WO2013116987A1

WO2013116987A1 - Method and apparatus for channel state information feedback

Info

Publication number: WO2013116987A1
Application number: PCT/CN2012/070934
Authority: WO
Inventors: Jianchi Zhu; Zhi Zhang
Original assignee: Nokia Corporation
Priority date: 2012-02-07
Filing date: 2012-02-07
Publication date: 2013-08-15

Abstract

In accordance with an example embodiment of the present invention, a method, comprising measuring channel state information over a measurement set, wherein the measurement set comprises at least two cells to be measured; determining a channel state information pattern group which comprises a plurality of channel state information patterns, wherein each of channel state information patterns indicates channel state information feedback for at least one of the cells of the measurement set; selecting a channel state information pattern from the channel state information pattern group based at least in part on the measured channel state information over the measurement set; and transmitting channel state information feedback based on the selected channel state information pattern, is disclosed.

Description

METHOD AND APPARATUS FOR CHANNEL STATE INFORMATION FEEDBACK

TECHNICAL FIELD

[0001] The present application relates generally to channel state information feedback.

BACKGROUND

[0002] In the third generation partnership project (3GPP) standardization, with long term evolution advanced (LTE-A) work, a bunch of new features, for example coordinated multi-point transmission (CoMP), earner aggregation (CA), downlink single-user multiple input multiple output (DL SU-MIMO), and multi-user multiple input multiple output (MU-MIMO), have been identified as ways to improve downlink (eNB towards user equipment) performance.

[0003] The motivation for CoMP is to allow fast coordination among different transmission points to improve coverage of high data rate, cell-edge throughput and/or to increase system throughput. In downlink (DL) CoMP, the transmissions from multiple cells are coordinated by a serving cell (eNB) so as to mitigate inter-cell interference among the cells at a given user equipment (UE). This type of operation requires channel state information (CSI) feedback from the UE to the eNB. The CSI feedback could take the form of, for example, a precoding matrix indication (PMI) or other form of CSI that allows weighting the eNB' antennas in order to mitigate interference in the spatial domain. Typically the UE also needs to feedback channel quality indication (CQI) to allow proper link adaptation at the eNB, preferably taking into account the inter-cell coordination to reflect correct interference level after coordination, he CQI calculation at the UE requires not only estimating the downlink channels associated with the cooperating cells, which relates to the associated CSI (for example PMI), but also the interference level outside of the set of cooperating cells.

[0004] Carrier aggregation, where two or more component carriers (CCs) are aggregated, is considered for LTE-A in order to support transmission bandwidths larger than 20MHz. The carrier aggregation may be contiguous or non-contiguous. This technique, as a bandwidth extension, may provide significant gains in terms of peak data rate and cell throughput as compared to non- aggregated operation as in LTE release 8 (Rel-8). [0005] Figure 1 shows an example of the carrier aggregation, where M Rel-8 component carriers are combined together to form MxRel-8 BW (for example, 5 x 20MHz = 100MHz given M = 5). Rel-8 UEs receive/transmit on one component carrier, whereas LTE-A UEs may receive/transmit on multiple component carriers simultaneously to achieve higher (wider) bandwidths depending on its capabilities. It is required that LTE-A should be backwards compatible with Rel-8 LTE in the sense that a Rel-8 LTE UE should be operable in the LTE-A system, and that a LTE-A UE should be operable in a Rel-8 LTE system.

SUMMARY

[0006] Various aspects of examples of the invention are set out in the claims.

[0007] According to a first aspect of the present invention, a method, comprising: measuring channel state information over a measurement set, wherein the measurement set comprises at least two cells to be measured; determining a channel state information pattern group which comprises a plurality of channel state information patterns, wherein each of channel state infomiation patterns indicates channel state information feedback for at least one of the cells of the measurement set; selecting a channel state information pattern from the channel state information pattern group based at least in part on the measured channel state information over the measurement set; and transmitting channel state information feedback based on the selected channel state information pattern, is disclosed.

[0008] According to a second aspect of the present invention, an apparatus, comprising: at least one processor; and at least one memory including computer program code; the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to perform at least the following: measuring channel state information over a measurement set, wherein the measurement set comprises at least two cells to be measured; determining a channel state information pattern group which comprises a plurality of channel state information patterns, wherein each of channel state information patterns indicates channel state information feedback for at least one of the cells of the measurement set; selecting a channel state information pattern from the channel state infonnation pattern group based at least in part on the measured channel state information over the measurement set; and transmitting channel state infonnation feedback based on the selected channel state information pattern, is disclosed. [0009] According to a third aspect of the present invention, a method, comprising: blind decoding a channel state information feedback received from a user equipment on a resource pool, wherein the resource pool comprises predefined resources for a channel state information group which comprises a plurality of channel state information patterns; and scheduling transmissions for the user equipment based on the decoded channel state information feedback, is disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] 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:

