Abstract:
User Equipment reports single-cell or multi-cell channel state information to a base station on a Physical Uplink Control Channel (PUCCH) Format 3 (PF 3) resource. The PF 3 resource selected depends on whether ACK/NACK needs to be reported simultaneously. Different coding and/or scrambling and/or interleaving schemes are used depending on whether ACK/NACK bits are present, as well as the number of ACK/NACK and/or CSI bits. Resource compatibility is maintained independently of the details of coding, interleaving, or scrambling—that is, all formats can be orthogonally multiplexed onto the same time-frequency resources. The format used for CSI only is PF 3c whereas the format used for CSI and ACK/NACK is PF 3b. PUCCH Formats 3b and 3c may be further differentiated depending on whether a CSI from a single or multiple cells are reported, or from which cells (PCell, SCell) an ACK/NACK is reported.

Description:
TECHNICAL FIELD 
       [0001]    The present Invention relates generally to wireless communication networks, and in particular to a system and method for Channel State information feedback in LTE carrier aggregation. 
       BACKGROUND 
       [0002]    The 3 rd  Generation Partnership Project (3GPP) oversees and governs 3 rd  Generation (3G) networks, including 3G Long Term Evolution (LTE) networks. 3G LTE provides mobile broadband to User Equipment (UE) within the 3G LTE network at higher data rates than generally available with other networks. For example, the air interface for 3G LTE, Evolved Universal Mobile Telecommunication System (UMTS) Terrestrial Radio Access Network (E-UTRAN), utilizes multi-antenna and multi-user coding techniques to achieve downlink data rates of 100 s of Mbps and uplink data rates of 10 s of Mbps. 
         [0003]    LTE uses Orthogonal Frequency Division Multiplexing (OFDM) in the downlink and Discrete Fourier Transform (DFT)-spread OFDM in the uplink. The basic LTE downlink physical resource can thus be seen as a time-frequency grid as illustrated in  FIG. 1 , where each resource element corresponds to one OFDM subcarrier during one OFDM symbol interval. In the time domain, LTE downlink transmissions are organized into radio frames of 10 ms, each radio frame comprising ten equally-sized subframes of length T subframe =1 ms, as shown in  FIG. 2 . Furthermore, the resource allocation in LTE is typically described in terms of resource blocks, where a resource block corresponds to one slot (0.5 ms) in the time domain and 12 contiguous subcarriers in the frequency domain. Resource blocks are numbered in the frequency domain, starting with 0 from one end of the system bandwidth. 
         [0004]    Downlink transmissions are dynamically scheduled, e.g., in each subframe the base station transmits control information about to which terminals data is transmitted and upon which resource blocks the data is transmitted. In the current downlink subframe. This control signaling is typically transmitted in the first 1, 2, 3 or 4 OFDM symbols in each subframe. A downlink system with 3 OFDM symbols for control signaling is illustrated in  FIG. 3 . 
         [0005]    LTE uses Hybrid-Automatic Repeat Request (Hybrid-ARQ, or HARQ), where, after receiving downlink data in a subframe, the terminal attempts to decode it and reports to the base station whether the decoding was successful with an acknowledgement (ACK) or not successful with a negative acknowledgement (NACK). In case of an unsuccessful decoding attempt, the base station can retransmit the erroneous data. 
         [0006]    Uplink control signaling, or L1/L2 control information, from the terminal to the base station includes: HARQ acknowledgements for received downlink data; terminal reports related to the downlink channel conditions, called Channel State Information (CSI) reports, used as assistance for the downlink scheduling; and scheduling requests, indicating that a mobile terminal needs uplink resources for uplink data transmissions. 
         [0007]    if the mobile terminal has not been assigned an uplink resource for data transmission, the L1/L2 control information (channel state reports, HARQ acknowledgments, and scheduling requests) is transmitted using uplink resources (resource blocks) specifically assigned for uplink L1/L2 control on the Physical Uplink Control CHannel (PUCCH). As illustrated in  FIG. 4 , these resources are located at the edges of the total available cell bandwidth. Each such resource comprises 12 subcarriers (one resource block) within each of the two slots of an uplink subframe. In order to provide frequency diversity, these frequency resources use frequency hopping on the slot boundary, e.g., one “resource” comprises 12 subcarriers at the lower part of the spectrum during the first slot of a subframe and an equally sized resource at the upper part of the spectrum during the second slot of the subframe, or vice versa. If more resources are needed for the uplink L1/L2 control signaling, e.g., in case of very large overall transmission bandwidth supporting a large number of users, additional resource blocks can be assigned next to the previously assigned resource blocks. 
         [0008]    There are two primary reasons for locating the PUCCH resources at the edges of the overall available spectrum. First, together with the frequency hopping described above, this maximizes the frequency diversity experienced by the control signaling. Second, assigning uplink resources for the PUCCH at other positions within the spectrum, e.g., not at the edges, would fragment the uplink spectrum, making it impossible to assign very wide transmission bandwidths to a single mobile terminal and still retain the single-carrier property of the uplink transmission. 
         [0009]    The bandwidth of one resource block during one subframe is too large for the control signaling needs of a single terminal. Therefore, to efficiently exploit the resources set aside for control signaling, multiple terminals can share the same resource block by some form of orthogonal spreading. Three formats for PUCCH have been defined. They are briefly summarized as:
       PUCCH Format 1 (PF 1): Used for scheduling request transmissions,   PUCCH Format 1a/1 b (PF 1a/1b): Used for the transmission of one ACK/NACK bit (1a) or two ACK/NACK bits (1b). In Carrier Aggregation (CA) PF 1a/1b can be used together with channel selection to Increase the number of HARQ ACK/NACK bits that can be transported.   PUCCH Format 2 (PF 2): Used for the transmission of CSI bits.   PUCCH Format 2a/2b (PF 2a/2b): Used for the transmission of CSI bits together with one ACK/NACK bit (2a) or two ACK/NACK bits (2b).   PUCCH Format 3 (PF 3): Used in carrier aggregation and Time Division Duplexing (TDD) to transmit HARQ ACK/NACK bits from multiple cells and/or subframes. The payload capacity of PF 3 is 11 bits with standard Reed-Muller encoding and 21 bits with dual Reed-Muller encoding. Recently it has been proposed to use a similar format to transmit CSI reports together with multi-cell ACK/NACK resources or only multi-cell CSI reports, where “similar” means a scheme that can be orthogonally multiplexed onto the same resources as PF 3, but may use different processing of the payload.
 
The PUCCH Formats 1 and 2 are described in greater detail:
       
 
       PUCCH Format 1 
       [0015]    PUCCH Format 1 is used for Hybrid-ARQ acknowledgements and, if necessary, scheduling requests. Hybrid-ARQ acknowledgements are used to acknowledge the reception of one (or two in the case of spatial multiplexing) transport blocks in the DL. An ACK is reported to Indicate successful decoding; a NACK is reported if the downlink transmission was received with errors; and no Hybrid-ARQ is reported when the terminal did not receive any assignment. The ACK/NACK can be one or two bits. A single ACK/NACK bit, related to one transport block, is used to generate a BPSK symbol, and is transmitted on PUCCH Format 1a. In the case of spatial multiplexing, two ACK/NACK bits are used to generate a QPSK symbol, which is transmitted on PUCCH Format 1 b. 
         [0016]    Scheduling requests are used to request UL transmission resources from the base station. Unlike ACK/NACK indicators, no explicit information bit is transmitted by the scheduling request; instead, the information is conveyed by the presence (or absence) of energy on the corresponding PUCCH. 
         [0017]    To multiplex multiple terminals onto PUCCH, each terminal is assigned a different orthogonal phase rotation of a cell-specific, length-12 frequency-domain sequence (equivalent to a cyclic sift in the time domain). To provide for an even larger number of terminals to share the PUCCH, the BPSK/QPSK symbol for a terminal is multiplied by a length-4 orthogonal cover sequence; this product then modulates the terminal&#39;s assigned rotated length-12 sequence. A PUCCH Format 1 resource, used to transmit either an ACK/NACK and/or a scheduling request, is represented by a scalar Index, which identifies the phase rotation and orthogonal cover sequence. 
         [0018]    The phase rotation and orthogonal cover sequence provides Intra-cell orthogonally between all terminals sharing the same time-frequency resource on PUCCH. To provide immunity to Inter-cell interference (which arises as the sequences are not orthogonal between different cells), the phase rotation of the sequence used in a cell varies on a symbol-by-symbol basis in a slot according to a hopping pattern derived from the physical-layer cell identity. Additionally, slot-level hopping is applied to the orthogonal cover and phase rotation to further randomize the interference. 
       PUCCH Format 2 
       [0019]    PUCCH Format 2 is used for Channel State Information (CSI) reports, which provide the base station information on the quality of the received channel, to facilitate channel-dependent scheduling. A CSI can comprise multiple bits per subframe. Because PF 1 is limited to two bits, a different format definition is necessary to transmit CSI. 
         [0020]    In PF 2, QPSK modulated CSI data modulate per-terminal assigned orthogonal phase rotation of the cell-specific, length-12 frequency-domain sequence as in PF 1, but without orthogonal spreading. Each rotated sequence can be used for one PF 2 instance or three PF 1 instances. PF 2a is used to transmit CSI together with one ACK/NACK bit; PF 2b is used to transmit CSI together with two ACK/NACK bits (e.g., for spatial multiplexing). 
