EXTENDING PHYSICAL DOWNLINK CONTROL CHANNELS

Abstract

Disclosed is a method for monitoring downlink control information in a communication system, including receiving information for an orthogonal frequency division multiplex (OFDM) symbol and information for frequency resources through higher layer signaling, and monitoring the downlink control information on a control region defined based on the information for the OFDM symbol and the information for the frequency resources, wherein the control region includes a user equipment (UE)-dedicated search space and a UE-common search space.

Claims

1. A method for monitoring downlink control information in a communication system, the method comprising: receiving information for an orthogonal frequency division multiplex (OFDM) symbol and information for frequency resources through higher layer signaling; and monitoring the downlink control information on a control region defined based on the information for the OFDM symbol and the information for the frequency resources, wherein the control region includes a user equipment (UE)-dedicated search space and a UE-common search space.

2. The method of claim 1, wherein the downlink control information is monitored by using a UE identity.

3. The method of claim 1, wherein the control region further includes a physical hybrid automatic repeat request indicator channel.

4. The method of claim 1, wherein a first control region and a second control region are configured for the control region.

5. The method of claim 4, wherein the control region is one of the first control region and the second control region.

6. An apparatus for monitoring downlink control information in a communication system, the apparatus comprising: a transceiver configured to receive information for an orthogonal frequency division multiplex (OFDM) symbol and information for frequency resources through higher layer signaling; and a controller configured to monitor the downlink control information on a control region defined based on the information for the OFDM symbol and the information for the frequency resources, wherein the control region includes a user equipment (UE)-dedicated search space and a UE-common search space.

7. The apparatus of claim 6, wherein the downlink control information is monitored by using a UE identity.

8. The apparatus of claim 6, wherein the control region further includes a physical hybrid automatic repeat request indicator channel.

9. The apparatus of claim 6, wherein a first control region and a second control region are configured for the control region.

10. The apparatus of claim 9, wherein the control region is one of the first control region and the second control region.

11. A method for transmitting downlink control information in a communication system, the method comprising: transmitting information for an orthogonal frequency division multiplex symbol and information for frequency resources through higher layer signaling; and transmitting the downlink control information on a control region defined based on the information for the OFDM symbol and the information for the frequency resources, wherein the control region includes a user equipment (UE)-dedicated search space and a UE-common search space.

12. The method of claim 11, wherein the downlink control information is monitored by using a UE identity.

13. The method of claim 11, wherein the control region further includes a physical hybrid automatic repeat request indicator channel.

14. The method of claim 11, wherein a first control region and a second control region are configured for the control region.

15. The method of claim 14, wherein the control region is one of the first control region and the second control region.

16. An apparatus for monitoring downlink control information in a communication system, the apparatus comprising: a transceiver configured to: transmit information for an orthogonal frequency division multiplex symbol and information for frequency resources on higher layer signaling; and transmit the downlink control information on a control region defined based on the information for the OFDM symbol and the information for the frequency resources, wherein the control region includes a user equipment (UE)-dedicated search space and a UE-common search space.

17. The apparatus of claim 16, wherein the downlink control information is monitored by using a UE identity (ID).

18. The apparatus of claim 16, wherein the control region further includes a physical hybrid automatic repeat request indicator channel.

19. The apparatus of claim 16, wherein a first control region and a second control region are configured for the control region.

20. The apparatus of claim 19, wherein the control region is one of the first control region and the second control region.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The above and other aspects, features, and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0062] FIG. 1 is a diagram illustrating a conventional structure for PDCCH transmission;

[0063] FIG. 2 is a block diagram illustrating a conventional processing chain for transmitting a DCI format;

[0064] FIG. 3 is a block diagram illustrating a conventional processing chain for receiving a DCI format;

[0065] FIG. 4 is a diagram illustrating a conventional PDCCH transmission process;

[0066] FIG. 5 is a diagram illustrating a principle of carrier aggregation;

[0067] FIG. 6 is a diagram illustrating a conventional heterogeneous network deployment;

[0068] FIG. 7 is a diagram illustrating a conventional PUSCH scheduling in a UL of multiple cells through PDCCH transmission in a single cell;

[0069] FIG. 8 is a diagram illustrating a conventional PDSCH scheduling in a DL of multiple cells through PDCCH transmission in a single cell;

[0070] FIG. 9 is a diagram illustrating a conventional PDCCH transmission in a first cell (macro-cell) and in a second cell (micro-cell);

[0071] FIG. 10 is a diagram illustrating a method of informing an A-UE whether a CI IE is included in DCI formats in a UE-specific manner, according to an embodiment of the present invention;

[0072] FIG. 11 is a diagram illustrating an E-PDCCH multiplexing structure where A-UEs assume a maximum PDCCH size to determine a first E-PDCCH symbol, according to an embodiment of the present invention;

[0073] FIG. 12 is a diagram illustrating an E-PDCCH multiplexing structure where A-UEs decode a PCFICH to determine an actual PDCCH size and a first E-PDCCH symbol, according to an embodiment of the present invention;

[0074] FIG. 13 is a diagram illustrating an assignment of different CI values to different cells, according to an embodiment of the present invention;

[0075] FIG. 14 is a diagram illustrating placement of CCEs for multiple UE-CSS, according to an embodiment of the present invention;

[0076] FIG. 15 is a diagram illustrating an operation for generating a distinct UE-DSS for each cell through a respective distinct initialization of a variable determining the location of a UE-DSS, according to an embodiment of the present invention;

[0077] FIG. 16 is a diagram illustrating an extension of a PDCCH size by configuring a set of possible values and using a PCFICH to indicate one value in the set, according to an embodiment of the present invention; and

[0078] FIG. 17 is a diagram illustrating a combination of explicit and implicit indication by a Node B of a UE-CSS size, according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0079] Various embodiments of the present invention will now be described in detail with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art.

[0080] Additionally, although the present invention is described in relation to an Orthogonal Frequency Division Multiple Access (OFDMA) communication system, it also applies to Frequency Division Multiplexing (FDM) systems and to Single-Carrier Frequency Division Multiple Access (SC-FDMA), OFDM, FDMA, Discrete Fourier Transform (DFT)-spread OFDM, DFT-spread OFDMA, SC-OFDMA, and SC-OFDM.

[0081] In accordance with an embodiment of the present invention, an A-UE is semi-statically configured, for example, through Radio Resource Control (RRC) signaling, the cells over which it may have PDSCH reception or PUSCH transmission. A link between the DL and the UL in those cells may also be configured. The inclusion of the CI IE in DCI formats can be either UE-specific or cell-specific. When the CI IE in DCI formats is UE-specific, each A-UE is informed through higher layer signaling (MAC or RRC signaling) whether its assigned DCI formats in a cell include a CI IE. When the CI IE in DCI formats is cell-specific, the Node B may broadcast whether a CI IE is included in the DCI formats. In both cases, the values of the CI to be monitored by an A-UE are also included. The DCI formats having the CI IE may be all DCI formats or a predetermined subset of DCI formats. For example, DCI formats in the UE-CSS may not contain CI while DCI formats in the UE-DSS may contain CI.

[0082] FIG. 10 is a diagram illustrating a method of informing an A-UE whether a CI IE is included in DCI formats in a UE-specific manner, according to an embodiment of the present invention.

[0083] Referring to FIG. 10, an A-UE is configured in the DL of Cell1 1010, Cell2 1020, and Cell3 1030 for PDSCH reception and in the UL of Cell1 1040 and Cell2 1050 for PUSCH transmission. The cells of PDCCH transmission are also informed to the A-UE through higher layer signaling.

[0084] In FIG. 10, a PDCCH is transmitted only in Cell1 1060. For example, the DL and UL for Cell1 may correspond to a macro-cell, while the DL and UL of Cell2 may correspond to a first micro-cell and the DL of Cell3, and the UL of Cell2 can correspond to a second micro-cell. DCI formats associated with PUSCH transmissions or with TPC for PUSCH or PUCCH transmissions (DCI format 3) will be referred to as UL DCI formats. The remaining DCI formats are associated with PDSCH receptions and will be referred to as DL DCI formats.

[0085] For the setup in FIG. 10, DL DCI formats to the UE include a CI IE having 2 bits. For example, for the DL, the CI values of ‘00’, ‘01”, and “10” can correspond to Cell1, Cell2, and Cell3, respectively, while the CI value “11” is unused. Similarly, for the UL, the CI values of ‘0’ and “1” can correspond to Cell1 and Cell2, respectively. In general, the number of bits for the CI IE can be different between DL DCI formats and UL DCI formats (including, for example, not having any CI IE bits in UL DCI formats while having CI IE bits in DL DCI formats). The association between CI values and Cells may also be implicitly determined. For example, ascending CI values of “00”, “01”, “10”, and “11” can be mapped to Cells in order of increasing carrier frequency.

