(12) INTERNA TlONAL APPLICATION PUBLISH ED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`<••> w:~i:Ei:~=-•e,ty
`
`~~":
`
`IDll llllllll 1111111110111111111111111 IIID 111111111111111111 IIII IIIIDII
`~ (10) International Publieation Number
`WO 2013/123961 Al
`
`(43) International Publication Date
`29 August 2013 (29.08.2013) WI PO I PCT
`
`(51) lnternatlonal Pate nt Classification:
`H04L 1100 (2006.01)
`
`(21) lnternatlonal Application Number:
`
`PCT /EP2012/052828
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`(22) International Filing Date:
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`(25) Filing Lau1,.,uage:
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`(26) Publication Language:
`
`20 Febniary2012 (20.02.2012)
`
`English
`
`English
`
`(71) A pplicant (for all designated States except US): NOKIA
`SIEMENS NETWORKS OY [FUFI]; Karaportti 3, FI-
`026 IO Espoo (FI).
`
`(72) lnventors; and
`(75) lnventors/Appllcant~ (for US only): LAH ETKANGAS,
`Eeva [FUFI); Kangasriune 6 A I, FI-90240 Oulu (FI).
`RAAF, Be rnhard [DE/DE]; KnoUerweg 14, 82061 Neur(cid:173)
`ied (DE). PAJUKOSKI, Karl Pekka [Fl/FI]; Purantie 3,
`Fl-90240 Oulu (FI). TllROLA, Esa Tapanl [Fl/Fl]; Port(cid:173)
`tikellonkuja 12, FI-90450 Kempele (FI).
`
`(81) Designated States (unless otherwise indicated. for eve1y
`kind of national protection available): AE, AG, AL, AM,
`AO, AT, AU, AZ, BA, BB, BG, BH, BR, BW, BY, BZ,
`CA, CH, CL, CN, CO, CR, CU, CZ, DE, DK, DM, DO,
`DZ, EC, EE, EG, ES, FI, GB, GD, GE, GH, Gtvl, GT, HN,
`HR, HU, ID, IL, lN, IS, JP, KE, KG, KM, KN, KP, KR,
`KZ, LA, LC, LK, LR, L5, LT, LU, LY, MA, MD, ME,
`MG, MK, MN, MW, MX, MY, MZ, NA, NG, NI, NO, NZ,
`OM, PE, PG, PH, PL, PT, QA, RO, RS, RU, RW, SC, SD,
`SE, SG, SK, SL, SM, ST, SV, SY, TH, TJ, TM, TN, TR,
`TI, TZ, UA, UG, US, UZ, VC, VN, ZA, ZM, ZW.
`
`(84)
`
`Designated States (unless otherwfa·e indicated. for eve,y
`kind of regional protection available): ARIPO (BW, GH,
`GM, KE, LR, LS, M\V, MZ, NA, RW, SD, SL, SZ, TZ,
`UG, ZM, ZW), Eurasian (AM, AZ, BY, KG, KZ, MD, RU,
`TJ, TM), European (AL, AT, BE, BG, CH, CY, CZ, OE,
`DK, EE, ES, FI, FR, GB, GR, HR, HU, IE, IS, IT, LT, LU,
`LV, MC, MK, MT, NL, NO, PL, PT, RO, RS, SE, SI, SK,
`SM, TR), OAP! (BF, BJ, CF, CG, CI, CM, GA, GN, GQ,
`GW, ML, MR, NE, SN, TD, TG).
