Method and apparatus for scheduling communication for low capability devices
11659570 · 2023-05-23
Assignee
Inventors
Cpc classification
H04W72/23
ELECTRICITY
H04L5/0053
ELECTRICITY
H04L1/1671
ELECTRICITY
International classification
H04L1/00
ELECTRICITY
H04L1/1822
ELECTRICITY
Abstract
Methods and apparatus are described for a User Equipment (UE) with reduced processing capabilities (e.g., Machine Type Communication (MTC) UE) to transmit and receive signaling are provided. The Downlink Control Information (DCI) formats scheduling a transmission of a Physical Uplink Shared CHannel (PUSCH) or a reception of a Physical Downlink Shared CHannel (PDSCH) are designed and have a smaller size than respective DCI formats for conventional UEs. DCI formats scheduling PUSCHs to or PDSCHs for a group of MTC UEs are also designed and can have a same size as DCI formats scheduling PUSCH or PDSCH for an individual MTC UE.
Claims
1. A method for a user equipment (UE), the method comprising: receiving first physical downlink control channel (PDCCH) candidates based on a first fixed number of PDCCH candidates per respective control channel element (CCE) aggregation levels for a first set of CCE aggregation levels, during an initial access process; receiving, via a higher layer signaling, configuration information related to a second number of PDCCH candidates per respective CCE aggregation levels in a second set of CCE aggregation levels; and receiving second PDCCH candidates based on the second number of PDCCH candidates per respective CCE aggregation levels in the second set of CCE aggregation levels, after receiving the configuration information.
2. The method of claim 1, further comprising: detecting, from the first PDCCH candidates, a PDCCH to schedule a physical downlink shared channel (PDSCH) conveying the configuration information.
3. The method of claim 1, wherein the configuration information includes the second number for the second PDCCH candidates per respective CCE aggregation levels and the second set of CCE aggregation levels.
4. The method of claim 1, further comprising: detecting, from the second PDCCH candidates, a first PDCCH scheduling a physical downlink shared channel (PDSCH), the first PDCCH comprising a first resource allocation (RA) information element (IE) which is represented by a first number of bits and allocating first resources for a transmission of the PDSCH; and detecting, from the second PDCCH candidates, a second PDCCH scheduling a physical uplink shared channel (PUSCH), the second PDCCH comprising a second RA IE which is represented by a second number of bits and allocating second resources for a transmission of the PUSCH, wherein the first RA IE indicates the first resources with a bandwidth (BW) granularity for the PDSCH, the second RA IE indicates the second resources with a reduced BW granularity for the PUSCH.
5. An apparatus in a user equipment (UE), the apparatus comprising: a transceiver; and a processor configured to control the transceiver to: receive first physical downlink control channel (PDCCH) candidates based on a first fixed number of PDCCH candidates per respective control channel element (CCE) aggregation levels for a first set of CCE aggregation levels, during an initial access process, receive, via higher layer signaling, configuration information of a second number of PDCCH candidates per respective CCE aggregation levels in a second set of CCE aggregation levels, and receive second PDCCH candidates based on the second number of PDCCH candidates per respective CCE aggregation levels in the second set of CCE aggregation levels, after receiving the configuration information.
6. The apparatus of claim 5, wherein the processor is configured to: detect, from the first PDCCH candidates, a PDCCH to schedule a physical downlink shared channel (PDSCH) conveying the configuration information.
7. The apparatus of claim 5, wherein the configuration information includes the second number for the second PDCCH candidates per respective CCE aggregation levels and the second set of CCE aggregation levels.
8. The apparatus of claim 5, wherein the processor is configured to: detect, from the second PDCCH candidates, a first PDCCH scheduling a physical downlink shared channel (PDSCH), the first PDCCH comprising a first resource allocation (RA) information element (IE) which is represented by a first number of bits and allocating first resources for a transmission of the PDSCH; and detect, from the second PDCCH candidates, a second PDCCH scheduling a physical uplink shared channel (PUSCH), the second PDCCH comprising a second RA IE which is represented by a second number of bits and allocating second resources for a transmission of the PUSCH, wherein the first RA IE indicates the first resources with a bandwidth (BW) granularity for the PDSCH, the second RA IE indicates the second resources with a reduced BW granularity for the PUSCH.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The above and other aspects, features, and advantages of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:
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(20) Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
(21) The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness.
(22) The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention is provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
(23) It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces.
(24) Additionally, although the exemplary embodiments of the present invention will be described with reference to Orthogonal Frequency Division Multiplexing (OFDM), exemplary embodiments of the present invention are also applicable to all Frequency Division Multiplexing (FDM) transmissions in general and to Discrete Fourier Transform (DFT)-spread OFDM in particular. Moreover, although the exemplary embodiments of the present invention will be described with reference to Physical DownLink Control CHannel (PDCCH), unless explicitly noted, exemplary embodiments of the present invention are also applicable for Enhanced Physical DownLink Control CHannel (EPDCCH).
(25) The first exemplary embodiment of the present invention considers a design of Downlink Control Information (DCI) formats for Physical Downlink Shared CHannel (PDSCH) transmissions to and Physical Uplink Shared CHannel (PUSCH) transmissions from a Machine Type Communication (MTC) User Equipment (UE).
(26) The first exemplary embodiment of the present invention considers modifications to DCI format 0 and DCI format 1A used for conventional UEs. The respective modified DCI formats will be referred to as DCI format 0_MTC and DCI format 1A_MTC. One design objective is to determine necessary IEs and their size in
(27) DCI format 0_MTC and DCI format 1A_MTC while considering reduced capabilities and operational characteristics of MTC UEs in order to reduce an associated PDCCH signaling overhead. Another design objective is to minimize a number of PDCCH decoding operations an MTC UE performs per subframe by designing DCI format 0_MTC and DCI format 1A_MTC to include a same number of bits.
(28) For a design of DCI formats for MTC UEs, exemplary embodiments of the present invention incorporate principles described in the U.S. Pat. No. 8,238,297 titled “METHOD AND SYSTEM FOR DIMENSIONING SCHEDULING ASSIGNMENTS IN A COMMUNICATION SYSTEM” in which a compact DCI format 0 or a compact DCI format 1A is designed to serve a second class of UEs in a communication system in which the second class of UEs transmits PUSCH or receives PDSCH using a smaller BW or a smaller TBS than a first class of UEs.
(29) DCI format 0_MTC incorporates attributes of smaller transmission BW or smaller TBS of a compact DCI format 0 and includes one or more additional restrictions as described below.
(30) Table 3 describes IEs included in DCI format 0_MTC for an FDD system.
(31) TABLE-US-00003 TABLE 3 DCI Format 0_MTC for PUSCH Scheduling of an MTC IE Number of Bits Flag for DCI Format 1 Differentiation RA ┌log.sub.2 (N.sub.RB_MTC.sup.UL (N.sub.RB_MTC.sup.UL + 1)/2┐ MCS and RV 3 FH Flag 0 NDI 1 HARQ Process Number 0-3 TPC Command for PUSCH 2 CS and OCC Index .sup.n.sub.DMRS 0-1 CSI Request 1 SRS Request 1 Padding Bits for 0 = 1A 0 RNTI 16 Total (FDD) 30-34
(32) A 1-bit flag IE provides differentiation between DCI format 0_MTC and DCI format 1A MTC because, as for DCI format 0 and DCI format 1A, exemplary embodiments of the present invention consider that these two DCI formats have a same size.
(33) An RA IE can be reduced in scope to address only a PUSCH transmission BW for an MTC UE, expressed in a number of N.sub.RB_MTC.sup.UL UL RBs, which can be smaller than a PUSCH transmission BW for a conventional UE.
(34) An MCS and RV IE can be reduced from 5 bits to, for example, 3 bits as an MCS corresponding to QAM16 or QAM64 may not be supported by MTC UEs or as an MCS granularity can be smaller than for conventional UEs. Moreover, the RV may be always assumed to be zero as, for HARQ retransmissions of a data TB, if such retransmissions are supported by the physical layer, IR has similar performance with chase combining for small data TBs.
(35) A FH flag IE can be removed from DCI format 0_MTC because, if a small UL BW is used by MTC UEs, a performance difference between a format having an FH and a format having no FH for PUSCH transmissions will be small. A PUSCH transmission type (e.g., with or without FH) can be a default operational characteristic or the PUSCH transmission type can be configured to an MTC UE by higher layer signaling. For example, if a frequency diversity offered by FH is small, a PUSCH transmission can be made without FH to obtain better channel estimation from possible DMRS averaging across slots of a PUSCH subframe as illustrated in
(36) A HARQ process number IE can be included if multiple HARQ processes are supported for PUSCH transmissions from MTC_UEs. If so, a number of HARQ processes for MTC UEs may be smaller than for conventional UEs, in order to reduce buffering requirements and therefore reduce Digital Base-Band (DBB) complexity, and can be represented with a smaller number of bits for MTC UEs, such as 2 bits for 4 HARQ processes, than for conventional UEs (e.g., 3 bits for 8 HARQ processes).
(37) A CS and OCC index IE, n.sub.DMRS, can be either removed from DCI format 0_MTC or be reduced in scope. The CS and OCC index IE, n.sub.DMRS, can be either removed from DCI format 0_MTC or be reduced in scope because if a PUSCH transmission BW includes only a few RBs, using spatial multiplexing for PUSCH transmissions from different MTC UEs does not provide meaningful UL throughput gains and therefore a large range for n.sub.DMRS to index a PHICH resource in response to each PUSCH transmission is not needed. Therefore, n.sub.DMRS may be either omitted or n.sub.DMRS may be represented by a single bit rather than 3 bits as conventional UEs use. If n.sub.DMRS is omitted, a CS and OCC value for a DMRS transmission may be either configured by higher layer signaling or be set to a default value, such as CS 0 and OCC {1, 1}.