[0086] The use of CI to indicate the cell for which a DCI format is intended may not be necessary for cells with different BWs because the respective DCI formats may have different sizes. For example, for 2 cells, where the PDCCH is transmitted only in one cell, the CI inclusion in the DL DCI formats is not necessary if, for example, one cell has a BW of 20 MHz and the other cell has a BW of 5 MHz. In general, the primary reason for having a different DCI format size for different BWs is the Resource Allocation (RA) IE in the DCI formats, which should have a larger size for cells with larger BWs, as it addresses a larger number of PRBs.

[0087] The transmission of DCI formats to L-UEs is supported with the conventional PDCCH structure. The PDCCH transmission to A-UEs having PDSCH reception or PUSCH transmission in the same cell is also supported with the conventional PDCCH structure. There is no differentiation between these A-UEs and the L-UEs with respect to the PDCCH transmission, although different DCI formats may be used. For ease of reference, such A-UEs will be referred to as Primary-UEs (P-UEs) and the cell with the PDCCH transmission as Primary-cell (Pcell). Conversely, A-UEs having PDSCH reception or PUSCH transmission in a cell other than the Pcell will be referred to as Secondary-UEs (S-UEs) and the corresponding cells as Secondary-cells (Scells).

[0088] For example, in FIG. 10, UEs receiving PDSCH in Cell1 are P-UEs and Cell1 is the Pcell, while UEs receiving PDSCH in Cell2 are S-UEs and Cell2 is an Scell. An A-UE can be both a P-UE and an S-UE depending on the cell (Pcell or Scell, respectively). Therefore, the classification of an A-UE as a P-UE or an S-UE is unique for each cell and may be different among cells as an A-UE can be a P-UE in the Pcell and the S-UE in an Scell.

[0089] For the PDCCH transmission to S-UEs in Scells, the conventional PDCCH structure or a separate PDCCH structure may be used. For example, for lightly loaded systems for which the capacity (first M OFDM symbols of the DL sub-frame) of the conventional PDCCH structure is not reached for scheduling P-UEs, it is also possible to support the transmission of DCI formats to S-UEs while, for heavily loaded systems, an additional PDCCH structure may be needed to support the PDCCH transmission to S-UEs.

[0090] Whether the conventional PDCCH structure or an Extended PDCCH (E-PDCCH) structure is used can be predetermined or be informed by the Node B through broadcast signaling or through UE-specific higher layer signaling. The PDCCH CCEs for an A-UE can be either in the PDCCH or in the E-PDCCH, but not in both. Whether an A-UE monitors the PDCCH or the E-PDCCH for scheduling a PDSCH or a PUSCH in a specific cell can be semi-statically configured either through higher layer signaling or through broadcast signaling.

[0091] If the E-PDCCH in the Pcell is used for scheduling a PDSCH or a PUSCH in Scells, the following is considered, in accordance with an embodiment of the present invention:

[0092] E-PDCCH Contents

[0093] The E-PDCCH provides an extension to the PDCCH and therefore, conveys information of the same nature. In addition to DCI formats for S-UEs, the E-PDCCH may include a respective PCFICH (referred to as an E-PCFICH) and a PHICH (referred to as an E-PHICH) for PUSCH transmissions in Scells served by the E-PDCCH. The E-PCFICH and the E-PHICH have the same structure as the PCFICH and the PHICH, respectively.

[0094] Frequency Resources for E-PDCCH

[0095] The DCI formats in the E-PDCCH are transmitted in CCEs, but the CCE allocation is in PRBs as the E-PDCCH is orthogonally multiplexed with the PDSCH. The PRBs for the E-PDCCH can be semi-statically or dynamically configured. A semi-static configuration of E-PDCCH PRBs ensures adequate separation in the frequency domain in order to obtain frequency diversity or that the PRBs are selected according to an interference co-ordination technique minimizing interference from adjacent cells.

[0096] Time Resources for E-PDCCH

[0097] The first E-PDCCH symbol can be the first OFDM symbol after the last actual PDCCH OFDM symbol or the first symbol after the last PDCCH OFDM symbol, assuming the maximum number of PDCCH OFDM symbols. When the first E-PDCCH symbol is the first OFDM symbol after the last actual PDCCH OFDM symbol, S-UEs decode the PCFICH to determine the E-PDCCH start. When the first E-PDCCH symbol is the first symbol after the last PDCCH OFDM symbol assuming the maximum number of PDCCH OFDM symbols, maximum E-PDCCH decoding latency results, but errors from incorrect PCFICH detection, which will lead in PDCCH decoding failure, are avoided.

