FEEDBACK

TECHNICAL FIELD:

The exemplary and non-limiting embodiments of this invention relate generally to wireless communication systems, methods, devices and computer programs and, more specifically, relate to single user and multi-user multiple input, multiple output transmissions from a network access node to a mobile node, and to feedback concerning same sent from the mobile node to the network access node.

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 and is not admitted to be prior art by inclusion in this section.

The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:

3 GPP third generation partnership project

CB codebook

CoMP coordinated multi-point transmission/reception

CQI channel quality indicator

CRC cyclic redundancy check

CSI channel state information (includes, e.g., CQI, PMI, and RI)

CSI-RS channel state information reference symbols

DoA direction of arrival

DL downlink (eNB towards UE)

eNB E-UTRAN Node B (evolved Node B, base station)

EPC evolved packet core

E-UTRAN evolved UTRAN (LTE)

LTE long term evolution of UTRAN (E-UTRAN)

LTE-A LTE advanced MAC medium access control (layer 2, L2)

MCS modulation and coding scheme

MIMO multiple-input, multiple-output

MM/MME mobility management/mobility management entity

MU-MIMO multi-user MIMO

OFDMA orthogonal frequency division multiple access

O&M operations and maintenance

PDCP packet data convergence protocol

PDCCH physical downlink control channel

PHY physical (layer 1, LI)

PRB physical resource block

PMI precoding matrix indicator

PUCCH physical uplink control channel

PUSCH physical uplink shared channel

Rel release

RI rank indicator

RLC radio link control

RRC radio resource control

RRM radio resource management

RS reference symbols

SGW serving gateway

SC-FDMA single carrier, frequency division multiple access

SU-MIMO single-user MIMO

TBS transport block size

Tx transmission

UE user equipment, e.g., a mobile station, mobile node or mobile terminal

UL uplink (UE towards eNB)

UTRAN universal terrestrial radio access network

The specification of a communication system known as evolved UTRAN (E -UTRAN, also referred to as UTRAN-LTE or as E-UTRA) is currently nearing completion within the 3GPP. As specified the DL access technique is OFDMA, and the UL access technique is SC-FDMA.

One specification of interest is 3 GPP TS 36.300, V8.8.0 (2009-04), "3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (EUTRA) and Evolved Universal Terrestrial Access Network

(EUTRAN); Overall description; Stage 2 (Release 8)". This system may be referred to for convenience as LTE Rel-8. In general, the set of specifications given generally as 3GPP TS 36.xyz (e.g., 36.211, 36.311, 36.312, etc.) may be seen as describing the Release 8 LTE system. More recently, Release 9 versions of at least some of these specifications have been published including 3 GPP TS 36.300, V9.1.0 (2009-9).

Figure 1A reproduces Figure 4-1 of 3GPP TS 36.300 V8.8.0, and shows the overall architecture of the EUTRAN system 2 (Rel-8). The E-UTRAN system 2 includes eNBs 3, providing the E-UTRAN user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UE (not shown). The eNBs 3 are interconnected with each other by means of an X2 interface. The eNBs 3 are also connected by means of an SI interface to an EPC, more specifically to a MME by means of a SI MME interface and to an S-GW by means of a S I interface (MME/S-GW 4). The SI interface supports a many-to-many relationship between MMEs/S-GWs and eNBs.

The eNB hosts the following functions:

• functions for RRM: RRC, Radio Admission Control, Connection Mobility Control, Dynamic allocation of resources to UEs in both UL and DL (scheduling);

• IP header compression and encryption of the user data stream;

• selection of a MME at UE attachment;

• routing of User Plane data towards the EPC (MME/S-GW);

• scheduling and transmission of paging messages (originated from the MME);

• scheduling and transmission of broadcast information (originated from the MME or O&M); and

• a measurement and measurement reporting configuration for mobility and scheduling.

Of particular interest herein are the further releases of 3GPP LTE (e.g., LTE Rel-10) targeted towards future IMTA systems, referred to herein for convenience simply as LTE-Advanced (LTE-A). Reference in this regard may be made to 3 GPP TR 36.913, V9.0.0 (2009-12), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Requirements for Further Advancements for EUTRA (LTE-Advanced) (Release 9). A goal of LTE-A is to provide significantly enhanced services by means of higher data rates and lower latency with reduced cost. LTE-A is directed toward extending and optimizing the 3 GPP LTE Rel-8 radio access technologies to provide higher data rates at lower cost. LTE-A will be a more optimized radio system fulfilling the ITU-R requirements for IMT -Advanced while keeping the backward compatibility with LTE Rel-8.

As is specified in 3GPP TR 36.913, LTE-A should operate in spectrum allocations of different sizes, including wider spectrum allocations than those of LTE Rel-8 (e.g., up to 100MHz) to achieve the peak data rate of lOOMbit/s for high mobility and 1 Gbit/s for low mobility. It has been agreed that carrier aggregation is to be considered for LTE-A in order to support bandwidths larger than 20 MHz. 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 could be contiguous or non-contiguous. This technique, as a bandwidth extension, can provide significant gains in terms of peak data rate and cell throughput as compared to non-aggregated operation as in LTE Rel-8.

A terminal may simultaneously receive one or multiple component carriers depending on its capabilities. A LTE-A terminal with reception capability beyond 20 MHz can simultaneously receive transmissions on multiple component carriers. A LTE Rel-8 terminal can receive transmissions on a single component carrier only, provided that the structure of the component carrier follows the Rel-8 specifications. Moreover, it is required that LTE-A should be backwards compatible with Rel-8 LTE in the sense that a Rel-8 LTE terminal should be operable in the LTE-A system, and that a LTE-A terminal should be operable in a Rel-8 LTE system.

During the ongoing standardization of LTE Rel-10 in 3GPP there has been input from network operators to further improve the competitiveness of LTE DL MIMO operation, as compared to what has been specified in Rel-8 and Rel-9. More specifically, the requirements concentrate on the following:

support for eight transmit and receive antenna ports: up to 8-layer DL MIMO operation; support for enhanced MU-MIMO operation;

support for UE-specific demodulation reference symbols (DMRS);

support for periodic channel state information reference symbols (CSI-RS); and

support for coordinated multi-point transmission/reception (CoMP).

An important aspect of providing DL MIMO enhancements is the channel state information (CSI) feedback provided to the eNB by the UE. Without accurate feedback the gains from the use of advanced MIMO techniques are diminished. Moreover, DL MU-MIMO has received considerable interest. With regard then to UE feedback enhancements, one issue relates to how to design efficient and unified UE feedback in support of both DL SU-MIMO and MU-MIMO, which are likely to be intrinsically tied together within the same DL transmission mode. Note that some form of CoMP may be included as well in Rel-10.

At present it appears to be clear that so-called implicit feedback will remain as the main type of UE feedback for DL SU-/MU-MIMO operation in LTE Rel-10. Under the implicit feedback paradigm, the CSI reports that the UE sends to the eNB give a direct recommendation for the DL transmission format (e.g. MCS/TBS, precoding weights for each antenna port, supportable transmission rank, etc.)

Examples of a concept/framework to be considered in beyond Release 8/9, have been proposed in 3 GPP TSG RAN WGl#59bis, Rl-100256, Valencia, Spain, January 18-22, 2010, Agenda Item: 7.2.4.4, Source: Huawei, Title: Downlink 8TX codebook considerations and in 3 GPP TSG-RAN WG1 #59bis, Rl-100051, Valencia, Spain, January 18 - 22, 2010, Source: Ericsson, ST-Ericsson, Title: A Flexible Feedback Concept, Agenda Item: 7.2.4.1.

The basic principle, which builds on adaptive feedback methodology, is to specify two sets of codebooks instead of a single codebook, where one codebook represents the long term channel characteristics (referred to for convenience as Wl) and the other codebook (referred to for convenience as W2) describes the short term variations. In other words, the long term channel characteristics or long term CSI depict large scale fast-fading in a wideband fashion that depends primarily on transmit correlation at the eNB, and that does not necessarily depend on the transmission rank. This is complemented by the short term CSI representing small scale fading in a frequency selective manner (with a granularity of from one up to a few PRBs), and which is typically rank specific (e.g., rank adaptation is performed at the UE on the short term part of the feedback). As the long term CSI is not expected to change as often as its short term counterpart, the long term component can be decoupled from the short term one from an UE feedback reporting perspective, allowing to report the long term part with lower time periodicity, and hence it is possible to achieve efficient feedback compression and hence lower associated UL overhead

The motivation for such adaptive and modular feedback stems from the MU-MIMO perspective: it is widely acknowledged that most MU-MIMO gains over SU-MIMO are achieved in scenarios with closely spaced Tx antennas and small azimuth (angular) spread at the eNB, which is precisely the scenario in which there exists long term wideband correlation in the wireless channel. Multi-user separation/multiplexing is then performed efficiently based on long term CSI (direction of arrival (Do A) is one example of such long term channel property) while UE-specific rank adaptation occurs mostly based on short term CSI (the case of rank > 1 per UE in MU-MIMO mode is feasible and supported). With practical eNB antenna deployments comprising cross-polarized antenna arrays, this translates to MU-MIMO (wideband) beamforming (e.g., UE separation) in the beam domain via groups of co-polarized antenna elements, while UE-specific rank adaptation occurs within each (UE-specific) beam by adequately combining the two polarizations. Clearly, then, there is a motivation to optimize the UE feedback in this direction. On the other hand, such an approach does not preclude either achieving gains from SU-/MU-MIMO in an uncorrected scenario: in this case the long term (wideband) CSI is expected to be of less importance while the short term CSI will play an increased role.

The rank of the channel refers to the number of independent spatial data streams that can be simultaneously transmitted between the antennas of the transmitter and receiver over a given radio channel resource. In a rich scattering environment, the maximum achievable rank is the minimum between the number of transmit and receive antennas. Such independent streams can be transmitted also in correlated scenarios under some circumstances, by employing cross polarized antennas at both the transmitter and receiver. The polarization dimension creates an extra degree of freedom, allowing the system to transmit simultaneously up to two spatial streams, even in line-of-sight scenarios where typically the transmission rank is close to one in practice. The rank of the radio channel indicates the number of layers that can be transmitted to the UE experiencing that radio channel.

In terms of codebook design, this implies that the long term channel statistics should be supported by wideband feedback with sufficiently high granularity (e.g., 4-5 bits and probably a little more if one desires good performance) and optimized for typical antenna configuration (e.g., ULA or cross-polarized arrays), while for the short term part IID codebooks will be most likely adequate. Reusing the 2-Tx and 4-Tx codebooks from Rel-8 is an appealing baseline for the feedback of the short term CSI from UE implementation and specification perspective. In order to support transmission ranks above 4 (not supported by Rel-8 codebooks) a design is needed that applies to the case of 8-Tx antennas, where most likely an 8 Tx codebook is needed for the short term feedback part (e.g. W2 codebook) supporting transmission ranks from 1 to 8. In uncorrected scenarios, the wideband part of the feedback becomes less significant and may be omitted (e.g. assuming an identity matrix for Wl) as there is no specific subspace/direction in the channel where to steer energy.

Reference with regard to Rel-8/Rel-9 codebooks can be made to 3 GPP TS 36.211 V9.0.0 (2009-12) Technical Specification 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA);Physical Channels and Modulation(Release 9), section 6.3.4.2.3, "Codebook for precoding". The following contributions serve as examples of differential/refinement codebook principles: 3 GPP TSG RAN WG1 Meeting #59bis, Rl-1001 16, Valencia, Spain, January 18- January 22, 2010, Agenda Item: 7.2.4.1, Source: Samsung, Title: Comparisons and performance evaluation of differential feedback proposals for Rel. 8 PMI enhancements; 3GPP TSG-RAN WG1 Meeting #58bis, Rl-093867, Miyazaki, Japan, Oct 12-16, 2009, Agenda Item: 7.5, Source: NEC, Title: Multi-resolution Precoding Codebook; and 3 GPP TSG RAN WG1 Meeting #56bis, Tdoc Rl-091288, Seoul, Korea, 23rd - 27th March 2009, Agenda Item: 15.6, Source: Philips, Title: CSI feedback improvements for LTE-A based on multiple codebooks. SUMMARY

The below summary section is intended to be merely exemplary and non-limiting.

The foregoing and other problems are overcome, and other advantages are realized, by the use of the exemplary embodiments of this invention.

In a first aspect thereof an exemplary embodiment of this invention provides a method for signaling support for MIMO CSI feedback. The method includes composing, using a first CB, a self-contained first report including wideband long-term CSI. Sending the first report from a UE to a network access node is also included in the method. The method also includes receiving from the network access node a grant to send a second report. The grant includes an indication informing the UE how to premise the second report. Composing, using a second CB, the second report including frequency selective short-term information is also included in the method. The second report is composed premised on the indication received with the grant. The method also includes sending the second report to the network access node.

In a further aspect thereof an exemplary embodiment of this invention provides a method for signaling support for MIMO CSI feedback. The method includes receiving a self-contained first report from a UE at a network access node. The first report includes wideband long-term CSI and the first report is composed using a first CB. Sending, from the network access node to the UE, a grant to send a second report is also included in the method. The grant includes an indication informing the UE how to premise the second report. The method also includes receiving the second report from the UE at the network access node. The second report is composed using a second CB. Deriving frequency selective short-term information from the second report based on the first report is also included in the method.

In another aspect thereof an exemplary embodiment of this invention provides an apparatus for signaling support for MIMO CSI feedback. The apparatus includes 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: to compose, using a first CB, a self-contained first report including wideband long-term CSI; to send the first report from a UE to a network access node; to receive from the network access node a grant to send a second report; to compose, using a second CB, the second report including frequency selective short-term information; and to send the second report to the network access node. The grant includes an indication informing the UE how to premise the second report and the second report is composed premised on the indication received with the grant.

In a further aspect thereof an exemplary embodiment of this invention provides an apparatus for signaling support for MIMO CSI feedback. The apparatus includes 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: to receive a self-contained first report from a UE at a network access node; to send, from the network access node to the UE, a grant to send a second report; to receive the second report from the UE at the network access node. The second report is composed using a second CB; and to derive frequency selective short-term information from the second report based on the first report. The first report includes wideband long-term CSI and the first report is composed using a first CB, the grant includes an indication informing the UE how to premise the second report and the second report is composed using a second CB.

In another aspect thereof an exemplary embodiment of this invention provides a computer readable medium for signaling support for MIMO CSI feedback. The computer readable medium is tangibly encoded with a computer program executable by a processor to perform actions. The actions include: composing, using a first CB, a self-contained first report including wideband long-term CSI; sending the first report from a UE to a network access node; receiving from the network access node a grant to send a second report; composing, using a second CB, the second report including frequency selective short-term information; and sending the second report to the network access node. The grant includes an indication informing the UE how to premise the second report and the second report is composed premised on the indication received with the grant.

In a further aspect thereof an exemplary embodiment of this invention provides a computer readable medium for signaling support for MIMO CSI feedback. The computer readable medium is tangibly encoded with a computer program executable by a processor to perform actions. The actions include receiving a self-contained first report from a UE at a network access node; sending, from the network access node to the UE, a grant to send a second report; receiving the second report from the UE at the network access node; and deriving frequency selective short- term information from the second report based on the first report. The first report includes wideband long-term CSI and the first report is composed using a first CB, the grant includes an indication informing the UE how to premise the second report and the second report is composed using a second CB

In another aspect thereof an exemplary embodiment of this invention provides an apparatus for signaling support for MIMO CSI feedback. The apparatus includes means for composing, using a first CB, a self-contained first report including wideband long-term CSI. Means for sending the first report from a UE to a network access node are also included. The apparatus also includes means for receiving from the network access node a grant to send a second report. The grant includes an indication informing the UE how to premise the second report. Means for composing, using a second CB, the second report including frequency selective short-term information are also included. The second report is composed premised on the indication received with the grant. The apparatus also includes means for sending the second report to the network access node.

In a further aspect thereof an exemplary embodiment of this invention provides an apparatus for signaling support for MIMO CSI feedback. The apparatus includes means for receiving a self-contained first report from a UE at a network access node. The first report includes wideband long-term CSI and the first report is composed using a first CB. Means for sending, from the network access node to the UE, a grant to send a second report are also included. The grant includes an indication informing the UE how to premise the second report. The apparatus also includes means for receiving the second report from the UE at the network access node. The second report is composed using a second CB. Means for deriving frequency selective short-term information from the second report based on the first report are also included.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects of exemplary embodiments of this invention are made more evident in the following Detailed Description, when read in conjunction with the attached Drawing Figures, wherein:

Figure 1 reproduces Figure 4-1 of 3GPP TS 36.300, and shows the overall architecture of the

EUTRAN system;

Figure 2 shows a simplified block diagram of various electronic devices that are suitable for use in practicing the exemplary embodiments of this invention;

Figure 3 shows an exemplary timing relationship of Report- A and Report-B; Figure 4 is a logic flow diagram that illustrates the operation of a method, and a result of execution of computer program instructions embodied on a computer readable memory, in accordance with the exemplary embodiments of this invention; and

Figure 5 is a logic flow diagram that illustrates the operation of a method, and a result of execution of computer program instructions embodied on a computer readable memory, further in accordance with the exemplary embodiments of this invention.

DETAILED DESCRIPTION

Various exemplary embodiments of this invention relate at least in part to the LTE -Advanced system which will be part of 3GPP LTE Rel-10, and more specifically relate to design aspects of downlink (DL) MIMO operation in LTE -Advanced, taking into account the extension to support 8 Tx antenna ports as well as enhanced Multi-User MIMO (MU-MIMO), which will be part of Rel-10 enhanced DL MIMO.

There are ongoing discussions in 3GPP regarding UE feedback signaling required to support DL MIMO extensions in LTE Rel-10. The exemplary embodiments pertain to those UE signaling aspects required to support flexible, reliable and efficient DL single (SU) and multiuser (MU) MIMO operation in LTE Rel-10 (an beyond).

While various feedback schemes have been presented thus far in 3 GPP RANI, several of these proposed schemes have issues relating to, for example, associated UL feedback overhead and a lack of testability. Considering the needed support for 8 Tx closed-loop (CL) MIMO, it is important to define a versatile feedback design, able to cope with various scenarios and eNB antennas deployments (e.g., cross-polarized and uniform linear array (ULA)), while maintaining a realistic balance between performance gains, UE complexity, testability, overall UL feedback and UL/DL signaling overhead.

The concept proposed by the above referenced Rl- 100256 and Rl- 100051 , based on two codebooks, is potentially promising. However, rather than being a complete proposal this can be better viewed as a framework or a design principle. What remains to be accomplished is to design the actual codebook and signaling details. From the signaling perspective such a dual- codebook approach imposes at least one problem: the frequency selective short-term CSI report is always dependent on the long term CSI report (conditioned on it) and is not self-contained, i.e., it is not usable alone. Hence, it is important that the eNB and UE have at all times a common understanding about the long term CSI used in deriving the short term report, otherwise the short term CSI report will be useless to the eNB. One solution to this problem is to put both the long term CSI and short term CSI in the same feedback report. However, such an approach does not allow decoupling of the two reports, as it may be useful for the eNB to be able to, for example, trigger short-term reports only when the UE is going to be scheduled in SU-MIMO (or, in general, rank>l) mode. Moreover, to fully re- use Rel-8 structures the short-term CSI report should preferably be the same as in Rel-8 (note that re-using Rel-8 codebooks would allow this), hence not including the long-term wideband part. Transmitting two separate reports on the other hand raises the problem that the UE and eNB might not have the same understanding about the long term CSI due to, e.g., uplink feedback channel errors.

A similar problem arises in other feedback mechanisms involving dual codebooks where the

UE report relative to the second codebook is conditioned on the UE report relative to the first codebook. One example relates to the differential/refinement codebooks proposed in the above referenced Rl-100116, Rl-093867 and Rl-091288. These proposals aim at improving the channel state information knowledge at the eNB by improving the CSI provided by a codeword chosen from a base codebook. This is to be achieved by utilizing a differential/refinement codebook that is conditional on the base codeword. In other words, the channel state described by Wl is refined by a codeword W2 into an improved CSI W as, for instance, W=W1 *W2 (or alternatively W is the Kronecker product of Wl and W2), where W2 is conditioned on Wl . The claimed benefit is an improved CSI with no increase in uplink overhead. Again, it can be noted that W2 is not self-contained: one needs information on both Wl and W2 in order to form the resulting transmit precoder

In this case it is obvious that Wl and W2 should not be put in the same report: typically one would obtain the performance of an N-bit base codebook + N-bit differential codebook (or better) by utilizing just one 2N-bit codebook. Hence, the overhead reduction provided by such schemes is lost if the two codewords are placed in the same report. Rather one should, for example, time-multiplex between Wl and W2. However, this again raises the issue of the possibility of mismatched knowledge between the UE and eNB concerning Wl.

The approaches described above are a few non-limiting examples of possible UE feedback in support of DL SU-/MU-MIMO. In more general terms, it is likely that a goal of the feedback framework for LTE Rel-10 (and beyond) will be to increase the feedback accuracy itself. The UE feedback with multiple CSI (PMI) /CQI reports is one generic way to achieve this goal. The reports themselves may be possibly of different types and/or purposes, and may be self- contained or not. Various exemplary embodiments of this invention pertain to signaling support for such modular UE feedback concepts with multiple CSI (PMI)/CQI reports, and more specifically pertain to how to make the two (or more) reports independent of one another, while preserving reliability, e.g., such that conditional CSI report(s) is (are) reported based on a correct assumption concerning the self-contained baseline report.

As was noted above, the use of dual codebook schemes has been suggested. However, these previous and other proposals have not suggested how to achieve the detailed signaling in support of efficient DL SU-/MU-MIMO operation.

Before describing in further detail various exemplary embodiments of this invention, reference is made to Figure 2 for illustrating a simplified block diagram of various electronic devices and apparatus that are suitable for use in practicing various exemplary embodiments of this invention. In Figure 2 a wireless network 1 is adapted for communication over a wireless link 1 1 with an apparatus, such as a mobile communication device which may be referred to as a UE 10, via a network access node, such as a Node B (base station), and more specifically an eNB 12. The network 1 may include a network control element (NCE) 14 that may include the MME/SGW functionality shown in Figure 1, and which provides connectivity with a further network, such as a telephone network and/or a data communications network (e.g., the internet).

The UE 10 includes a controller, such as a computer or a data processor (DP) 10A, a computer-readable memory medium embodied as a memory (MEM) 10B that stores a program of computer instructions (PROG) IOC, and a suitable wireless interface, such as radio frequency (RF) transceiver 10D for bidirectional wireless communications with the eNB 12 via one or more antennas 11 A.

The eNB 12 also includes a controller, such as a computer or a data processor (DP) 12 A, a computer-readable memory medium embodied as a memory (MEM) 12B that stores a program of computer instructions (PROG) 12C, and a suitable wireless interface, such as RF transceiver 12D for communication with the UE 10 via a plurality of antennas 11B (e.g., possibly 8 Tx antennas). The eNB 12 is coupled via a data/control path 13 to the NCE 14. The path 13 may be implemented as the SI interface shown in Figure 1. The eNB 12 may also be coupled to another eNB via data/control path 15, which may be implemented as the X2 interface shown in Figure 1.

The NCE 14 includes a controller, such as a computer or a data processor (DP) 14A, a computer-readable memory medium embodied as a memory (MEM) 14B that stores a program of computer instructions (PROG) 14C.

For the purposes of describing various exemplary embodiments of this invention the UE 10 may be assumed to also include a MIMO feedback (FB) functionality 10E that operates in accordance with various exemplary embodiments of this invention, and the eNB 12 includes a

MIMO functionality 12E that is responsive to MIMO FB reporting received from the UE 10 as described below. It can also be assumed that the UE 10 and eNB 12 each store a copy of any relevant codebooks, such as the codebooks Wl and W2 10F and 12F shown as stored in the memories 10B and 12B, respectively.

At least the PROGs IOC and 12C are assumed to include program instructions that, when executed by the associated DP, enable the device to operate in accordance with various exemplary embodiments of this invention, as will be discussed below in greater detail. That is, various exemplary embodiments of this invention may be implemented at least in part by computer software executable by the DP 10A of the UE 10 and/or by the DP 12A of the eNB 12, or by hardware, or by a combination of software and hardware (and firmware).

In general, the various embodiments of the UE 10 can include, but are not limited to, cellular telephones, 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 computer readable MEMs 10B and 12B 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. The DPs 10A and 12A 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 architectures, as non-limiting examples. The wireless interfaces (e.g., RF transceivers 10D and 12D) may be of any type suitable to the local technical environment and may be implemented using any suitable communication technology such as individual transmitters, receivers, transceivers or a combination of such components.

In accordance with various exemplary embodiments of this invention, there is defined the signaling to enable a CSI/CQI reporting scheme assuming multiple and possibly different reports in support of DL SU-/MU-MIMO operation in, for example, LTE Rel-10 (and beyond). The signaling scheme preserves the reliability in the signaling, e.g., the common understanding about the CSI between the eNB 12 and the UE 10. CSI is to be understood in this context in a broad sense as including, for example, PMI and transmission rank (RI).

More specifically, the exemplary embodiments provide a generic feedback signaling comprised of two reports (which can be referred to for convenience as Report-A and Report-B), and also provide DL control signaling to enable the combined usage of Report-A and Report-B that avoids issues with error propagation when one of the reports is erroneously received.

Two types of CSI feedback reports are thus described below.

Report-A: This first type of UE 10 report may be seen as a base report (with respect to other types of reports) on which the Report-B is conditioned. Report-A may be configured to be transmitted by the UE 10 over the UL. For example, in the non-limiting case of LTE Rel-10, several signaling alternatives for transmitting the report can include:

periodically on the PUCCH-in this case there will most likely be no error protection (no error detection/correction capability, e.g., no use of a CRC);

periodically on the PUSCH-in this case the CRC protection will most likely be applied; and aperiodically using the PUSCH-again in this case the Report-A will be most likely CRC protected.

The Report-A is preferably be self-contained (i.e., it is usable by the eNB 12 as is without additional information from other reports) in the sense that it allows for both MU-MIMO and SU-MIMO operation with at least rank = 1. The Report-A includes at least:

an index pointing to a preferred wideband precoder (PMI) in the long term codebook Wl, and

a corresponding wideband CQI assuming, e.g., open- loop rank-1 spatial multiplexing (e.g. via pre-defined precoder cycling) is performed over the short term codebook W2.

In a case where the precoder Wl is not self-contained by nature, the UE 10 may still compute and report the corresponding CQI(s) under a predefined assumption on the other type(s) of report(s) which would make the entire Report-A self-contained. One non-limiting example of such a Report-A is a wideband CSI report representing long term channel characteristics.

Additionally, it is possible to report the wideband PMI from the W2 codebook. The reported CQI applies to the combination of the reported Wl and an assumption on PMI(s) from the W2 codebook (either implicit as for open-loop, or explicitly reported such as wideband PMI from W2 codebook) leading to the self-contained Report-A. Furthermore, the report based on the Wl codebook may also contain frequency selective information concerning CQI, PMI and RI. As another example, this could present the baseline codeword as in the differential/refinement codebook schemes mentioned above (e.g., as presented in Rl- 100116, Rl-093867 and Rl-091288. referenced above).

The Report-B is conditioned upon Report-A and, hence, is not herein considered to be self- contained. It is requested by the eNB 12 on a per need basis (e.g., as an aperiodic CQI report).

The UE 10 derives Report-B under the hypothesis that the CSI from Report-A is being used as the transmit precoder at the eNB 12. A non-limiting example for Report-B is to consider a frequency selective short term CSI report, as also mentioned in Rl- 100256 and Rl- 100051 dual codebook proposal. In the case of two or four eNodeB antenna ports the structure of this report may directly correspond to the Aperiodic CQI defined for LTE Rel-8. Hence there is not a strict need to specify any additional signaling mechanisms. In case an enhanced feedback granularity is needed, new and larger 2-Tx and 4-Tx codebooks can be specified with a corresponding CSI report, but the principle remains the same as for LTE Rel-8. A difference compared to LTE Rel- 8 is that the UE 10 calculates the short term report assuming that the eNB 12 uses Wl as the wideband precoder.

This approach may also be viewed as corresponding to codeword(s) chosen from a differential/refinement codebook, conditioned on the baseline codeword.

Described now is the associated DL control signaling.

The DL control signaling supports the dual report operation in order to avoid error propagation in the case where the reception and/or decoding of the Report-A fails. When triggering the UE 10 to transmit Report-B, the eNB 12 sends to the UE 10 its current understanding of Report-A, and the UE 10 should then make its selection of Report-B based on this information. At least the following two cases can be distinguished:

Case A: Report-A is not CRC protected over the UL (e.g., as typically in the PUCCH case in the context of LTE). In this case the eNB 12 cannot know whether it has decoded the Report-A correctly. In order to mitigate any issues that can arise from this uncertainty the eNB 12 signals the CSI from Report-A (e.g., the long term PMI from the Wl codebook with an expected payload of 4-5 bits) explicitly to the UE 10 (e.g., in an UL grant that is used to trigger the sending of the Report-B, or by using some other mechanism).

Case B: Report-A is CRC protected over the UL (e.g., as typically in the PUSCH case in the context of LTE). In this case the eNB 12 can determine if an error occurs upon reception of the Report-A. Hence it is sufficient to add, for example, a one or two-bit indicator or confirmation to the indication (e.g., the UL grant) used for requesting the Report-B from the UE 10. The indication signaling can thus indicate to the UE 10 whether the last transmitted Report-A was correctly received by the eNB 12. If the reception of Report-A was successful, the UE 10 derives the Report-B under the assumption of the latest sent Report-A. If the reception of the last Report- A by the eNB 12 has failed, there is a pre-defined "fall-back" assumption on which kind of hypothesis the UE 10 should use for deriving Report-B. For example, the UE 10 can assume the last correctly received Report-A is used in the calculation of Report-B (e.g., the last Report-A that was acknowledged as being correctly received by the eNB 12), or it can assume some predefined open-loop mechanism.

One example of a predefined open- loop mechanism is to perform open- loop rank-1 spatial multiplexing over the short term codebook W2 (e.g. as in LTE Rel-8 via pre-defined precoder cycling) and report the corresponding CQI. The latter applies to the combination of the reported Wl and implicit/pre-defined assumption on open-loop precoding over the codebook W2. As an alternative to a predefined open-loop mechanism it is possible to report a wideband PMI from the W2 codebook explicitly in Report-A together with the long term channel properties from codebook Wl . The reported CQI then applies to the combination of the reported Wl and wideband PMI from the W2 codebook leading to a self-contained Report-A.

For convenience, the dual codebook proposal of Rl- 100256 and Rl- 100051 may be assumed to be in use, and the following example then is based on this (non- limiting) assumption.

The signaling framework in this case can be described with the following distinct steps, as shown in Figure 3.

Step 1. (Not shown in Figure 3) The eNodeB 12 configures via RRC signaling the UE 10 reporting parameters for both Report-A (e.g., periodic long term CSI/CQI report and corresponding PUCCH resources, or periodic or aperiodic PUSCH CQI, etc.) and Report-B (e.g., a Rel-8 similar aperiodic reporting mode).

Step 2. The UE 10 measures the DL channel from, e.g., the common RS and/or CSI-RS, derives the Report-A CSI. For example, this can include the long term CSI information in the form of the wideband PMI from the Wl codebook, and the corresponding CQI (e.g., wideband, assuming rank-1 open- loop precoding over the W2 codebook or an explicitly signaled assumption on the wideband PMI from the W2 codebook. The UE 10 transmits Report-A to the eNodeB 12 over the UL (e.g., on the PUCCH resources given in the RRC configuration, or the PUSCH resources indicated in the aperiodic or periodic CQI procedure).

Step 3. The eNodeB 12 sends to the UE 10 a request to transmit Report-B (e.g., a command via PDCCH UL grant to transmit an aperiodic CSI report on the PUSCH resources indicated in the UL grant) together with one of the following: a. An explicit indication of the Report-A upon which to condition the requested Report-B

(e.g., an explicit indication of the wideband PMI from Wl to condition upon for deriving a short term frequency selective PMIs from codebook W2). The explicit signaling of the hypothesis on Report-A resolves the potential issues related to the Report-B not being self-contained, whenever the transmission of Report-B is requested the UE 10 is signaled simultaneously with the hypothesis on Report-A to use as a basis for deriving Report-B.

b. A one-bit indicator indicating whether the eNodeB 12 correctly received the last Report-A Step 4. Following the request to transmit Report-B, the UE 10 sends Report-B to the eNodeB

12 over the UL (e.g. on the resources indicated in the triggering UL grant) sent in Step 3. The contents of Report-B are derived conditioned on the hypothesis on Report-A signaled earlier by eNodeB 12 together with its request for Report-B. For example, from the format point of view the report can be exactly the same as defined in LTE Rel-8. A difference is that the UE 10 assumes the eNodeB 12 will use the signaled information on the wideband PMI from the Wl codebook as assumed "base" precoder for the long term (e.g., wideband) precoding, while deriving the frequency selective short term CSI from the W2 codebook and associated CQI(s) for Report-B

Step 5. (Not visible in Figure 3) After receiving the Report-B the eNodeB 12 may combine the information from the Report-A and Report-B to derive the optimum precoding scheme and precode the downlink transmission accordingly.

Note that the steps 3, 4 and 5 may be repeated multiple times as shown in Figure 3, assuming that the update rate of Report-A is sufficiently low.

It should be appreciated that the use of these exemplary embodiments provides a number of technical effects and technical advantages.

For example, the structured and modular design makes the disclosed technique easy to standardize and implement. Further, the Report-A is usable also as a stand-alone report capable of providing good performance for a MU-MIMO or rank-1 SU-MIMO UE 10. In addition, the Report-A can be seen as a direct enhancement to MU-MIMO (as in correlated scenarios it serves as a beam selector), hence enhancing the ability to provide improved MU-MIMO performance as compared to conventional single codebook based implicit (PMI-based) UE feedback in LTE Rel- 8. In addition, signaling of the Wl information or the one-bit indicator in the PDCCH UL grant removes the possibility for error propagation due to erroneous reception of Report-A. Furthermore, the use of the explicit signaling of Wl enables the eNB 12 to override the recommendation of the UE 10 regarding Wl when deemed necessary. Also, new aperiodic CSI formats are not needed to be defined for W2, as the existing (e.g., Rel-8) aperiodic CSI formats may be reused, assuming the long term precoder given in Report-A. As a still further technical effect and advantage, optimization of the short term feedback is possible by allowing improved Report-B definitions (for 2- and 4-Tx antenna configurations at the eNB 12). Furthermore, and as compared to joint signaling of Wl and W2, the use of these exemplary embodiments has the significant benefit of maintaining the UE 10 CSI calculation latency budget at the same level as in LTE Rel-8, thereby avoiding a need to perform excessive computation operations to derive CSI.

Based on the foregoing it should be apparent that various exemplary embodiments of this invention provide a method, apparatus and computer program(s) to provide enhanced MIMO operation with enhanced, efficient and reliable feedback signaling.

Figure 4 is a logic flow diagram that illustrates the operation of a method, and a result of execution of computer program instructions, in accordance with various exemplary embodiments of this invention. In accordance with these exemplary embodiments a method performs, at Block 4A, a step of composing, using a first codebook, a self-contained first report comprising wideband long-term channel state information. At Block 4B there is a step of sending the first report from a user equipment to a network access node. At Block 4C these is a step of receiving from the network access node a grant to send a second report, where the grant is comprised of an indication of whether the first report was correctly received by the network access node. At Step 4D there is a step of composing, using a second codebook, the second report comprising frequency selective short-term information, where the second report is composed premised on the indication received with the grant. At Block 4E there is a step of sending the second report to the network access node.

In accordance with the method as shown in Figure 4, wherein composing the second report is conditioned on an assumption that channel state information that comprises part of the first report is being used as a transmit precoder at the network access node.

In accordance with the method as shown in Figure 4, wherein the first report is sent with error detection/correction.

In accordance with the method as shown in Figure 4, wherein the first report comprises an index pointing to a preferred wideband precoder (precoding matrix indicator) in the first codebook and a corresponding wideband channel quality indicator.

In accordance with the method as described in the preceding paragraph, wherein the first report assumes open- loop rank-1 spatial multiplexing is performed over the second codebook.

In accordance with the method as described in the preceding paragraph, wherein the wideband precoding matrix indicator is reported from the second codebook. In accordance with the method as described in the preceding paragraphs, wherein the reported channel quality indicator is based on an assumption on precoding matrix indicator(s) from the second codebook.

In accordance with the method as described in the preceding paragraphs, wherein the first report comprises frequency selective information concerning the channel quality indicator, the precoding matrix indicator and a rank indicator.

In accordance with the method as described in Figure 4, wherein the first report presents a baseline codeword in a differential/refinement codebook.

In accordance with the method as described in Figure 4, wherein the second report comprises a frequency selective short term channel state information report.

In accordance with the method as described in the preceding paragraph, wherein the structure of the second report directly corresponds to an aperiodic channel quality indicator defined for LTE Rel-8.

In accordance with the method as described in Figure 4, wherein the first report is sent without error detection/correction, and where the indication received with the grant comprises information that formed a part of the first report.

In accordance with the method as described in the preceding paragraph, wherein the information comprises a long term precoding matrix indicator.

In accordance with the method as described in Figure 4, wherein the first report is sent with error detection/correction, and where the indication received with the grant comprises information specifying whether the last transmitted first report was correctly received by the network access node.

In accordance with the method as described in the preceding paragraph, wherein if the information specifies that the last transmitted first report was correctly received, then the second report is composed premised on information contained in the last transmitted first report, while if the information specifies that the last transmitted first report was not correctly received, then the second report is composed premised on information contained in a previously transmitted first report that the network access node has previously acknowledged as being correctly received.

In accordance with the method as described in Figure 4, wherein after the first report is sent a plurality of grants are aperiodically received for triggering the user equipment to compose and send individual ones of a plurality of second reports to the network access node.

Various exemplary embodiments of this invention also encompass a tangible computer- readable memory medium that stores computer software code comprised of instructions that, when executed by at least one data processor, result in performance of the various method steps described above with respect to Figure 4. The computer-readable memory medium may be a non-transitory medium, for example, RAM, ROM, flash memory media, magnetic memory media, optical memory media, etc.

Figure 5 is a logic flow diagram that illustrates the operation of a method, and a result of execution of computer program instructions, further in accordance with various exemplary embodiments of this invention. In accordance with these exemplary embodiments a method performs, at Block 5A, a step of composing, using a first codebook, a self-contained first report comprising wideband long-term channel state information. At Block 5B there is a step of sending the first report from a user equipment to a network access node. At Block 5C these is a step of receiving from the network access node a grant to send a second report, where the grant is comprised of an indication of which codeword from the first codebook to assume when composing the second report. At Step 5D there is a step of composing, using a second codebook, the second report comprising frequency selective short-term information, where the second report is composed premised on the indication received with the grant. At Block 5E there is a step of sending the second report to the network access node.

An exemplary embodiment in accordance with this invention is a method for signaling support for MIMO CSI feedback. The method includes composing (e.g., by a processor), using a first CB, a self-contained first report including wideband long-term CSI. Sending (e.g., by a transmitter) the first report from a UE to a network access node is also included in the method. The method also includes receiving (e.g., by a receiver) from the network access node a grant to send a second report. The grant includes an indication informing the UE how to premise the second report. Composing (e.g., by a processor), using a second CB, the second report including frequency selective short-term information is also included in the method. The second report is composed premised on the indication received with the grant. The method also includes sending (e.g., by a transmitter) the second report to the network access node.

In a further exemplary embodiment of the method above, the indication is an indication of whether the first report was correctly received by the network access node. The second report is composed premised on information provided in the first report.

In another exemplary embodiment of the method above, the indication is an indication of which codeword from the first CB to assume when composing the second report.

In a further exemplary embodiment of the method above, composing the second report is conditioned on an assumption that CSI that includes part of the first report is being used as a transmit precoder at the network access node. In another exemplary embodiment of the method above, the first report is sent with error detection/ correction.

In a further exemplary embodiment of the method above, the first report includes an index pointing to a preferred wideband precoder (e.g., a PMI) in the first CB and a corresponding wideband CQL The first report may assume open- loop rank-l spatial multiplexing is performed over the second CB. Also, the wideband PMI may be reported from the second CB.

In another exemplary embodiment of any one of the methods above, a reported CQI is based on an assumption on at least one PMI from the second CB.

In a further exemplary embodiment of any one of the methods above, the first report includes frequency selective information concerning a CQI, the PMI and a RI.

In another exemplary embodiment of the method above, the first report presents a baseline codeword in a differential/refinement CB.

In a further exemplary embodiment of the method above, the second report includes a frequency selective short term CSI report. The structure of the second report may directly correspond to an aperiodic CQI.

In another exemplary embodiment of the method above, the first report is sent without error detection/correction. The indication received with the grant includes information that formed a part of the first report. The information may include a long term PMI.

In a further exemplary embodiment of the method above, the first report is sent with error detection/correction. The indication received with the grant includes information specifying whether the last transmitted first report was correctly received by the network access node. If the information specifies that the last transmitted first report was correctly received, then the second report may be composed premised on information contained in the last transmitted first report, while if the information specifies that the last transmitted first report was not correctly received, then the second report may be composed premised on information contained in a previously transmitted first report that the network access node has previously acknowledged as being correctly received.

In another exemplary embodiment of the method above, after the first report is sent a plurality of grants are aperiodically received for triggering the UE to compose and send individual ones of a plurality of second reports to the network access node.

A further exemplary embodiment in accordance with this invention is a method for signaling support for MIMO CSI feedback. The method includes receiving (e.g., by a receiver) a self- contained first report from a UE at a network access node. The first report includes wideband long-term CSI and the first report is composed using a first CB. Sending (e.g., by a transmitter), from the network access node to the UE, a grant to send a second report is also included in the method. The grant includes an indication informing the UE how to premise the second report. The method also includes receiving (e.g., by a receiver) the second report from the UE at the network access node. The second report is composed using a second CB. Deriving (e.g., by a processor) frequency selective short-term information from the second report based on the first report is also included in the method.

In another exemplary embodiment of the method above, the indication is an indication of whether the first report was correctly received by the network access node.

In a further exemplary embodiment of the method above, the indication is an indication of which codeword from the first CB to assume when composing the second report.

In another exemplary embodiment of the method above, the first report is received with error detection/ correction.

In a further exemplary embodiment of the method above, the first report includes an index pointing to a preferred wideband precoder (e.g., a PMI) in the first CB and a corresponding wideband CQI. The first report may assume open- loop rank-1 spatial multiplexing is performed over the second CB. Also, the wideband PMI may be reported from the second CB.

In another exemplary embodiment of any one of the methods above, a reported CQI is based on an assumption on at least one PMI from the second CB.

In a further exemplary embodiment of any one of the methods above, the first report includes frequency selective information concerning a CQI, the PMI and a RI.

In another exemplary embodiment of the method above, the first report presents a baseline codeword in a differential/refinement CB.

In a further exemplary embodiment of the method above, the second report includes a frequency selective short term CSI report. The structure of the second report may directly correspond to an aperiodic CQI.

In another exemplary embodiment of the method above, the first report is received without error detection/correction, and the indication sent with the grant includes information that formed a part of the first report. The information may include a long term PMI.

In a further exemplary embodiment of the method above, the first report is sent with error detection/correction, and the indication received with the grant includes information specifying whether the last transmitted first report was correctly received by the network access node.

In another exemplary embodiment of the method above, after the first report is received a plurality of grants are aperiodically sent for triggering the UE to compose and send individual ones of a plurality of second reports to the network access node. A further exemplary embodiment in accordance with this invention is an apparatus for signaling support for MIMO CSI feedback. The apparatus includes 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: to compose, using a first CB, a self-contained first report including wideband long-term CSI; to send the first report from a UE to a network access node; to receive from the network access node a grant to send a second report; to compose, using a second CB, the second report including frequency selective short-term information; and to send the second report to the network access node. The grant includes an indication informing the UE how to premise the second report and the second report is composed premised on the indication received with the grant.

In another exemplary embodiment of the apparatus above, the indication is an indication of whether the first report was correctly received by the network access node. The at least one memory and the computer program code are further configured to cause the apparatus to compose the second report premised on information provided in the first report.

In a further exemplary embodiment of the apparatus above, the indication is an indication of which codeword from the first CB to assume when composing the second report.

In another exemplary embodiment of the apparatus above, the at least one memory and the computer program code are further configured to cause the apparatus to compose the second report conditioned on an assumption that CSI that includes part of the first report is being used as a transmit precoder at the network access node.

In a further exemplary embodiment of the apparatus above, the at least one memory and the computer program code are further configured to cause the apparatus to send the first report with error detection/correction.

In another exemplary embodiment of the apparatus above, the first report includes an index pointing to a preferred wideband precoder (e.g., a PMI) in the first CB and a corresponding wideband CQL The first report may assume open- loop rank-l spatial multiplexing is performed over the second CB. Also, the wideband PMI may be reported from the second CB.

In a further exemplary embodiment of any one of the apparatus above, a reported CQI is based on an assumption on at least one PMI from the second CB.

In another exemplary embodiment of any one of the apparatus above, the first report includes frequency selective information concerning a CQI, the PMI and a RI.

In a further exemplary embodiment of the apparatus above, the first report presents a baseline codeword in a differential/refinement CB. In another exemplary embodiment of the apparatus above, the second report includes a frequency selective short term CSI report. The structure of the second report may directly correspond to an aperiodic CQI.

In a further exemplary embodiment of the apparatus above, the at least one memory and the computer program code are further configured to cause the apparatus to send the first report without error detection/correction, and the indication received with the grant includes information that formed a part of the first report. The information may include a long term PMI.

In another exemplary embodiment of the apparatus above, the at least one memory and the computer program code are further configured to cause the apparatus to send the first report with error detection/correction, and the indication received with the grant includes information specifying whether the last transmitted first report was correctly received by the network access node.

In a further exemplary embodiment of the apparatus above, the at least one memory and the computer program code are further configured to cause the apparatus to compose the second report premised on information contained in the last transmitted first report if the information specifies that the last transmitted first report was correctly received. The at least one memory and the computer program code are further configured to cause the apparatus to compose the second report premised on information contained in a previously transmitted first report that the network access node has previously acknowledged as being correctly received if the information specifies that the last transmitted first report was not correctly received.

In another exemplary embodiment of the apparatus above, the at least one memory and the computer program code are further configured to cause the apparatus to receive aperiodically, after the first report is sent, a plurality of grants for triggering the UE to compose and send individual ones of a plurality of second reports to the network access node.

In a further exemplary embodiment of any one of the apparatus above, the apparatus is embodied on an integrated circuit.

Another exemplary embodiment in accordance with this invention is an apparatus for signaling support for MIMO CSI feedback. The apparatus includes 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: to receive a self-contained first report from a UE at a network access node; to send, from the network access node to the UE, a grant to send a second report; to receive the second report from the UE at the network access node. The second report is composed using a second CB; and to derive frequency selective short-term information from the second report based on the first report. The first report includes wideband long-term CSI and the first report is composed using a first CB, the grant includes an indication informing the UE how to premise the second report and the second report is composed using a second CB.

In a further exemplary embodiment of the apparatus above, the indication is an indication of whether the first report was correctly received by the network access node.

In another exemplary embodiment of the apparatus above, the indication is an indication of which codeword from the first CB to assume when composing the second report.

In a further exemplary embodiment of the apparatus above, the at least one memory and the computer program code are further configured to cause the apparatus to receive the first report with error detection/correction.

In another exemplary embodiment of the apparatus above, the first report includes an index pointing to a preferred wideband precoder (e.g., a PMI) in the first CB and a corresponding wideband CQL The first report may assume open- loop rank-l spatial multiplexing is performed over the second CB. Also, the wideband PMI may be reported from the second CB.

In a further exemplary embodiment of any one of the apparatus above, a reported CQI is based on an assumption on at least one PMI from the second CB.

In another exemplary embodiment of any one of the apparatus above, the first report includes frequency selective information concerning a CQI, the PMI and a RI.

In a further exemplary embodiment of the apparatus above, the first report presents a baseline codeword in a differential/refinement CB.

In another exemplary embodiment of the apparatus above, the second report includes a frequency selective short term CSI report. The structure of the second report may directly correspond to an aperiodic CQI.

In a further exemplary embodiment of the apparatus above, the at least one memory and the computer program code are further configured to cause the apparatus to receive the first report without error detection/correction, and the indication sent with the grant includes information that formed a part of the first report. The information may include a long term PMI.

In another exemplary embodiment of the apparatus above, the at least one memory and the computer program code are further configured to cause the apparatus to send the first report with error detection/correction, and the indication received with the grant includes information specifying whether the last transmitted first report was correctly received by the network access node.

In a further exemplary embodiment of the apparatus above, the at least one memory and the computer program code are further configured to cause the apparatus to aperiodically send, after the first report is received, a plurality of grants for triggering the UE to compose and send individual ones of a plurality of second reports to the network access node.

In another exemplary embodiment of any one of the apparatus above, the apparatus is embodied on an integrated circuit.

A further exemplary embodiment in accordance with this invention is a computer readable medium for signaling support for MIMO CSI feedback. The computer readable medium is tangibly encoded with a computer program executable by a processor to perform actions. The actions include: composing, using a first CB, a self-contained first report including wideband long-term CSI; sending the first report from a UE to a network access node; receiving from the network access node a grant to send a second report; composing, using a second CB, the second report including frequency selective short-term information; and sending the second report to the network access node. The grant includes an indication informing the UE how to premise the second report and the second report is composed premised on the indication received with the grant.

In another exemplary embodiment of the computer readable medium above, the indication is an indication of whether the first report was correctly received by the network access node. The second report is composed premised on information provided in the first report.

In a further exemplary embodiment of the computer readable medium above, the indication is an indication of which codeword from the first CB to assume when composing the second report.

In another exemplary embodiment of the computer readable medium above, composing the second report is conditioned on an assumption that CSI that includes part of the first report is being used as a transmit precoder at the network access node.

In a further exemplary embodiment of the computer readable medium above, the first report is sent with error detection/correction.

In another exemplary embodiment of the computer readable medium above, the first report includes an index pointing to a preferred wideband precoder (e.g., a PMI) in the first CB and a corresponding wideband CQI. The first report may assume open- loop rank-1 spatial multiplexing is performed over the second CB. Also, the wideband PMI may be reported from the second CB.

In a further exemplary embodiment of any one of the computer readable media above, a reported CQI is based on an assumption on at least one PMI from the second CB.

In another exemplary embodiment of any one of the computer readable media above, the first report includes frequency selective information concerning a CQI, the PMI and a RI. In a further exemplary embodiment of the computer readable medium above, the first report presents a baseline codeword in a differential/refinement CB.

In another exemplary embodiment of the computer readable medium above, the second report includes a frequency selective short term CSI report. The structure of the second report may directly correspond to an aperiodic CQI.

In a further exemplary embodiment of the computer readable medium above, the first report is sent without error detection/correction, and the indication received with the grant includes information that formed a part of the first report. The information may include a long term PMI.

In another exemplary embodiment of the computer readable medium above, the first report is sent with error detection/correction, and the indication received with the grant includes information specifying whether the last transmitted first report was correctly received by the network access node. If the information specifies that the last transmitted first report was correctly received, then the second report may be composed premised on information contained in the last transmitted first report, while if the information specifies that the last transmitted first report was not correctly received, then the second report may be composed premised on information contained in a previously transmitted first report that the network access node has previously acknowledged as being correctly received.

In a further exemplary embodiment of the computer readable medium above, after the first report is sent a plurality of grants are aperiodically received for triggering the UE to compose and send individual ones of a plurality of second reports to the network access node.

In another exemplary embodiment of any one of the computer readable media above, the computer readable media is a non-transitory computer readable media (e.g., ROM, RAM, flash media, etc.).

A further exemplary embodiment in accordance with this invention is a computer readable medium for signaling support for MIMO CSI feedback. The computer readable medium is tangibly encoded with a computer program executable by a processor to perform actions. The actions include receiving a self-contained first report from a UE at a network access node; sending, from the network access node to the UE, a grant to send a second report; receiving the second report from the UE at the network access node; and deriving frequency selective short- term information from the second report based on the first report. The first report includes wideband long-term CSI and the first report is composed using a first CB, the grant includes an indication informing the UE how to premise the second report and the second report is composed using a second CB In another exemplary embodiment of the computer readable medium above, the indication is an indication of whether the first report was correctly received by the network access node.

In a further exemplary embodiment of the computer readable medium above, the indication is an indication of which codeword from the first CB to assume when composing the second report.

In another exemplary embodiment of the computer readable medium above, the first report is received with error detection/correction.

In a further exemplary embodiment of the computer readable medium above, the first report includes an index pointing to a preferred wideband precoder (e.g., a PMI) in the first CB and a corresponding wideband CQI. The first report may assume open- loop rank-1 spatial multiplexing is performed over the second CB. Also, the wideband PMI may be reported from the second CB.

In another exemplary embodiment of any one of the computer readable media above, a reported CQI is based on an assumption on at least one PMI from the second CB.

In a further exemplary embodiment of any one of the computer readable media above, the first report includes frequency selective information concerning a CQI, the PMI and a RI.

In another exemplary embodiment of the computer readable medium above, the first report presents a baseline codeword in a differential/refinement CB.

In a further exemplary embodiment of the computer readable medium above, the second report includes a frequency selective short term CSI report. The structure of the second report may directly correspond to an aperiodic CQI.

In another exemplary embodiment of the computer readable medium above, the first report is received without error detection/correction, and the indication sent with the grant includes information that formed a part of the first report. The information may include a long term PMI.

In a further exemplary embodiment of the computer readable medium above, the first report is sent with error detection/correction, and the indication received with the grant includes information specifying whether the last transmitted first report was correctly received by the network access node.

In another exemplary embodiment of the computer readable medium above, after the first report is received a plurality of grants are aperiodically sent for triggering the UE to compose and send individual ones of a plurality of second reports to the network access node.

In a further exemplary embodiment of any one of the computer readable media above, the computer readable media is a non-transitory computer readable media (e.g., ROM, RAM, flash media, etc.). Another exemplary embodiment in accordance with this invention is an apparatus for signaling support for MIMO CSI feedback. The apparatus includes means for composing (e.g., a processor), using a first CB, a self-contained first report including wideband long-term CSI. Means for sending (e.g., a transmitter) the first report from a UE to a network access node are also included. The apparatus also includes means for receiving (e.g., a receiver) from the network access node a grant to send a second report. The grant includes an indication informing the UE how to premise the second report. Means for composing (e.g., a processor), using a second CB, the second report including frequency selective short-term information are also included. The second report is composed premised on the indication received with the grant. The apparatus also includes means for sending (e.g., a transmitter) the second report to the network access node.

In a further exemplary embodiment of the apparatus above, the indication is an indication of whether the first report was correctly received by the network access node. The second report is composed premised on information provided in the first report.

In another exemplary embodiment of the apparatus above, the indication is an indication of which codeword from the first CB to assume when composing the second report.

In a further exemplary embodiment of the apparatus above, composing the second report is conditioned on an assumption that CSI that includes part of the first report is being used as a transmit precoder at the network access node.

In another exemplary embodiment of the apparatus above, the first report is sent with error detection/ correction.

In a further exemplary embodiment of the apparatus above, the first report includes an index pointing to a preferred wideband precoder (e.g., a PMI) in the first CB and a corresponding wideband CQI. The first report may assume open- loop rank-1 spatial multiplexing is performed over the second CB. Also, the wideband PMI may be reported from the second CB.

In another exemplary embodiment of any one of the apparatus above, a reported CQI is based on an assumption on at least one PMI from the second CB.

In a further exemplary embodiment of any one of the apparatus above, the first report includes frequency selective information concerning a CQI, the PMI and a RI.

In another exemplary embodiment of the apparatus above, the first report presents a baseline codeword in a differential/refinement CB.

In a further exemplary embodiment of the apparatus above, the second report includes a frequency selective short term CSI report. The structure of the second report may directly correspond to an aperiodic CQI. In another exemplary embodiment of the apparatus above, the first report is sent without error detection/correction, and the indication received with the grant includes information that formed a part of the first report. The information may include a long term PMI.

In a further exemplary embodiment of the apparatus above, the first report is sent with error detection/correction, and the indication received with the grant includes information specifying whether the last transmitted first report was correctly received by the network access node. If the information specifies that the last transmitted first report was correctly received, then the second report may be composed premised on information contained in the last transmitted first report, while if the information specifies that the last transmitted first report was not correctly received, then the second report may be composed premised on information contained in a previously transmitted first report that the network access node has previously acknowledged as being correctly received.

In another exemplary embodiment of the apparatus above, after the first report is sent a plurality of grants are aperiodically received for triggering the UE to compose and send individual ones of a plurality of second reports to the network access node.

A further exemplary embodiment in accordance with this invention is an apparatus for signaling support for MIMO CSI feedback. The apparatus includes means for receiving (e.g., a receiver) a self-contained first report from a UE at a network access node. The first report includes wideband long-term CSI and the first report is composed using a first CB. Means for sending (e.g., a transmitter), from the network access node to the UE, a grant to send a second report are also included. The grant includes an indication informing the UE how to premise the second report. The apparatus also includes means for receiving (e.g., a receiver) the second report from the UE at the network access node. The second report is composed using a second CB. Means for deriving (e.g., a processor) frequency selective short-term information from the second report based on the first report are also included.

In another exemplary embodiment of the apparatus above, the indication is an indication of whether the first report was correctly received by the network access node.

In a further exemplary embodiment of the apparatus above, the indication is an indication of which codeword from the first CB to assume when composing the second report.

In another exemplary embodiment of the apparatus above, the first report is received with error detection/correction.

In a further exemplary embodiment of the apparatus above, the first report includes an index pointing to a preferred wideband precoder (e.g., a PMI) in the first CB and a corresponding wideband CQL The first report may assume open- loop rank-l spatial multiplexing is performed over the second CB. Also, the wideband PMI may be reported from the second CB.

In another exemplary embodiment of any one of the apparatus above, a reported CQI is based on an assumption on at least one PMI from the second CB.

In a further exemplary embodiment of any one of the apparatus above, the first report includes frequency selective information concerning a CQI, the PMI and a RI.

In another exemplary embodiment of the apparatus above, the first report presents a baseline codeword in a differential/refinement CB.

In a further exemplary embodiment of the apparatus above, the second report includes a frequency selective short term CSI report. The structure of the second report may directly correspond to an aperiodic CQI.

In another exemplary embodiment of the apparatus above, the first report is received without error detection/correction, and the indication sent with the grant includes information that formed a part of the first report. The information may include a long term PMI.

In a further exemplary embodiment of the apparatus above, the first report is sent with error detection/correction, and the indication received with the grant includes information specifying whether the last transmitted first report was correctly received by the network access node.

In another exemplary embodiment of the apparatus above, after the first report is received a plurality of grants are aperiodically sent for triggering the UE to compose and send individual ones of a plurality of second reports to the network access node.

The various blocks shown in Figures 4 and 5 may be viewed as method steps, and/or as operations that result from operation of computer program code stored in a tangible memory medium, and/or as a plurality of coupled logic circuit elements constructed to carry out the associated function(s).

It can be further appreciated that an aspect of various exemplary embodiments of this invention is an apparatus that comprises a processor and a memory including computer program code. The memory and computer program code are configured to, with the processor, cause the apparatus at least to perform composing, using a first codebook, a self-contained first report comprising wideband long-term channel state information; sending the first report from a user equipment to a network access node; receiving from the network access node a grant to send a second report, where the grant is comprised of an indication of whether the first report was correctly received by the network access node; composing, using a second codebook, the second report comprising frequency selective short-term information, where the second report is composed premised on the indication received with the grant; and sending the second report to the network access node.

It can be further appreciated that an aspect of various exemplary embodiments of this invention is an apparatus that comprises means for composing, using a first codebook, a self- contained first report comprising wideband long-term channel state information; means for sending the first report from the apparatus to a network access node; means for receiving from the network access node a grant to send a second report, where the grant is comprised of an indication of whether the first report was correctly received by the network access node; means for composing, using a second codebook, the second report comprising frequency selective short-term information, where the second report is composed premised on the indication received with the grant; and means for sending the second report to the network access node

In general, the various exemplary embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. For example, some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the invention is not limited thereto. While aspects of various exemplary embodiments of this invention may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

It should thus be appreciated that at least some aspects of various exemplary embodiments of the inventions may be practiced in various components such as integrated circuit chips and modules, and that various exemplary embodiments of this invention may be realized in an apparatus that is embodied as an integrated circuit. The integrated circuit, or circuits, may comprise circuitry (as well as possibly firmware) for embodying at least one or more of a data processor or data processors, a digital signal processor or processors, baseband circuitry and radio frequency circuitry that are configurable so as to operate in accordance with various exemplary embodiments of this invention.

Various modifications and adaptations to the foregoing exemplary embodiments of this invention may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. However, any and all modifications will still fall within the scope of the non-limiting and exemplary embodiments of this invention. For example, while the exemplary embodiments have been described above in the context of the LTE-A system, it should be appreciated that the exemplary embodiments of this invention are not limited for use with only this particular type of wireless communication system, and that they may be used to advantage in other wireless communication systems.

It should be noted that the terms "connected," "coupled," or any variant thereof, mean any connection or coupling, either direct or indirect, between two or more elements, and may encompass the presence of one or more intermediate elements between two elements that are "connected" or "coupled" together. The coupling or connection between the elements can be physical, logical, or a combination thereof. As employed herein two elements may be considered to be "connected" or "coupled" together by the use of one or more wires, cables and/or printed electrical connections, as well as by the use of electromagnetic energy, such as electromagnetic energy having wavelengths in the radio frequency region, the microwave region and the optical (both visible and invisible) region, as several non-limiting and non-exhaustive examples.

Further, the various names used for the described parameters (e.g., PMI, CQI, RI, etc.) are not intended to be limiting in any respect, as these parameters may be identified by any suitable names. Further, the various names assigned to different channels (e.g., PUCCH, PUSCH, PDCCH, etc.) are not intended to be limiting in any respect, as these various channels may be identified by any suitable names.

Furthermore, some of the features of the various non-limiting and exemplary embodiments of this invention may be used to advantage without the corresponding use of other features. As such, the foregoing description should be considered as merely illustrative of the principles, teachings and exemplary embodiments of this invention, and not in limitation thereof.