         [0021]    The LTE Rel-8 standard has been standardized, supporting bandwidths up to 20 MHz. However, in order to meet the international Mobile Telecommunications (IMT)-Advanced requirements, 3GPP also recently finalized LTE Rel-10, which describes supporting bandwidths larger than 20 MHz. One important requirement on LTE Rel-10 is to assure backward compatibility with LTE Rel-8. This should also Include spectrum compatibility, which implies that an LTE Rel-10 carrier wider than 20 MHz should appear as a number of LTE carriers to an LTE Rel-8 terminal. Each such carrier can be referred to as a cell. In particular for early LTE Rel-10 deployments it can be expected that there will be a smaller number of LTE Rel-10-capable terminals compared to many LTE legacy terminals. Therefore, it is necessary to also assure an efficient use of a wide carrier for legacy terminals, e.g., that it is possible to implement carriers where legacy terminals can be scheduled in all parts of the wideband LTE Rel-10 carrier. The straightforward way to obtain this would be by means of Carrier Aggregation (CA). CA implies that an LTE Rel-10 terminal can receive multiple cells, where the cells have, or at least the possibility to have, the same structure as a Rel-8 carrier. CA is Illustrated in FIG.  5 Error!Reference source not found. 
         [0022]    The number of aggregated cells, as well as the bandwidth of the individual cells, may be different for uplink and downlink. A symmetric configuration refers to the case where the number of downlink and uplink cells is the same, whereas an asymmetric configuration refers to the case that the number of downlink and uplink cells is different. It is important to note that the number of cells configured in the network may be different from the number of cells seen by a terminal. A terminal may for example support more downlink cells than uplink cells, even though the network offers the same number of uplink and downlink cells. 
         [0023]    During Initial access, a LTE Rel-10 terminal behaves similar to an LTE Rel-8 terminal. Upon successful connection to the network a terminal may—depending on Its own capabilities and the network—be configured with additional downlink (DL) cells and corresponding uplink (UL) cells. Configuration is based on Radio Resource Control (RRC). 
         [0024]    Scheduling of a cell is done on the Physical Downlink Control CHannel (PDCCH) or enhanced PDCCH (ePDCCH) via downlink assignments. Control Information on the PDCCH or ePDCCH Is formatted as a Downlink Control Information (DCI) message. In Rel-8 a terminal only operates with one DL cell and one UL cell, the association between the DL assignment, the UL grants, and the corresponding DL and UL cells Is therefore clear. In Rel-10 two modes of CA needs to be distinguished. The first case is very similar to the operation of multiple Rel-8 terminals, where a DL assignment or UL grant contained in a DCI message transmitted on a DL is either valid for the DL cell itself or for the UL associated with the DL cell (either via cell-specific or terminal specific linking). A second case augments a DCI message with the Carrier Indicator Field (CIF). A DCI containing a DL assignment with a CIF Is valid for the DL cell Indicted with CIF, and a DCI containing an UL grant with a CIF is valid for the UL associated with the Indicated DL cell. 
         [0025]    One of the aggregated cells—the primary cell (PCell)—is special, compared to secondary cells (SCell). The UL of the PCell carries PUCCH. In the DL radio link monitoring is only defined for the PCell, e.g., a radio connection is reset if the terminal loses DL PCell connectivity but not if the terminal loses DL SCell connectivity. 
         [0026]    From a LIE perspective, both symmetric and asymmetric uplink/downlink configurations are supported. For some of the configurations, one may consider the possibility to transmit the uplink control information on multiple PUCCH or UL of multiple cells. However, this option is likely to result in higher UE power consumption and a dependency on specific UE capabilities. It may also create implementation issues due to Inter-modulation products, and would lead to generally higher complexity for implementation and testing. 
         [0027]    Therefore, the transmission of the PUCCH should have no dependency on the uplink/downlink configuration, e.g. all uplink control information for a UE is transmitted on a single UL. This is the UL of the semi-statically configured primary cell PCell (also referred to as the “anchor carrier”). 
         [0028]    Terminals only configured with a single cell (one DL and the associated UL, which is then the PCell) operate with dynamic ACK/NACK on PUCCH according to Rel-8. The first Control Channel Element (CCE) used to transmit PDCCH for the DL assignment determines the dynamic ACK/NACK resource on Rel-8 PUCCH. 
         [0029]    Terminals configured with multiple DL cells use PF 3 or PF 1a/1b, together with channel selection, to provide HARQ feedback from all scheduled DL cells. Which of these formats is used is RRC configured. 
         [0030]    Even a terminal configured with multiple DL cells, which receives only a PCell assignment, uses Rel-8 PUCCH. A terminal configured with multiple DL cells which receives multiple DL assignments, or at least one DL SCell assignment, uses PF 3 or PF 1 a/1b together with channel selection. A terminal is configured with multiple resources for PF 3 or channel selection to Increase scheduling flexibility and avoid PUCCH collisions. Which PF 3 or channel selection resource to use is indicated in each SCell DL assignment by the ACK/NACK Resource Indicator (ARI); HARQ feedback of configured cells for which no DL assignment is received is set to NACK. 
         [0031]    If reporting of HARQ feedback and CSI feedback collides, different behaviors can be configured. In case the terminal reports ACK/NACK with Rel-8 PUCCH it can be configured to drop CSI and report only ACK/NACK or to use PF 2a/2b and report CSI together with ACK/NACK. If CSI from multiple cells should be reported it drops all but one CSI report according to a priority rule. 