(38) A NDI IE, a TPC command IE, a CSI request IE, and a SRS request IE, can be included in DCI format 0_MTC as in DCI format 0.
(39) For DCI format 1A_MTC, as for DCI format 0_MTC, exemplary embodiments of the present invention consider a reduced DBB capability of an MTC UE and incorporate respective attributes while designing a same size for DCI format 1A_MTC and DCI format 0_MTC. Relative to DCI format 1A, DCI format 1A_MTC includes one or more additional restrictions as they are subsequently described.
(40) Table 4 describes IEs included in DCI format 1A_MTC for a Frequency Division Duplex (FDD) system.
(41) TABLE-US-00004 TABLE 4 DCI Format lA_MTC for PDSCH Scheduling of an MTC IE Number of Bits Flag for 0_MTC/1A_MTC 1 RA ┌log.sub.2 (N.sub.RB_MTC.sup.DL (N.sub.RB_MTC.sup.DL + 1)/2┐ MCS 3 Distributed/Localized 0 Transmission Flag NDI 1 RV 0 HARQ Process Number 0-3 TPC Command for PUCCH 0-2 CSI Request 0-2 SRS Request 1-2 Padding Bits for 0 = 1A ≥0 RNTI 16 Total 27-35
(42) A 1-bit flag IE provides differentiation between DCI format 0_MTC and DCI format 1A_MTC.
(43) A RA IE can be reduced in scope to address only a PDSCH transmission BW for an MTC UE, expressed in a number of N.sub.RB_MTC.sup.DL RBs, which can be smaller than a PDSCH transmission BW for a conventional UE.
(44) An MCS IE can be reduced from 5 bits to 3 bits as MCS corresponding to QAM16 or QAM64 modulations may not be supported by MTC UEs or an MCS granularity may be reduced relative to conventional UEs. As for DCI format 0_MTC, a subset of MCS corresponding to QPSK for a conventional UE may only be supported (a highest MCS corresponding to QPSK is always included).
(45) A distributed or localized PDSCH transmission flag IE can be removed from DCI format 1A_MTC as, if a total available PDSCH transmission BW for MTC UEs is only a few RBs, a performance difference between the two PDSCH transmission types (e.g., distributed or localized) will be small in practice. Whether a PDSCH transmission is distributed or localized can be a default operational choice or can be configured to an MTC UE by higher layer signaling, for example depending on an MTC UE's mobility. Also, if PDSCH demodulation is based on a CRS, a PDSCH transmission can be distributed because there is no penalty to channel estimation accuracy. If PDSCH demodulation is based on DMRS, a PDSCH transmission can be localized to enable averaging of DMRS across the two slots per subframe.
(46) A RV IE can be removed from DCI format 1A_MTC as processing of a data TB for HARQ retransmissions may be based on chase combining. Alternatively, in order to minimize buffering requirements at an MTC UE, physical layer HARQ retransmissions may not be supported.
(47) A HARQ process number IE can be included if multiple asynchronous HARQ processes are supported for PDSCH transmissions to an MTC_UE. Otherwise, a HARQ process number IE is not included. As for PUSCH transmissions to MTC UEs, the number of HARQ processes for PDSCH transmissions can be smaller than for conventional UEs in order to reduce buffering requirements and therefore reduce DBB complexity. The HARQ process number IE can be represented with a smaller number of bits for MTC UEs, such as 2 bits for 4 HARQ processes, than for conventional UEs (3 bits for 8 HARQ processes). Moreover, a number of HARQ processes for PDSCH transmissions can be different from a number of HARQ processes for PUSCH transmissions. For example, considering asymmetric traffic requirements of MTC UEs (more UL traffic than DL traffic), more HARQ processes can be supported for PUSCH transmissions.
(48) A TPC command IE can be maintained using 2 bits or, if HARQ-ACK signaling in a PUCCH is not supported, the TPC command IE can be completely removed.
(49) A NDI IE and a SRS request IE can be included in DCI format 1A_MTC as in DCI format 1A.
(50) As a DCI format 1A_MTC will be smaller than a DCI format 0_MTC, assuming at least same reductions in a number of bits for IEs common to these two DCI formats, and as it is desirable to maintain a same size for DCI format 0_MTC and DCI format 1A_MTC in order to avoid increasing a number of PDCCH decoding operations at an MTC UE, padding bits are necessary for DCI format 1A_MTC to make its size same as that of DCI format 0_MTC.
