Patent Publication Number: US-8995377-B2

Title: PHICH resource provisioning in time division duplex systems

Description:
FIELD OF THE DISCLOSURE 
     The present disclosure relates to control channels in wireless telecommunications systems. 
     BACKGROUND 
     As used herein, the term “user equipment” (alternatively “UE”) might in some cases refer to mobile devices such as mobile telephones, personal digital assistants, handheld or laptop computers, and similar devices that have telecommunications capabilities. Such a UE might include a device and its associated removable memory module, such as but not limited to a Universal Integrated Circuit Card (UICC) that includes a Subscriber Identity Module (SIM) application, a Universal Subscriber Identity Module (USIM) application, or a Removable User Identity Module (R-UIM) application. Alternatively, such a UE might include the device itself without such a module. In other cases, the term “UE” might refer to devices that have similar capabilities but that are not transportable, such as desktop computers, set-top boxes, or network appliances. The term “UE” can also refer to any hardware or software component that can terminate a communication session for a user. Also, the terms “user equipment,” “UE,” “user agent,” “UA,” “user device,” and “mobile device” might be used synonymously herein. 
     As telecommunications technology has evolved, more advanced network access equipment has been introduced that can provide services that were not possible previously. This network access equipment might include systems and devices that are improvements of the equivalent equipment in a traditional wireless telecommunications system. Such advanced or next generation equipment may be included in evolving wireless communications standards, such as long-term evolution (LTE). For example, an LTE system might include an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) node B (eNB), a wireless access point, or a similar component rather than a traditional base station. Any such component will be referred to herein as an eNB, but it should be understood that such a component is not necessarily an eNB. Such a component may also be referred to herein as an access node. 
     LTE may be said to correspond to Third Generation Partnership Project (3GPP) Release 8 (Rel-8 or R8) and Release 9 (Rel-9 or R9), while LTE Advanced (LTE-A) may be said to correspond to Release 10 (Rel-10 or R10) and possibly also to Release 11 (Rel -11 or R11) and other releases beyond Release 11. As used herein, the terms “legacy”, “legacy UE”, and the like might refer to signals, UEs, and/or other entities that comply with LTE Release 10 and/or earlier releases but do not fully comply with releases later than Release 10. The terms “advanced”, “advanced UE”, and the like might refer to signals, UEs, and/or other entities that comply with LTE Release 11 and/or later releases. While the discussion herein deals with LTE systems, the concepts are equally applicable to other wireless systems as well. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts. 
         FIG. 1  is a diagram of frequency division duplex and time division duplex modes. 
         FIG. 2  is a table showing LTE time division duplex uplink/downlink configurations. 
         FIG. 3  is a diagram of a PHICH modulation process. 
         FIG. 4  is a diagram of a PCFICH modulation process. 
         FIG. 5  is a diagram of generation and detection of the PHICH and the PCFICH. 
         FIG. 6  is a diagram of uplink HARQ linkage in inter-band carrier aggregation with uplink/downlink configuration  1  on a PCell and configuration  0  on an SCell. 
         FIG. 7  is a flowchart of provisioning PHICH resources for a carrier aggregation UE, according to an embodiment of the disclosure. 
         FIG. 8  is a simplified block diagram of an exemplary network element according to one embodiment. 
         FIG. 9  is a block diagram with an example user equipment capable of being used with the systems and methods in the embodiments described herein. 
         FIG. 10  illustrates a processor and related components suitable for implementing the several embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     It should be understood at the outset that although illustrative implementations of one or more embodiments of the present disclosure are provided below, the disclosed systems and/or methods may be implemented using any number of techniques, whether currently known or in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents. Embodiments are described herein in the context of an LTE wireless network or system, but can be adapted for other wireless networks or systems. 
     In an LTE system, downlink and uplink transmissions are organized into one of two duplex modes, frequency division duplex (FDD) mode and time division duplex (TDD) mode. The FDD mode uses paired spectrum where the frequency domain is used to separate the uplink (UL) and downlink (DL) transmissions. In TDD systems, on the other hand, unpaired spectrum is used where both UL and DL are transmitted over the same carrier frequency. The UL and DL are separated in the time domain.  FIG. 1  illustrates both duplex modes. 
     In a 3GPP LTE TDD system, a subframe of a radio frame can be a downlink, an uplink or a special subframe. The special subframe comprises downlink and uplink time regions separated by a guard period for downlink to uplink switching. 3GPP Technical Specification (TS) 36.211 defines seven different UL/DL configuration schemes in LTE TDD operations. The schemes are listed in  FIG. 2 , where D represents downlink subframes, U represents uplink subframes, and S represents a special frame. A special frame includes three parts: the downlink pilot time slot (DwPTS), the uplink pilot time slot (UpPTS), and the guard period (GP). Downlink transmissions on the Physical Downlink Shared Channel (PDSCH) may be made in DL subframes or in the DwPTS portion of the special subframe. 
     As  FIG. 2  shows, there are two switching point periodicities specified in the LTE standard, 5 milliseconds (ms) and 10 ms. 5 ms switching point periodicity is introduced to support the co-existence between LTE and low chip rate UTRA TDD systems, and 10 ms switching point periodicity is for the coexistence between LTE and high chip rate UTRA TDD systems. The supported configurations cover a wide range of UL/DL allocations from a DL-heavy 1:9 ratio to a UL-heavy 3:2 ratio. The DL allocations in these ratios include both DL subframes and special subframes, which can also carry downlink transmissions in the DwPTS. Compared to FDD, TDD systems have more flexibility in terms of the proportion of resources assignable to uplink and downlink communications within a given assignment of spectrum. Specifically, it is possible to distribute the radio resources unevenly between the uplink and the downlink. Such a distribution may allow the radio resources to be utilized efficiently through the selection of an appropriate UL/DL configuration based on the interference situation and different traffic characteristics in the DL and the UL. 
     The UL and DL transmissions may not be continuous in an LTE TDD system. That is, UL or DL transmissions may not occur in every subframe. Therefore, the data channel transmissions with their scheduling grant and Hybrid Automatic Repeat Request (HARQ) timing relationships are separately defined in the 3GPP specifications. Currently, the HARQ acknowledgement/negative acknowledgement (ACK/NACK) timing relationship for downlink data channel transmission is defined by Table 10.1.3.1-1 in 3GPP TS 36.213. This timing relationship is shown in Table 1 below. Table 1 associates a UL ACK/NACK transmission at sub-frame n, with a DL PDSCH transmission at sub-frames n−ki, i=0 to M −1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Downlink HARQ association set index K: {k 0 , k 1 , . . . k M−1 } 
               
            
           
           
               
               
            
               
                 UL-DL 
                   
               
               
                 Config- 
                 Subframe n 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 uration 
                 0  
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 8 
                 9 
               
               
                   
               
               
                 0 
                 — 
                 — 
                 6 
                 — 
                 4 
                 — 
                 — 
                 6 
                 — 
                 4 
               
               
                 1 
                 — 
                 — 
                 7, 6 
                 4 
                 — 
                 — 
                 — 
                 7, 6 
                 4 
                 — 
               
               
                 2 
                 — 
                 — 
                 8, 7, 4, 6 
                 — 
                 — 
                 — 
                 — 
                 8, 7, 
                 — 
                 — 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 4, 6 
               
               
                 3 
                 — 
                 — 
                 7, 6, 11 
                 6, 5 
                 5, 4 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 4 
                 — 
                 — 
                 12, 8, 
                 6, 5, 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                   
                   
                   
                 7, 11 
                 4, 7 
               
               
                 5 
                 — 
                 — 
                 13, 12, 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                   
                   
                   
                 9, 8, 7, 
               
               
                   
                   
                   
                 5, 4, 
               
               
                   
                   
                   
                 11, 6 
               
               
                 6 
                 — 
                 — 
                 7 
                 7 
                 5 
                 — 
                 — 
                 7 
                 7 
                 — 
               
               
                   
               
            
           
         
       
     
     The uplink HARQ ACK/NACK timing linkage with the PUSCH transmission is listed in Table 8.3-1 of 3GPP TS 36.213, which is provided as Table 2 below. Table 2 indicates that the Physical HARQ Indicator Channel (PHICH) carrying an ACK/NACK received in DL sub-frame i is linked with the UL data transmission in UL sub-frame i-k, where k is given in Table 2. For UL/DL configuration  0 , in sub-frames  0  and  5 , if I PHICH =1, then k=6. Otherwise k=7. This is because there may be two ACK/NACKs for a UE transmitted on the PHICH in subframes  0  and  5 . 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 k for Uplink HARQ ACK/NACK association 
               
            
           
           
               
               
            
               
                 TDD UL/DL 
                 subframe number i 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Configuration 
                 0 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 8 
                 9 
               
               
                   
               
               
                 0 
                 7 or 6 
                 4 
                   
                   
                   
                 7 or 6 
                 4 
                   
                   
                   
               
               
                 1 
                   
                 4 
                   
                   
                 6 
                   
                 4 
                   
                   
                 6 
               
               
                 2 
                   
                   
                   
                 6 
                   
                   
                   
                   
                 6 
               
               
                 3 
                 6 
                   
                   
                   
                   
                   
                   
                   
                 6 
                 6 
               
               
                 4 
                   
                   
                   
                   
                   
                   
                   
                   
                 6 
                 6 
               
               
                 5 
                   
                   
                   
                   
                   
                   
                   
                   
                 6 
               
               
                 6 
                 6 
                 4 
                   
                   
                   
                 7 
                 4 
                   
                   
                 6 
               
               
                   
               
            
           
         
       
     
     The relationship of a UL grant and/or an ACK/NACK with a UL transmission/retransmission is listed in Table 8.2 of 3GPP TS 36.213, which is provided as Table 3 below. The UE, upon detection of a Physical Downlink Control Channel (PDCCH) with Downlink Control Information (DCI) format  0  and/or a PHICH transmission in sub-frame n intended for the UE, sends the corresponding PUSCH transmission in sub-frame n +k, where k is given in Table 3. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 k for Uplink PUSCH grant association 
               
            
           
           
               
               
            
               
                 TDD UL/DL 
                 subframe number n 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Configuration 
                 0 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 8 
                 9 
               
               
                   
               
               
                 0 
                 4 
                 6 
                   
                   
                   
                 4 
                 6 
                   
                   
                   
               
               
                 1 
                   
                 6 
                   
                   
                 4 
                   
                 6 
                   
                   
                 4 
               
               
                 2 
                   
                   
                   
                 4 
                   
                   
                   
                   
                 4 
               
               
                 3 
                 4 
                   
                   
                   
                   
                   
                   
                   
                 4 
                 4 
               
               
                 4 
                   
                   
                   
                   
                   
                   
                   
                   
                 4 
                 4 
               
               
                 5 
                   
                   
                   
                   
                   
                   
                   
                   
                 4 
               
               
                 6 
                 7 
                 7 
                   
                   
                   
                 7 
                 7 
                   
                   
                 5 
               
               
                   
               
            
           
         
       
     
     For TDD UL/DL configuration  0 , if the Least Significant Bit (LSB) of the UL index in DCI format  0  is set to 1 in sub-frame n or a PHICH is received in sub-frame n=0 or 5 in the resource corresponding to I PHICH =1 or a PHICH is received in sub-frame n=1 or 6, the UE sends the corresponding Physical Uplink Shared Channel (PUSCH) transmission in sub-frame n+7. If, for TDD UL/DL configuration  0 , both the Most Significant Bit (MSB) and the LSB of the UL index in DCI format  0  are set to 1 in sub-frame n, the UE sends the corresponding PUSCH transmission in both sub-frames n+k and n+7, where k is given in Table 3. 
     It can be seen that both grant and HARQ timing linkage in TDD are more complicated than the fixed time linkages used in FDD. Accordingly, TDD usually requires more attention in design. 
     The PHICH specified in 3GPP TS 36.211 is used to transmit a HARQ-ACK, which indicates whether the eNB has correctly received UL shared channel (UL-SCH) data on the PUSCH. Multiple PHICHs can be transmitted in the same set of resource elements as a PHICH group. In the same PHICH group, multiple PHICHs may be multiplexed with different complex orthogonal Walsh sequences. In the case of a normal cyclic prefix, eight PHICHs can be multiplexed within one PHICH group as the length of the sequences is four and the PHICHs are also multiplexed in the complex domain. For an extended cyclic prefix, four PHICHs can be multiplexed within a PHICH group with length-2 Walsh sequences.  FIG. 3  illustrates the PHICH modulation flow at the eNB. 
     For PHICH resource configuration, two parameters are signaled in the Master Information Block (MIB): the PHICH duration and the number of PHICH groups. The PHICH duration defines the number of Orthogonal Frequency Division Multiplexing (OFDM) symbols over which the PHICH is distributed. To avoid a dependency on the Physical Control Format Indicator Channel (PCFICH), the PHICH duration is independently signaled and can be different from the control region for the PDCCH. The number of PHICH groups is used to define the amount of PHICH resources. The correspondence between PHICH resources and UL-SCH transmission is implicit. That is, there is a predefined representation rule between the PHICH resource index and the PUSCH Physical Resource Block (PRB) index transmitting the UL-SCH. Because there is a PUSCH transmission without a PDCCH in the case of resource non-adaptive retransmission, a PHICH resource is linked to the actual PUSCH PRB index instead of the PDCCH Control Channel Element (CCE) index. 
     The PHICH resource is identified by the index pair (n PHICH   group , n PHICH   seq ) where n PHICH   group  is the PHICH group number and n PHICH   seq  is the orthogonal sequence index within the group. As PHICH resource is implicitly linked to the PUSCH PRB index that is used to transmit the corresponding PUSCH, a UE may derive the assigned index pair with the scheduled PUSCH PRB index. If a PHICH resource is smaller than the number of PUSCH PRBs or if multiple users are scheduled in the same PUSCH PRBs, a collision can happen. That is, the same PHICH resource may be assigned to multiple UEs. To avoid a collision, a different cyclic shift value that is indicated in the uplink DCI format may be used to derive the assigned PHICH resource. The following equations are used to determine the PHICH group number and the orthogonal sequence index within the group:
 
 n   PHICH   group =( I   PRB     —     RA   lowest     —     index   +n   DMRS )mod  N   PHICH   group   +I   PHICH   N   PHICH   group  
 
 n   PHICH   seq =(└ I   PRB     —     RA   lowest     —     index   /N   PHICH   group   ┘+n   DMRS )mod 2 N   SF   PHICH  
 
     In the above equations, n DMRS  is mapped from the cyclic shift for a Demodulation Reference Signal (DMRS) field according to the most recent PDCCH with uplink DCI format, as described in 3GPP TS 36.212 for the transport block or blocks associated with the corresponding PUSCH transmission. n DMRS  is set to zero if there is no PDCCH with uplink DCI format for the same transport block, and if the initial PUSCH for the same transport block is semi-persistently scheduled or if the initial PUSCH for the same transport block is scheduled by a random access response grant. N SF   PHICH  is the spreading factor size used for PHICH modulation as described in section 6.9.1 of 3GPP TS 36.211. I PRB     —     RA   lowest     —     index  is the lowest PRB index in the first slot of the corresponding PUSCH transmission. N PHICH   group  is the number of PHICH groups configured by higher layers as described in section 6.9 of 3GPP TS 36.211. 
     
       
         
           
             
               I 
               PHICH 
             
             = 
             
               { 
               
                 
                   
                     1 
                   
                   
                     
                       
                         
                           
                             for 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             T 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             D 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             D 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             U 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               L 
                               / 
                               D 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             L 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             configuration 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             0 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             with 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             PUSCH 
                           
                         
                       
                       
                         
                           
                             
                               transmission 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               in 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               subframe 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               n 
                             
                             = 
                             
                               4 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               or 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               9 
                             
                           
                         
                       
                     
                   
                 
                 
                   
                     0 
                   
                   
                     
                       otherwise 
                       . 
                     
                   
                 
               
             
           
         
       
     
     For FDD, the index n PHICH   group  ranges from 0 to N PHICH   group −1. For TDD, the number of PHICH groups may vary between downlink subframes and is given by m i ·N PHICH   group  where m i  is given by Table 4. The index n PHICH   group  in a downlink subframe with non-zero PHICH resources ranges from 0 to m i ·N PHICH   group −1. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 The factor m i  for TDD 
               
            
           
           
               
               
            
               
                 Uplink-downlink 
                 Subframe number i 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 configuration 
                 0 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 8 
                 9 
               
               
                   
               
               
                 0 
                 2 
                 1 
                 — 
                 — 
                 — 
                 2 
                 1 
                 — 
                 — 
                 — 
               
               
                 1 
                 0 
                 1 
                 — 
                 — 
                 1 
                 0 
                 1 
                 — 
                 — 
                 1 
               
               
                 2 
                 0 
                 0 
                 — 
                 1 
                 0 
                 0 
                 0 
                 — 
                 1 
                 0 
               
               
                 3 
                 1 
                 0 
                 — 
                 — 
                 — 
                 0 
                 0 
                 0 
                 1 
                 1 
               
               
                 4 
                 0 
                 0 
                 — 
                 — 
                 0 
                 0 
                 0 
                 0 
                 1 
                 1 
               
               
                 5 
                 0 
                 0 
                 — 
                 0 
                 0 
                 0 
                 0 
                 0 
                 1 
                 0 
               
               
                 6 
                 1 
                 1 
                 — 
                 — 
                 — 
                 1 
                 1 
                 — 
                 — 
                 1 
               
               
                   
               
            
           
         
       
     
     The PCFICH is currently used to indicate the number of OFDM symbols used for transmission of PDCCHs in each subframe. This number is called the Control Format Indicator (CFI). There are three different CFI code words used in the current version of LTE and a fourth one is reserved for future use. Each codeword is 32 bits in length.  FIG. 4  illustrates the PCFICH modulation flow at an eNB. 
     In the current LTE specification, the PCFICH and the PHICH use different resource elements. The PCFICH takes four Resource Element Groups (REGs) and the PHICH consumes three REGs.  FIG. 5  shows the modulation chain at an eNB and the demodulation chain at a UE. 
     To meet LTE-A requirements, the Rel-10 LTE specification defines carrier aggregation (CA) for TDD systems. However, the Rel-10 specification supports CA only with the same UL/DL configuration on the aggregated carriers because intra-band CA is prioritized, and having different UL/DL configurations is impossible to support in intra-band CA, especially when one single RF chain is used. 
     To achieve bandwidth flexibility and coexistence with legacy TDD systems, inter-band carrier aggregation with different TDD UL/DL configurations on the carriers from different bands has been proposed in LTE Rel-11. Many design details, such as supporting both half duplex and full duplex modes, supporting both separate scheduling (s-scheduling) and cross-carrier scheduling (c-scheduling), transmitting the PHICH on the cell carrying the UL grant, and transmitting the PUCCH only on the primary cell, have been agreed upon. Some agreements have also been reached on HARQ timing linkage. 
     It should be noted that a component carrier (CC) is also known as a serving cell or a cell. Furthermore, when multiple CCs are scheduled, for each UE, one of the CCs is designated as the primary carrier which is used for PUCCH transmission, semi-persistent scheduling, etc., while the remaining CCs are configured as secondary CCs. This primary carrier is also known as a PCell (Primary cell), while the secondary CC is known as an SCell (Secondary cell). 
     As discussed above, the timing linkage in TDD systems is not as simple as in FDD systems. The degree of complexity increases when CA with different TDD configurations is considered. This is because, with different TDD configurations, there are some time instances with conflicting subframes among aggregated CCs. For example, a UL subframe on CC1 may occur at the same time that CC2 has a DL subframe. Also, the timing linkage may be different for each different TDD configuration and, furthermore, certain control signals may have to be on a specific carrier. For example, the PHICH may have to be transmitted on the cell carrying the UL grant. These conditions may lead to a need to transmit a PUSCH ACK/NACK at a DL subframe that does not have a PHICH resource configured according to Table 4 above. 
     One of the 3GPP design agreements indicates that the PHICH can be transmitted only on the cell carrying the UL grant in the case of inter-band CA with different UL/DL configurations. Therefore, a PUSCH ACK/NACK may need to be transmitted at a DL subframe that does not have a PHICH resource configured. 
     In an example case, two TDD carriers may be aggregated, the PCell may be set as UL/DL configuration  1 , and the SCell may have UL/DL configuration  0 , in full duplex mode. Based on the 3GPP design principles, the PCell follows its own UL HARQ timing relationship, which is configuration  1 , and the SCell UL HARQ follows the timing of configuration  0 . In this case, the PCell with UL/DL configuration  1  is the scheduling cell and carries the UL grant for the SCell, so the PUSCH ACK/NACK should be on the PCell as well.  FIG. 6  illustrates the UL HARQ timing of the above scenario. The solid arrows represent the SCell UL grant for transmission/retransmission, and the dashed arrows represent the UL HARQ-ACK timing of the SCell. 
     It can be seen that the ACK/NACK for PUSCH transmission at subframe # 3  or # 4  of the SCell should be at subframe # 0  of the PCell. However, with UL/DL configuration  1 , referring to Table 4 above, there is no PHICH resource provisioned in the control region of PCell subframe # 0 . The same issue occurs for the PUSCH transmission at subframes # 8  and # 9  of the SCell. Additionally, there is no PHICH resource provisioned at subframe # 5  of the PCell. 
     Embodiments of the present disclosure can resolve these PHICH resource issues by provisioning PHICH resources for a CA UE. New PHICH resources are provisioned in the control region of a DL subframe where the SCell PUSCH transmissions for CA UEs need to be acknowledged. The newly provisioned PHICH resource is recognized only by CA UEs. 
     In an embodiment, a new PHICH resource specifically for a CA UE is provisioned, if needed, in the control region of the previous zero-PHICH DL subframe, for example, subframe # 0  or # 5  in  FIG. 6 . The newly provisioned PHICH resource is recognized only by CA UEs. Legacy UEs will consider that this resource is being used for PDCCH transmission. The new resource will be discarded by legacy UEs because the PDCCH blind decoding is not able to pick the resource up. Therefore, there is no backward compatibility impact to legacy UEs. 
     This PHICH resource provisioning is performed on an as-needed basis. For example, in  FIG. 6 , when there is no cross-carrier scheduled PUSCH on SCell subframe # 3  and # 4 , there is no requirement to provision any PHICH resource at subframe # 0  of the PCell. The resource at that subframe may still be used for PDCCH purposes. 
     The following steps may be used in this method. (1) Given the UL/DL configurations of the PCell and the SCell, config(P) and config(S), identify the reference configuration, config(R), which the SCell PUSCH HARQ timing follows. (2) Identify the PHICH resource factor m i  for config(P) and config(R) based on Table 4, Pm i , Rm i , i=0, 1, 2, . . . 9. (3) On a radio frame basis, determine if there is an index i, such that Pm i =0 and Rm i &gt;0. If ‘Yes’, go to step (4). Otherwise, go to step (5) as there is no need to provision a PHICH resource. (4) Further determine if there is a need to provision a PHICH resource at subframe #i of the PCell by checking if there is a PUSCH transmission on the SCell that requires an ACK/NACK on subframe #i of the PCell. If ‘Yes’, provision the PHICH resource. Otherwise, go to Step (5) as there is no need to provision a PHICH resource. (5) End. 
       FIG. 7  presents a flowchart depicting these steps. At block  710 , the PHICH resource factor m i  for config(P) and config(R) is identified based on Table 4, Pm i , Rm i , i=0, 1, 2, . . . 9. At block  720 , it is determined if there is i such that Pm i =0 and Rm i &gt;0. If the determination in block  720  is negative, then at block  730 , PHICH resources are provisioned as in Rel 8/9/10. If the determination in block  720  is positive, then at block  740 , it is determined whether an SCell PUSCH ACK/NACK is needed on subframe #i of the PCell. If the determination in block  740  is negative, then at block  750 , it is determined that there is no need to provision a PHICH resource at PCell subframe #i. If the determination in block  740  is positive, then at block  760 , a PHICH resource is provisioned for a carrier aggregation UE based on Rm i . It can be seen that the scheme in this flowchart will provision the PHICH resource at zero-PHICH subframes of the PCell if needed. 
     At least two schemes can be used to provision a PHICH resource for a CA UE in the control region. A first scheme involves puncturing onto the existing control region. In this scheme, the control region resource allocation still follows the previous release rule at the zero-PHICH DL subframe. Advanced CA UE PHICH resource allocation may follow the same method as in previous releases for a non-zero-PHICH subframe. However, the CA UE PHICH resource is punctured onto the existing control region. The puncturing may damage the PDCCH common search space, but since a higher aggregation level (4 or 8) is used in the PDCCH common search space, the punctured REG is only 1/32 or 1/72, and the UEs (both advanced and legacy) should still be able to correctly decode the PDCCH in the common search space. The impact on error detection probability is expected to be low in this approach. Moreover, the puncturing loss on the PDCCH can be compensated by boosting the power on the PDCCH. An advanced UE may have an advantage since it may know the position of the punctured resource elements. In a UE-specific search space, an eNB can purposely put the PDCCH at the candidates that are not punctured. 
     Alternatively, the CA UE PHICH resource may be punctured onto one CCE at a UE-specific search space. This CCE may be at a fixed location which is known to all advanced CA UEs or may be set semi-statically by higher layer signaling. One group of PHICHs takes three REGs, and one CCE contains nine REGs. So, three groups of PHICH resources can be available in this scheme. An eNB can purposely avoid using the punctured CCE for the PDCCH. 
     A second scheme that can be used to provision a PHICH resource for a CA UE in the control region involves using a special PDCCH. In this scheme, the control region resource allocation still follows the previous release rule at the zero-PHICH DL subframe. For an advanced CA UE, the PHICH is inside a special PDCCH. A special Radio Network Temporary Identifier (RNTI), which is known to all CA UEs, may be assigned for this purpose. The previous PHICH process may be maintained inside the special PDCCH. Alternatively, instead of using a special RNTI to locate the special PDCCH, a fixed location known to all CA UEs or a semi-statically signaled location may be used for this special PDCCH. In this way, the 16-bit Cyclic Redundancy Check (CRC) will not be transmitted, and more PHICH groups can be accommodated inside the special PDCCH. A third alternative is to use the same PDCCH generation process to treat ACK/NACK bits as DCI payload, using a special RNTI, channel coding, rate matching, and QPSK modulation. The channel coding rate may be semi-statically adjustable to obtain the best performance and capacity trade-off. This second scheme for provisioning a PHICH resource in the control region may extend to the PDSCH resource region as well, such as an enhanced PHICH (ePHICH). 
     As the provisioned PHICH resource for a CA UE may otherwise be used for the PDCCH, the PDCCH capacity may be slightly impacted. However, compared to an adaptive retransmission solution, this second solution is more resource efficient since the same resource allocation method as in Release 8/9/10 can be used. Multiple PHICHs are transmitted over the same set of resource elements. 
     The above may be implemented by a network element. A simplified network element is shown with regard to  FIG. 8 . In  FIG. 8 , network element  3110  includes a processor  3120  and a communications subsystem  3130 , where the processor  3120  and communications subsystem  3130  cooperate to perform the methods described above. 
     Further, the above may be implemented by a UE. An example of a UE is described below with regard to  FIG. 9 . UE  3200  may comprise a two-way wireless communication device having voice and data communication capabilities. In some embodiments, voice communication capabilities are optional. The UE  3200  generally has the capability to communicate with other computer systems on the Internet. Depending on the exact functionality provided, the UE  3200  may be referred to as a data messaging device, a two-way pager, a wireless e-mail device, a cellular telephone with data messaging capabilities, a wireless Internet appliance, a wireless device, a smart phone, a mobile device, or a data communication device, as examples. 
     Where the UE  3200  is enabled for two-way communication, it may incorporate a communication subsystem  3211 , including a receiver  3212  and a transmitter  3214 , as well as associated components such as one or more antenna elements  3216  and  3218 , local oscillators (LOs)  3213 , and a processing module such as a digital signal processor (DSP)  3220 . The particular design of the communication subsystem  3211  may be dependent upon the communication network in which the UE  3200  is intended to operate. 
     Network access requirements may also vary depending upon the type of network  3219 . In some networks, network access is associated with a subscriber or user of the UE  3200 . The UE  3200  may require a removable user identity module (RUIM) or a subscriber identity module (SIM) card in order to operate on a network. The SIM/RUIM interface  3244  is typically similar to a card slot into which a SIM/RUIM card may be inserted. The SIM/RUIM card may have memory and may hold many key configurations  3251  and other information  3253 , such as identification and subscriber-related information. 
     When required network registration or activation procedures have been completed, the UE  3200  may send and receive communication signals over the network  3219 . As illustrated, the network  3219  may consist of multiple base stations communicating with the UE  3200 . 
     Signals received by antenna  3216  through communication network  3219  are input to receiver  3212 , which may perform such common receiver functions as signal amplification, frequency down conversion, filtering, channel selection, and the like. Analog to digital (A/D) conversion of a received signal allows more complex communication functions, such as demodulation and decoding to be performed in the DSP  3220 . In a similar manner, signals to be transmitted are processed, including modulation and encoding for example, by DSP  3220  and are input to transmitter  3214  for digital to analog (D/A) conversion, frequency up conversion, filtering, amplification, and transmission over the communication network  3219  via antenna  3218 . DSP  3220  not only processes communication signals but also provides for receiver and transmitter control. For example, the gains applied to communication signals in receiver  3212  and transmitter  3214  may be adaptively controlled through automatic gain control algorithms implemented in DSP  3220 . 
     The UE  3200  generally includes a processor  3238  which controls the overall operation of the device. Communication functions, including data and voice communications, are performed through communication subsystem  3211 . Processor  3238  also interacts with further device subsystems such as the display  3222 , flash memory  3224 , random access memory (RAM)  3226 , auxiliary input/output (I/O) subsystems  3228 , serial port  3230 , one or more keyboards or keypads  3232 , speaker  3234 , microphone  3236 , other communication subsystem  3240  such as a short-range communications subsystem, and any other device subsystems generally designated as  3242 . Serial port  3230  may include a USB port or other port currently known or developed in the future. 
     Some of the illustrated subsystems perform communication-related functions, whereas other subsystems may provide “resident” or on-device functions. Notably, some subsystems, such as keyboard  3232  and display  3222 , for example, may be used for both communication-related functions, such as entering a text message for transmission over a communication network, and device-resident functions, such as a calculator or task list. 
     Operating system software used by the processor  3238  may be stored in a persistent store such as flash memory  3224 , which may instead be a read-only memory (ROM) or similar storage element (not shown). The operating system, specific device applications, or parts thereof, may be temporarily loaded into a volatile memory such as RAM  3226 . Received communication signals may also be stored in RAM  3226 . 
     As shown, flash memory  3224  may be segregated into different areas for both computer programs  3258  and program data storage  3250 ,  3252 ,  3254  and  3256 . These different storage types indicate that each program may allocate a portion of flash memory  3224  for their own data storage requirements. Processor  3238 , in addition to its operating system functions, may enable execution of software applications on the UE  3200 . A predetermined set of applications that control basic operations, including at least data and voice communication applications for example, may typically be installed on the UE  3200  during manufacturing. Other applications may be installed subsequently or dynamically. 
     Applications and software may be stored on any computer-readable storage medium. The computer-readable storage medium may be tangible or in a transitory/non-transitory medium such as optical (e.g., CD, DVD, etc.), magnetic (e.g., tape), or other memory currently known or developed in the future. 
     One software application may be a personal information manager (PIM) application having the ability to organize and manage data items relating to the user of the UE  3200  such as, but not limited to, e-mail, calendar events, voice mails, appointments, and task items. One or more memory stores may be available on the UE  3200  to facilitate storage of PIM data items. Such a PIM application may have the ability to send and receive data items via the wireless network  3219 . Further applications may also be loaded onto the UE  3200  through the network  3219 , an auxiliary I/O subsystem  3228 , serial port  3230 , short-range communications subsystem  3240 , or any other suitable subsystem  3242 , and installed by a user in the RAM  3226  or a non-volatile store (not shown) for execution by the processor  3238 . Such flexibility in application installation may increase the functionality of the UE  3200  and may provide enhanced on-device functions, communication-related functions, or both. For example, secure communication applications may enable electronic commerce functions and other such financial transactions to be performed using the UE  3200 . 
     In a data communication mode, a received signal such as a text message or web page download may be processed by the communication subsystem  3211  and input to the processor  3238 , which may further process the received signal for output to the display  3222 , or alternatively to an auxiliary I/O device  3228 . 
     A user of the UE  3200  may also compose data items, such as email messages for example, using the keyboard  3232 , which may be a complete alphanumeric keyboard or telephone-type keypad, among others, in conjunction with the display  3222  and possibly an auxiliary I/O device  3228 . Such composed items may then be transmitted over a communication network through the communication subsystem  3211 . 
     For voice communications, overall operation of the UE  3200  is similar, except that received signals may typically be output to a speaker  3234  and signals for transmission may be generated by a microphone  3236 . Alternative voice or audio I/O subsystems, such as a voice message recording subsystem, may also be implemented on the UE  3200 . Although voice or audio signal output may be accomplished primarily through the speaker  3234 , display  3222  may also be used to provide an indication of the identity of a calling party, the duration of a voice call, or other voice call-related information, for example. 
     Serial port  3230  may be implemented in a personal digital assistant (PDA)-type device for which synchronization with a user&#39;s desktop computer (not shown) may be desirable, but such a port is an optional device component. Such a port  3230  may enable a user to set preferences through an external device or software application and may extend the capabilities of the UE  3200  by providing for information or software downloads to the UE  3200  other than through a wireless communication network. The alternate download path may, for example, be used to load an encryption key onto the UE  3200  through a direct and thus reliable and trusted connection to thereby enable secure device communication. Serial port  3230  may further be used to connect the device to a computer to act as a modem. 
     Other communications subsystems  3240 , such as a short-range communications subsystem, are further optional components which may provide for communication between the UE  3200  and different systems or devices, which need not necessarily be similar devices. For example, the subsystem  3240  may include an infrared device and associated circuits and components or a Bluetooth™ communication module to provide for communication with similarly enabled systems and devices. Subsystem  3240  may further include non-cellular communications such as WiFi, WiMAX, near field communication (NFC), and/or radio frequency identification (RFID). The other communications element  3240  may also be used to communicate with auxiliary devices such as tablet displays, keyboards or projectors. 
     The UE and other components described above might include a processing component that is capable of executing instructions related to the actions described above.  FIG. 10  illustrates an example of a system  3300  that includes a processing component  3310  suitable for implementing one or more embodiments disclosed herein. In addition to the processor  3310  (which may be referred to as a central processor unit or CPU), the system  3300  might include network connectivity devices  3320 , random access memory (RAM)  3330 , read only memory (ROM)  3340 , secondary storage  3350 , and input/output (I/O) devices  3360 . These components might communicate with one another via a bus  3370 . In some cases, some of these components may not be present or may be combined in various combinations with one another or with other components not shown. These components might be located in a single physical entity or in more than one physical entity. Any actions described herein as being taken by the processor  3310  might be taken by the processor  3310  alone or by the processor  3310  in conjunction with one or more components shown or not shown in the drawing, such as a digital signal processor (DSP)  3380 . Although the DSP  3380  is shown as a separate component, the DSP  3380  might be incorporated into the processor  3310 . 
     The processor  3310  executes instructions, codes, computer programs, or scripts that it might access from the network connectivity devices  3320 , RAM  3330 , ROM  3340 , or secondary storage  3350  (which might include various disk-based systems such as hard disk, floppy disk, or optical disk). While only one CPU  3310  is shown, multiple processors may be present. Thus, while instructions may be discussed as being executed by a processor, the instructions may be executed simultaneously, serially, or otherwise by one or multiple processors. The processor  3310  may be implemented as one or more CPU chips. 
     The network connectivity devices  3320  may take the form of modems, modem banks, Ethernet devices, universal serial bus (USB) interface devices, serial interfaces, token ring devices, fiber distributed data interface (FDDI) devices, wireless local area network (WLAN) devices, radio transceiver devices such as code division multiple access (CDMA) devices, global system for mobile communications (GSM) radio transceiver devices, universal mobile telecommunications system (UMTS) radio transceiver devices, long term evolution (LTE) radio transceiver devices, worldwide interoperability for microwave access (WiMAX) devices, and/or other well-known devices for connecting to networks. These network connectivity devices  3320  may enable the processor  3310  to communicate with the Internet or one or more telecommunications networks or other networks from which the processor  3310  might receive information or to which the processor  3310  might output information. The network connectivity devices  3320  might also include one or more transceiver components  3325  capable of transmitting and/or receiving data wirelessly. 
     The RAM  3330  might be used to store volatile data and perhaps to store instructions that are executed by the processor  3310 . The ROM  3340  is a non-volatile memory device that typically has a smaller memory capacity than the memory capacity of the secondary storage  3350 . ROM  3340  might be used to store instructions and perhaps data that are read during execution of the instructions. Access to both RAM  3330  and ROM  3340  is typically faster than to secondary storage  3350 . The secondary storage  3350  is typically comprised of one or more disk drives or tape drives and might be used for non-volatile storage of data or as an over-flow data storage device if RAM  3330  is not large enough to hold all working data. Secondary storage  3350  may be used to store programs that are loaded into RAM  3330  when such programs are selected for execution. 
     The I/O devices  3360  may include liquid crystal displays (LCDs), touch screen displays, keyboards, keypads, switches, dials, mice, track balls, voice recognizers, card readers, paper tape readers, printers, video monitors, or other well-known input/output devices. Also, the transceiver  3325  might be considered to be a component of the I/O devices  3360  instead of or in addition to being a component of the network connectivity devices  3320 . 
     In an embodiment, a method for communication in a wireless telecommunication system is provided. The method comprises provisioning, by a network element, for a carrier aggregation-capable UE, in a control region of a downlink subframe, at least one resource for a PHICH. 
     In another embodiment, a network element in a wireless telecommunication system is provided. The network element comprises a processor configured such that the network element provisions, for a carrier aggregation-capable UE, in a control region of a downlink subframe, at least one resource for a PHICH. 
     The following are incorporated herein by reference for all purposes: 3GPP TS 36.211, 3GPP TS 36.212, and 3GPP TS 36.213. 
     The embodiments described herein are examples of structures, systems or methods having elements corresponding to elements of the techniques of this application. This written description may enable those skilled in the art to make and use embodiments having alternative elements that likewise correspond to the elements of the techniques of this application. The intended scope of the techniques of this application thus includes other structures, systems or methods that do not differ from the techniques of this application as described herein, and further includes other structures, systems or methods with insubstantial differences from the techniques of this application as described herein. 
     While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods may be embodied in many other specific forms without departing from the scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented. 
     Also, techniques, systems, subsystems and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component, whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein.