WO2013166714A1

WO2013166714A1 - Complexity restricted feedback for cooperative multipoint operation

Info

Publication number: WO2013166714A1
Application number: PCT/CN2012/075381
Authority: WO
Inventors: Xiaoyi Wang; Klaus Hugl
Original assignee: Nokia Siemens Networks Oy; Nokia Inc
Current assignee: Nokia Solutions and Networks Oy; Nokia Inc
Priority date: 2012-05-11
Filing date: 2012-05-11
Publication date: 2013-11-14
Anticipated expiration: 2014-11-11

Description

COMPLEXITY RESTRICTED FEEDBACK FOR COOPERATIVE

MULTIPOINT OPERATION

TECHNICAL FIELD:

[0001] 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 feedback of channel conditions/channel state information in the context of cooperative multipoint CoMP.

BACKGROUND:

[0002] Coordinated multi-point (CoMP) transmission entails the coordination of multiple distinct transmission points to cooperate in the transmission of substantive data or control information to a single receiving party. Generally the advantages of CoMP are considered to be most pronounced in the downlink (DL) direction, and so for example the CoMP transmission points for a given user equipment (UE) might be a macro cell and a micro/pico cell in the E-UT AN (evolved universal terrestrial access network) system or alternatively different macro cells. The micro/pico cells may each be served by a remote radio head controlled by the eNB in one example deployment. Another example is multiple eNBs (macro E-UTRAN access nodes or base stations).

[0003] For downlink CoMP, different kinds of operations can be envisioned. One example is the case of joint transmission (JT) CoMP, the multiple distinct transmission points jointly transmit the same substantive data or control information to a single receive party. Another example is dynamic point selection (DPS), where a single transmission point for transmission of downlink data or control information to a single receive party is dynamically selected from the set of multiple transmission points. In general, the DL transmission the UE receives may be from multiple transmit antennas, and/or the UE may receive them on multiple receive antennas. Co-located antennas may form one CoMP transmission point, and each distinct CoMP transmission point may be geographically separate from each other CoMP transmission point.

[0004] To facilitate the most effective CoMP, channel state information (CSI) for these multiple radio links needs to be measured by the UE and sent to the network. In E-UTRAN Release 10 the UE measures CSI from channel state information reference signals (CSI-RSs) sent from the network. As Release 10 supports only a single CSI-RS resource to be configured, CoMP operation is not supported in Rel. 10. The UE performs some hypothesis testing on the received CSI-RS before it decides what CSI to report and so there are more computations at the UE than simply computing one CSI candidate value and reporting it. If E-UTRAN Release 1 1 enables CoMP by extending the CSI concept from Release 10 such that each transmission point sends a CSI-RS on its own CoMP downlink channel and the UE is requested to calculate CSI for several CSI-RS resources, the result will be a large increase in the UE's computational requirements. This impacts battery life for the UE, and will require the UE to improve its computational performance in order to report the required computations and measurements of several CSI-RSs in time for the reported CSI to be useful for the next DL CoMP data transmission.

[0005] These and other problems are resolved by the exemplary teachings set forth below. But while the context of 3GPP and E-UTRAN systems are used below for specific examples to better explain these teachings, those contexts are not limiting to the broader teachings and principles which are presented herein.

SUMMARY:

[0006] According to a first exemplary aspect the invention there is a method comprising: selecting one or more feedback modes for each of a plurality of channel state information reference signal resources so as not to exceed a predetermined maximum complexity; and configuring a user equipment with the selected feedback modes.

[0007] According to a second exemplary aspect the invention there is an apparatus comprising: at least one processor and at least one memory including computer program code. In this aspect the at least one memory and the computer program code are configured, with the at least one processor and in response to execution of the computer program code, to cause the apparatus to perform at least: selecting one or more feedback modes for each of a plurality of channel state information reference signal resources so as not to exceed a predetermined maximum complexity; and configuring a user equipment with the selected feedback modes. [0008] According to a third exemplary aspect the invention there is a computer readable memory storing a program of instructions which when executed by at least one processor result in actions comprising: selecting one or more feedback modes for each of a plurality of channel state information reference signal resources so as not to exceed a predetermined maximum complexity; and configuring a user equipment with the selected feedback modes.

[0009] According to a fourth exemplary aspect the invention there is a method comprising: receiving a configuration comprising one or more selected feedback modes for each of a plurality of channel state information reference signal resources; and in response to determining that a complexity for calculating channel state information for all of the selected feedback modes for all of the plurality of channel state information reference signal resources exceeds a predetermined maximum complexity, the method further comprises taking an action other than adopting the received configuration, such as for example disregarding the received configuration as being in error.

[0010] According to a fifth exemplary aspect the invention there is an apparatus comprising: at least one processor and at least one memory including computer program code. In this aspect the at least one memory and the computer program code are configured, with the at least one processor and in response to execution of the computer program code, to cause the apparatus to perform at least: receiving a configuration comprising one or more selected feedback modes for each of a plurality of channel state information reference signal resources; and in response to determining that a complexity for calculating channel state information for all of the selected feedback modes for all of the plurality of channel state information reference signal resources exceeds a predetermined maximum complexity, taking an action other than adopting the received configuration, such as for example disregarding the received configuration as being in error. [0011 ] According to a sixth exemplary aspect the invention there is a computer readable memory storing a program of instructions which when executed by at least one processor result in actions comprising: receiving a configuration comprising one or more selected feedback modes for each of a plurality of channel state information reference signal resources; and in response to determining that a complexity for calculating channel state information for all of the selected feedback modes for all of the plurality of channel state information reference signal resources exceeds a predetermined maximum complexity, taking a further action other than adopting the received configuration, such as for example disregarding the received configuration as being in error.

[0012] According to a seventh exemplary aspect the invention there is a method comprising: for each of a plurality of channel state information reference signal resources, storing in a local memory an association of a respective channel state information reference signal resource with a respective set of allowed feedback modes, in which at least one of the sets has a fewer number of allowed feedback modes than at least one other of the sets; and in response to receiving a configuration that selects, for at least one of the channel state information reference signal resources, a feedback mode that is not in the respectively associated set, the method further comprises taking an action other than adopting the received configuration, such as for example disregarding the received configuration as being in error.

[0013] According to a eighth exemplary aspect the invention there is an apparatus comprising: at least one processor and at least one memory including computer program code. In this aspect the at least one memory and the computer program code are configured, with the at least one processor and in response to execution of the computer program code, to cause the apparatus to perform at least: for each of a plurality of channel state information reference signal resources, storing in a local memory an association of a respective channel state information reference signal resource with a respective set of allowed feedback modes, in which at least one of the sets has a fewer number of allowed feedback modes than at least one other of the sets; and in response to receiving a configuration that selects, for at least one of the channel state information reference signal resources, a feedback mode that is not in the respectively associated set, taking an action other than adopting the received configuration, such as for example disregarding the received configuration as being in error. [0014] According to a ninth exemplary aspect the invention there is a computer readable memory storing a program of instructions which when executed by at least one processor result in actions comprising: for each of a plurality of channel state information reference signal resources, storing in a local memory an association of a respective channel state information reference signal resource with a respective set of allowed feedback modes, in which at least one of the sets has a fewer number of allowed feedback modes than at least one other of the sets; and in response to receiving a configuration that selects, for at least one of the channel state information reference signal resources, a feedback mode that is not in the respectively associated set, taking a further action other than adopting the received configuration, such as for example disregarding the received configuration as being in error.

[0015] These and other aspects are detailed further below.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0016] Figure 1 is a schematic diagram illustrating a heterogeneous radio environment with macro and micro/pico eNBs as the cooperative multipoint transmission points of a transmission to a UE, and is an exemplary radio environment in which embodiments of these teachings may be practiced to advantage.

[0017] Figures 2-3 are prior art tables of respective periodic and aperiodic feedback modes, reproduced from Table 7.2.2-1 and Table 7.2.1- 1 of 3GPP TS 36-213.

[0018] Figure 4 is a process flow diagram from the perspective of a network access node/eNB that illustrates a method, and a result of execution by one or more processors of a set of computer program instructions embodied on a computer readable memory, in accordance with the exemplary embodiments of this invention. [0019] Figure 5 is a simplified block diagram of a UE, a macro eNB and a micro/pico eNB from Figure 1 which are exemplary electronic devices suitable for use in practicing the exemplary embodiments of the invention.

DETAILED DESCRIPTION:

[0020] Consider Figure 1 which is an example radio environment for the below non-limiting examples. There is a heterogeneous network (hetnet) in which the macro and micro eNBs are deployed within proximity of each other and both are cooperatively transmitting to the UE 10; the macro eNB 20 on link 15 and the micro/pico eNB 21 on link 16. By example, this pico node 21 may have been deployed to extend the range of the macro cell, and may be embodied as a remote radio head or as a stand-alone access node under coordination with the macro eNB 20. The macro 20 and pico 21 cells that are used for the CoMP transmissions to the UE 10 thus form a virtual distributed antenna system from the UE's perspective. There are multiple other possible CoMP scenarios, including but not limited to two macro cell transmission points, two pico cell transmission points, and more than two transmission points.

[0021] In the CoMP scenario, the single UE 10 can be configured with multiple CSI-RS resources. Each CSI-RS resource is a parameter set for configuring a set of CSl-RSs, typically only antenna ports of a single transmission point. In the Figure 1 scenario the UE 10 would be configured with a minimum of two, one CSI-RS resource on the macro link 15 and one CSI-RS resource on the micro/pico link 16. But either or both of the eNBs 20, 21 can use more than only one CSI-RS, and the whole of the CSI-RSs that the UE is to measure for one CoMP scenario (one set of transmission points) is termed the CoMP measurement set. The UE 10 should measure each CSI-RS resource and generate CSI feedback.

[0022] The maximum size of the CoMP measurement set is currently under discussion for implementation in E-UTRAN Release 11 ; the maximum size of this measurement set is closely related to UE complexity as implied in the background section above. Since in the near term LTE Release 1 1 is expected to typically utilize two transmission points per CoMP scenario, generally the discussions are whether the maximum size of the CoMP measurement set should be two or three. Generally, each additional CSI-RS in the CoMP measurement set will result in a linear increase to the UE's computational complexity when finding the proper CSIs to signal uplink, because each CSI-RS resource has the similar impact to the UE behavior.

[0023] If three CSI-RS resources are used, they may be from three transmission points or, if from only two, the third CSI-RS may be used to enable the network to obtain some inter-transmission point CSI, such as that set forth in document Rl -121272 by Nokia and Nokia Siemens Networks entitled: UE TRANSPARENT INTER-TP PHASE FEEDBACK (3 GPP TSG-RAN WG1 Meeting #68bis; Jeju, Korea; 24-30 March 2012).

[0024] From the above the inventors have determined that not all CSI-RS resources necessarily impose the same computational burden on the UE. It is not necessary that the UE test as many hypotheses for the inter-transmission point CSI mentioned above as it does for the CSI-RSs on the macro and micro links 15, 16.

[0025] The inventors refined this general insight into the concept of limiting the set of feedback modes from which the network selects some for the UE and for which the UE must compute per CSI-RS resource CSI feedback. As detailed below this serves as a mechanism to restrict the amount of complexity the UE will undertake in calculating its CoMP feedback. As an overview of the principles detailed by example below, for each CSI-RS resource there is a specific set of feedback modes (each set having one or more modes), and a restriction in terms of UE complexity for CoMP specific CSI feedback. Not all potential feedback modes may be allowed for all CSI-RS resources, and so the allowed feedback mode(s) for each CSI-RS resource may be different from one another. The calculations for the UE's CoMP CSI feedback can then be limited in order to restrict complexity at the UE.

