Patent Publication Number: US-2015085720-A1

Title: Reduced delay harq process timeline for fdd-tdd carrier aggregation

Description:
CROSS REFERENCES 
     The present application for patent claims priority to U.S. Provisional Patent Application No. 61/883,173 by Gaal et al., entitled “Reduced Delay HARQ Process Timeline For FDD-TDD Carrier Aggregation,” filed Sep. 26, 2013, assigned to the assignee hereof, and expressly incorporated by reference herein. 
    
    
     BACKGROUND 
     Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, and the like. These wireless networks may be multiple-access networks capable of supporting multiple users by sharing the available network resources. 
     A wireless communication network may include a number of base stations that can support communication for a number of mobile devices. A mobile device may communicate with a base station via downlink (DL) and uplink (UL) transmissions. The downlink (or forward link) refers to the communication link from the base station to the mobile device, and the uplink (or reverse link) refers to the communication link from the mobile device to the base station. 
     Multiple access technologies may use Frequency Division Duplexing (FDD) or Time Division Duplexing (TDD) to provide uplink and downlink communications over one or more carriers. TDD operation offers flexible deployments without requiring paired spectrum resources. TDD formats include transmission of frames of data, each including a number of different subframes in which different subframes may be uplink or downlink subframes. In systems that operate using TDD, different formats may be used in which uplink and downlink communications may be asymmetric. Flexible TDD DL/UL configuration provides efficient ways to use unpaired spectrum resources and TDD configuration may be adaptive based on traffic conditions (e.g., UL/DL loading at the base station or mobile device). 
     The wireless communication networks including the base stations and UEs may support operation on multiple carriers which may be called carrier aggregation. Carrier aggregation may be used to increase throughput between a base station supporting multiple component carriers and a mobile device, and mobile devices may be configured to communicate using multiple component carriers associated with multiple base stations. Other techniques for increasing throughput using multiple carriers may be used where base stations performing joint operations have non-ideal backhaul (e.g., dual-connectivity, etc.). 
     In some instances, transmission errors between mobile devices and base stations are avoided or corrected by utilizing an automatic repeat request (ARQ) scheme. An ARQ scheme may be employed to detect whether a received packet is in error. For example, in an ARQ scheme, a receiver may notify a transmitter with a positive acknowledgment (ACK), when a packet is received free from errors; and the receiver may notify the transmitter with a negative acknowledgment (NAK), if an error is detected. In some case, a hybrid ARQ (HARQ) scheme is employed to correct some errors and to detect and discard certain uncorrectable packets. In some multi-carrier scenarios, however, the overall HARQ delay may cause certain inefficiencies in wireless communications. 
     SUMMARY 
     Methods, systems, and devices are described which minimize HARQ delay for multi-carrier scheduling in a wireless communications network utilizing one or more TDD component carriers and one or more FDD component carriers. HARQ periodicity may be adjusted, and tools and techniques for scheduling TDD UL and DL grants and HARQ indicators may be employed. 
     A method of wireless communication is described. The method may include determining a configuration for a set of component carriers in carrier aggregation, the set of component carriers including a time-division duplexing (TDD) secondary component carrier (SCC) and a frequency-division duplexing (FDD) SCC, identifying a scheduling timing and an uplink hybrid automatic repeat request (HARQ) timing of the FDD SCC based at least in part on a time duration of each frame of the TDD SCC, and communicating with a node based at least in part on the identified scheduling timing and uplink HARQ timing of the FDD SCC. 
     An apparatus for wireless communication is also described. The apparatus may include a processor, memory in electronic communication with the processor, and instructions stored on the memory. The instructions may executable by the processor to determine a configuration for a set of component carriers in carrier aggregation, the set of component carriers including a time-division duplexing (TDD) secondary component carrier (SCC) and a frequency-division duplexing (FDD) SCC, identify a scheduling timing and an uplink hybrid automatic repeat request (HARQ) timing of the FDD SCC based at least in part on a time duration of each frame of the TDD SCC, and communicate with a node based at least in part on the identified scheduling timing and uplink HARQ timing of the FDD SCC. 
     A further apparatus for wireless communication is also described. The apparatus may include means for determining a configuration for a set of component carriers in carrier aggregation, the set of component carriers including a time-division duplexing (TDD) secondary component carrier (SCC) and a frequency-division duplexing (FDD) SCC, means for identifying a scheduling timing and an uplink hybrid automatic repeat request (HARQ) timing of the FDD SCC based at least in part on a time duration of each frame of the TDD SCC, and means for communicating with a node based at least in part on the identified scheduling timing and uplink HARQ timing of the FDD SCC. 
     A non-transitory computer-readable medium is also described. The non-transitory computer-readable medium may include code comprising instruction for determining a configuration for a set of component carriers in carrier aggregation, the set of component carriers including a time-division duplexing (TDD) secondary component carrier (SCC) and a frequency-division duplexing (FDD) SCC, identifying a scheduling timing and an uplink hybrid automatic repeat request (HARQ) timing of the FDD SCC based at least in part on a time duration of each frame of the TDD SCC, and communicating with a node based at least in part on the identified scheduling timing and uplink HARQ timing of the FDD SCC. 
     A further method of wireless communication is also described. The method may include configuring a set of component carriers in carrier aggregation to serve a user equipment (UE), where the set of component carriers may include a time-division duplexing (TDD) secondary component carrier (SCC) and a frequency-division duplexing (FDD) SCC, determining a scheduling timing and an uplink hybrid automatic repeat request (HARQ) timing of the FDD SCC based at least in part on a time duration of each frame of the TDD SCC, and communicating with the UE based at least in part on the determined scheduling timing and uplink HARQ timing of the FDD SCC. 
     A further apparatus for wireless communication is also described. The apparatus may include a processor, memory in electronic communication with the processor, and instructions stored on the memory. The instructions may be executable by the processor to configure a set of component carriers in carrier aggregation to serve a user equipment (UE), where the set of component carriers may include a time-division duplexing (TDD) secondary component carrier (SCC) and a frequency-division duplexing (FDD) SCC, determine a scheduling timing and an uplink hybrid automatic repeat request (HARQ) timing of the FDD SCC based at least in part on a time duration of each frame of the TDD SCC, and communicate with the UE based at least in part on the determined scheduling timing and uplink HARQ timing of the FDD SCC. 
     A further apparatus for wireless communication is also described. The apparatus may include means for configuring a set of component carriers in carrier aggregation to serve a user equipment (UE), where the set of component carriers may include a time-division duplexing (TDD) secondary component carrier (SCC) and a frequency-division duplexing (FDD) SCC, means for determining a scheduling timing and an uplink hybrid automatic repeat request (HARQ) timing of the FDD SCC based at least in part on a time duration of each frame of the TDD SCC, and means for communicating with the UE based at least in part on the determined scheduling timing and uplink HARQ timing of the FDD SCC. 
     A further non-transitory computer-readable medium is described. The non-transitory computer-readable medium may include code comprising instruction for configuring a set of component carriers in carrier aggregation to serve a user equipment (UE), where the set of component carriers may include a time-division duplexing (TDD) secondary component carrier (SCC) and a frequency-division duplexing (FDD) SCC, determining a scheduling timing and an uplink hybrid automatic repeat request (HARQ) timing of the FDD SCC based at least in part on a time duration of each frame of the TDD SCC, and communicating with the UE based at least in part on the determined scheduling timing and uplink HARQ timing of the FDD SCC 
     In some examples of the methods, apparatuses, or computer-readable media described above, the time duration of each frame of the TDD SCC may be ten (10) milliseconds. In some examples, the scheduling timing of the FDD SCC is four (4) milliseconds. 
     In some examples of the methods, apparatuses, or computer-readable media described above, the scheduling timing of the FDD SCC may be a time difference between an uplink grant or physical hybrid indicator channel (PHICH) transmission and a physical uplink shared channel (PUSCH) transmission, and the uplink HARQ timing of the FDD SCC may be a time difference between the PUSCH transmission and a subsequent PHICH transmission. In some examples, the set of component carriers further comprises an frequency-division duplexing (FDD) primary cell (PCC). FDD SCC may be cross-carrier scheduled from the TDD SCC. Additionally or alternatively, the TDD SCC may include an downlink-uplink (DL/UL) configuration selected from a plurality of DL/UL configurations. 
     Some examples of the method, apparatus, or computer-readable medium described above further include features of, means for, or instructions for indicating the configuration of the set of component carriers to the UE via radio resource control (RRC) signaling. 
     The foregoing has outlined rather broadly the features and technical advantages of examples according to the disclosure in order that the detailed description that follows may be better understood. Further scope of the applicability of the described methods and apparatuses will become apparent from the following detailed description, claims, and drawings. The detailed description and specific examples are given by way of illustration only, since various changes and modifications within the spirit and scope of the description will become apparent to those skilled in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A further understanding of the nature and advantages of the present invention may be realized by reference to the following drawings. In the appended figures, similar components or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label. 
         FIG. 1  shows a diagram illustrating an example of a wireless communications system; 
         FIG. 2  shows a frame structure for a TDD carrier; 
         FIG. 3  shows a system employing carrier aggregation; 
         FIGS. 4A and 4B  shows a device(s) configured for multi-carrier scheduling; 
         FIG. 5  shows a block diagram of a MIMO communication system; 
         FIG. 6  shows a block diagram of a user equipment configured for multi-carrier scheduling; 
         FIG. 7  shows a system configured for multi-carrier scheduling; 
         FIGS. 8A-8E  show diagrams of multi-carrier scheduling; 
         FIG. 9  shows a flow diagram of a method(s) of multi-carrier scheduling; 
         FIG. 10  shows a flow diagram of a method(s) of multi-carrier scheduling; 
         FIG. 11  shows a flow diagram of a method(s) of multi-carrier scheduling; 
         FIG. 12  shows a flow diagram of a method(s) of multi-carrier scheduling; and 
         FIG. 13  shows a flow diagram of a method(s) of multi-carrier scheduling. 
     