[0098] The last E-PDCCH symbol can be statically, semi-statically, or dynamically configured. With static configuration, the last E-PDCCH symbol can be, for example, the seventh symbol of the DL sub-frame. With semi-static configuration, the last E-PDCCH symbol can be informed by the Node B through a broadcast channel With dynamic configuration, the last E-PDCCH symbol can be informed through the E-PCFICH.

[0099] The range of OFDM symbols indicated by the E-PCFICH for the E-PDCCH can be different than the range of OFDM symbols indicated by the PCFICH for the PDCCH. For example, the E-PCFICH may also indicate 0 OFDM symbols for the E-PDCCH in which case the E-PCFICH and the E-PHICH may be transmitted in the PDCCH.

[0100] FIG. 11 illustrates an E-PDCCH multiplexing structure where A-UEs assume a maximum PDCCH size to determine a first E-PDCCH symbol, according to an embodiment of the present invention.

[0101] Referring to FIG. 11, the PDCCH transmission 1110 has 2 OFDM symbols, out of a maximum of 3 PDCCH OFDM symbols. The first E-PDCCH symbol is the first OFDM symbol after the PDCCH transmission, assuming the maximum of 3 OFDM symbols. Therefore, the first E-PDCCH symbol is the fourth OFDM symbol of the DL sub-frame. The E-PCFICH transmission (not shown) is always in the first E-PDCCH symbol and, for the structure of FIG. 11, it indicates that the E-PDCCH is transmitted in 2 OFDM symbols 1120. The E-PDCCH transmission PRBs 1130 are semi-statically configured through broadcast signaling by the Node B (for example, in an SIB). The E-PDCCH transmission is multiplexed with PDSCH transmissions to various UEs, 1140, 1150, and 1160. PDSCH transmissions to L-UEs may or may not occur in PRBs used for E-PDCCH transmission. As an L-UE cannot be aware of the E-PDCCH existence, if it is assigned PDSCH reception in E-PDCCH PRBs, it will treat such PRBs as PRBs that include a PDSCH. Although this will degrade the PDSCH reception quality for the L-UEs, it is up to the Node B to determine whether or not perform such scheduling. A-UEs can be aware of the E-PDCCH PRBs and apply the appropriate rate matching for their respective PDSCH receptions.

[0102] FIG. 12 illustrates an E-PDCCH multiplexing structure where A-UEs decode a PCFICH to determine an actual PDCCH size and a first E-PDCCH symbol, according to an embodiment of the present invention.

[0103] Referring to FIG. 12, a PDCCH transmission 1210 has 2 OFDM symbols. The first E-PDCCH symbol is the third OFDM symbol, which is the first OFDM symbol after the PDCCH transmission. The E-PCFICH transmission (not shown) is always in the first E-PDCCH symbol and, in the structure illustrated in FIG. 12, it indicates that the E-PDCCH is transmitted in 2 OFDM symbols 1220. The E-PDCCH transmission PRBs 1230 are predetermined.

[0104] If the transmission of DCI formats for multiple Scells is conveyed through the E-PDCCH, in accordance with an embodiment of the present invention, all E-PDCCH CCEs are jointly considered for all Scells, instead of having a separate set of CCEs for each S cell. Therefore, there is only a single set of CCEs in the E-PDCCH, where each S-UE may have its UE-CSS and its UE-DSS. This also enables the transmission of a single E-PCFICH, instead of multiple E-PCFICH with each one corresponding to a different Scell in the E-PDCCH.

[0105] UE-CSS

[0106] In a first alternative, the UE-CSS for S-UEs is separately configured and its size, in number of CCEs, may be broadcasted by the Node B. For example, the UE-CSS size may take one of four predetermined values and the Node B broadcasts 2 bits to indicate that value (for example, through an SIB in the Pcell) or to indicate that the UE-CSS size is either 1, 2, 3, or 4 times a basic size of K CCEs. The CCEs for the UE-CSS in the E-PDCCH are placed first, i.e., before the CCEs for the UE-DSS. Once an S-UE is informed of the UE-CSS size, it needs to determine the CCEs corresponding to each Scell.

[0107] In a first option for the first alternative, the S-UE is informed of the order of Scells either through higher layer signaling, for UE-specific CI configuration, or as part of the system information for cell-specific CI configuration. This is equivalent to an S-UE being informed of the CI value for its DCI formats. In case a CI may not exist, such as, for example, when the cells have unequal BWs, the order may be in terms of decreasing BWs, e.g., the larger BWs are ordered first.