[0011] FIGURE 1 shows an example of carrier aggregation as proposed for the LTE-A system;

[0012] FIGURE 2 depicts an example CoMP system within which the embodiments of the invention may be implemented;

[0013[ FIGURE 3 is a flow diagram showing operations for UE for channel state information feedback according to the embodiments of the invention;

[0014] FIGURE 4 shows an example resource allocation for channel state information according to an embodiment of the invention;

[0015] FIGURE 5 shows a second example resource allocation for channel state information according to an embodiment of the invention;

[0016] FIGURE 6 shows a third example resource allocation for channel state information according to an embodiment of the invention;

[0017] FIGURE 7 shows a fourth example resource allocation for channel state information according to an embodiment of the invention;

[0018] FIGURE 8 is a flow diagram showing operations for eNB according to an embodiment of the invention;

[0019] FIGURE 9 is a simplified block diagram of an embodiment of a device that provides an environment for application of the example embodiments of the invention; and

[0020] FIGURE 10 is a simplified block diagram of an embodiment of another device that provides an environment for application of the example embodiments of the invention. DETAILED DESCRIPTON OF THE DRAWINGS

[0021] An example embodiment of the present invention and its potential advantages are understood by referring to FIGURES 2 through 10 of the drawings.

[0022] FIGURE 2 depicts an example CoMP system within which the embodiments of the invention may be implemented.

[0023] In an example embodiment, a system 200 comprises at least one UE 202 and at least one eNB 210 (for example a serving eNB for the UE 202). The eNB 210 defines a macro cell (cell-m) 220 of coverage. Within the macro cell 220 is at least one transmission point (TP1 21 1 , TP2 212, TP3 213, TP4 214) coupled at least to the eNB 210 and, in some example embodiments, to one another. Each transmission point defines a corresponding local cell of coverage (cell-1 221 , cell-2 222, cell-3 223, cell-4 224) that may be entirely within the macro cell 220 or, alternatively, may overlap with a portion of the macro cell 220. Each transmission point may comprise remote radio heads (RRHs) or additional eNBs. In example embodiments, the transmission points are coupled to the eNB 210 to enable at least coordinated transmission to the UE 202. The one or more (at least one) local cells of coverage may also be referred to as hotspots, hotspot cells or local hotspots, as non-limiting examples.

[0024] The eNB 210 may be coupled to the at least one transmission point via at least one data and control path, which may be implemented as an X2 interface for the case of another logical base station or may be a direct eNB internal interface (for example an optical fiber connection) for connection to another type of transmission point such as at least one RRH.

Typically, the eNB 210 covers a single macro cell (cell-m 220) via one or more antennas.

[0025] The UE 202 is attached to the eNB 210 and communicates with the eNB 210 for uplink (UE towards eNB) control, uplink data, or downlink control channels. For CoMP reception, the UE 202 may receive a joint transmission from any subset of eNB 210, TP 1 21 1 , TP2 212, TP3 213, and TP4 214 (also known as Joint Transmisison); the UE 202 may receive transmission from a single transmission point, the single transmission point may change dynamically within the set of eNB 210, TP1 21 1, TP2 212, TP3 213, and TP4 214 (also known as Dynamic Point Selection), The transmission points may or may not be assigned a same cell-id. The transmission points may or may not belong to a same eNB. Typically CoMP clusters are defined geographically to prevent and/or minimize overlap of macro cells or overlap of CoMP clusters.

[0026] In example embodiments, each transmission point may include a controller, such as at least one data processor, at least one computer-readable memory medium (for example, embodied as a memory) that stores a program of computer instructions, at least one suitable transmitter and at least one suitable receiver (for example, at least one RF transceiver) operable for communication with the UE 202 via one or more antennas (typically several when MIMO operation is in use). In example embodiments, for single-cell operation the transmission points may be under control of a single eNB, although dispersed control is also possible. Further, there is generally a central unit to which several transmission points (for example, RRHs) are connected. Thus, the transmission points and the macro eNB may be centrally controlled together. While the control is typically at the location of the macro eNB, in other example embodiments it may be at a location that is connected to the eNB and/or the transmission points,

[0027] For better CoMP performance, appropriate transmission point selection and accurate CSI feedback (from UE to eNB) are desirable. To provide better transmission point selection, large CSI measurement set is required so that CSI regarding more transmission points may be compared. Nevertheless, with the CSI measurement set increasing, there is an issue of large CSI feedback overhead if all CSI measurements need to be reported from UE to eNB. For example, if there are five transmission points in the measurement set, CSI feedback overhead increases by at least five times more than that in LTE Release 10 where, for example, only one cell's CSI feedback is reported in a corresponding reporting instance. However, actual CoMP operation may use CSI information for two transmission points only. Furthermore, the necessary CSI feedback for different CoMP scheme may differ. For dynamic point selection (DPS), the CSI information for the selected transmission point is needed. For joint transmission (JT), the CSI information for the joint transmission points are needed. In case CSI information

corresponding to each transmission point in the CSI measurement set is reported from UE to eNB, the not necessary CSI information introduces large unnecessary overhead.

