Allocating a control channel for carrier aggregation

Methods for allocating a physical downlink control channel (PDCCH) to reduce a number of PDCCH candidates in a search space for carrier aggregation on a user equipment (UE) are disclosed. The method comprises the step of selecting a control channel element (CCE) aggregation level for a PDCCH allocation for each of a plurality of user equipments (UEs) at an evolved NodeB (eNB). The operation of identifying a transmission mode for each of a plurality of component carriers (CCs) associated with the PDCCH at the eNB follows. The next operation of the method is assigning each CC's downlink control information (DCI) into CCEs in a PDCCH search space in the PDCCH starting at a CCE location based on the CC's transmission mode and the CCE aggregation level for the UE receiving the CC.

BACKGROUND

Wireless mobile communication technology uses various standards and protocols to transmit data between a base transceiver station (BTS) and a wireless mobile device. In the third generation partnership project (3GPP) long term evolution (LTE) systems, the BTS is a combination of evolved Node Bs (eNode Bs or eNBs) and Radio Network Controllers (RNCs) in a Universal Terrestrial Radio Access Network (UTRAN), which communicates with the wireless mobile device, known as a user equipment (UE). Data is transmitted from the eNode B to the UE via a physical downlink shared channel (PDSCH). A physical downlink control channel (PDCCH) is used to transfer downlink control information (DCI) that informs the UE about resource allocations or scheduling related to downlink resource assignments on the PDSCH, uplink resource grants, and uplink power control commands. The PDCCH can be transmitted prior to the PDSCH in each subframe transmitted from the eNode B to the UE.

DETAILED DESCRIPTION

Before the present invention is disclosed and described, it is to be understood that this invention is not limited to the particular structures, process steps, or materials disclosed herein, but is extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular examples only and is not intended to be limiting. The same reference numerals in different drawings represent the same element.

EXAMPLE EMBODIMENTS

A system and method is provided for allocating a physical downlink control channel (PDCCH) to reduce a number of PDCCH candidates in a search space for carrier aggregation on a user equipment (UE). A control channel element (CCE) aggregation level is selected for a PDCCH allocation for each of a plurality of user equipments (UEs) at an evolved NodeB (eNB). A transmission mode is identified for each of a plurality of component carriers (CCs) associated with the PDCCH at the eNB. Each CC's downlink control information (DCI) is assigned into CCEs in a PDCCH search space starting at a CCE location based on the CC's transmission mode and the CCE aggregation level for the UE receiving the CC. The eNode B can provide the allocation of the PDCCH and assignment of the CCEs to a search space using a transmission mode to create more search spaces for the CCs of the UE. Using the transmission mode can generate up to eight additional search space starting locations by partitioning the search space. The UE may use the carrier index (CI) or the DCI size along with the transmission mode to assign the CCEs to a PDCCH search space.

After the CCEs are assigned to a PDCCH search space, the PDCCH can be transmitted to a UE. At the UE, the PDCCH can be searched by the UE for each of the UE's CC's DCI. The UE may use the transmission mode, the carrier index (CI), and/or the DCI size to efficiently search smaller PDCCH search spaces in the PDCCH.

Data in wireless mobile communication can be transmitted on the physical (PHY) layer by the eNode B (also commonly denoted as an enhanced Node B, evolved Node B, or eNB) to the user equipment (UE) using a generic long term evolution (LTE) frame structure, as illustrated inFIG. 1. A radio frame100of a signal used to transmit the data is configured to have a duration, Tf, of 10 milliseconds (ms). Each radio frame can be segmented or divided into ten subframes110ithat are each 1 ms long. Each subframe can be further subdivided into two slots120aand120b, each with a duration, Tslot, of 0.5 ms. The first slot (#0)120acan include a physical downlink control channel (PDCCH)160and a physical downlink shared channel (PDSCH)166, and the second slot (#1)120bcan include data using the PDSCH. Each slot for a component carrier (CC) used by the eNode B and the UE can include multiple resource blocks (RBs)130a,130b,130i,130m, and130nbased on the CC frequency bandwidth. Each RB130ican include twelve 15 kHz subcarriers136(on the frequency axis) and 6 or 7 orthogonal frequency-division multiplexing (OFDM) symbols132(on the time axis) per subcarrier. The RB uses seven OFDM symbols if a short or normal cyclic prefix is employed. The RB uses six OFDM symbols if an extended cyclic prefix is used. The resource block can be mapped to 84 resource elements (REs)140iusing short or normal cyclic prefixing, or the resource block can be mapped to 72 REs (not shown) using extended cyclic prefixing. The RE can be a unit of one OFDM symbol142by one subcarrier (i.e., 15 kHz)146. Each RE can transmit two bits150aand150bof information in case of quadrature phase shift keying (QPSK) modulation. Other types of modulation may be used as well. For instance, when bi-phase shift keying (BPSK) modulation is used, then only a single bit of information is transmitted.