(51) As padding bits do not carry information, the padding bits can be exchanged for additional functionality in DCI format 1A_MTC relative to DCI format 1A. For example, a CSI request IE can be included in DCI format 1A_MTC although the CSI request IE is not included in DCI format 1A. One or more PUCCH resources can be configured to an MTC UE by higher layer signaling for CSI transmission triggered by DCI format 1A_MTC. A CSI request IE value determines whether an MTC UE should report CSI and, if so, which PUCCH resource to use for a respective transmission. A SRS request may also be expanded from one bit to two bits in order to provide more flexibility for resources, such as a CS or a BW location, used by a SRS transmission.
(52) Unlike DCI format 1A which is associated with PDSCH demodulation using a CRS, DCI format 1A_MTC may also support PDSCH demodulation using a DMRS if a DL operation for an MTC UE is DMRS based.
(53) As a TBS for MTC UEs can be as small as a few tens of bits, a BW granularity of one RB for PDSCH transmissions to an MTC UE or for PUSCH transmissions from an MTC UE may be too large. Reducing a BW granularity to half RB can improve PDSCH or PUSCH spectral efficiency by better aligning a TBS to allocated resources. A half RB granularity can be accommodated by DCI format 0_MTC and DCI format 1A_MTC by simply setting N.sub.RB_MTC.sup.UL=2.Math.N.sub.RB_MTC.sup.UL in Table 3 and N.sub.RB_MTC.sup.DL=2.Math.N.sub.RB_MTC.sup.DL in Table 4.
(54) Although DCI format 0_MTC in Table 3 and DCI format 1A_MTC in Table 4 assume an FDD system, the same IEs are also applicable for a TDD system. Regarding the two additional IEs of DCI formats for conventional UEs in TDD systems, namely the Downlink Assignment Index (DAI) IE and the UL index IE, their necessity for MTC UEs can be reconsidered. As communication with MTC UEs is typically more UL than DL intensive, PUSCH transmissions from MTC UEs are more frequent than PDSCH transmissions to MTC UEs that usually provide higher layer control signaling information. Therefore, MTC UEs do not typically require multiple PDSCH transmissions within a bundling window and a DAI IE may be omitted from DCI format 0_MTC and DCI format 1A_MTC. The conventional UL index IE should be included in DCI format 0_MTC as TDD UL-DL configurations aiming to primarily support MTC UEs may have more UL subframes than DL subframes per frame. Two additional padding bits can be included in DCI format 1A_MTC to maintain a same size with DCI format 0_MTC when an UL index IE of 2 bits is included in DCI format 0_MTC.
(55) A number of PDCCH decoding operations an MTC UE performs for each Control Channel Element (CCE) AL can be configured by a NodeB through higher layer signaling. Alternatively, or prior to a configuration by higher layer signaling, a fixed number of PDCCH decoding operations for respective CCE ALs can be supported in order to enable detection of a DCI format scheduling PDSCH before any higher layer signaling can be provided. For example, an MTC UE may perform 2 decoding operations for AL of 4 CCEs and 2 decoding operations for AL of 8 CCEs to detect a DCI format in a PDCCH that schedules a PDSCH with configuration information after the MTC UE performs initial system access. Additionally, as communication with MTC UEs is more UL than DL intensive, if a size of a DCI format scheduling PUSCH is different than a size of a DCI format scheduling PDSCH then, unlike conventional UEs, an MTC UE may perform a larger number of decoding operations for DCI formats scheduling PUSCH than for DCI formats scheduling PDSCH.
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(57) Referring to
(58) Unlike a conventional UE which is assumed to decode at least a DL TM dependent DCI format having a different size than DCI format 0/1A, communication with an MTC UE can be based only on DCI format 0_MTC and DCI format 1A_MTC having a same size. Consequently, an MTC UE performs at most half a number of PDCCH decoding operations that a conventional UE performs.
(59) As Digital Base-Band (DBB) complexity is dominated by the receiver and as communication with MTC UEs is more UL than DL intensive, PUSCH transmissions from MTC UEs may be over a larger BW than PDSCH transmissions to MTC UEs. As a result, having a same size for DCI formats 0_MTC and 1A_MTC is practically not possible without imposing additional restrictions to a RA IE of DCI format 0_MTC. In this case, exemplary embodiment of the present invention considers that a resource unit in DCI format 0_MTC can be different than a resource unit in DCI format 1A_MTC. For example, if a total available UL BW is 25 RBs and a total available DL BW is 6 RBs, a same size for a RA IE can be achieved if a resource unit in DCI format 0_MTC is 4 RBs (for a maximum UL resource allocation of 24 RBs) and a resource unit in DCI format 1A_MTC is 1 RB.
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(61) Referring to
(62) In addition to a capability of an MTC UE to have a PUSCH transmission BW larger than a PDSCH reception BW, a PUSCH transmission may also use a larger TBS or a higher MCS than a PDSCH transmission uses. Then, either an MCS IE in DCI format 0_MTC may have a coarser granularity than an MCE IE in DCI format 1A_MTC or one additional bit may be included in an MCS IE in DCI format 0_MTC.