[0108] FIG. 13 is a diagram illustrating an assignment of different CI values to different cells, according to an embodiment of the present invention.

[0109] Referring to FIG. 13, the CCEs for the UE-CSS of the macro-cell 1310 are placed in the PDCCH. The CCEs for the UE-CSS for micro-cell 1 1320 are ordered first in the E-PDCCH (CI=1) and the CCEs for the UE-CSS for micro-cell 2 1330 are ordered second in the E-PDCCH (CI=2). Once the CI values have been assigned to Scells, the CCEs of the UE-CSS of S-UEs are placed in the same order in the logical domain.

[0110] FIG. 14 is a diagram illustrating placement of CCEs for multiple UE-CSS, according to an embodiment of the present invention.

[0111] Referring to FIG. 14, the L.sub.1 CCEs for a first UE-CSS of S-UEs (micro-cell 1 or for a first set of S-UEs, CI=1) are placed first 1410, followed by the L.sub.2 CCEs for a second UE-CSS of S-UEs (micro-cell 2 or for a second set of S-UEs, CI=2) 1420. The placement of the CCEs for the UE-DSS 1430 occurs after the placement of the CCEs for the UE-CSS in the logical domain. The number of CCEs of the UE-CSS for S-UEs for the different CI values, denoted by L.sub.1 and L.sub.2 in FIG. 14, may be implicitly determined from the total UE-CSS size or may be informed by the Node B through broadcast signaling. Alternatively, the number of CCEs for the UE-CSS of S-UEs can be the same for all CI values, regardless of the DL or UL operating BW in each Scell (that is, L.sub.1=L.sub.2 in FIG. 14).

[0112] The CCEs for the UE-CSS of S-UEs are ordered as illustrated in FIG. 14 to reduce the associated number of Blind Decoding Operations (BDOs) because, for each UE-CSS, an S-UE searches a sub-set of the total set of CCEs allocated to the total UE-CSS. Moreover, by ordering the UE-CSSs for S-UEs, it is not necessary to include the CI IE in DCI formats transmitted in each UE-CSS.

[0113] In a second option for the first alternative, the ordering of individual UE-CSS for S-UEs is not applied and the respective CCEs may be distributed over the entire set of CCEs for the total UE-CSS. Thereafter, CI inclusion in the DCI formats is performed and the UE search process for DCI formats can be performed for the UE-DSS of S-UEs as will be described below.

[0114] In a second alternative, the UE-CSS remains unchanged, the S-UEs are treated as P-UEs with respect to the transmission of DCI format 3 and DCI format 1C in Scells, and there is no differentiation of UEs into different categories with respect to the UE-CSS.

[0115] The PCH can be transmitted to all S-UEs in the cell with the PDCCH transmission (Pcell).

[0116] Assuming no transmission of synchronization signals from cells (such as micro-cells) without PDCCH transmission (Scells), S-UEs acquire the synchronization signal of the cell (such as a macro-cell) with PDCCH transmission (Pcell). Thereafter, the RACH process is completed through the Pcell and no additional RACH response signaling, corresponding to cells without PDCCH transmission (Scells), is necessary.

[0117] The SIBs for cells (such as micro-cells) without PDCCH transmission (Scells) can also be transmitted from the cell (such as macro-cell) with PDCCH transmission (Pcell) using different CRC masks in DCI format 1C to indicate the cell corresponding to the SIB transmission.

[0118] DCI format 3 multiplexes TPC commands corresponding to UEs in the cell (such as a macro-cell) with PDCCH transmission (Pcell) and to UEs in the cells (such as micro-cells) without PDCCH transmission (Scells).

[0119] Accordingly, P-UEs have their UE-CSS for DCI format transmission in the PDCCH as in a backward compatible system including a single cell. For S-UEs, either a new UE-CSS is defined in the E-PDCCH, as described above in the first alternative, or no additional UE-CSS is defined and all UEs (P-UEs and S-UEs) use the same UE-CSS in the PDCCH, as described above in the second alternative.

[0120] UE-DSS

[0121] For the UE-DSS and single-cell operation, using the previously defined notation, the CCEs corresponding to a PDCCH candidate m are given by Equation (2).

S.sub.k.sup.(L)=L.Math.{(Y.sub.k+m)mod └N.sub.CCE,k/L┘}+i  (2)

[0122] In Equation (2), N.sub.CCE,k is the total number of CCEs in sub-frame k, i=0, . . . , L−1, m=0, . . . , M.sup.(L)−1, and M.sup.(L) is the number of candidates in the UE-DSS.