In carrier aggregation (CA), CCs for a Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network can be combined together to form a larger bandwidth for the UE, as illustrated inFIG. 2. For example, the UMTS may have a system bandwidth210of 100 MHz in a frequency spectrum216with each CC212having a 20 MHz bandwidth. Each CC may comprise a plurality of subcarriers214. Some UEs230may use the entire 100 MHz system bandwidth by aggregating five 20 MHz CCs together to achieve a 100 MHz UE bandwidth220. In another example, two UEs232aand232beach with a 40 MHz bandwidth capability may each use two 20 MHz CCs together to achieve a 40 MHz UE bandwidth222for each UE. In another example, each UE234a,234b,234c,234d, and234emay use a single 20 MHz CC to achieve a 20 MHz UE bandwidth224. The CCs at an eNode B may be aggregated for some UEs while other UEs may use a single CC during the same interval. For example, one UE with a 40 MHz bandwidth may be configured while three UEs that each use a single 20 MHz CC are employed in a 100 MHz bandwidth system (not shown). Carrier aggregation allows the bandwidth for a UE to be adjusted and adapted based on the system limitations, the UEs capabilities and bandwidth requirements, the bandwidth available to the system and/or loading on the system.

Each UMTS may use a different carrier bandwidth, as illustrated inFIG. 3. For example, the LTE Release 8 (Rel-8) carrier bandwidths and Release 10 (Rel-10) CC bandwidths can include: 1.4 MHz310, 3 MHz312, 5 MHz314, 10 MHz316, 15 MHz318, and 20 MHz320. The 1.4 MHz CC can include 6 RBs comprising 72 subcarriers. The 3 MHz CC can include 15 RBs comprising 180 subcarriers. The 5 MHz CC can include 25 RBs comprising 300 subcarriers. The 10 MHz CC can include 50 RBs comprising 600 subcarriers. The 15 MHz CC can include 75 RBs comprising 900 subcarriers. The 20 MHz CC can include 100 RBs comprising 1200 subcarriers.

Each subframe of a CC may include downlink control information (DCI) found in a PDCCH, as illustrated inFIG. 4. The PDCCH in the control region may include one to three columns of the first OFDM symbols in each subframe or RB. The remaining 11 to 13 OFDM symbols in the subframe may be allocated to the PDSCH for data. The control region can include Physical Control Format Indicator Channel (PCFICH), physical hybrid automatic repeat request (hybrid-ARQ) indicator channel (PHICH), and the PDCCH. The control region has a flexible control design to avoid unnecessary overhead. The number of OFDM symbols in the control region used for the PDCCH can be determined by the control channel format indicator (CFI) transmitted in the Physical Control Format Indicator Channel (PCFICH). The PCFICH is located in the first OFDM symbol of each subframe. The PCFICH and PHICH can have priority over the PDCCH, so the PCFICH and PHICH are scheduled prior to the PDCCH.

The CFI and the PDCCH can be illustrated by the example ofFIG. 4. Subframe A110a, including slot #0120aand slot #1120b, has a CFI410equal to one indicating the first column of OFDM symbols in a CC's subframe A are used for the PDCCH420and the remaining 13 columns of OFDM symbols (in short cyclic prefixing) are used for the PDSCH430. Each CC includes a plurality of subcarriers436mapped to a plurality of RBs. Subframe B110bhas a CFI412equal to three indicating the first three columns of OFDM symbols in a CC's subframe B are used for PDCCH422and the remaining 11 columns of OFDM symbols (in short cyclic prefixing) are used for PDSCH432. Subframe C110chas a CFI414equal to two indicating the first two columns of OFDM symbols in a CC's subframe C are used for PDCCH424and the remaining 12 columns of OFDM symbols (in short cyclic prefixing) are used for PDSCH434. In the example illustrated inFIG. 4, the subframe A is followed by subframe B and subframe C in time400.