[0026] Consider a few examples to more clearly explain this concept. Assume for this example that the maximum size of the CoMP measurement set is three. The first CSI-RS resource allows a selection from the full set of feedback modes. The full set of possible feedback modes in LTE is illustrated in Figure 2 and Figure 3. In Figure 2, the periodic CSI feedback modes are shown, consisting of mode 1-0, 1-1, 2-0 and 2-1 which are to be fed back on PUCCH. In Figure 3, the aperiodic feedback modes are illustrated consisting of mode 1-2, 2-0, 2-2, 3-0 and 3-1. The network is in normal operation allowed to select from the full set of transmission modes with the assumption of selecting at maximum one mode for periodic feedback from the set in Figure 2 and one mode for aperiodic feedback from the set in Figure 3. Looking now at the complexity, having one mode configured for periodic feedback and in addition one mode for aperiodic feedback of course has a higher overhead than just having one mode only (either periodic or aperiodic). Moreover, from a UE complexity point of view not all modes in the set for periodic feedback and not all the modes in the set for aperiodic feedback are equally computationally complex. As an example for periodic feedback, Mode 1-0 only requires the UE to determine a single wideband CQI whereas for Mode 2-0 two or more subband CQIs are need to be calculated. For the related Mode 3-0 of aperiodic feedback, one CQI for each subband needs to be calculated resulting in again much higher computational complexity compared to Mode 1-0 and 2-0.

[0027] For example, in an E-UTRAN deployment with CoMP enabled by Release 11 , for the 1^st CSI-RS resource configured to the UE, the full set of possible feedback modes may be all the feedback modes specified in Release 10 (see Figure 2). The second CSI-RS resource allows in this example only to choose from periodical feedback modes 1 -0, 2-0, and 1-1 (but excluding Mode 2-1 for complexity reasons) and aperiodical feedback modes: 2-0; 3-0 (excluding the other modes from the set). Each feedback mode corresponds to a set of PMI/CQI/RI feedback messages (PMI=precoding matrix index; CQI=channel quality indicator; RI=rank indicator), so for example mode 2-2 means wideband+subband CQI and wideband+subband PMI should be reported. Having these more limited feedback modes for the second CSI-RS resource means that the maximum complexity for the UE for the second CSI-RS resource is lower than that of the first CSI-RS resource. By choosing a CSI-RS resource whose associated set of allowable modes exclude those which require the most computations, the eNB can limit the potential maximum complexity the UE will need to undertake when generating its CSI feedback report.

[0028] Continuing with this same example, assume also there is a third CSI-RS resource which allows only periodical feedback mode 1-0; 2-0; and 1-1 ; and no support for any aperiodical feedback modes. In this case the maximum complexity for the UE arising from CSI feedback operations for the third CSI-RS resources is even smaller than that arising from the second CSI-RS resource, and of course also arising from the first CSI-RS resource where the network has the full flexibility to choose from the full set of periodic and potentially an additional aperiodic feedback modes.

[0029] So for example if we distinguish the three possible CSI-RS resources in the maximum-size measurement set as CSI-RS resource 1 , 2 and 3, the eNB may separately configure each of them for different feedback modes. Which CSI-RS resource support which feedback mode can be specified in written standards.

[0030] In the above example, the UE's potential maximum complexity for each CSI-RS resource is reduced for each subsequent CSI-RS resource described; highest for CSI-RS 1 and lowest for CSI-RS 3. In a further extension of these teachings this characteristic (a per-CSI-RS resource complexity constraint) is used to limit the total potential maximum complexity for a given UE across all the CSI-RS resources. In this manner the eNB can choose the feedback modes so as to limit the potential maximum total complexity at the UE.

[0031 ] The amount of this maximum possible complexity depends on (a) the number of CSI-RS resources; and (b) the number M of independently configured feedback modes for the i-th CSI-RS resource, e.g. if only periodic/aperiodic or periodic as well as aperiodic feedback is configured; and also (c) the FBjnode which is the complexity of the feedback mode selected by the network. The total complexity over all the CSI-RS resources could therefore be given by equation [1] below, and which might be imposed system- wide by a standardized limit that the total complexity C is less than or equal to C max.