         [0032]    If the terminal reports ACK/NACK using PF 3 it drops all CSI reports and only reports ACK/NACK. Dropped CSI reports never reach the base station, which implies that the base station has only older (maybe even outdated) CSI reports from cells which CSI reports have been dropped. Outdated or old CSI reports have a negative Impact on DL throughput. 
         [0033]    The Background section of this document is provided to place embodiments of the present invention in technological and operational context, to assist those of skill in the art in understanding their scope and utility. Unless explicitly identified as such, no statement herein is admitted to be prior art merely by its inclusion in the Background section. 
       SUMMARY 
       [0034]    The following presents a simplified summary of the disclosure in order to provide a basic understanding to those of skill in the art. This summary Is not an extensive overview of the disclosure and is not intended to identify key/critical elements of embodiments of the invention or delineate the scope of the invention. The sole purpose of this summary is to present some concepts disclosed herein in a simplified form as a prelude to the more detailed description that is presented later 
         [0035]    According to one or more embodiments described and claimed herein, a terminal reports single-cell or multi-cell CSI on a PUCCH Format 3 resource. Depending on whether ACK/NACK needs to be reported simultaneously, a different PUCCH Format 3 resource can be selected. The presence of ACK/NACK bits also impacts the processing of the payload, where different coding and/or scrambling and/or Interleaving scheme is used depending on whether ACK/NACK bits are present. Also the number of ACK/NACK and/or CSI bits impacts coding and/or scrambling and/or Interleaving. However, independent of the details of coding, Interleaving, or scrambling, resource compatibility Is maintained that is, all formats can be orthogonally multiplexed onto the same time-frequency resources. The format used for CSI only is PUCCH Format 3c (PF 3c) whereas the PUCCH Format used for CSI and ACK/NACK is PUCCH Format 3b (PF 3b). PUCCH Formats 3b and 3c may be further differentiated depending on whether a CSI from a single or multiple cells are reported, or from which cells (PCell, SCell) an ACK/NACK is reported. 
         [0036]    One embodiment relates to a method, by UE operative in a wireless communication network supporting carrier aggregation, of transmitting uplink channel state Information on a PUCCH. The PCell and any SCell assignments are determined. Any DL transmissions on PCell or SCell(s) are decoded and any corresponding Hybrid-ARQ acknowledgements are generated. If the UE has no Hybrid-ARQ acknowledgement to report, CSI is reported on a CSI resource using PUCCH Format 3c. If the UE has a Hybrid-ARQ acknowledgement only for a received PCell DL transmission, the Hybrid-ARQ acknowledgement is reported on a CSI_PCell_AN resource using PUCCH Format 3b. If the LIE has a Hybrid-ARQ acknowledgement for one or more received SCell DL transmissions, the Hybrid-ARQ acknowledgement is reported on an ARI resource using PUCCH Format 3b. 
         [0037]    Another embodiment relates to a method, by a base station operative in a wireless communication network supporting carrier aggregation, of processing UL channel state information reports received from a UE, on a PUCCH. The PCell and any SCell assignments for the UE are determined. Any corresponding expected Hybrid-ARQ acknowledgements are determined, from downlink transmissions to the UE. If the base station expects no Hybrid-ARQ acknowledgement from the UE, a channel state information report on a CSI resource using PUCCH Format 3c is processed. If the base station expects a Hybrid-ARQ acknowledgement only for a PCell DL transmission, a Hybrid-ARQ acknowledgement on a CSI_PCell_AN resource using PUCCH Format 3b is processed. If the base station expects a Hybrld-ARQ acknowledgement for one or more SCell DL transmissions, a Hybrid-ARQ acknowledgement on an ARI resource using PUCCH Format 3b is processed. 
         [0038]    Yet another embodiment relates to UE operative in a wireless communication network supporting carrier aggregation. The UE Includes a transceiver, memory, and a controller operatively connected to the transceiver and the memory. The controller is operative to determine the PCell and any SCell assignments, and decode any DL transmissions on PCell or SCell(s) and generate any corresponding Hybrld-ARQ acknowledgements. If the UE has no Hybrid-ARQ acknowledgement to report, the controller is operative to cause the transceiver to report channel state Information on a CSI resource using PUCCH Format 3c. If the UE has a Hybrid-ARQ acknowledgement only for a received PCell DL transmission, the controller is operative to cause the transceiver to report the Hybrld-ARQ acknowledgement on a CSI_PCell_AN resource using PUCCH Format 3b. If the UE has a Hybrid-ARQ acknowledgement for one or more received SCell DL transmissions, the controller Is operative to cause the transceiver to report the Hybrid-ARQ acknowledgement on an ARI resource using PUCCH Format 3b. 