[0028] While discussed herein with respect to CoMP, it should be understood that this is by way of convenience and for purposes of clarity, and thus should not be viewed as limiting the example embodiments of the invention. The example embodiments of the invention apply to other features, such as CA, where channel state information feedback is used for multiple downlink component carriers as well.

[0029] As for CA, the problem is similar with CoMP, the CSI overhead increases linearly with the number of component carriers (CCs). For example, if there are five downlink CCs, CSI feedback overhead increases by five times compared with single CC. However, the actual scheduling results may be that only two CCs are allocated to UE which means the CSI information of other three CCs may not need to be reported.

[0030] In LTE release 10, when multiple periodic CSI reports for respectively multiple cells are to be transmitted in the same subframe, only one periodic CSI report is transmitted and the remaining ones are dropped. The prioritization is according to the periodic CSI report type, for example rank indicator (RI) is prioritized over wideband CQI/PMI, and wideband CQI/PMI is prioritized over narrowband CQI/PMI. For the same periodic CSI report type, prioritization is according to the cell index.

[0031] Another possible solution is to have eNB semi-statically configure UE to feedback which cells' CSI information via RRC signaling. However, it may be hard to capture the best configuration in time due to the large channel fluctuation. For example, in CoMP UE may experience good channel in one transmission point in one time period, and experience good channel in several transmission points in the other time period. In this case, the semi-static configuration may not adapt to the fast channel fluctuation.

[0032] FIGURE 3 is a flow diagram showing operations for UE for channel state information feedback according to the embodiments of the invention.

[0033] At block 300, the UE measures channel state information (CSI) over a measurement set. The measurement set information may be signaled to the UE by eNB via radio resource control (RRC) signaling beforehand. The measurement set comprises at least two cells to be measured. In an example embodiment, the measurement set comprises at least two transmission points for CoMP, each transmission point relates to a frequency carrier for transmitting downlink transmissions to the UE. In another example embodiment, the

measurement set comprises at least two component carriers for CA, the UE may receive downlink transmissions on each component carrier. [0034] As non-limiting examples, the channel state information may take the form of channel quality indication (CQI), precoding matrix indication (PMI), rank indicator (RI), or other form of CSI that conveys the radio channel quality that the UE is experiencing.

[0035] In an example embodiment, the UE measures instantaneous channel quality over the cells in the measurement set. The instantaneous channel refers to the channel response, including amplitude and phase, may change from time to time. The instantaneous channel quality is measured within a subframe period, for example on some pilot symbols that are carried on a downlink pilot channel/sequence. The instantaneous channel quality may take the form of PMI, CQI, RI, channel direction indication (CDI), channel matrix, channel covariance matrix, eigen of channel matrix, or eigen of channel covariance matrix, as non-limiting examples. In another example embodiment, the UE measures channel quality over the cells for a certain time period. The time period may be longer than one subframe period, but shorter than the time required for scheduling (for example transmission point selection, or component carrier selection) in order to provide eNB accurate information about the radio channel quality that the UE is experiencing.

[0036] At block 302, the UE determines a channel state information pattern group. The channel state information pattern group comprises a plurality of channel state information patterns. Each of channel state information patterns indicates a channel state information feedback for at least one of the cells of the measurement set.

[0037] In an example embodiment, the channel state information pattern group is predefined and commonly known by the UE and eNB. In another example embodiment, the channels state information pattern group is signaled to the UE by eNB using RRC signaling. The RRC signaling may be common RRC signaling transmitted to a plurality of UEs, or dedicated RRC signaling transmitted to a certain UE.

[0038] In an example embodiment, a channel state information pattern (CSI pattern) may indicate for which cell(s) the UE would report CSI. The CSI pattern may indicate whether aggregated CSI should be reported for CoMP. The aggregated CSI may reflect multiple transmission points' CSI information. The aggregated CSI may be based on channel state information reference signal (CSI-RS) resources. The CSI-RS resources may correspond to one set of antenna ports.

