetical transmission scheme for CSI feedback. This selection may provide recommendation to eNB about which transmission scheme to use as well as corresponding scheduling and link adaption.

In an example embodiment， the information of the selected MIMO transmission scheme， such as for example， the index of the selected MIMO transmission scheme， is feedback to eNB together with the CSI， separately or jointly encoded.

In an example embodiment， a selected MIMO transmission scheme may have different CSI feedback formats. For example， as an implicit feedback， ifthe UE selects open loop spatial multiplexing， the CSI may include rank indicator (RI) and channel quality indicator (CQI) information； ifthe UE selects close loop spatial multiplexing， CSI feedback may include RI， PMI and CQI. In another example， as an explicit feedback， if the UE selects close loop spatial multiplexing， it may feedback quantized Eigen vectors plus quantized interference. In an example embodiment， multiple candidate MIMO transmission schemes of the set may be associated with one same CSI quantization type， and their associated CSI feedback formats are corresponding to different quantization granularities.

In an example embodiment， once receiving the CSI feedback selected by the UE， the eNB may use the recommended MIMO transmission scheme for future data or control transmission. The eNB may generate a message for the UE to acknowledge the CSI feedback， hence， the recommended MIMO transmission scheme. In another example embodiment， the eNB may over-write the recommend MIMO transmission scheme and choose by itself. For example， if UE selects close-loop MIMO， however， eNB finds the historical BLER of this user is very bad， it may overwrite it to transmission diversity.

Figure 1 illustrates a flowchart in accordance with an example embodiment of the application. In the example of Figure 1， a network element (NE) ， such as for example， an eNB， determines a set of candidate MIMO transmission scheme at step 101. Each MIMO transmission scheme is associated with a CSI calculation mechanism and a CSI feedback format. The eNB indicates the determined set of candidate MIMO transmission schemes to a UE at step 102. At step 103 the eNB may optionally determine an uplink resource and indicate the uplink resource to the UE. At step 104 the eNB receives a CSI feedback with a format associated with a MIMO transmission scheme selected from the set. The eNB may acknowledge the received CSI and hence the MIMO transmission scheme selected by the UE and adopt it for future transmission at step 105.

Figure 2 illustrates another flowchart in accordance with an example embodiment of the application. In the example of Figure 2， a UE receives from a NE， such as for example， an eNB， a set of candidate MIMO transmission scheme at step 201. Each MIMO transmission scheme is associated with a CSI calculation mechanism and a CSI feedback format. The UE selects a MIMO transmission scheme from the received set at step 202. At step 203 the UE calculates a CSI and determines a CSI feedback format based on the selected MIMO transmission scheme. The UE may receive an uplink resource from the NE at step 204， and indicate the CSI with the determined feedback format to the NE on the received uplink resource at step 205. At step 206 the UE may receive an acknowledgement from the NE acknowledging the indicated CSI and hence the selected MIMO transmission scheme that may be adopted by the NE for future transmission.

Reference is made to Figure 3 for illustrating a simplified block diagram of various example apparatuses that are suitable for use in practicing various example embodiments of this application. In Figure 3， a NE 301， is adapted for communication with a UE 311. The UE 311 includes at least one processor circuitry 315， at least one memory (MEM) 314 coupled to the at least one processor circuitry 315， and a suitable transceiver (TRANS) 313 (having a transmitter (TX) and a receiver (RX) ) coupled to the at least one processor circuitry 315. The at least one MEM 314 stores a program (PROG) 312. The TRANS 313 is for bidirectional wireless communications with the NE 301.

The NE 301 includes at least one processor circuitry 305， at least one memory (MEM) 304 coupled to the at least one processor circuitry 305， and a suitable transceiver (TRANS) 303 (having a transmitter (TX) and a receiver (RX) ) coupled to the at least one processor circuitry 305. The at least one MEM 304 stores a program (PROG) 302. The TRANS 303 is for bidirectional wireless communications with the UE 311. The NE 301 may be coupled to one or more cellular networks or systems， which is not shown in this figure.

As shown in Figure 3， the NE 301 may further include a MIMO TS control unit 306. The unit 306， together with the at least one processor circuitry 305 and the PROG 302， may be utilized by the NE 301 in conjunction with various example embodiments of the application， as described herein.

As shown in Figure 3， the UE 311 may further include a MIMO TS process unit 316. The unit 316， together with the at least one processor circuitry 315 and the PROG 312， may be utilized by the UE 311 in conjunction with various example embodiments of the application， as described herein.

At least one of the

PROGs

302 and 312 is assumed to include program instructions that， when executed by the associated processor， enable the electronic apparatus to operate in accordance with the example embodiments of this disclosure， as discussed herein.

In general， the various example embodiments of the apparatus 311 can include， but are not limited to， cellular phones， personal digital assistants (PDAs) having wireless communication capabilities， portable computers having wireless communication capabilities， image capture devices such as digital cameras having wireless communication capabilities， gaming devices having wireless communication capabilities， music storage and playback appliances having wireless communication capabilities， Internet appliances permitting wireless Internet access and browsing， as well as portable units or terminals that incorporate combinations of such functions.

The example embodiments of this disclosure may be implemented by computer software or computer program code executable by one or more of the

processor circuitries

305， 315 of the NE 301 and the UE 311， or by hardware， or by a combination of software and hardware.

The

MEMs

304 and 314 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， flash memory， magnetic memory devices and systems， optical memory devices and systems， fixed memory and removable memory， as non-limiting examples. The

processor circuitries

305 and 315 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 multi-core processor architecture， as non-limiting examples.

Without in any way limiting the scope， interpretation， or application of the claims appearing below， a technical effect of one or more of the example embodiments disclosed herein may be unifying CSI feedback inside one framework to support both control and data channels. It also allows UE to observe the full channel and interference， and to select the best transmission scheme. That results in a more efficient feedback and improved overall performance.

Embodiments of the present invention may be implemented in software， hardware， application logic or a combination of software， hardware and application logic. The software， application logic and/or hardware may reside on an apparatus such as a user equipment， an eNB or other mobile communication devices. If desired， part of the software， application logic and/or hardware may reside on a network element 301， part of the software， application logic and/or hardware may reside on a UE 311， and part of the software， application logic and/or hardware may reside on other chipset or integrated circuit. In an example embodiment， the application logic， software or an instruction set is maintained on any one of various conventional computer-readable media. In the context of this document， a “computer-readable medium” may be any media or means that can contain， store， communicate， propagate or transport the instructions for use by or in connection with an instruction execution system， apparatus， or device. A computer-readable medium may comprise a non-transitory computer-readable storage medium that may be any media or means that can contain or store the instructions for use by or in connection with an instruction execution system， apparatus， or device.

It is also noted herein that while the above describes example embodiments of the invention， these descriptions should not be viewed in a limiting sense. Rather， there are several variations and modifications which may be made without departing from the scope of the present invention. For example， the described example embodiments may focus on trigger based CSI feedback， i.e.， aperiodical feedback. But it may also be applied in the case of periodical feedback.

Further， the various names， such as for example， the names of timers used for the described parameters are not intended to be limiting in any respect， as these parameters may be identified by any suitable names.

If desired， the different functions discussed herein may be performed in a different order and/or concurrently with each other. Furthermore， if desired， one or more of the above-described functions may be optional or may be combined. As such， the foregoing description should be considered as merely illustrative of the principles， teachings and example embodiments of this invention， and not in limitation thereof.

Claims

A method， comprising：

by an apparatus，

determining a set of candidate multiple input multiple output (MIMO) transmission schemes， wherein each MIMO transmission scheme is associated with a channel state information (CSI) calculation mechanism and a feedback format for channel state information；

indicating the determined set of candidate MIMO transmission schemes to a user equipment； and

receiving a channel state information with a feedback format associated with a MIMO transmission scheme selected from the set of candidate MIMO transmission schemes.
The method according to claim 1， wherein a transmission scheme is a data channel transmission scheme or a control channel transmission scheme.
The method according to claim 1 or 2， further comprising：

determining an uplink resource； and

indicating the determined uplink resource to the user equipment.
The method according to claim 3， wherein receiving the channel state information comprising receiving the channel state information on the determined uplink resource.
The method according to any of claims 1 to 4， wherein determining the set of candidate MIMO transmission schemes comprising precluding a MIMO transmission scheme from the set.
The method according to any of claims 1 to 5， further comprising receiving an information indicating the selected MIMO transmission scheme.
The method according to any of claims 1 to 6， wherein multiple candidate MIMO transmission schemes of the set are associated with one same CSI quantization type， and their associated CSI feedback formats are corresponding to different quantization granularities.
The method according to any of claims 1 to 7， further comprising adopting the selected MIMO transmission scheme for future transmission.
The method according to any of claims 1 to 8， further comprising sending to the user equipment a message acknowledging the selected MIMO transmission scheme.
The method according to any of claims 1 to 9， wherein the set of candidate MIMO transmission schemes includes at least one of transmission diversity scheme， open loop spatial multiplexing scheme， close loop spatial multiplexing scheme， distributed control channel element configuration scheme， and localized control channel element configuration scheme.
An apparatus， comprising：