         [0039]    Still another embodiment relates to a base station operative in a wireless communication network supporting carrier aggregation. The base station includes communication circuits operative to communicate with other network nodes, a transceiver, memory, and a controller operatively connected to the communication circuits, the transceiver and the memory. The controller is operative to determine the PCell and any SCell assignments for the UE, and determine, from downlink transmissions to the UE, any corresponding expected Hybrid-ARQ acknowledgements. If the base station expects no Hybrid-ARQ acknowledgement from the UE, the controller is operative to process a channel state information report on a CSI resource using PUCCH Format 3c. If the base station expects a Hybrid-ARQ acknowledgement only for a PCell DL transmission, the controller is operative to process a Hybrid-ARQ acknowledgement on a CSI_PCell_AN resource using PUCCH Format 3b. If the base station expects a Hybrid-ARQ acknowledgement for one or more SCell DL transmissions, the controller is operative to process a Hybrid-ARQ acknowledgement on an ARI resource using PUCCH Format 3b. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0040]      FIG. 1  is a time-frequency grid representative of an exemplary LTE downlink physical resource. 
           [0041]      FIG. 2  is a diagram of the LTE time-domain structure. 
           [0042]      FIG. 3  is a diagram of an exemplary downlink subframe. 
           [0043]      FIG. 4  is a diagram of an exemplary uplink L1/L2 control signal transmission on PUUCH. 
           [0044]      FIG. 5  is a frequency diagram of carrier aggregation. 
           [0045]      FIGS. 6   a  and  6   b  are flow graphs depicting PUCCH Format 3b and 3c processing according to embodiments of the present invention. 
           [0046]      FIGS. 7   a  and  7   b  are flow graphs depicting PUCCH Formats 3b and 3c according to embodiments of the present invention. 
           [0047]      FIG. 8  is a flow diagram of a method of processing by a UE. 
           [0048]      FIG. 9  is a flow diagram of a method of processing by a base station. 
           [0049]      FIG. 10  is a functional block diagram of processing circuits configured to implement the flow diagram of  FIG. 8  and/or  FIG. 9 . 
           [0050]      FIG. 11  is a flow diagram of a method of ambiguity avoidance. 
           [0051]      FIG. 12  is a functional block diagram of processing circuits configured to implement the flow diagram of  FIG. 11 . 
           [0052]      FIG. 13  is a functional block diagram of a base station. 
           [0053]      FIG. 14  is a functional block diagram of a UE. 
       
    
    
     DETAILED DESCRIPTION 
       [0054]    With the advent of carrier aggregation, the need arises for a terminal to feedback multiple Hybrid-ARQ acknowledgement bits, one (or two) for each DL component carrier on which it receives data. While PF 1 can be used with resource selection to transmit up to four ACK/NACK bits, this is not an efficient solution for more than four bits. 
         [0055]    PUCCH Format 3 is based on DFT-precoded OFDM. ACK/NACK bits and an optional scheduling request bit are concatenated and block coded using one or two Reed-Muller codes. The coded bits are scrambled using a cell-specific scrambling sequence to randomize inter-cell Interference. The resulting 48 bits are QPSK modulated and DFT-precoded, and 12 QPSK symbols are transmitted in each PUCCH slot. Five of seven OFDM symbols per slot are available for control information bits (two transmit reference signals). A cyclic shift of the 12 inputs to the DFT, varying between OFDM symbols in a cell-specific manner, is applied to the block of 12 QPSK symbols prior to DFT precoding, to further randomize inter-cell interference. 
         [0056]    Each of the five OFDM symbols per slot is multiplied by one element of a length-5 orthogonal cover code sequence. This allows up to five terminals to share the same resource-block pair for PF 3. Different length-5 sequences are used in the two PUCCH slots. 
         [0057]    A PF 3 resource can be represented by a single Index, from which the orthogonal sequence and the resource-block number can be derived. A terminal can be configured with four different PF 3 resources; these are assigned in a scheduling assignment, allowing the scheduler to avoid PUCCH collisions by assigning different resources to different terminals. Resources cannot be shared between PF 3 and PF 1/2. 
         [0058]    According to embodiments of the present invention, PUCCH Format 3 resources are defined to report ACK/NACK and/or CSI according to Table 1. 
         [0000]                                                        TABLE 1                   PUCCH Format 3 and resources used for CSI and ACK/NACK reporting                        At least           No   Only PCell   one SCell           ACK/NACK   ACK/NACK   ACK/NACK                        single-cell CSI   PF 3c, CSI   PF 3b, CSI_PCell_AN   PF 3b, ARI       multi-cell CSI   PF 3c, CSI   PF 3b, CSI_PCell_AN   PF 3b, ARI                    
Whether a terminal should use PF 3b and PF 3c to report ACK/NACK and/or CSI Is RRC configured.
 
         [0059]    The PUCCH resource labelled “CSI” Is semi-statically configured. It can be a resource on its own or it can coincide with one of the four resources already configured for PF 3 ACK/NACK feedback. It is possible that this resource Is always one of the 4 already configured resources—e.g. the first. In this case, no extra signalling is required to configure this resource. 
         [0060]    The PUCCH resource labelled “CSI_PCell_AN” is semi-statically configured. It can be a resource on Its own or it can coincide with one of the four resources already configured for PF 3 ACK/NACK feedback or it can coincide with resource “CSI”. It is possible that this resource is always one of the four already configured resources—e.g. the first. In this case, no extra signalling is required to configure this resource. It is possible that this resource is always the same as the “CSI” resource; In this case no extra signalling Is required to configure this resource. 