^■num. CSI ^■RS ^Mi

[1] In equation [1]: , is the number of different feedbacks the UE needs to generate for the ;^'th CSI-RS resource; FBjnodet which represents the complexity of the feedback mode that is chosen from the set of available feedback modes for the i^th CSI-RS resource; and i indexes from 1 through the total number (num) of CSI-RS resources (so i indexes from 1 through 3 in the above example).

[0032] Consider another example to more clearly explain this concept of limiting the UE's total computations/complexity. If the UE is configured with one CSI-RS resource, then one of any of the periodic and in addition one of any of the aperiodic CSI feedback modes in E-UTRAN Release 10 can be enabled for this CSI-RS resource. For this case the UE's actual complexity, assuming one periodic and one aperiodic CSI feedback mode is configured, is given by Ci__actuai= FB_mode_perioiji_C+ FBjnode_aperi0(n_c. Considering the maximum complexity for the UE arising from the single CSI-RS resource and the availability of the full set is given by Ci__max- max{FBjnode_peri₀dic}⁺ max{FB_mode _aperiod c}* Here the maximum refers to the complexity of the feedback mode selected from the set of available CSI-feedback modes for periodic and aperiodic CSI reporting, respectively. Please again note, that according to Rel. 10 behavior a maximum of one periodic and one aperiodic CSI feedback mode can be configured for the UE.

[0033] In another example assume the UE is configured with two CSI-RS resources. In case all CSI feedback modes in E-UTRAN Release 10 are supported for each CSI-RS resource the maximum complexity out of the possible configured would be given as an example by

[0034] Doubling the maximum potential complexity for the UE compared to the case of a single CSI-RS resource might be not possible, due to the fact that there is a need to restrict the UE complexity for CoMP CSI feedback. In this respect it is proposed to restrict the set of available feedback modes as indicated earlier as an example for the second CSI-RS resource in contrast to allow the full set of CSI feedback modes for both CSI-RS resources in order to not exceed total specified UE complexity. In this case the maximum complexity for the UE could be as an example expressed as C2_max_resiricted⁼fnax{FB_mode_periodic_}+Max{FBjnode_ape +max{FB_mode_peri₀₍ii_C{Set2 jperiodic}}+max{FB jnode_aperi_0dic{Set2 _aperiodic}}. The set of feedback modes in the set thereby is a subset of the full available set of CSI feedback formats in Rel. 10. [0035] As a third example, if the UE is configured with three CSI-RS resources, again further restriction is needed here and only some of the E-UTRAN Release 10 feedback modes may be configured. If for example only periodic feedback with differently restricted sets is allowed for each CSI-RS resource, the resulting maximum potential UE complexity C is then

max{FBjnode_periodi_C{Setl _periodic}} +

+max{FB_mode_pert₀di_c{Set2 _periodic}} +

+max{FB_mode_periodic{Set3 jperiodic}}..

The intention overall is, that the complexity is limited in a way, that none of the potential configurations leads to a case of exceeding the overall allowed CSI complexity for the UE.

[0036] If by some miscommunication the UE received a CSI feedback configuration that exceeds the specified maximum complexity (for example, three CSI-RS resources each with a high-complexity feedback modes for periodic and aperiodic feedback), the UE can treat this as an error configuration rather than attempt to comply.

[0037] The principles of these teachings are more clearly described with reference to the process flow diagram of Figure 4, which also shows internal processes of the eNB 20. At block 402 the eNB selects one or more feedback modes for each of a plurality of CSI-RS resources so as not to exceed a predetermined maximum complexity. By example that predetermined maximum complexity is given above at equation [1], and in an embodiment may be published in a radio standard for the appropriate radio access technology (RAT) so all eNBs using the same RAT use the same maximum. [0038] Then at block 404 of Figure 4, the eNB configures a user equipment with the selected feedback modes, such as via signaling. In some deployments the eNB 20 may coordinate with its other CoMP transmission point for sending of their respective CSI-RS resources on their respective downlinks, and the UE configuration tells if and how the UE is to compute and report its CSI on each as well as what CSI to report.

[0039] Further portions of Figure 4 summarize some of the non-limiting embodiments from above. Blok 406 tells that for at least one of the CSI-RS resources, the selected feedback mode comprises one feedback mode for periodic feedback and/or one feedback mode for aperiodic feedback. But as noted above in some embodiments only periodic feedback will be configured for the UE.

[0040] In one example above there were three CSI-RS resources: a first one of them is associated with all possible feedback modes; a third one of them is associated with a smallest set of feedback modes; and a second one of them is associated with a subset of feedback modes fewer than all possible and greater than the smallest. Block 408 gives the principle behind this a bit more generally. Each of the CSI-RS resources is associated with a respective set of allowed feedback modes; at least one of these sets consists of a fewer number of feedback modes than at least one other of these sets. The larger set may or may not be all of the possible feedback modes and the smaller set may be a subset of the larger set. And as noted above, the eNB can manage the complexity easiest if it excludes from the smaller set one or more of the most complex feedback modes out of all the possible feedback modes or restrains to only request periodic or aperiodic feedback.

[0041] 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 the exemplary embodiments of this invention. The various steps and processes shown in Figure 4 may be viewed as method steps, and/or as operations that result from operation of computer program code embodied on a memory and executed by a processor, and/or as a plurality of coupled logic circuit elements constructed to carry out the associated function(s).

[0042] From the UE 10 perspective, above was described two ways by which these teachings can cause the UE to reject a configuration it receives. In one aspect the UE receives a configuration comprising one or more selected feedback modes for each of a plurality of CSI-RS resources; and in response to the UE determining that a complexity for calculating CSI for all of the selected feedback modes for all of the plurality of CSI-RS resources exceeds a predetermined maximum complexity (i.e., equation [1]), the UE can take some action other than adopting the received configuration, such as for example disregarding the received configuration as being in error. In another aspect the UE has stored in its local memory and for each of a plurality of CSI-RS resources, an association of a respective CSI-RS resource with a respective set of allowed feedback modes. At least one of those sets will have a fewer number of allowed feedback modes than at least one other of those sets. Then if the UE receives a configuration that selects, for at least one of the CSI-RS resources, a feedback mode that is not in the respectively associated set, the UE in response can take an action other than adopting the received configuration, such as for example disregarding the received configuration as being in error.

[0043] Reference is made to Figure 5 for illustrating a simplified block diagram of various electronic devices and apparatus that are suitable for use in practicing the exemplary embodiments of this invention. In Figure 5 a wireless network is adapted for communication over a macro wireless link 15 and a micro/pi co wireless link 1 with an apparatus, such as a mobile communication device which above is referred to as a UE 10, via a macro network access node such as a Node B (base station), and more specifically a macro eNB 20 and a micro/pico eNB 21. The network may include a network control element (NCE) 22 that may include mobility management entity/serving gateway MME/S-GW functionality that is specified for LTE/LTE-A. The NCE 22 also provides connectivity with a different network, such as a publicly switched telephone network and/or a data communications network (e.g., the Internet). While only one wireless link 15, 16 is shown for each transmission point 20, 21 , each representing multiple logical and physical channels.

[0044] 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 radio frequency (RF) transmitter 10D and receiver 10E for bidirectional wireless communications with the eNBs 20, 21 via one or more antennas (two shown). The UE 10 may have one or more than one radios 10D for communicating with the eNBs 20, 21. [0045] The macro eNB 20 also includes a controller, such as a computer or a data processor (DP) 20A, a computer-readable memory medium embodied as a memory (MEM) 20B that stores a program of computer instructions (PROG) 20C, and suitable RF transmitters and receivers (two shown as 20D and 20E) for communication with the UE 10 via one or more antennas (also two shown). The macro eNB 20 is coupled via a data / control path 30 to the NCE 22. The path 30 may be implemented as the SI interface known in the E-UTRAN system. The macro eNB 20 may also be coupled to the micro/pico eNB 21 via data / control path 17, which may be implemented as the X2 interface known in the E-UTRAN system.