at least one processor；

and at least one memory including computer program code，

wherein the at least one memory and the computer program code are configured to， with the at least one processor， cause the apparatus at least to：

determine a set of candidate multiple input multiple output (MIMO) transmission schemes， wherein each MIMO transmission scheme is associated with a channel state information (CSI) calculation mechanism and a feedback format for channel state information；

indicate the determined set of candidate MIMO transmission schemes to a user equipment； and

receive a channel state information with a feedback format associated with a MIMO transmission scheme selected from the set of candidate MIMO transmission schemes.
The apparatus according to claim 11， wherein a transmission scheme is a data channel transmission scheme or a control channel transmission scheme.
The apparatus according to claim 11 or 12， wherein the at least one memory and the computer program code are configured to， with the at least one processor， cause the apparatus further to：

determine an uplink resource； and

indicate the determined uplink resource to the user equipment.
The apparatus according to claim 13， wherein when receiving the channel state information， the at least one memory and the computer program code are configured to， with the at least one processor， cause the apparatus to receive the channel state information on the determined uplink resource.
The apparatus according to any of claims 11 to 14， wherein when determining the set of candidate MIMO transmission schemes， the at least one memory and the computer program code are configured to， with the at least one processor， cause the apparatus to preclude a MIMO transmission scheme from the set.
The apparatus according to any of claims 11 to 15， wherein the at least one memory and the computer program code are configured to， with the at least one processor， cause the apparatus further to receive an information indicating the selected MIMO transmission scheme.
The apparatus according to any of claims 11 to 16， wherein multiple candidate MIMO transmission schemes of the set are associated with one same CSI quantization type， and their associated CSI feedback formats are corresponding to different quantization granularities.
The apparatus according to any of claims 11 to 17， wherein the at least one memory and the computer program code are configured to， with the at least one processor， cause the apparatus further to adopt the selected MIMO transmission scheme for future transmission.
The apparatus according to any of claims 11 to 18， wherein the at least one memory and the computer program code are configured to， with the at least one processor， cause the apparatus further to send to the user equipment a message acknowledging the selected MIMO transmission scheme.
The apparatus according to any of claims 11 to 19， wherein the set of candidate MIMO transmission schemes includes at least one of transmission diversity scheme， open loop spatial multiplexing scheme， close loop spatial multiplexing scheme， distributed control channel element configuration scheme， and localized control channel element configuration scheme.
A computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer， the computer program code comprising code for：

determining a set of candidate multiple input multiple output (MIMO) transmission schemes， wherein each MIMO transmission scheme is associated with a channel state information (CSI) calculation mechanism and a feedback format for channel state information；

indicating the determined set of candidate MIMO transmission schemes to a user equipment； and

receiving a channel state information with a feedback format associated with a MIMO transmission scheme selected from the set of candidate MIMO transmission schemes.
An apparatus， comprising：

means for determining a set of candidate multiple input multiple output (MIMO) transmission schemes， wherein each MIMO transmission scheme is associated with a channel state information (CSI) calculation mechanism and a feedback format for channel state information；

means for indicating the determined set of candidate MIMO transmission schemes to a user equipment； and

means for receiving a channel state information with a feedback format associated with a MIMO transmission scheme selected from the set of candidate MIMO transmission schemes.
A method， comprising：

by an apparatus，

receiving from a network element a set of candidate multiple input multiple output (MIMO) transmission schemes， wherein each MIMO transmission scheme is associated with a channel state information (CSI) calculation mechanism and a feedback format for channel state information；

selecting a MIMO transmission scheme from the received set of candidate MIMO transmission schemes；

calculating a channel state information and determining a feedback format based on the selected MIMO transmission scheme； and

sending to the network element the channel state information with the determined feedback format.
The method according to claim 23， wherein a transmission scheme is a data channel transmission scheme or a control channel transmission scheme.
The method according to claim 23 or 24， further comprising：