         [0061]    The “ARI” resource Is the PF 3 resource which is indicated in the SCell DL assignment. 
         [0062]    In the case that the terminal has only single-cell CSI or single-cell CSI together with PCell ACK/NACK to report, it could also use PF 2/2a/2b. However, because for the other cases it has to use a PF 3 resource anyway, it would be a waste of resources if a terminal needs to be configured with both PF 2/2a/2b and PF 3 resources. 
         [0063]    Even a terminal that uses PF 1a/1b with channel selection to report multi-cell ACK/NACK could be configured with the above outlined reporting mode and resources to enable CSI reporting on PF 3 resources. 
       Error Cases 
       [0064]    PDCCH signalling Is not 100% reliable. It is possible that a terminal is scheduled on a cell but does not receive the assignment. For example, a terminal could be scheduled on the PCell and an SCell and is expected to report CSI and ACK/NACK on the “ARI” resource. However, since the terminal did not receive the SCell assignment it reports CSI and ACK/NACK on the “CSI_PCell_AN” resource. 
       Terminal Scheduled on PCell Only, and PCell+SCell 
       [0065]    If the terminal receives the PCell assignment it should report CSI on the “CSI_PCell_AN” resource using PF 3b. If it misses the PCell assignment it will use the “CSI” resource instead with PF 3c. 
         [0066]    If the “CSI” resource and the “CSI_PCell_AN” resource are different, the base station has to attempt to decode both resources and choose the resource which delivers the better decoding metric. Based on that, the base station also knows if PCell assignment has been missed or not. On the “CSI” resource the base station uses PF 3c, whereas on the “CSI_PCell_AN” resource the base station uses PF 3b. 
         [0067]    If “CSI” and “CSI_PCell_AN” resource are the same, the base station does not know whether to use PF 3b or PF 3c. Resolution of this ambiguity is discussed below. 
         [0068]    If the terminal receives all assignments—e.g., PCell and one or more SCells—it will use PF 3b on the “ARI” resource. 
         [0069]    If the terminal has also been scheduled on the PCell but misses the PCell assignment, it will still use the same resource and format. It will set the ACK/NACK bits for the non-received assignment to NACK (as in Rel-10). 
         [0070]    If the terminal misses some SCell assignments but at least receives one SCell assignment, it will still use the same resource and format. It will set the ACK/NACK bits for the non-received assignment to NACK (as in Rel-10). 
         [0071]    If the terminal misses all SCell assignments but receives a PCell assignment, it will use PF 3b on the “CSI_PCell_AN” resource. The terminal will set the ACK/NACK bits for the non-received assignment to NACK (as in Rel-10). 
         [0072]    If the terminal misses all SCell assignments and also receives no PCell assignment (not scheduled or missed), it will use PF 3c on the “CSI” resource. 
         [0073]    The base station must monitor the “ARI” resource (at least one SCell is received), the “CSI_PCell_AN” resource (only if PCell is scheduled, this resource would be used if all SCells assignments are missed but PCell assignment is received), and the “CSI” resource (no assignment is received). 
         [0074]    The base station assumes, for decoding, the PF 3c on the “CSI” resource and the PF 3b on “CSI_PCell_AN” and “ARI” resource. If the CSI resource coincides with any or both of the “CSI_PCell_AN” and “ARI” resource, the base station does not know which format to use for decoding. Resolution of this ambiguity is discussed below. 
       Avoiding Ambiguity 
       [0075]      FIG. 6   a depicts the processing for PUCCH Format  3b, and  FIG. 6   b  depicts the same for PF 3c. Both formats are based on PF 3 and use the same spreading sequences for reference signal modulation, e.g. [1 1]. The payload processing is different. 
         [0076]    If the base station does not know which format has been used, it has to test both formats. However, in many circumstances the decoding of both formats will deliver “valid” bit sequences for ACK/NACK and/or CSI, and the base station cannot tell which format has been used, and therefore also cannot tell if the bit represents an ACK/NACK and/or a CSI. 
         [0077]      FIGS. 7   a  and  7   b  depict modifications to  FIGS. 6   a  and  6   b , respectively, where different spreading codes are used to modulate reference signals. PF 3b, depicted in  FIG. 7   a , uses the sequence a to modulate (spread) the reference signals, and PF 3c, depicted in  FIG. 7   b , uses sequence b. Here, the reference signals are modulated differently. Instead of using [1 1] to modulate reference signals of both PUCCH formats, the sequences a=[a 0  a 1 ] and b=[b 0  b 1 ] are used to modulate the reference signals for PF 3b and PF 3c, respectively, with a≠b. For example, a=[1 1] could be used for PF 3b, while b=[1 −1] could be used for PF 3c. If the terminal transmits PF 3b, it uses sequence a to modulate Its reference signals, and if the terminal transmits PF 3c, it uses sequence b to modulate its reference signals. 
