(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`(19) World Intellectual Property Organization
`International Bureau
`
`( 43) International Publication Date
`26 February 2009 (26.02.2009)
`
`PCT
`
`(51) International Patent Classification:
`H04L 1/00 (2006.01)
`
`(21) International Application Number:
`PCT/SE2008/050951
`
`(22) International Filing Date: 22 August 2008 (22.08.2008)
`
`(25) Filing Language:
`
`(26) Publication Language:
`
`English
`
`English
`
`(30) Priority Data:
`0701915-1
`
`23 August 2007 (23.08.2007)
`
`SE
`
`(71) Applicant (for all designated States except US): TELE(cid:173)
`FONAKTIEBOLAGET LM ERICSSON
`(PUBL)
`[SE/SE]; S-164 83 Stockholm (SE).
`
`(72) Inventors; and
`(75) Inventors/Applicants (for US only): GORANSSON, Bo
`[SE/SE]; Silverdalsvagen 67, S-191 38 Sollentuna (SE).
`JONGREN, George [SE/SE]; Karlsviksgatan 15, S-112
`41 Stockholm (SE).
`
`(74) Agent: HASSELGREN, Joakim; Ericsson AB, Patent
`Unit LTE, S-164 80 Stockholm (SE).
`
`(81) Designated States ( unless otherwise indicated, for every
`kind of national protection available): AE, AG, AL, AM,
`
`!!!!!!!!
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`1111111111111111 IIIIII IIIII 11111111111111111111111111111111111 IIIII IIIII IIII IIIIIII IIII IIII IIII
`
`(10) International Publication Number
`WO 2009/025619 A2
`AO, AT, AU, AZ, BA, BB, BG, BH, BR, BW, BY, BZ, CA,
`CH, CN, CO, CR, CU, CZ, DE, DK, DM, DO, DZ, EC, EE,
`EG, ES, Fl, GB, GD, GE, GH, GM, GT, HN, HR, HU, ID,
`IL, IN, IS, JP, KE, KG, KM, KN, KP, KR, KZ, LA, LC, LK,
`LR, LS, LT, LU, LY, MA, MD, ME, MG, MK, MN, MW,
`MX, MY, MZ, NA, NG, NI, NO, NZ, OM, PG, PH, PL, PT,
`RO, RS, RU, SC, SD, SE, SG, SK, SL, SM, ST, SV, SY, TJ,
`TM, TN, TR, TT, TZ, UA, UG, US, UZ, VC, VN, ZA, ZM,
`zw.
`
`(84) Designated States (unless otherwise indicated, for every
`kind of regional protection available): ARIPO (BW, GH,
`GM, KE, LS, MW, MZ, NA, SD, SL, SZ, TZ, UG, ZM,
`ZW), Eurasian (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM),
`European (AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, Fl,
`FR, GB, GR, HR, HU, IE, IS, IT, LT, LU, LV, MC, MT, NL,
`NO, PL, PT, RO, SE, SI, SK, TR), OAPI (BF, BJ, CF, CG,
`CI, CM, GA, GN, GQ, GW, ML, MR, NE, SN, TD, TG).
`
`Declarations under Rule 4.17:
`as to applicant's entitlement to apply for and be granted a
`patent (Rule 4.17(ii))
`as to the applicant's entitlement to claim the priority of the
`earlier application (Rule 4.17(iii))
`of inventorship (Rule 4.17(iv))
`
`Published:
`without international search report and to be republished
`upon receipt of that report
`
`!!!!!!!!
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`M
`Q
`~ (54) Title: FEEDBACK REDUCTION FOR CODEBOOK SUBSET RESTRICTION
`Q
`M (57) Abstract: Systems and methods according to these exemplary embodiments provide for methods and systems for reducing
`0 uplink overhead from a user equipment, UE, (14) when performing communications in a mobile network. Reductions in uplink
`
`: , overhead may be achieved by using different control channel structures depending upon, for example, a subset of permissible transmit
`;;, parameters which are under consideration for a particular connection.
`
`LG Elecs. Ex. 1020
`LG Elecs. v. Pantech Corp.
`IPR2023-01273 Page 1
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`Feedback Reduction for Codebook Subset Restriction
`
`RELATED APPLICATION
`
`[0001)
`
`This application is related to, and claims priority from, Swedish Patent
`
`Application Serial No. 0701915-1, filed on August 23, 2007, entitled "Method and
`
`Arrangement in a Telecommunication System" to Bo Goransson and George Jongren, the
`
`entire disclosure of which is incorporated here by reference.
`
`TECHNICAL FIELD
`
`(0002)
`
`The present invention relates generally to telecommunications systems, and in
`
`particular to methods and systems for improving efficiency in radiocommunications systems.
`
`BACKGROUND
`
`(0003)
`
`Radiocommunication networks were originally developed primarily to
`
`provide voice services over circuit-switched networks. The introduction of packet-switched
`
`bearers in, for example, the so-called 2.50 and 30 networks enabled network operators to
`
`provide data services as well as voice services. Eventually, network architectures will likely
`
`evolve toward all Internet Protocol (IP) networks which provide both voice and data services.
`
`However, network operators have a substantial investment in existing infrastructures and
`
`would, therefore, typically prefer to migrate gradually to all IP network architectures in order
`
`to allow them to extract sufficient value from their investment in existing infrastructures.
`
`Also to provide the capabilities needed to support next generation radiocommunication
`
`applications, while at the same time using legacy infrastructure, network operators could
`
`deploy hybrid networks wherein a next generation radiocommunication system is overlaid
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`onto an existing circuit-switched or packet-switched network as a first step in the transition to
`
`an all IP-based network.
`
`[0004]
`
`One example of such a hybrid network involves an existing second generation
`
`(20) radiocommunication system, such as the Global System for Mobile communication
`
`(GSM), onto which a next generation "long term evolution" (L TE) system is overlaid. As
`
`will be appreciated by those skilled in the art, GSM systems have been modified and updated
`
`over time. For example, GSM release 1997 added packet data capabilities using General
`
`Packet Radio Service (GPRS) and GSM release 1999 introduced higher speed data
`
`transmissions through a system called Enhanced Data Rates for GSM Evolution (EDGE).
`
`Although not yet standardized, L TE systems will ultimately be designed in accordance with a
`
`new version of the UMTS standards, see, e.g., 3GPP TR 25.913 available online at
`
`www.3gpp.org. Target performance goals for LTE systems currently include, for example,
`
`support for 200 active calls per 5 MHz cell and sub 5 ms latency for small IP packets. Each
`
`new generation, or partial generation, of mobile communication systems add complexity and
`
`abilities to mobile communication systems and this can be expected to continue with either
`
`enhancements to proposed systems or completely new systems in the future.
`
`[0005)
`
`As these mobile communication systems continue to evolve, more data at
`
`higher bandwidths is expected to be transferred over mobile communication networks. One
`
`method for boosting the capacity and coverage of a wireless communication system involves
`
`the use of multiple antennas at the transmitter and/or the receiver end. These Multiple-Input(cid:173)
`
`Multiple-Output (MIMO) systems exploit the spatial dimension of a communication channel
`
`in order to improve performance by, for example, transmitting several parallel information
`
`carrying signals. By adapting the transmission to the current channel conditions, significant
`
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`additional gains can be achieved in a wireless system. One form of adaptation is to
`
`dynamically adjust, from one transmission time interval (TTI) to another TTI, the number of
`
`simultaneously transmitted information carrying signals to what the channel can support.
`
`This is commonly referred to as (transmission) rank adaptation. Another form of adaptation
`
`is precoding, wherein the phases and amplitudes of the signals are adjusted to better fit the
`
`current channel properties. The signals form a vector-valued signal and the adjustment can
`
`be described as multiplication by a precoder matrix. A common approach is to select the
`
`precoder matrix from a finite and countable set, e.g., as contained within a codebook. Such a
`
`codebook based precoding is likely to be an integral part of various mobile communication
`
`networks, e.g., LTE or MIMO for High Speed Downlink Packet Access (HSDPA) in
`
`Wideband Code Division Multiple Access (WDCMA) system.