`
`(54) Title: CONTROLLING A MODULATION AND CODING SCHEME FOR A TRANSMlSSlON BETWEEN A BASE STA(cid:173)
`TION AND A USER EQUlPMENT
`
`{Continued on next page}
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`FIG 1
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`103
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`100
`~
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`(57) Abstract: It is described a method for controUing a
`modulation and coding scheme for a transmis- sion between
`a base station (101) and a user equipment (102), wherein the
`modulation and coding scheme is selectable based on a first
`modulation and coding scheme table comprising entries cor(cid:173)
`responding to a plurality of modulation and coding schemes
`with a fast maximum modulation order or based ou a second
`modulation and coding scheme table comprising entries cor(cid:173)
`responding to a plurality of modulation and coding schemes
`with a second maximum modulation order. The method
`comprises selecting, by the base station (IOI), the first mod(cid:173)
`ulation and coding scheme table or the secoud modulatiou
`and coding scbe1ne table, and controlling, by the base station
`(IOI}, the modulation and coding scheme for the transmis (cid:173)
`sion between the base station (IOI) and the user equipment
`(102) based on the selected modulation and coding scheme
`table.
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`WO 2013/123 961 Al I lllllllllllll 11111111111111111111111 IIII I 111111111111111 lllll llllllllll 11111111111111111111111
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`Published:
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`with international search report (Art. 21(3))
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`DESCRIPTION
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`5
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`Controlling a modulation and coding scheme for a transmission between a base station
`and a user equipment
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`1 O
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`Field of invention
`
`The present invention relates to the field of cellular networks, especially to an evolution of
`L TE networks, and in particular to networks comprising L TE networks and evolved L TE
`networks.
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`Art Background
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`2 O
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`There have been further developments for L TE, for instance relating to a Beyond 4G
`(B4G) radio system which is assumed to be commercially available in 2020. It might how(cid:173)
`ever also be introduced in an evolution of L TE at any date within any new release.
`
`LTE provides a peak bit rate of 30 bps/Hz by using 64QAM modulation and 8x8 MIMO
`transmission. As a result, B4G may require a higher order modulation, for instance
`256QAM, than 64QAM in order to meet future requirements. Higher order modulations
`may be relevant for example in relay backhaul due to better channel quality and better
`radio frequency (RF) properties which are more easily feasible for relays than for user
`equipments (UEs) or for isolated indoor cells where the UEs are close by and therefore
`both having a good link to the access point and no or very little interference from other
`access points due to attenuation by the walls.
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`3 O
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`The modulation order determination of LTE Release 10 is described in TS 36.213 V10.3,
`chapter 7.1.7 and CQI definition in chapter 7.2.3. In L TE (and L TE-Advanced), theoretical
`spectral efficiency is restricted by 64QAM modulation. An improved spectral efficiency
`35 may be gained with extension to 256QAM.
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`In the L TE standard, there is defined a MCS (modulation and coding scheme) index and
`modulation table and CQI (channel quality indicator) table. These are used for determining
`and selecting appropriate modulation and coding schemes. The current tables support up
`to 64QAM. The problem is how to introduce a 256QAM extension or any other higher or-
`der modulation extension for L TE while maintaining backward compatibility and avoiding
`too much complexity.
`
`There may be a need for an improved and flexible system and method being adapted to
`allow an extension to a higher order modulation while remaining backward compatible for
`L TE. In particular it is desirable to maintain signaling formats in particular utilize the same
`number of bits as otherwise different encoding schemes need to be used and potentially
`so called blind decoding has to be applied.
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`Summary of the Invention
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`This need may be met by the subject matter according to the independent claims. Advan(cid:173)
`tageous embodiments of the present invention are described by the dependent claims.
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`2 O According to a first aspect of the invention there is provided a method for controlling a
`modulation and coding scheme for a transmission between a base station and a user
`equipment, wherein the modulation and coding scheme is selectable based on a first
`modulation and coding scheme table comprising entries corresponding to a plurality of
`modulation and coding schemes with a first maximum modulation order or based on a
`second modulation and coding scheme table comprising entries corresponding to a plu(cid:173)
`rality of modulation and coding schemes with a second maximum modulation order. The
`method comprises selecting, by the base station, the first modulation and coding scheme
`table or the second modulation and coding scheme table, and controlling, by the base
`station, the modulation and coding scheme for the transmission between the base station
`and the user equipment based on the selected modulation and coding scheme table.
`
`3 O
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`This aspect of the invention is based on the idea to extend the modulation and coding
`scheme table to a higher order modulation while remaining backward compatible. The first
`table may support for instance up to 64QAM (quadrature amplitude modulation) and the
`second table may support for instance up to 256QAM, or any other higher order modula(cid:173)
`tion extension. It should be noted that although 256QAM is explicitly mentioned herein,
`any other higher modulation order than that used for the first table may be used, for in-
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`stance also 128QAM or in general a higher modulation and coding scheme (MCS) which
`may be characterized by either modulation order or coding scheme of both.
`
`The idea of this method is to introduce a higher order modulation while still supporting a
`5 modulation and coding scheme (MCS) table being introduced for a lower modulation or(cid:173)
`der.
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`The term "modulation order'' in this context may be determined by the number of the
`different symbols that can be transmitted using it. In general MCS also considers different
`code rates and thus indicates the average number of payload bits that can be transmitted
`per symbol. The first maximum modulation order and the second maximum modulation
`order may be the same or may be different.
`
`The term "modulation and coding scheme table" may refer to the MCS table being defined
`in L TE and being used for determining and selecting appropriate modulation and coding
`schemes. The second table may be an extended MCS table being based on the MCS as
`defined in L TE but comprising entries corresponding to a higher order modulation. For
`instance, the backward compatibility may be ensured by having a first table exactly as it is
`currently defined in the L TE standard.
`
`The first and the second table may be different in some respects. For instance, one table
`may be biased more towards low MCS and the second towards high MCS values. For
`example, one table may have more MCS values below a certain threshold MCS. Also the
`density of MCS values at lower MCS may be higher in one table or the center of gravity or
`average of the MCS values may be lower in one table. In one embodiment, one table is a
`mirror image of the other, for instance being mirrored at the middle MCS.
`
`The term "base station" in this context may denote any kind of physical entity being able to
`communicate with a user equipment or any other network device by selecting a modula-
`tion and coding scheme from such a MCS table. A base station in this context may be any
`kind of network device providing the required functionality for the method, it may also be a
`transceiver node in communication with a centralized entity. The base station may be for
`example a NodeB or eNB.
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`The base station may either inform the U E explicitly about a change of the used MCS ta(cid:173)
`ble or may inform and select the MCS table implicitly as part of the capability enquiry pro(cid:173)
`cedure.
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`According to an embodiment of the invention, the second maximum modulation order is
`higher than the first maximum modulation order. In particular, the first maximum modula(cid:173)
`tion order corresponds to 64QAM and the second maximum modulation order corre-
`spends to 256QAM.
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`It should be noted that also other modulation orders may be used, for instance 128QAM.
`
`Furthermore, a few high MCSs may be included in the first table to be able to quickly react
`in case the channel gets suddenly better.
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`1 O
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`According to a further embodiment of the invention, the maximum modulation order may
`correspond to the highest modulation and coding scheme (MCS). Further, the highest
`modulation and coding scheme may be the same for both tables.
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`According to a further embodiment of the invention, the method further comprises deter(cid:173)
`mining, by the base station, actual channel conditions of a radio transmission channel
`being used for the transmission between the base station and the user equipment, deter(cid:173)
`mining, by the base station, a maximum supported modulation order based on the deter-
`2 O mined actual channel conditions, and selecting, by the base station, the first modulation
`and coding scheme table or the second modulation and coding scheme table based on a
`comparison of the maximum supported modulation order with the first maximum modula(cid:173)
`tion order and the second maximum modulation order.
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`If the actual channel conditions do not support the higher order modulation or if the user
`equipment (UE) is not able to support the higher order modulation, the base station may
`perform the modulation and coding for the transmission based on the first table. If the ac(cid:173)
`tual channel conditions are good enough for the higher order modulation and if the UE
`supports the higher order modulation, the base station may perform the modulation and
`coding based on the second table supporting a higher order modulation, for instance up to
`256QAM.
`
`According to a further embodiment of the invention, the method further comprises trans(cid:173)
`mitting information to the user equipment being indicative for the selected modulation and
`coding scheme table.
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`The base station may provide a signal to the UE comprising information about these(cid:173)
`lected and used MCS table. The UE may then perform, based on this information, further
`actions, like CQI reports.
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`According to a further embodiment of the invention, transmitting information to the user
`equipment is based on radio resource control signalling.
`
`By using a common signalling, the UE may be easily informed about the selected MCS
`table. This information may also be included in any information signal comprising informa-
`tion for the UE in view of any other resource control.
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`l O
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`According to a further embodiment of the invention, transmitting information to the user
`equipment is based on implicit signalling.
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`This may refer to the case, wherein the UE may receive information from the base station
`and may determine based on this information the selected MCS table. This may be the
`case for instance as part of the capability enquiry procedure which also makes the capa(cid:173)
`bility available to the eNB. During this kind of set up procedure, where the eNB determines
`capabilities of the UE, the tables may be switched and the UE may be informed implicitly
`2 O without specific signalling.
`
`According to a further embodiment of the invention, the method further comprises receiv(cid:173)
`ing confirmation information from the user equipment being indicative for a performed
`change of the selected modulation and coding scheme table.
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`The base station may carry out the change from one table to the selected MCS table after
`receiving the confirmation signal from the UE. The confirmation signal may thus be indica(cid:173)
`tive for a final change of the MCS tables to be carried out by the base station.
`
`3 O According to a further embodiment of the invention, the first modulation and coding
`scheme table and the second modulation and coding scheme table each comprise a
`common subset of equal entries being arranged at same positions within the first modula(cid:173)
`tion and coding scheme table and the second modulation and coding scheme table. In
`particular, the method further comprises after transmitting the information to the user
`equipment being indicative for the selected modulation and coding scheme table and be(cid:173)
`fore receiving the confirmation information from the user equipment, controlling the mod(cid:173)
`ulation and coding scheme for the transmission between the base station and the user
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`equipment based on the selected modulation and coding scheme table based on the
`common subset of entries.
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`5
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`By using common entries in both MCS tables, the base station may use the common en-
`tries as long as there is no confirmation signal from the UE. This may provide the advan(cid:173)
`tage that there is no misunderstanding and wrong modulation and coding as both parts
`(base station and UE) are using the same modulation and coding scheme (although they
`may possibly use different tables).
`
`1 O According to a further embodiment of the invention, controlling an initial transmission be(cid:173)
`tween the base station and the user equipment is based on the first modulation and cod(cid:173)
`ing scheme table.
`
`The base station and the UE may use the MCS table having the lower maximum modula-
`tion order at the start of each communication. This may provide the advantage that each
`communication starts with the same table and afterwards the base station may decide
`whether to change the MCS table or not. The change may then be performed based on
`the actual channel conditions if the U E can support the MCS table supporting the higher
`order modulation.
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`According to a further embodiment of the invention, the bits of carrying a modulation and
`coding scheme index are the same for the first modulation and coding scheme table and
`for the second modulation and coding scheme table.
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`2 5
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`Thus, it may be ensured that there is a backward compatibility without having to amend
`the MCS tables in their existing form nor the coding and transmission mechanisms that
`are employed to convey the selection out of that table. In a more specific embodiment, the
`tables may have the same size. In particular, parts of the first MCS table and the second
`MCS table are equal, providing common entries as explained above. Entries of the first
`3 O MCS table relating to very low modulation orders may be exchanged (redefined) for the
`second MCS table and may comprise the higher order modulations.
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`3 5
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`According to a further embodiment of the invention, the actual channel conditions are de(cid:173)
`termined based on a channel quality indicator being selectable based on a first channel
`quality indicator table supporting the first maximum modulation order or based on a
`second channel quality indicator table supporting the second maximum modulation order,
`the method comprising receiving, by the base station, a channel quality indicator from the
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`user equipment, and determining, by the base station, the actual channel conditions of the
`radio transmission channel being used for the transmission between the base station and
`the user equipment based on the received channel quality indicator.
`
`Like the MCS tables, also the CQI tables may be selected based on the selection of the
`MCS tables. If there is a switch or change from the first MCS table to the second MCS
`table, there may also be change from the first CQI table to the second CQI table. The UE
`may thus determine the CQI based on a table which corresponds to the selected MCS
`table.
`
`According to a further embodiment of the invention, the method further comprises select(cid:173)
`ing, by the base station, the first channel quality indicator table or the second channel
`quality indicator table based on the selected modulation and coding scheme table, and
`transmitting information to the user equipment being indicative for the selected channel
`quality indicator table.
`
`The information of the selected CQI table may be provided to the UE from the base sta(cid:173)
`tion. The information may also be provided implicitly by informing the user equipment of
`the selected MCS table.
`
`According to a further embodiment of the invention, the first channel quality indicator table
`and the second channel quality indicator table each comprise a common subset of equal
`entries being arranged at same positions within the first channel quality indicator table and
`the second channel quality indicator table.
`
`Like the MCS tables, also the CQI tables may comprise a common subset. Thus, it may
`be ensured that, during switching, there are no misunderstandings between the UE and
`the base station.
`
`According to a second aspect of the invention, there is provided a base station for control(cid:173)
`ling a modulation and coding scheme for a transmission between the base station and a
`user equipment, wherein the modulation and coding scheme is selectable based on a first
`modulation and coding scheme table comprising entries corresponding to a plurality of
`modulation and coding schemes with a first maximum modulation order or based on a
`second modulation and coding scheme table comprising entries corresponding to a plu(cid:173)
`rality of modulation and coding schemes with a second maximum modulation order. The
`base station comprises a selection unit being adapted to select the first modulation and
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`coding scheme table or the second modulation and coding scheme table, and a control
`unit being adapted to control the modulation and coding scheme for the transmission be(cid:173)
`tween the base station and the user equipment based on the selected modulation and
`coding scheme table.
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`5
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`The base station may be any type of access point or point of attachment, which is capable
`of providing a wireless access to a cellular network system. Thereby, the wireless access
`may be provided for a user equipment or for any other network element, which is capable
`of communicating in a wireless manner. The base station may be a NodeB, eNB, home
`1 O NodeB or HeNB, or any other kind of access point or also a multihop node or relay. The
`base station may in particular be used for a B4G, L TE or 3GPP cell and communication.
`
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`The base station may comprise a receiving unit, for example a receiver as known by a
`skilled person. The base station may also comprise a transmitting or sending unit, for ex-
`ample a transmitter. The receiver and the transmitter may be implemented as one single
`unit, for example as a transceiver. The transceiver or the receiving unit and the sending
`unit may be adapted to communicate with the user equipment via an antenna.
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`2 O
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`The base station further comprises a selection unit and a control unit. The selection unit
`and the control unit may be implemented as single units or may be implemented for ex(cid:173)
`ample as part of a standard control unit, like a CPU or a microcontroller.
`
`In one embodiment, the base station may further comprise a determination unit being
`adapted to determine actual channel conditions of a radio transmission channel being
`used for the transmission between the base station and the user equipment, and being
`adapted to determine a maximum supported modulation order based on the determined
`actual channel conditions. The selection unit may be adapted to select the first modulation
`and coding scheme table or the second modulation and coding scheme table based on a
`comparison of the maximum supported modulation order with the first maximum modula-
`tion order and the second maximum modulation order.
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`2 5
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`3 O
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`The determination unit may be implemented as a single unit or may be implemented for
`example as part of a standard control unit, like a CPU or a microcontroller.
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`The user equipment (UE) may be any type of communication end device, which is capable
`of connecting with the described base station. The UE may be in particular a cellular mo-
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`bile phone, a Personal Digital Assistant (PDA), a notebook computer, a printer and/or any
`other movable communication device.
`
`The user equipment may comprise a receiving unit or receiver which is adapted for receiv-
`ing signals from the base station. The user equipment may comprise a transmitting unit for
`transmitting signals. The transmitting unit may be a transmitter as known by a skilled per(cid:173)
`son. The receiver and the transmitting unit may be implemented as one single unit, for
`example as a transceiver. The transceiver or the receiver and the transmitting unit may be
`adapted to communicate with the base station via an antenna.
`
`The user equipment may further comprise a control unit for controlling and configuring the
`transmission based on information received from the base station being indicative for a
`selected MCS table. The control unit may be implemented as a single unit or may be im(cid:173)
`plemented for example as part of a standard control unit, like a CPU or a microcontroller.
`
`According to a third aspect of the invention, there is provided a cellular network system.
`The cellular network system comprises a base station as described above.
`
`Generally herein, the method and embodiments of the method according to the first
`aspect may include performing one or more functions described with regard to the second
`or third aspect or an embodiment thereof. Vice versa, the base station or cellular network
`system and embodiments thereof according to the second and third aspect may include
`units or devices for performing one or more functions described with regard to the first
`aspect or an embodiment thereof.
`
`According to a fourth aspect of the herein disclosed subject-matter, a computer program
`for controlling a modulation and coding scheme for a transmission between a base station
`and a user equipment is provided, the computer program being adapted for, when
`executed by a data processor assembly, controlling the method as set forth in the first
`aspect or an embodiment thereof.
`
`As used herein, reference to a computer program is intended to be equivalent to a refer(cid:173)
`ence to a program element and/or a computer readable medium containing instructions for
`controlling a computer system to coordinate the performance of the above described me-
`thod.
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`The computer program may be implemented as computer readable instruction code by
`use of any suitable programming language, such as, for example, JAVA, C++, and may be
`stored on a computer-readable medium (removable disk, volatile or non-volatile memory,
`embedded memory/processor, etc.). The instruction code is operable to program a com-
`puter or any other programmable device to carry out the intended functions. The computer
`program may be available from a network, such as the World Wide Web, from which it
`may be downloaded.
`
`The herein disclosed subject matter may be realized by means of a computer program
`respectively software. However, the herein disclosed subject matter may also be realized
`by means of one or more specific electronic circuits respectively hardware. Furthermore,
`the herein disclosed subject matter may also be realized in a hybrid form, i.e. in a combi(cid:173)
`nation of software modules and hardware modules.
`
`In the above there have been described and in the following there will be described exem(cid:173)
`plary embodiments of the subject matter disclosed herein with reference to a cellular net(cid:173)
`work system, a base station and a method of controlling a modulation and coding scheme
`for a transmission between a base station and a user equipment. It has to be pointed out
`that of course any combination of features relating to different aspects of the herein dis-
`closed subject matter is also possible. In particular, some embodiments have been de(cid:173)
`scribed with reference to apparatus type embodiments whereas other embodiments have
`been described with reference to method type embodiments. However, a person skilled in
`the art will gather from the above and the following description that, unless otherwise noti(cid:173)
`fied, in addition to any combination of features belonging to one aspect also any combina-
`tion between features relating to different aspects or embodiments, for example even be(cid:173)
`tween features of the apparatus type embodiments and features of the method type em(cid:173)
`bodiments is considered to be disclosed with this application.
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`The aspects and embodiments defined above and further aspects and embodiments of
`the present invention are apparent from the examples to be described hereinafter and are
`explained with reference to the drawings, but to which the invention is not limited.
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`Brief Description of the Drawing
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`Figure 1 shows a cellular network system according to an exemplary embodiment of the
`present invention.
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`Samsung Ex. 1011
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`Figure 2 shows a simulation of spectral efficiency for 64QAM and 256QAM.