    
    
     DETAILED DESCRIPTION 
     Described examples are directed to methods, systems, and devices that minimize HARQ delay for multi-carrier scheduling in a wireless communications network utilizing one or more TDD component carriers and one or more FDD component carriers. The methods, systems, and devices include tools and techniques for adjusting HARQ periodicity scheduling TDD UL and DL transmission, grants, and transfers to minimize HARQ process round trip time (RTT). 
     Techniques described herein may be used for various wireless communications systems such as cellular wireless systems, Peer-to-Peer wireless communications, wireless local access networks (WLANs), ad hoc networks, satellite communications systems, and other systems. The terms “system” and “network” are often used interchangeably. These wireless communications systems may employ a variety of radio communication technologies such as Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal FDMA (OFDMA), Single-Carrier FDMA (SC-FDMA), or other radio technologies. Generally, wireless communications are conducted according to a standardized implementation of one or more radio communication technologies called a Radio Access Technology (RAT). A wireless communications system or network that implements a Radio Access Technology may be called a Radio Access Network (RAN). 
     Examples of Radio Access Technologies employing CDMA techniques include CDMA2000, Universal Terrestrial Radio Access (UTRA), etc. CDMA2000 covers IS-2000, IS-95, and IS-856 standards. IS-2000 Releases 0 and A are commonly referred to as CDMA2000 1x, 1x, etc. IS-856 (TIA-856) is commonly referred to as CDMA2000 1xEV-DO, High Rate Packet Data (HRPD), etc. UTRA includes Wideband CDMA (WCDMA) and other variants of CDMA. Examples of TDMA systems include various implementations of Global System for Mobile Communications (GSM). Examples of Radio Access Technologies employing OFDM or OFDMA include Ultra Mobile Broadband (UMB), Evolved UTRA (E-UTRA), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM, etc. UTRA and E-UTRA are part of Universal Mobile Telecommunication System (UMTS). 3GPP Long Term Evolution (LTE) and LTE-Advanced (LTE-A) are new releases of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A, and GSM are described in documents from an organization named “3rd Generation Partnership Project” (3GPP). CDMA2000 and UMB are described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2). The techniques described herein may be used for the systems and radio technologies mentioned above as well as other systems and radio technologies. 
     Thus, the following description provides examples, and is not limiting of the scope, applicability, or configuration set forth in the claims. Changes may be made in the function and arrangement of elements discussed without departing from the spirit and scope of the disclosure. Various embodiments may omit, substitute, or add various procedures or components as appropriate. For instance, the methods described may be performed in an order different from that described, and various steps may be added, omitted, or combined. Also, features described with respect to certain embodiments may be combined in other embodiments. 
     Referring first to  FIG. 1 , a diagram illustrates an example of a wireless communications system  100 . The system  100  includes base stations (or cells)  105 , communication devices  115 , and a core network  130 . The base stations  105  may communicate with the communication devices  115  under the control of a base station controller (not shown), which may be part of the core network  130  or the base stations  105  in various embodiments. Base stations  105  may communicate control information and user data with the core network  130  through backhaul links  132 . Backhaul links  132  may be wired backhaul links (e.g., copper, fiber, etc.) or wireless backhaul links (e.g., microwave, etc.). In embodiments, the base stations  105  may communicate, either directly or indirectly, with each other over backhaul links  134 , which may be wired or wireless communication links. The system  100  may support operation on multiple carriers (waveform signals of different frequencies). Multi-carrier transmitters can transmit modulated signals simultaneously on the multiple carriers. For example, each communication link  125  may be a multi-carrier signal modulated according to the various radio technologies described above. Each modulated signal may be sent on a different carrier and may carry control information (e.g., reference signals, control channels, etc.), overhead information, data, etc. 
     The base stations  105  may wirelessly communicate with the devices  115  via one or more base station antennas. Each of the base station  105  sites may provide communication coverage for a respective coverage area  110 . In some embodiments, base stations  105  may be referred to as a base transceiver station, a radio base station, an access point, a radio transceiver, a basic service set (BSS), an extended service set (ESS), a NodeB, eNodeB (eNB), Home NodeB, a Home eNodeB, or some other suitable terminology. The coverage area  110  for a base station may be divided into sectors making up only a portion of the coverage area (not shown). The system  100  may include base stations  105  of different types (e.g., macro, micro, or pico base stations). There may be overlapping coverage areas for different technologies. 
     The communication devices  115  are dispersed throughout the wireless network  100 , and each device may be stationary or mobile. A communication device  115  may also be referred to by those skilled in the art as a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a user equipment, a mobile client, a client, or some other suitable terminology. A communication device  115  may be a cellular phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a tablet computer, a laptop computer, a cordless phone, a wireless local loop (WLL) station, or the like. A communication device may be able to communicate with macro base stations, pico base stations, femto base stations, relay base stations, and the like. 
     The transmission links  125  shown in network  100  may include uplink (UL) transmissions from a mobile device  115  to a base station  105 , or downlink (DL) transmissions, from a base station  105  to a mobile device  115 . The downlink transmissions may also be called forward link transmissions while the uplink transmissions may also be called reverse link transmissions. 
     In embodiments, the system  100  is an LTE/LTE-A network. In LTE/LTE-A networks, the terms evolved Node B (eNB) and user equipment (UE) may be generally used to describe the base stations  105  and communication devices  115 , respectively. The system  100  may be a Heterogeneous LTE/LTE-A network in which different types of eNBs provide coverage for various geographical regions. For example, each eNB  105  may provide communication coverage for a macro cell, a pico cell, a femto cell, or other types of cell. A macro cell generally covers a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscriptions with the network provider. A pico cell would generally cover a relatively smaller geographic area and may allow unrestricted access by UEs with service subscriptions with the network provider. A femto cell would also generally cover a relatively small geographic area (e.g., a home) and, in addition to unrestricted access, may also provide restricted access by UEs having an association with the femto cell (e.g., UEs in a closed subscriber group (CSG), UEs for users in the home, and the like). An eNB for a macro cell may be referred to as a macro eNB. An eNB for a pico cell may be referred to as a pico eNB. And, an eNB for a femto cell may be referred to as a femto eNB or a home eNB. An eNB may support one or multiple (e.g., two, three, four, and the like) cells. 
     The communications system  100  according to an LTE/LTE-A network architecture may be referred to as an Evolved Packet System (EPS)  100 . The EPS  100  may include one or more UEs  115 , an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN), an Evolved Packet Core (EPC)  130  (e.g., core network  130 ), a Home Subscriber Server (HSS), and an Operator&#39;s IP Services. The EPS may interconnect with other access networks using other Radio Access Technologies. For example, EPS  100  may interconnect with a UTRAN-based network or a CDMA-based network via one or more Serving GPRS Support Nodes (SGSNs). To support mobility of UEs  115  or load balancing, EPS  100  may support handover of UEs  115  between a source eNB  105  and a target eNB  105 . EPS  100  may support intra-RAT handover between eNBs  105  or base stations of the same RAT (e.g., other E-UTRAN networks), and inter-RAT handovers between eNBs or base stations of different RATs (e.g., E-UTRAN to CDMA, etc.). The EPS  100  may provide packet-switched services, however, as those skilled in the art will readily appreciate, the various concepts presented throughout this disclosure may be extended to networks providing circuit-switched services. 
     The E-UTRAN may include the eNBs  105  and may provide user plane and control plane protocol terminations toward the UEs  115 . The eNBs  105  may be connected to other eNBs  105  via backhaul link  134  (e.g., an X2 interface, and the like). The eNBs  105  may provide an access point to the EPC  130  for the UEs  115 . The eNBs  105  may be connected by backhaul link  132  (e.g., an  51  interface, and the like) to the EPC  130 . Logical nodes within EPC  130  may include one or more Mobility Management Entities (MMES), one or more Serving Gateways, and one or more Packet Data Network (PDN) Gateways (not shown). Generally, the MME may provide bearer and connection management. All user IP packets may be transferred through the Serving Gateway, which itself may be connected to the PDN Gateway. The PDN Gateway may provide UE IP address allocation as well as other functions. The PDN Gateway may be connected to IP networks and the operator&#39;s IP Services. These logical nodes may be implemented in separate physical nodes or one or more may be combined in a single physical node. The IP Networks/Operator&#39;s IP Services may include the Internet, an Intranet, an IP Multimedia Subsystem (IMS), or a Packet-Switched (PS) Streaming Service (PSS). 
     The UEs  115  may be configured to collaboratively communicate with multiple eNBs  105  through, for example, Multiple Input Multiple Output (MIMO), Coordinated Multi-Point (CoMP), or other schemes. MIMO techniques use multiple antennas on the base stations or multiple antennas on the UE to take advantage of multipath environments to transmit multiple data streams. CoMP includes techniques for dynamic coordination of transmission and reception by a number of eNBs to improve overall transmission quality for UEs as well as increasing network and spectrum utilization. Generally, CoMP techniques utilize backhaul links  132  or  134  for communication between base stations  105  to coordinate control plane and user plane communications for the UEs  115 . 
     The communication networks that may accommodate some of the various disclosed embodiments may be packet-based networks that operate according to a layered protocol stack. In the user plane, communications at the bearer or Packet Data Convergence Protocol (PDCP) layer may be IP-based. A Radio Link Control (RLC) layer may perform packet segmentation and reassembly to communicate over logical channels. A Medium Access Control (MAC) layer may perform priority handling and multiplexing of logical channels into transport channels. The MAC layer may also use hybrid automatic repeat request (HARQ) techniques to provide retransmission at the MAC layer to ensure reliable data transmission. In the control plane, the Radio Resource Control (RRC) protocol layer may provide establishment, configuration, and maintenance of an RRC connection between the UE and the network used for the user plane data. At the Physical layer, the transport channels may be mapped to Physical channels. 
     The downlink physical channels may include at least one of a physical downlink control channel (PDCCH) or enhanced PDCCH (EPDCCH), a physical HARQ indicator channel (PHICH), and a physical downlink shared channel (PDSCH). The uplink physical channels may include at least one of a physical uplink control channel (PUCCH) and a physical uplink shared channel (PUSCH). The PDCCH may carry downlink control information (DCI), which may indicate data transmissions for UEs on the PDSCH as well as provide UL resource grants to UEs for the PUSCH. The UE may transmit control information in the PUCCH on the assigned resource blocks in the control section. The UE may transmit only data or both data and control information in the PUSCH on the assigned resource blocks in the data section. 
     LTE/LTE-A utilizes orthogonal frequency division multiple-access (OFDMA) on the downlink and single-carrier frequency division multiple-access (SC-FDMA) on the uplink. An OFDMA or SC-FDMA carrier may be partitioned into multiple (K) orthogonal subcarriers, which are also commonly referred to as tones, bins, or the like. Each subcarrier may be modulated with data. The spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may be dependent on the system bandwidth. For example, K may be equal to 72, 180, 300, 600, 900, or 1200 with a subcarrier spacing of 15 kilohertz (KHz) for a corresponding system bandwidth (with guardband) of 1.4, 3, 5, 10, 15, or 20 megahertz (MHz), respectively. The system bandwidth may also be partitioned into sub-bands. For example, a sub-band may cover 1.08 MHz, and there may be 1, 2, 4, 8 or 16 sub-bands. 
     The carriers may transmit bidirectional communications using FDD (e.g., using paired spectrum resources) or TDD operation (e.g., using unpaired spectrum resources). Frame structures for FDD (e.g., frame structure type 1) and TDD (e.g., frame structure type 2) may be defined. Time intervals may be expressed in multiples of a basic time unit T S =1/30720000. Each frame structure may have a radio frame length T f =307200·T S =10 ms and may include two half-frames or slots of length 153600·T S =5 ms each. Each half-frame may include five subframes of length 30720·T S =1 ms. 
     LTE/LTE-A networks support multi-process Type II HARQ with a configurable number of independent HARQ processes. Each HARQ process waits to receive an acknowledgement (ACK) before transmitting a new data or transport block. LTE/LTE-A uses asynchronous HARQ transmission on the downlink and synchronous HARQ transmission on the uplink. In both asynchronous and synchronous HARQ, ACK/NAK information may be provided a certain number of subframes after a DL or UL transmission. Generally, for LTE/LTE-A FDD carriers, ACK/NAK information for a HARQ process is transmitted 4 subframes after a data transmission. In asynchronous HARQ, a DL or UL scheduled for subsequent transmissions is not predetermined and the eNB provides instructions to the UE regarding which HARQ process are transmitted in each subframe. For synchronous HARQ in FDD, UEs perform a second transmission of a particular HARQ process a predetermined number of subframes after receiving a NAK. Generally, for LTE/LTE-A FDD carriers subsequent UL transmissions of the same HARQ process occur 4 subframes after receiving a NAK. For synchronous HARQ in TDD, ACK/NAK information may be received in a subframe i associated with UL transmissions in a subframe i-k, where k may be defined according to TDD DL/UL configuration. Subsequent transmissions of particular HARQ processes may be performed in a subframe n for a NAK received in a subframe n-k, where k may be defined according to TDD UL/DL configuration. 
       FIG. 2  illustrates a frame structure  200  for a TDD carrier. For TDD frame structures, each subframe  210  may carry UL or DL traffic, and special subframes (“S”)  215  may be used to switch between DL to UL transmission. Allocation of UL and DL subframes within radio frames may be symmetric or asymmetric and may be reconfigured semi-statically or dynamically. Special subframes  215  may carry some DL and UL traffic and may include a Guard Period (GP) between DL and UL traffic. Switching from UL to DL traffic may be achieved by setting timing advance at the UEs without the use of Special subframes or a guard period between UL and DL subframes. TDD configurations with switch-point periodicity equal to the frame period (e.g., 10 ms) or half of the frame period (e.g., 5 ms) may be supported. For example, TDD frames may include one or more Special frames, and the period between Special frames may determine the TDD DL-to-UL switch-point periodicity for the frame. 
     For LTE/LTE-A, seven different TDD DL/UL configurations are defined that provide between 40% and 90% DL subframes as illustrated in Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 TDD Configurations 
               