[0039] Assuming a CSI measurement set for CoMP comprises TP A, TP B, and TP C, below are two example embodiments regarding the CSI pattern group. [0040] In an example embodiment, the CSI pattern group may be:

Pattern 1: TP index + CSI of TP A

Pattern 2: TP index + CSI of TP B

Pattern 3: TP index + CSI of TP C

Pattern 4: TP group index + CSI of TP A + CSI of TP B (+optional: aggregated CSI)

Pattern 5: TP group index + CSI of TP A + CSI of TP C (+optional: aggregated CSI)

Pattern 6: TP group index + CSI of TP B + CSI of TP C (+optional: aggregated CSI)

Pattern 7: TP group index (optional) + CSI of TP A + CSI of TP B + CSI of TP C (+optional: aggregated CSI)

[0041] The TP index is identifier to identify different transmission points. For this example, the TP index may comprise at least two bits of information to identify the three possible TPs (TP A, TP B, TP C). The TP group index is identifier to identify different combinations of TPs. For this example, the TP group index may comprise at least two bits of information to identify the four possible combinations of TPs,

[0042] In an example embodiment, the CSI pattern group may be;

Pattern 1 : pattern index + CSI of TP A

Pattern 2: pattern index + CSI of TP B

Pattern 3: pattern index + CSI of TP C

Pattern 4: pattern index + CSI of TP A + CSI of TP B (+optional: aggregated CSI)

Pattern 5: pattern index + CSI of TP A + CSI of TP C (+optional: aggregated CSI)

Pattern 6: pattern index + CSI of TP B + CSI of TP C (+optional: aggregated CSI)

Pattern 7: pattern index + CSI of TP A + CSI of TP B + CSI of TP C (+optional: aggregated CSI)

[0043] The pattern index is identifier to identify different patterns. For this example, the pattern index may comprise at least three bits of information to identify the seven different possible patterns.

[0044] In an example embodiment, a set of CSI pattern groups may be pre-defined. Each CSI pattern group corresponds to a certain size of measurement set. Let S represent the size of the measurement set. S equals to the number of cells to be measured in the measurement set.

[0045] In case S equals to 2, there are two cells, cl and c2, to be measured. The CSI pattern group for S=2 may be defined as:

Pattern 1 : pattern index + CSI of cl Pattern 2: pattern index + CSI of c2

Pattern 3: pattern index + CSI of cl + CSI of c2

[0046] In case S equals to 3, there are three cells, cl, c2, and c3, to be measured. The

CSI pattern group for S=3 may be defined as:

Pattern 1 : pattern index + CSI of cl

Pattern 2: pattern index + CSI of c2

Pattern 3: pattern index + CSI of c3

Pattern 4: pattern index + CSI of cl + CSI of c2

Pattern 5: pattern index + CSI of cl + CSI of c3

Pattern 6: pattern index + CSI of c2 + CSI of c3

Pattern 7: pattern index + CSI of cl + CSI of c2 + CSI of c3

[0047] In case S equals to 4, there are four cells, cl, c2, c3, and c4, to be measured. The

CSI pattern group for S=4 may be defined as:

Pattern 1 : pattern index + CSI of cl

Pattern 2: pattern index + CSI of c2

Pattern 3: pattern index + CSI of c3

Pattern 4: pattern index + CSI of c4

Pattern 5: pattern index + CSI of cl + CSI of c2

Pattern 6: pattern index + CSI of cl + CSI of c3

Pattern 7: pattern index + CSI of cl + CSI of c4

Pattern 8: pattern index + CSI of c2 + CSI of c3

Pattern 9: pattern index + CSI of c2 + CSI of c4

Patternl O: pattern index + CSI of c3 + CSI of c4

Pattern 11 : pattern index + CSI of cl + CSI of c2 + CSI of c3

Pattern 12: pattern index + CSI of cl + CSI of c2 + CSI of c4

Pattern 13: pattern index + CSI of cl + CSI of c3 + CSI of c4

Pattern 14: pattern index + CSI of c2 + CSI of c3 + CSI of c4

Pattern 15: pattern index + CSI of cl + CSI of c2 + CSI of c3 + CSI of c4

[0048] In an example embodiment, the channel state information pattern groups may be predefined and commonly known by the UE and eNB. The UE may derive the value of S from its measurement set configured by eNB. In another example embodiment, the UE may directly receive the value of S from eNB by dedicated RRC signaling. After having the value of S, the UE may utilize the corresponding channel state infonnation pattern group from the set of channel state information groups.

[0049] At block 304, the UE selects a channel state information pattern (CSI pattern) from the CSI pattern group that is determined at block 302. The UE may select a CSI pattern based on the CSI results that are measured at block 300.

[0050] In an example embodiment, the criterion for selecting CSI pattern may be defined by UE. For example, the UE may set a threshold for deciding which measured CSI may be included in the CSI feedback content to be transmitted to eNB. In another example embodiment, the criterion for selecting CSI pattern may be controlled by eNB. For example, eNB may signal the UE a predefined threshold.

[0051] In an example embodiment, in case the measured CSI difference between a serving cell and a non-serving cell is less than the threshold, the UE may consider the measured CSI of the non-serving cell as a part of the CSI feedback content when selecting CSI pattern. In another example embodiment, in case the measured CSI of a certain cell is above the threshold, the UE may consider the measured CSI of that certain cell as a part of the CSI feedback content when selecting CSI pattern. Please note, herein cell is used for explanation convenience, it may be component carrier or transmission point when applies.

[0052] Taken the above mentioned case of CoMP with TP A, TP B, and TP C as example, assuming the threshold is set as about 0.5 and the measured CSI of TP A, TP B, and TP C is about 0.3, about 0.6, and about 0.45 respectively. Then, the measured CSI of TP B is above the threshold, the measured CSI of TP B is to be included in the CSI feedback to be transmitted to eNB. The UE may select Pattern 2: TP index + CSI of TP B, or Pattern 2: pattern index + CSI of TP B according to the above depicted CSI pattern group embodiments.

[0053] At block 306, the UE transmits channel state information feedback (CSI feedback) to eNB based on the CSI pattern selected by block 304. In an example embodiment, the UE may select a portion of resources from a resource pool to transmit the CSI feedback, The resource may comprise at least one subcarrier in frequency domain, at least one symbol in time domain, or at least one sequence on code domain.The resource pool comprises resources for all CSI patterns of a CSI pattern group. Each CSI pattern may correspond to a portion of resources. The UE selects the portion of resources corresponds to the selected CSI pattern, and transmits the CSI feedback on the selected portion of resources. [0054] FIGURE 4 shows an example resource allocation for channel state information according to an embodiment of the invention.

|0055] In FIGURE 4, the horizontal axis represents time domain, the vertical axis represents frequency domain. Block 400 shows a resource pool for a plurality of CSI patterns. The block 400 spans tO to t4 in time domain and f0 to β in frequency domain. Point 410 represents the start point (tO, fO) of the resource pool. Point 420 represents the end point (t4, f3) of the resource pool.

[0056] Block 401 (filled with vertical lines) spans tO to t2 in time domain and fO to fl in frequency domain. The block 401 represents resources (Resource 1) for transmitting a first CSI pattern. Block 402 (filled with horizontal lines) spans tO to tl in time domain and fO to f3 in frequency domain. The block 402 represents resources (Resource 2) for transmitting a second CSI pattern. Block 403 (filled with crossed lines) spans tO to t3 in time domain and fO to f2 in frequency domain. The block 403 represents resources (Resource 3) for transmitting a third CSI pattern.

[0057] The resource pool may be predefined and commonly known by eNB and UE. Alternatively, eNB may signal the resource pool to UE via common RRC signaling or dedicated RRC signaling. For example, the eNB may signal the UE: the start point and the end point of the resource pool; and/or the start point and the end point of the resource for the CSI patterns.

[0058] In an example embodiment, a mapping table between CSI patterns and resources may be defined as Table 1 :

Table 1 : Mapping table between CSI pattern and resources for without pattern indicator or joint pattern indicator encoding

[0059] The mapping table 1 may be commonly known to eNB and UE, or be signaled from eNB to UE. [0060] In case without pattern indicator transmitted to eNB from UE, or pattern indicator is jointly encoded with CSI feedback, the example embodiments of FIGURE4 may be utilized. Joint encoding refers to the pattern indicator and the CSI feedback content are encoded together. They are transmitted on the same resources.

[0061] FIGURE 5 shows a second example resource allocation for channel state information according to an embodiment of the invention.

[0062] In FIGURE 5, block 500 shows a resource pool for a plurality of CSI patterns. The block 500 spans tO to t5 in time domain and fO to f3 in frequency domain. Point 510 represents the start point (tO, ID) of the resource pool. Point 520 represents the end point (t5, f3) of the resource pool,

[0063] Block 504 (filled with dotted lines) spans tO to tl in time domain and fO to f3 in frequency domain. The block 504 represents resources (Resource 1) for transmitting pattern indicator. The pattern indicator comprises at least one bit of information to indicate which CSI pattern is to be transmitted. It may be in form of the above mentioned TP index, TP group index, pattern index, or something alike. Block 501 (filled with vertical lines) spans tl to t3 in time domain and fO to fl in frequency domain. The block 501 represents resources (Resource 2) for transmitting a first CSI pattern. Block 502 (filled with horizontal lines) spans tl to t2 in time domain and fO to £3 in frequency domain. The block 502 represents resources (Resource 3) for transmitting a second CSI pattern. Block 503 (filled with crossed lines) spans tl to t4 in time domain and fO to £2 in frequency domain. The block 503 represents resources (Resource 4) for transmitting a third CSI pattern.

[0064] The resource pool may be predefined and commonly known by eNB and UE. Alternatively, eNB may signal the resource pool to UE via common RRC signaling or dedicated RRC signaling. For example, the eNB may signal the UE: the start point and the end point of the resource pool, the start point and the end point of the resource for the pattern indicator, and/or the start point and the end point of the resource for the CSI patterns.