[0123] The above UE-DSS structure leads to identical UE-DSSs for different cells (Pcell or Scells) as they are assumed to share the same UE-DSS in the E-PDCCH (or in the PDCCH when it supports the transmission of DCI formats for multiple cells).

[0124] In order to provide distinct UE-DSS, in addition to the UE_ID, in accordance with an embodiment of the present invention, the UE-DSS also depends on the Cell_ID. This can substantially decrease the probability that a DCI format transmission is blocked due to the unavailability of CCEs in the UE-DSS. Reducing this blocking probability increases the probability that a PDSCH or PUSCH scheduling occurs and therefore, improves the respective DL or UL system throughput and enhances operating quality and reliability.

[0125] The Cell_ID may be the CI value allocated to each cell. For example, the UE may be informed of the Cell_ID through higher layer signaling. At least when the cells have equal BWs (and a respective CI is defined), the Cell_ID may be the same as the respective CI. The UE may obtain the Cell_ID during initial synchronization with the respective cell, or if the cell does not transmit synchronization signals, the UE may obtain the respective Cell_ID through higher layer signaling from the cell transmitting synchronization signals after synchronization. Additionally, the Cell_ID may be UE-specific and informed to each UE through higher layer signaling. For example, for 3 cells, instead of having three different respective Cell_IDs, the Cell_ID for each UE can depend on the number of cells the UE is configured for. If UE1 is configured for Cell1 and Cell2, the respective Cell_IDs can be Cell_ID1 and Cell_ID2. If UE2 is configured for Cell2 and Cell3, the respective Cell_IDs can also be Cell_ID1 and Cell_ID2.

[0126] The following example further demonstrates the occurrence of transmission blocking for a DCI format. Assuming that DCI formats to a UE are transmitted with 4 CCEs, then, as there are only 2 candidates in the UE-DSS for this CCE aggregation level, transmission of DCI formats for at most 2 cells can be supported (or one cell, for both PDSCH reception and PUSCH transmission). Also, due to randomization through interleaving, the UE-DSSs for different UEs may have overlapping CCEs, and for this reason it will often be likely that the transmission of a DCI format for only a single cell can be supported.

[0127] An embodiment of the invention to construct separate UE-DSS for each cell considers that the initialization of the variable Y.sub.k includes the Cell_ID. When 0⊕0=0, 0⊕1=1, 1⊕0=1, 1⊕1=0, where ⊕ denotes the binary modulo add operation, an A-UE receives multiple PDSCH or transmits multiple PUSCH in multiple cells while the respective DCI formats are transmitted in a single cell, and Y.sub.−1=(UE_ID)⊕(Cell_ID)≠0 for the UE-DSS of the respective cell.

[0128] FIG. 15 illustrates an initialization of a variable Y.sub.k with a Cell_ID according to an embodiment of the present invention.

[0129] Referring to FIG. 15, the binary UE_ID 1510 and the binary Cell_ID 1520 are added by a binary adder 1530 to provide the initial value Y.sub.−1 1540 of the variable Y.sub.k, randomizing the CCEs in the UE-DSS in sub-frame k for DCI formats corresponding to the respective cell. Assuming a 16-bit UE_ID, the requirement Y.sub.−1≠0 prevents the use of a small number of UE IDs, which has only a minor impact on the total number of 2.sup.16=65536 available UE Ids, considering that the total number of cells for which the DCI formats are transmitted in a single cell is less than 10. Also, as the variable Y.sub.k depends on the Cell_ID, it should be denoted as Y.sub.k.sup.c with c=0, 1, . . . , N.sub.c−1, where N.sub.c is the number of cells for which the respective DCI formats are conveyed in a single cell (Pcell).

[0130] In another embodiment of the invention to construct separate UE-DSS for each cell, denoting as ƒ(c) a function of the CI or of the Cell_ID for cell c, each UE-DSS can be obtained by Equation (3).

S.sub.k,c.sup.(L)=L.Math.{(Y.sub.k+m+ƒ(c))mod └N.sub.CCE,k/L┘}+i  (3)

[0131] One condition for S.sub.k,c.sup.(L) may be that the UE-DSS corresponding to PDSCH/PUSCH scheduling in the Pcell should be defined as for L-UEs. This is useful for maintaining the legacy operation when all cells, other than the Pcell, are deactivated. Therefore, if c.sub.P is the CI or Cell_ID for the Pcell, then ƒ(c.sub.P)=0.