DCI can be mapped to the PDCCH using resource element groups (REGs) except both the PCFICH and PHICH, as illustrated inFIG. 5A. REGs can be used for defining the mapping of control channels to resource elements. A RB may include reference signal REs (reference signal OFDM symbols)522used for transmitting reference signals for a specific antenna port and unused REs (unused OFDM symbols)520not used for transmission on the specific port, which allow other antenna ports to transmit their reference signals. The number of reference signal REs and unused REs used in the RB can depend on the number of antenna ports. REGs can be used to map control channels to the remaining resource elements. REGs include a symbol quadruplet or four REs that do not include reference signal REs.

For example, a two antenna port configured RB502with a CFI=3 can include seven REGs512in the control region or seven REGs used for the PDCCH (if no REGs are used for PCFICH and PHICH), as illustrated inFIG. 5A. A four antenna port configured RB504with a CFI=3 can include six REGs in the control region or six REGs used for the PDCCH (if no REGs are used for PCFICH and PHICH), as illustrated inFIG. 5B. The REGs in the control region of the RBs for a CC can comprise the PDCCH. Each CCE used in the PDCCH can include 9 REGs. The PDCCH can be formed with one or more successive CCEs. A plurality of PDCCHs can be transmitted in a single subframe.

The PDCCH in the control region of a subframe can provide DCI that informs the UE about scheduling on a CC related to downlink resource assignments on the PDSCH, uplink resource grants, and uplink power control commands. Each CC can provide scheduling in the PDCCH (in the control region) for the data in the PDSCH, as illustrated inFIG. 6A. A PDCCH in the control region620afor CC1on CC1600acan provide the scheduling for a PDSCH630afor CC1in a subframe610a. A PDCCH in the control region620bfor CC2on CC2600bcan provide the scheduling for a PDSCH630bfor CC2. A PDCCH in the control region620cfor CC3on CC3600ccan provide the scheduling for a PDSCH630cfor CC3. The subframes610a,610b, and610cfor the CC1, CC2, and CC3may represent the same time duration. Each CC can provide its own PDCCH for the PDSCH scheduling.

In another example, one CC can provide the PDCCH for scheduling downlink resource assignments on the PDSCH of another CC, as illustrated inFIG. 6B. The DCI of one CC can be included or mapped to another CC's PDCCH. For example, the control region for CC1622a, the control region for CC2622b, and the control region for CC3622ccan be contained in the PDCCH on CC1600a. The control region for CC1provides the scheduling for the PDSCH632aon CC1, the control region for CC2provides the scheduling for the PDSCH632bon CC2, and the control region for CC3provides the scheduling for the PDSCH632con CC3. 3GPP LTE systems can provide for cross carrier scheduling of the PDSCH where the PDCCH is transmitted on a CC different from the CC transmitting the PDSCH.

The eNode B may schedule the CCEs in the PDCCH and code the DCI based on a predetermined process, and the UE may receive the transmission and may search for the DCI in the PDCCH and decode the DCI based on the predetermined process. The PDCCH can be formed with one or more successive CCEs. The total number of CCEs in the PDCCH can vary in every subframe k, where kε{0,1,2,3,4,5,6,7,8,9}, of a radio frame. The number of CCEs in the PDCCH can be represented by NCCE,k.

For example, the PDCCH700can include 86 CCEs710, as illustrated inFIG. 7A. Each CCE may include nine REGs512a,512b,512c,512d,512e,512f,512g,512h, and512i. Each REG may include four REs140a,140b,140c, and140d.

The PDCCH can provide control information to multiple UEs in a cell for each subframe k. The UE can perform blind decoding since the UE may be aware of the detailed control channel structure, including the number of control channels (CCHs) and the number of CCEs to which each control channel is mapped. Multiple PDCCHs can be transmitted in a single subframe k which may or may not be relevant to a particular UE. Because the UE does not know the precise location of the DCI information in a PDCCH, the UE searches and decodes the CCEs in the PDCCH until the DCI is found for the UE's CCs. The PDCCH can be referred to as a search space. The UE finds the PDCCH specific to the UE (or the UE's CCs) by monitoring a set of PDCCH candidates (a set of consecutive CCEs on which the PDCCH could be mapped) in a PDCCH search space in each subframe.

The UE can use a Radio Network Temporary Identifier (RNTI) assigned to the UE by the eNode B to try and decode candidates. The RNTI can be used to demask a PDCCH candidate's cyclic redundancy check (CRC) that was originally masked by the eNode B using the UE's RNTI. If the PDCCH is for a specific UE, the CRC can be masked with a UE unique identifier, for example a Cell-RNTI (C-RNTI). If no CRC error is detected the UE can determine that a PDCCH candidate carries the DCI for the UE. If a CRC error is detected then the UE can determine that PDCCH candidate does not carry the DCI for the UE and the UE can increment to the next PDCCH candidate. The UE may increment to the next PDCCH candidate in the search space based on the CCE aggregation level. The CCE aggregation level will be discussed more fully in the following paragraphs.

To reduce the burden and improve the process performance of the UE, the PDCCH can be composed of a search space within the PDCCH to improve searching and decoding of the PDCCH candidates. Each search space can have a starting address determined by the RNTI. The PDCCH can be divided into a common search space710, which can provide scheduling information for system information received by a group of UEs in a cell, and a UE specific space712allocated to control information for a particular UE. The common search space can be composed of the first 16 CCEs (CCE0through CCE15) the remaining CCEs may to allocated to the UE specific space712.

The number of CCEs used to transmit one piece of control information can be determined according to the receiving quality of the PDCCH allocated to a UE or the channel quality of the UE, and the number of CCEs is referred to as a CCE aggregation level or an aggregation level Lε{1,2,4,8}. The aggregation level can be used to determine the size of a search space or the number of CCEs forming a search space, and/or the number of control channel (CCH) candidates in a search space, as illustrated in table702ofFIG. 7B.

In another example, if a search space800includes 8 CCEs810,812,814,816,818,820,818, and820, the total number of CCH candidates that can be decoded may be 15. Eight CCH candidates830,832,834,836,838,840,842, and844can represent the candidates that can be decoded with an aggregation level of one (L=1). The UE can increment through the search space by the aggregation level until the DCI for the CCs of the UE is found.

Four CCH candidates846,848,850, and852can represent the candidates that can be decoded with an aggregation level of two (L=2). Two CCH candidates854and856can represent the candidates that can be decoded with an aggregation level of four (L=4). One CCH candidate858can represent the candidates that can be decoded with an aggregation level of eight (L=8). Searching and decoding the CCH candidates (PDCCH candidates) for the DCI in each subframe can be referred to as blind decoding.

Each decode takes a certain amount of time to process. The UE may have a limited number of blind decodes (for the candidates in the PDCCH) available in the timeframe allotted for decoding before the PDSCH or next subframe is transmitted for processing. For example, a UE may be able to handle up to 44 blind decodes before the PDSCH or next subframe is transmitted for processing. When the number (e.g., 300) of CCH candidates for an aggregation level is greater than a blind decode limit for the UE, then the UE may fail to obtain the CCH information and fail to process the PDSCH. Reducing the number of potential search spaces can be used to assist the UE to find and decode the DCI in the PDCCH efficiently and within an available time limit.

The 3GPP transport stream (TS) 36.2211 V8.4.0 defines a PDCCH allocation procedure for a search space Sk(L). A starting address of a UE specific search space that contains the DCI for a UE can be allocated by Equation 1 defined based on an aggregation level Lε{1,2,4,8}, where Ykis defined by Equation 2, NCCE,kis the total number of CCEs in a kthsubframe (kε{0,1,2,3,4,5,6,7,8,9}), i=0, . . . , L−1 is a constant, m=0, . . . , M(L)−1, and M(L)is the number of PDCCH candidates to monitor in a given search space.
Sk(L)=L·{(Yk+m)mod └NCCE,k/L┘}+i[Equation 1]

The variable Ykis defined by Equation 2, where Y−1=nRNTI≠0, nRNTIis the RNTI number assigned to a UE, A=39827, D=65537, k=└ns/2┘, and ns(nε{0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19}) is the slot number within the radio frame.
Yk=(A·Yk-1)modD[Equation 2]

The 3GPP TS 36.2211 V8.4.0 assignment procedure does not involve CC aggregation. 3GPP Rel-8 and Rel-9 do not support the scheduling of cross carriers and the UE is allocated one C-RNTI in CC aggregation. Using the RNTI and aggregation level of a UE maps the DCI of a UE to a single UE search space. As UE bandwidths increase, the number of PDCCH increase, the number of CCs increase, and the PDCCH search space sizes increase, then the number of decodes used to successfully decode PDCCH candidates will increase.