[0065] In an example embodiment, a mapping table between CSI patterns and resources may be defined as Table 2:

CSI pattern Resources

Pattern index Resource 1 CSI pattern 1 Resource 2

CSI pattern 2 Resource 3

CSI pattern 3 Resource 4

CSI pattern 4 Resource 5

Table 2: Mapping table between CSI pattern and resources for separate pattern indicator encoding

[0066] The mapping table 2 may be commonly known to eNB and UE, or be signaled from eNB to UE.

[0067] In case pattern indicator is separately encoded or independently encoded with CSI feedback, the example embodiments of FIGURE 5 may be utilized. Separate encoding refers to the pattern indicator and CSI feedback content is independently encoded. They are transmitted on different resources.

[0068] FIGURE 6 shows a third example resource allocation for channel state information according to an embodiment of the invention.

[0069] The example resource allocation in FIGURE 6 is designed for the above mentioned case of CoMP (with TP A, TP B, and TP C, there are seven CSI patterns defined in one CSI pattern group) for the cases of: without pattern indicator transmitted to eNB from UE, or pattern indicator is jointly encoded with CSI feedback.

[0070] Block 601 (filled with horizontal lines) spans tO to tl in time domain and fO to fl in frequency domain. The block 601 represents resources (Resource 1) for transmitting CSI pattern 1, CSI pattern 2, or CSI pattern 3. Block 602 (filled with vertical lines) spans tO to t2 in time domain and fO to fl in frequency domain. The block 602 represents resources (Resource 2) for transmitting CSI pattern 4, CSI pattern 5, or CSI pattern 6. Block 603 (filled with crossed lines) spans tO to t3 in time domain and fO to fl in frequency domain. The block 603 represents resources (Resource 3) for transmitting CSI pattern 7.

[0071] A mapping table between CSI patterns and resources may be defined as Table 3:

CSI pattern Resources

CSI pattern 1 ,2,3 Resource 1

CSI pattern 4,5,6 Resource 2 CSI pattern 7 Resource 3

Table 3: Mapping table between CSI pattern and resources for CoMP with three TPs (without pattern indicator or joint pattern indicator encoding)

[0072] FIGURE 7 shows a fourth example resource allocation for channel state information according to an embodiment of the invention.

[0073] The example resource allocation in FIGURE 7 is designed for the above mentioned case of CoMP when separate pattern indicator encoding is utilized.

[0074] Block 720 (filled with dotted lines) spans tO to tl in time domain and fO to fl in frequency domain. The block 720 represents resources (Resource 1) for transmitting pattern indicator. Block 701 (filled with horizontal lines) spans tl to t2 in time domain and fO to fl in frequency domain. The block 701 represents resources (Resource 2) for transmitting CSI pattern 1, CSI pattern 2, or CSI pattern 3. Block 702 (filled with vertical lines) spans tl to t3 in time domain and fO to fl in frequency domain. The block 702 represents resources (Resource 3) for transmitting CSI pattern 4, CSI pattern 5, or CSI pattern 6. Block 703 (filled with crossed lines) spans tl to t4 in time domain and fO to fl in frequency domain. The block 703 represents resources (Resource 4) for transmitting CSI pattern 7.

[0075] A mapping table between CSI patterns and resources may be defined as Table 4:

Table 4: Mapping table between CSI pattern and resources for CoMP with three TPs

(separate pattern indicator encoding)

[0076] FIGURE 8 is a flow diagram showing operations for eNB according to an embodiment of the invention.

[0077] At block 800, eNB blindly decodes a channel state information feedback (CSI feedback) received from a user equipment (UE) on a resource pool. The resource pool comprises predefined resources for at least one CSI group. One CSI group comprises a plurality of CSI patterns.

[0078] In an example embodiment, the eNB may decode the CSI feedback based on a mapping between the CSI patterns and resources. For example, using the above mapping table 3, the eNB may try to decode CSI pattern on Resource 1 firstly, in case the eNB successfully decodes CSI pattern 1, CSI pattern 2, or CSI pattern 3 on Resource 1, the eNB may stop the CSI pattern decoding operation; otherwise the eNB may try to decode CSI pattern on Resource 2, in case the eNB successfully decodes CSI pattern 4, CSI pattern 5, or CSI pattern 6, the eNB may stop the CSI pattern decoding operation; otherwise the eNB may try to decode CSI pattern 7 on Resource 3.

[0079] In an example embodiment, in case separate coding pattern indicator is utilized, the eNB may firstly decode the pattern indicator to determine which CSI pattern the UE is selected. After that, the eNB may decode the determined CSI pattern on the resource specifically defined for that CSI pattern. For example, using the above mapping table 4, the eNB may firstly try to decode pattern indicator on Resource 1. According to the pattern indicator, the eNB may determine which CSI pattern the UE selected to transmit the CSI feedback. Then, the eNB may try to decode Resource 2, Resource 3, or Resource 4 to find the CSI feedback that is reported by the UE.

[0080J The CSI patterns and/or the mapping between the CSI patterns and resources may be predefined, for example, in technical specification texts, or defined by the eNB and signaled to the UE from the eNB by RRC signaling.

[0081] At block 802, eNB schedules transmissions for the user equipment based on the decoded channel state information feedback. For example, the eNB may decide which

transmission points to be included in the UE's CoMP set. The eNB may decide on which downlink component carriers to transmit data to the UE.

[0082] In an example embodiment, according to the scheduling to the UE, the eNB may transmit a measurement set information to the UE. The measurement set may comprise at least two cells, for example two transmission points for CoMP or two component carriers for CA.

[0083] In an example embodiment, the eNB may transmit a trigger signaling to trigger the UE to report CSI feedback based on the CSI patterns. The trigger signaling may be physical layer signaling or RRC signaling. [0084] FIGURE 9 is a simplified block diagram of an embodiment of a device that provides an environment for application of the example embodiments of the invention. The device may represent an user equipment, a mobile station, or the like.

[0085] The device may include, but are not limited to, a cellular telephone, a personal digital assistant (PDA) having wireless communication capabilities, a portable and desktop computer having wireless communication capabilities, an image capture device such as digital camera having wireless communication capabilities, a gaming device having wireless communication capabilities, a music storage and playback appliance having wireless communication capabilities, an Internet appliance permitting wireless Internet access and browsing, as well as a portable unit or terminal that incorporate combinations of such functions.

[0086] The device comprises one or more antenna 900, a processor 901, a radio frequency transceiver 902, and memory 904, The memory 904 is coupled to processor 901 for storing programs and data of a temporary or more permanent nature. The CSI patterns may be stored in the memory 904. The radio frequency transceiver 902 is coupled to the antenna 900 and to the processor 901 for bidirectional wireless communications. The transceiver 902 modulates information onto a carrier waveform for transmission of the information or data via the antenna 900 to another communication device. The transceiver 902 demodulates information or data received via the antenna 900 for further processing by the processor 901.

[0087] The processor 901 includes a CSI measurement module 906, a CSI pattern selection module 908, and a CSI report module 910. The CSI measurement module 906 is configured to measure channel state information over a measurement set, for example as block 300 of FIGURE 3. The CSI pattern selection module 908 is configured to select a CSI pattern from a CSI patter group, for example as block 304 of FIGURE 3. The CSI report module 910 is configured to compile CSI feedback based on the selected CSI pattern, for example as block 306 of FIGURE 3. The CSI measurement module 906 output its measurement results to the CSI pattern selection module 908 for CSI pattern selection and to the CSI report module 910 for CSI feedback compiling. The CSI pattern selection module 908 outputs its selected CSI pattern to the CSI report module 910. The CSI report module 910 compiles CSI feedback based on the selected CSI pattern, and sends the complied CSI feedback to the transceiver 902 to be transmitted to the eNB. [0088] FIGURE 10 is a simplified block diagram of an embodiment of another device that provides an environment for application of the example embodiments of the invention. The device of FIGURE 10 may represent a network element such as eNB, a base station, or the like.

[0089] In an example embodiment, the device comprises one or more antenna 1000, a processor 1001, a radio frequency transceiver 1002, and memory 1004. The memory 1004 is coupled to processor 901 for storing programs and data of a temporary or more permanent nature. The memory 1004 may include program instructions (PROG), for example executable by the processor 1001, for operation in accordance with the example embodiments of this invention. The PROGs may be embodied in software, firmware and/or hardware, as appropriate.

[0090] The radio frequency transceiver 1002 is coupled to the antenna 1000 and to the processor 1001 for bidirectional wireless communications. The transceiver 1002 modulates information onto a carrier waveform for transmission of the information or data via the antenna 1000 to another communication device, for example the device of FIGURE 9. The transceiver 1002 demodulates information or data received via the antenna 1000 for further processing by the processor 1001.

[0091] The processor 1001 includes a CSI blind decoder 1006, a scheduler 1008, and a measurement controller 1010. The CSI blind decoder 1006 may be configured to blindly decoding a CSI feedback on a resource pool, as block 800 of FIGURE 8. The scheduler 1008 may be configured to schedule transmissions for a UE as block 802 of FIGURE 8. The measurement block 1010 may be configured to control the measurement set of the UE.

[0092] The CSI blind decoder 1006 outputs its decoded CSI feedback from a UE to the scheduler 1008. The scheduler 1008 takes the CSI feedback into account to make scheduling for the UE, and outputs its scheduling allocation to the measurement controller 1010 to assist the measurement controller 1010 to control the measurement set of the UE. The scheduler 1008 may output its scheduling allocation to the transceiver 1002 to transmit control signaling, for example CSI pattern group related signaling, to the UE. The measurement controller 1010 outputs the measurement set of the UE to the CSI blind decoder 1006 to assist the blind decoding. The measurement controller 1010 may also output the measurement set of the UE to the transceiver 1002 to transmit control signaling, for example measurement set configuration, to the UE. [0093] 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 is CS1 feedback saving. Another technical effect of one or more of the example embodiments disclosed herein is better conveying channel fluctuation information. Another technical effect of one or more of the example embodiments disclosed herein is improved spectrum utilization.

[0094] 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 UE, or eNB. If desired, part of the software, application logic and/or hardware may reside on UE, part of the software, application logic and/or hardware may reside on eNB. 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, such as a computer, with one example of a computer described and depicted in FIGURE 9 or FIGURE 10, A computer-readable medium may comprise a 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, such as a computer.

[0095] 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.

[0096] Although various aspects of the invention are set out in the independent claims, other aspects of the invention comprise other combinations of features from the described embodiments and/or the dependent claims with the features of the independent claims, and not solely the combinations explicitly set out in the claims.

[0097] 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 as defined in the appended claims.

Claims

WHAT IS CLAIMED IS

1. A method, comprising:

measuring channel state information over a measurement set, wherein the measurement set comprises at least two cells to be measured;

determining a channel state information pattern group which comprises a plurality of channel state information patterns, wherein each of channel state information patterns indicates channel state information feedback for at least one of the cells of the measurement set;

selecting a channel state information pattern from the channel state information pattern group based at least in part on the measured channel state information over the measurement set; and

transmitting channel state information feedback based on the selected channel state information pattern.

2. The method according to claim 1, wherein the measurement set comprises at least two transmission points for coordinated multi-point transmission, or at least two component earners for carrier aggregation.

3. The method according to claim 1, wherein the channel state information pattern group is predefined commonly known by eNB and a user equipment, or signaled to the user equipment by eNB using radio resource control signaling.

4. The method according to claim 1, wherein the measured channel state information comprises instantaneous channel quality measured by the user equipment over the measurement set.

5. The method according to claim 1 , wherein the selecting comprises comparing the measured channel state information with a predefined threshold.

6. The method according to claim 1, wherein the transmitting comprises transmitting the channel state information feedback on a portion of resources corresponding to the selected channel state information pattern, wherein the portion of resources is selected from a resource pool which comprises resources for all channel state information patterns.

7. An apparatus, comprising:

at least one processor; and

at least one memory including computer program code;

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

determining a channel state information pattern group which comprises a plurality of channel state information patterns, wherein each of channel state information patterns indicates channel state information feedback for at least one of the cells of the

measurement set;

8. The apparatus according to claim 7, wherein the measurement set comprises at least two transmission points for coordinated multi-point transmission, or at least two component carriers for carrier aggregation.

9. The apparatus according to claim 7, wherein the channel state information pattern group is predefined commonly known by eNB and a user equipment, or signaled to the user equipment by eNB using radio resource control signaling.

10. The apparatus according to claim 7, wherein the measured channel state information comprises instantaneous channel quality measured by the user equipment over the measurement set.

11. The apparatus according to claim 7, wherein the selecting comprises comparing the measured channel state information with a predefined threshold.

12. The apparatus according to claim 7, wherein the transmitting comprises transmitting the channel state information feedback on a portion of resources

corresponding to the selected channel state information pattern, wherein the portion of resources is selected from a resource pool which comprises resources for all channel state information patterns.

13. A method, comprising:

blind decoding a channel state information feedback received from a user equipment on a resource pool, wherein the resource pool comprises predefined resources for a channel state information group which comprises a plurality of channel state information patterns; and

scheduling transmissions for the user equipment based on the decoded channel state information feedback.

14. The method according to claim 13, wherein the blind decoding is based on a mapping between the channel state information patterns and the resources.

15. The method according to claim 13, further comprising:

transmitting a measurement set information to the user equipment, wherein the measurement set comprises at least two ceils to be measured; and/or

transmitting a trigger signaling to trigger the user equipment to report channel state information feedback based on the channel state information patterns.

16. An apparatus, comprising: at least one processor; and

at least one memory including computer program code;

17. The apparatus according to claim 16, wherein the blind decoding is based on a mapping between the channel state information patterns and the resources.

18. The apparatus according to claim 16, further caused to perform at least one of: transmitting a measurement set information to the user equipment, wherein the measurement set comprises at least two cells to be measured; or

19. A computer program, comprising:

code for measuring channel state information over a measurement set, wherein the measurement set comprises at least two cells to be measured;

code for determining a channel state information pattern group which comprises a plurality of channel state information patterns, wherein each of channel state information patterns indicates channel state information feedback for at least one of the cells of the measurement set;

code for selecting a channel state information pattern from the channel state information pattern group based at least in part on the measured channel state information over the measurement set; and code for transmitting channel state information feedback based on the selected channel state information pattern;

when the computer program is run on a processor.

20. The computer program according to claim 19, wherein the computer program is a computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer,