Patent Publication Number: US-2013242881-A1

Title: Explicit indication of uplink control channel resources in carrier aggregation systems

Description:
CLAIM OF PRIORITY 
     The present application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/612,132 filed Mar. 16, 2012. 
    
    
     FIELD 
     The present disclosure pertains to uplink control channel resource collisions, and more particularly to physical uplink control channel resource collisions that may occur in systems using in inter-band carrier aggregation with different TDD UL/DL configurations. 
     BACKGROUND 
     In wireless communications systems, such as long term evolution (LTE) systems, downlink and uplink transmissions may be organized into two duplex modes: frequency division duplex (FDD) mode and time division duplex (TDD) mode. The FDD mode uses a paired spectrum where the frequency domain is used to separate the uplink (UL) and downlink (DL) transmissions.  FIG. 1A  is a graphical illustration of an uplink and downlink subframe separated in the frequency domain for the FDD mode. In TDD systems, an unpaired spectrum may be used where both UL and DL are transmitted over the same carrier frequency. The UL and DL are separated in the time domain.  FIG. 1B  is a graphical illustration of uplink and downlink subframes sharing a carrier frequency in the TDD mode. In LTE-Advanced, carrier aggregation allows expansion of effective bandwidth delivered to a user terminal through concurrent utilization of radio resources across multiple carriers. Multiple component carriers are aggregated to form a larger overall transmission bandwidth. Carrier aggregation may be performed in LTE-Advanced TDD or LTE-Advanced FDD systems. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a graphical illustration of an uplink and downlink subframe separated in the frequency domain for the FDD mode. 
         FIG. 1B  is a graphical illustration of uplink and downlink subframes sharing a carrier frequency in the TDD mode. 
         FIG. 2  is a schematic representation of an example wireless cellular communication system based on 3GPP long term evolution (LTE). 
         FIG. 3  is a schematic block diagram illustrating an access node device according to one embodiment. 
         FIG. 4  is a schematic block diagram illustrating a user equipment device according to one embodiment. 
         FIG. 5  is a schematic diagram of a physical uplink control channel format 1a/1b slot structure with normal cyclic prefix. 
         FIG. 6  is a schematic diagram showing an example physical uplink control channel resource mapping scheme. 
         FIG. 7A  is an example schematic diagram illustrating downlink hybrid automatic repeat request timing linkages in inter-band carrier aggregation with UL/DL configuration  6  on the primary cell and UL/DL configuration  2  on the secondary cell. 
         FIG. 7B  is an example schematic diagram illustrating downlink hybrid automatic repeat request timing linkages in inter-band carrier aggregation with UL/DL configuration  1  on the primary cell and UL/DL configuration  4  on secondary cell. 
         FIG. 8  is a process flowchart for using an explicit PUCCH resource mapping. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure pertains to uplink control channel resource collisions, and more particularly to physical uplink control channel resource collision that may occur in systems using carrier aggregation. Specific embodiments described herein relate to physical uplink control channel (PUCCH) resources in a system using inter-band carrier aggregation with different UL/DL TDD configurations. In the various implementations described in this disclosure, PUCCH resources may be used more effectively by avoiding, preventing, detecting, resolving, or mitigating various types of PUCCH resource collisions described herein. 
     Certain aspects of the systems, methods, and apparatuses are part of a wireless communications network. Downlink (DL) hybrid automatic repeat request (HARD) timing linkages associated with a first component carrier and a second component carrier can be determined, the first component carrier having a different uplink (UL) and DL configuration than the second component carrier. A derived downlink association set can be determined. A physical uplink control channel (PUCCH) resource can be identified for the second component carrier. An indicator of the PUCCH resource can be sent to a user equipment. 
     In certain aspects, the PUCCH resource is indicated based, at least in part, on at least one acknowledgement/negative acknowledgement resource indicator (ARI) bit. The at least one ARI bit is communicated with at least one transmit power control (TPC) bit. 
     In certain aspects, the first component carrier comprises a primary cell and the second component carrier comprises a secondary cell. 