[0046] For completeness, the micro/pico eNB 21 is also shown to include a data processor (DP) 21 A, a computer-readable memory medium embodied as a memory (MEM) 2 IB that stores a program of computer instructions (PROG) 21C, and suitable RF transmitters 21 D and receivers 21 E for communication with the UE 10 via one or more antennas (two shown). The NCE 22 also has a DP 22A, a MEM 22B storing a PROG 22C and a modem 22D for communicating over the data/control link 30 with the macro eNB.

[0047] At least one of the PROGs IOC and 20C is assumed to include program instructions that, when executed by the associated DP, enable the device to operate in accordance with the exemplary embodiments of this invention, as detailed above. That is, the exemplary embodiments of this invention may be implemented at least in part by computer software executable by the DP 1 OA of the UE 10 and/or by the DP 20A of the macro eNB 20, or by hardware, or by a combination of software and hardware (and firmware).

[0048] For the purposes of describing the exemplary embodiments of this invention the macro eNB 20 may be assumed to also include a program or algorithm to cause the macro eNB 20 to configure the UE with feedback modes for CSI-RS resources so that a (predetermined) total maximum complexity for the UE is not exceeded as shown at 20G. Inherent within the eNB's feedback mode selection is that for a given CSI-RS resource it can select a periodic (and if it chooses also an aperiodic) feedback mode only from the set of allowable modes which is associated with a given CSI-RS resource, and not all (if any) sets include all of the possible feedback modes. Further the UE 10 includes a program or algorithm to cause the UE 10 to look up from its memory the feedback mode set that is associated with each CSI-RS resource it receives, and to check whether a CSI-RS configuration (with the selected feedback modes) it receives from the eNB is in error as shown at 10G, according to the non- limiting examples presented above. Two examples above show the UE checking the total complexity, and checking that the feedback mode which the eNB configured the UE for a given CSI-RS resource is one of the allowable feedback modes for that CSI-RS resource. [0049] 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.

[0050] The computer readable MEMs 10B and 20B 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 20A 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 a multicore processor architecture, as non-limiting examples.

[0051] 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 embodied firmware or software which maybe executed by a controller, microprocessor or other computing device, although the invention is not limited thereto. While various aspects of the 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 maybe implemented in, as non-limiting examples, hardware, embodied software and/or firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof, where general purpose elements may be made special purpose by embodied executable software.

[0052] It should thus be appreciated that at least some aspects of the exemplary embodiments of the inventions may be practiced in various components such as integrated circuit chips and modules, and that the 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 the exemplary embodiments of this invention.

[0053] While the exemplary embodiments have been described above in the context of the E-UTRAN system, it should be appreciated that the exemplary embodiments of this invention are not limited for use with only this one particular type of wireless communication system that uses CoMP and/or different feedback modes for CSI-RS resources. [0054] 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.

Claims

WHAT IS CLAIMED IS:

1. A method comprising:

selecting one or more feedback modes for each of a plurality of channel state information reference signal resources so as not to exceed a predetermined maximum complexity; and

configuring a user equipment with the selected feedback modes. 2. The method according to claim 1 , in which the selected feedback modes comprise, for at least one of the channel state information reference signal resources, one feedback mode for periodic feedback and one feedback mode for aperiodic feedback.

3. The method according to claim 1, in which each of the channel state information reference signal resources is associated with a respective set of allowed feedback modes, and:

at least one of the sets consists of a fewer number of feedback modes than at least one other of the sets.

4. The method according to claim 3, in which at least a most complex feedback mode out of all possible feedback modes is excluded from the said at least one of the sets.

5. The method according to any one of claims 1 through 4, in which the predetermined maximum complexity is C, where

num CSI-RS M¾

rnoae_im

f =l m=l

where: M_t is a total number of different feedbacks the user equipment needs to generate for the i^th channel state information reference signal resource;

FBjnode m represents complexity of the m^th selected feedback mode for the z^'th channel state information reference signal resource;

m indexes from 1 through M,- ; and i indexes from 1 through all of the plurality of the channel state information reference signal resources.