Instead of using a single search space for a UE, the search spaces may be further partitioned to decrease the search space size for a CC on a UE to reduce the number of blind decodes of PDCCH candidates and allow more efficient decoding of PDCCH candidates. In accordance with one embodiment of the present invention, the starting address of a UE specific search space can utilize the partial or full combinations of the transmission (TX) modes (Tc,m) for a carrier (c), the carrier index (CI) in the DCI format, and the DCI size (S) of different cross carriers. The total possible number of search spaces created using the method can be a product of the transmission (TX) modes (Tc,m) for a carrier (c), the carrier index (CI) in the DCI format, and the DCI size (S).

The eNode B can identify at least one value associated with each CC's PDCCH, where the at least one value represents at least one of a transmission mode for the CC, the carrier index in the DCI format, and/or the DCI size. The eNode B can assign or map the CC's control information (e.g., DCI) into CCEs in a search space based on the at least one value associated with the CC. The UE can receive the transmitted control channel (e.g., PDCCH) from the eNode B. The UE can search for the selected CC's control information in a search space using the CC's value and the CCE aggregation level for the UE receiving the selected CC. The UE can decode each control channel candidate in the search space until a validly decoded control channel candidate is decoded or until all validly decoded control channel candidates in a search space are decoded. The CC's control information, such as the DCI, may be obtained from the validly decoded control channel candidate.

In one embodiment, the eNode B can signal the transmission mode to the UE via a layer three communication link, such as Radio Resource Control (RRC) signaling, in advance of sending the PDCCH for a subframe. The transmission modes for PDSCH reception can include 8 modes: Mode1(single antenna port, port0), mode2(transmit diversity), mode3(large-delay Cyclic Delay Diversity (CDD)), mode4(closed-loop spatial multiplexing), mode5(multi-user multiple-input and multiple-output (MU-MIMO)), mode6(closed loop spatial multiplexing, single layer), mode7(single antenna port, UE-specific reference signal (RS) (port5)), and mode8(single or dual-layer transmission with UE-specific RS (ports7and/or8)). The transmission mode can be changed per subframe via RRC signaling. Usually the transmission changes slowly. Changes in the transmission mode may be based on changes in the environment that the UE is operating. Each CC used by the UE can have independent transmission modes from other CCs. For a system with eight available transmission modes, up to eight additional search spaces for each UE may be partitioned using the transmission modes for scheduling and searching. The DCI size, which can also be used for scheduling and searching, can be related to transmission modes and can be determined from the transmission mode.

The carrier index (CI) can be CIF values or the index of sorted CIF values at the ascending order. The eNode B can configure the CIF values of each CC to UE via Radio Resource Control (RRC) signaling prior to the transmission of the PDCCH for the subframe. The CI can change depending on RRC reconfiguration. Other information transmitted by RRC signaling may also be used for scheduling and searching PDCCH search spaces.

The variable Ykcan be modified to utilize at least one of the transmission modes (Tc,m), the carrier index (CI), and/or the DCI size (S) input parameters for the search space. Using an existing PDCCH assignment procedure and the transmission modes (Tc,m), Ykcan be defined by Equation 3 to increase the number of starting addresses for search spaces based on the transmission mode, where Y−1=nRNTI≠0, A=39827, D=65537, k=└ns/2┘, and nsis the slot number within the radio frame.
Yk=[A·(Yk-1+ƒ(Tc,m))] modD[Equation 3]

The ƒ(Tc,m) can be a function of transmission modes for a carrier (c). The carrier (c) can be a CC used by the UE. The ƒ(Tc,m) can be an integer based on the transmission modes (Tc,m). Equation 3 can be used to distinguish individual PDCCH search spaces for the different CCs in carrier aggregation. Equation 3 can specify that the PDCCHs with the same transmission modes can be located in a shared search space and the PDCCHs having different transmission modes can be located in an different shared search space. The DCI for a carrier may be allocated and mapped by an eNode B to CCEs in the PDCCH based on the transmission mode.

For example, the PDCCH on a subframe610for multiple CCs (600a-600d) may be transmitted by CC1660a, referred to as PDCCH1920, as illustrated inFIG. 9. A first transmission mode search space950starting location for a 1st transmission mode940on an independent search space on PDCCH1918may be calculated to be at a CCE location x962. The independent search space on PDCCH1may have N CCEs (NCCE,k)970for a subframe (k).

A PDCCH922for CC1with the first transmission mode may be assigned to the first transmission mode search space beginning at the CCE location x. The PDCCH for CC1can provide the PDSCH972scheduling for CC1. A PDCCH924for CC2600bwith the first transmission mode may be assigned to the first transmission mode search space950at a CCE location after the PDCCH for CC1. The PDCCH for CC2can provide the PDSCH974scheduling for CC2.