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`Figure 3 shows a simulation of spectral efficiency for 4x4 MIMO and 2x2 MIMO, each for
`64QAM and 256QAM.
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`Figure 4 shows a base station and a user equipment within a cellular network system ac(cid:173)
`cording to an exemplary embodiment of the invention.
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`It is noted that in different figures, similar or identical elements are provided with the same
`reference signs.
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`Detailed Description
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`In the following, embodiments of the herein disclosed subject matter are illustrated with
`reference to the drawings and reference to aspects of current standards, such as L TE,
`and their further developments. However, such reference to current standards is only ex(cid:173)
`emplary and should not be considered as limiting the scope of the claims.
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`Figure 1 shows a cellular network system 100. A user equipment 102 is served by a first
`cell 103 of the cellular network system. The first cell is assigned to a base station 101.
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`The transmission and communication between the base station and the user equipment is
`controlled based on a modulation and coding scheme. The modulation and coding
`scheme is selectable based on a first modulation and coding scheme table comprising
`entries corresponding to a plurality of modulation and coding schemes with a first maxi(cid:173)
`mum modulation order or based on a second modulation and coding scheme table com(cid:173)
`prising entries corresponding to a plurality of modulation and coding schemes with a
`second maximum modulation order. In one embodiment, the second maximum modulation
`order is higher (for instance up to 256QAM) than the first maximum modulation order (for
`instance up to 64QAM).
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`The base station may determine actual channel conditions of the radio transmission chan-
`nel being used for the transmission between the base station and the user equipment.
`Then, the base station may determine a maximum supported modulation order based on
`the determined actual channel conditions and eventually based on information from the
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`Samsung Ex. 1011
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`WO 2013/123961
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`PCT/EP2012/052828
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`user equipment which modulation order can be supported by the user equipment. The
`base station then selects the first modulation and coding scheme table or the second
`modulation and coding scheme table based on a comparison of the maximum supported
`modulation order with the first maximum modulation order and the second maximum
`5 modulation order. Thus, the modulation and coding scheme (MCS) for the transmission
`between the base station and the user equipment is controlled based on the selected
`modulation and coding scheme table.
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`The base station may also select the table based on any other information, for instance
`based on predefined selection criteria.
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`In L TE (and L TE-Advanced), theoretical spectral efficiency is restricted by 64QAM mod(cid:173)
`ulation. Figure 2 presents the simulated LTE-Advanced throughput with 8x8-MIMO and
`modulation restricted to 64QAM (reference number 201) (coding rate 8/9) in 1-tap Ray-
`leigh channel with no spatial correlation. Spectral efficiency that would be gained with ex(cid:173)
`tension to 256QAM is also plotted to Figure 2 for comparison (reference number 202). It
`can be seen that extension to 256QAM starts to have effect around 25dB SNR range. In
`these figures the average SINR is plotted against the throughput. Even if the average is
`below the area whether 256QAM provides gain, due to fading the channel conditions may
`still be good for some time.
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`Throughput in L TE is restricted by MCS also in a more practical scenario (for example in
`case of relay backhaul) where there is high spatial channel correlation that restricts the
`usage of large ranks. This is illustrated in the Figure 3 where spectral efficiencies for 2x2
`and 4x4 MIMO schemes with adaptive rank and MCS selections in high spatial correlation
`scenario are plotted as a function of average signal-to-noise ratio. For both 2x2 and 4x4
`schemes two curves are presented, in one of which MCS is restricted to 64QAM (2x2:
`304, 4x4: 302) and another one with MCS set extension to 256QAM (2x2: 303, 4x4: 301).
`It can be seen that extension to 256QAM increases the throughput already from around
`10dB SNR range in these scenarios. That means the throughput is already compromised
`well below the maximum throughput that is possible with 64QAM.
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`The problem is how to introduce 256QAM for L TE to maintain backward compatibility and
`avoid too much complexity. 256QAM addition might need to be done to both MCS index
`and modul