            
           
           
               
               
               
            
               
                 TDD 
                 Period 
                 Subframe 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Configuration 
                 (ms) 
                 0 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 8 
                 9 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 0 
                 5 
                 D 
                 S 
                 U 
                 U 
                 U 
                 D 
                 S 
                 U 
                 U 
                 U 
               
               
                 1 
                 5 
                 D 
                 S 
                 U 
                 U 
                 D 
                 D 
                 S 
                 U 
                 U 
                 D 
               
               
                 2 
                 5 
                 D 
                 S 
                 U 
                 D 
                 D 
                 D 
                 S 
                 U 
                 D 
                 D 
               
               
                 3 
                 10 
                 D 
                 S 
                 U 
                 U 
                 U 
                 D 
                 D 
                 D 
                 D 
                 D 
               
               
                 4 
                 10 
                 D 
                 S 
                 U 
                 U 
                 D 
                 D 
                 D 
                 D 
                 D 
                 D 
               
               
                 5 
                 10 
                 D 
                 S 
                 U 
                 D 
                 D 
                 D 
                 D 
                 D 
                 D 
                 D 
               
               
                 6 
                 5 
                 D 
                 S 
                 U 
                 U 
                 U 
                 D 
                 S 
                 U 
                 U 
                 D 
               
               
                   
               
            
           
         
       
     
     Because some TDD DL/UL configurations have fewer UL subframes than DL subframes, several techniques may be used to transmit ACK/NAK information for an association set within a PUCCH transmission in the uplink subframe. For example, bundling may be used to combine ACK/NAK information to reduce the amount of ACK/NAK information to be sent. ACK/NAK bundling may combine the ACK/NAK information into a single bit that is set to an acknowledgement (ACK) value only if the ACK/NAK information for each subframe of the association set is an ACK. For example, ACK/NAK information may be a binary ‘1’ to represent ACK and a binary ‘0’ to represent a negative acknowledgement (NAK) for a particular subframe. ACK/NAK information may be bundled using a logical AND operation on the ACK/NAK bits of the association set. Bundling reduces the amount of information to be sent over the PUCCH and therefore increases the efficiency of HARQ ACK/NAK feedback. Multiplexing may be used to transmit multiple bits of ACK/NAK information in one uplink subframe. For example, up to four bits of ACK/NAK may be transmitted using PUCCH format 1b with channel selection. 
     Wireless network  100  may support operation on multiple carriers, which may be referred to as carrier aggregation (CA) or multi-carrier operation. A carrier may also be referred to as a component carrier (CC), a layer, a channel, etc. The terms “carrier,” “layer,” “CC,” and “channel” may be used interchangeably herein. A carrier used for the downlink may be referred to as a downlink CC, and a carrier used for the uplink may be referred to as an uplink CC. A combination of a downlink CC and an uplink CC may be referred to as a cell. It is also possible to have a cell consisting of a downlink CC only. A UE  115  may be configured with multiple downlink CCs and one or more uplink CCs for carrier aggregation. Multi-layer eNBs  105  may be configured to support communications with UEs over multiple CCs on the downlink and uplink. Thus, a UE  115  may receive data and control information on one or more downlink CCs from one multi-layer eNB  105  or from multiple eNBs  105  (e.g., single or multi-layer eNBs). The UE  115  may transmit data and control information on one or more uplink CCs to one or more eNBs  105 . Carrier aggregation may be used with both FDD and TDD component carriers. For DL carrier aggregation, multiple bits of ACK/NAK are fed back when multiple DL transmissions occur in one subframe. Up to 22 bits of ACK/NAK may be transmitted using PUCCH format 3 for DL carrier aggregation. 
       FIG. 3  shows a system  300  employing carrier aggregation in accordance with various embodiments. The system  300  may illustrate aspects of the system  100 . The system  300  can include one or more eNBs  105  using one or more component carriers  325  (CC 1 -CC N ) to communicate with UEs  115 . The eNBs  105  can transmit information to the UEs  115  over forward (downlink) channels on component carriers  325 . In addition, the UEs  115  can transmit information to the eNB  105 - a  over reverse (uplink) channels on component carriers  325 . In describing the various entities of  FIG. 3 , as well as other figures associated with some of the disclosed embodiments, for the purposes of explanation, the nomenclature associated with a 3GPP LTE or LTE-A wireless network is used. However, it is to be appreciated that the system  300  can operate in other networks such as, but not limited to, an OFDMA wireless network, a CDMA network, a 3GPP2 CDMA2000 network and the like. One or more of the component carriers CC 1 -CC N    325  can be in the same frequency operating band (intra-band) or in different operating bands (inter-band) and intra-band CCs can be contiguous or non-contiguous within the operating band. 
     In the system  300 , UEs  115  may be configured with multiple CCs associated with one or more eNBs  105 . One CC is designated as the primary CC (PCC) for a UE  115 . PCCs may be semi-statically configured by higher layers (e.g., RRC, etc.) on a per-UE basis. Certain uplink control information (UCI) (e.g., ACK/NAK, channel quality information (CQI), scheduling requests (SR), etc.), when transmitted on PUCCH, are carried by the PCC. Thus, UL SCC&#39;s may not be used for PUCCH for a given UE. The UEs  115  may be configured with asymmetric DL to UL CC assignments. In LTE/LTE-A, up to 5:1 DL to UL mapping is supported. Thus, one UL CC (e.g., PCC UL) may carry UCI (e.g., ACK/NAK) on PUCCH for up to 5 DL CCs. 
     In the example illustrated in  FIG. 3 , UE  115 - a  is configured with PCC  325 - a  and SCC  325 - b  associated with eNB  105 - a  and SCC  325 - c  associated with eNB  105 - b . The system  300  may be configured to support carrier aggregation using various combinations of FDD and TDD CCs  325 . For example, some configurations of system  300  may support CA for FDD CCs (e.g., an FDD PCC and one or more FDD SCCs). Other configurations may support CA using TDD CCs (e.g., a TDD PCC and one or more TDD SCCs). In some examples, the TDD SCCs for CA have the same DL/UL configuration while other examples support TDD CA with CCs of different DL/UL configurations. 
     In some embodiments, the system  300  may support TDD-FDD joint operation, including CA and other types of joint operation (e.g., dual-connectivity when eNBs  105  of the multiple CCs configured for a UE  115  have reduced backhaul capabilities, etc.). TDD-FDD joint operation may allow UEs  115  supporting FDD and TDD CA operation to access both FDD and TDD CCs using CA or in single CC mode. In addition, legacy UEs with various capabilities (e.g., single mode UEs, FDD CA capable UEs, TDD CA capable UEs, etc.), may connect to FDD or TDD carriers of system  300 . 
     In CA scenarios employing a TDD CC and an FDD CC, HARQ UL processes may follow a TDD timeline. In cases of cross-carrier scheduling utilizing an FDD PCC, an UL HARQ process on a TDD SCC may follow the timeline of the FDD PCC. For example, on the DL, a data transmission and corresponding grant for the TDD CC may be sent in the same subframe. Then an ACK/NAK for the TDD DL data transmission may be sent four milliseconds (4 ms) later via the UL FDD PCC. On the UL, a TDD UL transmission may be sent 4 ms after the grant or a NAK on the FDD PCC. Then, an ACK/NAK for the TDD UL subframe may be sent 4 ms later. Thus, the scheduling may generally include 4 ms gaps between a grant, UL transmissions, and ACK/NAKs. 
     In some instances, feedback delay may be minimized for FDD PCC and TDD SCC cross-carrier scheduling by employing scheduling with these 4 ms gaps. In other cases, however, an FDD HARQ timeline aligns with a TDD SCC subframe timeline in a manner such that overall HARQ RTT is substantially greater than the FDD HARQ timeline. If, for instance, an UL HARQ process with an eight millisecond (8 ms) periodicity is used with the TDD SCC following the FDD PCC HARQ timeline, and the TDD SCC has ten millisecond (10 ms) radio frame configuration, a HARQ UL retransmission for a specific HARQ process may occur several frames after an initial transmission. By way of example, in a cross-carrier scenario involving an FDD PCC with an 8 ms HARQ process, a TDD SCC utilizing a DL-UL configuration 5 would realize a forty millisecond (40 ms) HARQ retransmission RTT, if scheduled according to the typical FDD HARQ 4 ms spacing described above. 
     In order to minimize the HARQ RTT, a TDD SCC HARQ process periodicity with an FDD PCC may be adjusted to correspond to the subframe periodicity of a TDD SCC. UL transmissions and ACK/NAK transfers may be scheduled accordingly. 
     A scheduling timing between a first uplink grant and a corresponding uplink transmission for the TDD SCC may be determined based on a scheduling timing of the FDD PCC. A number of UL HARQ processes may be determined based on a DL/UL configuration of the TDD SCC. Then UL transmissions and ACK/NAK transfers may be made according to the determined scheduling timing and the determined number of uplink HARQ processes. In some embodiments, an HARQ process timeline of the TDD SCC is adjusted such that the aggregate of the number of subframes between data transmissions and corresponding ACK/NAK indicators, and the number of subframes between ACK/NAK indicators and HARQ process retransmissions corresponds to the number of subframes in a frame period of the TDD SCC. In some embodiments, HARQ process timelines are adjusted for HARQ processes of the TDD SCC that are cross-carrier scheduled on the FDD PCC. In other embodiments, HARQ process timelines are adjusted for all HARQ processes including HARQ processes scheduled on the FDD PCC. 
     In one embodiment, scheduling timing for the joint FDD PCC and TDD SCC CA includes: sending a TDD UL subframe 4 ms after a PDCCH grant; receiving an ACK/NAK (e.g., PHICH), which may be sent 4 ms after the TDD UL subframe; and sending a subsequent TDD UL subframe 6 ms after a NAK. Such HARQ rules may be applied to various TDD DL-UL configurations. Additionally, the number of UL HARQ processes for a TDD SCC with an FDD PCC may be based on the TDD SCC DL/UL configuration. 
     Other scheduling timing may also lead to reductions in HARQ delay. For example, a TDD UL subframe is sent 4 ms after a PDCCH grant, then a PHICH ACK/NAK is sent 6 ms after the TDD UL subframe, and a subsequent TDD UL subframe is sent 4 ms after a PHICH NAK. 
     Additionally or alternatively, an ACK/NAK may be overwritten by a subsequent grant sent on PDCCH. In some cases, a grant on PDCCH sent two milliseconds (2 ms) (e.g., 2 subframes) after an ACK/NAK may overwrite the ACK/NAK. For example, if the PHICH NAK is received in a current subframe, n, and a corresponding HARQ retransmission would be scheduled for 6 ms later in subframe n+6 (as previously described), the HARQ retransmission may be superseded or overwritten when it would coincide with an UL transmission scheduled by a PDCCH received in subframe n+2 (also scheduled to occur in subframe n+6 due to the 4 ms spacing). In other embodiments, a grant sent in the same subframe as the ACK/NAK may overwrite the ACK/NAK. 
     Turning next to  FIG. 4A , which shows a block diagram  400  of a device  405  for multi-carrier scheduling in accordance with various embodiments. Device  405  may illustrate, for example, aspects of UEs  115  illustrated in  FIG. 1  or  FIG. 3 . Additionally or alternatively, device  405  may illustrate aspects of eNBs  105  described with reference to  FIG. 1  or  FIG. 3 . Device  405  may include a receiver module  410 , a multi-carrier scheduling module  415 , and a transmitter module  420 . Each of these components may be in communication with each other. In some embodiments, device  405  is a processor. 
     Device  405  may be configured for operation in a CA scheme including a TDD CC and an FDD CC. In some cases, the multi-carrier scheduling module  415  is configured to determine, based on an FDD PCC, a scheduling time between a control channel transfer (e.g., a grant on PDCCH or EPDCCH of the FDD PCC) and a corresponding UL transmission on a TDD SCC. The multi-carrier scheduling module  415  also may be configured to determine a number of UL HARQ processes of the TDD SCC based on a DL/UL configuration of the TDD SCC. 
     The receiver module  410  may receive a resource grant on PDCCH, and the transmitter module  420  may transmit a TDD UL subframe according to the grant. The receiver module  410  may also receive an ACK/NAK on PHICH, and the transmitter module  420  may transmit a subsequent TDD UL subframe in response to a received NAK. In some cases, the receiver module  410  may receive a grant on PDCCH that overwrites an earlier received ACK/NAK. 
     Next,  FIG. 4B  shows a block diagram  400 - a  of a device  405 - a  for multi-carrier scheduling in accordance with various embodiments. Device  405 - a  may illustrate, for example, aspects of UEs  115  illustrated in  FIG. 1  or  FIG. 3 . In some cases, device  405 - a  illustrates aspects of eNBs  105  described with reference to  FIG. 1  or  FIG. 3 . Device  405  may include a receiver module  410 - a , a multi-carrier scheduling module  415 - a , and a transmitter module  420 - a . Each of these components may be in communication with each other; and each may perform substantially the same functions as the corresponding modules illustrated in  FIG. 4A . According to some embodiments, device  405 - a  is a processor. 
     The multi-channel scheduling module  415 - a  may be configured with a timing determination module  450 , a HARQ determination module  460 , a cross scheduling module  470 , a time gap determination module  480 , and an overwrite module  490 . The modules, alone or in combination, may be means for performing various functions described herein. For example, the timing determination module may be configured to determine a scheduling timing between a first control channel transfer and a corresponding uplink transmission for a TDD SCC based on a scheduling timing for an FDD PCC. In some cases, the timing determination module  450  determines (e.g., establishes or identifies) a 4 ms gap between a grant on PDCCH and a corresponding UL transmission. 
     The HARQ determination module  460  may be configured to determine a number of uplink HARQ processes for a TDD CC based on a DL/UL configuration of the TDD CC. For example, the HARQ determination module  460  may determine the number of uplink HARQ processes for the TDD SCC is equal to a number of uplink subframes in a frame of the TDD SCC. In some embodiments, a determined number of UL subframes of a common UL HARQ process includes a ten millisecond (10 ms) gap. 
     The receiver module  410 - a  and the transmitter module  420 - a  may receive and transmit, respectively, control and data signals according to the determined scheduling timing and the determined uplink HARQ processes. 
     In some embodiments, the cross scheduling module  470  may be configured to cross schedule component carriers, such that the DL/UL transmission on one CC are based on grants carried by another CC. For example, UL transmissions of a TDD SCC may be based on grants from another CC (e.g., FDD PCC, etc.). 
     The timing gap determination module  480  may be configured to determine a gap between HARQ indicator transfers and UL transmissions. For example, the timing gap determination module  480  may determine a timing gap between a UL transmission and a corresponding ACK/NAK. In some cases, the determined timing gap is 6 ms. In other embodiments, the determined timing gap is 4 ms. Additionally or alternatively, the timing gap determination module  480  may be configured to determine a timing gap between a NAK and a corresponding retransmission. For instance, such a gap me be 6 ms, or it may be 4 ms. 
     In some embodiments, the overwrite module  490  is configured to overwrite an ACK/NAK with a subsequent or concurrent grant on, e.g., PDCCH. The overwrite module  490  may be configured to overwrite an HARQ retransmission triggered by an ACK/NAK sent 2 ms or two subframes earlier, when it would coincide with an UL grant scheduled by PDCCH. In other cases, the overwrite module  490  is configure to overwrite an ACK/NAK sent in the same subframe. 
     The components of the devices  405  and  405 - a  may, individually or collectively, be implemented with one or more application-specific integrated circuits (ASICs) adapted to perform some or all of the applicable functions in hardware. Alternatively, the functions may be performed by one or more other processing units (or cores), on one or more integrated circuits. In other embodiments, other types of integrated circuits may be used (e.g., Structured/Platform ASICs, Field Programmable Gate Arrays (FPGAs), and other Semi-Custom ICs), which may be programmed in any manner known in the art. The functions of each unit may also be implemented, in whole or in part, with instructions embodied in a memory, formatted to be executed by one or more general or application-specific processors. 
       FIG. 5  is a block diagram of a MIMO communication system  500  including a base station or eNB  105 - c  and a mobile device or UE  115 - b . The base station  105 - c  may be an example of the base stations  105  of  FIG. 1  or  FIG. 2 , while the mobile device  115 - b  may be an example of the communication devices  115  of  FIG. 1  or  FIG. 3 . This system  500  may illustrate aspects of the system  100  of  FIG. 1  or system  300  or  FIG. 3 . The base station  105 - c  may be equipped with M antennas  534 - a  through  534 - x , and the mobile device  115 - b  may be equipped with N antennas  552 - a  through  552 - y . In the system  500 , the base station  105 - c  may employ multiple antenna techniques for transmission over communication links. For example, the base station  105 - c  may employ transmit diversity to improve robustness of transmissions received by the mobile device  115 - b . The mobile device  115 - b  may employ receive diversity using multiple receive antennas to combine signals received at multiple antennas. 
     At the base station  105 - c , a transmit (Tx) processor  520  may receive data from a data source. The transmit processor  520  may process the data. The transmit processor  520  may also generate reference symbols, and a cell-specific reference signal. A transmit (Tx) MIMO processor  530  may perform spatial processing (e.g., precoding) on data symbols, control symbols, or reference symbols, if applicable, and may provide output symbol streams to the transmit modulators  532 - a  through  532 - m . Each modulator  532  may process a respective output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator  532  may further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink (DL) signal. In one example, DL signals from modulators  532 - a  through  532 - m  may be transmitted via the antennas  534 - a  through  534 - x , respectively. 
     At the mobile device  115 - b , the mobile device antennas  552 - a  through  552 - n  may receive the DL signals from the base station  105 - c  and may provide the received signals to the demodulators  554 - a  through  554 - n , respectively. Each demodulator  554  may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. Each demodulator  554  may further process the input samples (e.g., for OFDM, etc.) to obtain received symbols. A MIMO detector  556  may obtain received symbols from all the demodulators  554 - a  through  554 - n , perform MIMO detection on the received symbols if applicable, and provide detected symbols. A receive (Rx) processor  558  may process (e.g., demodulate, deinterleave, and decode) the detected symbols, providing decoded data for the mobile device  115 - b  to a data output, and provide decoded control information to a processor  580 , or memory  582 . 
     The base station  105 - c  or the mobile device  115 - b  may employ multi-carrier scheduling. By way of example, either processor  540  or processor  580 , or both, may determine the number of HARQ processes and HARQ process timelines based on an FDD-TDD CA configuration. For example, HARQ process timelines for HARQ processes using cross carrier scheduling may be adjusted to correspond to the number of subframes in a frame of a TDD SCC. In some examples, the number of UL HARQ for a TDD SCC processes may be determined based on a DL/UL configuration of the TDD SCC. Then UL transmissions and ACK/NAK transfers may be made according to the determined scheduling timing and the determined number of uplink HARQ processes. 
     On the uplink (UL), at the mobile device  115 - b , a transmit (Tx) processor  564  may receive and process data from a data source or a processor  540  coupled with memory  542 . The transmit processor  564  may also generate reference symbols for a reference signal. The symbols from the transmit processor  564  may be precoded by a transmit (Tx) MIMO processor  566  if applicable, further processed by the demodulators  554 - a  through  554 - n  (e.g., for SC-FDMA, etc.), and be transmitted to the base station  105 - c  in accordance with the transmission parameters received from the base station  105 - c . At the base station  105 - c , the UL signals from the mobile device  115 - b  may be received by the antennas  534 , processed by the demodulators  532 , detected by a MIMO detector  536  if applicable, and further processed by a receive (Rx) processor  538 . The receive processor  538  may provide decoded data to a data output and to the processor  540 . 
     The components of the base station  105 - c  may, individually or collectively, be implemented with one or more Application Specific Integrated Circuits (ASICs) adapted to perform some or all of the applicable functions in hardware. Each of the noted modules may be a means for performing one or more functions related to operation of the system  1000 . Similarly, the components of the mobile device  115 - b  may, individually or collectively, be implemented with one or more Application Specific Integrated Circuits (ASICs) adapted to perform some or all of the applicable functions in hardware. Each of the noted components may be a means for performing one or more functions related to operation of the system  1000 . 
     Turning now to  FIG. 6 , a block diagram  600  of a mobile device  115 - c  configured for HARQ in FDD-TDD CA in accordance with various embodiments. The mobile device  115 - c  may have any of various configurations, such as personal computers (e.g., laptop computers, netbook computers, tablet computers, etc.), cellular telephones, PDAs, smartphones, digital video recorders (DVRs), internet appliances, gaming consoles, e-readers, etc. The mobile device  115 - c  may have an internal power supply (not shown), such as a small battery, to facilitate mobile operation. In some embodiments, the mobile device  115 - c  may be the mobile devices  115  of  FIG. 1 ,  FIG. 3 , or  FIG. 5 . 
     The mobile device  115 - c  may generally include components for bi-directional voice and data communications including components for transmitting communications and components for receiving communications. The mobile device  115 - c  may include a transceiver module  610 , antenna(s)  605 , memory  680 , and a processor module  670 , which each may communicate, directly or indirectly, with each other (e.g., via one or more buses  675 ). The transceiver module  610  may be configured to communicate bi-directionally, via the antenna(s)  605  or one or more wired or wireless links, with one or more networks, as described above. For example, the transceiver module  610  may be configured to communicate bi-directionally with base stations  105  of  FIG. 1  or  FIG. 3 . The transceiver module  610  may include a modem configured to modulate the packets and provide the modulated packets to the antenna(s)  605  for transmission, and to demodulate packets received from the antenna(s)  605 . While the mobile device  115 - c  may include a single antenna  605 , the mobile device  115 - c  may have multiple antennas  605  capable of concurrently transmitting and receiving multiple wireless transmissions. The transceiver module  610  may be capable of concurrently communicating with multiple eNBs  105  via multiple component carriers. 
     The memory  680  may include random access memory (RAM) and read-only memory (ROM). The memory  680  may store computer-readable, computer-executable software/firmware code  685  containing instructions that are configured to, when executed, cause the processor module  670  to perform various functions described herein (e.g., call processing, database management, capture of handover delay, etc.). Alternatively, the software/firmware code  685  may not be directly executable by the processor module  670  but be configured to cause a computer (e.g., when compiled and executed) to perform functions described herein. 
     The processor module  670  may include an intelligent hardware device, e.g., a central processing unit (CPU), a microcontroller, an application-specific integrated circuit (ASIC), etc. The mobile device  115 - c  may include a speech encoder (not shown) configured to receive audio via a microphone, convert the audio into packets (e.g., 20 ms in length, 30 ms in length, etc.) representative of the received audio, provide the audio packets to the transceiver module  610 , and provide indications of whether a user is speaking. 
     According to the architecture of  FIG. 6 , the mobile device  115 - c  may further include a multi-carrier scheduling module  415 - b , which may be substantially the same as the multi-carrier scheduling devices  415  of  FIGS. 4A and 4B . In some cases, the multi-carrier scheduling device  415 - b  is configured to perform the functions of one or more of the modules  450 ,  460 ,  470 ,  480 , or  490  of  FIG. 4B . By way of example, the multi-carrier scheduling module  415 - b  may be a component of the mobile device  115 - c  in communication with some or all of the other components of the mobile device  115 - c  via a bus. Alternatively, functionality of these modules may be implemented as a component of the transceiver module  610 , as a computer program product, or as one or more controller elements of the processor module  670 . 
     The mobile device  115 - c  may be configured to perform HARQ for FDD-TDD CA as described above. The components for mobile device  115 - c  may be configured to implement aspects discussed above with respect to UEs  115  of  FIG. 1  or  FIG. 3  or devices  405  and  405 - a  of  FIGS. 4A and 4B . For example, the UE  115 - c  may be configured to determine, based on an FDD-TDD CA configuration, a scheduling time between a control channel transfer (e.g., a grant on PDCCH or EPDCCH) and a corresponding UL transmission for a TDD SCC. The multi-carrier scheduling module  415  also may be configured to determine a number of UL HARQ process of the TDD UL based on a DL/UL configuration of the TDD SCC. 
       FIG. 7  shows a block diagram of a communications system  700  that may be configured for multi-carrier scheduling in accordance with various embodiments. This system  700  may be an example of aspects of the systems  100  or  300  depicted in  FIG. 1  or  FIG. 3 . The system  700  includes a base station  105 - d  configured for communication with UEs  115  over wireless communication links  125 . Base station  105 - d  may be capable of receiving communication links  125  from other base stations (not shown). Base station  105 - d  may be, for example, an eNB  105  as illustrated in systems  100  or  300 . 
     In some cases, the base station  105 - d  may have one or more wired backhaul links. Base station  105 - d  may be, for example, a macro eNB  105  having a wired backhaul link (e g., Si interface, etc.) to the core network  130 - a . Base station  105 - d  may also communicate with other base stations  105 , such as base station  105 - m  and base station  105 - n  via inter-base station communication links (e.g., X2 interface, etc.). Each of the base stations  105  may communicate with UEs  115  using the same or different wireless communications technologies. In some cases, base station  105 - d  may communicate with other base stations such as  105 - m  and  105 - n  utilizing base station communication module  715 . In some embodiments, base station communication module  715  may provide an X2 interface within an LTE/LTE-A wireless communication network technology to provide communication between some of the base stations  105 . In some embodiments, base station  105 - d  may communicate with other base stations through core network  130 - a . In some cases, the base station  105 - d  may communicate with the core network  130 - a  through network communications module  765 . 
     The components for base station  105 - d  may be configured to implement aspects discussed above with respect to base stations  105  of  FIG. 1  and  FIG. 3  or devices  405  and  405 - a  of  FIGS. 4A and 4B , and may not be repeated here for the sake of brevity. For example, the base station  105 - d  may be configured to determine, based on an FDD-TDD CA configuration, a scheduling time between a control channel transfer (e.g., a grant on PDCCH or EPDCCH) and a corresponding UL transmission for a TDD SCC. The multi-carrier scheduling module  415  also may be configured to determine a number of UL HARQ processes of the TDD UL based on a DL/UL configuration of the TDD SCC. 
     The base station  105 - d  may include antennas  745 , transceiver modules  750 , memory  770 , and a processor module  760 , which each may be in communication, directly or indirectly, with each other (e.g., over bus system  780 ). The transceiver modules  750  may be configured to communicate bi-directionally, via the antennas  745 , with the UEs  115 , which may be multi-mode devices. The transceiver module  750  (or other components of the base station  105 - d ) may also be configured to communicate bi-directionally, via the antennas  745 , with one or more other base stations (not shown). The transceiver module  750  may include a modem configured to modulate the packets and provide the modulated packets to the antennas  745  for transmission, and to demodulate packets received from the antennas  745 . The base station  105 - d  may include multiple transceiver modules  750 , each with one or more associated antennas  745 . 
     The memory  770  may include random access memory (RAM) and read-only memory (ROM). The memory  770  may also store computer-readable, computer-executable software code  775  containing instructions that are configured to, when executed, cause the processor module  760  to perform various functions described herein (e.g., call processing, database management, message routing, etc.). Alternatively, the software  775  may not be directly executable by the processor module  760  but be configured to cause the computer, e.g., when compiled and executed, to perform functions described herein. 
     The processor module  760  may include an intelligent hardware device, e.g., a central processing unit (CPU), a microcontroller, an application-specific integrated circuit (ASIC), etc. The processor module  760  may include various special purpose processors such as encoders, queue processing modules, base band processors, radio head controllers, digital signal processors (DSPs), and the like. 
     According to the architecture of  FIG. 7 , the base station  105 - d  may further include a communications management module  740 . The communications management module  740  may manage communications with other base stations  105 . The communications management module may include a controller or scheduler for controlling communications with UEs  115  in cooperation with other base stations  105 . For example, the communications management module  740  may perform scheduling for transmissions to UEs  115  or various interference mitigation techniques such as beamforming or joint transmission. 
     Additionally or alternatively, the base station  105 - d  may include a multi-carrier scheduling module  415 - c , which may be configured substantially the same as devices  415  and  415 - b  of  FIGS. 4A and 4B . In some cases, the multi-carrier scheduling device  415 - c  is configured to perform the functions of at least one of the modules  450 ,  460 ,  470 ,  480 , or  490  of  FIG. 4B . In some embodiments, the multi-carrier scheduling module  415 - c  is a component of the base station  105 - d  in communication with some or all of the other components of the base station  105 - d  via a bus. Alternatively, functionality of the multi-carrier scheduling module  415 - c  may be implemented as a component of the transceiver module  750 , as a computer program product, as one or more controller elements of the processor module  760 , or as a an element of the communications management module  740 . 
     Turning now to  FIGS. 8A ,  8 B,  8 C,  8 D, and  8 E, which show diagrams of FDD-TDD CA according to various embodiments.  FIG. 8A  depicts a set of CCs  800 - a . The CCs  800 - a  include a TDD SCC  805 - a  (with a DL/UL configuration 5), an FDD DL PCC  810 - a , and an FDD UL PCC  815 - a . The TDD SCC  805 - a  has a subframe configuration  820 - a  of 10 ms, and the FDD DL PCC  810 - a  has UL HARQ process identification  825 - a . A grant may be transmitted, and a corresponding UL subframe sent, as shown with arrows  830 - a . In  800 - a , the FDD DL PCC  810 - a  has an UL HARQ periodicity of 8 ms. Thus, if a 4 ms gap is employed between a TDD UL subframe and an ACK/NAK, a particular HARQ process may have an RTT of 40 ms. 
       FIG. 8B  depicts a set of CCs  800 - b . The set of CCs  800 - b  includes a TDD SCC  805 - b  (with a DL/UL configuration 5), an FDD DL PCC  810 - b , and an FDD UL PCC  815 - b . The TDD SCC  805 - b  has a subframe configuration  820 - b  of 10 ms, and the FDD DL PCC  810 - b  has UL HARQ process identification  825 - b . A grant may be sent, and a corresponding UL subframe transmitted, as shown with arrows  830 - b . According to the present disclosure,  FIG. 8B  shows an adjustment to the TDD SCC HARQ timeline such that the number of HARQ processes are based on the TDD SCC DL/UL configuration. In  800 - b , the TDD UL SCC  805 - b  has an UL HARQ periodicity of 10 ms. In  800 - a , a UL grant in each 10 ms is associated with UL HARQ processes 0, 2, 4, 6, 0, . . . etc. In  800 - b , a UL grant in each 10 ms is associated with UL HARQ process 0. A 4 ms gap is employed between a TDD UL subframe and an ACK/NAK. Thus, in  800 - b , HARQ retransmission for a particular HARQ process may have a delay less than that of  800 - a  (e.g., 10 ms rather than 40 ms). 
       FIG. 8C  depicts a set of CCs  800 - c . The set of CCs  800 - c  includes a TDD SCC  805 - c  (with a DL/UL configuration 0), an FDD DL PCC  810 - c , and an FDD UL PCC  815 - c . The TDD SCC  805 - c  has a subframe configuration  820 - c  of 10 ms, and the FDD DL PCC  810 - c  has UL HARQ process identification  825 - c . A grant may be sent, and a corresponding UL subframe transmitted, as shown with arrows  830 - c . In  800 - c , the TDD UL  805 - c  has an UL HARQ periodicity of 10 ms. In  800 - c , a UL grant in every 10 ms is associated with a fixed UL HARQ process 0, 1, 2, 3, 4, or 5. A 4 ms gap is employed between a TDD UL subframe and an ACK/NAK. Thus, in  800 - c , HARQ retransmission for a particular HARQ process may have a delay less than that of  800 - a  (e.g., 10 ms rather than 40 ms). 
       FIG. 8D  depicts a set of CC  800 - d . The set of CC  800 - d  includes a TDD SCC  805 - d  (with a DL/UL configuration 5), an FDD DL PCC  810 - d , and an FDD UL PCC  815 - d . The TDD SCC  805 - d  has a subframe configuration  820 - d  of 10 ms, and the FDD DL PCC  810 - d  has UL HARQ process identification  825 - d . A grant may be sent, and a corresponding UL subframe transmitted, as shown with arrows  830 - d . In  800 - d , the TDD UL  805 - d  has an UL HARQ periodicity of 10 ms. A 6 ms gap is employed between a TDD UL subframe and an ACK/NAK. In  800 - d , HARQ retransmission for a particular HARQ process may have a delay less than that of  800 - a  (e.g., 10 ms rather than 40 ms). 
       FIG. 8E  depicts a set of CCs  800 - e . The set of CCs  800 - e  includes a TDD SCC  805 - e  (with a DL/UL configuration 0), an FDD DL PCC  810 - e , and an FDD UL PCC  815 - e . The TDD SCC  805 - e  has a subframe configuration  820 - e  of 10 ms, and the FDD DL PCC  810 - e  has UL HARQ process identification  825 - e . A grant may be sent, and a corresponding UL subframe transmitted, as shown with arrows  830 - e . In  800 - e , the TDD UL  805 - e  has an UL HARQ periodicity of 10 ms. A 6 ms gap is employed between a TDD UL subframe and an ACK/NAK. In  800 - e , HARQ retransmission for a particular HARQ process may have a delay less than that of  800 - a  (e.g., 10 ms rather than 40 ms). 
     Those skilled in the art will recognize that the scheduling timing described above (e.g., a TDD UL subframe sent 4 ms after a grant, ACK/NAK sent 6 ms after the TDD UL subframe, and a subsequent TDD UL subframe sent 4 ms after a NAK; or a TDD UL subframe sent 4 ms after a grant, ACK/NAK sent 4 ms after the TDD UL subframe, and a subsequent TDD UL subframe sent 6 ms after a NAK) may apply to any DL/UL configuration, and it may result in a 10 ms HARQ delay when UL HARQ periodicity corresponds to the TDD SCC subframe configuration. 
     In some embodiments, the number of UL HARQ processes equals the number of UL subframes in a frame based on the DL/UL configuration. Table 2 shows the number of UL HARQ processes for each TDD SCC DL/UL configuration. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 UL HARQ Processes per TDD DL/UL Configuration 
               
            
           
           
               
               
               
            
               
                   
                 TDD SCC DL/UL 
                 Number of UL HARQ 
               
               
                   
                 Configuration 
                 Processes 
               
               
                   
                   
               
               
                   
                 0 
                 6 
               
               
                   
                 1 
                 4 
               
               
                   
                 2 
                 2 
               
               
                   
                 3 
                 3 
               
               
                   
                 4 
                 2 
               
               
                   
                 5 
                 1 
               
               
                   
                 6 
                 5 
               
               
                   
                   
               
            
           
         
       
     
     According to some embodiments, for the DL, a grant and a data transmission are in the same subframe and asynchronous HARQ is employed. In such cases, no strict DL HARQ timeline or periodicity is defined. But, in some instances, a number of DL HARQ processes may be defined. For example, the number of HARQ processes may be defined such that the same HARQ process can be reused in a first available DL subframe separated by at least eight milliseconds (8 ms) from the previous transmission of the same HARQ process. Table 3 shows the number of DL HARQ processes for each TDD SCC DL/UL configuration for such cases. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 DL HARQ Processes per TDD DL/UL Configuration 
               
            
           
           
               
               
               
            
               
                   
                 TDD SCC DL/UL 
                 Number of DL HARQ 
               
               
                   
                 Configuration 
                 Processes 
               
               
                   
                   
               
               
                   
                 0 
                 4 
               
               
                   
                 1 
                 6 
               
               
                   
                 2 
                 7 
               
               
                   
                 3 
                 7 
               
               
                   
                 4 
                 8 
               
               
                   
                 5 
                 8 
               
               
                   
                 6 
                 5 or 6* 
               
               
                   
                   
               
               
                   
                 *For some embodiments, such as those employing LTE Release 8 soft buffer partitioning. 
               
            
           
         
       
     
     Next,  FIG. 9  shows a flow diagram of a method  900  for performing HARQ for FDD-TDD CA according to various embodiments. The method  900  may be implemented by the base stations  105  and UEs  115  of  FIG. 1 ,  FIG. 3 ,  FIG. 5 ,  FIG. 6  or  FIG. 7  or by the devices  405  and  405 - a  of  FIGS. 4A and 4B . 
     At block  905 , the method may include determining a scheduling timing between a first control channel transfer and a corresponding uplink transmission for a TDD CC based on a scheduling timing for the an FDD CC. The operations at block  905  may, in some embodiments, be performed by the multi-carrier scheduling modules  415  of  FIG. 4A ,  4 B,  6 , or  7  or by the timing determination module  450  of  FIG. 4B . The scheduling timing may be a 4 ms gap. In some embodiments, the TDD CC is an SCC and the FDD CC is a PCC. The control channel transfer may be a resource grant on PDCCH or EPDCCH. 
     At block  910 , the method may involve determining a number of UL HARQ processes for the TDD CC based on a DL/UL configuration of the TDD CC. The operations at block  910  may be performed by the multi-carrier scheduling modules  415  of  FIG. 4A ,  4 B,  6 , or  7  or the HARQ determination module  470  of  FIG. 4B . In some embodiments, the determined number of uplink subframes of a common UL HARQ process includes 10 ms gap. 
     At block  915 , the method may include communicating based on the determined scheduling timing and the determined number of uplink HARQ processes. The operations at block  915  are, in various embodiments, performed by the receiver modules  410  of  FIG. 4A  or  4 B, the transmitter modules  420  of  FIG. 4A  or  4 B, the transceiver module  610  of  FIG. 6 , or the transceiver module  750  of  FIG. 7 . 
     Next,  FIG. 10  depicts a flow diagram of a method  1000  for performing HARQ in FDD-TDD CA according to various embodiments. The method  1000  may be implemented by the base stations  105  and UEs  115  of  FIG. 1 ,  FIG. 3 ,  FIG. 5 ,  FIG. 6  or  FIG. 7  or by the devices  405  and  405 - a  of  FIGS. 4A and 4B . 
     At block  1005 , the method may include determining a scheduling timing between a first control channel transfer and a corresponding uplink transmission for a TDD CC based on a scheduling timing for the an FDD CC. The operations at block  1005  may be, in some embodiments, performed by the multi-carrier scheduling modules  415  of  FIG. 4A ,  4 B,  6 , or  7  or by the timing determination module  450  of  FIG. 4B . 
     At block  1010 , the method may involve determining a number of UL HARQ processes for the TDD CC based on a DL/UL configuration of the TDD CC. The operations at block  1010  may be performed by the multi-carrier scheduling modules  415  of  FIG. 4A ,  4 B,  6 , or  7  or the HARQ determination module  470  of  FIG. 4B . 
     At block  1015 , the method may include communicating based on the determined scheduling timing and the determined number of uplink HARQ processes. The operations at block  1015  are, in various embodiments, performed by the receiver modules  410  of  FIG. 4A  or  4 B, the transmitter modules  420  of  FIG. 4A  or  4 B, the transceiver module  610  of  FIG. 6 , or the transceiver module  750  of  FIG. 7 . 
     At block  1020 , the method may include cross carrier scheduling transmissions on the TDD CC from the FDD CC. The operations of block  1020  are, in some cases, performed by the multi-carrier scheduling modules  415  of  FIG. 4A ,  4 B,  6 , or  7  or by the cross scheduling module  470  of  FIG. 4B . 
       FIG. 11  shows a flow diagram of a method  1100  for multi-carrier scheduling according to various embodiments. The method  1100  may be implemented by the base stations  105  and UEs  115  of  FIG. 1 ,  FIG. 3 ,  FIG. 5 ,  FIG. 6  or  FIG. 7  or by the devices  405  and  405 - a  of  FIGS. 4A and 4B . 
     At block  1105 , the method may include determining a scheduling timing between a first control channel transfer and a corresponding uplink transmission for a TDD CC based on a scheduling timing for the an FDD CC. The operations at block  1105  may be, in some embodiments, performed by the multi-carrier scheduling modules  415  of  FIG. 4A ,  4 B,  6 , or  7  or by the timing determination module  450  of  FIG. 4B . 
     At block  1110 , the method may involve determining a number of UL HARQ processes for the TDD CC based on a DL/UL configuration of the TDD CC. The operations at block  1110  may be performed by the multi-carrier scheduling modules  415  of  FIG. 4A ,  4 B,  6 , or  7  or the HARQ determination module  470  of  FIG. 4B . 
     At block  1115 , the method may include communicating based on the determined scheduling timing and the determined number of uplink HARQ processes. The operations at block  1115  are, in various embodiments, performed by the receiver modules  410  of  FIG. 4A  or  4 B, the transmitter modules  420  of  FIG. 4A  or  4 B, the transceiver module  610  of  FIG. 6 , or the transceiver module  750  of  FIG. 7 . 
     At block  1120 , the method may involve determining a first timing gap between a first UL shared channel transmission and a corresponding HARQ indicator channel transfer (e.g., an ACK/NAK). The operations of block  1120  may be performed by the multi-carrier scheduling modules  415  of  FIG. 4A ,  4 B,  6 , or  7  or the timing gap determination module  480  of  FIG. 4B . In some embodiments, the determined first timing gap is 6 ms. In other cases, the determined first timing gap is four milliseconds 4 ms. 
     At block  1125 , the method may further involve determining a second timing gap between the HARQ indicator channel transfer (e.g., NAK) and a corresponding second uplink shared channel transmission, which may be a HARQ retransmission. The operations of block  1125  may be performed by the multi-carrier scheduling modules  415  of  FIG. 4A ,  4 B,  6 , or  7  or the timing gap determination module  480  of  FIG. 4B . In some instances, the determined first timing gap is four milliseconds 4 ms. But in other embodiments, the determined first timing gap is 6 ms. 
       FIG. 12  shows a flow diagram of a method  1200  for multi-carrier scheduling according to various embodiments. The method  1200  may be implemented by the base stations  105  and UEs  115  of  FIG. 1 ,  FIG. 3 ,  FIG. 5 ,  FIG. 6  or  FIG. 7  or by the devices  405  and  405 - a  of  FIGS. 4A and 4B . 
     At block  1205 , the method may include determining a scheduling timing between a first control channel transfer and a corresponding uplink transmission for a TDD CC based on a scheduling timing for the an FDD CC. The operations at block  1205  may be, in some embodiments, performed by the multi-carrier scheduling modules  415  of  FIG. 4A ,  4 B,  6 , or  7  or by the timing determination module  450  of  FIG. 4B . 
     At block  1210 , the method may involve determining a number of UL HARQ processes for the TDD CC based on a DL/UL configuration of the TDD CC. The operations at block  1210  may be performed by the multi-carrier scheduling modules  415  of  FIG. 4A ,  4 B,  6 , or  7  or the HARQ determination module  470  of  FIG. 4B . 
     At block  1215 , the method may include communicating based on the determined scheduling timing and the determined number of uplink HARQ processes. The operations at block  1215  are, in various embodiments, performed by the receiver modules  410  of  FIG. 4A  or  4 B, the transmitter modules  420  of  FIG. 4A  or  4 B, the transceiver module  610  of  FIG. 6 , or the transceiver module  750  of  FIG. 7 . 
     At block  1220 , the method may involve determining a first timing gap between a first UL shared channel transmission and a corresponding HARQ indicator channel transfer (e.g., an ACK/NAK). The operations of block  1220  may be performed by the multi-carrier scheduling modules  415  of  FIG. 4A ,  4 B,  6 , or  7  or the timing gap determination module  480  of  FIG. 4B . 
     At block  1225 , the method may further involve determining a second timing gap between the HARQ indicator channel transfer (e.g., NAK) and a corresponding second uplink shared channel transmission, which may be a HARQ retransmission. The operations of block  1225  may be performed by the multi-carrier scheduling modules  415  of  FIG. 4A ,  4 B,  6 , or  7  or the timing gap determination module  480  of  FIG. 4B . 
     At block  1230 , the method may also include overwriting the HARQ indicator channel transfer (e.g., ACK/NAK) with a second control channel transfer. The operation of block  1230  may be performed by the multi-carrier scheduling modules  415  of  FIG. 4A ,  4 B,  6 , or  7  or the overwrite module  490  of  FIG. 4B . In some cases, the second control channel transfer is a grant on PDCCH or EPDCCH sent 2 ms (or two subframes) after the ACK/NAK. In other embodiments, the second control channel transfer is a grant sent on PDCCH or EPDCCH in the same subframe as the ACK/NAK. 
     Next,  FIG. 13  shows a flow diagram of a method  1300  for multi-carrier scheduling according to various embodiments. The method  1300  may be implemented by the base stations  105  and UEs  115  of  FIG. 1 ,  FIG. 3 ,  FIG. 5 ,  FIG. 6  or  FIG. 7  or by the devices  405  and  405 - a  of  FIGS. 4A and 4B . 
     At block  1305 , the method may include configuring a set of component carriers in carrier aggregation. In some examples, this may include configuring component carriers by a base station; and the configuration may be indicated to a UE—e.g., via RRC signaling. In other cases, a UE may determine a configuration of a set of component carriers—e.g., via received RRC signaling. The set of component carriers may include a TDD SCC and an FDD SCC, which may be cross-carrier scheduled from one another. The operation of block  1305  may be performed by the multi-carrier scheduling modules  415  of  FIG. 4A ,  4 B,  6 , or  7  or by the cross scheduling module  470  of  FIG. 4B . 
     At block  1310 , the method may include determining a scheduling timing an UL HARQ timing of an FDD SCC based, wholly or partially, on a time duration of a TDD SCC. In some examples, a UE may identify scheduling timing and UL HARQ timing based on RRC signaling from a base station. The operation of block  1310  may be performed by the multi-carrier scheduling modules  415  of  FIG. 4A ,  4 B,  6 , or  7 , by the timing determination module  450  of  FIG. 4B , or by the HARQ determination module  460  of  FIG. 4B . 
     At block  1315 , the method may include communicating based on the determined scheduling timing and the determined number of UL HARQ process. The operation of block  1315  may be performed by the receiver modules  410  of  FIG. 4A  or  4 B, the transmitter modules  420  of  FIG. 4A  or  4 B, the transmitter module  610  and the receiver module  615  of  FIG. 6 , or the transceiver modules  750  of  FIG. 7 . 
     Those skilled in the art will recognize that the methods  900 ,  1000 ,  1100 ,  1200  and  1300  are example implementations of the tools and techniques described herein. The methods may be performed with more or fewer steps; and they may be performed in an order other than indicated. 
     The detailed description set forth above in connection with the appended drawings describes exemplary embodiments and does not represent the only embodiments that may be implemented or that are within the scope of the claims. The term “exemplary” used throughout this description means “serving as an example, instance, or illustration,” and not “preferred” or “advantageous over other embodiments.” The detailed description includes specific details for the purpose of providing an understanding of the described techniques. These techniques, however, may be practiced without these specific details. In some instances, well-known structures and devices are shown in block diagram form in order to avoid obscuring the concepts of the described embodiments. 
     Information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof. 
     The various illustrative blocks and modules described in connection with the disclosure herein may be implemented or performed with a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
     The functions described herein may be implemented in hardware, software/firmware, or combinations thereof. If implemented in software/firmware, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Other examples and implementations are within the scope and spirit of the disclosure and appended claims. For example, due to the nature of software/firmware, functions described above can be implemented using software/firmware executed by, e.g., a processor, hardware, hardwiring, or combinations thereof. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations. Also, as used herein, including in the claims, “or” as used in a list of items prefaced by “at least one of” indicates a disjunctive list such that, for example, a list of “at least one of A, B, or C” means A or B or C or AB or AC or BC or ABC (i.e., A and B and C). 
     Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage medium may be any available medium that can be accessed by a general-purpose or special-purpose computer. By way of example, and not limitation, computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, any connection is properly termed a computer-readable medium. For example, if the software/firmware is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, include compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above are also included within the scope of computer-readable media. 
     The previous description of the disclosure is provided to enable a person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Throughout this disclosure the term “example” or “exemplary” indicates an example or instance and does not imply or require any preference for the noted example. Thus, the disclosure is not to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.