     Mobile electronic devices may operate in a communications network, such as the network shown in  FIG. 2 , which is based on the third generation partnership project (3GPP) long term evolution (LTE), also known as Evolved Universal Terrestrial Radio Access (E-UTRA). More specifically,  FIG. 2  is a schematic representation of an example wireless communication system  200  based on 3GPP LTE. The system  200  shown in  FIG. 2  includes a plurality of base stations  212  (i.e.,  212   a  and  212   b ). In the LTE example of  FIG. 2 , the base stations are shown as evolved Node B (eNB)  212   a,b . In this disclosure, references to eNB are intended to refer to an access node device, such as a base station or any other communications network node that provides service to a mobile station including femtocell, picocell, or the like. The example wireless communication system  200  of  FIG. 2  may include one or a plurality of radio access networks  210 , core networks (CNs)  220 , and external networks  230 . In certain implementations, the radio access networks may be Evolved Universal Mobile Telecommunications System (UMTS) terrestrial radio access networks (EUTRANs). In addition, in certain instances, core networks  220  may be evolved packet cores (EPCs). Further, there may be one or more mobile electronic devices  202  obtaining communication services via the example wireless communication system  200 . In some implementations, 2G/3G systems  240 , e.g., Global System for Mobile communication (GSM), Interim Standard 95 (IS-95), Universal Mobile Telecommunications System (UMTS) and CDMA2000 (Code Division Multiple Access) may also be integrated into the communication system  200 . 
     In the example LTE system shown in  FIG. 2 , the EUTRAN  210  includes eNB  212   a  and eNB  212   b . Cell  214   a  is the service area of eNB  212   a  and Cell  214   b  is the service area of eNB  212   b . The term cell is intended to describe a coverage area associated with a base station regardless and may or may not overlap with the coverage areas associated with other base stations. In  FIG. 2 , User Equipment (UE)  202   a  and UE  202   b  operate in Cell  214   a  and are served by eNB  212   a . The EUTRAN  210  can include one or a plurality of eNBs  212  and one or a plurality of UEs can operate in a cell. The eNBs  212  communicate directly to the UEs  202 . In some implementations, the eNB  212  may be in a one-to-many relationship with the UE  202 , e.g., eNB  212   a  in the example LTE system  200  can serve multiple UEs  202  (i.e., UE  202   a  and UE  202   b ) within its coverage area Cell  214   a , but each of UE  202   a  and UE  202   b  may be connected only to one eNB  212   a  at a time. In some implementations, the eNB  212  may be in a many-to-many relationship with the UEs  202 , e.g., UE  202   a  and UE  202   b  can be connected to eNB  212   a  and eNB  212   b . The eNB  212   a  may be connected to eNB  212   b  with which handover may be conducted if one or both of UE  202   a  and UE  202   b  travels from cell  214   a  to cell  214   b . UE  202  may be any communications device used by an end-user to communicate, for example, within the LTE system  200 . The UE  202  may alternatively be referred to as mobile electronic device, user equipment, user device, mobile device, mobile station, subscriber station, or wireless terminal. In some embodiments, UE  202  may be a cellular phone, personal data assistant (PDA), smart phone, laptop, tablet personal computer (PC), pager, portable computer, or other types of mobile communications device, including communications apparatus used in wirelessly connected automobiles, appliances, or clothing. 
     UEs  202  may transmit voice, video, multimedia, text, web content and/or any other user/client-specific content. On the one hand, the transmission of some of these contents, e.g., video and web content, may require high channel throughput to satisfy the end-user demand. On the other hand, the channel between UEs  202  and eNBs  212  may be contaminated by multipath fading, due to the multiple signal paths arising from many reflections in the wireless environment. Accordingly, the UEs&#39; transmission may adapt to the wireless environment. In short, UEs  202  generate requests, send responses or otherwise communicate in different means with Enhanced Packet Core (EPC)  220  and/or Internet Protocol (IP) networks  230  through one or more eNBs  212 . 
     A radio access network is part of a mobile telecommunication system which implements a radio access technology, such as UMTS, CDMA2000, and 3GPP LTE. In many applications, the Radio Access Network (RAN) included in a LTE telecommunications system  200  is called an EUTRAN  210 . The EUTRAN  210  can be located between UEs  202  and EPC  220 . The EUTRAN  210  includes at least one eNB  212 . The eNB can be a radio base station that may control all or at least some radio related functions in a fixed part of the system. The at least one eNB  212  can provide radio interface within their coverage area or a cell for UEs  202  to communicate. eNBs  212  may be distributed throughout the communications network to provide a wide area of coverage. The eNB  212  directly communicates to one or a plurality of UEs  202 , other eNBs, and the EPC  220 . 
     The eNB  212  may be the end point of the radio protocols towards the UE  202  and may relay signals between the radio connection and the connectivity towards the EPC  220 . In certain implementations, the EPC  220  is the main component of a core network (CN). The CN can be a backbone network, which may be a central part of the telecommunications system. The EPC  220  can include a mobility management entity (MME), a serving gateway (SGW), and a packet data network gateway (PGW). The MME may be the main control element in the EPC  220  responsible for the functionalities including the control plane functions related to subscriber and session management. The SGW can serve as a local mobility anchor, such that the packets are routed through this point for intra EUTRAN  210  mobility and mobility with other legacy 2G/3G systems  240 . The SGW functions may include the user plane tunnel management and switching. The PGW may provide connectivity to the services domain including external networks  230 , such as the IP networks. The UE  202 , EUTRAN  210 , and EPC  220  are sometimes referred to as the evolved packet system (EPS). It is to be understood that the architectural evolvement of the LTE system  200  is focused on the EPS. The functional evolution may include both EPS and external networks  230 . 