`
`[0006]
`
`Codebook based precoding is a form of channel quantization. A typical
`
`approach when using a system, such as, L TE or MIMO in WDCMA, is to let the receiver
`
`recommend a suitable precoder matrix to the transmitter by signaling the precoder index over
`
`a feedback link. The transmitter may choose to override the recommendation of the receiver
`
`so that it might be necessary to signal the precoder index that is actually used in the
`
`transmission to the receiver. In order to limit signaling overhead, it may be desirable to keep
`
`the codebook size as small as possible. This design desire, however, needs to be balanced
`
`against the performance impact, since a larger codebook allows a better match to the current
`
`channel conditions.
`
`[0007)
`
`Accordingly, methods, devices, systems and software for communicating
`
`codebook-related information, or other transmission parameters, are desirable.
`
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`SUMMARY
`
`10008)
`
`According to one exemplary embodiment, a method for communicating in a
`
`mobile network includes the steps of: receiving a message at a user equipment, wherein the
`
`message identifies a permissible subset associated with a set of transmission parameters,
`
`selecting, by the user equipment, one of the transmission parameters from the permissible
`
`subset, and transmitting an indication of the selected one of the transmission parameters using
`
`one of a plurality of different uplink control channel structures, the one of the plurality of
`
`different uplink control channel structures being selected based on the permissible subset.
`
`[0009)
`
`According to another exemplary embodiment a user terminal includes a
`
`transceiver for sending and receiving signals, including receiving a signal which identifies a
`
`permissible subset associated with a set of transmission parameters, a memory device for
`
`storing the set of transmission parameters, and a processor, connected to the transceiver and
`
`the memory device, and for selecting one of the transmission parameters from the permissible
`
`subset, wherein the transceiver transmits an indication of the selected one of the transmission
`
`parameters using one of a plurality of different uplink control channel structures, the one of
`
`the plurality of different uplink control channel structures being selected based on the
`
`permissible subset.
`
`[0010)
`
`According to still another exemplary embodiment, a method for
`
`communicating in a mobile network includes the steps of transmitting a message, wherein the
`
`message identifies a permissible subset associated with a set of transmission parameters, and
`
`receiving an indication of one of the transmission parameters which has been selected from
`
`the permissible subset on one of a plurality of different uplink control channel structures, the
`
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`one of the plurality of different uplink control channel structures being selected based on the
`
`permissible subset.
`
`(0011)
`
`According to still another exemplary embodiment, a network node includes a
`
`transceiver for sending and receiving signals, including transmitting a signal which identifies
`
`a permissible subset associated with a set of transmission parameters, a memory device for
`
`storing the set of transmission parameters, and a processor, connected to the transceiver and
`
`the memory device, wherein the transceiver receives an indication of a selected one of the
`
`transmission parameters on one of a plurality of different uplink control channel structures,
`
`the one of the plurality of different uplink control channel structures being selected based on
`
`the permissible subset.
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`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0012)
`
`[0013)
`
`The accompanying drawings illustrate exemplary embodiments, wherein:
`
`Figure I depicts elements of a radiocommunications system according to
`
`exemplary embodiments;
`
`[0014]
`
`Figure 2 depicts elements of another radiocommunication system according to
`
`exemplary embodiments;
`
`(0015]
`
`Figure 3 illustrates elements of still another radiocommunication system
`
`according to exemplary embodiments;
`
`[0016)
`
`Figure 4 shows a block diagram representation of, for example, a mobile
`
`terminal or a network node according to exemplary embodiments;
`
`[0017]
`
`[0018)
`
`Figure 5 depicts a codebook according to exemplary embodiments;
`
`Figure 6 shows a plurality of different control channel structures according to
`
`exemplary embodiments;
`
`[0019)
`
`Figure 7 is a flowchart illustrating a method for communicating according to
`
`an exemplary embodiment; and
`
`[0020]
`
`Figure 8 is a flowchart illustrating another method for communicating
`
`according to an exemplary embodiment.
`
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`DETAILED DESCRIPTION
`
`(0021)
`
`The following detailed description of the exemplary embodiments refers to the
`
`accompanying drawings. The same reference numbers in different drawings identify the
`
`same or similar elements. Also, the following detailed description does not limit the
`
`invention. Instead, the scope of the invention is defined by the appended claims. The
`
`following embodiments are discussed, for simplicity, with regard to the terminology and
`
`structure of L TE systems. However, the embodiments to be discussed next are not limited to
`
`L TE systems but may be applied to other existing telecommunications systems.
`
`(0022]
`
`Reference throughout the specification to "one embodiment" or "an
`
`embodiment" means that a particular feature, structure, or characteristic described in
`
`connection with an embodiment is included in at least one embodiment of the present
`
`invention. Thus, the appearance of the phrases "in one embodiment" or "in an embodiment"
`
`in various places throughout the specification are not necessarily all referring to the same
`
`embodiment. Further, the particular features, structures or characteristics may be combined
`
`in any suitable manner in one or more embodiments.
`
`(0023)
`
`Codebook subset restrictions (CBSSRs) can be used by the system to restrict
`
`the user equipment (UE) from using the complete set of available precoders. One reason for
`
`using CBSSRs is that only parts of the entries in a codebook may be suitable for a particular
`
`antenna arrangement. For example, if a correlated array (also known as a traditional
`
`beamformer) is used at the cell site, only elements in the codebook corresponding to
`
`beamforming vectors are of value for selection and use. To ensure that a UE selects an
`
`appropriate beamforming vector, the system can restrict the UE to search for the "best"
`
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`precoder among the subset of precoders which containing suitable beamforming vectors, and
`
`prevent the UE from using and/or evaluating other codebook elements, i.e., those which do
`
`not provide such beamforming vectors.
`
`[0024)
`
`To provide some context for the following exemplary embodiments related to
`
`restricted codebooks and associated signaling, consider the exemplary radiocommunication
`
`system as shown from two different perspectives in Figures 1 and 2, respectively. To
`
`increase the transmission rate of the systems, and to provide additional diversity against
`
`fading on the radio channels, modern wireless communication systems include transceivers
`
`that use multi-antennas (often referred to as a MIMO systems). The multi-antennas may be
`
`distributed to the receiver side, to the transmitter side and/or provided at both sides as shown
`
`in Figure I. More specifically, Figure 1 shows a base station 10 having four antennas 12 and
`
`a user terminal (also referred to herein as "user equipment" or "UE") 14 having two antennas
`
`12. The number of antennas shown in Figure 1 is exemplary and is not intended to limit the
`
`actual number of antennas used at the base station or at the user terminal in the exemplary
`
`embodiments to be discussed below. Additionally, the term "base station" is used herein as a
`
`generic term. As it is known by those skilled in the art, in the Wideband Code Division
`
`Multiple Access (WCDMA) architecture, a NodeB may correspond to the base station. In
`
`other words, a base station is a possible implementation of the NodeB. However, the term
`
`"NodeB" is also broader than the conventional base station since the NodeB refers, in
`
`general, to a logical node. A NodeB in a WCDMA system handles transmission and
`
`reception in one or several cells, as shown for example in Figure 2.
`
`[0025]
`
`Figure 2 shows two NodeB IO and one user terminal 14. The user terminal 14
`
`uses dedicated channels 16 to communicate with the NodeB 10. The two NodeBs 10 are
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`wired to corresponding Radio Network Controllers (RNC) 18. One RNC 18 may control
`
`more than one NodeB 10. The RNCs 18 are connected to a Core Network 20. For the L TE
`
`architecture, there is a single node, the eNodeB. One possible L TE architecture is shown in
`
`Figure 3, in which the eNodeB 22 may include a physical layer PHY 24, a medium access
`
`control MAC 26, a radio link control RLC 28, and a packet data convergence protocol PDCP
`
`30. Although conventionally the term "base station" is narrower than the NodeB of the
`
`WCDMA architecture or the eNodeB of the L TE architecture, the term "base station" is used
`
`in the following embodiments as defining the NodeB, eNodeB or other nodes specific for
`
`other architectures. Thus, the term "base station" defined and used in the present disclosure
`
`is not limited to the conventional base station unit of a network.
`
`(0026)
`
`When using a restricted codebook, a mobile communications system can
`
`restrict a UE 14 from searching the whole codebook and reporting the complete results to a
`
`network node which, in turn, can result in an increase in system performance. However, this
`
`increased performance does not necessarily improve the overhead associated with uplink
`
`(UL) transmissions. For example, consider a codebook which contains 64 elements (i.e.,
`
`represented by six bits of data) and a UE 14 that is restricted to use only eight of those
`
`elements by CBSSR. In this case, the UE 14 will then search (only) over the eight allowed
`
`elements and then report the index which corresponds to the "best" one of the restricted
`
`subset precoder selection. However, since the codebook contains 64 elements, six bits are
`
`used to convey the precoder information (per layer) from the UE 14 to the network node 10,
`
`22 (e.g., base station or eNodeB). This use of six bits from the UE 14 to the network node
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`10, 22 is wasteful of capacity since only eight out of the possible 64 elements are allowed to
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`be selected by the UE 14, which implies that only three bits are needed to convey the identity
`
`of this particular selection.
`
`[0027)
`
`Exemplary embodiments of the present invention use this recognition to save
`
`uplink (UL) capacity by adapting the uplink control channel structure dependent upon
`
`whether, for example, a restricted codebook is being used for a particular connection between
`
`UE 14 and node 10, 22, or not. According to some exemplary embodiments, the number of
`
`different control channel structures can vary as a function of the number of bits used to
`
`convey the selected codebook, e.g., one control channel structure for each different number
`
`of bits which can be used to convey the codebook information, one control channel structure
`
`for every second different number of bits, down to the provision of only two different control
`
`channel structures overall. It will be appreciated that the number of different UL control
`
`channel structures which are provided in any given implementation will vary based upon, for
`
`example, the competing design considerations associated with, on the one hand, improved
`
`capacity and, on the other hand, system complexity. Moreover, although these exemplary
`
`embodiments are provided in the context of codebook signaling generally, and restricted
`
`codebook signaling, specifically, it will be appreciated that the present invention is not so
`
`limited. More generally, exemplary embodiments provide also for using different uplink
`
`control channel structures to convey other types of variable feedback from the UE 14 to
`
`network node 10, 22, e.g., modulation alphabet information, transmit power information,
`
`transport block size information, channelization code information, channel quality indicator
`
`(CQI) information, etc.
`
`[0028)
`
`Figure 4 shows a generic structure of the user terminal or UE 14 according to
`
`an exemplary embodiment which can be used to transmit, e.g., restricted codebook selection
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`information, on an uplink channel having a format which is selected based upon the number
`
`of selection items in the subset. The user terminal 14 includes one or more antennas 40
`
`connected to processor 42. The processor 42 is configured to analyze and process signals
`
`received via the antennas 40. The processor 42 is connected to a memory 44 via a bus 46.
`
`One skilled in the art would understand from Figure 4 that various ones of the elements
`
`shown therein may be implemented as electrical circuitry, software instructions or a
`
`combination of these two possibilities. The user terminal 14 may also include a switching
`
`unit 48 configured to switch from a first transmission mode, e.g., using a first uplink control
`
`channel structure, to a second transmission mode, e.g., a second uplink control channel
`
`structure which is different from the first uplink control channel structure. Other units and/or
`
`elements are, for example, an input/output unit 50 that allows a user to input commands to the
`
`processor 42 or a communication port 52 that allows the user terminal 14 to receive data from
`
`another communication system. Further units, not shown, for performing various operations
`
`as encoding, decoding, modulation, demodulation, encryption, scrambling, precoding, etc.
`
`may optionally be implemented not only as electrical components but also in software or a
`
`combination of these two possibilities as would be appreciated by those skilled in the art.
`
`The elements illustrated in Figure 4 can also be found in a network node used in exemplary
`
`embodiments, e.g., a base station.
`
`(0029)
`
`The memory 44 may also contain a stored version of a codebook. An
`
`exemplary codebook 60 is shown in Figure 5, which table is reproduced from section
`
`6.3.4.2.3 of 3GPP TS 36.211, which is a standards document entitled "Evolved Universal
`
`Terrestrial Radio "Access (E-UTRA), Physical Channels and Modulation" available from the
`
`3GPP organization at www.3gpp.org. Some or all of the information illustrated in Figure 5
`
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`can be stored, e.g., as a matrix, in memory 44. It will be appreciated that codebooks may
`
`come in numerous different sizes and that the one illustrated in Figure 5 is purely illustrative.
`
`[0030)
`
`According to exemplary embodiments, codebook subset restrictions
`
`(CBSSRs) can be signaled to a UE 14 using a bitmap mask which differentiates between
`
`allowed entries and disallowed entries within a codebook, such as that illustrated in Figure 5.
`
`For example, using the exemplary codebook in Figure 5 having a size of 16, a bitmap mask
`
`pattern of [O 1 1 0 0 1 1 0 0 0 0 0 0 0 0 O] could be applied to that codebook to indicate that
`
`only options 2, 3, 6 and 7 are allowed as selectable options from the codebook. This bitmap
`
`mask can then be signaled to the UE 14 from a network node 10, 22 in a downlink (DL)
`
`control signal, e.g., an RRC configuration command signal mapped to, at least ultimately,
`
`ultimately the physical downlink shared channel (PDSCH) in an L TE system. Different
`
`combinations of codebooks and bitmap masks, e.g., 2 bits, 4 bits, etc., can be used as desired.
`
`Additionally, other methods for restricting options within a codebook (or equivalent data
`
`structure) can be used.
`
`[0031)
`
`Continuing with this example, the UE 14 may then select one of the four
`
`unrestricted codebook options from its codebook 60 using any desired technique, e.g.,
`
`knowledge of channel conditions, etc. Thus the UE 14 restricts its choice to, and reports back
`
`to the network node 10, 22, one out of the four permissible codebook entries as the preferred
`
`choice. This response from UE 14 only requires two bits of feedback as compared to the
`
`three bits of feedback that would have been required if the codebook had not been restricted,
`
`i.e., using the original unrestricted codebook. According to exemplary embodiments of the
`
`present invention, this feedback information can be reported back to the network node using
`
`one of a plurality of different uplink control channel structures. Conceptually, this can be
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`visualized as shown in Figure 6, wherein three different control channel structures are defined
`
`for an exemplary system, each of which has a different number of bits assigned to the field
`
`"Precoder Set.". As mentioned earlier, the number of different control channel structures
`
`which are defined for a given implementation may be different than three, e.g., 2, 4, or any
`
`other number. However, for this example, the UE 14 would select the uplink control channel
`
`structure of CC# 1 since it has a precoder selection field with the fewest number of bits which
`
`can identify its selection given the number of permissible choices due to the codebook
`
`restriction. When the network node I 0, 22 receives this uplink signal from the UE 14, it will
`
`know that the structure selected will be CC# 1, since it sent the UE 14 the original CBS SR
`
`message restricting it to four possible codebook choices and, thus, will process the received
`
`signal using this knowledge of the correct control channel structure.
`
`(0032)
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`Of course the actual, physical structure of the uplink channel will vary based
`
`upon the system implementation such that the illustration of Figure 6 should be considered
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`merely illustrative of the concept of varying uplink control channel structures according to an
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`exemplary embodiment. For example, in an LTE system such as that shown in Figure 3, the
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`codebook selection information can be transmitted as part of the Layer I/Layer 2 (Ll/L2)
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`signaling information, e.g., as part of, or in a manner similar to CQI/PMI/RI (i.e., feedback of
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`channel state information parameters). This information can be conveyed on the physical
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`uplink control channel (PUCCH), e.g., as part of an OFDM subframe assigned for uplink
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`Ll/L2 control or, alternatively, as part of the control information field on a physical uplink
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`shared channel (PUSCH), wherein it is multiplexed together with uplink data from the UE 14.
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`(0033]
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`One challenge that can arise from having a multitude of combinations for
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`both the original codebook size and the different restriction sizes, e.g., different sized bitmap
`
`masks, is the potentially large number of control channels to be accounted for if, for example,
`
`a different control channel structure is available for every different minimum number of bits
`
`which can be used to convey a particular selection. For example, the absolute minimum
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`number of bits needed to convey a selection of one of two elements or parameters is one, a
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`selection of one of four elements or parameters is two, a selection of one of eight elements or
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`parameters is three, a selection of one of sixteen elements or parameters is four, a selection of
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`one of 32 elements or parameters is five, a selection of one of 64 elements or parameters is
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`six, and so on. Thus, for an exemplary codebook having 64 elements and defined subsets of
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`4, 6, 12, 20, 36 and 40 elements, one system implementation according to these exemplary
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`embodiments would involve defining six different uplink control channel structures each of
`
`which used a different number of bits to convey an indicator of which codebook element was
`
`selected by the UE 14. Alternatively, to balance the complexity of having a greater number
`
`of control channels against, while still obtaining uplink overhead reduction (i.e., potential
`
`efficiency improvement), from a reduced number of bits to be transmitted, exemplary
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`systems and methods provide for fewer different control channel structures.
`
`(0034]
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`For example, a restriction can be introduced by defining only two (or a few)
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`control channel structures, i.e., some number of control channel structures fewer than the
`
`different number of minimum bits needed to convey the indicator. For example, one control
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`channel structure could be used to convey indicators associated with selection of an
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`unrestricted codebook and one (or a few) different control channel structure(s) could be used
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`to convey precoder information (or other desired information as previously described above)
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`for a restricted codebook. For example, if the original codebook contains 64 elements, the
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`main control channel structure would carry six bits of precoder information (per layer). If an
`
`additional control channel structure is defined that can carry four bits, then all CBSSR
`
`resulting in a restricted codebook with less than 16 entries could use this control channel
`
`structure.
`
`(0035)
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`According to another exemplary embodiment, a control channel structure can
`
`be defined in such a way that it can carry two bits of precoder information. This exemplary
`
`control channel structure can be used whenever the CBSSR leads to a restricted codebook
`
`smaller than 4 elements. Alternatively, different amounts of bits of precoder information can
`
`be defined to be carried over a control channel structure dependent upon system needs and
`
`codebook size. From this reduction in response bits the uplink overhead can be reduced
`
`which potentially leads to an increase in system performance or, alternatively, allow for other
`
`information to be transmitted in unused bits within this space.
`
`(0036)
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`It will be appreciated from the foregoing that the number of bits used to
`
`convey the indicator of a transmission parameter from the UE 14 back to the network node
`
`10, 22 may, in some cases, equal an absolute minimum number of bits necessary to convey
`
`such information or may be more than the absolute minimum number of bits, i.e., a relative
`
`minimum number of bits based upon the decision to limit the number of different control
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`channel structures which are provided in a given system. Thus, as used herein, the phrase
`
`"minimum number of bits which are needed for transmitting" may be the absolute minimum,
`
`or may be more than the absolute minimum but represent a relative minimum given the
`
`number of different control structures which are defined.
`
`(0037)
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`Thus, a method for communicating in a mobile network from the UE 14's
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`perspective can include the steps illustrated in Figure 7. Therein, at step 700, a message is
`
`received at a user equipment which message identifies a permissible subset associated with a
`
`set of transmission parameters, e.g., a set of codebook elements or other types of transmission
`
`parameters as described above. The user equipment selects one of the transmission
`
`parameters from the permissible subset at step 702 and transmits an indication of the selected
`
`one of the transmission parameters using one of a plurality of different uplink control channel
`
`structures (step 704), which can be selected based on said permissible subset. For example, if
`
`the permissible subset includes four elements, then the selected uplink control channel
`
`structure could be the one which provides the closest number to (but at least) two bits for
`
`conveying such information.
`
`[0038)
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`Similarly, a method for communicating in a mobile network from the
`
`network's perspective can include the steps illustrated in the flow chart of Figure 8. Therein,
`
`at step 800, a message is transmitted which identifies a permissible subset associated with a
`
`set of tr