In one embodiment, the PDCCHs may be scheduled in a search space based on the order in which the PDCCHs are processed by an eNode B, and not necessarily based on a CC number or the RNTI. In another embodiment, the PDCCHs with the same transmission mode may be assigned to a search space in any order determined by the eNode B.

A second transmission mode search space952starting location for a second transmission mode942on the independent search space on PDCCH1may be calculated to be at a CCE location s964. A PDCCH926for CC3660chaving the second transmission mode may be assigned to the second transmission mode search space beginning at the CCE location s. The PDCCH for CC2can provide the PDSCH976scheduling for CC3. A third transmission mode search space954starting location for a third transmission mode944on the independent search space on PDCCH1918may be calculated to be at a CCE location v966. A PDCCH928for CC4600dwith the third transmission mode may be assigned to the third transmission mode search space beginning at the CCE location v. The PDCCH for CC4can provide the PDSCH978scheduling for CC4. A fourth transmission mode search space954with a starting location for a fourth transmission mode on the independent search space on PDCCH1may be calculated to be at a CCE location y968when a PDCCH for a fourth transmission mode is used. In the illustration ofFIG. 9, the PDCCHs for the CCs have an aggregation level of two. The first transmission mode, the second transmission mode, the third transmission mode, and the fourth transmission mode does not refer to a mode1, a mode2, a mode3, a mode4, but the terms first, second, third, and fourth are used to distinguish between the available transmission mode that is used.

The UE may search the independent search space on PDCCH1918for the PDCCH for each CC using the existing PDCCH searching procedure and the transmission modes (Tc,m). The transmission mode for a CC can be transmitted to the UE by RRC signaling prior to the subframe transmission. The PDCCH922for CC1600acan be searched in the first transmission mode search space950until the DCI for the CC1is validly decoded. Likewise, the PDCCH924for CC2600bcan be searched in the first transmission mode search space, the PDCCH926for CC3600ccan be searched in the second transmission mode search space952, and the PDCCH928for CC3600ccan be searched in the third transmission mode search space954.

In another example, the PDCCH for a subframe610for multiple CCs (600a-600c) may be transmitted by CC1660a, referred to as PDCCH11020, as illustrated inFIG. 10. A same transmission mode search space1050starting location for a same transmission mode1040as CC1on an independent search space on PDCCH11018may be calculated to be at a CCE location x1062. The independent search space on PDCCH1may have N CCEs (NCCE,k)1068for a subframe (k). A PDCCH1022for CC1with the same transmission mode as CC1may be assigned to the same transmission mode search space beginning at the CCE location x. The PDCCH for CC1can provide the PDSCH1072scheduling for CC1.

A first PDCCH1024for CC2600bwith the same transmission mode as CC1may be assigned to the same transmission mode search space1050at a CCE location after the PDCCH for CC1, such as x+2 in this example. The first PDCCH for CC2can provide the first PDSCH1074scheduling for CC2. A first different transmission mode search space1052starting location for a first different transmission mode1042that is different from the transmission mode of CC1on the independent search space on PDCCH11018may be calculated to be at a CCE location s1064. A second PDCCH1026for CC2with the first different transmission mode may be assigned to the first different transmission mode search space beginning at the CCE location s. The second PDCCH for CC2can provide the second PDSCH1076scheduling for CC2.

A second different transmission mode search space1054having a starting location for a second different transmission mode1044that is different from the transmission mode of CC1on the independent search space on PDCCH1may be calculated to start at a CCE location v1066. A PDCCH1028for CC3600cwith the second different transmission mode may be assigned to the second different transmission mode search space beginning at the CCE location v1066. The PDCCH for CC3may have an aggregation level of four. The PDCCH for CC3can provide the PDSCH1078scheduling for CC3.

The variable Ykcan be modified to utilize the transmission modes (Tc,m) and the carrier index (CI) input parameters to further segment the search space. Using an existing PDCCH assignment procedure, the transmission modes (Tc,m), and the carrier index (CI), Ykcan be defined by equation 4 to increase the number of starting addresses for search spaces based on the transmission mode and CI, where Y−1=nRNTI≠0, A=39827, D=65537, k=└ns/2┘, and nsis the slot number within the radio frame.
Yk=[A·(Yk-1+ƒ(CI,Tc,m))] modD[Equation 4]

The ƒ(CI,Tc,m) can be a function of transmission modes for a carrier (c) and the carrier index (CI) in the DCI formats. The ƒ(CI,Tc,m) can be an integer based on the transmission modes (Tc,m) and the carrier index (CI). The DCI for a carrier may be allocated and mapped by an eNode B to CCEs in the PDCCH based on the transmission mode and the carrier index.