6. An apparatus comprising:

at least one processor and at least one memory including computer program code;

in which the at least one memory and the computer program code are configured, with the at least one processor and in response to execution of the computer program code, to cause the apparatus to perform at least:

configuring a user equipment with the selected feedback modes.

7. The apparatus according to claim 6, in which the selected feedback modes comprise, for at least one of the channel state information reference signal resources, one feedback mode for periodic feedback and one feedback mode for aperiodic feedback.

8. The apparatus according to claim 6, in which each of the channel state information reference signal resources is associated with a respective set of allowed feedback modes, and:

9. The apparatus according to claim 8, in which at least a most complex feedback mode out of all possible feedback modes is excluded from the said at least one of the sets.

10. The apparatus according to any one of claims 6 through 9, in which the predetermined maximum complexity is C, where

num. CSI-RS Mi

where: ,· is a total number of different feedbacks the user equipment needs to generate for the ;^lh channel state information reference signal resource;

FBjnode m represents complexity of the m^th selected feedback mode for the i^lh channel state information reference signal resource;

m indexes from 1 through ,- ; and

/ indexes from 1 through all of the plurality of the channel state information reference signal resources.

1 1. A computer readable memory storing a program of instructions which when executed by at least one processor result in actions comprising:

configuring a user equipment with the selected feedback modes.

12. The computer readable memory according to claim 1 1, in which each of the channel state information reference signal resources is associated with a respective set of allowed feedback modes, and:

13. A method comprising:

receiving a configuration comprising one or more selected feedback modes for each of a plurality of channel state information reference signal resources;

in response to determining that a complexity for calculating channel state information for all of the selected feedback modes for all of the plurality of channel state information reference signal resources exceeds a predetermined maximum complexity, taking an action other than adopting the received configuration. 14. The method according to claim 13, in which the action comprises disregarding the received configuration as being in error. apparatus comprising: at least one processor and at least one memory including computer program code;

receiving a configuration comprising one or more selected feedback modes for each of a plurality of channel state information reference signal resources; and

in response to determining that a complexity for calculating channel state information for all of the selected feedback modes for all of the plurality of channel state information reference signal resources exceeds a predetermined maximum complexity, taking an action other than adopting the received configuration.

16. The apparatus according to claim 15, in which the action comprises disregarding the received configuration as being in error.

17. A computer readable memory storing a program of instructions which when executed by at least one processor result in actions comprising:

in response to determining that a complexity for calculating channel state information for all of the selected feedback modes for all of the plurality of channel state information reference signal resources exceeds a predetermined maximum complexity, taking a further action other than adopting the received configuration. 18. The computer readable memory according to claim 17, in which the further action comprises disregarding the received configuration as being in error.

19. A method comprising:

for each of a plurality of channel state information reference signal resources, storing in a local memory an association of a respective channel state information reference signal resource with a respective set of allowed feedback modes, in which at least one of the sets has a fewer number of allowed feedback modes than at least one other of the sets; and in response to receiving a configuration that selects, for at least one of the channel state information reference signal resources, a feedback mode that is not in the respectively associated set, taking an action other than adopting the received configuration.

20. The method according to claim 19, in which the action comprises disregarding the received configuration as being in error.

21. An apparatus comprising:

at least one processor and at least one memory including computer program code;

for each of a plurality of channel state information reference signal resources, storing in a local memory an association of a respective channel state information reference signal resource with a respective set of allowed feedback modes, in which at least one of the sets has a fewer number of allowed feedback modes than at least one other of the sets; and

in response to receiving a configuration that selects, for at least one of the channel state information reference signal resources, a feedback mode that is not in the respectively associated set, taking an action other than adopting the received configuration. 22. The apparatus according to claim 21 , in which the action comprises disregarding the received configuration as being in error.

23. A computer readable memory storing a program of instructions which when executed by at least one processor result in actions comprising:

in response to receiving a configuration that selects, for at least one of the channel state information reference signal resources, a feedback mode that is not in the respectively associated set, taking a further action other than adopting the received configuration.

24. The computer readable medium according to claim 20, in which the further action comprises disregarding the received configuration as being in error.