         [0078]    When decoding PF 3b, the base station uses a to de-spread the reference signals, and uses b in the case of PF 3c. The base station hypothesis that matches the transmission will result in a reasonable channel estimate and a good decoding metric. The hypothesis on the de-spreading sequence that does not match the transmission will result in a completely wrong channel estimate and in a very bad decoding metric. By comparing the decoding metrics, the base station can therefore decide which format has been used, and thus also identify if the decoded bits are ACK/NACK and/or CSI. 
         [0079]      FIG. 8  depicts an exemplary method  100  implemented by the terminal (also referred to herein as the UE). After the UE checks Its assignments (block  110 ), the UE determines if there is an ACK/NACK to report (block  120 ). If there is no ACK/NACK to report, the UE uses PF 3c on the CSI resource (block  130 ). If there is an ACK/NACK to report, the UE determines if the ACK/NACK is a PCell only ACK/NACK (block  140 ). If the ACK/NACK is a PCell only ACK/NACK, the UE uses PF 3b on the CSI_PCell_AN resource (block  150 ). Otherwise, the UE uses PF 3b on the ARI resource (block  160 ). 
         [0080]      FIG. 9  depicts an exemplary method  200  implemented by the base station (also referred to herein as the eNB). After the eNB checks the UE assignments (block  210 ), the eNB determines if the UE has an ACK/NACK to report (block  220 ). If there is no ACK/NACK to report, the eNB uses PF 3c on the CSI resource (block  230 ). If there Is an ACK/NACK to report, the eNB determines if the ACK/NACK is a PCell only ACK/NACK (block  240 ). If the ACK/NACK is a PCell only ACK/NACK, the eNB uses PF 3b on the CSI_PCell_AN resource, and PF 3c on the CSI resource (block  250 ). Otherwise, the eNB uses PF 3b on the CSI_PCell_AN resource (if a PCELL has been scheduled) and on the ARI resource, and PF 3c on the CSI resource (block  280 ). 
         [0081]      FIG. 10  is a functional block diagram of circuits  400  that may be implemented in a terminal and/or a base station. The diagram  400  includes an ACK/NACK circuit  410 , a PCell check circuit  420 , and a controller  430 . ACK/NACK circuit  410  checks the assignments and forwards whether the terminal has an ACK/NACK to report to the PCell check circuit  420  and/or the controller  430 . If there is no ACK/NACK to report, the controller  430  indicates PF 3c should be used on the CSI resource. If there is an ACK/NACK to report, the PCell check circuit  420  determines if the ACK/NACK is a PCell only ACK/NACK. If the PCell check unit  420  determines ACK/NACK Is a PCell only ACK/NACK, the controller  430  indicates PF 3b should be used on the CSI_PCell_AN resource (and if the circuit  400  is implemented in a base station controller  430  also Indicates PF 3c should be used on the CSI resource). Otherwise, controller  430  indicates PF 3b should be used on the ARI resource (and if the circuit  400  is implemented in a base station controller  430  also indicates to use PF3b on CSI_PCell AN resource (If PCELL has been scheduled) and PF 3c on the CSI resource). As used herein, a “circuit” may comprise a dedicated digital, analog, or mixed electronic circuit, or may comprise a software module executing on a processing circuit, such as a microprocessor or Digital Signal Processor (DSP). 
         [0082]      FIG. 11  depicts an exemplary method  300  implemented by the eNB for ambiguity avoidance. When the eNB has to decode the PF 3b and PF 3c on the same resource (block  310 ). It forms two hypotheses. In hypothesis 1, PF 3b is assumed, and a sequence a is used for RS demodulation (block  320 ). In hypothesis 2, PF 3c is assumed, and a sequence b is used for RS demodulation (block  330 ). The eNB compares the decoding metrics obtained with both hypotheses (block  340 ), and determines whether hypothesis 1 has a better metric (block  350 ). If hypothesis 1 has a better decoding metric, the eNB concludes that PF 3b has been used, and that the decoded bits are ACK/NACK and CSI (block  360 ). Otherwise, the eNB assumes PF 3c has been used, and that the decoded bits are CSI (block  370 ). 
         [0083]      FIG. 12  is a functional block diagram of circuits  500  configured to avoid ambiguity in a base station by determining which PUCCH format was used. The diagram  500  comprises a hypothesis circuit  510 , a decoding metric circuit  520 , and a comparator  630 . The hypothesis circuit  510  forms two hypotheses. In hypothesis 1, PF 3b Is assumed, and a sequence a is used for RS demodulation. In hypothesis 2, PF 3c Is assumed, and a sequence b is used for RS demodulation. The decoding metric circuit  520  demodulates the reference signals using the assumed sequences for each hypothesis, and outputs a decoding metric for each hypothesis. The comparator  530  compares the decoding metrics obtained with both hypotheses, and determines whether hypothesis 1 has a better metric. If hypothesis 1 has a better metric, the eNB assumes PF 3b has been used, and that the decoded bits are ACK/NACK and CSI. Otherwise, the eNB assumes PF 3c has been used, and that the decoded bits are CSI. As used herein, a “circuit” may comprise a dedicated digital, analog, or mixed electronic circuit, or may comprise a software module executing on a processing circuit, such as a microprocessor or Digital Signal Processor (DSP). 