     Though described in terms of  FIG. 2 , the present disclosure is not limited to such an environment. In general, telecommunication systems may be described as communications networks made up of a number of radio coverage areas, or cells that are each served by a base station or other fixed transceiver. Example telecommunication systems include Global System for Mobile Communication (GSM) protocols, Universal Mobile Telecommunications System (UMTS), 3GPP Long Term Evolution (LTE), and others. In addition to telecommunication systems, wireless broadband communication systems may also be suitable for the various implementations described in the present disclosure. Example wireless broadband communication systems include IEEE 802.11 wireless local area network, IEEE 802.16 WiMAX network, etc. 
     Referring to  FIG. 3 , an access node device (for example, eNB  212   a  in  FIG. 2 ) according to one embodiment will be described below. The illustrated device  300  includes a processing module  302 , a wired communication subsystem  304 , and a wireless communication subsystem  306 . The processing module  302  can include a processing component (alternatively referred to as “processor” or “central processing unit (CPU)”) capable of executing instructions related to one or more of the processes, steps, or actions described above in connection with one or more of the embodiments disclosed herein. The processing module  302  can also include other auxiliary components, such as random access memory (RAM), read only memory (ROM), secondary storage (for example, a hard disk drive or flash memory). The processing module  302  can execute certain instructions and commands to provide wireless or wired communication, using the wired communication subsystem  304  or the wireless communication subsystem  306 . A skilled artisan will readily appreciate that various other components can also be included in the device  300 . 
       FIG. 4  is a schematic block diagram illustrating a user equipment device (for example, UEs  202   a ,  202   b  in  FIG. 2 ) according to one embodiment. The illustrated device  400  includes a processing unit  402 , a computer readable storage medium  404  (for example, ROM or flash memory), a wireless communication subsystem  406 , a user interface  408 , and an I/O interface  410 . 
     Similar to the processing module  302  of  FIG. 3 , the processing unit  402  can include a processing component configured to execute instructions related to one or more of the processes, steps, or actions described above in connection with one or more of the embodiments disclosed herein. The processing unit  402  can also include other auxiliary components, such as random access memory (RAM) and read only memory (ROM). The computer readable storage medium  404  can store an operating system (OS) of the device  400  and various other computer executable software programs for performing one or more of the processes, steps, or actions described above. 
     The wireless communication subsystem  406  is configured to provide wireless communication for data and/or control information provided by the processing unit  402 . The wireless communication subsystem  406  can include, for example, one or more antennas, a receiver, a transmitter, a local oscillator, a mixer, and a digital processing (DSP) unit. In some embodiments, the wireless communication subsystem  406  can support a multiple input multiple output (MIMO) protocol. 
     The user interface  408  can include, for example, a screen or touch screen (for example, a liquid crystal display (LCD), a light emitting display (LED), an organic light emitting display (OLED), a microelectromechanical system (MEMS) display), a keyboard or keypad, a trackball, a speaker, or a microphone. The I/O interface  410  can include, for example, a universal serial bus (USB) interface. A skilled artisan will readily appreciate that various other components can also be included in the device  400 . 
     In the 3GPP LTE TDD system, a subframe of a radio frame can be a downlink, an uplink or a special subframe (the special subframe includes downlink and uplink time regions separated by a guard period for downlink to uplink switching). Currently, there are seven different UL/DL configuration schemes that may be used in LTE TDD operations, as shown in Table 1 below. Table 1 shows LTE TDD Uplink-Downlink Configurations. D represents downlink subframes, U represents uplink subframes and S represents special subframes. In each special subframe S, there are three parts which are: i) the downlink pilot time slot (DwPTS), ii) the guard period (GP) and iii) the uplink pilot time slot (UpPTS). Downlink transmissions on the physical downlink shared channel (PDSCH) may be made in DL subframes or in the DwPTS portion of a special subframe. Uplink transmissions on the physical uplink control channel (PUCCH) or physical uplink shared channel (PUSCH) may only be made in UL subframes, since the UpPTS portion of a special subframe is too short to accommodate these channels. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 LTE TDD Uplink-Downlink Configurations 
               
            
           
           
               
               
               
            
               
                 Uplink-downlink 
                 Downlink-to-Uplink 
                 Subframe number 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 configuration 
                 Switch-point periodicity 
                 0 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 8 
                 9 
               
               
                   
               
               
                 0 
                 5 ms 
                 D 
                 S 
                 U 
                 U 
                 U 
                 D 
                 S 
                 U 
                 U 
                 U 
               
               
                 1 
                 5 ms 
                 D 
                 S 
                 U 
                 U 
                 D 
                 D 
                 S 
                 U 
                 U 
                 D 
               
               
                 2 
                 5 ms 
                 D 
                 S 
                 U 
                 D 
                 D 
                 D 
                 S 
                 U 
                 D 
                 D 
               
               
                 3 
                 10 ms  
                 D 
                 S 
                 U 
                 U 
                 U 
                 D 
                 D 
                 D 
                 D 
                 D 
               
               
                 4 
                 10 ms  
                 D 
                 S 
                 U 
                 U 
                 D 
                 D 
                 D 
                 D 
                 D 
                 D 
               
               
                 5 
                 10 ms  
                 D 
                 S 
                 U 
                 D 
                 D 
                 D 
                 D 
                 D 
                 D 
                 D 
               
               
                 6 
                 5 ms 
                 D 
                 S 
                 U 
                 U 
                 U 
                 D 
                 S 
                 U 
                 U 
                 D 
               
               
                   
               
            
           
         
       
     
     As shown in Table 1, there are two switch point periodicities specified in the LTE standard, 5 ms and 10 ms. 5 ms switch point periodicity is introduced to support the co-existence between LTE and low chip rate UTRA TDD systems, and 10 ms switch 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 “DL heavy” 1:9 ratio to “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 DwPTS).) Therefore, compared to FDD, TDD systems have more flexibility in terms of the proportion of resources assignable to uplink and downlink communications within a given amount of spectrum. Specifically, it is possible to unevenly distribute the radio resources between uplink and downlink. This will provide a way to utilize the radio resources more efficiently by selecting an appropriate UL/DL configuration based on interference situation and different traffic characteristics in DL and UL. 
     As understood to persons of skill in the art, UL (or DL) transmissions do not occur in every subframe in an LTE TDD system. Since the UL and DL transmissions are not continuous, scheduling and hybrid automatic repeat request (HARQ) timing relationships for an LTE TDD system are defined in the specifications. Currently, the HARQ ACK/NACK timing relationship for downlink is defined in Table 2 below. Table 2 may be used to show which uplink subframes should carry uplink HARQ ACK/NACK transmissions associated with M multiple downlink subframes. Table 2 shows downlink association set index K: {k 0 , k 1 , . . . k M−1 }. It associates an UL sub-frame n, which conveys ACK/NACK, with DL sub-frames n−k i , i=0 to M−1. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Downlink Association Set Index K: {k 0 , k 1 , . . . k M−1 } 
               
            
           
           
               
               
            
               
                 UL-DL 
                 Subframe n 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Configuration 
                 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, 7, 11 
                 6, 5, 4, 7 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 5 
                 — 
                 — 
                 13, 12, 9, 8, 7, 5, 4, 11, 6 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 6 
                 — 
                 — 
                 7 
                 7 
                 5 
                 — 
                 — 
                 7 
                 7 
                 — 
               
               
                   
               
            
           
         
       
     
     As an illustrative example, when using TDD UL/DL configuration  6 , there are uplink subframes that occur in subframes  2 ,  3 ,  4 ,  7 , and  8 . (see also UL/DL configuration  6  in Table 1). Referring to Table 2, for the UL/DL configuration  6 , at subframe  2 , the downlink association set index K: {k 0 , k 1 , . . . k M−1 } can be represented as K:{7}. 
     The uplink HARQ ACK/NACK timing linkage is shown in Table 3 below. As understood to a person of skill in the art, a timing linkage represents a relationship between when downlink data is transmitted in downlink subframes and when corresponding HARQ ACK/NACK feedback is transmitted in one or more subsequent uplink subframes. Table 3 shows k values for HARQ ACK/NACK. It indicates that the physical hybrid ARQ indicator channel (PHICH) ACK/NACK received in DL sub-frame i is linked with the UL data transmission in UL sub-frame i−k, k is given in Table 3. In addition, for UL/DL configuration  0 , in sub-frames  0  and  5 , when I PHICH =1, k=6. This is because there may be two ACK/NACKs for a UE transmitted on the PHICH in subframes  0  and  5 . 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 k for HARQ ACK/NACK 
               
            
           
           
               
               
            
               
                 TDD UL/DL 
                 subframe number i 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Configuration 
                 0 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 8 
                 9 
               
               
                   
               
               
                 0 
                 7 
                 4 
                   
                   
                   
                 7 
                 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 UL grant, ACK/NACK and transmission/retransmission relationship is in Table 4 below. Table 4 shows k values for physical uplink shared channel (PUSCH) transmission. The UE shall upon detection of a physical downlink control channel (PDCCH) with DCI format 0 and/or a PHICH transmission in sub-frame n intended for the UE, adjust the corresponding PUSCH transmission in sub-frame n+k, with k given in Table 4. 
     For TDD UL/DL configuration  0 , if the LSB of the UL index in the 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 PHICH is received in sub-frame n=1 or 6, the UE shall adjust the corresponding PUSCH transmission in sub-frame n+7. If, for TDD UL/DL configuration  0 , both the most significant bit (MSB) and least significant bit (LSB) of the UL index field in the DCI format 0 are set in sub-frame n, the UE shall adjust the corresponding PUSCH transmission in both sub-frames n+k and n+7, with k given in Table 4. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 k for PUSCH transmission 
               
            
           
           
               
               
            
               
                 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 
               
               
                   
               
            
           
         
       
     
     Both grant and HARQ timing linkage in TDD are more complicated than the fixed time linkages used in an LTE FDD system. 
     The physical uplink control channel (PUCCH) format 1a/1b may be used to transmit the ACK/NACK signalling (when ACK/NACK is not multiplexed into a PUSCH transmission). The slot structure of PUCCH formats 1a and 1b with normal cyclic prefix is shown in  FIG. 5 .  FIG. 5  is a schematic diagram of a physical uplink control channel format 1a/1b slot structure with normal cyclic prefix. Each format 1a/1b PUCCH is in a subframe made up of two slots. The same modulation symbol is used in both slots. Without channel selection, formats 1a and 1b carry one and two ACK/NACK bits, respectively. These bits are encoded into the modulation symbol using either BPSK or QPSK modulation based on the number of ACK/NACK bits. The symbol is multiplied by a cyclic-shifted sequence with length-12. Then, the samples are mapped to the 12 subcarriers which the PUCCH is to occupy and then converted to the time domain via an IDFT. The spread signal is then multiplied with an orthogonal cover sequence with the length of 4, w(m), where mε{0,1,2,3} corresponds to each one of 4 data bearing symbols in the slot. There are three reference symbols in each slot (located in the middle symbols of the slot) that allow channel estimation for coherent demodulation of formats 1a/1b. 
     Similar to FDD, for TDD, the PUCCH resource which a UE is to use may be signalled via either implicit or explicit signaling. 
     In the case of implicit signaling, for a PDSCH transmission indicated by the detection of corresponding PDCCH or a PDCCH indicating downlink SPS release in sub-frame n−k i  where k i εK defined in Table 2, the PUCCH resource n PUCCH,i   (1) =(M−i−1)·N c +i·N c+1 +n CCE,i +N PUCCH   (1) , where c is selected from {0, 1, 2, 3} such that N c ≦n CCE,i &lt;N c+1 , where M is the number of elements in the set K defined in Table 2. N c =max{0,└[N RB   DL ·(N sc   RB ·c−4)]/36┘}, n CCE,i  is the number of the first control channel element (CCE) used for transmission of the corresponding PDCCH in subframe n−k i , and N PUCCH   (1)  is configured by higher layers. 
     In the case of explicit signalling, the PUCCH resource may be indicated via the ACK/NACK resource indicator (ARI) bits and/or higher layer configuration.  FIG. 6  illustrates the PUCCH resource mapping scheme.  FIG. 6  is a schematic diagram showing an example physical uplink control channel resource mapping scheme. In carrier aggregation (CA), PUCCH resources may be signalled implicitly using the location of the scheduling grant for the UE on the PDCCH of its primary cell (PCell). PUCCH resources may also be explicitly indicated using the ARI bits contained in the grant for the UE on the PDCCH of one of the UE&#39;s secondary cells (SCells). In some implementations, resources of the SCell may be cross carrier scheduled by the PCell. For example, a PDCCH transmitted on PCell may provide scheduling for a PDSCH on SCell. In cross carrier scheduling, the PUCCH resource allocated to a UE may be implicitly signalled by the first CCE index of the PDCCH. In other implementations, the SCell is separate-scheduled by PDCCH on SCell itself (i.e. a PDCCH on SCell refers to a PDSCH grant also on SCell), and the PUCCH resource index is determined by the ARI bits in the grant transmitted on the SCell PDCCH. 
     LTE-Advanced Release-10 currently only supports CA when using the same UL/DL configuration on all the aggregated carriers. Inter-band carrier aggregation with different TDD UL/DL configurations on the carriers from different bands may facilitate the bandwidth flexibility and coexistence with legacy TDD systems. 
     It is 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 can be designated as a primary carrier which is used for PUCCH transmission, semi-persistent scheduling, etc., while the remaining one or more CCs are configured as secondary CCs. This primary carrier is also known as primary cell (PCell), while the secondary CC is known as secondary cell (SCell). 
     The timing linkage complexity in TDD systems increases, especially in view of CA with different TDD configurations, because with different TDD configurations, there are time instances with direction conflicting subframes among aggregated CCs (e.g. an UL subframe on CC1 at the same time as CC2 has a DL subframe). Also the timing linkage is different for each different TDD configuration and, furthermore, certain control signals have to be on a specific carrier, e.g. PUCCH has to be on PCell, etc. This may lead to a much greater control channel resource collision possibility in some scenarios. 
     Because PUCCH is transmitted on PCell in the case of inter-band CA with different UL/DL configurations, it increases the possibility of PUCCH resource collision. Described in this disclosure are two types of PUCCH resource collision. One type is that collision takes place between different UEs when ACK/NACKs from different UEs happen to use the same PUCCH resource, which may be referred to as a Type 1 collision or an inter-UE collision. Another type of collision occurs within the same UE when the PUCCH format 1a/1b resources from PCell and SCell are mapped onto the same PUCCH resource: this type of collision may be referred to as a Type 2 collision or an intra-UE collision. We consider both scenarios in this disclosure. 
       FIG. 7A  is an example schematic diagram illustrating downlink hybrid automatic repeat request (HARQ) timing linkages in inter-band carrier aggregation. In  FIG. 7A , a primary cell (PCell) is utilizing UL/DL configuration  6  and a secondary cell (SCell) is utilizing UL/DL configuration  2 . In the example scenario shown in  FIG. 7A , two TDD carriers are aggregated, and the PCell  702  is set as UL/DL configuration  6  and SCell  704  is with UL/DL configuration  2 , in full duplex mode. PCell  702  follows its own DL HARQ timing relationship, which is UL/DL configuration  6 , and SCell  704  DL HARQ follows the timing of UL/DL configuration  2 . The PCell  702  is shown with PDCCH configuration  706  and PUCCH configuration  708 ; SCell  704  is shown with PDCCH configuration  712  (PDCCH may or may not be configured on SCell). The arrows  710  represent the DL HARQ timing for a first (e.g., non-CA legacy) UE served by PCell  702 ; while the arrows  716  represent the DL HARQ timing of SCell  704  for a second (e.g., CA) UE. A non-CA legacy UE on the carrier with UL/DL configuration  6  will follow the original Rel. 8/9/10 timing linkage of UL/DL configuration  6 . 
     For legacy UEs on PCell PUCCH resource is determined by the first CCE for subframe  0  grant; while for CA UEs SCell PUCCH resources are based on four different subframes. 
     Turning to the PUCCH format 1a/1b resource at subframe # 7   720  in  FIG. 7A , for a legacy non-CA UE whose serving cell has UL/DL configuration  6 , the PUCCH resource is determined by the first CCE index for transmission of the corresponding PDCCH in subframe # 0  as described above. For a CA UE, it may require four PUCCH resources at subframe # 7   720  for ACK/NACKs from four different PDSCH subframes, # 9 , # 0 , # 1  and # 3 . In the case of cross carrier scheduling, these PUCCH resources are determined by the same fashion as described above, but the CCE indexes used in the calculation are from the different subframes for transmission of the corresponding PDCCHs. Therefore, it may result in the same PUCCH channel resource index for the non-CA UE and the CA UE at the same UL subframe. 
       FIG. 7B  is an example schematic  750  diagram illustrating DL HARQ timing linkages in inter-band carrier aggregation with UL/DL configuration  1  on the PCell  752  and UL/DL configuration  4  on SCell  754 . PCell  752  follows its own DL HARQ timing relationship, which is UL/DL configuration  1 , and SCell  754  DL HARQ follows the timing of UL/DL configuration  4 . The arrows  760  represent the DL HARQ timing of PCell  752 , the arrows  766  represent the DL HARQ timing of SCell  754 . PCell  752  includes PDCCH configuration  756  and PUCCH configuration  758 . SCell  754  includes PDCCH configuration  762 . 
     As shown in  FIG. 7B , for cross carrier scheduling, the PUCCH format 1a/1b resources at subframes # 2  are determined by the first CCE index for transmission of the corresponding PDCCH in subframes # 5  and # 6  of PCell  752  and subframes # 0 , # 1 , # 4 , # 5  of SCell  754 . Therefore, it may result in PUCCH resource collision between PCell  752  and SCell  754  within the CA UE at subframe  2 . It should be understood that the PUCCH channel index mapped from different subframes may have the same number. In  FIG. 7B , a potential PUCCH resource collision may also occur in subframe  3 . 
     In one aspect of the present disclosure include, an algorithm can be used to determine PUCCH format 1a/1b resource mapping. The algorithm may be used throughout the system, or may be selectively used in the case of inter-band CA with different TDD UL/DL configurations. Because PUCCH is transmitted only on a single cell (PCell), we have to design a single PUCCH resource mapping rule which can be applied to all component carriers in CA. 
     In Table 2 above, each entry represents the downlink association set index K at a subframe n for a given UL/DL configuration. For convenience in expression, two additional indexes can be assigned to K: K j,n , with n indicating subframe number in a frame (from 0 to 9) and j representing UL/DL configuration (from 0 to 6). For example, K 1,2  refers to the subframe  2  of a carrier using UL/DL configuration  1 . Referring to the information of Table 2, the following expression should be understood as representing the downlink association set index K associated for UL/DL configuration  1 , subframe  2 : K 1,2 ={7,6}. Similarly, the downlink association set index K for UL/DL configuration  2 , subframe  2  is represented by the expression K 2,2 ={8,7,4,6}. The downlink association set is null at any DL or special subframe. 
     A CA UE can use the currently existing Rel 8/9/10 PUCCH mapping rule for the PCell PDSCH ACK/NACK. The non-CA UE served by the PCell follows the existing mapping rule as well. Therefore, no collision will occur. For SCell PDSCH ACK/NACK, if using different DL HARQ timing than PCell, an explicit signalling can be used to directly indicate the PUCCH resource to the UE. In certain implementation, the ACK/NACK Resource Indicator (ARI) bit(s) can be used to convey the exact location of PUCCH resource as is done for separate scheduling case in Rel 10. Table 5 below shows the correspondence between Transmit Power Control (TPC) bits (used as ARI bits) and PUCCH resource. Two TPC bits are contained in all UE-specific Downlink Control Information (DCI) formats which are signalled on the PDCCH to indicate downlink (PDSCH) and uplink (PUSCH) grants to a UE. These TPC bits are normally used to perform uplink power control for PUCCH and PUSCH transmissions. However, when carrier aggregation is used, it may not be necessary to use the TPC bits in all signalled DCIs for power control purposes, and hence it is possible to reuse one or both of these TPC bits for other purposes when they are not required for power control. Table 5 shows PUCCH resource values for HARQ ACK Resource for PUCCH. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 PUCCH Resource Value for HARQ-ACK Resource for PUCCH 
               
            
           
           
               
               
            
               
                 Value of ‘TPC command for 
                 n PUCCH,j   (1)  or 
               
               
                 PUCCH’ 
                 (n PUCCH,j   (1) , n PUCCH,j+1   (1) ) 
               
               
                   
               
               
                 ‘00’ 
                 The 1st PUCCH resource 
               
               
                   
                 value configured by the higher 
               
               
                   
                 layers 
               
               
                 ‘01’ 
                 The 2 nd  PUCCH resource 
               
               
                   
                 value configured by the higher 
               
               
                   
                 layers 
               
               
                 ‘10’ 
                 The 3 rd  PUCCH resource 
               
               
                   
                 value configured by the higher 
               
               
                   
                 layers 
               
               
                 ‘11’ 
                 The 4 th  PUCCH resource 
               
               
                   
                 value configured by the higher 
               
               
                   
                 layers 
               
               
                   
               
            
           
         
       
     
       FIG. 8  is a process flowchart  800  for using an explicit PUCCH resource mapping. The DL HARQ timing linkage can be determined ( 802 ). Depending on the combination of TDD UL/DL configurations for CCs (i.e., timing rules) ( 804 ), a single PUCCH mapping rule may work for ACK/NACKs of both PCell and SCell ( 808 ). However, other times, the explicit resource mapping is used ( 806 ). For example, when multiple timing rules exist for CA UEs, the PCell may still use the implicit PUCCH mapping rules, consistent with Rel10; for SCell, an explicit PUCCH resource mapping can be used ( 806 ). 
       FIG. 8  above describes a method executed in a base station in a wireless communications network that utilizes explicit signalling. The base station can determine a downlink (DL) hybrid automatic repeat request (HARQ) timing for a first component carrier and a second component carrier. The first component carrier may have a different DL HARQ timing configuration than the second component carrier. The first component carrier may be a primary cell (PCell) and the second component carrier may be a secondary cell (SCell). A physical uplink control channel (PUCCH) resource for the second component carrier can be identified, e.g., explicitly. The explicit identification of the PUCCH resource can be associated with (or represented by) a resource indicator. The base station can send the resource indicator of the PUCCH resource to a user equipment. The PUCCH resource may be identified based, at least in part, on at least one acknowledgement/negative acknowledgement resource indicator (ARI) bit. The at least one ARI bit may be communicated with at least one transmit power control (TPC) bit. The term “identified” is meant to capture different functional aspects, such as choosing, selecting, receiving an indication of, determining, calculating, mapping, etc. 
     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. 
     While the above detailed description has shown, described, and pointed out the fundamental novel features of the invention as applied to various embodiments, it will be understood that various omissions and substitutions and changes in the form and details of the system illustrated may be made by those skilled in the art, without departing from the intent of the disclosure.