For example, the PDCCH on a subframe610for multiple CCs may be transmitted by CC1600a, referred to as PDCCH11120, as illustrated inFIG. 11. A same transmission mode and carrier index search space1150starting location for a same transmission mode and carrier index1140as CC1on an independent search space on PDCCH11118may be calculated to be at a CCE location x1162. The independent search space on PDCCH1may have N CCEs (NCCE,k)1170for a subframe (k). A first PDCCH1122for CC1with the same transmission mode and carrier index as CC1may be assigned to the same transmission mode and carrier index search space beginning at the CCE location x. The first PDCCH for CC1can provide the first PDSCH1172scheduling for CC1. A second PDCCH1124for CC1with the same transmission mode and carrier index as CC1may be assigned to the same transmission mode and carrier index search space at the CCE location after the first PDCCH for CC1. The second PDCCH for CC1can provide the second PDSCH1174scheduling for CC1.

A first different transmission mode and/or carrier index search space1152starting location for a first different transmission mode and/or carrier index1142different from the transmission mode and/or carrier index of CC1on the independent search space on PDCCH1may be calculated to be at a CCE location j1164. A first PDCCH1126for CC2600bwith the different transmission mode and/or carrier index as CC1may be assigned to the first different transmission mode and/or carrier index search space beginning at the CCE location j. The first PDCCH for CC2can provide the first PDSCH1176scheduling for CC2. A second PDCCH1128for CC2with the first different transmission mode and/or carrier index may be assigned to the first different transmission mode and/or carrier index search space at the CCE location after the first PDCCH for CC2. The second PDCCH for CC2can provide the second PDSCH1178scheduling for CC2.

A second different transmission mode and/or carrier index search space1154starting location for a second different transmission mode and/or carrier index1144different from the transmission mode and/or carrier index of CC1on the independent search space on PDCCH1may be calculated to be at a CCE location g1166. A first PDCCH1130for CC3600cwith the second transmission mode and/or carrier index may be assigned to the second transmission mode and/or carrier index search space beginning at the CCE location g. The first PDCCH for CC3can provide the first PDSCH1180scheduling for CC3. A second PDCCH1132for CC3with the second different transmission mode and/or carrier index may be assigned to the second different transmission mode and/or carrier index search space at the CCE location after the first PDCCH for CC3. The second PDCCH for CC3can provide the second PDSCH1182scheduling for CC3. In the illustration ofFIG. 11, the PDCCHs for the CCs have an aggregation level of two.

The variable Ykcan be modified to utilize the transmission modes (Tc,m), the carrier index (CI), and the DCI size (S) input parameters for the search space. Using an existing PDCCH assignment procedure, the transmission modes (Tc,m), the carrier index (CI), and the DCI size (S), Ykcan be defined by Equation 5 to increase the number of starting addresses for a search spaces based on the transmission mode, CI, and S, where Y−1=nRNTI≠0, A=39827, D=65537, k=└ns/2┘, and nsis the slot number within the radio frame.
Yk=[A·(Yk-1+ƒ(CI,Tc,m,S))] modD[Equation 5]

The ƒ(CI,Tc,m,S) can be a function of transmission modes Tc,mfor a carrier (c), the carrier index (CI) in the DCI formats, and the DCI size (S). The ƒ(CI,Tc,m,S) can be an integer based on the transmission modes (Tc,m), the carrier index (CI), and the DCI size (S). The DCI for a carrier may be allocated and mapped by an eNode B to CCEs in the PDCCH based on the transmission mode, the carrier index, and the DCI size.

For example, the PDCCH for a subframe610on multiple CCs may be transmitted by CC1600a, referred to as PDCCH11220, as illustrated inFIG. 12. A same transmission mode, carrier index, and DCI size search space1250starting location for a same transmission mode, carrier index, and DCI size1240as CC1on an independent search space on PDCCH11218may be calculated to be at a CCE location x1262. The independent search space on PDCCH1may have N CCEs (NCCE,k)1270for a subframe (k). A first PDCCH1222for CC1with the same transmission mode, carrier index, and DCI size as CC1may be assigned to the same transmission mode, carrier index, and DCI size search space beginning at the CCE location x. The first PDCCH for CC1can provide the first PDSCH1272scheduling for CC1. A second PDCCH1224for CC1with the same transmission mode, carrier index, and DCI size as CC1may be assigned to the same transmission mode, carrier index, and DCI size search space at the CCE location after the first PDCCH for CC1. The second PDCCH for CC1can provide the second PDSCH1274scheduling for CC1.

A first different transmission mode, carrier index, and/or DCI size search space1252starting location for a first different transmission mode, carrier index, and/or DCI size1242different from the transmission mode and/or carrier index of CC1on the independent search space on PDCCH1may be calculated to be at a CCE location j1264. A first PDCCH1226for CC2600bwith the different transmission mode, carrier index, and/or DCI size as CC1may be assigned to the first different transmission mode, carrier index, and/or DCI size search space beginning at the CCE location j. The first PDCCH for CC2can provide the first PDSCH1276scheduling for CC2. A second PDCCH1228for CC2with the first different transmission mode, carrier index, and/or DCI size may be assigned to the first different transmission mode, carrier index, and/or DCI size search space at the CCE location after the first PDCCH for CC2. The second PDCCH for CC2can provide the second PDSCH1278scheduling for CC2.

A second different transmission mode, carrier index, and/or DCI size search space1254starting location for a second different transmission mode, carrier index, and/or DCI size1244different from the transmission mode and/or carrier index of CC1on the independent search space on PDCCH1may be calculated to be at a CCE location g1266. A first PDCCH1230for CC3600cwith the second transmission mode, carrier index, and/or DCI size may be assigned to the second transmission mode, carrier index, and/or DCI size search space beginning at the CCE location g. The first PDCCH for CC3can provide the first PDSCH1280scheduling for CC3. A second PDCCH1232for CC3with the second different transmission mode, carrier index, and/or DCI size may be assigned to the second different transmission mode, carrier index, and/or DCI size search space at the CCE location after the first PDCCH for CC3. The second PDCCH for CC3can provide the second PDSCH1282scheduling for CC3. In the illustration ofFIG. 12, the PDCCHs for the CCs have an aggregation level of two.

In another example illustrated byFIG. 13, an eNode B1310includes a coding unit1334and a scheduling unit1332. The coding unit may map the PDCCH bits from a DCI message after performing CRC attachment (using each UE's RNTI1336aand1136b), channel coding, and rate matching. The scheduling unit may use the UE's RNTI, the UE's aggregation level, the transmission mode for each of the UE's CC, the carrier index for each of the UE's CC, and/or the DCI size to schedule the CCEs of a PDCCH in a search space. The PDCCH can then be transmitted to the UEs. The UEs1320aand1320bcan have a searching unit1342aand1342band a decoding unit1342aand1342b, respectively, for blind decoding a PDCCH search space. Each UE may use the UE's RNTI1346aand1346bassigned by the eNode B to de-mask or decode the PDCCH candidates in a search space.

Another example provides a method1400for allocating a PDCCH to reduce a number of PDCCH candidates in a search space for carrier aggregation on a UE, as shown in the flow chart inFIG. 14. The method includes the operation of selecting1410a control channel element (CCE) aggregation level for a PDCCH allocation for each of a plurality of UEs at an eNode B. The operation of identifying1420a transmission mode for each of a plurality of CCs associated with the PDCCH at the eNode B follows. The next operation of the method may be assigning1430each CC's DCI into CCEs in a PDCCH search space in the PDCCH starting at a CCE location based on the CC's transmission mode and the CCE aggregation level for the UE receiving the CC.

The method and system for allocating a PDCCH to reduce a number of PDCCH candidates in a search space for carrier aggregation on a UE may be implemented using a computer readable medium having executable code embodied on the medium. The computer readable program code may be configured to provide the functions described in the method. The computer readable medium may be a RAM, EPROM, flash drive, optical drive, magnetic hard drive, or other medium for storing electronic data. Additionally, the method and system for allocating a PDCCH to reduce a number of PDCCH candidates in a search space for carrier aggregation on a UE may be downloaded as a computer program product transferred from a server or eNode B to a requesting or wireless device by way of machine readable data signals embodied in a carrier wave or other propagation medium.

Modules may also be implemented in software for execution by various types of processors. An identified module of executable code may, for instance, comprise one or more physical or logical blocks of computer instructions, which may, for instance, be organized as an object, procedure, or function.

Nevertheless, the executables of an identified module need not be physically located together, but may comprise disparate instructions stored in different locations which, when joined logically together, comprise the module and achieve the stated purpose for the module.