(63) The second exemplary embodiment of the present invention considers scheduling for a group of MTC UEs using a single DCI format which can schedule either PDSCH or PUSCH transmissions to or from, respectively, multiple MTC UEs.
(64) An MTC UE can be configured both with an MTC-UE-Radio Network Temporary Identifier (RNTI) and with an MTC-group-RNTI. A size of a DCI format scheduling PDSCH or PUSCH for a group of MTC UEs is designed to be the same as a size of a DCI format scheduling PDSCH or PUSCH, respectively, for an individual MTC UE. This constraint avoids increasing a number of PDCCH decoding operations for an MTC UE due to support of group scheduling and therefore avoids increasing a respective DBB receiver complexity. In one example, in order to adapt to traffic variations, a NodeB may decide to simultaneously (re)-configure to a group of MTC UEs, by higher layer signaling in respective PDSCHs, parameters for transmissions or receptions of various signals such as UL control signals, SRS, and so on. In another example, based on a Buffer Status Report (BSR) from some MTC UEs (not necessarily in a same subframe) in a group of MTC UEs for delay non-sensitive traffic such as metering, a NodeB may perform group scheduling of respective PUSCH transmissions from a group of MTC UEs.
(65) In order to provide efficient support for group scheduling of MTC UEs while fulfilling a constraint for a respective DCI format to have a same size as a DCI format for individual scheduling of an MTC UE (either for PDSCH or for PUSCH transmission), a DCI format for group scheduling of MTC UEs should provide less flexibility, including no flexibility, in dynamically setting values of IEs included in a DCI format scheduling an individual MTC UE.
(66) A NodeB has freedom to determine whether to use a DCI format with CRC scrambled by an MTC-UE-RNTI or with an MTC-group-RNTI. A determination by a NodeB can be based on considerations such as a DL control overhead (e.g., group scheduling is advantageous), an optimization for spectral efficiency of each PDSCH or PUSCH transmission (e.g., individual MTC UE scheduling is advantageous), a traffic type from each MTC UE (e.g., individual scheduling is advantageous for delay sensitive traffic while group scheduling is advantageous otherwise), a BSR from each MTC UE (e.g., individual scheduling may be used if a RA size associated with group scheduling is not appropriate), and so on.
(67) A DCI format scheduling a group of MTC UEs (UEs assigned a same MTC-group-RNTI) should also be able to identify scheduled MTC UEs as not all MTC UEs may need to receive PDSCH or transmit PUSCH. Otherwise, if an MTC UE always assumes that it is scheduled a PDSCH or a PUSCH when it receives a DCI format with an MTC-group-RNTI, a respective waste of DL or UL resources may occur in order to maintain robust system operation. Therefore, a DCI format scheduling a group of MTC UEs should include an MTC UE identification IE in a form of a bit-map indicating which MTC UEs in a group of MTC UEs are actually being scheduled. For this MTC UE identification IE, a one-to-one correspondence exists between each MTC UE, in a group of MTC UEs, and a binary element in a bit-map. This correspondence is represented by an MTC-index IE which, together with a configuration to an MTC UE for group scheduling by an MTC-group-RNTI, is informed by a NodeB to an MTC UE in advance through higher layer signaling.
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(69) Referring to
(70) Under an objective of having a same size for a DCI format scheduling an individual MTC UE and a DCI format scheduling a group of MTC UEs, a treatment of IEs in the former DCI format is now considered in a design of the latter DCI format.
(71) A 1-bit DCI format differentiation flag IE indicates whether a DCI format is applicable to PDSCH group scheduling or PUSCH group scheduling. A functionality of this IE is same as for individual MTC UE scheduling with DCI format 0_MTC or DCI format 1A_MTC. An alternative is to configure a UE with a first MTC-group-RNTI for PDSCH group scheduling and with a second MTC-group-RNTI for PUSCH group scheduling or to configure a UE for only PDSCH group scheduling or for only PUSCH group scheduling.
(72) An RA IE is not included in a DCI format scheduling a group of MTC UEs. Instead, resources allocated to each MTC UE in a group are predetermined and, although not necessary, all MTC UEs in a same group can have a same size of resources. This leads to a simpler implementation because an MTC UE in a group does not need additional explicit signaling to derive its allocated resources. A resource allocation unit MTC.sub.group_RA-unit can be a multiple or a sub-multiple of a RB and can be informed to an MTC UE by a NodeB through higher layer signaling or be predetermined in the operation of a communication system. Available resources may start from a predetermined resource MTC.sub.group_RA_first, which may be informed to an MTC UE by higher layer signaling or be implicitly determined, and continue in a sequential order in steps of a resource allocation unit MTC.sub.group_RA-unit. An MTC UE determines a starting point of its assigned MTC.sub.group_RA-unit RBs for PDSCH reception or PUSCH transmission, MTC.sub.RA-start, based on a sum of elements in an MTC UE identification IE located prior to a location (MTC-index) configured to the MTC.sub.run_sum, and MTC.sub.RA-start=MTC.sub.group_RA_first+MTC.sub.run_sum.Math.MTC.sub.group_RA-unit.