       Hardware and Software 
       [0084]      FIG. 13  depicts a base station  600  operative in embodiments of the present Invention. As those of skill in the art are aware, a base station  600  is a network node providing wireless communication services to one or more UE In a geographic region (known as a cell or sector, not to be confused with the term cell used herein to refer to component carriers in carrier aggregation, such as PCell or SCell). The base station  600  in LTE is called an e-NodeB or eNB; however the present invention is not limited to LTE or eNBs. A base station  600  includes communication circuitry  610  operative to exchange data with other network nodes; a controller  620 ; memory  630 ; and radio circuitry, such as a transceiver  640 , one or more antennas  650 , and the like, to effect wireless communication across an air interface to one or more UE. According to embodiments of the present invention, the memory  630  is operative to store, and the controller  620  operative to execute, software  635  which when executed is operative to cause the base station  600  to perform methods and functions described herein. In particular, the software  635  may implement a hypothesis circuit  510 , decoding metric circuit  520 , and/or comparator  530 , as described herein with reference to  FIG. 12 . 
         [0085]      FIG. 14  depicts a UE  700  operative in embodiments of the present invention. As those of skill in the art are aware, a UE  700  is a device, which may be battery-powered and hence mobile, operative within a wireless communication network. UE  700  are also known in the art as mobile stations or mobile terminals, and may include laptop computers, pad computers, cellular radiotelephones (including “smartphones”), and the like. The UE  700  includes a user interface  710  (display, touchscreen, keyboard or keypad, microphone, speaker, and the like); a controller  720 ; memory  730 ; and a radio circuitry, such as one or more transceivers  740 , antennas  760 , and the like, to effect wireless communication across an air interface to one or more base stations  600 . The UE  700  may additionally include features such as a camera, removable memory Interface, short-range communication interface (Wi-Fi, Bluetooth, and the like), wired interface (USB), and the like (not shown in  FIG. 14 ). According to embodiments of the present invention, the memory  730  is operative to store, and the controller  720  operative to execute, software  735  which when executed is operative to cause the UE  700  to perform methods and functions described herein. In particular, the software  735  may Implement an ACK/NACK circuit  410 , PCell check circuit  420 , and/or controller  430 , as described herein with reference to  FIG. 10 . 
         [0086]    In all embodiments, the controller  620 ,  720  may comprise any sequential state machine operative to execute machine instructions stored as machine-readable computer programs in the memory, such as one or more hardware-implemented state machines (e.g., in discrete logic, FPGA, ASIC, etc.); programmable logic together with appropriate firmware; one or more stored-program, general-purpose processors, such as a microprocessor or Digital Signal Processor (DSP), together with appropriate software; or any combination of the above. 
         [0087]    In all embodiments, the memory  630 ,  730  may comprise any non-transient machine-readable media known in the art or that may be developed. Including but not limited to magnetic media (e.g., floppy disc, hard disc drive, etc.), optical media (e.g., CD-ROM, DVD-ROM, etc.), solid state media (e.g., SRAM, DRAM, DDRAM, ROM, PROM, EPROM, Flash memory, solid state disc, etc.), or the like. 
         [0088]    In all embodiments, the radio circuitry may comprise one or more transceivers  640 ,  740  used to communicate with one or more other transceivers  640 ,  740  via a Radio Access Network according to one or more communication protocols known in the art or that may be developed, such as IEEE 802.xx, CDMA, WCDMA, GSM, LTE, UTRAN, WiMax, or the like. The transceiver  640 ,  740  implements transmitter and receiver functionality appropriate to the Radio Access Network links (e.g., frequency allocations and the like). The transmitter and receiver functions may share circuit components and/or software, or alternatively may be implemented separately. In particular, a UE  700  according to embodiments of the present invention may include a transceiver  740  having two or more sets of receiver circuits and/or two or more sets of transmitter circuits, each independently tunable to a different component carrier frequency (e.g., PCell and SCell). 
         [0089]    In all embodiments, the communication circuitry  610  may comprise a receiver and transmitter Interface used to communicate with one or more other nodes over a communication network according to one or more communication protocols known in the art or that may be developed, such as Ethernet, TCP/IP, SONET, ATM, or the like. The communication circuitry  610  implements receiver and transmitter functionality appropriate to the communication network links (e.g., optical, electrical, and the like). The transmitter and receiver functions may share circuit components and/or software, or alternatively may be implemented separately. 
         [0090]    The embodiments disclosed herein enable simultaneous reporting of channel state information from multiple cells. The base station always has up-to-date CSI from multiple cells, which improves DL throughput. The embodiments furthermore avoid the need to configure a terminal with both PF 2/2a/2b and PF 3 resources. Because it very difficult to reuse currently unused resources, such an avoidance is beneficial because it reduces recourse waste on the PUCCH. 
         [0091]    The present invention may, of course, be carried out in other ways than those specifically set forth herein without departing from essential characteristics of the invention. The present embodiments are to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are Intended to be embraced therein.