receiving from the network element an uplink resource.
The method according to claim 25， wherein sending the channel state information comprising sending the channel state information on the received uplink resource.
The method according to any of claims 23 to 26， wherein selecting the MIMO transmission scheme is based on at least one of observed channel changing rate， credibility of channel station information accuracy， and link adaptation efficiency between a control channel and a data channel.
The method according to any of claims 23 to 27， further comprising sending to the network element an information indicating the selected MIMO transmission scheme.
The method according to any of claims 23 to 28， wherein multiple candidate MIMO transmission schemes of the set are associated with one same CSI quantization type， and their associated CSI feedback formats are corresponding to different quantization granularities.
The method according to any of claims 23 to 29， further comprising receiving future transmission according to the selected MIMO transmission scheme.
The method according to any of claims 23 to 30， further comprising receiving from the network element a message acknowledging the selected MIMO transmission scheme.
The method according to any of claims 23 to 31， wherein the set of candidate MIMO transmission schemes includes at least one of transmission diversity scheme， open loop spatial multiplexing scheme， close loop spatial multiplexing scheme， distributed control channel element configuration scheme， and localized control channel element configuration scheme.
An apparatus， comprising：

at least one processor；

and at least one memory including computer program code，

wherein the at least one memory and the computer program code are configured to， with the at least one processor， cause the apparatus at least to：

receive from a network element a set of candidate multiple input multiple output (MIMO) transmission schemes， wherein each MIMO transmission scheme is associated with a channel state information calculation mechanism and a feedback format for channel state information； select a MIMO transmission scheme from the received set of candidate MIMO transmission schemes；

calculate a channel state information and determine a feedback format based on the selected MIMO transmission scheme； and

send to the network element the channel state information with the determined feedback format.
The apparatus according to claim 33， wherein a transmission scheme is a data channel transmission scheme or a control channel transmission scheme.
The apparatus according to claim 33 or 34， wherein the at least one memory and the computer program code are configured to， with the at least one processor， cause the apparatus further to：

receive from the network element an uplink resource.
The apparatus according to claim 35， wherein when sending the channel state information， the at least one memory and the computer program code are configured to， with the at least one processor， cause the apparatus to send the channel state information on the received uplink resource.
The apparatus according to any of claims 33 to 36， wherein when selecting the MIMO transmission scheme， the at least one memory and the computer program code are configured to， with the at least one processor， cause the apparatus to select the MIMO transmission scheme based on at least one of observed channel changing rate， credibility of channel station information accuracy， and link adaptation efficiency between a control channel and a data channel.
The apparatus according to any of claims 33 to 37， wherein the at least one memory and the computer program code are configured to， with the at least one processor， cause the apparatus further to send to the network element an information indicating the selected MIMO transmission scheme.
The apparatus according to any of claims 33 to 38， wherein multiple candidate MIMO transmission schemes of the set are associated with one same CSI quantization type， and their associated CSI feedback formats are corresponding to different quantization granularities.
The apparatus according to any of claims 33 to 39， wherein the at least one memory and the computer program code are configured to， with the at least one processor， cause the apparatus further to receive future transmission according to the selected MIMO transmission scheme.
The apparatus according to any of claims 33 to 40， wherein the at least one memory and the computer program code are configured to， with the at least one processor， cause the apparatus further to receive from the network element a message acknowledging the selected MIMO transmission scheme.
The apparatus according to any of claims 33 to 41， wherein the set of candidate MIMO transmission schemes includes at least one of transmission diversity scheme， open loop spatial multiplexing scheme， close loop spatial multiplexing scheme， distributed control channel element configuration scheme， and localized control channel element configuration scheme.
A computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer， the computer program code comprising code for：

receiving from a network element a set of candidate multiple input multiple output (MIMO) transmission schemes， wherein each MIMO transmission scheme is associated with a channel state information calculation mechanism and a feedback format for channel state information； selecting a MIMO transmission scheme from the received set of candidate MIMO transmission schemes；

calculating a channel state information and determining a feedback format based on the selected MIMO transmission scheme； and

sending to the network element the channel state information with the determined feedback format.
An apparatus， comprising：

means for receiving from a network element a set of candidate multiple input multiple output (MIMO) transmission schemes， wherein each MIMO transmission scheme is associated with a channel state information calculation mechanism and a feedback format for channel state information；

means for selecting a MIMO transmission scheme from the received set of candidate MIMO transmission schemes；

means for calculating a channel state information and determining a feedback format based on the selected MIMO transmission scheme； and

means for sending to the network element the channel state information with the determined feedback format.