(73) For example, for a DCI format performing PDSCH scheduling to a group of 4 MTC UEs, a first MTC UE with bit-map value (MTC-index value) of 1 may be allocated a RB with a lowest index MTC.sub.group_RA-unit is 1 RB, MTC.sub.group_RA_first=0, and MTC.sub.run_sum=0), a second MTC UE with bit-map value of 1 may be allocated a RB with a second lowest index (MTC.sub.run_sum=1), and so on. In a case in which E-CCHs are used, respective RBs may be excluded by MTC UEs in a determination of their respective resources and MTC.sub.group_RA_first may still be implicitly determined by excluding resources allocated to a transmission of E-CCHs.
(74)
(75) Referring to
(76) A transmission type IE (distributed/localized transmission IE or FH flag IE) may not be included in a DCI format scheduling a group of MTC UEs. Instead, all transmissions may have a same type which can be either predetermined in the operation of a communication system or be configured to each MTC UE in the group of MTC UEs by higher layer signaling. For example, all PDSCH transmissions may be distributed and all PUCCH transmissions may perform FH.
(77) An MCS and RV IE for PUSCH transmission or an MCS IE for PDSCH transmission may or may not be included in a DCI format scheduling a group of MTC UEs. If an MCS and RV IE is not included, an MCS is configured to each MTC UE in a group of MTC UEs by higher layer signaling. For example, an MCS can be based on the long term SINR an MTC UE experiences in an UL channel or in a DL channel. If an MCS and RV IE is included, a number of respective bits can be reduced compared to a number of bits in a DCI format scheduling an individual MTC UE, for example from 3 to 2. At least in case of PUSCH transmissions, an RV is always zero (e.g., only initial transmissions of a TB may be supported by group scheduling as is subsequently discussed).
(78) An NDI IE may not be included in a DCI format scheduling a group of MTC UEs and respective PDSCH or PUSCH transmissions can always be initial transmissions. A reason for not supporting group scheduling for retransmissions of an HARQ process, if such retransmissions are supported at the physical layer, is because of a much smaller likelihood that a predetermined group of MTC UEs will need such retransmissions. For example, if a DCI format schedules PDSCH transmissions to a group of MTC UEs, a retransmission will only be needed for MTC UEs that did not correctly receive an initial PDSCH transmission and, for typical PDSCH error rates, a retransmission is more likely to be needed for much fewer MTC UEs than ones having an initial transmission. A DCI format scheduling an individual MTC UE can then be used for retransmissions of an HARQ process, if such retransmissions are supported at the physical layer.
(79) An RV IE may not be included in a DCI format scheduling a group of MTC UEs for respective PDSCH transmissions for the same reasons as for not including an NDI IE as mentioned above.
(80) A HARQ process IE may or may not be included in a DCI format scheduling PDSCH or PUSCH transmissions to or from, respectively, a group of MTC UEs. If a HARQ process IE is not included, a HARQ process number (e.g., assuming that more than one HARQ process is supported) can be implicitly determined for example by linking a HARQ process to a subframe number (e.g., synchronous HARQ in both DL and UL).
(81) A TPC command IE may or may not be included in a DCI format scheduling PDSCH or PUSCH transmissions to or from, respectively, a group of MTC UEs. If HARQ-ACK signaling is not supported for MTC UEs then, instead of a TPC command, a DCI format can include an MCS for PDSCH or PUSCH transmissions to or from, respectively, a group of MTC UEs. Link adaptation is then performed based on MCS adaptation instead of power adaptation (e.g., an MTC UE can assume a TPC command indicating no power adjustment).
(82) In another alternative, a TPC command IE including 1 bit is included in a DCI format scheduling PDSCH or PUSCH transmissions to or from, respectively, a group of MTC UEs. The 1-bit TPC command IE may indicate, for example, a power adjustment of {−1 1} dB instead of a power adjustment of {−3, −1, 0 1} dB that can be supported by a 2-bit TPC command IE.
(83) In another alternative, neither a TPC IE nor an MCS IE is included in a DCI format for PDSCH or PUSCH scheduling to a group of MTC UEs. In a case in which a negative TPC command would be needed, a consequence is a somewhat increased interference. In a case in which a positive TPC command would be needed, a consequence is a somewhat increased error rate.
(84) A CS and OCC Index IE, n.sub.DMRS, may not be included in a DCI format scheduling a group of MTC UEs for PUSCH transmissions. Instead, all MTC UEs can use a same CS and OCC which can be either predetermined, such as for example CS=0 and OCC={1, 1}, or can be configured by higher layer signaling. A resource for PHICH transmission, if any, can be derived from a MTC.sub.run_sum value for a respective UE as described below.
(85) A CSI request IE may not be included in a DCI format scheduling PUSCH transmissions from a group of MTC UEs. As CSI feedback is associated with PDSCH scheduling, not all MTC UEs scheduled PUSCH transmissions may need to report CSI in respective PUSCHs. Alternatively, a DCI format with an MTC-UE-RNTI can be used or MTC UEs can be configured with a separate MTC-group-RNTI triggering CSI feedback using PUSCH or PUCCH and a determination of transmission parameters can be similar to that of data in a PUSCH as it was previously described.
(86) A SRS request IE may not be included in a DCI format scheduling PDSCH transmissions to or PUSCH transmissions from a group of MTC UEs as not all MTC UEs may need to also transmit SRS. Alternatively, a DCI format with an MTC-UE-RNTI can be used or MTC UEs can be configured with a separate MTC-group-RNTI triggering SRS transmission with parameters previously configured by a NodeB through higher layer signaling for each MTC UE in a group of MTC UEs.
(87) Therefore, a DCI format scheduling a group of MTC UEs can include only a respective MTC-group-RNTI and an MTC UE identification IE (bit-map) without including any IEs provided by a DCI format scheduling an individual MTC UE. Alternatively, a DCI format scheduling a group of MTC UEs can also include a minimal number of IEs provided by a DCI format scheduling an individual MTC UE such as an MCS IE or a TPC IE.
(88) Table 5 provides contents for a DCI format with CRC scrambled by an MTC-group-RNTI scheduling PDSCH transmissions to or PUSCH transmissions from a group of MTC UEs under previously discussed alternatives for included IEs. A size of a DCI format scheduling a group of MTC UEs is same as a size of a DCI format scheduling an individual MTC UE and assumed to be bits.
(89) TABLE-US-00005 TABLE 5 DCI Formats for Group Scheduling of MTC UEs Group DCI Group DCI Format- Format- IE Option 1 Option 2 Flag for DL/UL Scheduling 1 1 MTC UE identification Q-17 └(Q − 17)/ (I + 1)┘ Additional IEs (bits per — I MTC UE) Padding Bits — Q − 17 − └(Q − 17)/ (I + 1)┘ .Math. (I + 1) MTC-group-RNTI 16 16 Total Q Q
(90) If a DCI format scheduling a group of MTC UEs includes only an MTC-group-RNTI/CRC and a flag for distinguishing between PDSCH and PUSCH, a maximum number of MTC UEs in a group is Q−17. For example, for Q=29, a group may include up to 12 MTC UEs.
(91) If a DCI format scheduling a group of MTC UEs additionally includes other IEs, such as a TPC IE or an MCS IE, corresponding to bits per MTC UE, a maximum number of MTC UEs in a group is └(Q−17)/(I+1)┘. For example, for 2 and Q=29, a group can include up to 4 MTC UEs. A number of IEs included in a DCI format scheduling an individual MTC UE that are also included in a DCI format scheduling a group of MTC UEs should be as small as possible even with some acceptable performance degradation or loss of flexibility, as, otherwise, a number of MTC UEs in a group can become too low for group scheduling to be useful.
(92) An advantage of supporting a large number of MTC UEs by group scheduling is in allowing a NodeB scheduler to address any subset of these UEs with a single DCI format, thereby improving scheduler flexibility without transmitting multiple DCI formats and incurring a corresponding signaling overhead. For a total PDSCH BW or a total PUSCH BW including about 6 RBs (e.g., at least for DBB operation), a maximum of 10-12 MTC UEs may be scheduled per subframe (assuming a resource unit of half RB). Therefore, for group scheduling, both a DCI format being able to address up to 12 MTC UEs (but not schedule all of the 12 MTC UEs) and a DCI format being able to address 4 MTC UEs (and possibly schedule all of the 4 MTC UEs) are applicable.
(93) The second exemplary embodiment of the present invention so far assumed that a DCI format scheduling PDSCH for an individual MTC UE has a same size as a DCI format scheduling PUSCH for an individual UE as described by the first exemplary embodiment of the present invention. This is however not a necessary condition for the second exemplary embodiment of the present invention for which an only condition is that a DCI format scheduling a group of MTC UEs for PDSCH or PUSCH has a same size with a DCI format scheduling PDSCH or PUSCH for an individual MTC UE, respectively. If a size of a DCI format for PDSCH scheduling is not same as a size of the DCI format for PUSCH scheduling, whether for an individual MTC UE or for a group of MTC UEs, a flag IE for differentiating DL scheduling from UL scheduling is not needed.
(94) An HARQ-ACK signal transmission from or to an MTC UE in response to a reception of a PDSCH or a transmission of a PUSCH, respectively, through group scheduling by a respective DCI format with CRC scrambled by an MTC-group-RNTI is subsequently considered. An objective is to provide a technique for a communication system to support such HARQ-ACK signaling and for an MTC UE to derive a respective PUCCH or PHICH resource. A PUCCH or PHICH resource determination, as described by Equation (2) and Equation (1), respectively, is assumed but any other reference resource determination may apply.
(95) If an MTC UE transmits an HARQ-ACK signal in response to a detection of a DCI format with CRC scrambled by an MTC-group-RNTI, or in general in response to a detection of a DCI format associated with DL group scheduling, exemplary embodiments of the present invention considers that an MTC UE determines a PUCCH resource for HARQ-ACK signal transmission based on its MTC.sub.run_sum value as determined from an MTC UE identification IE included in the DCI format.
(96) In a first approach, each MTC UE configured for PDSCH group scheduling and with an MTC-group-RNTI is also configured by higher layer signaling a set of PUCCH resources for HARQ-ACK signal transmission. A PUCCH resource for HARQ-ACK signal transmission from a first MTC UE, which is the MTC UE for which a first bit in a bit-map of an MTC UE identification IE is equal to one, may be determined as for a conventional UE and derived from the first CCE used to transmit a PDCCH conveying the DCI format as in Equation (2). A PUCCH resource for HARQ-ACK signal transmission from each remaining MTC UE with actual scheduling, as determined by an MTC UE identification IE, is determined from a set of configured PUCCH resources based on a respective MTC.sub.run_sum value.
(97)
(98) Referring to
(99) In a modification of the first approach, a PUCCH resource for HARQ-ACK signal transmission from a first MTC UE with actual scheduling may also be determined from a set of configured PUCCH resources by associating each MTC.sub.run_sum value with a configured PUCCH resource in an ascending order starting from a MTC.sub.run_sum value of 0.
(100) In a second approach, all PUCCH resources may be implicitly derived from a first CCE used to transmit a PDCCH conveying a DCI format scheduling a group of MTC UEs and a MTC.sub.run_sum value for each scheduled MTC UE as determined by an MTC UE identification IE. In this case, it is up to a NodeB scheduler to avoid HARQ-ACK signal transmissions from multiple UEs using a same PUCCH resource.
(101)
(102) Referring to
(103) If a HARQ-ACK signal is transmitted by a NodeB to an MTC UE in response to a PUSCH transmission scheduled by a DCI format with CRC scrambled by an MTC-group-RNTI, the MTC UE may also determine a respective PHICH resource based on a MTC.sub.run_sum value as determined from an MTC UE identification IE using similar approaches as for PUCCH resource determination for HARQ-ACK signal transmission from the MTC UE.
(104) In a first approach, PHICH resources for HARQ-ACK signal transmissions to MTC UEs with PUSCH transmissions through group scheduling are configured by higher layer signaling. Each scheduled MTC UE determines a respective PHICH resource, from a configured set of resources, according to a one-to-one mapping between each configured PHICH resource and an MTC.sub.run_sum value where a first configured PHICH resource is mapped to MTC.sub.run_sum=0, a second configured PHICH resource is mapped to MTC.sub.run_sum=1, and so on.
(105)
(106) Referring to
(107) In a second approach, PHICH resources for HARQ-ACK signal transmissions to MTC UEs with PUSCH transmissions through group scheduling are determined from a first resource MTC.sub.RA-start for a respective PUSCH transmission. This is similar to a conventional approach for determining a PHICH transmission resource but n.sub.DMRS may not exist and I.sub.PRB_RA.sup.lowest_index is replaced by the MTC.sub.run_sum which an MTC UE determines from an MTC UE identification IE.
(108)
(109) Referring to
(110) The third exemplary embodiment of the present invention considers a data encoding method in a PDSCH transmitted to an MTC UE and a data encoding method in a PUSCH transmitted from an MTC UE.
(111) Unlike conventional UEs for which a TBS typically exceed about 70 bits and a TC is always used, most data information payloads to MTC UEs are only in the order of a few tens of bits. Moreover, considering a DBB receiver complexity of an MTC UE, a convolutional decoder is preferable to a turbo decoder. Furthermore, an MTC UE already includes convolutional decoders for PDCCH decoding. Therefore, unlike a conventional UE, a data TB transmitted in a PDSCH to an MTC UE may be encoded using a TBCC. A TBS transmitted from an MTC UE in a PUSCH is typically larger than a TBS transmitted to an MTC UE in a PDSCH and, as a turbo encoder complexity is much smaller than a turbo decoder complexity, either a turbo encoder or a convolutional encoder may be used to encode data transmitted from an MTC UE. For a same or similar maximum MCS of data transmitted in a PDSCH or in a PUSCH, a larger maximum TBS for data in a PUSCH than in a PDSCH implies a larger maximum size of frequency resources for a PUSCH than for a PDSCH.
(112)
(113) Referring to
(114) While the invention has been shown and described with reference to certain exemplary 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 their equivalents.