[0132] For CI or Cell_ID values c other than c.sub.P, ƒ(c) may be determined as ƒ(c)=1, 2, . . . , 7 (assuming a 3-bit CI), which can be ranked in ascending order based on the assigned CI values. Only active cells are considered in order to reduce the self-blocking probability for the UE-DSS of an A-UE. The exact values for Scells (excluding the Pcell) are not material as long as they are consecutive and the condition ƒ(c.sub.P)=0 is satisfied for the Pcell. For example, for CI or Cell_ID values c other than c.sub.P, the function ƒ (c) may be determined as ƒ(c)=−3, −2, −1,1,2,3, or in general, by alternating assignments of positive and negative integer values in a consecutive manner around ƒ(c.sub.P)=0 (starting from 1, and continuing with −1, 2, −2, and so on).

[0133] The transmission of DCI formats for scheduling in multiple S cells increases the number of BDOs an A-UE performs. Without any restrictions in the locations of these possible DCI formats, this increase in the number of BDOs is linear with the number of Scells. This increases the UE receiver complexity and also increases the probability of a false CRC test (resulting to a UE incorrectly considering a DCI format as intended for it).

[0134] Several alternative designs exist for reducing the number of BDOs. All consider that the possible locations of DCI formats in the multiple UE-DSSs for a reference UE are mutually dependent. In addition to reducing the number of BDOs and CRC tests, these designs maintain the same receiver architecture (bank of decoders) for the basic single-cell UE-DSS decoding process regardless of the number of cells a UE is configured.

[0135] A first design uses the same aggregation level L for all DCI formats to a reference UE. If for the reference cell c.sub.1 a candidate m is identified by the UE in position L.Math.{(Y.sub.k.sup.c.sup.1+m)mod └N.sub.CCE,k/L┘}+i, m=0, . . . , M.sup.(L)−1, i=0, . . . , L−1, an additional cell c.sub.2 can have a potential candidate n in position L.Math.{(Y.sub.k.sup.c.sup.2+m)mod └N.sub.CCE,k/L┘}+i, n=0, . . . , M.sup.(L)−1. Therefore, after the UE identifies a DCI format for cell c.sub.1, it performs an additional M.sup.(L) BDOs (for n=0, . . . , M.sup.(L)−1) to determine if it also has one for cell c.sub.2.

[0136] A second design enables different aggregation levels to be used for the PDCCH, but imposes a restriction in the possible candidates for each aggregation level. If for cell c.sub.1 a PDCCH is identified for candidate m in position L.sub.1.Math.{(Y.sub.k.sup.c.sup.1+m)mod └N.sub.CCE,k/L┘}+i, m=0, . . . , M.sup.(L)−1, i=0, . . . , L.sub.1−1, an additional cell c.sub.1 can have a potential PDCCH candidate in position L.sub.2.Math.{(Y.sub.k.sup.c.sup.1+m.Math.mod(min(L.sub.1, L.sub.2)))mod └N.sub.CCE,k/L.sub.2┘}+j, j=0, . . . , L.sub.2−1. Therefore, after the UE identifies a PDCCH for cell c.sub.1, it performs a number additional BDOs equal to the number of possible aggregation levels to determine if it also has a PDCCH for cell c.sub.2. In accordance with an embodiment of the present invention, this number of additional BDOs is 4, as the possible aggregation levels are {1,2,4,8}. This process can directly extend to additional cells.

[0137] A third design is a combination of the first and second designs, where the aggregation level used for the PDCCH in a reference cell (Pcell) affects the possible aggregation levels for the PDCCH for the remaining cells (Scells) for which a UE is configured. For example, the aggregation levels used for the PDCCH for the remaining cells may only have the same or the next larger value relative to the one used for the PDCCH for the reference cell (if L=8 is used in the reference cell, then L=8 is also used in the remaining cells). Additionally, the position of the PDCCH for the reference cell affects the possible PDCCH positions for the remaining cells. For example, if the PDCCH position for the reference cell is odd or even numbered, then the position of the potential PDCCH for the remaining cells is also odd or even numbered, respectively. Therefore, for the third design, if for the cell c.sub.1 a PDCCH is identified for candidate m in position L.sub.1.Math.{(Y.sub.k.sup.c.sup.1+m)mod └N.sub.CCE,k/L.sub.1┘}+i, with L.sub.1 ε{1,2,4,8}, m=0, . . . , M.sup.(L.sup.1.sup.)−1, i=0, . . . , L.sub.1−1, an additional cell c.sub.2 can have a potential PDCCH candidate in position L.sub.2.Math.{(Y.sub.k.sup.c.sup.1+2n+mod(m,2)))mod └N.sub.CCE,k/L.sub.2┘}+j, L.sub.2ε{L.sub.1, 2L.sub.1} if L.sub.1<8, L.sub.2=L.sub.1 if L.sub.1=8, n=0, . . . , M.sup.(L.sup.2.sup.)/2−1, j=0, . . . , L.sub.2−1. This process can directly extend to additional cells.

[0138] Additional restrictions for the third design are possible, for example, by requiring the same CCE aggregation level to be used in all cells. The potential combinations are covered by combinations of the principles for the first and second designs as described by the third design.

[0139] The previously described PDCCH extension was compatible with existing single-cell communications. However, PDCCH extension may also be supported in a non-compatible manner. For this case, in accordance with an embodiment of the present invention, a different interpretation of the PCFICH values and a different configuration of the UE-CSS and UE-DSS may apply. Unlike legacy systems for which the PCFICH conveys 3 predetermined values for the PDCCH size, such as for example 1, 2, or 3 OFDM symbols, the PCFICH for non-compatible PDCCH extension can convey more values, which are not predetermined but can semi-statically vary. The Node B may broadcast a configuration of PDCCH sizes, from a set of possible configurations, and the PCFICH may then simply indicate one size from the broadcasted configuration of PDCCH sizes. For example, the Node B may indicate one of the {1, 2, 3, 4}, {2, 3, 4, 5}, {3, 4, 5, 6} and {4, 5, 6, 7}, in number of OFDM symbols, for the PDCCH size configuration. The 2 bits in the PCFICH can then be used to inform the UEs of the PDCCH size within the configuration broadcasted by the Node B.

[0140] FIG. 16 illustrates a PDCCH size extension by configuring a set of possible values and using a PCFICH to indicate one value in the set, according to an embodiment of the present invention.

[0141] Referring to FIG. 16, the Node B broadcasts 2 bits, for example, “10”, to indicate the PDCCH size configuration of {3, 4, 5, 6} symbols 1610. The PDCCH size configuration may take effect at a predetermined sub-frame after the Node B broadcasts it, such as, for example, in the first sub-frame S, such that modulo(S, 40)=0. The PCFICH transmitted in each sub-frame indicates an element from the PDCCH size configuration set, such as, for example, the third element 1620. The UE determines the PDCCH size based on both the broadcasted PDCCH size configuration and the PCFICH value 1630.

[0142] In addition to configuring a total PDCCH size, an individual size of the UE-CSS or UE-DSS can also be configured. For example, the Node B may broadcast the UE-CSS size. Consequently, A-UEs can know that the UE-CSS size may have one of four predetermined values and the Node B simply broadcasts 2 bits to indicate that value or to indicate that the UE-CSS size is 1, 2, 3, or 4 times the basic UE-CSS size of 16 CCEs. The indication of the UE-CSS size may also be implicit based on the PDCCH configuration size. For example, if the Node B broadcasts the third PDCCH configuration size in FIG. 16, A-UEs can identify that the UE-CSS is 3 times the basic UE-CSS size of 16-CCEs, i.e., the UE-CSS size is 48 CCEs or it is determined by the third element in a configured set of UE-CSS sizes such as, for example, a set of {16, 28, 36, 44} CCEs.

[0143] FIG. 17 illustrates explicit and implicit indication by the Node B of a UE-CSS size to A-UEs, according to an embodiment of the present invention.

[0144] Referring to FIG. 17, for explicit indication, the Node B informs A-UEs of the UE-CSS size through a broadcast channel, e.g., an SIB transmission. For example, the Node B transmits 2 bits with a value “10” to indicate 36 CCEs, which is the third element in a set of 4 possible UE-CSS sizes 1710. A-UEs, upon reception of that broadcast information, determine the UE-CSS for each cell 1720, as described above, for PDCCH extension compatible with legacy systems. For implicit indication, the Node B broadcasts the PDCCH size configuration (for example, in an SIB), as described in FIG. 17, and based on this configuration, A-UEs determine the UE-CSS size and the UE-CSS for each cell. For example, the Node B may broadcast the third PDCCH size configuration 1730 and the then A-UEs determine the UE-CSS size to be 36 CCEs 1740.

[0145] While the present invention has been shown and described with reference to certain embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims, and any equivalents thereof.